Showing papers on "Micro heat exchanger published in 1997"

Heat Transfer: A Practical Approach

Abstract: Part 1 Fundamentals: basic concepts of thermodynamics and heat transfer heat conduction steady heat conduction transient heat conduction numerical methods in heat transfer forced convection natural convection boiling and condensation radiation heat transfer heat exchangers mass transfer. Part 2 Applications: heating and cooling of buildings refrigeration and freezing of foods cooling of electronic equipment property tables and charts (SI units and English units) about the software.

Heat Exchangers: Selection, Rating, and Thermal Design

Abstract: CLASSIFICATIONS OF HEAT EXCHANGERS Introduction Recuperation and Regeneration Transfer Processes Geometry of Construction Heat Transfer Mechanisms Flow Arrangements Applications Selection of Heat Exchangers BASIC DESIGN METHODS OF HEAT EXCHANGERS Introduction Arrangement of Flow Path in Heat Exchangers Basic Equations in Design Overall Heat Transfer Coefficient The LMTD Method for Heat Exchangers Analysis The e-NTU Method for Heat Exchangers Analysis Heat Exchanger Design Calculation Variable Overall Heat Transfer Coefficient Heat Exchanger Design Methodology FORCED CONVECTION CORRELATIONS FOR SINGLE-PHASE SIDE OF HEAT EXCHANGERS Introduction Laminar Forced Convection The Effect of Variable Physical Properties Turbulent Forced Convection Turbulent Flow in Smooth Straight Noncircular Ducts The Effect of Variable Physical Properties in Turbulent Forced Convection Summary of Forced Convection in Straight Ducts Heat Transfer from Smooth-Tube Bundles Heat Transfer in Helical Coils and Spirals Heat Transfer in Bends HEAT EXCHANGER PRESSURE DROP AND PUMPING POWER Introduction Tube-Side Pressure Drop Pressure Drop in Tube Bundles in Cross-Flow Pressure Drop in Helical and Spiral Coils Pressure Drop in Bends and Fittings Pressure Drop for Abrupt Contraction, Expansion, and Momentum Change Heat Transfer and Pumping Power Relationship FOULING OF HEAT EXCHANGERS Introduction Basic Considerations Effects of Fouling Aspects of Fouling Design of Heat Exchangers Subject to Fouling Operation of Heat Exchangers Subject to Fouling Techniques to Control Fouling DOUBLE-PIPE HEAT EXCHANGERS Introduction Thermal and Hydraulic Design of Inner Tube Thermal and Hydraulic Analysis of Annulus Parallel-Series Arrangements of Hairpins Total Pressure Drop Design and Operational Features DESIGN CORRELATIONS FOR CONDENSERS AND EVAPORATORS Introduction Condensation Film Condensation on a Single Horizontal Tube Film Condensation on Tube Bundles Condensation Inside Tubes Flow Boiling SHELL-AND-TUBE HEAT EXCHANGERS Introduction Basic Components Basic Design Procedure of a Heat Exchanger Shell-Side Heat Transfer and Pressure Drop COMPACT HEAT EXCHANGERS Introduction Heat Transfer and Pressure Drop THE GASKETED-PLATE HEAT EXCHANGERS Introduction Mechanical Features Operational Characteristics Passes and Flow Arrangements Applications Heat Transfer and Pressure Drop Calculations Thermal Performance CONDENSERS AND EVAPORATORS Introduction Shell and Tube Condensers Steam Turbine Exhaust Condensers Plate Condensers Air Cooled Condensers Direct Contact Condensers Thermal Design of Shell-and-Tube Condensers Design and Operational Considerations Condensers for Refrigeration and Air Conditioning Evaporators for Refrigeration and Air Conditioning Thermal Analysis Standards for Evaporators and Condensers APPENDICES Physical Properties of Metals and Nonmetals Physical Properties of Air, Water, Liquid Metals, and Refrigerants Each chapter also contains sections of Nomenclature, References, and Problems

