Sulian Tao

In order to improve the convective heat transfer efficiency of a shell-and-tube heat exchanger, a novel ladder-shaped bridge finned tube (LBFT) is presented. The LBFT possesses outer low helical integral fins, two layers of staggered transverse bridge, upper passage, middle passage, and bottom passage. The convective heat transfer performance of the LBFT is studied and experimental results show that the Nusselt numbers outside the tube and the overall heat transfer coefficients of the LBFT are significantly greater than those of the smooth tube. The bridges, bridge roots, and pores formed on the outer fins contribute to the larger heat transfer coefficient. Both the Nusselt number and the overall heat transfer coefficient decrease, while the friction resistance coefficient increases with outer helical fin pitch increasing and bridge width increasing. As the Reynolds number increases, the comprehensive performance evaluation criterion (PEC) decreases at first and then increases. The maximum PEC occurs at the Re number of 2300 and is up to 1.34.

A kind of stainless-steel heat pipe with sintered fiber wick is investigated with the aim to improve the heat dissipation when it is used in spent fuel pools in nuclear power plants. The effects of test angle, porosity, and the filling rate on the heat transfer performance of the heat pipe are studied. At a test angle of 90 deg, the permeability plays an important role in the power limit since gravity can provide the necessary driving force. Larger porosity involves poor heat conductivity although it results in better permeability. When the test angle is zero, gravity is no longer the driving force. In this case, the evaporation section can still avoid dry burning because part of the evaporation section is dipped in deionized water. Therefore, permeability and filling ratio are two important factors influencing the power limit. Filling rate determines the vapor-flowing space. When the test angle is smaller than zero, gravity becomes a resistance force. Then, the lag tension and the filling rate exert the greatest influence on the performance of the heat pipe. Smaller porosity corresponds to a smaller contact angle.

Heat sinks are widely used in electronic devices with high heat flux. The design and build of microstructures on heat sinks has shown effectiveness in improving heat dissipation efficiency. In this paper, four kinds of treatment methods were used to make different microstructures on heat sink surfaces, and thermal radiation coating also applied onto the heat sink surfaces to improve thermal radiation. The surface roughness, thermal emissivity and heat dissipation performance with and without thermal radiation coating of the heat sinks were studied. The result shows that with an increase of surface roughness, the thermal emissivity can increase up to 2.5 times. With thermal radiation coating on a surface with microstructures, the heat dissipation was further improved because the heat conduction at the coating and heat sink interface was enhanced. Therefore, surface treatment can improve the heat dissipation performance of the heat sink significantly by enhancing the thermal convection, radiation and conduction.