Matrix Heat Exchanger Research Articles

The thermal modeling of a matrix heat exchanger using a porous medium and the thermal non-equilibrium model

Heat transfer and fluid flow characteristics through a porous medium were investigated using numerical simulations and experiment. For the numerical simulations two models were created: a two-dimensional numerical model and a Fluent™ computational fluid dynamics (CFD) porous media model. The experimental investigation consisted of a flow channel with a porous medium section that was heated from below by a heat source. The results of the numerical models were compared to the experimental data in order to determine the accuracy of the models. The numerical model was then modified to better simulate a matrix heat exchanger. This numerical model then generated temperature profiles that were used to calculate the heat transfer coefficient of the matrix heat exchanger and develop a correlation between the Nusselt number and the Reynolds number.

Simulation Algorithm for Multistream Plate Fin Heat Exchangers Including Axial Conduction, Heat Leakage, and Variable Fluid Property

The effect of axial conduction through heat exchanger matrix, heat exchange with the surroundings, and variable fluid properties are included in the simulation algorithm of multistream plate fin heat exchangers. The procedure involves partitioning of the exchanger in both axial and normal directions, writing conservation equations for each segment, and solving them using an iterative procedure. In the normal direction, the exchanger is divided into a stack of overlapping two-stream exchangers interacting through their common streams. In the axial direction, the exchanger is successively partitioned to 2k segments, the final value of k being determined by the point where further partitioning has only marginal effect. The effects of axial conduction, heat leakage, and variable fluid properties are illustrated with the help of multistream heat exchanger examples solved by the above-mentioned technique.

An analytical model of a matrix heat exchanger with longitudinal heat conduction in the matrix in application for the exchanger dynamics research

The paper presents an analytical method for the solution of the problem of a fixed matrix heat exchanger with axial heat conduction within the matrix. The small parameter method and Laplace transform have been applied. A general solution has been obtained for the unsteady state in the form of function series, using single and double convolutions of functions, as well as a particular solution for both the uniform and non-uniform initial temperature of the matrix and for an arbitrary function of the fluid temperature at the inlet. Particular solutions have been used in the study of the matrix dynamics in determining dynamic characteristics for the standard input signals in the form of: Dirac δ pulse, Heaviside function and the function of sinusoidal variable temperature of the fluid at the inlet. The results obtained both illustrate and enable the assessment of the effect of axial heat conduction in the matrix on the dynamic properties of the heat exchanger.

Compact Tubular Ceramic Heat Exchangers ForMicro Gas Turbine Engines

Skid-mounted power plants have been finding ever-widening application on the power generation market [1]. Flexibility, compactness and the light weight of small GTEs promote their use as the main components of such power generating plants. However, to increase their cost-effectiveness, a notable elevation of the working media parameters is a must. What constrains the above elevation is the problems of reliability and durability of operation of hot parts of the turbine which need to be cooled but, first and foremost, it is a degradation of the effectiveness of the small-size blades for compressors and turbines. Furthermore, at turbine cooling, a power is consumed which is connected with heat removal and, also, the power consumption for treatment and circulation of the cooling agent tends to increase as well. This results in an extra lowering of the level of the temperature increase effectiveness and restriction of the critical costeffectiveness of a GTE. Findings of the convective heat transfer and hydraulic resistance studies in the internal path of the path of the high-temperature gas ceramic cooler are presented. It was demonstrated that the application of the combined technique of heat exchange enhancement using a string of ballturbolators separated by fin inserts allows an increase in the compactness factor for the heat exchanger matrix up to 400-600 m/m.

