WorldWideScience
1

Heat exchange method using natural flow of heat exchange medium  

International Nuclear Information System (INIS)

Heat exchange is effected in a simple and economical manner by allowing natural flow, i.e., without mechanical compressors, pumps, etc., of a heat exchange fluid such as a conventional refrigerant liquid between two heat exchangers which are exposed to air at different temperatures. The two heat exchangers, which may conveniently take the form of fin-tube heat exchangers, for example, are arranged with one end at a higher elevation than the other, the upper ends of the two exchangers being connected in direct communication and the lower ends being likewise connected. As the refrigerant liquid absorbs heat and evaporates in the heat exchanger exposed to the warmer air the vapor travels through the upper connecting line to the other heat exchanger, where it rejects heat and is condensed, the liquid flows through the lower connecting line back to the first heat exchanger, and so on, with heat exchange between the two air streams or masses occurring during the natural, continuous flow of the refrigerant in gaseous and liquid form

2

Buoyancy driven flow in counter flow heat exchangers  

International Nuclear Information System (INIS)

The temperature distribution, the buoyancy head and the flow rate have been studied in a counter flow heat exchanger having buoyancy driven flow on at least one side. The assumptions made for heat flux distribution are varied and the resulting effects on the flow rate and fluid temperatures are studied. A network model is used to simulate the temperature distribution and oil flow rates in an oil-filled power transformer cooled by radiators. It is found that for operating conditions normally found for mineral oil the counter flow assumptions for heat flux distribution gives approximately the same results as assuming uniform heat flux. When a more viscous oil type is used or the radiators are placed lower than normal relative to the heat generating parts, the counter flow assumptions give more reliable results.

3

Simulation Studies on A Cross Flow Plate Fin Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available Compact heat exchangers which were initially developed for the aerospace industries in the1940s have been considerably improved in the past few years. The main reasons for the goodperformance of compact heat exchangers are their special design which includes turbulent which inturn use high heat transfer coefficient and resists fouling, and maximum temperature driving forcebetween the hot and cold fluids. Numerous types use special enhancement techniques to achieve therequired heat transfer in smaller plot areas and, in many cases, less initial investment. One such type ofcompact heat exchanger is the Plate-fin heat exchanger. The complexity of compact heat exchangerdesign equations results from the exchangers unique ability to transfer heat between multiple processstreams and a wide array of possible flow configurations. This paper presents the performanceevaluation of cross flow plate fin heat exchanger with several different Gas-Liquid systems.Experimental results such as exchanger effectiveness, overall heat transfer coefficients were calculatedfor the flow systems of Cross flow Heat Exchangers. A steady state model for the outlet temperature ofboth the cold and hot fluid and overall heat transfer coefficient of a plate-fin cross flow heat exchangerwas developed and simulated using MATLAB, which was verified with the experiments conducted.

M. Thirumarimurugan

2008-01-01

4

Characteristics of heat flow in recuperative heat exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available A simplified model of heat flow in cross-flow tube recuperative heat exchangers (recuperators was presented in this paper. One of the purposes of this investigation was to analyze changes in the values of some parameters of heat transfer in recuperators during combustion air preheating. The logarithmic mean temperature (Atm and overall heat transfer coefficient (U, are two basic parameters of heat flow, while the total heated area surface (A is assumed to be constant. The results, presented as graphs and in the form of mathematical expressions, were obtained by analytical methods and using experimental data. The conditions of gaseous fuel combustions were defined by the heat value of gaseous fuel Qd = 9263.894 J.m-3, excess air ratio ?= 1.10, content of oxygen in combustion air ?(O2 = 26%Vol, the preheating temperature of combustion air (cold fluid outlet temperature tco = 100-500°C, the inlet temperature of combustion products (hot fluid inlet temperature thi = 600-1100°C.

Lalovi? Milisav

2005-01-01

5

Constructal tree-shaped parallel flow heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

The paper reports the performance of balanced two-stream parallel flow heat exchangers, in which each stream flows as a tree network through its allotted space. The two trees are in parallel flow, and are arranged like two palms pressed against each other. The relationships between effectiveness and number of heat transfer units are developed for several parallel tree flow configurations: (i) constructal dichotomous trees covering uniformly a rectangular area, (ii) trees on a disk-shaped area, and (iii) trees on a square-shaped area. In configurations (ii) and (iii) each stream flows between the center and the periphery of the area. Configurations (i) and (ii) are trees with minimal resistance to fluid flow. Configuration (iii) is designed by minimizing the length of each duct in the network. The performance of the parallel flow configurations is compared with the performance of counterflow configurations. The future use of dendritic heat exchangers in devices with maximal heat transport density is proposed. (author)

Zimparov, V.D. [Department of Mechanical Engineering, Gabrovo Technical University, 4 Hadji Dimitar Str., 5300 Gabrovo (Bulgaria); Da Silva, A.K. [Department of Mechanical Engineering, University of Hawaii, Manoa, Honolulu, HI 96822 (United States); Bejan, A. [Department of Mechanical Engineering and Materials Science, Duke University, Box 90300, Durham, NC 27708-0300 (United States)

2006-11-15

6

Oscillating flow loss test results in Stirling engine heat exchangers  

Science.gov (United States)

The results are presented for a test program designed to generate a database of oscillating flow loss information that is applicable to Stirling engine heat exchangers. The tests were performed on heater/cooler tubes of various lengths and entrance/exit configurations, on stacked and sintered screen regenerators of various wire diameters and on Brunswick and Metex random fiber regenerators. The test results were performed over a range of oscillating flow parameters consistent with Stirling engine heat exchanger experience. The tests were performed on the Sunpower oscillating flow loss rig which is based on a variable stroke and variable frequency linear drive motor. In general, the results are presented by comparing the measured oscillating flow losses to the calculated flow losses. The calculated losses are based on the cycle integration of steady flow friction factors and entrance/exit loss coefficients.

Koester, G.; Howell, S.; Wood, G.; Miller, E.; Gedeon, D.

1990-01-01

7

Geothermal heat exchanger with coaxial flow of fluids  

OpenAIRE

The paper deals with a heat exchanger with coaxial flow. Two coaxial pipes of the secondary part were placed directly into a geothermal boring in such a way that geothermal water flows around the outer pipe. Starting from the energy balance of the exchanger formed in this way and the assumption of a study-state operating regime, a mathematical model was formulated. On the basis of the model, the secondary circle output temperature was determined as a function of the exchanger geometry, the co...

Peji? Dragan M.; Stojiljkovi? Dragan T.; Stojiljkovi? Staniša T.; ?urovi?-Petrovi? Maja; Miti? Nebojša

2005-01-01

8

Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger  

OpenAIRE

Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by ...

Pavel Neuberger; Radomír Adamovský; Michaela Še?ová

2014-01-01

9

Optimization of cross flow heat exchangers for thermoelectric waste heat recovery  

International Nuclear Information System (INIS)

Thermoelectric waste heat recovery is investigated for current thermoelectric materials with advanced heat exchangers. Numerical heat exchanger models integrated with models for Bi2Te3 thermoelectric modules are validated against experimental data from previous cross flow heat exchanger studies as well as experiments using thermoelectrics between counterflow hot water and cooling air flow channels. The models are used in optimization studies of thermoelectric waste heat recovery with air cooling in a cross flow heat exchanger. Power losses from an air fan and a fluid pump result in an optimal configuration at intermediate cooling air and hot fluid flows. Results show that heat exchangers with Bi2Te3 thermoelectrics can achieve net power densities over 40 W/l

10

A novel compact heat exchanger using gap flow mechanism  

Science.gov (United States)

A novel, compact gap-flow heat exchanger (GFHE) using heat-transfer fluid (HTF) was developed in this paper. The detail design of the GFHE coaxial structure which forms the annular gap passage for HTF is presented. Computational fluid dynamics simulations were introduced into the design to determine the impacts of the gap width and the HTF flow rate on the GFHE performance. A comparative study on the GFHE heating rate, with the gap widths ranged from 0.1 to 1.0 mm and the HTF flow rates ranged from 100 to 500 ml/min, was carried out. Results show that a narrower gap passage and a higher HTF flow rate can yield a higher average heating rate in GFHE. However, considering the compromise between the GFHE heating rate and the HTF pressure drop along the gap, a 0.4 mm gap width is preferred. A testing loop was also set up to experimentally evaluate the GFHE capability. The testing results show that, by using 0.4 mm gap width and 500 ml/min HTF flow rate, the maximum heating rate in the working chamber of the as-made GFHE can reach 18 °C/min, and the average temperature change rates in the heating and cooling processes of the thermal cycle test were recorded as 6.5 and 5.4 °C/min, respectively. These temperature change rates can well satisfy the standard of IEC 60068-2-14:2009 and show that the GFHE developed in this work has sufficient heat exchange capacity and can be used as an ideal compact heat exchanger in small volume desktop thermal fatigue test apparatus.

Liang, J. S.; Zhang, Y.; Wang, D. Z.; Luo, T. P.; Ren, T. Q.

2015-02-01

11

Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by the heat-exchangers, has been characterised by meticulous measurements. These reveal that high concentrations of antifreeze mix in the heat-transfer fluid of the heat exchanger have an adverse impact on heat flows discharged into the soil.

Pavel Neuberger

2014-02-01

12

Applications of two-phase flow and heat transfer in compact heat exchangers  

OpenAIRE

Three applications of two-phase flow and heat transfer in plate-fin heat exchangers have been studied. A dephlegmator is a heat exchanger in which reflux condensation of a vapour mixture occurs, and plate-fln versions have importance in cryogenic gas separation processes. Numerical calculations for different binary mixtures show that the number of transfer units can be expressed as a simple function of the inlet vapour state and flow rate, heat load, and channel geometry. Th...

Lintern, Andrew Charles

2008-01-01

13

A review of flow induced vibrations in heat exchangers  

International Nuclear Information System (INIS)

Flow induced vibrations are widely recognized as a major concern in the design of modern tube and shell heat exchangers. Tube failures caused by excessive vibrations are relatively commonplace and often very expensive to repair. While considerable progress has been made in the development of predictive tools, many uncertainties still remain. This paper reviews our state of understanding of the flow excitation mechanisms and presents design guidelines. Also discussed are the research needs in this field. (author)

14

Turbulent flow heat transfer from externally roughened tubes in axial flow in concentric pipe heat exchangers  

International Nuclear Information System (INIS)

Results are presented from an experimental investigation of annulus side flow friction and heat transfer to water from different externally roughened tubes in turbulent axial flow in a concentric pipe heat exchanger. The roughened tubes studied include tubes with (i) transverse ribbing, (ii) spiral wire wrapping and (iii) knurling on the outside surface, having wide ranges of aspect ratios of geometrical roughness parameters, (e/D), (p/e) and (p/D). Correlations are proposed for turbulent friction and heat transfer coefficients, and the most efficient tube giving increased heat duty was identified on the criterion of constant pumping power. Comparison with the published results of similar internally roughened tubes reveals that externally rough tubes also perform better around Reynolds numbers of 5000 to 15000 for water flow and for surface roughness severity factors, (e/sup 2/ /pD) in the range, 0.01 to 0.025

15

Heat exchanger  

International Nuclear Information System (INIS)

The arrangement described relates particularly to heat exchangers for use in fast reactor power plants, in which heat is extracted from the reactor core by primary liquid metal coolant and is then transferred to secondary liquid metal coolant by means of intermediate heat exchangers. One of the main requirements of such a system, if used in a pool type fast reactor, is that the pressure drop on the primary coolant side must be kept to a minimum consistent with the maintenance of a limited dynamic head in the pool vessel. The intermediate heat exchanger must also be compact enough to be accommodated in the reactor vessel, and the heat exchanger tubes must be available for inspection and the detection and plugging of leaks. If, however, the heat exchanger is located outside the reactor vessel, as in the case of a loop system reactor, a higher pressure drop on the primary coolant side is acceptable, and space restriction is less severe. An object of the arrangement described is to provide a method of heat exchange and a heat exchanger to meet these problems. A further object is to provide a method that ensures that excessive temperature variations are not imposed on welded tube joints by sudden changes in the primary coolant flow path. Full constructional details are given. (U.K.)

16

Flow distribution and tube vibration in heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

A project was initiated to study flow distribution and tube vibration in heat exchangers. An experimental program was carried out on a full-size heat exchanger in four test phases of parametric study. The flow induced vibration data were used to quantify and develop non-intrusive vibration monitoring techniques for online problem evaluation and to study the influence of design features and conditions on the vibration. The in-tube vibration data obtained have shown that the vibroacoustic and microphone monitoring techniques to be reliable and accurate methods for the detection of tube impacting in an operating heat exchanger. Development of work on the use of a two-accelerator vibroacoustic technique for the location of impacting zones in a bundle showed promise and is currently being employed in the field. The in-tube vibration data have demonstrated the effects that changes in the design of a bundle can have on tube vibration in that bundle. These results indicate that an important factor in bundle design is the local flow distribution in areas of high vibration susceptibility. The in-tube data have demonstrated that tubes in zones other than the inlet region can be susceptible to a form of periodic resonant excitation. This observation has implications for cases where flow reduction is implemented to avoid an instability problem. Such a reduction could bring the tube bundle into a flow regime where it is susceptible to the resonant excitation. 10 refs., 55 figs., 4 tabs.

Anderson, H.L.

1985-07-01

17

Flow induced vibration in shell and tube heat exchangers  

International Nuclear Information System (INIS)

Assessing heat exchanger designs, from the standpoint of flow induced vibration, is becoming increasingly important as shell side flow velocities are increased in a quest for better thermal performance. This paper reviews the state of the art concerning the main sources of vibration excitation, i.e. vortex shedding resonance, turbulent buffeting, fluidelastic instability and acoustic resonance, as well as the structural dynamics of the tubes. It is concluded that there are many areas which require further investigation but there are sufficient data available at present to design, with reasonable confidence, units that will be free from flow induced vibration. Topics which are considered to be key areas for further work are listed

18

Flow induced acoustic resonance in tubular heat exchangers  

Science.gov (United States)

This Data Item 88028, an addition to the Sub-series on Heat Transfer, and complements ESDU 87019, which provides prediction methods for vibration of heat exchanger bundles. After outlining the nature of acoustic resonance, calculation methods are given for the acoustic frequency in both rectangular and cylindrical ducts. Procedures, based on a correlation of all the available acoustic data (all data on periodic wake shedding derived from measurements in the flow field were discarded because of their inapplicability), are given for the prediction of resonance. Possible damage caused by accoustic resonance is considered, and the means by which a design can be modified, before or after fabrication, are discussed. The methods apply to bundles in a rectangular cross-section duct, to shell-and-tube heat exchangers and to helical coil arrangements.

1988-12-01

19

Heat and flow analysis inside a parallel-flow heat exchanger  

International Nuclear Information System (INIS)

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header

20

Analysis of flow induced vibration in heat exchangers  

International Nuclear Information System (INIS)

A description will be given of three different types of heat exchangers developed by the Dutch Nuclear Industry Group ''Neratoom'' in cooperation with TNO for the sodium-cooled fast breeder reactor SNR-300 at Kalkar. Moreover, the research related with flow induced vibrations carried out by TNO (Organization for Applied Scientific Research) will be presented. The flow induced forces on the tubes of the straight-tube steam generators were measured at the inlet and outlet section where partial crossflow occurs. With the measured flow induced forces the response of a tube was calculated as a function of the tube-to-supportbush clearances taking into account the non-linear damping effects from the sodium. The theoretical results showed that for this particular design no tube impact damage is to be expected which was confirmed later by a full scale experiment. Special attention will be devoted to the steam generator with helical-coil tube-bundles, where the sodium flows in a counter cross-flow over the tube-bundle. Extensive measurements of the power spectra of the flow induced forces were carried out since no information could be found in the literature. The vibration analysis will be presented and vibration modes of the entire bundle will be compared with experimentally obtained results. Finally a description of the vibration tests to be carried out on the intermediate heat exchanger (IHX) will be presented. (author)

21

Thermal induced flow oscillations in heat exchangers for supercritical fluids  

Science.gov (United States)

Analytical model has been developed to predict possible unstable behavior in supercritical heat exchangers. From complete model, greatly simplified stability criterion is derived. As result of this criterion, stability of heat exchanger system can be predicted in advance.

Friedly, J. C.; Manganaro, J. L.; Krueger, P. G.

1972-01-01

22

Microcomputer analysis of regenerative heat exchangers for oscillating flow  

Energy Technology Data Exchange (ETDEWEB)

Regenerative heat exchangers for use in oscillating flows such as those occurring in Stirling engines present considerable analytical problems to the thermal engineer. A simplified finite element analysis has been implemented in a spreadsheet, providing improved access to analytical assumptions and allowing parametric analysis of current heat transfer data. In addition, an irreversibility analysis has been implemented using the thermal and friction results in the spreadsheet. It is suited for evaluation and insights into loss tradeoffs inside operating regenerators, to suggest new regenerator design concepts, and to focus experimental work. 22 refs., 13 figs.

Hutchinson, R.A.; Lyke, S.E.

1987-03-01

23

Investigation of heat exchange at the laminar flow of liquids in the pipe  

Directory of Open Access Journals (Sweden)

Full Text Available The results of the experimental investigation of heat exchange of various liquids at the laminar flow in pipes are presented in the paper. The design formula is received. Possibilities of heat exchange intensification are shown.

Ilyin Roman Albertovich

2011-12-01

24

Plate heat exchanger - inertia flywheel performance in loss of flow transient  

Energy Technology Data Exchange (ETDEWEB)

One of the most versatile types of heat exchangers used is the plate heat exchanger. It has principal advantages over other heat exchangers in that plates can be added and/or removed easily in order to change the area available for heat transfer and therefore its overall performance. The cooling systems of Egypt's second research reactor (ETRR 2) use this type of heat exchanger for cooling purposes in its primary core cooling and pool cooling systems. In addition to the change in the number of heat exchanger cooling channels, the effect of changing the amount of mass flow rate on the heat exchanger performance is an important issues in this study. The inertia flywheel mounted on the primary core cooling system pump with the plate heat exchanger plays an important role in the case of loss of flow transients. The PARET code is used to simulate the effect of loss of flow transients on the reactor core. Hence, the core outlet temperature with the pump-flywheel flow coast down is fed into the plate heat exchanger model developed to estimate the total energy transferred to the cooling tower, the primary side heat exchanger temperature variation, the transmitted heat exchanger power, and the heat exchanger effectiveness. In addition, the pressure drop in both, the primary side and secondary side of the plate heat exchanger is calculated in all simulated transients because their values have limits beyond which the heat exchanger is useless. (orig.)

Abou-El-Maaty, Talal; Abd-El-Hady, Amr [Atomic Energy Authority, Cairo (Egypt). Reactors Dept.

2009-04-15

25

Effect of flow maldistribution and axial conduction on compact microchannel heat exchanger  

Science.gov (United States)

When a compact microchannel heat exchanger is operated at cryogenic environments, it has potential problems of axial conduction and flow maldistribution. To analyze these detrimental effects, the heat exchanger model that includes both axial conduction and flow maldistribution effect is developed in consideration of the microchannel heat exchanger geometry. A dimensionless axial conduction parameter (?) is used to describe the axial conduction effect, and the coefficient of variation (CoV) is introduced to quantify the flow maldistribution condition. The effectiveness of heat exchanger is calculated according to the various values of the axial conduction parameter and the CoV. The analysis results show that the heat exchanger effectiveness is insensitive when ? is less than 0.005, and effectiveness is degraded with the large value of CoV. Three microchannel heat exchangers are fabricated with printed circuit heat exchanger (PCHE) technology for validation purpose of the heat exchanger model. The first heat exchanger is a conventional heat exchanger, the second heat exchanger has the modified cross section to eliminate axial conduction effect, and the third heat exchanger has the modified cross section and the cross link in parallel channel to mitigate flow maldistribution effect. These heat exchangers are tested in cryogenic single-phase, and two-phase environments. The third heat exchanger shows the ideal thermal characteristic, while the other two heat exchangers experience some performance degradation due to axial conduction or flow maldistribution. The impact of axial conduction and flow maldistribution effects are verified by the simulation results and compared with the experimental results.

Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon

2014-03-01

26

The black box model of a double-tube counter-flow heat exchanger  

Science.gov (United States)

Variable working conditions of a double-tube counter-flow heat exchanger were analysed. During operation of the heat exchanger, the parameters (temperatures and mass flow rates) of both fluids at its inlet change, which leads to a change in its performance. Heat transfer effectiveness is commonly used to assess the heat exchanger performance, defined as the ratio of the actual to the maximum heat flow rate. In the present paper, the heat exchanger was considered to be a `black box', and the aim was to investigate how the inlet parameters (temperatures and mass flow rates of both fluids) affect the outlet ones (temperatures of both fluids), and thus to attempt to introduce a new relation for the heat transfer effectiveness of a counter-flow heat exchanger as a function of only inlet parameters. Following the analysis, a relation for the heat transfer effectiveness as a function of inlet parameters with five constant coefficients was obtained. These coefficients depend on the heat exchanger geometry and on the properties of the heat transfer fluids; they are not general-purpose, but specific to a counter-flow heat exchanger. The form of the proposed relation for the heat transfer effectiveness of a counter-flow heat exchanger is not satisfactory as it involves five constant coefficients; therefore, a new approach was chosen, consisting in analysing a parameter defined as the ratio of the minimum to the actual arithmetic mean temperature difference. Using the parameter defined in this way, the relation for the heat transfer effectiveness of a counter-flow heat exchanger was obtained as a function of two parameters: the ratio of the heat capacity rates of both fluids, and NTU, with no constant coefficients. The proposed relations were verified against the data produced by a simulator of a double-tube counter-flow heat exchanger.

Laskowski, Rafa?

2014-12-01

27

Heat exchanger  

International Nuclear Information System (INIS)

This invention concerns a heat exchanger between a fluid flowing through a tube and a gas. Such an exchanger can be used, inter alia, for removing calories that cannot be used for generating electricity in a thermal or nuclear power station. This exchanger can withstand any pressure surges in the system and even the use of a high vapour pressure coolant such as ammonia, since the fluid flows in a round tube with low pressure drops (both with respect to the fluid to be cooled and the cooling air). It is rigid enough to stand up to being moved and handled as well as to gusts of wind. It is formed of units that can be handled without difficulty and that are easily dismantable and interchangeable, even in service, and it is easily maintained. The exchange area is high for a minimum frontal area and this enables the size of the supporting frame to be reduced and makes it easy to hide it behind a screen of trees should this prove necessary. Finally, it is composed of a small number of standard units thus reducing the industrial production cost. These units are rectangular plates, each one being a flat tubular coil fitted between two flat parallel sheet metal plates having on their outer sides flat top raised bosses. These units are assembled together by the tops of the bosses so as to form an exchanger bank, each bank comprising two collectors to which the bank coils are tightly connected

28

Characteristics of flow distribution in compact parallel flow heat exchangers, part II: Modified inlet header  

International Nuclear Information System (INIS)

This study presents the experimental results of liquid flow distribution in compact parallel flow heat exchanger through a rectangular and 5 modified inlet headers (i.e., 1 trapezoidal, one multi-step, 2 baffle plates and 1 baffle tubes header). The basic header has a rectangular shape with 9 x 9 mm cross section and 90 mm long header length having a 4 mm inlet tube for flow into the header and distributed to nine 3 mm parallel tubes with 400 mm length. A jet stream induced at the header inlet associated with vortexes affecting the flow distribution to the front tubes. The flow distribution in the header highly depends on the header shape and the total flow rate. Normally the first several tubes have the lowest flow ratios for the conventional headers and the flow distribution is significantly improved by lifting the jet stream using the modified header with baffle tube, followed by the baffle plate and multi-step header. The baffle tube yields the best flow distribution for it removed the vortex flow, and it is applicable for all the flow rates. - Highlights: ? This study investigates flow distribution in parallel flow heat exchanger through 5 modified inlet headers. ? Jet flow induces at the header inlet with vortexes affecting the flow distribution to front tubes. ? The modified header with baffle tube removes the vortex flow and yields the best flow distribution.

29

Characteristics of flow distribution in compact parallel flow heat exchangers, part I: Typical inlet header  

International Nuclear Information System (INIS)

This study experimentally and numerically investigates the single-phase flow into parallel flow heat exchangers with inlet and outlet rectangular headers having square cross section and 9 circular tubes. The effects of inlet flow condition, tube diameter, header size, area ratio, flow directions (Z and U-type), as well as the gravity are investigated. The experimental results indicate that flow distribution for U-type flow is more uniform than Z-type flow. Depending on the inlet volumetric flow rate, the flow ratio at the first several tubes can be lower than 50% of the last tube for Z-type arrangement, and this phenomenon becomes more and more pronounced with the rising velocity at the intake conduit. The mal-distribution can be eased via reducing the branching tube size or increasing the entrance settling distance at the intake conduit. It is found that the influence of gravity on mal-distribution is negligible and the mal-distribution is associated with the jet flow pattern. - Highlights: ? The flow distribution into parallel flow heat exchangers with rectangular headers is examined. ? The first several tubes may show only 50% flow rate of the last tube. ? The mal-distribution becomes more severe with the rising velocity at the intake conduit. ? The mal-distribution is mainly associated with the jet flow pattern. ? Flow distribution is improved via smaller tubes or increasing the inlet distance at the intake conduit.

30

Heat exchangers  

International Nuclear Information System (INIS)

This invention relates to a heat exchanger, more particularly intended, although not exclusively, for transferring the thermal power acquired by an initial fluid medium cooling the core assemblies of a nuclear reactor to another fluid medium isolated from the first, therefore having low activity and suitable them to generate steam in a separate generator. The invention applies particularly in the case where the first fluid medium or primary fluid is a liquid metal, generally sodium, used as coolant in a fast nuclear reactor, the second fluid medium or secondary fluid also being liquid sodium, flowing through tubes between two tube plates respectively to enter an intake manifold and an outlet manifold of the secondary sodium. These tubes are externally steeped in the primary sodium. The exchanger concerned comprises two tube plates fitted inside an external envelope crossed by a primary fluid. These two tube plates are joined by a bundle of tubes extending vertically over the major part of their length and through which a secondary fluid flows, these tubes being covered externally by the primary fluid exchanging heat with the secondary fluid through these tubes

31

Heat exchangers  

International Nuclear Information System (INIS)

A heat exchanging apparatus comprises an elongate chamber which is part filled with a heat transfer medium, and a pair of U-shaped pipes. The pipes are spaced from one another, but are generally mutually adjacent so that heat from a liquid flowing in one pipe can be transferred through a medium to the liquid in the other pipe. If one or other of the pipes ruptures the escaping liquid can be vented and will not intermix with the liquid in the other pipe. A level detector detects a rise in the level of the material in the chamber when a pipe ruptures and closes valves to prevent further loss of liquid. The apparatus is particularly suitable for use in the food industry or where one of the liquids is toxic or radioactive. (author)

32

Special problems of heat- and flow transfer in heat exchangers of HTGR type reactors  

International Nuclear Information System (INIS)

A heat pipe with an oblique flow is one in which the angle between the initial direction of flow and the pipe axis is larger than 00 and smaller than 900. A brief outline is given of two examples of an oblique flow in heat exchangers. In one of the apparatuses, the main-flow direction of the fluid bypassing the pipes runs parallel to the pipe axle; the angle of attack therefore is 00. In the inflow and outflow areas of the heat exchanger the pipes admit a cross flow and/or an oblique flow. Under conventional operating conditions, this area, which is geometrically small by comparison with the total length of the apparatus, is of secondary importance; as regards heat exchangers with a high thermal stress, accurate knowledge of temperature and velocity distributions in the inflow and outflow areas is decisive for the operational life of the components. In the other heat exchanger, the pipes admit an oblique flow through their entire length. The chain-dotted lines symbolize pipe cylinders on which the pipes are helically coiled around a central pipe. A special feature of the pipe arrangement shown - this should be noted - lies in the fact that the pipes are coiled in opposite directions on adjacent pipe cylinders. As a result, intersecting pipe coils emerge with special fluidic characteristics. These features, which result from the transition of the inclination of all the pipes in the same direction to their crosswise inclination, need to n to their crosswise inclination, need to be described more profoundly here. (orig./GL)

33

Heat transfer enhancement in cross-flow heat exchangers using oval tubes and multiple delta winglets  

Energy Technology Data Exchange (ETDEWEB)

A three-dimensional study of laminar flow and heat transfer in a channel with built-in oval tube and delta winglets is carried out through the solution of the complete Navier-Stokes and energy equations using a body-fitted grid and a finite-volume method. The geometrical configuration represents an element of a gas-liquid fin-tube cross-flow heat exchanger. The size of such heat exchangers can be reduced through enhancement of transport coefficients on the air (gas) side, which are usually small compared to the liquid side. In a suggested strategy, oval tubes are used in place of circular tubes, and delta-winglet type vortex generators in various configuration's are mounted on the fin-surface. An evaluation of the strategy is attempted in this investigation. The investigation is carried out for different angles of attack of the winglets to the incoming flow for the case of two winglet pairs. The variation of axial location of the winglets is also considered for one pair of winglets mounted in common-flow-down configuration. The structures of the velocity field and the heat transfer characteristics have been presented. The results indicate that vortex generators in conjunction with the oval tube show definite promise for the improvement of fin-tube heat exchangers. (author)

Tiwari, S.; Maurya, D.; Biswas, G.; Eswaran, V. [Indian Institute of Technology, Kanpur (India). Dept. of Mechanical Engineering

2003-07-01

34

A simple and accurate numerical network flow model for bionic micro heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Heat exchangers are often associated with drawbacks like a large pressure drop or a non-uniform flow distribution. Recent research shows that bionic structures can provide possible improvements. We considered a set of such structures that were designed with M. Hermann's FracTherm {sup registered} algorithm. In order to optimize and compare them with conventional heat exchangers, we developed a numerical method to determine their performance. We simulated the flow in the heat exchanger applying a network model and coupled these results with a finite volume method to determine the heat distribution in the heat exchanger. (orig.)

Pieper, M.; Klein, P. [Fraunhofer Institute (ITWM), Kaiserslautern (Germany)

2011-05-15

35

A simple and accurate numerical network flow model for bionic micro heat exchangers  

Science.gov (United States)

Heat exchangers are often associated with drawbacks like a large pressure drop or a non-uniform flow distribution. Recent research shows that bionic structures can provide possible improvements. We considered a set of such structures that were designed with M. Hermann's FracTherm® algorithm. In order to optimize and compare them with conventional heat exchangers, we developed a numerical method to determine their performance. We simulated the flow in the heat exchanger applying a network model and coupled these results with a finite volume method to determine the heat distribution in the heat exchanger.

Pieper, M.; Klein, P.

2011-05-01

36

A REVIEW ON EFFECT OF VORTEX GENERATORS ON FLOW CHARACTERISTICS AND HEAT TRANSFER IN HEAT EXCHANGERS  

Directory of Open Access Journals (Sweden)

Full Text Available The development of high-performance thermal systems has increased interest in heat transfer enhancement techniques. The high thermal performance enhancement of heat exchanger systems is needed to use energy source efficiently due to the sky-rocketing prices of petroleum and coal fuels. Heat exchangers are widely used in industry both for cooling and heating. Insertion of turbulator in the flow passage is one of the favorable passive heat transfer augmentation techniques due to their advantages of easy fabrication, operation as well as low maintenance. The purpose of this experiment is to find the efficient shape and size of the vortex generator by using and comparing various types of Winglet pairs.

S.A.Wani

2015-02-01

37

Modeling of turbulent heat transfer and thermal dispersion for flows in flat plate heat exchangers  

International Nuclear Information System (INIS)

In this paper, heat transfer and dispersion for both laminar and turbulent regimes in heat exchangers and nuclear cores are considered. Such hydraulic systems might be seen as spatially periodic porous media. The existence of a turbulent flow within a porous medium structure suggests the use of a spatial average operator, combined to a statistical average operator. Previous works [M.H.J. Pedras, M.J.S. De Lemos, Macroscopic turbulence modeling for incompressible flow through un-deformable porous media, Int. J. Heat Mass Transfer 44 (2001) 1081-1093; F. Kuwahara, A. Nakayama, H. Koyama, A numerical study of thermal dispersion in porous medium, J. Heat Transfer 118 (1996) 756-761] have applied a double average procedure to the thermal balance equation, which led to a macroscopic turbulent transport and a subsequent macro-scale equation featuring dynamic dispersion. Considering the heat flux at the solid surfaces as a boundary condition for the fluid energy balance, the model proposed in this paper allows one to take into account this dispersion as the sum of two contributions. The first one is the classical dispersion due to velocity heterogeneities [G. Taylor, Dispersion of solute matter in solvent flowing slowly through a tube, Proc. Roy. Soc. Lond. A 219 (1953) 186-203] and the second one is due to wall heat transfer. Applying Whitaker up-scaling method [S. Whitaker, Theory and. applications of transport in porous media: the method of volume averaging, Kluwer Academimethod of volume averaging, Kluwer Academic Publishers, 1999], a 'closure problem' is then derived for a representative elementary volume, using the so-called Boussinesq approximation to account for small scale turbulence. The model is used to compute macro-scale heat transfer properties for turbulent flows inside a flat plate heat exchanger. It is shown that, for such flows, both dispersive fluxes strongly predominate over the macroscopic turbulent. heat flux. (authors)

38

Flow boiling heat transfer of ammonia/water mixture in a plate heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

The objective of this work is to contribute to the development of plate heat exchangers as desorbers for ammonia/water absorption refrigeration machines driven by waste heat or solar energy. In this study, saturated flow boiling heat transfer and the associated frictional pressure drop of ammonia/water mixture flowing in a vertical plate heat exchanger is experimentally investigated. Experimental data is presented to show the effects of heat flux between 20 and 50 kW m{sup -2}, mass flux between 70 and 140 kg m{sup -2} s{sup -1}, mean vapour quality from 0.0 to 0.22 and pressure between 7 and 15 bar, for ammonia concentration between 0.42 and 0.62. The results show that for the selected operating conditions, the boiling heat transfer coefficient is highly dependent on the mass flux, whereas the influence of heat flux and pressure are negligible mainly at higher vapour qualities. The pressure drop increases with increasing mass flux and quality. However, the pressure drop is independent of the imposed heat flux. (author)

Taboas, Francisco [Universidad de Cordoba, Campus de Rabanales, Edificio Leonardo da Vinci, 14014 Cordoba (Spain); Valles, Manel; Bourouis, Mahmoud; Coronas, Alberto [CREVER - Universitat Rovira i Virgili, Av. Paisos Catalans No. 26, 43007 Tarragona (Spain)

2010-06-15

39

Analysis of fluid flow and heat transfer in a double pipe heat exchanger with porous structures  

Energy Technology Data Exchange (ETDEWEB)

A numerical study of flow and heat transfer characteristics is made in a double pipe heat exchanger with porous structures inserted in the annular gap in two configurations: on the inner cylinder (A) and on both the cylinders in a staggered fashion (B). The flow field in the porous regions is modelled by the Darcy-Brinkman-Forchheimer model and the finite volume method is used to solve the governing equations. The effects of several parameters such as Darcy number, porous structures thickness and spacing and thermal conductivity ratio are considered in order to look for the most appropriate properties of the porous structures that allow optimal heat transfer enhancement. It is found that the highest heat transfer rates are obtained when the porous structures are attached in configuration B especially at small spacing and high thicknesses. (author)

Targui, N.; Kahalerras, H. [Faculty of Mechanical and Process Engineering, Houari Boumediene University of Sciences and Technology, B.P. 32, El Alia, Bab Ezzouar, 16111 Algiers (Algeria)

2008-11-15

40

Analysis of fluid flow and heat transfer in a double pipe heat exchanger with porous structures  

International Nuclear Information System (INIS)

A numerical study of flow and heat transfer characteristics is made in a double pipe heat exchanger with porous structures inserted in the annular gap in two configurations: on the inner cylinder (A) and on both the cylinders in a staggered fashion (B). The flow field in the porous regions is modelled by the Darcy-Brinkman-Forchheimer model and the finite volume method is used to solve the governing equations. The effects of several parameters such as Darcy number, porous structures thickness and spacing and thermal conductivity ratio are considered in order to look for the most appropriate properties of the porous structures that allow optimal heat transfer enhancement. It is found that the highest heat transfer rates are obtained when the porous structures are attached in configuration B especially at small spacing and high thicknesses

41

Heat Exchange Between a Liquid Flowing in a Tube and an External Flow Around it with Intense Stirring  

Science.gov (United States)

A mathematical model of heat exchange between a tube (a coil) with a liquid flowing inside it and an external flow around it is considered. Limiting equations of the process with intense stirring are derived. Some solutions of the proposed equations are obtained that can be used in modeling the processes occurring in heat exchangers.

Moshinskii, A. I.

2014-11-01

42

Numerical Analysis of Heat Transfer and Fluid Flow in Heat Exchangers with Emphasis on Pin Fin Technology  

OpenAIRE

One of the most important industrial processes is heat transfer, carried out by heat exchangers in single and multiphase flow applications. Despite the existence of well-developed theoretical models for different heat transfer mechanisms, the expanding need for industrial applications requiring the design and optimization of heat exchangers, has created a solid demand for experimental work and effort. This thesis concerns the use of numerical approaches to analyze and optimize heat transfer a...

Nabati, Hamid

2012-01-01

43

Borehole Heat Exchangers: heat transfer simulation in the presence of a groundwater flow  

Science.gov (United States)

The correct design of the Borehole Heat Exchanger is crucial for the operation and the energy performance of a Ground Source Heat Pump. Most design methods and tools are based on the assumption that the ground is a solid medium where conduction is the only heat transfer mechanism. In turn in regions rich in groundwater the groundwater flow influence has to be assessed, by including the convection effects. In this paper a numerical model of a 100 m U-pipe in a saturated porous medium is presented. The model is created adopting MT3DMS coupled to MODFLOW. A Darcy flow is imposed across the medium. The typical operation of a Borehole Heat Exchanger operating both in winter and in summer is simulated for two years, under different groundwater velocities. The energy injected to and extracted from the ground is derived as a function of the Darcy velocity and compared with the purely conductive case. Temperature fields in the ground at key moments are shown and discussed. From both the energy and the aquifer temperature field points of view, the velocity ranges for respectively negligible and relevant influence of the groundwater flow are identified.

Angelotti, A.; Alberti, L.; La Licata, I.; Antelmi, M.

2014-04-01

44

Thermoacoustics and related oscillatory heat and fluid flows in microheat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Classical linear thermoacoustic theory is applied to compact micro heat exchangers and the validity of such calculus applied to micro scale is discussed. Expressions for the radial profiles and average values of the fluid axial velocity and temperature are demonstrated, formulations for first order friction and heat transfer coefficients of oscillating flows are deduced. It is shown how aerodynamic and thermal performances of a micro heat exchanger in pulsed flow regime can be characterized with three factors: a thermal characteristic time, an aerodynamic matrix of transfer and a thermal efficiency. The model proposed is devoted to design the micro heat exchangers of micro refrigerators dedicated to the cooling of electronic components. (author)

Nika, P.; Bailly, Y.; Guermeur, F. [UMR CNRS, Belfort (France). Dept. CREST FEMTO-ST UMR

2005-08-01

45

Pressure loss and heat transfer studies performed on axial-flow finned-tube bundle heat exchangers  

International Nuclear Information System (INIS)

The experimental studies intend to determine the dependence on the parameters of influence state of flow, tube length, and bundle pitch of the heat transfer and pressure loss characteristic of two tube types in the bundle. By means of suitable parameters for heat flow and pressure loss a comparison will be made of the heat transfer and pressure loss power of the axial-flow furried-tube bundle systems investigated here and conventional heat exchangers. (orig.)

46

Heat exchanger  

International Nuclear Information System (INIS)

Heat exchangers for use in uranium enrichment plant are subject to particularly stringent safety requirements and should be capable of being repaired and maintained quickly. It is proposed to improve a heat exchanger which has a roller type of design consisting of heat exchanger tubes arranged around a core tube, which are connected together in tube floors. According to the invention the tube floors are connected solidly to the outer jacket (possibly via intermadiate pieces), while the heat exchanger tubes end at the side near the inside of the jacket in the tube floors. Manufacture can be further simplified if core tube, roller and outer jacket which are solidly connected form a compact unit. (UWI)

47

Theoretical investigation on thermal performance of heat pipe flat plate solar collector with cross flow heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

Based on the heat transfer characteristics of absorber plate and the heat transfer effectiveness-number of heat transfer unit method of heat exchanger, a new theoretical method of analyzing the thermal performance of heat pipe flat plate solar collector with cross flow heat exchanger has been put forward and validated by comparisons with the experimental and numerical results in pre-existing literature. The proposed theoretical method can be used to analyze and discuss the influence of relevant parameters on the thermal performance of heat pipe flat plate solar collector. (orig.)

Xiao, Lan; Wu, Shuang-Ying; Zhang, Qiao-Ling; Li, You-Rong [Chongqing University, Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education, Chongqing (China); Chongqing University, College of Power Engineering, Chongqing (China)

2012-07-15

48

Numerical simulation of fluid flow and heat transfer in a concentric tube heat exchanger  

International Nuclear Information System (INIS)

In this paper, numerical simulation of a concentric tube heat exchanger is presented to determine the convective heat transfer coefficient and friction factor in a smooth tube. Increasing the convective heat transfer coefficient can increase heat transfer rate in a concentric tube heat exchanger from a given tubular surface area. This can be achieved by using heat transfer augmentation devices. This work constitutes the initial phase of the numerical simulation of heat transfer from tubes employing augmentation devices, such as twisted tapes, wire-coil inserts, for heat transfer enhancement. A computational fluid dynamics (CFD) simulation tool was developed with CFX software and the results obtained from the simulations are validated with the empirical correlations for a smooth tube heat exchanger. The difficulties associated with the simulation of a heat exchanger augmented with wire-coil inserts are discussed. (author)

49

Two models for the dynamics of a cross flow heat exchanger  

International Nuclear Information System (INIS)

Two models of a cross flow heat exchanger, a concentric tube counter flow model and a cross flow model, are studied theoretically. Differential equations describing the behaviour of the models are derived and from them equations for the steady state temperatures and the temperature transfer functions are obtained. (author)

50

Investigation of the flow conditions in a high-performance heat exchanger  

Science.gov (United States)

CFD (Computational Fluid Dynamics) computations are carried out in order to investigate the flow distribution and its influence on the heat transfer processes in the high-performance heat exchanger. The subject of this investigation is the classical model of the high-performance heat exchanger with elliptical tubes and rectangular fins. It is possible to find the flow domains where the heat transfer conditions are impaired due to the fully developed turbulent flow. Therefore, the considerable thermal loads occur that may cause the breakdown of the heat exchanger. The emphasis of this investigation is put on the zones and the locations where the tubes are not properly fed with liquid, that result in occurrence of cavitation.

?opata, Stanis?aw; Oc?oñ, Pawe?

2010-09-01

51

3D numerical simulation on fluid flow and heat transfer characteristics in multistage heat exchanger with slit fins  

Energy Technology Data Exchange (ETDEWEB)

In this paper, a numerical investigation is performed for three-stage heat exchangers with plain plate fins and slit fins respectively, with a three-dimensional laminar conjugated model. The tubes are arranged in a staggered way, and heat conduction in fins is considered. In order to save the computer resource and speed up the numerical simulation, the numerical modeling is carried out stage by stage. In order to avoid the large pressure drop penalty in enhancing heat transfer, a slit fin is presented with the strip arrangement of ''front coarse and rear dense'' along the flow direction. The numerical simulation shows that, compared to the plain plate fin heat exchanger, the increase in the heat transfer in the slit fin heat exchanger is higher than that of the pressure drop, which proves the excellent performance of this slit fin. The fluid flow and heat transfer performance along the stages is also provided. (orig.)

Tao, W.Q. [Xi' an Jiaotong University, State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an (China); Cheng, Y.P.; Lee, T.S. [National University of Singapore, Laboratory of Fluid Mechanics, Department of Mechanical Engineering, Singapore (Singapore)

2007-11-15

52

Low flow velocity, fine-screen heat exchangers and vapor-cooled cryogenic current leads  

International Nuclear Information System (INIS)

The design, construction, and testing of three compact, low temperature heat exchangers are reported. A method is given for the construction of a small (approximately = 20-cm3 volume) exchanger that can handle 6 g/s helium flow with low pressure drops (?P/P = 10 percent) and adequate heat transfer (N/sub tu/ = 3). The use of screen for simple, vapor-cooled current leads into cryogenic systems is also discussed

53

Analysis of flow boiling of ammonia and R-114 in a matrix heat exchanger  

Science.gov (United States)

An analysis is carried out for flow boiling in a vertical matrix aluminum heat exchanger. The prediction model, developed for thin film evaporation in a previous study, is extended to include heat transfer in the slug-flow regime that exists at low mass qualities. Appropriate criteria is used to switch from slug-flow to thin-film annular-flow analysis. The two-phase-flow convective heat transfer enhancement for the slug-flow is correlated with inclusion of fluid Reynolds and Prandtl numbers in addition to commonly used Martinelli parameter. This approach reflects transient nature of heat transfer in the slug-flow regime. The thin-film annular-flow analysis developed in the previous study is refined with inclusion of a reliable two-phase friction factor correlation. The experimentally measured pressure drop is used to validate the friction factor correlation. The resulting prediction method is used to predict exit mass qualities for ammonia and R-114. The experimental analysis includes flow boiling of ammonia and R-114 in a vertical brazed-aluminum matrix heat exchanger. The test unit has straight perforated fins on the fluid side and extruded rectangular channels on the single-phase (water) heating-media side. Only two parameters are adjusted to validate the analytical prediction method, the constant in the friction factor correlation, and the constant in the slug-flow heat transfer correlation. The results show that the combination of slug-flow and thin-film annular-flow model gives better prediction of the overall performance of the matrix heat exchanger than a single model applied for the whole range of mass qualities.

Panchal, C. B.

1989-05-01

54

Heat exchanger  

International Nuclear Information System (INIS)

A heat exchanger such as forms, for example, part of a power steam boiler is made up of a number of tubes that may be arranged in many different ways, and it is necessary that the tubes be properly supported. The means by which the tubes are secured must be as simple as possible so as to facilitate construction and must be able to continue to function effectively under the varying operating conditions to which the heat exchanger is subject. The arrangement described is designed to meet these requirements, in an improved way. The tubes are secured to a member extending past several tubes and abutment means are provided. At least some of the abutment means comprise two abutment pieces and a wedge secured to the supporting member, that acts on these pieces to maintain the engagement. (U.K.)

55

Dynamic model of counter flow air to air heat exchanger for comfort ventilation with condensation and frost formation  

OpenAIRE

In cold climates heat recovery in the ventilation system is essential to reduce heating energy demand. Condensation and freezing occur often in efficient heat exchangers used in cold climates. To develop efficient heat exchangers and defrosting strategies for cold climates, heat and mass transfer must be calculated under conditions with condensation and freezing. This article presents a dynamic model of a counter flow air to air heat exchanger taking into account condensation and freezing and...

