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1

Auxiliary Heat Exchanger Flow Distribution Test  

International Nuclear Information System (INIS)

The Auxiliary Heat Exchanger Flow Distribution Test was the first part of a test program to develop a water-cooled (tube-side), compact heat exchanger for removing heat from the circulating gas in a high-temperature gas-cooled reactor (HTGR). Measurements of velocity and pressure were made with various shell side inlet and outlet configurations. A flow configuration was developed which provides acceptable velocity distribution throughout the heat exchanger without adding excessive pressure drop

2

Stirling Engine With Radial Flow Heat Exchangers  

Science.gov (United States)

Conflict between thermodynamical and structural requirements resolved. In Stirling engine of new cylindrical configuration, regenerator and acceptor and rejector heat exchangers channel flow of working gas in radial direction. Isotherms in regenerator ideally concentric cylinders, and gradient of temperature across regenerator radial rather than axial. Acceptor and rejector heat exchangers located radially inward and outward of regenerator, respectively. Enables substantial increase in power of engine without corresponding increase in diameter of pressure vessel.

Vitale, N.; Yarr, George

1993-01-01

3

Cryogenic Heat Exchanger with Turbulent Flows  

Science.gov (United States)

An evaporator-type cryogenic heat exchanger is designed and built for introducing fluid-solid heat exchange phenomena to undergraduates in a practical and efficient way. The heat exchanger 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…

Amrit, Jay; Douay, Christelle; Dubois, Francis; Defresne, Gerard

2012-01-01

4

Stokes flow heat transfer in an annular, rotating heat exchanger  

International Nuclear Information System (INIS)

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 heat exchanger-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 transfer rate is a maximum. - Highlights: ? The eccentric, annular, rotating heat exchanger is studied for periodic Stokes flow. ? Counter-rotating the inner tube with a periodic velocity enhances the heat transfer. ? The heat-transfer enhancement under such conditions is due to chaotic advection. ? For a given axial flow rate there is a frequency that maximizes the heat transfer. ? There is also an optimum value of the eccentricity ratio.

5

Simulation Studies on A Cross Flow Plate Fin Heat Exchanger  

Directory of Open Access Journals (Sweden)

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

M. Thirumarimurugan

2008-01-01

6

Two-phase Flow Distribution in Heat Exchanger Manifolds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO2 and HFC-134a were used as refrigerants.

Vist, Sivert

2004-01-01

7

Auxiliary heat-exchanger flow-distribution test  

International Nuclear Information System (INIS)

The Auxiliary Heat Exchanger Flow Distribution Test was the first part of a test program to develop a water-cooled (tube-side), compact heat exchanger for removing heat from the circulating gas in a High-Temperature Gas-Cooled Reactor (HTGR). The function of this heat exchanger is to provide emergency cooldown for the HTGR. It is designed to operate over a wide range of helium or helium mixture conditions from depressurized to pressurized reactor operations

8

Thermal performance modeling of cross-flow heat exchangers  

CERN Document Server

This monograph introduces a numerical computational methodology for thermal performance modeling of cross-flow heat exchangers, with applications in chemical, refrigeration and automobile industries. This methodology allows obtaining effectiveness-number of transfer units (e-NTU) data and has been used for simulating several standard and complex flow arrangements configurations of cross-flow heat exchangers. Simulated results have been validated through comparisons with results from available exact and approximate analytical solutions. Very accurate results have been obtained over wide ranges

Cabezas-Gómez, Luben; Saíz-Jabardo, José Maria

2014-01-01

9

Flow and vibration analysis to upgrade a CANDU heat exchanger  

International Nuclear Information System (INIS)

This paper presents an example to illustrate the use of two-dimensional flow calculations to optimize the location of sealing strips and rods in a shell-and-tube heat exchanger. This is done to minimize flow maldistribution and potential flow-induced vibration damage without significantly de-rating the unit. The calculations are carried out for an existing design

10

Entropy resistance analyses of a two-stream parallel flow heat exchanger with viscous heating  

International Nuclear Information System (INIS)

Heat exchangers are widely used in industry, and analyses and optimizations of the performance of heat exchangers are important topics. In this paper, we define the concept of entropy resistance based on the entropy generation analyses of a one-dimensional heat transfer process. With this concept, a two-stream parallel flow heat exchanger with viscous heating is analyzed and discussed. It is found that the minimization of entropy resistance always leads to the maximum heat transfer rate for the discussed two-stream parallel flow heat exchanger, while the minimizations of entropy generation rate, entropy generation numbers, and revised entropy generation number do not always. (general)

11

Geothermal heat exchanger with coaxial flow of fluids  

Directory of Open Access Journals (Sweden)

Full Text Available The paper deals with a heat exchanger with coaxial flow. Two coaxial pipes of the secondary part were placed directly into a geothermal boring in such a way that geothermal water flows around the outer pipe. Starting from the energy balance of the exchanger formed in this way and the assumption of a study-state operating regime, a mathematical model was formulated. On the basis of the model, the secondary circle output temperature was determined as a function of the exchanger geometry, the coefficient of heat passing through the heat exchange areas, the average mass isobaric specific heats of fluid and mass flows. The input temperature of the exchanger secondary circle and the temperature of the geothermal water at the exit of the boring were taken as known values. Also, an analysis of changes in certain factors influencing the secondary water temperature was carried out. The parameters (flow temperature of the deep boring B-4 in Sijarinska Spa, Serbia were used. The theoretical results obtained indicate the great potential of this boring and the possible application of such an exchanger.

Peji? Dragan M.

2005-01-01

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Oscillating flow loss test results in Stirling engine heat exchangers  

Science.gov (United States)

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

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

1990-01-01

13

Geothermal heat exchanger with coaxial flow of fluids  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2005-01-01

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On turbulence modelling of industrial heat exchanger flows  

International Nuclear Information System (INIS)

The present research is focussed on the prediction of shell-side flow in shell-and-tube heat exchangers. In order to simplify the analysis, the flow field is divided into three regions: (a) the tube-free region, away from the shell, baffles and tubes, (b) the tube-filled region, and (c) the near-wall region. The flow within each region is modelled separately, but the solutions within consecutive regions must be matched near the corresponding boundaries. (author)

15

A survey of oscillating flow in Stirling engine heat exchangers  

Science.gov (United States)

Similarity parameters for characterizing the effect of flow oscillation on wall shear stress, viscous dissipation, pressure drop and heat transfer rates are proposed. They are based on physical agruments and are derived by normalizing the governing equations. The literature on oscillating duct flows, regenerator and porous media flows is surveyed. The operating characteristics of the heat exchanger of eleven Stirling engines are discribed in terms of the similarity parameters. Previous experimental and analytical results are discussed in terms of these parameters and used to estimate the nature of the oscillating flow under engine operating conditions. The operating points for many of the modern Stirling engines are in or near the laminar to turbulent transition region. In several engines, working fluid does not pass entirely through heat exchangers during a cycle. Questions that need to be addressed by further research are identified.

Simon, Terrence W.; Seume, Jorge R.

1988-01-01

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Measurement of flow field and local heat transfer distribution on a scraped heat exchanger crystalliser surface  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In a cylindrical scraped heat exchanger crystallizer geometry the flow field influence on the local heat transfer distribution on an evenly cooled scraped heat exchanger surface has been studied by direct measurements of the heat exchanger surface temperature and the fluid velocity field inside the crystallizer. Liquid Crystal Thermometry revealed that the local heat transfer is higher in the middle area of the scraped surface. Stereoscopic PIV measurements demonstrated that the secondary flo...

Rodriguez, Marcos; Ravelet, Florent; Delfos, Rene; Witkamp, Geert-jan

2008-01-01

17

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

Directory of Open Access Journals (Sweden)

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

Pavel Neuberger

2014-02-01

18

Segmented heat exchanger  

Science.gov (United States)

A segmented heat exchanger system for transferring heat energy from an exhaust fluid to a working fluid. The heat exchanger system may include a first heat exchanger for receiving incoming working fluid and the exhaust fluid. The working fluid and exhaust fluid may travel through at least a portion of the first heat exchanger in a parallel flow configuration. In addition, the heat exchanger system may include a second heat exchanger for receiving working fluid from the first heat exchanger and exhaust fluid from a third heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the second heat exchanger in a counter flow configuration. Furthermore, the heat exchanger system may include a third heat exchanger for receiving working fluid from the second heat exchanger and exhaust fluid from the first heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the third heat exchanger in a parallel flow configuration.

Baldwin, Darryl Dean (Lafayette, IN); Willi, Martin Leo (Dunlap, IL); Fiveland, Scott Byron (Metamara, IL); Timmons, Kristine Ann (Chillicothe, IL)

2010-12-14

19

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

International Nuclear Information System (INIS)

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

20

Effect of nanoparticles on heat transfer in mini double-pipe heat exchangers in turbulent flow  

Science.gov (United States)

In this work, heat transfer of a fluid containing nanoparticles of aluminum oxide with the water volume fraction (0.1-0.3) percent has been reported. Heat transfer of the fluid containing nano water aluminum oxide with a diameter of about 20 nm in a horizontal double pipe counter flow heat exchanger under turbulent flow conditions was studied. The results showed that the heat transfer of nanofluid in comparison with the heat transfer of fluid is slightly higher than 12 percent.

Aghayari, Reza; Maddah, Heydar; Ashori, Fatemeh; Hakiminejad, Afshin; Aghili, Mehdi

2014-07-01

 
 
 
 
21

Heat and flow analysis inside a parallel-flow heat exchanger  

International Nuclear Information System (INIS)

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

22

A simplified method of calculating heat flow through a two-phase heat exchanger  

International Nuclear Information System (INIS)

A simplified method of calculating the heat flow through a heat exchanger in which one or both heat carrying media are undergoing a phase change is proposed. It is based on enthalpies of the heat carrying media rather than their temperatures. The method enables the determination of the maximum rate of heat flow provided the thermodynamic properties of both heat-carrying media are known. There will be no requirement to separately simulate each part of the system or introduce boundaries within the heat exchanger if one or both heat-carrying media undergo a phase change. The model can be used at the pre-design stage, when the parameters of the heat exchangers may not be known, i.e., to carry out an assessment of a complex energy scheme such as a steam power plant. One such application of this model is in thermal simulation exercises within the TRNSYS modeling environment

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A simplified method of calculating heat flow through a two-phase heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

A simplified method of calculating the heat flow through a heat exchanger in which one or both heat carrying media are undergoing a phase change is proposed. It is based on enthalpies of the heat carrying media rather than their temperatures. The method enables the determination of the maximum rate of heat flow provided the thermodynamic properties of both heat-carrying media are known. There will be no requirement to separately simulate each part of the system or introduce boundaries within the heat exchanger if one or both heat-carrying media undergo a phase change. The model can be used at the pre-design stage, when the parameters of the heat exchangers may not be known, i.e., to carry out an assessment of a complex energy scheme such as a steam power plant. One such application of this model is in thermal simulation exercises within the TRNSYS modeling environment.

Yohanis, Y.G. [Thermal Systems Engineering Group, Faculty of Engineering, University of Ulster, Newtownabbey, Co Antrim, BT37 0QB Northern Ireland (United Kingdom)]. E-mail: yg.yohanis@ulster.ac.uk; Popel, O.S. [Non-traditional Renewable Energy Sources, Institute for High Temperatures, Russian Academy of Sciences, 13/19 Izhorskaya str., IVTAN, Moscow 125412 (Russian Federation); Frid, S.E. [Non-traditional Renewable Energy Sources, Institute for High Temperatures, Russian Academy of Sciences, 13/19 Izhorskaya str., IVTAN, Moscow 125412 (Russian Federation)

2005-10-01

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Numerical simulation of two phase flows in heat exchangers  

International Nuclear Information System (INIS)

The author gives an overview of his research activity since 1981. He first gives a detailed presentation of properties and equations of two-phase flows in heat exchangers, and of their mathematical and numerical investigation: semi-local equations (mass conservation, momentum conservation and energy conservation), homogenized conservation equations (mass, momentum and enthalpy conservation, boundary conditions), equation closures, discretization, resolution algorithm, computational aspects and applications. Then, he reports the works performed in the field of turbulent flows, hyperbolic methods, low Mach methods, the Neptune project, and parallel computing

25

Heat transfer enhancement in cross-flow heat exchanger using vortex generator  

International Nuclear Information System (INIS)

Fouling is very serious problem in heat exchanger because it rapidly deteriorates the performance of heat exchanger. Cross-flow heat exchanger with vortex generators is developed, which enhance heat transfer and reduce fouling. In the present heat exchanger, shell and baffle are removed from the conventional shell-and-tube heat exchanger. The naphthalene sublimation technique is employed to measure the local heat transfer coefficients. The experiments are performed for single circular tube, staggered array tube bank and in-line array tube bank with and without vortex generators. Local and average Nusselt numbers of single tube and tube bank with vortex generator are investigated and compared to those of without vortex generator

26

Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger  

DEFF Research Database (Denmark)

The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger 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 heat exchanger 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.

Knudsen, SØren; Furbo, Simon

2005-01-01

27

Laminar fluid flow and heat transfer in a fin-tube heat exchanger with vortex generators  

Energy Technology Data Exchange (ETDEWEB)

Development of heat transfer enhancement techniques for fin-tube heat exchangers has great importance in industry. In recent years, heat transfer augmentation by vortex generators has been considered for use in plate fin-tube heat exchangers. 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 heat exchangers, in terms of large heat transfer enhancement and small pressure loss penalty. (author)

Yanagihara, J.I.; Rodriques, R. Jr. [Polytechnic School of Univ. of Sao Paolo, Sao Paolo (Brazil). Dept. of Mechanical Engineering

1996-12-31

28

Experimental study on the cross flow air cooled plate heat exchanger using fin with electric pump.  

Directory of Open Access Journals (Sweden)

Full Text Available Experimental study on the cross flow air cooled plate heat exchanger using fin with electric pump was performed. Two prototype plate heat exchanger were manufactured in a stack of single wave plates and double plates in parallel. Cooling air flows through the plate heat exchanger in across wise direction against internal cooling water. In this study prototype heat exchanger were tested in a laboratoryscale experiments. From test double wave plates heatexchanger shows approximately 52.50 % enhanced heat transfer performance compare to single wave plates heat exchanger . However double wave heat exchanger costs 30%additional pressure drop .

Pankaj kumar mishra

2013-03-01

29

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

International Nuclear Information System (INIS)

method of volume averaging, Kluwer Academic Publishers, 1999], a 'closure problem' is then derived for a representative elementary volume, using the so-called Boussinesq approximation to account for small scale turbulence. The model is used to compute macro-scale heat transfer properties for turbulent flows inside a flat plate heat exchanger. It is shown that, for such flows, both dispersive fluxes strongly predominate over the macroscopic turbulent. heat flux. (authors)

30

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

Directory of Open Access Journals (Sweden)

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

Ilyin Roman Albertovich

2011-12-01

31

Flow length effect in heat exchangers with turbulent flow at low Prandtl number  

International Nuclear Information System (INIS)

This work brings out the effect of energy length on the mean overall heat transfer coefficient of a heat exchanger for turbulent flow with low Prandtl number. For this purpose simple heat transfer correlations are proposed in the thermal energy length region and with these correlations the correction factors are calculated for selected special cases. The effect of flow parameters and total heat exchanger length has also been investigated. Finally comments are made regarding thermal boundary conditions and in its light the commonly used design method is assessed

32

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

International Nuclear Information System (INIS)

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

33

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-04-15

34

Heat exchanger panel having reference indicia and improved flow distribution  

Energy Technology Data Exchange (ETDEWEB)

In a heat exchanger panel for use in a solar energy collector system, said panel comprising a plurality of spaced parallel individual tubular passageways connecting opposed headers defined by numerous island-like bonded portions connected by a plurality of tubular channels passing therebetween, the boundaries of said headers defining a generally triangular shape with at least one of said boundaries being inclined with respect to an edge of said panel, said headers including entry and exit portions to said panel, siad entry and exit portions being laterally displaced from the center of said panel to permit a heat exchange medium to flow into said panel and across said headers so that said medium flows through each of the plurality of spaced parallel indiviual tubular passageways connecting said headers; and said parallel individual tubular passageways being interconnected by further tubular interconnecting portions spaced from said headers the improvement wherein said tubular interconnecting portions are arranged across said panel at an inclination generally corresponding to the inclination of said at least one boundary.

Kleine, C.; Middleton, V.

1980-07-01

35

Heat transfer in tube bundles of heat exchangers with flow baffles induced forced mixing  

International Nuclear Information System (INIS)

Thermal analysis of shell-and-tube heat exchangers is being investigated through geometric modeling of the unit configuration in addition to considering the heat transfer processes taking place within the tube bundle. The governing equations that characterize the heat transfer from the shell side fluid to the tube side fluid across the heat transfer tubewalls are indicated. The equations account for the heat transfer due to molecular conduction, turbulent thermal diffusion, and forced fluid mixing among various shell side fluid channels. The analysis, though general in principle, is being applied to the Clinch River Breeder Reactor Plant-Intermediate Heat Exchanger, which utilizes flow baffles appropriately designed for induced forced fluid mixing in the tube bundle. The results of the analysis are presented in terms of the fluid and tube wall temperature distributions of a non-baffled and baffled tube bundle geometry. The former case yields axial flow in the main bundle region while the latter is associated with axial/cross flow in the bundle. The radial components of the axial/cross flow yield the necessary fluid mixing that results in reducing the thermal unbalance among the heat transfer to the allowable limits. The effect of flow maldistribution, present on the tube or shell sides of the heat exchangers, in altering the temperature field of tube bundles is also noted

36

CFD Based Evaluation Of Effectiveness Of Counter Flow Heat Exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available Engineers are continually being asked to improve effectiveness of heat transfer equipments. These requests may arise as a result of the need to increase profitability or accommodate capital limitations. Processes which use heat transfer equipment i.e. heat exchanger must frequently be improved for these reasons. Artifical roughness is important technique for enhancing the effectiveness of heat exchanger. In this work effectiveness of smooth as well as roughened tube in heat exchanger is theoretically investigated by using ring type roughness geometry. The performance obtained is then compared with smooth tube. Ringed tube has a significant effect on effectiveness of heat exchanger. The effectiveness is 3.2 times as compared with plane tube was reported. The effectiveness found to be increased with increasing roughness and decreasing pitch between the rings.

Gurpreet Kour

2014-04-01

37

Effects of pulsating flow on the performance of a plate heat exchanger  

International Nuclear Information System (INIS)

The effects of pulsating flow, such as pulsating frequency and flow rate, on the heat transfer as well as pressure drop in a plate heat exchanger has been studied in detail. Reynolds number in cold side of a plate heat exchanger is varied 100?530 while that of hot side is fixed 620. The pulsating frequency is considered in the range of 5?30Hz. The result of the pulsating flow are also compared with those of steady flow. It is found that the average heat transfer rate as well as pressure drop is increased as flow rate is increased for both steady flow and pulsating flow cases. When pulsating flow is applied to the plate heat exchanger, heat transfer could be substantially increased in particular ranges of pulsating frequency or Strouhal number; St=0.36?0.60 and pressure drop is also increased, compare with those of steady flow

38

Modeling heat efficiency, flow and scale-up in the corotating disc scraped surface heat exchanger  

DEFF Research Database (Denmark)

A comparison of two different scale corotating disc scraped surface heat exchangers (CDHE) was performed experimentally. The findings were compared to predictions from a finite element model. We find that the model predicts well the flow pattern of the two CDHE's investigated. The heat transfer performance predicted by the model agrees well with experimental observations for the laboratory scale CDHE whereas the overall heat transfer in the scaled-up version was not in equally good agreement. The lack of the model to predict the heat transfer performance in scale-up leads us to identify the key dimensionless parameters relevant for scale-up.

Friis, Alan; Szabo, Peter

2002-01-01

39

Heat exchangers  

International Nuclear Information System (INIS)

The aim of this invention is to provide improvements in the circulation of the fluids in shell type heat exchangers used in the generation of steam, especially those operating by indirect heat exchange with a fluid circulating through a nuclear reactor. It is claimed that the improvements described promote the natural circulation both in the radial and axial directions and also reduce or eliminate sludge buildup within the exchanger. Thus the possibility of tube failure in a heat exchanger is reduced and the operation and maintenance of a heat exchanger are improved such that its useful life is enhanced and its efficiency increased. (U.K.)

40

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-06-15

 
 
 
 
41

Thermographic analysis of flow distribution in compact heat exchangers for a Formula 1 car  

Science.gov (United States)

A non-intrusive approach is investigated to calculate the internal flow distribution in heat exchangers. In particular, the liquid flow rate can be determined in each tube of an air-liquid finned-tube heat exchanger. A purposely designed test bench impresses a sudden change of temperature of the liquid flowing through the heat exchanger. The thermal transient that follows is monitored by a thermographic camera. This measures the rise of surface temperature along each tube. The temperature evolution pattern is then correlated to the flow rate in the tube by simple mathematical processing. The heat exchanger is tested in still air. Modification is not required. The approach is tested on heat exchangers for a F1 race car, with encouraging results.

Caffagni, E.; Levoni, P.; Piraccini, M.; Muscio, A.; Corticelli, M. A.; Barozzi, G. S.

2007-01-01

42

Thermal design of multi-fluid mixed-mixed cross-flow heat exchangers  

Science.gov (United States)

A fast analytical calculation method is developed for the thermal design and rating of multi-fluid mixed-mixed cross-flow heat exchangers. Temperature dependent heat capacities and heat transfer coefficients can iteratively be taken into account. They are determined at one or two special reference temperatures. Examples are given for the application of the method to the rating of special multi-fluid multi-pass shell-and-tube heat exchangers and multi-fluid cross-flow plate-fin heat exchangers. The accuracy of the method is tested against numerical calculations with good results.

Roetzel, W.; Luo, X.

2010-11-01

43

Heat transfer and flow characteristics around a finned-tube bank heat exchanger in fluidized bed  

Science.gov (United States)

Principal heat transfer mechanisms in a fluidized bed have been classified into three categories, i.e. solid convection, gas convection and radiation. Among these mechanisms, the solid convection is a dominant mechanism in the bubbling fluidized bed. This solid convection is substantially caused by the bubble movement, thus the visualization of the void fraction distribution becomes a very useful method to understand the characteristics of the fluidized-bed heat exchanger. In this study, the heat transfer coefficient and the void fraction around the heat transfer tube with annuler fin were measured. For the quantitative measurement of the void fraction, neutron radiography and image processing technique were employed. Owing to the existence of the annuler fin, the restriction of the particle movements was put. This restriction suppressed the disturbance caused by tubes, and the influence of the tube arrangement on the flow and heat transfer characteristics could be clearly expressed.

Honda, Ryosuke; Umekawa, Hisashi; Ozawa, Mamoru

2009-06-01

44

Heat transfer and flow characteristics around a finned-tube bank heat exchanger in fluidized bed  

International Nuclear Information System (INIS)

Principal heat transfer mechanisms in a fluidized bed have been classified into three categories, i.e. solid convection, gas convection and radiation. Among these mechanisms, the solid convection is a dominant mechanism in the bubbling fluidized bed. This solid convection is substantially caused by the bubble movement, thus the visualization of the void fraction distribution becomes a very useful method to understand the characteristics of the fluidized-bed heat exchanger. In this study, the heat transfer coefficient and the void fraction around the heat transfer tube with annuler fin were measured. For the quantitative measurement of the void fraction, neutron radiography and image processing technique were employed. Owing to the existence of the annuler fin, the restriction of the particle movements was put. This restriction suppressed the disturbance caused by tubes, and the influence of the tube arrangement on the flow and heat transfer characteristics could be clearly expressed.

45

The combined effects of wall longitudinal heat conduction and inlet fluid flow maldistribution in crossflow plate-fin heat exchangers  

Science.gov (United States)

An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effect of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow distribution on both hot and cold fluid sides is carried out using a finite element method. Using the fluid flow maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of wall longitudinal heat conduction and inlet fluid flow nonuniformity on crossflow plate-fin heat exchanger.

Ranganayakulu, Ch.; Seetharamu, K. N.

46

New counter flow heat exchanger designed for ventilation systems in cold climates  

DEFF Research Database (Denmark)

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 heat exchanger, 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 flow heat exchanger designed for cold climates are presented. The developed heat exchanger 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 heat exchangers. In this paper, the new heat exchanger's efficiency is calculated theoretically and measured experimentally. The experiment shows that the heat exchanger 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 heat exchanger will be described in future articles.

Kragh, Jesper; Rose, JØrgen

2007-01-01

47

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

Science.gov (United States)

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

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

2014-04-01

48

Cross-flow heat exchangers for anti-freezing of liquid nitrogen  

Science.gov (United States)

Cross-flow heat exchangers are proposed and experimentally investigated as an anti-freezing scheme of liquid nitrogen. The possibility of freeze-out of liquid nitrogen is an important design issue in developing long superconducting cables, as the supply temperature of liquid nitrogen is close to its freezing temperature (63.3 K). Plate-fin heat exchangers are fabricated as typical counter-flow and newly proposed two-pass cross-flow in laboratory scale, and tested with cold helium gas at temperatures below 60 K. The experimental results show that the cross-flow heat exchanger is less vulnerable to the freeze-out condition, since the temperature distribution is basically two-dimensional. The cross-flow heat exchangers are effective in avoiding a complete clog-up of all passages and reducing the risk of freeze-out of liquid nitrogen.

Chang, Ho-Myung; Gwak, Kyung Hyun; Yang, Hyung Suk; Hwang, Si-Dole

2013-10-01

49

Two-phase flow instability in a liquid nitrogen heat exchanger  

International Nuclear Information System (INIS)

Experimental results on two-phase flow instability in a liquid nitrogen heat exchanger are shown. A preliminary visual observation study reveals that two unstable regions exist at low flow rate and high flow rate conditions, and that the corresponding flow patterns are the slug flow and the annular flow, respectively. Experiments with a heat exchanger are carried out for three cases with various combinations of tube length, attitude of the heat exchanger and the secondary flow fluid. A stability map and periods of flow oscillations are obtained in each experiment. A computer code LUSH-EX is developed based on a linear analysis technique with the density wave oscillation model. With this code, experimental data are analysed, and the oscillations in these experiments are found to be those of the density wave type. (orig.)

50

Experimental and Exergy Analysis of A Double Pipe Heat Exchanger for Parallel Flow Arrangement  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents For Experimental and Exergy Analysis of a Double Pipe Heat Exchanger for Parallel- flow Arrangement. The Double pipe heat exchanger is one of the Different types of heat exchangers. double-pipe exchanger because one fluid flows inside a pipe and the other fluid flows between that pipe and another pipe that surrounds the first.In a parallel flow, both the hot and cold fluids enter the Heatexchanger at same end andmove in same direction. The present work is taken up to carry experimental work and the exergy analysis based on second law analysis of a Double-Pipe Heat Exchanger. In experimental set up hot water and cold water will be used working fluids. The inlet Hot water will be varied from 40 0C and 50 0C and cold water temperature will be varied from between 15 and 20 0C. It has been planned to find effects of the inlet condition of both working fluid flowing through the heat exchanger on the heat transfer characteristics, entropy generation, and Exergy loss. The Mathematical modelling of heat exchanger will based on the conservation equation of mass, energy and based on second law of thermodynamics to find entropy generation and exergy losses.

Parth P. Parekh

2014-07-01

51

Heat exchange in the laminar flow of a viscous liquid in channels with spiral wire insertions  

International Nuclear Information System (INIS)

A mathematical model of convective heat exchange intensification in laminar flow of a viscous liquid by means of spiral wire insertions is described. The model is developed in the Galerkin approximation. Numerical investigation results are given

52

Numerical calculation of the transient behaviour of two pure cross-flow heat exchangers coupled by a circulating flow stream  

Energy Technology Data Exchange (ETDEWEB)

The transient thermal behaviour of a heat shifting system consisting of two pure cross-flow heat exchangers coupled by a circulating flow stream is studied theoretically. A suitable mathematical description of the system is based on the energy balance equation for general flow processes yielding a system of coupled hyperbolic partial differential equations in two dimensions. System responses to perturbations of inlet temperatures and mass flow rates are numerically calculated with an explicit finite difference method. A criterion for the generation of computational grids minimising effects of numerical dispersion and dissipation is applied to the system of coupled pure cross-flow heat exchangers which has not been considered up to now. Due to its internal circulation the coupled system shows a different behaviour compared to single cross-flow heat exchangers like inverse response and oscillatory behaviour to non-oscillating input signals. (orig.)