Optimization of Matrix Heat Exchanger Geometry

Matrix heat exchangers are used in a number of applications such as helium liquefiers, sorption refrigerators, and in Kleemenko cryocoolers. In this paper the methods for the optimum sizing of balanced flow and unbalanced flow matrix heat exchangers of rectangular and circular shapes are presented. Using the methods developed, the relative size of matrix heat exchangers of rectangular and circular shapes are compared. [S0022-1481(00)01503-6]

Mixed Convection in a Horizontal Porous Duct With a Sudden Expansion and Local Heating From Below

Results are reported for an experimental and numerical study of forced and mixed convective heat transfer in a liquid-saturated horizontal porous duct. The cross section of the duct has a sudden expansion with a heated region on the lower surface downstream and adjacent to the expansion. Within the framework of Darcy’s formulation, the calculated and measured Nusselt numbers for 0.1 < Pe < 100 and 50 < Ra < 500 are in excellent agreement. Further, the calculated Nusselt numbers are very close to those for the bottom-heated flat duct. This finding has important implications for convective heat and mass transfer in geophysical systems and porous matrix heat exchangers. The calculations were also carried out for glass bead-packed beds saturated with water using non-Darcy’s formula. The streamlines in the forced convection indicate that, even with non-Darcy effects included, recirculation is not observed downstream of an expansion and the heat transfer rate is decreased but only marginally.

Transient testing of perforated plate matrix heat exchangers

Till recently, perforated plate matrix heat exchangers (MHEs) were used mainly in helium liquefaction systems and Brayton cycle refrigerators. Currently they are also being used in Kleemenko or J-T refrigerators operating with a mixture of gases. It is now well understood that the effectiveness of a MHE is strongly dependent on the number of plate–spacer pairs used. It has also been shown that the traditional methods used for reducing the transient single blow method to determine the heat transfer coefficients cannot be used for MHEs. In this paper we show that the traditional methods can indeed be used for determining the heat transfer coefficients using the transient testing methods, provided certain conditions are met.

Transient response of perforated plate matrix heat exchangers

Perforated plate matrix heat exchangers are used in a number of applications such as helium liquefiers, Joule–Thompson cryocoolers operating with pure fluids and mixtures, etc. The time taken for cool down of cryocoolers is very critical in many applications, for example, those used in mobile applications (e.g. missiles). In this paper we study the effect of different parameters on the transient response of perforated plate matrix heat exchangers.

Application of matrix heat exchangers to thermomechanical exergy recovery from liquid hydrogen

This paper reports the outcome of a project aimed at exploring thermomechanical exergy recovery from liquid hydrogen. The basis of this project was the conceptual design, development and testing of a new process for CO 2 removal from air for use in alkaline fuel cells operating with hydrogen stored as a liquid, addressing simultaneously: • thermomechanical exergy recovery from liquid hydrogen, and • its application to CO 2 removal from atmospheric air. This project was an attempt to address these issues by using the cooling available from the vaporisation of liquid hydrogen and/or boil-off vapour, to remove CO 2 from the alkaline fuel cell feed air by refrigeration purification, ie. by freezing the CO 2 out of the air. A schematic description of the process and an energy balance for refrigeration purification for the CO 2 removal are presented, showing that the process relies on high effectiveness heat exchangers and water re-vaporisation. The high effectiveness heat transfer is achieved using perforated plate matrix heat exchangers. Implicit in this work were: • The development of a new sizing procedure for matrix heat exchangers based on an approximate analytical solution for their performance, published recently in this journal. • The development of a new method for construction of perforated plate matrix heat exchangers. • Experimental testing of matrix heat exchanger performance. • The application of matrix heat exchangers to mass transfer, and their use as reversing heat exchangers. Certain questions relating to the recent analysis published in this journal are raised and modifications suggested. Experimental results of heat exchanger effectiveness tests and CO 2 removal tests showed that heat exchangers of the requisite effectiveness were designed and manufactured, and that the proposed process was successful in exergy recovery and CO 2 removal

Discussion: “Analysis of Matrix Heat Exchanger Performance” (Venkatarathnam, G., and Sarangi, S., 1991, ASME J. Heat Transfer, 113, pp. 830–836)

Recently, a new numerical scheme for solving the equations governing matrix heat exchanger thermal performance was published in this journal. It was found that this scheme does not include the full effect of longitudinal heat transfer in the said heat exchangers. This effect is demonstrated by correcting the parameter related to longitudinal heat transfer in the approximate analytical solution for the balanced flow case and finding it to deviate considerably from the numerically calculated result.

