Matrix Heat Exchanger Research Articles

Correlating Young's Modulus with High Thermal Conductivity in Organic Conjugated Small Molecules.

Attaining elevated thermal conductivity in organic materials stands as a coveted objective, particularly within electronic packaging, thermal interface materials, and organic matrix heat exchangers. These applications have reignited interest in researching thermally conductive organic materials. The understanding of thermal transport mechanisms in these organic materials is currently constrained. This study concentrates on N, N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), an organic conjugated crystal. A correlation between elevated thermal conductivity and augmented Young's modulus is substantiated through meticulous experimentation. Achievement via employing the physical vapor transport method, capitalizing on the robust C═C covalent linkages running through the organic matrix chain, bolstered by π-π stacking and noncovalent affiliations that intertwine the chains. The coexistence of these dynamic interactions, alongside the perpendicular alignment of PTCDI-C8 molecules, is confirmed through structural analysis. PTCDI-C8 thin film exhibits an out-of-plane thermal conductivity of 3.1±0.1Wm-1K-1, as determined by time-domain thermoreflectance. This outpaces conventional organic materials by an order of magnitude. Nanoindentation tests and molecular dynamics simulations elucidate how molecular orientation and intermolecular forces within PTCDI-C8 molecules drive the film's high Young's modulus, contributing to its elevated thermal conductivity. This study's progress offers theoretical guidance for designing high thermal conductivity organic materials, expanding their applications and performance potential.

Design, Fabrication, and Test of a Prototype of Matrix Heat Exchanger for Cryogenic Distillation of Hydrogen Isotopes

The following properties are needed to increase the efficiency of refrigeration, liquefaction, and cryogenic separation cycles: Heat exchangers must have high effectiveness doubled by high compactness; small temperature differences between incoming and outgoing flows must be ensured to increase efficiency; there must be a large heat transfer surface, relative to the volume of the heat exchanger, to minimize heat loss; there must be a high heat transfer rate to reduce the transfer area; there must be a small pressure drop to reduce compression costs; and there must be high reliability with minimal maintenance. All these properties are entirely fulfilled by the designed matrix heat exchangers (MHEs). This paper presents the results of the research program developed by the team of the Cryogenic Laboratory from INC-DTCI ICSI Ramnicu Valcea, which included procedural stages of the realization and preliminary results of the characterization of the MHE-type heat exchanger in a narrow range of values to achieve a proper solution for a heat exchanger to be used for cryogenic purposes, such as cooling the gas mixture at the entrance of a distillation column of hydrogen isotopes and running at low pressure (typically regimes of 0.5 to 2.0 bars) and flows. Within several experimental campaigns, different assembly and testing techniques of the matrix heat exchanger (MHE) prototype were performed to achieve numerical data for the temperature and pressure drops along the heat exchanger and to verify ANSYS Fluent numerical simulation results. The results showed that for the designed and tested MHE prototype, a temperature drop of up to almost 230 K can be obtained at the established parameters correlated with pressure losses within a few millibars (the maximum recorded pressure drop is 80 mbars), small dimensions (64 mm high), and accessible weight (up to 2000 g).

Особенности проектирования высокотемпературных пластинчатых теплообменников для малоразмерных газотурбинных двигателей

An increase in the fuel efficiency of small-sized gas turbine engines can be achieved by regenerating the heat of the turbine exhaust gases. A rational layout solution in this case is a turboshaft scheme, where the effective power is generated on the shaft of a free turbine, and the turbine exhaust gases are released into the environment without doing useful work. When creating a turboshaft engine with heat recovery, the concept of developing engine family on the base of unified gas-generator was considered. The concept involves the development of a modular system, where the addition or exclusion of individual large units allows changing the type of engine at minimal cost. The article presents the layout solution of a small-sized turboshaft gas turbine engine with heat recovery, developed on the basis of a unified gas-generator and using a gearbox to transfer effective power to a propeller or a rotor. A plate heat exchanger module with a corrugated heat exchange surface for a small-sized turboshaft gas turbine engine has been designed. The heat exchange matrix was developed using a complex techniques of computer-aided design, calculation and manufacture of plate heat exchangers. Some design features of high-temperature plate heat exchangers are identified, the most important of which is the non-uniformity of temperature fields in the heat exchange matrix. Taking into account the non-uniformity of temperature fields, the heat exchanger module is a collapsible structure allowing the replacement of the heat exchange matrix and providing compensation for thermal expansion of the heat exchanger elements. The designed plate heat exchanger module for a small turboshaft gas turbine engine will be manufactured and tested on the bench

