Porous Heat Exchanger Research Articles

Overview of the application of open cell foam heat exchangers

PURPOSE. Review modern highly porous cellular heat exchangers. METHODS. We conducted a broad literature review on highly porous cellular structures used as heat exchangers. We studied both domestic and foreign literature. RESULTS. We analyzed highly porous heat exchangers of various structures: stochastic (foam with open and closed cells) and ordered (honeycombs and lattices). Methods for producing open/closed cell foams and additive technologies for producing honeycomb and lattice structures have been studied. The basic properties of highly porous structures are described. The factors influencing heat transfer and hydrodynamics in highly porous cellular heat exchangers are analyzed. A review of theapplication areas of highly porous metal heat exchangers is carried out. CONCLUSION. Heat transfer and hydrodynamics in highly porous materials depend on structural parameters, such as porosity, cell size and geometry, diameter, and geometry of the strands. Increasing porosity and cell size leads to a decrease in heat transfer coefficient and pressure drop. Changing the cell geometry affects the specific surface area of the heat exchanger and the pressure drop. Cells with complex geometries, such as octet, have a large surface area and provide a high heat transfer coefficient but high resistance to coolant flow. Cells with simple geometries, such as a cube, on the other hand, provide low flow resistance and low heat transfer coefficient. In general, any structural parameter change affects heat transfer and hydrodynamics.

Experimental and numerical investigation of porous heat exchangers with Kelvin cell structured foam at high temperatures: Coupled conduction-convection and radiation heat transfer

Heat recovery is crucial in the energy sector, especially for industries operating at high temperatures. One way to achieve high-efficiency heat recovery is to use porous materials in heat exchangers. In this work, the performance of a high temperature heat exchanger was investigated. For this purpose, a tube containing a porous cast iron structure was externally heated by radiation inside a tubular furnace and air at ambient temperature was blown into the tube. Experiments were conducted at different temperatures of up to ▪ and different airflow velocities in a specialized bench, considering the combined effects of conduction, convection, and radiation. Temperature profiles in three sections of the porous structure were measured by using sheathed thermocouples brazed to the porous structure. Power and exergy flow rate extracted from the porous structure to the air flow were calculated and analyzed to quantify recovered heat. In addition, a numerical modeling performed at the pore level using Fluent showed an average relative error of 15% compared to experimental results, indicating acceptable agreement with observed trends. This numerical model will serve as a valuable reference tool for future parametric analyses of porous structures in heat exchanger configurations.

Experimental and numerical study on the offshore adaptability of new FLH2 floating hydrogen liquefaction production storage and offloading unit

With the development of hydrogen production technology from offshore wind power and natural gas, the deep-sea energy interconnection system using hydrogen energy as the medium is constantly improving. The floating hydrogen liquefaction production storage and offloading unit (LH2-FPSO, FLH2) is an effective method for large-scale utilization of offshore hydrogen energy. By filling the heat exchanger with ortho-parahydrogen conversion catalyst, a new porous medium heat exchange channel is formed. Integrating the spiral wound heat exchanger with the ortho-parahydrogen catalytic conversion reactor can reduce the deck area of FLH2 process system and lower the investment cost of floating hydrogen liquefaction device. The performance of FLH2 can be influenced by the offshore wave and typhoon. In this paper, the methods of floating cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the coupled flow and heat transfer mechanism of working fluid applied in FLH2 under offshore conditions. The results show that the sea state has little influence on the ortho-parahydrogen conversion and cooling process of hydrogen in the porous heat exchange tube. The complex flow and heat transfer challenges brought by the integrated process of new floating hydrogen liquefaction and ortho-parahydrogen conversion have been overcome. With the effect of co-current shear of gas-phase mixed refrigerant, a large dry area will not appear on the outer wall surface of porous tube under offshore conditions. The FLH2 process system shows good adaptability at sea.

