being used in government and industry for heat transfer analysis of practical problems. Depending on ...... Average and Maxima for Blocks of Nodes ...... flowheatexchangers, cross flowheatexchangers, condensing heatexchangers, and any ...
An air heating and cooling system for a building includes an expansion-type refrigeration circuit and a heat engine. The refrigeration circuit includes two heatexchangers, one of which is communicated with a source of indoor air from the building and the other of which is communicated with a source of air from outside the building. The heat engine includes a heat rejection circuit having a source of rejected heat and a primary heatexchanger connected to the source of rejected heat. The heat rejection circuit also includes an evaporator in heatexchange relation with the primary heatexchanger, a heat engine indoor heatexchanger, and a heat engine outdoor heatexchanger. The indoor heatexchangers are disposed in series air flow relationship, with the heat engine indoor heatexchanger being disposed downstream from the refrigeration circuit indoor heatexchanger. The outdoor heatexchangers are also disposed in series air flow relationship, with the heat engine outdoor heatexchanger disposed downstream from the refrigeration circuit outdoor heatexchanger. A common fluid is used in both of the indoor heatexchanges and in both of the outdoor heatexchangers. In a first embodiment, the heat engine is a Rankine cycle engine. In a second embodiment, the heat engine is a non-Rankine cycle engine.
This patent describes a heating system, comprising a heating compartment, a tubular heatexchanger within the heating compartment, heat input means for supplying hot fluid into the heatexchanger for flowing therein, and means for causing other fluid to flow across the heatexchanger in a direction generally transverse to the longitudinal axis of the heatexchanger for transfer of thermal energy from the heatexchanger to such other fluid flowing thereacross. The heatexchanger has an egg-shaped cross-section oriented with its narrow end facing downstream of the flow of such other fluid, the heating compartment having wall means cooperatively positioned with respect to the heatexchanger further to direct flow of such other fluid on both sides of the heatexchanger. The wall means includes a wall adjacent to and generally parallel to the longitudinal axis of the heatexchanger, and the major axis of the egg-shape cross-section is oriented at an angle to the direction of flow of such other fluid and at an angle to the wall with its narrower end nearest the wall to define with such wall a restricted flow passage for such other fluid at the narrower end. Here such other fluid flowing across the heatexchanger will be caused to flow closely over substantially the entire exterior extent thereof to maximize thermal energy transfer while minimizing heat concentration at the downstream side of the heatexchanger.
A spray generator for an absorption refrigeration system that includes a heatexchanger comprised of a multiplicity of variably spaced heatexchange tubes. The tubes are spaced close together near the top of the heatexchanger and spaced more widely apart near the bottom of the heatexchanger. Dilute absorbent solution is sprayed down through the heatexchanger. The close nesting of the tubes in the top portion of the heatexchanger retards liquid flow and aids heating of the solution. The wide spacing of the tubes in the lower section of the heatexchanger facilitate vapor flow out of the heatexchanger and eliminates liquid "blow-off". The top tubes are covered by a baffle to prevent the liquid solution from splashing out of the heatexchanger off of these top tubes.
A triple loop heatexchanger for an absorption refrigeration system is disclosed. The triple loop heatexchanger comprises portions of a strong solution line for conducting relatively hot, strong solution from a generator to a solution heatexchanger of the absorption refrigeration system, conduit means for conducting relatively cool, weak solution from the solution heatexchanger to the generator, and a bypass system for conducting strong solution from the generator around the strong solution line and around the solution heatexchanger to an absorber of the refrigeration system when strong solution builds up in the generator to an undesirable level. The strong solution line and the conduit means are in heatexchange relationship with each other in the triple loop heatexchanger so that, during normal operation of the refrigeration system, heat is exchanged between the relatively hot, strong solution flowing through the strong solution line and the relatively cool, weak solution flowing through the conduit means. Also, the strong solution line and the bypass system are in heatexchange relationship in the triple loop heatexchanger so that if the normal flow path of relatively hot, strong solution flowing from the generator to an absorber is blocked, then this relatively, hot strong solution which will then be flowing through the bypass system in the triple loop heatexchanger, is brought into heatexchange relationship with any strong solution which may have solidified in the strong solution line in the triple loop heatexchanger to thereby aid in desolidifying any such solidified strong solution.
Design details of a compact heatexchanger and supporting hardware for heat recuperation in a high-temperature electrolysis application are presented. The recuperative heatexchanger uses a vacuum-brazed plate-fin design and operates between 300 and 800°C. It includes corrugated inserts for enhancement of heat transfer coefficients and extended heat transfer surface area. Two recuperative heatexchangers are required per each four-stack electrolysis module. The heatexchangers are mated to a base manifold unit that distributes the inlet and outlet flows to and from the four electrolysis stacks. Results of heatexchanger design calculations and assembly details are also presented.
The invention discloses a heat pump including an indoor heatexchanger, a main outdoor heatexchanger and an auxiliary outdoor heatexchanger provided underneath the main outdoor heatexchanger and connected between the indoor and main outdoor heatexchangers in a closed refrigerant flow circuit. The refrigerant flow circuit includes a compressor and a reversal valve which can be adjusted (1) during cooling operation to direct the hot compressed gaseous refrigerant from the compressor to the main outdoor heatexchanger and thence to the auxiliary heatexchanger acting as a sub-cooler into the indoor heatexchanger for extracting heat from air of the interior of a building and (2) during heating operation to direct the hot compressed gaseous refrigerant to the indoor heatexchanger to supply heat to the indoor air and then to the auxiliary heatexchanger now acting as a defroster for melting a block of ice which may have accumulated under the main outdoor heatexchanger and into the main outdoor heatexchanges. 9 claims.
In this paper, a cross flow plate type heatexchanger, operating with unmixed fluids, was analysed with balanced cross flow. For this aim, a cross flow plate type heatexchanger was developed and manufactured in the laboratory. The heatexchanger was tested with an applicable experimental set up, and temperatures, velocity of the air and the pressure losses occurring in the system were measured so that the effectiveness of the heatexchanger has been determined. The minimum entropy generation number has been taken into consideration with respect to the second law of thermodynamics for the heatexchanger in this analysis. The minimum entropy generation number depends on parameters such as optimum flow path length, dimensionless mass velocity, dimensionless heat transfer area and dimensionless heat transfer volume. The variations between the entropy generation number and these parameters were analysed for the manufactured heatexchanger and introduced with their graphics. (author)
An annular heatexchanger assembly includes a plurality of low thermal growth ceramic heatexchange members with inlet and exit flow ports on distinct faces. A mounting member locates each ceramic member in a near-annular array and seals the flow ports on the distinct faces into the separate flow paths of the heatexchanger. The mounting member adjusts for the temperature gradient in the assembly and the different coefficients of thermal expansion of the members of the assembly during all operating temperatures.
The present study addresses fluid flow and heat transfer in a high temperature compact heatexchanger which will be used as a chemical decomposer in a hydrogen production plant. The heatexchanger is manufactured using fused ceramic layers that allow creation of channels with dimensions below 1 mm. The main purpose of this study is to increase the thermal performance of the heatexchanger, which can help to increase the sulfuric acid decomposition rate. Effects of various channel geometries of the heatexchanger on the pressure drop are studied as well. A three-dimensional computational model is developed for the investigation of fluid flow and heat transfer in the heatexchanger. Several different geometries of the heatexchanger channels, such as straight channels, ribbed ground channels, hexagonal channels, and diamond-shaped channels are examined. Based on the results, methods on how to improve the design of the heatexchanger are recommended. (orig.)
It is well known that significant fouling by particulate matter can have a deleterious effect on the performance of enhanced surface heatexchangers, and the same is true for hybrid heatexchangers. Hybrid heatexchangers are heatexchangers that are typically run in dry mode to reject heat. When the ambient conditions require more heat rejection than can be provided by sensible heat transfer, a water pump is turned on and water flows over the fins, and the evaporation of water provides a further cooling effect. Fouling in dry-mode operation is physically similar to that of air-cooled heatexchangers, but in evaporative mode the flow of the water over the coil eliminates the impact of fouling. A hybrid dry cooler heatexchanger of 60 cm × 60 cm frontal area has been installed in a wel...
This patent describes a closed system with no moving parts for providing cryogenic cooling to a load heatexchanger, comprising: an electrochemical pump for pressurizing an ionizable cryogenic gas; a high-pressure flow path adapted to direct pressurized gas from the electrochemical pump to the load heatexchanger. The path includes a first heatexchanger for cooling the gas to below its inversion temperature and a Joule-Thomson flow restrictor to further cool the gas to a cryogenic temperature for delivery to the load heatexchanger; and, a low-pressure flow path adapted to receive the gas from the load heatexchanger and to return the gas to the electrochemical pump. The low-pressure flow path includes a second heatexchanger for warming the gas to a predetermined temperature.
A sodium-to-sodium heatexchanger has been widely used in a sodium-cooled fast reactor as an intermediate heatexchanger (IHX) or a decay heatexchanger (DHX). It is basically a shell-and-tube type counter-current flowheatexchanger, and sodium flows along the tube bundles on the shell-side of the heatexchanger. An accurate prediction of a heat transfer performance is very important for the heatexchanger thermal sizing in a sodium-cooled fast reactor (SFR) design application. To this end, a proper heat transfer coefficient for the appropriate design conditions should be provided for a better design of sodium heatexchangers. However, the experimental correlations for a heat transfer of liquid metal are very rare in the literature and they have large uncertainties since the experiment is very expensive and difficult. The most difficult thing is that the differences among the correlations are so serious that it is difficult to decide which correlation should be used for a particular flow situation. In the present study, we surveyed the conventional heat transfer correlations for single-phase liquid metal flows in a heatexchanger design. The thermal sizing results of sodium heatexchangers with respect to the Nusselt (Nu) number correlations were quantitatively discussed
Flow-induced vibration in heatexchangers has been a major cause of concern in the nuclear industry for several decades. Many incidents of failure of heatexchangers due to apparent flow-induced vibration have been reported through the USNRC incident reporting system. Almost all heatexchangers 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 heatexchangers.
A novel heatexchanger computational procedure is described which provides a means of rapidly calculating the distributions of fluid and wall temperatures, deposit formation, and pressure loss at various points in a heatexchanger. The procedure is unique in that it is capable of treating wide variations in heatexchanger geometry without recourse to restrictive assumptions concerning heatexchanger type (e.g., co-flow, counterflow, cross flow devices, etc.). The analysis has been used extensively to predict the performance of cross-counterflow heatexchangers in which one fluid behaves as a perfect gas (e.g., air) while the other fluid is assumed to be a distillate fuel. The model has been extended to include the effects on heatexchanger performance of time varying inflow conditions. Heatexchanger performance degradation due to deposit formation with time can be simulated, making this procedure useful in predicting the effects of temperature-dependent fouling.
Double-spiral-type equipment is proposed as a new compact heatexchanger. Initially, the behavior of heat transfer coefficients is quantitatively determined through experiments of the heatexchange between hot and cold water flows in the exchanger. Subsequently, the heat-recipient water is changed with phase change material (PCM)–water slurry to ascertain the effects of PCM-melting on heat transfer enhancement through direct measurements of heat transfer rates. By appropriately evaluating the physical properties of the slurries with PCM-melting, we finally propose a heat transfer correlation which is applicable to both the water and slurry flows.
In this invention for providing fuel gas from a storage tank containing liquefied natural gas, the naturally vaporized gas from the dome above the liquid gas surface is compressed and fed into a heatexchanger. If required, liquefied gas from the tank is also pumped into the heatexchanger, which is of a combined type with separate channels for the two flows. The two flows are heated by heatexchange against an external hot flow, usually steam, and the liquefied gas evaporates. The two gas flows are mixed at the outlet of the heatexchanger and then flows as fuel gas to the consumer. Since only one of the gas components is compressed, a relatively small compressor with a simple capacity regulation will suffice, although it must work with gases at temperatures down to -140{sup o}C. The combined heatexchanger can be designed for a high pressure loss, with small mantle dimensions and thus low production cost. 1 figure
Heatexchangers 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 heatexchangers, we developed a numerical method to determine their performance. We simulated the flow in the heatexchanger applying a network model and coupled these results with a finite volume method to determine the heat distribution in the heatexchanger. (orig.)
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 heatexchanger. The model has been used to determine the heat transfer capacity, which expresses the thermal performance of heat pipe heatexchanger. 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 heatexchanger.
On the basis of experimental verification of mathematical model, the influence of honeycomb ceramic on heat extraction is numerically studied under the steady state condition. The calculation results show the packed honeycomb ceramic influences the extracted heat of heatexchanger by changing the flow field while not radiation heat transfer of heatexchanger outer wall, and the difference between the extracted heat of heatexchanger embedded in packed bed and that of heatexchanger in empty bad is gradually obvious with gas temperature increasing under the condition of the same gas mass flow rate. In addition, under the same operating condition, when the two characteristic sizes of heat extraction zone honeycomb ceramic in the vertical gas flow direction increase, the extracted heat of emb...
A cascade connection of efficient flue gas heated ejector drifts and recuperative flue gas heatexchangers is needed in highly efficient absorption refrigerating machines with direct firing or with the use of flue gas heat. Nevertheless, the permissible pressure loss in the flue gas flow is strongly limited. The present study showed that heatexchangers with cross-flow through a bundle of pipes enable significantly higher heat transfer values at the same pressure loss than the set-up with pipe flow. A variation of the pipe separation ratio or the rib cutting of the exterior pipe in the back part of the heatexchanger enables a flexible adaptation of the heat transfer coefficients in heating tubes. This allows generating a balanced heat flux density in the whole heatexchanger. (orig.)
A numerical analysis using FLUENT code was carried out to investigate flow characteristics and heat transfer development of heatexchangers. The analysis results for both cases of the fin-circular tube and the fin-flat tube heatexchanger with the vortex generator show relatively higher heat transfer coefficient than that for both cases of the fin-circular tube and the fin-flat tube heatexchangers without the vortex generator. Also, the analysis result for the fin-circular tube heatexchanger with the vortex generator has relatively higher heat transfer coefficient and higher pressure loss than those for the fin-flat tube heatexchanger with the vortex generator. The results of this study can be used to design the heatexchanger with relatively low pressure loss and maximum heat transfer coefficient. 28 figs., 15 refs. (Author) .new.
HEATEXCHANGER POWER INCREASE POTENTIAL . .... An in-space fission power system is developed by ground-testing, evaluating, and improving ... the flow annuli in the test model, where most of the heat transfer takes place, are ...
1 Thermal Systems Engineer, Crew and Thermal Systems Division, Mail Code EC-2. .... the heat acquisition function using various coldplates and heatexchangers, ... The internal loop is driven by a centrifugal pump, and the system flow rate is ...
Reactor. Analysis. Methods ............................. Reactor. Design and Critical. Experiments ... Lateral support .................................. Vibration ..................................... FLUID. SYSTEMS .... tube. The removal of heat is provided by pumping the water through the .... a water flow loop and a heatexchanger .... into six shell-and-tube ...
In the present work, the design and analysis of a multi-block heatexchanger has been carried out by applying the concept of constructal theory proposed by Bejan. The heatexchanger works on the principle of developing laminar flow in each block carefully designed to avoid fully developed heat transfer coefficient. The additional thermal interaction is provided by the special design allowing heat transfer in ports as well as collecting and distributing channels. Numerical simulations were carried out for different values of heat capacity rate ratios on finned and unfinned constructal heatexchangers and four cross flowheatexchangers (two finned and two unfinned). In all the heatexchangers the heat transfer area is kept the same. To validate the numerical results, experiments were conduc...
In a fluidized bed of solid particles having one or more heatexchange tubes immersed therein, the rate of heat transfer between the fluidized particles and a fluid flowing through the immersed heatexchange tubes is controlled by rotating an arcuate shield apparatus about each tube to selectively expose various portions of the tube to the fluidized particles.
In a fluidized bed of solid particles having one or more heatexchange tubes immersed therein, the rate of heat transfer between the fluidized particles and a fluid flowing through the immersed heatexchange tubes is controlled by rotating an arcuate shield apparatus about each tube to selectively expose various portions of the tube to the fluidized particles.
An improved heating and cooling system utilizing recovered heat is described comprising: a water heater having a tank provided with a cold water inlet and a hot water outlet; compressor means for effecting heating and cooling functions within the system and having an outlet means for heated compression gases communicating with the desuperheater means and the water circulating in the water circulation means and dissipating heat from the compression gases; heatexchange means operatively connected to the compressor means; and blower means associated with the heatexchange means to provide air flow across the heatexchange means and provide circulation of conditioned air outside a cabinet.
Jul 13, 1998 ... The nested soil layer approach of BATS has b een converted to a discrete ... Parameters involved in heat and moisture exchange b etween the canopy ... including overland flow and runoff into streams, lateral sub-surface flow, ...
Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heatexchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heatexchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heatexchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heatexchanger. The model is used to guide design decisions on heatexchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heatexchanger ...
The objective of this work is to obtain the Performance test data for the passive residual heat removal (RHR) heatexchanger in the advanced PWR. The RHR heatexchanger 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 heatexchanger. The one is the single bundle test model which consisted of a finned tubular heatexchanger unit. The other is the multi-bundle test model which has the finned tubular heatexchanger 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 heatexchanger were investigated.
In the present work, the design and analysis of a multi-block heatexchanger has been carried out by applying the concept of constructal theory proposed by Bejan. The heatexchanger works on the principle of developing laminar flow in each block carefully designed to avoid fully developed heat transfer coefficient. The additional thermal interaction is provided by the special design allowing heat transfer in ports as well as collecting and distributing channels. Numerical simulations were carried out for different values of heat capacity rate ratios on finned and unfinned constructal heatexchangers and four cross flowheatexchangers (two finned and two unfinned). In all the heatexchangers the heat transfer area is kept the same. To validate the numerical results, experiments were conducted keeping the heat transfer area and boundary conditions same as that of the numerical simulations. The results show that the effectiveness of the constructal heatexchangers, both finned and unfinned, are higher by around 20% compared to that of the conventional cross flowheatexchangers under similar conditions. The experimental result confirms this enhancement and brings out the immense potential of this new type of heatexchanger. (author)
This study presents the flow and heat transfer characteristics of tetra-n-butyl ammonium bromide (TBAB) aqueous solution and clathrate hydrate slurry (CHS) in a double-tube heatexchanger (DHE). Both the TBAB aqueous solutions at the supercooling state and normal state were tested to understand the influence of supercooling state on the flow and heat transfer of TBAB aqueous solution. Pressure drops of 5-25wt% TBAB CHS flowing through DHE without heatexchange were measured and the corresponding flow friction factor was obtained, while the pressure drops of the flow melting and generating of TBAB CHS were also obtained. Single side heat transfer coefficients of the flow melting of 10-25wt% TBAB CHS in the heatexchanger were presented, and the local heat transfer correlation was developed ...
A thermal storage heater system for heating fluids includes a storage tank for accumulating and storing energy in the form of a quantity liquid heated to a high temperature by an electric immersion heating element in the tank. A source of a first fluid to be heated is connected to the inlets of pilot and primary heatexchangers immersed in the high temperature liquid for transferring heat to the first fluid. A first circuit connects the outlet of the pilot heatexchanger to a point of use. A second fluid circuit connects the outlet of the primary heatexchanger to the point of use and includes a spring-loaded pressure sensitive check valve responsive to the flow rate in the first circuit for regulating the flow of fluid through the primary heatexchanger in response to a change in flow indicative of insufficient heating of the fluid by the pilot heatexchanger. The system includes an additional heatexchanger for heating a second fluid to be heated. The pilot, primary and additional heatexchangers each comprise at least one U-shaped tube immersed in the liquid with each tube having an inlet and an outlet aligned in a horizontal plane. A condenser is provided at the outlet of the pilot heatexchanger and additional heatexchanger for condensing any entrained steam in the heated fluid. The condenser for the additional heatexchanger includes a central spray tube connecting the source of second fluid to the inlet of the U-shaped tube, a concentric outer shell connecting the outlet of the U-shaped tube to the point of use, and a radially corrugated imperforate baffle therebetween.
Shell and tube heatexchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heatexchanger with single segmental baffles. Effect of shell-side nozzles configurations on heatexchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heatexchanger with twisted tube bundle is lower than that of the heatexchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the latter. The comparison of heat transfer rate per unit pressure drop versus shell-side mass flow rate show...
A novel system for space heating has been developed taking advantage of the favourable characteristics of the transcritical CO{sub 2} cycle, where heat is rejected by cooling of supercritical gas at gliding temperature. By a proper design of a counter flowheatexchanger it is possible to heat air to high temperatures and thereby giving the driving force for circulation of air through the heatexchanger, in consequence without using a fan. A concept without a fan, here called a fan-less concept, would give several advantages; no noise, no power consumption for the fan and increased comfort with reduced air draft in the room. The concept may also be used for heat rejection in systems for light commercial applications or other applications where fan assisted heat rejection concepts are used today. An experimental study of a CO{sub 2} to air heatexchanger has been performed. The heatexchanger was made of a vertically finned aluminium profile. Tubes for CO{sub 2} were mounted in the base of the profile. CO{sub 2} at supercritical pressure flowing downwards through the profile was heating air flowing in the channels formed by the fins of the profile. In this way a perfect counter flowheatexchange was obtained. The prototype heatexchanger was 2000mm high and 190mm wide, with 45mm deep fins. A simulation model was developed and verified to give good accordance with the experimental data. The model was then used to study how different design parameters influence the efficiency of the heatexchanger. By altering the number of fins and the fin thickness of the tested profile, the heat output at a given condition could be increased to almost double, meaning that the initial design was relatively far from optimal. With the original heatexchanger profile design concept a heatexchanger with height, width and depth of, respectively 2000, 750 and 200mm, would be required in order to achieve a heat output of 2500W if the constraints for assumed acceptable efficiency was applied. If a heatexchanger with less height is preferred, the width will have to be increased in order to maintain about the same front area, width times height. Ideas have also been introduced for how to improve both the compactness and efficiency of the heatexchanger by introducing a compact counter flowheatexchanger in the lower part of the air flow channel. It is concluded that the new concept looks promising for use as the indoor heatexchanger in an air-to-air heat pump or as a gascooler for heat rejection in small commercial equipment, when using CO{sub 2} as refrigerant. (author)
Correlations for heat transfer and flow friction coefficients are provided for plane parallel plates and offset strip-fin plates over the ranges used in compact heatexchangers. Closed form expressions have been used to present these correlations. The proposed correlations allow one to adequately predict experimental data available for the heatexchanged and pressure losses in compact plate-type heatexchangers. The correlation cover continuously the full range from laminar to turbulent flow, for both short and long pipes. Suggestions to extend the correlations to other flow conditions are provided.
The transient and steady-state heat transfer, fluid flow, and stability of a toroidal thermosyphon have been studied theoretically. The thermosyphon is heated over the lower half and cooled over the upper half by an annular parallel-flowheatexchanger. Under some conditions the system becomes unstable and the interaction between the fluids in the thermosyphon and in the heatexchanger is of special interest. Indeed, two neutrally stable curves are obtained for the same heatexchanger conditions. Detailed results and discussion are presented for the stability of the system as well as for the temperature, velocity, pressure drop, and efficiency.
Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heatexchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heatexchangers such as nuclear steam generators, reboilers, coolers, service water heatexchangers, condensers, and moisture-separator-reheaters. Part 2 of this paper covers forced vibration excitation mechanisms, vibration response prediction, resulting damage assessment, and acceptance criteria.
This gas-fired water heater contains two heat-exchanging coils submerged in the tank. Water jets within the tank draw the combustion gases from the burner and wash the gas molecules to remove any particulate matter. Undissolved flue gases bubble to the surface, transfer additional heat to the exchanger liquid (preferably water), and then flow out through a vent at the top of the tank. Pressure from an auxiliary pump powers the jets and also withdraws the heat-exchange liquid.
Combustion deposits reduce transfer of heat. Instrument measures fouling like that on gas side of heatexchanger in direct-fired boiler or heat-recovery system. Heat-flux probe includes tube with embedded meter in outer shell. Combustion gases flow over probe, and fouling accumulates on it, just as fouling would on heatexchanger. Embedded heat-flow meter is sandwich structure in which thin Chromel layers and middle alloy form thermopile. Users determine when fouling approaches unacceptable levels so they schedule cleaning and avoid decreased transfer of heat and increased drop in pressure fouling causes. Avoids cost of premature, unnecessary maintenance.
The invention comprises a dense pack heatexchanger for a steam generator having a circulating fluidized bed combustion system whereby a bed of solid particles comprising fuel and inert material is entrained in the furnace gas stream. Means are provided for collecting high temperature bed solid particles downstream of the furnace. The dense pack heatexchanger directs the hot collected particles down over heat transfer surface, such surface being a portion of the steam generator fluid circuits. Flow is induced by gravity means. The dense compaction of the solid particles around the fluid heatexchange circuits results in high heat transfer rates as the fluid cools the compacted solid material. The heatexchange surface is arranged to facilitate flow of the solid particles through the heatexchanger.
The Heat Pipe Stirling Engine (HP-1000), a free-piston Stirling engine incorporating three heatexchanger 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 heatexchanger modules were designed to reduce the number of potential flow leak paths in the heatexchanger 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 heatexchanger modules. This paper describes heatexchanger module and engine performance during baseline testing. Condenser temperature profiles, brake power, and efficiency are presented and discussed.
Highlights: Black-Right-Pointing-Pointer Air side heat transfer and flow characteristics of mesochannel cross-flowheatexchanger are studied experimentally. Black-Right-Pointing-Pointer Hot ethylene glycol-water mixture (50:50) at constant mass flow rate is used against varying air flow. Black-Right-Pointing-Pointer Air side heat transfer and fluid flow key parameters such as Nusselt number, Colburn factor, friction factor are obtained. Black-Right-Pointing-Pointer General correlations are proposed for air side heat transfer and fluid flow parameters. - Abstract: Air side force convective heat transfer and flow characteristics of cross-flow mesochannel heatexchanger are investigated experimentally. A series of experiments representing 36 different operating conditions have been conducted on a finned mesochannel heatexchanger through the fully automated dynamic single-phase experimental facility which is capable of handling a wide variety of working fluids in air-to-liquid cross-flow orientation. The mesochannel heatexchanger is made of 15 aluminum slabs with arrays of wavy fins between slabs; 68 one millimeter circular diameter port located at each slab, and the air side frontal area of 304-mm Multiplication-Sign 304-mm. The ethylene glycol-water mixture as the working fluid in the liquid side was forced to flow through mesochannels maintaining constant inlet temperature and flow rate at 74 Degree-Sign C and 0.0345 kg/s respectively whereas the inlet flowing air into the arrays of wavy fins was changed at four different temperature levels from 28 Degree-Sign C to 43 Degree-Sign C. Frontal air velocity was altered in nine steps from 3 m/s to 11 m/s at each temperature level corresponding range of Reynolds number 752 < Re{sub a} < 3165. The air side heat transfer and flow characteristics of mesochannel heatexchanger were evaluated during air heating, and heat transfer and fluid flow correlations were derived accordingly. The air side Nusselt number (Nu{sub a}) and Colburn factor (j{sub a}) were found higher in comparison with other studies.
In cold climates, mechanical ventilation systems with highly efficient heat recovery will experience problems with condensing water from the extracted humid indoor air. If the condensed water changes to ice in the heatexchanger, the airflow rate will quickly fall due to the increasing pressure drop. Preheating the inlet air (outdoor air) to a temperature above 0 degrees C before it enters the exchanger is one solution often used to solve the problem, however, this method reduces the energy saving potential significantly. To minimize the energy cost, a more efficient way to solve the freezing problem is therefore desirable. In this paper, the construction and test measurements of a new counter flowheatexchanger designed for cold climates are presented. The developed heatexchanger is capable of continuously defrosting itself without using supplementary heating. Other advantages of the developed beat exchanger are low pressure loss, cheap materials and a simple construction. The disadvantage is that the exchanger is big compared with other heatexchangers. In this paper, the new heatexchanger's efficiency is calculated theoretically and measured experimentally. The experiment shows that the heatexchanger is capable of continuously defrosting itself at outside air temperatures well below the freezing point while still maintaining a very high efficiency. Further analysis and development of a detailed simulation model of a counter flow air-to-air heatexchanger will be described in future articles.
This newsletter from Electricite de France (EdF) laboratory of hydraulics and fluid dynamics, reports on recent computer simulation studies of fluid flow in the domain of energy. Five papers were selected which deal with: unsteady flows in turbine blades of turbo-machineries, thermal exchanges between fluid and structures, multi-fluid thermal interactions in heatexchangers, heat transfers through windows, and flows induced by dam breaking. (J.S.)
An air heating and cooling system for a building includes an expansion type refrigeration circuit and a vapor power circuit. The refrigeration circuit includes two heatexchangers, one of which is communicated with a source of indoor air from the building and the other of which is communicated with a source of air from outside the building. The vapor power circuit includes two heatexchangers, one of which is disposed in series air flow relationship with the indoor refrigeration circuit heatexchanger and the other of which is disposed in series air flow relationship with the outdoor refrigeration circuit heatexchanger. Fans powered by electricity generated by a vapor power circuit alternator circulate indoor air through the two indoor heatexchangers and circulate outside air through the two outdoor heatexchangers. The system is assembled as a single roof top unit, with a vapor power generator and turbine and compressor thermally insulated from the heatexchangers, and with the indoor heatexchangers thermally insulated from the outdoor heatexchangers.
The objective of this study is to obtain the performance test data for the passive residual heat removal heatexchanger being designed to remove the decay heat with combined effects of the natural circulation of water by means of thermosyphon at the inside and the natural convection of air at the outside. Through the tests, the following results were obtained : (1) The thermosyphon flow between the heater and the finned tubular heatexchanger was smoothly established and flow rates of the thermosyphon were in good agreement with theoretical values. (2) Maximum heat removal rate per unit length of heatexchanger at equilibrium state were measured as 405 W/m for single bundle and 285 W/m for multi-bundle. (3) Natural convective heat transfer coefficients of air at the heatexchanger were ranging from 6 W/m{sup 2} K to 15 W/m{sup 2} K. 35 figs, 2 tabs, 8 refs. (Author).
- The flow structure in vertical mantle heatexchangers was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the mantle were measured using a particle Image Velocimetry (PIV) system. A CFD simulation model of vertical mantle heatexchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle was evaluated for both high and low temperature input flows.
In order to reduce the plant cost of a pool type LMFBR, technology for more effective design of intermediate heatexchangers is being developed. This time, a zigzag-flow internal heatexchanger which has baffle plates and whose secondary coolant has a cro...
Papers are presented on heat conduction, natural and forced heat convection, two-phase flows and visualization, boiling heat transfer, condensation heat transfer, thermal radiation, heat and mass transfer in porous media, and heatexchangers. Also considered are nuclear reaction heat transfer, combustion heat transfer, high-temperature heat transfer, enhanced heat transfer, and industrial heat transfer. Topics considered include an enthalpy method for the solution of the temperature field during the alloy solidification process, laminar heat transfer and flowfield downstream of backward-facing steps, thermal analysis and optimum design for radiating spines of various geometries, and thermal radiation properties of refractory metals and electrically conductive ceramics at high temperatures.
A generalized method was developed to evaluate the thermal performance of heatexchangers with different geometries and fluids. By this method the heatexchanger can be decomposed in three types of discrete nodes: parallel current flow, countercurrent flow and cross flow. The thermal energy equation is applied to each node, in terms of non-dimensional variables and forms a linear algebraic equation system. The solution of this system is the temperature distribution within the heatexchanger and the thermal performance parameters for the particular configuration under analysis. (author) 4 refs., 5 figs., 3 tabs.
A three-dimensional numerical model for seasonal heat storage in the ground by vertical heatexchanger pipes is presented. The model also accounts for convective heatflows in the ground. The storage is employed in a district solar heating system with a h...
LBL has constructed a facility for testing various performance aspects of residential air-to-air heatexchangers. When used in conjunction with a mechanical ventilation system, a residential heatexchanger permits the adequate ventilation of a residence while recovering most of the energy normally lost during ventilation. By constructing or retrofitting a home so that it has low natural infiltration rates and by using a heatexchanger-ventilation system, a homeowner can save energy, reduce heating and cooling costs, and prevent the buildup of indoor-generated air contaminants. Results obtained on five different residential heatexchangers are presented. The performance criteria and the test facility are described. The performance parameters measured were heatexchanger effectiveness (a measure of heat transfer ability), airstream static pressure drop, and fan system performance. The performance of the five heatexchangers differed greatly. The ability to transfer heat ranged from 43% to 75% of the theoretical maximum. The resistance to air flow varied by a factor of two. One of the heatexchangers was highly susceptible to leakage between airstreams and one had an unstable performance. In the future, additional heatexchangers will be tested, a new test system will be used to measure cross-stream leakage, and the possibility and consequences of freeze-up within the heatexchangers will be investigated.
A mass and heatexchanger includes at least one first substrate with a surface for supporting a continuous flow of a liquid thereon that either absorbs, desorbs, evaporates or condenses one or more gaseous species from or to a surrounding gas; and at least one second substrate operatively associated with the first substrate. The second substrate includes a surface for supporting the continuous flow of the liquid thereon and is adapted to carry a heatexchange fluid therethrough, wherein heat transfer occurs between the liquid and the heatexchange fluid.
