Pei-Xue Jiang

Thermal–hydraulic performance of small scale micro-channel and porous-media heat-exchangers

Abstract Fluid flow and forced convection heat transfer in micro-heat-exchangers with either micro-channels or porous media have been investigated experimentally. The influence of the dimensions of the micro-channels on the heat transfer performance was first analyzed numerically. Based on these computations, deep micro-channels were used for the experimental studies reported here. The measured performance of both micro-channel and porous-media micro-heat-exchangers are compared with those of similar heat-exchangers tested by other researchers. It is shown that the heat transfer performance of the micro-heat-exchanger using porous media is better than that of the micro-heat-exchanger using micro-channels, but the pressure drop of the former is much larger. Over the range of test conditions, the maximum volumetric heat transfer coefficient of the micro-heat-exchanger using porous media was 86.3 MW/(m 3 K) for a water mass flow rate of 0.067 kg/s and a pressure drop of 4.66 bar. The maximum volumetric heat transfer coefficient of the micro-heat-exchanger using deep micro-channels was 38.4 MW/(m 3 K) with a corresponding mass flow rate of 0.34 kg/s and a pressure drop of 0.7 bar. Considering both the heat transfer and pressure drop characteristics of these heat-exchangers, the deep micro-channel design offers a better overall performance than either the porous media or shallow micro-channel alternatives.

Numerical investigation of forced convection heat transfer in porous media using a thermal non-equilibrium model

Abstract In the present paper, the effects of viscous dissipation, the boundary condition assumptions, thermal dispersion, particle diameters and the variable properties of oil on convection heat transfer are analyzed using a numerical model including thermal non-equilibrium assumption. The results, which are compared with experimental data, show that the convection heat transfer in porous media can be predicted numerically using the thermal non-equilibrium model with the ideal constant wall heat flux boundary condition. Viscous dissipation weakens the convection heat transfer from the fluid to the wall in the porous media. However, under practical conditions the influence of viscous dissipation on the convection heat transfer is small. The fluid temperature in the bottom part of the channel is higher than in the core region of the channel when the lower plate is adiabatic due to the effect of viscous dissipation. The variation of the thermal physical properties of oil has a profound influence on the convection heat transfer coefficient, which increases as the heat flux increases. When the upper and lower plates are heated with the same heat flux, the convection heat transfer coefficient on the upper plate surface is higher than when one side is heated and the other is insulated. However, the differences caused by these two kinds of boundary conditions in porous media are less than that in an empty channel.

NUMERICAL SIMULATION OF FORCED CONVECTION HEAT TRANSFER IN POROUS PLATE CHANNELS USING THERMAL EQUILIBRIUM AND NONTHERMAL EQUILIBRIUM MODELS

A numerical study of fluid flow and convection heat transfer in a plate channel filled with metallic or nonmetallic particles using both the local thermal equilibrium model and a nonlocal thermal equilibrium model is presented in this paper. The numerical simulation results are compared with our experimental data, and a new modified thermal dispersion conductivity model is presented. The effects of the assumption of local thermal equilibrium versus nonlocal thermal equilibrium and the thermal dispersion effect on the convection heat transfer are investigated. The nonlocal thermal equilibrium model is appropriate for either nonmetallic or metallic porous media. The velocity distribution and the temperature fields are presented.

Simulation of mixed convection heat transfer to carbon dioxide at supercritical pressure

Abstract Computational simulations of turbulent mixed convection heat transfer experiments using carbon dioxide at supercritical pressure have been performed by solving the Reynolds averaged transport equations using an elliptic formulation. A number of two-equation low Reynolds number turbulence models have been used and the results have been compared directly with the experimental data. It has been shown that most of the models were to some extent able to reproduce the effects of the very strong influences of buoyancy on heat transfer in these experiments. However, the performance of the models varied significantly from one to another in terms of the predicted onset of such effects.

Experimental research of fluid flow and convection heat transfer in plate channels filled with glass or metallic particles

Fluid flow and forced convection heat transfer was investigated experimentally in a plate channel filled with glass, stainless steel or bronze spherical particles. The test section was mm with water as the working fluid. The local wall temperature distribution was measured along with the inlet and outlet fluid temperature and pressures. The porous media greatly increased the heat transfer coefficient although the hydraulic resistance was increased even more. The effects of particle diameter, particle thermal conductivity and fluid velocity were examined for a wide range of thermal conductivities (from 75.3 W/(mK) for bronze to 0.744 W/(mK) for glass) and for three nominal particle sizes (0.278, 0.428 and 0.7 mm). The coolant water flow rate in the porous plate channel ranged from 0.01568 to 0.1992 kg/s. The Nusselt number and the heat transfer coefficient increased with decreasing bronze particle diameter, but decreased with decreasing glass particle diameter. A modified criterion was developed to judge the effect of dp on the heat transfer coefficient. The Nusselt number and the heat transfer coefficient increased with increasing thermal conductivity of the packing material.

