Conventional design methods start from an existing engine and determine basic engine specifications by introducing similarity laws such as Beale's number. Then, detailed engine specifications are determined by trial and error under the desired conditions using Schmidt theory, isothermal models, adiabatic models, and so on. In the case of high temperature difference type engines, where sufficient temperature difference is available, there is no problem with the above method because the basic design does not need to be changed significantly according to the temperature difference. In the case of the low-temperature-difference type, however, the balance between the volume change of the working space that produces the output and the volume transfer that generates the pressure change is different depending on the available temperature difference. Therefore, in order to enable the optimal design of Stirling engines under various temperature difference conditions, including low temperature difference types, a new design index focusing on the ratio of the volume transfer to the total working space volume and the ratio of the volume transfer to the volume change are derived.

It is valuable to develop a code to analyze Stirling engine performance in a high accuracy with a low calculation load. A program that solve at first assuming uniform pressure at every time, then adjust pressure distribution to satisfy pressure drop due to friction has such possibility. Such a program employing Runge-Kutta method, however, will become numerically unstable for a large time step. This prevents efficient calculation. This study made clear the stable time-step limit. It is employed as the stable condition that all absolute of eigen values of time-evolution matrix A which is multiplied to the vector consists of the node temperatures are less than unity. This condition was found as det(A–γE) becomes zero when the argument of complex g in the determinant changed along |γ|=1 around –1 and as the time step is increased. The followings are the results. When the conduction along the flow direction is negligible, the calculation is stable when hA_w, _jΔt/ρc_pV_j≤1.65. When the conduction is significant, no recommended correlation was found for the stability limit. The dimensionless parameter is, however, applicable for various crank angles once the value is determined. The scheme similar to Crank-Nicolson’s was found to be stable for all time step.

A heat and power supply system is constructed by connecting a 1kW class Stirling engine generator and a wood-fired boiler. Performance evaluation test of the wood boiler, which is installed an L-shaped chimney on the back to improve the combustion gas flow, was conducted to determine the amount of wood input and interval. It was found that combustion gas temperature in furnace required to drive the Stirling engine generator was more than 600°C, and that 19.5 kg of firewood per hour was proper to meet this requirement. Based on this result, the system was tested, so that the power output of 207.9 W and the heat output of 27.1 kW was obtained. Thus, the system performance was improved more than performance reported previously, but the heater needs to design again to input heat from combustion gas into the Stirling engine generator and to get the target performance.

In this report, wire meshes are stacked in a reciprocating flow field with a constant volume, and pressure is measured by changing the reciprocating frequency of the piston. The experimental apparatus is filled with nitrogen or helium. The measured pressure is used to investigate flow characteristics and to calculate the heat transfer rate utilizing that the internal energy of the gas that changed due to heating or cooling is a unique function of its pressure. When the amplitude of the differential pressure (amplitude of the fundamental frequency of the Fourier series expansion) is plotted versus velocity, the order of magnitude is comparable to that of the correlation equations by Hamaguchi et al. and Tanaka et al. The velocity dependence is closer to that of Tanaka et al. Heat added to the gas during a heat cycle is compared with the theoretical value that is found as all the gas in the cooler side is at the cooler temperature and the temperature gas in the regenerator has a linear distribution boom the heat and the heat and the cooler temperature. The experimental value is about 25% of the theoretical value.

When sound waves propagate in a tube, a secondary flow called acoustic streaming is sometimes generated. This study focuses on the circulating acoustic mass flow that flows in one direction in a looped tube and is a type of acoustic streaming. A heat transport device based on the circulating acoustic mass flow was developed by Backhaus and Swift, and they called it a self-circulating heat exchanger. It consists of a loop tube and an acoustic flow generator. This acoustic flow generator plays an important role; however, its structure and installation method—to efficiently generate the circulating acoustic mass flow—have not yet been clarified. Therefore, this study aims to establish a design method for a self-circulating heat exchanger. In previous studies, the generation of circulating acoustic mass flow was confirmed and a method for measuring the mass flow rate was established. In this study, we experimentally investigated how the circulating acoustic mass flow changes by changing the installation position of the acoustic flow generator and the driving power of the speaker. It was found that the magnitude of the circulating acoustic mass flow changed by changing the installation position of the acoustic flow generator.

To understand the flow in the pulse tube, a model pulse tube refrigerator was made for visualization, and the Schlieren method was used for visualization and the velocity distribution was estimated by Optical Flow. To obtain accurate velocity distribution, two types of averaging were performed: image averaging and velocity distribution average. As a result, Velocity estimation was possible where the flow boundary was clear. However, inside the flow, the velocity distribution was negative. It was found that averaging of images and velocity distributions is necessary to obtain an accurate flow.