Heat transfer coefficients in a liquid/solid fluidized bed heatexchanger are investigated for application in ice slurry generators. A range of temperature driving forces is determined in which ice slurry generation is stable. In this range ice crystal formation or growth does not affect heat transfer coefficients. A model is proposed that accurately predicts heat transfer coefficients in the fluidized bed ice slurry generator. Due to lower temperatures and higher viscosity in ice slurry generation, heat transfer coefficients measured are lower than predicted with heat transfer correlations specific for liquid/solid fluidized bed heatexchangers. Heat transfer coefficients measured are however significantly higher than for single phase fluid flow. (author)
The objectives of the program reported were: to determine the heat transfer and friction characteristics on the outside of spiral fluted tubing in single phase flow of water, and to assess the relative cost of a heatexchanger constructed with spiral fluted tubing with one using conventional smooth tubing. An application is examined where an isolation water/water heatexchanger was used to transfer the heat from a gaseous diffusion plant to an external system for energy recovery. (LEW)
Recently developed fluid bed heatexchangers offer several advantages over conventional shell-and-tube air-to-air heatexchangers commonly employed in utilizing hot combustion gases to preheat combustion or process air, or to preheat process gases that are to be recycled or incinerated. These advantages include higher heat transfer rates, elimination of tubecleaning requirements, the ability to preheat air and process gases to a constant temperature over a range of combustion gas temperatures and flow rates, and the ability to vary the preheat temperature of fumes to be incinerated according to their hydrocarbon content and flow rate. The fluid bed heatexchanger is approximately 85% efficient in comparison with a maximum shell-and-tube heatexchanger efficiency of about 55%. The fluid bed heatexchanger also offers several advantages over other regenerative-type heatexchangers. They are generally less expensive, take up less floor space, do not require multiple heat-exchange media beds, and do not require valves, dampers, and controls for alternately directing the high and low temperature gases through the stationery media beds. Contaminants in the gases will not adhere to heatexchange media to possibly restrict or block gas flow.
If a large difference in heat transfer coefficients between two sides of an indirect heatexchanger occurs, the transfer area on the side with the lower transfer coefficient is enlarged with fins. A finned tube heatexchanger is one of the most often used compact heatexchanges in automobiles, air-conditioners, and chemical industries. Here, flow and conjugate heat transfer in a high-performance finned oval tube heatexchanger element have been calculated for a thermally and hydrodynamically developing three-dimensional laminar flow. The influence of Reynolds number in the range 100--500 has been studied. Computations have been performed with a finite volume method based on the SIMPLEC algorithm for pressure correction. Flow patterns and pressure distributions are presented. A helical vortex in the tube wake is observed. The shape of the separation zone in the tube wake shows a paraboloid.
In relation to a method of heatexchange between a heat emitting sulphurous, gaseous medium (especially flue gas) and a heat absorbing liquid medium (especially water) in a heatexchanger with a number of heat conducting tubes, the gaseous medium flows outside the tubes and has an intake temperature which is above sulphuric acid's dew point (ca. 150 degrees centigrade) whilst the liquid medium flows into the tubes and has an intake temperatuer which is higher than the dew point of water (50 degrees centigrade). At intervals, the tubes are covered with a layer of a substance which neutralizes sulphuric acid, expecially calcium hydroxide, whilst the gaseous medium, during its flow through the heatexchanger, is cooled to the extent that it has an outlet temperature under the dew point of sulphuric acid. In this way recovery of the heat energy from the gaseous medium is achieved, yet corrosion of the heat tubes is avoided. In the heatexchanger utilized within this method the tubes are placed in vertical sections which can be swung out of the heatexchanger's ''house''. The heatexchanger can especially be used in connection with district heating plants. (AB).
This book presents the papers given at a conference which examined mechanical vibrations in pipes caused by fluid flow. Topics considered at the conference included fluid excitation forces, axial flow induced vibration, fluid damping, crossflow induced vibration of multiple cylinders, two-phase flow, a computer program for vibration analysis, hydrodynamics, heatexchangers, and flow-induced vibrations of condenser tubes.
An experimental heat transfer study of two-phase water flow in vertical thin rectangular channels with side vents is conducted. A multiple, heated channel configuration with up- and down-flow conditions is investigated. Parallel heated and unheated flow channels test the effects of cross flow on the onset of nucleate boiling (ONB) and critical heat flux (CHF). The test apparatus provides pressure and substrate temperature data and visual data of the boiling regimes and side-vent flow patterns. The objectives are to determine the two-phase, heat and mass transfer characteristics between adjacent channels as permitted by side-vent cross flow. These data will help develop ONB and CHF correlations for flow geometries typical of plate-type nuclear reactors and heatexchangers. Fundamentally, the data shows how the geometry, flow conditions, and channel configurations affect the heat transfer characteristics of interior channel flows, essential in understanding the ONB and CHF phenomena.
There are many factors for designing the cross flow fan. Therefore, the performance of cross flow fan is not clear yet. We can analyze the transient flow of a cross flow fan using sliding mesh approach. One of the tasks using Computational Fluid Dynamics (CFD) is a way of modeling for analysis heatexchangers with cross flow fan. These tasks are very important for design. The paper has a modeling of heatexchangers and meshing the fan blades. The next tasks, we focus the ability of cross flow fan when we change the geometry of fan blades.
Using mechanical ventilation with highly efficient heat-recovery in northern European or arctic climates is a very efficient way of reducing the energy use for heating in buildings. However, it also presents a series of problems concerning condensation and frost formation in the heat-exchanger. Developing highly efficient heat-exchangers and strategies to avoid/remove frost formation implies the use of detailed models to predict and evaluate different heat-exchanger designs and strategies. This paper presents a quasi-steady-state model of a counter-flow air-to-air heat-exchanger that takes into account the effects of condensation and frost formation. The model is developed as an Excel spreadsheet, and specific results are compared with laboratory measurements. As an example, the model is used to determine the most energy-efficient control strategy for a specific heat-exchanger under northern European and arctic climate conditions. (C) 2007 Elsevier Ltd. All rights reserved.
An advanced heatexchanger (AHX) was designed, built, and tested in the flue gas stream of a hazardous waste incinerator (HWI). The AHX utilized ceramic composite tubes with stainless steel inner tubes mounted in a bayonet configuration. Bayonet mounting of the tubes was used to enhance heat transfer and to minimize mechanical stresses on the tubes and seals. This represented the first successful industrial operation of a ceramic composite based heatexchanger. During the test, the AHX was exposed to conditions of high-temperature and highly corrosive flue gas, which traditional metal heatexchangers cannot survive. In the six-month field test, the AHX operated continuously for four to five days per week, with shutdown on weekends. During each day of operation, the AHX was subjected to large variations in flue gas flow rates and temperatures. Operating data collected included temperatures and flow rates of the incinerator flue gas and heatexchanger air, pressure drops through the heatexchanger system, and surface temperatures of the ceramic tubes. The degree of air preheat and the ratio of air flow to flue gas flow were varied to determine the effects on heatexchanger performance. Data were evaluated to determine heatexchanger thermal and hydraulic performance. An assessment of ceramic tube performance and predicted life were also made.
A concept for an artificial upwelling driven by salinity differences in the ocean to supply nutrients to a mariculture farm is described and analyzed. A long shell-and-tube counterflow heatexchanger built of inexpensive plastic and concrete is suspended vertically in the ocean. Cold, nutrient rich, but relatively fresh water from deep in the ocean flows up the shell side of the heatexchanger, and warm but relatively saline water from the surface flows down the tube side. The two flowsexchangeheat across the thin plastic walls of the tubes, maintaining a constant temperature difference along the heatexchanger. The plastic tubes are protected by the concrete outer shell of the heatexchanger. The flow is maintained by the difference in density between the deep and surface water due to their difference in salinity. This phenomenon was first recognized by the oceanographer Stommel, who termed it The Perpetual Salt Fountain. The heat transfer and flow rate as a function of tube number and diameter is analyzed and the size of the heatexchanger optimized for cost is determined for a given flow of nutrients for various locations. Reasonable sizes (outer diameter on the order of 5 m) are obtained. The incremental capital cost of the salinity-driven artificial upwelling is compared to the incremental capital cost and present value of the operating cost of an artificial upwell fueled by liquid hydrocarbons.
The goal of this research program is to understand the phenomenon of soil heat transfer coupled with fluid flow, soil moisture freezing, soil moisture migration, and ground surface temperature variation. From these studies, comprehensive ground coil mathematical models are being developed to better predict ground coil heatexchanger performance. The program has been loosely divided into three phases. Phase I was for ground coils involving heat transfer only, which was suitable for deep-well, tube-in-tube type ground heatexchanger analyses. A mathematical model based on energy balance coupled with fluid flow was solved numerically. The model was validated with laboratory experimental data obtained from a vertical, tube-in-tube heatexchanger 47 m (155 ft) deep. Figure 1 shows the configuration of the heatexchanger. Figure 2 shows the excellent agreement between the calculated and experimental results. The parametric study indicates that the size and material of the exchanger casing and the length of the exchanger are important factors in determining the performance of the ground heatexchanger. Table 1 shows monthly ground coil cooling and heating performance. The ground coil system performs better than an air-source heat pump system in the heating season, but the latter is better for the cooling season. Nevertheless, the ground coil system achieved a respectable annual performance factor of 2.4. We have developed various advanced ground coil models for different types of ground coils and various factors affecting soil heat transfer. 13 refs., 8 figs., 1 tab.
Based on the heat transfer characteristics of absorber plate and the heat transfer effectiveness-number of heat transfer unit method of heatexchanger, a new theoretical method of analyzing the thermal performance of heat pipe flat plate solar collector with cross flowheatexchanger 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.
This 4th part deals with heat recovery and the necessary switching for the liquefier. Block diagrams describe various ways of utilizing the heat of hot gas (additional heatexchanger within and outside the boiler). Utilization of hot gas heat does not influence the operation of the refrigerating system (most economic solution). The construction of the heatexchanger is briefly described. Utilization of the total liquefaction heat is dealt with. A specially well suited serial switching system of a compound refrigeration plant is introduced (heat condenser installed before plants regular condenser in flow direction of refrigerant) remarks on the individual valve control steps. (HWJ).
The influence is discussed of the Reynolds number and of the degree and scale of turbulence upon heatexchange at the forward critical point in turbulent flow. It is found that there is a great scatter of the experimental data.
to use mobile robots, automated control, and automated interpretation of .... e.g., inspection of heatexchanger tubes in nuclear power ... into the flow of passenger aircraft ..... and sequential methods with interline-polarization and passive ...
a series of stair-cased deployable rectangular panels that are contained ... source heatexchanger (HSHX), to the main radiator through the gas ..... flow rates and operating temperatures are maintained at ... Total cumulated gamma dose at ...
turbcpumps, gas generators, heatexchangers, valves, flow-ccntrollers ..... system so %hat ea v%sW mems of control will. be avail- able to the we83 edsty .... testing area, 480 square feet for hydraulic component cleaning equip- ment, and 420 ...
control of air pressure in the water vapor measurement subsystem are discussed. ..... where the refrigeration heatexchanger was running colder than the ambient air temperature to effect ..... the ejector to accurately control the sample flow rate.
A practical application of standard convection heatexchangers to preheat combustion air on an unusual shuttle-kiln design is described. This design uses downdraft gas flow and recirculation of the kiln atmosphere throughout the setting during the burn.
A method to optimize the maintenance of large plate heatexchanger installations using conditioning monitoring is developed. The maintenance of large plate heatexchangers is very expensive. An unexpected failure can have dramatic economic consequences. Today regular service is done every 4-5 year. There is a great need to improve the background for deciding the maintenance interval. Slightly decreasing performance (fouling) results in increasing efficiency loss in the heat production system. The lifetime of the gaskets varies depending on especially the water temperature and variation of the temperature. Unexpected gasket failure can lead to water leak and to a close down of the heatexchanger in winter situation, where the heatexchanger is needed. The developed method measures the actual working condition and gives the operator an idea of the condition of the heatexchanger. The method includes a combination of heatexchanger models, models for degradation of the gaskets rubber material based on continuous measurement of water flow and temperatures which is combined with algorithms for degradation of heatexchangers. A procedure is made for analysis of water quality to control the quality especially on the secondary (distribution) side. Another procedure is made for closing down the heatexchanger in summertime, where the needed energy is low. The heatexchanger is kept in a warm condition, to avoid corrosion and to make it easy to start again. The models will be adaptive and practical experience is included. (EG) 18 refs.
The flow structure inside the inner tank and inside the mantle of a vertical mantle heatexchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heatexchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (Author)
The flow structure inside the inner tank and inside the mantle of a vertical mantle heatexchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heatexchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C) 2004 Elsevier Ltd. All rights reserved.
The flow boiling heat transfer characteristics of R134a in the multiport minichannel heatexchangers are presented. The heatexchanger was designed as the counter flow tube-in-tube heatexchanger with refrigerant flowing in the inner tube and hot water in the gap between the outer and inner tubes. Two inner tubes were made from extruded multiport aluminium with the internal hydraulic diameter of 1.1mm for 14 numbers of channels and 1.2mm for eight numbers of channels. The outer surface areas of two inner test sections are 5979mm2 and 6171m2, while the inner surface areas are 13,545mm2 and 8856mm2 for 14 and eight numbers of channels, respectively. The outer tube of heatexchanger was made from circular acrylic tube with an internal hydraulic diameter of 25.4mm. The experiments were perform...
ABSTRACT: This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heatexchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heatexchanger to assess its heatexchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heatexchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heatexchange. The maximum enhanced ratio of heatexchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heatexchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heatexchanger is another important factor to be taken into consideration. PMID:21827644
Due to the presence of large interfaces, heat transfer can be enhanced by the vortices in liquid plugs in microchannel heatexchangers. The heat transfer in liquid plugs moving in microcapillaries with constant-surface-heat-flux boundary condition is investigated. The effects of the Peclet number and the plug length are studied. Higher Peclet numbers and shorter plug length result in higher Nusselt numbers and lower maximum fluid temperature. However, higher Peclet numbers require higher flow speed, while shorter plug lengths result in higher flow resistance coefficients. The pressure drop needs to be considered in the optimization of microchannel heatexchangers.
Numerical analysis of non-isothermal Newtonian flows in plate heatexchanger passages is carried out in the laminar flow region. The results of this analysis are compared with information available in the literature. Some interesting trends are observed for both heat transfer and pressure drop with ...
Optical properties of human whole blood were measured in vitro, at 633 nm with a double integrating sphere set-up, The blood was kept at constant flow through a flow cell while slowly heating the blood from approximately 25 degrees C to 55 degrees C in a heatexchanger, The results show a small but ...
This report describes and documents the development of a counter flowheatexchanger with efficiency of approximately 90% and a highly efficient axial fan both developed for small mechanical ventilation systems for use in single family houses. The report also treats problems concerning condensation and ice formation in efficient counter flowheatexchangers. The influence of condensate and ice is investigated by measurements on an efficient heatexchanger and different strategies for de-icing are tested. A computer program is developed to calculate how condensation and frost influence the heatexchange under stationary conditions. In the project a counter flowheatexchanger of aluminium is developed with a calculated efficiency of approximately 90%. The heatexchanger is hereby legal for ventilation of more than one fire section. CAD drawings of the exchanger are coded to a CNC milling machine and two cylinders (a positive and a negative mould) are produced. The joints of the heatexchanger are glued and placed in a protecting aluminium frame. (BA)
A solar collector having a copper panel in a contiguous space relationship with a condenser-evaporator heatexchanger located under the panel, the panel having a honeycomb-like structure on its interior defining individual cells which are filled with zeolite loaded, in its adsorbed condition, with 18 to 20% by weight of water. The interior of the panel and heatexchanger are maintained at subatmospheric pressure of about 0.1 to 1 psia. The panel and heatexchanger are insulated on their lateral sides and bottoms and on the top of the heatexchange. The panel has a black coating on its top which is exposed to and absorbs solar energy. Surrounding the insulation (which supports the panel) is an extruded aluminum framework which supports a pair of spaced-apart glass panels above the solar panel. Water in conduits from a system for heating or cooling or both is connected to flow into an inlet and discharge from outlet of a finned coil received within the heatexchanger. The collector panel provides heat during the day through desorption and condensing of water vapor from the heated solar panel in the heatexchanger and cools at night by the re-adsorption of the water vapor from the heatexchanger which lowers the absolute pressure within the system and cools the heatexchange coils by evaporation.
A solar collector having a copper panel in a contiguous space relationship with a condenser-evaporator heatexchanger located under the panel, the panel having a honeycomb-like structure on its interior defining individual cells which are filled with zeolite loaded, in its adsorbed condition, with 18 to 20% by weight of water. The interior of the panel and heatexchanger are maintained at subatmospheric pressure of about 0.1 to 1 psia. The panel and heatexchanger are insulated on their lateral sides and bottoms and on the top of the heatexchange. The panel has a black coating on its top which is exposed to and absorbs solar energy. Surrounding the insulation (which supports the panel) is an extruded aluminum framework which supports a pair of spaced-apart glass panels above the solar panel. Water in conduits from a system for heating or cooling or both is connected to flow into an inlet and discharge from outlet of a finned coil received within the heatexchanger. The collector panel provides heat during the day through desorption and condensing of water vapor from the heated solar panel in the heatexchanger and cools at night by the re-adsorption of the water vapor from the heatexchanger which lowers the absolute pressure within the system and cools the heatexchange coils by evaporation.
The study is conducted to evaluate the heat transfer characteristics of two new and versatile enhancement configurations in a double tube heatexchanger annulus. The novelty is that they are usable in single phase forced convection, evaporation and condensation. Heat transfer coefficients are determined by the Wilson Plot technique in laminar and turbulent flow and correlations are proposed for Nusselt numbers. Comparisons are then made between heat transfer and flow friction.
The study is conducted to evaluate the heat transfer characteristics of two new and versatile enhancement configurations in a double tube heatexchanger annulus. The novelty is that they are usable in single phase forced convection, evaporation and condensation. Heat transfer coefficients are determined by the Wilson Plot technique in laminar and turbulent flow and correlations are proposed for Nusselt numbers. Comparisons are then made between heat transfer and flow friction.
Experiments are carried out to investigate the flow characteristics with/without heatexchange in a narrow annulus. In the experiments, directions of flow include horizontal, upstream and downstream flow. Experimental results show that the flow characteristics of water through the narrow annulus are different from those in normal tubes. Flow directions have little influences on the flow friction for the fluid flow in the narrow annulus with/without heatexchange. The flow characteristics in the narrow annulus have relations to the liquid temperature difference at the inlet and outlet of the annulus. Their influences on the flow characteristics are relatively obvious in the laminar flow area. When the Reynolds number is larger than 10{sup 4}, there are little differences between the flow friction factors with/without heatexchange. It is also found that the asymmetrical flow can make the friction factor increase, whereas the symmetrical flow can reduce the flow friction. In the experiments, the transition from laminar to turbulent flow is carefully observed. In the narrow annulus, the flow transition is initiated earlier than that in normal pipes at a Reynolds number range from 1,100 to 1,500, which is different from the heat transfer transition. The results are gained to provide bases for the further investigations on the two-phase flow in narrow annuli. (orig.)
Heatexchanger tube spacers were examined on the basis of their fabricability and resistance to water flow. For current liquid metal heatexchangers, strut spacers are recommended because of their ease of fabrication and superior tube bundle support. This spacer gives exact tube location, no critical welds, and no tube-to-tube tolerances. Tube insent spacers offer the least resistance to flow of all spacers (rings. spirals. and struts) tested, but presented critical tube-to-spacer welds. Total pressure losses in triangular pitch heatexchangers require calculation of pure frictional losses and spacer losses. (auth)
Laboratory experiments of co-axial heatexchangers were carried out in a sand layer. The experiments were intended to investigate characteristics of heatexchange performance under various groundwater flow conditions. Results of laboratory experiments showed that heatexchange rates increase with the increase of groundwater velocity. A three-dimensional numerical model considering advection effect of groundwater flow was developed. The model was verified with the experiment results. Finally, the relationship between apparent thermal conductivity and groundwater velocity was estimated by the developed numerical model in a field scale. The relationship showed that the apparent thermal conductivity increases with the increase of groundwater velocity.
Earth heatexchangers are essential parts of the ground-source heat pumps and the accurate prediction of their performance is of fundamental importance. This paper presents the development and validation of a numerical model for the simulation of energy flows and temperature changes in and around a borehole heatexchanger when a fluid circulates through a U-tube. Based on the time-dependent convection-diffusion equation, the FlexPDE software package is employed to solve the resulting boundary value problem that model a heatexchanger. First, the mathematical model is validated through a comparison with data obtained from experiments with real borehole set-ups in Cyprus. Then the validated model is used to study the heatflow and the temperature variation in the heat-exchanger. Finally conc...
Ice slurry performance in a concentric corrugated tube heatexchanger is experimentally studied in this work in order to compare experimental results to theoretical prediction obtained using the correlations proposed in previous papers. Once the validity of those correlations is verified, the behaviour of the studied heatexchanger is analyzed for different ice slurry flow conditions and compared to the results obtained when a heterogeneous storage is used and only carrier fluid flows through the heatexchanger. According to the performance evaluation criterion used - variation in heat transfer rate for equal pressure drop and surface area - the most remarkable conclusion obtained is that slurry improves the behaviour of the heatexchanger studied for all the cases analyzed, although the increase in heat transfer rate is always lower than 15%, being in most cases lower than 5%. (author)
This experimental work was carried out to obtain basic information on frost melting on a heatexchanger used as a heat pump air conditioner. The heatexchanger working fluid used in this experiment was a 50 wt% propylene glycol aqueous solution. The flow amount G and the temperature T{sub b} of the working fluid were 0.1 {lt} G m{sup 3}/hour {lt} 0.2 and 10 {lt} T{sub b}0{degrees}C {lt} 34, respectively. A melting thermal efficiency {eta} is defined in this paper as the ratio of the net heat for melting to the heat supplied to the heatexchanger until the critical time for melting t{sub c}. {eta} strongly depends on t{sub c}, and t{sub c} is strongly affected by G and T{sub b}. In conclusion, it was found that the heat supplied to the heatexchanger can be utilized with a high {eta} when t{sub c} becomes small.
When liquid helium is supplied to a heatexchanger block upon liquefication/solidification of hydrogen, pressures often fluctuate to change the flowrate and cause temperature pulsation in pipelines and the heatexchanger block from a liquid helium storage vessel to a solid hydrogen injection device. In view of the above, when if gasified helium from the liquid helium storage vessel is transferred by a vacuum heat insulative pipe and the heat is transferred in a state of single-phase flow in the heatexchanger block through the temperature elevation by heat intrusion, flow instability is not caused. After heatexchange, the temperature is elevated to a room temperature at the outside of a vacuum container, the flowrate is controlled by a valve and then it is discharged to the atmospheric air or a gas absorbing system. The temperature for each of heatexchanger blocks is controlled by heating while feeding back signals of a thermometer measuring element. Thus, the problem of flow instability caused by boiling of liquid helium in the heatexchanger blocks and coolants supply pipelines is eliminated, to improve temperature stability. (N.H.).
The papers in this conference were divided into the following sections: Radiation Heat Transfer in Fires; Computational Fluid Dynamics Methods in Two-Phase Flow; Heat Transfer in Microchannels; Thin Film Heat Transfer; Thermal Design of Electronics; Enhanced Heat Transfer I; Porous Media Convection; Contact Resistance Heat Transfer; Materials Processing in Solidification and Crystal Growth; Fundamentals of Combustion; Challenging Modeling Aspects of Radiative Transfer; Fundamentals of Microscale Transport; Laser Processing and Diagnostics for Manufacturing and Materials Processing; Experimental Studies of Multiphase Flow; Enhanced Heat Transfer II; Heat and Mass Transfer in Porous Media; Heat Transfer in Turbomachinery and Gas Turbine Systems; Conduction Heat Transfer; General Papers; Open Forum on Combustion; Combustion and Instrumentation and Diagnostics I; Radiative Heat Transfer and Interactions in Participating and Nonparticipating Media; Applications of Computational Heat Transfer; Heat Transfer and Fluid Aspects of HeatExchangers; Two-Phase Flow and Heat Transfer Phenomena; Fundamentals of Natural and Mixed Convection Heat Transfer I; Fundamental of Natural and Mixed Convection Heat Transfer II; Combustion and Instrumentation and Diagnostics II; Computational Methods for Multidimensional Radiative Transfer; Process Heat Transfer; Advances in Computational Heat and Mass Transfer; Numerical Methods for Porous Media; Transport Phenomena in Manufacturing and Materials Processing; Practical Combustion; Melting and Solidification Heat Transfer; Transients in Dynamics of Two-Phase Flow; Basic Aspects of Two-Phase Flow; Turbulent Heat Transfer; Convective Heat Transfer in Electronics; Thermal Problems in Radioactive and Mixed Waste Management; and Transport Phenomena in Oscillatory Flows. Separate abstracts were prepared for most papers in this conference.
Development of heat transfer enhancement techniques for fin-tube heatexchangers has great importance in industry. In recent years, heat transfer augmentation by vortex generators has been considered for use in plate fin-tube heatexchangers. The present work describes a numerical investigation about the influence of delta winglet pairs of vortex generators on the flow structure and heat transfer of a plate fin-tube channel. The Navier-Stokes and Energy equations are solved by the finite volume method using a boundary-fitted coordinate system. The influence of vortex generators parameters such as position, angle of attack and aspect ratio were investigated. Local and global influences of vortex generators in heat transfer and flow losses were analyzed by comparison with a model using smooth fin. The results indicate great advantages of this type of geometry for application in plate fin-tube heatexchangers, in terms of large heat transfer enhancement and small pressure loss penalty. (author)
The 57 papers are divided into 12 sections covering the following aspects of flow induced vibrations: the analysis of the flow field and excitation forces within arrays of cylinders in cross flow, the analysis of simulation of engineering structures, hydraulic structures and machines, vibration of tube bundles due to two-phase flow, vortex shedding and acoustics, bridges; deck and related sections, vortex shedding, self-excited vibration, structural dynamics and wear of heatexchanger tubes and vibration induced by axial and annular flow. Nine papers concern fluid-structure interaction causing vibrations in reactor steam generators, heatexchangers or fuel assemblies and these are indexed separately. (U.K.).
In the present work the field synergy principle is applied to the optimization design of the shell-and-tube heatexchanger with segmental baffles. The field synergy number which is defined as the indicator of the synergy between the velocity field and the heatflow is taken as the objective function. The genetic algorithm is employed to solve the heatexchanger optimization problems with multiple design variables. The field synergy number maximization approach for heatexchanger optimization design is thus formulated. In comparison with the initial design, the optimal design leads to a significant cost cut on the one hand and an improvement of the heatexchanger performance on the other hand. The comparison with the traditional heatexchanger optimization design approach with the total cost as the objective function shows that the field synergy number maximization approach is more advantageous. (author)
An enhanced decay heat removal system for removing heat from the inert gas-filled gap space between the reactor vessel and the containment vessel of a liquid metal-cooled nuclear reactor. Multiple cooling ducts in flow communication with the inert gas-filled gap space are incorporated to provide multiple flow paths for the inert gas to circulate to heatexchangers which remove heat from the inert gas, thereby introducing natural convection flows in the inert gas. The inert gas in turn absorbs heat directly from the reactor vessel by natural convection heat transfer.
Particulate fouling in an Alfa-Laval P20 plate heatexchanger was investigated using a suspension of aluminum oxide particles in heptane. Process parameters such as flow velocity, heat flux, and particle concentration were varied over a considerable range. In this paper, the influence of the above parameters on the asymptotic fouling resistance is discussed. Measured values of fouling resistance are compared with results for a double-pipe heatexchanger and with the prediction of a fouling model from the literature.
On the basis of analyzing equations of motion, mass transfer, and energy of two-component flux there were determined conditions under which the analogy between heatexchange and mass exchange on their separate and combined occurrence, taking account of the Stefan flux, is valid. It has been established that the difference in heat capacity of flow components has an influence on heat transport by the Stefan flux.
This report describes the work carried out for the development of a downhole bundle heatexchanger for heat recovery from mine water. The temperature of water flowing through mine shafts remains essentially constant at approximately 60 F throughout the year. Therefore, it is warmer than the working fluid in the heating season and colder than the working fluid in the cooling season. In addition, it is available at zero fuel cost, thus making it an ideal candidate for space-conditioning applications. The heat transfer performance of the heatexchanger in a constant temperature water reservoir was studied and experimentally evaluated by installing the heatexchanger in the mine water shafts at Scranton, Pennsylvania and also subsequently at the Ohio State University and the lake at Lackawanna State Park. All these sites provided a stationary water column for installing a heatexchanger, where heatexchange through natural convection could be obtained. Depending on the requirements of the system cycle the heatexchanger could either function on the heating or cooling modes of operation. In tests, spanning over a period of many months, the performance of the downhole bundle heatexchanger was evaluated for both cooling and heating modes of operation.
Electric heating represents the second rank of electricity uses in the industry, behind the rotating machines. Since 1987, a new concept of electric resistance has been developed which is called current flow tube. This technique combines the advantages of electricity (simpleness and easiness of use, preciseness) and the performances of heatexchangers (large surface of exchange and good transfer coefficient). The current flow tube has several applications such as the processing of chemical products, gases, sensible food industry fluids, powders, and the processes involving evaporation or chemical reactions. This technical document presents the principle, installation and uses of current flow tubes in the industry: 1 - definitions: principle, heat transfers, electrical equations; 2 - installation: different parts, thermal and electrical dimensioning, power supply, thermoregulation, safety and regulatory aspects; 3 - differences with other heatexchangers and industrial applications: differences, heating of liquids and gases, thermal processing of thermo-sensible fluids, tracing and un-coagulating, heating of partitioned solids, vaporizing and concentrating, chemical reactors. (J.S.)
Disclosed is a method and apparatus for generating high pressure steam within a well bore. The steam vapor generator is constructed for receiving and mixing high pressure water, fuel and oxidant in a down-hole configuration. High pressure water is received within a heatexchanger constructed around a combustion chamber in an annular sleeve configuration and heated through a thermal wall region forming a lower portion thereof. The combustion chamber utilizes the heat energy of radiation to heat the water flowing in the annular sleeve to the point of steam. The heatexchanger further includes a series of open ended flow tubes which triplicate the length of the flow path of the water prior to egressing from the sleeve. A collection chamber is provided beneath the combustion chamber in communication with the heatexchanger for the mixing of the high pressure vapor and the exhaust thereof into the adjacent well formation.
The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heatexchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.
Nusselt numbers are measured in three counterflow tube-in-shell heatexchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heatexchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under more realistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.
The aim of this article is to take stock of todays knowledge about heat transfers with state change in a phase change material when both liquid and solid phases are in presence: 1 - fundamental aspects: phase change thermodynamics and kinetics, state change with pure conduction heat transfer, state change under forced flow, state change with conduction-natural convection coupling, solidification of multi-compound mixtures; 2 - system aspects: exchange concept (heatexchanges threw a wall, direct contact exchanges), examples of applications (fusion enthalpy heat storage, interface materials, direct induction in cold crucible, metal coating, core meltdown of a nuclear reactor, freezing in dispersed environments). (J.S.)
A fuel delivery system is presented wherein first and second heatexchanger means are each adapted to provide the transfer of heat between the fuel and a second fluid such as lubricating oil associated with the gas turbine engine. Valve means are included which are operative in a first mode to provide for flow of the second fluid through both first and second heatexchange means and further operative in a second mode for bypassing the second fluid around the second heatexchanger means.
A system for protecting components including the heatexchangers of a fluidized bed boiler against thermal mismatch. The system includes an injection tank containing an emergency supply of heated and pressurized feedwater. A heater is associated with the injection tank to maintain the temperature of the feedwater in the tank at or about the same temperature as that of the feedwater in the heatexchangers. A pressurized gas is supplied to the injection tank to cause feedwater to flow from the injection tank to the heatexchangers during thermal mismatch.
A powerful and useful method for heatexchanger analysis is the effectiveness-NTU method. The equations for this technique presented in textbooks, however, are limited to the case where all of the heat transfer occurs between the two fluid streams. In an application of interest to us, cryogenic heatexchangers, we wish to consider a heat leak term. Thus, we have derived equations for the {var_epsilon}-NTU method with heat leak involved. The cases to be studied include evaporators, condensers, and counter-flow, with heat leak both in and out.
An improved system for separating higher boiling hydrocarbon products from methane in a gas/liquid extraction plant. The improvements lies in combining the fractionating tower with a counterflow plate and tube heatexchanger through which the refrigerated low pressure gas flows from top end to bottom end, and the precooled high pressure gas flows upwardly in counterflow relation. The heatexchanger is in the form of an annular chamber with tubes running the full length from bottom to top and plates forcing a zig-zag flow of the cold gas. This sets up a more or less linear temperature gradient which is impressed on the fractionating tower inside of the heatexchanger, which forms the inner wall of the heatexchanger and makes for more efficient and effective fractionation of the entering gas and vapor mixture.
Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heatexchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heatexchangers such as nuclear steam generators, reboilers, coolers, service water heatexchangers, condensers, and moisture-separator-reheaters. Generally, a heatexchanger vibration analysis consists of the following steps: (i) flow distribution calculations, (ii) dynamic parameter evaluation (i.e. damping, effective tube mass, and dynamic stiffness), (iii) formulation of vibration excitation mechanisms, (iv) vibration response prediction, and (v) resulting damage assessment (i.e., comparison against allowables). The requirements applicable to each step are outlined in this paper. Part 1 of this paper covers flow calculations, dynamic parameters and fluidelastic instability.
For reducing the initial cost of geothermal heat pump (GeoHP) systems, the existence of groundwater flow is considered important since the advection effect of groundwater flow can significantly enhance the heatexchange rate at ground heatexchangers (GHEs). In most of the planes of Japan, however, the advection effect cannot be utilized due to the slowness of the groundwater flow. In this study, therefore, we carried out field tests and numerical simulations to evaluate the effects of groundwater pumping, which could generate artificial groundwater flow around the GHEs and hence enhance the heatexchange rates. In the field tests, we carried out four thermal response tests (TRTs) in two types GHEs drilled in Hirosaki City, Japan. The results of TRTs showed that the grouting with permeable materials is more preferable than the grouting with impermeable materials in terms of heatexchange rates since the use of the permeable grouting material allows a closer contact between the heatexchange pipes and the groundwater flow. The effect of groundwater pumping was not clearly observed in the TRTs due to the existence of natural groundwater flow. In the next step, a 3D numerical simulation model was developed to simulate the heatexchange performance of the GHEs with groundwater pumping and was validated using TRT results. Sensitivity studies using the simulation model showed that groundwater pumping can remarkably enhance heatexchange rates in case groundwater flow is slow, though the effect tended to decrease as groundwater flow becomes faster. Cost calculations were also carried out on the basis on the sensitivity studies to conclude that the application groundwater pumping in GHEs could remarkably improve the feasibility of GeoHP systems.