Na Ranong, Chakkrit; Hapke, Jobst [Hamburg University of Technology, Institute of Process and Plant Engineering, Hamburg (Germany); Roetzel, Wilfried [University of the Federal Armed Forces, Institute of Thermodynamics, Helmut-Schmidt-University, Hamburg (Germany)

2010-11-15

53

Heat exchanger  

International Nuclear Information System (INIS)

The invention concerns a safety device in a heat exchanger, which is situated between the nuclear reactor and the boiler of a sodium cooled nuclear reactor in a power station. A piece of pipe which slides in the lid of the heat exchanger is connected to the housing by bellows. According to the invention an additional sliding packing seal is provided outside the bellows between the piece of pipe and the housing, which acts as secondary safety device, in case the bellows fracture. (UWI)

54

Heat exchanger  

International Nuclear Information System (INIS)

A heat exchanger having primary and secondary conduits in heat-exchanging relationship is described comprising: at least one serpentine tube having parallel sections connected by reverse bends, the serpentine tube constituting one of the conduits; a group of open-ended tubes disposed adjacent to the parallel sections, the open-ended tubes constituting the other of the conduits, and forming a continuous mass of contacting tubes extending between and surrounding the serpentine tube sections; and means securing the mass of tubes together to form a predetermined cross-section of the entirety of the mass of open-ended tubes and tube sections

55

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

Science.gov (United States)

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

Tao, W. Q.; Cheng, Y. P.; Lee, T. S.

2007-11-01

56

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

International Nuclear Information System (INIS)

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

57

Heat exchanger  

International Nuclear Information System (INIS)

In order to fasten the tubes of a tube bundle inside a heat exchanger of the type used in nuclear reactors to the tube wall or tube plate, it is proposed to seal the tubes with the aid of pressure pipe couplings, thus avoiding welded joints. (RW)

58

Flow-induced vibration test and analysis of heat exchanger in NPP  

International Nuclear Information System (INIS)

A method of comparing the results of calculation with test is used to verify the reliability and adequacy of the program in order to evaluate the flow-induced vibration of heat-exchanger tubes, so the program can be applied to design of safety related heat-exchanger in NPP. The shell side flow velocity and tube vibration are measured. The results of measurement show that there is a margin of safety in general for the results of calculated by program TASC and PIPO 1, but it should be noted that the flow velocities may be higher at a few points of the shell side. (7 refs., 10 figs., 4 tabs.)

59

Heat transfer coefficient in a shallow fluidized bed heat exchanger with a continuous flow of solid particles  

Directory of Open Access Journals (Sweden)

Full Text Available 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 700degreesC. 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 heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger 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 heat exchanger.

Pécora Araí A. Bernárdez

2006-01-01

60

Heat transfer coefficient in a shallow fluidized bed heat exchanger with a continuous flow of solid particles  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English 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 d [...] istance 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 heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger 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 heat exchanger.

Araí A. Bernárdez, Pécora; Maria Regina, Parise.

2006-09-01

 
 
 
 
61

Heat transfer coefficient in a shallow fluidized bed heat exchanger with a continuous flow of solid particles  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English 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 d [...] istance 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 heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger 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 heat exchanger.

Araí A. Bernárdez, Pécora; Maria Regina, Parise.

62

Development of a compact laminar flow heat exchanger with stainless steel micro-tubes  

Science.gov (United States)

The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger. We presented in a previous paper that some compact heat exchangers with good performance in the temperature range of less than 4 K are required for a subcooled He II refrigerator cycle to be worked with 3He turbo-compressors (F. Doty, et al., A new look at the closed brayton cycle, Proceedings, IECEC-90 Reno, NV, 1991, p. 116). For this requirement, we developed a micro-tube strip counter flow type heat exchanger, which consists of 12 elements with a total of 4800 stainless steel micro-tubes. Each element is formed with 400 tubes and a newly developed vacuum brazing method was applied for the bonding to the side plate. Each tube has an inner diameter of 0.5 mm, an outer diameter of 0.7 mm and is 310 mm long. We developed a cladding plate with two layers of gold brazing sheet sandwiched inside. In aerodynamic and thermal design of the element, the laminar flow conditions were adopted for the flows of inner and outer tubes to keep a high heat transfer rate and a low pressure loss.

Saji, N.; Nagai, S.; Tsuchiya, K.; Asakura, H.; Obata, M.

2001-05-01

63

Flow distribution analysis in nuclear heat exchangers with application to CRBRP-IHX  

International Nuclear Information System (INIS)

The shell side flow distribution of a shell-and-tube heat exchanger, in which the shell side fluid moves downwards in an axial/cross flow combination dictated by the design of the flow baffles, is examined. Depending on the degree of overlapping and perforation of the baffles, the magnitude of the cross flow component can be controlled in a manner compatible with the unit design. Axial/cross flow field would yield a relatively small pressure drop on the shell side, and in the meantime it creates sufficient fluid mixing to minimize any thermal unbalance among the heat transfer tubes. Such requirements are essential in the design of nuclear heat exchangers similar to the CRBRP-IHX. The present flow distribution analysis utilizes two models: The lumped model and the detailed model. The lumped model employs an overall flow distribution and pressure drop approach to determine the magnitudes of the axial and cross flow components as a function of the baffle overlapping and baffle perforation. The detailed model utilizes more of a fundamental approach in solving the governing equations for the conservation of mass and momentum of a turbulent flowing fluid in a nodal mesh. The mesh incorporates distributed resistances resulting from the presence of the heat transfer tubes and the flow baffles in the tube bundle. The model employs a modified version of the computer code VARR II tailored specifically to the analysis of the shell side flow of heat exchangers. The results of bothow of heat exchangers. The results of both models are indicated and compared with emphasis on demonstrating the influence of the baffle overlapping and baffle perforation on the flow field and the pressure distribution

64

Heat exchangers in oscillating flow, with application to thermoacoustic devices that have neither stack nor regenerator  

Science.gov (United States)

The performance of parallel-plate heat exchangers in oscillating flow is studied empirically and theoretically, with the goal of improving the models of heat exchangers used in the design of thermoacoustic engines and refrigerators. A novel style of thermoacoustic device, the "no-stack" device, provides the framework for study. In a no-stack engine or refrigerator, the porous medium (the stack or regenerator) that is found in other thermoacoustic devices is eliminated, replaced by a small "no-stack gap." A no-stack device, then, consists of two heat exchangers strategically placed in an enclosure containing oscillating pressure and flow. Such devices lie beyond the boundaries of the acoustic theory that has been used to model and design thermoacoustic devices based on stacks and regenerators. The theory developed here to study no-stack devices combines original calculations and conventional thermoacoustic theory with results from fluids engineering, which are used on an ad hoc basis as required. Further studies are carried out on those parts of this semi-analytical model that are deemed least reliable. In particular, measurements are made of heat transfer between two identical parallel-plate heat exchangers under conditions of oscillating flow over a range of frequencies and amplitudes. The results are analyzed and summarized in terms of heat-exchanger effectiveness, the ratio of the actual heat transfer rate to the maximum possible heat transfer rate. Measured results are compared to the DeltaE model that is often used in the design of conventional thermoacoustic devices, and possible improvements to the model are offered. The influence of nonuniform velocity profiles on minor losses at the exit from oscillating-flow heat exchangers is studied. Heat exchanger performance in an environment with both oscillating flow and oscillating pressure is examined with a time-stepping computational method. Combined with the heat transfer measurements, the time-stepping model indicates that extremely effective exchangers would be required for successful no-stack devices, and that pressure oscillations give rise to significant changes in performance of heat exchangers at more typical pressure amplitudes, enhancing heat transfer in stack-based refrigerators and degrading it in stack-based engines.

Wakeland, Ray Scott

65

Two-phase gas-liquid flow characteristics inside a plate heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)

Nilpueng, Kitti [Department of Mechanical Engineering, South East Asia University, Bangkok 10160 (Thailand); Wongwises, Somchai [Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, King Mongkut' s University of Technology Thonburi, Bangmod, Bangkok 10140 (Thailand)

2010-11-15

66

Heat and mass exchanger  

Science.gov (United States)

A mass and heat exchanger 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 heat exchange fluid therethrough, wherein heat transfer occurs between the liquid and the heat exchange fluid.

Lowenstein, Andrew (Princeton, NJ); Sibilia, Marc J. (Princeton, NJ); Miller, Jeffrey A. (Hopewell, NJ); Tonon, Thomas (Princeton, NJ)

2011-06-28

67

Microtube strip heat exchanger  

Science.gov (United States)

During the last quarter, Doty Scientific, Inc. (DSI) continued to make progress on the microtube strip (MTS) heat exchanger. The DSI completed a heat exchanger stress analysis of the ten-module heat exchanger bank; and performed a shell-side flow inhomogeneity analysis of the three-module heat exchanger bank. The company produced 50 tubestrips using an in-house CNC milling machine and began pressing them onto tube arrays. The DSI revised some of the tooling required to encapsulate a tube array and press tubestrips into the array to improve some of the prototype tooling.

Doty, F. D.

1991-07-01

68

Plate-fin heat exchanger performance reduction in special two-phase flow conditions  

Science.gov (United States)

This paper discusses the occurrence of various flow patterns of a cold, upflowing two-phase stream in an aluminium plate-fin heat exchanger (PFHE) and their impact on the overall heat exchanger performance. Various flow patterns were observed in a flow visualization rig comprising a single PFHE passage. At high gas mass fluxes both phases flow uniformly upwards. When decreasing the gas flow, a reversing slug flow becomes more and more pronounced. In this flow pattern fluid particles of significantly different temperatures can mix within the same passage. If the number of transfer units (NTU) is high, the effective temperature difference against a hot stream of the exchanger decreases. At very low gas mass fluxes a sudden static instability with liquid logging was observed. The liquid zones thus appearing can cover and thus deactivate large portions of the heating area. In PFHE design both phenomena should be taken into account, particularly for exchangers with low mean temperature differences and heated multicomponent streams with large boiling ranges.

Müller-Menzel, T.; Hecht, T.

69

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-04-15

70

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

International Nuclear Information System (INIS)

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

71

Heat exchanger  

International Nuclear Information System (INIS)

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

72

Heat exchanger  

International Nuclear Information System (INIS)

The invention relates to the improvement of the seal of a conduit flexibly attached to the housing of a heat exchanger. When these heat exchangers are used as steam generators for nuclear power plants, they must meet high thermal and mechanical requirements. It is proposed to use a labyrinth seal with several annular disks surrounding the conduit instead of the metal bellows customarily applied so far. The annular disks are positioned one beside the other with the sides facing each other pointing in the direction of the axis of the conduit, while the faces extending at right angles to this direction alternately abut against the conduit or the housing. They have different thicknesses. The labyrinth seal may additionally be enclosed in a jacket. (UWI)

73

A Numerical Investigation of Gas flow and Heat Transfer in Proton Exchange Membrane Fuel Cells  

DEFF Research Database (Denmark)

Gas flow and heat transfer in both cathode and anode channels have been modeled and analyzed for proton exchange membrane fuel cells. The simulated channel consists of a porous electrode layer (anode or cathode), gas flow duct, and solid current collector. The characteristics of gas flow and heat transfer in terms of friction factor and Nusselt number were investigated by a three-dimensional computational fluid dynamics code (CFD). A combined thermal boundary condition, which is unique for fuel cells and interfacial conditions between the porous layer, the gas flow duct, and the solid current collector, were clarified and applied in the calculation. The heat generation and mass transport processes have been modeled and implemented into the code by proper source terms. Furthermore, the effects of various parameters on the generation of heat, mass transport process, gas flow, and heat transfer are assessed also. These parameters include current density and permeability, effective thermal conductivity, and thickness of porous diffusion layer.

Yuan, Jinliang; Rokni, Masoud

2003-01-01

74

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

Directory of Open Access Journals (Sweden)

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

Yasin Ramezani

2013-05-01

75

Flow model test development of CRBRP intermediate heat exchanger  

International Nuclear Information System (INIS)

The details of these tests, flow data achieved, finalized design configurations of the flow distribution devices, and final interpretation of the results are given in this paper. The tests consist of the: Primary Inlet Plenum Flow Model Test which has the objective of finalizing the design of the primary flow inlet plenum configuration that results in a circumferentially uniform flow entering the tube bundle; Tube Bundle Flow Model Test which has the objective of achieving optimum design configurations for the flow baffles in the bundle, which is based on the baffles capability to create the necessary forced fluid mixing of the shell side flow within the pressure drop limitation imposed on the unit's design; and Intermediate Flow Model Test with its objective of confirming the design of the intermediate flow inlet plenum, which has a hemispherical shape with a ring baffle attached, in distributing the flow evenly among the tubes. The paper includes details of the flow fields within various test models in a wide range of operating flow rates. 2 refs

76

Numerical simulation of two phase flows in heat exchangers  

International Nuclear Information System (INIS)

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

77

Flow and heat transfer characteristics of indirect dry cooling system with horizontal heat exchanger A-frames at ambient winds  

International Nuclear Information System (INIS)

Ambient winds are key issues in the operation of indirect dry cooling system in power plants, so it is of use to make clear the thermo-hydraulic performances of indirect dry cooling system at ambient winds. On the basis of two indirect dry cooling systems with horizontally arranged heat exchanger bundles in the patterns of radial and rectangular A-frames, the computational models of air-side flow and heat transfer coupled with the performances of the circulating water and exhaust steam are developed. The velocity, pressure and temperature fields of cooling air in the absence and presence of winds are presented and the average mass flow rate of cooling air, inlet air temperature as well as the heat rejection for the A-frames of each cooling sector of the air-cooled heat exchanger are calculated, by which the outlet water temperature of heat exchanger and the back pressure of turbine are obtained. The results show that the wind effects on the thermo-hydraulic performances of indirect dry cooling system differ completely from those with vertically arranged air-cooled heat exchanger outside. The velocity and temperature fields present central symmetric characteristics for the heat exchanger in the radial pattern, however, the differences are observed for the heat exchanger A-frames in the rectangular pattern. The thermo-hydraulic performances of the upwind A-frames are most deteriorated by the adverse impacts of ambient winds, but they are improved for the downwind ones, just similar to those of direct dry cooling system. As the wind speed increases, the mass flow rate and heat rejection of the downwind A-frames increase, but they are reduced for the upwind ones. The outlet water temperature of the heat exchanger and back pressure of turbine increase with increasing wind speed. The investigation of wind effects on the flow and heat transfer characteristics of indirect dry cooling system with horizontal heat exchanger A-frames is of benefit to the design and operation of air-cooled heat exchangers and cooling towers. (authors)

78

Effectiveness-ntu computation with a mathematical model for cross-flow heat exchangers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Due to the wide range of design possibilities, simple manufactured, low maintenance and low cost, cross-flow heat exchangers are extensively used in the petroleum, petrochemical, air conditioning, food storage, and others industries. In this paper a mathematical model for cross-flow heat exchangers [...] with complex flow arrangements for determining epsilon -NTU relations is presented. The model is based on the tube element approach, according to which the heat exchanger outlet 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 heat exchangers performance.

H. A., Navarro; L. C., Cabezas-Gómez.

79

Effectiveness-ntu computation with a mathematical model for cross-flow heat exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available Due to the wide range of design possibilities, simple manufactured, low maintenance and low cost, cross-flow heat exchangers are extensively used in the petroleum, petrochemical, air conditioning, food storage, and others industries. In this paper a mathematical model for cross-flow heat exchangers with complex flow arrangements for determining epsilon -NTU relations is presented. The model is based on the tube element approach, according to which the heat exchanger outlet 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 heat exchangers performance.

H. A. Navarro

2007-12-01

80

Study of flow distribution and its improvement on the header of plate-fin heat exchanger  

Science.gov (United States)

In order to enhance the uniformity of flow distribution, an improved header configuration of plate-fin heat exchanger is put forward in this paper. Based on the analysis of the fluid flow maldistribution for the conventional header used in industry, a baffle with small holes of three different kinds of diameters is recommended to install in the header. The flow maldistribution parameter S is obtained under different header configuration. When the baffle is properly installed with an optimum length, with stagger arranged and suitably distributed holes from axial line to baffle boundary, the ratio of the maximum flow velocity to the minimum flow velocity drops from 3.44-3.04 to 1.57-1.68 for various Reynolds numbers. The numerical results indicate that the improved header configuration can effectively improve the performance. The conclusion of this paper is of great significance in the improvement of plate-fin heat exchanger.

Wen, Jian; Li, Yanzhong

2004-11-01

 
 
 
 
81

Microscale Regenerative Heat Exchanger  

Science.gov (United States)

The device described herein is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a "regenerator" in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle.

Moran, Matthew E.; Stelter, Stephan; Stelter, Manfred

2006-01-01

82

An experimental study of a cross-flow type plate heat exchanger for dehumidification/cooling  

Energy Technology Data Exchange (ETDEWEB)

The thermal and dehumidification behaviour of a standard cross-flow type plate heat exchanger, intended for use as a dehumidifier/cooler, has been investigated both experimentally and numerically. Three sets of experiments have been carried out where air is blown into the primary and secondary sides of the exchanger, while water and liquid desiccant were being sprayed in a counter flow arrangement. The first set represents the indirect evaporative cooling of the primary stream by the secondary air stream. The second set is with liquid desiccant only and no indirect evaporative cooling. In the third set of experiments the primary air stream is indirectly evaporatively cooled by the secondary air stream and dehumidified by the liquid desiccant sprayed into the primary side of the exchanger. The above experiments indicate that the heat exchanger performs well when used with liquid desiccant. Furthermore, for an exchanger angle of 45{sup o}, there is an optimum value of air mass flow rate at which the effectiveness and dehumidification efficiency of the plate heat exchanger are maxima. To investigate the effect of the ambient air conditions on the PHE performance, further experiments were carried out using a heater element and a humidifier. The results show that under laboratory conditions the exchanger effectiveness and dehumidification efficiency increase with increasing primary air inlet temperature and humidity ratio. The experimental results were used to validate a computer model developed for the cross-flow type plate heat exchanger/dehumidifier. Comparison indicates that the numerical results are in good agreement with the experiments. (Author)

Saman, W.Y.; Alizadeh, S. [University of South Australia, Mawson Lakes (Australia). School of Mechanical Engineering

2002-07-01

83

Microtube strip heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

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 heat exchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.

Doty, F.D.

1991-10-16

84

Thermal-hydraulic issues of flow boiling and condensation in organic Rankine cycle heat exchangers  

Science.gov (United States)

In the paper presented are the issues related to the design and operation of micro heat exchangers, where phase changes can occur, applicable to the domestic micro combined heat and power (CHP) unit. Analysed is the stability of the two-phase flow in such unit. A simple hydraulic model presented in the paper enables for the stability analysis of the system and analysis of disturbance propagation caused by a jump change of the flow rate. Equations of the system dynamics as well as properties of the working fluid are strongly non-linear. A proposed model can be applicable in designing the system of flow control in micro heat exchangers operating in the considered CHP unit.

Mikielewicz, Jaros?aw; Mikielewicz, Dariusz

2012-08-01

85

Experimental and numerical simulations of flow and heat transfer in heat exchanger elements using liquid crystal thermography  

Science.gov (United States)

Experimental and numerical investigation of heat transfer and fluid flow were conducted for classic heat exchanger elements (flat plate with fin-tubes in-line, staggered and with vortex generators) and corrugated-undulated ducts under transitional and weakly turbulent conditions. The dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters was investigated. Distributions of local heat transfer coefficient were obtained by using liquid crystal thermography and surface-averaged values were computed. Three-dimensional numerical simulations were conducted by a finite-volume method using a low-Reynolds number k-? model under the assumption of fully developed flow. Computed flow fields provided otherwise inaccessible information on the flow patterns and the mechanisms of heat transfer enhancement.

Stasiek, Jan; Ciofalo, Michele; Wierzbowski, Maciej

2004-05-01

86

Criteria for the cross-flow-induced tube vibrations in tube bank heat exchangers  

International Nuclear Information System (INIS)

Properties of the various excitation sources of cross-flow-induced vibrations in tube bank heat exchangers, such as Karman vortex shedding, wake swing, jet switch, jet instability and fluid-elastic whirling are shown. The working charts are examined using the experimental results obtained on a heat exchanger with mixed cross-parallel flow. It is shown for the present case that only the coupled second bending mode of the entire tube can be excited by the flow due to its S-shaped pattern. The hydrodynamic added mass is then discussed. The investigation shows that the added mass of a tube in a cross flow is far less than that in a stationary fluid. It is therefore recommended that great care be taken when transferring data from stationary fluid tests to prototypes working with dense fluid across tubes. (author)

87

HEAT TRANSFER AND FLUID FLOW ANALYSIS IN PLATE-FIN AND TUBE HEAT EXCHANGERS WITH DIFFERENT SHAPED VORTEX GENERATORS  

Directory of Open Access Journals (Sweden)

Full Text Available Numerical analyses were carried out to study the heat transfer and flow in the plate-fin and tube heat exchangers with different shaped vortex generators mounted behind the tubes. The effects of different span angles a (? = 30°, 45° and 60° are investigated in detail for the Reynolds number ranging from 500 to 2500. Numerical simulation was performed by computational fluid dynamics of the heat transfer and fluid flow. The results indicated that the triangle shaped winglet is able to generate longitudinal vortices and improve the heat transfer performance in the wake regions. The case of ? = 45° provides the best heat transfer augmentation than rectangle shape winglet generator in case of inline tubes. Common flow up configuration causes significant separation delay, reduces form drag, and removes the zone of poor heat transfer from the near wake of the tubes.

K.Thirumalai kannan

2012-03-01

88

PIV experimental investigation of entrance configuration on flow maldistribution in plate-fin heat exchanger  

Science.gov (United States)

Flow characteristics of flow field in the entrance of plate-fin heat exchanger have been investigated by means of particle image velocimetry (PIV). The velocity fields were measured using the two-frame cross-correlation technique. A series of velocity vector and streamline graphs of different cross-sections are achieved in the experiment. The experimental results indicate that performance of fluid maldistribution in conventional entrance configuration is very serious, while the improved entrance configuration with punched baffle can effectively improve the performance of fluid flow distribution in the entrance. Based on the analysis of the fluid flow maldistribution, a baffle with small holes is recommended to install in the entrance configuration in order to improve the performance of flow distribution. When the punched baffle is proper in length, the small holes is distributed in staggered arrangement, and the punched ratio gradually increases from central axis to the boundary along with the baffle length, the performance of flow distribution in plate-fin heat exchanger is effectively improved by the optimum design of the entrance configuration. The flow maldistribution parameter S in plate-fin heat exchanger has been reduced from 1.21 to 0.209 and the ratio of the maximum velocity to the minimum ? is reduced from 23.2 to 1.76 by installing the punched baffle. The results validate that PIV is well suitable to investigate complex flow pattern and the conclusion of this paper is of great significance in the optimum design of plate-fin heat exchanger.

Wen, Jian; Li, Yanzhong; Zhou, Aimin; Zhang, Ke; Wang, Jiang

2006-01-01

89

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

Directory of Open Access Journals (Sweden)

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

Adrian Bejan

1999-12-01

90

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

Science.gov (United States)

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

Onstad, Andrew J.

91

Study of junction flows in louvered fin round tube heat exchangers using the dye injection technique  

Energy Technology Data Exchange (ETDEWEB)

Detailed studies of junction flows in heat exchangers with an interrupted fin design are rare. However, understanding these flow structures is important for design and optimization purposes, because the thermal hydraulic performance of heat exchangers is strongly related to the flow behaviour. In this study flow visualization experiments were performed in six scaled-up models of a louvered fin round tube heat exchanger. The models have three tube rows in a staggered layout and differ only in their fin spacing and louver angle. A water tunnel was designed and built and the flow visualizations were carried out using dye injection. At low Reynolds numbers the streakline follows the tube contours, while at higher Reynolds numbers a horseshoe vortex is developed ahead of the tubes. The two resulting streamwise vortex legs are destroyed by the downstream louvers (i.e. downstream the turnaround louver), especially at higher Reynolds numbers, smaller fin pitches and larger louver angles. Increasing the fin spacing results in a larger and stronger horseshoe vortex. This illustrates that a reduction of the fin spacing results in a dissipation of vortical motion by mechanical blockage and skin friction. Furthermore it was observed that the vortex strength and number of vortices in the second tube row is larger than in the first tube row. This is due to the thicker boundary layer in the second tube row, and the flow deflection, which is typical for louvered fin heat exchangers. Visualizations at the tube-louver junction showed that in the transition part between the angled louver and the flat landing a vortex is present underneath the louver surface which propagates towards the angled louver. (author)

Huisseune, H.; Willockx, A.; De Paepe, M. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); T' Joen, C. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); Department Radiation, Radionuclides and Reactors, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); De Jaeger, P. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); NV Bekaert SA, Bekaertstraat 2, 8550 Zwevegem (Belgium)

2010-11-15

92

Heat exchange in multilayer flow-through cooling systems under one-sided heating  

International Nuclear Information System (INIS)

Under conditions of one-sided thermal loading ratios for the calculation of temperature fields, heat fluxes, coefficients of reduced heat transfer for multilayer cooling systems of flow type were obtained. The solution is analyzed from the viewpoint of heat transfer intensification and conditions for the achievement of the structure thermal isolation. The solutions obtained were tested using a channel-type two-layer system of cooling (Re = 102-2x104; Pr = 5-9)

93

Modeling pressure drop of inclined flow through a heat exchanger for aero-engine applications  

International Nuclear Information System (INIS)

In the present work further numerical predictions for the flow field through a specific type of a heat exchanger, which is planned to be used in the exhaust nozzle of aircraft engines. In order to model the flow field through the heat exchanger, a porous medium model is used based on a simple quadratic relation, which connects the pressure drop with the inlet air velocity in the external part of the heat exchanger. The aim of this work is to check the applicability of the quadratic law in a variety of velocity inlet conditions configured by different angles of attack. The check is performed with CFD and the results are compared with new available experimental data for these inlet conditions. A detailed qualitative analysis shows that although the quadratic law has been derived for a zero angle of attack, it performs very well for alternative non-zero angles. These observations are very helpful since this simple pressure drop law can be used for advanced computations where the whole system of the exhaust nozzle together with the heat exchangers can be modeled within a holistic approach

94

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

International Nuclear Information System (INIS)

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

95

Heat transfer to an in-containment heat exchanger in natural convection flow: Validation of the AEA Technology computational fluid dynamics code CFDS-FLOW3D  

International Nuclear Information System (INIS)

Validation is presented of an appropriate computer code for modelling heat transfer from the containment atmosphere to an in-containment heat exchanger using new data from ENEL. This work has been carried out in collaboration with ENEL, CISE and ANSALDO. The study helps to identify conditions under which natural circulation induced by the heat exchanger does initiate. The Computational Fluid Dynamics (CFD) code CFDS-FLOW3D, developed by AEA Technology, has been used, initially in a 2-dimensional mode, to simulate the natural convection flow generated within a test vessel by an internal heat exchanger operating in a steam-air gas mixture. The model incorporates a calculations of the heat exchanger condensation rate based on local conditions. Calculational parameters have identified which allow the transient timesteps to converge sufficiently but without using excessive CPU time. Results of pre-test calculations performed for 2 different geometrical configurations are presented. These calculations suggest that the heat exchanger will operate as intended and, at the design values of pressure and temperature, would exceed the planned test power by up to 28%. Post-test simulation results are presented for the first test performed. Good general agreement with major measured parameters is found and a possible explanation for the high upward velocity measured outside the heat exchanger exit is offered. The simulation underestimated the total condenser power by about 16%; thise total condenser power by about 16%; this is believed to be due to unpredicting the steady state steam fraction in the vessel. CFDS-FLOW3D is found to be a suitable tool for simulating the details of complex buoyancy driven flows, including non-condensibles, in passive containment cooling applications. The code is sufficiently flexible to be able to represent correctly heat exchanger condensation effects and to be able to simulate the resultant natural convection flows in either 2-D or, if required, in 3-D. (author). 3 refs, 9 figs

96

The Design of Heat Exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available A relation between heat transferred and energy loss, for turbulent flow. In different tube arrangements, is made. The conditions are determined which decide the dimensions and velocities for a heat exchanger. Also, a reference to the economic dimensioning of heat exchangers is presented. In this study, the conditions which a heat exchanger must satisfy represent the best balance between the amounts of material employed. The investigation is restricted to the case of turbulent flow.

Arturo Reyes-León

2011-09-01

97

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-10-15

98

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

International Nuclear Information System (INIS)

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

99

Numerical simulation of flow field in a fin tube heat exchanger  

International Nuclear Information System (INIS)

This paper reports on the computation of the flow field and heat transfer between two plate fins of a compact cross flow heat exchanger with staggered arrangement of tubes that has been carried out in Reynolds number range of 40 to 2000. Three Nusselt number plots on the fin show deterioration of heat transfer by 50%, or more in the stagnation zone of the rear tube due to the wake of the preceding tube. The Nusselt number distributions on the tube near the juncture of the tube and the fin deviates substantially from the two dimensional prediction. The Nusselt numbers on the midplane of the first tube in stagnation area compares well available experimental results of Nusselt number distribution on a cylinder in unbounded cross flow

100

Experiments on flow induced vibrations in a heat exchanger tube bundle  

International Nuclear Information System (INIS)

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

 
 
 
 
101

Velocity Boundary Layer Analysis of a Flat Plate Heat Exchanger in Laminar Flow: A Case Study  

Directory of Open Access Journals (Sweden)

Full Text Available In this article, a behavioral analysis of velocity boundary layer in a flat plate heat exchanger in laminar flow condition through CFD simulation using FLUENT software is done. The main objective of this study is to determine the velocity vectors between the flat plates of the heat exchanger. In addition, wake occurrence, differences of velocity at different surfaces between plates, angles of velocity vectors and the effect of wake phenomenon on the shear stresses exerted on the plates are discussed in detail. The study graphically illustrates results based on fluid’s behavior by a 3D and 2D simulation with air and water as cold and hot streams that affect plate’s situation and its hydro dynamical operations. Consequently, some important design features regarding wake point occurrence and pressure loss are investigated. In addition, eddy current and reverse flows in the wake area and the angles of the velocity vectors are described.