Global Change Observation Mission-Climate (GCOM-C) “Shikisai” is a satellite observe global climate change. It was launched on December 23, 2017 by H2A launch vehicle from Tanegashima space center. The Second-generation GLobal Imager (SGLI) on GCOM-C is a multi-channel optical sensor to observe aerosols, vegetation and temperatures. Through long-term monitoring，understanding climate change mechanism will be improved. InfraRed Scanner (IRS) on SGLI has a Thermal InfraRed (TIR) detector. The detector is requested to operate at 55K. A Cooler Dewar Assembly (CDA) was developed to keep the detector at 55K. The CDA is designed to minimize heat load for the small cooler. The detector is supported on thermal isolator made of Glass FRP and thermally connected to the cooler by flexible thermal link. A Cooler Control Electronics (CCE) compensates fluctuation of heat load by using heater to maintain temperature and its stability. Heater power gradually decrease in 5 years. This means decrease of cooling power. Although degradation of the cooler，the detector is successfully kept in temperatures 55±0.1K for 5years in orbit and continue operating with 36W power consumption. This paper describes the cooler Dewar Assembly and its 5 years operation in orbit.

Sumitomo Heavy Industries, Ltd. (SHI) has been supplying 1-stage and 2-stage Stirling cryocoolers and J-T cryocoolers as cooling systems for earth observation satellites and scientific satellites for sensor cooling and shield cooling applications. The performance of the 2-stage Stirling cryocooler used as a pre-cooler for the J-T cryocooler has a cooling capacity of 0.2 W at 20 K/1 W at 100 K at a maximum electrical input power of 90 W [1]. In the future, it is planned to increase the size of the sensor to improve the observation capability, which will require an increase in the cooling capacity of the cryocoolers. Furthermore, measures to reduce vibration to the sensor are necessary, and in the case of the Stirling cryocooler, a driver is also installed in the expander to actively control vibration to achieve low vibration. Currently, SHI is using 1-stage Stirling cryocooler as a pre-cooler for a 2-stage Stirling cryocooler to increase cooling capacity and improve system efficiency by operating each cryocooler at a specialized frequency for 80 K and 15 K, the pre-cooling temperature of the J-T cryocooler. However, a total of six drivers are required for low-vibration cryocoolers and the heat bridges used for conduction cooling of the 1-stage and 2-stage Stirling cryocoolers have a large heat transfer loss to make them rigid enough not to load the cylinder of the expander, which increases the temperature of the cold head and reduces cooling efficiency. Furthermore, there is a need to extend the life of cryocoolers from the current 5 years to 10 years, and the 1-stage Stirling cryocoolers and J-T cryocoolers are on track to have a 10year life based on the knowledge obtained from past tests. However, for the 2-stage Stirling cryocooler, it is difficult to maintain the clearance seal of the 2-stage displacer and achieving a 10-year life is a tough challenge. To solve the vibration and life issues, we have been considering the use of a pulse tube expander without moving parts in the expander.

This paper describes the results of performance tests using a previously developed 1-stage pulse tube cryocooler with a cooling capacity of 5 W at 77 K as a pre-cooler (Figure 2) and a 2-stage PT expander designed and fabricated using a compressor for a 2-stage Stirling cryocooler.

Sumitomo Heavy Industries，Ltd. (SHI) supplies 4K-class and 1K-class cooler for space use. The 4K-class and 1K-class cooler consists of Joule-Thomson (JT) cooler and two-stage Stirling cooler as a pre-cooler. To improve the cooling capacity of 4K-class and 1K-class coolers， we are developing the cooling capacity of two-stage Stirling cooler below 20K. The performance of the two-stage Stirling cooler essentially depends on the volumetric heat capacity of its regenerator. We investigated new materials which has higher volumetric heat capacity than stainless steel used in current model. This paper describes the results of cooling tests of the two-stage Stirling cooler using new materials.

In order to expand the opportunities for low temperature difference Stirling engine to be adapted to teaching material for engineering education, we tried more difficult challenge for low temperature difference Stirling engine. RC-class in Stirling Technorally is much more difficult challenge because of many functions required as the machine is required to run 50 m by radio control and rough surface of the course. So, we tried to develop a model car equipped with low temperature difference Stirling engine that can complete the RC class in Stirling Technorally. By equipping a low temperature difference Stirling engine that has arrayed plastic regenerator and continuously variable transmission manufactured by 3D printers, it could successfully complete RC-class in 26th Stirling Technorally. By this achievement, it was shown that more possibility of low temperature difference Stirling engine for education.