Natural ventilation systems assisted by passive stacks are currently designed without incorporating heat recovery, leading to wasteful heat loss. Heat recovery is not used because the pressure loss caused by a conventional heatexchanger is large and could cause the ventilation system to fail. The heat pipe promises higher capacity because it has much higher thermal conductance than conventional heatexchangers. Individual heat pipes can be independently located in ventilation stacks, making it easier to achieve lower pressure drops. Experimental results show that for a heat recovery efficiency of 50% and stack flow speed of 0.5 m/s, the pressure loss across an existing type of heat-pipe assembly is about 1 Pa. Computer simulation of pressure and flow loss caused by heat pipes was carried out using computational fluid dynamics. It has been shown that heat pipes located at the bottom of the stack produce greater insertion flow loss (IFL) than those located at the top and heat pipes next to the stack walls give rise to less IFL than those in the centre. Furthermore, it has been shown that the IFL is the preferred indicator. The temperature of the heat pipe has a small effect on flow loss performance of the heatexchangers. (author)
Recuperative and regenerative heatexchangers are described. Methods of exhaustion of convective air flows are analyzed in order to find ways of energy conservation. An air flow balance is established, and room air flows and concentrations are specified. A chip- and dust-collecting exhaust ventilation system is proposed in which room air is exhausted only for the machinery in use.
In order to investigate the performance of the micro channel heatexchanger, three-dimensional numerical simulations and experiments on heat transfer behavior and pressure loss were carried out. So far as the heat transfer phenomena is concerned, results obtained using a silicon chip micro channel model showed a very small thermal resistance, about 0.1 (Kcm2/W). And, measured pressure loss showed good agreement with that of analytical result obtained on the basis of fully developed laminar pipe flow assumption. Furthermore, a practical setup was made with a micro channel heatexchanger to clarify the possibility of using the micro channel heatexchanger in electrical equipment. As a result, it was confirmed that the performance of the micro channel heatexchanger system is sufficient to cool a silicon chip which generates a large amount of heat, and the scale of the system is compact compared to that of the whole setup of electrical equipment.
This paper reports the 4th ISAIF including 74 presented papers from 21 countries which was held in Dresden, Germany for 3 days from August 31, 1999. Fields concerned with internal flow are as follows: flows on fan, compressor, turbine and pump, flows in channel, tube, inlet and nozzle, subsonic flow, impact wave boundary layer interference, boundary layer flow, laminar flow, transition flow, turbulent flow, turbulent flow model, heat transfer, mass transfer, heatexchanger, thermal device, chemical process, flow of energy systems, unsteady flow, aerosound, aeroelasticity, multi-phase flow, combustion, non-equilibrium reaction flow, biothermal fluid dynamics, fluid measurement, visualization, experimental technology, and active/passive flow control. 7 keynote addresses were also given. Although the presented papers ranged over various fields, most of them were concerned with internal flow of rotating machines. The author observed the research low-speed axial compressor, supersonic/hypersonic wind tunnel, and cogeneration gas turbine power plant in Dresden Institute of Technology. (NEDO)
A microchannel crossflow fluid heatexchanger and a method for its fabrication are disclosed. The heatexchanger is formed from a stack of thin metal sheets which are bonded together. The stack consists of alternating slotted and unslotted sheets. Each of the slotted sheets includes multiple parallel slots which form fluid flow channels when sandwiched between the unslotted sheets. Successive slotted sheets in the stack are rotated ninety degrees with respect to one another so as to form two sets of orthogonally extending fluid flow channels which are arranged in a crossflow configuration. The heatexchanger has a high surface to volume ratio, a small dead volume, a high heat transfer coefficient, and is suitable for use with fluids under high pressures. The heatexchanger has particular application in a Stirling engine that utilizes a liquid as the working substance.
Ice slurry performance in a concentric corrugated tube heatexchanger is experimentally studied in this work in order to compare experimental results to theoretical prediction obtained using the correlations proposed in previous papers. Once the validity of those correlations is verified, the behaviour of the studied heatexchanger is analyzed for different ice slurry flow conditions and compared to the results obtained when a heterogeneous storage is used and only carrier fluid flows through the heatexchanger. According to the performance evaluation criterion used - variation in heat transfer rate for equal pressure drop and surface area - the most remarkable conclusion obtained is that slurry improves the behaviour of the heatexchanger studied for all the cases analyzed, although the i...
This progress report is for the September--October 1991 quarter. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heatexchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.
The authors examine a coil heatexchanger of the throttle stage of cryogenic helium plants made of tubes with wire fins. The coil heatexchanger represents a bundle of tubes with wire fins encased in a shell and is shown. This heatexchanger design offers a pure countercurrent flow to achieve small temperature differences. The coefficient of hydraulic resistance was investigated under isothermal conditions. The geometrical parameters of the experimental coil heatexchangers with different finning parameters, the composition of the bundle, and the diameter of the coil are given. The investigated designs of coil heatexchangers are being used in the throttle stage of cryogenic helium plants with low and medium refrigerating capacities and as supercoolers in air fractionation units with low refrigerating capacities. Their applications may be expanded to microcryogenic technology.
The structure of a multiple-pass heatexchanger composed of pipes and plate fins is similar to that of heatexchangers used for melting snow. In this study, we investigated the characteristics of a multiple-pass heatexchanger having two types, a regular pitch type and an irregular one, focusing on the brine pipe pitch of the multiple-pass heatexchanger. The perfect melting condition and the melting efficiency were related to the dimensionless parameters of the heatexchanger and its operating conditions. The calculated results for the perfect melting condition and the melting efficiency agreed with the results obtained from field tests on melting of falling snow. Applying the irregular pitch extends the critical condition for perfect melting when the flow rate of brine is low or the area for melting of falling snow is large. Also, the melting efficiency of the irregular pitch is higher than that of the regular pitch.
An evaporator-type cryogenic heatexchanger is designed and built for introducing fluid-solid heatexchange phenomena to undergraduates in a practical and efficient way. The heatexchanger functions at liquid nitrogen temperature and enables cooling of N[subscript 2] and He gases from room temperatures. We present first the experimental results of various parameters which characterize the heatexchanger (efficiency, number of transfer units, heatexchange coefficient, etc) as a function of the mass flow rate of the gas to be cooled. An analysis of the "Nu-Re" diagram is also presented. All experiments were conducted with N[subscript 2] gas. The scope of this tool is readily extended to research purposes. (Contains 9 figures and 1 table.)
A novel laser flow visualization technique is presented together with examples of its use in visualizing complex flow patterns and plans for its further development. This technique has been successfully used to study (1) the flow in a horizontal pipe subject to temperature transients, to view the formation and breakup of thermally stratified flow and to determine instantaneous velocity distributions in the same flow at various axial locations; (2) the discharge of a stratified pipe flow into a plenum exhibiting a periodic vortex pattern; and (3) the thermal-buoyancy-induced flow channeling on the shell side of a heatexchanger with glass tubes and shell. This application of the technique to heatexchangers is unique. The flow patterns deep within a large tube bundle can be studied under steady or transient conditions. This laser flow visualization technique constitutes a very powerful tool for studying single or multiphase flows in complex thermal system components.
This paper addresses the implications of potential flow-induced acoustic and tube vibration problems to the design of a shell-and-tube heatexchanger. Specific design limitations are described in light of the current understanding of flow-induced vibration phenomena. Although various design alternatives can be used to avoid vibration problems, they all exact a penalty in performance or cost. Representative examples are presented where the results from an analysis to check for possible flow-induced vibration problems have voided designs that were otherwise attractive. Design alternatives to avoid these vibration problems are described to illustrate the importance of flow-induced vibration in the final selection of a heatexchanger.
In the present study, the pressure drop characteristics during the boiling of R134a as it flows through the multiport minichannel heatexchangers are presented. The heatexchangers are counter flow tube-in-tubes. The refrigerant flow runs through the inner tube, while the hot water flows through the 25.4mm round tube at outer edge of the heatexchanger. Two inner test sections are made from aluminium tubing with hydraulic diameters of 1.1mm for 14 channels and 1.2mm for eight channels. The experiments were carried out at mass fluxes ranging from 350 to 980kg/(m2s), heat fluxes ranging from 18 to 80kW/m2, and saturation pressures of 4, 5 and 6bar, at constant inlet quality of 0.05. The effect of relevant parameters on the frictional pressure drop, such as the saturation pressure, mass flux,...
This article focuses on the behavior in heatexchangers of an ice slurry composed of fine ice particles inside an ethanol-water solution. The heat transfer and friction characteristics were studied in two double pipe heatexchangers, one with a smooth surface and another with an improved surface. Heat transfer coefficients and pressure drops were experimentally investigated for the slurry flowing in the internal tube with ice mass fractions ranging from 0 to 30% and with flow velocities between 0.3 and 1.9 m s{sup -1}. For some flow velocities, the results showed that an increase in the ice fractions caused a change in the slurry flow structure influencing the evolution of the pressure drops and the heat transfer coefficients. Critical ice fraction values were determined corresponding to a change flow structure from laminar to turbulent motion revealed by the evolution of the friction factor. (author)
Oct 13, 1972 ... An ion-exchange resin, ... CO and these resins provides a CO- removal method which is feasible for cabin ... flows back to the cabin via a condensing heatexchanger. Two of ...... This leads to a gravity-independent gas-liquid ...
While numerous studies have been undertaken to characterize the heat transfer and flow characteristics in microchannels, literature investigating the air-side performance of microchannel heatexchangers is scarce. Air-side heat transfer and flow characteristics were studied through an air to de-ionized water cross-flow serpentine microchannel heatexchanger through air cooling. In the single phase, twenty distinct operating conditions were maintained within the range of air and de-ionized water-side Reynolds number 283Rea1384 and 105Rew159 respectively, retaining the constant inlet temperatures of both fluids (Ta,i=38+-0.5degreeC and Tw,i=9+-0.5degreeC). Heat transfer and fluid flow key parameters were evaluated from experimental data. Heat balance performance was observed within 4% throug...
In these days, studying and developing algorithms which calculate fluid flows which have interfaces or bodies on cartesian grid become trend of computational fluid dynamics area. In this paper, we propose Virtual Flux Method (VFM) which calculates heat and fluid flow around interfaces or bodies on cartesian grid. This method enables to seamlessly calculate heat convection on the surface of the bodies and fluid and heat conduction inside bodies. In three dimensional calculations of shell and tube type heatexchangers, there is a possibility that fluid inside and outside tubes and heatflow between these fluid and tube bodies are calculated without any kind of extra algorithms but VFM. (author)
In pool type Fast Breeder Reactors (FBR) a passive Safety Grade Decay Heat Removal (SGDHR) system removes decay heat produced in the core when normal heat removal path through steam water system is not available. This is essential to maintain the core temperatures within limits. A Decay HeatExchanger (DHX) picks the heat from the pool and transfers the heat to atmosphere through sodium to Air HeatExchanger (AHX) situated at high elevation. Due to the temperature differences existent in the system density differences are generated causing a buoyant convective heat transfer. The system is completely passive as primary sodium, secondary sodium and air flows under natural convection. DHX is a sodium to sodium counter flowheatexchanger with primary sodium on shell side and secondary sodium on tube side. AHX is a cross flowheatexchanger with sodium on tube side and air flows in cross flow across the finned tubes. Capacity of a single loop of SGDHR is 8 MW. Four such loops are available for the decay heat removal. It has been seen that the decay heat removal to a large extent depends on the AHX performance. AHX tested have shown reduced heat removal capacity much as 30 to 40%, essentially due to the bypassing of the finned tubes by the air. It was felt that a geometrically similar AHX be tested in sodium. Towards this a 2 MW Sodium to air heatexchanger (AHX) was tested in the Steam Generator Test Facility (SGTF) constructed at Indira Gandhi Center for Atomic Research (IGCAR), Kalpakkam. The casing arrangement of the AHX was designed to minimise bypassing of air. (authors)
Water flow through model porous media was studied in the presence of surface relaxation, internal magnetic field inhomogeneities and exchange with stagnant water pools with different relaxation behavior, demonstrating how the apparent flow parameters average velocity, volume flow and flow conducting area in these situations depend on the observation time. To investigate the water exchange process a two component biological model system consisting of water flowing through a biofilm reactor (column packed with methanogenic granular sludge beads) was used, before and after a heat treatment to introduce exchange. We show that correction of the stagnant fluid signal amplitude for relaxation at increasing observation time using the observed relaxation times reveals exchange between the two fractions in the system. Further it is demonstrated how this exchange can be quantified.
This thesis, 'Investigation and optimisation of heat storage tanks for low-flow SDHW systems', describes a study of the heat transfer and flow structure in vertical mantle heatexchangers for low-flow Solar Domestic Hot Water (SDHW) systems. The heat storage is a key component in SDHW systems and the vertical mantle heatexchanger is one of the most promising heat storage designs for low-flow SDHW systems. The study was carried out using a combination of experimental and numerical methods. Thermal experiments of mantle heatexchangers with different mantle inlet designs showed that the mantle inlet port with advantage can be located a distance from the top of the mantle. Consequently, the mantle heatexchangers marketed today can be improved by changing the mantle inlet position. The heat transfer and flow structure in mantle heatexchangers are rather complex and the thermal experiments were followed by investigations by means of advanced experimental and numerical techniques such as Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD). Using a transparent glass mantle tank, experimental flow visualisation was carried out with a PIV system. The flow structures inside the mantle and inside the tank were visualised and then compared with the flow structures predicted by CFD-models. The investigations showed that the CFD-models were able to model the flow in the mantle and in the tank correctly. The CFD-models were also validated by means of thermal experiments with a steel mantle tank. With the verified CFD-models, a parameter analysis was carried out for differently designed mantle heatexchangers for different typical conditions to reveal how the mantle tank parameters influence the flow structure and heat transfer in mantle heatexchangers. The heat transfer in the mantle near the mantle inlet port showed to be in the mixed convection regime, and as the distance from the inlet increased, natural convection started to dominate. The heat transfer between the tank wall and the domestic water in the tank is governed by natural convection. Dimensionless heat transfer theory was applied, and Nusselt number correlations for the heat transfer in vertical mantle heatexchangers were developed, based on the CFD-analysis. The CFD-calculations and PIV measurements revealed that thermal stratification is built up in the inner tank above the mantle due to natural convection flow along the tank wall. Based on CFD-calculations, a method was developed for determining the heat transfer caused by the natural convection flow inside the tank. Furthermore, a method was developed for determining the mixing inside the mantle due to the mantle inlet jet. The developed heat transfer correlations, the method for determining the heat transfer in the inner tank caused by natural convection and the method for determining the mixing in the mantle were implemented in a simulation program for SDHW systems, MantlSim. The simulation program predicts the yearly thermal performance of low-flow SDHW systems based on mantle tanks. MantlSim was verified and afterwards used as a tool for heat storage design analysis. The heat storage design analysis showed that vertical mantle heatexchangers could be designed in a better way than done today. (au)
The purpose of the work is to study two-phase mixture heatexchange composed of water particles suspended in silicone oil circulating in a closed loop. Water, contained in polymer porous matrix, is freezing by successive passages in plane plate heatexchanger. Thermo-hydraulic literature data analysis about these fluids in exchangers shows important blanks in exchange coefficient and pressure drop forecast methods and in experimental data. Experimental results, outcome of global energy balance on a test section specifically conceived and made for this study, show doping effect on exchange coefficient. Before phase change, micro-convective effects of rotating particles improve exchange coefficient of 2,3 factor. Supplementary enhancement included between 2 and 16 appeared during phase change. Trial measured discrepancy are certainly induced by bed layer formation due to low flow speed. At the end of particle freezing, when latent heat is not involved anymore in exchange enhancement, important heat transfer reduction is observed. This is attributed to the cooling suspension rheological evolution and the change of flow particle distribution. Modelling results corroborate heatexchange improvement due to phase change: particles act as sources when discharging there latent heat. They stop fluid temperature dropping and enable to keep a high wall temperature gradient. A deepened suspension rheological study is necessary for a better understanding of observed phenomenon, nevertheless these first results show already an important energetic profit brings by particles in range temperature of 0 and -6 deg. C. (author)
For development of a compact SiC heatexchanger, numerical heat transfer analysis was conducted to investigate its performance for a wide range of thermal media, liquid LiPb and helium gas, flow rates. The numerical model used was based on the heatexchanger test module developed by the authors. Within the authors' experimental range, the heat quantity transferred from high temperature liquid LiPb to helium gas and the overall heat transfer coefficients obtained numerically are in agreement with the experimental results. Therefore, the numerical model has proved to be valid for estimation of heat transfer phenomena in the heatexchanger in incompressible regime. The heat quantity transferred from LiPb to He amounts up to 3.7kW at helium pressure of 0.5MPa. On the basis of the numerical res...
Part 1 of this study discusses the diagonal Cartesian method for temperature analysis. The application of this method to the analysis of flow and conjugate heat transfer in a compact heatexchanger is given in Part 2. In addition to a regular (i.e., Cartesian-oriented) fin arrangement, two complex fin arrangements are modeled using the diagonal Cartesian method. The pressure drop and heat transfer characteristics of the different configurations are compared. It is found that enhanced heat transfer and reduced pressure drop can be obtained with the modified fin arrangements for this compact heatexchanger.
This paper presents the relationships for the heat transfer performance of two-stream heatexchangers (THEs) and two-stream heatexchanger networks (THENs) with the entropy generation, the entropy generation number, the revised entropy generation number, the entransy dissipation, the entransy dissipation number and the entransy-dissipation-based (EDB) thermal resistance. The results indicate that the effectiveness only increases with decreasing revised entropy generation number, entransy dissipation number and EDB thermal resistance when the heat capacity flow rates and the inlet temperatures are both fixed. The heat transfer rate increases with decreasing thermal resistance, increasing entropy generation and increasing entransy dissipation for prescribed inlet temperatures and prescribed ...
An investigation of the thermal hydraulic characteristics in the passive residual heat removal system of the System integrated Modular Advanced ReacTor-P (SMART-P) has been carried out using the MARS code, which is a best estimate system analysis code. The SMART-P is designed to cool the system during accidental conditions by a natural convection. The dominant heat transfer in the steam generator is a boiling mode under a forced convection condition, and it is a single-phase liquid and a boiling heat transfer under a natural convection condition. Most of the heat is removed in the heatexchanger of the passive residual heat removal system by a condensation heat transfer. The passive residual heat removal system can remove the energy from the primary side as long as the heatexchanger is submerged in the refueling water tank. The mass flow is stable under a natural circulation condition though it oscillates periodically with a small amplitude. The parameter study is performed by considering the effects of an effective height between the steam generator and the heatexchanger, a hydraulic resistance, an initial pressure, a non-condensable gas fraction in the compensating tank, and a valve actuation time, which are useful for the design of the passive residual heat removal system. The mass flow in the passive residual heat removal system has been affected by the height between the steam generator and the heatexchanger, and the hydraulic resistance of the loop.
Ice slurries can be used both for cold storage in place of chilled water or ice and as a secondary refrigerant since, up to certain concentrations, they can be pumped directly through distribution pipeworks and heatexchangers. For ice slurries to become more widely accepted, however, more engineering information is required on fluid flow and heat transfer characteristics.This paper reports on the results of experimental investigations into the melting heat transfer and pressure drop of 5% propylene/water ice slurry flowing in a commercial plate heatexchanger. Measurements were obtained for ice fractions between 0% and 25% by weight, and flow rates between 1.0 and 3.7 m{sup 3}/h. In this flow range, increasing the ice fractions from 0% to 20% caused around a 15% increase in the pressure drop over the flow range tested. The overall heat transfer coefficient, based on the logarithmic mean temperature difference, was found to remain fairly constant as the ice fraction increased from 5% to 20%. The heat transfer capacity of the heatexchanger was found to increase by more than 30% with melting ice slurry flow compared to chilled water flow.In a practical application, for a given thermal load this would lead to greater than 60% reduction in flow rate and pressure drop compared to chilled water cooling systems. (Author)
The tube plug comprises a one piece mechanical plug having one open end and one closed end which is capable of being inserted in a heatexchange tube and internally expanded into contact with the inside surface of the heatexchange tube for preventing flow of a coolant through the heatexchange tube. The tube plug also comprises a groove extending around the outside circumference thereof which has an elastomeric material disposed in the groove for enhancing the seal between the tube plug and the tube.
According to the invention, the heatexchanger has an array of vertical tubes arranged along one or, preferentially, several cylindrical and coaxial rows and two toroidal collectors; the tubes are extending between the upper and the lower toroidal collectors. A deflector and a casing enveloping the tubes allow the cooling air to flow in contact with the tubes between a vertical inlet conduit and a vertical outlet conduit. The invention applies, more particularly, to heatexchangers used for cooling the secondary liquid sodium coming from a sodium-sodium heatexchanger immerged in the vessel of a fast neutron reactor.
This research investigates the effect of fly-ash deposit on thermal performance of a cross-flowheatexchanger having a set of spiral finned-tubes as a heat transfer surface. A stream of warm air having high content of fly-ash is exchangingheat with a cool water stream in the tubes. In this study, the temperature of the heatexchanger surface is lower than the dew point temperature of air, thus there is condensation of moisture in the air stream on the heatexchanger surface. The affecting parameters such as the fin spacing, the air mass flow rate, the fly-ash mass flow rate and the inlet temperature of warm air are varied while the volume flow rate and the inlet temperature of the cold water stream are kept constant at 10 l/min and 5 C, respectively. From the experiment, it is found that as the testing period is shorter than 8 h the thermal resistance due to the fouling increases with time. Moreover, the deposit of fly-ash on the heat transfer surface is directly proportional to the dust-air ratio and the amount of condensate on heatexchange surface. However, the deposit of fly-ash is inversely proportional to the fin spacing. The empirical model for evaluating the thermal resistance is also developed in this work and the simulated results agree well with those of the measured data. (author)
The heatexchange system in geothermal wells is a system that replaces the air source heat pump and uses underground beds or groundwater as a heat source to heat rooms by collecting underground heat in winter, and cool rooms in summer by operating a heat media circuit in reverse direction through the action of a reverse flow valve to discharge heat underground. This paper describes feasibility investigations on the system including its technical trend for introducing the system technology. Technological and economic discussions were given by classifying the intra-well heatexchange device in its installation direction (horizontal loop type and vertical installation type), underground heatexchange media (antifreeze solution/water cyclic system and direct expansion system), and underground heat transfer (heat conduction system and heat convection system). As a result of discussing each system, it was concluded that the following two systems are promising: A = vertical installation, antifreeze solution/water cyclic and heat conduction system, and B = vertical installation, antifreeze solution/water cyclic and heat convection system. Since the system B was found to have better efficiency and economy among both systems, it is necessary to verify an intra-well heatexchange system and operation methods that suit the system B effectively. 21 refs., 8 tabs.
This report presents the results of an effort to develop and design a unique thermoplastic film heatexchanger for use in an industrial heat pump evaporator system and other energy recovery applications. The concept for the exchanger is that of individual heatexchange elements formed by two adjoining and freely hanging plastic films. Liquid flows downward in a regulated fashion between the films due to the balance of hydrostatic and frictional forces. The fluid stream on the outside of film may be a free-falling liquid film, a condensing gas, or a noncondensing gas. The flow and structural principles are similar to those embodied in an earlier heatexchange system developed for use in waste water treatment systems (Sanderson). The design allows for high heat transfer rates while working within the thermal and structural limitations of thermoplastic materials. The potential of this new heatexchanger design lies in the relatively low cost of plastic film and the high inherent corrosion and fouling resistance. This report addresses the selection of materials, the potential heat transf er performance, the mechanical design and operation of a unit applied in a low pressure steam recovery system, and the expected selling price in comparison to conventional metallic shell and tube heatexchangers.
One of the main components of a closed ice slurry system is the heatexchanger in which ice slurry absorbs heat resulting in the melting ice crystals. Design calculations of heatexchangers are mainly based on heat transfer coefficient and pressure drop data. But experiments presented in this paper show the effect of ice slurry mass flux on heat transfer rate and heat transfer coefficient during melting. For the experiments, ice slurry was made from 6.5% ethylene glycol-water solution, flowing through a 16.91mm internal diameter, 1500mm long horizontal copper tube. The ice slurry was heated by hot water circulated at the annulus gap of the heatexchanger. Experiments of the melting process were conducted with changing the ice slurry mass flux and the ice fraction from 800 to 3500kgm{sup -2}s{sup -1} and 0 to 25%, respectively. During the experiment, it was found that the measured heat transfer rates increase with the mass flow rate and ice fraction; however, the effect of ice fraction appears not to be significant at high mass flow rate. At the region of low mass flow rates, a sharp increase in the heat transfer coefficient was observed when the ice fraction was more than a certain value. Experiments were also conducted to investigate the effect of hot water temperature on the heat transfer coefficient. (author)
An isotopic heat source is formed using stacks of thin individual layers of a refractory isotopic fuel, preferably thulium oxide, alternating with layers of a low atomic weight diluent, preferably graphite. The graphite serves several functions: to act as a moderator during neutron irradiation, to minimize bremsstrahlung radiation, and to facilitate heat transfer. The fuel stacks are inserted into a heat block, which is encased in a sealed, insulated and shielded structural container. Heat pipes are inserted in the heat block and contain a working fluid. The heat pipe working fluid transfers heat from the heat block to a heatexchanger for power conversion. Single phase gas pressure controls the flow of the working fluid for maximum heatexchange and to provide passive cooling.
An isotopic heat source is formed using stacks of thin individual layers of a refractory isotopic fuel, preferably thulium oxide, alternating with layers of a low atomic weight diluent, preferably graphite. The graphite serves several functions: to act as a moderator during neutron irradiation, to minimize bremsstrahlung radiation, and to facilitate heat transfer. The fuel stacks are inserted into a heat block, which is encased in a sealed, insulated and shielded structural container. Heat pipes are inserted in the heat block and contain a working fluid. The heat pipe working fluid transfers heat from the heat block to a heatexchanger for power conversion. Single phase gas pressure controls the flow of the working fluid for maximum heatexchange and to provide passive cooling.
A high-resolution, cryogenic side-entry type specimen stage includes a copper block within which a specimen can be positioned in the electron beam of an electron microscope, one end of the copper block constituting a specimen heatexchanger, means for directing a flow of helium at cryogenic temperature into the heatexchanger, and electrical leads running from the specimen to the exterior of the microscope for four point D.C. electrical resistivity measurements.
This article focuses on the behavior in heatexchangers of an ice slurry composed of fine ice particles inside an ethanol-water solution. The heat transfer and friction characteristics were studied in two double pipe heatexchangers, one with a smooth surface and another with an improved surface. Heat transfer coefficients and pressure drops were experimentally investigated for the slurry flowing in the internal tube with ice mass fractions ranging from 0 to 30% and with flow velocities between 0.3 and 1.9m s-1. For some flow velocities, the results showed that an increase in the ice fractions caused a change in the slurry flow structure influencing the evolution of the pressure drops and the heat transfer coefficients. Critical ice fraction values were determined corresponding to a change...
Abstract in english This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700°C. Experiments were carried out in order to verify the influence of solid particle flow rate and distance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide h (more) eat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heatexchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heatexchanger were experimentally obtained and heat balances for differential control volumes of the heatexchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heatexchanger.
The thermal resistance of heatexchangers has a strong influence on the electric power produced by a thermoelectric generator (TEG). In this work, a real TEG device is applied to three configurations of micro plate-fin heat sink. The distance between certain microchannels is varied to find the optimum heat sink configuration. The particular focus of this study is to reduce the coolant mass flow rate by considering the thermal resistances of the heat sinks and, thereby, to reduce the coolant pumping power in the system. The threedimensional governing equations for the fluid flow and the heat transfer are solved using the finite-volume method for a wide range of pressure drop laminar flows along the heat sink. The temperature and the mass flow rate distribution in the heat sink are discussed. The results, which are in good agreement with previous computational studies, show that using suggested heat sink configurations reduces the coolant pumping power in the system.
The conceptual design of a 600MWe demonstration sodium-cooled fast reactor (hereafter called DSFR-600) has been performed by the Korea Atomic Energy Research Institute (KAERI). In order to enhance plant safety, reliable decay heat removal (DHR) systems with natural circulation flow have been considered, and different kinds of sodium-to-air heatexchangers were employed as an ultimate heat sink for this type of DHR system. The DHR system comprises two diverse heat removal loops, and the heat load imposed on the primary sodium pool is safely rejected into the environment through different shapes of final aircoolers. Serpentine- and helical-coil type sodium-to-air heatexchangers have been considered for the purpose. The former is called FDHX (Forced-draft sodium-to-air heatexchanger) and the latter is simply called AHX. For a general sodium-to-air heatexchanger design, convection resistance at shell-side air flow path becomes a dominant factor affecting the mechanism of conjugate heat transfer from the sodium flow inside the tube to the air path across the sodium tube wall. To this end, performance evaluation of a sodium-to-air heatexchanger is one of the most important tasks to secure the overall performance of a DHR system. This study introduces one-dimensional design approach of a finned-tube sodium-to-air heatexchanger using reasonable heat transfer and pressure drop models, and provides detailed design parameters with heat transfer tube arrangement including the factors of fin-effect. The operational strategy regarding sodium freezing protection of the FDHX unit was briefly discussed as well
The heating load and coefficient of performance (COP) of a class of generalized irreversible universal steady-flowheat pump cycle model with variable-temperature heat reservoirs and the losses of heat transfer, heat leakage and internal irreversibility are investigated by using the theory of finite-time thermodynamics. The universal heat pump cycle model consists of two heat-absorbing branches, two heat-releasing branches and two adiabatic branches. Expressions of heating load and COP of the universal heat pump cycle model are deduced, respectively. By means of numerical calculations, the heat conductance distributions between hot- and cold-side heatexchangers are optimized by taking the maximum heating load as objective. There exist both optimal heat conductance distributions and optima...
A 1032-hr corrosion test was made of two geothermal heatexchanger materials, Allegheny-Ludlum Alloy 29-4 and Alloy 29-4C. Coupons of the two metals were exposed under conditions simulating flow in a geothermal heatexchanger tube. Continuous flow and cyclic exposure tests were made. No signs of localized corrosion were observed in either the base metal, tube weld seam, or heat affected zone. Most coupons showed statistically insignificant weight change. A corrosion rate of less than 0.5 mil/yr is indicated. No significant difference in the performance of the two alloys is reported. (LEW)
An alcohol fuel burner and decomposer in which one stream of fuel is preheated by passing it through an electrically heated conduit to vaporize the fuel, the fuel vapor is mixed with air, the air-fuel mixture is ignited and combusted, and the combustion gases are passed in heatexchange relationship with a conduit carrying a stream of fuel to decompose the fuel forming a fuel stream containing hydrogen gas for starting internal combustion engines, the mass flow of the combustion gas being increased as it flows in heatexchange relationship with the fuel carrying conduit, is disclosed.
The particle image velocimetry has been developed to measure the typical two-phase flow of various work conditions in Membrane Micropore Aeration Bioreactor. The fluid phase is separated out using image processing techniques, which provided accurate measurements for the Bioreactor’s flow field, and makes it possible for quantitative analysis of the momentum exchange, heatexchange and the process of micro-admixture, and initiates a new way for the Bioreactor which mainly designed by the experience at present.
The purpose of this invention is in operating an absorption heat pump to use energy inherent in the stack gases of the heat source of the ejector, where further condensation in the subsequent pipelines should be avoided. According to the invention, this problem is solved by heating the rich solution by means of the stack gases of the heat source, and mixing the stack gases with the air flow feeding the evaporator, after they were previously dried by the air leaving the evaporator by subcooling. A stack-gas heatexchanger and a drying heatexchanger are situated in the stack gas pipe. The drying heatexchanger is situated in the evaporator air duct. The outlet of the stack gas pipe is situated in the air duct upstream of the evaporator.
Heatexchange methods must be efficient in order to minimize the patient's pump time. However, comparisons of heatexchangers have been rare. Therefore, the in vivo functions of the most popular, currently available heatexchangers, Sarns, Cobe, Medtronics Maxima, and an experimental model manufactured by Haemonetics were compared. Thirty-two pigs weighing between 63-74 kg were placed on cardiopulmonary bypass with right atrial and ascending aorta cannulation through a right thoracotomy. Thermocouples were placed in the pump tubing before and after the heatexchangers, in the water line before and after the heatexchangers, in the inlet and outlet line of the pump, and the esophagus, brain, bladder, rectum, liver, myocardium, and tympanic membranes of the pigs. They were cooled until the bladder temperature was reduced to 14 degrees C, and maintained at that temperature for 10 minutes. Rewarming was begun until the bladder temperature became 37 degrees C. The pump flow was maintained between 50-60 ml/kg/min with standard ventilation. Cobe, Sarns, Maxima, and Haemonetics heatexchangers were tested and their function determined by comparing the time necessary for rewarming. The Haemonetics heatexchanger required a significant shorter time than the others to rewarm the pigs to normal bladder temperature (Cobe 82.0 +/- 12.0, Sarns 80.3 +/- 15.4, Maxima 89.0 +/- 13.9 Haemonetics 68.7 +/- 13.4, p < 0.05). The principal advantage was seen at the lowest temperatures between the Haemonetics experimental heatexchanger and the other heatexchangers. No statistically significant superiority was seen at higher temperatures. The current heatexchangers are relatively comparable but improved performance is possible with available technology. PMID:8922264
In the present work an experimental investigation was conducted to obtain a correlation for the determination of convective heat transfer coefficients of stirred yoghurt in a plate heatexchanger. A rheological study was carried out in order to characterise the stirred yoghurt flow behaviour, evalua...