Performance of plate finned tube heat exchangers under dehumidifying conditions

Abstract: Systematic studies of continuous fin-and-tube tube heat exchangers under dehumidifying conditions are reported in the present study. The heat exchangers consist of nine fin-and-tube heat exchangers having plane fins. The effects of fin spacing, the number of tube row, and inlet conditions are investigated. Data are presented in terms of j factors and friction factors f . It is found that the inconsistencies in the open literature may be associated with the wet fin efficiency. A correlation is proposed for the present plate fin configuration; this correlation can describe 92 percent of j , and 91 percent of the f data within ±10 percent.

Heat exchanger for electronic equipment

Abstract: A heat transfer apparatus is disclosed The heat transfer apparatus includes a heat pipe containing heat transfer liquid Disposed in the heat pipe is a centrifugal rotor assembly having fixed magnets on the rotor blades A magnetic field is generated by a magnetic coil assembly that surrounds the heat pipe The rotor assembly rotates in response to the magnetic field, agitating the heat transfer liquid A second embodiment is a liquid heat transfer system that includes a heat absorption chamber, a pump, and a heat exchanger where circulation and cooling of the heat transfer liquid occurs outside of the heat absorption chamber

Experiments and Analyses of Flat Miniature Heat Pipes

Abstract: Two flat copper-water axially grooved miniature heat pipes are fabricated employing the electric-discharge-machining (EDM) wire-cutting method. Because of the advantage of the EDM method, axial grooves are provided around the entire interior perimeters of the miniature heat pipes. The two miniature heat pipes are tested under different heat inputs, cooling temperatures, and orientations. The maximum heat transfer rate for the heat pipes tested is about 40 W, and the maximum heat flux achieved is about 20 W/cm 2 , based on the outer surface of the evaporator. The effective thermal conductance of the heat pipe is on the order of 40 times that of copper based on the external cross-sectional area of the miniature heat pipe. If the effective thermal conductance is evaluated based on the interior cross-sectional area of the heat pipe, it can be 100 times higher than the thermal conductivity of copper. Analyses for heat-pipe limitations are also performed based on certain analytical relations. It is found that the capillary limit is the dominant heat transfer limitation for the miniature heat pipes tested in this paper. To improve the accuracy of the analytical model, the hydraulic radius in the capillary limit is corrected using the exact two-dimensional solutions found in the literature, and the expression for the friction factor that takes into account the shear stress at the liquid/vapor interface is adopted. The analytical results based on these modifications are compared with corresponding experimental results with good agreement.

Pressure drop on the shell side of shell-and-tube heat exchangers with segmental baffles

Abstract: A procedure is presented for evaluating the shell side pressure drop in shell-and-tube heat exchangers with segmental baffles. The procedure is based on correlations for calculating the pressure drop in an ideal tube bank coupled with correction factors, which take into account the influence of leakage and bypass streams, and on equations for calculating the pressure drop in a window section from the Delaware method. The proposed equations were checked by comparing experimental measurements available in the literature with the theoretical predictions. The ranges of the geometrical and operational parameters, for which the deviations between the experimental measurements and the theoretical predictions were within ± 35%, are presented in the paper

Heat Transfer and Friction Correlations for Wavy Plate Fin-and-Tube Heat Exchangers

Abstract: This paper deals with heat exchangers having plate fins of herringbone wave configuration. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of flow conditions and geometric variables of the heat exchanger. Correlations are provided for both staggered and in-line arrays of circular tubes. A multiple regression technique was used to correlate 41 wavy fin geometries by Beecher and Fagan (1987), Wang et al. (1995) and Beecher (1968). For the staggered layout, 92% of the heat transfer data are correlated within {+-}10%, and 91% of the friction data are correlated within {+-}15%.