Computational fluid dynamics modelling of expanded metal porous matrix heat exchangers for intensified carbon capture applications

Expanded Metal Porous Matrix Heat Exchangers (EM-PMHE) use a fin structure based on stacked sheets of expanded metal. This fin structure creates a three-dimensional flow that also enhances heat transfer. EM-PMHEs are of interest for potential applications in carbon-capture processes. Their compact design could intensify heat exchange processes in the amine absorption cycle. The transport properties of EM-PMHEs are also of interest for applications in rotating packed beds, where expanded metal can make an effective packing material. This work examines a EM-PMHE using computational fluid dynamics. The heat transfer prediction of the model is validated against experimental data from literature. A simple 1D model is also presented for comparison. The model is used to evaluate the potential of EM-PMHEs in amine-based carbon-capture applications. The modelling results indicate that EM-PMHEs could be used to achieve intercooling in the rotating packed bed absorber. This would allow amine concentrations to be increased to 70 wt% in the carbon-capture process, achieving 2x volume reduction in comparison to conventional amine concentrations. Elsewhere in the carbon-capture process, EM-PMHEs could also achieve an 10x size reduction in the lean/rich heat exchanger, a major item of plant equipment in the carbon capture process.

Gas Turbine Tubular Coilpipes Regenerators Optimized According to the Minimum Mass Criterion

The aim of this work is to determine the effect of the elements, which do not participate in heat transfer, on the mass of the regenerator of a gas turbine plant X, as well as to define the re-strictions that are imposed on the regenerator design based on the conditions of manufacturabil-ity, placement at the facility and transportability. This goal is achieved using an algorithm for finding rational geometric parameters of the heat exchange matrix with minimization of the re-generator mass by Newton's method. It has been determined that the mass of the heat exchange matrix can be 0.48–0.58 of the mass of the regenerator. This makes it necessary, even at the initial design stages, to take into account the effect of the above factors on the mass of the re-generator and the choice of the rational geometrical parameters. A significant result of the stud-ies performed is determination of the effect of dimensional restrictions and requirements for the shape of the regenerator to be increased in its mass. The values of the geometrical parameters of the heat exchange matrix were obtained, at which the mass of the regenerator takes on a mini-mum value. The significance of the work is that the obtained relationships between the mass of the regenerator and its geometry makes it possible to reduce the metal consumption of the regen-erator and the gas turbine plant, which allows designing the heat exchangers for power plants

PRELIMINARY DEVELOPMENT OF A CONCEPTUAL MODEL OF MATRIX HEAT EXCHANGER

While the basic principles of thermodynamics have remained the same, the necessity for heat exchangers to have good effectiveness in a small volume is constantly growing. Heat exchangers type Matrix Heat Exchanger (MHE), which can meet these requirements, does not have an optimal design variant for its use. These heat exchangers have been approached for 60 years, by many researchers, currently offering only an overview of the process. The mechanism of heat transfer in a matrix heat exchanger is complex, having three different thermal convection paths as well as thermal conduction through two different surfaces. This paper presents the simulations performed in ANSYS Workbench, combining all these heat transfer modes, for developing an optimal model of a perforated plate matrix heat exchanger, used for the pre-cooling of a hydrogen isotopes stream mixture, for purification purposes, as well as, for preparing the inlet temperature in cryogenic distillation columns of hydrogen isotopes.