M. Mirdrikvand

2012-01-01

102

Influence of the Flow from an Axial Fan on the Performance of a Heat Exchanger  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Limited water supplies in arid regions that have abundant solar resources eliminates the use of water as a feasible means of cooling condensers in a Concentrated Solar Power (CSP) plant condenser. This has triggered the need to optimise existing air-cooled condenser technology, which is currently extremely inefficient. This paper aims to investigate the influence of various fan parameters on the performance of a cross-flow heat exchanger. The study first focuses on the effect of varying the d...

Moore, J.; Grimes, R.; Walsh, E.

2012-01-01

103

Condensation heat transfer and pressure drop of refrigerant R-410A flow in a vertical plate heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

Heat transfer and associated frictional pressure drop in the condensing flow of the ozone friendly refrigerant R-410A in a vertical plate heat exchanger (PHE) are investigated experimentally in the present study. In the experiment two vertical counter flow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60{sup o}. Downflow of the condensing refrigerant R-410A in one channel releases heat to the upflow of cold water in the other channel. The effects of the refrigerant mass flux, imposed heat flux, system pressure (saturated temperature) and mean vapor quality of R-410A on the measured data are explored in detail. The results indicate that the R-410A condensation heat transfer coefficient and associated frictional pressure drop in the PHE increase almost linearly with the mean vapor quality, but the system pressure only exhibits rather slight effects. Furthermore, increases in the refrigerant mass flux and imposed heat flux result in better condensation heat transfer accompanying with a larger frictional pressure drop. Besides, the imposed heat flux exhibits stronger effects on the heat transfer coefficient and pressure drop than the refrigerant mass flux especially at low refrigerant vapor quality. The friction factor is found to be strongly influenced by the refrigerant mass flux and vapor quality, but is almost independent of the imposed heat flux and saturated pressure. Finally, an empirical correlation for the R-410A condensation heat transfer coefficient in the PHE is proposed. In addition, results for the friction factor are correlated against the Boiling number and equivalent Reynolds number of the two-phase condensing flow. (author)

Kuo, W.S.; Lie, Y.M.; Lin, T.F. [Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Hsieh, Y.Y. [Department of Mechanical Engineering, Nan Kai Institute of Technology, Nantou, Taiwan (China)

2005-12-01

104

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2005-01-01

105

Modeling of flow-induced vibrations in heat exchangers and nuclear reactors  

International Nuclear Information System (INIS)

Appropriate scaling factors for the modeling of the fluid-mechanical interaction of complex structures are discussed. The possible mechanisms of flow-excited vibration are described, and scaling parameters are derived from considerations of the mechanical and fluid systems. Emphasis is placed on flow-induced vibrations of banks of cylinders in single phase, high Reynolds number, turbulent, cross flow, as occur for example in light water nuclear reactors and heat exchangers. It is concluded that the modeling of the tube banks in light water nuclear reactors will involve a mismatch of Reynolds number, but that the major phenomena of fluid-solid interaction in the single-phase flow region will probably be closely replicated if the Reynolds number is high enough so that the entering flow is turbulent and if the scaling ratio is not too large. (auth)

106

Heat exchanger restart evaluation  

International Nuclear Information System (INIS)

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

107

Low Reynolds number flow heat exchangers; Proceedings of the Fourth Advanced Study Institute, Ankara, Turkey, July 13-24, 1981  

Science.gov (United States)

A review of thermal-hydraulic fundamental principles is presented, focusing on the design of heat exchangers with low-Reynolds number flows. Attention is given to aspects of laminar forced convection, low-Reynolds number turbulent flow, and laminar non-Newtonian flow. The investigations were performed in tubes, tube bundles, and in a gravity flow over vertical or horizontal tubes. Heat exchanger configurations and materials were examined, as were compact and noncompact versions and heat transfer and fouling. Finally, research directions that are necessary to further characterize thermal design parameters, produce better flow visualization, and study single-phase fluid flows in heat exchangers are discussed. No individual items are abstracted in this volume

Kakac, S.; Shah, R. K.; Bergles, A. E.

108

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

International Nuclear Information System (INIS)

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

109

Heat exchanger performance monitoring guidelines  

International Nuclear Information System (INIS)

Fouling can occur in many heat exchanger applications in a way that impedes heat transfer and fluid flow and reduces the heat transfer or performance capability of the heat exchanger. Fouling may be significant for heat exchanger surfaces and flow paths in contact with plant service water. This report presents guidelines for performance monitoring of heat exchangers subject to fouling. Guidelines include selection of heat exchangers to monitor based on system function, safety function and system configuration. Five monitoring methods are discussed: the heat transfer, temperature monitoring, temperature effectiveness, delta P and periodic maintenance methods. Guidelines are included for selecting the appropriate monitoring methods and for implementing the selected methods. The report also includes a bibliography, example calculations, and technical notes applicable to the heat transfer method

110

Experimental study of the flow induced vibration of multi-span heat exchanger tube bundles in liquid cross-flow  

International Nuclear Information System (INIS)

It is well known that flow induced vibration is one of the factors which imposes limits on the design of heat exchangers and steam generators employed in the Nuclear Power Industry. The results of numerous liquid cross-flow tests conducted on single span laboratory tube bundles have already been reported by the author. These test results have been utilized to develop criterion for design purposes. It remains a fact, nevertheless, that there exists a strong need for test results acquired on multi-span bundles. Such bundles much more closely approximate real heat exchangers and steam generators. Like real heat exchangers, their resonant frequencies are clustered close together, thereby overcoming one of the principal shortcomings of single span test facilities. In this paper, the design of a new four span test facility along with the results of a series of vibration tests are discussed in detail. Using spectral analysis equipment the tube response is carefully examined for the resonant frequencies which it contains and fluidelastic instability measurements have been made. To the author's knowledge, this constitutes one of the first reports in the literature of the results of systematic laboratory vibration tests conducted on a realistic multi-span tube bundle facility subjected to liquid cross-flow. It is expected that these test results, coupled with the results of tests planned for the future, will throw significant new light on this important industrial problem. (orion this important industrial problem. (orig.)

111

Experimental and numerical investigation of the flow field through a heat exchanger for aero-engine applications  

International Nuclear Information System (INIS)

An experimental and computational study for the flow development through a heat exchanger for aero-engine applications is presented. The heat exchanger consists of elliptic tubes in a U formation, the ends of which are attached to the collector pipe, which has a cylindrical cross section. In this way, two identical packages (named as matrices) are formed and located at a certain distance between them. The elliptic tubes are placed in a staggered arrangement. Detailed flow measurements using a 3-hole pitot-static probe were carried out on a 1:1 scale model of the heat exchanger in order to measure the pressure drop through the heat exchanger and the velocity distribution behind it. The flow through the heat exchanger was modeled with a computational fluid dynamics approach. The heat exchanger matrices were modeled using a porous medium assumption. The pressure drop through each element of the porous medium was linked to an effective local velocity. In order to check the validity of the computational modeling, the results were compared to the measured flow parameters such as pressure and velocity distributions. Two sets of modeling were performed assuming a laminar and a turbulent flow. The results showed that the laminar approach gave better results and this is supported by the corresponding Reynolds numbers, which indicated that the global flow field is transitional

112

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

Directory of Open Access Journals (Sweden)

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

Nuntaphan, A.

2006-05-01

113

Steady-state and transient behaviour of two heat exchangers coupled by a circulating flow-stream  

Energy Technology Data Exchange (ETDEWEB)

Systems consisting of two heat exchangers coupled by a circulating flow-stream are studied. The systems differ in the flow configurations of the single heat exchangers. For steady-state operation there exists a heat capacity rate of the circulating flow-stream which maximizes the temperature changes of the external flow-streams. Until now this optimum has been calculated, assuming that the overall heat transfer coefficients of the heat exchangers do not depend on the mass flow rate of the circulating flow-stream. In this paper the dependence of the overall heat transfer coefficient on mass flow rate of the circulating flow-stream is taken into account. For transient operating conditions the system response to perturbations of inlet temperatures and mass flow rates is calculated by the method of Laplace-transforms and an explicit finite difference method. The most significant features of the coupled system become apparent considering outlet temperature transients induced by perturbations of the mass flow rate of the circulating flow-stream. (authors)

Na Ranong, Chakkrit; Roetzel, Wilfried [Institut fuer Thermodynamik, Universitaet der Bundeswehr Hamburg, D-22039, Hamburg (Germany)

2002-11-01

114

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

International Nuclear Information System (INIS)

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

115

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-07-01

116

Experiments on vibration of heat exchanger tube arrays in cross flow  

International Nuclear Information System (INIS)

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

117

The concept of a new approximate relation for heat transfer effectiveness for a cross-flow heat exchanger with unmixed fluids  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents an approximate relation for the heat transfer effectiveness for a counter-flow heat exchanger, which was compared with the exact solution. Based on the obtained approximate relation for a counter-flow heat exchanger the approximate heat transfer effectiveness for a cross-flow heat exchanger in which both fluids do not mix is proposed. This approximate heat transfer effectiveness was compared with the exact solution proposed by Mason, the most well-known relation. A comparison between the most frequently used approximate formula and the exact solution proposed by Mason was made, too. The heat transfer effectiveness was analyzed for the ratio of the heat capacity of fluids C in the range from 0 to 1 and the number of transfer units NTU from the most common range 0 – 5.

Rafal Marcin Laskowski

2011-01-01

118

An Empirical Study of Helical Coil Heat Exchanger Used in Liquid Evaporization and Droplet Disengagement for a Laminar Fluid Flow  

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchanger is an important component in industrial systems especially in process industries. Many commercial designs and types of heat exchangers are available in market for transfer of heat as well as for recovery of waste heat for the process plants. As helical coil have compact size and higher heat transfer coefficient they are widely used in industrial applications such as food preservation, refrigeration, process plant, power generation, etc. An attempt has been made to study the parallel flow and counter flow of inner higher temperature fluid flow and lower temperature fluid flow, which are separated by copper surface in a helical coil heat exchanger. Helical geometry allows the effective handling at higher temperatures and extreme temperature differentials without any highly induced stress or expansion of joints. These heat exchanger consists of series of stacked helical coiled tubes and the tube ends are connected by manifolds, which also acts as fluid entry and exit locations. In this paper, we focus on design parameters and heat transfer conditions of a vaporizer or generator of a simple vapour absorption refrigeration system having flow condition of refrigerant taken as laminar flow.

Kapil Dev*1,

2014-04-01

119

Oscillating-Coolant Heat Exchanger  

Science.gov (United States)

Devices useful in situations in which heat pipes inadequate. Conceptual oscillating-coolant heat exchanger (OCHEX) transports heat from its hotter portions to cooler portions. Heat transported by oscillation of single-phase fluid, called primary coolant, in coolant passages. No time-averaged flow in tubes, so either heat removed from end reservoirs on every cycle or heat removed indirectly by cooling sides of channels with another coolant. Devices include leading-edge cooling devices in hypersonic aircraft and "frost-free" heat exchangers. Also used in any situation in which heat pipe used and in other situations in which heat pipes not usable.

Scotti, Stephen J.; Blosser, Max L.; Camarda, Charles J.

1992-01-01

120

3D Numerical heat transfer and fluid flow analysis in plate-fin and tube heat exchangers with electrohydrodynamic enhancement  

Science.gov (United States)

Three-dimensional laminar fluid flow and heat transfer over a four-row plate-fin and tube heat exchanger with electrohydrodynamic (EHD) wire electrodes are studied numerically. The effects of different electrode arrangements (square and diagonal), tube pitch arrangements (in-line and staggered) and applied voltage (VE=0-16 kV) are investigated in detail for the Reynolds number range (based on the fin spacing and frontal velocity) ranging from 100 to 1,000. It is found that the EHD enhancement is more effective for lower Re and higher applied voltage. The case of staggered tube pitch with square wire electrode arrangement gives the best heat transfer augmentation. For VE=16 kV and Re = 100, this study identifies a maximum improvement of 218% in the average Nusselt number and a reduction in fin area of 56% as compared that without EHD enhancement.

Lin, Chia-Wen; Jang, Jiin-Yuh

2005-05-01

 
 
 
 
121

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

International Nuclear Information System (INIS)

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

122

Heat exchanger with ceramic elements  

Science.gov (United States)

An annular heat exchanger assembly includes a plurality of low thermal growth ceramic heat exchange 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 heat exchanger. 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.

Corey, John A. (North Troy, NY)

1986-01-01

123

Tubed heat exchanger  

International Nuclear Information System (INIS)

A tubed heat exchanger is described, which has at least one tube with transverse flow over it. The invention concerns the improvement of efficiency by avoiding thick boundary layers on the tube. It has transverse ribs set on it with special projections, which, according to the invention lie only on one side of the main plane of the ribs. Eight pictures illustrate the proposal. (RW)

124

A computational study of flow mal-distribution on the thermal hydraulic performance of an intermediate heat exchanger in LMFBR  

International Nuclear Information System (INIS)

The flow and thermal non-uniformities occurring in the intermediate heat exchanger (IHX) of a liquid metal-cooled fast breeder reactor have been characterized through numerical simulations. For modeling the primary and secondary sodium flow through the IHX, an equivalent anisotropic porous medium approach has been used. The pressure drop in the equivalent porous medium is accounted through the inclusion of additional pressure drop terms in the Navier–Stokes equations, with the help of standard correlations for cross flow or parallel flow over tubes. For secondary sodium flow, the effects of a flow distributor device with orifices and baffles at the inlet have also been included, in addition to axial flow through the tubes. The heat exchange between primary and secondary streams is incorporated in the form of a volumetric heat source or sink term, which is corrected iteratively. The resulting flow distributions are in reasonable agreement with available experimental results. The study shows that the temperature of the secondary sodium flow at the exit can be made more uniform by exchanging less heat near the inner wall of IHX, as compared to the region close to the outer wall, using suitable flow distribution devices. (author)

125

Investigations of flow characteristics in a plate fin and tube heat exchanger model composed of single cylinder  

International Nuclear Information System (INIS)

The flow structure in a plate fin and tube heat exchanger 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 heat exchanger flow 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

126

Evaluating certain ambiguities in results of calculations of radiative-convective heat exchange in hypersonic flow about a body  

Science.gov (United States)

Estimates are made of the effect of using several models of optical properties of the gaseous medium of a compressed layer, use of the method of equivalent line width, and use of a binary diffusion approximation on the results of calculations of radiative-convective heat exchange in hypersonic flow about a body. A method is proposed for correcting the results of calculations of heat transfer on permeable surfaces obtained without allowance for the effect of advance heating.

Rolin, M. N.; Iurevich, F. B.

1985-09-01

127

Thermal modeling of a greenhouse integrated to an aquifer coupled cavity flow heat exchanger system  

Energy Technology Data Exchange (ETDEWEB)

A thermal model is developed for heating and cooling of an agricultural greenhouse integrated with an aquifer coupled cavity flow heat exchanger system (ACCFHES). The ACCFHES works on the principal of utilizing deep aquifer water available at the ground surface through an irrigation tube well already installed in every agricultural field at constant year-round temperature of 24 C. The analysis is based on the energy balance equations for different components of the greenhouse. Using the derived analytical expressions, a computer program is developed in C{sup ++} for computing the hourly greenhouse plant and room air temperature for various design and climatic parameters. Experimental validation of the developed model is carried out using the measured plant and room air temperature data of the greenhouse (in which capsicum is grown) for the winter and summer conditions of the year 2004-2005 at Chandigarh (31 N and 78 E), Punjab, India. It is observed that the predicted and measured values are in close agreement. Greenhouse room air and plant temperature is maintained 6-7 K and 5-6 K below ambient, respectively for an extreme summer day and 7-8 K and 5-6 K above ambient, respectively for an extreme winter night. Finally, parametric studies are conducted to observe the effect of various operating parameters such as mass of the plant, area of the plant, mass flow rate of the circulating air and area of the ACCFHES on the greenhouse room air and plant temperature. (author)

Sethi, V.P. [Department of Mechanical Engineering, Punjab Agricultural University, Ludhiana 141 008, Punjab (India); Sharma, S.K. [Energy Research Centre, Panjab University, Chandigarh 160 017, Punjab (India)

2007-06-15

128

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

International Nuclear Information System (INIS)

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

129

Heat transfer in turbulent flow  

International Nuclear Information System (INIS)

This book reports on heat transfer and turbulent flow. The topics covered include fundamental research on turbulence in heat transfer processes, boundary layer flows, temperature turbulence spectrum, turbulence modeling, and applications to heat exchangers, gas turbines, and other engineering problems

130

An experimental and numerical study of a jetfire stop material and a new helical flow heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

This thesis consists of two parts. Part 1: Experimental and numerical study of jetfire stop, and Part 2: Experimental and numerical study of a new kind of shell and tube heat exchanger with helical flow on shell side. Part 1 describes the development of the model for simulation of the temperature development through Viking jetfirestop. A simulation program is developed that calculates the temperature development through Viking 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 heat exchanger. It consists of the development of a porosity model and a model for pressure drop and heat transfer as well as experiments in non-standard tube layouts. Results from the simulation program are compared with experiments on a helical flow shell and tube heat exchanger. There is a separate appendix volume. 62 refs., 152 figs., 22 tabs.

Austegard, Anders

1997-12-31

131

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

Directory of Open Access Journals (Sweden)

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

A. Barzegar

2009-01-01

132

Direct-contact heat exchanger for swirling countercurrent flow of hot gas and finely divided solids: A parametric study  

Science.gov (United States)

A vertically oriented solid-to-gas direct-contact heat exchanger (DCHX) has been proposed for heat recovery in high temperature plants that process finely divided solids. The flows are countercurrent, with the inlet gas flow entering on the centerline and swirling strongly. Swirling enhances heat transfer and centrifuges the solid particles from the center to the wall in order to minimize entrainment and permit gravity separation. A computer program was written to calculate particle trajectories and heat transfer rates (and, therefore, temperature profiles) for gas and solid phases. The flow model considers interactions between the particles and the flow field of the gas. The results of the computer program showed that the introduction of swirl significantly reduced the vertical distance required to achieve a given thermal efficiency. The countercurrent flow arrangement achieves high thermal efficiency in one contacting stage, unlike existing cocurrent suspension preheater systems, which require four or five stages. The practical application of this design to the cement industry appears unlikely, because very low gas velocities and correspondingly large areas of cross-sectional flow are required to prevent elutriation of the 74 micron particles required for the chemical reactions. The computer program can be modified for spray-dryer applications by the addition of mass transfer terms and a spray-formation model. In addition, the concept of a swirling flow heat exchanger may be applicable to other processes in which larger and heavier particles are used.

Bell, K. J.; Arman, B.

1991-06-01

133

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

Directory of Open Access Journals (Sweden)

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

Suneela Sardar

2013-10-01

134

Dehumidification: Prediction of Condensate Flow Rate for Plate-Fin Tube Heat Exchangers Using the Latent j Factor  

Energy Technology Data Exchange (ETDEWEB)

Condensate flow rate is an important factor in designing dehumidifiers or evaporators. In this paper, the latentj fimtor is used to analyze the dehumidification performance of two plate-fin tube heat exchangers. This latent j factor, analogous to the total j factor, is a flmction of the mass transfa coefllcient, the volumetric air flow rate, and the Schmidt number. This latent j factor did predict condensate flow rate more directly and accurately than any other sensiblej factor method. The Iatentj factor has been used in the present study because the sensible j factor correlations presented in the literature failed to predict the condensate flow rate at high Reynolds numbers. Results show that the latent j i%ctor em be simply correlated as a fhnction of the Reynolds number based on the tube outside diameter and number of rows of the heat exchanger.

Baxter, V.D.; Chen, D.T.; Conklin, J.C.

1999-03-15

135

Damping of heat exchanger tubes  

International Nuclear Information System (INIS)

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

136

Modelling and performance analysis of a cross-flow type plate heat exchanger for dehumidification/cooling  

Energy Technology Data Exchange (ETDEWEB)

This paper describes the performance analysis of a cross-flow type plate heat exchanger for use as a liquid desiccant absorber (dehumidifier) and indirect evaporative cooler. The proposed absorber can be described as a direct contact, cross-flow, heat and mass exchanger, with the flow passages separated from each other by thin plastic plates. One air stream (primary air) is sprayed by liquid desiccant solution, while the other stream (secondary air) is evaporatively cooled by a water spray. Each thin plate, besides separating the water/air passage from the solution/air passage, also provides the contact area for heat and mass transfer between the fluids flowing in each passage. A parametric study for the primary air stream at 33degC, 0.0171 kg/kg humidity ratio and secondary air stream at 27degC and 0.010 kg/kg humidity ratio using calcium chloride solution was performed in this study. The results showed a strong dependence on the heat and mass transfer areas, solution concentration and ratio of secondary to primary air mass flow rates. However, negligible differences were found between the performance of a counter flow and a parallel flow arrangement. The results demonstrate that the proposed absorber will not offset both the latent and sensible load of the primary air and, therefore, an auxiliary cooler or more dehumidification/indirect evaporate cooling stages will generally be required to meet the sensible and latent load in a typical comfort application. (Author)

Saman, W.Y.; Alizadeh, S. [South Australia Univ., School of Mechanical Engineering, Levels Campus, SA (Australia)

2001-07-01

137

Optimization of Heat Exchangers  

Energy Technology Data Exchange (ETDEWEB)

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

Ivan Catton

2010-10-01

138

The effect of unbalance flow on the performance of compact heat exchanger for HTGR-GT system  

International Nuclear Information System (INIS)

As for the design of the compact heat exchanger (recuperator) of HTGR-GT system by the helium gas turbine, heat exchanger effectiveness (HEE) is set to the goal in 92% of very high values. A recuperator is consisted of multi-layer core element with the combination of ultra fine offset fins (fin height x pitch x offset x thickness, 1.1-1.5 mm x 1.1-1.5 mm x 3 mm x 0.15 mm), separator, header with ultra fine straight fins (fin height x pitch x thickness, 1.1-1.5 mm x 3 mm x 0.15 mm) and ducts. By the concept design of this recuperator, it got the prospect that 95% of HEE can be achieved by making this ultra-fine offset fin-type core element with the flow channel width x height x length, 890 mm x 6,800 mm x 940 mm. However, there is possibility that the flow unbalance occurs to the cold flow, which is supplied to the direction of the core element height from the header when the recuperator size becomes large-sized in this way and as results, that the performance of the recuperator declines. Therefore, by implementing the three-dimensional heat transfer flow analysis of the recuperator, it evaluated a performance about the heat transfer of the recuperator when the virtual flow unbalance occurs to the direction of the height of the duct of the side of cold flow. As a result, the following conclusion was derived; (1) Helium flow unbalance in the cold flow header is caused by the maximum, -20% to 14% to all the helium flow rate. (2) When the flow unbalance which is identicalWhen the flow unbalance which is identical with cold flow along the header occurs on the hot flow header, it declines by about 0.5% to HEE per recuperator 1 unit when the flow unbalance does not occur on the cold flow. (3)When the symmetrical flow unbalance in cold flow header occur on the hot flow header, the rate with the declining heat transfer performance of the recuperator is the biggest. It declines by about 1.3% to the HEE per recuperator 1 unit when the flow unbalance does not occur on the cold flow header of the case. When above result, the assumed flow unbalance occurred, the thing about which it is possible to design the recuperator which meets a design request specification was concluded. (author)

139

Heat transfer and pressure drop of supercritical carbon dioxide flowing in several printed circuit heat exchanger channel patterns  

International Nuclear Information System (INIS)

chord length facing into the flow. Heat transfer coefficients and bulk temperatures are calculated from measured local wall temperatures and local heat fluxes. The experimental results are compared to several methods for estimating the friction factor and Nusselt number of cooling-mode flows at supercritical pressures in millimeter-scale channels. (authors)

140

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

International Nuclear Information System (INIS)

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

 
 
 
 
141

Analytical Entropy Analysis of Recuperative Heat Exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract: The analytical solutions for the temperature variation of two streams in parallel flow, counter flow and cross-flow heat exchangers and related entropy generation due to heat exchange between the streams are presented. The analysis of limiting cases for the relative entropy generation is performed, and corresponding analytical expressions are given. The obtained results may be included in a more general procedure concerning optimal heat exchanger design.

Marija Zivic

2003-12-01

142

Experimental and numerical study of mixed convection with flow reversal in coaxial double-duct heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Velocity vectors in a vertical coaxial double-duct heat exchanger for parallel ascending flow of water under conditions of laminar mixed convection have been determined experimentally using the particle image velocimetry technique. The measured velocity distributions for large annular flow rates, resulting in an essentially isothermal environment for the stream in the inner tube, are in very good agreement with corresponding numerical predictions. For flow rates of the same order of magnitude in the inner tube and the annulus, and corresponding temperature differences of about 20 C, experimental observations show that flow reversal occurs simultaneously in both streams over large axial distances for both heating and cooling of the flow in the inner tube. (author)

Mare, Thierry; Voicu, Ionut; Miriel, Jacques [Laboratoire de Genie Civil et de Genie Mecanique (LGCGM), INSA de Rennes, IUT Saint Malo, 35043 Rennes (France); Galanis, Nicolas [Faculte de genie, Universite de Sherbrooke, Sherbrooke, QC (Canada); Sow, Ousmane [Laboratoire d' Energie Appliquee, Ecole superieure Polytechnique, Dakar (Senegal)

2008-04-15

143

Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement  

Energy Technology Data Exchange (ETDEWEB)

Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program were to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined was iterative and intended to systematically (i) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, to be (ii) evaluated at 'in-service' loads at service temperatures and environments. Our report outlines the significant hoop creep enhancements possible via secondary cross-rolling and/or flow-forming operations. Each of the secondary processes i.e. hot rotary forming and ambient-temperature flow forming exhibited improvement over the base-line hoop-creep performance. The flow formed MA956 tubes exhibited performance superior to all other rolling/forming variants. At the conclusion of this program 2ksi creep-test exposure for flow formed materials exceeded 7300 hours, 7694 hours and 4200 hours for creep tests operating at 950 C, 975 C and 1000 C respectively. The Larsen-Miller parameter for these improvised flow-formed tubes now exceeds 54.14, i.e., better than ever recorded previously. The creep performance enhancement in cross-rolled MA956 material samples versus the base creep property is elucidated. At least 2-3 orders of magnitude of improvement in creep rates/day and concomitant increases in creeplife are demonstrated for the flow formed tubes versus the base reference tests.

Bimal Kad

2007-09-30

144

Numerical simulation of heat exchanger  

International Nuclear Information System (INIS)

Accurate and detailed knowledge of the fluid flow field and thermal distribution inside a heat exchanger becomes invaluable as a large, efficient, and reliable unit is sought. This information is needed to provide proper evaluation of the thermal and structural performance characteristics of a heat exchanger. It is to be noted that an analytical prediction method, when properly validated, will greatly reduce the need for model testing, facilitate interpolating and extrapolating test data, aid in optimizing heat-exchanger design and performance, and provide scaling capability. Thus tremendous savings of cost and time are realized. With the advent of large digital computers and advances in the development of computational fluid mechanics, it has become possible to predict analytically, through numerical solution, the conservation equations of mass, momentum, and energy for both the shellside and tubeside fluids. The numerical modeling technique will be a valuable, cost-effective design tool for development of advanced heat exchangers

145

Numerical simulation of heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

Accurate and detailed knowledge of the fluid flow field and thermal distribution inside a heat exchanger becomes invaluable as a large, efficient, and reliable unit is sought. This information is needed to provide proper evaluation of the thermal and structural performance characteristics of a heat exchanger. It is to be noted that an analytical prediction method, when properly validated, will greatly reduce the need for model testing, facilitate interpolating and extrapolating test data, aid in optimizing heat-exchanger design and performance, and provide scaling capability. Thus tremendous savings of cost and time are realized. With the advent of large digital computers and advances in the development of computational fluid mechanics, it has become possible to predict analytically, through numerical solution, the conservation equations of mass, momentum, and energy for both the shellside and tubeside fluids. The numerical modeling technique will be a valuable, cost-effective design tool for development of advanced heat exchangers.

Sha, W.T.