The optimum thermal design of microchannel heat sinks

Abstract: A thermal resistance model was set up to analyse the flow and heat transfer in microchannel heat sinks. Laminar, turbulent, developed and developing flow and heat transfer were considered in the analysis. Optimum thermal design of the heat sink was then studied using this model and a self-developed software package, where the influences of the heat sink's channel aspect ratio, fin width to channel width ratio, and the channel width on heat sink performance under three flow constraints-constant coolant volume flow rate, constant pressure drop and constant pumping power-were extensively investigated over wide flow and heat transfer regimes. This paper documents the modelling or analysis methodologies and the results of the investigation which include guidelines for the optimum thermal design of microchannel heat sinks.

Radiation and natural convection heat transfer from wire-and-tube heat exchangers in refrigeration appliances

Abstract: The air-side heat transfer from wire-and-tube heat exchangers of the kind widely used in small refrigeration appliances has been studied. Radiation and free-convection components have been separately investigated. The radiation component was theoretically computed using a diffuse, gray-body network with interactions between each part of the heat exchanger and the surroundings. For the free-convection heat transfer component, a semiempirical correlation was developed on the basis of experimental tests conducted on a set of 42 low-emittance exchangers with various geometrical characteristics. Comparisons between overall heat transfer predictions and a second, independent set of experiments on eight high-emittance exchangers showed satisfactory agreement. The proposed analysis is suitable either to determine the heat transfer performance of an existing (already sized) exchanger or to design a new one for prescribed heat duty and working temperatures.

A heat exchanger model for mixtures and pure refrigerant cycle simulations

Abstract: This paper describes a heat exchanger simulation developed for transient and steady state cycle simulations of mixtures and pure components. The simulation focuses on air to refrigerant condensers and evaporators found in residential heat pumps. The refrigerant differential momentum, continuity, species and energy equations are solved for these components and the steady state results are verified experimentally. Ten different heat transfer correlations for condensation and evaporation are evaluated to determine which best reproduces experimental data. Of those tested Jung and Radermacher's (1989, Int. J. Heat Mass Transfer 32 2435–2446) heat transfer correlation worked the best for evaporation while Dobson et al.'s (1994, ACRC Project 37) correlation worked the best for condensation. The experimentally determined capacity of four cross flow heat exchangers operating as condensers and evaporators with four different refrigerants is compared to the simulation results. The capacities predicted by the simulation agreed with the experimental results within ±8.0%. Furthermore, the simulation is used to quantify the effects of using a zeotropic mixture, R-407C, with cross, parallel and counter flow heat exchangers. As compared to a typical cross flow heat exchanger at typical heat pump operating conditions, the simulation predits that a pure parallel flow heat exchanger can decrease capacity by as much as 8.3% while a pure counter flow heat exchanger can increase performance by up to 4.4%.

Heat exchanger having microchannel tubing and spine fin heat transfer surface

Abstract: A heat exchanger for an air conditioner outdoor unit includes tubing of the microchannel type which is internally partitioned into separate, parallel refrigerant flow passages and a wrapping of heat conductive flexible heat transfer material, commonly known as spine fin. The heat exchanger provides for greater heat transfer and a more compact package. Further, such heat exchangers allow for a reduced refrigerant charge in the air conditioning unit in which they are used.

Transition from nucleate boiling to convective boiling in compact heat exchangers

Abstract: The boiling of pure fluids has been experimentally studied in several types of compact heat exchanger channels. Plate fin and corrugated heat exchangers have been studied (seven geometries). Controlling the flow parameters (mass flux and vapour quality), the heat flux and measuring the wall temperature, have allowed characterization of the local heat transfer coefficient. The results clearly show that the dominant mechanisms occurring could be nucleate or convective boiling. The transition between these two mechanisms depends on the flow characteristics and also on the channel geometry. Based on these measurements, an objective criteria can be established to identify the flow boiling regime. The knowledge of such a criteria is useful if we want to extend the use of compact heat exchanger to boiling of mixtures.