Nielsen, Toke Rammer; Rose, Jørgen; Kragh, Jesper

2007-01-01

56

Experimental research on heat transfer coefficients for cryogenic cross-counter-flow coiled finned-tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

The aim of present experimental research is to find out the suitable correlations for designing the coiled finned-tube heat exchangers used in cryogenic applications. In order to conduct above experimental study, cross-counter-flow coiled finned-tube heat exchangers were developed in our lab and used in actual refrigeration cycle. The experiments were conducted in the range of effective Reynolds number 500-1900. The effect of diametrical clearance on the prediction of overall heat transfer coefficient is also investigated experimentally. The results from present study were compared in the form of overall heat transfer coefficient. Results of present experimental research indicate that different correlations selected in the study can be used with reasonable accuracy for designing the coiled finned-tube heat exchangers, if they are applied with suitable method of calculation of free-flow cross-sectional area. A more accurate new correlation has also been proposed that fitted experimental data within {+-}10% error band. (author)

Gupta, Prabhat Kumar; Kush, P.K. [Cryogenics Section, Raja Ramanna Centre for Advanced Technology (RRCAT), Indore 452013, Madhya Pradesh (India); Tiwari, Ashesh [Institute of Engineering and Technology, DAVV, Indore, Madhya Pradesh (India)

2009-08-15

57

Double tube heat exchanger with novel enhancement: Part I - flow development length and adiabatic friction factor  

Energy Technology Data Exchange (ETDEWEB)

The study is conducted to evaluate the flow characteristics in a double tube heat exchanger using two new and versatile enhancement configurations. The novelty is that they are usable in single phase forced convection, evaporation and condensation. Correlations are proposed for flow development length and friction factor for use in predicting fluid pumping power in thermal equipment as well as in subsequent heat transfer characterization of the surface. (orig.)

Tiruselvam, R.; Raghavan, Vijay R. [Universiti Teknologi PETRONAS, Faculty of Mechanical Engineering, Tronoh (Malaysia)

2012-04-15

58

Air side flow analysis of fin-tube heat exchanger with vortex generator  

Energy Technology Data Exchange (ETDEWEB)

Fin-tube heat exchangers are widely used in refrigeration systems. To improve the performance of fin-tube heat exchangers, the shape of plain fin was developed in slit fin and louver fin. These pins have higher heat transfer performance as well as larger pressure drop. Recent studies of a Delta Winglet Vortex Generator (DWVG) show less heat transfer capacity than louver fin. However, the DWVG has very small pressure drop. This paper compares the performance for the plain fin and DWVG fin in terms of flow characteristics and heat transfer based on CFD analyses. The DWVG generates vortex and delayed flow separation and leads to a reduction of a wake region behind a tube. The results show that the DWVG produces improved heat transfer and reduced pressure drop compared to a plain fin. This result is opposite to the Reynolds analogy.

Hwang, Seong Won; Jeong, Ji Hwan [Pusan National University, Busan (Korea, Republic of)

2009-07-01

59

Velocity Boundary Layer Analysis: A Flat Plate Heat Exchanger in Laminar Flow  

Directory of Open Access Journals (Sweden)

Full Text Available Plate heat exchangers (PHEs are among the most applicable thermal facilities in diverse industries, particularly in oil and gas operations. Due to their high thermal efficiencies, PHEs are widely used in industries.Plate heat exchangers are mainly made of thin plates that are pressed into a whole frame and shaped in a package. They are designed in various types based on which the plates might be flat or curved with different angles according to their applications. PHEs are much more sensitive to temperature and pressure than other heat exchangers. Their sensitivity is due to their structures that are mainly specified by plate perforations and gasket designs.In this article, a behavioral analysis of velocity Boundary layer in a flat plate heat exchanger in laminar flow condition through CFD simulation using software is done. The main objective of this study is to determine the velocity vectors between the flat plates of heat exchanger. In addition wake occurrence, differences of velocity at different surfaces between plates, angles of velocity vectors and effect of wake phenomenon on the shear stresses exerted on the plates are discussed in detail. The study reveals results graphically based on fluid’s behavior in co-current and counter current flows and discusses thermal indexes consisting of heat transfer coefficient, Nusslet and total heat flux in both conditions.

Yasin Ramezani

2013-05-01

60

Oscillating flow loss test results in Stirling engine heat exchangers. Final Report  

Energy Technology Data Exchange (ETDEWEB)

The results are presented for a test program designed to generate a database of oscillating flow loss information that is applicable to Stirling engine heat exchangers. The tests were performed on heater/cooler tubes of various lengths and entrance/exit configurations, on stacked and sintered screen regenerators of various wire diameters and on Brunswick and Metex random fiber regenerators. The test results were performed over a range of oscillating flow parameters consistent with Stirling engine heat exchanger experience. The tests were performed on the Sunpower oscillating flow loss rig which is based on a variable stroke and variable frequency linear drive motor. In general, the results are presented by comparing the measured oscillating flow losses to the calculated flow losses. The calculated losses are based on the cycle integration of steady flow friction factors and entrance/exit loss coefficients.

Koester, G.; Howell, S.; Wood, G.; Miller, E.; Gedeon, D.

1990-05-01

61

Heat exchangers  

International Nuclear Information System (INIS)

Reference is made to ''tube-in-shell'' heat exchangers. Hitherto it has been the practice to seal the tubes to a tube sheet by welding, but frequently the welds fail, probably as a result of stress corrosion, and repair is a very difficult operation because there are so many closely spaced tubes. In the arrangement described welding is avoided by employing what are known as compression pipe couplings, the construction of which is described. The arrangement is particularly applicable to liquid metal cooled reactors. (UK)

62

Analysis of loss-of-flow transients in the intermediate heat exchanger using the COMMIX code  

International Nuclear Information System (INIS)

The intermediate heat exchanger (IHX) is an important component of the liquid-metal fast breeder reactor (LMFBR). It plays a very important role in the safe and reliable operation of a nuclear plant. Evaluation of thermal-hydraulic conditions are important in the design and development of a reliable and economical heat exchanger. These evaluations would provide complete maps of the temperature field of both the working fluids and the heat transfer tube. The maps are used for a large range of operating conditions, including nominal as well as off-nominal. Knowledge of temperature and flow distribution in both the shell and the tube side will ensure that the unit will meet its thermal performance requirements. Moreover, information is needed to provide proper evaluation of the thermal performance characteristics of a heat exchanger under the natural circulation conditions that result from a loss of coolant. The flow pattern and the thermal map of a shell-and-tube heat exchanger may be obtained either through actual testing of a scale model or by using analytical methods. To provide these evaluations multidimensional thermal-hydraulic codes are assessed for heat exchanger applications. The purpose of this paper is to present the thermal performance evaluation of the IHX of the Fast Flux Test Facility (FFTF) during a loss-of-coolant transient using the COMMIX-1B code and to compare the results with experimental data

63

Calculation of temperature field and flow field in 200 MW NHR's primary heat exchanger  

International Nuclear Information System (INIS)

The Primary Heat Exchanger (PHE) is a key component of the Nuclear Heating Reactor (NHR), which transfers heat from the primary circuit to the secondary circuit. The temperature field and the flow field in the PHE are very important for the PHE design. the flow field and the temperature field were analyzed numerically. The U-tubes are first divided into 4 regions in a planar network. The calcination can be divided into two parts, calculating the temperature field with a given flow field and calculating the flow field with a given temperature field. The temperature field is calculated using the energy balance equation. The flow field is calculated using pressure drop balance equations. Newton iteration is used to solve the non-linear equations. The results describe the thermal power distribution and the heat transfer coefficient

64

Algebraic solution of capillary tube flows. Part II: Capillary tube suction line heat exchangers  

International Nuclear Information System (INIS)

Capillary tube suction line heat exchangers have been modeled using both numerical and analytical approaches. The former requires a reasonable understanding of the governing heat and fluid flow equations, thermodynamic relations, numerical methods, and computer programming, and therefore are not suitable for most refrigeration and air-conditioning practitioners. Alternatively, empirical algebraic formulations for diabatic capillary tube flows have been proposed in the literature, in spite of their lack of generality and accuracy. This paper introduces a physically consistent, unconditionally convergent, easy-to-implement semi-empirical algebraic model for capillary tube suction line heat exchangers, with the same level of accuracy as found with more sophisticated first-principles models. The methodology treats the refrigerant flow and the heat transfer as independent phenomena, thus allowing the derivation of explicit algebraic expressions for the refrigerant mass flow rate and the heat exchanger effectiveness. The thermal and hydraulic models are then conflated through the so-called Buckingham-? theorem using in-house experimental data collected for diabatic capillary tube flows of refrigerants HFC-134a and HC-600a. Comparisons between the model predictions and the experimental data revealed that more than 90% and nearly 100% of all data can be predicted within ±10% and ±15% error bands, respectively.

65

Theoretical and experimental investigation of wickless heat pipes flat plate solar collector with cross flow heat exchanger  

International Nuclear Information System (INIS)

In this work, a wickless heat pipes flat plate solar collector with a cross flow heat exchanger was investigated theoretically and experimentally under the meteorological conditions of Cairo, Egypt. The author's earlier simulation program of wickless heat pipes flat plate solar water heaters was modified to be valid for the present type of wickless heat pipes solar collector by including the solution of the dimensionless governing equations of the present analysis. For verifying the modified simulation program, a wickless heat pipes flat plate solar collector with a cross flow heat exchanger was designed, constructed, and tested at different meteorological conditions and operating parameters. These parameters include different cooling water mass flow rates and different inlet cooling water temperatures. The comparison between the experimental results and their corresponding simulated ones showed considerable agreement. Under different climatic conditions, the experimental and theoretical results showed that the optimal mass flow rate is very close to the ASHRAE standard mass flow rate for testing conventional flat plate solar collectors. Also, the experimental and theoretical results indicated that the number of wickless heat pipes has a significant effect on the collector efficiency

66

Empirical correlation for the time lag of double pipe heat exchanger operating with variable flow rates  

International Nuclear Information System (INIS)

The behavior of a heat exchanger in variable regime can be described by a two parameter model with a time lag and a time constant. In many studies, the analytical calculation based on the energy balance permitted to express the time constant in various configurations of the device operating. However, the time lag is only experimentally determined. We propose in this paper an empirical method for the prediction of this parameter when a double pipe heat exchanger is submitted to a flow rate step at the entrance. Experimental data are used for developing correlations of both hot and cold fluids

67

INTENSIFICATION OF HEAT TRANSFER AND FLOW IN HEAT EXCHANGER WITH SHELL AND HELICALLY COILED TUBE BY USING NANO FLUIDS  

Directory of Open Access Journals (Sweden)

Full Text Available This article presents an experimental study on enhancement of heat transfer and pressure drop of nanofluids flow. In this study the method using to enhancement of heat transfer and pressure drop, by used the helically coiled tube heat exchange and the nanofluids instead of the base fluid (oil. The concentrations of nanofluid used are ranging from (5 – 30 wt%. The shell of the heat exchanger is constant wall temperature (CWT . Two types of nanoparticles used in this paper silver (Ag (30nm and Titanium Oxide (TiO2 (50nm as well as the base fluid (oil. The effect of different parameters such as flow Reynolds number, nanofluid temperature, concentration and type of nanoparticle on heat transfer coefficient and pressure drop of the flow are studied at constant wall temperature. The obtained results show an increase in heat transfer coefficient of 45.35% for Ag + oil and 32.29% for TiO2 + oil at concentration of 30 wt % compared with base fluid (oil. The heat transfer coefficient and pressure drop is increased by using nanofluids (Ag, TiO2 – oil instead of the base fluid (oil. In addition the results indicated that by using heat exchanger with shell and helically coiled tube, the heat transfer performance is improved as well as the pressure drop enhancement due to the curvature of the tube. Furthermore, a maximum increase of 34.15% (Ag + Oil and 27.23% (TiO2+ Oil in Nusselt number ratio for a range of Reynolds numbers between 20 and 200. This paper decided that the nanofluid behaviors are close to typical Newtonian fluids through the relationship between viscosity and shear rate. Moreover to performance index are used to present the corresponding flow and heat transfer technique. The type and size nanoparticles play an important role in enhancement of heat transfer rate

Dr. Khalid Faisal Sultan

2015-01-01

68

Numerical investigation of a high-temperature counter-flow compact heat exchanger  

International Nuclear Information System (INIS)

Very High Temperature Reactors (VHTRs) require high temperature, high integrity, and highly effective heat exchangers during normal and off-normal conditions. A class of compact plate-type heat exchanger, Printed Circuit Heat Exchangers (PCHEs) is being considered for use in VHTRs. In the current study, simplified and full-size PCHE models are investigated numerically using FluentTM software. The geometry considered in the study replicate the PCHEs that were fabricated using Alloy 617 plates for use in a high-temperature helium test facility at The Ohio State University. The cases considered are based upon the design conditions of the high-temperature test facility: operating pressure of 3 MPa, hot side inlet temperature of 1,173 K, cold side inlet temperature of 813 K, and mass flow rates ranging from 10 to 80 kg/h. The ranges of mass flow rates and temperatures correspond to laminar and laminar-to-turbulent transition flows in the PCHE flow passages. Heat transfer and pressure drop are evaluated in both models to provide preliminary performance data for the laboratory scale PCHEs to be operated at temperatures similar to those of the VHTRs. Local convective heat transfer coefficients are calculated for channels on the hot and cold sides and compared to published experimental results for the laminar flow cases and the Gnielinski correlation for the transition flow cases. The overall heat transfer coefficient ranges from 563-1,697 W/m2-K. The max from 563-1,697 W/m2-K. The maximum pressure drop in this particular PCHE is found to be approximately 1.5% of the system operating pressure. The calculated convective heat transfer coefficients and pressure drop compare well with the models in the literature. (author)

69

Random excitation of heat exchanger tubes by cross-flows  

International Nuclear Information System (INIS)

This paper investigates the random excitation mechanism of tube arrays in cross-flow, also often called ''turbulent buffeting''. It summarizes the experimental data obtained so far at CEA-Saclay on various tube bundles subjected to single and to two-phase flows. An attempt is made to put them into an appropriate theoretical framework. The formalism used to reduce the force spectra produced by single-phase cross-flow is first reviewed. It allows the determination of a reduced force spectrum which is found to be fairly independent of the tube array geometry. On the other hand, the situation in two-phase flow still remains insufficiently documented. Based on the restricted data set obtained at Saclay in the high void fraction range, random forces produced by air-water and by steam-water mixtures would be of the same order of magnitude. Only a crude estimate of it can be produced by using the single-phase force spectrum together with the homogenous two-phase flow model without slip. Further investigations are still clearly required to confirm such preliminary conclusions and to derive the physically relevant scaling factors to reduce conveniently the two-phase data. (author)

70

Flow-induced vibration analysis of heat exchanger and steam generator designs  

International Nuclear Information System (INIS)

Tube and shell heat exchange components such as steam generators, heat exchangers and condensers are essential parts of CANDU (CANadian Deuterium Uranium) nuclear power stations. A flow-induced vibration analysis is presented. In cross-flow three basic flow-induced vibration excitation mechanisms are considered, namely: fluidelastic instability, forced vibration response due to random flow turbulence and periodic wake shedding (the first two mechanisms in both liquid and two-phase cross-flow). Periodic wake shedding has not been detected in two-phase flow but is possible in liquid flow. It is only significant for upstream tube rows. Random flow turbulence is he dominant excitation in both liquid and two-phase axial flow. These vibration excitation mechanisms and the dynamics of multispan tubes are formulated in a computer model. The model predicts tube vibration response and critical velocities for fluidelastic instability. A description of the model is given. The vibration analysis of a steam generator is outlined as an example. The parameters required to formulate the vibration excitation mechanisms are discussed. Periodic wake shedding excitation is formulated in terms of a Strouhal No. and a lift coefficient which is generally less than unity. Fluidelastic instability thresholds are related to dimensionless flow velocity and dimensionless damping for both liquid and two-phase cross-flow. Some statistical parameters to describe random flow turbulence excitation areribe random flow turbulence excitation are deduced from experimental data. The power spectral density of the latter is related to a power of the flow velocity. The velocity exponent is roughly two for liquid flow and near unity for two-phase flow. For a given mass flux, the random excitation reaches a maximum at a steam quality of roughly 15%. Damping in two-phase flow is found to be at least four times greater than in liquid flow

71

Entropy Generation Minimization in a Ram-Air Cross-Flow Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents the constrained thermodynamic optimization of a crossflow heat exchanger with ram air on the cold side. The ram-air stream passes through a diffuser before entering the heat exchanger, and exits through a nozzle. This configuration is used in the environmental control systems of aircraft. In the first part of the study the heat exchanger is optimized alone, subject to fixed total volume and volume fraction occupied by solid walls. Optimized geometric features such as the ratio of channel spacings and flow lengths are reported. It is found that the optimized features are relatively insensitive to changes in other physical parameters of the installation. In the second part of the study the entropy generation rate also accounts for the irreversibility due to discharging the ram-air stream into the atmosphere. The optimized geometric features are relatively insensitive to this additional effect, emphasizing the robustness of the thermodynamic optimum.

Adrian Bejan

1999-12-01

72

Buffeting of heat exchanger tube arrays in a cross flow  

International Nuclear Information System (INIS)

A model for turbulence-induced vibration of tube arrays in a cross flow is presented and compared with experimental data. The model is based on random vibration theory. The model is found to provide reasonable agreement with experimental data for tube arrays not subject to instability. (author)

73

Additions to compact heat exchanger technology: Jet impingement cooling & flow & heat transfer in metal foam-fins  

Science.gov (United States)

Compact heat exchangers have been designed following the same basic methodology for over fifty years. However, with the present emphasis on energy efficiency and light weight of prime movers there is increasing demand for completely new heat exchangers. Moreover, new materials and mesoscale fabrication technologies offer the possibility of significantly improving heat exchanger performance over conventional designs. This work involves fundamental flow and heat transfer experimentation to explore two new heat exchange systems: in Part I, large arrays of impinging jets with local extraction and in Part II, metal foams used as fins. Jet impingement cooling is widely used in applications ranging from paper manufacturing to the cooling of gas turbine blades because of the very high local heat transfer coefficients that are possible. While the use of single jet impingement results in non-uniform cooling, increased and more uniform mean heat transfer coefficients may be attained by dividing the total cooling flow among an array of smaller jets. Unfortunately, when the spent fluid from the array's central jets interact with the outer jets, the overall mean heat transfer coefficient is reduced. This problem can be alleviated by locally extracting the spent fluid before it is able to interact with the surrounding jets. An experimental investigation was carried out on a compact impingement array (Xn/Djet = 2.34) utilizing local extraction of the spent fluid (Aspent/Ajet = 2.23) from the jet exit plane. Spatially resolved measurements of the mean velocity field within the array were carried out at jet Reynolds numbers of 2300 and 5300 by magnetic resonance velocimetry, MRV. The geometry provided for a smooth transition from the jet to the target surface and out through the extraction holes without obvious flow recirculation. Mean Nusselt number measurements were also carried out for a Reynolds number range of 2000 to 10,000. The Nusselt number was found to increase with the Reynolds number to the 0.6 power with peak Nusselt numbers near 75 at a Reynolds number of 10,000. Open-celled metallic foams offer three important characteristics which enable them to perform well in heat exchange applications. They contain a very large surface area to volume ratio, a highly complex flow passage through the foam, and in many cases, significant thermal conductivity in the solid phase. Unfortunately, difficulty arises when metal foams are implemented in heat exchanger designs. The performance of the foam has not been characterized in a way which is conducive to analytical design of high performance heat exchangers. The second part of this work provides both flow and heat transfer measurements for metal foam geometries. Full-field velocity measurements through a foam sample were acquired using MRV. The measurements show transverse velocities on the order of 25-30% of the Darcy velocity, UD, which produce enhanced thermal dispersion within the foam matrix. A mechanical dispersion coefficient, DM, was formed which demonstrates the transverse dispersion to be 13 times the kinematic viscosity and 9 times the thermal diffusivity of air at 20°C and 1 atm. To describe the heat transfer performance of the foam as a fin, we have developed a new method that utilizes a well documented, periodic heat exchanger core test and a new one heated wall (OHW) test which when used in conjunction are shown to determine the convective performance (hmAc), the conductive performance (ksAc), and the effective bond resistance associated to attaching metal foams to primary heat transfer surfaces (RBond). Small pore diameter foams, d ? 1 mm, where found to perform approximately a factor of 2 greater per unit volume than a comparable fine-fin heat exchanger surface at the same pumping power which points to the fact the foam as a system is conduction limited not convection limited.

Onstad, Andrew J.

74

Study of two-phase flow redistribution between two passes of a heat exchanger  

International Nuclear Information System (INIS)

The object of the present thesis deals with the study of two-phase flow redistribution between two passes of a heat exchanger. Mass flow rate measurements of each component performed at each channel outlet of the second pass allowed us to determine the influence of mass flow, gas quality, flow direction (upward or downward) and common header geometry upon flow redistribution. Local void fraction inside common header was measured with an optical probe. A two-dimensional two-phase flow computational code was developed from a two-fluid model. Modelling of interfacial momentum transfer was used in order to take into account twp-phase flow patterns in common headers. Numerical simulation results show qualitative agreement with experimental results. Present theoretical model limitations are analysed and future improvements are proposed

75

A 2-D oscillating flow analysis in Stirling engine heat exchangers  

Science.gov (United States)

A two-dimensional oscillating flow analysis was conducted, simulating the gas flow inside Stirling heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10800 (Va = 272), 19300 (Va = 272), and 60800 (Va = 126). The results are compared with experimental results of previous investigators. Also, predictions of the flow regime on present oscillating flow conditions were checked by comparing velocity amplitudes and phase differences with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, performance evaluation of the K-epsilon model was made to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.; Ibrahim, Mounir B.

1991-01-01

76

Numerical computations on flow and heat transfer characteristics of a helically coiled heat exchanger using different turbulence models  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • This study investigates thermal–hydraulic behaviors of helically coiled tube HXs. • Three turbulence models are incorporated with N–S equations in simulations. • Flow and heat transfer characteristics in a helically coiled tube HX are captured. • Existing experimental data on Nu number validate the present CFD model. -- Abstract: This study investigates the thermal–hydraulic characteristics of helically coiled tube heat exchangers applied in high temperature gas reactors. In the heat exchanger, the high-temperature helium and the low-temperature water flow through the shell side and the coiled tube, respectively. Three turbulence models are incorporated with Navier–Stokes equations in the numerical simulations: realizable k–?, low-Reynolds k–? and Reynolds stress. Existing experimental data on the Nusselt (Nu) number validate the present CFD simulations using these turbulence models.

Lin, Wei-Cheng [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Ferng, Yuh-Ming, E-mail: ymferng@ess.nthu.edu.tw [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Chieng, Ching-Chang [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon (Hong Kong)

2013-10-15

77

Flow measurement and characterization in shallow geothermal systems used for downhole heat exchanger applications  

Energy Technology Data Exchange (ETDEWEB)

In the largest non-electrical application of geothermal energy presently occurring in the United States, over 400 relatively shallow wells are being used for extraction of energy with downhole heat exchangers. Despite this large amount of application, the exact nature of the flows in the wells has not before been characterized. Knowledge to date on the nature of flows in the systems is summarized, and an ongoing experimental program for making appropriate downhole measurements to determine flows is described in detail. Flow characterization was a principal object of this study. Horizontal cross-flows of geothermal fluid may occur at upper and/or lower levels in the well where perforations in the well casing are situated. In addition, natural convection may induce vertical flows within the well casing which would be influenced by the presence or absence of a heat exchanger. Three main aspects of the experimental program are reported on: (i) a review of potentially applicable methods for measuring vertical and horizontal flows in wells, (ii) the limitations and preliminary results of using a vane anemometer for measuring vertical flows, and (iii) the description of the selected hot-film probe, its associated pressurized calibration facility, and means of making well measurements.

Churchill, D.; Culver, G.G.; Reistad, G.M.

1977-01-01

78

Experiments on flow induced vibrations in a heat exchanger tube bundle  

International Nuclear Information System (INIS)

Most structure and equipment used in nuclear power plant and process plant, such as reactor internals, fuel rod bundles, steam generator tubes and heat exchanger tubes are sub-merged in the fluid. These structures are subjected to flow-induced vibration. An experimental study has been carried out for Reynolds number (7.15 x 103 3) and reduced velocities (1 r < 19) on a research heat exchanger tube bundle to simulate the real conditions. Effect of thermal loading has also been considered. Experimental natural frequencies have been compared to existing literature. Effect of flow rate and pressure on tube drag, lift and axial forces has been analyzed. It has been shown that temperature increase results favorably with respect to stability against vibration as indicated by decrease in volumetric fretting wear loss at loose supports which is due to increase in damping with temperature (thermal damping). (authors)

79

Heat transfer and flow studies of the liquid droplet heat exchanger  

International Nuclear Information System (INIS)

This paper describes a lightweight, highly effective liquid droplet heat exchanger (LDHX) concept for thermal management in space. Heat is transferred by direct contact between fine droplets (100 to 300 micron diameter) of a low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the microgravity environment is accomplished by configuring the LDHX as a vortex chamber. A quasi-one-dimensional, two-phase heat transfer model of the LDHX is developed and used to investigate the potential use of the LDHX for both heating and cooling the working gas in a 100-k W(e) Brayton cycle. Experimental studies on a small scale LDHX chamber, using air and water as the two media, show excellent agreement with the theoretical model. 21 references

80

Simulation of Cross Flow Heat Exchanger for Multi Tubes Using FLUENT 6.3.26  

OpenAIRE

In chemical engineering a lot of work is done to improve the results of the equipment to make its widespread applications be possible. Simulation is extensively used as the power of the computer is well known nowadays. Simulation is frequently used to study both real and virtual behavior. In this paper experimentation, simulation and development of mathematical models are performed. Practical experiments are made on a cross flow heat exchanger for a multi tube layout with staggered arrangemen...

Suneela Sardar; Shahid Raza Malik

2013-01-01

81

Microtube strip heat exchanger  

Science.gov (United States)

Doty Scientific (DSI) believes their microtube-strip heat exchanger will contribute significantly to the following: (1) the closed Brayton cycles being pursued at MIT, NASA, and elsewhere; (2) reverse Brayton cycle cryocoolers, currently being investigated by NASA for space missions, being applied to MRI superconducting magnets; and (3) high-efficiency cryogenic gas separation schemes for CO2 removal from exhaust stacks. The goal of this current study is to show the potential for substantial progress in high-effectiveness, low-cost, gas-to-gas heat exchangers for diverse applications at temperatures from below 100 K to above 1000 K. To date, the highest effectiveness measured is about 98 percent and relative pressure drops below 0.1 percent with a specific conductance of about 45 W/kgK are reported. During the pre-award period DSI built and tested a 3-module heat exchanger bank using 103-tube microtube strip (MTS) modules. To add to their analytical capabilities, DSI has acquired computational fluid dynamics (CFD) software. This report describes the pre-award work and the status of the ten tasks of the current project, which are: analyze flow distribution and thermal stresses within individual modules; design a heat exchanger bank of ten modules with 400 microtube per module; obtain production quality tubestrip die and AISI 304 tubestrips; obtain production quality microtubing; construct revised MTS heat exchanger; construct dies and fixtures for prototype heat exchanger; construct 100 MTS modules; assemble 8 to 10 prototype MTS heat exchangers; test prototype MTS heat exchanger; and verify test through independent means.

Doty, F. D.

1990-12-01

82

Heat exchanger restart evaluation  

International Nuclear Information System (INIS)

On December 24, 1991, the K-Reactor was in the shutdown mode with full AC process water flow and full cooling water flow. Safety rod testing was being performed as part of the power ascension testing program. The results of cooling water samples indicated tritium concentrations higher than allowable. Further sampling and testing confirmed a Process Water System to Cooling Water System leak in heat exchanger 4A (HX 4A). The heat exchanger was isolated and the plant shutdown. Heat exchanger 4A was removed from the plant and moved to C-Area prior to performing examinations and diagnostic testing. This included locating and identifying the leaking tube or tubes, eddy current examination of the leaking tube and a number of adjacent tubes, visually inspecting the leaking tube from both the inside as well as the area surrounding the identified tube. The leaking tube was removed and examined metallurgically to determine the failure mechanism. In addition ten other tubes that either exhibited eddy current indications or would represent a baseline condition were removed from heat exchanger 4A for metallurgical examination. Additional analysis and review of heat exchanger leakage history was performed to determine if there are any patterns which can be used for predictive purposes. Compensatory actions have been taken to improve the sensitivity and response time to any future events of this type. The results of these actions are summarized

83

Modeling free convection flow of liquid hydrogen within a cylindrical heat exchanger cooled to 14 K  

OpenAIRE

A liquid hydrogen in a absorber for muon cooling requires that up to 300 W be removed from 20 liters of liquid hydrogen. The wall of the container is a heat exchanger between the hydrogen and 14 K helium gas in channels within the wall. The warm liquid hydrogen is circulated down the cylindrical walls of the absorber by free convection. The flow of the hydrogen is studied using FEA methods for two cases and the heat transfer coefficient to the wall is calculated. The first case is when the wa...

Yang, Sq; Green, Ma; Lau, W.

2005-01-01

84

Comparison of calculated results from two analytical models with measured data from a heat-exchanger flow test  

International Nuclear Information System (INIS)

Predicted results from both a network flow model and a turbulent flow model were compared with measured results from an air flow test on a half-scale model of the auxiliary heat exchanger for a high-temperature gas-cooled reactor. Measurements of both velocity and pressure were made within the heat exchanger shell side flow field. These measurements were compared with calculated results from both a network flow model and a turbulent flow model. Both analytical models predicted early identical results which, except for some minor anomalies, compared favorably with the measured data

85

Vibration of heat exchange components in liquid and two-phase cross-flow  

International Nuclear Information System (INIS)

Heat exchange components must be analysed at the design stage to avoid flow-induced vibration problems. This paper presents information required to formulate flow-induced vibration excitation mechanisms in liquid and two-phase cross-flow. Three basic excitation mechanisms are considered, namely: 1) fluidelastic instability, 2) periodic wake shedding, and 3) response to random flow turbulence. The vibration excitation information is deduced from vibration response data for various types of tube bundles. Sources of information are: 1) fundamental studies on tube bundles, 2) model testing, 3) field measurements, and 4) operating experiences. Fluidelastic instability is formulated in terms of dimensionless flow velocity and dimensionless damping; periodic wake shedding in terms of Strouhal number and lift coefficient; and random turbulence excitation in terms of statistical parameters of random forces. Guidelines are recommended for design purposes. (author)

86

Heat exchange effectiveness and pressure drop for air flow through perforated plates with and without crosswind  

Science.gov (United States)

Low-porosity perforated plates are being used as absorbers for heating ambient air in a new type of unglazed solar collector. This paper investigates the convective heat transfer effectiveness for low-speed air flow through thin, isothermal perforated plates with and without a crosswind on the upstream face. The objective of this work is to provide information that will allow designers to optimize hole size and spacing. In order to obtain performance data, a wind tunnel and small lamp array were designed and built. Experimental data were taken for a range of plate porosities from 0.1 to 5 percent, hole Reynolds numbers from 100 to 2000, and wind speeds from 0 to 4 m/s. Correlations were developed for heat exchange effectiveness and also for pressure drop. Infrared thermography was used to visualize the heat transfer taking place at the surface.

Kutscher, C. F.

1994-05-01

87

Effect of nonuniform inlet air flow on air-cooled heat-exchanger performance  

International Nuclear Information System (INIS)

Blowers used to propel air across tube bundles generate a non-uniform flow field due to their construction details. A formalism to evaluate heat transfer degradation due to non-uniform airflow has been developed. Certain symmetry relations for cross flowheat exchangers, heretofore unavailable in the open literature, have been derived. The solution presented here was developed to model a 4 tube pass air blast heat exchanger for the Clinch River Breeder Reactor Plant Project. This case is utilized to show how this method can be used as a design tool to select the most suitable blower construction for a particular application. A numerical example is used to illustrate the salient points of the solution

88

Effect of nonuniform inlet air flow on air-cooled heat-exchanger performance  

Energy Technology Data Exchange (ETDEWEB)

Blowers used to propel air across tube bundles generate a non-uniform flow field due to their construction details. A formalism to evaluate heat transfer degradation due to non-uniform airflow has been developed. Certain symmetry relations for cross flowheat exchangers, heretofore unavailable in the open literature, have been derived. The solution presented here was developed to model a 4 tube pass air blast heat exchanger for the Clinch River Breeder Reactor Plant Project. This case is utilized to show how this method can be used as a design tool to select the most suitable blower construction for a particular application. A numerical example is used to illustrate the salient points of the solution.

Soler, A.I.; Singh, K.P.; Ng, T.L.

1983-01-01

89

Performance testing of cross flow heat exchanger operating in the atmosphere of flue gas particulate with vapor condensation  

Directory of Open Access Journals (Sweden)

Full Text Available Performance testing of a cross flow heat exchanger operating under the atmosphere of flue gas particulate from combustion was carried out in this work. This heat exchanger exchanges heat between flue gas from the fuel oil combustion and cold water. The heat exchanger is composed of a spiral finned tube bank having 3 rows and 8 tubes per row with a staggered arrangement. The fin spacings considered are 2.85 and 6.10 mm. The theories of thermodynamics and heat transfer are used for analyzing the performance of this system.In this experiment, the flue gas temperature of 200ºC from combustion having 0.35 kg/s mass flow rate flows along outside surface of the heat exchanger and transfers heat to the 25ºC cooling water having 0.15 kg/s mass flow rate flowing in the tube side. Each experiment uses 750 hr for testing. During the testing, part of flue gas condenses on the heat transfer surface.From the experiment, it was found that the heat transfer rate of both heat exchangers tended to decrease with time while the airside pressure drop increased. These results come from the fouling on the heat transfer surface. Moreover, it is found that the heat exchanger having 2.85 mm fin spacing has an approximately 4 times higher fouling resistance than that of the 6.10 mm fin spacing.In this work a model for calculating the fouling resistance is also developed as a the function of time. The model is developed from that of Kern and Seaton and the mean deviation of the model is 0.789.

Nuntaphan, A.

2006-05-01

90

Co-flow anode/cathode supply heat exchanger for a solid-oxide fuel cell assembly  

Science.gov (United States)

In a solid-oxide fuel cell assembly, a co-flow heat exchanger is provided in the flow paths of the reformate gas and the cathode air ahead of the fuel cell stack, the reformate gas being on one side of the exchanger and the cathode air being on the other. The reformate gas is at a substantially higher temperature than is desired in the stack, and the cathode gas is substantially cooler than desired. In the co-flow heat exchanger, the temperatures of the reformate and cathode streams converge to nearly the same temperature at the outlet of the exchanger. Preferably, the heat exchanger is formed within an integrated component manifold (ICM) for a solid-oxide fuel cell assembly.

Haltiner, Jr., Karl J.; Kelly, Sean M.

2005-11-22

91

Optimization of zigzag flow channels of a printed circuit heat exchanger for nuclear power plant application  

International Nuclear Information System (INIS)

Printed circuit heat exchanger (PCHE) is recently considered as a recuperator for the high-temperature gas cooled reactor. In this study, shape optimization of zigzag flow channels in a PCHE has been performed to enhance heat transfer performance and reduce the friction loss based on three-dimensional Reynolds-averaged Navier-Stokes analysis with the Shear Stress Transport Turbulence model. A multi-objective genetic algorithm is used for the multi-objective optimization. Two non-dimensional objective functions related to heat transfer performance and friction loss are employed. The shape of a flow channel is defined by two geometric design variables, viz. the cold channel angle and the ellipse aspect ratio of the cold channel. The experimental points within the design space are selected using Latin hypercube sampling as the design of the experiment. The response surface approximation model is used to approximate the Pareto-optimal front. Five optimal designs on the Pareto-optimal front have been selected using k-means clustering. The flow and heat transfer characteristics, as well as the objective function values, of these designs have been compared with those of the reference design. (author)

92

Assessment of flow induced vibration in a sodium-sodium heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

The 500 MWe Prototype Fast Breeder Reactor (PFBR) is under construction at Kalpakkam. It is a liquid metal sodium cooled pool type fast reactor with all primary components located inside a sodium pool. The heat produced due to fission in the core is transported by primary sodium to the secondary sodium in a sodium to sodium Intermediate Heat Exchanger (IHX), which in turn is transferred to water in the steam generator. PFBR IHX is a shell and tube type heat exchanger with primary sodium on shell side and secondary sodium in the tube side. Since IHX is one of the critical components placed inside the radioactive primary sodium, trouble-free operation of the IHX is very much essential for power plant availability. To validate the design and the adequacy of the support system provided for the IHX, flow induced vibration (FIV) experiments were carried out in a water test loop on a 60 deg. sector model. This paper discusses the flow induced vibration measurements carried out in 60 deg. sector model of IHX, the modeling criteria, the results and conclusion.

Prakash, V. [Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu (India)], E-mail: prakash@igcar.gov.in; Thirumalai, M.; Prabhakar, R.; Vaidyanathan, G. [Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu (India)

2009-01-15

93

Assessment of flow induced vibration in a sodium-sodium heat exchanger  

International Nuclear Information System (INIS)

The 500 MWe Prototype Fast Breeder Reactor (PFBR) is under construction at Kalpakkam. It is a liquid metal sodium cooled pool type fast reactor with all primary components located inside a sodium pool. The heat produced due to fission in the core is transported by primary sodium to the secondary sodium in a sodium to sodium Intermediate Heat Exchanger (IHX), which in turn is transferred to water in the steam generator. PFBR IHX is a shell and tube type heat exchanger with primary sodium on shell side and secondary sodium in the tube side. Since IHX is one of the critical components placed inside the radioactive primary sodium, trouble-free operation of the IHX is very much essential for power plant availability. To validate the design and the adequacy of the support system provided for the IHX, flow induced vibration (FIV) experiments were carried out in a water test loop on a 60 deg. sector model. This paper discusses the flow induced vibration measurements carried out in 60 deg. sector model of IHX, the modeling criteria, the results and conclusion

94

Air flow test of MK-III dump heat exchanger tube arrays for JOYO  

International Nuclear Information System (INIS)

The reactor thermal power of JOYO MK-III is to be increased from 100MWt to 140MWt due to high performance of reactor core. So, Dump Heat Exchanger(DHX) of MK-III was designed to improve its heat removal capability by changing U type heat transport tube arrays to ? type tube arrays and increasing air flow. Natural frequency between support and support of MK-III DHX's tube arrays was about 15Hz, and Karman vortex shedding frequency of tube arrays was about 90Hz by Y.N.Chen's report. Then, a possibility of piling up of Karman vortex shedding frequency in high frequency mode was to be considered. And, air velocity of flow tube arrays is also increased compared to the MK-II DHX. Sodium leak accident of MONJU was caused by a flow-induced vibration of thermometer well. Therefore, the air flow test to tube arrays of MK-III DHX was conducted. High cycles fatigue damage of tube arrays was evaluated. Since, peak stress is below 2kg/mm2, it can be said that high cycles fatigue damage of tube arrays by Karman vortex shedding vibration will not be caused. (J.P.N.)

95

Air flow test of MK-III dump heat exchanger tube arrays for JOYO  

Energy Technology Data Exchange (ETDEWEB)

The reactor thermal power of JOYO MK-III is to be increased from 100MWt to 140MWt due to high performance of reactor core. So, Dump Heat Exchanger(DHX) of MK-III was designed to improve its heat removal capability by changing U type heat transport tube arrays to {Sigma} type tube arrays and increasing air flow. Natural frequency between support and support of MK-III DHX`s tube arrays was about 15Hz, and Karman vortex shedding frequency of tube arrays was about 90Hz by Y.N.Chen`s report. Then, a possibility of piling up of Karman vortex shedding frequency in high frequency mode was to be considered. And, air velocity of flow tube arrays is also increased compared to the MK-II DHX. Sodium leak accident of MONJU was caused by a flow-induced vibration of thermometer well. Therefore, the air flow test to tube arrays of MK-III DHX was conducted. High cycles fatigue damage of tube arrays was evaluated. Since, peak stress is below 2kg/mm{sup 2}, it can be said that high cycles fatigue damage of tube arrays by Karman vortex shedding vibration will not be caused. (J.P.N.)

Isozaki, Kazunori; Kawahara, Hirotaka; Tomita, Naoki [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

1997-07-01

96

Local convective heat exchanges and flow structure in a rotor-stator system  

Energy Technology Data Exchange (ETDEWEB)

This work deals with an experimental study of the flow structure and the local convective exchanges in the air-gap of a rotor-stator system. The experimental technique uses infrared thermography to measure the surface temperatures of the rotor and the numerical solution of the steady state heat equation to determine the local heat transfer coefficients. The analysis of the flow structure between the rotor and the stator is obtained by PIV (Particle Image Velocimetry). Tests are carried out for rotational Reynolds numbers ranging from 5.87 x 10{sup 4} to 1.76 x 10{sup 5} and for gap ratios ranging from 0.01 to 0.17. Analysis of the experimental results has determined the influence of the rotational Reynolds number and the gap ratio on the flow structure and the convective exchanges in the gap between the rotor and the stator. Some correlations expressing the local Nusselt number as a function of the rotational Reynolds number and the gap ratio are proposed. (authors)

Boutarfa, Rachid; Harmand, Souad [Laboratoire de Mecanique et Energetique, Universite de Valenciennes et du Hainaut Cambresis, Le Mont Houy, 59313 cedex 9, Valenciennes (France)

2003-12-01

97

Experiments on vibration of heat exchanger tube arrays in cross flow  

International Nuclear Information System (INIS)

A series of tests have been made at the Commissariat a l'Energie Atomique, in cooperation with General Atomic Company, SAN DIEGO (U.S.A.) on the flow-induced vibration of heat exchanger tube bundles in cross flow. These tests were made in air on tube bundles which simulated heat exchangers in the high temperature gas cooled reactors. The tests were of two types. In the first type, an instrumented tube was inserted at various locations into a tube bundle. Measurements were made of pressure at a number of points along the tube and about the circumference of the tube. These measurements were processed to obtain the spectra of turbulent pressure fluctuations on the tube, the spanwise correlation and the lift force. The second set of tests was made on tube bundles with flexible tubes. As the flow velocity was increased, these tests clearly show an instability. Nine tube configurations were tested with both plastic and metallic tubes and the effect of tube-to-tube difference in natural frequency was investigated

98

Entropy Generation Minimization in a Ram-Air Cross-Flow Heat Exchanger  

OpenAIRE

This paper presents the constrained thermodynamic optimization of a crossflow heat exchanger with ram air on the cold side. The ram-air stream passes through a diffuser before entering the heat exchanger, and exits through a nozzle. This configuration is used in the environmental control systems of aircraft. In the first part of the study the heat exchanger is optimized alone, subject to fixed total volume and volume fraction occupied by solid walls. Optimized geometric features such as the r...

Adrian Bejan; Asad Alebrahim

1999-01-01

99

Liquid-Metal/Water Direct Contact Heat Exchange: Flow Visualization, Flow Stability, and Heat Transfer Using Real-Time X-Ray Imaging  

International Nuclear Information System (INIS)

Advanced reactor system designs are being considered with liquid-metal cooling connected to a steam power cycle. In addition, current reactor safety systems are considering auxiliary cooling schemes that assure ex-vessel debris coolability utilizing direct water injection into molten material pools to achieve core quenching and eventual coolability. The phenomenon common in both applications is direct contact heat exchange. The current study focuses on detailed measurements of liquid-metal/water direct contact heat exchange that is directly applicable to improvements in effective heat transfer in devices that are being considered for both of these purposes.In this study, a test facility was designed at the University of Wisconsin-Madison to map the operating range of liquid-metal/water direct contact heat exchange. The test section (184-cm height, 45.75-cm width, and 10-cm depth) is a rectangular slice of a larger heat exchange device. This apparatus was used not only to provide measurements of integral thermal performance (i.e., volumetric heat transfer coefficient), but also local heat transfer coefficients in a bubbly flow regime with X-ray imaging based on measured parameters such as bubble formation time, bubble rise velocity, and bubble diameters.To determine these local heat transfer coefficients, a complete methodology of the X-ray radiography for two-phase flow measurement has been developed. With this methodology, a high-energy X-ray imaging system is optimihigh-energy X-ray imaging system is optimized for our heat exchange experiments. With this real-time, large-area, high-energy X-ray imaging system, the two-phase flow was quantitatively visualized. An efficient image processing strategy was developed by combining several optimal digital image-processing algorithms into a software computational tool written in MATLAB called T-XIP. Time-dependent heat transfer-related variables such as bubble volumes and velocities, were determined. Finally, an error analysis associated with these measurements has been given based on two independent procedures. This methodology will allow one to utilize X-ray attenuation for imaging vapor bubbles with acceptable errors (bubbles ?1 to 5 cm ± 5 to 20%).Subcooled water (Tsat - Twater [approximately equal to] 10 deg. C) was brought into contact with liquid lead (or lead alloys) at an elevated temperature (Tlm = 500 deg. C and Tlm - Tmelting [approximately equal to] 200 deg. C). The study was conducted over a range of ambient pressures (1 to 10 bar) with four different water injection rates (1.5 to 8 g/s; 0.1 to 1 kg/m2.s). The results showed that the system pressure has a slight effect on volumetric heat transfer coefficient, the bubble formation time, and the bubble rise velocity. Increasing the system pressure, however, resulted in an increase in the bubble average heat transfer coefficient. Increasing the water injection rate directly had only a small effect on the bubble rise velocity or formation rate. Increasing the water injection rate resulted in a decrease in the local bubble heat transfer coefficient.Direct contact heat transfer also has some key disadvantages; e.g., flow instabilities caused by local vapor explosion is one of the issues related to direct contact heat exchange, particularly for liquid/liquid exchange with high temperature differences. In this study, the region of stable heat transfer was mapped and the effects of the liquid metal temperature, the water injection rate, and the operating pressure were investigated. The pressure required to stabilize the heat exchange process was found to be a function of the water injection rate but generally increasing the system pressure helped stabilize the system. It was also found that the larger the injection rate, the higher the pressure required to stabilize the system

100

Effect of corrugation angle on the thermal behaviour of power-law fluids during a flow in plate heat exchangers  

OpenAIRE

In this study, CFD calculations were made in order to analyze the thermal behaviour of a power-law fluid in the channels of plate heat exchangers with corrugation angles of 30º and 60º. For the observed laminar flow, the numerical results show the absence of a typical local temperature profile in the 3D channel. Local Nusselt numbers and transversal variations of viscosity along the plate heat exchangers were studied and simulations considering and discarding the influence of temperature...

Fernandes, Carla S.; Dias, Ricardo P.; No?brega, Joa?o M.; Maia, Joa?o M.

