Youqu Zheng

Experimental Study of the Heat Transfer Enhancement from a Circular Cylinder in Laminar Pulsating Cross-flows

Experiments were designed to investigate the heat transfer enhancement from a single heated circular cylinder in laminar pulsating cross-flows. Several parameters were explored, including Strouhal number between 0.18 and 2.80, Reynolds number between 205 and 822, and pressure amplitude prms between 40 Pa and 276 Pa. It was observed that the heat transfer enhancement factor increased up to 2.10, and an empirical correlation between the convection heat transfer coefficient and pulsating flows was developed. Results found that the heat transfer enhancement factor decreases with Strouhal number. Increasing Reynolds number was found to have a negative impact on the heat transfer enhancement factor when the pulsating frequency is relatively low, but with a higher pulsating frequency, an increasing Reynolds number increases the heat transfer enhancement factor. Larger pressure amplitude was found to continuously produce larger heat transfer enhancement factor when both Strouhal number and Reynolds number are kept constant.

Heat Transfer Enhancement from A Rectangular Flat Plate With Constant Heat Flux in Pulsating Flows

Experiments have been carried out to study heat transfer enhancement from a heated rectangular flat plate in pulsating flows. A heat transfer empirical formula of the heated rectangular flat plate in pulsating flows was developed that correlates the heat transfer enhancement factor to the Womersley number (α = 3.3–23.8), the Reynolds number (Re = 527–4,217), and the pressure coefficient (C p = 41.3–31,644.6). The results demonstrate that heat transfer from the rectangular flat plate was enhanced significantly under proper conditions. In addition, the influence of the Reynolds number on the heat transfer enhancement factor increases as the pressure amplitude increases.

Mathematical Modelling of Flow and Heat/Mass Transfer During Reactive Spraying Deposition Technology (RSDT) Process for High Temperature Fuel Cells

Abstract A three-dimensional mathematical model of flow and heat/mass transfer coupling with chemical reactions for fuel gas and droplet combustion during reactive spraying deposition technology (RSDT) is presented in this paper. The RNG k- ε model is employed in the numerical simulation of turbulent combustion gas flow. The droplet particle is tracked and analyzed in a Lagrangian frame. The heating and vaporization histories of the injected droplet are also calculated during its movement. The three-dimensional distributions of velocity, species concentration and temperature are numerically obtained. The results indicate that the droplet will disappear over a very short distance and the vaporized fuel gas will burn immediately. Both the methods and the results described in this paper will help in the control of the final catalyst particle size and the optimization of the microstructure of the catalyst layer.

Testing and Optimizing a Stove-Powered Thermoelectric Generator with Fan Cooling

In order to provide heat and electricity under emergency conditions in off-grid areas, a stove-powered thermoelectric generator (STEG) was designed and optimized. No battery was incorporated, ensuring it would work anytime, anywhere, as long as combustible materials were provided. The startup performance, power load feature and thermoelectric (TE) efficiency were investigated in detail. Furthermore, the heat-conducting plate thickness, cooling fan selection, heat sink dimension and TE module configuration were optimized. The heat flow method was employed to determine the TE efficiency, which was compared to the predicted data. Results showed that the STEG can supply clean-and-warm air (625 W) and electricity (8.25 W at 5 V) continuously at a temperature difference of 148 °C, and the corresponding TE efficiency was measured to be 2.31%. Optimization showed that the choice of heat-conducting plate thickness, heat sink dimensions and cooling fan were inter-dependent, and the TE module configuration affected both the startup process and the power output.

Influence of conduction heat loss on enhancing the heat transfer performance of a square flat plate with constant heat flux by an impinging jet in cross-flows

ABSTRACT An experimental setup was built to study the influence of conduction heat loss on the convective heat transfer performance enhanced by an impinging jet in cross-flows. Results revealed that the conduction heat loss ratio (Ec/E) is between 12.0% and 40.1%, and it decreases nonlinearly with the ratio of jet-to-cross-flow velocity. The relative Nusselt number increases with the ratio of jet-to-cross-flow velocity. The maximum peak value and the average are 8.1 and 6.4, respectively. The distribution of the relative Nusselt number seems to be flattened by assuming a constant conduction heat loss ratio.

Numerical Simulation of Driven Convective Heat Transfer Based Lattice Boltzmann Method in a Porous Cavity

A lattice Boltzmann model of the uniform velocity, driven convective thermal conductivity in a porous cavity is studied. The Darcy, Richardson, and Reynolds numbers are shown to have a significant influence on the heat transfer behavior and the horizontal velocity of the flow field, while the porosity has little influence on either. The model is validated by the average Nusselt number at different Reynolds numbers, and the numerical results are in good agreement with available published data.