Two‐phase flow properties of a sandstone rock for the CO2/water system: Core‐flooding experiments, and focus on impacts of mineralogical changes

The two-phase flow characterization (CO2/water) of a Triassic sandstone core from the Paris Basin, France, is reported in this paper. Absolute properties (porosity and water permeability), capillary pressure, relative permeability with hysteresis between drainage and imbibition, and residual trapping capacities have been assessed at 9 MPa pore pressure and 28°C (CO2 in liquid state) using a single core-flooding apparatus associated with magnetic resonance imaging. Different methodologies have been followed to obtain a data set of flow properties to be upscaled and used in large-scale CO2 geological storage evolution modeling tools. The measurements are consistent with the properties of well-sorted water-wet porous systems. As the mineralogical investigations showed a nonnegligible proportion of carbonates in the core, the experimental protocol was designed to observe potential impacts on flow properties of mineralogical changes. The magnetic resonance scanning and mineralogical observations indicate mineral dissolution during the experimental campaign, and the core-flooding results show an increase in porosity and water absolute permeability. The changes in two-phase flow properties appear coherent with the pore structure modifications induced by the carbonates dissolution but the changes in relative permeability could also be explained by a potential increase of the water-wet character of the core. Further investigations on the impacts of mineral changes are required with other reactive formation rocks, especially carbonate-rich ones, because the implications can be significant both for the validity of laboratory measurements and for the outcomes of in situ operations modeling.

Numerical Simulation of Transpiration Cooling for Sintered Metal Porous Strut of the Scramjet Combustion Chamber

The strut structure in a scramjet combustion chamber is used to inject fuel into the main stream. The environment surrounding the strut in the scramjet chamber is supersonic flow at very high temperatures. Thus, the leading edge of the strut is easily ablated due to aerodynamic heating. This study analyzes the effect of a transpiration cooling scheme using a sintered metal porous media surface to protect the strut from ablation. Numerical simulations are used to study the transpiration cooling for different strut structures and coolant conditions. The influences of these parameters on the transpiration cooling of the strut are analyzed for a main stream Mach number of 2.5 and a total temperature of 1700 K. The surface temperature can be reduced to a safe temperature with a coolant mass flow rate through the porous media of 27.5 kg/ m2-s. The coolant flow near the leading edge is most important, with less flow needed downstream.

Forced convective heat transfer in a plate channel filled with solid particles

A numerical study of fluid flow and convective heat transfer in a plate channel filled with solid (metallic) particles is presented in this paper. The study uses the thermal equilibrium model and a newly developed numerical model which does not assume idealized local thermal equilibrium between the solid particles and the fluid. The numerical simulation results are compared with the experimental data in reference [2]. The paper investigates the effects of the assumption of local thermal equilibrium versus non-thermal equilibrium, the thermal conductivity of the solid particles and the particle diameter on convective heat transfer.For the conditions studied, the convective heat transfer and the temperature field assuming local thermal equilibrium are much different from that for the non-thermal equilibrium assumption when the difference between the solid and fluid thermal conductivities is large. The relative values of the thermal conductivities of the solid particles and the fluid also have a profound effect on the temperature distribution in the channel. The pressure drop decreases as the particle diameter increases and the convective heat transfer coefficient may decrease or increase as the particle diameter increases depending on the values of ɛ, λs, λf, λd, αv, ρu.

Convective heat and mass transfer in water at super-critical pressures under heating or cooling conditions in vertical tubes

Forced and mixed convection heat and mass transfer are studied numerically for water containing metallic corrosion products in a heated or cooled vertical tube with variable thermophysical properties at super-critical pressures. The fouling mechanisms and fouling models are presented. The influence of variable properties at super-critical pressures on forced or mixed convection has been analyzed. The differences between heat and mass transfer under heating and cooling conditions are discussed. It is found that variable properties, especially buoyancy, greatly influence the fluid flow and heat mass transfer.

Injector Head Transpiration Cooling Coupled with Combustion in H2/O2 Subscale Thrust Chamber

Transpiration cooling coupled with combustion was investigated in an H2/O2 liquid rocket thrust chamber with a transpiration-cooled injector plate. A numerical model was developed using the real gas equation of state. The H2 and O2 combustion process was modeled by the eddy dissipation concept model, which includes the detailed chemical reaction mechanisms in turbulent flows. The permeability and the inertia coefficient of the metal mesh, porous media used for the injector plate were obtained experimentally. The simulation results for the porous plate temperatures and H2 fluxes compare well with hot firing experiments, giving reliable predictions of the combustion, flow, and heat transfer processes in the liquid rocket thrust chamber. The model was also used to investigate the effects of the inlet conditions and the plate material on the transpiration cooling. The results show that locations near the chamber wall and the ignition hole on the plate surface have higher temperatures than other locations. The...