Development of a high-effectiveness slotted plate cryogenic heat exchanger

High-effectiveness heat exchangers are a ubiquitous component of cryogenic systems, but their performance typically falls short of model-based expectations. The following paper summarizes modeling efforts of a heat exchanger designed to achieve an effectiveness in excess of 99% within a prescribed envelope of volume, weight, pressure drop, and operating conditions. Simulation efforts focus on employing minimal assumptions and accounting for many loss mechanisms to avoid overestimation of predicted effectiveness. Axial conduction and parallel passage flow imbalance are major contributing factors to heat exchanger inefficiency. Consequently, a staggered stacked slotted plate geometry, also known as a matrix heat exchanger, was chosen as the most promising type to achieve the desired effectiveness. High thermal conductivity, high surface area finned copper plates separated by low thermal conductivity, low cross-sectional area stainless steel spacers achieve high stream-to-stream heat transfer while limiting axial conduction and allowing for fluid redistribution between plates. The number of design parameters was reduced based on manufacturing limitations and conceptual reasoning. ANSYS Fluent computational fluid dynamics was used to form Nusselt number and Darcy friction factor correlations for the geometry and flow conditions. A finite difference MATLAB model accounted for axial conduction, parasitic heat loads, and material property variation with temperature and pressure. The Fluent-derived correlations were used as inputs to the MATLAB model. The MATLAB model was validated by comparing its results to an analytic, constant property effectiveness-NTU solution for stacked plate heat exchangers, as well as experimental data collected from a similar heat exchanger. Trade-offs between weight, pressure drop, and effectiveness were studied.

Design optimization of perforated plate matrix heat exchangers for cryogenic applications using Teaching Learning Based Optimization (TLBO) method

A perforated plate matrix heat exchanger (PPHE) is a bonded stack of alternately arranged plates and spacers. Because of their high surface area density and high effectiveness, PPHEs are highly suitable for cryogenic applications such as cryogenic refrigeration and liquefaction systems. The aim of this study is to arrive at the optimized shape and design variables of a PPHE that satisfy the specified constraints, namely effectiveness and pressure drop, while the volume of the heat exchanger (as objective function) is minimized. A Teaching-Learning-Based Optimization (TLBO) method is used for optimum sizing of the PPHE.

Experimental and numerical investigation of thermal and fluid-flow processes in a matrix heat exchanger

The need for compact heat exchangers has led to the development of many types of surfaces that enhance the rate of heat transfer, among them the matrix heat exchangers. These heat exchangers consist of a series of perforated plates mutually separated and sealed by spacers. The goal of this research was to investigate the heat transfer process of matrix heat exchangers on the air side, at the close to ambient conditions. The research was conducted in two directions ? experimental research and CFD research. The experimental investigation was carried out over a perforated plate package with the porosity of 25.6%. The air/water matrix heat exchanger was heated by hot water and was installed in an experimental chamber at which entrance was a fan with the variable flow rate and heated by hot water. The thermocouples were attached to the surface of the perforated plate at the upwind and downwind sides, as well as at the inlet and the outlet of the chamber. During each experiment, the thermocouple readings and the air and water-flow and temperatures were recorded. In the numerical part of the research, the matrix heat exchangers with different plate porosity from 10 to 50% were investigated. The results of the numerical simulations were validated against the experimental results. On the basis of the experimental and numerical results, equations for heat transfer as the function of Reynolds number and geometrical parameters was established.

Optimization of micro gas-turbine-recuperator heat transfer surface

Making highly efficient recuperator, that will have minimal dimensions, high recovery rate, and low-pressure loss is one of the key tasks in a micro gas turbine design process. This paper presents recuperator with Frenkel-type heat-exchange matrix. Design and dimension choice of envelopes, which comprise recuperator heat-exchange surface is validated through gas-dynamic calculations, which are described in this paper.