Analysis of complete boiling process inside double pipe porous heat exchanger filled with NanoFluids

This study involves an investigation on fully evaporation process inside annular porous heat exchanger using Cu/distilled water nano-fluid. Emphasis has been placed on how the use of Cu/distilled water affected two-stage flux predictions. Two-phase mixture model, based on the considerations of Local Thermal Equilibrium (LTE), has been reformulated to involve the influences of employing nano-fluid instead of only water. To display the actions of employing nano-fluid, the predictions of liquid saturation and temperature, obtained using Cu/distilled water and only water, have been presented and compared for a wide ranges of geometric conditions, operating conditions and properties of porous media. The outcomes displayed that the using Cu particle to water has a large impacts on the heat diffusivity, where the boiling and condensation fronts are considerably moved to downstream and upstream sections, respectively, as compared to the predictions of only water due to rising the axial diffusion. The temperature at the pipe exit is considerably decreased when adding Cu particles to water as compared to the pure water case. The predications of Cu/distilled water show that the nano-fluid volume fraction, geometric parameters, operating parameters and porous structure properties have high actions on the locations of initiation and termination of phase change process. Since the fluid temperature for pure water case is extremely high at the superheated vapour region, the addition of Cu particles to water considerably reduces the fluid temperature in this region and hence, the use of nano-fluid can be considered as a safety factor in the applications that used heat exchangers (boiling processes) due to it improves the mechanism of heat transfer during the boiling process.

Experimental Approach for Enhancing the Natural Convection Heat Transfer by Nanofluid in a Porous Heat Exchanger Unit

Natural convection heat transfer is a significant component in the energy transfer mechanism and plays an essential role in a wide range of scientific and industrial technologies. This research seeks to enhance the energy transfer by nanofluid, which is compatible with some applications, such as heat exchanger thermal energy storage (HXTES). For this purpose, a triplex tube heat exchanger (TTHX) is designed to receive the hot and cold flow by two pumps from two thermal baths, respectively. Samples of the Copper (Cu) nanoparticles were then carefully selected in a volume concentration range of 0.05 ≤ ∅ ≤ 0.5 to promote the thermal conductivity of the base fluid, which consists of 55% water and 35% ethylene glycol (EG), and to form nanofluid. On the other side, the effect of the porous medium of glass spheres inside a TTHX is considered. Experimentally, and after preparing the nanofluid, temperature readings of six various thermocouples locations have been investigated. The effects of Cu volume concentrations under different temperatures of 20 °C, 30 °C and 50 °C on nanofluid heat transfer are evaluated, respectively. One more result: the yields in the heat transfer coefficient of the hot tube were higher compared to those of the cold tube under Reynolds number (Re) between 200 and 7000. The efficiency of transition and turbulent flow through TTHX is clearly appointed. Overall, these findings support the supposition that the heat transfer enhancement is optimized by 0.05% nanoparticle volume concentration due to increasing thermal conductivity and fluid movement effectiveness. Ultimately, a natural progression of this work is to analyze more convective form using controlled trial applications, such as solar collectors.

Optimization of microencapsulated phase change material slurry-based porous heat exchanger

Microencapsulated phase change material (MPCM) is one of the promising methods for thermal energy storage systems. However, the feasibility of their implementation in different systems, especially heat exchangers, is still questionable. In this study, the MPCM slurry flow within a porous double-pipe heat exchanger is evaluated and optimized. To have a better understanding of characteristic parameters impact, including Reynolds number, Darcy number, MPCM mass concentration and inlet temperature difference, on the performance of the heat exchanger, response surface methodology is applied. The effectiveness and Performance Evaluation Criterion (PEC) with three levels are selected as the response variables. The results showed that the simultaneous use of MPCM and a porous medium is not reasonable in terms of pressure losses inside the pipes. However, increasing the permeability of porous media can increment and decrement the PEC and effectiveness by 83 and 5.2 %, respectively, at any MPCM mass concentration. Also, MPCM can improve the cost-effectiveness at lower PEC which demands finding optimum values depending on the application. Increasing the mass concentration of MPCM has shown a high negative impact on PEC at high Reynolds numbers in which up to 13 % reduction is observed by changing the mass concentration from 5 to 15 %.