The convective heat transfer characteristics in a periodic converging-diverging heatexchanger channel are investigated experimentally. Experiments were performed for Prandtl number 0.7, for corrugation angle of 30 . In order to determine the channel having the best performance, the channels also compared by considering the flow area goodness factor. (orig.)
The convective heat transfer characteristics in a periodic converging?diverging heatexchanger channel are investigated experimentally. Experiments were performed for Prandtl number 0.7, for corrugation angle of 30?. In order to determine the channel having the best performance, the channels also compared by considering the flow area goodness factor.
A continuous two-phase (air-liquid), slug flow, tubular heatexchanger was developed for microbial thermal inactivation research to give exposure times and temperatures in the range of high-temperature, short-time milk pasteurization as well as heat-treated sample volumes of at least 2 ml. The use o...
Uranine, chloride, and ?D breakthrough curves are nearly identical. Water exchangesheat with aquifer, producing a modified thermal signal at spring. Thermal signal and heat transport model are used to estimate hydraulic diameter. Different tracers provide unique information about flow path.
TRANSIENT HEAT TRANSFER MODEL OF THE JPL BOILER- .... temperature differences in the liquid metal heatexchanger are in the order of 100°F, .... The idealization that thermal delay times due to finite liquid flow velocities ...... '2d '2d. 7 '= 2. 3. An analytical expression for the vapor pressure - temperature relation- ...
A heat pump system is described having a heatexchange circuit including a hot side and a cold side and having a hot side heatexchanger (HSHE) and a cold side heatexchanger (CSHE). The CSHE is connected to a water supply circuit, the improvement wherein the CSHE is provided with conduit means through which water flows, a cooling refrigerant externally of the conduit means and in contact therewith. The conduit means have a very small internal diameter as compared to its length whereby the water is capable of being supercooled in its quasi-stable liquid state to temperatures below OC and on a continuous basis in the conduit means of the cold side heatexchanger. The conduit means have an isolated area immediately upstream of the cooling refrigerant to thermally isolate the water from the cooling refrigerant to prevent freezing of the water prior to entry into the conduit means in contact with the refrigerant.
The availability of computational methods to simulate fluid flow in the complex, three-dimensional geometry of heatexchangers recently prompted the development of a HeatExchanger Vibration Analysis (HXVA) method that accounts for nonuniform flow velocity distributions in the determination of fluidelastic tube bundle instabilities. The concurrent acquisition of flow-induced vibration (FIV) test data for several configurations of an industrial-size shell-and-tube heatexchanger made possible this evaluation of the HXVA method for six cases. The ability to predict the overall heatexchanger pressure drop with the hydrodynamic code COMMIX-IHX was good. Another useful capability of the HXVA method is the ability to predict the general location of the tubes most susceptible to FIV instabilities, in particular, those tubes located along the baffle cut in the baffle flow windows. However, finer discrimination of susceptibility between the tubes along the baffle cut was not possible and is believed to be beyond the current state-of-the-art. Also, global prediction of critical flowrates was better than local predictions. The predicted lowest critical flowrate (for safe heatexchanger operation) was less than 20% too large in four of the six cases and less than 50% too large in the other two cases. However, errors in predicting the critical flowrates of individual tubes were as large as 100%. Recommendations to improve the prediction capability were made, with priority on the excitation mechanism for dense fluid flows with nonuniform velocity distributions.
Proceedings includes 8 papers dealing with flow-induced vibration in conjunction with the advancement in nuclear power reactor technology. Topics covered include: flow of fluids, ship joints, heatexchangers, steam condensers, and structural design procedures for submerged structures. All papers are abstracted and indexed separately.
This paper discusses the creation of heatexchangers where their energy capacity and metal content may be reduced to increase their productivity by an average of 10%. The author considers a unified economical method of numerical solution of conjugate problems of heatexchange, in both the detailed and semidetailed statements, for one-sided and two-sided concurrent flow and counterflow over a solid body by heat-transfer agents, in orthogonal coordinate systems, the coordinate lines of which coincide with the boundaries of the solid body (in this case the temperature field of the heat-transfer agents can be analyzed in other coordiante systems). The method is developed for the case when heat transfer by heat conduction in the heat-transfer agents in the direction of their flow can be neglected.
Heat pump systems using treated sewage water as the heat source were used in the Beijing Olympic Village for domestic heating and cooling. However, considerable biofouling occurred in the plate heatexchangers used in the heat pump system, greatly limiting the system efficiency. This study investigates the biofouling characteristics using a plate heatexchanger in parallel with a flow cell system to focus on the effect of calcium ions on the biofilm development. The interactions between the microorganisms and Ca^2^+ enhances both the extent and the rate of biofilm development with increasing Ca^2^+ concentration, leading to increased heat transfer and flow resistances. Three stages of biofouling development were identified in the presence of Ca^2^+ from different biofouling mass growth rat...
An experimental and analytical project to study the design of vertical, concentric-tube ground-coupled heatexchangers for use in heat pump applications is described. The experimental apparatus consists of a concentric configuration of two 155-ft (47.2-m) polyvinylchloride (PVC) pipes (sealed at both ends with connections so that hot or cold water could be pumped through the system) with instrumentation to measure heat transfer. This heatexchanger was placed in a well with an 8-in (0.20-m) inside diameter (ID), which was backfilled with sand to establish good thermal contact. Heat transfer was measured for heatexchanger operation under several sets of operating conditions. A mathematical model was developed and converted into a computer program to simulate the operation of the ground-coupled heatexchanger. Data collected using the experimental apparatus was used to validate the computer program, and the computer model was then used to study the effects of variations in heatexchanger length, diameter, flow rate, and thermal conductivity and the thermal conductivity of the ground on the heatexchanger performance. Results are presented.
An experimental and analytical project to study the design of vertical, concentric-tube ground-coupled heatexchangers for use in heat-pump applications is described. The experimental apparatus consists of a concentric configuration of two 47.7-m (155-ft) PVC pipes (sealed at both ends with connections so that hot or cold water could be pumped through the system) with instrumentation to measure heat transfer. This heatexchanger was placed in a 0.20-m (8-in.) inside-diameter well and backfilled with sand to establish good thermal contact. Heat transfer was measured for heat-exchanger operation under several sets of operating conditions. A mathematical model was developed and converted into an ANSI standard FORTRAN IV computer program to simulate the operation of the ground-coupled heatexchanger. Data collected using the experimental apparatus was used to validate the computer program, and the computer model was then used to study the effects of variations in heat-exchanger length, diameter, flow rate, and thermal conductivity and the thermal conductivity of the ground on the heat-exchanger performance. Results are presented.
Various design parameters of compact heatexchanger-reactors have been characterized in order to develop a new methodology for their design and optimization. This process, combining heatexchange and chemical reaction at the same place, achieves a technological break. Nowadays, most of the batch processes could be carried out continuously. The use of compact heatexchanger as a chemical reactor constitutes a significant break trough towards a new approach of chemical processes. Indeed, mixing heat transfer and chemical reaction at the same place could improve largely on one hand the final product quality and on the other hand the process safety. In order to answer the compelling operation requirements, heat and mass transfer phenomena must be precisely investigated. This knowledge allows to set up criteria for the channel basic geometry selection. These studied structures are close to those used in compact heatexchangers for their good thermal and hydraulics characteristics (Offset Strip Fins and metallic foams). Therefore, by using an original physico-chemical method, micro-mixing and thermohydraulics of turbulent flows have been studied to compare heat and mass transfer performance of selected geometries. Moreover, a process simulation based on serial mixer connection model has been validated by experimental exothermic reactions achieved with a heatexchanger reactor prototype. Finally, a thermo-hydrodynamic and micro-mixing database has been built. Based on the results of this study a substantial data base is built. Using this database a novel process modeling has led to a creative design of future compact heat-exchanger reactors. (author)
In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results. (author)
Significant improvements in efficiency for electricity generation from coal can be achieved by cycles that employ a high-temperature, highly recuperative gas turbine topping cycle. The principal difficulty of employing a gas turbine in a coal-fired power generation system is the possible erosion and corrosion of the high-temperature rotating gas turbine components caused by the coal`s inorganic and organically bound constituents (ash, sulfur, and alkali metals). One route to overcome this problem is the development of an externally fired gas turbine system employing a coal fired heatexchanger. The solution discussed in this paper is the design of a Radiatively Enhanced, Aerodynamically Cleaned Heat-Exchanger (REACH-Exchanger). The REACH-Exchanger is fired by radiative an convective heat transfer from a moderately clean fuel stream and radiative heat transfer from the flame of a much larger uncleaned fuel stream, which supplies most of the heat. The approach is to utilize the best ceramic technology available for high-temperature parts of the REACH-Exchanger and to shield the high-temperature surfaces from interaction with coal minerals by employing clean combustion gases that sweep the tube surface exposed to the coal flame. This paper presents a combined experimental/computational study to assess the viability of the REACH-Exchanger concept. Experimental results indicated that the REACH-Exchanger can be effectively fired using radiation from the coal flame. Both computation and experiments indicate that the ceramic heatexchanger can be aerodynamically protected by a tertiary stream with an acceptably low flow rate.
A method and apparatus are described to recover thermal energy from the exhaust air from a paint spray booth for painting of automobile chasses. Heatheat from the relatively warm exhaust air is transferred to the relatively cold supply air to the booth. The outgoing air is mixed with water or other heat-exchange liquid, and the liquid is then separated in a separation-chamber adjacent the ventilation outlet of the booth, and is circulated between the chamber and a heatexchanger, through which the supply air flows.
The velocity field in a vortex heat cell was investigated experimentally using laser Doppler velocimetry for a wide range of flow conditions. Experimental results point out the three dimensionality of the exchanger's flow, which is composed into a main vortex flow developing along the side walls. The strength of the flow increases up to a limiting value reached for a Reynolds number ranging between 15,000 and 30,000; a secondary flow, caused by interaction between centrifugal and inertial forces, extends perpendicularly to the main flow and remains Reynolds number dependent. It is composed of multiple counter-rotating structures occurring at the exchanger periphery with low inlet Reynolds numbers, thus reducing the rate of centripetal momentum transfer. With increasing inlet Reynolds number, the secondary flow extends across the whole exchanger radius, thus increasing the rate of mixing of the treated fluid. The appearance of so-called Taylor-Goertler vortices tends to reduce the z- and r-axis vorticity transfer. (orig.)
The thermal resistance of heatexchangers has a strong influence on the electric power produced by a thermoelectric generator (TEG). In this work, a real TEG device is applied to three configurations of micro plate-fin heat sink. The distance between certain microchannels is varied to find the optimum heat sink configuration. The particular focus of this study is to reduce the coolant mass flow rate by considering the thermal resistances of the heat sinks and, thereby, to reduce the coolant pumping power in the system. The three-dimensional governing equations for the fluid flow and the heat transfer are solved using the finite-volume method for a wide range of pressure drop laminar flows along the heat sink. The temperature and the mass flow rate distribution in the heat sink are discusse...
The simulation studies are made to understand the concept of heat transfer by convection in a rectangular coiled type heatexchanger. The rectangular coil heatexchanger consists of inner and outer coil arrangements with several straight portions and bends so that the exterior flow is very similar to flow within tube-bundles. The present work focuses mainly on exploring the various flow pattern and temperature distribution through the pipe. Computer simulation studies were performed for four different angle of tube bundle inclination (0°, 30°, 60°, and 90°) with two set flow arrangements (inline and staggered arrangement) in the shell side of the heatexchanger. The simulation results show that the effect of the tube bundle inclination on the fluid velocity distribution and the heat transfer performance is observed maximum for the coil with tube bundle inclination angle between 30 degrees and 60 degrees with the staggered arrangement than with the inline arrangement due to proper mixing in the shell side and the outside flow over the tube bundle helps to create turbulence without increasing the velocity in the shell side of the heatexchanger.
This paper dealt with the flow and cold heat-storage characteristics of the oil (tetradecane, C{sub 14}H{sub 30}, freezing point 278.9 K)/water emulsion as a latent heat-storage material having a low melting point. A coiled double-tube heatexchanger was used for the cold heat storage experiment. The pressure drop, the heat transfer coefficient, and the finishing time of cold heat storage in the coiled tube were measured as experimental parameters. It was understood that the flow behavior of the emulsion as a non-Newtonian fluid had an important role in the present cold heat storage. The useful nondimensional correlation equations for the additional pressure loss coefficient, the heat transfer coefficient, and the cold heat storage time were derived in terms of modified Dean number and heat capacity ratio. 11 refs., 13 figs., 1 tab.
We are currently investigating the engineering feasibility of drilling into an active magma body at a depth of roughly 5 km from the earth's surface, establishing a downhole heatexchange region, and extracting thermal energy from the magma body by circulating fluid through this heatexchange region. In the present paper, we evaluate the overall thermodynamic performance of various conceptual magma energy systems in which energy is added as heat to the fluid within the magma region and is converted to useful work in a power conversion cycle at the surface. Unusually high return temperatures and pressures may be available at the wellhead of such a circulating well. Cycles investigated here are an open Rankine power system in which steam from the magma well is circulated directly through a power conversion cycle and a closed Rankine cycle where the heated fluid from downhole is circulated through an aboveground heatexchanger to heat the cycle fluid. The downhole heatexchange region is established during the drilling process. As drilling proceeds into the magma, a solidified layer forms about the drilling tube due to heatexchange to the fluid. This solidified layer thermally fractures because of large temperature gradients between the cooled inner region and the heated outer region, thereby opening secondary flow paths. Two models of the downhole behavior have been used. In the simplest approach, denoted as the ''infinite area model,'' the water entering the pipe to return to the surface is assumed to be always at the temperature of the magma, independent of mass flow rate and other parameters. The other model is more detatiled and the fractured heatexchange region is modelled as a cylindrical porous layer through which fluid flows vertically. The net power and the performance aspects for the systems are investigated in terms of various parameters, including the characteristics of the downhole heat transfer.
The shell and tube heatexchangers were introduced to apply to a big capacity condenser and a high pressure feed water heater for power plant in the beginning of 1990s. Design and manufacturing technology for shell and tube heatexchangers have been developed until now. But it is very difficult to calculate the expected performance characteristics of the shell and tube heatexchanger, because there are many design parameters to be considered according to internal structure and the shell side heat transfer mechanism complicately related to the design parameters. Design parameters to be considered in the design stage of shell and tube heatexchanger are shell and tube side fluids, flow rate, inlet and outlet temperature, physical properties, type of heatexchanger, outer diameter, thickness, length of tube, tube arrangement, tube pitch, permissive pressure loss on both sides, type of baffle plate, baffle cutting ratio. The propose of study is an analysis TEMA(Tubular Exchanger Manufacturers Association) E shell and tube heatexchanger performance with changing a number of baffles(3, 5, 7, 9, 11) and tubes(16, 20) and determined optimal baffle spacing. (author). 11 refs., 12 figs., 2 tabs.
The flow structure in a plate fin and tube heatexchanger model composed of single cylinder located between two parallel plates for duct height-to-cylinder diameter ratio of 0.365 for Reynolds numbers of 4000 and 7500 is investigated experimentally. Particle image velocimetry (PIV) technique is employed to obtain instantaneous, time-averaged and phase-averaged turbulent flow characteristics in the heatexchangerflow passage. Interactions between the main flow and the secondary flow are examined in detail in the horizontal and vertical planes of the flow passage. Horseshoe vortex system formed in close region of cylinder-plate junction and convected downstream in the main flow direction and its evolution in the circumference of the cylinder is also investigated in detail.
Simplified mathematical models are developed to describe the extraction of thermal energy from magma based on the concept of a counterflow heatexchanger inserted into the magma body. Analytical solutions are used to investigate influence of the basic variables on electric power production. Calculations confirm that the proper heatexchangerflow path is down the annulus with hot fluid returning to the surface through the central core. The core must be insulated from the annulus to achieve acceptable wellhead temperatures, but this insulation thickness can be quite small. The insulation is effective in maintaining the colder annular flow below expected formation temperatures so that a net heat gain from the formation above a magma body is predicted. The analyses show that optimum flow rates exist that maximize electric power production. These optimum flow rates are functions of the heat transfer coefficients that describe magma energy extraction. 15 refs., 3 figs.
Several solutions are currently being tested to improve the thermal efficiency of ground heatexchangers (GHEs) employed in geothermal closed loops. For shallow exchangers, the main effort is towards maximizing the surface available for heatexchange, while reducing the interference among exchangers; popular solutions towards this end are the slinky coil and the radiator shape. Recently, the flat panel has been proposed as a novel alternative to horizontal exchangers. In this study, the performance and thermal impact of the radiator and flat panel installations are compared by solving the transient flow and heat transport problem within the surrounding ground via a numerical model. Adopting the same computational conditions, the two installations yield different resulting domain thermal fi...
Ammonia, an environment friendly natural refrigerant with attractive thermo-physical properties is a potential replacement of the synthetic refrigerants with high ozone depletion and global warming potentials. Experimental heat transfer and pressure drop data are obtained for two phase evaporation of ammonia in a commercial plate heatexchanger for symmetric 30^o/30^o chevron plates. The plate heatexchanger was configured in a single pass U-type counter flow arrangement with liquid ammonia evaporating in upward flow direction and glycol/water solution simulating the heat load in counter flow. Experiments were carried out for saturation temperatures ranging from -25 ^oC to -2 ^oC. The heat flux was varied between 21 kW m^-^2 and 44 kW m^-^2. Experimental results show significant effect of ...
The papers in the first section cover falling films and heat transfer. Papers in the second section address issues associated with heatexchangers, such as: plate-and-frame heatexchanger technology; thermal design issues; condensation; and single-phase flows. The papers in the third section deal with studies related to: the turbulent velocity field in a vertical annulus; the effects of curvature and a dissolved noncondensable gas on nucleate boiling heat transfer; the effects of flow obstruction on the onset of a Ledinegg-type flow instability; pool boiling from a large-diameter tube; and two-dimensional wall temperature distributions and convection in a single-sided heated vertical tube. Separate abstracts were prepared for most papers in this volume.
The new concept of the safety graded decay heat removal system (SGDHRS) is suggested to complement the weakness of the existing passive decay heat removal circuit (PDRC) of KALIMER-600 in the long-term cooling capability. Components of the decay heat removal system in both concepts are the same. The system is operated by natural circulation flow which consists of a DHX (Decay HeateXchanger), an AHX (Air HeateXchanger), and piping system connecting two heatexchangers. The DHX of PDRC partly submerged in the cold pool; on the other hand, it is fully submerged in hot pool side. For the comparison of the long-term cooling capability of both systems, a LOOP (Loss Of Offsite Power) of KALIMER- 600 reactor was analyzed using two types of DHX's using the MARS-LMR system analysis code
For hypersonic potential-use pulse detonation rocket engines (PDREs), the detonation chamber must stand against the high intensity of waste heat by fuel active cooling which in turn preheats and promotes liquid hydrocarbon fuel to crack into lower-molecular-weight carbon alkenes. The purpose of this research was to study the beneficial effects of the fuel pretreatments on PDRE performance, which comprised preheating and adding additives. Firstly, five concentric-counter-flowheatexchangers based on active cooling were tested to investigate the effect of geometric dimension on the heating efficiency. The results showed that the optimum length and thickness of annular heatexchange section were 300mm and 5mm, respectively. The heating capacity of the heatexchanger based on active cooling w...
Recently, fluidized bed heatexchangers with circulating liquid are widely used in a number of places-chemical, process, food concentration, waste water treatment facilities, etc. In a circulating heatexchanger. solid particles circulate with the liquid, thereby increase the heat transfer and reduce the fouling potential of the heatexchanger. In this study, glass beads were circulated through a vertical tube. The pressure loss and the heat transfer coefficient were measured. At low flow velocities, glass beads enhanced the heat transfer considerably. The enhancement increased as the volume fraction of the glass beads increased. The pressure loss showed a similar trend. From the observed particle behavior near tube wall, a possible explanation of the trend is provided. (author). 15 refs., 13 figs.
This article investigates the effectiveness of embedded vortex generators in enhancing the heat transfer performance of a plate-fin heatexchanger with a four-row staggered oval tube bundle. Two different types of vortex generator are considered, namely annular and inclined block. Numerical simulations are performed to analyze the effects of the three-dimensional turbulence induced by the vortex generators on the heat transfer and fluid flow characteristics of the heatexchanger. The results indicate that compared to a plate-fin heatexchanger with circular tubes, the use of oval tube fins and vortex generators increases the heat transfer rate by 3 to 16% and reduces the pressure drop by 17 to 35% for inlet velocities in the range of 1 to 8 m/s. Furthermore, the vortex generators make poss...
Direct magma energy extraction forces water into magma using a single pipe to flow it into fractured and solidified magma and exchangesheat to recover hot water. With an objective to acquire knowledge about behavior of solidified region around the heatexchanging portion and transitional response for the heat extraction rate, this paper describes preparation and discussion on a three-dimensional axially symmetrical model. As a result, a number of useful findings were obtained which may be summarized as follows: the solidification region grows as time passes, but upon elapsing about 3,000 hours after starting the heat extraction, the growth rate slows down remarkably; coefficient for average heat transfer from the solidification region to the fracture region, the fracture radius, and water temperature and flow rate at the fracture region entrance were varied to calculate the heat extraction rates, and as a result, the water flow rate at which the maximum output may be anticipated to be obtained is 10 to 20 kg/s; and in order to execute magma heatexchange efficiently, it is effective to keep the water temperature at the fracture region entrance high at a certain degree by exchanging the heat at a depth shallower than magma. 12 refs., 10 figs.
The present work describes the optimisation of a compact steam reformer for light fuel oil and diesel fuel. The reformer is based upon a catalytically coated micro heatexchanger that thermally couples the reforming reaction with a catalytic combustion. Since the reforming process is sensitive to reaction temperatures and internal flow patterns, the reformer was modelled using a commercial CFD code in order to optimise its geometry. Fluid flow, heat transfer and chemical reactions were considered on both sides of the heatexchanger. The model was successfully validated with experimental data from reformer tests with 4kW, 6kW and 10kW thermal inputs of light fuel oil. In further simulations the model was applied to investigate parallel flow, counter flow and cross flow conditions along with...
The diagnosis of heatexchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet-outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heatexchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow mal-distribution diagnosis in the case of multi-phase heatexchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. 81mKr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer re...
The study is conducted to evaluate the flow characteristics in a double tube heatexchanger 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.
In order to investigate the optimum locations for the installation of ground-coupled heat pump system, heatexchange rate maps in the Fukui Plain were developed. For the estimation of the heatexchange performance at difference location in the plain, a single ground heatexchanger (GHE) model was constructed. The results of the field-wide groundwater flow-heat transfer modeling by Uchida et al. (2010), such as local hydraulic head and the distribution of subsurface temperature, were used as the boundary and initial conditions of the single GHE model. And then, the heatexchange rates in the cases of the snow melting and the air conditioning were estimated at 13 locations in the plain. The developed ground heatexchange rate maps using the results from the single GHE models were compared with the geological, hydrological and thermal information of the plain. As the result, the geological information (the rate of sand gravel layer thickness) was successfully linked with the ground heatexchange rate maps.
Experiments were conducted to evaluate four techniques to improve the energy efficiency of electrically-heated domestic clothes dryers. Reduced air flow rate and heater input led to energy savings around 8%, while recirculation of a portion of the exhaust air back into the clothes dryer reduced energy consumption by approximately 18%. These two measures are attractive because of their low cost. Two modes of using an air-to-air heatexchanger for heat recovery were considered. The first is to preheat the inlet air with heat from the exhaust air, which resulted in 20 to 26% energy savings. The second mode is 100% recirculation of air through the dryer and a heatexchanger and condensation of water from this air in the heatexchanger by using indoor air. as a heat sink. This resulted in 100% heat recovery (i.e., all heat was rejected to indoors) but the energy consumption of the dryer was increased by up to 6%. To maximize energy savings, a clothes dryer with a heatexchanger can be equipped to operate in the preheating mode in the summer and in the recirculation/condensation mode in the winter. The last measure investigated recirculation, through a heat pump (i.e., dehumidifier), also resulted in a 100% heat recovery and, in addition, up to a 33% reduction in dryer energy consumption, but this technique also yielded long drying times.
The ''standard heatexchanger network problem'' has been suprisingly difficult to solve. It is only now that simple and reliable methods have evolved to synthesize the most efficient network of heatexchangers to heat and cool known process streams between stated temperature bounds. This has taken over a decade of research and scores of publications. The ''resilient heatexchanger network problem'' requires a solution that can cope with the uncertainties of industrial design. Fixed flow rates and temperature bounds rarely occur industrially. Rather, an industrial heatexchanger network problem necessarily involves ranges of flow rates and ranges of temperature bounds, and must include ease of operation and control. In this paper we make several fundamental advances in the design of resilient heatexchangers networks. (1) An efficient design procedure is developed to yield resilient designs which handle fluctuations within the condition of maximum energy efficiency. (2) A control structure and operating policy are developed to adjust flow distributions in the network to meet temperature constraints with minimum utility usage. These developments are based on several new theorems concerning resiliency in network design.
In order to scale-up Circulating Fluidized Bed boilers (up to 600 MWe), Electricite de France has initiated a Research and Development program including: laboratory work on mock-up, numerical modeling and on-site tests in the 125 MWe CFB Emile Huchet plant. This paper is devoted to on-site measurements analysis in two main components of this industrial unit: the external fluidized bed heatexchangers and the backpass. This study particularly concerns hydrodynamics and heat transfer with the final target of developing a physical model of a CFB unit. The first part of this paper describes the specific instrumentation set up on external fluidized bed heatexchangers. The comparison between experimental data collected on these heatexchangers and the theoretical heat transfer models mainly used, shows a great difference about the value of the overall heat transfer coefficient. To explain this discrepancy, the particle flow pattern initially used in the thermal balance calculation is modified and a solid bypass is introduced. The analysis of the by-pass behavior, connected to the geometrical and operating parameters of each exchanger, confirms the particle flow pattern suggested. The second part of this paper shows an analysis of the specific measurements set up on the backpass to study heat transfer. The physical model of heat transfer used to assess the importance of each convection, radiation and conduction components is presented. This model allows one to assess the influence of heatexchangers design on heat transfer. Moreover, the analysis of heat transfer variations during sweeping cycles gives the amount of dust that is removed from the heatexchanger tubes. These results are used to evaluate the amount of power that can be recovered by optimizing both design and sweeping of the backpass.
In this study, we developed neon refrigeration system using commercial helium compressor which was originally designed for GM cryocooler. We performed this research as precedent study before developing neon refrigeration system for small-scale hydrogen liquefaction system. The developed system is based on precooled Linde-Hampson system with liquid nitrogen as precoolant. Design parameters of heatexchangers are determined from thermodynamic cycle analysis with operating pressure of 2 MPa and 0.4 MPa. Heatexchangers have concentric-tube heatexchanger configuration and orifice is used as Joule- Thomson expansion device. In experiments, pressure, temperature, mass flow rate and compressor input power are measured as charging pressure. With experimental results, the characteristics of heatexchanger, Joule-Thomson expansion and refrigeration effect are discussed. The developed neon refrigeration system shows the lowest temperature of 43.9 K.
A two-dimensional (2D) cone shape has been added to the normal circular tubes of heatexchangers to minimize the area of stagnation and to streamline the air flow around the heatexchanger tubes. An experimental setup has been developed to study the influence of the apex angle of the cone-shaped tubes on particulate fouling of heatexchangers. Fouling experiments have been performed in which calcium carbonate particles are injected during the experiments and the deposition of particles on the tubes of the heatexchanger is monitored. Four sets of experiments have been performed, in which normal cylindrical tubes and coned tubes with an apex angle of 60°, 90°, and 120° are examined. It was found that particulate fouling ceased if the apex angle of the cone-shaped tubes is sma...
We have developed an efficient cryogenic system with heatexchange and associated gas purification system, as a prototype for the XENON1T experiment. The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a temperature of 175K as target and detection medium for a dark matter search. In this paper we report results on the cryogenic system performance focusing on the dynamics of the gas circulation-purification through a heated getter, at flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114 SLPM has been achieved, and using two heatexchangers in parallel, a heatexchange efficiency better than 96% has been measured.
The Cascade ICF reactor features a flowing blanket of solid BeO and LiAlO/sub 2/ granules with very high temperature capability (up to approx. 2300 K). The authors present here the design of a high temperature granule transport and heatexchange system, and two options for high efficiency power conversion. The centrifugal-throw transport system uses the peripheral speed imparted to the granules by the rotating chamber to effect granule transport and requires no additional equipment. The heatexchanger design is a vacuum heat transfer concept utilizing gravity-induced flow of the granules over ceramic heatexchange surfaces. A reference Brayton power cycle is presented which achieves 55% net efficiency with 1300 K peak helium temperature. A modified Field steam cycle (a hybrid Rankine/Brayton cycle) is presented as an alternate which achieves 56% net efficiency.
Rotorua township is situated on top of a shallow geothermal reservoir within the Taupo Volcanic Zone of New Zealand. The resource is easy to access for private users and is commonly used for domestic and commercial heating. The Rotorua Hospital is located on one of the up flows of the geothermal reservoir and uses a doublet geothermal heating system that was commissioned in 1977. The performance of the heating system is evaluated and the impact on the geothermal reservoir is assessed. The heatingexchanger system has a unique design of 18 once through counter flow 4m long heatexchangers connected in series. It was built with significant safety margin of 300% in redundant production well capacity and is reliably serving the hospital's heating requirements at 100% availability with the pote...
This paper presents results of an experimental investigation of surface-averaged, time-wise variation of the heat transfer rate during melting and freezing of a PCM (commercial paraffin wax) contained in a large pool; the heat transfer fluid flows through a coil immersed in the pool of PCM. Heat transfer measurements are made during melting as well as freezing. Since in the most realistic application of a PCM storage-type heatexchanger, the PCM is subjected to cycling i.e. alternating melting (during the storage mode) and freezing (during the heat recovery mode), the present study included an evaluation of the effect of controlled cycling. Heat transfer data were obtained for varying cycle times (i.e. 30 mon., 60 min., 180 min. etc). Also, data were obtained with different temperatures of the heat transfer fluid. Implications of the results in the light of practical heatexchanger design using immersed coils will be discussed.
Conjugate heat transfer in a high-performance finned oval tube heatexchanger element has been calculated for a thermally and hydrodynamically developing three-dimensional laminar flow. The influence of Reynolds number in the range 100--500 and of a fin parameter Fi, the product of the dimensionless fin thickness and its thermal conductivity, on the heat transfer behavior have been studied. In part 1, the computed velocity field was presented. Here the authors present the heat transfer behavior, including heat flux on the tube, fin temperatures, fin Nusselt numbers and heat flux distributions, fin efficiencies, Colburn j factor, and apparent friction factor f{sup app}. For the investigated configuration, the ratio of heat transfer on the tube to that on the fin remains under 10%. The fin temperature and fin efficiency depend weakly on Fi. Finned tube heatexchangers are used in air conditioners and the chemical industry.
The above-mentioned firm has a glasshouse with an area of 3500 m{sup 2} with a solar plant. The heat energy is transported via an energy umbrella which can be closed (outside black, reflecting on the inside) and via air ducts (foil hose) by means of fans to a heatexchanger. Water tanks with a content of 50 m{sup 3} each act as energy heat reservoirs. Heatexchangers emit the heat gained into 18 km of floor heating pipes laid by Witte. Heat sensors in the floor monitor the heat emission. The hydro-culture plants are cultivated by the ebb and flow system, flooded at night to 20 mm and flooded four times by day to 50 mm. (orig.).
Today, large buildings requiring both cooling and heating are climatized with separate systems, so any surplus heat is lost. This report investigates the energy economical consequences of estabilishing an air conditioning system consisting of small reversible heat pumps connected to a single-string water loop. It also includes a central heat pump/cooling unit as well as an air/water heatexchanger. The annual electricity saving is calcuated in comparison to the traditional climate system. Small reversible heat pumps meet the different cooling and heating requirements in the individual climatic zones of the loop which serves as heat source for the heat pumps when heating is required. When cooling is required, the water loop is used as heat drain for the reversible heat pumps. The energy surplus/deficit of the water loop is equalized centrally in the water loop by means of a reversible heat pump/heatexchanger. By doing so, this climate system makes use of any surplus heat. Simulations show that it is possible to save up to 60% of the energy consumption compared with a traditional system when using a climate system with reversible heat pumps. However, in order to achieve that effect, a control system must be established to control the central unit and the decentralized heat pumps. The purpose of this control system is to control the temperature and the capacity flow in the water loop as well as the synchronism of the individual decentralized reversible heat pumps. (author).
