Showing papers by "Liang-Bi Wang published in 2021"

Thermal and flow characteristics of a channel formed by aligned round tube bank fins stamped with curve delta-winglet vortex generators

Abstract: The primary purpose of present study is to reveal the roles played by CDVGs in vectoring the airflow and breeding longitudinal vortices for enhancing heat transfer. The thermal-hydraulic characteristics of a finned aligned round tube heat exchanger with stamped CDVGs were numerically studied by using the custom code with SIMPLE algorithm in a nonorthogonal curvilinear coordinate system. Four geometric parameters including vortex generator height, radial position, peripheral position and fin pitch, were programmed to ascertain parametric effects on fin side thermal performance, and the regression formulas of Nusselt number and resistance coefficient in the fin side passage with Reynolds numbers and four geometric parameters were secured. The findings suggest that the mean Nusselt number, resistance coefficient and secondary flow strength for the novel fin with CDVGs are all prevail over that in the reference plain fin under a certain Reynolds number. The body fitted CDVGs are ideally situated for finned round tube exchanger in aligned arrangement. The action of CDVGs can not only efficiently lessen the size of recirculation area behind tube but also produce strong longitudinal vortices, accordingly heighten evidently the fin side heat transfer ability in the recirculation zone. Using the studied optimum geometric parameters can make the thermal property factor up to 1.35 under the same pumping power constraint in comparison with the reference plain fin geometry when Reynolds number equals to 3000. This study can be a real application in compact heat exchanger with finned round tubes when heat transfer augmentation is under consideration.

Enhanced Effective Thermal Conductivity of Composite Materials by Incorporating Constructal Fillers

Abstract: It is a feasible way to use constructal filler to increase the effective thermal conductivity of polymer. However, the combined effect of filler constructal-shape, contact, anisotropy and interface thermal resistance on the effective thermal conductivity of the composites has not been considered, and the heat transfer mechanisms remain unclear. In this study, these effects are evaluated at the same time. The results show that the filler contact is a key factor in increasing the effective thermal conductivity of composite. The constructal fillers are easy to contact and form heat conduction network than common filler. The filler content of 5 % is the percolation threshold of constructal filler. It is lower than common filler and previous reports. The enhanced heat transfer performance of constructal filler is insensitive to directional angle and has no significant anisotropy. The composite with constructal filler has high effective thermal conductivity in different directions. Series numerical models are proposed to predict the effective thermal conductivity of composite. These models have high accuracy and reliability, the deviations with experiment results is in an acceptable range. The interface thermal resistance should be considered in predicting the effective thermal conductivity of composite with nano-fillers.