Двухконтурный рекуперативный теплообменный аппарат с межканальным движением теплоносителя в металлических сетчатых материалах

The paper considers a dual-circuit recuperator using the principle of interchannel movement of coolant through a porous metal mesh. This interchannel coolant movement schematic and the metal mesh manufactured via vacuum diffusion welding of woven metal meshes form the basis for developing compact high-performance recuperators for aircraft. Employing porous metal mesh materials characterised by a well-developed heat exchange surface and transitioning from conventional longitudinal coolant movement within channels to interchannel coolant movement through metal meshes are the factors that ensure operation at low Reynolds numbers and maximum heat exchange efficiency. The principle of interchannel coolant movement combined with the intermesh coolant movement within the metal mesh yields a highly efficient porous heat exchange path, leading in turn to developing a recuperator featuring interchannel coolant movement that will enable greater heat exchange efficiency than that provided by the best finned heat exchangers.

GeoChemFoam: Direct modelling of flow and heat transfer in micro-CT images of porous media

GeoChemFoam is an open-source OpenFOAM-based numerical modelling toolbox that includes a range of custom packages to solve complex flow processes including multiphase transport with interface transfer, single-phase flow in multiscale porous media, and reactive transport with mineral dissolution. In this paper, we present GeoChemFoam’s novel numerical model for simulation of conjugate heat transfer in micro-CT images of porous media. GeoChemFoam uses the micro-continuum approach to describe the fluid-solid interface using the volume fraction of fluid and solid in each computational cell. The velocity field is solved using Brinkman’s equation with permeability calculated using the Kozeny-Carman equation which results in a near-zero permeability in the solid phase. Conjugate heat transfer is then solved with heat convection where the velocity is non-zero, and the thermal conductivity is calculated as the harmonic average of phase conductivity weighted by the phase volume fraction. Our model is validated by comparison with the standard two-medium approach for a simple 2D geometry. We then simulate conjugate heat transfer and calculate heat transfer coefficients for different flow regimes and injected fluid analogous to injection into a geothermal reservoir in a micro-CT image of Bentheimer sandstone and perform a sensitivity analysis in a porous heat exchanger with a random sphere packing.

DIFFUSION-VACUUM TECHNOLOGY OF MANUFACTURING LARGE AXISYMMETRIC ASSEMBLIES OF METAL MESH MATERIALS FOR HEAT EXCHANGE PATHS

Requirements for improving the reliability, service life, and increasing a specific pulse of liquid-propellant rocket engines justify a need for transfer to new designs and manufacturing technologies of regenerative engine cooling system. The paper describes a advanced diffusion-vacuum technology of manufacturing a regenerative cooling circuit for liquid-propellant rocket engine based on the concept of inter-channel coolant transpiration through a porous metal mesh material. The method of diffusion welding of metal wire mesh in vacuum makes it possible to obtain large axisymmetric blanks of metal mesh materials necessary to manufacture the regenerative cooling path of the liquid-propellant rocket engine and recuperative heat exchanger (RHE). The possibility of developing a high-efficient low-gradient porous heat exchange path obtained using a metal mesh material (MMM) has been experimentally confirmed. It is recommended to use metal woven cloth and twill filter screens of standard size П24–П60, С120 as a basic material for manufacturing MMM. Key words: diffusion-vacuum technology, porous mesh material, regenerative cooling system, inter-channel coolant transpiration.