Closure to “Discussion of ‘Analysis of Matrix Heat Exchanger Performance’” (1998, ASME J. Heat Transfer, 120, pp. 801–803)

Closure to “Discussion of ‘Analysis of Matrix Heat Exchanger Performance’” (1998, ASME J. Heat Transfer, 120, pp. 801–803)

Carbon dioxide removal from air for alkaline fuel cells operating with liquid hydrogen — A synergistic advantage

This paper reports the outcome of a project undertaken to explore the synergistic use of alkaline fuel cells and liquid hydrogen. An experimental program was conducted to develop and test a system to address simultaneously: • thermomechanical exergy recovery from liquid hydrogen; • the need to remove CO 2 from air so that the purified air can be used in hydrogen-air alkaline fuel cells. An earlier paper by Ahuja and Green (Ahuja, V. and Green, R., International Journal of Hydrogen Energy, 1996, 21(5), 415-121) discussed the use of thermomechanical exergy recovery in CO 2 removal from air for alkaline fuel cells operating with hydrogen stored as liquid. An energy balance for refrigeration purification for the CO 2 removal, a schematic description of the process, and an overview of the thermal analysis of matrix heat exchangers were presented. These were used to show that the proposed process of CO 2 removal by refrigeration purification using thermomechanical exergy recovery from liquid hydrogen depended on very high effectiveness heat exchangers. Results of heat exchanger effectiveness tests were given to show that heat exchangers of the requisite effectiveness could be built. This paper presents results from the experimental program used to evaluate this CO 2 removal process. Results of tests on CO 2 removal, the use of a reversing heat exchanger to process natural humidity, regeneration of the heat exchanger where CO 2 is removed, pressure drop, single heat exchanger and overall system effectiveness, are shown. The results establish that a regenerable process for CO 2 removal from alkaline fuel cell feed air by refrigeration purification, using the cooling available from thermomechanical exergy recovery from liquid hydrogen, is achievable.

Manufacture of a matrix heat exchanger by diffusion bonding

The solid-state diffusion bonding technique is employed to manufacture a matrix heat exchanger made of cooper and stainless steel. The matrix heat exchanger so fabricated has good strength, leak tightness and free flow of the heat-exchanging fluids.

Composite material for construction of matrix heat exchangers

Composite material for construction of matrix heat exchangers

CO 2 removal from air for alkaline fuel cells operating with liquid hydrogen — Heat exchanger development

Two independent problems when using hydrogen as an energy source in vehicles are: (i) gaseous hydrogen boil-off from stored liquid hydrogen, its associated pressure rise and hence necessary venting; and (ii) CO 2 removal from air for hydrogen-air alkaline fuel cells. An experimental program has been undertaken to see if in a system using an alkaline fuel cell running on hydrogen stored as liquid, both these problems may be solved concurrently. For vehicular hydrogen storage the most suitable system in terms of low mass and volume, is cryogenic storage of liquid hydrogen. Unfortunately, with liquid hydrogen there is always a small amount of boil-off, which necessitates venting of gaseous hydrogen from the storage vessel. Vented boil-off is hazardous and wasteful, and so it is essential that it be rendered safe, and preferably utilized efficiently. For electrochemical power generation, alkaline fuel cells offer the highest efficiency, as well as the possibility of using electrocatalysts that do not include platinum. However, since they operate at low temperatures they do not support hydrogen production by reformation of carbonaceous fuels. Further, they are rendered inoperative by the CO 2 content of the (reformed) fuel and or air. Their application to vehicular use is impaired by this inability to use other than pure hydrogen and complexity of on-board CO 2 removal. This paper describes a novel and simple process whereby H 2 boil-off can be used to continuously sublime and remove CO 2 from air, prior to the purified air and hydrogen being supplied to an alkaline fuel cell. It includes a schematic description of the process and an energy balance for refrigeration purification for the CO 2 removal. It is shown that the process relies on high effectiveness heat exchangers and water re-vaporization. An overview of thermal analysis of matrix heat exchangers is presented along with experimental results of heat exchanger effectiveness tests, which indicate that heat exchangers of the required effectiveness are easily designed and manufactured.