1985-01-01

146

An experimental analysis of the flow pattern in heat exchangers with an egg carton configuration (parallel, convergent and divergent cases)  

Energy Technology Data Exchange (ETDEWEB)

An experimental analysis about the flow patterns that appear in the channel formed between two corrugated plates with an egg carton configuration is reported. The types of flow instabilities caused by the corrugated plates are identified and described by means of flow visualization experiments, and photographic sequences illustrate the flow features present for each case. The influence on flow instabilities of Reynolds number, phase angle, convergence/divergence angle and spacing between corrugated plates is investigated. The corrugated plates are set divergent and convergent in order to investigate if recirculations are broken by chaotic advection. The improvement of heat transfer in the laminar regime has become an essential task in many applications and therefore the experiments are conducted in this regime. The corrugated plates geometry provides two main advantages over the conventional plane plates: the recirculation zones observed in the longitudinal direction and the three-dimensionality of the flow, i.e. the recirculations reduce the thermal resistances while the three-dimensionality of flow generates a better mixing and a more uniform temperature distribution. This experimental study contributes to the general knowledge on the subject being the first that addresses the analysis of convergent and divergent egg carton plates. It is expected that the results presented here will shed some light as to advantageously use these geometries in the near-future heat exchangers. (Because of the improve chaotic mixing in divergent corrugated plates, this configuration may be a good option to improve heat exchangers performance, because a better mixing is always related to the presence of core fluid near exchange surfaces, and consequently an increase in temperature gradients and heat transfer.)

Giron-Palomares, B. [Facultad de Ingenieria, Universidad de Guanajuato, Tampico 912, Salamanca, Guanajuato, 36730 (Mexico); Hernandez-Guerrero, A. [Facultad de Ingenieria, Universidad de Guanajuato, Tampico 912, Salamanca, Guanajuato, 36730 (Mexico)], E-mail: abelh@salamanca.ugto.mx; Romero-Mendez, R. [Facultad de Ingenieria, Universidad Autonoma de San Luis Potosi, Av. Dr. Manuel Nava 8, Zona Universitaria, San Luis Potosi, SLP 78290 (Mexico)], E-mail: rromerom@uaslp.mx; Oviedo-Tolentino, F. [Facultad de Ingenieria, Universidad Autonoma de San Luis Potosi, Av. Dr. Manuel Nava 8, Zona Universitaria, San Luis Potosi, SLP 78290 (Mexico)

2009-02-15

147

A study of heat and fluid flow phenomena on the gas side of circular-tube plate-fin heat exchangers  

Science.gov (United States)

The heat transfer and pressure drop characteristics of a circular-tube, plate-fin heat exchanger geometry were investigated. These parameters, expressed as the Colburn J factor and a friction factor f, are presented for Reynolds numbers from 100 to 3200, for exchanger samples with 1, 2 and 4 tube rows and 8, 10 and 12 fins per inch. These results are presented graphically and as a mathematical predictor model. The Taylor first order expansion and a Monte-Carlo numerical simulation of data were used to estimate the uncertainty in the values of J and f due to instrument discretization and random error. Comparisons with earlier work by other authors using simplified equations were undertaken. Dye-streak flow visualization was undertaken to study the flow field in four times scale models of circular-tube exchanger geometries with louvred and un-louvred plate-fins. Local heat transfer coefficients were obtained for the plain exchanger using a phase change paint in a transient condition. Correlations between the flow field and local heat transfer coefficient distribution were identified on the plain geometry and used to estimate the trends in heat transfer coefficient distribution for a louvred geometry. Numerical prediction of the flow fields present in a three dimensional plain circular-tube, plate-fin exchanger geometry, and two designs of multi-fin louvre bank were undertaken using the PHOENICS 81 code. Comparisons of predicted flow fields and experimental flow visualization showed good qualitative agreement. The development and manufacture of the various rigs, tools, and techniques used in the investigation are described.

Baldwin, Stephen

148

Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement  

Energy Technology Data Exchange (ETDEWEB)

Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (a) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (b) evaluated at ''in-service'' loads at service temperatures and environments. In this 12th quarter of performance, program activities are concluded for Task 2 and continuing for Tasks 3, 4 and reported herein. Two sets of MA956 tubes rotary cross-rolled at rolling angles of {Beta}=2{sup o} and 8{sup o} and two sets of flow formed and recrystallized tubes are being evaluated under hoop creep conditions in air. While, the rotary cross-rolled samples exhibit improvement over the baseline performance, it is he flow formed tubes that exhibit superior performance. Current test exposure for flow formed materials exceeds 6000 hours for a creep test operating at 950 C at 2Ksi stress. The Larsen-Miller parameter for these improvised flow-formed tubes now exceeds 52.4, i.e., better than ever recorded previously. These samples are at various stages of creep testing and evaluation in Task 4. The creep performance enhancement in cross-rolled MA956 material samples versus the base creep property is elucidated. At least 2-3 orders of magnitude of improvement in creep rates/day and concomitant increases in creep-life are demonstrated for the flow formed tubes versus the base reference tests.

Bimal K. Kad

2006-09-30

149

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

Directory of Open Access Journals (Sweden)

Full Text Available An Ionanofluids are a new and innovative class of heat transfer fluids which exhibit fascinating thermo physical properties compared to their base ionic liquids. In this paper (1-Butyl-3-methylimidazolium chloride (BmimCLionic fluid is used comparison with Distilled Water. Distilled Water is non Ionic form in nature, so, results using (BmimCLis Overall good efficient in heat transfer device, were obtained with experimental work results on thermal conductivity and heat capacity,. As compared to (BmimCL those of their base ionic liquids such as (mineral oils and ethylene glycol etc are less thermophysical properties . as coolants in heat exchanger are also used to access their feasibility and performance in heat transfer devices.

N.D.Shirgire

2014-07-01

150

Thermoelectric heat exchange element  

Science.gov (United States)

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

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

2007-08-14

151

Design evaluation of flow-induced vibrations for a large shell and tube type nuclear heat exchanger  

International Nuclear Information System (INIS)

Increased flow requirements for a large sized shell and tube type nuclear heat exchanger during advanced stage of manufacturing required re-evaluation of the Design to withstand flow-induced vibrations and suggest suitable Design alternatives within the constraints imposed at this advanced stage of manufacturing. Detailed flow-induced vibration analysis was done and two design alternatives offered. The first one consisted in attaching a wire-netted grid mounted alongside the baffle supports and the second considered removal of tubes from the vibration prone double span window region, which was counter-checked for heat-transfer adequacy requirement. Of the two alternatives, the second one was accepted due to its easy application at the advanced manufacturing stage. While the application of the wire-netted grid was not considered in the specific case, this might find application wherever the vibration prone double span tubes cannot be removed due to heat transfer requirements of Design

152

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

International Nuclear Information System (INIS)

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

153

Plate-Type Heat Exchanger  

International Science & Technology Center (ISTC)

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

154

Identification of some cross flow heat exchanger dynamic responses by measurement with low level binary pseudo-random input signals  

International Nuclear Information System (INIS)

An experiment was performed to assess the usefulness of the binary cross-correlation method in the context of the identification problem. An auxiliary burner was excited with a discrete interval binary code and the response to the perturbation of the input heat was observed by recording the variations of the primary inlet, primary outlet and secondary outlet temperatures. The observations were analysed to yield cross-correlation functions and frequency responses were subsequently determined between primary inlet and primary outlet temperatures and also between primary inlet and secondary outlet temperatures. The analysis verified (1) that these dynamic responses of this cross flow heat exchanger may be predicted theoretically, (2) in so far as this heat exchanger is representative of the generality of plant, that the binary cross-correlation method provides adequate identification of plant dynamics for control purposes in environments where small input variations and low signal to noise ratio are obligatory. (author)

155

Shell side numerical analysis of a shell and tube heat exchanger considering the effects of baffle inclination angle on fluid flow using CFD  

Directory of Open Access Journals (Sweden)

Full Text Available In this present study, attempts were made to investigate the impacts of various baffle inclination angles on fluid flow and the heat transfer characteristics of a shell-and-tube heat exchanger for three different baffle inclination angles namely 0°,10° and 20°. The simulation results for various shell and tube heat exchangers, one with segmental baffles perpendicular to fluid flow and two with segmental baffles inclined to the direction of fluid flow are compared for their performance. The shell side design has been investigated numerically by modeling a small shell-and-tube heat exchanger. The study is concerned with a single shell and single side pass parallel flow heat exchanger. The flow and temperature fields inside the shell are studied using non-commercial CFD software tool ANSYS CFX 12.1. For a given baffle cut of 36 %, the heat exchanger performance is investigated by varying mass flow rate and baffle inclination angle. From the CFD simulation results, the shell side outlet temperature, pressure drop, recirculation near the baffles, optimal mass flow rate and the optimum baffle inclination angle for the given heat exchanger geometry are determined.

Raj Karuppa Thundil R.

2012-01-01

156

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

International Nuclear Information System (INIS)

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

157

CROSSMIX; A mathematical model of a multi-pass cross-flow heat exchanger with primary fluid mixing  

International Nuclear Information System (INIS)

A two-dimensional model of a multi-pass cross-flow heat exchanger incorporating the interaction between primary and secondary fluids has been developed. Turbulent mixing and the cross flows due to temperature induced density gradients in the primary fluid are also included. The modelling equations are solved numerically using finite difference methods. The model is applicable to either serpentine or helical boilers and enables the effects of blanked-off tubes and other asymmetries to be predicted. An essential input to the model is the turbulent diffusivity within the relevant boiler geometry and the acquisition of these experimental data is discussed. (author)

158

Counterflow Regolith Heat Exchanger  

Science.gov (United States)

A problem exists in reducing the total heating power required to extract oxygen from lunar regolith. All such processes require heating a great deal of soil, and the heat energy is wasted if it cannot be recycled from processed material back into new material. The counterflow regolith heat exchanger (CoRHE) is a device that transfers heat from hot regolith to cold regolith. The CoRHE is essentially a tube-in-tube heat exchanger with internal and external augers attached to the inner rotating tube to move the regolith. Hot regolith in the outer tube is moved in one direction by a right-hand - ed auger, and the cool regolith in the inner tube is moved in the opposite direction by a left-handed auger attached to the inside of the rotating tube. In this counterflow arrangement, a large fraction of the heat from the expended regolith is transferred to the new regolith. The spent regolith leaves the heat exchanger close to the temperature of the cold new regolith, and the new regolith is pre-heated close to the initial temperature of the spent regolith. Using the CoRHE can reduce the heating requirement of a lunar ISRU system by 80%, reducing the total power consumption by a factor of two. The unique feature of this system is that it allows for counterflow heat exchange to occur between solids, instead of liquids or gases, as is commonly done. In addition, in variants of this concept, the hydrogen reduction can be made to occur within the counterflow heat exchanger itself, enabling a simplified lunar ISRU (in situ resource utilization) system with excellent energy economy and continuous nonbatch mode operation.

Zubrin, Robert; Jonscher, Peter

2013-01-01

159

Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes for Hoop Creep Enhancement  

Energy Technology Data Exchange (ETDEWEB)

Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (2) evaluated at ''in-service'' loads at service temperatures and environments. This research program is being conducted in collaboration with the DOE's Oak Ridge National Laboratory and the vested industrial partner Special Metals Corporation. In this ninth quarter of performance, program activities are continued for Tasks 2, 3 and 4 and are reported herein. Two sets of MA956 tube material samples rotary crossrolled at rolling angles of {beta} = 2{sup o} and 8{sup o} are processed in Task 3 and available for mechanical property testing in the remainder of this project. These samples are at various stages of creep testing and evaluation in Task 4. The creep rigs are being upgraded to handle long term testing at 1000 C and above. Reduced test times at accelerated temperatures will allow for additional testes to be conducted resulting in overall robust creep data statistics. The creep performance enhancement in cross-rolled MA956 material samples versus the base creep property is elucidated. Additional creep enhancements are derived when flow formed tubes are flattened at 900 C and recrystallized. The Larsen-Miller parameter for the improvised thermo-mechanical processing now approaches 52. At least 2-3 orders of magnitude of improvement in creep rates/day are demonstrated for the cross-rolled samples versus the base reference tests.

Bimal K. Kad

2006-04-10

160

Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement  

Energy Technology Data Exchange (ETDEWEB)

Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in crossrolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (2) evaluated at 'in-service' loads at service temperatures and environments. This research program is being conducted in collaboration with the DOE's Oak Ridge National Laboratory and the vested industrial partner Special Metals Corporation. In this eighth quarter of performance, program activities are continued for Tasks 2, 3 and 4 and are reported herein. Two sets of MA956 tube material samples cross-rolled at rolling angles of {beta} = 2{sup o} and 8{sup o} are processed in Task 3 and available for mechanical property testing in the remainder of this project. These samples are in preparation for creep testing in Task 4. The creep performance enhancement in cross-rolled MA956 material samples versus the base creep property is elucidated. Additional creep enhancements are derived when flow formed tubes are flattened at 900 C and recrystallized. The Larsen-Miller parameter for the improvised thermo-mechanical processing now approaches 52. At least 2-3 orders of magnitude of improvement in creep rates/day are demonstrated for the cross-rolled samples versus the base reference tests.

Bimal K. Kad

2005-11-23

 
 
 
 
161

Corrosion protected reversing heat exchanger  

International Nuclear Information System (INIS)

A reversing heat exchanger of the plate and fin type having multiple aluminum parting sheets in a stacked arrangement with corrugated fins separating the sheets to form multiple flow paths, means for closing the ends of the sheets, an input manifold arrangement of headers for the warm end of of the exchanger and an output manifold arrangement for the cold end of the exchanger with the input air feed stream header and the waste gas exhaust header having an alloy of zinc and aluminum coated on the inside surface for providing corrosion protection to the stack

162

PIPO-FE: an updated computer code to evaluate heat exchanger and steam generator flow-induced vibration  

International Nuclear Information System (INIS)

PIPO-FE is the latest version of a computer code that has been developed over the past 30 years to assess the flow-induced vibration of heat exchanger and steam generator tubes due to fluidelastic instability, random-turbulence excitation and vortex shedding. The code has recently been updated to include design guidelines prepared by Chalk River Laboratories of Atomic Energy of Canada Ltd. and the Department of Mechanical Engineering of Ecole Polytechnique, Montreal, and to estimate fretting-wear damage caused by random-turbulence vibration. This paper provides a general description of the updated code and includes examples to illustrate how the code can be used to support the design and modification of power plant heat exchangers and related research activities. (author)

163

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

International Nuclear Information System (INIS)

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

164

Monogroove liquid heat exchanger  

Science.gov (United States)

A liquid supply control is disclosed for a heat transfer system which transports heat by liquid-vapor phase change of a working fluid. An assembly (10) of monogroove heat pipe legs (15) can be operated automatically as either heat acquisition devices or heat discharge sources. The liquid channels (27) of the heat pipe legs (15) are connected to a reservoir (35) which is filled and drained by respective filling and draining valves (30, 32). Information from liquid level sensors (50, 51) on the reservoir (35) is combined (60) with temperature information (55) from the liquid heat exchanger (12) and temperature information (56) from the assembly vapor conduit (42) to regulate filling and draining of the reservoir (35), so that the reservoir (35) in turn serves the liquid supply/drain needs of the heat pipe legs (15), on demand, by passive capillary action (20, 28).

Brown, Richard F. (Inventor); Edelstein, Fred (Inventor)

1990-01-01

165

Microgravity condensing heat exchanger  

Science.gov (United States)

A heat exchanger having a plurality of heat exchanging aluminum fins with hydrophilic condensing surfaces which are stacked and clamped between two cold plates. The cold plates are aligned radially along a plane extending through the axis of a cylindrical duct and hold the stacked and clamped portions of the heat exchanging fins along the axis of the cylindrical duct. The fins extend outwardly from the clamped portions along approximately radial planes. The spacing between fins is symmetric about the cold plates, and are somewhat more closely spaced as the angle they make with the cold plates approaches 90.degree.. Passageways extend through the fins between vertex spaces which provide capillary storage and communicate with passageways formed in the stacked and clamped portions of the fins, which communicate with water drains connected to a pump externally to the duct. Water with no entrained air is drawn from the capillary spaces.

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor); North, Andrew (Inventor); Weislogel, Mark M. (Inventor)

2011-01-01

166

Probe Measures Fouling As In Heat Exchangers  

Science.gov (United States)

Combustion deposits reduce transfer of heat. Instrument measures fouling like that on gas side of heat exchanger 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 heat exchanger. 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.

Marner, Wilbur J.; Macdavid, Kenton S.

1990-01-01

167

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

International Nuclear Information System (INIS)

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

168

Numerical study of a novel counter-flow heat and mass exchanger for dew point evaporative cooling  

International Nuclear Information System (INIS)

The paper presents numerical investigation of a novel counter-flow heat and mass exchanger used in the indirect evaporative dew point cooling systems, a potential alternative to the conventional mechanical compression air conditioning systems. Numeric simulation was carried out to optimise the geometrical sizes and operating conditions of the exchanger in order to enhance the cooling (dew point and wet bulb) effectiveness of the exchanger and maximise the energy efficiency of the dew point cooling system. The results of the simulations indicated that cooling (dew point and wet bulb) effectiveness and energy efficiency are largely dependent on the dimensions of the airflow passages, air velocity and working-to-intake-air ratio, and less dependent on the temperature of the feed water. It is recommended that exchanger intake air velocity should be controlled to a value below 0.3-0.5 m/s; height of air passage (channel) should be set to 6 mm or below and the length of the passage should be 200 time the height; the working-to-intake-air ratio should be around 0.4. Under the UK summer design condition, i.e., 28 deg. C of dry bulb temperature, 20 deg. C of wet bulb temperature and 16 deg. C of dew point temperature, the exchanger can achieve wet-bulb effectiveness of up to 1.3 and dew-point effectiveness of up to 0.9

169

Cooling device for a heat exchange fluid  

International Nuclear Information System (INIS)

The invention refers to a system for cooling process or operation fluids, in which the local or general superheating of the coolant must be avoided. It particularly applies to the bleed fluid of a nuclear power station steam generator. This invention aims to create a heat exchange system that uses static components only and that is therefore completely reliable whilst remaining simple and relatively economical. This system includes a regeneration heat exchanger (with a primary and secondary system) and a triple flow heat exchanger with three circuits. The first and second circuits are in fluid communication with the primary and secondary circuits of the regeneration heat exchanger. The fluid communication between the regeneration heat exchanger and the triple circuit heat exchanger is such that the process fluid first goes through one of the circuits of the regeneration heat exchanger where it is cooled, then through one of the first two circuits of the triple circuit heat exchanger where it is cooled still more, then through the other of the circuits of the regeneration exchanger where it is heated and finally through the second of the first two circuits of the triple circuit heat exchanger where it is cooled again. A coolant flows through the third circuit in order to cool the process fluid concerned

170

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Transient thermal behavior of a vertical storage tank of a domestic solar heating system with a mantle heat exchanger has been investigated numerically in the charging mode. It is assumed that the tank is initially filled with uniform cold water. At an instant of time, the hot fluid from collector outlet is uniformly injected in the upper section of the mantle heat exchanger and after heat transfer with the fluid inside the tank, withdrawn from the bottom part of the heat excha...

Barzegar, A.; Dehghan, A. A.

2009-01-01

171

Detection of flow mixing processes using transmission methods in high-duty heat exchanging apparatus  

International Nuclear Information System (INIS)

The COBRA-IIIC program modified by MIT has been further improved for verifying the experimental studies described in the thesis. This work has been accompanied by a review and modification of the relevant analytical equations. A mathematical relationship has been set up for the cross-mixing phenomenon of shearing flow in narrowest cross-section between two heating rods, the relationship being taken into account in the sub-channel analysis. Despite the very complex and superposing processes of the problem studied, the results obtained by the improved sub-channel analysis program using the nearly derived cross-mixing approach are quantitatively well confirmed by comparison with experimental data. Applying the improved sub-channel analysis program to describing the author's two-phase flow experiments (air-water and water-steam) with rod bundle geometries to be found in the literature, the cross-mixing approach presented in the thesis is shown to be reliable (orig./GL)

172

Experimental evaluation of vibrations in heat exchangers  

International Nuclear Information System (INIS)

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

173

The numerical analysis of the flow fields near fin surface of a plate fin-oval tube heat exchanger with delta wing vortex generators  

International Nuclear Information System (INIS)

In present study, the flow field near the fin surface of plate fin - oval tube heat exchanger with delta wing vortex generator was numerically analyzed. As results, the well developed vortex behind delta wing was observed. These vortex can improve heat transfer fin surface behind delta wing vortex generators

174

Matrix heat exchanger  

International Nuclear Information System (INIS)

Heat exchangers for nuclear reactors cooled with liquid metal are often of matrix construction. The invention deals with the improvement of the heat transfer behaviour of such aggregates. A small gap between the matrix and pipeline is to be filled with a liquid medium of good thermal conductivity (e.g. melted metal such as Bi, Pb, Hg or their alloys). Additions of Zr, Mg or Ti are to prevent the cooling pipe walls from corrosion. Advantageous variations of the composition and arrangement are given in detail. (HP)

175

The effect of flow-hole structure and water chemistry on scale adhesion at the leading edge of a flow hole in a heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

In the heat exchangers of power plants, scale deposition may occur, especially at the leading edge of contraction. The growth of scale can lead to an increase in pressure and cause oscillation of the water level. In our previous study, the dependence of flow on contraction geometry was analyzed numerically and empirically. It was shown that the contraction ratio of hydraulic diameter of the flow path contributed greatly to the difference in pressure drop and turbulent kinetic energy at the leading edge of the flow path. In this study, the effect of contraction geometry and flow rate on scale adhesion was studied in AVT chemistry at 270degC using a high-velocity scale-adhesion test loop. The differential pressure and the amount of scale deposited due to scale adhesion at the leading edge of the flow path increased more in a quatrefoil-type flow path than in drill-type flow path. The differential pressure and the amount of scale deposited also increased with increasing flow rate. Based on the results of the previous study, the flow behavior around the two different contractions under the above test conditions was also analyzed numerically. The test and analysis results indicated that the increase in scale adhesion at the leading edge of a quatrefoil-type flow path might be correlated with the localized increase in turbulent kinetic energy and pressure drop at the contraction inlet. (author)

Hirano, Hideo; Miyajima, Kaori; Kawamura, Hirotaka; Yoneda, Kimitoshi; Yasuo, Akira [Central Research Inst. of Electric Power Industry, Komae, Tokyo (Japan). Komae Research Lab

1999-05-01

176

The effect of flow-hole structure and water chemistry on scale adhesion at the leading edge of a flow hole in a heat exchanger  

International Nuclear Information System (INIS)

In the heat exchangers of power plants, scale deposition may occur, especially at the leading edge of contraction. The growth of scale can lead to an increase in pressure and cause oscillation of the water level. In our previous study, the dependence of flow on contraction geometry was analyzed numerically and empirically. It was shown that the contraction ratio of hydraulic diameter of the flow path contributed greatly to the difference in pressure drop and turbulent kinetic energy at the leading edge of the flow path. In this study, the effect of contraction geometry and flow rate on scale adhesion was studied in AVT chemistry at 270degC using a high-velocity scale-adhesion test loop. The differential pressure and the amount of scale deposited due to scale adhesion at the leading edge of the flow path increased more in a quatrefoil-type flow path than in drill-type flow path. The differential pressure and the amount of scale deposited also increased with increasing flow rate. Based on the results of the previous study, the flow behavior around the two different contractions under the above test conditions was also analyzed numerically. The test and analysis results indicated that the increase in scale adhesion at the leading edge of a quatrefoil-type flow path might be correlated with the localized increase in turbulent kinetic energy and pressure drop at the contraction inlet. (author)

177

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

International Nuclear Information System (INIS)

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

178

Heat exchanger tube tool  

International Nuclear Information System (INIS)

Certain types of heat-exchangers have tubes opening through a tube sheet to a manifold having an access opening offset from alignment with the tube ends. A tool for inserting a device, such as for inspection or repair, is provided for use in such instances. The tool is formed by a flexible guide tube insertable through the access opening and having an inner end provided with a connector for connection with the opening of the tube in which the device is to be inserted, and an outer end which remains outside of the chamber, the guide tube having adequate length for this arrangement. A flexible transport hose for internally transporting the device slides inside of the guide tube. This hose is long enough to slide through the guide tube, into the heat-exchanger tube, and through the latter to the extent required for the use of the device. The guide tube must be bent to reach the end of the heat-exchanger tube and the latter may be constructed with a bend, the hose carrying anit-friction elements at interspaced locations along its length to make it possible for the hose to negotiate such bends while sliding to the location where the use of the device is required

179

Fluid exchange flows  

Science.gov (United States)

Flow flows from one container to another play important roles in many natural and industrial situations. The talk will describe the latest work on some of these. 1. The exchange flow of relatively dense, viscous fluid in a container connected by a vertical pipe to a container beneath it, initially full of relatively light fluid, will be discussed. This mimics the important exchange flow between a volcanic crater and a deep magma reservoir. A quantitative analysis of the flow will be presented. For the volcanic situation this allows the conduit radius to be evaluated from observations of the sulphur dioxide flux from the crater to the atmosphere. 2. A closed container initially full of liquid, which can drain into the atmosphere through a very long tube, displays different phenomena, which are associated with the compressibility of the air that exchanges space with the liquid. Three distinct regimes are observed, which we term: `popping'; `glugging'; and `slugging'. During each of these the container drains at a quite different rate. 3. Hot air in a house can be exchanged through doors and windows with the cooler air outside. The form and rate of exchange and its dependence on window geometry is of considerable architectural interest at the moment, if only to make our working environment as green as possible. New experiments and the associated concepts for this problem will be discussed.

Huppert, Herbert

2006-11-01

180

The combined effects of inlet fluid flow and temperature nonuniformity in cross flow plate-fin compact heat exchanger using finite element method  

Science.gov (United States)

An analysis of a crossflow plate-fin heat exchanger accouning for the combined effects of inlet fluid flow nonuniformity and temperature nonuniformity on both hot and cold fluid sides is carried out using a Finite Element Model. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in inlet fluid flow. Using these fluid flow maldistribution models, the exchanger effectiveness and its deteriorations due to flow/temperature nonuniformity are calculated for entire range of design and operating conditions. It was found that the performance deteriorations are quite significant in some typical applications due to inlet fluid flow/temperature nonuniformity. Zusammenfassung Mit Hilfe der Finitelement-Methode wird der zusammenwirkende Einfluß ungleichförmiger Strömungs- und Temperaturverteilungen am Eintritt des kalten, wie des warmen Fluids eines kreuzstrombetriebenen, berippten Kompakt-Plattenwärmetauschers untersucht. Über eine mathematische Beziehung lassen sich verschiedene Arten ungleichmäßiger Strömungs bzw. Temperaturverteilungen in den Eintrittsquerschnitten generieren. Unter Verwendung dieser Fehlverteilungsmodelle wird deren Einfluß auf den Austauscher-Gütegrad im gesamten Auslegungs- und Betriebsbereich ermittelt. Es zeigte sich, daß diese Auswirkungen bei typischen Ungleichförmigkeiten der Strömungs- bzw. Temperaturfelder in den Eintrittsquerschnitten erheblich sein können.

Ranganayakulu, C.; Seetharamu, K. N.

 
 
 
 
181

Heat Exchangers Analysis  

Directory of Open Access Journals (Sweden)

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

S.C. Pang

2013-01-01

182

Heat transport characteristics of flow fields in proton exchange membrane fuel cells  

Energy Technology Data Exchange (ETDEWEB)

Since the electrochemical reaction at electrodes of PEMFC is a form of exothermic reaction, three-dimensional non-isothermal numerical simulation was developed including the energy equation with all heat source terms such as reversible heat generation and irreversible heat release attributed to ohmic and activation polarization. The results show that the maximum temperature is observed at the cathode because of reaction heat from water formation reaction and temperature at the electrolyte along channel increases due to accumulative heat addition and heat is mainly generated by irreversible loss at a low voltage and by water formation loss at a low current density. (author)

Cho, Son Ah; Lee, Pil Hyong; Han, Sang Seok; Hwang, Sang Soon [Department of Mechanical Engineering, University of Incheon, Dohwa-dong 177, Nam-gu, Incheon 402-749 (Korea)

2008-04-01

183

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

Energy Technology Data Exchange (ETDEWEB)

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

Culver, G.

1990-11-01

184

Comparative Study of Heat Exchangers Using CFD  

Directory of Open Access Journals (Sweden)

Full Text Available A parallel flow heat exchanger and a corresponding ribbed tube heat exchanger is modeled and numerically analysed using a commercial finite volume CFD package. Pro-E & ANSYS 14.5 softwares are used for the designing and the analysis. CFD predictions of effectiveness of the two heat exchangers are obtained and compared. After selecting the best modeling approach, the sensitivity of the results to particular flow rate is investigated. It is observed that the flow and the temperature fields obtained from CFD simulations provide valuable information about the parts of the heat exchanger design that need improvement. Correlation based approaches may indicate the existence of the weakness but CFD simulations can also pin point the source and the location of it. Using CFD may speed up the design process and may improve the final design.