Impact of using triple adiabatic obstacles on natural convection inside porous cavity under non-darcy flow and local thermal non-equilibrium model

This work displays a numerical investigation on free convection inside non-Darcy porous cavity having a vertical triple adiabatic obstacles under conditions of Local thermal non-equilibrium (LTNE). Interesting has been focused on how the obstacles lengths arrangements manipulates the enhancement of free convection. Based on obstacles lengths, seven cases have been tested under large ranges of heat transfer coefficient (0.1 ≤ H ≤ 100), ratio of thermal conductivity (0.1 ≤ Kr ≤ 100), obstacles length (0.25 L ≤ Z ≤ 0.75 L), modified Rayleigh number (200 ≤ Ra* ≤ 1000) and inertia coefficient (10−4 ≤ Fs/Pr* ≤ 10−2). Results indicate that the optimum improvement in Nu can be obtained when using small length of all obstacles or the obstacle length should be set in ascending order. The presence of obstacles reduces the heat transfer as compared to its absence. Therefore, the case that has a minimum obstacles length is advised to be used for applications of porous heat exchangers that involved adiabatic obstacles. A significant improvement in Nu is obtained with rising in Ra*, H and Kr and reducing in Fs/Pr*. The density of LTNE region is extremely reduced with rising in H, Kr and Ra* and reducing in Z and Fs/Pr*. The thermal equilibrium case can be reached when using large values of H and Kr.

A Numerical Approach to Study the Steady State Heat Transfer Characteristics of an Annular Porous Heat Exchanger

Heat exchangers are one of the most heavily studied devices and extensive work has been performed over the years to increase their effectiveness. The present work investigates the heat transfer characteristics of an APHE (annular porous heat exchanger) in terms of different parameters. A modified design for the APHE is proposed, which resembles a conventional double pipe heat exchanger, with the annular portion of the outer pipe filled with a specific type of porous medium in order to intensify the heat transfer process. Commercial CFD package ANSYS Fluent has been utilized to investigate the performance of the proposed design numerically. Introduction of porous medium induces an increase in pressure loss which is undesirable; hence, a trade-off is present between hydrodynamic and thermodynamic performance. In the present work different inlet parameters have been modified such as different values of porosity (70% to 90%), different inlet velocities of hot fluid (1 m/s to 9 m/s), different inlet velocities of cold fluid (5 mm/s to 25 mm/s), and different inlet temperature of hot fluid (400 K to 480K), and their effects on the outlet parameters have been studied. The change in heat transfer has been presented quantitatively along with other significant parameters such as mass flow rate, pressure drop and hot gas outlet temperature. These results have been compared with the values for conventional heat exchangers in order to establish the effectiveness of APHE.

Analysis of two-phase flow in a double-pipe heat exchanger filled with porous media

In this article, two-phase flow in a double-pipe porous heat exchanger and associated phase change processes has been numerically analysed to investigate the impacts of the relative permeabilities. The modified h-formulation along with the assumption of Local Thermal Equilibrium condition has been employed. Finite Volume Method (FVM) has been used to discretise the governing equations. The solutions of incomplete evaporation process have been validated with the experiments and they show an excellent agreement between them. The pertinent parameters have been systematically investigated to demonstrate the importance of the above mentioned influences on the complete evaporation process. It has been observed that the power index of the relative permeabilities for either liquid or vapour region has a significant effects on the beginning and ending of phase change operation, especially when the steam is formed inside the pipe. Comparison between results obtained with maximum and minimum values of the power index indicated that the latter value must be used while simulating the complete evaporation process, particularly for very low inlet Reynolds number and very high wall temperature. It is also evident that the operating conditions and geometric parameters of the heat exchanger have been substantially changed the location of the beginning and ending of the phase change process. On the other hand, the properties of porous media have only minor influence.

Porous Materials in Heat Exchangers Used in Heating

This paper proposes using porous metals to boost heat exchanger efficiency. One coolant (Freon) flows through the porous metal, while the other coolant (water) flows through the narrow tubes laid inside the porous metal. The paper presents a mathematical model for a porous-metal heat exchanger, which can find metal temperature changes in any section of the heat exchanger to compare the heat transfer rate of metals of different porosity. Calculation by standard methods is not an option, as the inner surface of pores is unknown. The temperature of hot water inside the heat exchanger is to be found analytically. The obtained equations help determine the degree of cooling the first coolant (hot water). Porous heat exchangers can be used in heating systems.