Effectiveness- Ntu relationship in perforated plate matrix heat exchangers

Perforated plate matrix heat exchangers (MHEs), invented nearly 40 years ago, are finding increasing use in small cryogenic liquefaction and refrigeration systems. There are two different approaches for analysis of the performance of MHEs: (i) to consider the MHE as a conventional exchanger with the plate acting as a fin; and (ii) to treat the MHE as a discrete set of plate-spacer pairs, with the number of plates being a very important parameter. The latter approach involves numerical solution of governing equations. In this paper a simple analytical approach is presented for analysis of the performance and design of MHEs. Closed-form expressions are presented for the effectiveness of the MHE in terms of different resistances and a finite number of plates. It is shown analytically that the first approach is only a special case of the second approach and that the solutions obtained with the present method are very close to those obtained with complex numerical models (in the second approach).

An apparatus for the testing of small cryogenic heat exchangers

Most cryogenic processes demand high effectiveness heat exchangers. The performance of these exchangers is determined not only by convective heat transfer resistance, but also by other irreversibilities such as axial conduction, flow maldistribution, heat transfer with surroundings, and finite number of lateral heat transfer paths. While determination of heat transfer correlations for exchanger cores is sufficient in most conventional applications, high‐Ntu cryogenic exchangers must be tested under true operating conditions. As a part of our matrix heat exchanger development program, an apparatus has been constructed for testing small, compact heat exchangers at low temperature. The apparatus, enclosed in a vacuum vessel, provides a variable cold end temperature and means for direct measurement of ineffectiveness. Temperature approaches at both ends and pressure drop in both channels are also measured. The construction of the apparatus as well as the instrumentation and data acquisition methods are discussed. The results of a test on a small matrix heat exchanger using the test apparatus are also presented.

Heat Transfer Performance of Heat Exchanger with a Stacked-Sphere Matrix Formed by Diffusion Bonding.

A new type of heat exchanger with a stacked-sphere matrix is proposed. This heat exchanger comprises several segments separated by spacers. Each segment has a stacked copper sphere matrix formed by diffusion bonding. The ratio between the effective conductivity of the test heat exchanger matrix λe and the conductivity of copper λCu was 0.09. Experiments were conducted to ivestigate the heat transfer in the proposed heat exchanger. The following results were obtained. (1) The overall heat transfer coefficient of the proposed heat exchanger is about 5 times as high as that without diffusion bonding. (2) The friction factor of the proposed heat exchanger is about 1.5 times as high as that without diffusion bonding. (3) Calculated overall heat transfer coefficients are almost the same as measured overall heat transfer coefficients. (4) The heat exchanger effectiveness is constant for λe/λCu above 0.2.

Axial conduction in a thick-wall matrix heat exchanger

Solutions are developed for temperature distributions and ineffectiveness for a high Ntu matrix heat exchanger having simultaneous axial conduction in the single phase (matrix/fluid) flow channels and separating wall. A scale analysis of the governing equations shows a large disparity in length scales for the conduction and convection effects, thus indicating a singular perturbation problem. Solutions for both balanced and imbalanced flow are obtained by analytical methods with appropriate scaling so that all terms of the solution are well behaved in the limit of large Ntu. The limiting cases of only wall conduction and only matrix conduction are treated, the results from which are favourably compared with past works. Ineffectiveness resulting from simultaneous matrix and wall conduction from the present work is compared with a traditional heat exchanger model for axial conduction. Good agreement is found for only small ratios of axial and wall conductance to Ntu. Finally, the results are compared with earlier laboratory data. These data are found to be bracketed from below by the results of this work and, from above, by an earlier model for high Ntu performance which neglected axial conduction.

Experimental prediction of heat transfer coefficients by use of a double-blow method

A new method is proposed for evaluating heat transfer coefficients in a heat exchanger matrix. In comparison with the well known single-blow method, a new double-blow method offers prediction of heat transfer coefficients on both sides of the heat exchanger wall by using one run only, because temperatures of both fluids flowing through the heat exchanger matrix are changed and measured.