Melvinraj C R

2014-05-01

185

Cryogenic regenerative heat exchangers  

CERN Document Server

An in-depth survey of regenerative heat exchangers, this book chronicles the development and recent commercialization of regenerative devices for cryogenic applications. Chapters cover historical background, concepts, practical applications, design data, and numerical solutions, providing the latest information for engineers to develop advanced cryogenic machines. The discussions include insights into the operation of a regenerator; descriptions of the cyclic and fluid temperature distributions in a regenerator; data for various matrix geometries and materials, including coarse and fine bronze, stainless steel-woven wire mesh screens, and lead spheres; and unique operating features of cryocoolers that produce deviations from ideal regenerator theory.

Ackermann, Robert A

1997-01-01

186

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

Science.gov (United States)

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

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

2007-12-01

187

Triple loop heat exchanger for an absorption refrigeration system  

Science.gov (United States)

A triple loop heat exchanger for an absorption refrigeration system is disclosed. The triple loop heat exchanger comprises portions of a strong solution line for conducting relatively hot, strong solution from a generator to a solution heat exchanger of the absorption refrigeration system, conduit means for conducting relatively cool, weak solution from the solution heat exchanger to the generator, and a bypass system for conducting strong solution from the generator around the strong solution line and around the solution heat exchanger 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 heat exchange relationship with each other in the triple loop heat exchanger 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 heat exchange relationship in the triple loop heat exchanger 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 heat exchanger, is brought into heat exchange relationship with any strong solution which may have solidified in the strong solution line in the triple loop heat exchanger to thereby aid in desolidifying any such solidified strong solution.

Reimann, Robert C. (Lafayette, NY)

1984-01-01

188

Plate heat exchanger  

International Nuclear Information System (INIS)

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

189

Numerical simulation of a three-layered radiant porous heat exchanger including lattice Boltzmann simulation of fluid flow  

International Nuclear Information System (INIS)

radiative heat flux in the porous medium. The numerical results consist of the gas and porous media temperature distributions. The variation of radiative heat flux are also presented. Furthermore, the effects of scattering albedo, optical thickness and inlet gas temperature on the efficiency of the proposed porous heat exchanger are investigated. It is revealed that this type of heat exchanger has high efficiency in comparison to conventional one. Also, the present numerical results for a porous radiant burner are compared with theoretical finding by the other investigator and good agreement is found.

190

Improvements in or relating to heat exchangers  

International Nuclear Information System (INIS)

A 'tube-in-shell' heat exchanger is described for effecting heat exchange between liquid metal and water. In conventional heat exchangers of this type a condition can arise wherein Na passing through the tube plate at the water inlet end of the heat exchanger may be above the saturation temperature of the water, and although resultant boiling of the water in the region of the tube plate would tend to counter stagnation there is a possibility that sub-cooled boiling associated with stagnation may occur in the central area of the tube plate, and this could be the source of corrosion. The design of heat exchanger described is directed towards a solution of this problem. The heat exchanger comprises an elongated shell having two spaced transverse tube plates sealed to the shell so as to provide end and intermediate chambers. A bundle of spaced parallel heat exchange tubes extends between the tube plates, interconnecting the end chambers with an inlet port for liquid metal flow to one of the end chambers and an outlet port for liquid metal flow from the other of the end chambers, and inlet and outlet ports for flow of water through the intermediate chamber, these ports being at opposite ends of the intermediate chamber. The intermediate chamber has a tube closed to liquid metal flow extending between the tube plates, this tube having an inlet port for water adjacent to the tube plate at the inlet region of the intermediate chamber and an outlet port at the outlet region. This tube has open ends and is laterally supported by neighbouring heat exchange tubes, or alternatively may have closed ends and be end supported by penetration of the tube plates, the inlet and outlet ports for flow of water being perforations in the wall of the tube. (U.K.)

191

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

International Nuclear Information System (INIS)

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

192

Dynamic Behaviour of a Continuous Heat Exchanger/Reactor after Flow Failure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The intensified technologies offer new prospects for the development of hazardous chemical syntheses in safer conditions: the idea is to reduce the reaction volume by increasing the thermal performances and preferring the continuous mode to the batch one. In particular, the Open Plate Reactor (OPR) type “reactor/ exchanger” also including a modular block structure, matches these characteristics perfectly. The aim of this paper is to study the OPR behaviour during a normal operation, that ...

Benaissa, Wassila; Elgue, Se?bastien; Gabas, Nadine; Cabassud, Michel; Carson, Douglas; Demissy, Michel

2008-01-01

193

Tube bundle heat exchanger  

International Nuclear Information System (INIS)

The heat exchanger consists of tube bundles mounted in parallel. Each bundle consists of a jacket in which tubes for a first coolant are mounted. Straight tubes are connected with their open ends to tube plates which, in turn, are connected to the jacket provided with the inlet and outlet for a second coolant. This passes between the outer surfaces of straight tubes and the inner jacket surface. Spacers are inserted between the tube bundles, this along the whole length of the bundles. The second coolant enters one tube plate through the open ends of inlet tubes. It leaves through the other tube plate of the respective bundle, through the open ends of the outlet tubes. The other open ends of the inlet and/or outlet tubes are inserted in auxiliary tube plates mounted in the jacket on both sides of the tube bundles. (H.S.)

194

Evaluation of heat transfer performance on drum side of orthogonal flow type Na heat exchanger. Application of inviscid vortex-free flow model to zig-zag tube arrangement system  

International Nuclear Information System (INIS)

Recently, for the purpose of heightening the economical efficiency and performance of FBRs, it has been attempted to evaluate the performance of intermediate heat exchangers and steam generators with large computation codes. If the heat transfer characteristics of individual heating tubes can be grasped with the required accuracy by numerical analysis, it is most economical and realistic. There is the possibility of being able to forecast the heat transfer coefficient using the inviscid vortex-free flow model considering only the basic features of flow fields with the practical accuracy. In this research, first, the visualization experiment on the flow orthogonally crossing the tube nest of zig-zag arrangement using water was carried out to elucidate the features. Based on the observed results, the analysis of the heat transfer coefficient of alkali metals orthogonally crossing the tube nest of zig-zag arrangement was carried out for single tube heating and whole tube heating systems, using the inviscid vortex-free flow model. The visualization experiment and the numerical analysis are reported. (K.I.)

195

Design study of plastic film heat exchanger  

Science.gov (United States)

This report presents the results of an effort to develop and design a unique thermoplastic film heat exchanger for use in an industrial heat pump evaporator system and other energy recovery applications. The concept for the exchanger is that of individual heat exchange 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 heat exchange 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 heat exchanger 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 heat exchangers.

Guyer, E. C.; Brownell, D. L.

1986-02-01

196

Generalized thermal characteristic of a heat exchanger  

International Nuclear Information System (INIS)

Thermal characteristics of a heat exchanger are presented in the form of a single generalized dependence. Such a dependence provides acceleration both of numerical and experimental determination of output temperatures of actuating media. This characteristic is derived for single-pass cross-flow plate-finned heat exchanger. Experimental checking the dependence obtained confirms the correctness of theoretical suppositions forming the basis of the analytical solution made

197

Performance test of miniature heat exchangers with microchannels  

International Nuclear Information System (INIS)

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

198

Interfacing heat exchanger network synthesis and detailed heat exchanger design  

Energy Technology Data Exchange (ETDEWEB)

Current heat exchanger network synthesis targeting and design procedures involve the use of assumed stream heat transfer coefficients. However, during detailed heat exchanger design, allowable pressure drops are often the most critical factors. The result can be big differences between the exchanger sizes and costs anticipated by the network designer and those realised by the exchanger designer. This in turn prejudices any optimisation attempted at the network design stage. In this paper it is shown how allowable pressure drop can be used as a basis of network design and consistency between expectation and realisation achieved. (author).

Polley, G.T.; Panjeh Shahi, M.H. (Manchester Univ. (United Kingdom). Inst. of Science and Technology)

1991-11-01

199

Heat exchanger leakage problem location  

Directory of Open Access Journals (Sweden)

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

Jícha Miroslav

2012-04-01

200

Heat exchanger leakage problem location  

Science.gov (United States)

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

Hej?ík, Ji?í; Jícha, Miroslav

2012-04-01

 
 
 
 
201

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

International Nuclear Information System (INIS)

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

202

Rotor bore and turbine rotor wheel/spacer heat exchange flow circuit  

Science.gov (United States)

In a turbine having closed-circuit steam-cooling passages about the rim of the rotor during steady-state operation, compressor discharge air is supplied to the rotor bore for passage radially outwardly into the wheel space cavities between the wheels and spacers. Communicating slots and channels in the spacers and wheels at circumferentially spaced positions enable egress of the compressor discharge air into the hot gas flow path. At turbine startup, cooling air flows through the closed-circuit steam passages to cool the outer rim of the rotor while compressor discharge air pre-warms the wheels and spacers. At steady-state, cooling steam is supplied in the closed-circuit steam-cooling passages and compressor discharge air is supplied through the bore and into the wheel space cavities to cool the rotor.

Caruso, Philip M. (Selkirk, NY); Eldrid, Sacheverel Quentin (Saratoga Springs, NY); Ladhani, Azad A. (Niskayuna, NY); DeMania, Alan Richard (Niskayuna, NY); Palmer, Gene David (Clifton Park, NY); Wilson, Ian David (Clifton Park, NY); Rathbun, Lisa Shirley (Scotia, NY); Akin, Robert Craig (Schenectady, NY)

2002-01-01

203

Performance Investigation of Plate Type Heat Exchanger (A Case Study  

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchanger is a thermodynamic system which is most commonly used in the process industry for exchanging heat energy between the fluids. flowing in the same or opposite direction. It is desired that effectiveness of heat exchanger should remain as large as possible. Heat exchanger's performance may be improved by the addition of fins or corrugations. These investigations include design of plate type heat exchanger, heat transfer enhancement, flow phenomenon and cleanliness factor. In process plants, this type of heat exchange is generally used for recovering heat content of exhaust steam. However, with the flow of fluid for a long period, fouling occurs on the plate surface. Therefore, it is required to investigate the effect of fouling, wherever the heat exchanger is installed. An extensive experimental investigation has been carried out under clean and dirty condition of the said plate type heat exchanger. Heat transfer and flow data were collected in experiment. From collected data heat transfer rate, overall heat transfer coefficient, fouling factor and cleanliness factor were evaluated. Based upon the cleanliness factor data, next date of cleanliness for plate type heat exchanger was predicted. It is felt that the outcome of the present research work may be quite useful for efficient operation of plate type heat exchanger installed in Process plants.

Simarpreet Singh

2014-04-01

204

Component Cooling Heat Exchanger Heat Transfer Capability Operability Monitoring  

International Nuclear Information System (INIS)

The ultimate heat sink (UHS) is of highest importance for nuclear power plant safe and reliable operation. The most important component in line from safety-related heat sources to the ultimate heat sink water body is a component cooling heat exchanger (CC Heat Exchanger). The Component Cooling Heat Exchanger has a safety-related function to transfer the heat from the Component Cooling (CC) water system to the Service Water (SW) system. SW systems throughout the world have been the root of many plant problems because the water source, usually river, lake, sea or cooling pond, are conductive to corrosion, erosion, biofouling, debris intrusion, silt, sediment deposits, etc. At Krsko NPP, these problems usually cumulate in the summer period from July to August, with higher Sava River (service water system) temperatures. Therefore it was necessary to continuously evaluate the CC Heat Exchanger operation and confirm that the system would perform its intended function in accordance with the plant's design basis, given as a minimum heat transfer rate in the heat exchanger design specification sheet. The Essential Service Water system at Krsko NPP is an open cycle cooling system which transfers heat from safety and non-safety-related systems and components to the ultimate heat sink the Sava River. The system is continuously in operation in all modes of plant operation, including plant shutdown and refueling. However, due to the Sava River impurities and our limited abilities of the water treatment, the system is subject to fouling, sedimentation buildup, corrosion and scale formation, which could negatively impact its performance being unable to satisfy its safety related post accident heat removal function. Low temperature difference and high fluid flows make it difficult to evaluate the CC Heat Exchanger due to its specific design. The important effects noted are measurement uncertainties, nonspecific construction, high heat transfer capacity, and operational specifics (e.g. using CC Heat Exchanger bypass valves for CC temperature control, variation of plant heat loads, pumps performance, and day-night temperature difference, with lagging effects on heat transfer dynamics). Krsko NPP is continuously monitoring the Component Cooling (CC) Heat Exchanger performance using the on-line process information system (PIS). By defining the mathematical algorithm, it is possible to continuously evaluate the CC Heat Exchanger operability by verifying if the heat transfer rate calculation is in accordance with the heat exchanger design specification sheet requirements. These calculations are limited to summer periods only when the bypass valves are neither throttled nor open.(author).

205

High Temperature Heat Exchanger Project  

Energy Technology Data Exchange (ETDEWEB)

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

Anthony E. Hechanova, Ph.D.

2008-09-30

206

Heat pipes in modern heat exchangers  

International Nuclear Information System (INIS)

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

207

Heat pipes in modern heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Heat pipes are very flexible systems with regard to effective thermal control. They can easily be implemented as heat exchangers inside sorption and vapour-compression heat pumps, refrigerators and other types of heat transfer devices. Their heat transfer coefficient in the evaporator and condenser zones is 10{sup 3}-10{sup 5} W/m{sup 2} K, heat pipe thermal resistance is 0.01-0.03 K/W, therefore leading to smaller area and mass of heat exchangers. Miniature and micro heat pipes are welcomed for electronic components cooling and space two-phase thermal control systems. Loop heat pipes, pulsating heat pipes and sorption heat pipes are the novelty for modern heat exchangers. Heat pipe air preheaters are used in thermal power plants to preheat the secondary-primary air required for combustion of fuel in the boiler using the energy available in exhaust gases. Heat pipe solar collectors are promising for domestic use. This paper reviews mainly heat pipe developments in the Former Soviet Union Countries. Some new results obtained in USA and Europe are also included. (author)

Vasiliev, L.L. [Academy of Science, Minsk (Russian Federation). A.V. Luikov Heat and Mass Transfer Institute

2005-01-01

208

Quantitative flow visualization of fluidized-bed heat exchanger by neutron radiography  

International Nuclear Information System (INIS)

Quantitative flow visualization of a gas-solid fluidized-bed installed vertical tube-bank has been successfully conducted using neutron radiography and image processing technique. The quantitative data of void fraction distribution as well as the fluctuation data are presented. The time-averaged void fraction is well correlated by the drift-flux model. The bubbles formed in the bed, rise along the vertical tubes and the observed bubble size is smaller than that in a free bubbling bed without tube-banks. The bubble diameter is well correlated by the modified Mori and Wen's correlation taking into account the pitch of tube arrangement. The bubble rise velocity is also well correlated by applying the drift-flux model. These results are consistent for both bed materials of Geldart's B- and A-particles, while the bubble size is significantly different between two kinds of particles

209

A method for cleaning heat exchanger pipes with flow energy usage  

Energy Technology Data Exchange (ETDEWEB)

This paper describes the application of an effective hydro-dynamical vibrational device for cleaning inner surfaces of pipes from sediments. The device is based on the phenomenon of vortex shedding behind spheres in fluid flow (Karman vortex street), which leads to vibration and sphere rotation. Forces of impact interactions of a sphere with the pipe wall exceed 25 N. This value allows cleaning of pipe inner surfaces irrespective of the sediment type. The ability to vary the sphere oscillations and a range of up to 125 Hz provide very flexible intensity control for the cleaning process. The pressure pulsations caused by the working device greatly increase the efficiency of sediment removal. Experimental results are provided, showing good agreement between practice and theoretical models. Laboratory tests show the high efficiency of the cleaning device. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

Grinis, L. [Sami Shamoon College of Engineering, Bialik/Basel Sts., Beer Sheva 84100 (Israel)

2005-05-01

210

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

CERN Document Server

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

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

2012-01-01

211

Viscous exchange flows  

Science.gov (United States)

Gravitationally driven exchange flows of viscous fluids with different densities are analysed theoretically and investigated experimentally within a horizontal channel. Following initiation from rest when there is a vertical boundary dividing the two fluids, the denser fluid slumps under the less dense along the underlying boundary, while the less dense fluid intrudes along the upper boundary. The motion is driven by the pressure gradients associated with the density differences between the two fluids, resisted by viscous stresses, and mathematically modelled by a similarity solution that depends on the ratio of the viscosities of the two fluids. When the viscosity of the less dense fluid is much smaller than the viscosity of the denser fluid, the shape of the interface between the fluids varies rapidly close to the upper boundary and depends weakly on the viscosity ratio within the interior of the flow. Matched asymptotic expansions are employed in this regime to determine the shape of the interface and the rates of its propagation along the boundaries. The similarity solutions are shown to be linearly stable and thus are expected to represent the intermediate asymptotics of the flow. Experiments confirm the similarity form of solutions and demonstrate close agreement with the theoretical predictions when the viscosities of the fluids are comparable, but exhibit some discrepancies when the viscosities differ more substantially. It is suggested that these discrepancies may be due to mixing between the fluids close to the boundaries, which is induced by the no-slip boundary condition. Exchange flows within porous domains are also investigated to determine the shape of the interface as a function of the ratio of the viscosities of the two fluids and using asymptotic analysis, this shape is determined when this ratio is much larger, or smaller, than unity.

Matson, Gary P.; Hogg, Andrew J.

2012-02-01

212

Computer aided design of heat pipe type heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Heat pipe type heat exchangers have been extensively used for heat recovery applications in several countries. However, in Turkey heat pipe type heat exchangers are not commercially common and a great attention should be paid to these type of heat exchangers. For this goal, a prototype heat pipe type heat exchanger was designed and constructed. This paper gives a general design aspects of this heat pipe type heat exchanger, its thermal calculations, experimental description and discussions. (authors)

Turan, M.; Gungor, A. [Ege Universitesi, Dept. Mechanical Engineering, Izmir (Turkey)

2000-07-01

213

Sleeving repair of heat exchanger tubes  

International Nuclear Information System (INIS)

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

214

Heat exchanger using graphite foam  

Science.gov (United States)

A heat exchanger is disclosed. The heat exchanger may have an inlet configured to receive a first fluid and an outlet configured to discharge the first fluid. The heat exchanger may further have at least one passageway configured to conduct the first fluid from the inlet to the outlet. The at least one passageway may be composed of a graphite foam and a layer of graphite material on the exterior of the graphite foam. The layer of graphite material may form at least a partial barrier between the first fluid and a second fluid external to the at least one passageway.

Campagna, Michael Joseph; Callas, James John

2012-09-25

215

Influence of SiC particles on the heat exchange at the metal-mould interface during composite flow along the mould channel  

Directory of Open Access Journals (Sweden)

Full Text Available Calculation results concerning the heat transfer coefficient at the metal-mould interface during flow of the AlMg10 alloy matrix composites containing various fractions of solid SiC particles and, for the purpose of comparison, of the pure AlMg10 alloy in the channel-like cavity of the spiral castability test mould have been presented. Cooling curves and flow velocities have been determined on the basis of metal temperature measured during flow. These experimental data have been used for calculation of the heat transfer coefficient values at given points of a metal stream along the mould channel. Comparison of obtained values and the analysis of the influence of SiC particles on the heat exchange have been presented.

Z. Konopka

2008-07-01

216

Tube in shell heat exchangers  

International Nuclear Information System (INIS)

An improved tube-in-shell heat exchanger to be used between liquid metal and water is described for use in the liquid metal coolant system of fast breeder reactors. It is stated that this design is less prone to failures which could result in sodium water reactions than previous exchangers. (UK)

217

High-temperature self-circulating thermoacoustic heat exchanger  

Science.gov (United States)

Thermoacoustic and Stirling engines and refrigerators use heat exchangers to transfer heat between the oscillating flow of their thermodynamic working fluids and external heat sources and sinks. An acoustically driven heat-exchange loop uses an engine's own pressure oscillations to steadily circulate its own thermodynamic working fluid through a physically remote high-temperature heat source without using moving parts, allowing for a significant reduction in the cost and complexity of thermoacoustic and Stirling heat exchangers. The simplicity and flexibility of such heat-exchanger loops will allow thermoacoustic and Stirling machines to access diverse heat sources and sinks. Measurements of the temperatures at the interface between such a heat-exchange loop and the hot end of a thermoacoustic-Stirling engine are presented. When the steady flow is too small to flush out the mixing chamber in one acoustic cycle, the heat transfer to the regenerator is excellent, with important implications for practical use.

Backhaus, S.; Swift, G. W.; Reid, R. S.

2005-07-01

218

Transient heat transfert in coflow heat exchanger  

Science.gov (United States)

More than ever before, dynamic investigation techniques are becoming widely used in the control systems, parameter implementation and state estimators. Indeed, dynamical models describing the response of process systems that are subject to disturbances play a vital role in controlling and optimising these systems. Recently developed in literature, the method of step response analysis provides a promising means towards solving some of the problems associated with the characterisation of transient response of heat exchangers. In Abdelghani-Idrissi et al. (Int J Heat Mass Transfer 44:3721-3730, 2001), authors present analytical expressions of fluids temperatures response time of counter-current heat exchanger when hot fluid step change is applied in the internal tube. This paper describes the extension of this technique to a coflow heat exchanger for which the exact solution of its mathematical model is unavailable.

Bagui, F.; Chafouk, H.

2006-07-01

219

Advantages of brazed heat exchangers in the gas processing industry  

Energy Technology Data Exchange (ETDEWEB)

Brazed aluminum heat exchangers have superior heat transfer capabilities and can be cost effective for non-corrosive gases and liquids as compared with traditional shell-and-tube exchangers. Even so, brazed aluminum exchangers are often not considered because of complicated design equations and complex stacking arrangements. The simpler yet less efficient shell-and-tube exchangers or networks of shell-and-tubes are employed instead. Recently, the design equations for multistream brazed aluminum heat exchangers for both single and multiphase flow have been added to the Heat Exchanger Rating package of the process simulator PROSIM{reg_sign}.

Lunsford, K.M. [Bryan Research and Engineering, Bryan, TX (United States)

1996-12-31

220

Analysis of Heat Transfer Enhancement in Spiral Plate Heat Exchanger  

Directory of Open Access Journals (Sweden)

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

Kaliannan Saravanan

2009-02-01

 
 
 
 
221

Multidimensional numerical modeling of heat exchangers  

Science.gov (United States)

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

Sha, W. T.; Yang, C. I.; Kao, T. T.; Cho, S. M.

222

Experimental research on heat transfer in a coupled heat exchanger  

Directory of Open Access Journals (Sweden)

Full Text Available The heat exchanger is a devise used for transferring thermal energy between two or more different temperatures. The widespreadly used heat exchanger can only achieve heat exchange between two substances. In this paper, a coupled heat exchanger is proposed, which includes a finned heat exchanger and a double pipe heat exchanger, for multiple heat exchange simultaneously. An experiment is conducted, showing that the average heating capacity increases more than 35%, and the average heating efficiency increases more than 55%, compared with the ordinary air-source heat pump.

Liu Yin

2013-01-01

223

Studies on CO2 heat exchangers and heat transfer  

Energy Technology Data Exchange (ETDEWEB)

The thermodynamic and transport properties of carbon dioxide differ considerably from those of conventional fluorocarbon refrigerants. High working pressures and operation close to the critical point result in heat exchanger designs with high optimum refrigerant-side flow velocities and efficient heat transfer. The slope of the CO2 saturation pressure curve allows for evaporator refrigerant-side pressure drops that are 5-10 times higher than with conventional fluids, and low liquid/vapour density ratio of CO2 makes the two-phase flow more homogeneous than with low-pressure fluids. Liquid specific heat of CO2 is also high, typically three times that of the refrigerant HFC-134a. At supercritical pressures, the low viscosity and high operating pressure allows for very high flow velocities, giving extremely efficient refrigerant-side heat transfer. Even though this is single-phase flow, the heat transfer coefficients exceed typical values for condensing HFC by a factor of 3 to 5. Air-to-refrigerant heat exchangers for CO2 are designed with small-diameter tubes or ducts, in order to effectively handle high pressures without excessive wall thickness and material weight. For car air-conditioning systems, mechanically expanded tube-in-fin evaporators and gas coolers with inside tube diameters of 2-3 mm have been developed and tested. Results show that these units offer competitive performance at equal or lower size and weight compared to baseline HFC-134a units. New heat exchanger concepts based on extruded multiport tubes with 0.8 mm diameter ports are now under development. Detailed computer-based design models (EVAC, GCSIM) for the heat exchangers are used for thermal optimization and performance estimation, as well as studies on internal conduction effects in gas coolers and dehumidification characteristics in evaporators. The mathematical heat exchanger models rely on local heat transfer and pressure drop data on the air- and refrigerant-side. Refrigerant-side heat transfer data are quite important since refrigerant-side surfaces tend to be small in CO2 heat exchangers. Local heat transfer and pressure drop data are generated and correlations developed from experiments on laboratory test rigs. Data for evaporation in an electrically heated ID 7 mm tube have been measured, and experiments in a new rig for small-diameter multiport tubes will be started shortly. The latter rig can handle evaporation, gas cooling and condensation. The influence of lubricant will also be studied. The overview on the title subject is presented in the form of copies of overhead sheets, presented in Session 3 on Development of Components

Bredesen, A.M.; Aflekt, K. [Norwegian University of Science and Technology NTNU, Trondheim (Norway); Pettersen, J.; Hafner, A.; Neksaa, P.; Skaugen, G. [SINTEF Energy, Trondheim (Norway)

1998-12-31

224

Calculation of heat-mass exchange and friction in near-wall flows based on the two-scale four-parametric model of turbulence  

International Nuclear Information System (INIS)

The calculational results on heat-mass exchange and friction in near-wall flows by injection through a gap and porous surface of homogeneous or extraneous gases in the main flow are presented. The above results are obtained on the basis of the turbulence model, including two expressions for the turbulence scale and four transfer equations for the second order velocity fields, enthalpy and concentration. The agreement of the calculational results with the known experimental data made it possible to prove more substantially satisfactory compliance of the calculations with the published experimental data by injection of extraneous gas into super-sound area of the Laval's nozzle

225

Tube in shell heat exchangers  

International Nuclear Information System (INIS)

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

226

Study on heat transfer of heat exchangers in the Stirling engine - Performance of heat exchangers in the test Stirling engine  

Science.gov (United States)

The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the shell-and-tube-type heat exchanger and is chilled by water. It is shown that the experimental results of heat transfer performance of the heater and cooler of the test Stirling engine are in good agreement with the results calculated by the correlation proposed in our previous heat transfer study under the periodically reversing flow condition. Our correlation is thus confirmed to be applicable to the evaluation of the heat transfer coefficient and the thermal design of the heat exchangers in the Stirling engine.

Kanzaka, Mitsuo; Iwabuchi, Makio

1992-11-01

227

Heat transfer enhancement in heat exchangers by longitudinal vortex generators  

International Nuclear Information System (INIS)

In this paper heat transfer enhancement and flow losses are computed for the interaction of a laminar channel flow with a pair of counterrotating longitudinal vortices generated by a pair of delta-winglets punched out of the channel wall. The geometry simulates an element of a fin-plate or fin-tube heat exchanger. The structure of the vortex flow and temperature distribution, the local heat transfer coefficients and the local flow losses are discussed for a sample case. For a Reynolds number of Red = 1000 and a vortex generator angle of attack of ? = 25 degrees heat transfer is enhanced locally by more than 300% and in the mean by 50%. These values increase further with Re and ?

228

Planning heat exchange systems  

International Nuclear Information System (INIS)

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

229

Carbon nanotube heat-exchange systems  

Science.gov (United States)

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

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

2008-11-11

230

Membrane and plastic heat exchangers performance  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The performance of a membrane-based heat exchanger utilizing porous paper as the heat and moisture transfer media is presented. The measured performance is compared with a plastic film heat exchanger. This novel heat exchanger is used in ventilation energy recovery systems. The results show that the sensible effectiveness is higher than the latent effectiveness. When a similar experiment was conducted using a plastic film heat exchanger surface instead of paper, where only heat is transferred...

Masud Behnia; Mohammad Shakir Nasif; Morrison, Graham L.

2005-01-01

231

Flow visualization and void fraction measurement in liquid-metal/water direct contact heat exchange by X-ray attenuation technique  

Science.gov (United States)

One concept being considered for steam generation in particular next generation nuclear reactor designs, involves water coming into direct contact with a circulating molten metal. To optimize the design of such direct contact heat exchange and vaporization systems, detailed knowledge is necessary of the various flow regimes, interfacial transport phenomena, heat transfer and operational stability. With the development of high performance digital detectors, radiography using X-rays or neutrons maybe a suitable technique to obtain information about that direct-contact interaction; i.e., void volume fractions, length scales and dynamic behavior. Under the basis of previous investigations, a complete methodology of the X-ray radiography for two-phase flow measurement has been developed from the facility and imaging analysis aspects. Through this developed methodology, a high energy X-ray imaging system is optimized for the direct-contact heat exchange experiment. Beside an on-line calibration procedure which practically quantifies the imaging system's performance, the extended linear system theory and Rose's model have also been used to evaluate the imaging system's performance, respectively. The bottleneck of the current imaging system and the future of system improvement direction have been pointed out. With our real-time, large-area high energy X-ray imaging system, the two-phase flow was visualized and stored digitally. An efficient image processing strategy has also been established by combining several optimal digital image processing algorithms. The approach has been implemented into a software computational tool written in MATLAB called T-XIP. Time-dependent heat transfer related variables, such as void fraction (void volume), local heat transfer coefficient, etc., were calculated using this software tool. Finally, an error analysis associated with the void fraction measurement has been given based on two procedures.

