Research On Thermodynamic Characteristics Of Microstructure Materials In Heat Transfer And Flow Process

Microstructure materials with peculiar function can be applied to various fields, such as optics, acoustics, thermodynamics, it has wide prospects in national defense and tiny chips. Nowadays, with the development of preparation technology and precision measuring instruments, and the researches on microstructure materials by international scholars, transmission mechanism of energy and momentum of microstructure materials in heat transfer and flow process has become one of the focuses of research.The simulation calculation of a thermal concentrator which consists of polydimethylsiloxane(PDMS) and copper with circumferential arrangement were carried out. The irreversible dissipation of transmission process was analyzed with the theory of entropy generation. The thermal concentrator can control the direction of heat flow well, and create few influences on the ambient temperature field and dissipation distribution. Based on temperature rise and entropy generation rate, a parameter named thermal concentration ratio were put forward. In the process of heat conduction, thermal concentration ratio of the thermal concentrator has fluctuant changes, which is biggest in the early time and eventually stabilizes at around zero. The thermal performance of the thermal concentrator with different temperature differences between two sides of 60 K, 100 K, 140 K and that of the semicircular thermal concentrator units with different center distances of 4 mm and 8 mm were analyzed and evaluated, which shows that larger temperature differences or smaller center distances presents a better thermal control effect.According to the flow of nanofluids with different concentration in microstructure conical diffusor, numerical results were got with different nanoparticles concentrations, respectively 0.4, 1.0, 1.8, 2.8, 4.0, and different Re, respectively 50, 100, 150, 200, 300. The irreversible loss was investigated using flow entropy generation and heat transfer entropy generation in the process of flow and heat transfer. Transmission characteristics were analyzed from the view of property regulation. When the concentration of nanoparticles or Re increases, irreversible dissipation of flow increases and irreversible dissipation of heat transfer decreases. The numerical value of irreversible dissipation of heat transfer is much larger than that of flow, playing a dominant role in the total dissipation.Three-dimensional simulation of fluid-solid conjugate heat transfer and flow for the inner region and outer region of the vacuum layer in Decoupled Poisoned Hydrogen Moderator of Chinese Spallation Neutron Source, was carried out with non-uniform complex heat source, and transmission characteristics were analyzed using the theory of entropy generation. Because of the non-uniform heat source, the distribution of temperature is non-uniform, with the maximum value of temperature in a corner of the container, which is 354.4K. In the outside of the vacuum layer, helium container has the biggest value of temperature and the largest heat transfer irreversible loss. Cooling water can take heat away timely, so the temperature and the irreversible dissipation is low. In the inside of the vacuum layer, the asymmetric shunt effect of poisoned plate causes the different flow and the temperature distribution at the two sides. In the liquid hydrogen container, the irreversible dissipation of flow and heat transfer are comparable, mainly concentrating in the area at the bottom of the container. Along the direction of liquid hydrogen flow, flow loss and heat loss decreases firstly, and then increases. A fast increase occurs in the bottom of the container. Optimization schemes were designed based on the length of the inlet-pipe of hydrogen. The comprehensive analysis of the temperature and the irreversible dissipation, shows that it is the best when the distances between the inlet-pipe of hydrogen and the bottom of the container is around 15 mm or 50 mm.