2005-01-01

101

Experimental study of turbulent flow heat transfer and pressure drop in a plate heat exchanger with chevron plates  

Energy Technology Data Exchange (ETDEWEB)

Experimental data for isothermal pressure drop and heat transfer in single-phase water flows in a plate heat exchanger (PHE) with chevron plates are presented. A single-pass, U-type, counterflow PHE, with three different chevron plate arrangements is employed: two symmetric plate arrangements with {beta} = 30/30{degree} and 60/60{degree}, and a mixed-plate arrangement with {beta} = 30/60{degree}. With water flow rates in the turbulent flow regime (600 < Re < 10{sup 4} and 2 < Pr < 6), effects of the chevron corrugation inclination angle {beta} on Nu and f characteristics of the PHE are investigated. As {beta} increases and compared to a flat-plate pack, up to 2 to 5 times higher Nu are obtained; the concomitant f, however, are 13 to 44 times higher. Based on the experimental data for Re {le} 1,000, predictive correlations of the form Nu = C{sub 1}{beta} Re{sup p1({beta})} Pr{sup 1/3} ({mu}/{mu}{sub w}){sup 0.14} and f = C{sub 2}{beta} Re{sup p2({beta})} are devised. Also, at constant pumping power and depending upon {beta}, the heat transfer is found to be enhanced over 1.8 times that in equivalent flat-plate channels.

Muley, A.; Manglik, R.M.

1997-07-01

102

Effect of corrugation angle on the hydrodynamic behaviour of power-law fluids during a flow in plate heat exchangers  

OpenAIRE

In this study, CFD calculations were made in order to analyze the hydrodynamic behaviour of a power-law fluid in the channels of plate heat exchangers with corrugation angles of 30º and 60º during a non-isothermal flow. For the observed laminar flow, the numerical results show that a typical velocity profile in the 3D channel of the plate heat exchanger with corrugation angle 30º assumes an approximate parabolic shape and that for a corrugation angle of 60º the profile have a irregular...

Fernandes, Carla S.; Dias, Ricardo P.; No?brega, Joa?o M.; Maia, Joa?o M.

2005-01-01

103

A relaxation-projection method for compressible flows. Part II: Artificial heat exchanges for multiphase shocks  

International Nuclear Information System (INIS)

The relaxation-projection method developed in Saurel et al. [R. Saurel, E. Franquet, E. Daniel, O. Le Metayer, A relaxation-projection method for compressible flows. Part I: The numerical equation of state for the Euler equations, J. Comput. Phys. (2007) 822-845] is extended to the non-conservative hyperbolic multiphase flow model of Kapila et al. [A.K. Kapila, Menikoff, J.B. Bdzil, S.F. Son, D.S. Stewart, Two-phase modeling of deflagration to detonation transition in granular materials: reduced equations, Physics of Fluids 13(10) (2001) 3002-3024]. This model has the ability to treat multi-temperatures mixtures evolving with a single pressure and velocity and is particularly interesting for the computation of interface problems with compressible materials as well as wave propagation in heterogeneous mixtures. The non-conservative character of this model poses however computational challenges in the presence of shocks. The first issue is related to the Riemann problem resolution that necessitates shock jump conditions. Thanks to the Rankine-Hugoniot relations proposed and validated in Saurel et al. [R. Saurel, O. Le Metayer, J. Massoni, S. Gavrilyuk, Shock jump conditions for multiphase mixtures with stiff mechanical relaxation, Shock Waves 16 (3) (2007) 209-232] exact and approximate 2-shocks Riemann solvers are derived. However, the Riemann solver is only a part of a numerical scheme and non-conservative variables pose extra difficulties for the projection or cell a difficulties for the projection or cell average of the solution. It is shown that conventional Godunov schemes are unable to converge to the exact solution for strong multiphase shocks. This is due to the incorrect partition of the energies or entropies in the cell averaged mixture. To circumvent this difficulty a specific Lagrangian scheme is developed. The correct partition of the energies is achieved by using an artificial heat exchange in the shock layer. With the help of an asymptotic analysis this heat exchange takes a similar form as the 'pseudoviscosity' introduced by Von Neumann and Richtmyer [J. Von Neumann, R.D. Richtmyer, A method for the numerical calculation of hydrodynamic shocks, J. Appl. Phys. 21 (1950) 232-237]. The present Lagrangian numerical scheme thus combines Riemann solvers and artificial heat exchanges. An Eulerian variant is then obtained by using the relaxation-projection method developed earlier by the authors for the Euler equations. The method is validated against exact solutions based on the multiphase shock relations as well as exact solutions of the Euler equations in the context of interface problems. The method is able to solve interfaces separating pure fluids or heterogeneous mixtures with very large density ratio and with very strong shocks

104

Experimental studies on pressure drop characteristics of cryogenic cross-counter flow coiled finned tube heat exchangers  

Science.gov (United States)

Cross-counter flow coiled finned tube heat exchangers used in medium capacity helium liquefiers/refrigerators were developed in our lab. These heat exchangers were developed using integrated low finned tubes. Experimental studies have been performed to know the pressure drop characteristics of tube side and shell side flow of these heat exchangers. All experiments were performed at room temperature in the Reynolds number range of 3000-30,000 for tube side and 25-155 for shell side. The results of present experiments indicate that available correlations for tube side can not be used for prediction of tube side pressure drop data due to complex surface formation at inner side of tube during formation of fins over the outer surface. Results also indicate that surface roughness effect becomes more pronounced as the value of di/ D m increases. New correlations based on present experimental data are proposed for predicting the friction factors for tube side and shell side.

Gupta, Prabhat Kumar; Kush, P. K.; Tiwari, Ashesh

2010-04-01

105

Damping of heat exchanger tubes  

International Nuclear Information System (INIS)

Damping information is required for flow-induced vibration analyses of heat exchangers. There are several possible energy dissipation mechanisms that contribute to overall tube damping, including structural damping, friction damping, tube-to-fluid viscous damping and squeeze-film damping. These mechanisms and their relative contribution to overall tube damping are discussed. The approach is to identify the more important energy dissipation mechanisms and to formulate them in terms of heat exchanger tube parameters. This will give the designer a method to evaluate overall tube damping. The results of recent measurements on a simple two-span heat exchanger tube, on tube bundles in two-phase cross-flow, and on real heat exchangers in the field are disscussed

106

Transient Thermal Behavior of a Vertical Solar Storage Tank with a Mantle Heat Exchanger During No-Flow Operation  

Directory of Open Access Journals (Sweden)

Full Text Available Transient thermal behavior of a vertical storage tank of a domestic solar heating system with a mantle heat exchanger has been investigated numerically in the charging mode. It is assumed that the tank is initially filled with uniform cold water. At an instant of time, the hot fluid from collector outlet is uniformly injected in the upper section of the mantle heat exchanger and after heat transfer with the fluid inside the tank, withdrawn from the bottom part of the heat exchanger. The conservation equations in the cylindrical coordinate and in axis-symmetric condition have been used according to the geometry under investigation. Governing equations have been discretized by employing the finite volume method and the SIMPLER algorithm has been used for coupling between momentum and pressure equations. The Low Reynolds Number (LRN k ?? model is utilized for treating turbulence in the fluid. First, the transient thermal behavior of heat storage tank and the process of formation of thermal stratification in the heat storage tank were investigated. Then, the influence of Rayleigh number in the heat storage tank, Reynolds number in the mantle heat exchanger and vertical positioning of mantle on the flow and thermal fields and the formation of the thermal stratification was investigated. It is found that for higher values of Rayleigh number, a more suitable thermal stratification is established inside the tank. Also it is noticed that increasing the incoming fluid velocity through the mantle heat exchanger causes a faster formation of the thermal stratification. A superior thermal performance was achieved when the mantle heat exchanger is positioned at the middle height of the storage tank.

A. Barzegar

2009-01-01

107

Experimental study on flow-induced vibration and heat transfer characteristics of heat exchanger with helically coiled tube bundles  

International Nuclear Information System (INIS)

An experimental study was carried out to investigate flow-induced vibration, heat transfer and pressure drop of helically coiled tube bundles of an intermediate heat exchanger (IHX) for the HTTR, using a full-size partial model and air as a testing fluid. The test model has 54 helically coiled tubes separated into three layer bundles, surrounding the center pipe. The vibration behavior in the fluid was investigated focussing on vortex-induced and fluidelastic vibrations which are main ones to cause failure of tubes. The vibration of the tube bundles was mainly at the center pipe, and their vibration amplitude was less than 0.1 mm. As the results, it was clarified that individual vibrations of the tube bundles were not significant under the operation conditions of the IHX. The Nusselt number of the tube outside, due to forced convection, was obtained as a function of Re0.56, and the drag coefficient was proportional to Re-0.14. Furthermore, effect of radiative plates on heat transfer was clarified. (author)

108

An experimental study on the flow and heat transfer of flinak molten salt in small channels for the application to the VHTR intermediate heat exchanger  

International Nuclear Information System (INIS)

To make the design of the Very High Temperature Reactor (VHTR) complete and plausible, the designs of the Intermediate Heat Transport Loop (IHTL) as well as the Intermediate Heat Exchanger (IHX) are known to be one of the difficult engineering tasks due to its high temperature operating condition (up to 950degC). In this study, the Flinak molten salt, an eutectic mixture of LiF, NaF and KF (46.5:11.5:42.0 mole %) is considered as the heat transporting fluid in the IHTL. To evaluate the flow and heat transfer performance of the Flinak molten salt in small channels of millimeter-range hydraulic diameters, a double-pipe type heat exchanger was constructed using small-diameter tubes for the heat exchange between the Flinak and gas flow. The inner diameters of the inner tube and the outer tube are 1.4 mm and 4.6 mm, respectively, and the length of the tubes is 500 mm. The molten salt flows through the inner tube. The molten salt is prepared in a crucible made of Inconel 600 placed in an electric furnace. The molten salt flow is produced by differential pressure between a twin set of molten salt crucibles without using a mechanical pump. The flow rate of the molten salt is reduced from the weight change of a crucible measured by load cells. Temperatures of the two heat exchanging fluids at various points as well as pressure drop across the test tube are measured to obtain flow and heat transfer characteristics of the molten salt flow. For laminar flow of the Flinak in 1.4 mm inner-diameter circular tube, the measured friction factors were smaller than the 64/Re curve by 50%. Also the measured Nusselt numbers were generally in the range between 3.66 and 4.36, although the data were scattered due to the measurement error in such a high temperature condition. (author)

109

Optimization of Heat Exchangers  

International Nuclear Information System (INIS)

The objective of this research is to develop tools to design and optimize heat exchangers (HE) and compact heat exchangers (CHE) for intermediate loop heat transport systems found in the very high temperature reator (VHTR) and other Generation IV designs by addressing heat transfer surface augmentation and conjugate modeling. To optimize heat exchanger, a fast running model must be created that will allow for multiple designs to be compared quickly. To model a heat exchanger, volume averaging theory, VAT, is used. VAT allows for the conservation of mass, momentum and energy to be solved for point by point in a 3 dimensional computer model of a heat exchanger. The end product of this project is a computer code that can predict an optimal configuration for a heat exchanger given only a few constraints (input fluids, size, cost, etc.). As VAT computer code can be used to model characteristics (pumping power, temperatures, and cost) of heat exchangers more quickly than traditional CFD or experiment, optimization of every geometric parameter simultaneously can be made. Using design of experiment, DOE and genetric algorithms, GE, to optimize the results of the computer code will improve heat exchanger design.

110

Optimization of Heat Exchangers  

Energy Technology Data Exchange (ETDEWEB)

The objective of this research is to develop tools to design and optimize heat exchangers (HE) and compact heat exchangers (CHE) for intermediate loop heat transport systems found in the very high temperature reator (VHTR) and other Generation IV designs by addressing heat transfer surface augmentation and conjugate modeling. To optimize heat exchanger, a fast running model must be created that will allow for multiple designs to be compared quickly. To model a heat exchanger, volume averaging theory, VAT, is used. VAT allows for the conservation of mass, momentum and energy to be solved for point by point in a 3 dimensional computer model of a heat exchanger. The end product of this project is a computer code that can predict an optimal configuration for a heat exchanger given only a few constraints (input fluids, size, cost, etc.). As VAT computer code can be used to model characteristics )pumping power, temperatures, and cost) of heat exchangers more quickly than traditional CFD or experiment, optimization of every geometric parameter simultaneously can be made. Using design of experiment, DOE and genetric algorithms, GE, to optimize the results of the computer code will improve heat exchanger disign.

Ivan Catton

2010-10-01

111

Simulation of Cross Flow Heat Exchanger for Multi Tubes Using FLUENT 6.3.26  

Directory of Open Access Journals (Sweden)

Full Text Available In chemical engineering a lot of work is done to improve the results of the equipment to make its widespread applications be possible. Simulation is extensively used as the power of the computer is well known nowadays. Simulation is frequently used to study both real and virtual behavior. In this paper experimentation, simulation and development of mathematical models are performed. Practical experiments are made on a cross flow heat exchanger for a multi tube layout with staggered arrangement to study the rate of heat transfer. Simulation is carried out when experimental results are obtained. For designing and meshing of plate geometries GAMBIT 2.3.16 is used and then solution and analysis are accomplished on FLUENT 6.3.26. By comparing experimental and simulated results, it is found that both validate each other with minor differences. Empirical relationships have been also developed. Re and Nu relationships are developed mathematically and compared to the models found in literature concerned. The developed models are found in good agreement with theoretically available models. The future research in this regard can be done by using viscous fluids and an advanced version of the software like Cubit for designing and meshing the plate geometry.DOI: http://dx.doi.org/10.5755/j01.erem.65.3.4453

Suneela Sardar

2013-10-01

112

Compact heat exchangers modeling: Condensation  

Energy Technology Data Exchange (ETDEWEB)

A model for the analysis of compact heat exchangers working as either evaporators or condensers is presented. This paper will focus exclusively on condensation modeling. The model is based on cell discretization of the heat exchanger in such a way that cells are analyzed following the path imposed by the refrigerant flowing through the tubes. It has been implemented in a robust code developed for assisting with the design of compact heat exchangers and refrigeration systems. These heat exchangers consist of serpentine fins that are brazed to multi-port tubes with internal microchannels. This paper also investigates a number of correlations used for the calculation of the refrigerant side heat transfer coefficient. They are evaluated comparing the predicted data with the experimental data. The working fluids used in the experiments are R134a and R410A, and the secondary fluid is air. The experimental facility is briefly described and some conclusions are finally drawn. (author)

Garcia-Cascales, J.R.; Vera-Garcia, F. [Technical University of Cartagena, Thermal and Fluid Engineering Department, C/Dr. Fleming, s/n 30202 Cartagena, Murcia (Spain); Gonzalvez-Macia, J.; Corberan-Salvador, J.M. [Technical University of Valencia, Applied Thermodynamic Department, Valencia (Spain); Johnson, M.W.; Kohler, G.T. [Modine Manufacturing Company, Commercial Products Group, Racine, WI (United States)

2010-01-15

113

Non-Newtonian flows in laminar regime in chevron plate heat exchangers: the influence of geometrical configuration  

OpenAIRE

Physical processing brings about irreversible textural and sensorial properties of nearly all the fluids on the food industry. In liquid food processing, plate heat exchangers (PHEs) are commonly used in the heating or cooling stages due to their advantages, such as high efficiency, ease of maintenance and cleaning and flexibility on account of the modular design. Although, laminar or low Reynolds number flows are usually obtained when liquid foods are processed in PHEs, the behaviour is s...

Fernandes, Carla S.; Dias, Ricardo P.; No?brega, Joa?o M.; Maia, Joa?o M.

2007-01-01

114

Second law analysis and heat transfer in a cross-flow heat exchanger with a new winglet-type vortex generator  

Energy Technology Data Exchange (ETDEWEB)

In this paper a second law analysis of a cross-flow heat exchanger (HX) is studied in the presence of a balance between the entropy generation due to heat transfer and fluid friction. The entropy generation in a cross-flow HX with a new winglet-type convergent-divergent longitudinal vortex generator (CDLVG) is investigated. Optimization of HX channel geometry and effect of design parameters regarding the overall system performance are presented. For the HX flow lengths and CDLVGs the optimization model was developed on the basis of the entropy generation minimization (EGM). It was found that increasing the cross-flow fluid velocity enhances the heat transfer rate and reduces the heat transfer irreversibility. The test results demonstrate that the CDLVGs are potential candidate procedure to improve the disorderly mixing in channel flows of the cross-flow type HX for large values of the Reynolds number. (author)

Kotcioglu, Isak [Department of Mechanical Engineering, Faculty of Engineering, University of Atatuerk, 25240 Erzurum (Turkey); Caliskan, Sinan [Department of Mechanical Engineering, Faculty of Engineering, University of Hitit, 19030 Corum (Turkey); Cansiz, Ahmet [Department of Electrical-Electronics Engineering, Faculty of Engineering, University of Atatuerk, 25240 Erzurum (Turkey); Baskaya, Senol [Department of Mechanical Engineering, Faculty of Engineering and Architecture, Gazi University, Maltepe 06570, Ankara (Turkey)

2010-09-15

115

Experimental Research on Gas-Solid Flow in an External Heat Exchanger with Double Outlets  

Science.gov (United States)

A new type scaling-up scheme of CFB boiler that takes separator as center and furnaces are laid around was put forward in this paper. In the recycle system, a new type heat exchanger device with double outlets was designed for this disposal scheme. As we know, the external heat exchanger is very important for the CFB, which be able no only to adjust the steam temperature, but also to adjust the bed temperature. In this paper, through the adjustment of air speed in different room of the heat exchanger, the adjusting performance of the new type heat exchanger was analyzed. Moreover, the test of the pressure in the whole recycle system was analyzed. The pressure balance system of the circulating circuit with this new arrangement scheme was realized. Through this test research, the main conclusions were got as follows: The external heat exchanger, which has two recycled solid outlets, could run flexibly and stably and could successfully discharge the materials from the standpipe into either of the furnaces. This test device has a good pressure and material balance system.

Liu, H. Z.; Lu, X. F.

116

Dendritic counterflow heat exchanger experiments  

Energy Technology Data Exchange (ETDEWEB)

In this paper we report experimentally the hydraulic and thermal behavior of a balanced counterflow heat exchanger in which each stream flows through a tree-shaped structure covering a circular area. The tree structure is the same on both sides of the heat exchanger: they have three channels reaching/leaving the center, and three branching levels (i.e., 24 channels on the periphery of the circular area). On the hot side, fluid is pumped from the center to the periphery. On the cold side, fluid is pumped from the periphery to the center, and leaves the heat exchanger as a single stream. Two experimental apparatuses were built and tested. In the first design, the body of the heat exchanger was made out of plexiglass and a peripheral plenum was used to collect or distribute the working fluid to the tree structure. The measurements showed that the use of a plenum generates undesirable volumetric flow asymmetries. These lessons led to a second design, which has two major improvements: (i) the heat exchanger core was made out of aluminum and (ii) individual ports (inlets/outlets) were used for each of the peripheral channels. The hydraulic results show a relation between the appearance of volumetric flow rate asymmetries and the bifurcation angles throughout the dendritic structure. The heat transfer results are also discussed. (author)

da Silva, Alexandre K.; Bejan, Adrian [Department of Mechanical Engineering and Materials Science, Duke University, Box 90300, Durham, NC 27708-300 (United States)

2006-09-15

117

Distribution of air-water R134a in a header of a parallel flow heat exchanger  

International Nuclear Information System (INIS)

Flow distribution in a header of a parallel flow heat exchanger was experimentally investigated using R-134a. Both downward and upward flow configuration were tested with tubes protruded to the center of the header. For the test range, the flow pattern at the inlet of the header was identified as stratified flow. It was observed that, for the downward flow, most of the liquid was extracted from the frontal part of the header. For the upward flow, however, most of the liquid was extracted from the rear part of the header. For the downward configuration, better distribution was obtained at a low mass flux and at a low quality. For the upward configuration, however, the mass flux or quality had minor influence on the flow distribution

118

Overview of numerical methods for predicting flow-induced vibration and wear of heat-exchanger tubes  

International Nuclear Information System (INIS)

Practical interest in performing predictive analysis of vibration and wear risks of industrial tube bundles, e.g. in nuclear reactor heat exchangers, subjected to cross flow is broadly recognized. A predictive analysis of an heat-exchanger design against severe vibration and wear has to cope with experimental data on FIV and fretting wear, together with the use of analytical and numerical methods for predicting linear and nonlinear tube response. This paper describes a general approcah of the problem currently under development at C.E.A. Attention is especially paid to some key aspects of the numerical techniques, namely, the modelisation of flow-induced forcing functions and the modelisation of impact and sliding at tube-support gaps. These topics are exemplified by numerical results related to some typical situations including the case of random vibration induced by flow turbulence and fluid-elastic vibration

119

Rotating fluidized bed heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

A rotating fluidized bed heat exchanger particularly adaptable as a heat exchange unit in the recuperator section of conventional gas turbine engines is disclosed comprising an annular fluidized bed, defined by inner and outer spaced apart coaxial cylindrical, perforated walls, which rotates about the longitudinal axis of the cylinders. The bed is comprised of pulverulent inert particulate material and includes fluid-containing heat exchange tubes passing substantially longitudinally therethrough. Hot gases, such as turbine exhaust gases, enter the bed through the outer perforated wall, heat and fluidize the bed particles, heat the fluid, usually compressed air, in the tubes, and exit the bed through the inner perforated wall. The heat exchange tubes direct the fluid flowing therein from an inlet adjacent the inner perforated wall to an outlet adjacent the outer perforated wall such that the fluid flows substantially countercurrently to the hot fluidizing gas. In a preferred embodiment, the heat exchange tubes comprise an inlet tube extending longitudinally adjacent the inner perforated wall, an outlet tube extending longitudinally adjacent the outer perforated wall and a plurality of tubes interconnecting the inlet and outlet tubes.

Belke, W.H.; Goloff, A.; Grim, G.B.

1982-02-02

120

Tertiary heat exchanger  

International Nuclear Information System (INIS)

The invention deals with the improvement of a tertiary heat exchanger possessing a contact medium besides a heating and working medium. These kind of heat exchangers are used in sodium-cooled nuclear power plants. The contact medium used so far should be reploced by a metal granulate which is used in porous bulk of single grains of varying size. It is advantageous to use copper as granulate. (RW)

121

Determining the heat exchanger capacity of the 6.5/10 MW reactor as a function of temperature and water coolant flow  

International Nuclear Information System (INIS)

This paper describes the possibility of increasing the thermal power of the RA reactor, since there is a possibility to increase the heat flow of the heat exchanger. It is shown that the heat flow of the heat exchanger can be represented as a function of flow and the temperature of the incoming cooling fluid: Q = f (Q',t1'). Calculated values of the heat transfer coefficient are reduced by 25% because it has been found that the measured value was 25% higher than the real value of the heat transfer coefficient. Obtained data and diagrams can be used for determining the heat exchanger operating conditions for specific reactor operation regimes. The diagram shows that the the existing heat exchanger enables reactor operation at 10 MW power under any cooling condition, and even at 15 MW power under some conditions

122

Thermoelectric heat exchange element  

Science.gov (United States)

A thermoelectric heat exchange module includes a first substrate including a heat receptive side and a heat donative side and a series of undulatory pleats. The module may also include a thermoelectric material layer having a ZT value of 1.0 or more disposed on at least one of the heat receptive side and the heat donative side, and an electrical contact may be in electrical communication with the thermoelectric material layer.

Callas, James J. (Peoria, IL); Taher, Mahmoud A. (Peoria, IL)

2007-08-14

123

Plate-Type Heat Exchanger  

International Science & Technology Center (ISTC)

Conduction of Experimental Studies of Heat Exchange Element of Plate-Type Heat Exchanger Aiming at Enhancement of its Effectiveness Owing to Design Improvement and Optimization of Used Heat Exchange Intensifiers

124

Flow-induced vibration specifications for steam generators and liquid heat exchangers  

International Nuclear Information System (INIS)

It is desirable to avoid vibration problems by following appropriate guidelines and specifications at the design stage. Accordingly, design specifications were developed to prevent tube failures due to vibration in nuclear steam generators and liquid heat exchangers. These specifications are outlined in this report. (author). 14 refs., 2 figs

125

Heat exchanger design handbook  

CERN Document Server

Completely revised and updated to reflect current advances in heat exchanger technology, Heat Exchanger Design Handbook, Second Edition includes enhanced figures and thermal effectiveness charts, tables, new chapter, and additional topics--all while keeping the qualities that made the first edition a centerpiece of information for practicing engineers, research, engineers, academicians, designers, and manufacturers involved in heat exchange between two or more fluids.See What's New in the Second Edition: Updated information on pressure vessel codes, manufacturer's association standards A new c

Thulukkanam, Kuppan

2013-01-01

126

Visualization and void fraction measurement of gas-liquid two-phase flow in heat exchangers by neutron radiography  

International Nuclear Information System (INIS)

Gas-liquid two-phase flows in a plate heat exchanger and a vertical tube with a wire coil were visualized by a neutron radiography method to clarify the effect of configurations on phase distribution. For plate heat exchangers, adiabatic air-water flows and boiling R141b two-phase flows in a simulated test section with a single channel were visualized. From the results, it was shown that the effect of inlet configuration on the phase distribution was strongly dependent on the inlet configuration and inlet flow conditions. Especially, in the case where the incoming flow was a gas-liquid two-phase flow, liquid stagnation in an enlarged inlet section caused unsymmetrical phase distribution. Liquid mixing in the ribbed channel was weak. On the other hand, for a vertical tube with a wire coil, adiabatic air-water flows were visualized and cross-sectional void fraction distributions were calculated by a CT method from projection images from only one direction. The effect of a wire on the liquid distribution was clearly shown. Under the high gas velocity condition, liquid fraction on the wall at the upstream of the wire was lower than that at the downstream. (orig.)

127

Thermosyphon heat exchanger  

Science.gov (United States)

Report summarizes final development, testing, and certification of pumpless, liquid-to-air heat exchanger for solar heating. System requires blower but no pump in water loop. Output is 35,000 Btu/hr when water temperature is 49 C.

Hankins, J. D.

1980-01-01

128

Heat exchange enhancement structure  

International Nuclear Information System (INIS)

A passive heat exchange enhancement structure which operates by free convection includes a flat mounting portion having a plurality of integral fins bent outwardly from one side edge thereof. The mounting portion is securable around a stovepipe, to a flat surface or the like for transferring heat from the pipe through the fins to the surrounding air by rotation-enhanced free convection

129

Computational thermal-fluid dynamics analysis of the laminar flow regime in the meander flow geometry characterizing the heat exchanger used in high temperature superconducting current leads  

International Nuclear Information System (INIS)

Highlights: • The laminar regime in the meander flow geometry has been analysed with a previously validated computational strategy. • Several meander flow geometries as well as flow conditions have been analysed. • A range for the Reynolds number has been defined in which the flow can be considered laminar. • Correlations for the pressure drop and the heat transfer coefficients in the laminar regime have been derived. • A comparison between the computed the experimental pressure drop of the W7-X HTS current lead prototype is presented. -- Abstract: The Karlsruhe Institute of Technology and the Politecnico di Torino have developed and validated a computational thermal-fluid dynamics (CtFD) strategy for the systematic analysis of the thermal-hydraulics inside the meander flow heat exchanger used in high-temperature superconducting current leads for fusion applications. In the recent past, the application of this CtFD technique has shown that some operating conditions occurring in these devices may not reach the turbulent regime region. With that motivation, the CtFD analysis of the helium thermal-fluid dynamics inside different meander flow geometries is extended here to the laminar flow regime. Our first aim is to clarify under which operative conditions the flow regime can be considered laminar and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and for the heat transfer coefficient in the meander flow geometry have been derived, which are applicable with good accuracy to the design of meander flow heat exchangers over a broad range of geometrical parameters

130

Chapter 11. Heat Exchangers  

Energy Technology Data Exchange (ETDEWEB)

Most geothermal fluids, because of their elevated temperature, contain a variety of dissolved chemicals. These chemicals are frequently corrosive toward standard materials of construction. As a result, it is advisable in most cases to isolate the geothermal fluid from the process to which heat is being transferred. The task of heat transfer from the geothermal fluid to a closed process loop is most often handled by a plate heat exchanger. The two most common types used in geothermal applications are: bolted and brazed. For smaller systems, in geothermal resource areas of a specific character, downhole heat exchangers (DHEs) provide a unique means of heat extraction. These devices eliminate the requirement for physical removal of fluid from the well. For this reason, DHE-based systems avoid entirely the environmental and practical problems associated with fluid disposal. Shell and tube heat exchangers play only a minor role in low-temperature, direct-use systems. These units have been in common use in industrial applications for many years and, as a result, are well understood. For these reasons, shell and tube heat exchangers will not be covered in this chapter.

Rafferty, Kevin D.; Culver, Gene

1998-01-01

131

NUMERICAL SIMULATION OF VERTICAL GROUND HEAT EXCHANGERS FOR GROUND SOURCE HEAT PUMPS  

OpenAIRE

Abstract: This paper presents the numerical simulation of several types of vertical ground heat exchangers. The ground heat exchangers (GHEs) such as U-tube, double-tube and multi-tube were simulated using the commercial CFD software FLUENT. Water flows through the heat exchangers and exchanges the heat to the ground. The inlet and outlet water temperatures, flow rate, and heat exchange rate are presented. The heat exchange rates in discontinuous short-time period of operation ...

Jalaluddin

2011-01-01

132

Air-side performance of a parallel-flow parallel-fin (PF{sup 2}) heat exchanger in sequential frosting  

Energy Technology Data Exchange (ETDEWEB)

The thermal-hydraulic performance in periodic frosting conditions is experimentally studied for the parallel-flow parallel-fin heat exchanger, henceforth referred to as a PF{sup 2} heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal. Typically, it takes a few frosting/defrosting cycles to come to repeatable conditions. The criterion for the initiation of defrost and a sufficiently long defrost period are determined for the test PF{sup 2} heat exchanger and test condition. The effects of blower operation on the pressure drop, frost accumulation, water retention, and capacity in time are compared under the conditions of 15 sequential frosting cycles. Pressure drop across the heat exchanger and overall heat transfer coefficient are quantified under frost conditions as functions of the air humidity and air face velocity. The performances of two types of flat-tube heat exchangers, PF{sup 2} heat exchanger and conventional parallel-flow serpentine-fin (PFSF) heat exchanger, are compared and the results obtained are presented. (author)

Zhang, Ping [Zhejiang Vocational College of Commerce, Hangzhou, Binwen Road 470 (China); Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801 (United States); Hrnjak, P.S. [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801 (United States)

2010-09-15

133

Duct acoustic resonances induced by flow over coiled and rectangular heat exchanger test banks, of plain and finned tubes  

International Nuclear Information System (INIS)

The generation of acoustic resonances in ducts of rectangular and circular cross-section by gas flow over straight and coiled tube heat exchanger banks contained in the ducts has been studied. It has been shown that there is a distinct difference in behaviour between shallow heat exchanger banks, ie less than 40 rows deep, and deep banks, ie greater than 50 rows deep. It has also been shown that there is a distinct difference between the behaviour of finned tubes and plain tubes which is also dependent on the method of supporting the tubes. Some of these features can be predicted from theory but other aspects cannot as yet be explained by theory. (author)

134

Modular heat exchanger  

International Nuclear Information System (INIS)

A heat exchanger for use in nuclear reactors is disclosed which includes a heat exchange tube bundle formed from similiar modules each having a hexagonal shroud containing a large number of thermally conductive tubes which are connected with inlet and outlet headers at opposite ends of each module, the respective headers being adapted for interconnection with suitable inlet and outlet manifold means. In order to adapt the heat exchanger for operation in a high temperature and high pressure environment and to provide access to all tube ports at opposite ends of the tube bundle, a spherical tube sheet is arranged in sealed relation across the chamber with an elongated duct extending outwardly therefrom to provide manifold means for interconnection with the opposite end of the tube bundle

135

Vortex structure of a flow in a heat exchanger with twisted tubes  

International Nuclear Information System (INIS)

Experimental study on the intensity of longitudinal rate pulsations, autocorrelation function, spectral density and turbulence macroquantities in twisted tube beams with relative twisting pitches S/d=12.5 and 25 is carried out, therewith analogue thermoanemometric equipment, computers and digital signal analyser with tape interrecording, that allows an accurate X-ray analysis, was used. It is noticed that in the flow core an appreciable anisotropy of properties is detected that is due to presence of open channels and places of the tube contact. With high Reynolds numbers turbulent structure in this flow region yields to isotropic that may be used in designing heat mass transfer calculations in such beams

136

Experimental study of heat exchange coefficients, critical heat flux and charge losses, using water-steam mixtures in turbulent flow in a vertical tube  

International Nuclear Information System (INIS)

Two stainless steel tubes were used (with diameters of 5 and 10 mm, lengths 400 and 600 mm respectively), heated electrically (50 Hz). The mixture flows from top to bottom. The work was carried out mainly on mixtures of high concentration (x > 0.1), at pressures between 50 and 60 kg/cm2, flowing as a liquid film on the walls of the tube with droplets suspended in the central current of steam. By analysis of the heat transfer laws the exchange mechanisms were established, and the conditions under which the critical heat flux may be exceeded without danger of actual burnout were determined. In this way high output concentrations (xs > 0.9) may be obtained. An attempt has been made to find out to what extent existing correlation formulae can be used to account for the phenomena observed. It is shown that those dealing with exchange coefficients can only be applied in a first approximation in cases where exchange by convection is preponderant, and only below the critical flux. The formulae proposed by WAPD and CISE do not give a satisfactory estimation of the critical heat flux, and the essential reasons for this inadequacy are explained. Lastly, the Martinelli and Nelson method may be used to an approximation of 30 per cent for the calculation of charge losses. (author)

137

Cryogenic heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

A heat exchanger for vaporizing a cryogenic fluid comprises a conduit through which the fluid is passed and a heat transfer sleeve surrounding the conduit. The sleeve is comprised of two heat transfer sections, each having a central arcuate portion in close partial circumferential contact with the conduit, a plurality of radially extending heat transfer fins, and a pair of interlocking members located on the fins at a predetermined distance from the central portion for assembling the two sections together around the conduit. In the assembled state, the resiliency of the fins on which the interlocking members are located provides a continuous clamping for which permits the two central portions to maintain intimate contact with the conduit as it undergoes thermal contraction, while also facilitating assembly and disassembly of the two sections. Each heat transfer fins is also provided with a corrugated or rippled surface near its tip to increase its surface area and the rate of heat transfer and vaporization.

Lutjens, R. D.; Duron, P. P.

1984-12-11

138

Experimental evaluation of vibrations in heat exchangers  

International Nuclear Information System (INIS)

Flow induced vibrations may produce damage of heat exchangers, condensers and steam generators tubes. To evaluate this problem a set of tests were developed to know the real support state of the tubes, which have great influence on the vibration response. This paper include a description of the tests and the results obtained applying them on a heat exchanger equipment. (author)

139

Helically coiled tube heat exchanger  

International Nuclear Information System (INIS)

In a heat exchanger such as a steam generator for a nuclear reactor, two or more bundles of helically coiled tubes are arranged in series with the tubes in each bundle integrally continuing through the tube bundles arranged in series therewith. Pitch values for the tubing in any pair of tube bundles, taken transverse to the path of the reactor coolant flow about the tubes, are selected as a ratio of two unequal integers to permit efficient operation of each tube bundle while maintaining the various tube bundles of the heat exchanger within a compact envelope. Preferably, the helix angle and tube pitch parallel to the path of coolant flow are constant for all tubes in a single bundle so that the tubes are of approximately the same length within each bundle

140

Manufacture of heat exchangers  

International Nuclear Information System (INIS)

A tube bundle for use in a heat exchanger has a series of spaced parallel tubes supported by tube plates and is manufactured by depositing welding material around the end of each tube, machining the deposited material to form an annular flange around the end of the tube and welding the flange into apertures in the tube plate. Preferably the tubes have a length which is slightly less than the distance between the outer surfaces of the tube plates and the deposited material is deposited so that it overlaps and protects the end surfaces of the tubes. A plug may be inserted in the bore of the tubes during the welding material deposition which, as described, is effected by manual metal arc welding. One use of heat exchangers incorporating a tube bundle manufactured as above is in apparatus for reducing the volume of, and recovering nitric acid from, radioactive effluents from a nuclear reprocessing plant. (author)

141

Membrane Based Heat Exchanger  

OpenAIRE

Reduction of the energy used to acclimatise buildings is a huge challenge simultaneously with the implementation of air tight low energy buildings. In residential buildings with several living units centralised air handling units are the most energy efficient system. However, in a centralised system there is important to avoid leakages of pollutions between the exhaust air and the supply air. This leads to that flat plate heat exchangers are used instead of the more energy efficient rotary he...

Aarnes, Sofie Marie

2012-01-01

142

Experimental investigation of heat transfer performance coefficient in tube bundle of shell and tube heat exchanger in two-phase flow  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN6 and K4Fe(CN6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.

Kara? Marcin

2014-03-01

143

Heat exchangers for advanced reactors  

International Nuclear Information System (INIS)

Manufacturing and operating experience has been gained from different types of nuclear heat exchangers, in particular from steam generators built for gas-cooled reactor power stations. This expertise was used to advantage in the development and construction of heat exchangers for advanced nuclear systems. Design and thermal and structural analysis of heat exchanging equipment are accompanied by an extensive research and development program

144

Transient two-phase flow with heat exchange in a horizontal annular tube  

International Nuclear Information System (INIS)

An experimental system was designed and installed to investigate the effects of depressurisation in a horizontal annular test section; Freon-113 was used as a coolant in the experimental system with a maximum operating pressure of 194 kN/m2 and the test conditions covered a range of initial circulating velocities up to 0.55 m/s. Thermodynamic non-equilibrium was found experimentally from measuring both the pressure and temperature of the coolant at the outlet of the test section during the blowdown. The void fraction and the local heat transfer coefficient were increasing throughout the blowdown while the local surface temperature of the inner heated pipe decreased mainly due to the turbulence and agitation in the bulk of the flowing coolant created by bubble formation. Nucleate boiling and flash evaporation are the two mechanisms responsible for bubble formation. Satisfactory agreement was found between the heat transfer coefficient results and Chen correlation in the later stages of the transient

145

Simulation of the resistance and heat exchange under conditions of its intensification for the turbulent flow in channels of coolants with variable properties  

International Nuclear Information System (INIS)

The theoretical model for calculating the resistance and heat exchange under the conditions of its intensification by the turbulent flow of various types of coolants (gas, dropwise liquid) with variable monotonically changing thermophysical properties, is developed for the first time. The calculated data on the wide range of changes in the turbulators and flow modes parameters are obtained

146

Heat Exchangers Analysis  

Directory of Open Access Journals (Sweden)

Full Text Available Current research performs mathematics correlations between engine speed, coolant flow, vehicle speed and driving gear. A step-by-step procedure is described to obtain the engine cooling system parameters mathematically (include a CFD model. After obtaining the parameters, the thermal equilibrium of engine cooling system is studied thoroughly. The study of thermal equilibrium provides some insights on how to reduce engine cooling load and when the interference of cooling fan is required. A segmented spread sheet model is developed in order to explain the phenomenon which air flow driven by uniform ram air could dissipate higher amount of heat flow than air flow driven by cooling fan. The segmentation analysis concluded that minimum mCp fluid is switched to coolant when the air flow is concentrated at small portion of area.

S.C. Pang

2013-01-01

147

Numerical Simulation of Passive Residual Heat Removal Heat Exchanger  

International Nuclear Information System (INIS)

FLUENT software was employed to simulate the temperature-field and flow-field of AP1000 passive residual heat removal heat exchanger (PRHR HX), and investigate its heat-transferring and flow characteristics. Through comparative analysis of the distributions of temperature-field and flow-field in different locations at the same time, and the variations of temperature-field and flow-field in the same location at different time, heat-transferring process and natural convection situation of PRHR HX were understood deeply. It contributes to analyze the natural circulation capacity of PRHR HX, and provides some references for the effective operation of passive residual heat removal system. (authors)

148

Magnetic heat pump flow director  

Science.gov (United States)

A fluid flow director is disclosed. The director comprises a handle body and combed-teeth extending from one side of the body. The body can be formed of a clear plastic such as acrylic. The director can be used with heat exchangers such as a magnetic heat pump and can minimize the undesired mixing of fluid flows. The types of heat exchangers can encompass both heat pumps and refrigerators. The director can adjust the fluid flow of liquid or gas along desired flow directions. A method of applying the flow director within a magnetic heat pump application is also disclosed where the comb-teeth portions of the director are inserted into the fluid flow paths of the heat pump.

Howard, Frank S. (inventor)

1995-01-01

149

DHE (downhole heat exchangers). [Downhole Heat Exchangers (DHE)  

Energy Technology Data Exchange (ETDEWEB)

The use of downhole heat exchangers (DHE) for residential or commercial space and domestic water heating and other applications has several desirable features. Systems are nearly or completely passive -- that is, no or very little geothermal water or steam is produced from the well either reducing or completely eliminating surface environmental concerns and the need for disposal systems or injection wells. Initial cost of pumps and installation are eliminated or reduced along with pumping power costs and maintenance costs associated with pumping often corrosive geothermal fluids. Many residential and small commercial systems do not require circulating pumps because the density difference in the incoming and outgoing sides of the loop are sufficient to overcome circulating friction losses in the entire system. The major disadvantage of DHEs is their dependence on natural heat flow. In areas where geological conditions provide high permeability and a natural hydraulic gradient, DHEs can provide a substantial quantity of heat. A single 500-ft (152 m) well in Klamath Falls, Oregon, supplies over one megawatt thermal and output is apparently limited by the surface area of pipe that can be installed in the well bore. In contrast, DHEs used in conjunction with heat pumps may supply less than 8 KW from a well of similar depth. Here output is limited by conductive heat flow with perhaps a small contribution from convection near the well bore. The highest capacity DHE reported to date, in Turkey, supplies 6 MW thermal from an 820-ft (250 m) well. There were two main goals for this project. The first was to gather, disseminate and exchange internationally information on DHES. The second was to perform experiments that would provide insight into well bore/aquifer interaction and thereby provide more information on which to base DHE designs. 27 refs., 31 figs., 3 tabs.

Culver, G.

1990-11-01

150

Flow visualization of annular and delta winglet vortex generators in fin-and-tube heat exchanger application  

Energy Technology Data Exchange (ETDEWEB)

This study presents flow visualization and frictional results of enlarged fin-and-tube heat exchangers with and without the presence of vortex generators. Two types of vortex generators and a plain fin geometry were examined in this study. For plain fin geometry at Re=500, the horseshoe vortex generated by the tube row is not so pronounced, and the horseshoe vortex separates into two streams as it flows across the second row and consequently loses its vortical strength. This phenomenon may support the ''maximum phenomenon'' in low Reynolds number region reported by previous studies. With the presence of annular vortex generator, the presence of a pair of longitudinal vortices formed behind the tube is seen. The strength of the counter-rotating vortices increases with the annular height and the strength of the longitudinal vortices is so strong that may swirl with the horseshoe vortices and other flow stream. For the same winglet height, the delta winglet shows more intensely vortical motion and flow unsteadiness than those of annular winglet. This eventually leads to a better mixing phenomenon. However, it is interesting to know that the corresponding pressure drops of the delta winglet are lower than those of annular winglet. Compared to the plain fin geometry, the penalty of additional pressure drops of the proposed vortex generators is relatively insensitive to change of Reynolds number. (author)

Wang, C.-C.; Wei, C.-S. [Energy and Resources Labs., Hsinchu (Taiwan); Lo, J.; Lin, Y.-T. [Yuan Ze Univ., Taiwan (Taiwan). Dept. of Mechanical Engineering

2002-08-01

151

Surface Chemical Composition Effect on Internal Gas Flow and Molecular Heat Exchange in a Gas-Solids System  

Science.gov (United States)

On the basis of classical knowledge about movement of atoms and lattice theory of F. Goodman and G. Wachman the program modeling helium atom interaction with a three-dimensional crystal tungsten lattice taking into account partial surface covering by chemisorbed oxygen atoms is developed. An efficiency of molecular heat exchange of helium for pure and partially chemisorbed tungsten surface is calculated for different temperatures. Similar model of the surface and procedure of calculations have been applied for description of free-molecular gas flow in long cylindrical channel with clean and fully chemisorbed metal surface. Within the limits of the developed approach the results of calculations for both problems agree well with available experiments with surface contamination control.

Ukhov, Alexander; Borisov, Sergey; Porodnov, Boris

2011-05-01

152

Plate heat exchanger  

International Nuclear Information System (INIS)

In a plate heat exchanger required to handle corrosive, toxic or radioactive fluids, wherein each plate has a peripheral recess or like formation adapted for receiving an elastomeric gasket, the plates are welded together in pairs by the method comprising the steps of inserting into the gasket recess of a first plate of said pair a metal packing piece and welding the second place (e.g. by a laser or electron beam weld running along the base of the recess) superimposing a second plate on to the first in contact with the packing piece and welding the second plate to the packing piece (e.g. by a laser or electron beam weld). The packing piece may be of hollow or solid cross section and is preferably of the same material (e.g. titanium or stainless steel) as the plates. In use a service fluid in heat exchange with the said corrosive etc. fluid is confined by peripheral and normally elastomeric gaskets. (author)

153

Heat exchanger for liquid metals  

International Nuclear Information System (INIS)

The heat exchanger is for liquid metals, such as sodium, whereby the secondary liquid metal is fed through parallel pipes in one or more pipe bundles, and wherein the pipes, between pipe plates or other assembly pieces, are introduced, and the primary liquid metal flows or circulates along the outside of the pipes, characterised by that the pipes of the pipe handles consist of molybdenum, tantalum or niobium, or alloys thereof, and the outside diameter lies between 6 and 16 mm at least. (G.C.)