A criterial analysis of the effectiveness of air-to-air heat exchangers with periodic change of airflow direction

The physico-mathematical model of the regenerative heat exchanger with periodic changes of air flow direction has been developed. The model takes into account phase transitions both on the surface of air channels of heat exchange matrix and directly in the airflow. In this paper, the results of the influence of parameter groups on the heat exchanger effectiveness are generalized. Such generalization is reached by identifying the governing dimensionless groups in the system of equations. The analysis using the generalized parameters allows considerably simplifying the study of processes with a large number of parameters. In addition, the influence of air humidity and temperature on the sensible and latent effectiveness of the heat exchanger has been analyzed. Computations enable determining the heat exchange matrix material that is the most suitable in terms of its thermophysical properties.

Perforated plate convective heat transfer analysis

The need for high performance heat exchangers has led to the development of many types of surfaces that enhance the rate of heat transfer. One of the heat exchanger types are the matrix heat exchangers. Matrix heat exchangers consist of a series of perforated plates, separated by a series of spacers. The present study experimentally investigates the overall heat transfer characteristics of flow through a perforated plate with 2 mm in diameter, the hole length to diameter ratio of 1 and 25.6% porosity. Numerical simulations were performed to determine the overall heat transfer in the function of geometric parameters. Reynolds numbers based on the perforated plate pitch were set in the range from 50 to 500. The results of the average Nusselt number prediction were compared with the related experimental correlations. The experimental data agreed on qualitatively with the results obtained using a CFD. Using these data, a Nusselt criterial equation was obtained.

Comparison of stationary and rotary matrix heat exchangers using teaching-learning-based optimization algorithm

In this paper, two kinds of compact heat exchanger including plate fin heat exchanger and rotary regenerator, respectively the stationary and rotary matrix heat exchanger, are compared. For this purpose, both heat exchangers are optimized by considering three simultaneous objective functions including effectiveness, heat exchanger volume, and total pressure drop using multi-objective teaching learning based optimization algorithm. Six different design parameters are considered for the both plate fin heat exchanger and rotary regenerator. Optimization is performed for the same and different hot and cold side mass flow rates. The optimum results reveal 13.26% growth in the effectiveness, 475.17% increase in the volume, and 95.45% reduction in the pressure drop in RR as compared with plate fin heat exchanger and for the final optimum point. As a result, rotary regenerator is more suitable in the case of high effectiveness and low pressure drop while plate fin heat exchanger is more suitable in the case of space limitation (lower heat exchanger volume).

Coordination analysis of cross-flow heat exchanger under high variations in thermodynamic properties

Supercritical pressure CO2 was employed to investigate the improvement of a cross-flow heat exchanger with variable properties in the present work. The whole heat exchanger was uniformly divided into M×N heat exchange units, and the matrix analysis indicated that the total heat load of the heat exchange matrix depends not only on the vector norms of local heat transfer coefficient and local temperature difference, but also on their distributed coordination. A numerical example confirmed that the total heat load increased as the coordinative degree between the two vectors of local heat transfer coefficient and local temperature difference improved when the other conditions remained unchanged. The further analysis indicated that the coordination improvement between the two vectors of local heat flux density and local heat transfer area also increased the total heat load. A coordination angle was proposed to measure the coordination degree between the distributions of different parameters in heat exchange matrix; the smaller coordination angle means the better distributed coordination when the other conditions remain the same. The present work might provide a new approach to the improvement of heat exchange matrix for the fluids with drastic changes of properties.

Heat transfer and flow friction correlations for perforated plate matrix heat exchangers

Perforated plate matrix heat exchangers (MHE) are constructed of high conductivity perforated plates stacked alternately with low conductivity spacers. They are being increasingly used in many cryogenic applications including Claude cycle or Reversed Brayton cycle cryo-refrigerators and liquefiers. Design of high NTU (number of (heat) transfer unit) cryogenic MHEs requires accurate heat transfer coefficient and flow friction factor. Thermo-hydraulic behaviour of perforated plates strongly depends on the geometrical parameters. Existing correlations, however, are mostly expressed as functions of Reynolds number only. This causes, for a given configuration, significant variations in coefficients from one correlation to the other. In this paper we present heat transfer and flow friction correlations as functions of all geometrical and other controlling variables. A FluentTM based numerical model has been developed for heat transfer and pressure drop studies over a stack of alternately arranged perforated plates and spacers. The model is validated with the data from literature. Generalized correlations are obtained through regression analysis over a large number of computed data.

