Takao Koshimizu

Numerical simulation of heat and fluid flow in basic pulse tube refrigerator

Purpose – To clarify the physical working principle of refrigeration in basic pulse tube refrigerators (BPTRs).Design/methodology/approach – A numerical simulation was performed. Transient compressible NS equation was solved utilizing the TVD scheme coupled with energy equation.Findings – The periodic flow and temperature field were obtained. The movement of the gas particles and heat transfer between the gas particles and wall were analyzed. These numerical results explained the mechanism of surface heat pumping (SHP) which is known as the working principle of refrigeration in BPTR.Research limitations/implications – Pulse tube refrigerator (PTR) is classified into the third generation. BPTR is the first generation. It is needed to clarify the working principle of refrigeration in the second and third generation by analyzing heat and fluid flow in the tube.Practical implications – A very useful source of information to understand the physical working principle of refrigeration in BPTR.Originality/value –...

Numerical Simulation of Heat and Fluid Flow in a Basic Pulse-Tube Refrigerator

The working principle of refrigeration in basic pulse-tube refrigerators (BPTR) has been explained by the mechanism called surface heat pumping (SHP) that heat is conveyed from the cold end to the hot end of the pulse tube by the successive heat exchange between the working gas and the wall. In this study, a numerical simulation has been performed to clarify the effect of the wall in BPTRs by comparing the numerical results in two physical models; one is the model considering the heat exchange between the working gas and the wall (HE model), and the other is the model ignoring that (AW model). As a result, the importance in the effect of the wall was shown clearly. In addition, the mechanism of refrigeration other than the SHP was made clear in the AW model.Copyright

Numerical Simulation of Heat Pumping in a Pulse Tube Refrigerator

Numerical simulation of heat and fluid flow in a basic and an orifice pulse tube refrigerator have been performed to visualize heat pumping generated in the regenerator and the pulse tube, and to clarify the difference in heat pumping caused by the phase difference between pressure and displacement of gas. Common components of the regenerator and the pulse tube are used in the basic and the orifice pulse tube refrigerator. The flow in the tube is assumed to be one-dimensional and compressible. As governing equations, the continuity, momentum and energy equations are used in this study. From the temperature and velocity field obtained as a result of the simulation, the relation between the displacement and the temperature change of gas elements is visually clarified, and consequently it is found that the characteristic that the temperatures of gas elements are nearly higher than those of the regenerator material or the pulse-tube wall during compression and lower during expansion is very important for the heat pumping in basic and orifice pulse tube refrigerators. Furthermore, the behavior of heat pumping in the basic and the orifice pulse tube refrigerator is illustrated by analyzing the relation between the displacement of gas elements and heat quantity transferred to the wall from the gas elements, and the difference in heat pumping between the basic and the orifice pulse tube refrigerator is made clear.© 2007 ASME

Micro-Refrigerator Fabricated on Silicon Wafer

A prototype Joule-Thomson micro-cooler was fabricated on silicon wafer by making use of photofabrication. The micro-cooler uses ethylene as a refrigerant and it consists mainly of heat exchanger and evaporator. The cooling power of 20mW at evaporator temperature of 272K was attained at the inlet and outlet gas pressures of 2.5MPa and 0.1MPa, respectively. To understand the low cooling performance, numerical analysis of heat exchanger has been done and the effects of mass flow rate and thermal conductivity of solid on temperature profiles and effectiveness were examined. It was found that the flow rate of present experiment is too large and the decrease in flow rate gives better temperature effectiveness of heat exchanger. It was also found that the low thermal conductivity of solid improves the performance of heat exchanger.Copyright