154

Two phase heat exchanger symposium  

International Nuclear Information System (INIS)

This book compiles the papers presented at the conference on the subject of heat transfer mechanics and instrumentation. Theoretical and experimental data are provided in each paper. The topics covered are: temperature effects of steel; optimization of design of two-phase heat exchanges; thermosyphon system and low grade waste heat recovery; condensation heat transfer in plate heat exchangers; forced convective boiling; and performance analysis of full bundle submerged boilers

155

A two Layer Convecting Mantle With Exchange : A Unified Model Based on Geochemical, Seismic and Heat Flow Observations  

Science.gov (United States)

The question of layered versus whole mantle convection has been pending since early models of mantle convection (Oxburgh and Turcotte, 1967; McKenzie and Richter, 1978). In a first phase, layered mantle models appeared to be the winners, because they explained most of geochemical observations. They of course also explained the seismic focal solutions (compressive/ non compressive) in subducting plate and the heat flow constraints (Richter, 1980). Later on, the discovery that slabs could penetrate the lower mantle was considered as proof of whole mantle convection. Most numerical experiments were then developed in this context, overlooking many geochemical observations such as rare gas isotopes or radioactive elements. In this presentation, we will examine the different data one by one. a) geochemical constraints include the budget equations for Sr, Nd, Hf, isotopes, the budget equation for He, Ne, Ar, the budget for heat producing elements U, Th, K (including Th/U and K/U ratios). (Allègre and al., 1979, 1982; De Paolo and Wasserburg, 1977; O'Nions and al.,1977). b) Constrains linking geochemical observations and geodynamics. How the so-called depleted mantle is generated ? Continuities and affinities between MORB and OIB, including the Dupal and Non Dupal provinces: The non-pristine source for OIB based on Pb isotope data. The marble cake structure for upper mantle. Continental crust recycling via sediments and delamination processes. In thise respect, we emphasize the difference in statistical variance of isotope or trace element ratios in the different/types of basalts reflecting the difference in stirring intensity in their sources. We also use information from extinct radioactivities 142Nd and 129Xe. In each case, we estimate the errors for measurements and models. c) The seismic evidence of slab penetration into the lower mantle are from Creager and Jordan(1984) to Van der Hilst et al.(1991), Sparkman and al.(1993), with the counter example of non-penetrating slabs as emphasized by Fukao and al.(2001) and the recent observation of the large energy spectrum differences at 670 km depth (Gu and al., 2006). We discuss the problem of return flow, which is crucial for both energy budget and convection regime. The recent work on plume by Montelli and al. (2004, 2006) shows the existence of broad plumes in the lower mantle and thin plumes in the upper mantle. d) The estimate of heat flow coming from the lower mantle of 35-32 TW. The work of Davies(1990) and Sleep(1992) shows clearly that this transfer is not the result of plumes reaching the surface, because they correspond at most to 3TW. At the reverse the estimated heat flow carried by the lower mantle plumes is much higher (Nolet and al., 2006). We also discuss the heat flow paradox to explain a Urey ratio of 0.4 with whole mantle convection. In conclusion, we propose mantle with two layers convecting separately but with some exchange of matter, this global exchange corresponding to 1.1024kg since 4.4 Gy. Plume genesis is a two-stage process. Lower mantle plumes heat the Mesosphere boundary layer generating second generation plumes which reach the surface (Allègre and Turcotte; 1983; Allègre, 1987). In the upper mantle itself, we have to distinguish between a vigorously convecting asthenosphere and a sluggish convecting transition zone, both convecting in same cells.

Allègre, C. J.; Jaupart, C.; Nolet, G.

2007-12-01

156

Performance test of miniature heat exchangers with microchannels  

International Nuclear Information System (INIS)

Etched microchannel heat exchanger, a subfield within MEMS, has high heat flux capability. This capability makes microchannels well-suited for a wide variety of application of cooling and chemical reaction. In this study, counter flow type miniature heat exchangers, which have flat metal plates with chemically etched microchannels, were manufactured by brazing method. Four type of the heat exchangers, which have straight microchannels, wavy shape microchannels, pin-fin channels and serpentine shape microchannels, were investigated to compare their thermal and hydraulic performance. Gas to gas heat exchange experiments were performed to measure the pressure drop and effectiveness of the heat exchangers at given gas flow rates and temperature difference

157

Microchannel heat exchangers for advanced climate control  

Science.gov (United States)

This paper presents details of fabrication and performance testing of prototype microchannel heat exchangers. The microchannel heat exchangers are being developed for advanced cooling and climate control applications, and are designed for heat loads of 100 W/cm2. Bulk and surface micromachining techniques are used to fabricate the test devices. Each heat exchanger section consists of over 150 microchannels etched in silicon substrates by either chemical etching or ion milling processes. The channels are 100-micrometers deep, 100-micrometers wide, and spaced 50- to 100-micrometers apart and connected with headers. Other heat exchangers have also been fabricated in copper and aluminum using machining and ion milling processes. Process steps involved photolithographic patterning, deposition of etch masks, ion or chemical etching, electrostatic bonding of the silicon to glass, insulator deposition, lamination of silicon to metals, application of thin heater coatings with busbars, and installation of the inlet/outlet hardware and valves. Recent hear exchangers have the silicon laminated to copper substrates. Performance testing focuses on determining the performance characteristics of the microchannel heat exchangers over a wide range of flow and heat transfer conditions. The working fluid for heat transfer is restricted to water or SUVA refrigerant HCFC-124 (R-124). Testing with water is run under single-phase conditions. The tests with R-124 are run under single-and two-phase flow conditions.

Martin, Peter M.; Bennett, Wendy D.; Johnston, John W.

1995-09-01

158

Next Generation Microchannel Heat Exchangers  

CERN Document Server

In Next Generation Microchannel Heat Exchangers, the authors’ focus on the new generation highly efficient heat exchangers and presentation of novel data and technical expertise not available in the open literature.  Next generation micro channels offer record high heat transfer coefficients with pressure drops much less than conventional micro channel heat exchangers. These inherent features promise fast penetration into many mew markets, including high heat flux cooling of electronics, waste heat recovery and energy efficiency enhancement applications, alternative energy systems, as well as applications in mass exchangers and chemical reactor systems. The combination of up to the minute research findings and technical know-how make this book very timely as the search for high performance heat and mass exchangers that can cut costs in materials consumption intensifies.

Ohadi, Michael; Dessiatoun, Serguei; Cetegen, Edvin

2013-01-01

159

Tube bundle assembly for a heat exchanger  

International Nuclear Information System (INIS)

An improved type of tube bundle assembly for a heat exchanger is described which can be used as a reheater section of a vapour generator in a gas-cooled nuclear reactor. The assembly has a compact annular configuration while providing effective heat exchange capabilities, maintains minimum gas flow resistance and allows for differential expansion without the use of unheated cross-over connections. (U.K.)

160

Influence of Ionic Fluid in Counter flow in Shell and Tube Heat Exchanger  

OpenAIRE

An Ionanofluids are a new and innovative class of heat transfer fluids which exhibit fascinating thermo physical properties compared to their base ionic liquids. In this paper (1-Butyl-3-methylimidazolium chloride) (BmimCL)ionic fluid is used comparison with Distilled Water. Distilled Water is non Ionic form in nature, so, results using (BmimCL)is Overall good efficient in heat transfer device, were obtained with experimental work results on thermal conductivity and heat capacity,. As compare...

Shirgire, N. D.; Bhansali, S. S.; Bhagat, A. R.; Padgelwar, A. G.; Ghawade, P. S.

2014-01-01

161

Appendix to the thesis an experimental and numerical study of a jetfire stop material and a new helical flow heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

This thesis consists of two parts. Part 1: Experimental and numerical study of jetfire stop, and Part 2: Experimental and numerical study of a new kind of shell and tube heat exchanger with helical flow on shell side. Part 1 describes the development of the model for simulation of the temperature development through Viking jetfirestop. A simulation program is developed that calculates the temperature development through Viking jetfirestop. In the development of the model, measurements of reaction energy, pyrolysis and heat conductivity at low temperatures are made. The conductivity at higher temperatures and when pyrolysis reactions are going on is estimated experimentally and by numerical calculations. Full-scale jet fire test and small-scale xenon lamp experiments are made to test the simulation model. Part 2 contains the development of a model that simulate the fluid flow and heat transfer in a helical flow shell and tube heat exchanger. It consists of the development of a porosity model and a model for pressure drop and heat transfer as well as experiments in non-standard tube layouts. Results from the simulation program are compared with experiments on a helical flow shell and tube heat exchanger. This is a separate appendix volume, including computer codes and simulated results. 316 figs., 11 tabs.

Austegard, Anders

1997-12-31

162

Heat exchanger with auxiliary cooling system  

International Nuclear Information System (INIS)

A heat exchanger with an auxiliary cooling system is described which is capable of cooling a nuclear reactor should the normal cooling mechanism become inoperable. A cooling coil is disposed around vertical heat transfer tubes that carry secondary coolant therethrough and is located in a downward flow of primary coolant that passes in heat transfer relationship with both the cooling coil and the vertical heat transfer tubes. A third coolant is pumped through the cooling coil which absorbs heat from the primary coolant which increases the downward flow of the primary coolant thereby increasing the natural circulation of the primary coolant through the nuclear reactor

163

Regenerative heat exchangers. Regeneratiivinen kuulalaemmoensiirrin  

Energy Technology Data Exchange (ETDEWEB)

The aim of this research was to develop a computer program that could be used for simulating heat transfer and pressure drop in a regenerative particle heat exchanger for gases. Particles were considered spherical. Two cases were studied, counterflow- and crossbow heat exchangers. Heat transfer by conduction and radiation were considered small compared to heat transfer by forced convection. The convection heat transfer coefficient and pressure drop are calculated by using empirical correlations developed for packed beds. In the program there is a possibility to choose different correlations in different cases. The heat transfer equation in spherical coordinates is discretized by using implicit difference method and solved by the matrix inversion method. (orig.)

Vaittinen, P.

1998-01-01

164

Regenerative heat exchangers; Regeneratiivinen kuulalaemmoensiirrin  

Energy Technology Data Exchange (ETDEWEB)

The aim of this research was to develop a computer program that could be used for simulating heat transfer and pressure drop in a regenerative particle heat exchanger for gases. Particles were considered spherical. Two cases were studied, counterflow- and crossbow heat exchangers. Heat transfer by conduction and radiation were considered small compared to heat transfer by forced convection. The convection heat transfer coefficient and pressure drop are calculated by using empirical correlations developed for packed beds. In the program there is a possibility to choose different correlations in different cases. The heat transfer equation in spherical coordinates is discretized by using implicit difference method and solved by the matrix inversion method. (orig.)

Vaittinen, P.

1998-12-31

165

Asymptotic analysis of the flow of shear-thinning foodstuffs in annular scraped heat exchangers  

OpenAIRE

The problem of isothermal flow of a shear-thinning (pseudoplastic) fluid in the gap between two concentric cylinders is considered. A pump provides an axial pressure gradient which causes flow down the device. The outer cylinder is fixed and has 'scrapers' attached to it to cause flow mixing, whilst the inner cylinder rotates about its axis to provide shear and thus thin the fluid. The goal is to determine the optimal distribution of power between rotation and pumping. Although ostensibly the...

Fitt, Ad; Please, Cp

2001-01-01

166

Heat exchanger leakage problem location  

Directory of Open Access Journals (Sweden)

Full Text Available Recent compact heat exchangers are very often assembled from numerous parts joined together to separate heat transfer fluids and to form the required heat exchanger arrangement. Therefore, the leak tightness is very important property of the compact heat exchangers. Although, the compact heat exchangers have been produced for many years, there are still technological problems associated with manufacturing of the ideal connection between the individual parts, mainly encountered with special purpose heat exchangers, e.g. gas turbine recuperators. This paper describes a procedure used to identify the leakage location inside the prime surface gas turbine recuperator. For this purpose, an analytical model of the leaky gas turbine recuperator was created to assess its performance. The results obtained are compared with the experimental data which were acquired during the recuperator thermal performance analysis. The differences between these two data sets are used to indicate possible leakage areas.

Jícha Miroslav

2012-04-01

167

Computation of two-dimensional isothermal flow in shell-and-tube heat exchangers  

International Nuclear Information System (INIS)

A computational procedure is outlined whereby two-dimensional isothermal shell-side flow distributions can be calculated for tube bundles having arbitrary boundaries and flow blocking devices, such as sealing strips, defined in arbitrary locations. The procedure is described in some detail and several computed results are presented to illustrate the robustness and generality of the method

168

Heat pipes in modern heat exchangers  

International Nuclear Information System (INIS)

Heat pipes are very flexible systems with regard to effective thermal control. They can easily be implemented as heat exchangers inside sorption and vapour-compression heat pumps, refrigerators and other types of heat transfer devices. Their heat transfer coefficient in the evaporator and condenser zones is 103-105 W/m2 K, heat pipe thermal resistance is 0.01-0.03 K/W, therefore leading to smaller area and mass of heat exchangers. Miniature and micro heat pipes are welcomed for electronic components cooling and space two-phase thermal control systems. Loop heat pipes, pulsating heat pipes and sorption heat pipes are the novelty for modern heat exchangers. Heat pipe air preheaters are used in thermal power plants to preheat the secondary-primary air required for combustion of fuel in the boiler using the energy available in exhaust gases. Heat pipe solar collectors are promising for domestic use. This paper reviews mainly heat pipe developments in the Former Soviet Union Countries. Some new results obtained in USA and Europe are also included

169

High Temperature Heat Exchanger Project  

Energy Technology Data Exchange (ETDEWEB)

The UNLV Research Foundation assembled a research consortium for high temperature heat exchanger design and materials compatibility and performance comprised of university and private industry partners under the auspices of the US DOE-NE Nuclear Hydrogen Initiative in October 2003. The objectives of the consortium were to conduct investigations of candidate materials for high temperature heat exchanger componets in hydrogen production processes and design and perform prototypical testing of heat exchangers. The initial research of the consortium focused on the intermediate heat exchanger (located between the nuclear reactor and hydrogen production plan) and the components for the hydrogen iodine decomposition process and sulfuric acid decomposition process. These heat exchanger components were deemed the most challenging from a materials performance and compatibility perspective

Anthony E. Hechanova, Ph.D.

2008-09-30

170

Expanded microchannel heat exchanger: design, fabrication and preliminary experimental test  

CERN Document Server

This paper first reviews non-traditional heat exchanger geometry, laser welding, practical issues with microchannel heat exchangers, and high effectiveness heat exchangers. Existing microchannel heat exchangers have low material costs, but high manufacturing costs. This paper presents a new expanded microchannel heat exchanger design and accompanying continuous manufacturing technique for potential low-cost production. Polymer heat exchangers have the potential for high effectiveness. The paper discusses one possible joining method - a new type of laser welding named "forward conduction welding," used to fabricate the prototype. The expanded heat exchanger has the potential to have counter-flow, cross-flow, or parallel-flow configurations, be used for all types of fluids, and be made of polymers, metals, or polymer-ceramic precursors. The cost and ineffectiveness reduction may be an order of magnitude or more, saving a large fraction of primary energy. The measured effectiveness of the prototype with 28 micro...

Denkenberger, David C; Pearce, Joshua M; Zhai, John; 10.1177/0957650912442781

2012-01-01

171

Thermodynamic Optimization of GSHPS Heat Exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available

In this paper, a new method for determining the optimized dimensions of a ground source heat pump system (GSHPS heat exchanger is presented. Using the GSHPS is one of the ways for utilization of infinite, clean and renewable energies in the environment. In recent years, due to limitation of physical space for installing the heat exchangers and avoiding the environmental effects on heat exchanger operation, vertical GSHP systems are used more than the other ones. Determination of optimum heat exchanger size is one of the most important parameters in the optimization of the heat exchanger design. In this study, optimum length and diameter for the heat exchanger is determined for different mass flows by using the second law of thermodynamics. The optimal length and diameter minimize entropy generation and therefore result in increased efficiency of the heat pump.

  • An initial version of this pa per was published in May of 2004 in the proceedings of Second International Applied Thermodynamics Conference, Istanbul, Turkey.

Ahmad Kahrobaeian

2007-09-01

172

Method for removing coronene from heat exchangers  

International Nuclear Information System (INIS)

A method for removing a coronene deposit in a reforming process is described that consists of (A) contacting a hydrocarbonacous feedstock with a catalyst in the presence of added hydrogen at reforming conditions in a reforming zone; (B) splitting the total reforming zone effluent into a first stream and a second stream; (C) passing said first stream into a first train of heat exchangers arranged in parallel with a second train of heat exchangers; (D) passing said second stream into said second train of heat exchangers, said reforming zone effluent comprising coronene, at least a portion of which deposits in said heateexchangers; (E) separating the heat exchanged total reforming zone effluent into a hydrogen-rich gaseous phase and a liquid hydrocarbon phase comprising normally liquid hydrocarbons and normally gaseous hydrocarbons, the improvement which comprises reducing the flow of said first stream in said first train of heat exchangers to produce a temperature sufficient to condense at least a portion of said reformer effluent therein such that the resulting condensate contacts said coronene deposit, and simultaneously increasing the flow of said second stream in said second train of heat exchangers

173

Visualization and void fraction distribution of downward gas-liquid two-phase flow in a plate heat exchanger by neutron radiography  

International Nuclear Information System (INIS)

Adiabatic vertically downward air-water two-phase flows in a commercial plate heat exchanger were visualized by a neutron radiography method as a non-destructive test in order to clarify the flow characteristics and the differences of the liquid distributions from those of the vertically upward flows. Flow behaviors in a single channel and a multi-channel plate heat exchanger were investigated. From the visualized results of the flows in a single channel, it was shown that water fell down without a spreading at a lower gas volumetric flux of less than about 2 m/s. In the case of a higher gas volumetric flux above 2 m/s, liquid spread around the enlarged section and the liquid distribution in the main part of the heat exchanger seemed to be homogenous. Measured average void fractions for the air-water downward flows showed almost the same tendency as those for the upward flows in spite of the difference of the flow patterns. On the other hand, liquid distributions into 18 parallel channels were evaluated from the measured results of the liquid volumetric fractions in each channel. It was shown that the liquid distribution depended on the inlet liquid flow rate. However, the effect of the gas flow rate was a little. In the case of higher liquid flow rate, the liquid fraction became higher with a deeper channel due to a larger liquid momentum. However, in the case of a lower liquid flow rate, the opposite tendency was observed, i.e., the liquid fraction in the nearest ch.e., the liquid fraction in the nearest channel to the inlet was higher

174

Experimental study on the heat transfer and pressure drop of a cross-flow heat exchanger with different pin-fin arrays  

Science.gov (United States)

In this study, convective heat transfer and pressure drop in a cross-flow heat exchanger with hexagonal, square and circular (HSC) pin-fin arrays were studied experimentally. The pin-fins were arranged in an in-line manner. For the applied conditions, the optimal spacing of the pin-fin in the span-wise and stream-wise directions has been determined. The variable parameters are the relative longitudinal pitch ( S L / D = 2, 2.8, 3.5), and the relative transverse pitch was kept constant at S T / D = 2. The performances of all pin-fins were compared with each other. The experimental results showed that the use of hexagonal pin-fins, compared to the square and circular pin-fins, can lead to an advantage in terms of heat transfer enhancement. The optimal inter-fin pitches are provided based on the largest Nusselt number under the same pumping power, while the optimal inter-fin pitches of hexagonal pin-fins are S T / D = 2 and S L / D = 2.8. Empirical equations are derived to correlate the mean Nusselt number and friction coefficient as a function of the Reynolds number, pin-fin frontal surface area, total surface area, and total number. Consequently, the general empirical formula is given in the present form. NuD = a(ReD )b ( {{{Nt Af }/{A_{{total} }}}} )c quad {{and}}quad f = a(ReD )b

Kotcioglu, Isak; Caliskan, Sinan; Baskaya, Senol

2011-09-01

175

Heat transfer coefficients of shell and coiled tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

In the present study, the heat transfer coefficients of shell and helically coiled tube heat exchangers were investigated experimentally. Three heat exchangers with different coil pitches were selected as test section for both parallel-flow and counter-flow configurations. All the required parameters like inlet and outlet temperatures of tube-side and shell-side fluids, flow rate of fluids, etc. were measured using appropriate instruments. Totally, 75 test runs were performed from which the tube-side and shell-side heat transfer coefficients were calculated. Empirical correlations were proposed for shell-side and tube-side. The calculated heat transfer coefficients of tube-side were also compared to the existing correlations for other boundary conditions and a reasonable agreement was observed. (author)

Salimpour, M.R. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran)

2009-01-15

176

Air-sand heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

This paper summarizes research activities that analyse the thermodynamic behaviour of an Air / Sand Heat Exchanger, developed by Solar-Institut Juelich (SIJ) and the German Aerospace Centre (DLR). A numerical 3-D model, new results and a model validation of this particular cross-flow heat exchanger are presented. Simulation results were obtained for sand with 1-2 mm grain size. The simulation was validated with operational results of a new 15 kW prototype unit. Ansys, including Ansys-CFX, is used as modelling and simulation platform. The bulk material is modelled by a porous solid medium without structural dynamic interaction between fluid and solid phase. For pressure drop calculations, Ergun's model for bulk material is used. The model parameters were validated and fitted with measured values of a separate pressure drop test rig. The validation was done with quartz sand. To determine the suitability of available granular products for this application, tests have been conducted regarding the thermomechanical properties as well as their attrition behaviour and abrasion on various wall materials.

Baumann, Torsten; Zunft, Stefan [German Aerospace Center (DLR), Stuttgart (Germany); Boura, Cristiano; Eckstein, Julian; Felinks, Jan; Goettsche, Joachim; Hoffschmidt, Bernhard; Schmitz, Stefan [FH Aachen, Juelich (Germany). Solar-Inst. Juelich

2011-07-01

177

Sleeving repair of heat exchanger tubes  

International Nuclear Information System (INIS)

Defective heat exchanger tubes can be repaired using techniques that do not involve the cost and schedule penalties of component replacement. FTI's years of experience repairing steam generator tubes have been successfully applied to heat exchangers. Framatome Technologies heat exchanger sleeves can bridge defective areas of the heat exchanger tubes, sleeves have been designed to repair typical heat exchanger tube defects caused by excessive tube vibration, stress corrosion cracking, pitting or erosion. By installing a sleeve, the majority of the tube's heat transfer and flow capacity is maintained and the need to replace the heat exchanger can be delayed or eliminated. Both performance and reliability are improved. FTI typically installs heat exchanger tube sleeves using either a roll expansion or hydraulic expansion process. While roll expansion of a sleeve can be accomplished very quickly, hydraulic expansion allows sleeves to be installed deep within a tube where a roll expander cannot reach. Benefits of FTI's heat exchanger tube sleeving techniques include: - Sleeves can be positioned any where along the tube length, and for precise positioning of the sleeve eddy current techniques can be employed. - Varying sleeve lengths can be used. - Both the roll and hydraulic expansion processes are rapid and both produce joints that do not require stress relief. - Because of low leak rates and speed of installations, sleeves can be used to preventatively repair likely-to-f used to preventatively repair likely-to-fail tubes. - Sleeves can be used for tube stiffening and to limit leakage through tube defects. - Because of installation speed, there is minimal impact on outage schedules and budgets. FTI's recently installed heat exchanger sleeving at the Kori-3 Nuclear Power Station in conjunction with Korea Plant Service and Engineering Co., Ltd. The sleeves were installed in the 3A and 3B component cooling water heat exchangers. A total of 859 tubesheet and 68 freespan sleeves were installed in the 3A heat exchanger, and 1020 tubesheet and 244 freespan sleeves were installed in the 3B heat exchanger. Hydraulically expanded sleeves were used in the freespan areas while the tubesheet sleeves were roll expanded. (author)

178

Fluid-elastic instability of heat exchanger tube arrays in potential cross-flow  

International Nuclear Information System (INIS)

In order to study the fluid-elastic instability effects of tube arrays in a uniform cross-flow, Van der Hoogt and Van Campen (1984) adopted a two-dimensional complex velocity potential approach and calculations were performed on two tubes out of a tube array. A potential flow approach was used, because, for closely packed staggered tube arrays, the wakes behind the tubes are considerably suppressed and the flow distribution around the tubes shows a 'potential-like' character. In the present paper the model is extended to account for more complex configurations, followed by an examination of their dynamical features. For a specific staggered configuration the results of the critical flow velocities will be compared with Paidoussis (1984) data, who dealt with a comparable approach. In order to account for the influence of a phase lagging effect between the motions of the tubes and the fluid forces, a modification of the model was performed by introducing a phase lag angle ?. Dynamical (flutter) instability was found to occur for specific configurations of tubes whenever a non-zero phase lagging effect was incorporated in the calculations. For a specific configuration critical velocities were compared with the results obtained by Paidoussis et al. (1984), dealing with a similar approach. Although agreement was found for the critical buckling velocities using ? = 00, discrepancies occurred for the critical flutter velocities, using ? = 100 and ? ities, using ? = 100 and ? = 300 possibly due to the different way of incorporating the phase lag effect in the equations of motion. Although the present model predicts that the reduced critical velocity depends on the square root of the mass-damping parameter m?/?D2 in a similar way as found by Connors, the actual values are larger than the experimental values from literature. (orig./GL)

179

Observer-based monitoring of heat exchangers.  

Science.gov (United States)

The goal of this work is to provide a method for monitoring performance degradation in counter-flow double-pipe heat exchangers. The overall heat transfer coefficient is estimated by an adaptive observer and monitored in order to infer when the heat exchanger needs preventive or corrective maintenance. A simplified mathematical model is used to synthesize the adaptive observer and a more complex model is used for simulation. The reliability of the proposed method was demonstrated via numerical simulations and laboratory experiments with a bench-scale pilot plant. PMID:17706652

Astorga-Zaragoza, Carlos-Manuel; Alvarado-Martínez, Víctor-Manuel; Zavala-Río, Arturo; Méndez-Ocaña, Rafael-Maxim; Guerrero-Ramírez, Gerardo-Vicente

2008-01-01

180

Hierarchic modeling of heat exchanger thermal hydraulics  

International Nuclear Information System (INIS)

Volume Averaging Technique (VAT) is employed in order to model the heat exchanger cross-flow as a porous media flow. As the averaging of the transport equations lead to a closure problem, separate relations are introduced to model interphase momentum and heat transfer between fluid flow and the solid structure. The hierarchic modeling is used to calculate the local drag coefficient Cd as a function of Reynolds number Reh. For that purpose a separate model of REV is built and DNS of flow through REV is performed. The local values of heat transfer coefficient h are obtained from available literature. The geometry of the simulation domain and boundary conditions follow the geometry of the experimental test section used at U.C.L.A. The calculated temperature fields reveal that the geometry with denser pin-fins arrangement (HX1) heats fluid flow faster. The temperature field in the HX2 exhibits the formation of thermal boundary layer between pin-fins, which has a significant role in overall thermal performance of the heat exchanger. Although presented discrepancies of the whole-section drag coefficient Cd are large, we believe that hierarchic modeling is an appropriate strategy for calculation of complex transport phenomena in heat exchanger geometries.(author)

181

Explosive plugging of heat exchangers  

International Nuclear Information System (INIS)

The mechanism and development of explosive welding and particularly the application to tube-to-tubeplate welding is briefly reviewed. The need for plugging of heat exchangers in the power generating industry and the requirement for producing a high integrity weld are discussed. Details are given of the explosive plugging system developed for the reheater heat exchanger of the prototype fast reactor (PFR), including data on weld lengths and distortion of adjoining holes. Results of destructive and nondestructive tests on trial plugging of a seven hole array are given. The system described has been successfully applied to an actual heat exchanger and the procedure followed is briefly discussed

182

Fluid-elastic instability of heat exchanger tube arrays in potential cross-flow  

International Nuclear Information System (INIS)

Possibly occurring instabilities may be classified into buckling instability (divergence) and dynamical instability (flutter). Calculations revealed only instabilities of the divergence type, whenever a phase lagging angle equal to zero between the tube and fluid motion was used. The associated critical flow velocity appeared to be strongly dependent on the system geometry, thus on the number of tubes and their mutual distance. In order to account for the influence of a phase lagging effect between the motions of the tubes and the fluid sources, a modification of the model was performed by introducing a phase lag angle eta. Dynamical (flutter) instability was found to occur for specific configurations of tubes whenever a non-zero phase lagging effect was incorporated in the calculations. For a specific configuration critical velocities were compared with the results obtained by Paidoussis, dealing with a similar approach. Although agreement was found for the critical buckling velocities using eta = 0/sup o/, discrepancies occurred for the critical futter velocities, using eta = 10/sup o/ and eta = 30/sup o/ possibly due to the different way of incorporating the phase lag effect in the equations of motion. Although the present model predicts that the reduced critical velocity depends on the square root of the mass-damping parameter m?rhoD2 in a similar way as found by Connors, the actual values are larger than the experimental values from literatureperimental values from literature

183

Milk fouling in heat exchangers.  

OpenAIRE

The mechanisms of fouling of heat exchangers by milk were studied. Two major fouling mechanisms were indentified during the heat treatment of milk: (i) the formation and the subsequent deposition of activated serum protein molecules as a result of the heat denaturation; (ii) the precipitation of calcium phosphate as a result of the decreased solubility of this salt upon heating. Both foulants are formed in the bulk of the solution and are transported to the surface, where they can be deposite...

Jeurnink, Th J. M.

1996-01-01

184

Analysis of Heat Transfer Enhancement in Spiral Plate Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available In the present study, the heat transfer coefficients of benzene in a spiral plate heat exchanger are investigated. The test section consists of a Plate of width 0.3150 m, thickness 0.001 m and Mean hydraulic diameter of 0.01 m. The mass flow rate of water (Hot fluid is varying from 0.5 kg sec-1 to 0.8 kg sec-1 and the mass flow rate of benzene (cold fluid varies from 0.4 kg sec-1 to 0.7 kg sec-1. Experiments have been conducted by varying the mass flow rate, temperature and pressure of cold fluid, keeping the mass flow rate of hot fluid constant. The effects of relevant parameters on spiral plate heat exchanger are investigated. The data obtained from the experimental study are compared with the theoretical data. Besides, a new correlation for the nusselt number which can be used for practical applications is proposed.

Kaliannan Saravanan

2009-02-01

185

How flow dispersion affects exchanger performance  

International Nuclear Information System (INIS)

The Fluid Dynamics of the two streams in heat exchangers have not been analyzed sufficiently for studies of pressure drop. While the effect of axial dispersion of the process stream on the driving force is generally considered in the design of mass transfer operations, it is ignored for the design of the heat transmitting area. There may exist, however, large differences in heat exchanger efficiency as a result of different flow patterns, which may lie between perfect mixing and plug flow. In general, the heat transfer characteristics of different types of heat exchangers, e.g., single pass, cross flow, shell and tube, are represented by the correction factor F = Q/sub T//UA?T/sub iotan/ or the heat exchanger effectiveness E = Q/sub T//[(mc/sub p/)min (T/sub in/ - t/sub in/]. Graphical representations are generally given for plug flow and perfect mixing and are used to obtain the heat transfer, transfer area and the fluid outlet temperatures. In reality, however, neither of the extremes, plug or perfect mixing, are to be expected. The flow patterns will be of an intermediate type. In this article, graphical representations are given for this situation in terms of the factor, E, whose application is recommended when outlet temperatures are to be calculated

186

The dry heat exchanger calorimeter system  

International Nuclear Information System (INIS)

A radiometric isothermal heat flow calorimeter and preconditioner system that uses air instead of water as the heat exchange medium has been developed at Mound. The dry heat exchanger calorimeter is 42 inches high by 18 inches in diameter and the preconditioner is a 22 inch cube, making it extremely compact compared to existing units. The new system is ideally suited for transportable, stand-alone, or glovebox applications. Preliminary tests of the system have produced sample measurements with standard deviations less than 0.25% and sample errors less than 0.50%. These tests have shown that the dry heat exchanger system will yield acceptance data with an accuracy comparable to those of Mound water bath systems now in use. 4 figs., 1 tab

187

Vibration damping in multispan heat exchanger tubes  

International Nuclear Information System (INIS)

Heat exchanger tubes can be damaged or fail if subjected to excessive flow-induced vibration, either from fatigue or fretting-wear. Good heat exchanger design requires that the designer understands and accounts for the vibration mechanisms that might occur, such as vortex shedding, turbulent excitation or fluidelastic instability. To incorporate these phenomena into a flow-induced vibration analysis of a heat exchanger requires information about damping. Damping in multispan heat exchanger tubes largely consists of three components: viscous damping along the tube, and friction and squeeze-film damping at the supports. Unlike viscous damping, squeeze-film damping and friction damping are poorly understood and difficult to measure. In addition, the effect of temperature-dependent fluid viscosity on tube damping has not been verified. To investigate these problems, a single vertical heat exchanger tube with multiple spans was excited by random vibration. Tests were conducted in air and in water at three different temperatures (25, 60, and 90oC). At room temperature, tests were carried out at five different preloads. Frequency response spectra and resonant peak-fitted damping ratios were calculated for all tests. Energy dissipation rates at the supports and the rate of excitation energy input were also measured. Results indicate that damping does not change over the range of temperatures tested and friction damping is very dependent on preload. (author)ery dependent on preload. (author)

188

Numerical investigation into the effect of cross-flow on the performance of axial flow fans in forced draught air-cooled heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Air-cooled heat exchangers (ACHEs) which utilise large arrays of axial fans, commonly suffer from inlet flow losses related to off-axis flow into the fans. This investigation aims to extend current knowledge on the effect of off-axis inflow on the performance of axial fans in this type of installation. An actuator disk fan-model was developed for the Computational Fluid Dynamics (CFD) code, FLUENT, and validated against experimental data for off-axis inflow angles up to 45{sup o}. Agreement between numerical and experimental pressure rise was good, although fan power consumption and fan static efficiency were under and over-predicted respectively. Experimentally observed trends were confirmed numerically: fan static pressure rise and efficiency were adversely affected, while fan power consumption was not significantly affected by the presence of cross-flow into the fan. The investigation revealed that while the torque characteristics over the outer portion of the fan blades are fundamental in determining the global fan power requirements, the net effect of cross-flow in this region is very small. Local variations of blade torque at diametrically opposed orientations more or less cancel each other out, explaining the independence of fan power consumption to cross-flow conditions. The adverse effect of off-axis inflow on fan static pressure rise was attributed to two factors: increased kinetic energy per unit volume at the fan exit, and greater dissipation through the fan itself. Off-axis inflow was found to affect fan-blade loading characteristics, with implications for blade fatigue. (author)

Hotchkiss, P.J.; Meyer, C.J. [Department of Mechanical Engineering, University of Cape Town, Private Bag, Rondebosch 7701 (South Africa); Backstroem, T.W. von [Department of Mechanical Engineering, Private Bag X1, Matieland 7602 (South Africa)

2006-02-01

189

Liquid droplet heat exchanger studies  

International Nuclear Information System (INIS)

Recent studies at the University of Washington (Bruckner, et al., 1982, 1984, 1985) and elsewhere (Taussig, et al., 1985) have addressed the feasibility of direct contact heat exchanger concepts, such as the liquid droplet heat exchanger (LDHX), for space power systems. In the LDHX heat is transferred by direct contact between a recirculating cloud of finely dispersed liquid droplets and a working gas. A critical design requirements of the LDHX is effective separation of the heat exchange media following heat transfer. The principle of the cyclone dust separator, in which particulate matter is separated from a swirling gas by centrifugal forces, offers an effective approach to the problem. A variety of cyclone-based LDHX geometries have been investigated, culminating in a low aspect ratio vortex chamber configuration (Bruckner, et al., 1984, 1985)

190

Multidimensional numerical modeling of heat exchangers  

International Nuclear Information System (INIS)

A comprehensive, multidimensional, thermal-hydraulic model is developed for the analysis of shell-and-tube heat exchangers for liquid-metal services. For the shellside fluid, the conservation equations of mass, momentum, and energy for continuum fluids are modified using the concept of porosity, surface permeability and distributed resistance to account for the blockage effects due to the presence of heat-transfer tubes, flow baffles/shrouds, the support plates, etc. On the tubeside, the heat-transfer tubes are connected in parallel between the inlet and outlet plenums, and tubeside flow distribution is calculated based on the plenum-to-plenum pressure difference being equal for all tubes. It is assumed that the fluid remains single-phase on the shell side and may undergo phase-change on the tube side, thereby simulating the conditions of Liquid Metal Fast Breeder Reactor (LMFBR) intermediate heat exchangers (IHX) and steam generators (SG)

191

A Numerical Procedure for Flow Distribution and Pressure Drops for U and Z Type Configurations Plate Heat Exchangers with Variable Coefficients  

Science.gov (United States)

In Plate Heat Exchangers it is important to determine the flow distribution and pressure drops, because they affect directly the performance of a heat exchanger [1]. This work proposes an incompressible, one-dimensional, steady state, discrete model allowing for variable overall momentum coefficients to determine these magnitudes. The model consists on a modified version of the Bajura and Jones [2] model for dividing and combining flow manifolds. The numerical procedure is based on the finite differences approximation approach proposed by Datta and Majumdar [3]. A linear overall momentum coefficient distribution is used in the dividing manifold, but the model is not limited to linear distributions. Comparisons are made with experimental, numerical and analytical data, yielding good results.

López, R.; Lecuona, A.; Ventas, R.; Vereda, C.

2012-11-01

192

Analytical, one-dimensional frequency model for U-shaped heat exchangers with regard to disturbances of inlet temperature and inlet mass flow in the primary and secondary loop  

International Nuclear Information System (INIS)

A linear, one- dimensional analytical frequency response model for U-tube heat exchangers will be presented. The model calculates the frequency response behaviour of fluid- temperatures both on the primary and secondary side at any position (and in particular at the outlet) of the heat exchanger with respect to perturbations of inlet fluid temperatures and inlet fluid mass flows. (orig.)

193

Heat Exchanger for Motor Vehicle Cooling System  

OpenAIRE

Heat exchanger for a motor vehicle cooling system including a sleeve-like meter hermetically mounted on, and surrounding, a hollow tubular chassis meter of the vehicle. The sleeve is provided with inlets and outlets communicating with the space between the sleeve and the chassis meter and vehicle coolant flows through the inlet and outlet. Air, flowing over the outside surface of the sleeve and the inside surface of the chassis meter, cools the vehicle coolant. SMH - MCC Smart, car concepts (...

Thuliez, Jean-luc; Chevroulet, Tristan; Stoll, Daniel

1997-01-01

194

Tube in shell heat exchangers  

International Nuclear Information System (INIS)

An improved tube-in-shell heat exchanger is described for use as a boiler for generating steam by heat exchange with liquid metal. It comprises a bundle of spaced tubes that conduct the liquid metal between headers and that extends through a shell containing water, the ends of this shell being closed by tube sheets spaced from the headers. The heat exchange tubes have internal thermally insulating sleeves each of which comprises a pair of spaced co-axial tubes sealed together at each end to form a closed interspace that contains inert gas. In this arrangement the heat flux between the tubes and tube sheet adjacent the inlet header for liquid metal is greatly reduced and the deposition of salts on the water side of the tube sheet and on the outside of the tubes in the vicinity of the tube sheet is thereby greatly reduced. (UK)

195

Experimental evaluation of sodium to air heat exchanger performance  

International Nuclear Information System (INIS)

Highlights: ? Sodium to air heat exchangers are used to remove the decay heat produced in fast breeder reactor after shutdown. ? Finned tube sodium to air heat exchanger with sodium on tube side was tested for its heat transfer performance. ? A one dimensional computer code was validated by the experimental data obtained. ? Non uniform sodium and air flow distribution was present in the heat exchanger. - Abstract: Sodium to air heat exchangers (AHXs) is used in Prototype Fast Breeder Reactor (PFBR) circuits to reject the decay heat produced by the radioactive decay of the fission products after reactor shutdown, to the atmospheric air. The heat removal through sodium to air heat exchanger maintains the temperature of reactor components in the pool within safe limits in case of non availability of normal heat transport path. The performance of sodium to air heat exchanger is very critical to ensure high reliability of the decay heat removal systems in sodium cooled fast breeder reactors. Hence experimental evaluation of the adequacy of the heat transfer capability gives confidence to the designers. A finned tube cross flow sodium to air heat exchanger of 2 MW heat transfer capacity with sodium on tube side and air on shell side was tested in the Steam Generator Test Facility at Indira Gandhi Center for Atomic Research, India. Heat transfer experiments were carried out with forced circulation of sodium and air, which confirmed the adequacy of heat removal capacity of the heat exchanger. The testing showed that 2.34 MW of heat power is transferred from sodium to air at nominal flow and temperature conditions. A one dimensional computer code developed for design and analysis of the sodium to air heat exchanger was validated by the experimental data obtained. An equivalent Nusselt number, Nueq is derived by approximating that the resistance of heat transfer from sodium to air is contributed only by the film resistance of air. The variation of Nueq with respect to the Reynolds number was studied

196

Compact heat exchanger for power plants  

International Nuclear Information System (INIS)

Vahterus Oy, located at Kalanti, has manufactured heat exchangers since the beginning of 1990s. About 90% of the equipment produced are exported. In the PSHE (Plate and Shell) solution of the Vahterus heat exchanger the heat is transferred by round plated welded to form a compact package, which is assembled into a cylindrical steel casing. The heat exchanger contains no gaskets or soldered joints, which eliminates the leak risks. Traditional heat exchanges are usually operated at higher temperatures and pressures, but the heat transfer capacities of them are lower. Plate heat exchangers, on the other hand, are efficient, but the application range of them is narrow. Additionally, the rubber gasket of the heat exchange plates, sealing the joints of the heat exchanging plates, does not stand high pressures or temperatures, or corroding fluids. The new welded plate heat exchanger combine the pressure and temperature resistance of tube heat exchangers and the high heat exchange capacity of plate heat exchangers. The new corrosion resisting heat exchanger can be applied for especially hard conditions. The operating temperature range of the PSHE heat exchanger is - 200 - 900 deg C. The pressure resistance is as high as 100 bar. The space requirement of PSHE is only one tenth of the space requirement of traditional tube heat exchangers. Adjusting the number of heat exchanging plates can change the capacity of the heat exchanger. Power range of the heat exchanger can be as hig range of the heat exchanger can be as high as 80 MW. Due to the corrosion preventive construction and the small dimension the PSHE heat exchanger can be applied for refrigerators using ammonia as refrigerant. These kinds of new Vahterus heat exchangers are in use in 60 countries in more than 2000 refrigerators

197

Optimal Pin Fin Heat Exchanger Surface  

OpenAIRE

This research presents the results of numerical study of heat transfer and pressure drop in a heat exchanger that is designed with different shape pin fins. The heat exchanger used for this research consists of a rectangular duct fitted with different shape pin fins, and is heated from the lower plate. The pin shape and the compact heat exchanger (CHE) configuration were numerically studied to maximize the heat transfer and minimize the pressure drop across the heat exchanger. A three dimensi...

Nabati, Hamid

2008-01-01

198

Effect of the Moments of Probability Density Function for Non-uniform Air Flow Distribution on the Hydraulic Performance of a Fin-tube Heat Exchanger  

OpenAIRE

The work presented in this paper examines the effect of a non-uniform airflow velocity distribution on the air pressure drop through the fin passages of a single row fin-tube heat exchanger. Water flow rate through the tubes and its temperature are taken as constant. Maldistribution of the airflow increases the average pressure drop with respect to that of a uniform flow. As a result of this, the pumping power required by the fan or blower will also increase. The increase of the pumping power...

Wai Meng Chin; Raghavan, Vijay R.

2011-01-01

199

Planning heat exchange systems  

International Nuclear Information System (INIS)

Following a discussion on heating or cooling media, the possible faults arising when not keeping to the required technical specifications are firstly indicated. The soiling and cleaning, vibration and selection of material are discussed, as well as preventive planning measures recommended to avoid later trouble. Finally, some practical tips are given which should not be overlooked. (orig./HP)

200

AP600 passive residual heat removal heat exchanger test  

International Nuclear Information System (INIS)

The AP600 reactor is a pressurized water reactor being designed to utilize a passive residual heat removal (PRHR) heat exchanger as the safety grade means for residual heat removal. The PRHR heat exchanger is utilized during many design basis events and is especially important in mitigating non-loss-of-coolant accidents such as loss of normal feedwater and feedwater line break. The PRHR system transfers decay heat from the reactor coolant system to the containment by heating and boiling the water in the in-containment refueling water storage tank (IRWST). The steam produced transfers heat to the atmosphere by condensing on the inside of the containment shell. The condensate is collected by gutters on the containment shell and is returned to the IRWST, which provides a heat sink for an indefinite amount of time. The PRHR test facility is a prototypical representation of the PRHR heat exchanger with respect to tube material, diameter, pitch, and tube length, such that the gravity-induced flow characteristics in the pool are representative of the design. The main scaling parameter for the pool is the pool volume per tube, which preserves the buoyancy and pool mixing effects. A generalized PRHR boiling correlation was developed using the approach given by Rohsenow such that pressure effects can be induced

201

Carbon nanotube heat-exchange systems  

Science.gov (United States)

A carbon nanotube heat-exchange system (10) and method for producing the same. One embodiment of the carbon nanotube heat-exchange system (10) comprises a microchannel structure (24) having an inlet end (30) and an outlet end (32), the inlet end (30) providing a cooling fluid into the microchannel structure (24) and the outlet end (32) discharging the cooling fluid from the microchannel structure (24). At least one flow path (28) is defined in the microchannel structure (24), fluidically connecting the inlet end (30) to the outlet end (32) of the microchannel structure (24). A carbon nanotube structure (26) is provided in thermal contact with the microchannel structure (24), the carbon nanotube structure (26) receiving heat from the cooling fluid in the microchannel structure (24) and dissipating the heat into an external medium (19).

Hendricks, Terry Joseph (Arvada, CO); Heben, Michael J. (Denver, CO)

2008-11-11

202

An investigation of heat exchange of liquid metal during flow in a vertical tube with non-uniform heating in the transverse magnetic field  

Science.gov (United States)

The results of experimental investigations of heat exchange during the downflow of liquid metal in a vertical tube with non-uniform heating in the transverse magnetic field are presented. The experiment was more realistic in terms of conditions of the blanket of a fusion reactor of the tokamak type. Profiles of the average temperature, distribution of local and mean heat transfer coefficients (Nusselt numbers), and the intensities and spectra of temperature pulsations have been measured. On certain combinations of operating parameters in the strong magnetic field low-frequency temperature pulsations with abnormal intensity were found.

Mel'nikov, I. A.; Razuvanov, N. G.; Sviridov, V. G.; Sviridov, E. V.; Shestakov, A. A.

2013-05-01

203

Predict the temperature distribution in gas-to-gas heat pipe heat exchanger  

Science.gov (United States)

A theoretical model has been developed to investigate the thermal performance of a continuous finned circular tubing of an air-to-air thermosyphon-based heat pipe heat exchanger. The model has been used to determine the heat transfer capacity, which expresses the thermal performance of heat pipe heat exchanger. The model predicts the temperature distribution in the flow direction for both evaporator and condenser sections and also the saturation temperature of the heat pipes. The approach used for the present study considers row-by-row heat-transfer in evaporator and condenser sections of the heat pipe heat exchanger.

Azad, E.

2012-07-01

204

Predict the temperature distribution in gas-to-gas heat pipe heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

A theoretical model has been developed to investigate the thermal performance of a continuous finned circular tubing of an air-to-air thermosyphon-based heat pipe heat exchanger. The model has been used to determine the heat transfer capacity, which expresses the thermal performance of heat pipe heat exchanger. The model predicts the temperature distribution in the flow direction for both evaporator and condenser sections and also the saturation temperature of the heat pipes. The approach used for the present study considers row-by-row heat-transfer in evaporator and condenser sections of the heat pipe heat exchanger. (orig.)

Azad, E. [Iranian Research Organization for Science and Technology, Department of Advanced Materials and Renewable Energy, Tehran (Iran, Islamic Republic of)

2012-07-15

205

Control of heat exchanger using predictive approach  

Energy Technology Data Exchange (ETDEWEB)

A classical thermal process which occurs in a diverse range of industrial technologies, particularly in the energetic and chemical industry, is heat exchange. Most technological and chemical industrial processes are temperature dependant. Many of them can be performed only within a given temperature range. Biochemical processes in particular are highly nonlinear and optimum performance can be achieved only within very narrow temperature limits. The usage of water is an effective approach for maintaining the process temperature because of its high thermal capacitance. This paper focused on the problem of nonlinear heat exchanger control, and specifically, on the problem of production of liquid water with a given temperature course in time. It discussed the use of a multifunction process control teaching system (MPCTS), with particular reference to the description of the MPCTS; a description of the through-flow heat exchanger; analytical model of the through-flow heat process; and static characteristics of the model. The design of the controller was also presented, with particular reference to the model of the exchanger and model predictive control (MPC) criterion. It was concluded that the key advantage of using the quadratic criterion in the MPC is the smooth control. However, the pure quadratic criterion could not fulfil both zero steady state control error and economically optimal control. 10 refs., 9 figs.