Advances in Thermal Design of Heat Exchangers: A Numerical Approach: Direct-sizing, Step-wise rating, and Transients

Abstract: Preface Chapter 1: Classification 1.1 Class definition 1.2 Exclusions and extensions 1.3 Helical-tube, multi-start coil 1.4 Plate-fin exchangers 1.5 RODbaffle 1.6 Helically twisted flattened tube 1.7 Spirally wire-wrapped 1.8 Bayonet tube 1.9 Wire-woven heat exchangers 1.10 Porous matrix heat exchangers 1.11 Some possible applications Chapter 2: Fundamentals 2.1 Simple temperature distributions 2.2 Log mean temperature difference 2.3 LMTD-Ntu rating problem 2.4 LMTD-Ntu sizing problem 2.5 Link between Ntu values and LMTD 2.6 The 'theta' methods 2.7 Effectiveness and number of transfer units 2.8 1-Ntu rating problem 2.9 1-Ntu sizing problem 2.10 Comparison of LMTD-Ntu and 1-Ntu approaches 2.11 Sizing when Q is not specified 2.12 Optimum temperature profiles in contraflow 2.13 Optimum pressure losses in contraflow 2.14 Compactness and performance 2.15 Required values of Ntu in cryogenics 2.16 To dig deeper 2.17 Dimensionless groups Chapter 3: Steady-State Temperature Profiles 3.1 Linear temperature profiles in contraflow 3.2 General cases of contraflow and parallel flow 3.3 Condensation and evaporation 3.4 Longitudinal conduction in contraflow 3.5 Mean temperature difference in unmixed crossflow 3.6 Extension to two-pass unmixed crossflow 3.7 Involute-curved plate-fin exchangers 3.8 Longitudinal conduction in one-pass unmixed crossflow 3.9 Determined and undetermined crossflow 3.10 Possible optimization criteria 3.11 Cautionary remark about core pressure loss 3.12 Mean temperature difference in complex arrangements 3.13 Exergy destruction Chapter 4: Direct-Sizing of Plate-Fin Exchangers 4.1 Exchanger lay-up 4.2 Plate-fin surface geometries 4.3 Flow-friction and heat-transfer correlations 4.4 Rating and direct-sizing design software 4.5 Direct-sizing of an unmixed crossflow exchanger 4.6 Concept of direct-sizing in contraflow 4.7 Direct-sizing of a contraflow exchanger 4.8 Best of rectangular and triangular ducts 4.9 Best small, plain rectangular duct 4.10 Fine-tuning of ROSF surfaces 4.11 Overview of surface performance 4.12 Headers and flow distribution 4.13 Multi-stream design (cryogenics) 4.14 Buffer zone or leakage plate 'sandwich' 4.15 Consistency in design methods 4.16 Geometry of rectangular offset strip fins 4.17 Compact fin surfaces generally 4.18 Conclusions Chapter 5: Direct-Sizing of Helical-Tube Exchangers 5.1 Design framework 5.2 Consistent geometry 5.3 Simplified geometry 5.4 Thermal design 5.5 Completion of the design 5.6 Thermal design results for t/d =1.346 5.7 Fine tuning 5.8 Design for curved tubes 5.9 Discussion 5.10 Part-load operation with by-pass control 5.11 Conclusions Chapter 6: Direct-Sizing of Bayonet-Tube Exchangers 6.1 Isothermal shell-side conditions 6.2 Evaporation 6.3 Condensation 6.4 Design illustration 6.5 Non-isothermal shell-side conditions 6.6 Special explicit case 6.7 Explicit solution 6.8 General numerical solutions 6.9 Pressure loss 6.10 Conclusions Chapter 7: Direct-Sizing of RODbaffle Exchangers 7.1 Design framework 7.2 Configuration of the RODbaffle exchanger 7.3 Approach to direct-sizing 7.4 Flow areas 7.5 Characteristic dimensions 7.6 Design correlations 7.7 Reynolds numbers 7.8 Heat transfer 7.9 Pressure loss tube-side 7.10 Pressure loss shell-side 7.11 Direct-sizing 7.12 Tube-bundle diameter 7.13 Practical design 7.14 Generalized correlations 7.15 Recommendations 7.16 Other shell-and-tube designs 7.17 Conclusions Chapter 8: Exergy Loss and Pressure Loss Exergy loss 8.1 Objective 8.2 Historical development 8.3 Exergy change for any flow process 8.4 Exergy loss for any heat exchangers 8.5 Contraflow exchangers 8.6 Dependence of exergy loss number on absolute temperature level 8.7 Performance of cryogenic plant 8.8 Allowing for leakage 8.9 Commercial considerations 8.10 Conclusions Pressure loss 8.11 Control of flow distribution 8.12 Header design 8.13 Minimizing effects of flow maldistribution 8.14 Embedded heat exchangers 8.15 Pumping power Chapter 9: Transients in Heat Exchangers 9.1 Review of solution methods - contraflow 9.2 Contraflow with finite differences 9.3 Further considerations 9.4 Engineering