The thermal-hydraulics of the reactor hot pool is important in the sodium-cooled fast reactor (SFR) design. Many activities are concentrated in this region, and one of them is the natural convection situation during decay heat removal operation. In a SFR which is currently being developed in KAERI, the passive decay heat removal circuit (PDRC) is adopted as one of the safety grade systems, which cools the reactor by using the natural convections inside reactor vessel and PDRC loop. In the PDRC loop, the sodium flow is circulated through the piping which connects the decay heatexchanger (DHX) inside reactor vessel and the sodium-to- -air heatexchanger (AHX). Inside the reactor vessel, a part of the hot pool sodium is cooled by the DHX but a part of it goes directly to the intermediate heatexchanger (IHX) without cooling by DHX, as shown in Fig. 1. The amount of sodium flow to DHX is very important for ensuring the passive decay heat removal performance, and the flow division between DHX and IHX has the multidimensional characteristics which depend on the heat removal capacity of DHX, the hot pool geometry, the flow rate at core exit and so on. The multi-dimensional characteristics in the reactor hot pool are being analyzed by using a commercial CFD package to assess the flow through the DHX for various boundary conditions. In this study, a steady-state result is presented as the first step to assess the PDRC design condition at normal (100 %) operating condition
A test rig has been assembled to investigate the thermodynamic and hydraulic performance of a cylindrical graphite block heatexchanger consisting of three graphite blocks and a steel shell. The flow pattern in the heatexchanger was triple cross-flow on the shell-side (service side) with one pass per block and a single pass on the tube-side (process side). Overall heat transfer coefficients and pressure drops have been measured for a range of operating conditions. Shell-side leakage flows were significant, with values up to 19% with water and 38% with a heat transfer oil. Corresponding increases in the overall heat transfer coefficient withouth leakage flow were 8 and 21%, respectively. The mean difference between the theoretical and experimental overall heat transfer coefficients for the runs with leakage flow does not exceed 6% with water as the shell-side liquid. With oil the error does not exceed 8%. Pressure drop models were developed for both the shell-side and tube-side of the heatexchanger. The tube-side model predicted the pressure drop with a mean error of 5%. Errors within 20% can be expected for the shell-side pressure drop model. The pressure drop on the shell-side depends on a number of different losses and it is therefore difficult to be modelled accurately. (orig.)
The purpose of this review summarizes the important published articles on the enhancement of the convection heat transfer in heatexchangers using nanofluids on two topics. The first section focuses on presenting the theoretical and experimental results for the effective thermal conductivity, viscosity and the Nusselt number reported by several authors. The second section concentrates on application of nanofluids in various types of heatexchangers: plate heatexchangers, shell and tube heatexchangers, compact heatexchangers and double pipe heatexchangers.
An air cycle air conditioning system is provided with regenerative heatexchangers upstream and downstream of an expansion turbine. A closedloop liquid circulatory system serially connects the two regenerative heatexchangers for regeneration without the bulk associated with air-to-air heatexchange. The liquid circulatory system may also provide heat transport to a remote sink heatexchanger and from a remote load as well as heatexchange within the sink heatexchanger and load for enhanced compactness and efficiency.
Compact heatexchangers 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 heatexchanger (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 heatexchangers, 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 heatexchanger 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 heatexchangers, 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)
This work describes a systematic procedure to integrate a heatexchanger network (HEN) considering heat and flow exergy consumptions. The flow exergy consumption by the HEN is calculated by means of pressure drop correlation and stepwise optimization. Case studies reveal that the flow exergy loss changes the two-way trade-off between the operating cost and the capital cost in the traditional method. The introduction of heat exergy loss adds the weight of energy cost by considering both the external utility consumption and internal heat exergy loss in the HEN, which benefits heat recovery and energy conservation at the cost of more area and investment. In contrast, the flow exergy loss shifts the balance to the capital cost by adding the cost relating to area in terms of flow frictional dissipation. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Abstract This work describes a systematic procedure to integrate a heatexchanger network (HEN) considering heat and flow exergy consumptions. The flow exergy consumption by the HEN is calculated by means of pressure drop correlation and stepwise optimization. Case studies reveal that the flow exergy loss changes the two-way trade-off between the operating cost and the capital cost in the traditional method. The introduction of heat exergy loss adds the weight of energy cost by considering both the external utility consumption and internal heat exergy loss in the HEN, which benefits heat recovery and energy conservation at the cost of more area and investment. In contrast, the flow exergy loss shifts the balance to the capital cost by adding the cost relating to area in terms of flow frict...
A heatexchanger adapted for efficient operation alternatively as evaporator or condenser and characterized by flexible outer tube having a plurality of inner conduits and check valves sealingly disposed within the outer tube and connected with respective inlet and outlet master flow conduits and configured so as to define a parallel flow path for a first fluid such as a refrigerant when flowed in one direction and to define a serpentine and series flow path for the first fluid when flowed in the opposite direction. The flexible outer tube has a heatexchange fluid, such as water, flowed therethrough by way of suitable inlet and outlet connections. The inner conduits and check valves form a package that is twistable so as to define a spiral annular flow path within the flexible outer tube for the heatexchange fluid. The inner conduits have thin walls of highly efficient heat transfer material for transferring heat between the first and second fluids. Also disclosed are specific materials and configurations.
In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20mm internal diameter, 1000mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of i...
A test facility was designed and constructed to study forced flow boiling heat transfer in a closed loop long tube heatexchanger which is a two concentric-tube vertical design. The system consists of a 12 m long heatexchanger which can be operated at pressures to 689.3 kPa with pumped or natural convection flow rates from 0.0631 to 0.631 liters/second and which can be irradiated with a maximum steady heat flux rate of 50 kW/m/sup 2/ by a set of resistive heaters operable at temperatures up to 1250/sup 0/C. The facility was also designed so that other heatexchanger configurations can be tested with minimum difficulty (i.e., little or no modification of the system other than to replace the heatexchanger). The preliminary tests indicate that the system can be operated in a stable mode. This facility was motivated primarily by the magma energy research program where energy is extracted from magma by heatexchangers similar to the configuration in this report.
An acoustic cooling engine with improved thermal performance and reduced internal losses comprises a compressible fluid contained in a resonant pressure vessel. The fluid has a substantial thermal expansion coefficient and is capable of supporting an acoustic standing wave. A thermodynamic element has first and second ends and is located in the resonant pressure vessel in thermal communication with the fluid. The thermal response of the thermodynamic element to the acoustic standing wave pumps heat from the second end to the first end. The thermodynamic element permits substantial flow of the fluid through the thermodynamic element. An acoustic driver cyclically drives the fluid with an acoustic standing wave. The driver is at a location of maximum acoustic impedance in the resonant pressure vessel and proximate the first end of the thermodynamic element. A hot heatexchanger is adjacent to and in thermal communication with the first end of the thermodynamic element. The hot heatexchanger conducts heat from the first end to portions of the resonant pressure vessel proximate the hot heatexchanger. The hot heatexchanger permits substantial flow of the fluid through the hot heatexchanger. The resonant pressure vessel can include a housing less than one quarter wavelength in length coupled to a reservoir. The housing can include a reduced diameter portion communicating with the reservoir. The frequency of the acoustic driver can be continuously controlled so as to maintain resonance.
An indoor unit for an electric heat pump is provided in modular form including a refrigeration module 10, an air mover module 12, and a resistance heat package module 14, the refrigeration module including all of the indoor refrigerant circuit components including the compressor 36 in a space adjacent the heatexchanger 28, the modules being adapted to be connected to air flow communication in several different ways as shown in FIGS. 4-7 to accommodate placement of the unit in various orientations.
Film cooling is commonly used to protect surfaces exposed to high temperatures such as turbine vanes. Experimental measurements were made of the heat transfer between a planar heated plate subjected to hot injection within a cool external flow. Partial transfers were considered for two heatexchange coefficients at different injection velocities for double alternate rows of injectors. Results were discussed for athermanous and non-athermanous surfaces. 5 refs., 4 figs.
This book presents the papers given at a conference on thermoelectric energy conversion. Topics considered at the conference included thermoelectric materials, the computer calculation of thermoelectric properties, the performance of crss-flow thermoelectric liquid coolers, thermoelectric cooler performance corrections for soft heat sinks, heatexchange in a thermoelectric cooling system, the optimal efficiency of a solar pond and thermoelectric generator system, and thermoelectric generation utilizing industrial waste heat as an energy source.
An experimental and analytical project to study the design of vertical, concentric-tube ground-coupled heatexchangers for use in heat pump applications is described. A mathematical model was developed and converted into a computer program to simulate the operation of the ground-coupled heatexchanger. The experimental apparatus consisted of a concentric configuration of two 47.2-m (155-ft) polyvinyl chloride (PVC) pipes (sealed at both ends with connections so that hot or cold water could be pumped through the system) with instrumentation to measure heat transfer. This heat excanger was placed in a 0.20-m (8-in.) inside diameter (ID) well and backfilled with sand to establish good thermal contact with the surrounding ground. Heat transfer was measured for heatexchanger operation under several sets of operating conditions. Data collected using the experimental apparatus were used to validate the computer program, and the computer model was then used to study the effects of variations in heatexchanger length and diameter, flow rate, and tube and ground thermal conductivities on the heatexchanger performance. Results are presented.
The purpose of this contract has been to explore the limits of miniaturization of heatexchangers with the goals of (1) improving the theoretical understanding of laminar heatexchangers, (2) evaluating various manufacturing difficulties, and (3) identifying major applications for the technology. A low-cost, ultra-compact heatexchanger could have an enormous impact on industry in the areas of cryocoolers and energy conversion. Compact cryocoolers based on the reverse Brayton cycle (RBC) would become practical with the availability of compact heatexchangers. Many experts believe that hardware advances in personal computer technology will rapidly slow down in four to six years unless lowcost, portable cryocoolers suitable for the desktop supercomputer can be developed. Compact refrigeration systems would permit dramatic advances in high-performance computer work stations with ``conventional`` microprocessors operating at 150 K, and especially with low-cost cryocoolers below 77 K. NASA has also expressed strong interest in our MTS exchanger for space-based RBC cryocoolers for sensor cooling. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heatexchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.
The purpose of this contract has been to explore the limits of miniaturization of heatexchangers with the goals of (1) improving the theoretical understanding of laminar heatexchangers, (2) evaluating various manufacturing difficulties, and (3) identifying major applications for the technology. A low-cost, ultra-compact heatexchanger could have an enormous impact on industry in the areas of cryocoolers and energy conversion. Compact cryocoolers based on the reverse Brayton cycle (RBC) would become practical with the availability of compact heatexchangers. Many experts believe that hardware advances in personal computer technology will rapidly slow down in four to six years unless lowcost, portable cryocoolers suitable for the desktop supercomputer can be developed. Compact refrigeration systems would permit dramatic advances in high-performance computer work stations with conventional'' microprocessors operating at 150 K, and especially with low-cost cryocoolers below 77 K. NASA has also expressed strong interest in our MTS exchanger for space-based RBC cryocoolers for sensor cooling. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heatexchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.
OAK-B135 Flow-induced vibration in heatexchangers has been a major cause of concern in the nuclear industry for several decades. Many incidents of failure of heatexchangers due to apparent flow-induced vibration have been reported through the USNRC incident reporting system. Almost all heatexchangers 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 heatexchangers. In the nuclear industry, steam generators are often affected by this problem. However, flow-induced vibration is not limited to nuclear power plants, but to any type of heatexchanger used in many industrial applications such as chemical processing, refrigeration and air conditioning. Specifically, shell and tube type heatexchangers experience flow-induced vibration due to the high velocity flow over the tube banks. Flow-induced vibration in these heatexchangers leads to equipment breakdown and hence expensive repair and process shutdown. The goal of this research is to provide accurate measurements that can help modelers to validate their models using the measured experimental parameters and thereby develop better design criteria for avoiding fluid-elastic instability in heatexchangers. The research is divided between two primary experimental efforts, the first conducted using water alone (single phase) and the second using a mixture of air or steam and water as the working fluid (two phase). The outline of this report is as follows: After the introduction to fluid-elastic instability, the experimental apparatus constructed to conduct the experiments is described in Chapter 2 along with the measurement procedures. Chapter 3 presents results obtained on the tube array and the flow loop, as well as techniques used in data processing. The project performance is described and evaluated in Chapter 4 followed by a discussion of publications and presentations relevant to the project in Chapter 5, while the conclusions and recommendations for future work are presented in Chapter 6.
The Orbital Sciences Taurus II medium lift launch vehicle utilizes first stage engines fueled by liquid oxygen and RP-1. Performance of the Taurus II is enhanced by densifying the liquid oxygen from a saturation temperature of 94 K to a subcooled temperature of 77.9 K. Subcooling the 75.07 kg/s liquid oxygen flow is accomplished in a 1.907 megawatt heatexchanger cooled by a flow of 9.62 kg/s ambient pressure liquid nitrogen. Design, fabrication, insulation and testing of the densification heatexchanger is described in this paper.
An improved reactor vessel auxiliary cooling system for a sodium cooled nuclear reactor is disclosed. The sodium cooled nuclear reactor is of the type having a reactor vessel liner separating the reactor hot pool on the upstream side of an intermediate heatexchanger and the reactor cold pool on the downstream side of the intermediate heatexchanger. The improvement includes a flow path across the reactor vessel liner flow gap which dissipates core heat across the reactor vessel and containment vessel responsive to a casualty including the loss of normal heat removal paths and associated shutdown of the main coolant liquid sodium pumps. In normal operation, the reactor vessel cold pool is inlet to the suction side of coolant liquid sodium pumps, these pumps being of the electromagnetic variety. The pumps discharge through the core into the reactor hot pool and then through an intermediate heatexchanger where the heat generated in the reactor core is discharged. Upon outlet from the heatexchanger, the sodium is returned to the reactor cold pool. The improvement includes placing a jet pump across the reactor vessel liner flow gap, pumping a small flow of liquid sodium from the lower pressure cold pool into the hot pool. The jet pump has a small high pressure driving stream diverted from the high pressure side of the reactor pumps. During normal operation, the jet pumps supplement the normal reactor pressure differential from the lower pressure cold pool to the hot pool. Upon the occurrence of a casualty involving loss of coolant pump pressure, and immediate cooling circuit is established by the back flow of sodium through the jet pumps from the reactor vessel hot pool to the reactor vessel cold pool. The cooling circuit includes flow into the reactor vessel liner flow gap immediate the reactor vessel wall and containment vessel where optimum and immediate discharge of residual reactor heat occurs.
Ground-source heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems. For the design of a GSHP system, it is necessary to accurately predict the heat extraction and injection rates of the heatexchanger. Many models that combine ground heat conduction and heatexchangers have been proposed to predict heat extraction/injection rates from/into the ground in the research field of heating, ventilation and air-conditioning systems. However, most analysis models are inaccurate in their predictions for long periods because they are based on a thermal conduction model using a cylindrical coordinate model or an equivalent diameter model. In this paper, a numerical model that combines a heat transport model with ground water flow and a heatexchanger model with an exact shape is developed. Furthermore, a method for estimating soil properties based on ground investigations is proposed. Comparison between experimental results and numerical analysis based on the model developed above was conducted under the conditions of an experiment from 2004. The analytical results agreed well with the experimental results. Finally, the proposed model was used to predict the heatexchange rate for an actual office building in Japan. (author)
A two-step approach to conserving energy in the textile industry by decreasing gas consumption in dryer operations involves 1) the automatic control of dryer dampers to minimize the flow of exhaust heat and 2) the recovery and use of the exhaust heat to preheat incoming air. These measures could reduce natural gas consumption by 45-65%. Decreasing the exhaust flow rates entails increasing the dryer humidity to a maximum level (about 0.1 lb water/lb dry air) and controlling it by the stack dampers. Three types of air-to-air heatexchangers appear suitable for preheating the dryer air by the sensible exhaust heat.
A dry (refrigerantless) heat pump incorporates a single stage centrifugal (outward flow) compressor which extracts from the space to be air conditioned the stale air and compresses it. A single stage centripetal (inward flow) turbine, its rotor being mechanical and directly connected with that of the compressor is used to decompress the stale air, the power difference between compressor input and turbine output being provided by an electric motor preferably directly coupled with the shaft of the combined compressor and turbine rotor. In a regenerative or recuperative heatexchanger the compressed and hence heated stale air transfers part of its heat to the fresh air, provided by a blower, before being conducted into the space to be air conditioned. Apart from heating, cooling can be performed by expanding the stale air in the turbine thus reducing its pressure and hence temperature, extracting heat from the incoming fresh air so as to cool it in the heatexchanger before being led to the space to be cooled. Then the pressure of the stale air after having passed through the heatexchanger is raised by the compressor to atmospheric pressure before being expelled. The heat of the stale air after leaving the compressor can be utilised for water cooling. Other modified cycles with a similar heating and cooling effect and water heating capability are described as well as methods of control.
PWR steam generators, tubular heatexchangers and condensers, are basic components of nuclear power plants involving two-phase flows in tube bundles. The operation of these components lead to vibration and corrosion inside the tube bundle, deposits and thermal shocks on the tube sheet of steam generators. A knowledge of the detailed flow patterns on the shell side is necessary to predict, quantify and prevent these risks. Moreover it is also useful to assess the efficiency of new designs, such as the economizer of the N4 nuclear plant steam generator. Electricite de France has developed a general purpose code named THYC (Thermal HYdraulic Code) designed to study three-dimensional single and two-phase flows in tube bundle (pressurized water reactor cores, steam generators, condensers, heatexchangers). Two types of components in the 3D domain are taken into account: fluid and solids (i.e. porous media approach). The THYC model is obtained by space-time averaging of the instantaneous equations (mass, momentum and energy) of each fluid phase over control volumes including fluid and solids. The THYC-EXCHANGER version solves three to five conservation equations of the fluid outside the tubes, plus the energy equation of the fluid inside the tubes. That makes the code able to model all types of heatexchangers, from single phase heatexchangers, to components involving boiling or condensation. First, this paper describes the physical model and the numerical method used in THYC-EXCHANGER. Secondly, validation tests (comparison with experiments) and applications are presented. We present successively : (a) the single-phase heatexchanger mock-up VACARM; (b) the PALUEL steam generator with temperature measurement; (c) the steam generator mock-up CLOTAIRE with void fraction and gas velocity measurements. They emphasize the latest developments, the new capabilities and the adaptability of the code to compute the local thermal-hydraulics of various kinds of heatexchangers.
COBRA-SFS is used for steady-state and transient thermal hydraulic analysis of spent fuel storage systems as well as other heat transfer and fluid flow problems. It is designed to predict flow and temperature distributions under a wide range of flow conditions, including mixed and natural convection. Two auxiliary programs, RADX1 and RADGEN, generate blackbody view factors and calculate radiation exchange factors for unconsolidated spent fuel assemblies to be supplied as input to COBRA-SFS.
COBRA-SFS is used for steady-state and transient thermal hydraulic analysis of spent fuel storage systems as well as other heat transfer and fluid flow problems. It is designed to predict flow and temperature distributions under a wide range of flow conditions, including mixed and natural convection. Two auxiliary programs, RADX1 and RADGEN, generate blackbody view factors and calculate radiation exchange factors for unconsolidated spent fuel assemblies to be supplied as input to COBRA-SFS.
The paper production is water intensive. At the paper mill Palm in Eltmann (FRG), the produced wastewater flows through the own treatment plant. The waste water not only is treated biologically, but also recycled as process water. This can reduce the fresh water demand by about 40 %. Due to fluctuations in the temperatures and volume flows of the waste water, the paper mill uses a free flow plate heatexchanger.
This thesis examines gas-side fouling mechanisms in heatexchangers that involve the inertial impaction of small particles onto tubular exchanger surfaces. An aerosol processes wind tunnel was constructed that facilitates quantitative studies of particle interactions with heat-exchanger surfaces. Three sets of experiments were performed. First, single heat-exchanger tubes were exposed to a cross flow of particle-laden air. Stainless steel tubes coated with a thin layer of grease to ensure that particle collisions resulted in capture were used to verify a numerical model for the inertial transport of ammonium fluorescein particles to the tube surface. Particle bound was quantified for the case of clean tubes and solid particles. Second, the transient deposition of particles onto single heat-exchanger tubes in cross flow was studied. It was found that a steady-state condition could be reached for cases in which particle bounce occurred. Finally, the deposition patterns for the aerosol particles as they passed through a tube bank were studied. The quantities of aerosol deposited on various tubes depended on tube surface condition, tube position within the tube bank, and the overall geometry of the bank. Using these findings, heatexchangers can be designed that will resist gas-side fouling.
The safety graded decay heat removal system (SGDHRS) of KALIMER-600 is currently reviewed in the view point of long-term cooling capability. The SGDHRS is one of the main safety functions which must be assured for all operating conditions under design basis events of the plant. The system is operated by natural circulation flow which consists of a DHX (Decay HeateXchanger) suspended in the cold pool of the primary system, an AHX (Air HeateXchanger), and piping system connecting two heatexchangers. As a part of the analysis for the long-term cooling capability of the reactor, a LOHS (Loss Of Heat Sink) was analyzed using two types of DHX's using the MARS-LMR system analysis code
The features of heat and mass exchange during operation of the thermocatalytic sensor were analyzed. Diffusion and heating processes were studied and mathematical relationships deduced to find the value of methane transfer from the atmosphere into the reaction chamber through a cermet gas-exchange filter, to determine the methane flow that passes through the boundary layer to the surface of the sensing element inside the reaction chamber, and the quantity of methane oxidizing at the surface of an electrically heated catalytic element per unit time. The relationships for the heat and mass exchange processes associated with convective heat transfer and thermal radiation of the sensing element and current leads were also deduced. Based on the results of these studies, a new type of sensing element has been suggested that features an unequal-access diffusive supply of the mixture analyzed to its catalytic surface. A sensor and portable gas analyzers were developed. 1 ref., 2 figs.
The flow inside a thermoacoustic couple is investigated experimentally using particle image velocimetry. Measurements show the oscillation of the shear layers flowing out of a single stack, thus forming an asymmetric vortex street at high driving amplitudes. Development of vortices is also observed within the gap of a thermoacoustic couple. It causes the flow not to repeat from one acoustic period to another. The nonperiodicity of the flow will lead to unsteady heat transfer between the stack and heatexchangers and to the oscillation of the cooling load. PMID:17902740
Ambient winds are one of the key issues in the design and operation of indirect dry cooling system in a power plant. It is of benefit to the optimization of air-cooled heatexchangers and dry-cooling towers to investigate the impacts of ambient winds on the thermo-flow performances of indirect dry cooling system. Based on a representative 4 x 660 MW dry cooling power plant with the flue gas desulfurization and stack installed inside the dry-cooling tower, the physical and mathematical models of the air-side fluid and heatflows at various wind speeds and in various wind directions are developed. The velocity, pressure and temperature fields are presented, and the flow rate and heat rejection for the air-cooled heatexchangers and cooling towers are obtained by using CFD simulations. The re...
A detailed heat transfer model of GAXAC (generator-absorber-exchange absorption compression) cycle using ammonia-water as working fluid is reported. The effect of UA (heat transfer conductance, kW/K) of each component on COP and cycle capacity is investigated. The results show that UA of the absorber and high temperature generator (HTG) have significant impact on COP and cycle capacity. For a capacity of 11.56 kW, the maximized COP with minimum UA value for all heatexchanging components is found to be 1.185. Further the effect of mass flow rate and inlet temperatures of hot fluid, chilled water and cooling water are also investigated. (author)
This patent describes a heatexchanger of the type wherein elongated plates are laminated together to define passageways for movement of fluid therethrough, each of the passageways being formed by inwardly facing surfaces of a pair of laminated plates which define a central fluid conducting section located between reservoir sections at each end thereof. The adjacent of the passageways are so constructed and arranged that heat conductive fin strips are located between juxtaposed, outward facing surfaces thereof. The reservoirs of adjacent ones of the passageways are interconnected so that the fluid may flow through the plurality of laminated plates forming the heatexchanger.
This paper presents 3D numerical simulation of an air-cooled metal foam heatexchanger with potential application in thermal management of fuel cell systems in general and Proton Exchange Membrane Fuel Cells, PEMFCs, in particular. It has been shown that the new design can lead to a uniform temperature distribution for the heated plate especially at higher air flow speeds. The heat transfer enhancement because of the foams leads to an increase in the pressure drop which is, interestingly, comparable to that of water-cooled PEMFCs. Other potential benefits of the application of metal foams for fuel cell thermal management are briefly discussed and estimated.
Characteristics of vertical mantle heatexchanger tanks for SDHW systems have been investigated experimentally and theoretically using particle image velocimetry (PIV) and CFD modelling. A glass model of a mantle heatexchanger tank was constructed so that the flow distribution in the mantle could be studied using the PIV test facility. Two transient three-dimensional CFD-models of the glass model mantle tank were developed using the CFD-programmes CFX and FLUENT.The experimental results illustrate that the mantle flow structure in the mantle is complicated and the distribution of flow in the mantle is buoyancy dominated. The numerically predicted flow distribution was found to be in good agreement with the experimental results. The numerical results were also found to be independent of the grid system used to model the convection processes on either side of the mantle heat transfer wall.
J.D. Evans, Inc., House B, is an instrumented single-family residence in Columbia, Maryland with approximately 2250 square feet of conditioned space. The solar energy system has an array of flat-plate collectors with a gross area of 350 ft/sup 2/. Solar energy is stored in the basement in a 1000-gallon steel storage tank. Incoming city water is preheated in a liquid-to-liquid heatexchanger located in the storage tank and then flows into a conventional 40-gallon DHW tank. A heatexchanger within a heat pump and an electrical heating element in the air-distribution duct provide auxiliary energy for space heating. Similarly, an electrical heating element in the DHW tank provides auxiliary energy for water heating. The dwelling has been fully instrumented for performance evaluation since February 1977 and the data is integrated into the National Solar Data Network. Original cost estimates for provisioning and installation of the solar system are given.
Biological and/or chemical fouling in utility service water system heatexchangers 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 heatexchanger 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 heatexchanger 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 heatexchangers. This paper discusses the design, construction of the new monitor, and algorithm used to calculate service water heatexchanger fouling.
Energy and material savings, as well as economic incentives, have led to concentrated efforts over the past several decades in the field of heat transfer enhancement to produce more efficient and compact heatexchangers. Internally finned tubes are widely used for heat transfer enhancement, particularly in chemical process and petroleum industries. A finned tube heatexchanger with optimum geometry could offer 35--40% increase in heat duty for equal pumping power and size over a smooth tube heatexchanger or a comparable decrease in the heatexchanger size for a given heat duty. Developing mixed convection flow in internally finned tubes with variable viscosity was numerically investigated for a fin geometry range of 8 {le} N {le} 24, 0.1 {le} H {le} 0.3 and an operating condition range of 50 {le} Pr{sub in} {le} 1,250, 0 {le} Ra{sub in} {le} 10{sup 7}, and 0 {le} q{sub w}d/k{sub in} {le} 2,000. The numerical model was validated by comparison with existing numerical and experimental data. Internal finning was found to produce a complex two-cell, buoyancy-induced vortex structure. The results show that coring (retarded velocity in the interfin region) leads to poor heat transfer performance of tubes with large numbers of fins or with tall fins. The overall results indicated that large enhancement in the heat transfer can be obtained in the entrance region. Furthermore, variable viscosity effects are seen to have a pronounced effect on the friction factor and Nusselt number predictions.
Abstract in english Due to the wide range of design possibilities, simple manufactured, low maintenance and low cost, cross-flowheatexchangers are extensively used in the petroleum, petrochemical, air conditioning, food storage, and others industries. In this paper a mathematical model for cross-flowheatexchangers with complex flow arrangements for determining epsilon -NTU relations is presented. The model is based on the tube element approach, according to which the heatexchanger outle (more) t temperatures are obtained by discretizing the coil along the tube fluid path. In each cross section of the element, tube-side fluid temperature is assumed to be constant because the heat capacity rate ratio C*=Cmin/Cmax tends toward zero in the element. Thus temperature is controlled by effectiveness of a local element corresponding to an evaporator or a condenser-type element. The model is validated through comparison with theoretical algebraic relations for single-pass cross-flow arrangements with one or more rows. Very small relative errors are obtained showing the accuracy of the present model. epsilon -NTU curves for several complex circuit arrangements are presented. The model developed represents a useful research tool for theoretical and experimental studies on heatexchangers performance.
An experimental study is described in which the formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a cross-flow fabricated from a treated paper. The core of the second heatexchanger is a rotating heat wheel coated with lithium chloride. To reduce the transfer of gases by air leakage each core was installed in a specially fabricated case. Only 5% to 8% of the two tracer gases and 7% to 15% of the formaldehyde injected into the exhaust airstream was transferred to the supply airstream. Therefore, formaldehyde transfer between airstreams by processes other than air leakage does not seriously compromise the performance of these enthalpy exchangers. Theoretical calculations indicate, however, that the transfer of water vapor between airstreams in enthalpy exchangers can significantly diminish their ability to lower indoor formaldehyde concentrations because of the positive coupling between indoor humidity and the emission rates of formaldehyde from building materials.
The effect of flow distribution control on the design and performance of marine gas turbine waste heat steam generators was investigated. Major design requirements and critical problems associated with a waste heat steam generator were reviewed, and an existing two dimensional heatexchanger model based on the compact heatexchanger design criteria and the relaxation approach was modified and updated to estimate the waste heat steam generator performance at any inlet gas flow distribution. Performance estimates were made of the steam generator using uniform velocity distribution, and also actual flow distribution data available (at the diffuser inlet) with and without flow distribution controls, all at design and off design operating conditions of the gas turbine engine. Results indicate that the exit steam temperatures of the baseline waste heat steam generator with and without flow distribution controls would be 725 F and 450 F, respectively, for a constant design flow ratio of 7.9 lb/sec, and for a constant exit temperature of 700 F, the water flow rates would be 8.1 lb/sec and 6.6 lb/sec, respectively.
This technical report is concerned with the effect of flow distribution control on the design and performance of marine gas turbine waste-heat steam generators. Major design requirements and critical problems associated with a waste-heat steam generator were reviewed, and an existing two-dimensional heatexchanger model based on the compact heatexchanger design criteria and the relaxation approach was modified and updated to estimate the waste-heat steam generator performance at any inlet gas flow distribution. Performance estimates were made of the steam generator using a uniform velocity distribution, and also actual flow distribution data available (at the diffuser inlet) with and without flow distribution controls, all at design and off design operating conditions of the gas turbine engine. Results of the study indicate that the exit steam temperature of the baseline waste-heat steam generator with and without flow distribution controls would be 725 F and 450 F, respectively, for a constant design flow rate of 7.9 lb/sec, and for a constant exit temperature of 700 F, the water flow rates would be 8.1 lb/sec and 6.6 lb/sec, respectively. A suggested experimental program to provide information for comparison with the analytical results, and to obtain applicable operational experience is also described in this report.
Computer simulation was used in the development of an inward-burning, radial matrix gas burner and heat pipe heatexchanger. The burner and exchanger can be used to heat a Stirling engine on cloudy days when a solar dish, the normal source of heat, cannot be used. Geometrical requirements of the application forced the use of the inward burning approach, which presents difficulty in achieving a good flow distribution and air/fuel mixing. The present invention solved the problem by providing a plenum with just the right properties, which include good flow distribution and good air/fuel mixing with minimum residence time. CFD simulations were also used to help design the primary heatexchanger needed for this application which includes a plurality of pins emanating from the heat pipe. The system uses multiple inlet ports, an extended distance from the fuel inlet to the burner matrix, flow divider vanes, and a ring-shaped, porous grid to obtain a high-temperature uniform-heat radial burner. Ideal applications include dish/Stirling engines, steam reforming of hydrocarbons, glass working, and any process requiring high temperature heating of the outside surface of a cylindrical surface.
A combustor for generating a mixture of steam and combustion gas is located downhole in an oil well, so that the mixture can be injected directly into the reservoir, to displace heavy oil from the reservoir. The combustion is built up in stages, with each stage supplying hot air to the following stage. The first stage comprises a catalytic heatexchanger, which preheats the incoming air. One side of the exchanger is coated with catalyst. On this side of the exchanger the preheated air burns a clean fuel, so that heatflows through the metal wall of the exchanger to preheat the incoming air. The heated air from the first stage is used to ignite and burn a heavy fuel such as crude oil, which is burned in the second stage and following stages.
Abstract in english A green ceramic tape micro-heatexchanger was developed using Low Temperature Co-fired Ceramics technology (LTCC). The device was designed by using Computational Aided Design software and simulations were made using a Computational Fluid Dynamics package (COMSOL Multiphysics) to evaluate the homogeneity of fluid distribution in the microchannels. Four geometries were proposed and simulated in two and three dimensions to show that geometric details directly affect the dist (more) ribution of velocity in the micro-heatexchanger channels. The simulation results were quite useful for the design of the microfluidic device. The micro-heatexchanger was then constructed using the LTCC technology and is composed of five thermal exchange plates in cross-flow arrangement and two connecting plates, with all plates stacked to form a device with external dimensions of 26 x 26 x 6 mm³.
The different methods used to obtain load variations on circulating fluidised bed boilers are variation of the fluidisation speed, partial recycling of the exhaust gases, and bypassing of any external heatexchanger. The first part of this research project consisted of finding a way of progressively aerating the valve so as to vary the flow of solids. The heatexchanger subsequently developed is original in that: it consists of two compartments, one of which encases a compact bundle of tubes, this design enabling internal movement to be introduced with the circulation of solids, thus promoting heatexchange; its regulator valve is non-mechanical and is integrated with the exchanger, allowing adjustment of recovery power.
The objective of the present work is to design and fabricate a thermal management system (TMS) that commands a proton exchange membrane fuel cell (PEMFC) based cogeneration system to generate the electricity and hot water efficiently. Parametric studies include the external load (PL) and the regenerative temperature (TR). A thermostat valve is employed to optimize the stack operation temperature, while a thermal regenerative unit (TRU) containing a planar heatexchanger is used to recover the heat dissipated by the stack. First, the dynamics of thermal and electrical characteristics such as voltage, current, power, coolant temperature, coolant flow rate, and hydrogen flow rate are measured to check the reliability of the TMS. Then, the effectiveness of the planar heatexchanger is determin...
This paper presents an evaluation of flow-induced vibration problems of component cooling water heatexchangers in one of Taipower's nuclear power stations. Specifically, it describes flow-induced vibration phenomena, tests to identify the excitation mechanisms, measurement of response characteristics, analyses to predict tube response and wear, various design alterations, and modifications of the original design. Several unique features associated with the heatexchangers are demonstrated, including energy-trapping modes, existence of tube-support-plate (TSP)-inactive modes, and fluidelastic instability of TSP-active and -inactive modes. On the basis of this evaluation, the difficulties and future research needs for the evaluation of heatexchangers are identified. 11 refs., 19 figs., 3 tabs.