Chalupa, P.; Novak, J.; Bobal, V. [Tomas Bata Univ. in Zlin, Zlin (Czech Republic). Faculty of Applied Informatics, Dept. of Process Control

2010-03-09

206

Tube-in-shell heat exchangers  

International Nuclear Information System (INIS)

Tube-in-shell heat exchangers normally comprise a bundle of parallel tubes within a shell container, with a fluid arranged to flow through the tubes in heat exchange with a second fluid flowing through the shell. The tubes are usually end supported by the tube plates that separate the two fluids, and in use the tube attachments to the tube plates and the tube plates can be subject to severe stress by thermal shock and frequent inspection and servicing are required. Where the heat exchangers are immersed in a coolant such as liquid Na such inspection is difficult. In the arrangement described a longitudinally extending central tube is provided incorporating axially spaced cylindrical tube plates to which the opposite ends of the tubes are attached. Within this tube there is a tubular baffle that slidably seals against the wall of the tube between the cylindrical tube plates to define two co-axial flow ducts. These ducts are interconnected at the closed end of the tube by the heat exchange tubes and the baffle comprises inner and outer spaced walls with the interspace containing Ar. The baffle is easily removable and can be withdrawn to enable insertion of equipment for inspecting the wall of the tube and tube attachments and to facilitate plugging of defective tubes. Cylindrical tube plates are believed to be superior for carrying pressure loads and resisting the effects of thermal shock. Some protection against thermal shock can be effected by arranging that the secondary heat exchange fluid is on the tube side, and by providing a thermal baffle to prevent direct impingement of hot primary fluid on to the cylindrical tube plates. The inner wall of the tubular baffle may have flexible expansible region. Some nuclear reactor constructions incorporating such an arrangement are described, including liquid metal reactors. (U.K.)

207

Heat exchangers and methods of construction thereof  

International Nuclear Information System (INIS)

A heat exchanger is described comprising a shell having first inlet means and first outlet means for the flow of a first fluid therethrough, a plurality of tubes within the shell to provide a path for flow of a second fluid in heat exchange relation to the first fluid, second inlet means and second outlet means for flow of the second fluid to and from the tubes respectively, a tubular member concentric with at least a portion of the length of one of the tubes to define a space between the tube and the tubular member, at least one radially outwardly projecting portion on the tubular member, and a plurality of tube support means spaced apart and disposed generally perpendicular to the tube axes, wherein the tubular member is fixedly attached at one end to one of the tube support means and at the other end to an adjacent one of the tube support means, the space between the tube and the tubular member is closed to flow of both the first fluid and the second fluid, and the radially outwardly projecting portion on the tubular member extends longitudinally to allow flexing of the tubular member and expanding thereof radially outwardly during construction of the heat exchanger so as to allow insertion of the tube into the tubular member, the radially outwardly projecting portion defining a gap which contributes to the space between the tube and the tubular member. 6 figs

208

Circulating heat exchangers for oscillating wave engines and refrigerators  

Science.gov (United States)

An oscillating-wave engine or refrigerator having a regenerator or a stack in which oscillating flow of a working gas occurs in a direction defined by an axis of a trunk of the engine or refrigerator, incorporates an improved heat exchanger. First and second connections branch from the trunk at locations along the axis in selected proximity to one end of the regenerator or stack, where the trunk extends in two directions from the locations of the connections. A circulating heat exchanger loop is connected to the first and second connections. At least one fluidic diode within the circulating heat exchanger loop produces a superimposed steady flow component and oscillating flow component of the working gas within the circulating heat exchanger loop. A local process fluid is in thermal contact with an outside portion of the circulating heat exchanger loop.

Swift, Gregory W.; Backhaus, Scott N.

2003-10-28

209

Heat exchanger staybolt acceptance criteria  

International Nuclear Information System (INIS)

The structural integrity demonstration of the primary coolant piping system includes evaluating the structural capacity of each component against a large break or equivalent Double-Ended Guillotine Break. A large break at the inlet or outlet heads of the heat exchangers would occur if the restraint members of the heads become inactive. The structural integrity of the heads is demonstrated by showing the redundant capacity of the staybolts to restrain the head at design conditions and under seismic loadings. The Savannah River Site heat exchanger head is attached to the tubesheet by 84 staybolts. Access to the staybolts is limited due to a welded seal cap over the staybolts. An ultrasonic testing (UT) inspection technique to provide an in-situ examination of the staybolts has recently been developed at SRS. Examination of the staybolts will be performed to ensure their service condition and configuration is within acceptance limits. An acceptance criteria methodology has been developed to disposition flaws reported in the staybolt inspections while ensuring adequate restraint capacity of the staybolts to maintain integrity of the heat exchanger heads against collapse. The methodology includes an approach for the baseline and periodic inspections of the staybolts. The heat exchanger head is analyzed with a three-dimensional finite element model. The restraint provided by the staybolts is evaluated for several postulated cases of inactive or missing staybolts. Evaluation of specific, inactive staybolt configurations based on the UT results can be performed with the finite element model and fracture methodology in this report

210

The influence of radiative heat exchange on the character of gasdynamic flows under conditions of pulsed discharge in high-pressure cesium vapor  

Science.gov (United States)

The gasdynamics of pulse-periodic radiative discharge in high-pressure cesium vapor has been studied in the framework of a two-temperature multifluid model. It is established that, at a limited volume of the gas-discharge tube, the character of gasdynamic flows depends on the conditions of radiative heat exchange in discharge plasma. In cases in which the main contribution to radiative energy losses is related to a spectral region with optical thickness ? R (?) ˜ 1, there is nonlocal radiative heat exchange in discharge plasma, which is uniformly heated over the entire tube volume and moves from the discharge axis to tube walls during the entire pulse of discharge current. Under the conditions of radiative losses determined by the spectral region where ? R (?) ? 1, the reabsorption of radiation is absent and discharge plasma is nonuniformly heated by the current pulse. This leads to the appearance of reverse motions, so that the heated plasma is partly pushed toward the tube walls and partly returned to the discharge axis.

Baksht, F. G.; Lapshin, V. F.

2015-01-01

211

Tubular heat exchanger, for nuclear installations  

International Nuclear Information System (INIS)

The description is given of a heat exchanger comprising an elongated heat exchanger module suitable for group mounting with other similar modules. The module includes a long casing having a hexagonal cross section configuration to make it easy to group together a set of modules in an appreciably continuous set. A set of thermally conducting tubes is arranged in the casing and extends through its entire length. An intake collector is fitted to one end of the casing and communicates with one end of the tubes and an outlet collector is fitted to the other end of the casing and communicates with the other end of the tubes, a fluid passage being made inside the casing for the flow of primary fluid through it around the thermally conducting tubes. The intake and outlet collectors are each fitted for their respective coupling to an intake manifold and an outlet manifold for the flow of a primary fluid through the tubes in the casing

212

Effect of the Moments of Probability Density Function for Non-uniform Air Flow Distribution on the Hydraulic Performance of a Fin-tube Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available The work presented in this paper examines the effect of a non-uniform airflow velocity distribution on the air pressure drop through the fin passages of a single row fin-tube heat exchanger. Water flow rate through the tubes and its temperature are taken as constant. Maldistribution of the airflow increases the average pressure drop with respect to that of a uniform flow. As a result of this, the pumping power required by the fan or blower will also increase. The increase of the pumping power is calculated by means of a discretization technique and it is analyzed with respect to the non-uniform distribution statistical moments of probability density function, i.e., the mean, standard deviation, skew and kurtosis. The analysis reveals that the increase of pumping power is dependent on the exchanger NTU, standard deviation and skew of the velocity distribution. Kurtosis has no effect on the pressure drop. Correlations have been developed to predict this increase of pumping power from known statistical moments and resulting air temperatures. These can then be used as design tools to optimize the sizing of the heat exchanger within the air-conditioning unit, hence giving the best energy efficiency performance.

Wai Meng Chin

2011-01-01

213

Experimental investigation of passive residual heat removal system with air cooled heat exchanger  

International Nuclear Information System (INIS)

The objective of this work is to obtain the Performance test data for the passive residual heat removal (RHR) heat exchanger in the advanced PWR. The RHR heat exchanger is designed to remove the decay heat with combined effects of the natural circulation of water by means of the thermosyphon at the inside and the natural convection of the air at the outside. Two test models were made to simulate the RHR heat exchanger. The one is the single bundle test model which consisted of a finned tubular heat exchanger unit. The other is the multi-bundle test model which has the finned tubular heat exchanger consisting of ten bundles of tubular units. The Maximum heat removal capabilities of each model were investigated. The cooling water flow rates by the thermosyphon were measured and were in good agreement with the theoretical predictions. The effects of chimney and elevation between the heater and the heat exchanger were investigated

214

Analysis of spray-cooled finned-tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

This paper reports that a mathematical model has been developed for the analysis of spray-cooled finned-tube heat exchangers. An experimental study was conducted on a four-pass, finned-tube heat exchanger in a vertical air/water mist flow to validate the model, and the results compared well with the predicted performance. Significant performance enhancement (up to 3.5 times the dry performance) was found by spraying relatively small amounts of water onto the heat exchanger. The two-phase pressure drop across the heat exchanger was also measured, and the spray water mass flow rate was found to have a significant effect on the pressure drop across the tube bundle. The study helped to identify certain factors, such as the geometry of the finned tubes and the optimum air/spray water ratios, which have to be taken into consideration when designing spray-cooled heat exchangers.

Dreyer, A.A.; Kriel, D.E.; Erens, P.J. (Dept. of Mechanical Engineering, Univ. of Stellenbosch, Stellenbosch, 7600 (South Africa))

1992-12-01

215

Noise spectra measured on the Dragon reactor primary heat exchanges  

International Nuclear Information System (INIS)

The frequency spectra of secondary water flow and tube wall temperatures have been measured on Dragon primary heat exchangers. No indication of tube wall temperature oscillations leading to tube burnout was found from the noise spectra analysed. (author)

216

Heat exchanges in coarsening systems  

International Nuclear Information System (INIS)

This paper is a contribution to the understanding of the thermal properties of ageing systems where statistically independent degrees of freedom with greatly separated time scales are expected to coexist. Focusing on the prototypical case of quenched ferromagnets, where fast and slow modes can be respectively associated with fluctuations in the bulk of the coarsening domains and in their interfaces, we perform a set of numerical experiments specifically designed to compute the heat exchanges between different degrees of freedom. Our studies promote a scenario with fast modes acting as an equilibrium reservoir to which interfaces may release heat through a mechanism that allows fast and slow degrees to maintain their statistical properties independently

217

Flat tube heat exchangers – Direct and indirect noise levels in heat pump applications  

International Nuclear Information System (INIS)

In the outdoor unit of an air-source heat pump the fan is a major noise source. The noise level from the fan is dependent on its state of operation: high air-flow and high pressure drop often result in higher noise levels. In addition, an evaporator that obstructs an air flow is a noise source in itself, something that may contribute to the total noise level. To be able to reduce the noise level, heat exchanger designs other than the common finned round tubes were investigated in this study. Three types of heat exchanger were evaluated to detect differences in noise level and air-side heat transfer performance at varying air flow. The measured sound power level from all the heat exchangers was low in comparison to the fan sound power level (direct effect). However, the heat exchanger design was shown to have an important influence on the sound power level from the fan (indirect effect). One of the heat exchangers with flat tubes was found to have the lowest sound power level, both direct and indirect, and also the highest heat transfer rate. This type of flat tube heat exchanger has the potential to reduce the overall noise level of a heat pump while maintaining heat transfer efficiency. - Highlights: •The direct noise from a heat exchanger is negligible in heat pump applications. •The design of the heat exchanger highly influences the noise from an outdoor unit. •Flat tube heat exchangers can reduce the noise from the outdoor unit of a heat pump. •Flat tube heat exchangers can increase the energy efficiency of a heat pump

218

The Experimental Study on Heat Transfer Characteristics of The External Heat Exchanger  

Science.gov (United States)

Using the external heat exchanger in large-scale CFB boilers can control combustion and heat transfer separately, make the adjustments of bed temperature and steam temperature convenient. The state of gas-solid two phase flow in the external heat exchanger is bubbling fluidized bed, but differs from the regular one as there is a directional flow in it. Consequently, the temperature distribution changes along the flow direction. In order to study the heat transfer characteristics of the water cooled tubes in the bubbling fluidized bed and ensure the uniformity of heat transfer in the external heat exchanger, a physical model was set up according to the similarity principle and at the geometric ratio of 1?28 to an external heat exchanger of a 300MW CFB boiler. The model was connected with an electrically heated CFB test-bed which provides the circulating particles. The influencing factors and the distribution rule of the particles' heat transfer coefficient in the external heat exchanger were assessed by measuring the temperature changes of the water in the tubes and different parts of particles flow along the flow direction. At the end, an empirical correlation of particles' heat transfer coefficient in external heat exchanger was given by modifying the Veedendery empirical correlation.

Ji, X. Y.; Lu, X. F.; Yang, L.; Liu, H. Z.

219

Study of transient behavior of finned coil heat exchangers  

Science.gov (United States)

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Rooke, S. P.; Elissa, M. G.

1993-11-01

220

Design of intermediate heat exchanger for PFBR  

International Nuclear Information System (INIS)

Prototype fast breeder reactor (PFBR) is a sodium cooled 500 MWe pool type reactor. It has three heat transfer circuits viz. primary sodium circuit, secondary sodium circuit and water- steam circuit. The main vessel contains the pool of sodium and houses all the components of the primary sodium circuit. Two numbers of primary sodium pumps and four numbers of intermediate heat exchangers (IHX) have been provided. The nuclear heat generated in the core is transferred to secondary sodium in IHX by circulation of primary sodium. There are two secondary sodium circuits. Each circuit contains one sodium pump, one surge tank and four steam generators (in parallel) and is connected to two IHXs in the reactor. The secondary sodium circuits transfer the heat to water/steam in steam generators (SG). Super heated steam produced in the SGs is used to drive the turbo-alternator set to generate power. The IHX is a very important component of the reactor because it forms the boundary between radioactive primary sodium in the reactor pool and non-radioactive secondary sodium. The IHX is a counter flow shell-and-tube heat exchanger. The IHX is designed to meet the specified design requirements and constraints. This involves thermal, hydraulic, and structural design. In this paper, the design features, design conditions and design of IHX for PFBR are described. 4 figs., 3 tabs

221

Test results of a Stirling engine utilizing heat exchanger modules with an integral heat pipe  

Science.gov (United States)

The Heat Pipe Stirling Engine (HP-1000), a free-piston Stirling engine incorporating three heat exchanger modules, each having a sodium filled heat pipe, has been tested at the NASA-Lewis Research Center as part of the Civil Space Technology Initiative (CSTI). The heat exchanger modules were designed to reduce the number of potential flow leak paths in the heat exchanger assembly and incorporate a heat pipe as the link between the heat source and the engine. An existing RE-1000 free-piston Stirling engine was modified to operate using the heat exchanger modules. This paper describes heat exchanger module and engine performance during baseline testing. Condenser temperature profiles, brake power, and efficiency are presented and discussed.

Skupinski, Robert C.; Tower, Leonard K.; Madi, Frank J.; Brusk, Kevin D.

1993-04-01

222

Preliminary SP-100/Stirling heat exchanger designs  

International Nuclear Information System (INIS)

Analytic modeling of several heat exchanger concepts to couple the SP-100 nuclear reactor primary lithium loop and the Space Stirling Power Convertor (SSPC) was performed. Four 25 kWe SSPC's are used to produce the required 100 kW of electrical power. This design work focused on the interface between a single SSPC and the primary lithium loop. Manifolding to separate and collect the four channel flow was not modeled. This work modeled two separate types of heat exchanger interfaces (conductive coupling and radiative coupling) to explore their relative advantages and disadvantages. The minimum mass design of the conductively coupled concepts was 18 kg or 0.73 kg/kWe for a single 25 kWe convertor. The minimum mass radiatively coupled concept was 41 kg or 1.64 kg/kWe. The direct conduction heat exchanger provides a lighter weight system because of its ability to operate the Stirling convertor evaporator at higher heat fluxes than those attainable by the radiatively coupled systems. Additionally the conductively coupled concepts had relatively small volumes and provide potentially simpler assembly. Their disadvantages were the tight tolerances and material joining problems associated with this refractory to superalloy interface. The advantages of the radiatively coupled designs were the minimal material interface problems

223

NGNP Process Heat Utilization: Liquid Metal Phase Change Heat Exchanger  

International Nuclear Information System (INIS)

One key long-standing issue that must be overcome to fully realize the successful growth of nuclear power is to determine other benefits of nuclear energy apart from meeting the electricity demands. The Next Generation Nuclear Plant (NGNP) will most likely be producing electricity and heat for the production of hydrogen and/or oil retrieval from oil sands and oil shale to help in our national pursuit of energy independence. For nuclear process heat to be utilized, intermediate heat exchange is required to transfer heat from the NGNP to the hydrogen plant or oil recovery field in the most efficient way possible. Development of nuclear reactor--process heat technology has intensified the interest in liquid metals as heat transfer media because of their ideal transport properties. Liquid metal heat exchangers are not new in practical applications. An important rational for considering liquid metals is the potential convective heat transfer is among the highest known. Thus explains the interest in liquid metals as coolant for intermediate heat exchange from NGNP. For process heat it is desired that, intermediate heat exchangers (IHX) transfer heat from the NGNP in the most efficient way possible. The production of electric power at higher efficiency via the Brayton Cycle, and hydrogen production, requires both heat at higher temperatures and high effectiveness compact heat exchangers to transfer heat to either the power or process cycle. Compact heat exchangers maximize t cycle. Compact heat exchangers maximize the heat transfer surface area per volume of heat exchanger; this has the benefit of reducing heat exchanger size and heat losses. High temperature IHX design requirements are governed in part by the allowable temperature drop between the outlet and inlet of the NGNP. In order to improve the characteristics of heat transfer, liquid metal phase change heat exchangers may be more effective and efficient. This paper explores the overall heat transfer characteristics and pressure drop of the phase change heat exchanger with Na as the heat exchanger coolant. In order to design a very efficient and effective heat exchanger one must optimize the design such that we have a high heat transfer and a lower pressure drop, but there is always a trade-off between them. Based on NGNP operational parameters, a heat exchanger analysis with the sodium phase change will be presented to show that the heat exchanger has the potential for highly effective heat transfer, within a small volume at reasonable cost

224

Heat exchange phenomena and COP evaluation in heat pump systems coupled to single borehole heat exchangers  

OpenAIRE

In recent years a growing interest in Borehole Heat Exchangers (BHEs) has been shown in Europe thanks to the increase of installations in systems connected to Ground Source Heat Pumps (GSHPs) used for heating and cooling needs. Different geometries and technical solutions have been de- veloped in order to improve heat exchange with the ground, accompanied by several descriptive models. Recently, innovative technologies as optical fiber for a new Distributed Thermal Response Test (DTRT) have b...

Casellato, Francesco

2013-01-01

225

Optimum geometry of MEMS heat exchanger for heat transfer enhancement  

OpenAIRE

The study is based on an analysis of MEMS heat exchanger of three different geometries: wavy, triangular and rectangular using water as test fluid. The problem is solved using finite element method. The aim of this analysis is to evaluate the performance of MEMS heat exchanger for different geometry and to obtain an optimum design for better heat enhancement. It is apparent from this work that rectangular surface heat exchanger shows the best performance for heat enhancement technique in comp...

Chhanda, Nusrat J.; Muhannad Mustafa; Maglub Al Nur

2010-01-01

226

Heat Transport Study of the Laminar Heat Pipe Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this experiment is to analyze the performance of the Laminar Heat Pipe Heat Exchanger. The test samples were divided two groups, one is the metal corrugated sheet with heat pipe, and the other is the metal corrugated sheet only. By dipping these two group samples into hot water and to see the thermal image by Infrared thermal imager. The results shown the temperature risen of the sheet with heat pipe was faster than that of the sheet without heat pipe. In addition, the bigger of the temperature difference between hot water temperature and ambient temperature, the quicker of the temperature risen for the metal corrugated sheet, and the temperature of the metal corrugated sheet were homogenous as well. For example, when the water temperature is 30?, ambient temperature is 20?, the metal corrugated sheet with heat pipe rise rapidly to 26? within 1 minute, while the metal corrugated sheet without heat pipe rise to 22? only, this temperature difference would be more obvious with the increasing of the hot water temperature. When the hot water temperature is up to 40?, the metal corrugated sheet with heat pipe rise rapidly to 31? within 1 minute, while the metal corrugated sheet without het pipe is still rise up to 22? only. When the hot water temperature is up to 50?, The metal corrugated sheet with heat pipe rise rapidly to 33? within 1 minute, while the sheet without heat pipe still keep at 22?, the results shown the heat pipe affect the temperature rising speed is obvious, and it also implying heat pipe is a very important parameter for the heat transfer rate of the Laminar Heat Pipe Heat Exchanger.

Wei-Keng Lin

2012-11-01

227

NGNP Process Heat Utilization: Liquid Metal Phase Change Heat Exchanger  

Energy Technology Data Exchange (ETDEWEB)

One key long-standing issue that must be overcome to fully realize the successful growth of nuclear power is to determine other benefits of nuclear energy apart from meeting the electricity demands. The Next Generation Nuclear Plant (NGNP) will most likely be producing electricity and heat for the production of hydrogen and/or oil retrieval from oil sands and oil shale to help in our national pursuit of energy independence. For nuclear process heat to be utilized, intermediate heat exchange is required to transfer heat from the NGNP to the hydrogen plant or oil recovery field in the most efficient way possible. Development of nuclear reactor - process heat technology has intensified the interest in liquid metals as heat transfer media because of their ideal transport properties. Liquid metal heat exchangers are not new in practical applications. An important rational for considering liquid metals is the potential convective heat transfer is among the highest known. Thus explains the interest in liquid metals as coolant for intermediate heat exchange from NGNP. For process heat it is desired that, intermediate heat exchangers (IHX) transfer heat from the NGNP in the most efficient way possible. The production of electric power at higher efficiency via the Brayton Cycle, and hydrogen production, requires both heat at higher temperatures and high effectiveness compact heat exchangers to transfer heat to either the power or process cycle. Compact heat exchangers maximize the heat transfer surface area per volume of heat exchanger; this has the benefit of reducing heat exchanger size and heat losses. High temperature IHX design requirements are governed in part by the allowable temperature drop between the outlet and inlet of the NGNP. In order to improve the characteristics of heat transfer, liquid metal phase change heat exchangers may be more effective and efficient. This paper explores the overall heat transfer characteristics and pressure drop of the phase change heat exchanger with Na as the heat exchanger coolant. In order to design a very efficient and effective heat exchanger one must optimize the design such that we have a high heat transfer and a lower pressure drop, but there is always a trade-off between them. Based on NGNP operational parameters, a heat exchanger analysis with the sodium phase change will be presented to show that the heat exchanger has the potential for highly effective heat transfer, within a small volume at reasonable cost.

Piyush Sabharwall; Mike Patterson; Vivek Utgikar; Fred Gunnerson

2008-09-01

228

Microchannel Heat Exchangers with Carbon Dioxide  

Energy Technology Data Exchange (ETDEWEB)

The objective of the present study was to determine the performance of CO{sub 2} microchannel evaporators and gas coolers in operational conditions representing those of residential heat pumps. A set of breadboard prototype microchannel evaporators and gas coolers was developed and tested. The refrigerant in the heat exchangers followed a counter cross-flow path with respect to the airflow direction. The test conditions corresponded to the typical operating conditions of residential heat pumps. In addition, a second set of commercial microchannel evaporators and gas coolers was tested for a less comprehensive range of operating conditions. The test results were reduced and a comprehensive data analysis, including comparison with the previous studies in this field, was performed. Capacity and pressure drop of the evaporator and gas cooler for the range of parameters studied were analyzed and are documented in this report. A gas cooler performance prediction model based on non-dimensional parameters was also developed and results are discussed as well. In addition, in the present study, experiments were conducted to evaluate capacities and pressure drops for sub-critical CO{sub 2} flow boiling and transcritical CO{sub 2} gas cooling in microchannel heat exchangers. An extensive review of the literature failed to indicate any previous systematic study in this area, suggesting a lack of fundamental understanding of the phenomena and a lack of comprehensive data that would quantify the performance potential of CO{sub 2} microchannel heat exchangers for the application at hand. All experimental tests were successfully conducted with an energy balance within {+-}3%. The only exceptions to this were experiments at very low saturation temperatures (-23 C), where energy balances were as high as 10%. In the case of evaporators, it was found that a lower saturation temperature (especially when moisture condensation occurs) improves the overall heat transfer coefficient significantly. However, under such conditions, air side pressure drop also increases when moisture condensation occurs. An increase in airflow rate also increases the overall heat transfer coefficient. Air side pressure drop mainly depends on airflow rate. For the gas cooler, a significant portion of the heat transfer occurred in the first heat exchanger module on the refrigerant inlet side. The temperature and pressure of CO{sub 2} significantly affect the heat transfer and fluid flow characteristics due to some important properties (such as specific heat, density, and viscosity). In the transcritical region, performance of CO{sub 2} strongly depends on the operating temperature and pressure. Semi-empirical models were developed for predictions of CO{sub 2} evaporator and gas cooler system capacities. The evaporator model introduced two new factors to account for the effects of air-side moisture condensate and refrigerant outlet superheat. The model agreed with the experimental results within {+-}13%. The gas cooler model, based on non-dimensional parameters, successfully predicted the experimental results within {+-}20%. Recommendations for future work on this project include redesigning headers and/or introducing flow mixers to avoid flow mal-distribution problems, devising new defrosting techniques, and improving numerical models. These recommendations are described in more detail at the end of this report.

Zhao, Y.; Ohadi, M.M.; Radermacher, R.

2001-09-15

229

Thermodynamic analysis and optimization of air-cooled heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

In the present study, a thermodynamic second-law analysis was performed to investigate the effects of different geometry and flow parameters on the air-cooled heat exchanger performance. For this purpose, the entropy generation due to heat transfer and pressure loss of internal and external flows of the air-cooled heat exchanger was calculated; and it was observed that the total entropy generation has a minimum at special tube-side Reynolds number. Also, it was seen that the increasing of the tube-side Reynolds number resulted in the rise of the irreversibility of the air-cooled heat exchanger. The results also showed when air-side Reynolds number decreased, the entropy generation rate of the external flow reduced. Finally, based on the computed results, a new correlation was developed to predict the optimum Reynolds number of the tube-side fluid flow. (orig.)

Salimpour, Mohammad Reza; Bahrami, Zabihollah [Isfahan University of Technology, Department of Mechanical Engineering, Isfahan (Iran, Islamic Republic of)

2011-01-15

230

Condensation in horizontal heat exchanger tubes  

International Nuclear Information System (INIS)

Many innovative reactor concepts for Generation III nuclear power plants use passive safety equipment for residual heat removal. These systems use two phase natural circulation. Heat transfer to the coolant results in a density difference providing the driving head for the required mass flow. By balancing the pressure drop the system finds its operational mode. Therefore the systems depend on a strong link between heat transfer and pressure drop determining the mass flow through the system. In order to be able to analyze these kind of systems with the help of state of the art computer codes the implemented numerical models for heat transfer, pressure drop or two phase flow structure must be able to predict the system performance in a wide parameter range. Goal of the program is to optimize the numerical models and therefore the performance of computer codes analyzing passive systems. Within the project the heat transfer capacity of a heat exchanger tube will be investigated. Therefore the tube will be equipped with detectors, both temperature and pressure, in several directions perpendicular to the tube axis to be able to resolve the angular heat transfer. In parallel the flow structure of a two phase flow inside and along the tube will be detected with the help of x-ray tomography. The water cooling outside of the tube will be realized by forced convection. It will be possible to combine the flow structure measurement with an angular resolved heat transfer for a wide angular resolved heat transfer for a wide parameter range. The test rig is set up at the TOPLFOW facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), so that it will be possible to vary the pressure between 5 and 70 bar. The steam mass content will be varied between 0 and 100 percent. The results will be compared to the large scaled Emergency Condenser Tests performed at the INKA test facility in Karlstein (Germany). The paper will explain the test setup and the status of the project will be presented. (authors)

231

Analytical Study on Thermal and Mechanical Design of Printed Circuit Heat Exchanger  

Energy Technology Data Exchange (ETDEWEB)

The analytical methodologies for the thermal design, mechanical design and cost estimation of printed circuit heat exchanger are presented in this study. In this study, three flow arrangements of parallel flow, countercurrent flow and crossflow are taken into account. For each flow arrangement, the analytical solution of temperature profile of heat exchanger is introduced. The size and cost of printed circuit heat exchangers for advanced small modular reactors, which employ various coolants such as sodium, molten salts, helium, and water, are also presented.

Su-Jong Yoon; Piyush Sabharwall; Eung-Soo Kim

2013-09-01

232

Design considerations for compact heat exchangers  

International Nuclear Information System (INIS)

The next generation of nuclear power plants demand highly-effective, high integrity compact heat exchangers capable of meeting the mechanical challenges posed by the need for improved cycle efficiencies. Heatric offers a range of diffusion bonded compact heat exchangers to meet these challenges, each custom-designed and engineered by Heatric's dedicated Nuclear Engineering Department. Heatric currently offers three heat exchanger types: Printed Circuit Heat Exchangers (PCHEs); Formed Plate Heat Exchangers (FPHEs); and Hybrid Heat Exchangers (H2Xs). The thermal hydraulic design, selection, and optimisation of these heat exchangers must consider a wide range of factors, including process constraints, cost, size, and mechanical considerations. Each heat exchanger is a bespoke product, designed by iteration and consultation with customers to provide optimal cost and performance (i.e. pressure drop/effectiveness). This paper discusses the design and surface enhancement considerations that lead to optimal heat exchanger designs. In particular heat transfer versus pressure drop performance considerations for enhanced surfaces will be discussed, with reference made to other surface types. The versatility of Heatric's manufacturing techniques and their use in reducing heat transfer penalties are also discussed, including mechanical and construction considerations. The paper closes with an overview of the engineering capabilities and services offered by Heatric's Nuclear Enginervices offered by Heatric's Nuclear Engineering Department. (authors)

233

Improved ceramic heat exchange material  

Science.gov (United States)

Improved corrosion resistant ceramic materials that are suitable for use as regenerative heat exchangers for vehicular gas turbines is reported. Two glass-ceramic materials, C-144 and C-145, have superior durability towards sulfuric acid and sodium sulfate compared to lithium aluminosilicate (LAS) Corning heat exchange material 9455. Material C-144 is a leached LAS material whose major crystalline phase is silica keatite plus mullite, and C-145 is a LAS keatite solid solution (S.S.) material. In comparison to material 9455, material C-144 is two orders of magnitude better in dimensional stability to sulfuric acid at 300 C, and one order of magnitude better in stability to sodium sulfate at 1000 C. Material C-145 is initially two times better in stability to sulfuric acid, and about one order of magnitude better in stability to sodium sulfate. Both C-144 and C-145 have less than 300 ppm delta L/L thermal expansion from ambient to 1000 C, and good dimensional stability of less than approximately 100 ppm delta L/L after exposure to 1000 C for 100 hours. The glass-ceramic fabrication process produced a hexagonal honeycomb matrix having an 85% open frontal area, 50 micrometer wall thickness, and less than 5% porosity.

Mccollister, H. L.

1977-01-01

234

Design of a liquid metals heat exchanger  

International Nuclear Information System (INIS)

The method that has been used in this design is that of the summation of the partial resistances to the heat transference, permitting to obtain the value of the total coefficient of heat transfer which will be equal to the reciprocal of the summation of all the resistances. The obtained exchanger is of tubes and rod type shield with the primary sodium flowing through the tubes and the secondary sodium flowing in counter-current through the shield. The shield has a nominal diameter of 6 inches and the bundle of tubes is formed by 31 tubes with a nominal diameter of 1/2 inch. The shield as well as the tubes are of stainless steel. The total heat transfer area is of 7.299 square meters, and the effective length of heat transfer is of 3.519 meters. After sizing the interchanger it was proceeded to simulate its functioning through a computer program in which the effective length of heat transfer was divided in 150 points in such a way that according to the integration of the distinct parameters along these points a comparison can finally be made between the design values and those of the simulation, which show a concordance. (author)

235

Enhancement of heat transfer and structure of flow in a double-pipe heat exchanger with uniformly distributed perforated-plate baffles in the inner pipe  

International Nuclear Information System (INIS)

The effect of the number of baffles per meter of length on the average heat transfer coefficient and on the hydraulic drag coefficient of a 70 mm I.D. inner pipe at Re between 9 . 103 and 50 . 103 was investigated. The test data were correlated in dimensionless form. The length of the inlet stabilization zone proved to be two to three pipe diameters. The profiles of velocity and of the longitudinal component of fluctuations, and also the development of the flow through the baffles are analyzed

236

Thermal behavior of a heat exchanger module for seasonal heat storage  

DEFF Research Database (Denmark)

Experimental and theoretic investigations are carried out to study the heat transfer capacity rate of a heat exchanger module for seasonal heat storage with sodium acetate trihydrate (SAT) supercooling in a stable way. A sandwich heat storage test module has been built with the phase change material (PCM) storage box in between two plate heat exchangers. Charge of the PCM storage is investigated experimentally with solid phase SAT as initial condition. Discharge of the PCM storage with the presence of crystallization is studied experimentally. Fluid flow and heat transfer in the PCM module are theoretically investigated by Computational Fluid Dynamics (CFD) calculations. The heat transfer rates between the PCM storage and the heating fluid/cooling fluid in the plate heat exchangers are determined. The CFD calculated temperatures are compared to measured temperatures. Based on the studies, recommendations on how best to transfer heat to and from the seasonal heat storage module are given.

Fan, Jianhua; Furbo, Simon

2012-01-01

237

Hydraulic and thermal design of a gas microchannel heat exchanger  

Science.gov (United States)

In this paper investigations on the design of a gas flow microchannel heat exchanger are described in terms of hydrodynamic and thermal aspects. The optimal choice for thermal conductivity of the solid material is discussed by analysis of its influences on the thermal performance of a micro heat exchanger. Two numerical models are built by means of a commercial CFD code (Fluent). The simulation results provide the distribution of mass flow rate, inlet pressure and pressure loss, outlet pressure and pressure loss, subjected to various feeding pressure values. Based on the thermal and hydrodynamic analysis, a micro heat exchanger made of polymer (PEEK) is designed and manufactured for flow and heat transfer measurements in air flows. Sensors are integrated into the micro heat exchanger in order to measure the local pressure and temperature in an accurate way. Finally, combined with numerical simulation, an operating range is suggested for the present micro heat exchanger in order to guarantee uniform flow distribution and best thermal and hydraulic performances.

Yang, Yahui; Brandner, Juergen J.; Morini, Gian Luca

2012-05-01

238

A heat exchanger between forced flow helium gas at 14 to 18 K and liquid hydrogen at 20 K circulated by natural convection  

International Nuclear Information System (INIS)

The Muon Ionization Cooling Experiment (MICE) has three 350-mm long liquid hydrogen absorbers to reduce the momentum of 200 MeV muons in all directions. The muons are then re-accelerated in the longitudinal direction by 200 MHz RF cavities. The result is cooled muons with a reduced emittance. The energy from the muons is taken up by the liquid hydrogen in the absorber. The hydrogen in the MICE absorbers is cooled by natural convection to the walls of the absorber that are in turn cooled by helium gas that enters at 14 K. This report describes the MICE liquid hydrogen absorber and the heat exchanger between the liquid hydrogen and the helium gas that flows through passages in the absorber wall

239

The role of sealing strips in tubular heat exchangers  

International Nuclear Information System (INIS)

Tubular-type heat exchangers contain both baffle plates and sealing strips. The baffles force the flow to pass normal to the axes of the tubes and they serve to support the tubes. In order to facilitate assembly of the heat exchanger, a space exists between the tube bundle and the retaining shell. This space offers a hydraulic short circuit to the fluid, thus reducing the effectiveness of the device to exchange heat. Sealing strips, which are metal strips mounted on the shell and running parallel to the tubes, are introduced to partially block this leakage flow, thereby increasing the effectiveness of the device. The objectives of the research reported here are to experimentally determine the effectiveness of sealing strips, and to investigate the effects of their shape and location. Such results not only supply design information, but they serve to establish the accuracy of computer codes which have been developed for such heat exchangers. (author)

240

Damping of multispan heat exchanger tubes. Pt. 1: in gases  

International Nuclear Information System (INIS)

Flow-induced vibration analyses of heat exchanger tubes require the knowledge of damping. This paper treats the question of damping on multispan heat exchanger tubes in air and gases. The different energy dissipation mechanisms that contribute to tube damping are discussed. The available experimental data are reviewed and analysed. We find that the main damping mechanism in gases is friction between tube and tube-supports. Damping is strongly related to tube-support thickness. Damping values are recommended for design purposes. This study is interesting in the nuclear industry for it often uses heat exchangers

241

Passive Restriction of Blood Flow and Counter-Current Heat Exchange Via Lingual Retia in the Tongue of a Neonatal Gray Whale Eschrichtius robustus (Cetacea, Mysticeti).  

Science.gov (United States)

Retia mirabilia play broad roles in cetacean physiology, including thermoregulation during feeding and pressure regulations during diving. Vascular bundles of lingual retia are described within the base of the tongue of a neonatal female gray whale (Eschrichtius robustus). Each rete consists of a central artery surrounded by four to six smaller veins. The retia and constituent vessels decrease in diameter as they extend anteriorly within the hyoglossus muscle from a position anterior to the basihyal cartilage toward the apex of the tongue. The position of the retia embedded in the hyoglossus and the anterior constriction of the vessels differs from reports of similar vascular bundles that were previously identified in gray whales. The retia likely serve as a counter-current heat exchange system to control body temperature during feeding. Cold blood flowing toward the body center within the periarterial veins would accept heat from warm blood in the central artery flowing toward the anterior end of the tongue. Although thermoregulatory systems have been identified within the mouths of a few mysticete species, the distribution of such vascular structures likely is more widespread among baleen whales than has previously been described. Anat Rec, 298:675-679, 2015. © 2014 Wiley Periodicals, Inc. PMID:25737382

Ekdale, Eric G; Kienle, Sarah S

2015-04-01

242

Comparison of natural convection heat exchangers for solar water heating systems  

Energy Technology Data Exchange (ETDEWEB)

Thermosyphon heat exchangers are used in indirect solar water heating systems to avoid using a pump to circulate water from the storage tank to the heat exchanger. In this study, the authors consider the effect of heat exchanger design on system performance. They also compare performance of a system with thermosyphon flow to the same system with a 40W pump in the water loop. In the first part of the study, the authors consider the impact of heat exchanger design on the thermal performance of both one- and two-collector solar water heaters. The comparison is based on Solar Rating and Certification Corporation (SRCC) OG300 simulations. The thermosyphon heat exchangers considered are (1) a one-pass, double wall, 0.22 m{sup 2}, four tube-in-shell heat exchanger manufactured by AAA Service and Supply, Inc., (the Quad-Rod); (2) a two-pass, double wall, 0.2 m{sup 2}, tube-in-shell made by Heliodyne, Inc., but not intended for commercial development; (3) a one-pass, single wall, 0.28 m{sup 2}, 31 tube-in-shell heat exchanger from Young Radiator Company, and (4) a one-pass single-wall, 0.61 m{sup 2}, four coil-in-shell heat exchanger made by ThermoDynamics Ltd. The authors compare performance of the systems with thermosyphon heat exchangers to a system with a 40 W pump used with the Quad-Rod heat exchanger. In the second part of the study, the effects of reducing frictional losses through the heat exchanger and/or the pipes connecting the heat exchanger to the storage tank, and increasing heat transfer area are evaluated in terms of OG300 ratings.

Davidson, J.; Liu, W.

1998-09-15

243

RIBBED DOUBLE PIPE HEAT EXCHANGER: ANALYTICAL ANALYSIS  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents the findings obtained by modeling a Double Pipe Heat Exchanger (DPHE equipped with repeated ribs from the inside for artificial roughing. An analytical procedure was developed to analyze the thermal and hydraulic performance of the DPHE with and without ribbing. The procedure was verified by comparing with experimental reported results and they are in good agreement. Several parameters were investigated in this study including the effect of ribs pitch to height ratios, P/e= 5, 10, 15, and 20, and ribs to hydraulic diameter ratios, e/Dh= 0.0595, 0.0765, and 0.107. These parameters were studied at various operating Reynolds number ranging from 2500 to 150000. Different installation configurations were investigated, too. An enhan-cement of 4 times in the heat transfer in terms of Stanton number was achieved at the expense of 38 times increase of pressure drop across the flow in terms of friction facto values.

HUSSAIN H. AL-KAYIEM

2011-02-01

244

Plate heat exchangers design, applications and performance  

CERN Document Server

Heat exchangers are important, and used frequently in the processing, heat and power, air-conditioning and refrigeration, heat recovery, transportation and manufacturing industries. Such equipment is also important in electronics cooling and for environmental issues like thermal pollution, waste disposal and sustainable development.The present book concerns plate heat exchangers (PHEs), which are one of the most common types in practice. The overall objectives are to present comprehensive descriptions of such heat exchangers and their advantages and limitations, to provide in-depth thermal and

Wang, L; Manglik, R M

2007-01-01

245

Numerical simulation of two phase flows in heat exchangers; Simulation numerique des ecoulements diphasiques dans les echangeurs  

Energy Technology Data Exchange (ETDEWEB)

The report presents globally the works done by the author in the thermohydraulic applied to nuclear reactors flows. It presents the studies done to the numerical simulation of the two phase flows in the steam generators and a finite element method to compute these flows. (author)

Grandotto Biettoli, M

2006-04-15

246

Experimental Study on Heat Transfer of Plate Heat Exchanger and Application to Waste Heat Power Generation  

Science.gov (United States)

According to investigation on the steel plant, a large amount of low thermal energy is emitted directly to the environment without any utilization. It is apparent that energy cogeneration and energy conversion become a problem concerned by all countries. At present, the utilization of thermal energy stored in slag washing water is mainly confined to transformation to heating rather than electricity generation. The working mechanism of electricity generation using slag washing water and experimental study on heat transfer characteristics of plate heat exchanger are presented in this paper. The experimental results show the non-linear relationship between heat transfer coefficient of plate heat exchanger made by different materials and different flow velocity of clean water in the pipe. When the flow velocity is greater than 1 m/s, K retains a certain value while the resistance coefficient increases dramatically. By comparison of experimental data, it is found that the heat resistance outside plate heat exchanger is the main factor that influences performance of plate heat transfer.

Tang, X. Y.; Zhu, D. S.; Guo, C. Q.

2010-03-01

247

THE STUDY OF HEAT EXCHANGE DYNAMICS OF VENTILATION EMISSIONS ON HEAT UTILIZATION WITH CONSIDERATION FOR WATER VAPOUR CONDENSATION  

Directory of Open Access Journals (Sweden)

Full Text Available Problem statement. Known corrosion-resistant air heaters made from glass tubes have not received wide acceptance because of some defects (low mechanical strength, temperature deformation, complexity and unreliability of assemblies, etc., whereas the structure of insulated glazing heat exchange devices has some advantages. The aim of present paper is to study heat exchange dynamics of venti-lation emissions in insulated glazing air heater on heat utilization with considera-tion for water vapor condensation.Results and conclusions. The study of heat exchange in channel insulated glazing heat exchanger at heat utilization of corrosion-active ventilation emissions is car-ried out with consideration for water vapour condensation on heat-exchange sur-faces. It is shown that the rate of heat exchange under longitudinal flow of vertical glass surfaces air heated and steam-and-air cooled is 15—20 % lower than the rate of heat exchange at air cooling.

V. S. Ezhov

2010-10-01

248

Heat exchanger for power generation equipment  

Science.gov (United States)

A heat exchanger for a turbine is provided wherein the heat exchanger comprises a heat transfer cell comprising a sheet of material having two opposed ends and two opposed sides. In addition, a plurality of concavities are disposed on a surface portion of the sheet of material so as to cause hydrodynamic interactions and affect a heat transfer rate of the turbine between a fluid and the concavities when the fluid is disposed over the concavities.

Nirmalan, Nirm Velumylm; Bowman, Michael John

2005-06-14

249

Analysis of thermosyphon heat exchangers for use in solar domestic hot water heating systems  

Science.gov (United States)

A recent innovation in the solar industry is the use of thermosyphon heat exchangers. Determining the performance of these systems requires knowledge of how thermosyphon flow rate and heat exchanger performance vary with operating conditions. This study demonstrates that several thermosyphon heat exchanger designs operate in the laminar mixed convection regime. Empirical heat transfer and pressure drop correlations are obtained for three tube-in-shell heat exchangers (four, seven, and nine tube). Thermosyphon flow is on the shell side. Correlations are obtained with uniform heat flux on the tube walls and with a mixture of glycol and water circulating inside the tubes. Ranges of Reynolds, Prandtl, and Grashof numbers are 50 to 1800, 2.5 and 6.0, and 4×105 to 1×108, respectively. Nusselt number correlations are presented in a form that combines the contributions of forced and natural convection, Nu4Mixed=Nu4Forced+Nu4Natural. The Nusselt number is influenced by natural convection when the term Raq0.25/(Re0.5Pr0.33) is greater than unity. Pressure drop through these three designs is not significantly affected by mixed convection because most pressure drop losses are at the heat exchanger inlet and outlet. A comparison and discussion of the performance of several other heat exchanger designs (tube-in-shell and coil-in- shell designs) are presented. Generally, the coil-in- shell heat exchangers perform better than the tube-in- shell heat exchangers. Data from all heat exchanger designs is used to develop a new one-dimensional model for thermosyphon heat exchangers in solar water heating systems. The model requires two empirically determined relationships, pressure drop as a function of water mass flow rate and the overall heat transfer coefficient-area product (UA) as a function of Reynolds, Prandtl, and Grashof number. A testing protocol is presented that describes the procedure to obtain the data for the correlations. Two new TRNSYS component models are presented, for the thermosyphon heat exchanger and thermosyphon loop. Unlike previous models, which are based on forced flow relationships, the new heat exchanger model accounts for mixed convection heat transfer and accurately predicts pressure drop in the connecting piping around the thermosyphon loop. Comparison between the model and experimental data shows excellent agreement. Daily and annual ratings for a sample thermosyphon system are presented.