Performing multiobjective optimization on perforated plate matrix heat exchanger surfaces using genetic algorithm

Matrix Heat Exchanger is having wide spread applications in cryogenics and aerospace, where high effectiveness and compactness is essential. This can be achieved by providing high thermal conductive plates and low thermal conductive spacers alternately. These perforated plate matrix heat exchangers have near to 100% efficiency due to low longitudinal heat transfer. The heat transfer and flow friction characteristics of a perforated plate matrix heat exchanger can be represented using Colburn factor and friction factor. In this paper, dimensionless parameters like Reynolds number (Re ), porosity (p ), perforation perimeter factor (P f ), plate thickness to pore diameter ratio (l /d ) and spacer thickness to plate thickness ratio (s /l ) have been optimized for maximum Colburn factor and minimum friction factor using genetic algorithm. Two algorithms, one for single objective and the other for multi-objective problems, which are believed to be more efficient, are described. The algorithms coded with MATLAB, is used to perform multi-objective optimization on perforated plate matrix heat exchanger surfaces. The results show promising results.

Impact of damper opening time on work of storage matrix regenerative heat exchanger

Devices that by heat exchange take heat from exhaust air stream and transfer it to the external air stream in order to pre heat are called heat recovery heat exchangers. The heat exchange may take place through the wall (diaphragm) or using heat storage liquid (these devices are called recuperators) or by direct contact of exhaust and external air stream with the heat transfer surface - these devices are called regenerators. The publication presents the work characteristics of the storage matrix heat exchanger based on laboratory tests. In order to achieve the objectives the research station was designed and built.

Effective NTU of a counterflow heat exchanger with unbalanced flow and longitudinal heat conduction through fluid separating and outer walls

A closed form expression for effective NTU of a heat exchanger is very useful for performance prediction and design optimization of the heat exchanger with less computational efforts. However, in literature it is available only for some limited cases such as infinite design NTU, balanced flow etc. In this paper, we present effective NTU of heat exchangers with finite design NTUs and unbalanced flows. Three separate cases, (i) longitudinal conduction only through the fluid separating wall, (ii) longitudinal conduction only through the outer wall and (iii) longitudinal conduction through both fluid separating and outer walls, have been considered. Accuracy of the proposed expressions is verified with the numerical solution of the corresponding governing equations. It is proved that an existing expression for balanced flow can be used for unbalanced flow by using a modified axial conduction parameter. This principle is applied on perforated plate type matrix heat exchangers.

Influence of condensation on the efficiency of regenerative heat exchanger for ventilation

The paper presents a physical and mathematical model for calculating the air-to-air heat exchanger with periodically changing direction of the air flow. It accounts for vaporization and condensation on the channel walls of the heat exchange matrix with regular structure as well as possible formation of water fog directly in the air flow. The model can be used to analyze the influence of operating parameters, the geometric dimensions of the channels and properties of the used materials on the work efficiency of the heat exchanger. The results of calculations of the influence of indoor air humidity on heat and moisture transfer processes in the regenerative heat exchanger are provided. Sensible and latent efficiency of the regenerative heat exchanger as well as their dependence on relative humidity of indoor air are determined. The relationship between the outdoor air temperature and relative humidity of indoor air, at which ice formation begins in the channels of the heat exchange matrix, is found.

Effect of perforation shape and porosity on effective thermal conductivity of matrix heat exchanger plates

The effective thermal conductivity of a matrix heat exchanger plate is used to determine the heat transfer characteristics of the matrix exchanger in transient testing methods. In this paper, the influence of two parameters namely porosity, which is an indication of the void space and perforation shape, which is the geometry of the void, on effective thermal conductivity is analysed numerically and experimentally. The perforated copper plates of square, rhomboidal, rectangular and circular shapes of different porosities are used. A new parameter called perforation coefficient which generalises the different perforation shapes is coined. Correlations are developed using regression analysis to understand the effect of these parameters on effective thermal conductivity.