An exhaust gas purification system for a lean burn engine includes a thermal mass unit and a NO.sub.x conversion catalyst unit downstream of the thermal mass unit. The NO.sub.x conversion catalyst unit includes at least one catalyst section. Each catalyst section includes a catalytic layer for converting NO.sub.x coupled to a heatexchanger. The heatexchanger portion of the catalyst section acts to maintain the catalytic layer substantially at a desired temperature and cools the exhaust gas flowing from the catalytic layer into the next catalytic section in the series. In a further aspect of the invention, the exhaust gas purification system includes a dual length exhaust pipe upstream of the NO.sub.x conversion catalyst unit. The dual length exhaust pipe includes a second heatexchanger which functions to maintain the temperature of the exhaust gas flowing into the thermal mass downstream near a desired average temperature.
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 heatexchange 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.
The auxiliary power research program by Geoscience which encompasses both fundamental liquid metal boiling and condensation heat transfer analyses and experiments in linear and high gravity flow through ducts is discussed. This research will permit the development of design correlations and criteria necessary for the prediction of nuclear reactor and heatexchanger performance in space power systems. A review and summary of post liquid metal heat and momentum transfer research, two-phase flow analyses, two-phase flow measurements, a comparison of analytical and experimental two-phase flow results, a boiling heat transfer system design, Mollier diagrams and physical properties for mercury and potassium, and a study of the influence of sudden coolant density changes on core heat transfer rates are presented. (H.G.G.)
A hybrid ground source heat pump (HGSHP) combining a ground flow loop and a supplemental heat rejecter loop in parallel is proposed to overcome the degradation of the ground thermal condition. The objective of this study is to optimize the performance of the HGSHP with the parallel configuration by varying the amount of refrigerant charge, the secondary fluid flow rate of the ground loop, and the secondary fluid flow rate of the supplemental loop. The coefficient of performance (COP) of the HGSHP with the parallel configuration was 21% higher than that of the conventional ground source heat pump (GSHP), and the heat rejection rate of the ground flow loop was 42% lower than that of the GSHP at the entering fluid temperature (EFT) of 40 ^oC in the ground heatexchanger and the EFT of 28 ^oC ...
The heat transfer rate into highly viscous, low thermal-conductivity fluids can be enhanced significantly by chaotic advection in three-dimensional flows dominated by viscous forces. The physical effect of chaotic advection is to render the cross-sectional temperature field uniform, thus increasing both the wall temperature gradient and the heat flux into the fluid. A method of analysis for one such flow???the flow in the eccentric, annular, rotating heatexchanger???and a procedure to determine the best heat transfer conditions, namely the optimal values of the eccentricity ratio and time-periodic rotating protocol, are discussed. It is shown that in continuous flows, such as the one under consideration, there exists an optimum frequency of the rotation protocol for which the heat transfe...
Heat transfer for boiling and condensing carbon dioxide has been investigated.Heat transfer for carbon dioxide evaporating inside pipe has been measured and compared with Shah's correlation. The measured heat transfer coefficient is much higher than the value determined with the correlation.A shell-and-tube heatexchanger with carbon dioxide on the shell side and flow ice inside the tubes has been used to investigate the heat transfer for condensing carbon dioxide.At leats is mentioned results obtained with a frozen food display case using carbone dioxide as refrigerant.
An improved air conditioning system comprises a first medium in heatexchange relation with an air stream, means for controlling the temperature of the first medium to effect sufficient heatexchange to control the temperature of the air stream, a second medium having thermal storage capacity, thermal conducting means interposed between said first and second media for effecting heatexchange therebetween, the thermal conducting means being thermally coupled to a means for exchangingheat with the air stream, and a means for controlling the flow rate of the air stream through the heatexchange means in order to controllably apportion heatexchange between (A) the first medium and (B) the air stream and the second medium. The system also includes, as additions to the conventional sensors and controls, means for sensing the level of thermal storage effected by the second medium and providing an output signal indicative thereof, cycling means for activating the temperature control means in response to these sensing means output signals, and, for vehicular applications, means for sensing and cycling on the basis of vehicle operating mode.
All aspects of heatexchanger fouling are considered, from the basic science of how surfaces become fouled to very practical ways of mitigating the problem and from mathematical modeling of different fouling mechanisms to practical methods of heatexchanger cleaning. The problems that restrict the efficient operation of equipment are described and the costs, some of them hidden costs, that are associated with the fouling of heatexchangers are discussed. Some simple concepts and models of the fouling processes are presented as part of the introduction to the subject. Advice on the selection, design, installation and commissioning of heatexchangers to minimize fouling is given. A large part of the test is devoted to the use of chemical and other additives to reduce or eliminate the problem of fouling. Another large section is designed to give information on both on-line and off-line cleaning of heatexchangers. One of the difficulties faced by designers and operators of heatexchangers is anticipating the likely extent of fouling problems to be encountered with different flow streams. Another large section addresses the question and describes methods that have been used in attempting to define fouling potential. The book concludes with a chapter on how fouling information can be obtained using plant data, field tests and laboratory studies
Heat pipes are often proposed as cooling system components for small fission reactors. SAFE-300 and STAR-C are two reactor concepts that use heat pipes as an integral part of the cooling system. Heat pipes have been used in reactors to cool components within radiation tests (Deverall, 1973); however, no reactor has been built or tested that uses heat pipes solely as the primary cooling system. Heat pipe cooled reactors will likely require the development of a test reactor to determine the main differences in operational behavior from forced cooled reactors. The purpose of this paper is to describe the results of a systems code capable of modeling the coupling between the reactor kinetics and heat pipe controlled heat transport. Heat transport in heat pipe reactors is complex and highly system dependent. Nevertheless, in general terms it relies on heatflowing from the fuel pins through the heat pipe, to the heatexchanger, and then ultimately into the power conversion system and heat sink. A system model is described that is capable of modeling coupled reactor kinetics phenomena, heat transfer dynamics within the fuel pins, and the transient behavior of heat pipes (including the melting of the working fluid). The paper focuses primarily on the coupling effects caused by reactor feedback and compares the observations with forced cooled reactors. A number of reactor startup transients have been modeled, and issues such as power peaking, and power-to-flow mismatches, and loading transients were examined, including the possibility of heatflow from the heatexchanger back into the reactor. This system model is envisioned as a tool to be used for screening various heat pipe cooled reactor concepts, for designing and developing test facility requirements, for use in safety evaluations, and for developing test criteria for in-pile and out-of-pile test facilities.
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heatexchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Experiments have been conducted in a compact heatexchanger with two-phase inlet conditions and vertical upflow in order to study the flow behavior. The test section consists of an offset strip fin heatexchanger with a rectangular cross-section (dimensions: 1 m x 1 m x 7.13 mm). The distributor was designed to optimize two-phase flow distribution. In a preliminary step, pressure drop of single phase flow in offset strip fins is needed to assess the quality of the distribution in the single phase case. For that, pressure drop of single phase flow has been measured in the experimental loop. Pressure drop has also been analysed numerically via CFD simulations. For low Reynolds numbers, numerical results show good agreement with experimental measurements. In a second step, the two-phase flow ...
A multiphase program aimed at investigating the importance of thermal buoyancy to LMFBR steam-generator and heat-exchanger thermal hydraulics under low-flow transient conditions is being conducted in the Argonne Mixing Components Test Facility (MCTF) on a 60/sup 0/ sector shell-side flow model of the Westinghouse straight-tube steam generator being developed under the US/DOE large-component development program. A series of shell-side constant-flow thermal-downramp transient tests have been conducted focusing on the phenomenon of thermal-buoyancy-induced-flow channeling. In addition, it was discovered that a shell-inlet flow-distribution plenum can play a significant role in mitigating the severity of a thermal transient entering a steam generator or heatexchanger.
Encapsulation reduces engine noise below the specified limiting values. On the other hand, it increases the requirements on the car, e.g. by installation of heatexchangers. The authors investigated the effects of encapsulation on the temperature level in the cooling system and developed a simulation method for cooling system design. The temperature level in the cooling system is a function of the flow conditions inside the cooler and the heat load from the engine. Experiments with systematic variation of the construction parameters relevant for cooling air flow resulted in different variants of encapsulations in a wide region of relatively low influence of the position and size of the engine outlet on the cooling air flow. The problem that is more critical is the increasing rate of leakage flow past the heatexchangers with increasing clogging of the outlet, especially return flow of hot off-air from the cooler back to the cooler front. The cooling system is further loaded by interactions of heatflow removed via coolant and engine oil, although the oil pan is integrated in the encapsulation in order to reduce the surface heatflow in this region. The underseal structure can be used for optimal utilisation of the available energy for cooling air transport and also improve the air resistance by optimized mixing of cooling air. Air resistance measurements were carried out which validate the theoretical investigations, whose goal is the minimisation of the cooling air flow with parallel mixing with maximum outlet momentum.
Compact heatexchangers are becoming more attractive for applications in which energy conservation, space saving, and cost are important considerations. Applications exist in the process industries where phase-change heat transfer realizes more compact designs and improved performance compared to single-phase heat transfer. However, there have been only a few studies in the literature reporting on phase-change heat transfer and two-phase flow in compact heatexchangers, and validated design correlations are lacking. Recent data from experiments on flow boiling of refrigerants in small channels have led researchers to conclude that nucleation is the dominant heat transfer mechanism over a broad range of heat flux and wall superheats. Local heat transfer coefficients and overall two-phase pressure drops were measured for three different refrigerants with circular and non-circular channels in a range of pressures. This data base supports the nucleate boiling mechanism, and it was used to develop a new correlation for heat transfer in nucleate flow boiling. The correlation is based on the Rohsenow boiling model, introducing a confinement number defined by Kew and Cornwell. The new correlation predicts the experimental data for nucleate flow boiling of three refrigerants within {+-}15%.
What is disclosed is a heat pump apparatus for conditioning a fluid characterized by a fluid handler for circulating the fluid in heatexchange relationship with a refrigerant fluid; two refrigerant heatexchangers; one for effecting the heatexchange with the fluid and a second refrigerant-heatexchange fluid heatexchanger for effecting a low pressure ratio of compression of the refrigerant; a rotary compressor for compressing the refrigerant with low power consumption at the low pressure ratio; at least one throttling valve connecting at the inlet side of heatexchanger in which liquid refrigerant is vaporized; a refrigerant circuit serially connecting the above elements; refrigerant in the circuit; a source of heatexchange fluid; heatexchange fluid circulating device and heatexchange fluid circuit for circulating the heatexchange fluid in heatexchange relationship with the refrigerant.
The conjugate heat transfer in a high-performance finned-tube heatexchanger element was calculated for three-dimensional thermally and hydrodynamically developing laminar flows. The influence of Reynolds number Re and a fin efficiency parameter Fi (ratio of fin to fluid conductivity times fin thickness to fin pitch) on the heat transfer behavior has been studied. Flow patterns, pressure distribution, Nusselt number distribution, heat flux distribution, and fin efficiency are presented. The part of the fin upstream of the tube is much more efficient than the downstream part. A unique heat transfer phenomenon, a directional reversal of the heat transfer, occurred locally on the fin in the tube wake for small Fi and large Re. This can be interpreted as three-dimensional interaction of convection and the fin conduction in the tube wake, when the flow is dominated by a strong horseshoe vortex and a dead water zone with recirculation.
Due to the progress realised by the semiconductor manufacturers, power electronic components are now able to dissipate heat flux densities that can 400 w/cm{sup 2}. The use of water two-phase properties seems convenient to evacuate such high heat flux densities. This paper presents a methodology of an evaporator design versus power electronics specificities. After computed total pressure drop, critical heat flux, we determine channel diameter and the flow rate which minimise wall temperature and the required pumping power permitting the flow of water through the channels. Due to low flow rates, the two-phase heat transfer coefficient is obtained with a correlation based on nucleation instead of convection. Then, comparison with an evaporator with the same pressure drop and a pumping power single-pass heatexchanger allows us to show the advantages of the two-phase heat transfer. (authors) 11 refs.
Effects of nanofluid (Al2O3 in water 2, 3 and 4vol.%) and water as coolants on heat transfer, frictional losses, and exergy loss in a counter flow corrugated plate heatexchanger were experimentally investigated. The required properties of the nanofluid were measured. It was observed that the heat transfer characteristics improve with increase in Reynolds- and Peclet-number and with decrease in nanofluid concentration. For a given heat load, the required pumping power increased with increase in nanofluid concentration. Both power consumption and heat transfer rates were lower for water in comparison to the nanofluid for flow rates of 2-5lpm for hot and cold fluids. Further, for a given heat load the nanofluid required lower flow rate but suffered higher pressure drop than that for water. F...
The PS1 heatexchanger is one of three prototype heatexchangers built by Atomic Welders before Meyer was given the contract to build the Satellite Refrigerator HeatExchanger components. This heatexchanger was first put into operation in July 1983. In November 1991, this heatexchanger experienced a failure in the shell of heatexchanger 1 causing nitrogen to contaminate the helium in the refrigerator. The resulting contamination plugged heatexchanger 3. The break occurred at a weld that connects a 0.25 inch thick ring to heatexchanger 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.
This book presents the papers given at a symposium on the use of heatexchangers in the industrial plants. Topics considered include the US DOE and GRI research programs, advanced fixed boundary heatexchanger technology, commercial heatexchanger applications, thermo-hydraulic performance of heat-transfer equipment, field tests, the corrosion of heatexchanger materials, economics, cost benefit analysis, payback, and advanced assembly and materials.
A textile dryer heat recovery system includes a textile dryer and a heatexchanger. A duct is provided for directing dryer exhaust gas to the heatexchanger for preheating dryer input air. A cleaning system within the heatexchanger removes dryer exhaust gas contaminants deposited in the heatexchanger.
...I of the Pricing Schedule: Arena Pharmaceuticals Inc...will continue to attract order flow to the Exchange. Complex Order...transact additional Complex Order flow on the Exchange...route Customer Complex Order flow to the Exchange for...
Data from an indoor solar simulator experimental performance test is used to develop a systematic calibration procedure for a computer model of a thermosyphoning, solar domestic hot water heating system with a tank-in-tank heatexchanger. Calibration is performed using an indoor test with a simulated solar collector to adjust heat transfer in the heatexchanger and heat transfer between adjacent layers of water in the storage tank. An outdoor test is used to calibrate the calculation of the friction drop in the closed collector loop. Additional indoor data with forced flow in the annulus of the heatexchanger leads to improved heat transfer correlations for the inside and outside regions of the tank-in-tank heatexchanger. The calibrated simulation model is compared to several additional outdoor tests both with and without auxiliary heating. Integrated draw energies are predicted with greater accuracy and draw temperature profiles match experimental results to a better degree. Auxiliary energy input predictions improve significantly. 63 figs., 29 tabs.
A high efficiency water heating apparatus is described comprising a tank to contain water to be heated, means for withdrawing heated water from the upper end of the tank, heating means for heating water in the tank and comprising a tubular member disposed in an opening in the side wall of the tank and extending across the tank, a burner disposed in the tubular member, fuel supply means for supplying a combustible fuel to the burner, means for supplying air to the burner to provide a combustible fuel-air mixture, pilot light means for igniting the mixture and generating waste gases of combustion, a heatexchanger located beneath the tubular member, conduit means for conducting waste gases from the tubular member to the heatexchanger, a stack communicating with the heatexchanger for discharging the waste gases from the apparatus, means for flowing the waste gases from the combustion chamber through the heatexchanger to the stack, a vent tube separate from the stack, one end of the vent tube being disposed adjacent the pilot light means and extending along the outside of the tank and communicating with the atmosphere. The vent tube serves to vent gases generated by burning of the pilot light means.
Compact heatexchangers have traditionally found wide application in the transportation industry, where they are used as evaporators and condensers in vapor compression cycles for air conditioning and refrigeration. Such heatexchangers possess numerous attractive features including high thermal effectiveness, small size, low weight, design flexibility, and pure counterflow, and they can accommodate multiple streams. Today, there is a widespread interest in expanding the range of application of compact heatexchangers to include phase-change heat transfer in the process industries, among others. An overall objective of this effort is to provide the basis for establishing design technology in this area. In the present study, small channel flow boiling heat transfer was extended to a rectangular channel (4.06 {times} 1.70 mm) using refrigerant 12 (R-12). As with the circular tube studies, the flow channel wall was electrically heated providing a constant heat flux. Tests were performed over a quality range of 0.15 to 0.80, and large ranges of mass fluxes (50 to 400 kg/m{sup 2}s) and heat flux (4 to 34 kW/m{sup 2}). Heat transfer was measured and results are compared with correlation predictions.
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 heatexchanger 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 jetfire stop. 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 heatexchanger. 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 heatexchanger. There is a separate appendix volume. 62 refs., 152 figs., 22 tabs.
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 heatexchanger 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 heatexchanger. 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 heatexchanger. This is a separate appendix volume, including computer codes and simulated results. 316 figs., 11 tabs.
This paper deals with flow and cold heat storage characteristics of the oil (tetradecane, C14H30, freezing point 278.9 K, Latent heat 229 kJ/kg)/water emulsion as a latent heat storage material having a low melting point. The test emulsion includes a water-urea solution as a continuum phase. The freezing point depression of the continuum phase permits enhancement of the heat transfer rate of the emulison, due to the large temperature difference between the latent heat storage material and water-urea solution. The velocity of emulsion flow and the inlet temperature of coolant in a coiled double tube heatexchanger are chosen as the experimental parameters. The pressure drop, the heat transfer coefficient of the emulsion in the coiled tube are measured in the temperture region over solid and liquid phase of the latent heat storage material. The finishing time of the cold heat storage is defined experimentally in the range of sensible and latent heat storage. It is clarified that the flow behavior of the emulsion as a non-Newtonian fluid has an important role in cold heat storage. The useful nondimentional correlation equations for the additional pressure loss coefficient, the heat transfer coefficient and the finishing time of the cold heat storage are derived in terms of Dean number and heat capacity ratio.
A closed loop earth-tube heatexchanger was installed at an average depth of 10 feet below ground and used as a passive cooling device for a residential style house common to Florida. During this investigation a heat and mass transfer analysis was performed on the system, and the thermal properties of the soil surrounding the test apparatus were determined. The system consisted of a 24 in. corrugated galvanized steel culvert installed as a closed loop heatexchanger; air flow, temperature, and humidity sensors, with an inline centrifugal blower used to move the air. As the air passed through the heatexchanger it was cooled, dehumidified and subsequently distributed throughout the house. The thermal performance of the system was determined experimentally as well as theoretically through the use of a computer model. The results of these experiments which were performed during July 1995 show good agreement with the developed computer model allowing for the performance prediction of future systems.
Steady state simulation of a 3D model of supercritical CO2 based natural circulation loop with end heatexchangers has been carried out employing the commercial CFD (computational fluid dynamics) code, FLUENT. The simulation considers phenomena such as viscous dissipation in fluid, axial conduction in fluid as well as in solid wall. Study has been carried out at a constant CO2 operating pressure of 80?bar. Results are obtained for various inlet temperatures of water in the hot heatexchanger, within the range of 323?353?K, for a fixed inlet temperature of cooling water in the cold heatexchanger (305?K). Results show that heat transfer rate increases with increase in HHX water inlet temperature whereas mass flow rate of loop fluid decreases. Due to the presence of bends and strong buoyancy...
For heatexchanger applications needing extreme operation temperatures such as in the field of power generation or heat recovery a ceramic plate-fin heatexchanger is proposed, based on the "Offset Strip Fin" design. At first the principal selection of the materials and the environmental barrier coating (EBC) needed to protect the substrate from the aggressive flue gases is explained. Then a manufacturing process is described able to incorporate the EBC on all parts having contact to the flue gases. On the basis of a representative biomass fuelled externally fired combined cycle (EFCC) process with an electrical output of 6MW the thermal design is presented resulting in a counter flow ceramic heatexchanger block of weight 4.0t and surface area densities of 443mm2/mm3 on the flue gas side ...
For regenerative heat engines like Stirling engines or heat pumps using the Vuilleumier process the calculation of COP by means of only the two fundamental laws of thermodynamics is limited to ideal embodiments where pressure and temperature drops at heatexchangers, the losses produced by friction and heat conduction and the adiabatic behaviour of the working gas are neclected. By the use of the modelling method presented in this paper, the temperature differences and flow losses occuring within heatexchangers and thermal regenerators, the heat losses along cylinder and displacer piston and the mechanical friction losses are considered. The equations derived for a real engine with losses can be solved under these conditions by an iteration procedure; the resulting COP's are in fair agreement with relevant experimental values. (orig.).
An experimental evaluation was made of a 100-kw model of a concentric cylinder, countercurrent, spiralflow heatexchanger to determine its applicability in sodium-cooled reactor systems. The heatexchanger underwent a rigid program of rapid thermal transients, and the unit demonstrated a satisfactory resistance to thermal stresses. Heat transfer tests also were conducted, and expressions were developed for the liquid metal Nusselt numbers associated with two general heat transfer conditions for the essentially rectangular cross sections of the fluid passages. For net heat transmission through two opposite walls, where Nu is the Nusselt number and Pe is the Peclet number, the relation found was Nu = O.O55Pe/sup 0.8/. For a similar geometry with heatflow through only one wall, the relation found was Nu = 0 15 + O.l2Pe/ sup 0.6/. (auth)
Presents a new system of air source energy independence driven by internal-combustion engine (EIICE), which used natural gas or other fuels as an independent input energy, and could provide the heating, cooling and hot water for the buildings efficiently. It also could provide electricity for electric equipments of the system. The performance of air source EIICE system was investigated theoretically and experimentally. The experimental and simulation results indicated that the heat capacity of plate heatexchanger (P-HE), heat recovered from exhaust gas heatexchanger (EG-HE), input power of compressor, output power of engine and fuel consumption increased with the increase of the rotary speed, water flow rate of the P-HE and evaporation temperature. Heat recovered from the cylinder jacket...
Oak Ridge National Laboratory's graphite foam has the potential to be used as a heatexchanger for the Army's Future Combat System Manned Ground Vehicle and thus has the potential to improve its thermal performance. The computational fluid dynamics (CFD) program FLOW3D was used to develop a new CFD model for the graphite foam to be used in the development of a proper heatexchanger. The program was calibrated by first measuring the properties of the solid foams and determining the parameters to be used in the CFD model. Then the model was used to predict within 5% error the performance of finned foam heat sinks. In addition, the f factors and j factors commonly used to predict pressure drop and heat transfer were calculated for both the solid and finned structures. There was some evidence that corrugating the foams would yield higher j/f ratios than state of the art heatexchangers, confirming previously measured data. Because the results show that the CFD model was validated, it is recommended that the funding for Phases 2 through 5 be approved for the design of both the finned heatexchanger using tubes and round fin structures and the solid foam design using corrugated foams. It was found that the new CFD model using FLOW3D can predict both solid foam heat transfer and finned foam heat transfer with the validated model parameters. In addition, it was found that the finned foam structures exhibited j/f ratios that indicate that significant heat transfer is occurring within the fin structures due to aerodynamically induced flow, which is not present in solid aluminum fin structures. It is possible that the foam surfaces can act as turbulators that increase heat transfer without affecting pressure drop, like the vortex generators seen in state of the art heatexchangers. These numbers indicate that the foam can be engineered into an excellent heatexchanger. It was also found that corrugating the solid foams would increase the j/f ratio dramatically, allowing the solid foams to compete directly with standard heatexchangers. Although corrugated L1 foam samples have not been produced (attempts are under way), it is possible that their j/f ratio can be even higher than those of the finned structures.
Heatexchanger tubes can be damaged or fail if subjected to excessive flow-induced vibration, either from fatigue or fretting-wear. Good heatexchanger 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 heatexchanger requires information about damping. Damping in multispan heatexchanger 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 damage 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 heatexchanger tube with multiple spans was excited by random vibration. Tests were conducted in air and in water at three different temperatures (25, 60, and 90 C). 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.
Heatexchanger tubes can be damaged or fail if subjected to excessive flow-induced vibration, either from fatigue or fretting-wear. Good heatexchanger 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 heatexchanger requires information about damping. Damping in multispan heatexchanger 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 heatexchanger tube with multiple spans was excited by random vibration. Tests were conducted in air and in water at three different temperatures (25, 60, and 90{sup o}C). 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)
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 heatexchanger 4A (HX 4A). The heatexchanger was isolated and the plant shutdown. Heatexchanger 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 heatexchanger 4A for metallurgical examination. Additional analysis and review of heatexchanger 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 summary herein.
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 heatexchanger 4A (HX 4A). The heatexchanger was isolated and the plant shutdown. Heatexchanger 4kA 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 failure mechanism. In addition ten other tubes that either exhibited eddy current indications or would represent a baseline condition were removed from heatexchanger 4A for metallurgical examination. Additional analysis and review of heatexchanger 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 herein.
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 heatexchanger 4A (HX 4A). The heatexchanger was isolated and the plant shutdown. Heatexchanger 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 heatexchanger 4A for metallurgical examination. Additional analysis and review of heatexchanger 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 summary herein.
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 heatexchanger 4A (HX 4A). The heatexchanger was isolated and the plant shutdown. Heatexchanger 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 heatexchanger 4A for metallurgical examination. Additional analysis and review of heatexchanger 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.
Experiments were conducted in a wind tunnel to study open lane and peripheral gap effects in heatexchanger tube bundles subjected to cross flow. A rotated triangular array of tubes was tested to obtain critical velocities for uniform flow instability. By removing different rows of tubes, critical velocities for nonuniform flow caused by open lanes and peripheral gaps were recorded. Also, theoretical correction factors due to open lanes and peripheral gaps were developed to predict the critical velocities for nonuniform flow. The correction factor can be multiplied by the critical velocity predictions from existing models for uniform cross-flow. Correlations of the analytical model with experimental data are good. (orig.).
The executive summary includes the following topics of discussion: the state of affairs; the fundamental governing equations; the one-dimensional mixture model; the drift-flux model; the Denver Research Institute two-phase geothermal flow program; two-phase flow pattern transition criteria; a two-fluid model under development; the mixture model as applied to geothermal well flow; DRI downwell instrumentation; two-phase flow instrumentation; the Sperry Research Corporation downhole pump and gravity-head heatexchanger systems; and the Brown University two-phase flow experimental program. (MHR)
This paper has dealt with melting heat transfer characteristics of ice water slurry in an inside tube of horizontal double tube heatexchanger in which a hot water circulated in an annular gap between the inside and outside tubes. Two kinds of heatexchangers were used; one is made of acrylic resin tube for flow visualization and the other is made of stainless steel tube for melting heat transfer measurement. The result of flow visualization revealed that ice particles flowed along the top of inside tube in the ranges of small ice packing factor and low ice water slurry velocity, while ice particles diffused into the whole of tube and flowed like a plug built up by ice particles for large ice packing factor and high velocity. Moreover, it was found that the flowing ice plug was separated into numbers of small ice clusters by melting phenomenon. Experiments of melting heat transfer were carried out under some parameters of ice packing factor, ice water slurry flow rate and hot water temperature. Consequently, the correlation equation of melting heat transfer was derived as a function of those experimental parameters.
Ice slurries have been used as environmentally-friendly secondary refrigerants. In addition to such ice slurries, aqueous solutions in slurry-state have also been put to practical use at temperatures below 0 oC. Urea-water mixture is a multi-component substance that has a eutectic point. If we can form a two-phase fluid substance by the liquid-solid phases at the eutectic point, it can be used as a fluid latent heat storage material, which will maintain the secondary refrigerant in a heatexchanger at constant temperature. In the present study, we propose a urea-water mixture as a novel functional thermal fluid that can be used as a fluid latent heat material. To demonstrate its feasibility, we first measured the latent heat and density of a urea-water mixture, and then used a counter-flow double tube heatexchanger to produce a liquid-solid two-phase flow of the urea-water mixture. This work demonstrates that it is possible to make a fluid latent heat storage material continuously from an aqueous solution at the eutectic point by flowing it through a double tube heatexchanger equipped with a stirrer.
A cooling system is configured to control the flow of a refrigerant by controlling the rate at which the refrigerant is heated, thereby providing an efficient and reliable approach to cooling a load (e.g., magnets, rotors). The cooling system includes a conduit circuit connected to the load and within which a refrigerant circulates; a heatexchanger, connected within the conduit circuit and disposed remotely from the load; a first and a second reservoir, each connected within the conduit, each holding at least a portion of the refrigerant; a heater configured to independently heat the first and second reservoirs. In a first mode, the heater heats the first reservoir, thereby causing the refrigerant to flow from the first reservoir through the load and heatexchanger, via the conduit circuit and into the second reservoir. In a second mode, the heater heats the second reservoir to cause the refrigerant to flow from the second reservoir through the load and heatexchanger via the conduit circuit and into the first reservoir.
being released under U.S. Department of State export license TA 0042-05. Retransfer .... Transmitter HeatExchanger (HE in this document), which is a part of the 20 kW .... with valves to regulate the amount of flow through each circuit and with ...
Apr 7, 2002 ... It boosts the liquid oxygen's pressure from 100 psia to 422 psia. ... Another small flow path is tapped off and sent to the oxidizer heatexchanger. .... A support ring welded to the forward end of the nozzle is the engine attach ...
heatexchanger inboard of the radiator and by using a regenerator bypass flow ... 1 Assuming that the ground slopes away from the vehicle at 5° and adding in the 1.54° tilt of the lunar axis gives a ... using a simplified Excel thermal model.
The critical regimes of heatexchange at a laminar steady flow of a pseudo-plastic liquid in the initial interval of a coaxial duct are investigated with regard for both dissipative and chemical sources in the Arrhenius representation [5] under the conditions of an insignificant variation of the concentrations of reacting substances.
The transport phenomena in scraped heatexchanger (HE) crystallizers are critical for the process performance. Fluid flow and turbulence close to the HE surface as generated by stirring elements and scraper blades are crucial in this respect as they aim at avoiding an insulating scale layer on the H...
This patent describes a recuperator comprising a ceramic heat-exchanger core within a housing, the core having six faces, two solid and four having openings for the flow of gas therethrough, the improvement comprising a layer of intumescent material disposed between a solid face and the housing.
Senior Research Engineer, Gas Turbine Laboratory ... Compressor pre-cooling, either via a heatexchanger or mass-injection, ... passage level, by a decrease in the total pressure reduction coefficient and an increase in the flow ...... the shape of the loss bucket in the cooled case opens up slightly @e, the "minimum a" ...
The phosphoric acid mixed into the exhaust air of the fuel cell reacts chemically with the structural materials such as stainless steel of pipes in which fuel cell exhaust air flows and the air preheater, and produces phosphoric acid compound. This compound accumulates on the surface, grows with the passage of time to block up the exhaust air passage, and causes production of pin holes at welded area by corrosion. This invention is concerned with a phosphoric acid fuel cell, wherein an inlet for exhaust oxidizer gas to flow into the heatexchanger is provided at the lower part of the heatexchanger, and an outlet is provided at the upper part of the heatexchanger for flowing exhaust oxidizer gas from the heatexchanger. As a result, even when vapor in the exhaust oxide gas is condensed to become water, the water drops to contact with high temperature exhaust oxidizer gas at the lower area and evaporates to avoid production of strong acidic drain caused by phosphoric acid because high temperature exhaust oxidizer gas containing phosphoric acid forms upward flow ascending from the lower part to the upper part of the air preheater. 5 figs.
The objectives of this research are to: extend the range of pressure drop data for ice-water slurry flows; and design and build a prototypical ice slurry distribution system which demonstrates ice slurry handling at an end user's heatexchanger, without s...
The objectives of this research are to: extend the range of pressure drop data for ice-water slurry flows, and design and build a prototypical ice slurry distribution system which demonstrates ice slurry handling at an end user's heatexchanger, without s...
The mathematical model of furnace slagging integrated into the Sigma-Flow program system of computational hydrodynamics has been developed; this system makes it possible to calculate aerodynamics, processes of heat-and-mass exchange, and combustion processes in complex technological facilities, including pulverized-coal-firing furnaces.
Optimal heatexchanger temperature profiles of exothermic tubular reactors were determined under the assumption of steady-state and plug-flow characteristics. The minimum principle of Pontryagin (optimal control theory) was applied in a straightforward analytical sense. To enable a trade-off between...
Water tubes are endangered by corrosion and lime. Service life and reliability of heatexchangers are influenced by many parameters. Therefore a system with specific oscillation patterns, presented in this article, keeps fluids in flow and avoids deposits on tube walls. (GL)
Fouling is a complex phenomenon that (1) encompasses formation and transportation of precursors, and (2) attachment and possible removal of foulants. A basic understanding of fouling mechanisms should guide the development of effective mitigation techniques. The literature on fouling in complex flow passages of compact heatexchangers is limited; however, significant progress has been made with enhanced tubes.
leaving the blower flows through a heatexchanger cooled by the thermal .... The PAVS draws air through activated carbon filters and then forces the clean air through .... The motor was driven by an inverter which, in turn, was driven by a DC power supply. .... pV aero. ?. = x. (1). The simulation conditions correspond to air at ...
In support of the crystalline silicotitanate (CST) ion exchange project of High-Level Waste (HLW) Process Engineering, a transient two-dimensional heat transfer model that includes the conduction process neglecting the convection cooling mechanism inside the CST column has been constructed and heat transfer calculations made for the present design configurations. For this situation, a no process flow condition through the column was assumed as one of the reference conditions for the simulation of a loss-of-flow accident. The modeling and calculations were performed using a computational heat transfer approach.
Purpose - The purpose of this paper is to compare k-? shear-stress transport (SST) and large eddy simulation (LES) turbulence model application effect on numerical computation of flow pattern and heatexchange characteristics through the neutron beam window region for European spallation source setup model. Design/methodology/approach - Transient hydrodynamic and thermal calculations with appropriate heat sources are performed using both turbulence models and typical discrepancies in flow and thermal patterns are discussed, as well as, simulation results are qualitatively compared with experimental data for heat transfer coefficient distribution a at the window surface. Findings - Contribution of greater k-energy field obtained with LES calculation leads to prediction of more intensive hea...