Dahl, Scott David

1998-11-01

250

Experimental study on R-134a evaporation heat transfer characteristics in plate and shell heat exchanger  

International Nuclear Information System (INIS)

An experiment was carried out to investigate the characteristics of the evaporation heat transfer for refrigerant R-134a flowing in a plate and shell heat exchanger. The data are useful in designing more compact and effective evaporators for various refrigeration and air conditioning systems. Two vertical counterflow channels were formed in the exchanger. The R-134a flows up in one channel exchanging heat with the hot water flowing down in the other channel. The effects of the average heat flux, mass flux, saturation temperature and vapor quality were examined in detail. The present data show that the evaporation heat transfer coefficient increases with the vapor quality. A rise in the refrigerant mass flux causes an increase in the hr value. A rise in the average imposed heat flux causes an increase in the hr value at the low quality. Finally, at a higher refrigerant saturation temperature the hr value is found to be lower

251

Numerical study on boiling heat transfer enhancement in a microchannel heat exchanger  

International Nuclear Information System (INIS)

Flow boiling in a microchannel heat exchanger has received attention as an effective heat removal mechanism for high power-density microelectronics. Despite extensive experimental studied, the bubble dynamics coupled with boiling heat transfer in a microchannel heat exchanger is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulations are performed to further clarify the dynamics of flow boiling in a microchannel heat exchanger. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle and to treat an immersed solid surface. Based on the numerical results, the effects of modified channel shape on the bubble growth and heat transfer are quantified

252

Heat exchange apparatus for a reactor  

International Nuclear Information System (INIS)

A heat exchange apparatus for transferring heat from a reactor gas coolant to a secondary fluid medium is described. The heat exchange apparatus comprises an elongated vertically extending hole in a concrete shield. Supported within the hole in spaced relation to the wall thereof is an elongated vertical extending tubular shroud which shroud has a gas entry at its lower end and a gas exit at its upper end. Means are provided for dividing the annular space between the shroud 16 and the wall of the hole into an upper and a lower region. Disposed in the shield is an inlet for reactor coolant which communicates with the lower region and is positioned vertically so as to be spaced above the gas entry to the shroud to thereby suppress natural convection during nonoperating standby conditions of the apparatus. An outlet for reactor coolant, which is disposed in the shield, communicates with the upper region. A plurality of vertically extending, spaced apart bayonet tube assemblies are supported within the shroud and means are provided for passing secondary fluid through these tube assemblies. A circulator is provided for causing the reactor coolant to flow in through the inlet, downward in the annular space, into the shroud through the gas entry, upward through the shroud and out through the outlet during emergency conditions of the reactor

253

Heat exchanger network retrofit optimization involving heat transfer enhancement  

International Nuclear Information System (INIS)

Heat exchanger network retrofit plays an important role in energy saving in process industry. Many design methods for the retrofit of heat exchanger networks have been proposed during the last three decades. Conventional retrofit methods rely heavily on topology modifications which often result in a long retrofit duration and high initial costs. Moreover, the addition of extra surface area to the heat exchanger can prove difficult due to topology, safety and downtime constraints. Both of these problems can be avoided through the use of heat transfer enhancement in heat exchanger network retrofit. This paper presents a novel design approach to solve heat exchanger network retrofit problems based on heat transfer enhancement. An optimisation method based on simulated annealing has been developed to find the appropriate heat exchangers to be enhanced and to calculate the level of enhancement required. The physical insight of enhanced exchangers is also analysed. The new methodology allows several possible retrofit strategies using different retrofit methods be determined. Comparison of these retrofit strategies demonstrates that retrofit modification duration and payback time are reduced when heat transfer enhancement is utilised. Heat transfer enhancement can be also used as a substitute for increased heat exchanger network surface area to reduce retrofit investment costs.

254

Experimental testing and analytical analysis of a plastic panel heat exchanger for greenhouse heating  

Energy Technology Data Exchange (ETDEWEB)

The performance of a plastic panel-type heat exchanger, suitable for greenhouse heating using low-grade (25 to 60/sup 0/C water) power plant reject heat, was investigated theoretically and experimentally. The theoretical analysis showed that a plastic panel heat exchanger would have an overall heat transfer coefficient, U/sub 0/, of about 18 w/m/sup 2/-/sup 0/C compared to about 12 w/m/sup 2/-/sup 0/C for a fin-tube heat exchanger, under typical greenhouse conditions. Furthermore the plastic heat exchanger would require less fan power due to reduced air pressure losses. The experimental data revealed a similar functional relationship for U/sub 0/ and air flow when compared with the theoretical calculations, however the experimental values of U/sub 0/ were consistently larger by 20 to 30%. It was concluded that a properly designed plastic heat exchanger can compete with metal fin tube type exchangers on a performance basis, but the plastic heat exchangers are 3 to 4 times larger by volume. However, because of the lower cost of plastic, a substantial cost reduction is expected. It appears that further study, examining heat exchanger lifetime, performance and costs, is warranted.

Olszewski, M.; Thomas, J.F.

1980-02-01

255

Heat transfer characteristics of a new helically coiled crimped spiral finned tube heat exchanger  

Science.gov (United States)

In the present study, the heat transfer characteristics in dry surface conditions of a new type of heat exchanger, namely a helically coiled finned tube heat exchanger, is experimentally investigated. The test section, which is a helically coiled fined tube heat exchanger, consists of a shell and a helical coil unit. The helical coil unit consists of four concentric helically coiled tubes of different diameters. Each tube is constructed by bending straight copper tube into a helical coil. Aluminium crimped spiral fins with thickness of 0.5 mm and outer diameter of 28.25 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Ambient air is used as a working fluid in the shell side while hot water is used for the tube-side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. The effects of the inlet conditions of both working fluids flowing through the heat exchanger on the heat transfer coefficients are discussed. The air-side heat transfer coefficient presented in term of the Colburn J factor is proportional to inlet-water temperature and water mass flow rate. The heat exchanger effectiveness tends to increase with increasing water mass flow rate and also slightly increases with increasing inlet water temperature.

Srisawad, Kwanchanok; Wongwises, Somchai

2009-02-01

256

Graphite Foam Heat Exchangers for Thermal Management  

Energy Technology Data Exchange (ETDEWEB)

Improved thermal management is needed to increase the power density of electronic and more effectively cool electronic enclosures that are envisioned in future aircraft, spacecraft and surface ships. Typically, heat exchanger cores must increase in size to more effectively dissipate increased heat loads, this would be impossible in many cases, thus improved heat exchanger cores will be required. In this Phase I investigation, MRi aimed to demonstrate improved thermal management using graphite foam (Gr-foam) core heat exchangers. The proposed design was to combine Gr-foams from POCO with MRi's innovative low temperature, active metal joining process (S-Bond{trademark}) to bond Gr-foam to aluminum, copper and aluminum/SiC composite faceplates. The results were very favorable, so a Phase II SBIR with the MDA was initiated. This had primarily 5 tasks: (1) bonding, (2) thermal modeling, (3) cooling chip scale packages, (4) evaporative cooling techniques and (5) IGBT cold plate development. The bonding tests showed that the ''reflow'' technique with S-Bond{reg_sign}-220 resulted in the best and most consistent bond. Then, thermal modeling was used to design different chip scale packages and IGBT cold plates. These designs were used to fabricate many finned graphite foam heat sinks specifically for two standard type IC packages, the 423 and 478 pin chips. These results demonstrated several advantages with the foam. First, the heat sinks with the foam were lighter than the copper/aluminum sinks used as standards. The sinks for the 423 design made from foam were not as good as the standard sinks. However, the sinks made from foam for the 478 pin chips were better than the standard heat sinks used today. However, this improvement was marginal (in the 10-20% better regime). However, another important note was that the epoxy bonding technique resulted in heat sinks with similar results as that with the S-bond{reg_sign}, slightly worse than the S-bond{reg_sign}, but still better than the standard heat sinks. Next, work with evaporative cooling techniques, such as heat pipes, demonstrated some unique behavior with the foam that is not seen with standard wick materials. This was that as the thickness of the foam increased, the performance got better, where with standard wick materials, as the thickness increases, the performance decreases. This is yet to be completely explained. Last, the designs from the thermal model were used to fabricate a series of cold plates with the graphite foam and compare them to similar designs using high performance folded fin aluminum sinks (considered standard in the industry). It was shown that by corrugating the foam parallel to fluid flow, the pressure drop can be reduced significantly while maintaining the same heat transfer as that in the folded fin heat sink. In fact, the results show that the graphite foam heat sink can utilized 5% the pumping power as that required with the folded fin aluminum heat sink, yet remove the same amount of heat.

Klett, J.W.

2004-06-07

257

Heat exchange fluids and techniques. [US patents  

Energy Technology Data Exchange (ETDEWEB)

The detailed, descriptive information presented is based on US patents, issued since January 1975, that deal with heat exchange fluids and techniques, and their potential for energy saving. This book serves a double purpose in that it supplies detailed technical information and can be used as a guide to the US patent literature in this field. By indicating all the information that is significant, and eliminating legal jargon and juristic phraseology, an advanced, technically oriented review of heat exchange fluids and techniques is presented. Information is included on the design and construction of heat exchangers; heat transfer fluids; low temperature processes; heat storage; heat transfer control in buildings; solar and geothermal energy processes; and industrial, medical, and residential uses of heat exchangers. (LCL)

Ranney, M.W.

1979-01-01

258

Heat exchanger for nuclear power plants  

International Nuclear Information System (INIS)

A heat exchanger is designed for nuclear power plants whose heat transfer surface consists of U-shaped exchange elements with inner integral pipes on which is slipped a jacketed tube integral in bend. This heat transfer surface is arranged symmetrically or laterally with respect to the axis of the drums or steam separators. The exchange elements with the drum are arranged in an insulated assembly box and the drum is attached to swing suspensions. The exchange elements can thus swing together with the suspension drum and may shift in the direction of the thermal dilatation of the pipe conduit. (F.M.)

259

The use of downhole heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

The downhole heat exchanger (DHE), used extensively in Klamath Falls, Oregon, in over 500 installations, and in Turkey and New Zealand, provides heating for one or more homes, schools, and apartment buildings from a single geothermal well. The DHE eliminates the problem of disposal of geothermal fluid, since only heat is extracted from the well. The heat exchangers consist of a loop of pipes or tubes suspended in the geothermal well, through which ''clean'' secondary water is pumped or allowed to circulate by natural convection. The maximum output of large installations is typically less than 3 GJ/h or 0.8 MW{sub t}, with well depths up to about 150 m, and may be economical under certain conditions at a well depth of 500 m. However, the typical output for an individual home in Klamath Falls tends to be less than 265 MJ/h (0.07 MW{sub t}). In order to obtain maximum output, the well must be designed to have an open annulus between the wellbore and casing, with perforations near the top and bottom of the submerged heat exchanger, just below the water surface and at the hot aquifer at the bottom of the well. Natural convection circulates the well water down inside the casing, through the lower perforations, up through the annulus and back into the casing through the upper perforations, with the new geothermal water mixing with the old. This vertical convection cell exposes the DHE to the near-maximum temperature of the well water and thus increases the heat output of the DHE. The heat output from a DHE system is dependent on the bore diameter, casing diameter, DHE length, tube diameter, number of loops in the well, flow rate and temperature of the geothermal fluid. Based on local experience in Klamath Falls, the ''rule-of-thumb'' is that contractors estimate approximately ''1 foot of DHE pipe per 1500 Btu/h'' (5200 kJ/h/m or 1.44 kW/m) as an average output. (author)

Lund, J.W. [Oregon Institute of Technology, Klamath Falls, OR (United States). Geo-Heat Center

2003-12-01

260

Heat flow method  

International Nuclear Information System (INIS)

In this paper we study the heat flow of harmonic maps between two compact Riemannian manifolds. The global existence of the regular solution and the weak solution, as well as the blow up of the weak solution are discussed. (author). 14 refs

261

Compact interior heat exchangers for CO{sub 2} mobile heat pumping systems  

Energy Technology Data Exchange (ETDEWEB)

The natural refrigerant carbon dioxide (CO{sub 2}) offers new possibilities for design of flexible, efficient and environmentally safe mobile heat pumping systems. As high-efficient car engines with less waste heat are developed, extra heating of the passenger compartment is needed in the cold season. A reversible transcritical CO{sub 2} system with gliding temperature heat rejection can give high air delivery temperature which results in rapid heating of the passenger compartment and rapid defogging or defrosting of windows. When operated in cooling mode, the efficiency of transcritical CO{sub 2} systems is higher compared to common (HFC) air conditioning systems, at most dominant operating conditions. Several issues were identified for the design of compact interior heat exchangers for automotive reversible CO{sub 2} heat pumping systems. Among theses issues are: (1) Refrigerant flow distribution, (2) Heat exchanger fluid flow circuiting, (3) Air temperature uniformity downstream of the heat exchanger, (4) Minimization of temperature approach, (5) Windshield flash fogging due to retained water inside the heat exchanger, (6) Internal beat conduction in heating mode operation, and (7) Refrigerant side pressure drop In order to provide a basis for understanding these issues, the author developed a calculation model and set up a test facility and investigated different prototype heat exchangers experimentally.

Hafner, Armin

2003-07-01

262

Heat transfer of high thermal energy storage with heat exchanger for solar trough power plant  

International Nuclear Information System (INIS)

High temperature thermal energy storage was studied by a lab-scale cylindrical storage tank experiment. A heat exchanger of thermal energy storage is used for separating two fluids, storage medium, and heat transfer fluid (HTF). There are two types of pipe in the heat exchanger, a vertical straight pipe and a helical coiled pipe. The experimental results were validated with the created mathematical model of nonsteady state heat exchanger. The highest storage efficiency is 0.631 at the HTF flow rate of 0.1 kg/s in a helical coiled pipe heat exchanger. The HTF and storage medium temperatures were measured for validating the model at various HTF flow rates. The agreement between model and experiment was presented with the error below 10%. This model is able to calculate the storage temperature of solar thermal power plants that performs in the liquid temperature range of selected HTF and storage medium

263

High temperature alloys and ceramic heat exchanger  

International Nuclear Information System (INIS)

From the standpoint of energy saving, the future operating temperatures of process heat and gas turbine plants will become higher. For this purpose, ceramics is the most promissing candidate material in strength for application to high-temperature heat exchangers. This report deals with a servey of characteristics of several high-temperature metallic materials and ceramics as temperature-resistant materials; including a servey of the state-of-the-art of ceramic heat exchanger technologies developed outside of Japan, and a study of their application to the intermediate heat exchanger of VHTR (a very-high-temperature gas-cooled reactor). (author)

264

Heat Transfer Enhancement of Shell and Tube Heat Exchanger Using Conical Tapes.  

Directory of Open Access Journals (Sweden)

Full Text Available This paper provides heat transfer and friction factor data for single -phase flow in a shell and tube heat exchanger fitted with a helical tape insert. In the double concentric tube heat exchanger, hot air was passed through the inner tube while the cold water was flowed through the annulus. The influences of the helical insert on heat transfer rate and friction factor were studied for counter flow, and Nusselt numbers and friction factor obtained were compared with previous data (Dittus 1930, Petukhov 1970, Moody 1944 for axial flows in the plain tube. The flow considered is in a low Reynolds number range between 2300 and 8800. A maximum percentage gain of 165% in heat transfer rate is obtained for using the helical insert in comparison with the plain tube.

Dhanraj S.Pimple

2014-12-01

265

Damping of multispan heat exchanger tubes. Pt. 2: in liquids  

International Nuclear Information System (INIS)

Damping information is required for flow-induced vibration analyses of heat exchanger tubes. This paper treats the question of damping of multispan heat exchanger tubes in liquids. There are three important energy dissipation mechanisms that contribute to damping in liquids. These are: viscous damping between tube and liquid, squeeze-film damping in the clearance between tube and tube-support and friction damping at the tube-support. These mechanisms are discussed and formulated in terms of heat exchanger tube parameters. The available experimental data on damping in liquids are reviewed and analysed. Semi-empirical expressions have been developed to formulate damping. These expressions are recommended for design purposes. This study is interesting in the nuclear industry for it often uses heat exchangers

266

Heat transfer analysis of short helical borehole heat exchangers  

International Nuclear Information System (INIS)

Highlights: ? Vertical ground heat exchanger with a helical shaped pipe is analyzed. ? The model considers the interaction between the ground and the environment. ? The results of the model are in good agreement with the experimental values. ? The weather conditions considerably affect the fluid heat carrier temperature. ? The pitch between the turns does not affect the behaviour of the heat exchanger. -- Abstract: In this paper a numerical model to analyze the thermal behaviour of vertical ground heat exchangers with a helical shaped pipe is presented. This type of configuration can be a suitable alternative to conventional ground heat exchangers, especially when the heating and cooling loads of the building are very low. The model describes the heat transfer problem by means of a network of interconnected thermal resistances and capacitances. Moreover, as the investigated ground heat exchanger is usually installed in shallow depth, the model takes into account the interaction between the ground and the ambient environment which affects the fluid heat carrier temperature into the heat exchanger and, as a consequence, the energy efficiency of the heat pump. After a sensitivity analysis on the mesh parameters, the presented model is compared with experimental data and the simulation results show good agreement with the measurements. Finally, analyses to investigate the influence of the weather conditions, of the axial heat transfer and of the pitch between the turns of the helical pipe for two types of ground are carried out.

267

Heat exchanger device and method for heat removal or transfer  

Energy Technology Data Exchange (ETDEWEB)

Systems and methods for a forced-convection heat exchanger are provided. In one embodiment, heat is transferred to or from a thermal load in thermal contact with a heat conducting structure, across a narrow air gap, to a rotating heat transfer structure immersed in a surrounding medium such as air.

Koplow, Jeffrey P

2015-03-24

268

Optimisation of intermediate heat exchanger for PFBR  

International Nuclear Information System (INIS)

In the Prototype Fast Breeder Reactor (PFBR) intermediate heat exchangers (IHX) enable the transfer of thermal power from the active primary sodium to inactive secondary sodium which in turn transfers the heat to produce steam. The IHX is a vertical shell and tube heat exchanger with primary sodium on the shell side and secondary sodium on the tube side. For sizing the IHX parametric studies have been carried out and the results are given

269

Intermediate heat exchanger project for Super Phenix  

International Nuclear Information System (INIS)

The Super Phenix (1200 MWe) intermediate heat exchangers are derived directly from those of Phenix (250 MWe). The intermediate exchangers are housed in the reactor vessel annulus: as this annulus must be of the smallest volume possible, these IHX are required to work at a high specific rating. The exchange surface is calculated for nominal conditions. A range is then defined, consistent with the above requirements and throughout which the ratio between bundle thickness and bundle length remains acceptable. Experimental technics and calculations were used to determine the number of tube constraint systems required to keep the vibration amplitude within permissible limits. From a knowledge of this number, the pressure drop produced by the primary flow can be calculated. The bundle geometry is determined together with the design of the corresponding tube plates and the way in which these plates should be joined to the body of the IHX. The experience (technical and financial) acquired in the construction of Phenix is then used to optimize the design of the Super Phenix project. An approximate definition of the structure of the IHX is obtained by assuming a simplified load distribution in the calculations. More sophisticated calculations (e.g. finite element method) are then used to determine the behaviour of the different points of the IHX, under nominal and transient conditions

270

COMPARATIVE THERMAL ANALYSIS OF HELIXCHANGER WITH SEGMENTAL HEAT EXCHANGER USING BELL-DELAWARE METHOD  

OpenAIRE

Heat exchangers are important heat transfer apparatus in oil refining, chemical engineering, environmental protection, electric power generation etc. The present work modifies the existing Bell-Delaware method used for conventional heat exchanger, taking into consideration the helical geometry of Helixchanger. Thermal analysis was carried out to study the impacts of various baffle inclination angles on fluid flow and heat transfer of heat exchangers with helical baffles. The analysis was con...

Pavithran, S.; Hadgekar, P. V.; Shinde, S. S.

2012-01-01

271

Concept of irreversibility in heat exchanger design: Counterflow heat exchangers for gas-to-gas applications  

International Nuclear Information System (INIS)

The thermal design of counterflow heat exchangers for gas-to-gas applications is based on the thermodynamic irreversibility rate or useful power no longer available as a result of heat exchanger frictional pressure drops and stream-to-stream temperature differences. The irreversibility (entropy production) concept establishes a direct relationship between the heat exchanger design parameters and the useful power wasted due to heat exchanger nonideality. The paper presents a heat exchanger design method for fixed or for minimum irreversibility (number of entropy generation units N/sub s/). In contrast with traditional design procedures, the amount of heat transferred between streams and the pumping power for each side become outputs of the N/sub s/ design approach. To illustrate the use of this method, the paper develops the design of regenerative heat exchangers with minimum heat transfer surface and with fixed irreversibility N/sub s/

272

Negative Joule Heating in Ion-Exchange Membranes  

OpenAIRE

In ion-exchange membrane processes, ions and water flow under the influence of gradients in hydrostatic pressure, ion chemical potential, and electrical potential (voltage), leading to solvent flow, ionic fluxes and ionic current. At the outer surfaces of the membranes, electrical double layers (EDLs) are formed (Donnan layers). When a current flows through the membrane, we argue that besides the positive Joule heating in the bulk of the membrane and in the electrolyte outsi...

Biesheuvel, P. M.; Brogioli, D.; Hamelers, H. V. M.

2014-01-01

273

Forced convection heat exchange inside porous sintered metals  

International Nuclear Information System (INIS)

Methods and results of investigating heat exchange in the process of liquid flow inside porous sintered metals have been analyzed. It has been shown that experimental data available include extremely conflicting correlations between heat transfer coefficient and Reynolds number, porosity, and relative wall thickness. Scattering of the data can attain one order of magnitude. The volume coefficient of heat transfer inside pores determined in papers does not correspond to its real value in the initial equations of the inner problem of porous cooling. Calculating and experimental method of determining the heat transfer coefficient has been developed and realized on the unit of radiation heating. More accurate experimental data on intraporous heat exchange have been obtained. It has been established that relative wall thickness does not affect the intensity of heat transfer inside pores

274

Performances of heat exchangers on HTGR application  

International Nuclear Information System (INIS)

Rising oil price is making the high-temperature gas-cooled reactor (HTGR) an attractive alternative energy resource for high temperature process heat applications. Motivation and aspect of nuclear process applications to steam reforming and coal gasification, etc. are described. Studies on heat transfer problems are reviewed. The present status of designed high temperature heat exchangers is summarized. The performances of He-He high temperature heat exchanger tested in Japan is reported. Several problems in the future research and development of technologies for process heat application by HTGR are discussed. 29 refs

275

Heat exchanger and its manufacturing method  

International Nuclear Information System (INIS)

A plurality of helical type double-walled heat transfer tubes are disposed in an outer cylinder. Each of the helical type double-walled heat exchange tubes has an outer tube in a state where a gap is formed at the outer circumference of an inner tube. A porous metal is disposed in the gap between the inner tube and the outer tube. A leakage detection means is disposed for detecting leakage of fluid circulating in the heat exchange tubes by way of the gap between the inner and the outer tubes. The helical type double-walled heat transfer tube is formed by cold helical fabrication, and then heat treatment is applied in an argon gas atmosphere. Since a helical type double-walled heat transfer tube is used, a great heat transfer area per unit volume can be provided. Accordingly, the capacity of the heat exchanger can be increased without enlarging the size of the heat exchanger and increasing the number of the heat transfer tubes. In addition, since heat treatment is applied, the close bondability between the inner or the outer tube and the porous metal is restored, thereby enabling to make heat transfer performance satisfactory. (I.N.)

276

Pressure distribution and heat exchange in a gasdynamic model with combustion over which a high-enthalpy air stream flows  

Energy Technology Data Exchange (ETDEWEB)

This paper presents data on the pressure distribution and heat fluxes in the channel of a gasdynamic model with combustion. The geometry of the internal channel is described. Tests were conducted in a IT-301 pulsed tunnel with a conical nozzle. For hydrogen burning in the model presented, the system of equations for determining the parameters along the channel of the combustion chamber is presented.

Baev, V.K.; Shumskii, V.V.; Yaroslavtsev, M.I.

1986-03-01

277

On-line fouling monitor for heat exchangers  

International Nuclear Information System (INIS)

Biological and/or chemical fouling in utility service water system heat exchangers adversely affects operation and maintenance costs, and reduced heat transfer capability can force a power deaerating or even a plant shut down. In addition, service water heat exchanger performance is a safety issue for nuclear power plants, and the issue was highlighted by NRC in Generic Letter 89-13. Heat transfer losses due to fouling are difficult to measure and, usually, quantitative assessment of the impact of fouling is impossible. Plant operators typically measure inlet and outlet water temperatures and flow rates and then perform complex calculations for heat exchanger fouling resistance or ''cleanliness''. These direct estimates are often imprecise due to inadequate instrumentation. Electric Power Research Institute developed and patented an on-line condenser fouling monitor. This monitor may be installed in any location within the condenser; does not interfere with routine plant operations, including on-line mechanical and chemical treatment methods; and provides continuous, real-time readings of the heat transfer efficiency of the instrumented tube. This instrument can be modified to perform on-line monitoring of service water heat exchangers. This paper discusses the design, construction of the new monitor, and algorithm used to calculate service water heat exchanger fouling

278

The LUX prototype detector: Heat exchanger development  

International Nuclear Information System (INIS)

The LUX (large underground xenon) detector is a two-phase xenon time projection chamber (TPC) designed to search for WIMP–nucleon dark matter interactions. As with all noble element detectors, continuous purification of the detector medium is essential to produce a large (>1ms) electron lifetime; this is necessary for efficient measurement of the electron signal which in turn is essential for achieving robust discrimination of signal from background events. In this paper, we describe the development of a novel purification system deployed in a prototype detector. The results from the operation of this prototype indicated heat exchange with an efficiency above 94% up to a flow rate of 42 slpm, allowing for an electron drift length greater than 1 m to be achieved in approximately 2 days and sustained for the duration of the testing period

279

The LUX prototype detector: Heat exchanger development  

Energy Technology Data Exchange (ETDEWEB)

The LUX (large underground xenon) detector is a two-phase xenon time projection chamber (TPC) designed to search for WIMP–nucleon dark matter interactions. As with all noble element detectors, continuous purification of the detector medium is essential to produce a large (>1ms) electron lifetime; this is necessary for efficient measurement of the electron signal which in turn is essential for achieving robust discrimination of signal from background events. In this paper, we describe the development of a novel purification system deployed in a prototype detector. The results from the operation of this prototype indicated heat exchange with an efficiency above 94% up to a flow rate of 42 slpm, allowing for an electron drift length greater than 1 m to be achieved in approximately 2 days and sustained for the duration of the testing period.

Akerib, D.S. [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); Bai, X. [South Dakota School of Mines and Technology, 501 East St Joseph St., Rapid City, SD 57701 (United States); Bedikian, S. [Yale University, Department of Physics, 217 Prospect St., New Haven, CT 06511 (United States); Bernstein, A. [Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94551 (United States); Bolozdynya, A. [National Research Nuclear University MEPHI, Faculty of the Experimental and Theoretical Physics, Kashirskoe Sh., 31, Moscow 115409 (Russian Federation); Bradley, A. [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); Cahn, S.B. [Yale University, Department of Physics, 217 Prospect St., New Haven, CT 06511 (United States); Carr, D. [Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94551 (United States); Chapman, J.J. [Brown University, Department of Physics, 182 Hope St., Providence, RI 02912 (United States); Clark, K., E-mail: kjc20@psu.edu [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); Classen, T. [University of California Davis, Department of Physics, One Shields Ave., Davis, CA 95616 (United States); Curioni, A. [Yale University, Department of Physics, 217 Prospect St., New Haven, CT 06511 (United States); Dahl, C.E. [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); Dazeley, S. [Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94551 (United States); Viveiros, L. de [Brown University, Department of Physics, 182 Hope St., Providence, RI 02912 (United States); Dragowsky, M. [Department of Physics, Case Western Reserve University, Cleveland, OH 44106 (United States); Druszkiewicz, E. [University of Rochester, Department of Physics and Astronomy, Rochester, NY 14627 (United States); and others

2013-05-01

280

Condensing Heat Exchanger with Hydrophilic Antimicrobial Coating  

Science.gov (United States)

A multi-layer antimicrobial hydrophilic coating is applied to a substrate of anodized aluminum, although other materials may form the substrate. A silver layer is sputtered onto a thoroughly clean anodized surface of the aluminum to about 400 nm thickness. A layer of crosslinked, silicon-based macromolecular structure about 10 nm thickness overlies the silver layer, and the outermost surface of the layer of crosslinked, silicon-based macromolecular structure is hydroxide terminated to produce a hydrophilic surface with a water drop contact angle of less than 10.degree.. The coated substrate may be one of multiple fins in a condensing heat exchanger for use in the microgravity of space, which has narrow channels defined between angled fins such that the surface tension of condensed water moves water by capillary flow to a central location where it is pumped to storage. The antimicrobial coating prevents obstruction of the capillary passages.

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor)

2014-01-01

281

The explosive plugging of heat exchangers  

International Nuclear Information System (INIS)

The mechanism and development of explosive welding and particularly the application to tube to tubeplate welding is briefly reviewed. The need for plugging of heat exchangers in the power generating industry and the requirement for producing a high integrity weld are discussed. Details are given of the explosive plugging system developed for the reheater heat exchanger of the prototype fast reactor (PFR), including data on weld lengths and distortion of adjoining holes. Results of destructive and non-destructive tests on trial plugging of a seven hole array are given. The system described has been successfully applied to an actual heat exchanger and the procedure followed is briefly discussed. (author)

282

Enceladus' enigmatic heat flow  

Science.gov (United States)

Enceladus’ heat flow provides a fundamental constraint on its tidal dissipation mechanisms, orbital evolution, and the physical processes that generate the plumes. An initial estimate of this value, 5.8±1.3 GW, was made by Spencer et al. (2006) using Cassini Composite Infrared Spectrometer (CIRS) 600 to 1100 cm-1 observations. This number was refined using 10 to 600 cm-1 CIRS observations to 15.8±3.1 GW by Howett et al. (2011). However, recent reanalysis of high-spatial resolution 10 to 1100 cm-1 CIRS observations of Enceladus’ active south polar region conducted by Spencer and Howett gives a heat flow of 4.64±0.23 GW. Whilst all of these heat flow estimates are much larger than those expected in a steady state, 1.1 GW (Meyer and Wisdom, 2007), their obvious discrepancy is a puzzle. Was the passive emission component simply underestimated in the 15.8 GW determination, or is there significant between-stripe endogenic emission that is excluded in the most recent estimate, or is something else going on?

Howett, Carly; Spencer, John; Verbiscer, Anne

2014-11-01

283

Development of Design Criteria for Fluid Induced Structural Vibrations in Steam Generators and Heat Exchangers  

International Nuclear Information System (INIS)

Flow-induced vibration in heat exchangers has been a major cause of concern in the nuclear industry for several decades. Many incidents of failure of heat exchangers due to apparent flow-induced vibration have been reported through the USNRC incident reporting system. Almost all heat exchangers have to deal with this problem during their operation. The phenomenon has been studied since the 1970s and the database of experimental studies on flow-induced vibration is constantly updated with new findings and improved design criteria for heat exchangers

284

Development of Design Criteria for Fluid Induced Structural Vibrations in Steam Generators and Heat Exchangers  

Energy Technology Data Exchange (ETDEWEB)

Flow-induced vibration in heat exchangers has been a major cause of concern in the nuclear industry for several decades. Many incidents of failure of heat exchangers due to apparent flow-induced vibration have been reported through the USNRC incident reporting system. Almost all heat exchangers have to deal with this problem during their operation. The phenomenon has been studied since the 1970s and the database of experimental studies on flow-induced vibration is constantly updated with new findings and improved design criteria for heat exchangers.

Uvan Catton; Vijay K. Dhir; Deepanjan Mitra; Omar Alquaddoomi; Pierangelo Adinolfi

2004-04-06

285

Heat transfer and fluid flow in minichannels and microchannels  

CERN Document Server

Heat exchangers with minichannel and microchannel flow passages are becoming increasingly popular due to their ability to remove large heat fluxes under single-phase and two-phase applications. Heat Transfer and Fluid Flow in Minichannels and Microchannels methodically covers gas, liquid, and electrokinetic flows, as well as flow boiling and condensation, in minichannel and microchannel applications. Examining biomedical applications as well, the book is an ideal reference for anyone involved in the design processes of microchannel flow passages in a heat exchanger. Each chapter is accompan

Kandlikar, Satish; Li, Dongqing; Colin, Stephane; King, Michael R

2013-01-01

286

Heat transfer from oriented heat exchange areas  

OpenAIRE

This paper deals with the transfer of heat-driven heat transfer surface area in relation to the construction of the criterion equation for “n” horizontal pipe one about another. On the bases of theoretical models have been developed for calculating the thermal performance of natural convection by Churilla and Morgan, for various pipe diameters and temperatures. These models were compared with models created in CFD-Fluent Ansys the same boundary conditions. The aim of the analyse of heat a...

Vantuch Martin; Huzvar Jozef; Kapjor Andrej

2014-01-01

287

The use of helical heat exchanger for heat recovery domestic water-cooled air-conditioners  

International Nuclear Information System (INIS)

An experimental study on the performance of a domestic water-cooled air-conditioner (WAC) using tube-in-tube helical heat exchanger for preheating of domestic hot water was carried out. The main aims are to identify the comprehensive energy performance (space cooling and hot water preheating) of the WAC and the optimum design of the helical heat exchanger taking into account the variation in tap water flow rate. A split-type WAC was set up for experimental study at different indoor and outdoor conditions. The cooling output, the amount of recovered heat, and the power consumption for different hot water flow rates were measured. The experimental results showed that the cooling coefficient of performance (COP) of the WAC improves with the inclusion of the heat recovery option by a minimum of 12.3%. This can be further improved to 20.6% by an increase in tap water flow rate. Same result was observed for the comprehensive COP of the WAC. The maximum achievable comprehensive COP was 4.92 when the tap water flow rate was set at 7.7 L/min. The overall heat transfer coefficient of the helical heat exchanger under various operating conditions were determined by Wilson plot. A mathematical model relating the over all heat transfer coefficient to the outer pipe diameter was established which provides a convenient way of optimising the design of the helical heat exchanger

288

Performance evaluation criteria for use of enhanced heat transfer surfaces in heat exchanger design  

International Nuclear Information System (INIS)

Previous work of Bergles and Webb is extended to establish a broad range of Performance Evaluation Criteria (PEC) applicable to single phase flow in tubes. The equations include the effects of shell-side enhancement and fouling and are applicable to roughness and internally finned tubes. Detailed procedures are outlined to calculate the performance improvement and to select the 'optimum' surface geometry. PEC are presented for four design cases: (1) reduced heat exchanger material; (2) increased heat duty- (3) reduced log-mean temperature difference- and (4) reduced pumping power. The 11 cases discussed include fixed flow area and variable flow area. Appropriate PEC for two-phase exchangers are also discussed. (author)

289

Air heat exchangers with long heat pipes: Experiments and predictions  

Energy Technology Data Exchange (ETDEWEB)

This paper presents measurements and predictions of a heat pipe-equipped heat exchanger with two filling ratios of R134a, 19% and 59%. The length of the heat pipe, or rather thermosyphon, is long (1.5 m) as compared to its diameter (16 mm). The airflow rate varied from 0.4 to 2.0 kg/s. The temperatures at the evaporator side of the heat pipe varied from 40 to 70 C and at the condenser part from 20 to 50 C. The measured performance of the heat pipe has been compared with predictions of two pool boiling models and two filmwise condensation models. A good agreement is found. This study demonstrates that a heat pipe equipped heat exchanger is a good alternative for air-air exchangers in process conditions when air-water cooling is impossible, typically in warmer countries. (author)

Hagens, H. [VDL Klima b.v. Meerenakkerweg 30, 5652 AV Eindhoven (Netherlands); Ganzevles, F.L.A.; van der Geld, C.W.M.; Grooten, M.H.M. [Department of Mechanical Engineering, Technische Universiteit Eindhoven, Postbus 513, 5600 MB Eindhoven (Netherlands)

2007-10-15

290

Heat exchanger fouling: Prediction, measurement, and mitigation  

Science.gov (United States)

The US Department of Energy (DOE), Office of Industrial Programs (OIP) sponsors the development of innovative heat exchange systems. Fouling is a major and persistent cost associated with most industrial heat exchangers and nationally wastes an estimated 2.9 Quads per year. To predict and control fouling, three OIP projects are currently exploring heat exchanger fouling in specific industrial applications. A fouling probe has been developed to determine empirically the fouling potential of an industrial gas stream and to derive the fouling thermal resistance. The probe is a hollow metal cylinder capable of measuring the average heat flux along the length of the tube. The local heat flux is also measured by a heat flux meter embedded in the probe wall. The fouling probe has been successfully tested in the laboratory at flue gas temperatures up to 2200 F and a local heat flux up to 41,000 BTU/hr sq ft. The probe has been field tested at a coal-fired boiler plant. Future tests at a municipal waste incinerator are planned. Two other projects study enhanced heat exchanger tubes, specifically the effect of enhanced surface geometries on the tube bundle performance. Both projects include fouling in a liquid heat transfer fluid. Identifying and quantifying the factors affecting fouling in these enhanced heat transfer tubes will lead to techniques to mitigate fouling.

291

Joule-Thomson expander and heat exchanger  

Science.gov (United States)

The Joule-Thomson Expander and Heat Exchanger Program was initiated to develop an assembly (JTX) which consists of an inlet filter, counterflow heat exchanger, Joule-Thomson expansion device, and a low pressure jacket. The program objective was to develop a JTX which, when coupled to an open cycle supercritical helium refrigerating system (storage vessel), would supply superfluid helium (He II) at 2 K or less for cooling infrared detectors.

Norman, R. H.

1976-01-01

292

Tube-in-shell heat exchangers  

International Nuclear Information System (INIS)

A tube-in-shell heat exchanger is described for use in liquid metal cooled fast breeder reactor constructions. The system consists of a bundle of heat exchange tubes with a central spine extending longitudinally through the shell and a series of longitudinally spaced transverse grids resiliently mounted on the central spine within the shell to provide transverse support for bracing the tubes apart. (U.K.)

293

Device for supporting flat heat exchange packets for recuperative heat exchange  

International Nuclear Information System (INIS)

A honeycombed structure of the supporting framework allows to place very closely a great number of adjacent tube-shaped cases which contain the heat exchanger sets connected in parallel. Thus individual components of the heat exchangers are easily accessible fact which is of great advantage for heat exchangers operating in HTRs being subject to high dynamic loads which are due to pressure- and temperature variations. (GL)

294

Evaluation of heat exchange performance for intermediate heat exchanger in HTTR  

International Nuclear Information System (INIS)

In High Temperature Engineering Test Reactor (HTTR) of 30 MW, the generated heat at reactor core is finally dissipated at the air-cooler by way of the heat exchangers of the primary pressurized water cooler and the intermediate heat exchanger (IHX). The heat exchangers in the main cooling system of HTTR must satisfy two conditions, that is, achievement of reactor coolant outlet temperature 850degC/950degC and removal of reactor generated heat 30 MW. Therefore, the heat exchanges have to have the same performance as these in the design. In this report, heat exchange performance of the IHX in the main cooling system was evaluated with the rise-to-power-up test and the in-service operation data. Moreover, the validity of the IHX thermal-hydraulic design method was confirmed by comparison of evaluated data with designed value. (author)

295

PS1 satellite refrigerator heat exchanger: Failure of the LN2 heat exchanger to low pressure helium  

International Nuclear Information System (INIS)

The PS1 heat exchanger is one of three prototype heat exchangers built by Atomic Welders before Meyer was given the contract to build the Satellite Refrigerator Heat Exchanger components. This heat exchanger was first put into operation in July 1983. In November 1991, this heat exchanger experienced a failure in the shell of heat exchanger 1 causing nitrogen to contaminate the helium in the refrigerator. The resulting contamination plugged heat exchanger 3. The break occurred at a weld that connects a 0.25 inch thick ring to heat exchanger 1. The failure appears to be a fatigue of the shell due to temperature oscillations. The flow rate through the break was measured to be 1.0 scfm for a pressure drop over the crack of 50 psi. An ANSYS analysis of the failure area indicates that the stress would be 83,000 psi if the metal did not yield. This is based on cooling down the shell to 80K from 300K with the shell side helium on the outside of the shell at 300K. This is the largest change in temperature that occurs during operation. During normal operations, the temperature swings are not nearly this large, however temperatures down to 80K are not unusual (LN2 overflowing pot). The highest temperatures are typically 260K. The analysis makes no attempt to estimate the stress concentration factor at this weld but there is no doubt that it is greater than 1. No estimate as to the number of cycles to cause failure was calculated nor any estimate as to the actual number of cycles was made

296

CALCULATION OF DISTRIBUTION OF TEMPERATURE ALONG THE CORE AT NON-STATIONARY HEAT EXCHANGE USING THE METHOD OF LOCAL THERMAL FLOWS  

Directory of Open Access Journals (Sweden)

Full Text Available Statement of the problem. Engineering practice has to deal with the problems of non-stationary heat exchange in flat elements of building structures, however, the methods of its calculation are not sufficiently developed.Results. An engineering method for calculating a non-stationary temperature field in a core heat-insulated from the sides was proposed, based on local application of physical and mathematical models of non-stationary heat exchange on the core. The expression was obtained for the calcula-tion of a constant of time which all of the calculation formulas include. Using a constant of time, the upper boundary for each step in time was established.Conclusions. The developed calculation techniques are applicable for non-uniform cores. The method to be further described is applicable and for calculation of distribution of temperature on a thickness of flat elements of the building designs, which cross-section sizes much more a thickness.

I. Yu. Butusov

2013-02-01

297

Heat transfer of high thermal energy storage with heat exchanger for solar trough power plant  

Energy Technology Data Exchange (ETDEWEB)

Thermal energy storage equipment is used in conventional solar thermal power plants to ensure power stability. The highly efficient and low cost solar parabolic trough power plant consists of trough shaped mirrors that focus the sun's ray into a pipe in which heat transfer fluid (HTF) circulates. The 3 major components in a solar trough power plant are the solar energy collector, the energy storage system, and the steam generator. This study investigated the high temperature thermal energy storage in a lab-scale cylindrical storage tank experiment. A thermal energy storage heat exchanger was used to separate 2 fluids, notably the storage medium and heat HTF. Vertical straight pipes and helical coiled pipes are the two types of pipes in a heat exchanger. A newly developed mathematical model for non-steady state heat exchange was used to validate the experimental results. The highest storage efficiency was 0.631 when the HTF flow rate was 0.1 kg/s in a helical coiled pipe heat exchanger. The HTF and storage medium temperatures were measured for validating the model at various HTF flow rates. The model and experimental results were in good agreement, having an error below 10 per cent. Unsteady state heat exchange equations were used to calculate the temperature of the HTFs based on the principle of energy balance and heat convection. The temperature and thermal energy that transfers between the two fluids was determined by the storage equation. 8 refs., 1 tab., 9 figs.

Vaivudh, S. [Uttaradit Rajabhat Univ., Uttaradit (Thailand). Dept. of Physics

2007-07-01

298

Development of thermal-hydraulic model for condensation heat exchanger in APR+ (I)  

International Nuclear Information System (INIS)

In the present study, pervious researches for the design of condensation heat exchangers was collected and the characteristics of them was analyzed according to orientation, the flow regime map, which can be applied for the primary system of condensation heat exchanger, was proposed. the heat transfer models of boiling and condensation were developed

299

CFD Analysis of Plate Fin Tube Heat Exchanger for Various Fin Inclinations  

OpenAIRE

ANSYS Fluent software is used for three dimensional CFD simulations to investigate heat transfer and fluid flow characteristics of six different fin angles with plain fin tube heat exchangers. The numerical simulation of the fin tube heat exchanger was performed by using a three dimensional numerical computation technique. Geometry of model is created and meshed by using ANSYS Workbench software. To solve the equation for the fluid flow and heat transfer analysis ANSYS FLUENT ...

Subodh Bahirat,; Joshi, P. V.

2014-01-01

300

Heat transfer from oriented heat exchange areas  

Science.gov (United States)

This paper deals with the transfer of heat-driven heat transfer surface area in relation to the construction of the criterion equation for "n" horizontal pipe one about another. On the bases of theoretical models have been developed for calculating the thermal performance of natural convection by Churilla and Morgan, for various pipe diameters and temperatures. These models were compared with models created in CFD-Fluent Ansys the same boundary conditions. The aim of the analyse of heat and fluxional pipe fields "n" pipes one about another at natural convection is the creation of criterion equation on the basis of which the heat output of heat transfer from pipe oriented areas one above another with given spacing could be quantified. At presence a sum of criterion equations exists for simple geometrical shapes of individual oriented geometrical areas but the criterion equation which would consider interaction of fluxional field generated by free convection from multiple oriented areas is not mentioned in standardly accessible technical literature and other magazine publications.

Vantuch, Martin; Huzvar, Jozef; Kapjor, Andrej

2014-03-01

301

Heat transfer from oriented heat exchange areas  

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with the transfer of heat-driven heat transfer surface area in relation to the construction of the criterion equation for “n” horizontal pipe one about another. On the bases of theoretical models have been developed for calculating the thermal performance of natural convection by Churilla and Morgan, for various pipe diameters and temperatures. These models were compared with models created in CFD-Fluent Ansys the same boundary conditions. The aim of the analyse of heat and fluxional pipe fields „n“ pipes one about another at natural convection is the creation of criterion equation on the basis of which the heat output of heat transfer from pipe oriented areas one above another with given spacing could be quantified. At presence a sum of criterion equations exists for simple geometrical shapes of individual oriented geometrical areas but the criterion equation which would consider interaction of fluxional field generated by free convection from multiple oriented areas is not mentioned in standardly accessible technical literature and other magazine publications.

Vantuch Martin

2014-03-01

302

Numerical Study of Heat Transfer Enhancement on Microchannel Plate Heat Exchanger with Channel Shape  

International Nuclear Information System (INIS)

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena

303

Predicted and measured velocity distribution in a model heat exchanger  

International Nuclear Information System (INIS)

This paper presents a comparison between numerical predictions, using the porous media concept, and measurements of the two-dimensional isothermal shell-side velocity distributions in a model heat exchanger. Computations and measurements were done with and without tubes present in the model. The effect of tube-to-baffle leakage was also investigated. The comparison was made to validate certain porous media concepts used in a computer code being developed to predict the detailed shell-side flow in a wide range of shell-and-tube heat exchanger geometries

304

Mechanical design of heat exchangers and pressure vessel components  

International Nuclear Information System (INIS)

The twenty-two chapters in this book are prefaced by brief descriptions of the computer codes referenced or listed within the pages that follow. The first chapter, which contains an outline of the more accepted heat-exchanger types and basic design considerations, is followed by another outlining various design-stress criteria. The next twenty chapters contain considerable detailed information concerning the design and operation of heat exchangers. The authors devote 121 pages to one of the most important design considerations, flow-induced vibration. Another chapter is dedicated to methods of seismic analysis. The remaining chapters address mechanical and thermal design as well as manufacturing

305

A fundamentally new approach to air-cooled heat exchangers.  

