Heat Exchanger Core Research Articles

Boiling Refrigerant Type Panel Cooler. Refrigerant Circulation and Cooling Performance.

We have developed a new compact boiling refrigerant type panel cooler. It is a kind of closed two-phase loop thermosyphon constructed with heat exchanger cores for automobile air conditioning system. We confirmed higher performance of the natural refrigerant circulation type and tried to optimize the size of the refrigerant path in the boiling core by observing the internal refrigerant flow and successfully achieved much higher cooling performance.

Entropy generation minimization in parallel-plates counterflow heat exchangers

This paper shows that the main architectural features of a counterflow heat exchanger can be determined based on thermodynamic optimization subject to volume constraint. It is assumed that the channels are formed by parallel plates, the two fluids are ideal gases, and the flow is fully developed, laminar or turbulent. In the first part of the paper, it is shown that the irreversibility of the heat exchanger core is minimized with respect to (1) the ratio of the two-channel spacings, and (2) the total heat transfer area between the two streams. In the second part, the entropy generation rate also accounts for the irreversibility due to discharging the spent hot stream into the ambient. It is shown that the design can be optimized with respect to (1), (2) and (3) the ratio of the capacity rates of the two streams. The optimized features of the geometry are robust with respect to whether the external discharge irreversibility is included in the entropy generation rate calculation. Copyright © 2000 John Wiley & Sons, Ltd.

Fluidized tube heat exchanger

The presence of solid particles in a heat exchanger is important in keeping the surface clean, thus having a beneficial effect on heat transfer. Solids circulation in the system can be provided by means of a recycle tube mounted in the central core of the heat exchanger. In this study a pilot scale fluidized tube heat exchanger system which consists of six fluidization tubes together with the centrally located recycling tube was constructed and pressure drop, liquid-wall and solid-wall friction forces and the effects of the amount of solids introduced to the system on heat transfer were investigated. Experimental results indicate that although the recycle tube causes an approximately 35% decrease in the heat transfer coefficient when no solid is used, the presence of the solids in the system increases the heat transfer coefficient by about 45% above that of the solids-free system.

Transient Response of a Cross-Flow Charge Air Intercooler and Its Influence on Engine Operation

To examine the influence of intercooler thermal inertia on transient engine operation, a 2D model of an air-to-air, cross-flow heat exchanger has been developed. Finned passages of heat exchanger core have been subdivided into separate channels of charge and cooling air, respectively. A two-step Lax-Wendroff differential method has been used to solve one-dimensional, nonhomentropic, unsteady, compressible fluid flow in each channel. Simultaneously, the Saul’yev explicit method has been applied to compute the 2D temperature distribution along the dividing plate. The Wieting correlation has been used to compute the local convection heat transfer coefficient and friction factor. The model has been verified against steady-state experimental data and then incorporated into an engine cycle simulation program based on “Filling-Emptying” method. Two engine transients have been simulated; the acceleration of the engine from idle to rated engine speed at constant load, and deceleration from rated power to rated torque by increasing the load torque. The first example shows the warming up of the intercooler, while in the second example intercooler temperatures are decreasing. The results have been compared with the predictions of an additional set of simulations, where the NTU-effectiveness method has been used to simulate the intercooler, and the thermal inertia of intercooler has been neglected. The results of both sets of simulations are discussed in the paper. [S0022-0434(00)02003-7]

5538073 Balanced dual flow regenerator heat exchanger system and core driving system

5538073 Balanced dual flow regenerator heat exchanger system and core driving system

95/05111 Gas installation pipework, boosters and compressors on industrial and commercial premises

In this paper, a mathematical model is developed to quantitatively evaluate the effect of flow maldistribution in a multi-channel heat exchanger. A computational fluid dynamics (CFD) technology is used to obtain the fluid distribution in the core of heat exchanger, taking into account the effects of gross passages, headers and distributors, etc. Based on the CFD simulation profile, a heat exchanger model is then developed. A parallel plate-fin heat exchanger with N flow passages is divided into N sub-exchangers when only one fluid is in maldistribution mode or 2N-1 sub-exchangers when both fluids are in nonuniformity modes to guarantee the uniform flow patterns in each sub-exchanger. Based on ε-NTU theory, the effectiveness of the heat exchanger is calculated by modeling the heat exchanger as a parallel coupling of the sub-exchangers. The core pressure drop of the whole heat exchanger is taken as the average pressure drop of the sub-exchangers. The mathematical model combining with the achieved flow distribution was utilized to investigate the performance of the heat exchanger with conventional header configurations, a punched baffle header configuration and a quasi-S header configuration, respectively. Results indicated that a good synergy of flow rates for both cold and hot fluids in the adjacent sub-exchangers can effectively reduce effectiveness deterioration. The performance of the heat exchanger is improved by using the improved header configurations. And the performance with a quasi-S header configuration is the best. The proposed mathematical model provides a theoretical basis for multi-channel heat exchangers in solving the problem of flow maldistribution.

