Keynote 1 (August 25, 2015)
Prof. Yitung Chen
Department of Mechanical Engineering, University of Nevada Las Vegas.

Study on Local Thermal-hydraulic Performance, Optimization and Fabrication of Printed Circuit Heat Exchanger under High Temperature Conditions

A compact heat exchanger is one of the most important components to transfer heat from the first loop to the second loop in very high temperature reactors (VHTRs). In order to enhance the heat transfer performance, a mini-channel heat exchanger called the printed circuit heat exchanger (PCHE) has attracted more attention in recent years. In the first part of this talk, the thermal-hydraulic performance of a zigzag-type PCHE operating at a typical temperature of 900C is presented. It shows that the flow and temperature cannot achieve a fully-developed condition due to the significant variation of thermal physical properties arising from the large temperature difference. However, the non-dimensional velocity and temperature can become steady after the second pitch. It is recommended to put the channel with a larger inclined angle to the cold region when using the hybrid channels. The heat transfer enhancement method with inclined angles completely depends on the operating conditions. In the second part of this talk, a photochemical etching experiment to fabricate the PCHE plate is presented. The effect of etchant components, initial width and objective geometrical structure on the photochemical etching quality is discussed. The result indicates that the channel has endwall fillets, especially in the airfoil PCHE. In the last part of this talk, the effect of an actual fin-endwall fillet on the thermal-hydraulic performance of PCHE is presented. It shows that the fin-endwall fillet can increase the heat transfer and pressure drop in the cases where the longitudinal pitch is 6.5 mm. The effect of fin-endwall fillet on thermal-hydraulic performance decreases with an increase of transverse pitch, but the longitudinal pitch has little effect when the longitudinal pitch is greater than 7.5 mm. In the cases studied, the maximum difference of Nusselt number and friction factor between the two models with and without fin-endwall fillet is up to 6.7% and 6.4% respectively. This research project is collaborated with Professors Qiuwang Wang and Ting Ma at Xi'an Jiaotong University and the financial support is funded through the International Research Collaboration Program from the China National Natural Science Foundation (NNSF) from 2012 to 2016.