Energy Technology Data Exchange (ETDEWEB)

We describe breakthrough results obtained in a feasibility study of a fundamentally new architecture for air-cooled heat exchangers. A longstanding but largely unrealized opportunity in energy efficiency concerns the performance of air-cooled heat exchangers used in air conditioners, heat pumps, and refrigeration equipment. In the case of residential air conditioners, for example, the typical performance of the air cooled heat exchangers used for condensers and evaporators is at best marginal from the standpoint the of achieving maximum the possible coefficient of performance (COP). If by some means it were possible to reduce the thermal resistance of these heat exchangers to a negligible level, a typical energy savings of order 30% could be immediately realized. It has long been known that a several-fold increase in heat exchanger size, in conjunction with the use of much higher volumetric flow rates, provides a straight-forward path to this goal but is not practical from the standpoint of real world applications. The tension in the market place between the need for energy efficiency and logistical considerations such as equipment size, cost and operating noise has resulted in a compromise that is far from ideal. This is the reason that a typical residential air conditioner exhibits significant sensitivity to reductions in fan speed and/or fouling of the heat exchanger surface. The prevailing wisdom is that little can be done to improve this situation; the 'fan-plus-finned-heat-sink' heat exchanger architecture used throughout the energy sector represents an extremely mature technology for which there is little opportunity for further optimization. But the fact remains that conventional fan-plus-finned-heat-sink technology simply doesn't work that well. Their primary physical limitation to performance (i.e. low thermal resistance) is the boundary layer of motionless air that adheres to and envelops all surfaces of the heat exchanger. Within this boundary layer region, diffusive transport is the dominant mechanism for heat transfer. The resulting thermal bottleneck largely determines the thermal resistance of the heat exchanger. No one has yet devised a practical solution to the boundary layer problem. Another longstanding problem is inevitable fouling of the heat exchanger surface over time by particulate matter and other airborne contaminants. This problem is especially important in residential air conditioner systems where often little or no preventative maintenance is practiced. The heat sink fouling problem also remains unsolved. The third major problem (alluded to earlier) concerns inadequate airflow to heat exchanger resulting from restrictions on fan noise. The air-cooled heat exchanger described here solves all of the above three problems simultaneously. The 'Air Bearing Heat Exchanger' provides a several-fold reduction in boundary layer thickness, intrinsic immunity to heat sink fouling, and drastic reductions in noise. It is also very practical from the standpoint of cost, complexity, ruggedness, etc. Successful development of this technology is also expected to have far reaching impact in the IT sector from the standpointpoint of solving the 'Thermal Brick Wall' problem (which currently limits CPU clocks speeds to {approx}3 GHz), and increasing concern about the the electrical power consumption of our nation's information technology infrastructure.

Koplow, Jeffrey P.

2010-01-01

306

Dynamic responses of heat exchanger tube banks  

International Nuclear Information System (INIS)

Understanding and modeling fluid/structure interaction in cylinder bundles is a basic requirement in the development of analytical methods and guidelines for designing LMFBR heat exchanger and reactor fuel assemblies that are free from component vibration problems. As a step toward satisfying this requirement, an analytical and experimental study of tube banks vibrating in liquids is presented. A general method of analysis is presented for free and forced vibrations of tube banks including tube/fluid interaction, and numerical results are given for tube banks subjected to various types of excitations. Two cantilevered tubes were tested in a water tank, and the natural frequencies and forced responses of coupled motion were measured. Experimental data and analytical results are in reasonably good agreement. The analytical method presented is currently being extended to account for the flowing fluid in tube banks and will be used in the development of the mathematical models for crossflow- and parallel-flow-induced vibrations of tube bundles. Those models will be useful in predicting the response of tube bundles and in design to avoid detrimental vibration

307

Heat and mass transfer at rotary heat exchangers in consideration of the condensation potential  

Science.gov (United States)

In many industrial processes as well as in air conditioning systems heat and moisture is transferred by rotary heat exchangers from the warm exhaust air flow to the cold supply air flow. Rotary heat exchangers are classified as sorption rotors, hygroscopic rotors and condensation rotors. Basic mechanisms of heat and moisture transfer are presented. By means of the condensation potential as the difference between the moisture content of the warm air flow and the moisture content of the cold air flow at saturation the humidity transfer at the different rotor types is investigated. The condensation potential as a reference parameter provides the possibility to describe the influence of various air conditions in exhaust air and supply air flow on the humidity transfer of different rotary heat exchangers and to compare these rotors with each other. In order to give an overview of relevant design parameters, the influence of the speed of turning, the flute height of the rotor matrix and the velocity of the air flow regarding the heat and mass transfer is considered.

Dinglreiter, Udo

2011-08-01

308

Comparative Study and Analysis between Helical Coil and Straight Tube Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this study is to determine the relative advantage of using a helically coiled heat exchanger against a straight tube heat exchanger. It is found that the heat transfer in helical circular tubes is higher as compared to Straight tube due to their shape. Helical coils offer advantageous over straight tubes due to their compactness and increased heat transfer coefficient. The increased heat transfer coefficients are a consequence of the curvature of the coil, which induces centrifugal forces to act on the moving fluid, resulting in the development of secondary flow. The curvature of the coil governs the centrifugal force while the pitch (or helix angle influences the torsion to which the fluid is subjected to the centrifugal force results in the development of secondary flow. Due to the curvature effect, the fluid streams in the outer side of the pipe moves faster than the fluid streams in the inner side of the pipe. In current work the fluid to fluid heat exchange is taken into consideration. Most of the investigations on heat transfer coefficients are for constant wall temperature or constant heat flux. The effectiveness, overall heat transfer coefficient, effect of cold water flow rate on effectiveness of heat exchanger when hot water mass flow rate is kept constant and effect of hot water flow rate on effectiveness when cold water flow rate kept constant studied and compared for parallel flow, counter flow arrangement of Helical coil and Straight tube heat exchangers. All readings were taken at steady state condition of heat exchanger. The result shows that the heat transfer coefficient is affected by the geometry of the heat exchanger. Helical coil heat exchanger are superior in all aspect studied here.

N. D. Shirgire

2014-08-01

309

Pressurized-Flat-Interface Heat Exchanger  

Science.gov (United States)

High thermal conductance obtained without leakage between loops. Heat-exchanger interface enables efficient transfer of heat between two working fluids without allowing fluids to intermingle. Interface thin, flat, and easy to integrate into thermal system. Possible application in chemical or pharmaceutical manufacturing when even trace contamination of process stream with water or other coolant ruins product. Reduces costs when highly corrosive fluids must be cooled or heated.

Voss, F. E.; Howell, H. R.; Winkler, R. V.

1990-01-01

310

Review of Heat Transfer Augmentation Within A Plate Heat Exchanger By Different Shapes Of Ribs  

Directory of Open Access Journals (Sweden)

Full Text Available Heat transfer augmentation techniques (passive, active or a combination of passive and active methods are commonly used in areas such as process industries, heating and cooling in evaporators, thermal power plants, air-conditioning equipment, refrigerators, radiators for space vehicles, automobiles, etc. Passive techniques, where inserts are used in the flow passage to augment the heat transfer rate, are advantageous compared with active techniques, because the insert manufacturing process is simple and these techniques can be easily employed in an existing heat exchanger. In design of compact heat exchangers, passive techniques of heat transfer augmentation can play an important role if a proper passive insert configuration can be selected according to the heat exchanger working condition (both flow and heat transfer conditions. In the past decade, several studies on the passive techniques of heat transfer augmentation have been reported. Twisted tapes, wire coils, ribs, fins, dimples, etc., are the most commonly used passive heat transfer augmentation tools. In the present paper, emphasis is given to works dealing with different shapes of ribs, and there arrangement because, according to recent studies, these are known to be economic heat transfer augmentation tools. The present review is organized in four different sections: circular ribs with staggered at 90º; circular ribs with staggered at 45º, triangular ribs with staggered at 90ºand triangular ribs with staggered at 45º.

A. D. Yadav, V. M. Kirplani

2013-05-01

311

Study on numerical and experimental heat transfer characteristics of heat exchanger with helical turbulators  

International Nuclear Information System (INIS)

Heat exchangers have been widely used devices in the industry because of supply heat transfer between two fluids that are at different temperatures and separated by a solid wall. There are two groups: active and passive methods. The active methods requires extra external power sources, for instance, mechanical aids, surface and fluid vibration, electrostatic fields, injection or suction of fluid and jet impingement. The other is the passive methods, on the contrary, without additional external power, such as a surface coating, rough surfaces, extended surfaces, displaced enhancement devices, turbulent or swirl flow devices, coiled tubes and additives for liquids and gases. Experimental study of the heat exchangers is very useful but very expensive because of the high cost of the tools. A suitable computational fluid dynamics (CFD) code is run to compare to experimental studies, provides flow field information. Experimental analysis and three-dimensional numerical simulations for the concentric-tube heat exchanger with helical turbulators having different pitches distance were performed to reveal the effects of pitches distance on the heat transfer and pressure drop characteristics. The conclusions can be summarized; the FLUENT was applied successfully for the heat transfer and pressure drop analysis in the concentric-tube heat exchanger with helical turbulator. The numerical, experimental and empirical correlation results were in a good agreement with each others. Whe in a good agreement with each others. Whereas Nu number increases with increase of Re number, the friction factor reduces. The results indicated the effective enhancement of the heat transfer performance. It can be concluded that numerical calculations provided more detailed knowledge of the heat transfer and flow distribution than experimental studies. The values of the pressure drop can be negligible, when comparing with the heat transfer enhancement. The numerical and experimental results show as a validated computational technique using in this study. The obtained results for different pitch of helical turbulators can be applied to heat exchanger designs for commercial applications. (author)

312

Study of heat exchange between air and snow block with a vertical hole. Effect of air flow rate on heat exchange characteristics; Enchokuko wo yusuru setsukai to kuki tono netsu kokan ni kansuru kenkyu. Kuki no ryuryo ga reikyaku noryoku ni oyobosu eikyo  

Energy Technology Data Exchange (ETDEWEB)

It is very important to use many kinds of natural energy resources to keep environment clean and to reduce the energy consumption. Many simple and skilful methods to utilize the natural energy have to be developed. The authors have been proposing to utilize snow stored till summer as one of the natural cold and clean energy resources. In this study, the authors investigated the characteristics of direct heat exchange between hot air and snow block with a vertical hole. This heat transfer model, so called as the snow cooling system, may he applied to various air-conditioning systems of conventional living room and so on. As the heat transfer process of this model is very complicated because the shape of the snow block changes by the progress of melting, the characteristics of -the direct heat exchange were investigated by the experiment with a model of practical scale. The outlet air temperature through the snow hole and snow melting process were measured for various air flow rates at constant inlet air temperature 30 degree C. Experimental results show that the outlet air temperature from the snow cooling system was almost constant and enough lower to use for the actual air conditioning situations. Heat transfer coefficients on the snow surfaces of top plane, bottom plane and side wall of the snow hole were clear by those experimental results, and the correlative equations between the overall Nusselt number and the Reynolds number are presented for three surfaces mentioned above. (author)

Iijima, K. [Sanki Engineering Co. Ltd., Tokyo (Japan); Kobiyama, M.; Wang, A.R.; Hanaoka, Y.; Kawamura, M. [Muroran Institute of Technology, Hokkaido (Japan)

1999-08-25

313

Heat Pipe Blocks Return Flow  

Science.gov (United States)

Metal-foil reed valve in conventional slab-wick heat pipe limits heat flow to one direction only. With sink warmer than source, reed is forced closed and fluid returns to source side through annular transfer wick. When this occurs, wick slab on sink side of valve dries out and heat pipe ceases to conduct heat.

Eninger, J. E.

1982-01-01

314

Comparison between conventional heat exchanger performance and an heat pipes exchanger  

International Nuclear Information System (INIS)

The thermal performance of conventional compact heat exchanger and of exchanger with heat pipes are simulated using a digital computer, for equal volumes and the same process conditions. The comparative analysis is depicted in graphs that indicate which of the situations each equipment is more efficient. (author)

315

Compact heat exchanger technologies for the HTRs recuperator application  

International Nuclear Information System (INIS)

Modern HTR nuclear power plants which are now under development (projects GT-MHR, PBMR) are based on the direct cycle concept. This concept leads to a more important efficiency compared to the steam cycle but requires the use of high performance components such as an helium/helium heat exchanger called recuperator to guarantee the cycle efficiency. Using this concept, a net plant efficiency of around 50% can be achieved in the case of an electricity generating plant. As geometric constraints are particularly important for such a gas reactor to limit the size of the primary vessels, compact heat exchangers operating at high pressure and high temperature are attractive potential solutions for the recuperator application. In this frame, Framatome and CEA have reviewed the various technologies of compact heat exchangers used in industry. The first part of the paper will give a short description of the heat exchangers technologies and their ranges of application. In a second part, a selection of potential compact heat exchangers technologies are proposed for the recuperator application. This selection will be based upon their capabilities to cope with the operating conditions parameters (pressure, temperature, flow rate) and with other parameters such as fouling, corrosion, compactness, weight, maintenance and reliability. (author)

316

Experimental Study on Heat Transfer Characteristics of Shell and Tube Heat Exchanger Using Hitran Wire Matrix Turbulators As Tube Inserts.  

OpenAIRE

Shell and tube heat exchangers are extensively used in boilers, oil coolers, pre-heaters, condensers etc. They are also having special importance in process application as well as refrigeration and air conditioning industries. The present paper emphasizes on heat transfer characteristics of shell and tube heat exchangers with the aid of hiTRAN wire matrix inserts is been studied. Investigations were made on effect of mass flow rate of water on heat transfer characteristics in ...

Manoj; Mulla, A. M.

2014-01-01

317

Failure analysis of a heat exchanger  

International Nuclear Information System (INIS)

The rupture of a heat exchanger inside an inert atmosphere glovebox threatened to damage a radioactively fueled heat source intended to generate electricity on a future US space flight. Because of the potential for damage to heat sources in other gloveboxes, it was necessary to identify the cause of failure. The failure analysis was effected by listing possible causes of rupture and then determining which possibilities were consistent with evidence obtained from the failed heat exchanger. Macroscopic evaluation of the heat exchanger provided information as to the nature of the failure. Scanning electron microscopy and energy dispersive x-ray analysis were used to confirm the failure mechanism. Metallographic sections of both ruptured and deformed tubes gave clues as to the history of the material, as did microhardness measurements. Tensile tests on undeformed tubing provided estimates of strength. Burst tests on similar tubing were used to confirm the validity of the tensile data. Finally, the tensile data were used in models to determine which of the proposed scenarios of failure were most likely. It was concluded that failure had occurred because, periodically during the life of the heat exchanger, both the inlet and outlet valves had deliberately been closed. The subsequent rise in temperature caused expansion of the coolant, and a corresponding rise in hydrostatic pressure occurred which was sufficient to deform the tubing upon each repetition upon each repetition

318

Materials, Turbomachinery and Heat Exchangers for Supercritical CO2 Systems  

Energy Technology Data Exchange (ETDEWEB)

The objective of this project is to produce the necessary data to evaluate the performance of the supercritical carbon dioxide cycle. The activities include a study of materials compatibility of various alloys at high temperatures, the heat transfer and pressure drop in compact heat exchanger units, and turbomachinery issues, primarily leakage rates through dynamic seals. This experimental work will serve as a test bed for model development and design calculations, and will help define further tests necessary to develop high-efficiency power conversion cycles for use on a variety of reactor designs, including the sodium fast reactor (SFR) and very high-temperature gas reactor (VHTR). The research will be broken into three separate tasks. The first task deals with the analysis of materials related to the high-temperature S-CO{sub 2} Brayton cycle. The most taxing materials issues with regard to the cycle are associated with the high temperatures in the reactor side heat exchanger and in the high-temperature turbine. The system could experience pressures as high as 20MPa and temperatures as high as 650°C. The second task deals with optimization of the heat exchangers required by the S-CO{sub 2} cycle; the S-CO{sub 2} flow passages in these heat exchangers are required whether the cycle is coupled with a VHTR or an SFR. At least three heat exchangers will be required: the pre-cooler before compression, the recuperator, and the heat exchanger that interfaces with the reactor coolant. Each of these heat exchangers is unique and must be optimized separately. The most challenging heat exchanger is likely the pre-cooler, as there is only about a 40°C temperature change but it operates close to the CO{sub 2} critical point, therefore inducing substantial changes in properties. The proposed research will focus on this most challenging component. The third task examines seal leakage through various dynamic seal designs under the conditions expected in the S-CO{sub 2} cycle, including supercritical, choked, and two-phase flow conditions.

Anderson, Mark; Nellis, Greg; Corradini, Michael

2012-10-19

319

Modeling particle deposition on HVAC heat exchangers  

International Nuclear Information System (INIS)

Fouling of fin-and-tube heat exchangers by particle deposition leads to diminished effectiveness in supplying ventilation and air conditioning. This paper explores mechanisms that cause particle deposition on heat exchanger surfaces. We present a model that accounts for impaction, diffusion, gravitational settling, and turbulence. Simulation results suggest that some submicron particles deposit in the heat exchanger core, but do not cause significant performance impacts. Particles between 1 and 10(micro)m deposit with probabilities ranging from 1-20% with fin edge impaction representing the dominant mechanism. Particles larger than 10(micro)m deposit by impaction on refrigerant tubes, gravitational settling on fin corrugations, and mechanisms associated with turbulent airflow. The model results agree reasonably well with experimental data, but the deposition of larger particles at high velocities is underpredicted. Geometric factors, such as discontinuities in the fins, are hypothesized to be responsible for the discrepancy

320

Diffusion bonding in compact heat exchangers  

International Nuclear Information System (INIS)

Heatric's diffusion bonding process is a solid-state joining technology that produces strong, compact, all-metal heat exchanger cores. Diffusion bonding allows for a large quantity of joints to be made in geometries that would normally be inaccessible for conventional welding techniques. Since Heatric's diffusion bonding process uses no interlayer or braze alloy, the resulting heat exchanger core has consistent chemistry throughout and, under carefully controlled conditions, a return to parent metal strength can be reached. This paper will provide an overview of the diffusion bonding process and its origins, and also its application to compact heat exchanger construction. The paper will then discuss recent work that has been done to compare mechanical properties of Heatric's diffusion bonded material with material that has been conventionally welded, as well as with material tested in the as-received condition. (author)

321

Studies on direct liquid-liquid heat exchange in the context of seawater desalination  

International Nuclear Information System (INIS)

In order to lower the operational costs of a sea water desalination plant working by the evaporation principle, an economical heat flow must be provided for amongst other measures. This may be done by utilizing the heat content of newly condensed fresh water for preheating sea water. The easiest way would be a heat exchange between the sea water and the desalinated condensate, e.g. in a counter-flow tube bundle heat exchanger, and to compensate the heat loss by means of an additional heating unit. However, operational experience with this type of heat exchanger has shown that the metal walls on the sea water side get encrusted with hardly soluble salts even after only a short period of operation. Consequently, the heat-transmission resistance increases, so that expensive cleaning of the heat exchangers is necessary after only a few hours of operation already. (orig./TK)

322

Flow measurements related to gas exchange applications  

OpenAIRE

This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a st...

Laurantzon, Fredrik

2012-01-01

323

Enhanced two phase flow in heat transfer systems  

Science.gov (United States)

A family of structures and designs for use in devices such as heat exchangers so as to allow for enhanced performance in heat exchangers smaller and lighter weight than other existing devices. These structures provide flow paths for liquid and vapor and are generally open. In some embodiments of the invention, these structures can also provide secondary heat transfer as well. In an evaporate heat exchanger, the inclusion of these structures and devices enhance the heat transfer coefficient of the evaporation phase change process with comparable or lower pressure drop.

Tegrotenhuis, Ward E; Humble, Paul H; Lavender, Curt A; Caldwell, Dustin D

2013-12-03

324

Eddy current testing of heat exchanger tubes  

International Nuclear Information System (INIS)

Production-line testing of heat exchanger tubes for detection of manufacturing flaws is done with encircling outer coils switched in a difference system. Tubes with longitudinal welds and with larger cross-sectional areas are tested by means of saddle coils in order to detect flaws in the welds. Computerized testing of heat exchanger tubes on site, by means of encircling inner coils, in most cases is done for in-service inspection in order to defect flaws caused by operational conditions. The contribution here particularly discusses the in-service testing conditions and methods, and the use of microprocessors for defect analysis. (orig./HP)

325

Performance Evaluation of Plate-Fin-And Tube Heat Exchanger with Wavy Fins- A Review  

Directory of Open Access Journals (Sweden)

Full Text Available The plate fin-and-tube heat exchangers are widely used in variety of industrial applications, particularly in the heating, air-conditioning and refrigeration, HVAC industries. In most cases the working fluid is liquid on the tube side exchanging heat with a gas, usually air. It is seen that the performance of heat exchangers can be greatly increased with the use of unconventionally shaped flow passages such as plain, perforated offset strip, louvered, wavy, vortex generator and pin. The current study is focused on wavy-fin. The wavy surface can lengthen the path of airflow and cause better airflow mixing. In order to design better heat exchangers and come up with efficient designs, a thorough understanding of the flow of air in these channels is required. Hence this study focuses on the heat transfer and friction characteristics of the air side for wavy fin and tube heat exchanger.

Sandip S. Kale

2014-09-01

326

Experimental and theoretical analysis of the local condensation heat transfer in a plate heat exchanger  

International Nuclear Information System (INIS)

Plate heat exchanger (PHE) are today widely used in industrial heat transfer applications due to their good thermal performance, modest space requirement, easy accessibility to all areas and their lower capital and operating costs as compared to shell-and-tube heat exchangers. Although authoritative models for the design of PHE used as condensers are missing, the number of applications where a PHE is operating as a condenser increases. On the way to a reliable model based on physical approaches for the prediction of heat transfer and pressure drop during the condensation process inside a PHE, the flow and heat interactions as well as their dependence on the geometrical parameters of the corrugated plates and the operating conditions must be studied in detail. In this work the stepwise procedure for the fundamental construction of such a model is described. An experimental setup was built to analyze the characteristics of the two-phase-flow in PHE. A single gap, consisting of two transparent corrugated plates, was tested with a two-phase flow of air/water and also with boiling refrigerant R365mfc. Flow pattern maps were constructed for plates with corrugation angles of 27 and 63 degrees relative to the direction of flow. Investigations of the local heat transfer coefficients and the pressure drop were done with the same plates. The measurement of the local heat transfer coefficients was carried out by the use of the 'Temperature Oscillation InfraRed Thermography' (TOIRe Oscillation InfraRed Thermography' (TOIRT) method. Based on these results three main flow patterns are defined: film flow, bubbly flow and slug flow. For each of the three flow patterns an own model for the heat transfer and pressure drop mechanism are developed and the heat transfer coefficient and the friction factor is calculated with different equations depending on the actual steam quality, mass flow and geometrical parameters by means of a flow pattern map. The theory of the flow pattern based prediction models is proved with own experimental data. The measurements were carried out with an experimental setup in a technical scale. The refrigerant cycle works with R134a as refrigerant and involves two PHEs, used as condenser and evaporator, and a 55 kWel compressor for the compression of the vapor phase. The setup allows the measurement of quasi-local heat transfer coefficients inside the PHEs. Additional heat exchangers assure saturated vapor at the inlet and saturated liquid at the outlet of the condenser.

327

A numerical analysis on the heat transfer and pressure drop characteristics of welding type plate heat exchangers  

International Nuclear Information System (INIS)

Numerical analysis was carried out to examine the heat transfer and pressure drop characteristics of plate heat exchangers for absorption application using computational Fluid Dynamics(CFD) technique. A commercial CFD software package, FLUENT was used to predict the characteristics of heat transfer, pressure drop and flow distribution within plate heat exchangers. In this paper, a welded plate heat exchanger with the plate of chevron embossing type was numerically analyzed by controlling mass flow rate, solution concentration, and inlet temperatures. The working fluid is H2O/LiBr solution with the LiBr concentration of 50?60% in mass. The numerical simulation show reasonably good agreement with the experimental results. Also, the numerical results show that plate of the chevron shape gives better results than plate of the elliptical shape from the view points of heat transfer and pressure drop. These results provide a guideline to apply the welded PHE for the solution heat exchanger of absorption systems

328

Heat exchanger design for desalination plants  

International Nuclear Information System (INIS)

The Office of Saline Water (OSW) accomplished a very large amount of significant work related to the design and performance of large heat exchanger bundles and enhanced heat transfer surfaces. This work was undertaken to provide basic technical and economic data for the design of distillation plants for the desalination of seawater, and should be of value to other industrial applications as well. The OSW work covers almost every aspect of heat exchanger design, and ranges academic research to data gathering on commercial desalting plants. Exchanger design configurations include multistage flash plant condensers, vertical tube falling film and upflow evaporators, and horizontal tube spray film evaporators. Unfortunately, the data is scattered through a large number of reports of which many are concerned primarily with factors other than heat transfer, and the quality of reporting and the quality of the data are far from consistent. This report catalogues and organizes the heat exchanger data developed by the OSW. Some analysis as to the validity of the data is made and ranges of performance that can be expected are given. Emphasis is placed on the vertical tube, falling film evaporators. A thorough analysis of the large literature file that was surveyed was not possible. No analysis was made of the quality of original data, but apparent data discrepancies are pointed out where such discrepancies happen to be found

329

Heat transfer accompanying a falling fluid flow  

International Nuclear Information System (INIS)

Gravitational fluid flow with no head, as a rule, in the form of a thin layer (film), is employed in many areas of technology. Falling fluid flow, completely filling the transverse cross section of a pipe, is encountered. Both types of flow are observed in the channels of the safety and control system of reactors, where in one and the same vertical pipe a fluid can flow through the whole cross section or in an annular section (in the gap between the control unit and the channel) and in the form of a film. In heat-engineering calculations of such devices it is necessary to know the characteristics of heat exchange for both types of coolant flow. The possibility of obtaining general heat-transfer laws follows from the data of Emel'yanov, et al, 1979 and Gimbutis, 1978 where analogous hydrodynamic and thermal processes accompanying coolant flow in turbulent, fluid flow and is determined by its universal physical nature. The paper first derives equations of heat transfer for a headless falling flow, then transforms the equation to computational form for comparison with experiment, taking into account the local wave characteristic

330

Experimental Study on Heat Transfer Characteristics of Shell and Tube Heat Exchanger Using Hitran Wire Matrix Turbulators As Tube Inserts.  

Directory of Open Access Journals (Sweden)

Full Text Available Shell and tube heat exchangers are extensively used in boilers, oil coolers, pre-heaters, condensers etc. They are also having special importance in process application as well as refrigeration and air conditioning industries. The present paper emphasizes on heat transfer characteristics of shell and tube heat exchangers with the aid of hiTRAN wire matrix inserts is been studied. Investigations were made on effect of mass flow rate of water on heat transfer characteristics in case of plain tube without inserts. When hiTRAN wire matrix tube inserts are used, which effectively increases the turbulence of tube side flow due to the hydrodynamic and thermal agitation of boundary layer in turns increases additional pressure drop is available in the system. This results in increase in the wall shear, reduced wall temperature which enhances substantial increase in tube side heat transfer characteristics. Heat and cooling processes streams is a standard operation in many industries this operation is often performed in heat exchangers where the heated or cold fluid flows under laminar conditions inside the tubes the mechanisms of under those flow conditions are complex poorly understood since they can involve both forced and natural convection making accurate prediction for heat exchanger. Heat transfer in laminar flow regimes is low by default but can be greatly increased by the use of passive heat transfer enhancement such as tube inserts. The present analysis the hiTRAN wire matrix turbulators were used and increased heat transfer characteristics as expected outcomes.

Manoj

2014-06-01

331

Suction-liquid heat exchanger having accumulator and receiver  

International Nuclear Information System (INIS)

A suction-liquid heat exchanger for a heat pump is provided by utilizing an inner vessel as a suction line accumulator together with a surrounding high pressure outer vessel which is utilized as a receiver in the liquid line. Heat from the liquid refrigerant in the outer vessel is transferred to the cooler liquid accumulated in the inner vessel to vaporize it, preventing slugs of liquid refrigerant from entering the compressor. The exit and entry ports of the outer vessel are at different levels. This causes a greater amount of liquid refrigerant to remain in the outer vessel on heating mode operation than on reverse flow for cooling, thereby increasing the heat transfer to the accumulator as required for the greater volume of liquid in the suction line gas and compensating for the decreased quantity of refrigerant needed for heating

332

Heat transfer to immiscible liquid mixtures in a spiral plate heat exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available This work presents new predictive correlations for heat transfer to immiscible liquid-liquid mixtures in a spiral plate heat exchanger. Liquid-liquid heat transfer studies were carried out in spiral plate heat exchangers for the water-octane, water-kerosene, and water-dodecane systems. For each composition of the mixture, the mass flow rate of the cold fluid was varied, keeping that of the hot fluid and the fluid inlet temperatures constant. Two-phase cold flow rates were in the laminar range, while the hot fluid flow was turbulent. Calculations of the LMTD (log mean temperature difference correction factor showed that the flow was countercurrent. Heat transfer coefficients of the two-phase liquids were found to be strongly dependent on the composition of the liquid mixture and exhibited abrupt transitions as a function of the compositions. Given the absence of predictive correlations in the literature that sufficiently capture this compositiondependence, new empirical correlations were developed using part of the experimental data, with the composition of the cold fluid as an explicit variable. Statistical analysis of the regression yielded satisfactory results. The correlations were tested against the rest of the experimental data and were found to predict heat transfer coefficients within ± 15%. These preliminary studies should be useful in designing compact exchangers for handling two-phase water-organics mixtures.

S. Sathiyan

2013-06-01

333

Experimental analysis of an air–water heat pump with micro-channel heat exchanger  

International Nuclear Information System (INIS)

A multi-port extruded (MPE) aluminium flat tube air heat exchanger was compared to a round tube finned coil (FC). The MPE heat exchanger has parallel flow vertical tube configuration with headers in horizontal position and conventional folded louvred fins. The two heat exchangers were mounted on a 10 kW cooling capacity R410A packaged air heat pump. They were sized to approximately obtain the same cooling and heating capacities in chiller and heating mode, respectively. Climatic room steady state tests without frosting phenomena occurring during heat pump operation, demonstrated that the round tube and the flat tube heat exchanger performance are comparable. The MPE heat exchanger was tested with different refrigerant inlet distributor/outlet tubes configurations to investigate the effect of liquid refrigerant distribution. Cycling frosting/defrosting operations were tested with two equivalent machines placed in parallel outdoor and working at full load condition, one of the units was equipped with the MPE heat exchanger while the other mounted a standard finned coil. Penalization factors were analytically introduced to evaluate frosting associated heating energy and energy efficiency degradation. Test results indicate that both the heat pumps are penalized by frost formation but both the penalization factors are higher for the MPE-unit than the FC-unit one in the ?6 to 4 °C air dry bulb temperature range. For the two units, a roughly linear dependence of the heati roughly linear dependence of the heating energy penalization factor and of the energy efficiency factor from the difference between outdoor air and saturated air at the evaporation temperature humidity ratio can be pointed out. - Highlights: ? A multi-port aluminium flat tube heat exchanger was compared to a round tube finned one in a heat pump application. ? In steady state tests without frosting the round and the flat tube heat exchanger are comparable. ? Different inlet distributor/outlet tubes configurations were tested to investigate liquid distribution. ? Cycling frosting/defrosting operations were compared with two machines placed in parallel outdoor.

334

Heat Storage Characteristics of Latent-Heat Microcapsule Slurry Using Hot Air Bubbles by Direct-Contact Heat Exchange  

Science.gov (United States)

This study deals with the heat storage characteristics of latent-heat microcapsule slurry consisting of a mixture of fine microcapsules packed with latent-heat storage material and water. The heat storage operation for the latent-heat microcapsules was carried out by the direct-contact heat exchange method using hot air bubbles. The latent-heat microcapsule consisted of n-paraffin as a core latent-heat storage material and melamine resin as a coating substance. The relationship between the completion time of latent-heat storage and some parameters was examined experimentally. The nondimensional correlation equations for temperature efficiency, the completion time period of the latent-heat storage process and variation in the enthalpy of air through the microcapsule slurry layer were derived in terms of the ratio of microcapsule slurry layer height to microcapsule diameter, Reynolds number for airflow, Stefan number and modified Stefan number for absolute humidity of flowing air.

Inaba, Hideo; Horibe, Akihiko; Kim, Myoung-Jun; Tsukamoto, Hirofumi

335

Exergo-ecological evaluation of heat exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available Thermodynamic optimization of thermal devices requires information about the influence of operational and structural parameters on its behaviour. The interconnections among parameters can be estimated by tools such as CFD, experimental statistic of the deviceetc. Despite precise and comprehensive results obtained by CFD, the time of computations is relatively long. This disadvantage often cannot be accepted in case of optimization as well as online control of thermal devices. As opposed to CFD the neural network or regression is characterized by short computational time, but does not take into account any physical phenomena occurring in the considered process. The CFD model of heat exchanger was built using commercial package Fluent/Ansys. The empirical model of heat exchanger has been assessed by regression and neural networks based on the set of pseudo-measurements generated by the exact CFD model. In the paper, the usage of the developed empirical model of heat exchanger for the minimisation of TEC is presented. The optimisationconcerns operational parameters of heat exchanger. The TEC expresses the cumulative exergy consumption of non-renewable resources. The minimization of the TEC is based on the objective function formulated by Szargut. However, the authors extended the classical TEC by the introduction of the exergy bonus theory proposed by Valero. The TEC objective function fulfils the rules of life cycle analysis because it contains the investment expenditures (measured by the cumulative exergy consumption of non-renewable natural resources, the operation of devices and the final effects of decommissioning the installation.

Stanek Wojciech

2014-01-01

336

Heat exchanger for a contaminated fluid  

International Nuclear Information System (INIS)

A heat exchanger, in particular for a contaminated fluid in the nuclear industry. The tubes forming the tube core are welded and crimped across the whole width of the tubular plate which defines the floating head together with the sealing cover, and said tubular plate is also welded and crimped to the calandria along the whole of its periphery. (author)

337

Measurement of heat and moisture exchanger efficiency.  

Science.gov (United States)

Deciding between a passive heat and moisture exchanger or active humidification depends upon the level of humidification that either will deliver. Published international standards dictate that active humidifiers should deliver a minimum humidity of 33 mg.l(-1); however, no such requirement exists, for heat and moisture exchangers. Anaesthetists instead have to rely on information provided by manufacturers, which may not allow comparison of different devices and their clinical effectiveness. I suggest that measurement of humidification efficiency, being the percentage moisture returned and determined by measuring the temperature of the respired gases, should be mandated, and report a modification of the standard method that will allow this to be easily measured. In this study, different types of heat and moisture exchangers for adults, children and patients with a tracheostomy were tested. Adult and paediatric models lost between 6.5 mg.l(-1) and 8.5 mg.l(-1) moisture (corresponding to an efficiency of around 80%); however, the models designed for patients with a tracheostomy lost between 16 mg.l(-1) and 18 mg.l(-1) (60% efficiency). I propose that all heat and moisture exchangers should be tested in this manner and percentage efficiency reported to allow an informed choice between different types and models. PMID:24047355

Chandler, M

2013-09-01

338

A study on the formation of fouling in a heat exchanging system for river water  

International Nuclear Information System (INIS)

When the water flowing inside of the heat transfer equipment such as heat exchangers, condensers, and boilers is heated, calcium, magnesium sulfate, and other minerals in the water are deposited and built up for scales on the heat transfer surfaces. When those scales accumulate on the heat transfer surfaces, their performance of the heat transfer become progressively reduced due to the increase of the heat transfer resistance. The mechanism of this reduced heat transfer is called fouling. This study investigated the formation of the fouling in a heat exchanger with river and tap water flowed inside of it as a coolant. In order to visualize the formation of the fouling and to measure the fouling coefficients, a lab-scale heat exchanging system was used. Based on the experimental results, it was found that the formation of fouling for river water was quite different with the formation for tap water

339

Solution of operational problems utilization of an EX-IRT-2000 heat exchanger  

International Nuclear Information System (INIS)

The Bandung TRIGA Mark II Reactor has been successfully operated for 21 years, especially in low power operation or as neutron sources for various experiments. Most of the operating time, approximately 80% of routine operation, was dedicated for radio-isotope production. During routine operation for radio-isotope production, the reactor could not be operated at full power. The reactor was operated at 60% of the maximum power (1 MWth) due to the inability of the original heat exchanger to operate properly. The reason is that slack deposition was built-up on the secondary side of the heat exchanger. Therefore, it reduced the coefficient of heat transfer considerably. To solve the problems, a set of heat exchanger including the pump was installed In parallel with the original unit. The heat exchanger was an IRT-2000 Reactor Heat exchanger which was collected from the abandoned IRT-2000 Project. The heat exchanger has capacity of 1.25 MW. The new heat exchanger could reduced the outlet temperature of the primary coolant Into 42 deg. C. While the original-heat exchanger at the worst condition and at 600 kW of power reach outlet temperature 49 deg. C. The IRT Heat Exchanger is a counter flow heat exchanger. (author)

340

Magnetic Heat Pump Containing Flow Diverters  

Science.gov (United States)

Proposed magnetic heat pump contains flow diverters for suppression of undesired flows. If left unchecked, undesired flows mix substantial amounts of partially heated and partially cooled portions of working fluid, effectively causing leakage of heat from heated side to cooled side. By reducing leakage of heat, flow diverters increase energy efficiency of magnetic heat pump, potentially offering efficiency greater than compressor-driven refrigerator.

Howard, Frank S.

1995-01-01

341

Heat transfer phenomena in a thermally stratified energy storage with integrated heat exchanger coils  

Energy Technology Data Exchange (ETDEWEB)

Enhancement of thermal stratification in the heat store is known to be beneficial for the performance of a solar domestic hot water (SDHW) system. Thermal stratification might be destroyed though by a heat exchanger having a limited heat transfer rate. In this report attention is paid to an experimental investigation on the thermal behavior of the heat exchanger, and a numerical parameter variation study on the application of the heat exchanger in the Domestic Hot Water circuit. Insight in the tank flow pattern is obtained by thymol-blue visualization in a transparent tank. The observations show the presence of thermal buoyant plumes, originating from the heat exchanger tube. In the stratified tank the plumes are short, and spread horizontally before a neighboring tube is reached. Performance tests yield temperature step responses of the store which agree well with their numerical equivalents. The tests are conducted for three different tubes: (1) a 15x13 mm smooth tube, (2) a TRUFIN W/HT 45-11 14 100 13 finned tube, and (3) a standard wire finned SPIRO tube. With the numerical model developed earlier, a parameter sensitivity study is conducted for a solar system with integrated DHW heat exchanger, the program specifying the solar heat gain for the short (56 days) reference year. The optimal tube length is determined for the smooth and finned tube. The tube length costs effectiveness is determined based on the first year benefits (capitalized solar heat gain) and marginal tube costs at a 10% depreciation rate. It is concluded that application of a DHW heat exchanger is indeed beneficial from a cost effectiveness-, a construction- as well as from a hygienic (avoidance of legionella bacterial growth) point of view. A final selection of the configuration (tube length, construction) remains to be made by the manufacturers. 26 figs., 1 tab., 2 appendices, 7 refs.

Van Berkel, J.

1992-12-01

342

Predicting particle deposition on HVAC heat exchangers  

Science.gov (United States)

Particles in indoor environments may deposit on the surfaces of heat exchangers that are used in heating, ventilation and air conditioning (HVAC) systems. Such deposits can lead to performance degradation and indoor air quality problems. We present a model of fin-and-tube heat-exchanger fouling that deterministically simulates particle impaction, gravitational settling, and Brownian diffusion and uses a Monte Carlo simulation to account for impaction due to air turbulence. The model predicts that HVAC systems. For supermicron particles, deposition increases with particle size. The dominant deposition mechanism for 1-10 ?m particles is impaction on fin edges. Gravitational settling, impaction, and air turbulence contribute to deposition for particles larger than 10 ?m. Gravitational settling is the dominant deposition mechanism for lower air velocities, and impaction on refrigerant tubes is dominant for higher velocities. We measured deposition fractions for 1-16 ?m particles at three characteristic air velocities. On average, the measured results show more deposition than the model predicts for an air speed of 1.5 m s -1. The amount that the model underpredicts the measured data increases at higher velocities and especially for larger particles, although the model shows good qualitative agreement with the measured deposition fractions. Discontinuities in the heat-exchanger fins are hypothesized to be responsible for the increase in measured deposition. The model and experiments reported here are for isothermal conditions and do not address the potentially important effects of heat transfer and water phase change on deposition.

Siegel, Jeffrey A.; Nazaroff, William W.

343

Optimal cleaning schedule for heat exchangers in a heat exchanger network  

Energy Technology Data Exchange (ETDEWEB)

In process plants incorporating heat exchangers networks for heat recovery, fouling of heat-transfer surfaces hinders correct production activity and increases energy consumption thus giving rise to economic losses. The losses can be reduced if on-line cleaning of heat exchangers is applied. The scheduling of cleaning interventions on the individual exchangers in the HEN can be based on a priori knowledge of the time behaviour of the thermal resistance of fouling. In this paper, the mathematical model of the influence of fouling on heat exchanger and HEN operation is outlined and an example of its application is presented. Heat exchanger cleaning is postulated to maximise the avoided loss understood as the value of energy recovered if cleaning the HEN, minus the value of energy recovered without HEN cleaning, minus the cost of HEN cleaning. The mathematical formulation of the avoided loss is given and the computational approach to its maximisation is outlined. The example of optimal scheduling of cleaning interventions in a HEN comprising 10 heat exchangers is considered and numerical results are presented. (Author)

Markowski, M.; Urbaniec, K. [Warsaw Univ. of Technology, Plock (Poland). Dept. of Process Equipment

2005-05-01

344

Tube vibration in industrial size test heat exchanger  

International Nuclear Information System (INIS)

Tube vibration data from tests of a specially built and instrumented, industrial-type, shell-and-tube heat exchanger are reported. The heat exchanger is nominally 0.6 m (2 ft) in dia and 3.7 m (12 ft) long. Both full tube and no-tubes-in-window bundles were tested for inlet/outlet nozzles of different sizes and with the tubes supported by seven, equally-spaced, single-segmental baffles. Prior to water flow testing, natural frequencies and damping of representative tubes were measured in air and water. Flow testing was accomplished by increasing the flow rates in stepwise fashion and also by sweeping through a selected range of flow rates. The primary variables measured and reported are tube accelerations and/or displacements and pressure drop through the bundle. Tests of the full tube bundle configuration revealed tube rattling to occur at intermediate flow rates, and fluidelastic instability, with resultant tube impacting, to occur when the flow rate exceeded a threshold level; principally, the four-span tubes were involved in the regions immediately adjacent to the baffle cut. For the range of flow rates tested, fluidelastic instability was not achieved in the no-tubes-in-window bundle; in this configuration the tubes are supported by all seven baffles and are, therefore, stiffer

345

Heat-metric method of thermal energy estimation in ship heat-exchange systems  

Directory of Open Access Journals (Sweden)

Full Text Available A thermal energy estimation method is described in the paper. It may be taken as the base for creation special thermal energy audit devices in ship heat-exchange systems. The analysis of errors in thermal energy estimation, measuring circuit, installation diagram for calibration of heat flow density converters are given in the article. The considered method is direct in spite of the enthalpy method applied nowadays.

Krasnov Vladislav Alekseevich

2010-04-01

346

The dynamics of cross-inclined helically coiled heat exchangers  

International Nuclear Information System (INIS)

The dynamical behaviour of cross-inclined helically coiled heat exchangers in AGR pod boilers is examined. Studies of flow-induced excitation aero-elastic instability, acoustic excitation and aero-elastic coupling are reported. Work on fretting wear at the tube/support interaction site is described. Measurements taken during unfuelled engineering runs on pod units at Hartlepool and at Heysham are presented. (U.K.)

347

Numerical study of 2D heat transfer in a scraped surface heat exchanger  

OpenAIRE

A numerical study of fluid mechanics and heat transfer in a scraped surface heat exchanger with non-Newtonian power law fluids is undertaken. Numerical results are generated for 2D steady-state conditions using finite element methods. The effect of blade design and material properties, and especially the independent effects of shear thinning and heat thinning on the flow and heat transfer, are studied. The results show that the gaps at the root of the blades, where the blades are connected to...

Sun, Kh; Pyle, Dl; Fitt, Ad; Please, Cp; Baines, Mj; Hall-taylor, N.

2004-01-01

348

Experiments and Simulations on a Heat Exchanger of an Automotive Exhaust Thermoelectric Generation System Under Coupling Conditions  

Science.gov (United States)

The present experimental and computational study investigates an exhaust gas waste heat recovery system for vehicles, using thermoelectric modules and a heat exchanger to produce electric power. It proposes a new plane heat exchanger of a thermoelectric generation (TEG) system, producing electricity from a limited hot surface area. To investigate the new plane heat exchanger, we make a coupling condition of heat-flow and flow-solid coupling analysis on it to obtain the temperature, heat, and pressure field of the heat exchanger, and compared it with the old heat exchanger. These fields couple together to solve the multi-field coupling of the flow, solid, and heat, and then the simulation result is compared with the test bench experiment of TEG, providing a theoretical and experimental basis for the present exhaust gas waste heat recovery system.

Liu, X.; Yu, C. G.; Chen, S.; Wang, Y. P.; Su, C. Q.

2014-06-01

349

Numerical investigation of the influence of heat exchanger U-bends on temperature profile and heat transfer of secondary working fluids  

OpenAIRE

In this paper, numerical investigations, conducted using computational fluid dynamics, on the enhancement of internal convection heat transfer following a heat exchanger U-bend under laminar flow conditions in secondary working fluids are described. Under laminar flow conditions enhanced mixing within the heat exchanger U-bends is known to occur due to the development of secondary flows, known as Dean vortices. Numerical investigations indicated that within the U-bend, secondary flows partial...

Clarke, R.; Finn, Donal

2008-01-01

350

IMPROVED PERFORMANCE OF HELIXCHANGER OVER SEGMENTAL BAFFLE HEAT EXCHANGER USING KERN’S METHOD  

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchangers being one of the most important heat & mass transfer apparatus in industries like oil refining, chemical engineering, electric power generation etc. are designed with preciseness for optimum performance and long service life. This paper analyses the conventional segmental baffle heat exchanger using the Kern method with varied shell side flow rates. This is a proven method used in design of Heat Exchangers with a baffle cut of 25%. The paper also consists of the thermal analysis of a helixchanger (Continuous Helical baffled Heat Exchanger using the Kern method, modified to estimate the results for different flow rates at a fixed helical angle of 25?.The results obtained in this paper show us that the desired properties from a Heat exchanger i.e High Heat Transfer Co-efficient and lower pressure drop are more effectively obtained in a Helixchanger. The shell side zigzag flow induced by the Segmental baffle arrangement is completely eliminated in a Helixchanger. The flow pattern in the shell side of the continuous helical baffle heat exchanger is rotational & helical due to the geometry of continuous helical baffles. This flow pattern, at a certain fixed helical angle, results in significant increase in the heat transfer coefficient, however at the cost of lower pressure drop.

