Shiqiang Liang

Effects of Chemical Heat Sink Generated by an Oxalic Acid Cooling Stream on Film-Cooling Effectiveness

Based on the theory of heat transfer enhancement, a novel film-cooling method for turbine blades that involves a chemical heat sink generated by the use of oxalic acid as a cooling stream has been proposed. Experiments were conducted on a flat plate with a row of 30° angled holes, and the conventional method using air as the cooling stream was examined for comparison. Overall, the results of this study demonstrate that the proposed cooling method involving an oxalic acid-induced chemical heat sink is more effective than the conventional method.

Influence of Radial Thickness of Phase Change Material on Thermal Performance of Heat Pipe Receiver Under Microgravity

In this article, a unit heat pipe receiver in an advanced solar dynamic system is numerically simulated. Accordingly, a mathematical model is set up, a numerical method is offered, and numerical results are compared with numerical results of the National Aeronautics and Space Administration (NASA). With both void cavity and phase change considered, influence of radial thickness of phase change material (PCM) on thermal performance of heat pipe receiver is numerically analyzed under microgravity. Numerical results indicate that decreasing the radial thickness of PCM in each canister has an effect of decreasing the thermal resistance of PCM. The variation of heat pipe temperature decreases as the thermal resistance between the heat pipe and the melt front decreases. The variation in heat pipe temperature is seen to be substantially reduced as the radial thickness of PCM is decreased to between 14.5 and 17 mm. Beyond this point, the impact of further reductions appears limited. The effect can be achieved with far fewer canisters with some degree of increasing thermal enhancement. When the radial thickness of PCM for unit heat pipe receiver is between 14.5 and 17 mm, the thermal performance of the heat pipe receiver is stable, and thermal spot during sunlight periods and thermal ratcheting during eclipse periods may be alleviated. The research results can be used to guide the designing and optimization of a PCM canister for a heat pipe receiver.

Influence of Void Ratio on Phase Change in Thermal Storage Canister of Heat Pipe Receiver

In this paper, with both void cavity and phase change considered, influence of void ratio on phase change in thermal storage canister of heat pipe receiver under microgravity is numerically simulated. Accordingly, physical and mathematical models are built. A solidification–melting model upon the enthalpy–porosity method is specially provided to deal with phase changes. The change of liquid fraction with respect to void ratio and the liquid fraction distribution of different void ratios in a thermal storage canister of a heat pipe receiver are shown. Numerical results are compared with experimental ones. Research results indicate that the void cavity prevents the process of phase change significantly. Phase-change material (PCM) melts slowly during sunlight periods and freezes slowly during eclipse periods as void ratio increases. The utility ratio of PCM during both sunlight periods and eclipse periods decreases obviously as the void ratio increases. The void cavity prevents the heat transfer between the PCM zone and canister wall. The void cavity blocks the processes of both melting and solidification during cycle orbital periods.

Visualization Study of Dropwise Condensation on a Super-Hydrophobic Surface

Compared with conventional filmwise condensation, dropwise condensation has the advantage of high heat transfer coefficient when properly enhanced. To better understand the inherent mechanism of this outstanding performance and optimize the structure of the condensation surface, this paper focuses on the visualization experiments of dropwise condensation on a superhydrophobic surface to study the dynamic behaviors of droplet nucleation and growth. The surface is fabricated by chemically growing an n-octadecanethiol self-assembled monolayer coating with microscopic roughness on a copper surface. Some characteristics of interest such as the droplet nucleation, the droplet diameter, the number and the path of the droplets are obtained using image processing software. The experimental results indicate that the nucleation sites of the droplets are fixed, which in turn verifies the droplet nucleation theory. In addition, the nucleation of the small droplets together with the coalescence of the existing droplets contributes significantly to the variation of the number of the droplets.Copyright

Molecular Dynamics Computation of Thermal Properties in Si/Ge Nanocomposites

In this paper, an atomic scale study is carried out to characterize the thermal transport in Si/Ge nanocomposites by using the molecular dynamics (MD) simulation. The influence of size, heat flux, interface, as well as voids, on thermal properties and the inner temperature profiles of nanowire composites are studied. The results show that the thermal conductivity of nanowire composites is much lower than that of alloy, which accounts mainly for ZT enhancement and owes a great deal to the effect of interface thermal resistance. The results also indicate that a nonfourier phenomena what we call “reflecting effect” is remarkable at the Si/Ge interface, and the thermal conductivity is also dependent slightly on the bulk temperature and the specified heat flux in the range of selected system sizes and temperatures. It is also investigated that how the thermal conductivity of Si1−x Gex composites changes with the atomic percentage x of germanium for wire dimension of LSi = 10 nm. Simulation results reveal that for a constant silicon wire dimension, the thermal conductivity of the Si/Ge nanocomposites increases with x. An attempt study on the influence of the voids on thermal conductivity shows that the thermal conductivity decreases with the void density. Most of the presented results from the simulations in this work come to favorable agreement with previous work, suggesting a good reliability of the present simulation method for further analysis of thermal transportation phenomena in nanocomposites and even more complex composites with pores, dislocations and impurities.Copyright