A self-circulating heat exchanger is a device that connects a heat source and a high-temperature heat exchanger with a loop tube and generates acoustic streaming, a steady flow, in the loop tube. The word “self-circulating” means that the gas inside the heat exchanger is flowed by a thermoacoustic spontaneous gas oscillation. It is important to establish a design guideline for the self-circulating heat exchanger because the method to efficiently generate the circulating acoustic streaming has not yet been clarified. Therefore, the purpose of this study is to clarify the relationship between the mass flow rate of the acoustic streaming and the temperature. An experimental apparatus was constructed, in which external gas oscillation input from a loudspeaker is used instead of a thermoacoustic spontaneous gas oscillation. To accelerate the acoustic streaming, an acoustic streaming generator was installed in the loop tube with multiple holes to narrow the flow path. Since it is difficult to measure the mass flow rate directly, it was obtained indirectly by using the heat balance between the acoustic streaming generator and the working fluid. The mass flow rate obtained from the experiment showed that the mass flow rate was constant in the temperature range of 60 to 140℃.

The optimization of design parameters, the compression ratio, heat conductance ratios of the three heat exchangers was conducted. Three heat exchangers, the heater, the regenerator and the cooler are assumed to have zero-volume and finite heat conductance for simplicity. Finite flow loss is considered: Instantaneous pressure drop follows the laminar steady pressure drop for the instantaneous velocity of the fluid. The cross sectional area and the lengths of the heat exchangers are introduced in the calculation of flow loss, but it is neglected in the thermodynamic cycle calculation. Net power and efficiency take the maximum at a conductance ratio of the cooler and the heater of around unity. The conductance of the regenerator has opposite effects on net power and efficiency: Net power becomes larger for smaller conductance of the regenerator, and efficiency becomes higher for larger conductance. It is found to be possible to optimize the parameters by maximizing efficiency for a condition to produce a certain net power. This power is taken 50%, for instance, of the maximum power realized when the heat conductance of the regenerator is set zero.

Performance measurement and analysis on new mesh regenerator material M5, M6 and M7 at low temperature difference using a 2-piston alpha-type Stirling engine, NS03T are carried out. With nitrogen and helium as the working fluid, the engine performance is measured by changing the charge pressure, heating temperature, and engine speed. As a result of the measurement, M7 has the highest indicated power and indicated efficiency.

In Japan, large reduction of the carbon dioxide emission amount is demanded according to Paris agreement. Woody Biomass is defined as a new energy and desired to utilize an energy source beneficially. The authors present a combined heat and power system constructed by a firewood boiler and a Stirling engine generator. The firewood boiler has a maximum combustion ability of 16kg/h and is available for consecutive combustion by a kerosene burner. The Stirling engine generator is built up as a 2 piston type engine with driving mechanism including a PM synchronous generator. It is attached to the back wall of the firewood boiler and heated by combustion gas. This paper describes the design overview of the system and the examination results of the firewood. The authors burnt 14.9kg of firewood and got heat exchange of 20.9kW by warm water.

We analyze the rotation frequency of a flywheel-based traveling-wave thermoacoustic engine from the energy balance between the energy supply from the loop tube and the energy dissipation in the piston-crank-flywheel assembly. The energy supply from the looped tube was calculated numerically using the result of the thermoacoustic theory, and the energy dissipation in the piston-crank-flywheel assembly was determined from measurement of rotation angle during freely rotating state without the influence of the looped tube. Finally, we found that the operating frequency was in good agreement with that the engine made of the looped tube and the piston-crank-flywheel assembly under investigation.

Measurements and analysis of the critical temperature difference (ΔT_crit) and the oscillation temperature of the hot heat exchanger (T_H) of a wet standing wave thermoacoustic engine under various mean pressure (Pm) are presented. A standing wave thermoacoustic engine with the total length of 675 mm was constructed and operated under the vacuum pressure condition. A wet honeycomb ceramic with size 2/1200 and length 40 mm was used as the stack in this research. Experimental results showed that ΔT_crit and T_H has the tendency to decrease as the mean pressure decreases. The value of T_H did not exceed its boiling point for Pm ≥ 50 kPa. However, when Pm ≤ 40 kPa, the value of T_H exceeded its boiling point. In this research, no oscillation was observed when the mean pressure was equal or below 20 kPa.

Fluidyne is a Stirling engine consisting of a looped tube and a tuning column partially filled with liquid. In this study, for the purpose of lowering the critical oscillation temperature ratio of Fluidyne, it was calculated by linear stability analysis with changing the tuning column length and connection position. As a result, when the temperature on the low temperature side was 296K, the minimum critical oscillation temperature ratio of 1.10 was found with the tuning column length of 1.32 m and the length ratio of 2.7 between the liquid columns on the high and low temperature sides. We also calculated the Q value and confirmed that the enhancement of Q by the temperature ratio was responsible to the reduction of the oscillating temperature ratio. Finally, we focused on the pressure and velocity of the gas in the regenerator and discussed the acoustic power generation in the regenerator.

Our purpose is to clarify the effective control method with a plasma actuator to reduce the energy loss in the acoustic oscillatory flow in a curved duct. This flow appears in machinery related with sound such as speakers and thermoacoustic devices. In this study, simulations based on the compressible Navier-Stokes equations were conducted to clarify the flow and acoustic fields in a curved duct under acoustic excitation at the duct end. The excitation frequency was adjusted so that acoustic resonance with a three-quarter wavelength mode occurs in the duct. The curved section was positioned at the anti-node of the velocity fluctuations between straight sections. The acoustic Reynolds number based on the amplitude of velocity fluctuations at the anti-node was varied in the simulations. The predicted flow fields show the periodic occurrence of flow separation leading to the energy loss around the curvature. The flow control by a plasma actuator, which was installed between curved and straight sections, was applied to suppress the flow separation. It was shown that the acoustic energy loss around the curvature was reduced by the intermittent control of the plasma actuator with the duty ratio of 0.5. Moreover, the influence of the phase of the intermittent control with reference to the cross-sectional averaged velocity fluctuations around the curvature on the control effects is discussed.