S. Pavithran

2012-11-01

351

Selection and costing of heat exchangers  

Science.gov (United States)

ESDU 92013 gives guidance on the selection of heat exchanger types for a given duty against various criteria; they include the general characteristics, together with such detailed aspects as the ranges of pressure and temperature appropriate, compatibility with the fluids involved, space and weight requirements, and cleaning accessibility and maintenance. That allows an initial choice to be made from 18 principal types of exchangers. The various types are all illustrated. A final choice can then be made between the feasible types on the basis of costs. Detailed costing data provided by manufacturers are tabulated as a function of heat load, operating pressure and the types of cold- and hot-side fluids for the following types of exchangers: shell-and-tube, double-pipe, printed-circuit, plate-fin, air-cooled and welded plate. Costing data are also tabulated as a function of heat load and the types of cold- and hot-side fluids for gasketed-plate exchangers. Seven worked examples of selection based on technical suitability and using the tabulated cost data illustrate fully the use of the information.

1992-12-01

352

Role of heat exchangers in helium liquefaction cycles: Simulation studies using Collins cycle  

International Nuclear Information System (INIS)

Highlights: ? Role of heat exchangers in basic helium liquefier analyzed to design large-scale ones. ? Heat exchangers that determine inlet temperature to expanders are more significant. ? Limiting values of nondimensional UA for each heat exchanger have been determined. ? Extra area distributed such that effectiveness of all heat exchangers increase uniformly. ? Heat exchanger performance variation have little influence on the optimum expander flow. - Abstract: Energy efficiency of large-scale helium liquefiers generally employed in fusion reactors and accelerators is determined by the performance of their constituting components. Simulation with Aspen HYSYS® V7.0, a commercial process simulator, helps to understand the effects of heat exchanger parameters on the performance of a helium liquefier. Effective UA (product of overall heat transfer coefficient U, heat transfer surface area A and deterioration factor F) has been taken as an independent parameter, which takes into account all thermal irreversibilities and configuration effects. Nondimensionalization of parameters makes the results applicable to plants of any capacity. Rate of liquefaction is found to increase linearly with the effectiveness of heat exchangers. Performance of those heat exchangers that determine the inlet temperatures to expanders have more influence on the liquid production. Variation of sizes of heat exchangers does not affect the optimum rate of flow through expanderm rate of flow through expanders. Increasing UA improves the rate of liquid production; however, the improvement saturates at limiting UA. Maximum benefit in liquefaction is obtained when the available heat transfer surface area is distributed in such a way that the effectiveness remains equal for all heat exchangers. Conclusions from this study may be utilized in analyzing and designing large helium plants.

353

Experimental study of a novel manifold structure of micro-channel heat exchanger  

Science.gov (United States)

Refrigerant flow distribution with phase change heat transfer was experimentally studied for a micro-channel heat exchanger having horizontal headers. In order to solve the problem of maldistribution, a novel manifold structure with orifice and bypass tube was proposed and experimentally studied compared to the conventional structure. Tests were conducted with downward flow for mass flux from 70 to 110 kg m-2s-1 (air side flow velocity from 1 to 2ms-1). The surface temperature distribution of the heat exchanger recorded by thermal imager and the square deviation of it were used to judge the uniformity of flow distribution. It is shown that as mass flux increased, better flow distribution is obtained (small square deviation of temperature distribution means better flow distribution: conventional structure from 32 to 27, novel structure from 19 to 14), and flow distribution of the novel structure was much better than that of the conventional one. The heat transfer performances of the two heat exchangers were also studied. The cooling capacity of the novel heat exchanger was 14.8% higher than that of the conventional because of the better flow distribution. And the refrigerant pressure drop was 120% higher because of bigger mass flow and the resistance of the orifice. It's worth noting that the air pressure drop of novel heat exchanger was also higher (about 28.3%)than that of the conventional one, even when they have same fin and flat tube structure. From the pictures of the heat exchanger surfaces, it was found that some surface area of the conventional heat exchanger was not wet because of the low mass flow and high superheat, which leaded to a poor performance and relatively small air pressure drop.

Xu, Bo; Xu, Kunhao; Wei, Wei; Han, Qing; Chen, Jiangping

2013-07-01

354

Heating system with vapour compressor heat pump and vertical U-tube ground heat exchanger  

Science.gov (United States)

In the paper a heating system with a vapour compressor heat pump and vertical U-tube ground heat exchanger for small residential house is considered. A mathematical model of the system: heated object - vapour compressor heat pump - ground heat exchanger is presented shortly. The system investigated is equipped, apart from the heat pump, with the additional conventional source of heat. The processes taking place in the analyzed system are of unsteady character. The model consists of three elements; the first containing the calculation model of the space to be heated, the second - the vertical U-tube ground heat exchanger with the adjoining area of the ground. The equations for the elements of vapour compressor heat pump form the third element of the general model. The period of one heating season is taken into consideration. The results of calculations for two variants of the ground heat exchanger are presented and compared. These results concern variable in time parameters at particular points of the system and energy consumption during the heating season. This paper presents the mutual influence of the ground heat exchanger subsystem, elements of vapour compressor heat pump and heated space.

Hanuszkiewicz-Drapa?a, Ma?gorzata; Sk?adzie?, Jan

2010-10-01

355

Impact of exchange flows on wetland flushing  

OpenAIRE

The flushing of littoral regions is governed by barotropic river flows, QR, and baroclinic exchange flows, ?Q. This note presents field observations of two different flushing regimes in a shallow wetland that borders a lake. In spring, when river flows are high, the wetland circulation is river- or jet-dominated, ?Q/QR < 1, and the river short- circuits through the wetland in a much shorter time than the nominal residence time. During summer low flows, however, the wetland circulation is do...

Nepf, Heidi; Andradottir, Hrund O.

2001-01-01

356

Temperature Profile Data in the Zone of Flow Establishment above a Model Air-cooled Heat Exchanger with 0.56 m2 Face Area Operating under Natural Convection  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this study was to analyze the temperature profile in the Zone of Flow Establishment (ZFE above a 0.56 m2 hot screen placed at different height above an electrically heated model air-cooled heat exchanger operating under natural convection. Installation of screens increased the temperature difference from 30 to 140 K with respect to ambient that resulted in the air velocity increased at the inlet of the special duct from 0.67 m sec-1 to more than 2.0 m sec-1 under different heat loads ranging from 1 to 2.5 kW. The investigation of temperature profile was done above the hot screens placed at 0.35, 0.65, 0.95 and 1.25 m height over the electrically heated model air-cooled heat exchanger. The results show that the exit air temperature near to the electric heater and above the hot screens did not differ significantly but at heights of 0.09 m and upward the temperature difference differed by 2 to 6 K depending on the height of the hot screens. Maximum temperature difference was observed for hot screen placed at 0.65 and 0.95 m. Although, the temperatures at the beginning of the zone of flow establishment were almost the same for every heat load, the radial profile of temperature turned from parabolic in shape to uniformly flat for the configuration without screen and with screen respectively. This indicates turbulence increase above the hot screens.

Chu Chi Ming

2010-01-01

357

RECITAL SCRUTINY ON TUBE-INTUBE COMPACT HEAT EXCHANGERS  

Directory of Open Access Journals (Sweden)

Full Text Available This paper focused on the investigational cram of the recital characteristics of tube-in-tube compact heat exchangers. Experiments are conducted in the compact heat exchangers with R-134a and liquefiedpetroleum gas. The effectiveness of the heat exchangers was calculated using the experiment data and it was found that the effectiveness of heat exchanger-1 is above 75 and heat exchanger-2 is above 84% for R-134a.The effectiveness of heat exchanger-1 is about 60% and heat exchanger-2 is about 81% for liquefied petroleum gas. In this paper, details about the new tube-in-tube type compact heat exchanger, experimental setup, results and conclusions are discussed.

V.NATARAJAN,

2011-04-01

358

Thermal hydraulic parameter studies of heat exchanger for the TRIGA MARK II research reactor  

International Nuclear Information System (INIS)

Thermal Hydraulic studies have being conducted at PUSPATI TRIGA Mark II (RTP) Nuclear Research Reactor. The purpose of this study is to determine the heat transfer characteristic and heat exchanger performance at difference reactor power. Fundamental concept and a plate type application of heat exchanger in RTP are presented in this study. A plate type heat exchanger is a device for RTP reactor cooling system built for efficient heat transfer from one fluid to another. The study involves the observation of inlet and outlet temperature profile, flow rate and pressure at the reactor pool and heat exchanger. The observed parameters are compared to basic engineering calculation and the output of the study has been beneficial to evaluate the performance of newly-installed plate type heat exchanger. (author)

359

Thermodynamic optimization of a coiled tube heat exchanger under constant wall heat flux condition  

International Nuclear Information System (INIS)

In this paper the second law analysis of thermodynamic irreversibilities in a coiled tube heat exchanger has been carried out for both laminar and turbulent flow conditions. The expression for the scaled non-dimensional entropy generation rate for such a system is derived in terms of four dimensionless parameters: Prandtl number, heat exchanger duty parameter, Dean number and coil to tube diameter ratio. It has been observed that for a particular value of Prandtl number, Dean number and duty parameter, there exists an optimum diameter ratio where the entropy generation rate is minimum. It is also found that with increase in Dean number or Reynolds number, the optimum value of the diameter ratio decreases for a particular value of Prandtl number and heat exchanger duty parameter.

360

Thermodynamic optimization of a coiled tube heat exchanger under constant wall heat flux condition  

Energy Technology Data Exchange (ETDEWEB)

In this paper the second law analysis of thermodynamic irreversibilities in a coiled tube heat exchanger has been carried out for both laminar and turbulent flow conditions. The expression for the scaled non-dimensional entropy generation rate for such a system is derived in terms of four dimensionless parameters: Prandtl number, heat exchanger duty parameter, Dean number and coil to tube diameter ratio. It has been observed that for a particular value of Prandtl number, Dean number and duty parameter, there exists an optimum diameter ratio where the entropy generation rate is minimum. It is also found that with increase in Dean number or Reynolds number, the optimum value of the diameter ratio decreases for a particular value of Prandtl number and heat exchanger duty parameter. (author)

Satapathy, Ashok K. [Department of Mechanical Engineering, National Institute of Technology, Rourkela 769 008, Orissa (India)

2009-09-15

361

Exchange flow through multiple porous media  

Science.gov (United States)

Geological formations are crossed by multiscale fractures and/or faults, and conductive faults may mainly control reservoir performance. Conductive faults are modeled using small grids in a vertical two-dimensional domain to see the multiphase flow exchange between neighboring medium across the fault or the vertical fluid migration through the fault. A major limitation of this modeling approach is that faults appear as one-dimensional structures in which fluid migration occurs only by counter-current flows. This simplified model cannot capture unstable exchange flows within the fault that will determine the rate of leakage. In three-dimensional models, the fluids can bypass each other and the exchange will be much faster. Because the reservoir volume is large relative to the fault, a quasi-steady exchange flow across the fault will be developed and determine the leakage rate. We aim to quantify the quasi-steady exchange rate as a function of the fault properties and geometry, the fluid properties, and the type of fluid bypassing. Limitations of geophysical imaging and uncertainty in the fault properties makes it difficult to constrain numerical models of the dynamics of the exchange flow through the fault. Therefore, our experimental study complements the numerical model to understand the dynamics of the unstable exchange flow. This study is motivated by geological CO2 storage in brine-saturated aquifer, but the unstable exchange of multiphase fluids through conductive faults is also important in many other geological and engineering applications, in particular the migration of hydrocarbons in tectonic-driven faulting system or hydraulically developed fractures in unconventional reservoirs. Better understanding of the density-driven flow in a faulted system will allow more precise estimate of the reservoir capacity as well as more efficient operation of injection or production wells.

Chang, K.; Hesse, M. A.

2012-12-01

362

Constructal multi-scale tree-shaped heat exchangers  

Science.gov (United States)

This paper describes the conceptual design and performance of balanced two-stream counterflow heat exchangers, in which each stream flows as a tree network through its allotted space. The two trees in counterflow are like two palms pressed against each other. The paper develops the relationships between effectiveness and number of heat transfer units for several tree-counterflow configurations: (i) constructal dichotomous trees covering uniformly a rectangular area, (ii) trees on a disk-shaped area, and (iii) trees on a square-shaped area. In configurations (ii) and (iii) each stream flows between the center and the periphery of the area. Configurations (i) and (ii) are trees with minimal resistance to fluid flow. Configuration (iii) is designed by minimizing the length of each duct in the network. The paper reports the formula for the number of heat transfer units in each configuration. Unlike in counterflows formed by two parallel streams, in which the longitudinal temperature gradient is constant, in the counterflow formed by two trees the longitudinal temperature gradient is steeper as one approaches the periphery of the tree canopy. The application of dendritic heat exchangers to devices with maximal transport density is discussed, e.g., electronics cooling, fuel cell architectures, etc.

da Silva, Alexandre K.; Lorente, Sylvie; Bejan, Adrian

2004-08-01

363

Verification on reliability of heat exchanger for primary cooling system  

International Nuclear Information System (INIS)

Prior to the JMTR refurbishment, verification on reliability of the heat exchangers for primary cooling system was carried out to investigate an integrity of continuously use component. From a result of the significant corrosion, decrease of tube thickness, crack were not observed on the heat exchangers, and integrity of heat exchangers were confirmed. In the long terms usage of the heat exchangers, the maintenance based on periodical inspection and a long-term maintenance plan is scheduled. (author)

364

Preliminary thermal sizing of intermediate heat exchanger for NHDD system  

International Nuclear Information System (INIS)

Nuclear Hydrogen Development and Demonstration (NHDD) system is a Very High Temperature gascooled Reactor (VHTR) coupled with hydrogen production systems. Intermediate heat exchanger transfers heat from the nuclear reactor to the hydrogen production system. This study presented the sensitivity analysis on a preliminary thermal sizing of the intermediate heat exchanger. Printed Circuit Heat Exchanger (PCHE) was selected for the thermal sizing because the printed circuit heat exchanger has the largest compactness among the heat exchanger types. The analysis was performed to estimate the effect of key parameters including the operating condition of the intermediate system, the geometrical factors of the PCHE, and the working fluid of the intermediate system.

365

Design with constructal theory: Steam generators, turbines and heat exchangers  

Science.gov (United States)

This dissertation shows that the architecture of steam generators, steam turbines and heat exchangers for power plants can be predicted on the basis of the constructal law. According to constructal theory, the flow architecture emerges such that it provides progressively greater access to its currents. Each chapter shows how constructal theory guides the generation of designs in pursuit of higher performance. Chapter two shows the tube diameters, the number of riser tubes, the water circulation rate and the rate of steam production are determined by maximizing the heat transfer rate from hot gases to riser tubes and minimizing the global flow resistance under the fixed volume constraint. Chapter three shows how the optimal spacing between adjacent tubes, the number of tubes for the downcomer and the riser and the location of the flow reversal for the continuous steam generator are determined by the intersection of asymptotes method, and by minimizing the flow resistance under the fixed volume constraints. Chapter four shows that the mass inventory for steam turbines can be distributed between high pressure and low pressure turbines such that the global performance of the power plant is maximal under the total mass constraint. Chapter five presents the more general configuration of a two-stream heat exchanger with forced convection of the hot side and natural circulation on the cold side. Chapter six demonstrates that segmenting a tube with condensation on the outer surface leads to a smaller thermal resistance, and generates design criteria for the performance of multi-tube designs.

Kim, Yong Sung

366

Digital simulation of transients in a sodium-sodium intermediary heat exchanger  

International Nuclear Information System (INIS)

A computer program to simulate a sodium-sodium heat exchanger in normal and abnormal operation was developed. Two simplifications were used : rate of flow spatially uniform and shell and tube model. (E.G.)

367

Heating cooling flows with jets  

OpenAIRE

Active galactic nuclei are clearly heating gas in `cooling flows'. The effectiveness and spatial distribution of the heating are controversial. We use three-dimensional simulations on adaptive grids to study the impact on a cooling flow of weak, subrelativistic jets. The simulations show cavities and vortex rings as in the observations. The cavities are fast-expanding dynamical objects rather than buoyant bubbles as previously modelled, but shocks still remain extremely hard...

Omma, H.; Binney, J.; Bryan, G.; Slyz, A.

2003-01-01

368

Heat transfer in a direct contact turbulent exchanger/reactor  

International Nuclear Information System (INIS)

Transport of thermal energy between two co-current flows of immiscible liquids is of interest for the improvement of cooling or heating processes, in terms of characteristic time, compactness, and energy cost. The major benefit lays in the dramatic increase of the specific contact area between the two fluids, due to the dispersion of the internal phase in the main flow under the turbulent stresses, compared with a classical double-jacket heat exchanger. Moreover, the thermal resistance of the wall is eliminated, and the diffusive transfer in the drops is linked to the particle size. Hence, turbulence governs the heat transfer both in the dispersion process, and by the heat transfer mechanism at the interface. In this work, the dispersion is realized in a static mixer, namely HEV (High Efficiency Vortex, see figure 1). The study will be carried with the aim of comparing the efficiency of the direct contact system with two reference configurations: wall-transfer in the HEV and direct contact in a simple duct of the same hydraulic diameter, so that both dispersion and geometric advantages could be quantified. Experimental results will be confronted with the classical model of Whitaker to predict the global performance of the device. Moreover, an algebraic 1D model for the axial development of the specific area and the temperature profile will be developed in order to optimize the heat exchanger dimensions. (authors)

369

Local description of the energy transfer process in a packed bed heat exchanger  

International Nuclear Information System (INIS)

The energy transfer process in a packed-bed heat exchanger, in counter0flow arrangement is considered. The phenomenon is described through a Continuum Theory of Mixtures approach, in which fluid and solid (porous matrix) are regarded as continuous constituents possessing, each one, its own temperature and velocity fields. The heat 'exchangers consists of two channels, separated by an impermeable wall without thermal resistence, in which there exists a saturated flow. Some particular cases are simulated. (author)

370

Heat transfer and pressure loss of immediate heat exchanger  

International Nuclear Information System (INIS)

The immediate heat exchanger (IHX) is the key component to connect the high-temperature gas-cooled reactor with the helium turbine for high-temperature gas-cooled reactor coupled with indirect gas turbine cycle (indirect HTGR-GT) system. IHX transfers the high temperature energy generated by reactor to gas turbine loop. IHX can reduce the difficulties of the design,operation and maintenance of helium gas turbine. On the other hand, IHX will lower the cycle efficiency due to IHX's heat transfer and pressure loss. So the characteristics of heat transfer and pressure loss,material performance, compactness should be considered for the design and the choice of IHX because of its special operating conditions. The features of printed circuit heat exchanger (PCHE) and its feasibility in the indirect HTGR-GT were discussed. The characteristics of heat transfer and pressure loss of the PCHE were studied and the factors effecting heat transfer efficiency and pressure loss were analyzed. Furthermore, the measures to improve the performance of the IHX were presented. (authors)

371

Development and application of radiotracer technique for online leak detection in high pressure heat exchangers  

International Nuclear Information System (INIS)

A radiotracer technique for online leak detection in high-pressure heat exchanger systems have been developed and successfully applied in various process industries in India. Bromine-82 as dibromobiphenyl is used as a radiotracer for leak detection in heat exchangers involving flow of organic fluids. The radiotracer is injected into high pressure side of the heat exchanger system and monitored at strategically selected locations in low pressure side using NaI(Tl) scintillation detectors connected to a preset data acquisition system. The tracer concentration curves monitored as a function of time are analyzed to identify the leaking heat exchanger(s). A number of leak detection investigations have been carried out since year 2001 leading to high economical benefits to the industry. This paper discusses principle of leak detection in high-pressure heat exchanger systems using radiotracer technique with two specific case studies. (author)

372

Mean heat transfer coefficients during the evaporation of 1,1,1,2-tetrafluoroethane (R-134a) in a plate heat exchanger  

OpenAIRE

In this study the transfer coefficient of evaporation heat of the refrigerant 1,1,1,2-tetrafluoroethane (R-134a) in a vertical plate heat exchanger was experimentally investigated. The results are presented as the dependancy of the mean heat transfer coefficient for the whole heat exchanger on the mean vapor quality. The influences of mass flux, heat flux and flow configuration on the heat transfer coefficient were also taken into account and a comparison with previously published experimenta...

EMILA DJORDJEVIC; STEPHAN KABELAC; SLOBODAN SERBANOVIC

2007-01-01

373

Role of heat exchangers in helium liquefaction cycles: Simulation studies using Collins cycle  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Role of heat exchangers in basic helium liquefier analyzed to design large-scale ones. Black-Right-Pointing-Pointer Heat exchangers that determine inlet temperature to expanders are more significant. Black-Right-Pointing-Pointer Limiting values of nondimensional UA for each heat exchanger have been determined. Black-Right-Pointing-Pointer Extra area distributed such that effectiveness of all heat exchangers increase uniformly. Black-Right-Pointing-Pointer Heat exchanger performance variation have little influence on the optimum expander flow. - Abstract: Energy efficiency of large-scale helium liquefiers generally employed in fusion reactors and accelerators is determined by the performance of their constituting components. Simulation with Aspen HYSYS{sup Registered-Sign} V7.0, a commercial process simulator, helps to understand the effects of heat exchanger parameters on the performance of a helium liquefier. Effective UA (product of overall heat transfer coefficient U, heat transfer surface area A and deterioration factor F) has been taken as an independent parameter, which takes into account all thermal irreversibilities and configuration effects. Nondimensionalization of parameters makes the results applicable to plants of any capacity. Rate of liquefaction is found to increase linearly with the effectiveness of heat exchangers. Performance of those heat exchangers that determine the inlet temperatures to expanders have more influence on the liquid production. Variation of sizes of heat exchangers does not affect the optimum rate of flow through expanders. Increasing UA improves the rate of liquid production; however, the improvement saturates at limiting UA. Maximum benefit in liquefaction is obtained when the available heat transfer surface area is distributed in such a way that the effectiveness remains equal for all heat exchangers. Conclusions from this study may be utilized in analyzing and designing large helium plants.

Thomas, Rijo Jacob, E-mail: rijojthomas@gmail.com [Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur 721302 (India); Ghosh, Parthasarathi; Chowdhury, Kanchan [Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur 721302 (India)

2012-01-15

374

Experimental study of mixed convection heat transfer in vertical helically coiled tube heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

In this study the mixed convection heat transfer in a coil-in-shell heat exchanger for various Reynolds numbers, various tube-to-coil diameter ratios and different dimensionless coil pitch was experimentally investigated. The experiments were conducted for both laminar and turbulent flow inside coil. Effects of coil pitch and tube diameters on shell-side heat transfer coefficient of the heat exchanger were studied. Different characteristic lengths were used in various Nusselt number calculations to determine which length best fits the data and several equations were proposed. The particular difference in this study in comparison with the other similar studies was the boundary conditions for the helical coils. The results indicate that the equivalent diameter of shell is the best characteristic length. (author)

Ghorbani, N. [School of Mechanical Engineering, University of Leeds, Leeds, England (United Kingdom); Taherian, H. [Department of Engineering Technology and Industrial Distribution, Texas A and M University, College Station, TX (United States); Gorji, M. [Department of Mechanical Engineering, Babol Noushirvani University of Technology, Babol (Iran); Mirgolbabaei, H. [Department of Mechanical Engineering, Islamic Azad University, Jouybar branch, Jouybar (Iran)

2010-10-15

375

OXIDE DISPERSION-STRENGTHENED HEAT EXCHANGER TUBING  

Energy Technology Data Exchange (ETDEWEB)

Oxide dispersion strengthened (ODS) alloys (e.g. the INCOLOY{reg_sign} MA956 alloy) are known for their excellent high temperature properties and are prime candidate materials for the construction of very high temperature heat exchangers that will be used in Vision 21 power plants. The main limitation of these materials is their poor weldability. Commercially available ODS tubing also tends to exhibit relatively poor circumferential creep strength due to current processing practices resulting in a fine grain size in the transverse direction. Thus far, these two characteristics of the ODS tubing have restricted its use to mostly non-pressure containing applications. The objectives of this program are to develop: (a) an MA956 tube with sufficient circumferential creep strength for long term use as heat exchanger tubing for very high temperatures; (b) a welding technique(s) for producing adequate joints between an MA956 tube and an MA956 tube, and an MA956 tube and an INCONEL 601 tube; (c) the bending strain limits, below which recrystallization will not occur in a MA956 tube during normal operation; and (d) the high temperature corrosion limits for the MA956 alloy with respect to working-fluid side and fireside environments. Also, this program seeks to generate data for use by heat exchanger designers and the ASME Boiler and Pressure Vessel Code, and perform an analysis of the mechanical property, tube bending, and corrosion data in order to determine the implications on the design of a very high temperature heat exchanger (T>1093 C/2000 F). After one year, work is currently being conducted on increasing the circumferential strength of a MA956 tube, developing joining techniques for this material, determining the tube bending strain limits, and establishing the high temperature corrosion parameters for the MA956 alloy in environments expected to be present in Vision 21 power plants. Work in these areas will is continuing into the next fiscal year, with success anticipated to produce innovative developments that will allow the reliable use of ODS alloys for heat exchanger tubing, as well as a variety of applications previously not possible with metallic materials.

Harper, Mark A.

2001-11-06

376

Intensification of heat-transfer and mixing in multifunctional heat exchangers by artificially generated streamwise vorticity  

Energy Technology Data Exchange (ETDEWEB)

Compact heat exchangers are well known for their ability to transfer a large amount of heat while retaining low volume and weight. The purpose of this paper is to study the potential of using this device as a mixer as well as a chemical reactor, generally called a multifunctional heat exchanger (MHE). Indeed, the question arises: can these geometries combine heat transfer and mixing in the same device? Such a technology would offer many potential advantages, such as better reaction control (through the thermal aspect [S. Ferrouillat, P. Tochon, H. Peerhossaini, D. Della Valle, Open-loop thermal control of exothermal chemical reactions in multifunctional heat exchangers, Int. J. Heat Mass Transfer, in press]), improved selectivity (through intensified mixing, more isothermal operation and shorter residence time, and sharper residence time distribution (RTD)), byproduct reduction, and enhanced safety. Several geometries of compact heat exchanger based on turbulence generation are available. This paper focuses on one type: vortex generators. The main objective is to contribute to the determination of turbulent flow inside various geometries by computational fluid dynamics methods. These enhanced industrial geometries are studied in terms of their thermal-hydraulic performance and macro-/micro-mixing ability [S. Ferrouillat, P. Tochon, H. Peerhossaini, Micromixing enhancement by turbulence: application to multifunctional heat exchangers, Chem. Eng. Process., in press]. The longitudinal vortices they generate in a channel flow turn the flow perpendicular to the main flow direction and enhance mixing between the fluid close to the fin and that in the middle of the channel. Two kinds of vortex generators are considered: a delta winglet pair and a rectangular winglet pair. For both, good agreement is obtained between numerical results and data in the literature. The vortex generator concept is found to be very efficient in terms of heat-transfer enhancement and macro-mixing. Nevertheless, the micro-mixing level is poor due to strong inhomogeneities: the vortex generator must be used as a heat-transfer enhancement device or as a static mixer for macro- and meso-mixing. (author)

Ferrouillat, S.; Tochon, P.; Garnier, C. [Commissariat of Atomic Energy-GRETh, 17 avenue des Martyrs, F-38054 Grenoble Cedex 9 (France); Peerhossaini, H. [Thermofluids, Complex Flows and Energy Group, Laboratoire de Thermocinetique, CNRS-UMR 6607, Ecole Polytechnique de l' Universite de Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France)

2006-11-15

377

Assessment of thermoelectric module with nanofluid heat exchanger  

International Nuclear Information System (INIS)

For applications such as cooling of electronic devices, it is a common practice to sandwich the thermoelectric module between an integrated chip and a heat exchanger, with the cold-side of the module attached to the chip. This configuration results thermal contact resistances in series between the chip, module, and heat exchanger. In this paper, an appraisal of thermal augmentation of thermoelectric module using nanofluid-based heat exchanger is presented. The system under consideration uses commercially available thermoelectric module, 27 nm Al2O3-H2O nanofluid, and a heat source to replicate the chip. The volume fraction of nanofluid is varied between 0% and 2%. At optimum input current conditions, experimental simulations were performed to measure the transient and steady-state thermal response of the module to imposed isoflux conditions. Data collected from the nanofluid-based exchanger is compared with that of deionized water. Results show that there exist a lag-time in thermal response between the module and the heat exchanger. This is attributed to thermal contact resistance between the two components. A comparison of nanofluid and deionized water data reveals that the temperature difference between the hot- and cold-side, ?T = Th - Tc ? 0, is almost zero for nanofluid whereas ?T > 0 for water. When ?T ? 0, the contribution of Fourier effect to the overall heating is approximately zero hence enhancins approximately zero hence enhancing the module cooling capacity. Experimental evidence further shows that temperature gradient across the thermal paste that bonds the chip and heat exchanger is much lower for the nanofluid than for deionized water. Low temperature gradient results in low resistance to the flow of heat across the thermal paste. The average thermal contact resistance, R = ?T/Q, is 0.18 and 0.12 deg. C/W, respectively for the deionized water and nanofluid. For the range of optimum current, 1.2 ? current ? 4.1 A, considered in this study, the COP ranges between 1.96 and 0.68

378

Design experience with liquid-to-gas heat exchanger using finned heat pipes  

International Nuclear Information System (INIS)

Heat pipes are high capacity heat transfer devices. Therefore, many studies have been carried out on their theory and application in liquid-gas heat exchangers and radiators. In this present study, a heat exchanger composed of 18 thermosyphones ( heat pipes without wicks) arranged in two rows with staggered configuration was constructed. Heat was absorbed by lower part of the tube from hot water and removed from upper part of the tube by air stream. Analysis showed that the boiling limit is the lowest limit. Since the capacity of each thermosyphone is lower than this limit, it is assured that the designed thermosyphones operate securely at the design condition. Calculations showed that they are capable of transferring 1908 watts heat from a hot water with 80 degree centigrade temperature and 6 liters per minute flow. Experimental results approved a capacity of 1730 watts. Comparison of the two mentioned values indicates the satisfactory design and construction. Theoretical and experimental values of heat transfer coefficient of inside and outside of the condensing part of the tube are in good agreement. The inside heat transfer coefficient of the used heat pipes was 7900 w/m 2.K while this value is 230 for a similar metallic tube

379

Heat transfer and pressure drop amidst frost layer presence for the full geometry of fin-tube heat exchanger  

International Nuclear Information System (INIS)

The present study numerically solves the flow and thermal fields in the full geometry of heat exchanger modeling with frost layer presence on the heat exchanger surface. The effects of air inlet velocity, air inlet temperature, frost layer thickness, fin pitch, fin thickness, and heat exchanger shape on the thermo-hydraulic performance of a fin-tube heat exchanger are investigated. Heat transfer rate rises with increasing air inlet velocity and temperature, and decreasing frost layer thickness and fin pitch. Pressure drop rises with increasing air inlet velocity and frost layer thickness, and decreasing fin pitch. The effect of fin thickness on heat transfer and pressure drop is negligible. Based on the present results, we derived the correlations, which express pressure drop and temperature difference between air inlet and outlet as a function of air inlet velocity and temperature, as well as frost layer thickness

380

Fabrication experiments for large helix heat exchangers  

International Nuclear Information System (INIS)

The helical tube has gained increasing attention as a heat transfer element for various kinds of heat exchangers over the last decade. Regardless of reactor type and heat transport medium, nuclear steam generators of the helix type are now in operation, installlation, fabrication or in the project phase. As a rule, projects are based on the extrapolation of existing technologies. In the particlular case of steam generators for HTGR power stations, however, existing experience is with steam generators of up to about 2 m diameter whereas several projects involve units more than twice as large. For this reason it was felt that a fabrication experiment was necessary in order to verify the feasibility of modern steam generator designs. A test rig was erected in the SULZER steam generator shops at Mantes, France, and skilled personnel and conventional production tools were employed in conducting experiments relating to the coiling, handling and threading of large helices. (Auth.)

381

Pressure drop characteristics of cryogenic mixed refrigerant at macro and micro channel heat exchangers  

Science.gov (United States)

Mixed Refrigerant-Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. The temperature glide effect is one of the major features of using mixed refrigerants since a recuperative heat exchanger in a MR-JT refrigerator is utilized for mostly two-phase flow. Although a pressure drop estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in MR-JT refrigerator heat exchanger designs, it has been rarely discussed so far. In this paper, macro heat exchangers and micro heat exchangers are compared in order to investigate the pressure drop characteristics in the experimental MR-JT refrigerator operation. The tube in tube heat exchanger (TTHE) is a well-known macro-channel heat exchanger in MR-JT refrigeration. Printed Circuit Heat Exchangers (PCHEs) have been developed as a compact heat exchanger with micro size channels. Several two-phase pressure drop correlations are examined to discuss the experimental pressure measurement results. The result of this paper shows that cryogenic mixed refrigerant pressure drop can be estimated with conventional two-phase pressure drop correlations if an appropriate flow pattern is identified.

Baek, Seungwhan; Jeong, Sangkwon; Hwang, Gyuwan

2012-12-01

382

Intensification of batch chemical processes by using integrated chemical reactor-heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

This paper provides an overview of a collaborative project that was aimed at developing tools that will assist in the design and operation of integrated chemical reactor-heat exchangers (HEX reactors) for the advanced processing of fast exothermic chemical reactions. The tools are: (i) a chemical probe that is sensitive to both mixing intensity and heat transfer and (ii) a mathematical model that describes exothermic reacting flows in a simulated heat exchanger passage. Experimental and simulated reactive mixing data and measurements of local temperature and velocity profiles in a simulated heat exchanger passage are provided as examples to aid design engineers and industrial users of the HEX reactor technology. (author)

Phillips, C.H. [BHR Group Ltd., Bedford (United Kingdom); Lauschke, G. [Hoechst AG Verfahrenstechnik, Frankfurt am Main (Germany); Peerhossaini, H. [Thermofluids and Complex Flows Research Group, ISITEM, Nantes (France)

1997-08-01

383

The causes of milk deposit formation on the walls of the heat exchangers during the heat treatment of milk  

OpenAIRE

The results of research on finding the causes and preventing the formation of milk deposit are described in this paper.During the heat treatment of milk, an unwanted phenomenon occurs; the formation of milk deposit on heating surfaces of heat exchangers. This phenomenon causes the decrease of heat transfer coefficient as well as the pressure drop, it restricts the flow of milk, and causes additional production costs and increases production loss.The formation of milk deposit is a result of co...

Bojan Matijevi?; Josip ?ulig

2006-01-01

384

Numerical Investigation of Air-Side Heat Transfer and Pressure Drop in Circular Finned-Tube Heat Exchangers  

OpenAIRE

A three-dimensional numerical study is performed to investigate the heat transfer and pressure drop performance on the air-side of circular finned tube bundles in cross flow. New heat transfer and pressure drop correlations for the air-cooled heat exchangers have been developed with the Reynolds number ranging from 5000 to 70000. The heat transfer and pressure drop results agree well with several existing experimental correlations. In addition, the influence of the geometric parameters on the...

Mon, Mi Sandar

2009-01-01

385

Heat flow measurements in Egypt  

Energy Technology Data Exchange (ETDEWEB)

Temperature measurements in recent mineral exploration boreholes allow the first heat flow estimates to be made for Egypt. Gradients ranging from 15.6 to 32.0 mK m/sup -1/ have been determined from 22 boreholes at 4 locations in the Eastern Desert, and a range of 18.0 to 18.5 mK m/sup -1/ was measured in 3 boreholes at a single locality in the Western Desert. Uncorrected heat flow values have been estimated from these gradients and are considered to be reliable to within +-20 percent. Heat flow values for the localities in the Eastern Desert are as follows: Neweibi (25/sup 0/ 12'N; 34/sup 0/ 31'E) 60 mW m/sup -2/ (1.4 hfu); Abu Dabab (25/sup 0/ 21'N; 34/sup 0/ 33'E) 85 mW m/sup -2/ (2.0 hfu); Sukkari (24/sup 0/ 57'N; 34/sup 0/ 43'E) 55 mW m/sup -2/ (1.3 hfu); Abu Ghalga (-24/sup 0/ 20'N; -34/sup 0/ 55'E) 37 mW m/sup -2/ (.9 hfu). Except Abu Ghalga, these localities are all in granitic Precambrian Basement rocks, and indicate significantly high heat flow in the Precambrian of Egypt bordering the Red Sea. Abu Ghalga is in gabbroic Basement rocks, and estimates indicate that thermal refraction may reduce the heat flow by as much as 20 percent at this site. The high heat flow is associated with microseismic activity and is thought to be related to the opening of the Red Sea. Heat flow at the single locality in the Western Desert (Abu Tartur: 25/sup 0/ 26'N; 30/sup 0/ 02'E) was measured in Palaeocene sediments, and is estimated to be 42 mW m/sup -2/ ( 1.0 hfu). This value is consistent with other heat flow determinations from stable African shield and platform areas, and is in agreement with heat flow values of 42 to 47 mW m/sup -2/ (1.0 to 1.1 hfu) for the northern Western Desert, estimated using temperature data from oil wells.

Morgan, P. (New Mexico State Univ., Las Cruces); Blackwell, D.D.; Boulos, F.K.

1976-12-01

386

Heat Exchanger Design for Solar Gas-Turbine Power Plant  

OpenAIRE

The aim of this project is to select appropriate heat exchangers out of available gas-gas heat exchangers for used in a proposed power plant. The heat exchangers are to be used in the power plant for the purposes of waste heat recovery, recuperation and intercooling.In selecting an optimum heat exchanger for use, the PCHE was identified as the best candidate for waste heat recovery and recuperation. In order to ascertain the viability of this assertion the PCHE was designed and a 1D modeling ...

Yakah, Noah

2012-01-01

387

Heat flow in northern Thailand  

Science.gov (United States)

One hundred and two geothermal gradients have been obtained from water wells and mineral and oil prospecting holes in northern and northeastern Thailand. The geothermal gradients vary in the broad range of 8-95 mK/m. Two hundred and sixty-one rock samples and two hundred and nine rock-core samples of various types and formations were collected for the thermal conductivity measurement. A Quick Thermal Conductivity Meter (QTM) was used for the measurements both in wet and dry states: the latter values represent the in-situ condition and, therefore, were used for the heat flow determinations. Heat flow values have been obtained by the multiplication of the geothermal gradients and the thermal conductivity values of rocks which represented the lithology. The heat flow values obtained ranged in a broad interval of 17-320 mW/m 2. Using all stations as check points a simple heat flow density pattern for northern Thailand was proposed, which clearly shows four regions with high heat-flow (over 100 mW/m 2): the Fang oil fields, the San Kamphaeng geothermal area, Mae Sot and the western margin of Khorat plateau (Phetchabun province).

Thienprasert, Amnuaychai; Raksaskulwong, Manop

1984-03-01

388

A NUMERCIAL COMPARISON OF SINGLE-PHASE FORCED CONVECTIVE HEAT TRANSFER BETWEEN ROUND TUBE AND STRAIGHT MICROCHANNEL HEAT EXCHANGERS  

Directory of Open Access Journals (Sweden)

Full Text Available Three dimensional simulations of the single-phase laminar flow and forced convective heat transfer of water in round tube and straight microchannel heat exchangers were investigated numerically. This numerical method was developed to measure heat transfer parameters of round tube and straight microchannel tube geometries. Then, similarities and differences were compared between different geometries. The geometries and operating conditions of those indicated heat exchangers were created using a finite volume-based computational fluid dynamics technique. In this article, at each Z-location variation of dimensionless local temperature, nondimensional local heat flux variation and dimensionless local Nusselt number distribution along the tube length were compared between round tube and straight microchannel heat exchangers. Consequently, averaged computational Nusselt number was obtained for those indicated models and then validation study was performed for round tube counter flow type heat exchanger model. Finally, all of these numerical results for both kind of geometries in counter flow heat exchangers were discussed in details.

P. MOHAJERI KHAMENEH,

2010-11-01

389

Heat transfer characteristics and pressure drop in straight microchannel of the printed circuit heat exchangers  

International Nuclear Information System (INIS)

The performance experiments for a microchannel Printed Circuit Heat Exchanger (PCHE) of high-performance and high-efficiency on the two technologies of micro photo-etching and diffusion bonding were performed in this study. The microchannel PCHE were experimentally investigated for Reynolds number in ranges of 100 ? 700 under various flow conditions in the hot side and the cold side. The inlet temperatures of the hot side were conducted in range of 40 .deg. C ? 50 .deg. C while that of the cold-side were fixed at 20 .deg. C. In the flow pattern, the counter flow was provided 6.8% and 10 ? 15% higher average heat transfer rate and heat transfer performance than the parallel flow, respectively. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all the experiment. The increasing of inlet temperature in the experiment range has not an effect on the heat transfer performance while the pressure drop decrease slightly with that of inlet temperature. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the microchannel PCHE

390

Digital simulation of transients in sodium-sodium intermediary heat exchanger  

International Nuclear Information System (INIS)

The digital simulation of sodium-sodium heat exchangers considering uniform spatial flow and single tube model is presented. The discrete temperature field in the primary and secondary fluids and in the tube shell walls are obtained from the numerical integration of the energy and heat flow equations which are coupled by the heat transfer equation. A series of tests was performed in order to determine the precision of results and the program's efficiency. Data from the EBRII reactor to simulate the heat exchanger in the steady and transient states were used. The results show that the model satisfies the transient spectrum proposed. (F.E.)

391

Vapor Compression and Thermoelectric Heat Pump Heat Exchangers for a Condensate Distillation System: Design and Experiment  

Science.gov (United States)

Maximizing the reuse of wastewater while minimizing the use of consumables is critical in long duration space exploration. One of the more promising methods of reclaiming urine is the distillation/condensation process used in the cascade distillation system (CDS). This system accepts a mixture of urine and toxic stabilizing agents, heats it to vaporize the water and condenses and cools the resulting water vapor. The CDS wastewater flow requires heating and its condensate flow requires cooling. Performing the heating and cooling processes separately requires two separate units, each of which would require large amounts of electrical power. By heating the wastewater and cooling the condensate in a single heat pump unit, mass, volume, and power efficiencies can be obtained. The present work describes and compares two competing heat pump methodologies that meet the needs of the CDS: 1) a series of mini compressor vapor compression cycles and 2) a thermoelectric heat exchanger. In the paper, the system level requirements are outlined, the designs of the two heat pumps are described in detail, and the results of heat pump performance tests are provided. A summary is provided of the heat pump mass, volume and power trades and a selection recommendation is made.

Erickson, Lisa R.; Ungar, Eugene K.

2013-01-01

392

Microchannel heat exchanger for two-phase Mixed Refrigerant Joule Thomson process  

Science.gov (United States)

Mixed Refrigerant Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. Printed Circuit Heat Exchanger (PCHE) is one of the promising cryogenic compact recuperators for MR-JT refrigerators due to its compactness, high NTU and robustness. However, PCHE composed with microchannel bundles can cause flow mal-distribution, and it can cause the degradation of thermal performance of the system. To mitigate the flow mal-distribution problem, the cross link (or intra-layer bypass) can be adapted to parallel microchannels. Two heat exchangers are fabricated in this study; one has straight channels, and the other one has intra-layer bypass structure between channels to enhance the flow distribution. The MR-JT refrigerators are operated with these two heat exchanger and the no-load temperatures are compared. The lower no load temperature achieved with the intra-layer bypass structured heat exchanger. The results indicate that the flow mal-distribution in the microchannel heat exchanger can be mitigated with intra-layer bypass structure, and relaxation of flow mal-distribution in the heat exchanger guarantee the MR-JT refrigerator's performance.

Baek, Seungwhan; Lee, Jisung; Lee, Cheonkyu; Jeong, Sangkwon

2014-01-01

393

Heat exchange model in absorption chamber of water-direct-absorption-typed laser energy meter  

Science.gov (United States)

The interaction between laser and water flow is very complicated in the absorption chamber of a high energy laser (HEL) energy meter which directly uses water as an absorbing medium. Therefore, the heat exchange model cannot be studied through traditional methods, but it is the most important factor to improve heat exchange efficiency in the absorption chamber. After the exchanges of heat and mass were deeply analyzed, experimental study and numerical fitting were brought out. The original testing data of laser power and water flow temperature at one moment were utilized to calculate those at the next moment, and then the calculated temperature curve was compared with the measured one. If the two curves matched well, the corresponding coefficient was obtained. Meanwhile, numerous experiments were performed to study the effects of laser power, duration, focal spot scale, and water flow rate on heat exchange coefficient. In addition, the relationship between water phase change and heat exchange was analyzed. The heat exchange coefficient was increased by optimizing the construction of the absorption chamber or increasing water flow rate. The results provide the reference for design of water-direct-absorption-typed HEL energy meters, as well as for analysis of the interaction between other similar lasers and water flow.

Feng Wei, Ji; Qun Sun, Li; Zhang, Kai; Hu, XiaoYang; Zhou, Shan

2015-04-01

394

Heat Exchanger Anchors for Thermo-active Tunnels  

OpenAIRE

Shallow geothermal power represents an important energy resource for the heating and cooling of the buildings. Due to relatively low temperature levels encountered at shallow depths in the soil, between 10°C and 20°C, heat pumps are required to process the extracted heat, forming the so called ground source heat pump system. Different types of heat exchangers with the ground were developed in order to optimize the heat exchanges, from simple geothermal loops grouted in boreholes reaching de...

Mimouni, Thomas; Dupray, Fabrice; Minon, Sophie; Laloui, Lyesse

2013-01-01

395

Heat transfer studies in a spiral plate heat exchanger for water: palm oil two phase system  

Directory of Open Access Journals (Sweden)

Full Text Available Experimental studies were conducted in a spiral plate heat exchanger with hot water as the service fluid and the two-phase system of water ? palm oil in different mass fractions and flow rates as the cold process fluid. The two phase heat transfer coefficients were correlated with Reynolds numbers (Re in the form h = a Re m, adopting an approach available in literature for two phase fluid flow. The heat transfer coefficients were also related to the mass fraction of palm oil for identical Reynolds numbers. The two-phase multiplier (ratio of the heat transfer coefficient of the two phase fluid and that of the single phase fluid was correlated with the Lockhart Martinelli parameter in a polynomial form. This enables prediction of the two-phase coefficients using single-phase data. The predicted coefficients showed a spread of ± 10 % in the laminar range.

S. Ramachandran

2008-09-01

396

Thermal Analysis of Fin and Tube Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available This paper studied experimentally the effect of heat transfer of fin and tube type heat exchanger for different mass flow rate of fluid. The thermal stresses induced on fin and tube is also studied by ansys software at steady state condition by changing the width of fin and diameter of tube. Readings were taken experimentally by changing mass flow rate of fluid at respective temperatures. Comparison was done on theoretically and experimentally obtained results. It is observed that as the width of fin increases thermal stresses on fin also increases. Likewise for tube, by varying diameter of tube different values of stress are obtained. It is also observed at full valve position maximum thermal stresses are induced on fin as well as tube.

Ms N. B. Rairker

2014-06-01