Helically coiled heatexchangers, where one of the working fluids is flowing through helical coil, are used in various process industries due to better heat transfer characteristics and the resulting compact layout. Out of these, process requirements make some of the heatexchangers to operate in air-water two-phase region. Even though the characteristics of their operation with single-phase working fluids are well documented, it is not so for the case of two-phase flows. There do exist few experimental results on hydrodynamics of air-water flow through helical pipes. However numerical investigation, which can give much insight into the physics of the problem, is lacking and this is the subject matter of this paper. Two-fluid Eulerian-Eulerian scheme available in FLUENT 6.3 is used in this...
Abstract The flow of a shear thinning food product in a tube in tube in tube (TnTnT) heatexchanger (HE ) is modeled with a CFD (computational fluid dynamics) commercial code, FLUENT 6.1. Results are compared with in line industrial measurements. The heating medium was pressurized hot water in counter current flow and constant wall temperature. The equipment was modeled in five meshed sections: three TnTnT heatexchange domains and two 180 bends that connect them. Good agreement was obtained between measured and predicted values of the product outlet temperature at the end of the process. Agreement on temperature profiles in the different sections of the heater, in the center of the flow, was generally poor. Modeled temperature was higher at the outlet of the bend compared with the inlet i...
Technological applications in which porous materials are utilized include thermal energy storage, geophysical fluid engineering, thermal insulation, heat transfer enhancement, and heatexchangers. The author proposes a new method to estimate the heat transfer between fluid gas and solid material in a porous medium. In the first stage, the local Nusselt numbers on the heated wall of a flow passage with a porous medium are numerically obtained in advance for the parameter H{sub a}, including the volumetric heat transfer coefficient, h{sub {nu}}, between the fluid and the solid material in a porous medium. In the second stage, the experimental Nusselt numbers on the heated wall are obtained by measuring wall temperatures and heat flux. The volumetric heat transfer coefficient, h{sub {nu}}, is evaluated by comparing experimental Nusselt numbers with numerical ones. This method also gives the longitudinal characteristics of the heat transfer in a porous medium.
An experimental study on energy efficient electrical domestic clothes dryers is presented. A literature survey was performed and four basic energy saving techniques were identified: (1) reduced air flow rate and heater input, (2) recirculation of a portion of the exhaust air back into the clothes dryer, (3) heat recovery, utilizing an air-to-air heatexchanger, and (4) 100% recirculation of air through the dryer and a heat pump to condense water out of the air. Reduced air flow rate and heater input leads to energy savings around 8%, while recirculation of exhaust air reduces the energy consumption by approximately 18%. Because of the low cost of these two measures, they should be pursued by the manufacturers. When utilizing an air-to-air heatexchanger for heat recovery, two modes are considered. The first is to preheat the inlet air with heat from the exhaust air, which results in 20 to 26% energy savings depending upon the location of the dryer in the house. The second more attractive mode is 100% recirculation of air and condensation of water from this air in the heatexchanger (using indoor air as a heat sink) and represents a 100% heat recovery but leads to a 1 to 6% increase in energy consumption. The development of a clothes dryer equipped with an air-to-air heatexchanger and a summer/winter switch (preheating mode in the summer and recirculation/condenstion mode in the winter) should be pursued by the manufacturers. Recirculation through a heat pump with condensation again gives a 100% heat recovery and can save up to 33% in energy consumption but yields long drying times due to limitations of the condenser temperature.
Abstract in english Experiments were performed to determine average heat transfer coefficients and friction factors for turbulent flow through annular ducts with pin fins. The measurements were carried out by means of a double-pipe heatexchanger. The total number of pins attached to the inner wall of the annular region was 560. The working fluids were air, flowing in the annular channel, and water through the inner circular tube. The average heat transfer coefficients of the pinned air-side (more) were obtained from the experimental determination of the overall heat transfer coefficients of the heatexchanger and from the knowledge of the average heat transfer coefficients of the circular pipe (water-side), which could be found in the pertinent literature. To attain fully developed conditions, the heatexchanger was built with additional lengths before and after the test section. The inner circular duct of the heatexchanger and the pin fins were made of brass. Due to the high thermal conductivity of the brass, the small tube thickness and water temperature variation, the surface of the internal tube was practically isothermal. The external tube was made of an industrial plastic which was insulated from the environment by means of a glass wool batt. In this manner, the outer surface of the annular channel can be considered adiabatic. The results are presented in dimensionless forms, in terms of average Nusselt numbers and friction factors as functions of the flow Reynolds number, ranging from 13,000 to 80,000. The pin fin efficiency, which depends on the heat transfer coefficient, is also determined as a function of dimensionless parameters. A comparison of the present results with those for smooth sections (without pins) is also presented. The purpose of such a comparison is to study the influence of the presence of the pins on the pressure drop and heat transfer rate.
Isoelectric focusing is a high-resolution technique for separating and purifying large peptides, proteins, and other biomolecules. The apparatus described in the present paper constitutes a new approach to fluid stabilization and increased throughput. Stabilization is achieved by flowing the process fluid uniformly through an array of closely spaced filter elements oriented parallel both to the electrodes and the direction of the flow. This seems to overcome the major difficulties of parabolic flow and electroosmosis at the walls, while limiting the convection to chamber compartments defined by adjacent spacers. Increased throughput is achieved by recirculating the process fluid through external heatexchange reservoirs, where the Joule heat is dissipated.
Horizontal ground heatexchangers have been widely used in many countries as the heat source for ground-source heat pump systems. When abundant land space is available for the installation of ground heatexchangers, the horizontal ground heatexchangers provide a cost-effective choice because the installation costs of horizontal ground heatexchangers are much lower than those of vertical ground heatexchangers. Slinky-coil horizontal ground heatexchangers, which are basically coiled ground heatexchangers, require less land space than conventional straight horizontal ground heatexchangers because of the higher installation density of heatexchange pipes per given area. However, at present, the slinky-coil horizontal ground heatexchangers tend to be over- or undersized because of the la...
In this paper, a comparison of heat transfer and pressure drop characteristics of CuO/water nanofluids in a helically coiled heatexchanger held in horizontal and vertical positions is presented. Experiments were conducted in the turbulent flow regimes using water and CuO/water nanofluids of 0.1% and 0.2% volume concentrations. The experimental results show that there is no much difference between horizontal and vertical arrangements in the enhancement of convective heat transfer coefficient and friction factors of nanofluids compared to water. Irrespective of the positions of the helically coiled heatexchanger, the enhancement in internal Nusselt numbers is high for higher concentration nanofluids at turbulent flow. Also the experimental friction factors obtained are high for higher conc...
This Note presents the study of transient flow under forced convection in buried co-axial exchanger. The wall temperature as well as the wall heat flux and the heat transfer coefficient are unknown. A hybrid model consisting of a finite element method at the boundary (BEM) for the heat transfer problem on the boundary and a finite volume method (FVM) to solve the laminar flow inside solves this problem. The development of the BEM method is based on the Greens function theory. This conjugate method allows one to have fast results and to foresee the thermal behaviour of the exchanger. The heat transfer coefficients are investigated. The results are compared to those obtained using the commercial CFD package Fluent.
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 heatexchanger having a limited heat transfer rate. In this report attention is paid to an experimental investigation on the thermal behavior of the heatexchanger, and a numerical parameter variation study on the application of the heatexchanger 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 heatexchanger 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 heatexchanger, 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 heatexchanger 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.
Direct contact heatexchangers are characterized by the absence of any heatexchange wall between the two fluids. Examples are for instance: the cooling towers, the solid-gas recuperator exchangers, the gas-liquid direct contact exchangers for water heating using gaseous effluents, the air humidifiers, the bubble and barometric condensers etc.. These exchangers offer the possibility to reduce the investment costs and to increase the efficiency of heat transfers with respect to a classical exchanger. This paper presents the basic knowledge concerning direct contact heatexchangers: 1 - basic concepts and characteristics; 2 - dimensioning and modeling; 3 - liquid-liquid direct contact heatexchangers: design and performances, numerical analysis; 4 - gas-solid direct contact heatexchangers: different types of solid particle contactors, contactor with particles rainfall, exchanger-regenerator, fluidized beds; 5 - liquid-solid phase transition heatexchangers: granulometry of dispersed systems with liquid to solid state change, domains of use; 6 - liquid-vapor phase transition heatexchangers: evaporation, condensation, boiling. (J.S.)
This paper deals with fault detection and isolation (FDI) in sensors applied to a concentric-pipe counter-flowheatexchanger. The proposed FDI is based on the analytical redundancy implementing nonlinear high-gain observers which are used to generate residuals when a sensor fault is presented (as software sensors). By evaluating the generated residual, it is possible to switch between the sensor and the observer when a failure is detected. Experiments in a heatexchanger pilot validate the effectiveness of the approach. The FDI technique is easy to implement allowing the industries to have an excellent alternative tool to keep their heat transfer process under supervision. The main contribution of this work is based on a dynamic model with heat transfer coefficients which depend on temperature and flow used to estimate the output temperatures of a heatexchanger. This model provides a satisfactory approximation of the states of the heatexchanger in order to allow its implementation in a FDI system used to perform supervision tasks. PMID:21501838
This paper reports on an experimental study of air-water mixtures flowing through an idealised shell and tube, in-line heatexchanger. Void fraction measurements are reported for the minimum gaps between the tubes at near atmospheric conditions. The pressure distributions around some tubes are also reported. These data are combined with data available in the open literature to investigate pressure drop and void fraction prediction methods for these heatexchangers. The data are shown to be flow pattern dependent. Criteria for flow pattern boundaries are deduced from previously published flow maps. Void fraction data in the maximum gap between the tubes are shown to be compatible with the drift flux model and to be different in magnitude to the minimum gap values, which are shown to result ...
Topic of this article is a dryer for sludges. The dryer is a fluidized bed with a heatexchanger, heating media is steam or oil. The FluiDry process is shown with a flow sheet. (SR) [Deutsch] Fuer die Entsorgung kommunaler und industrieller Schlaemme setzt MAN GHH mit Flui-Dry ein thermisches Verfahren ein, das auf der Basis der Wirbelschichttechnologie mit hoher Sicherheit und Zuverlaessigkeit arbeitet und dabei Anspruechen an eine kostenbewusste Entsorgung der Schlaemme und eine hohe Trockenschlammqualitaet gerecht wird. (orig.)
In this study the thermal characteristics of horizontal mantle heatexchangers are investigated for application in active solar water heaters. Some important parameters such as flow rate, thermal short circuit, average temperature, and convection heat transfer coefficient and inlet velocity have been investigated too. The results show that the thermal efficiency of the storage tank is critically impaired by the effect of short circuit phenomenon and mixing caused by turbulence.
This book is a timely, accurate and comprehensive monograph which presents a solid foundation for the development of Stirling engine analysis by covering computer, mathematical and experimental techniques which affect the structured analysis. The subject requires a familiarity with the design and operational mode of the Stirling engine being analyzed, and the thermodynamics and aerodynamics of fluid flow and simultaneous heat transfer. Contents, abridged: Isothermal analysis. Free-piston machines. Heatexchanger analysis. Parasitic losses. Appendices. Index.
Part of the gas is heated before its entry into the filter in order to increase the temperature of the catalyst above the ignition temperature of particles, and a complementary amount of fuel is injected into the gas flow. After the initiation of the oxidation reaction the extra energy supply can be discontinued. The supplementary fuel is preferably preheated in a heatexchanger at the filter. (G.B.).
In this paper we are going to present the results of the measurements on two heatexchangers with smoothly and finned surface. Especially, we considered the influence of the strength of the sprinkling and the outer finning on the heat and mass transfer coefficient under different kinds of flowing fluids and under different operation conditions. Finally, the results have been analysed, discussed and some improvement suggestions have been derived. (orig.)
When exchanging old heating systems against new, it is essential to find out whether the old chimney is still suitable. The following changes to the heating system can cause problems in this context: lower performance and consequent lower exhaust gas mass flow; lower exhaust gas losses and consequent lower exhaust gas temperatures; longer burner operating time impeding the evaporation of moisture in the chimney. The article presents a comparison of different means of exhaust gas conducting systems. (BWI)
Experimental investigations in connection with the dimensioning of natural draught dry cooling towers undertaken by the Department for Heat Transfer and Climatology are aimed at discovering favourable tube arrangements for the heatexchange system, which permit small construction size for such cooling towers. Systematic variations in tube spacing in the direction of flow and of tube arrangement in a system comprising spiral finned tubes indicate that optimum configurations are available for prescribed cooling performance in relation to tower dimensions.
Laminar 2-D pulsating flow through homogeneous linear arrays of heated square tubes is simulated for pulsation frequencies of 0-80 Hz for tube diameter-based Reynolds numbers from 50 to 200. The objective is to examine the effects of flow pulsation on drag and heat transfer in heatexchanger tube bundles. Cycle-averaged and maximum drag coefficients, as well as the instantaneous and cycle-averaged Nusselt numbers are reported for each of the ten rows of tubes in the simulated array. The results show that flow pulsations can enhance heat transfer in tube bundles, and the level of enhancement increases with pulsation frequency and mean flow Reynolds number. A wake interference effect has been observed which significantly amplifies the drag on the leading rows and reduces and instantaneously ...
In this paper, the effects of inlet temperature and rib height on the fluid flow and heat transfer performances of the ribbed channel inside the high temperature heatexchanger are presented. The inlet temperature varies from 850K to 1250K and the ratio of rib height to channel height varies from 0.083 to 0.333. The results indicate that increasing the rib height can enhance the flow disturbance and hence improve the heat transfer performance. The inlet temperature has little effect on the basic structure of fluid flow and the heat transfer is enhanced due to the increased velocity. Compared to increasing the rib height, more heat can be transferred by increasing the inlet temperature with less pressure drop. The high pressure drop is more serious as the inlet temperature increases. It is ...
A multi-shell heatexchanger is described which consists of: (a) multiplicity of interconnected shells arranged one within the other, the shells including an innermost shell defining an enclosed space therein, the innermost shell being enclosed by a plurality of successively larger shells; (b) means supporting the shells in spaced relation so as to define annular flow spaces between the shells; (c) first fluid passage means defined at least in part by connector means forming a first continuous flow path for a cooling fluid circulating through the shells; and (d) second fluid passage means defined at least in part by connector means forming a second continuous and separate flow path for a heated fluid circulating through the shells, the heated fluid being cooled by heat transfer between the heated fluid and the cooling fluid occurring across the shells.
The thermal efficiency of the gas-turbine LMFBR system using the liquid sodium as a primary coolant and a gas turbine as a power conversion system is evaluated. And then the sodium/helium heatexchangers are analyzed. The evaluation models of the configuration of the sodium/helium heatexchanger having a single pass tube bank or a cross flow tube bank and their effects of the expansion of the heatexchange areas are developed to analyze the size and the performance of a heatexchanger. The design charts corresponding to the evaluation model of the heat technology in field of FBRs without intermediate loops, the concepts of the super critical steam coolant fast breeder reactors(SCFBRs) and of small gas turbine FBRs are reviewed. The thermal efficiency of a gas turbine LMFBR system is expected to reach about 35 % as the technology is developed. Sodium/helium heatexchanger using Phenix reactor as a primary side and a GA-modular gas turbine system as a secondary side, for an example, has the shell diameter of 2 to 3 meters and the tube height of 12 to 17 meters. 44 figs, 14 tabs, 32 refs. (Author).
This patent describes a nuclear system comprising a containment airspace in which a nuclear reactor pressure vessel is disposed there being a reactor core within the pressure vessel. It comprises a heatexchanger elevated a distance above the pressure vessel; a pool of water surrounding the heatexchanger; means for venting the pool of water to an environment outside the containment; a heatexchanger entry conduit within the containment, the entry conduit having an open lower end communicating with the containment space, and an upper end connected to the heatexchanger, water-containing heated fluid present in the containment airspace incident a pressure vessel loss of coolant event entering and flowing through the entry conduit into the heatexchanger for cooling the fluid to convert water vapor therein to a condensate and separate non-condensable gasses therefrom; a gravity driven cooling water pond-containing space, the gravity cooling water space being elevated a distance above the core in the pressure vessel sufficient for cooling water upon occurrence of an event and when pressure in the pressure vessel is reduced to a predetermined level, to gravity feed into the pressure vessel through a piping means connected therewith so that the water can cover the core.
This preliminary report for the Swiss Federal Office of Energy presents the results of study carried out to assess the influence of soiling (Biofilm formation) on the efficiency of heatexchangers for heat recovery from wastewater systems. The results of tests made from January to April 2003 on a test bed are presented. Firstly, the measuring equipment was calibrated and mathematical relationships between important experimental parameters were defined. The conduit with its integrated heatexchanger was then fed with wastewater and different experiments were carried out involving the growth of biofilms. The decrease in the efficiency of the heatexchanger in dependence of biofilm formation was quantified. Then, the influence of the hydraulics on biofilm formation was examined. In this case, it turned out that a significant amount of the biofilm could be washed away by appropriate modification of wastewater flow. In this way, the efficiency of the soiled heatexchanger, as compared with the efficiency of a clean heatexchanger, could be increased again from 61% before washing away the biofilm, to 87% after its washing. The washing away of the biofilm was repeated several times in succession.
A heat pump system includes, in an operable relationship for transferring heat between an exterior atmosphere and an interior atmosphere via a fluid refrigerant: a compressor; an interior heatexchanger; an exterior heatexchanger; an accumulator; and means for heating the accumulator in order to defrost the exterior heatexchanger.
This report presents the results of a study conducted to consider heatexchanger options and tritium transport in a very high temperature reactor (VHTR) system for the Next Generation Nuclear Plant Project. The heatexchanger options include types, arrangements, channel patterns in printed circuit heatexchangers (PCHE), coolant flow direction, and pipe configuration in shell-and-tube designs. Study considerations include: three types of heatexchanger designs (PCHE, shell-and-tube, and helical coil); single- and two-stage unit arrangements; counter-current and cross flow configurations; and straight pipes and U-tube designs in shell-and-tube type heatexchangers. Thermal designs and simple stress analyses were performed to estimate the heatexchanger options, and the Finite Element Method was applied for more detailed calculations, especially for PCHE designs. Results of the options study show that the PCHE design has the smallest volume and heat transfer area, resulting in the least tritium permeation and greatest cost savings. It is theoretically the most reliable mechanically, leading to a longer lifetime. The two-stage heatexchanger arrangement appears to be safer and more cost effective. The recommended separation temperature between first and second stages in a serial configuration is 800oC, at which the high temperature unit is about one-half the size of the total heatexchanger core volume. Based on simplified stress analyses, the high temperature unit will need to be replaced two or three times during the plant’s lifetime. Stress analysis results recommend the off-set channel pattern configuration for the PCHE because stress reduction was estimated at up to 50% in this configuration, resulting in a longer lifetime. The tritium transport study resulted in the development of a tritium behavior analysis code using the MATLAB Simulink code. In parallel, the THYTAN code, previously performed by Ohashi and Sherman (2007) on the Peach Bottom data, was revived and verified. The 600 MWt VHTR core input file developed in preparation for the transient tritium analysis of VHTR systems was replaced with the original steady-state inputs for future calculations. A Finite Element Method analysis was performed using COMSOL Multiphysics software to accurately predict tritium permeation through the PCHE type heatexchanger walls. This effort was able to estimate the effective thickness for tritium permeations and develop a correlation for general channel configurations, which found the effective thickness to be much shorter than the average channel distance because of dead spots on the channel side.
For the purpose of impoving the response to cooling load variations and the part load characteristics, the optimal operation of a double-effect absorption refrigerating machine was investigated. The test machine was designed to be able to control energy input and weak solution flow rate continuously. It is composed of a gas-fired high-temperature generator, a separator, a low-temperature generator, an absorber, a condenser, an evaporator, and high- and low-temperature heatexchangers. The working fluid is Lithium Bromide and water solution. The standard output is 80 kW. Based on the experimental data, a simulation model of the static characteristics was developed. The experiments and simulation analysis indicate that there is an optimal weak solution flow rate which maximizes the coefficient of performance under any given cooling load condition. The optimal condition is closely related to the refrigerant steam flow rate flowing from the separator to the high temperature heatexchanger with the medium solution. The heat transfer performance of heatexchangers in the components influences the COP. The change in the overall heat transfer coefficient of absorber has much effect on the COP compared to other components.
In present day low energy houses, due to the high thermal insulation and the fitting of multiple glazed heat protection windows, the transmission heat demand of the buildings has been reduced so much that any further energy saving potential is small here and can only be achieved with considerable expense. For the ventilation heat demand which has gained in importance due to the reduced transmission heat demand, there is still a considerable energy saving potential. The first step for reducing the ventilation heat losses is the fitting of controlled mechanical flat ventilation. In this way, the flow of external air is matched to the hygienic requirements in the flat. A further reduction of the ventilation heat demand can be achieved by heat recovery. The simplest way of using the high enthalpy of the waste air to heat the incoming air is by use of a plate heatexchanger. The ventilation heat demand is considerably reduced by this simple system. Complete covering of the ventilation heat demand is achieved by the addition of a subsequent air/air small heat pump. The possibility of using a regenerative energy source for flat ventilation is provided by using an earth heatexchanger. (orig.).
This paper presents a bench scale experiment of a water thermo-capillary loop which allows to improve the understanding of its functioning mechanisms thanks to the internal visualisation of each component using transparent walls. The advantages of water are its non-toxicity, its high chemical compatibility with several materials and its low functioning pressure. The experimental device is presented and the functioning regimes of each component is analyzed: condenser (flow visualization, influence of tilt), evaporator (quality of heatexchange between teeth and porous medium, bubbles, heatexchange coefficient). (J.S.)
A refrigeration system having a vapor compression cycle utilizing a liquid over-feeding operation with an integrated accumulator-expander-heatexchanger. Hot, high-pressure liquid refrigerant from the condenser passes through one or more lengths of capillary tubing substantially immersed in a pool liquid refrigerant in the accumulator-expander-heatexchanger for simultaneously sub-cooling and expanding the liquid refrigerant while vaporizing liquid refrigerant from the pool for the return thereof to the compressor as saturated vapor. The sub-cooling of the expanded liquid provides for the flow of liquid refrigerant into the evaporator for liquid over-feeding the evaporator and thereby increasing the efficiency of the evaporation cycle.
The present invention proposes a cooling system with intermediate gas flow which ensures the reactor core cooling when the primary pumps are stopped either directly by means of main heat-exchange circuits ensuring normally the reactor operation, or by means of separated loops, these ones being able so to operate in an autonomous way for they produce their own electricity needs and also an excedent which is added to the power plant production. The cooling circuit and the heatexchanger are described in detail.
A semiconductor cooling arrangement wherein a semiconductor is affixed to a thermally and electrically conducting carrier such as by brazing. The coefficient of thermal expansion of the semiconductor and carrier are closely matched to one another so that during operation they will not be overstressed mechanically due to thermal cycling. Electrical connection is made to the semiconductor and carrier, and a porous metal heatexchanger is thermally connected to the carrier. The heatexchanger is positioned within an electrically insulating cooling assembly having cooling oil flowing therethrough. The arrangement is particularly well adapted for the cooling of high power switching elements in a power bridge.
Advanced light water reactor systems are designed to use passive emergency core cooling systems with horizontal pipes that provide highly subcooled water from water storage tanks or passive heatexchangers to the reactor vessel core under accident conditions. Because passive systems are driven by density gradients, the horizontal pipes often do not flow full and thus have a free surface that is exposed to saturated steam and stratified flow is present.
Laboratory tests with stratification inlet pipes marketed by the German company SOLVISSolarsysteme GmbH were carried out in a small test heat storage. The tests showed that the stratification pipes ensure that water entering the heat storage through the pipes enters the heat storage in the 'right' level so that the temperature stratification in the heat storage is built up in the best possible way as long as the volume flow rate of the entering water is lower than 10 l/min. If the volume flow rate increases the water will enter the heat storage in different levels. For volume flow rates higher that 20 l/min. water enters the heat storage in all levels of the heat storage. It is estimated that the stratification inlet pipes secure a good thermal stratification in the heat storage as long as the volume flow rate is not higher than 15 l/min. Based on the laboratory tests a 10000 l hot water tank for Sundparkens solar heating system was designed. A 336 m{sup 2} solar domestic hot water system was built in Sundparken, Elsinore. The solar heating system is a low flow system with a 10000 l hot water tank. Half of the solar collectors are facing east, half of the solar collectors are facing west. The collector tilt is for all collectors 15 deg. from horizontal. Both the east-facing and west-facing collectors have their own solar collector loop, circulation pump, external heatexchanger and control system. The external heatexchangers are used to transfer the heat from the solar collector fluid to the domestic water. The domestic water is pumped from the bottom of the hot water tank to the heatexchanger and back to the hot water tank through the SOLVIS stratification inlet pipes. In this way the water will enter the tank in the 'right' level so that thermal stratification is built up in the best possible way. In the mornings the east-facing solar collectors produce a lot of heat and therefore high return temperatures of the domestic water. This water will enter the tank in the upper part of the tank while the relatively cold water returning from the heatexchanger of the west-facing collectors enters the tank at the lower part of the tank. In the afternoons/evenings when the west-facing solar collectors produce more heat than the eastfacing collectors, the water heated by the west-facing collectors enters the top part of the tank while the water heated by the east-facing collectors enters the bottom part of the tank. The tank design ensures an excellent thermal stratification in the tank during all hours. Therefore the thermal performance of the solar heating system will be high in spite of the fact that the collectors are not optimally facing south. Measurements showed that the yearly net utilized solar energy of the system was 123 MWh corresponding to 366 kWh/m{sup 2}. The solar fraction of the solar heating system was 8% and 16%, respectively, with and without regard for the heat loss of the circulation piping. 40% of the solar radiation on the solar collectors were utilized. Compared to other large Danish solar domestic hot water systems the system in Sundparken is performing well. This might be a surprise because the solar collectors are far from being orientated optimally. The utilization of the solar radiation on the collectors for Sundparkens solar heating system was higher than for any other system earlier investigated. The reason for the good thermal performance and for the excellent utilization of the solar radiation is the high hot-water consumption and the good system design. Based on the investigations it is recommended in the future to design large solar heating systems as low flow systems with hot water tanks with external heatexchangers and stratification inlet pipes. (au)
We investigate heat transfer characteristics of a turbulent swept flow in a channel with a wire placed over one of its walls using direct numerical simulation. This geometry is a model of the flow through the wire-wrapped fuel pins, the heatexchanger, typical of many civil nuclear reactor designs. The swept flow configuration generates a recirculation bubble with net mean axial flow. A constant inward heat flux from the walls of the channel is applied. A key aspect of this flow is the presence of a high temperature region at the contact line between the wire and the channel wall, due to thermal confinement (stagnation). We analyze the variation of the temperature in the recirculation bubble at Reynolds number based on the bulk velocity along the wire-axis direction and the channel half he...
Quantum coherence can affect the thermodynamics of small quantum systems. Coherences have been shown to affect the power generated by a quantum heat engine (QHE) which is coupled to two thermal photon reservoirs and to an additional cavity mode. We show that the fluctuations of the heatexchanged between the QHE and the reservoirs strongly depend on quantum coherence, especially when the engine operates as a refrigerator, i.e., heat current flows from the cold bath to the hot bath. Intriguingly, we find that the ratio of positive and negative (with respect to the thermodynamic force) fluctuations in the heat current satisfies a universal coherence-independent fluctuation theorem.
We describe breakthrough results obtained in a feasibility study of a fundamentally new architecture for air-cooled heatexchangers. A longstanding but largely unrealized opportunity in energy efficiency concerns the performance of air-cooled heatexchangers 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 heatexchangers 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 heatexchangers 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 heatexchanger 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 heatexchanger surface. The prevailing wisdom is that little can be done to improve this situation; the 'fan-plus-finned-heat-sink' heatexchanger 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 heatexchanger. 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 heatexchanger. No one has yet devised a practical solution to the boundary layer problem. Another longstanding problem is inevitable fouling of the heatexchanger 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 heatexchanger resulting from restrictions on fan noise. The air-cooled heatexchanger described here solves all of the above three problems simultaneously. The 'Air Bearing HeatExchanger' 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.
Fluid flow in geothermal production and injection wells can be strongly affected by heat transfer effects with the formations surrounding the wellbore. Various techniques and approximations to model wellbore heat transmission have been presented in the literature. The objective of the present work is to develop a treatment of conductive heat transfer in the formations surrounding a wellbore that is simple, yet provides good accuracy for transient effects at early time. This is accomplished by adapting the well known semi-analytical heat transfer method of Vinsome and Westerveld (1980) to the problem of heat transfer to and from a flowing well. The Vinsome-Westerveld method treats heatexchange between a reservoir and adjacent cap and base rocks by means of a hybrid numerical-analytical method, in which temperature distributions in the conductive domain are approximated by simple trial functions, whose parameters are obtained concurrently with the numerical solution for the flow domain. This method can give a very accurate representation of conductive heat transfer even for non-monotonic temperature variations over a broad range of time scales. The only enhancement needed for applying the method to wellbore heat transmission is taking account of the cylindrical geometry around a flowing well, as opposed to the linear flow geometry in cap and base rocks. We describe the generalization of trial functions needed for cylindrical geometry, and present our implementation into the TOUGH2 reservoir simulator. The accuracy of the method is evaluated through application to non-isothermal flow through a pipe.
A three-dimensional computational study on conjugate heatexchangers was conducted. Attention was specifically directed towards studying extended surfaces used to increase heat transfer. The strategy adopted in the present investigation of forced convection in a flow passage was to use the finite volume method. Our implementation incorporated a SIMPLE-based semi-implicit solution algorithm which was applied to working equations formulated within the single-phase catalog. The analysis allowed for marked changes in thermodynamic and flow properties. To justify using the proposed numerical model to simulate this conjugate heat transfer problem, we considered first a heatexchanger with a plane fin simply because experimental data are available for comparison. This validation study was followed by a study of how a newly designed fin pattern can provide increased heat transfer. The efficiency has been judged by considering several aspects, namely the span-averaged pressure drop, Nusselt number and heat flux. To better illuminate the flow and heat transfer characteristics in a flow passage bounded by two fins having wavy geometries, we have plotted solutions in a three-dimensional format. (author)
In aquifer thermal energy storage (ATES) installations, ground water is circulated between an aquifer and heatexchangers via a well field. It is often necessary to soften the water to prevent carbonate scaling in pipes, heatexchangers, and well screens. Most ATES projects requiring water softening will be best served by using synthetic ion-exchange resins. The size of the resin beds, the resin regeneration cycle, and the amount of NaCl brine used in each regeneration depend on several factors. These are (1) the chemistry of the native ground water, (2) allowable residual hardness after softening, (3) the maximum flow rate of water through the ATES plant, and (4) exchange characteristics of the resin. Example calculations are given for a three-bed water softening system.
An ice storage system with a closed ice-making device using supercooled water has been developed. This system is made up of a chiller, a closed ice-making device, a supercooling heatexchanger, an ice storage tank and two pumps (a water-circulating pump and a brine-circulating pump). These components are connected by pipes filled with water and brine. The water in the storage tank is pumped into the heatexchanger and supercooled to - 2 degree C by brine supplied from the chiller. The supercooled water flows into the ice-making device. A fluid two-phase mixture of water and ice (slurry ice) is produced in the ice-making device as the phase changes from supercooled water to ice, the slurry ice is then transported to the storage tank. All these operations take place in the closed system without exposure to the atmosphere. Therefore, the slurry ice produced by the ice-making device can easily be transported to the storage tank, wherever the tank is installed. For example, an ice storage system can be built even if the tank is a long distance from the ice-making device, e.g., several floors above or below. Moreover this system can enhance COP (coefficient of performance) of the chiller at ice-making through the use of a plate-type heat-exchanger for the supercooling heat-exchanger that has high performance of heat transfer. The plate-type supercooling heat-exchanger can produce supercooled water of -2 degree C from brine of -3 degree C. The supercooling heatexchanger and the ice-making device have a 1,800 kW ice-making capacity. Therefore this system can be used as a heat source for district heating and cooling plants. (author)
This study is the first to map the flow regimes, which identify the form and structure of liquid and vapor, of R-134a in small-channel cross-flow condensers. The condenser tested here is used in automotive applications and uses smaller internal volumes than conventional heatexchangers to perform the same task. The flow regimes are documented for the pipes, headers, and small-channel condenser tubes. Consistent with the Damianides flow map, intermittent flow is the predominate flow regime in the small channels. The flow transitioned from a dispersed liquid to a bubble flow regime through the inlet header. The flow regime in the outlet header was always a dispersed gravity-driven liquid in the core with a thin liquid annulus on the wall.
The flow between two concentric cylinders which is termed as Taylor-Couette flow has been studied in scraped surface heatexchanger with and without blades. Shear rate in annular flow with and without blades was measured by Dumont et al. (2000a) using electrochemical method and determined the onset of Taylor vortices at specific Taylor number in both cases for Newtonian flow. CFD simulations have been carried out to determine the transition zone from laminar Couette flow to Taylor vortex flow using the same geometry for which Dumont et al. (2000a) had carried out the experiments. The Reynolds stress model (RSM) and k-@? model are used for Taylor vortex flow (Ta>300) to characterize the flow pattern in annular flow and SSHE respectively. The aim of the present work is to analyze the effect ...
Annular flows are a well utilized flow regime in many industrial applications, such as, heatexchangers, chemical reactors and industrial process equipment. These flows are characterized by a droplet laden vapor core with a thin, wavy liquid film wetting the walls. The prediction of annular flows has been largely confined to one-dimensional modeling which typically correlates the film thickness, droplet loading, and phase velocities by considering the average flow conditions and global mass and momentum balances to infer the flow topology. In this paper, a methodology to predict annular flows using a locally based two-fluid model of multiphase flow is presented. The purpose of this paper is to demonstrate a modeling approach for annular flows using a multifield, multidimensional two-fluid model and discuss the need for further work in this area.
heatexchangers to be used in 100-kWe nuclear space ... heat-source exchanger, recuperator and rejection exchanger (gas ... A CBC PCS was modeled in a recent spacecraft ..... MiniBRU was a development program (ground test only), mass ...