Experimental Study of Porous Metals in Heat Exchangers

Use of porous materials in heat exchangers makes them more efficient in a smaller form-factor. Heat exchangers based on porous materials have uses in various industries, e.g. in power engineering. The latter currently relies on steam-to-water heat exchangers that load the environment. One promising way to make heat exchangers more eco-friendly is to use porous materials. An experimental setup was made to study heat transfer in porous materials. The setup enabled the research team to find the degree of cooling the hot coolant (water) passing through a porous heat exchanger. For comparison, experiments also involved a second heat exchanger (tubular, non-porous). The paper presents the installation diagram and the experiment methodology. It also reports the processed experimental data, draws conclusions, and suggests further experimentation.

Porous heat exchange tube with ultra-thin dense skin layer via NIPS for AGMD process

In this paper, a kind of poly(vinylidene fluoride) (PVDF) porous heat exchange tube (HET) was prepared via non-solvent induced phase separation (NIPS) method. This porous HET possessed an ultra-thin dense skin layer of 2 μm. Since the thermal conductivity of water is higher than that of PVDF, filling the pores with water can significantly improve the heat performance of the porous HET. A full plastic double-pipe air gap membrane distillation (AGMD) module was fabricated with the porous HETs and PVDF hollow fiber membranes. In the AGMD process, the wetting treatment can make the membrane distillation flux (J) and the gained output ratio (GOR) increased by 30%. During the long-term stability test, the maximum conductivity of distillate water was only 17.2 μS/cm. The experimental results demonstrated that the porous HET can be applied for the AGMD process to treat high saline brine, and the ultra-thin dense layer can prevent the leakage of saltwater.

A macroscopic particle modelling approach for non-isothermal solid-gas and solid-liquid flows through porous media

The complexity of multiphase flows in many engineering systems such as heat exchangers signify the need to develop new and advanced numerical models to analyse the interactions the working fluid and unwanted solid foulants. Fouling is present in a myriad of industrial and domestic processes and it has a negative impact on the economy and the environment. The mechanisms that govern non-isothermal solid-fluid flow through porous metal foam heat exchangers are complex and poorly understood. In this research, a coupled finite volume method (FVM) and macroscopic particle model (MPM) is developed and implemented in ANSYS Fluent to examine the transient evolution of a non-isothermal multiphase solid-fluid flow and the interaction between coupled interactions of solid particles, fluid, and porous media. The maximum particle temperature is dependent on the fluid and solid particle thermo-physical properties in addition to the temperature of the cylindrical ligaments of the porous media. The present results show that the smallest solid particles reach the highest temperatures in the porous heat exchanger and at low inlet velocities, the highest particle temperatures are realized. The results pertaining to maximum particle temperatures are prevalent in many industrial processes and acquiring knowledge of the maximum particle temperature serves as a steppingstone for comprehending complex multiphase solid-fluid flows such as the cohesiveness between the particles and the particle adhesion with the walls. The results of these studies could potentially be used in the future to optimize metal foam heat exchanger designs.