Experimental investigation of highly effective plate-fin heat exchanger surfaces

Results are presented of an experimental investigation of a new convective rational heat transfer augmentation law in plate-fin heat exchanger surfaces. This law is characterized by Nu/Nu sm ≥ ξ/ξ sm by comparing channels (heat transfer surfaces) with vortex promoters with similar smooth channels at equal Reynolds numbers. For experimental confirmation and investigation of this law, heat exchanger cores having three different plate-fin surfaces were developed and manufactured. Two surfaces are formed by short offset channels (interrupted surfaces) of equilateral triangular and rectangular cross sections. The third surface has channels of isosceles triangular cross sections, with transverse projections and grooves along the channel length direction. The experimental results and correlations are reported for the three surfaces. The experiments were conducted in a wind tunnel with specially developed precise instrumentation that ensured experimental uncertainties of δξ = ± 2.3% and δRe = 1.7% at a 0.997 confidence level. Analysis of the results indicated that the fundamental character and causes limiting rational heat transfer augmentation to Nu/Nu sm ≥ ξ/ξ sm depend upon the heat transfer surface configuration. This paper consolidates the author's research on the subject reported in the Russian language over the last 25 years.

247 フィンアンドチューブ熱交換器内の流れの可視化

In a heat exchanger, the behavior of air flow influences the peformance of heat transfer greatly. Understanding the flow will help in improving the peformance and the cost reduction in the system of the heat exchanger. The purpose of this study is to grasp the flow structure and its influence on the peformance of the heat transfer. Flow visualization test was conducted using scale up models of heat exchanger cores which were produced geometrically similar to the actual heat exchangers. By comparing the flow visualization results with those obtained by heat transfer test, the way how the flow in a core affects the heat transfer performance was disclosed.

Experimental study on heat transfer and pressure drop characteristics of four types of plate fin-and-tube heat exchanger surfaces

In this paper, air side heat transfer and pressure drop characteristics of twelve three-row plate fin-and-tube heat exchanger cores of four types of fin configurations have been experimentally investigated. The heat transfer and friction factor correlations for the twelve cores are provided in a wide range of Reynolds number. It is found that in the range of Reynolds number tested, the Nusselt number of the slotted fin surface is the largest and that of the plain plate fin is the lowest while the Nusselt numbers of two types of wavy fins are somewhere in between.

Compact liquid cooling system for small, moveable electronic equipment

A compact liquid cooling system has been evaluated in a benchmark of self-contained heat exchanger units that fit within small movable electronic equipment, such as PCs and workstations. The compact cooling system connects to a multichip module package via a pair of flexible stainless steel hoses. The system contains a fluid expansion chamber, a liquid-to-air heat exchanger core, a fan, and a pump and can operate entirely sealed. Pressures, package power dissipation, flow rate, and temperatures were recorded. The coolant liquid chosen for use in this system was 3M Fluorinert type FC-72, a chemically inert dielectric liquid. The 5.5 liter prototype system delivers 1.1 liter/min of FC-72. Test results showed the unit can remove up to 274 W of power dissipated with a 52 degrees C temperature difference between inlet liquid and air with a thermal resistance of 0.19 degrees C/W. Design improvements for a second generation system are proposed. >

Plots from Closed Solution for Plate Fin Heat Exchanger Core Volume

Abstract An equation for the core volume of two-fluid, flat plate, plate fin heat exchangers is put into closed form by using empirical relationships between j Re and f Re3. Fin effectiveness is included, and different core types may be used on the two sides of the exchanger. Although the equation cannot be solved explicitly, the results of an implicit solution for cross-flow cores may be plotted as volume/UA, with pumping power/UA on each side as independent variables. Using an additional fit of) versus Re, face area/flow for each side can be mapped on the same cross-flow plot, and plots for counterflow made. Such plots are useful for quickly indicating the relative volumes and shape of different core types for a given application and for system trade-off studies.