The conceptual design of a 600MWe demonstration SFR (Sodium-cooled Fast Reactor) has been performed by the Korea Atomic Energy Research Institute (KAERI). In order to enhance plant safety, reliable decay heat removal (DHR) systems with natural circulation flow have been considered, and a few types of sodium-to-air heatexchanger (AHX) have been employed as an ultimate heat sink for this type of DHR system. The DHR system comprises two diverse heat removal loops, and the heat load imposed on the primary sodium pool is safely rejected into the environment through different kinds of sodium-to-air heatexchangers. Serpentine-type and helical-coil sodium-to-air heatexchangers have been considered for air-coolers. The former is called as an FDHX (Forceddraft sodium-to-air HX) and the latter is simply called as an AHX. For a general AHX design, convection resistance in the shell-side air flow path becomes the dominant factor affecting the mechanism of the conjugate heat transfer from the sodium flow inside the tube to the air path across the sodium tube wall. To this end, verification of the AHX performance is one of the most important tasks to secure the overall performance of a DHR system. In order to assess the performance of the sodium-toair heatexchanger, KAERI is now constructing a largescale sodium thermal-hydraulic test facility, STELLA-1 (Sodium Integral Effect Test Loop for Safety Simulation and Assessment). The helical-coil AHX is to be installed at this facility, which is designed so that the local phenomena occurring at the sodium-to-air heatexchanger of the prototype is well preserved. Various scaling methodologies aimed at providing a suitable simulation for single-phase heat transfer with natural circulation of sodium and air have also been applied to obtain proper scaled design parameters. This study introduces the one-dimensional design approaches of the helical-coil AHX using reasonable heat transfer and pressure drop models, and provides the CFD analysis results to confirm the multi-dimensional flow effect coming from the complicated heat transfer tube arrangement. The feasibility of the helical-coil AHX design and some design features regarding the helical tube arrangement are discussed as well
We investigate the two-dimensional transport of heat through viscous flow between two parallel rough interfaces with a given fractal geometry. The flow and heat transport equations are solved through direct numerical simulations, and for different conduction-convection conditions. Compared with the behavior of a channel with smooth interfaces, the results for the rough channel at low and moderate values of the Peclet number indicate that the effect of roughness is almost negligible on the efficiency of the heat transport system. This is explained here in terms of the Makarov's theorem, using the notion of active zone in Laplacian transport. At sufficiently high Peclet numbers, where convection becomes the dominant mechanism of heat transport, the role of the interface roughness is to generally increase both the heat flux across the wall as well as the active length of heatexchange, when compared with the smooth channel. Finally, we show that this last behavior is closely related with the presence of recircul...
This work investigates the flow field and the heat transfer characteristics of a shell-and-tube heatexchanger for the cooling of syngas. Finite volume method based on FLUENT software was used and the RNG k-&z.epsiv; turbulence model was adopted for modeling turbulent flow. The porosity rate, the distribution of the resistance and the distribution of the heat source are introduced to FLUENT by coupling the user defined function. The pressure drop, the temperature distribution and the variation of local heat transfer are studied under the effects of the syngas components and the operating pressure, and the effect of the arrangement of the baffles on the heat transfer is studied. The results show that higher operation pressure can improve the heat transfer, however brings bigger pressure dro...
The Vuilleumier process allows to transform heat at different temperature levels; owing to thus, it may be used in heat pumps, for instance, in which heat is used as the driving energy. The process is realized by periodically changing the distribution of an inert gas across three volumes of different temperature levels using regenerators and heatexchangers. In theory, the Vuilleumier machine requires no mechanical driving work and will achieve Carnot efficiency under ideal conditions. High efficiency is expected to obtain under practical operation, too, since the temperature of the drive heatflow may be relatively high e.g. above 500/sup 0/C. Drive heatflow may be supplied, for instance, by external combustion of a fuel - preferably gas.
Silicon carbide ceramic foams are used to achieve high performances in many industrial heatexchange systems. This paper experimentally investigated the heat transfer characteristics of air flowing through high-temperature silicon carbide ceramic foams in an electric air heating furnace heated by resistance wires and silicon-carbon sticks. It was found that for an air inlet flow rate of 200m3/h, the air outlet temperature reached 981degreeC after about 2h when five silicon carbide ceramic foam panels were inserted inside the furnace, while it only reached about 650degreeC when no ceramic foam was inserted. The heat transfer enhancement was due to that the ceramic foams enlarged the heat transfer area between air and hot solid surfaces. The results also showed that the position of the ceram...
This study is concerned with an open absorption (liquid desiccant) system, capable of producing both cooling and dehumidification for air conditioning, utilizing low-grade heat. The system includes a novel solution heat and mass exchanger (HME) designed to serve as a desiccant solution reservoir for both the absorber and desorber, enabling mass transfer between them with minimum heat transfer losses and eliminating the need for an external recuperative heatexchanger. The use of this new HME together with an improved solution flow arrangement in the new system facilitates the use of adiabatic absorption/desorption with minimum circulation heat losses and wetting problems. The characteristic performance of the system was studied under varying operating conditions. The use of the new HME has...
This final report for the Swiss Federal Office of Energy (SFOE) presents the results of tests and measurements made at the University of Applied Science in Buchs, Switzerland, on a variable-speed, multi-cell, sliding-vane rotary compressor. The work forms part of a project that is to provide technical support for the evaluation of components for the so-called Swiss Retrofit Heat Pump Project. This heat pump must produce temperatures that are higher than those normally encountered for heat pumps in order to be able to replace old heating systems with high flow temperatures. The loading-test rig for the air-water heat pump built at the University is described and the performance of the compressor tested is discussed. Possibilities of using an economiser to boost performance at low ambient temperatures and to increase heating capacity are discussed, as are the effects on the heat pump's efficiency by varying heat-exchanger surface area.
Liquid-liquid direct-contact phenomena are abundant in nature. Being most efficient in heat transfer between two liquids, the direct-contact type has been applied to the process industry, for example, as direct-contact heatexchangers. This type of heat transfer equipment is characterized by a number of advantages, including higher heat transfer coefficients, a lower operating temperature difference, simple design, less scaling problems, and no fouling and corrosion in the absence of a separate on low-grade heat sources, with applications in latent-heat storage systems, industrial waste heat recover, ocean thermal energy conversion, water desalination, geothermal heat utilization, etc. This paper reports that an optical Fourier transform system is applied to visualize natural-convective flow patterns inside and evaporating liquid drop floating on an immiscible liquid. Strong cellular convective patterns prevail inside the drop at room temperature, which play an important role in the evaporation of the drop.
The flow of river water around large woody debris (LWD) creates pressure gradients along the riverbed that drive river-groundwater mixing, or hyporheic exchange, and heat transport within the hyporheic zone. We quantify hyporheic fluid and heatexchange induced by current interaction with channel-spanning logs using two approaches: laboratory flume experiments and numerical simulations that link turbulent open-channel fluid flow, porous fluid flow, and heat transport. Flume and numerical experiments show that logs produce a characteristic diel temperature pattern within sediment that shifts with log blockage ratio (a fraction of the channel depth blocked by the log), channel Froude number, and sediment permeability. Upstream of a log, downwelling water transports the river's diel thermal signal deep into the sediment. Downstream, upwelling water from shallow flow paths has a thermal signal similar to the surface water, while upwelling water from deep flow paths forms a wedge of buffered (low-amplitude) temperatures. Since most hyporheic water emerges from shallow flow paths, upwelling water has limited potential to buffer surface water temperature. Because of historic channel clearing practices, modern rivers have unnaturally low densities of LWD. A key implication is that LWD removal has contributed to thermal homogenization and potential degradation of hyporheic habitats. LWD reintroduction is a promising strategy to improve vertical connectivity in rivers and increase thermal patchiness within the hyporheic zone. However, hyporheic exchange near LWD may not impact diel surface water temperatures at the reach scale.
A heat pipe arrangement for exchangingheat between two different temperature fluids. The heat pipe arrangement is in a ounterflow relationship to increase the efficiency of the coupling of the heat from a heat source to a heat sink.
A framework for a method to predict fluidelastic instability in heatexchanger tube bundles is presented. The method relies on a three-dimensional, cylindrical coordinate, thermal-hydraulic analysis code to obtain a representation of the three-dimensional flow distribution within the heatexchanger. With this information, local crossflow velocities corresponding to each tube in the exchanger are obtained by interpolation and resultant crossflow velocity distributions are computed. With a knowledge of the vibration mode shapes and frequencies, reduced effective crossflow velocities are then computed for each tube. A comparison with experimental results shows excellent agreement: the tubes with high values of predicted reduced effective crossflow velocity are the same tubes that first experience fluidelastic instability in the flow tests and vibrate most violently; also, the simulation correctly predicts that the tubes directly exposed to the flow from the inlet nozzle have a low potential for fluidelastic instability. Very good agreement is also shown in the comparison of the predicted reduced effective crossflow velocities with the critical value obtained from a design guide. In summary, the feasibility of developing a heatexchanger tube vibration prediction method, based on a computer simulation of flow distribution, is demonstrated. Such a method would have immediate application in design optimization. However, further development and evaluation are required.
BEETIT Project: A2 is developing a building moisture and heatexchange technology that leverages a new material and design to create healthy buildings with lower energy use. Commercial building owners/operators are demanding buildings with greater energy efficiency and healthier indoor environments. A2 is developing a membrane-based heat and moisture exchanger that controls humidity by transferring the water vapor in the incoming fresh air to the drier air leaving the building. Unlike conventional systems, A2 locates the heat and moisture exchanger within the depths of the building’s wall to slow down the air flow and increase the surface area that captures humidity, but with less fan power. The system’s integration into the wall reduces the size and demand on the air conditioning equipment and increases liable floor area flexibility.
The supports for heatexchanger tubes are usually plates with drilled holes; other types of supports also have been used. To facilitate manufacture and to allow for thermal expansion of the tubes, small clearances are used between tubes and tube supports. The dynamics of tube/support interaction in heatexchangers is fairly complicated. Understanding tube dynamics and its effects is important for heatexchangers. This paper summarizes the current state of the art on this subject and to identify future research needs. Specifically, the following topics are discussed: dynamics of loosely supported tubes, tube/support gap dynamics, tube response in flow, tube damage and wear, design considerations, and future research needs. 55 refs., 1 fig.
It has long been known that carbon steel exposed to some geothermal brines is aggressively attacked, and large corrosion allowances must be made in the design of piping used in such environments. In addition, scaling of the pipes reduces the flow through within a short period of time. Several high temperature polymer concretes have been developed which can be used as non-corrosive liner materials. In addition, polymer concretes with high thermal conductivities have been developed which may be used as heatexchanger tubes for geothermal brines. Studies have indicated that polymer concretes will not scale as rapidly as carbon steel does, thus making them attractive alternatives for heatexchanger tubes. Thin walled, thermally conductive polymer concrete tubes have been made that can withstand pressures >4.1 MPa at 150/sup 0/C without leaking. Continuing studies are being made to characterize these materials and evaluate them for heatexchanger applications.
Compact tube-fin evaporators have been extensively used in refrigeration cassettes for light commercial applications. Such refrigeration systems are space constrained and, therefore, the heatexchangers (condenser and evaporator) must have a large area-to-volume ratio. In addition, such applications require a subfreezing evaporating temperature that induces the growth of a frost layer on the finned surface, which may block the evaporator if a proper defrost strategy is not used. Before completely blocking the evaporator, the frost layer depletes the heatexchanger performance by adding an extra thermal resistance and also by reducing the fan-supplied air flow rate. Understanding the way the frost forms on these compact heatexchangers and also the way the fan is affected by frost clogging ...
A method of forming a polyester resin from dicarboxylic acid anhydrides and monoepoxides in a specially designed mixing apparatus. The mixing apparatus is a vessel having a centrally disposed vertical draft tube and a centrifugal impeller at the lower end of the draft tube. A plurality of vertical heatexchange tubes surround the draft tube. The reactants are admitted into the vessel and drawn down through the draft tube by the impeller which mixes the reactants and forces the reactants up through the heatexchange tubes. The heatexchange tube portion of the vessel acts as a plug flow reactor, and the upper and lower portions of the vessel act as a back mix reactor. As reactants are admitted into the vessel, product is drawn off from the vessel.
This invention provides a heatexchanger, particularly useful for systems requiring cooling of hot particulate solids, such as the separated fines from the product gas of a carbonaceous material gasification system. The invention allows effective cooling of a hot particulate in a particle stream (made up of hot particulate and a gas), using gravity as the motive source of the hot particulate. In a preferred form, the invention substitutes a tube structure for the single wall tube of a heatexchanger. The tube structure comprises a tube with a core disposed within, forming a cavity between the tube and the core, and vanes in the cavity which form a flow path through which the hot particulate falls. The outside of the tube is in contact with the cooling fluid of the heatexchanger.
Internal boundaries in multiphase flow greatly complicate fluid-dynamic and heat-transfer descriptions. Different flow regimes or topological configurations can have radically dissimilar interfacial and wall mass, momentum, and energy exchanges. To model the flow dynamics properly requires estimates of these rates. In this paper the common flow regimes for gas-liquid systems are defined and the techniques used to estimate the extent of a particular regime are described. Also, the current computer-code procedures are delineated and introduce a potentially better method is introduced.
Abstract in english The study of non-Newtonian flow in plate heatexchangers (PHEs) is of great importance for the food industry. The objective of this work was to study the pressure drop of pineapple juice in a PHE with 50º chevron plates. Density and flow properties of pineapple juice were determined and correlated with temperature (17.4 (more) friction factor for non-isothermal flow of pineapple juice in the PHE was obtained for diagonal and parallel/side flow. Experimental results were well correlated with the generalized Reynolds number (20
This experimental study investigates the oblique inlet pressure loss for the entry of an annular swirling flow into an automotive catalyst substrate. The results are applicable to a wide range of compact heatexchangers. For zero swirl, the total pressure loss agrees with established expressions for pressure loss in developing laminar flow in parallel channels with finite wall thickness. For positive swirl, the additional pressure loss due to oblique flow entry is correlated to the tangential velocity upstream of the catalyst, measured using laser-Doppler anemometry. The obtained oblique inlet pressure loss correlation can improve the accuracy of numerical calculations of the flow distribution in catalysts. (author)
In the steam generator of the fast breeder prototype reactor ''Monju'', heatexchange tubes of helical coil type are utilized. Steam-water two-phase flows in the helical coil tube have unique characteristic due to effects of centrifugal acceleration. In this report, we visualized gas-liquid two-phase flows in the helical coil tube for providing the flow pattern map, and suggested the method for reconstructing the interfacial structures of gas-liquid two-phase flows in the cross-section of the tube. The method was applied to artificial images and experimental images, and the applicability was discussed. (author)
The efforts to establish a greater pool of knowledge in the field of low temperature heat transfer for the application of geothermal spring waters to space heating are described. A comprehensive set of heat loss experiments involving passive radiant heating panels is conducted and the results presented in an easily interpretable form. Among the conclusions are the facts that heating a 65 to 70 F/sup 0/ space with 90 to 100 F/sup 0/ liquids is a practical aim. The results are compared with the much lower rates published in the American Society of Heating Refrigeration and Air Conditioning Engineers SYSTEMS, 1976. A heatexchange chamber consisting of a 1000 gallon three compartment, insulated and buried tank is constructed and a control and pumping building erected over the tank. The tank is intended to handle the flow of geothermal waters from Pinkerton Hot Springs at 50 GPM prior to the wasting of the spring water at a disposal location. Approximately 375,000 Btu per hour should be available for heating assuming a 15 F/sup 0/ drop in water temperature. A combination of the panel heat loss experiments, construction of the heatexchange devices and ongoing collection of heat loss numbers adds to the knowledge available to engineers in sizing low temperature heat systems, useful in both solar and geothermal applications where source temperature may be often below 110 F/sup 0/.
Solids moving with a gas stream in a pipeline can be found in many industrial processes, such as power generation, chemical, pharmaceutical, food and commodity transfer processes. A mass flow rate of the solids is important characteristic that is often required to be measured (and controlled) to achieve efficient utilization of energy and raw materials in pneumatic conveying systems. The methods of measuring the mass flow rate of solids in a pneumatic pipeline can be divided into direct and indirect (inferential) measurements. A thermal solids' mass flow-meter, in principle, should ideally provide a direct measurement of solids flow rate, regardless of inhomogeneities in solids' distribution and environmental impacts. One key issue in developing a thermal solids' mass flow-meter is to characterize the heat transfer between the hot pipe wall and the gas-solids dense phase flow. The Eulerian continuum modeling with gas-solid two phases is the most common method for pneumatic transport. To model a gas-solid dense phase flow passing through a heated region, the gas phase is described as a continuous phase and the particles as the second phase. This study aims to describe the heat transfer characteristics between the hot wall and the gas-solids dense phase flow in pneumatic pipelines by modeling a turbulence gas-solid plug passing through the heated region which involves several actual and crucial issues: selections of interphase exchange coefficient, near-wall region functions and different wall surface temperatures. A sensitivity analysis was discussed to identify the influence on the heat transfer characteristics by selecting different interphase exchange coefficient models and different boundary conditions. Simulation results suggest that sensitivity analysis in the choice of models is very significant. The simulation results appear to show that a combination of choosing the Syamlal-O'Brien interphase exchange coefficient model and the standard k-? model along with the standard wall function model might be the best approach, by which, the simulation data seems to be closest to the experimental results.
An apparatus for generation of steam in a borehole for penetration into an earth formation wherein a spiral, tubular heatexchanger is used in the combustion chamber to isolate the combustion process from the water being superheated for conversion into steam. The isolation allows combustion of a relatively low pressure oxidant and fuel mixture for generating high enthalpy steam. The fuel is preheated by feedback of combustion gases from the top of the combustion chamber through a fuel preheater chamber. The hot exhaust gases of combustion at the bottom of the combustion chamber, after flowing over the heatexchanger enter an exhaust passage and pipe. The exhaust pipe is mounted inside the water supply line heating the water flowing into the heatexchanger. After being superheated in the heatexchanger, the water is ejected through an expansion nozzle and converts into steam prior to penetration into the earth formation. Pressure responsive doors are provided at a steam outlet downstream of the nozzle and close when the steam pressure is lost due to flameout.
The AP600 reactor is a pressurized water reactor being designed to utilize a passive residual heat removal (PRHR) heatexchanger as the safety grade means for residual heat removal. The PRHR heatexchanger 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 heatexchanger 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.
The NGNP Project is currently investigating the use of metallic, diffusion welded, compact heatexchangers to transfer heat from the primary (reactor side) heat transport system to the secondary heat transport system. The intermediate heatexchanger will transfer this heat to downstream applications such as hydrogen production, process heat, and electricity generation. The channeled plates that make up the heat transfer surfaces of the intermediate heatexchanger will have to be assembled into an array by diffusion welding.
Stream restoration structures such as large wood can enhance shallow river-groundwater exchange, or hyporheic exchange, and alter temperature dynamics in restored reaches. We added and then removed channel-spanning logs in a second-order mountain meadow stream to test short-term impacts on hyporheic exchange, streambed temperatures, and surface water temperatures. Based on vertical seepage measurements and numerical simulations of hyporheic fluid and heatflow, large wood addition increased hyporheic exchange and altered streambed temperatures. In this losing stream, meter-scale hyporheic exchange cells formed beneath large wood. Upwelling pore water downstream of logs stabilized diel temperature cycles across wood, which may indicate that surface storage zones rather than hyporheic storage zones increased thermal retardation. Losing conditions limited the spatial extent and rates of hyporheic exchange near large wood. Impacts of large wood reintroduction on hyporheic exchange depend on ambient groundwater discharge or recharge, streambed permeability, channel Froude number, large wood blockage ratio, and large wood spacing. In many streams, large wood reintroduction may increase hyporheic habitat volume and complexity but may not increase exchange rates enough to alter surface water temperature or chemistry. Surface storage zones such as eddies and pools can still influence heat and solute retention in the channel.
Steam reforming of hydrocarbons using a catalytic plate-type-heat-exchanger (CPHE) reformer is an attractive method of producing hydrogen for a fuel cell-based micro combined-heat-and-power system. In this study the flow distribution in a CPHE reformer, which uses a coated wire-mesh catalyst, is considered to investigate the effect of catalyst wire-mesh pressure drop characteristics on flow distribution in the CPHE reformer. Flow distribution in a CPHE reformer is rarely uniform due to inlet and exhaust manifold design. Poorly-designed manifolds may lead to severe flow maldistribution, flow reversal in some of the CPHE reformer channels and increased overall pressure drop. Excessive flow maldistribution can significantly reduce the CPHE reformer performance. Detailed three-dimensional mode...
A two-equation turbulence closure model (k-{omega}) using an h-adaptive grid technique and finite element method (FEM) has been developed to simulate low Mach flow and heat transfer. These flows are applicable to many flows in engineering and environmental sciences. Of particular interest in the engineering modeling areas are: combustion, solidification, and heatexchanger design. Flows for indoor air quality modeling and atmospheric pollution transport are typical types of environmental flows modeled with this method. The numerical method is based on a hybrid finite element model using an equal-order projection process. The model includes thermal and species transport, localized mesh refinement (h-adaptive) and Petrov-Galerkin weighting for the stabilizing the advection. This work develops the continuum model of a two-equation turbulence closure method. The fractional step solution method is stated along with the h-adaptive grid method (Carrington and Pepper, 2002). Solutions are presented for 2d flow over a backward-facing step.
In this paper, conjugate heat transfer associated with the flow of sodium in an annulus in the decay heat removal mode of advanced fast reactors is studied. The coupled governing equations of momentum and energy are solved numerically and analytically. The TEACH code with the SIMPLE algorithm has been used for the internal forced flow and wall regions. For turbulent flow, a k-{epsilon} model is employed. The integral method is used for natural convection, and one-dimensional analysis is performed for the stratified flow over and underneath the redan. Results are presented for the two-dimensional temperature field in the fluids and the solid for both laminar and turbulent flows. A substantial amount of energy exchange between the hot or cold pool and the sodium flowing in the annulus occurs via the liner. As a result, convective boundary layers form along the liner.
Two simulation models, an analysis and a design model, were developed to evaluate a multi-barn tobacco curing system. With data collected in 14 tests, the analysis model was used to study the energy supplies and demands. Energy was supplied by fuel, electricity, heatexchanger, solar collector, tobacco respiration and recycling conditioning. Energy demand associated with this system was used to change the enthalpy of the exchanged air, and elevate and maintain the temperature of the drying tobacco and curing structure. Results showed that the effectiveness of heatexchanger ranged from 0.39 to 0.99, with an average of 0.707. A regression equation of effectiveness, expressed as a function of temperatures of cold inlet and hot inlet air, exhaust air humidity and air mass flow rate, was obtained to describe the performance of the heatexchanger. With the aid of the analysis model, information of outside air temperature, solar radiation, moisture content of tobacco during curing, air-flow rates and curing schedule were obtained to develop a design model. The results of simulation from the design model indicated that increasing barn capacity will improve the efficiency of solar energy collection. Multi-barn systems were found to be better than single-barn systems in both solar energy collection and heat recovery. Six different sizes of heatexchangers were investigated for a six-barn expanded system. The results suggested that there may not be an economic advantage to increase heatexchanger size beyond about 3-m length, as number of barns are increased between three and seven.
An emerging issue relative to beryllium technology in fusion involves tritium interactions with molten beryllium-bearing salts. Innovative designs for fusion reactors, both magnetic and inertially confined, feature the molten salt mixture 2LiF.BeF{sub 2}, commonly called Flibe, as a tritium breeder and coolant. Tritium is bred in the Flibe as neutrons from the plasma are absorbed by Li atoms, which then transmute to tritium and helium. Transmutation of tritium from Be also occurs. Among the issues to be resolved for such coolant systems is the potential loss of tritium from the Flibe coolant to the walls of the system, particularly through heatexchanger tubes, and from there into secondary coolants or working fluids and the environment. Effectively removing tritium from Flibe in clean-up units is also important. In quiescent or low Reynolds number flow, tritium movement through Flibe is governed by diffusion. For Flibe in turbulent flow, as in heatexchanger tubes, transport is by turbulent mixing, and the same flow conditions and structural design features that maximize heat transfer to the heatexchanger walls will enhance the transport of tritium to those same surfaces. Analyses have been performed to estimate the fractional loss of tritium through heatexchanger tubes and release rates from Flibe droplets in vacuum disengagers in molten Flibe systems. The calculations suggest unacceptably large losses of tritium through heatexchanger tubes. The gravity of the implications of these estimates calls for experimental verification to determine if tritium losses through molten Flibe heatexchangers or other Flibe systems can really be so high and whether vacuum disengagers will really work. There is also a need for better information on evolution of tritium from Flibe droplets in a vacuum. Several experiments are presently being planned to address these issues and are discussed. These include experiments to induce tritium in Flibe using spontaneous fission neutrons, experiments in flowing loops to evaluated tritium losses through heatexchanger walls, and exploration of schemes for tritium extraction from molten Flibe. (orig.)
Compact fission power systems are under consideration for use in long duration space exploration missions. Power demands on the order of 500 W, to 5 kW, will be required for up to 15 years of continuous service. One such small reactor design consists of a fast spectrum reactor cooled with an array of in-core alkali metal heat pipes coupled to thermoelectric or Stirling power conversion systems. Heat pipes advantageous attributes include a simplistic design, lack of moving parts, and well understood behavior. Concerns over reactor transients induced by heat pipe instability as a function of extreme thermal transients require experimental investigations. One particular concern is rapid cooling of the heat pipe condenser that would propagate to cool the evaporator. Rapid cooling of the reactor core beyond acceptable design limits could possibly induce unintended reactor control issues. This paper discusses a series of experimental demonstrations where a heat pipe operating at near prototypic conditions experienced rapid cooling of the condenser. The condenser section of a stainless steel sodium heat pipe was enclosed within a heatexchanger. The heat pipe - heatexchanger assembly was housed within a vacuum chamber held at a pressure of 50 Torr of helium. The heat pipe was brought to steady state operating conditions using graphite resistance heaters then cooled by a high flow of gaseous nitrogen through the heatexchanger. Subsequent thermal transient behavior was characterized by performing an energy balance using temperature, pressure and flow rate data obtained throughout the tests. Results indicate the degree of temperature change that results from a rapid cooling scenario will not significantly influence thermal stability of an operating heat pipe, even under extreme condenser cooling conditions.
A space air heating or cooling device comprises an elongate box-like channel, a mixing chamber formed between a side wall of the device and the channel and a heatexchanger in the upper part of the mixing chamber. The mixing chamber has a bottom opening. The side wall of the channel has airflow openings from which fresh air is directed downwards into the mixing chamber to induce a flow of room air via the heatexchanger. The combined air flow is directed to the side from the mixing chamber bottom opening by a guide. The opening may be associated with a false ceiling. The air directing means associated with the openings are pressed from the sidewalls, or are defined by downwardly directed curved nozzle tubes
This study presents a theoretical and experimental analysis of the thermal performance of a solar water heater prototype with an internal exchanger using a thermosiphon system. The heatexchanger made of a rolled copper tube is placed diagonally in the storage tank so that the hot fluid crosses a significant mass of stored water. The results focus mainly on the levels of the heat fluxes, temperatures recorded, mass flow rate and efficiency of the collector. During the main insulation period, one obtains satisfactory qualitative and quantitative agreement between the experimental and theoretical results of mass flow rate and temperatures. Those indicate heat fluxes whose peak reaches 989 W/m{sup 2}, collector outlet water temperature levels of more than 85.5 C and a collector thermal effectiveness around 58%. (author)
An experimental study of bubble absorption in a plate heatexchanger using ammonia/lithium nitrate and ammonia/(lithium nitrate + water) mixtures has been carried at operating conditions of air-cooled absorption systems driven by low temperature heat sources. An experimental test has been layout and set-up for the absorber characterization at different operation conditions. Experiments have been performed at a nominal system pressure of 510 kPa absolute using a corrugated plate heatexchanger formed by three channels in which absorption takes place in the central one. A sensitive study of the main operating conditions such the weak solution inlet concentration and flow rate, and cooling-water inlet temperature and flow rate on the absorber efficiency parameters has been performed. For both...
Conceptual design for a free-piston Vuilleumier cycle heat pump machine was proposed. The machine was designed based upon the numerical results of a dynamic analysis method. The method included the effect of self excitation vibration with dissipation caused by the flow friction of an oscillating working gas flow and solid friction of seals. It was found that the design values of reciprocating masses and spring constants proposed in published papers related to this study were suitable for practical use. The fundamental effects of heatexchanger elements on dynamic behaviors of the machine were clarified. It has been pointed out that some improvements were required for thermodynamic analysis of heatexchangers and working spaces.
To minimize the negative effects of scale formation in heatexchangers, new anti-fouling strategies are focusing on the modification of heat transfer surfaces. These modifications should lead to tailor-made surfaces for different technical applications. The aim of this surface modification is the extension of the induction period to minimize the negative effects of fouling and maximize the endurance of the heatexchanger. To achieve this, different surface coatings on stainless steel were investigated with respect to fouling tendency. The effects of flow velocity with respect to Reynolds number on the induction time of CaSO4 crystallization fouling were tested in different test units. Diamond-like carbon (DLC) coatings extend the induction time at every measured flow velocity. At higher Re...
A double-pipe helical heatexchanger was numerically studied to determine the effects of thermally dependent viscosity and non-Newtonian flows on heat transfer and pressure drop for laminar flow. Thermally dependent viscosities were found to have very little effect on the Nusselt number correlations for Newtonian fluids; however significant effects on the pressure drop in the heatexchanger were predicted. Changing the flow rate in the annulus can significantly affect the pressure drop in the inner tube, since the average viscosity of the fluid in the inner tube would change due to the change in the average temperature. The effects of non-Newtonian power law fluids on the heat transfer and the pressure drop were determined for laminar flow in the inner tube and in the annulus. The Nusselt number was correlated with the Peclet number for heat transfer in the inner tube. For the annulus, the Nusselt number was found to correlate best with the Peclet number and the curvature ratio. Pressure drop data were compared by using ratios of the pressure drop of the non-Newtonian fluid to a Newtonian fluid at identical mass flow rates and consistency indices. (author)
The objectives of this research are to: extend the range of pressure drop data for ice-water slurry flows, and design and build a prototypical ice slurry distribution system which demonstrates ice slurry handling at an end user's heatexchanger, without sending ice slurry directly through the heatexchanger. The results of Phase 1 work demonstrated a 40% reduction in pump power required to move an ice-water slurry versus the same mass flow of water only. In addition to lower pressure drop, pumping ice slurries is advantageous because of the large latent and sensible heat cooling capacity stored in the ice compared to only sensible heat in chilled water. For example, an ice-water slurry with a 20% ice fraction (by mass) has a mass flow rate that is 70% less than the mass flow rate required for a chilled water system cooling and equivalent load. The greatly reduced mass flow combined with the friction reducing effects of ice-water slurries results in a total savings of 83% in pumping power. Therefore, a substantial savings potential exists for capital costs and system operating costs in ice-water slurry district cooling systems. One potential disadvantage of an ice-slurry district cooling system is the introduction of ice into equipment not so designed, such as air handlers at end user locations. A prototypic ice slurry distribution loop will demonstrate a cooling network which will provide ice slurry to an end user but sends ice free water into the actual heat transfer.
In order to enhance convective heat transfer of a heatexchanger, adding injection air to main air flow through a slit into the laminar boundary layer formed on a horizontal flat plate, the effect of injection of heat transfer and skin friction characteristics were experimentally investigated through augmentation of transient from a laminar flow to a turbulent one. Friction factor and heat transfer coefficient were measured for air flow with a range of Reynolds number from 3.0 * 10{sup 4} to 6.4 * 10{sup 5} and of injection rate from 0.005 to 0.1. Main results were obtained as follows: increasing the injection rate decreased local heat transfer coefficient around the front and behind ends of the slit, the flow accumulating zone and around the transition point to the turbulence flow of heat transfer; the heat transfer coefficient and the friction coefficient could be controlled through varying the injection rate since common points were observed between their average values; when a performance evaluation for enhanced heat transfer was made under the condition of constant pumping power, the maximum increasing rate of Staton number for the injection rate of 0.1 and 0.5 were 1.39 and 1.29 respectively. 14 refs., 11 figs.
Vahterus Oy, located at Kalanti, has manufactured heatexchangers since the beginning of 1990s. About 90% of the equipment produced are exported. In the PSHE (Plate and Shell) solution of the Vahterus heatexchanger the heat is transferred by round plated welded to form a compact package, which is assembled into a cylindrical steel casing. The heatexchanger contains no gaskets or soldered joints, which eliminates the leak risks. Traditional heatexchanges are usually operated at higher temperatures and pressures, but the heat transfer capacities of them are lower. Plate heatexchangers, on the other hand, are efficient, but the application range of them is narrow. Additionally, the rubber gasket of the heatexchange plates, sealing the joints of the heatexchanging plates, does not stand high pressures or temperatures, or corroding fluids. The new welded plate heatexchanger combine the pressure and temperature resistance of tube heatexchangers and the high heatexchange capacity of plate heatexchangers. The new corrosion resisting heatexchanger can be applied for especially hard conditions. The operating temperature range of the PSHE heatexchanger 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 heatexchangers. Adjusting the number of heatexchanging plates can change the capacity of the heatexchanger. Power range of the heatexchanger can be as high as 80 MW. Due to the corrosion preventive construction and the small dimension the PSHE heatexchanger can be applied for refrigerators using ammonia as refrigerant. These kinds of new Vahterus heatexchangers are in use in 60 countries in more than 2000 refrigerators.