Liu, Xin

232

Heat exchangers and methods of construction thereof  

International Nuclear Information System (INIS)

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

233

SP-100 Heat Source Heat Exchanger Design  

Science.gov (United States)

A conceptual design for a liquid metal to gas counterflow heat exchanger has been developed for use in the SP-100 Closed Brayton Cycle (CBC) Space Reactor Power System (SRPS). The Heat Source Heat Exchanger (HSHX) is required to transfer 80 kWt from the 1350 K lithium reactor coolant to the He/Xe working fluid of the Brayton Rotating Unit (BRU). Trade studies were performed to select a concept that best meets the performance requirements as well as the mass minimization goals and packaging requirements of the SRPS. The HSHX design is based on state-of-the-art fabrication techniques developed for use in the SP-100 Thermoelectric Converter Assembly (TCA) Heat Exchanger and a previously developed Mini-BRU space power system HSHX. The HSHX is a Nb-lZr finned flat plate assembly fabricated by the Hot Isostatic Process (HIP). The approximate size of the HSHX assembly is a 0.70 m x 0.15 m cross section over its 18 cm active length. The conceptual design meets all thermal-hydraulic and structural design requirements for a five-year mission while weighing less than 50 kg.

Fallas, T. Ted; Desepte, Andrew W.; Hill, Robert J.; Manjarrez, Georgi B.; Solorzano, Enrique R.; Salamah, Samir A.; Yahalom, Raphael

1994-07-01

234

Determination of the bending loading's resulting from the superheated steam flow path variation in an expansion pipe-bend for sodium-water heat exchangers  

International Nuclear Information System (INIS)

The structural design of an asymmetric stiffened pipe incorporating an expansion bend, as applied in a sodium-water heat exchanger, was presented in Energi Nucleare, vol. 23(10) p. 507 (October 1976). The present article describes a further theoretical approach required to make such design more complete and reliable. In particular, the bending loadings exerted on the pipe-bend, as resulting from the path variation of the running fluid, are evaluated. All correlations associated to such loadings are derived in terms of the expansion bend sizing parameters and superheated steam flow properties and presented in a quick-use form for practical design purposes

235

Analysis of flow-induced vibration of heat exchanger and steam generator tube bundles using the AECL computer code PIPEAU-2  

International Nuclear Information System (INIS)

PIPEAU-2 is a computer code developed at the Chalk River Nuclear Laboratories for the flow-induced vibration analysis of heat exchanger and steam generator tube bundles. It can perform this analysis for straight and 'U' tubes. All the theoretical work underlying the code is analytical rather than numerical in nature. Highly accurate evaluation of the free vibration frequencies and mode shapes is therefore obtained. Using the latest experimentally determined parameters available, the free vibration analysis is followed by a forced vibration analysis. Tube response due to fluid turbulence and vortex shedding is determined, as well as critical fluid velocity associated with fluid-elastic instability

236

Characteristics of Vertical Mantle Heat Exchangers for Solar Water Heaters  

DEFF Research Database (Denmark)

- The flow structure in vertical mantle heat exchangers 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 heat exchangers 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.

Shah, Louise Jivan

1999-01-01

237

Heat exchanger optimization for geothermal district heating systems: A fuel saving approach  

Energy Technology Data Exchange (ETDEWEB)

One of the most commonly used heating devices in geothermal systems is the heat exchanger. The output conditions of heat exchangers are based on several parameters. The heat transfer area is one of the most important parameters for heat exchangers in terms of economics. Although there are a lot of methods to optimize heat exchangers, the method described here is a fairly easy approach. In this paper, a counter flow heat exchanger of geothermal district heating system is considered and optimum design values, which provide maximum annual net profit, for the considered heating system are found according to fuel savings. Performance of the heat exchanger is also calculated. In the analysis, since some values are affected by local conditions, Turkey's conditions are considered. (author)

Dagdas, Ahmet [Department of Mechanical Engineering, Yildiz Technical University, 34349 Besiktas, Istanbul (Turkey)

2007-05-15

238

A study on the heat transfer development of heat exchanger with vortex generator  

International Nuclear Information System (INIS)

A numerical analysis using FLUENT code was carried out to investigate flow characteristics and heat transfer development of heat exchangers. The analysis results for both cases of the fin-circular tube and the fin-flat tube heat exchanger 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 heat exchangers without the vortex generator. Also, the analysis result for the fin-circular tube heat exchanger with the vortex generator has relatively higher heat transfer coefficient and higher pressure loss than those for the fin-flat tube heat exchanger with the vortex generator. The results of this study can be used to design the heat exchanger with relatively low pressure loss and maximum heat transfer coefficient. 28 figs., 15 refs. (Author) .new

239

Heat exchange in a channel with a sinusoidal magnetofluid coating  

International Nuclear Information System (INIS)

An interesting means of controlling the hydrodynamics and heat exchange in a fluid flow through the channels involves the use of magnetofluid coatings on the solid channel walls. The present study offers results from experimental research into the hydrodynamics and heat exchange in a plane channel with a sinusoidal magnetofluid coating at constant heat flux to one of the channel walls. The derived results provide convincing experimental confirmation of the possibility of heat-exchange intensification with simultaneous reduction in hydraulic resistance in the flow of fluids through channels with magnetofluid coatings. 5 refs., 5 figs

240

The Design on the Refrigerant Circuit of Heat Exchanger  

Science.gov (United States)

The efficient design method for plate fin-and-tube heat exchanger has been developed with the directed graph(graph-based traversal method) in graph theory and the distribution model of refrigerant flow rate. According to the experimental results of heat exchanger which is carried out under 98 experimental conditions of the changes of air velocity and the refrigerant flow rates and so on, by using the refrigerant R 22 and R 410A, we conclude the following deviations of analysis: the heat transfer rate is within ±10% and the pressure drop is within ±20%. Now this design method has being used for designing plate fin-and-tube heat exchangers efficiently.

Wang, Kaijian; Fukaya, Masaharu; Ding, Guoliang; Liu, Jian

 
 
 
 
241

Large intermediate heat exchangers for tank type FBRs  

International Nuclear Information System (INIS)

The intermediate heat exchangers for FBRs are the large heat exchangers which carry out the heat exchange between the primary sodium extracting heat generated in reactor cores and the secondary sodium transmitting this heat to steam generators. This intermediate heat exchanger is hung from a roof slab covering a reactor vessel together with a primary main circulating pump in the case of a tank type FBR. In order to heighten the economical efficiency of a tank type FBR, it is effective to make the reactor structures such as a reactor vessel, for which high reliability is required, compact. To use four intermediate heat exchangers, to increase the unit capacity and to make the heat exchangers compact are most effective to decrease the size of a reactor vessel. In order to develop the intermediate heat exchangers of large capacity and compact size, the uniformity of flow in the heat exchangers, the hydrodynamic vibration of heat transfer tubes and other thermo-hydrodynamic design problems, and structural soundness problems have been researched. Toshiba Corp. carried out the research on the method of manufacturing the intermediate heat exchangers for tank type FBRs from 1984 to 1986. It is reported in this paper. (Kako, I.)

242

Oil Circulation Effects on Evaporation Heat Transfer in Brazed Plate Heat Exchanger using R134A  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Experimental study was performed for oil circulation effects on evaporation heat transfer in the brazed type plate heat exchangers using R134A. In this study, distribution device was installed to ensure uniform flow distribution in the refrigerant flow passage, which enhances heat transfer performance of plate type heat exchanger. Tests were conducted for three evaporation temperature; 33?, 37?, and 41? and several oil circulation conditions. The nominal conditions of refrigerant are as...

Jang, Jaekyoo; Chang, Youngsoo; Kang, Byungha

2012-01-01

243

Cooling Flows or Heating Flows?  

CERN Document Server

It is now clear that AGN heat cooling flows, largely by driving winds. The winds may contain a relativistic component that generates powerful synchrotron radiation, but it is not clear that all winds do so. The spatial and temporal stability of the AGN/cooling flow interaction are discussed. Collimation of the winds probably provides spatial stability. Temporal stability may be possible only for black holes with masses above a critical value. Both the failure of cooling flows to have adiabatic cores and the existence of X-ray cavities confirm the importance of collimated outflows. I quantify the scale of the convective flow that the AGN Hydra would need to drive if it balanced radiative inward flow by outward flow parallel to the jets. At least in Virgo any such flow must be confined to r<~20 kpc. Hydrodynamical simulations suggest that AGN outbursts cannot last longer than ~25 Myr. Data for four clusters with well studied X-ray cavities suggests that heating associated with cavity formation approximately ...

Binney, J

2003-01-01

244

Pressurized bellows flat contact heat exchanger interface  

Science.gov (United States)

Disclosed is an interdigitated plate-type heat exchanger interface. The interface includes a modular interconnect to thermally connect a pair or pairs of plate-type heat exchangers to a second single or multiple plate-type heat exchanger. The modular interconnect comprises a series of parallel, plate-type heat exchangers arranged in pairs to form a slot therebetween. The plate-type heat exchangers of the second heat exchanger insert into the slots of the modular interconnect. Bellows are provided between the pairs of fins of the modular interconnect so that when the bellows are pressurized, they drive the plate-type heat exchangers of the modular interconnect toward one another, thus closing upon the second heat exchanger plates. Each end of the bellows has a part thereof a thin, membrane diaphragm which readily conforms to the contours of the heat exchanger plates of the modular interconnect when the bellows is pressurized. This ensures an even distribution of pressure on the heat exchangers of the modular interconnect thus creating substantially planar contact between the two heat exchangers. The effect of the interface of the present invention is to provide a dry connection between two heat exchangers whereby the rate of heat transfer can be varied by varying the pressure within the bellows.

Voss, Fred E. (inventor); Howell, Harold R. (inventor); Winkler, Roger V. (inventor)

1990-01-01

245

Tube-type heat exchanger  

International Nuclear Information System (INIS)

The tube-type heat exchanger consists of a cylindrical casing in which are mounted U shaped heat exchange tubes anchored in a tube plate. The individual tubes of the inlet and outlet branch are fitted in support partitions normal to the axis of the tubes and provided with fins. The length of the fin equals half of the length of the chord of the support partition. The fins of the partitions of the inlet branch fit close to the partitions of the outlet branch and vice versa. The fin nearest to the tube plate comes into contact with the inner wall of the tube plate. Support partitions, fins and the inner surface of the casing thus form a helical throughflow channel to which are tangentially connected the inlet and outlet necks. (E.S.)

246

Evaluation of the flow at the contraction of a heat exchanger. Pt. 2. Effect of thermal-hydraulic factors on scale deposition at the contraction  

International Nuclear Information System (INIS)

In heat exchangers used in power plants, scale may deposit on the tube support plates of heat transfer tubes, especially at the leading edge where the flow passes a sudden contraction. This phenomenon can lead to flow path blockage, which in turn can affect plant performance. As a result, the mechanism of scale deposition and growth needs to be clarified. This phenomenon is assumed to be caused by a complex of thermal-hydraulic and electrochemical factors. In this study, flashing induced by pressure drop and turbulence at the leading edge of a contraction were assumed to be the main factors from the thermal-hydraulic point of view. And these factors in two different type of contractions were evaluated with a High Pressure / High Temperature steam-water two-phase flow experiment and 3D numerical analysis. Considerable differences in amount of steam caused by flashing and turbulence magnitude were observed between the two contractions which have same flow path area but different hydraulic diameter. It was also found that the size of bubbles passing the leading edge of contraction were smaller than 1 mm, while the bubbles in the upstream part were more than 10 times larger than those of the leading edge. (author)

247

Comparative thermal analysis of theoretical and experimental studies of modified indirect evaporative cooler having cross flow heat exchanger with one fluid mixed and the other unmixed  

Directory of Open Access Journals (Sweden)

Full Text Available The comparative thermal analysis of theoretical and experimental studies of modified indirect evaporative cooler having cross flow heat exchanger with one fluid mixed and the other unmixed is presented in this research paper. A heat and mass transfer mathematical model is developed to simulate the properties of indirect evaporative cooler. The theoretical result analysis was done by plotting the curves between various performance parameters. This work presents the fabrication and experiments carried out on the indirect evaporative cooler at various outdoor air conditions. The data acquired by experiment were analyzed by plotting the curves between various performance parameters. The theoretical and experimental results were compared and analyzed. The theoretical model can be used to predict the performance of modified indirect evaporative cooler.

Trilok Singh Bisoniya, S.P.S. Rajput, Anil Kumar

2011-09-01

248

Heat Exchanger Design in Combined Cycle Engines  

Science.gov (United States)

Combined cycle engines employing both pre-cooled air-breathing and rocket modes of operation are the most promising propulsion system for achieving single stage to orbit vehicles. The air-breathing phase is purely for augmentation of the mission velocity required in the rocket phase and as such must be mass effective, re-using the components of the rocket cycle, whilst achieving adequate specific impulse. This paper explains how the unique demands placed on the air-breathing cycle results in the need for sophisticated thermodynamics and the use of a series of different heat exchangers to enable precooling and high pressure ratio compression of the air for delivery to the rocket combustion chambers. These major heat exchanger roles are; extracting heat from incoming air in the precooler, topping up cycle flow temperatures to maintain constant turbine operating conditions and extracting rejected heat from the power cycle via regenerator loops for thermal capacity matching. The design solutions of these heat exchangers are discussed.

Webber, H.; Feast, S.; Bond, A.

249

Noise spectra measured on the Dragon reactor primary heat exchanges  

International Nuclear Information System (INIS)

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

250

Modeling and Performance Analysis of Alternative Heat Exchangers for Heavy Vehicles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cross flow heat exchangers made from aluminum are common as radiators in vehicles. However, due to the increasing power requirement and the limited available space in vehicles, it is extremely difficult to increase the size of heat exchangers (HEXs) placed in the front of vehicles. Placing the heat exchanger on the roof or at the underbody of vehicles might offer opportunity to increase the size of the heat exchangers. A new configuration of heat exchangers has to be developed to accommodate ...

Lin, Wamei

2014-01-01

251

Fluidized bed heat exchanger utilizing angularly extending heat exchange tubes  

Science.gov (United States)

A fluidized bed heat exchanger in which air is passed through a bed of particulate material containing fuel disposed in a housing. A steam/water natural circulation system is provided and includes a steam drum disposed adjacent the fluidized bed and a series of tubes connected at one end to the steam drum. A portion of the tubes are connected to a water drum and in the path of the air and the gaseous products of combustion exiting from the bed. Another portion of the tubes pass through the bed and extend at an angle to the upper surface of the bed.

Talmud, Fred M. (Berkeley Heights, NJ); Garcia-Mallol, Juan-Antonio (Morristown, NJ)

1980-01-01

252

Preliminary SP-100/Stirling heat exchanger designs  

International Nuclear Information System (INIS)

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

253

The resistance and heat transfer in zigzag duct and the performance of plate heat exchangers  

International Nuclear Information System (INIS)

A comprehensive experimental set-up for investigation of heat transfer, resistance and flow visualization as well as a full scale heat exchanger experiment system to test plate heat exchangers are described in the present work. The set-up and the system are cooperated to make developmental researches of the plate heat exchanges. The experiment data to relate the resistance factors in various zigzag ducts with the Reynolds number are obtained. It shows that the resistance factors of flow in the zigzag ducts do not depend on both the length-height ratio and the Reynolds number. The flow visualization reveals that the critical Reynolds number at which the laminar flow in the ducts will translate into turbulent flow is about 100 to 150. The experiment results and the preliminary analysis on eleven plate heat exchanges are given in the present paper

254

Multidimensional numerical modeling of heat exchanges  

International Nuclear Information System (INIS)

A comprehensive, multidimensional, thermal-hydraulic model is developed for the analysis of shell-and-tube heat exchanges for liquid metal services. For the shellside fluid, the conservation equations of mass, momentum and energy for continuum fluids are modified using the concept of porosity, surface premeability and distributed resistance to account for the blockage effects due to the presence of heat transfer tubes, flow baffles/shrouds, the support plates, etc. On the tubeside, heat transfer tubes are connected in parallel between the inlet and outlet plenums, and tubeside flow distribution is calculated based on the plenum-to-plenum pressure difference being equal for all tubes. It is assumed that the fluid remains single-phased on the shell side and may undergo phase-change in the tube side, thereby simulating the conditions of Liquid Metal Fast Breeder Reaction (LMFBR) intermediate heat exchanges (IHX) and steam generators (SG). The analytical model predictions are compared with three sets of test data (one for IHX and two for SG) and favorable results are obtained, thus providing a limited validation of the model

255

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

Science.gov (United States)

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

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

1993-04-01

256

NGNP Process Heat Utilization: Liquid Metal Phase Change Heat Exchanger  

International Nuclear Information System (INIS)

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

257

Membrane and plastic heat exchangers performance  

Directory of Open Access Journals (Sweden)

Full Text Available The performance of a membrane-based heat exchanger utilizing porous paper as the heat and moisture transfer media is presented. The measured performance is compared with a plastic film heat exchanger. This novel heat exchanger is used in ventilation energy recovery systems. The results show that the sensible effectiveness is higher than the latent effectiveness. When a similar experiment was conducted using a plastic film heat exchanger surface instead of paper, where only heat is transferred, the sensible effectiveness values were lower than the effectiveness values recorded when the paper heat exchanger is used. Furthermore, energy analysis shows that utilizing a paper surface heat exchanger in a standard air conditioning system will lead to significant energy savings.

Masud Behnia

2005-09-01

258

Heat exchanger thermal insulation system  

International Nuclear Information System (INIS)

The heat exchanger insulation system described includes an outer ring, a bundle of circulation tubes connected at their ends to a tube plate and comprising a coaxial cylindrical sleeve around each tube with play along a part of its length near the ends connected to the tube plate. The sleeves are suspended by their upper ends to a perforated plate with holes into which the sleeves fit, the perforated plate being fixed to a ring fitted by its base to the tube plate by means of tie rods between the tube plate and the perforated plate. This system has been particularly designed for liquid sodium cooled reactors

259

Online performance assessment of heat exchanger using artificial neural networks  

Energy Technology Data Exchange (ETDEWEB)

Heat exchanger is a device in which heat is transferred from one medium to another across a solid surface. The performance of heat exchanger deteriorates with time due to fouling on the heat transfer surface. It is necessary to assess periodically the heat exchanger performance, in order to maintain at high efficiency level. Industries follow adopted practices to monitor but it is limited to some degree. Online monitoring has an advantage to understand and improve the heat exchanger performance. In this paper, online performance monitoring system for shell and tube heat exchanger is developed using artificial neural networks (ANNs). Experiments are conducted based on full factorial design of experiments to develop a model using the parameters such as temperatures and flow rates. ANN model for overall heat transfer coefficient of a design/ clean heat exchanger system is developed using a feed forward back propagation neural network and trained. The developed model is validated and tested by comparing the results with the experimental results. This model is used to assess the performance of heat exchanger with the real/fouled system. The performance degradation is expressed using fouling factor (FF), which is derived from the overall heat transfer coefficient of design system and real system. It supports the system to improve the performance by asset utilization, energy efficient and cost reduction interms of production loss.

Ahilan, C.; Kumanan, S. [Department of Production Engineering, National Institute of Technology Tiruchirappalli (India); Sivakumaran, N. [Department of Instrumentation and Control Engineering, National Institute of Technology Tiruchirappalli (India)

2011-07-01

260

Online performance assessment of heat exchanger using artificial neural networks  

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchanger is a device in which heat is transferred from one medium to another across a solid surface. The performance of heat exchanger deteriorates with time due to fouling on the heat transfer surface. It is necessary to assess periodically the heat exchanger performance, in order to maintain at high efficiency level. Industries follow adopted practices to monitor but it is limited to some degree. Online monitoring has an advantage to understand and improve the heat exchanger performance. In this paper, online performance monitoring system for shell and tube heat exchanger is developed using artificial neural networks (ANNs. Experiments are conducted based on full factorial design of experiments to develop a model using the parameters such as temperatures and flow rates. ANN model for overall heat transfer coefficient of a design/ clean heat exchanger system is developed using a feed forward back propagation neural network and trained. The developed model is validated and tested by comparing the results with the experimental results. This model is used to assess the performance of heat exchanger with the real/fouled system. The performance degradation is expressed using fouling factor (FF, which is derived from the overall heat transfer coefficient of design system and real system. It supports the system to improve the performance by asset utilization, energy efficient and cost reduction interms of production loss.

C. Ahilan, S. Kumanan, N. Sivakumaran

2011-09-01

 
 
 
 
261

Thermal energy storage by means of the latent heat of fusion of a mineral salt - Study of a direct contact dynamic exchanger with salt crystallization during flow  

Energy Technology Data Exchange (ETDEWEB)

The use of a heat exchanger in which the storage medium (a mineral salt) comes into direct contact with the heat transfer agent for the recovery of thermal energy stored in molten salt is investigated. Preliminary experiments on heat transfer and phase separation in a mixture of a molten NaNO/sub 2/, NaNO/sub 3/, KNO/sub 3/ eutectic (melting point 142 C) with a synthetic oil at a temperature below the melting point of the salt show that a dynamic heat exchanger with direct contact leads to greater heat recovery by the oil than a static exchanger with natural or forced convection. A device for injecting molten salt into the heat transfer medium is used to determine the relations between injection velocity, the temperature difference between the salt and the oil, and salt particle formation. Calculations have shown the heat recovery process to have an efficiency of about 85 percent.

Pantaloni, J.; Favre, O.; Bailleux, R.; Finiels, G.; Marchisio, J.

1979-01-01

262

Microchannel crossflow fluid heat exchanger and method for its fabrication  

Science.gov (United States)

A microchannel crossflow fluid heat exchanger and a method for its fabrication are disclosed. The heat exchanger 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 heat exchanger 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 heat exchanger has particular application in a Stirling engine that utilizes a liquid as the working substance.

Swift, Gregory W. (Los Alamos, NM); Migliori, Albert (Santa Fe, NM); Wheatley, John C. (Los Alamos, NM)

1985-01-01

263

Heat Transport Study of the Laminar Heat Pipe Heat Exchanger  

Directory of Open Access Journals (Sweden)

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

Wei-Keng Lin

2012-11-01

264

Condensation in horizontal heat exchanger tubes  

International Nuclear Information System (INIS)

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

265

Heat exchanger fouling and corrosion evaluation  

Science.gov (United States)

The experimental determination of acid corrosion and fouling effects upon a series of tubular heat exchanger modules exposed to the exhaust gases from a large (8900-hp) diesel engine, with different fin geometries and materials was studied. A study of the exhaust gas analysis was undertaken and acid dew point temperatures were determined. Heat exchanger test modules were then operated with metal surface temperatures below the acid dew point to allow for acid condensation and fouling. A continuous soot buildup was observed on the heat exchanger, as a function of the diesel engine operating time, heat transfer metal surface temperature, and fin geometry. The corrosion effects on the heat exchangers were minimal.

Deanda, E.

1981-10-01

266

Performance of a shell-and-tube heat exchanger with spiral baffle plates  

International Nuclear Information System (INIS)

In a conventional shell-and-tube heat exchanger, fluid contacts with tubes flowing up and down in a shell, therefore there is a defect in the heat transfer with tubes due to the stagnation portions. Fins are attached to the tubes in order to increase heat transfer efficiency, but there exists a limit. Therefore, it is necessary to improve heat exchanger performance by changing the fluid flow in the shell. In this study, a highly efficient shell-and-tube heat exchanger with spiral baffle plates is simulated three-dimensionally using a commercial thermal-fluid analysis code, CFX4.2. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffle plates is superior to the conventional heat exchanger in terms of heat transfer

267

Fluid dynamical considerations on heat exchanger networks  

Directory of Open Access Journals (Sweden)

Full Text Available The synthesis and analysis of heat exchanger networks are issues of great industrial interest due to the possibilities of decreasing plant costs, through the reduction of the utilities consumption and/or the number of equipments, in a grassroot design or retrofitting an existent network. The present paper explores a new design algorithm based on the Total Annual Cost (TAC optimization for a thermal equipment, with mean tubeside and shellside flow velocities constraints, studying also the influence of pumping cost in the network’s final cost.

A. J. M. Vieira

2000-03-01

268

Fluid dynamical considerations on heat exchanger networks  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The synthesis and analysis of heat exchanger networks are issues of great industrial interest due to the possibilities of decreasing plant costs, through the reduction of the utilities consumption and/or the number of equipments, in a grassroot design or retrofitting an existent network. The present [...] paper explores a new design algorithm based on the Total Annual Cost (TAC) optimization for a thermal equipment, with mean tubeside and shellside flow velocities constraints, studying also the influence of pumping cost in the network’s final cost.

A. J. M., Vieira; F. L. P., Pessoa; E. M., Queiroz.

2000-03-01

269

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

Energy Technology Data Exchange (ETDEWEB)

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

Grandotto Biettoli, M

2006-04-15

270

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-09-01

271

Alternative coiled heat exchangers; Alternativ gewickelte Kuehlschlangen  

Energy Technology Data Exchange (ETDEWEB)

Recent developments in energy costs demand efficient heat transfer apparatus. The question addressed here was if standard pipe fittings such as 180 - and 90 -bends can be used to build alternatively coiled heat exchangers with enhanced heat transfer. For that purpose a water tunnel was constructed. It was found that by employing standard fittings, an enhancement of heat transfer compared to standard coiled tube heat exchangers between 2 and 20% can be obtained. (orig.)

Buschmann, Matthias H. [Institut fuer Luft- und Kaeltetechnik gGmbH, Dresden (Germany)

2009-07-01

272

The role of sealing strips in tubular heat exchangers  

International Nuclear Information System (INIS)

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

273

Convective heat flow probe  

Science.gov (United States)

A convective heat flow probe device is provided which measures heat flow and fluid flow magnitude in the formation surrounding a borehole. The probe comprises an elongate housing adapted to be lowered down into the borehole; a plurality of heaters extending along the probe for heating the formation surrounding the borehole; a plurality of temperature sensors arranged around the periphery of the probe for measuring the temperature of the surrounding formation after heating thereof by the heater elements. The temperature sensors and heater elements are mounted in a plurality of separate heater pads which are supported by the housing and which are adapted to be radially expanded into firm engagement with the walls of the borehole. The heat supplied by the heater elements and the temperatures measured by the temperature sensors are monitored and used in providing the desired measurements. The outer peripheral surfaces of the heater pads are configured as segments of a cylinder and form a full cylinder when taken together. A plurality of temperature sensors are located on each pad so as to extend along the length and across the width thereof, with a heating element being located in each pad beneath the temperature sensors. An expansion mechanism driven by a clamping motor provides expansion and retraction of the heater pads and expandable packer-type seals are provided along the probe above and below the heater pads.

Dunn, James C. (Albuquerque, NM); Hardee, Harry C. (Albuquerque, NM); Striker, Richard P. (Albuquerque, NM)

1985-01-01

274

Minichannel heat exchanger; Minichannel-Waermeuebertrager  

Energy Technology Data Exchange (ETDEWEB)

This paper gives an overview of the application of minichannel heat exchangers in stationary refrigeration and airconditioning systems and describes the findings of a recent research project at Karlsruhe University of Applied Sciences. Benefits employing minichannel heat exchangers are reduced global warming impact of the refrigeration and air-conditioning system due to increased efficiency and reduced refrigerant charge, as well as improved recyclability, reduced size and weight as well as cost of the heat exchanger. (orig.)

