Ze-Pei Ren

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 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.

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.

GENERALIZED TIME DELAY BIOHEAT EQUATION AND PRELIMINARY ANALYSIS ON ITS WAVE NATURE

As a new developing field, the science of bioheat transfer is making its fundamental propositions and theories much more complete and thus postulates new concepts based on the new discovery and knowledge. In this note, an important improvement on the previously developed thermal wave models of bioheat transfer (TWMBT) is given.

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.

Qualitative Experimental Evidences for the Thermal Wave Mechanisms of Temperature Oscillations in Living Tissues

To make it possible for the thermal wave theory on temperature oscillation (TO) effects in living tissues to be founded on the substantial experimental basis, a series of typical decisive experiments in vivo as well as in artificially simulating constructions were carried out. Conclusions obtained including some other scholars’ animal experimental results all greatly support the thermal wave viewpoint qualitatively. A few experimental facts used not to be easily understood from the classical viewpoint are also well reinterpreted. The revealing on the thermal wave mechanisms of TO in living tissues is a brand new discovery and deep insight into this important thermophysiological phenomenon. It may possibly promote new investigations on the corresponding topics in the field of bioheat transfer science.

Natural convective heat and mass transfer of water with corrosion products at super-critical pressures under cooling conditions

A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures. The influence of variable properties at super-critical pressures on natural convection has been analyzed. The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.

Natural Convective Heat and Mass Transfer on a Vertical Heated Plate for Water Flow Containing Metal Corrosion Particles

Corrosion products of structural materials when contained in water usually are in two states: soluble state and colloidal particles with diameter about 10−3–10−1 µm. Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even result in accidents. A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the first or mixed kind of boundary conditions for high-pressure water (P=17MPa) containing metal corrosion products with consideration of variable thermophysical properties.

Turbulent convection mass transfer of water with internal mass sources

Convective turbulent mass transfer in heated tubes is modeled with internal mass sources resulting from crystallization. The analysis considers the influence of internal mass sources on the concentration distribution, average concentration of colloidal particles and dissolved impurities, and the mass flux at the wall. If the mass transfer coefficient in the case which considers internal mass sources is defined properly, the Sherwood number and the mass transfer coefficient with internal mass sources are equal to those without internal mass sources. The mass flux and the increase in the wall temperature beneath the iron oxide deposit layer were predicted using two crystallization models. The model predicting crystallization at the wall only is recommended based on predictions of the maximum increase in the wall temperature beneath the deposit layer