Analytical Solution of the Transient Response of Gas-to-Gas Crossflow Heat Exchanger With Both Fluids Unmixed

The dynamic response of a single-pass crossflow heat exchanger with both fluids unmixed to arbitrary time varying inlet temperatures of fluids is investigated analytically. The initial spatial temperature distribution of the heat exchanger core is arbitrary as well. Analytical solutions for temperature distributions of both fluids and the wall as well as the mean mixed fluid temperatures at the exit are presented. The solutions are found by using Laplace transform method and special functions in the form of series of modified Bessel functions.

A Transient Heat Exchanger Evaluation Test for Arbitrary Fluid Inlet Temperature Variation and Longitudinal Core Conduction

An improved version of the transient technique is described which utilizes a finite-difference model of the heat exchanger for the evaluation of an average hem transfer coefficient. The model, which can accommodate arbitrary inlet fluid temperature variation as well as longitudinal conduction in the heat exchanger core, is well suited for a computer-based data reduction procedure. The finite-difference model is validated by comparison with the predictions of exact solutions for a step change in inlet temperature. Actual tests on a core of known performance indicate that the overall accuracy of the technique can be within ± 2 percent.

A Study of the Flow Mechanisms Responsible for Heat Transfer Enhancement in Interrupted-Plate Heat Exchangers

Certain compact heat exchanger cores are modeled by assemblies of parallel plates. The heat transfer in these cores may be enhanced if the plate surfaces are interrupted. The results of an experimental study of the mechanisms responsible for enhancement are reported here along with quantitative measures of the magnitude of the enhancement and the pressure drop penalty incurred. The aim of this work is to identify the important parameters and provide guidelines for designers of heat transfer surfaces and to workers attempting to correlate experimental data. Arrays of parallel plates were tested in a wind tunnel. Fluid flow phenomena were identified using the Schlieren visualization technique. Three distinctly different flow regimes are found within cores composed of in-line plates. These are classified as steady, general unsteady, and periodic unsteady flows. The periodic unsteady flow is accompanied by the emission of a strong acoustic tone. The heat transfer performance of these cores was determined using a transient heating technique. The evolution of the enhancement and the associated changes in the flow regimes are documented over a range of Reynolds number as the streamwise spacing between in-line plates is increased from zero. The results of these experiments are used to interpret the measured performance of cores consisting of staggered arrays of parallel plates and of cores formed by assembling parallel-plate arrays so that alternate plates in the streamwise direction are perpendicular to each other.

One approach to irreversibility minimization in compact crossflow heat exchanger design

The minimum of enthalpy exchange irreversibility (EEI) as a selective criterion in heat exchanger design is considered. This concept is applied in the core sizing procedure of a compact crossflow heat exchanger for gas-to-gas application. This approach objectivizes, in the final analysis, the pressure drop choice in such a way that from the total set of possible heat exchanger core dimensions the thermodynamically optimal one is selected.

Three kinds of heat transfer augmentation in perforated surfaces

Heat exchanger cores, each consisting of a number of single or composite perforated plates separated by wooden spacers to form parallel flow channels, were tested in a subsonic wind tunnel. Three distinct types of augmentation in the heat transfer and friction loss performance have been identified: the transition-turbulent flow enhancement, the “second” laminar flow enhancement and the laminar flow enhancement. The first kind is observed to occur in the transition and turbulent flow regimes on low porosity surfaces [1]. The second type is detected in the “second” laminar flow regime on high porosity surfaces [2]. The present study has revealed the existence of the third pattern which occurs over the entire laminar flow region on low-porosity composite surfaces consisting of a short upstream section for producing vortices and a main section for heat transfer. An attempt is made to explain the enhancement mechanisms.

Fracture Strength and Thermal Shock Resistance of Thick And Thin-Wall Magnesium-Aluminum-Silicate Ceramic Heat Regenerators

Thin-wall regenerator cores offer the potential for higher effectiveness than comparable thick-wall cores. The fracture strength of magnesium-aluminum-silicate (MAS) ceramic heat-exchanger cores with wall thickness of 0.083 mm (0.003 in.) and 0.160 mm (0.006 in.) are compared. Thermal shock resistance calculations for these cores are also presented.

The Periodic Method for Testing Compact Heat Exchanger Surfaces

The regular periodic method for testing the heat transfer performance of heat exchanger cores is studied in detail. This method, which has received very limited attention in the past, has certain advantages over the more conventional steady-state technique. It is shown to be useful especially in testing matrix surfaces. A theoretical analysis is performed, forming the basis for the periodic method. Directions for use in the range 0.2 < Ntu < 50, an uncertainty analysis, and test results for 2.6 < Ntu < 36.6 are included. It is concluded that the periodic method has the major advantages of: a wide Ntu range, easily generated experimental temperature waves, and the accuracy of an integral technique.