Kauffeld, Michael; Maurath, Timo [Hochschule Karlsruhe - Technick und Wirtschaft, Karlsruhe (Germany). Inst. fuer Kaelte-, Klima- und Umwelttechnik

2011-08-15

275

OPTIMASI KINERJA HEAT EXCHANGER TABUNG KOSENTRIS  

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchanger effectiveness is affected by some factors such as pipe shape, temperature, cold and hot air direction and velocity entering the heat exchanger. Research about heat exchanger has been done but the significance level of the heat exchanger effectiveness resulted is unknown. A designed experiment should be done to optimize the performance of concentric tube heat exchanger with measured significance level. From the analysis of result of previous experiment, factors that seem to affect the effectiveness are velocity of cold air, velocity of hot air, and pipe shape of heat exchanger used (outlet and inlet similar to U, S and L shape. Experimental design that is used here is three-level factorial design. On the arrangement of factors as follows: velocity of cold air = 4 m/s, velocity of hot air = 7 m/s, and pipe of S shape, optimum effectiveness gained at significance level of 95 % is 0,39098. Abstract in Bahasa Indonesia : Efektifitas heat exchanger tabung konsentris bisa dipengaruhi oleh beberapa faktor, antara lain bentuk pipa, temperatur, arah aliran dan kecepatan udara masuk baik dingin maupun panas. Penelitian mengenai heat exchanger telah dilakukan sebelumnya namun tingkat signifikasi dari efektifitas heat exchanger yang dihasilkan tidak diketahui. Suatu eksperimen yang terancang perlu dilakukan untuk mengoptimalkan kinerja dari heat exchanger tabung kosentris dengan tingkat signifikasi yang terukur. Dari analisa terhadap hasil eksperimen terdahulu, tampak bahwa faktor yang berpengaruh adalah kecepatan udara dingin, kecepatan udara panas dan bentuk pipa heat exchanger (outlet dan inlet menyerupai bentuk U, S dan L yang digunakan. Rancangan eksperimen yang digunakan ialah rancangan faktorial 3 level. Pada pengaturan level faktor sebagai berikut: kecepatan udara dingin = 4 m/det, kecepatan udara panas = 7 m/det dan bentuk tabung yang digunakan ialah pipa berbentuk S, diperoleh efektifitas optimum pada tingkat signifikasi 95 % = 0,39098. Kata kunci: heat exchanger, desain eksperimen, efektifitas

Didik Wahjudi

2000-01-01

276

Experimental determination of correlations for mean heat transfer coefficients in plate fin and tube heat exchangers  

Science.gov (United States)

This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coefficients in the correlations defining heat transfer on the liquid- and air-side were determined using a nonlinear regression method. Correlation coefficients were determined from the condition that the sum of squared liquid and air temperature differences at the heat exchanger outlet, obtained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The uncertainty in estimated parameters was determined using the error propagation rule by Gauss. The outlet temperature of the liquid and air leaving the heat exchanger was calculated using the analytical model of the heat exchanger.

Taler, Dawid

2012-09-01

277

Feasibility study of improved heat exchanger  

International Nuclear Information System (INIS)

Generally shell and tube type heat exchangers have been used widely for many years in the auxiliary cooling systems of nuclear power plants. Recently, however, in general industrial facilities and so on many plate heat exchangers excellent in heat transfer performance have been used, compared with shell and tube heat exchangers, and their heat exchanger bodies and cooling system facilities have been rationalized. We carried out confirmation tests on the plate type heat exchangers in structural strength, aseismatic strength, heat transfer performance and maintenance regarding their application to nuclear power plants. As a result, we have confirmed that they can be applied to seawater systems of actual plants. The tests further provided useful information on their actual operation. (author)

278

Process for oil shale retorting using gravity-driven solids flow and solid-solid heat exchange  

Science.gov (United States)

A cascading bed retorting process and apparatus in which cold raw crushed shale enters at the middle of a retort column into a mixer stage where it is rapidly mixed with hot recycled shale and thereby heated to pyrolysis temperature. The heated mixture then passes through a pyrolyzer stage where it resides for a sufficient time for complete pyrolysis to occur. The spent shale from the pyrolyzer is recirculated through a burner stage where the residual char is burned to heat the shale which then enters the mixer stage.

Lewis, Arthur E. (Los Altos, CA); Braun, Robert L. (Livermore, CA); Mallon, Richard G. (Livermore, CA); Walton, Otis R. (Livermore, CA)

1986-01-01

279

Double tube heat exchanger with novel enhancement: part II—single phase convective heat transfer  

Science.gov (United States)

The study is conducted to evaluate the heat transfer characteristics of two new and versatile enhancement configurations in a double tube heat exchanger 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.

Tiruselvam, R.; Chin, W. M.; Raghavan, Vijay R.

2012-08-01

280

Condensate removal device for heat exchanger  

Science.gov (United States)

A set of perforated tubes disposed at the gas output side of a heat exchanger, in a position not to affect the rate of flow of the air or other gas is described. The tubes are connected to a common manifold which is connected to a sucking device. Where it is necessary to conserve and recirculate the air sucked through the tubes, the output of the manifold is run through a separator to remove the condensate from the gas. The perforations in the slurper tubes are small, lying in the range of 0.010 inch to 0.100 inch. The tubes are disposed in contact with the surfaces of the heat exchanger on which the condensate is precipitated, whether fins or plates, so that the water may be directed to the tube openings by means of surface effects, together with the assistance of the air flow. Only about 5 percent of the air output need be thus diverted, and it effectively removes virtually all of the condensate.

Trusch, R. B.; Oconnor, E. W. (inventors)

1975-01-01

 
 
 
 
281

Process for repairing a cryogenic heat exchanger  

International Nuclear Information System (INIS)

The patent describes a method for repairing leakage-causing cracks and fissures in a cryogenic heat exchanger. It comprises: reducing the interior pressure of the heat exchanger to a level which does not exceed the external pressure upon the hear exchanger while maintaining the temperature of the heat exchanger at a low level relative to the ambient external temperature; applying a curable liquid filler composition to the surface of the heat exchanger proximal the leakage site for seepage into the cracks and fissures located at the leakage. The composition upon a relatively short period of cure at low temperature forming a solid material which fills the cracks and fissures; curing the filler composition; and, applying a sealant composition to the surface of the heat exchanger at the filled leakage site. The sealant composition having long-term sealing performance under cyrogenic conditions

282

Microbial fouling control in heat exchangers  

International Nuclear Information System (INIS)

Biofilm formation in turbulent flow has been studied a great deal during the last 15 years. Such studies have provided the basis for further experiments designed to test the efficacy of industrial antimicrobials against biofilms in laboratory models and in actual real-world industrial water-treatment programs. Biofilm microbiology is relevant from the industrial perspective because adherent populations of microorganisms often cause an economic impact on industrial processes. For example, it is the adherent population of microorganisms in cooling-water systems that can eventually contribute to significant heat transfer and fluid frictional resistances. The microbiology of biofilms in heat exchangers can be related to the performance of industrial antimicrobials. The development of fouling biofilms and methods to quantitatively observe the effect of biofouling control agents are discussed in this paper

283

Heat exchanger with vertical flexible tubes of the 'descending' type  

International Nuclear Information System (INIS)

This invention concerns a heat exchanger with vertical flexible tubes of the 'descending' type, particularly intended for the evaporation of a saline solution. For the record, a vertical tube heat exchanger for heating a secondary fluid by a primary fluid is of the 'descending' type when the secondary fluid flows by gravity in thin films along the outside of the tubes in which the primary fluid is flowing. Specifically, the purpose of this invention is a heat exchanger of the above type comprising new arrangements for fixing the tubes by their upper ends and the creation on the outside of these tubes of a thin continuous descending film of secondary fluid to be heated

284

Design of heat exchangers by numerical methods  

International Nuclear Information System (INIS)

Differential equations describing the heat tranfer in shell - and tube heat exchangers are derived and solved numerically. The method of ?T sub(lm) is compared with the proposed method in cases where the specific heat at constant pressure, Cp and the overall heat transfer coefficient, U, vary with temperature. The error of the method of ?T sub (lm) for the computation of the exchanger lenght is less than + 10%. However, the numerical method, being more accurate and at the same time easy to use and economical, is recommended for the design of shell-and-tube heat exchangers. (Author)

285

Heat transfer with freezing in a scraped surface heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

An experimental study was carried out on a scraped surface heat exchanger used for freezing of water-ethanol mixture and aqueous sucrose solution. The influence of various parameters on heat transfer intensity was established: product type and composition, flow rate, blade rotation speed, distance between blades and wall. During starting (transient period) the solution is first supercooled, then ice crystals appear on the scraped surface (heterogeneous nucleation) and no more supercooling is observed. It seems that, when blades are 3 mm far from the surface, a constant ice layer is formed having this thickness and acting as a thermal resistance. But when the blades rotate at 1 mm from the surface, periodically all the ice layer is removed despite the surface is not really scraped. This could simplify ice generator technology. An internal heat transfer coefficient was defined; it depends mainly on rotation speed. Correlations were proposed for its prediction, which could be applied, at least as a first approach, for the most common freezing applications of scraped surface heat exchanger i.e. ice creams (which are derived from sucrose solutions) and two-phase secondary refrigerants (which are principally ethanol solutions). (author)

Lakhdar, M.B. [LGL France Refrigerating Division, Genas (France); Cerecero, R.; Alvarez, G.; Guilpart, J. [Cemagref, Antony cedex (France). Food Process Engineering; Flick, D. [Institut National Agronomique, Paris (France); Lallemand, A. [Institut National des Sciences Appliquees de Lyon (France). Centre de Thermique

2005-01-01

286

Conjugate heat and mass transfer in heat mass exchanger ducts  

CERN Document Server

Conjugate Heat and Mass Transfer in Heat Mass Exchanger Ducts bridges the gap between fundamentals and recent discoveries, making it a valuable tool for anyone looking to expand their knowledge of heat exchangers. The first book on the market to cover conjugate heat and mass transfer in heat exchangers, author Li-Zhi Zhang goes beyond the basics to cover recent advancements in equipment for energy use and environmental control (such as heat and moisture recovery ventilators, hollow fiber membrane modules for humidification/dehumidification, membrane modules for air purification, desi

Zhang, Li-Zhi

2013-01-01

287

Forced-Convection Heat Transfer in a Spherical-Annulus Heat Exchanger.  

Science.gov (United States)

Results are presented of a combined numerical and experimental study of steady forced-convection heat transfer in a spherical annulus heat exchanger with 50 exp 0 C heated water flowing in an annulus formed by an insulated outer sphere and a 0 exp 0 C coo...

D. B. Tuft, H. Brandt

1981-01-01

288

Optimum geometry of MEMS heat exchanger for heat transfer enhancement  

Directory of Open Access Journals (Sweden)

Full Text Available The study is based on an analysis of MEMS heat exchanger of three different geometries: wavy, triangular and rectangular using water as test fluid. The problem is solved using finite element method. The aim of this analysis is to evaluate the performance of MEMS heat exchanger for different geometry and to obtain an optimum design for better heat enhancement. It is apparent from this work that rectangular surface heat exchanger shows the best performance for heat enhancement technique in comparison to other geometry. Moreover, it is also easy to manufacture. Therefore, the rectangular surface may be used instead of other configurations of heat transfer surfaces. In this analysis, emphasis is given on enhancing heat transfer area of MEMS heat exchanger by reducing the pitch which shows that 0.475 mm is the optimum pitch as further decrease of pitch length does not have any significant effect on the effectiveness and heat transfer.

Nusrat J. Chhanda

2010-05-01

289

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

International Nuclear Information System (INIS)

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

290

Applicability of uniform heat flux Nusselt number correlations to thermosyphon heat exchangers for solar water heaters  

Energy Technology Data Exchange (ETDEWEB)

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers 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% ethylene glycol is circulated in the tubes. Actual Nusselt numbers are within 15% 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.

Dahl, S.; Davidson, J.

1999-07-01

291

Applicability of uniform heat flux Nusselt number correlations to thermosyphon heat exchangers for solar water heaters  

Energy Technology Data Exchange (ETDEWEB)

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers 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.

Dahl, S.; Davidson, J. [Univ. of Minnesota, Minneapolis, MN (United States). Mechanical Engineering Dept.

1999-05-01

292

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

Science.gov (United States)

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

Srisawad, Kwanchanok; Wongwises, Somchai

2009-02-01

293

Heat exchange intensification in evaporators of the ship refrigerating machinery with application of belt turbulence promoters  

Directory of Open Access Journals (Sweden)

Full Text Available The search of methods of intensification of the heat exchange process at boiling in evaporators of refrigerators is made to decrease mass-dimension pa-rameters of heat exchange equipment. The heat exchange process at boiling within belt six-ray turbulence promoter, made as a six-ray star is investigated. The results of the model experiment for hydrodynamics and heat exchange of two-phase flow observation are presented.

Proshkin Oleg Vladimirovich

2009-10-01

294

High temperature alloys and ceramic heat exchanger  

International Nuclear Information System (INIS)

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

295

Testing and plugging power plant heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

Heat Exchanger tubes fail for any number of reasons including but certainly not limited to the cumulative effects of corrosion, erosion, thermal stress and fatigue. This presentation will attempt to identify the most common techniques for determining which tubes are leaking and then introduce the products in use to plug the leaking tubes. For the sake of time I will limit the scope of this presentation to include feedwater heaters and secondary system heat exchangers such as Hydrogen Coolers, Lube Oil Coolers, and nuclear Component Cooling Water, Emergency Cooling Water, Regenerative Heat Recovery heat exchangers.

Sutor, F. [Expando Seal Tools, Inc., Montgomeryville, PA (United States)

1994-12-31

296

Performance Prediction of Cross-finned Tube Heat Exchangers  

Science.gov (United States)

An important issue in heat pumps is increasing their efficiency, in order to achieve a significant optimization for heat exchangers. Techniques to simulate the flow length averaged heat transfer coefficient and static pressure drop through the flow passage are presented in this paper. In addition, an analytical evaluation of the cost reduction for a cross-fined tube heat exchanger of outdoor heat pump units is instantiated. The dimensionless factors, Colburn's factor j and Fanning's friction factor f, express the heat transfer performance and frictional characteristics, as a function of Reynolds number. These depend on slit possession, an original parameter used in this study. Further, this paper describes an approximate expression of the fin efficiency, which can be used for to survey the fin parameters. The above three concepts were necessary to forecast the performance on the airside. In the results, the cost minimum point was obtained with a comparable performance.

Kondou, Chieko; Senshu, Takao; Matsumura, Kenji; Oguni, Kensaku

297

Improved ceramic heat exchanger materials  

Science.gov (United States)

The development and evaluation of materials for potential application as heat exchanger structures in automotive gas turbine engines is discussed. Test specimens in the form of small monolithic bars were evaluated for thermal expansion and dimensional stability before and after exposure to sea salt and sulfuric acid, followed by short and long term cycling at temperatures up to 1200 C. The material finally selected, GE-7808, consists of the oxides, ZrO2-MgO-Al2O3-S1O2, and is described generically as ZrMAS. The original version was based on a commercially available cordierite (MAS) frit. However, a clay/talc mixture was demonstrated to be a satisfactory very low cost source of the cordierite (MAS) phase. Several full size honeycomb regenerator cores, about 10.2 cm thick and 55 cm diameter were fabricated from both the frit and mineral versions of GE-7808. The honeycomb cells in these cores had rectangular dimensions of about 0.5 mm x 2.5 mm and a wall thickness of approximately 0.2 mm. The test data show that GE-7808 is significantly more stable at 1100 C in the presence of sodium than the aluminosilicate reference materials. In addition, thermal exposure up to 1100 C, with and without sodium present, results in essentially no change in thermal expansion of GE-7808.

Rauch, H. W.

1980-01-01

298

Experimental investigation on heat transfer analysis of conical coil heat exchanger with 90° cone angle  

Science.gov (United States)

In the present study, an experimental investigation on thermal performance of the conical coil heat exchanger with 90° conical coil heat exchanger is reported. Three different conical coil heat exchangers of same mean coil diameter (Dm = 200 mm) with different tube diameters (di = 8, 10, 12.5 mm) are analyzed under steady state condition. The analysis is carried out for the tube side hot fluid flow range of 10-100 lph (Re = 500-5,000), while the shell side flow range of 30-90 lph. The data available from experimentation leads to evaluate heat transfer coefficients for inside and outside the tube of the conical coil heat exchanger by Wilsons plot method. The calculations are further extended to estimate Nusselt Number (Nu) and effectiveness. The empirical correlations are proposed for predicting Nu and the outlet temperatures of hot and cold fluids. The predicted empirical correlations show reasonable agreement with the experimental results within the given range of parameters.

Purandare, Pramod S.; Lele, Mandar M.; Gupta, Raj Kumar

2014-08-01

299

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

Energy Technology Data Exchange (ETDEWEB)

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

Hafner, Armin

2003-07-01

300

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

International Nuclear Information System (INIS)

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

 
 
 
 
301

Intermediate heat exchanger project for Super Phenix  

International Nuclear Information System (INIS)

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

302

Heat transfer analysis of short helical borehole heat exchangers  

International Nuclear Information System (INIS)

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

303

Optimisation of intermediate heat exchanger for PFBR  

International Nuclear Information System (INIS)

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

304

Heat exchanger device and method for heat removal or transfer  

Science.gov (United States)

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

Koplow, Jeffrey P

2013-12-10

305

Heat exchanger, head and shell acceptance criteria  

International Nuclear Information System (INIS)

Instability of postulated flaws in the head component of the heat exchanger could not produce a large break, equivalent to a DEGB in the PWS piping, due to the configuration of the head and restraint provided by the staybolts. Rather, leakage from throughwall flaws in the head would increase with flaw length with finite leakage areas that are bounded by a post-instability flaw configuration. Postulated flaws at instability in the shell of the heat exchanger or in the cooling water nozzles could produce a large break in the Cooling Water System (CWS) pressure boundary. An initial analysis of flaw stability for postulated flaws in the heat exchanger head was performed in January 1992. This present report updates that analysis and, additionally, provides acceptable flaw configurations to maintain defined structural or safety margins against flaw instability of the external pressure boundary components of the heat exchanger, namely the head, shell, and cooling water nozzles. Structural and flaw stability analyses of the heat exchanger tubes, the internal pressure boundary of the heat exchangers or interface boundary between the PWS and CWS, were previously completed in February 1992 as part of the heat exchanger restart evaluation and are not covered in this report

306

Influence of the yaw angle on heat transfer and pressure drop of helical type heat exchangers  

International Nuclear Information System (INIS)

The influence of the flow angle ? between the tube axis and the flow direction on heat transfer and pressure drop has been studied at 15 deg. ? ? ? 90 deg. (cross flow). The Reynolds number was varied in the range 2.103 ? Re ? 105. Experimental data are given for a number of tube banks of straight tubes as well as a helical type heat exchanger with a large thread pitch of the tubes. (author)

307

Development and application of out-of-focus imaging in order to characterize heat and mass exchanges in two-phase flows  

International Nuclear Information System (INIS)

The aim of this paper is to present the capacity of the out-of-focus imaging in order to measure droplets size in presence of heat and mass exchanges. It is supported with optical simulations first based on geometrical optics, and then with the Lorenz-Mie theory. Finally, this technique is applied in presence of heat and mass transfers in the TOSQAN experiment. (authors)

308

Dimple in real world heat exchangers; Dellen und Noppen im Waermeuebertrager  

Energy Technology Data Exchange (ETDEWEB)

Experiments in a cross flow heat exchanger employing three different geometrical dimple/protrusion configurations show that these structures can enhance heat transfer significantly. It is found, that compared with the smooth wall heat exchanger, the transferred specific amount of heat can be increased up to 40%. A more sophisticated validation of the data employing thermal performance parameters indicates that the geometrical configuration has to be selected according to the specific case of operation of the heat exchanger. (orig.)

Pohl, Stefan [Hochschule Lausitz (Germany). Fakultaet Chemieingenieurwesen/Verfahrenstechnik; Friebe, Christian; Buschmann, Matthias H. [Institut fuer Luft- und Kaeltetechnik gGmbH, Dresden (Germany)

2010-07-15

309

The LUX prototype detector: Heat exchanger development  

International Nuclear Information System (INIS)

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

310

Heat transfer and fluid flow in minichannels and microchannels  

CERN Document Server

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

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

2013-01-01

311

Safety Investigation of Liquid-Metal-Cooled Nuclear Systems with Heat Exchanger in the Risers of Simple Flow-Path Pool Design  

International Nuclear Information System (INIS)

Safety investigations were performed on 600- and 1426-MW(thermal) liquid-metal-cooled reactors with the heat exchangers (HXs) located in the risers of simple flow-path pool designs. This includes both critical reactors and accelerator-driven systems (ADSs) using liquid-metal coolants. For the 600-MW(thermal) ADS, the safety implications were examined for vessel sizes of two heights (11 and 15 m) and two diameters (6 and 10 m). Then, the reference design of 11-m height and 6-m diameter was compared with a similar design, but with the HXs located in the downcomers. The transients investigated were total-loss-of-power (TLOP), unprotected-loss-of-flow (ULOF), protected-loss-of-flow, and unprotected loss-of-heat-sink accidents. The 600-MW(thermal) ADS of 11-m height and 6-m diameter peaks at 1041 K after 29 h during a TLOP accident. If the diameter is increased to 10 m, it will peak after 55 h at a 178 K lower temperature thanks to its larger thermal inertia. The difference between locating the HXs in the risers and the downcomers is insignificant for this accident type. With the HXs in the risers, the temperature peaks at 1045 K after 28 h. During a ULOF accident in an ADS at full power, the core outlet temperature stabilizes at 1010 K, which is 337 K above the nominal outlet temperature. When the vessel height is increased to 15 m, the natural convection is improved, and the core outlet temperature stabilizes at 911 K. A Pb-cooled 1426-MW(thermal) reactor of 11-m height d 1426-MW(thermal) reactor of 11-m height and 12-m diameter is also shown to be sufficiently coolable during a TLOP accident; i.e., it peaks at 1093 K after 49 h. In a pool-type design with a simple flow path, the use of HXs in the risers and flaps at their inlets that prevent a flow reversal will have significant safety advantages in case of HX tube failures. Steam or gas bubbles exiting from the secondary circuit cannot be dragged into the core region by the liquid-metal coolant. Instead, they would rise with the coolant and exit through the free surface. Another important effect from placing the HXs in the risers is the fact that the reactor vessel wall will be cooler during normal operation and during all accidents in which the HXs still operate. This is because the coolant passes through the HXs before it reaches the vessel wall. The idea to place the HXs in the risers of a simple flow-path design is protected by European patent No. 04 103 634.4. The computational fluid dynamics code STAR-CD was used in all calculations

312

On-line fouling monitor for heat exchangers  

International Nuclear Information System (INIS)

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

313

Calculation of the heat exchange in turbulent liquid-metal flow in ducts with infinite square assemblies of cylindrical fuel rods  

International Nuclear Information System (INIS)

There were made calculations and determined values for the temperature variation over the heat transfer surface and for the average heat transfer coefficients in turbulent liquid-metal flow (Pr = 0,02) along a bundle of cylindrical fuel rods in a square assembly. (orig.)

314

Assessment of heating dynamics in a prototype magnetic induction heat exchanger  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Magnetic induction (MI) heating has the potential to be used in food processing systems to heat flowing food material. Due to electromagnetic properties, MI heating theoretically has the ability to evenly distribute energy to heat exchanger surfaces in a manner that is more energy efficient and gentler to the processing stream than current steam-boiler systems. The goal of this project was to analyze the processing capabilities of an MI unit composed of a high-frequency power source, an induc...

Sadler, Philip C.

2011-01-01

315

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-04-06

316

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

Directory of Open Access Journals (Sweden)

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

I. Yu. Butusov

2013-02-01

317

Eddy current testing of heat exchangers tubes  

International Nuclear Information System (INIS)

An automatic system for Eddy Current testing of heat exchangers tubes of warships was developed. The advantages are an exposure of the controller limited at the time required to put in place the system and a reduced time of control

318

Heat exchanger fouling: Prediction, measurement, and mitigation  

Science.gov (United States)

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

319

A heat exchanger analogy of automotive paint ovens  

International Nuclear Information System (INIS)

Computational prediction of vehicle temperatures in an automotive paint oven is essential to predict paint quality and manufacturability. The complex geometry of vehicles, varying scales in the flow, transient nature of the process, and the tightly coupled conjugate heat transfer render the numerical models computationally very expensive. Here, a novel, simplified model of the oven is developed using an analogy to a three-stream cross flow heat exchanger that transfers heat from air to a series of moving bodies and supporting carriers. The analogous heat exchanger equations are developed and solved numerically. Steady state Computational Fluid Dynamics (CFD) simulations are carried out to model the flow field and to extract the heat transfer coefficients around the body and carriers. The air temperature distribution from the CFD models is used as a boundary condition in the analogous model. Correction coefficients are used in the analogy to take care of various assumptions. These are determined from existing test data. The same corrections are used to predict air temperatures for a modified configuration of the oven and a different vehicle. The method can be used to conduct control volume analysis of ovens to determine energy efficiency, and to study new vehicle or oven designs. -- Highlights: • Analogy of an automotive paint oven as a three stream cross flow heat exchanger. • The three streams are vehicle bodies, carriers and hot air. • Convection coefficients and inlet air stream temperatures from steady CFD simulations. • Analogy useful for overall energy efficiency analysis of conveyor ovens in general

320

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

International Nuclear Information System (INIS)

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

 
 
 
 
321

Exergy optimization in a steady moving bed heat exchanger.  

Science.gov (United States)

This work provides an energy and exergy optimization analysis of a moving bed heat exchanger (MBHE). The exchanger is studied as a cross-flow heat exchanger where one of the phases is a moving granular medium. The optimal MBHE dimensions and the optimal particle diameter are obtained for a range of incoming fluid flow rates. The analyses are carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the steady-state problem and an analytical solution of the simplified equations, neglecting the conduction terms. The numerical simulation considers, for the solid, the convection heat transfer to the fluid and the diffusion term in both directions, and for the fluid only the convection heat transfer to the solid. The results are compared with a well-known analytical solution (neglecting conduction effects) for the temperature distribution in the exchanger. Next, the analytical solution is used to derive an expression for the exergy destruction. The optimal length of the MBHE depends mainly on the flow rate and does not depend on particle diameter unless they become very small (thus increasing sharply the pressure drop). The exergy optimal length is always smaller than the thermal one, although the difference is itself small. PMID:19426351

Soria-Verdugo, A; Almendros-Ibáñez, J A; Ruiz-Rivas, U; Santana, D

2009-04-01

322

Experimental study on forced convection heat transfer characteristics in a converging diverging heat exchanger channel  

Energy Technology Data Exchange (ETDEWEB)

The convective heat transfer characteristics in a periodic converging-diverging heat exchanger 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.)

Taymaz, I.; Islamoglu, Y. [Sakarya University, Mechanical Engineering Department, Adapazari (Turkey); Koc, I. [Air Force Academy, Department of Aeronautical Engineering, Istanbul (Turkey)

2008-08-15

323

Inverse heat transfer problem in digital temperature control in plate fin and tube heat exchangers  

Science.gov (United States)

The aim of the paper is a steady-state inverse heat transfer problem for plate-fin and tube heat exchangers. The objective of the process control is to adjust the number of fan revolutions per minute so that the water temperature at the heat exchanger outlet is equal to a preset value. Two control techniques were developed. The first is based on the presented mathematical model of the heat exchanger while the second is a digital proportional-integral-derivative (PID) control. The first procedure is very stable. The digital PID controller becomes unstable if the water volumetric flow rate changes significantly. The developed techniques were implemented in digital control system of the water exit temperature in a plate fin and tube heat exchanger. The measured exit temperature of the water was very close to the set value of the temperature if the first method was used. The experiments showed that the PID controller works also well but becomes frequently unstable.

Taler, Dawid; Sury, Adam

2011-12-01

324

A Cell Model to Describe and Optimize Heat and Mass Transfer in Contact Heat Exchangers  

Directory of Open Access Journals (Sweden)

Full Text Available A cell model to describe and optimize heat and mass transfer in contact heat exchangers for utilization of exhaust gases heat is proposed. The model is based on the theory of Markov chains and allows calculating heat and mass transfer at local moving force of the processes in each cell. The total process is presented as two parallel chains of cells (one for water flow and one for gas flow. The corresponding cells of the chains can exchange heat and mass, and water and gas can travel along their chains according to their transition ma-trices. The results of numerical experiments showed that the most part of heat transfer occurs due to moisture condensation from gas and the most intense heat transfer goes near the inlet of gas. Experimental validation of the model showed a good correlation between calculated and experimental data for an industrial contact heat exchanger if appropriate empirical equations were used to calculate heat and mass transfer coefficient. It was also shown that there exists the optimum height of heat exchanger that gave the maximum gain in heat energy utilization.

Piotr Yakimychev

2011-05-01

325

Brayton-cycle heat exchanger technology program  

Science.gov (United States)

The following five tasks designed to advance this development of heat exchanger systems for close loop Brayton cycle power systems are presented: (1) heat transfer and pressure drop data for a finned tubular heat transfer matrix. The tubes are arranged in a triangular array with copper stainless steel laminate strips helically wound on the tubes to form a disk fin geometry; (2) the development of a modularized waste heat exchanger. Means to provide verified double containment are described; (3) the design, fabrication, and test of compact plate fin heat exchangers representative of full scale Brayton cycle recuperators; (4) the analysis and design of bellows suitable for operation at 1600 F and 200 psia for 1,000 cycles and 50,000 hours creep life; and (5) screening tests used to select a low cost braze alloy with the desirable attributes of a gold base alloy. A total of 22 different alloys were investigated; the final selection was Nicrobraz 30.

Killackey, J. J.; Coombs, M. G.; Graves, R. F.; Morse, C. J.

1976-01-01

326

Fouling characteristics of compact heat exchangers and enhanced tubes.  

Energy Technology Data Exchange (ETDEWEB)

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 heat exchangers is limited; however, significant progress has been made with enhanced tubes.

