Naotsugu Isshiki

Design, simulation, and test results of a heat-assisted three-cylinder Stirling heat pump (C-3)

This paper describes recent results in a project at KUBOTA to develop a gas engine-driven Stirling heat pump using both engine shaft power and engine exhaust heat source. The design, simulation and test results of the third prototype three-cylinder machine (C-3) are presented. The three-cylinder machine is modeled as a combination of two Stirling sub-systems, one a power producer and one a heat pump. These have been separately optimized then joined into the three-cylinder heat-assisted heat pump case. Shaft power is augmented by thermal power. Performance is effectively controlled by the phase shifting of the third piston to adjust the absorbing of thermal power. The test results of the C-3 prototype machine are given and are shown to compare well with predictions made in the Sage simulation code.

Performance characteristics of a gas engine driven Stirling heat pump

This paper describes recent results in a project at KUBOTA to develop an efficient CFC-free multifunctional heat supply system. A heat pump in the system is a gas engine driven Stirling heat pump. The heat pump is mainly driven by engine shaft power and is partially assisted by thermal power from the engine exhaust heat. By proportioning two energy sources to match the heat balance of the driving engine, this heat-assisted Stirling heat pump can be supplied with the maximum share of the original energy fueling the engine and can be operated at the most efficient point. The authors have developed a system heat pump composed of 6 cylinders, the doubled E-3 prototype. This prototype uses helium gas as a working gas and is constructed as two sets of three-cylinder machines, each a combination of two Stirling sub-systems (one a power producer and one a heat pump). Design and performance simulations of the prototype are presented in conjunction with the driving engine characteristics. This heat supply system is expected to produce cooling and heating water at high COP. Developing the system will provide a CFC-free thermal utilization system technology that satisfies both wide heat demands and various fuel systems.

Study on the Stirling Engine (2nd Report)

In the 1st report, the theoretical comparison of performance of various types of the Stirling engines and experimental work on the single acting L-type Stirling engine with atmospheric air as a working fluid were reported.From the 1st report, following results were obtained; 1) by the theoretical comparison, the output is decreased exponentially when dead volume ratio “a” is increased and the Inverted T type engine shows the best performance when “a” has same value for each type, 2) by the experimental results, regenerator material sizes (three kinds of diameter of steel balls were used) and the phase angle affect very much on the output performance of the engine.In this report, with the Inverted T type Stirling engine as shown in Fig. 1, the effects of the temperature of the working fluid in the expansion cylinder, various types of the regenerator material, kinds of the working fluid and the size and the number of piston rings on the output of the engine were investigated experimentally.Main results from this study are as follows; 1) fluid loss caused by reciprocating flow of the working fluid between the hot cylinder and the cold cylinder is proportional to the molecular weight of the working fluid and to the n-th power of the engine speed, 2) remarkable improvement in the engine output is obtained by use of thin piston rings (the thickness×height=1×3mm, the number of rings=15) instead of thick piston rings (6×7mm, 4) .

A Theoretical Analysis and an Analogue Test of Two-Dimensional Thermal Stress : The Case When the Temperature of Boundaries for a Rectangular Cross Sectional Solid is Suddenly Changed

Though there are many papers about thermal stress, it is generally fairly difficult to solve two-dimensional thermal stress problems exactly by means of theoretical analysis except in some special cases. So most of interesting problems from an engineering view point are frequently treated by approximate calculations such as the finite-difference methods, or by experimental approaches as photoelasticity method. Under these circumstances, we performed an analogue test of two dimensional thermal stress taking place in a rectangular block where boundary temperature is suddenly changed, using characteristics of laminar viscous flow and pressure expansion. On the other hand, we analyzed theoretically the thermal stress described above and compared the numerical calculations with the experimental results. By calculation and experiment, the general tendency in such a thermal stress can be made clear and this physical analogue technique is also applicable for two-dimensional problems.