applications - contraflow 9.5 Review of solution methods - crossflow 9.6 Engineering applications - crossflow Chapter 10: Single-Blow Test Methods 10.1 Features of the test method 10.2 Choice of theoretical model 10.3 Analytical and physical assumptions 10.4 Simple theory 10.5 Relative accuracy of outlet response curves in experimentation 10.6 Conclusions on test methods 10.7 Practical considerations 10.8 Solution by finite differences 10.9 Regenerators Chapter 11: Heat Exchangers in Cryogenic Plant 11.1 Background 11.2 Liquefaction concepts and components 11.3 Liquefaction of nitrogen 11.4 Hydrogen liquefaction plant 11.5 Preliminary direct-sizing of multi-stream heat exchangers 11.6 Step-wise rating of multi-stream heat exchangers 11.7 Future commercial applications 11.8 Conclusions Chapter 12: Heat Transfer and Flow Friction in Two-Phase Flow 12.1 With and without phase change 12.2 Two-phase flow regimes 12.3 Two-phase pressure loss 12.4 Two-phase heat-transfer correlations 12.5 Two-phase design of a double-tube exchanger 12.6 Discussion 12.7 Aspects of air conditioning 12.8 Rate processes Appendix A: Transient Equations with Longitudinal Conduction and Wall Thermal Storage A.1 Mass flow and temperature transients in contraflow A.2 Summarized development of transient equations for contraflow A.3 Computational approach Appendix B: Algorithms And Schematic Source Listings B.1 Algorithms for mean temperature distribution in one-pass unmixed crossflow B.2 Schematic source listing for direct-sizing of compact one-pass crossflow exchanger B.3 Schematic source listing for direct-sizing of compact contraflow exchanger B.4 Parameters for rectangular offset strip fins B.5 Longitudinal conduction in contraflow B.6 Spline-fitting of data B.7 Extrapolation of data B.8 Finite-difference solution schemes for transients Supplement to Appendix B - Transient Algorithms Appendix C: Optimization of Rectangular Offset Strip, Plate-Fin Surfaces C.1 Fine-tuning of rectangular offset strip fins C.2 Trend curves C.3 Optimization graphs C.4 Manglik & Bergles correlations Appendix D: Performance Data for RODbaffle Exchangers D.1 Further heat-transfer and flow-friction data D.2 Baffle-ring by-pass Appendix E: Proving the Single-Blow Test Method - Theory and Experimentation E.1 Analytical approach using Laplace transforms E.2 Numerical evaluation of Laplace outlet response E.3 Experimental test equipment Appendix F: Most Efficient Temperature Difference in Contraflow F.1 Calculus of variations F.2 Optimum temperature profiles Appendix G: Physical Properties of Materials and Fluids G.1 Sources of data G.2 Fluids G.3 Solids Appendix H: Source Books on Heat Exchangers H.1 Texts in chronological order H.2 Exchanger types not already covered H.3 Fouling - some recent literature Appendix I: Creep Life of Thick Tubes I.1 Applications I.2 Fundamental equations I.3 Early work on thick tubes I.4 Equivalence of stress systems I.5 Fail-safe and safe-life I.6 Constitutive equations for creep I.7 Clarke's creep curves I.8 Further and recent developments I.9 Acknowledgements Appendix J: Compact Surface Selection for Sizing Optimization J.1 Acceptable flow velocities J.2 Overview of surface performance J.3 Design problem J.4 Exchanger optimization J.5 Possible surface geometries Appendix K: Continuum Equations K.1 Laws of continuum mechanics K.2 Coupled continuum theory K.3 De-coupling the balance of energy equation Appendix L: Suggested Further Research L.1 Sinusoidal-lenticular surfaces L.2 Steady-state crossflow L.3 Header design L.4 Transients in contraflow Appendix M: Conversion Factors Notation Commentary Chapter 2: Fundamentals Chapter 3: Steady-state temperature profiles Chapter 4: Direct-sizing of plate-fin exchangers Chapter 5: Direct-sizing of helical-tube exchangers Chapter 6: Direct-sizing of bayonet-tube exchangers Chapter 7: Direct-sizing of RODbaffle exchangers Chapter 8: Exergy loss and pressure loss Chapter 9: Transients in heat exchangers Chapter 10: Single-blow test methods Chapter 11: Heat exchangers in cryogenic plant Chapter 12: Heat transfer and flow friction in two-phase flow Appendix A: Transient equations with longitudinal conduction and wall thermal storage Appendix I: Creep life of thick tubes Index