Effect of local thermal non-equilibrium model on natural convection in a nanofluid-filled wavy-walled porous cavity containing inner solid cylinder

In the current work, the impacts of local thermal non-equilibrium model and Al2O3-water nanofluid on natural convection heat transfer in a porous cavity consisting of a bottom heated wavy wall and an inner solid cylinder are investigated. The Galerkin weighted residual finite element method is utilized to simulate the dimensionless governing equations of the fluid flow and heat transfer. The effects of different parameters including Darcy number (10-6⩽Da⩽10-2), nanoparticle volume fraction (0⩽ϕ≤0.04), modified conductivity ratio (0.01⩽γ≤1000), number of undulations (1⩽N⩽4) and the porosity of the medium (0.2⩽ε⩽0.8) on the field of the flow and the heat transfer mechanisms are described. The Forchheimer-Brinkman-extended Darcy model along with the Boussinesq approximation are assumed to hold. A comprehensive validation of the present code is obtained by comparing the results with those of previous studies. The results show that all the mentioned parameters have significant impacts on the fluid flow and the temperature distributions. In addition, increasing the thermal conductivity of the nanoparticles leads to an increase in the rate of heat transfer for the nanofluid condition and reaches its maximum value at ϕ=0.04. Considering high values of ε, the average Nusselt number increases by the augmentation of ϕ, while at low values of the porosity, the average Nusselt number decreases after reaching a peak. The results of this study are very useful for designing a porous heat exchanger.

Heat Exchange in Unsaturated Porous Media with Heat Dependent Water Flow

We discuss the heat and mass transport in unsaturated-saturated porous mediaincluding heat exchange between inltrated water and matrix. We include the thermal inuenceon hydraulic permeability and on the water expansion which changes the water saturation.This consequently inuences the hydraulic permeability.Numerical modelling includes the direct and inverse solution of the problem, where model parametersare determined. Numerical experiments require only simple input/output measurementsof suitable ow characteristics in laboratory conditions with 3D cylindrical samples.The ow model is based on Richard's strongly non-linear parabolic equation based on empiricalvan Genuchten's capillary-pressure model. The transport includes longitudinal and transversaldispersion.

Determination Of Heat Transfer Characteristics Employing Modified Maximum Slope Method For Porous Media Heat Exchanger Using Al2O3–Water Nanofluids

It has been well documented in many literature that porous media and nanofluid can augment heat transfer in many engineering system. However the combined usage of these two media has not been given much attention in literature. The objective of the present work is to experimentally investigate porous media heat exchanger using Al2O3/water nanofluids. The heat transfer characteristics is determined using transient testing method wherein, only one fluid stream flows steadily throughthe test core, then a transient perturbation in the inlet fluid temperature is induced and the outletfluid temperature variation is measured continuously. The measured data is evaluated using the maximum slope method to obtain the heat transfer characteristics. The results show an increase in Nusselt number values with the use of nanofluids in porous media heat exchanger compared to water

Numerical simulations of MHD forced convection flow of micropolar fluid inside a right-angled triangular cavity saturated with porous medium: Effects of vertical moving wall

The present article explores the effects of moving lid on the forced convection flow of micropolar fluid inside a right-angle triangular cavity saturated with porous medium. The base and hypotenuse or inclined sides of the cavity are maintained at constant temperatures, while the vertical side of the enclosure is adiabatic and moving with constant velocity in upward or downward direction. The flow equations are simulated by using the robust finite element numerical technique. The pressure term from the momentum equations is eliminated by using the penalty parameter. For a consistent solution, the value of the penalty parameter is selected as 107. The simulations are performed for the cases based on the direction of moving lid. The numerical outcomes are shown in terms of streamlines, temperature contours, and local and average Nusselt numbers for sundry parameters, such as micropolar parameter, Reynolds number, Richardson number, Darcy number, Hartmann number, and Prandtl number. It is observed that the shape of the inner circulating cell is elliptic when the lid is moving in the upward direction and fluid is clear (Newtonian fluid). It is also found that average Nusselt number in both cases increases with increasing Prandtl number, Richardson number, micropolar parameter, and Darcy number, whereas it decreases with increasing Hartmann number. Further, it achieves a maximum when the lid is moving in the downward direction, regardless of the choice of involved parameters. The numerical code is also validated with previous published results. The investigation of the current study is beneficial in porous heat exchangers, construction of triangular-shaped solar collectors, rigid crystal, polymeric fluid transport, etc.