Panchal, C. B.; Rabas, T. J.

1999-07-15

327

Optimization of compact heat exchangers by numerical simulation  

International Nuclear Information System (INIS)

In the field of heat exchangers, researchers are pushing forward basic investigation of the mechanisms governing turbulent flows, of decisive importance but only partly understood, even as industrialists call for ever-higher-performing technological developments. At the center of these concerns, simulation tools play a major role. (authors)

328

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

International Nuclear Information System (INIS)

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

329

Heat transfer from oriented heat exchange areas  

Science.gov (United States)

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

Vantuch, Martin; Huzvar, Jozef; Kapjor, Andrej

2014-03-01

330

Simulation of multistream plate-fin heat exchangers of an air separation unit  

Science.gov (United States)

Hot and cold reversible heat exchangers of an air separation unit are simulated. Five fluid streams exchange heat with six fluid streams in parallel and counter flow. The numerical method employed divides the heat exchanger in a number of sections, for which fluid properties, capacity rates and heat transfer coefficients are considered constant. Single and two-phase streams are taken into account. Results obtained from the model are compared with field data.

Boehme, R.; Parise, J. A. R.; Pitanga Marques, R.

2003-06-01

331

Modelling of natural-convection driven heat exchangers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract: A lumped model is developed for shell-and-tube heat exchangers driven by natural convection, which is based on a one-dimensional approximation. The heat flux is driven by the logarithmic mean temperature difference. The volumetric air flow rate is driven by the buoyant force. Based on the Boussinesq aproximation, this force is characterised by an analytic expression of the inflow and outflow temperatures. The lumped model is finished by relating the buoyant force to the friction...

Dirkse, M. H.; Loon, W. K. P.; Stigter, J. D.; Bot, G. P. A.

2007-01-01

332

Quantification of the heat exchange of chicken eggs.  

Science.gov (United States)

In the incubation process of domestic avian eggs, the development of the embryo is mainly influenced by the physical microenvironment around the egg. Only small spatiotemporal deviations in the optimal incubator air temperature are allowed to optimize hatchability and hatchling quality. The temperature of the embryo depends on 3 factors: (1) the air temperature, (2) the exchange of heat between the egg and its microenvironment and (3) the time-variable heat production of the embryo. Theoretical estimates on the heat exchange between an egg and its physical microenvironment are approximated using equations that assume an approximate spherical shape for eggs. The objective of this research was to determine the heat transfer between the eggshell and its microenvironment and then compare this value to various theoretical estimates. By using experimental data, the overall and the convective heat transfer coefficients were determined as a function of heat production, air humidity, air speed, and air temperature. Heat transfer was not affected by air humidity but solely by air temperature, embryonic heat generation, and air speed and flow around eggs. Also, heat transfer in forced-air incubators occurs mainly by convective heat loss, which is dependent on the speed of airflow. A vertical airflow is more efficient than a horizontal airflow in transferring heat from the egg. We showed that describing an egg as a sphere underestimated convective heat transfer by 33% and was, therefore, too simplistic to accurately assess actual heat transfer from real eggs. PMID:15782902

Van Brecht, A; Hens, H; Lemaire, J L; Aerts, J M; Degraeve, P; Berckmans, D

2005-03-01

333

Gas Diodes for Thermoacoustic Self-circulating Heat Exchangers  

Science.gov (United States)

An asymmetrical constriction in a pipe functions as an imperfect gas diode for acoustic oscillations in the gas in the pipe. One or more gas diodes in a resonant loop of pipe create substantial steady flow, which can carry substantial heat between a remote heat exchanger and a thermoacoustic or Stirling engine or refrigerator; the flow is driven directly by the oscillations in the engine or refrigerator itself. This invention gives Stirling and thermoacoustic devices unprecedented flexibility, and may lead to Stirling engines of unprecedented power. We have built two of these resonant self-circulating heat exchangers, one as a fundamental test bed and the other as a demonstration of practical levels of heat transfer. Measurements of flow and heat transfer are in factor-of-two agreement with either of two simple calculation methods. One calculation method treats the oscillating and steady flows as independent and simply superimposed, except in the gas diodes. The other method accounts for the interaction between the oscillating and steady flow with the quasi-steady approximation. The mutual influence of superimposed turbulent oscillating and steady flows is a theoretical challenge.

Swift, Greg; Backhaus, Scott

2006-05-01

334

Research of heat exchange rate of the pulsating heat pipe  

Directory of Open Access Journals (Sweden)

Full Text Available Given article presents experimental research of heat transfer characteristics of the pulsating heat pipe (PHP which consists of seven coils with 1 mm inner diameter. Water was used as the heat carrier. PHP construction, measuring circuit and research technique are presented. It is shown that under PHP functioning there are two characteristic modes of operation, which can be distinguished by values of thermal resistance. PHP heat exchange features are disclosed.

Kravets V. Yu.

2010-02-01

335

Phase Change Material Heat Exchanger Life Test  

Science.gov (United States)

Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The IR environment of the space craft varies drastically from the light side to the dark side of the moon. The result is a situation where a radiator sized for the maximal heat load in the most adverse situation is subject to freezing on the dark side of the orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when there is too much being produced by the space craft to reject to space, and then feeding that energy back into the thermal loop when conditions are more favorable. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration LLO missions. In order to validate the performance of PCM Heat Exchangers, a life test is being conducted on four n-Pentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed.

Lillibridge, Sean; Stephan, Ryan

2009-01-01

336

Heat Pipe Blocks Return Flow  

Science.gov (United States)

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

Eninger, J. E.

1982-01-01

337

New developments in compact plate-fin heat exchangers  

International Nuclear Information System (INIS)

The extension of compact plate-fin heat exchanger capabilities in order to accommodate the performance requirements of regeneratively cooled hypersonic ramjet engines, laser weapons, aircraft engine infrared suppressors, and large high-efficiency gas turbine cycles is described. Attention is given to cooling fluid flow path geometry and heat exchanger fabrication techniques, such novel materials as alumina and silicon carbide, and space and weight constraints imposed on designs by airborne application. It is shown that operating temperatures, pressures and area densities have been significantly increased

338

Improvements in or relating to heat exchangers  

International Nuclear Information System (INIS)

A heat exchanger is described that is suitable for use with high temperature gas cooled reactors in which the heat is used as process heat. The construction which is of necessity of large size, is of much lighter weight than current constructions and is better able to withstand the high operating temperature (up to about 10000C). Carbon fibre reinforced carbon materials are employed as constructional materials. A method of fabrication is described. The heat exchanger comprises a tube or bundle of tubes associated with a header plate, and the tube can be of helical form. The carbon materials may be formed by carbonisation of a thermosetting plastic such as a phenolic resin. The exchanger is rendered substantially impermeable to gas by an infiltration treatment of the carbon material using a cracked hydrocarbon gas. (U.K.)

339

Effect of the axial scraping velocity on enhanced heat exchangers  

International Nuclear Information System (INIS)

Highlights: • The flow pattern has been obtained by means of PIV in an enhanced heat exchanger. • The effects of the Reynolds number and the scraping velocity have been analysed. • The turbulence level of the flow has been related to the scraping velocity. • A numerical RNG k–? turbulent model has been validated with the experimental data. -- Abstract: The flow pattern within an enhanced tubular heat exchanger equipped with a reciprocating scraping device is experimentally analysed. The insert device, specially designed to avoid fouling and to enhance heat transfer, has also been used to produce ice slurry. It consists of several circular perforated scraping discs mounted on a coaxial shaft. The whole is moved alternatively along the axial direction by a hydraulic cylinder. The phase-averaged velocity fields of the turbulent flow have been obtained with PIV technique for both scraping semi-cycles. Special attention has been paid to the effect of the non-dimensional scraping velocity and the Reynolds number in the flow field. CFD simulations provide support for the identification of the flow patterns and the parameter assessment extension. The results show how the scraping parameters affect the turbulence level produced in the flow and therefore the desired heat transfer enhancement

340

A fundamentally new approach to air-cooled heat exchangers.  

Energy Technology Data Exchange (ETDEWEB)

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

Koplow, Jeffrey P.

2010-01-01

 
 
 
 
341

Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties  

CERN Document Server

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 heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers 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 heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger ...

Hansen, B J; Klebaner, A; 10.1063/1.4706971

2012-01-01

342

Heat exchange and resistance in tubes under supercritical pressures of coolant. Pt. 2. Heat transfer and resistance under high thermal loads. Deteriorated heat exchange intensification  

International Nuclear Information System (INIS)

The basic peculiarities of turbulent heat exchange in tubes under supercritical pressures of coolant are considered, their physical nature is noted and recommendations on engineering calculations of thermohydraulic properties of the process are given. The principal similarity of the heat transfer deterioration mechanism by supercritical pressures with analogous events by gases heating and by mixed convections in drop liquids, which are conditioned by appearance under heat exchange conditions of new dynamic factors - thermal acceleration and the Archimedean forces, changing the liquid flow structure, is shown

343

Research of characteristics slot-hole heat exchanger with the developed surface of heat exchange  

Directory of Open Access Journals (Sweden)

Full Text Available Thermal characteristics of multichannel slot-hole heat exchanger with the developed surface of heat exchange inside the opened-cycle water cooling system are experimentally investigated. Graphic dependences of average value of temperature of the simulator of a heat current and temperatures of the heat exchanger base are presented on tapped-off power. Dependences of tapped-off power and hydraulic losses on the of water consumption are given. It is shown, that use of developed slot-hole heat exchanger provides higher values of tapped-off power as compared to well-known two-channel slot-hole heat exchanger: at the temperature of heat-generating component simulator of +60°? the tapped-off power increases with 307 up to 750 W. Recommendations on increase of adaptability of slot-hole heat exchanger manufacturing are given. Heat exchanger is suitable for application in microprocessors and others heat-generating components and electronic equipment units cooling.

Malkin E. C.

2010-03-01

344

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

Directory of Open Access Journals (Sweden)

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

N. D. Shirgire

2014-08-01

345

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

Directory of Open Access Journals (Sweden)

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

A. D. Yadav, V. M. Kirplani

2013-05-01

346

Compact heat exchanger technologies for the HTRs recuperator application  

International Nuclear Information System (INIS)

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

347

Simulation of induction heating process with radiative heat exchange  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: Numerical modelling of induction heating process is a complex issue. It needs analysis of coupled electromagnetic and thermal fields. Calculation models for electromagnetic field analysis as well as thermal field analysis need simplifications. In case of thermal field calculations, correct modelling of radiative heat exchange between the heated charge and inductor’s thermal insulation is essential. Most commercial calculation programs enabling coupled analysis of electromagnetic and thermal fields do not allow taking into consideration radiative heat exchange between calculation model components, which limits thermal calculations only to the charge area. The paper presents a supplementation of the program Flux 2D with radiative heat exchange procedures.Design/methodology/approach: Commercial program Flux 2D designed for coupled electromagnetic and thermal calculation (based on finite element method was supplemented with authors program for radiative heat exchange based on numerical integration of classic equations.Findings: Supplementation EM-T calculations with radiative heat exchange between charge and inductor enables to calculate thermal insulation parameters and increase precision of modelling.Research limitations/implications: Procedures for radiative heat exchange enables calculation of two surfaces (flat or cylindrical with finite dimensions. The surfaces can be displaced relative to each other (charge shorter or longer than thermal insulation of inductor. Material of surfaces is modelled as: flat, diffuse, radiant surfaces absorb energy evenly in the whole spectrum (grey bodies. The whole system is modelled as in a steady thermal state (quasi-steady.Originality/value: Authors program extends Flux 2D features with a possibility for calculating radiative heat transfer. The application of radiative process is possible between all components of the studied model, not only for the boundary conditions.

A. Kachel

2007-05-01

348

Liquid Salt Heat Exchanger Technology for VHTR Based Applications  

Energy Technology Data Exchange (ETDEWEB)

The objective of this research is to evaluate performance of liquid salt fluids for use as a heat carrier for transferring high-temperature process heat from the very high-temperature reactor (VHTR) to chemical process plants. Currently, helium is being considered as the heat transfer fluid; however, the tube size requirements and the power associated with pumping helium may not be economical. Recent work on liquid salts has shown tremendous potential to transport high-temperature heat efficiently at low pressures over long distances. This project has two broad objectives: To investigate the compatibility of Incoloy 617 and coated and uncoated SiC ceramic composite with MgCl2-KCl molten salt to determine component lifetimes and aid in the design of heat exchangers and piping; and, To conduct the necessary research on the development of metallic and ceramic heat exchangers, which are needed for both the helium-to-salt side and salt-to-process side, with the goal of making these heat exchangers technologically viable. The research will consist of three separate tasks. The first task deals with material compatibility issues with liquid salt and the development of techniques for on-line measurement of corrosion products, which can be used to measure material loss in heat exchangers. Researchers will examine static corrosion of candidate materials in specific high-temperature heat transfer salt systems and develop an in situ electrochemical probe to measure metallic species concentrations dissolved in the liquid salt. The second task deals with the design of both the intermediate and process side heat exchanger systems. Researchers will optimize heat exchanger design and study issues related to corrosion, fabrication, and thermal stresses using commercial and in-house codes. The third task focuses integral testing of flowing liquid salts in a heat transfer/materials loop to determine potential issues of using the salts and to capture realistic behavior of the salts in a small scale prototype system. This includes investigations of plugging issues, heat transfer, pressure drop, and the corrosion and erosion of materials in the flowing system.

Anderson, Mark; Sridhara, Kumar; Allen, Todd; Peterson, Per

2012-10-11

349

Negative Joule Heating in Ion-Exchange Membranes  

CERN Document Server

In ion-exchange membrane processes, ions and water flow under the influence of gradients in hydrostatic pressure, ion chemical potential, and electrical potential (voltage), leading to solvent flow, ionic fluxes and ionic current. At the outer surfaces of the membranes, electrical double layers (EDLs) are formed (Donnan layers). When a current flows through the membrane, we argue that besides the positive Joule heating in the bulk of the membrane and in the electrolyte outside the membrane, there is also negative Joule heating in one of the EDLs. We define Joule heating as the inner product of the two vectors current and field strength. Also when fluid flows through a charged membrane, at one side of the membrane there is pressure-related cooling, due to the osmotic and hydrostatic pressure differences across the EDLs.

Biesheuvel, P M; Hamelers, H V M

2014-01-01

350

Enhanced two phase flow in heat transfer systems  

Science.gov (United States)

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

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

2013-12-03

351

Materials, Turbomachinery and Heat Exchangers for Supercritical CO2 Systems  

Energy Technology Data Exchange (ETDEWEB)

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

Anderson, Mark; Nellis, Greg; Corradini, Michael

2012-10-19

352

Heat exchanger design for desalination plants  

International Nuclear Information System (INIS)

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

353

Friction and Heat Transfer in Twisted Flow inside a Pipe.  

Science.gov (United States)

Approximate calculations of the characteristics of heat exchange and friction during turbulent flow in tubes with band-type vortex generators are compared with experimental results obtained on an air unit. Graphs are given for hydraulic friction in tubes ...

V. K. Migai

1969-01-01

354

Hydrodynamics, heat transfer and flow boiling instabilities in microchannels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Boiling in microchannels is a very efficient mode of heat transfer with high heat and mass transfer coefficients achieved. Less pumping power is required for two-phase flows than for single-phase liquid flows to achieve a given heat removal. Applications include electronics cooling such as cooling microchips in laptop computers, and process intensification with compact evaporators and heat exchangers. Evaporation of the liquid meniscus is the main contributor to the high hea...

Barber, Jacqueline Claire

2010-01-01

355

Multi scale thermo-hydraulic modeling of cryogenic heat exchangers  

Energy Technology Data Exchange (ETDEWEB)

The cryogenic industry has experienced a continuous growth in the last decades, partially sustained by the worldwide development of Liquefaction of Natural Gas (LNG) projects. LNG technology provides an economically feasible way of transporting natural gas over long distances, and currently accounts for nearly 30% of the international trade of this resource. The economic feasibility of these projects, in terms of both capital and operating costs, is to a large extent controlled by the performance of the main cryogenic two-phase flow heat exchanger. This industrial scenario provides then the motivation for a detailed study of the heat exchanger from a design perspective. On the one hand, it is widely accepted that a highly detailed analysis is required at a micro scale to properly take account of the two phase heat transfer process. On the other hand, a process-level description corresponds to larger time and space scales. In general, determining the proper methodology for considering these scales and their interaction remains a challenging problem. For this reason, current techniques focus in only one particular scale. The main objective of this project is then to develop a multi scale model applicable for two-phase flow heat exchangers. In this context, a three-scale framework is postulated. This thesis was divided into macro, meso (medium) and micro scale analysis. First, a macroscopic analysis provides a broad description in terms of overall heat transfer and pressure drop, using simple models without taking into account the details of physical phenomena at lower scales. Second, at mesoscale level, flow in parallel channels is considered following a homogenization approach, thus including the effects of flow mal distribution and partial mixing. Third, the microscopic description conceives a phenomenological representation of boiling flows, following multi fluid formulations, for two specific flow patterns: annular-mist and post-dryout regimes. Finally, a multi scale design algorithm is proposed. (au)

Pacio, Julio Cesar

2012-07-01

356

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

International Nuclear Information System (INIS)

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

357

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

Science.gov (United States)

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

Grabenstein, V.; Kabelac, S.

2012-11-01

358

Comparing vertical ground heat exchanger models  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The main objective of this article is to establish a set of test cases for analytical verification and inter-model comparison of vertical ground heat exchanger (GHX) models used in building simulation programs. Several test cases are suggested. They range from steady-state heat rejection in a single borehole to varying hourly loads with relatively large yearly thermal imbalance in multiple borehole configurations. The usefulness of the proposed test cases is illustrated with different GHX mod...

Bertagnolio, Ste?phane; Bernier, Michel; Kummert, Michae?l

2012-01-01

359

Heat exchanges in a quenched ferromagnet  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The off-equilibrium probability distribution of the heat exchanged by a ferromagnet in a time interval after a quench below the critical point is calculated analytically in the large-N limit. The distribution is characterized by a singular threshold Qc < 0, below which a macroscopic fraction of heat is released by the k = 0 Fourier component of the order parameter. The mathematical structure producing this phenomenon is the same responsible of the order parameter condensatio...

Corberi, Federico; Gonnella, Giuseppe; Piscitelli, Antonio; Zannetti, Marco

2012-01-01

360

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

Directory of Open Access Journals (Sweden)

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

Sandip S. Kale

2014-09-01

 
 
 
 
361

Heat transfer in heat exchangers of sodium cooled fast reactor systems  

Energy Technology Data Exchange (ETDEWEB)

The present paper describes the heat transfer in heat exchangers of sodium cooled fast reactors. Practical empirical correlations regarding heat transfer coefficients for intermediate heat exchangers (IHXs) and air coolers (ACs) were derived using test data obtained at the fast reactor 'Monju' and 'Joyo' and also at the 50 MW steam generator facility (50 MW SG). The correlation proposed by Seban and Shimazaki was applicable to estimate the heat transfer coefficients in both flows of IHX, i.e., primary and secondary flows, when the Peclet number was larger than 30. When the Peclet number for shell-side was small, the Nusselt number decreased as a function of the Peclet number. It was clarified that this characteristic was not caused by the heat conduction in flow direction. The heat conduction effect can be neglected even in the natural circulation conditions of the Monju plant. As for the heat transfer coefficient of AC provided in the secondary heat transport system of the fast breeder reactor, data in the above mentioned three facilities were evaluated. As a result, empirical correlations were derived for the average heat transfer coefficients of a large capacity finned air cooler made of stainless steel. These correlations could contribute to analyze the plant dynamics with better accuracy than before.

Mochizuki, Hiroyasu [Nuclear Power and Energy Safety Engineering, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507 (Japan)], E-mail: mochizki@u-fukui.ac.jp; Takano, Masahito [Nuclear Power and Energy Safety Engineering, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507 (Japan)

2009-02-15

362

Radio frequency (RF) heated supersonic flow laboratory  

Energy Technology Data Exchange (ETDEWEB)

A unique supersonic flow apparatus which employs an inductively-coupled, radio frequency (RF) torch to supply high enthalpy source gas to the nozzle inlet is described. The main features of this system are the plasma tube, a cooled nozzle assembly, and a combustion/expansion chamber with a heat exchanger. A description of these components with current test data is presented. In addition, a discussion of anticipated experiments utilizing this system is included.

Wantuck, P.; Watanabe, H.

1990-01-01

363

Exergo-ecological evaluation of heat exchanger  

Directory of Open Access Journals (Sweden)

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

Stanek Wojciech

2014-01-01

364

Improvements relating to plate heat exchangers  

International Nuclear Information System (INIS)

A plate heat exchanger is described in which the whole pack of plates can be removed bodily from the containing frame for maintenance. The advantages of such a system to the nuclear industry in particular include the saving of time, the avoidance of disturbing connecting pipework and the possibility of carrying out plate maintenance remotely from the installation. (U.K.)

365

Tube-in-shell heat exchangers  

International Nuclear Information System (INIS)

A method is described for repairing a defective tube weld in a heat exchanger. A sleeve is inserted within the tube to bridge the defect, one end of the sleeve being brazed to the tube and the other end bonded to the tube sheet by explosive welding. (author)

366

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

Scientific Electronic Library Online (English)

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

S., Sathiyan; Murali, Rangarajan; S., Ramachandran.

2013-06-01

367

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

Scientific Electronic Library Online (English)

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

S., Sathiyan; Murali, Rangarajan; S., Ramachandran.

368

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

Directory of Open Access Journals (Sweden)

Full Text Available Heat exchangers are important heat transfer apparatus in oil refining, chemical engineering, environmental protection, electric power generation etc. The present work modifies the existing Bell-Delaware method used for conventional heat exchanger, taking into consideration the helical geometry of Helixchanger. Thermal analysis was carried out to study the impacts of various baffle inclination angles on fluid flow and heat transfer of heat exchangers with helical baffles. The analysis was conducted for conventional shell and tube heat Exchanger and Helixchanger for five baffle inclination angles. Analysis results indicate that continual helical baffles can reduce or even eliminate dead regions in the shell side of shell-and-tube heat exchangers. The pressure drop varies drastically with baffle inclination angle and shell-side Reynolds number. The variation of the pressure drop is relatively large for small inclination angle. However, for ?>350, the effect of ? on pressure drop is very small. Compared to the segmental heat exchangers, the heat exchangers with continual helical baffles have higher heat transfer coefficients to the same pressure drop. The detailed knowledge on the heat transfer and pressure drop across the shell side will provide further basis flow for further optimization of shell-and-tube heat exchangers.

S. Pavithran

2012-05-01

369

Polymer Material Heat Exchangers Application in Refrigerant Cycles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Special heat exchanger made out of polymer materials have been developed and applied in refrigeration systems. The initial purpose was to provide corrosion resistant heat exchangers for the rejection of heat into sea water for an improved efficiency compared to regular air cooling of A/C and refrigeration system condensers. Another application was the corrosion resistant heat exchanger for heat rejection or heat extraction to resp. from ground source water in A/C and heat pump installations. ...

Hesse, Ullrich; Weimer, Thomas

2012-01-01

370

Predicting particle deposition on HVAC heat exchangers  

Science.gov (United States)

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

Siegel, Jeffrey A.; Nazaroff, William W.

371

Brayton heat exchange unit development program  

Science.gov (United States)

A Brayton Heat Exchanger Unit (BHXU), consisting of a recuperator, a heat sink heat exchanger and a gas ducting system, was designed, fabricated, and tested. The design was formulated to provide a high performance unit suitable for use in a long-life Brayton-cycle powerplant. A parametric analysis and design study was performed to establish the optimum component configurations to achieve low weight and size and high reliability, while meeting the requirements of high effectiveness and low pressure drop. Layout studies and detailed mechanical and structural design were performed to obtain a flight-type packaging arrangement. Evaluation testing was conducted from which it is estimated that near-design performance can be expected with the use of He-Xe as the working fluid.

Morse, C. J.; Richard, C. E.; Duncan, J. D.

1971-01-01

372

Tube vibration in industrial size test heat exchanger  

International Nuclear Information System (INIS)

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

373

Improved spacers for high temperature gas-cooled heat exchangers  

International Nuclear Information System (INIS)

Experimental and analytical investigations in the field of heat exchanger thermohydraulics have been performed at EIR for many years, Basic studies have been carried out on heat transfer and pressure loss for tube bundles of different geometries and tube surfaces. As a part of this overall R+D programme for heat exchangers, investigations have been carried out on spacer pressure loss in bundles with longitudinal flow. An analytical spacer pressure loss model was developed which could handle different types of subchannel within the bundle. The model has been evaluated against experiments, using about 25 spacers of widely differing geometries. In a gas-cooled reactor it is important to keep the pressure loss over the primary circuit heat exchangers to a minimum. In exchangers with grid spacers these contribute a significant proportion of the overall bundle losses. For example, in the HHT Recuperator, with a shell-side pressure loss of 3.5 % of the inlet pressure, the spacers cause about one half of this loss. Reducing the loss to, say, 2.5 % results in an overall increase in plant efficiency by more than 1 % - a significant improvement Preliminary analysis identified 5 geometries in particular which were chosen for experimental evaluation as part of a joint project with the SULZER Company, to develop a low pressure-loss spacer for HHT heat exchangers (longitudinal counter-flow He/He and He/H2O designs). The aim of the tests was to verify the low pressure-loss characteristics of these spacer grid types, as well as the quality of the results calculated by the computer code analytical model. The experimental and analytical results are compared in this report

374

The dynamics of cross-inclined helically coiled heat exchangers  

International Nuclear Information System (INIS)

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

375

Heat exchangers with several heat exchanger matrices mounted in a common casing for separately conducted media  

International Nuclear Information System (INIS)

The heat exchanger is suited for plants with a closed gas cycle such as, e. g., HTR with a helium turbine or drive units for vehicles. It contains heat exchanger matrices running parallel to each other and formed by the folds of a uniformly folded band and by walls covering the saddles of the folds. Two neighbouring matrices each are combined to form a heat exchanger unit and supported between supporting walls. The heat exchanger unit is not firmly connected with these supporting walls and therefore can easily to be inserted or dismounted. For sealing purposes, the fold saddles are contacting the supporting walls because of the high pressure of the meUWIdium, Ior the remaining seals between hp and lp-compartments labyrinth boxes being provided. (UWI)

376

Selection and costing of heat exchangers  

Science.gov (United States)

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

1992-12-01

377

Improvement of efficiency on ball-cleaning method for JRR-3 heat exchanger  

International Nuclear Information System (INIS)

JRR-3 uses shell and tube heat exchangers. The secondary coolant flushes into the tubes and the primary coolant flows outside of the tubes. The heat exchangers are cleaned with the ball-cleaning method, which is a method to clean inside of the tubes by passing the sponge balls with secondary coolant. Decline in the performance of heat exchanger could rise temperature of the primary coolant and then influence the safe and stable reactor operation. The effective way of ball-cleaning for JRR-3 heat exchangers is examined based on past cleaning data. The results show the optimal ball size and the way to determine the cleaning time. (author)

378

Shell side CFD analysis of a small shell-and-tube heat exchanger  

Energy Technology Data Exchange (ETDEWEB)

The shell side design of a shell-and-tube heat exchanger; in particular the baffle spacing, baffle cut and shell diameter dependencies of the heat transfer coefficient and the pressure drop are investigated by numerically modeling a small heat exchanger. The flow and temperature fields inside the shell are resolved using a commercial CFD package. A set of CFD simulations is performed for a single shell and single tube pass heat exchanger with a variable number of baffles and turbulent flow. The results are observed to be sensitive to the turbulence model selection. The best turbulence model among the ones considered is determined by comparing the CFD results of heat transfer coefficient, outlet temperature and pressure drop with the Bell-Delaware method results. For two baffle cut values, the effect of the baffle spacing to shell diameter ratio on the heat exchanger performance is investigated by varying flow rate.

Ozden, Ender [Department of Mechanical Engineering, Middle East Technical University, 06531 Ankara (Turkey); Tari, Ilker, E-mail: itari@metu.edu.t [Department of Mechanical Engineering, Middle East Technical University, 06531 Ankara (Turkey)

2010-05-15

379

Shell side CFD analysis of a small shell-and-tube heat exchanger  

International Nuclear Information System (INIS)

The shell side design of a shell-and-tube heat exchanger; in particular the baffle spacing, baffle cut and shell diameter dependencies of the heat transfer coefficient and the pressure drop are investigated by numerically modeling a small heat exchanger. The flow and temperature fields inside the shell are resolved using a commercial CFD package. A set of CFD simulations is performed for a single shell and single tube pass heat exchanger with a variable number of baffles and turbulent flow. The results are observed to be sensitive to the turbulence model selection. The best turbulence model among the ones considered is determined by comparing the CFD results of heat transfer coefficient, outlet temperature and pressure drop with the Bell-Delaware method results. For two baffle cut values, the effect of the baffle spacing to shell diameter ratio on the heat exchanger performance is investigated by varying flow rate.