An Experimental Investigation of Convective Heat Transfer From Wire-On-Tube Heat Exchangers

Abstract: An experimental investigation of the air-side convective heat transfer from wire-on-tube heat exchangers is described. The study is motivated by the desire to predict the performance, in a forced flow, of the steel wire-on-tube condensers used in most refrigerators. Previous investigations of wire-on-tube heat exchangers in a forced flow have not been reported in the literature. The many geometrical parameters (wire diameter, tube diameter, wire pitch, tube pitch, etc.), the complex conductive paths in the heat exchanger, and the importance of buoyant forces in a portion of the velocity regime of interest make the study a formidable one. A key to the successful correlation of the experimental results is a definition of the convective heat transfer coefficient, h w , that accounts for the temperature gradients in the wires as well as the vast difference in the two key characteristic lengths-the tube and wire diameters. Although this definition results in the need to solve a transcendental equation in order to obtain h w from the experimental data, the use of the resulting empirical correlation is straightforward. The complex influence of the mixed convection regime on the heat transfer from wire-on-tube heat exchangers is shown, as well as the effects of air velocity and the angle of attack. The study covers a velocity range of 0 to 2 m/s (the Reynolds number based on wire diameter extends to 200) and angles of attack varying from 0 deg (horizontal coils) to ±90 deg. Heat transfer data from seven different wire-on-tube heat exchangers are correlated so that 95 percent of the data below a Richardson number of 0.004, based on the wire diameter, lie within ±16.7 percent of the proposed correlation.

Dehumidifier having two heat exchangers

Abstract: A pair of heat exchangers of generally cylindrical shape are coaxially coupled to the opposite ends of a cylindrical air-water separator. Each heat exchanger has a stack of heat transfer disks brazed together to define two alternating sets of intercommunicating flow paths. The first set of flow paths of the first heat exchanger receives high-temperature, high-humidity air under pressure, which is precooled by low-temperature, low-humidity air flowing to the second set of flow paths from the air-water separator. The precooled high-humidity air is directed through an internal passageway in the separator into the second heat exchanger, in which the air is cooled by heat exchange with a coolant. The cooled high-humidity air is then directed into the separator for reduction of the moisture. The low-temperature, low-humidity air is then afterheated by precooling the incoming high-temperature, high-humidity air in the first heat exchanger, for subsequent delivery to a load.