Makoto Nohtomi

Design, construction and evaluation of a standing wave thermoacoustic prime mover

A standing wave thermoacoustic prime mover (TAPM) has been succesfully designed, constructed, and evaluated. It consists of a resonator with length of 128u2005cm, a stainless-steel wire-mesh stack with 14 mesh number, two heat exchangers, and air at atmospheric pressure as the working gas inside the resonator. The stack is placed inside the resonator near one of its closed-ends and has 4u2005cm length. The hot and ambient heat-exchangers are attached at each end of the stack to provide a large temperature gradient along the stack which is required for generating acoustic energy. An electric heater with maximum power of 400u2005W is used to supply thermal energy to the TAPM. The temperatures and dynamic pressures are measured by using type-K thermocouples and pressure transducers, respectively. We evaluated the prime mover by experimentally investigating the influence of heat input power on the onset temperature difference, time to reach the onset condition, sound frequency, and sound pressure amplitude. It was found ...

Experimental Study on a Standing Wave Thermoacoustic Prime Mover with Air Working Gas at Various Pressures

Thermoacoustic prime mover is an energy conversion device which converts thermal energy into acoustic work (sound wave). The advantages of this machine are that it can work with air as the working gas and does not produce any exhaust gases, so that it is environmentally friendly. This paper describes an experimental study on a standing wave thermoacoustic prime mover with air as the working gas at various pressures from 0.05 MPa to 0.6 MPa. We found that 0.2 MPa is the optimum pressure which gives the lowest onset temperature difference of 355 °C. This pressure value would be more preferable in harnessing low grade heat sources to power the thermoacoustic prime mover. In addition, we find that the lowest onset temperature difference is obtained when rh /δ k ratio is 2.85, where r h is the hydraulic radius of the stack and δ k is the thermal penetration depth of the gas. Moreover, the pressure amplitude of the sound wave is significantly getting larger from 2.0 kPa to 9.0 kPa as the charged pressure increases from 0.05 MPa up to 0.6 MPa.

Critical temperature differences of a standing wave thermoacoustic prime mover with various helium-based binary mixture working gases

Thermoacoustic prime movers are energy conversion devices which convert thermal energy into acoustic work. The devices are environmentally friendly because they do not produce any exhaust gases. In addition, they can utilize clean energy such as solar-thermal energy or waste heat from internal combustion engines as the heat sources. The output mechanical work of thermoacoustic prime movers are usually used to drive a thermoacoustic refrigerator or to generate electricity.A thermoacoustic prime mover with low critical temperature difference is desired when we intend to utilize low quality of heat sources such as waste heat and sun light. The critical temperature difference can be significantly influenced by the kinds of working gases inside the resonator and stacks channels of the device. Generally, helium gas is preferred as the working gas due to its high sound speed which together with high mean pressure will yield high acoustic power per unit volume of the device. Moreover, adding a small amount of a heavy gas to helium gas may improve the efficiency of thermoacoustic devices.This paper presents numerical study and estimation of the critical temperature differences of a standing wave thermoacoustic prime mover with various helium-based binary-mixture working gases. It is found that mixing helium (He) gas with other common gases, namely argon (Ar), nitrogen (N2), oxygen (O2), and carbon dioxide (CO2), at appropriate pressures and molar compositions, reduce the critical temperature differences to lower than those of the individual components of the gas mixtures. In addition, the optimum mole fractions of Hegas which give the minimum critical temperature differences are shifted to larger values as the pressure increases, and tends to be constant at around 0.7 when the pressure increases more than 2 MPa. However, the minimum critical temperature differences slightly increase as the pressure increases to higher than 1.5 MPa. Furthermore, we found that the lowest critical temperature difference for He-Armixture gas is around 66 °C which is achieved in pressure range of 1.5 MPa - 2.0 MPa and mole fractions of helium of 0.55 - 0.65. The He-N2 and He-O2 mixture gases demonstrate almost the same performances, both have the lowest critical temperature difference around 59 °C atpressures of 1.0 MPa - 1.5 MPa and heliums mole fractions of 0.35 - 0.55. For all tested gases, the lowest critical temperature difference of around 51 °C is provided by He-CO2 mixture gas at pressures of 0.5 MPa - 1.0 MPa with heliums mole fractions of 0.15 - 0.40.

Experimental study on the influence of the porosity of parallel plate stack on the temperature decrease of a thermoacoustic refrigerator

Thermoacoustic refrigerators are cooling devices which are environmentally friendly because they dont use hazardous gases like chlorofuorocarbons (CFCs) or hydrofuorocarbons (HFCs) but rather air or inert gases as working medium. They apply sound wave with high intensity to pump heat from the cold to hot the regions through a stack in a resonator tube. One of the important parameters of thermoacoustic refrigerators is the porosity (blockage ratio) of stack which is a fraction of cross sectional area of the resonator unblocked for the gas movement by the stack. This paper describes an experimental study on how the porosity of parallel plate stack affects the temperature decrease of a thermoacoustic refrigerator. The porosity of parallel plate stack is specified by the thickness of plates and the spacing between plates. We measured the maximum temperature decreases of thermacoustic refrigerator using stacks with various porosities in the range of 0.5 – 0.85, with plate spacing from 0.5 mm to 1.5 mm and plate thicknesses 0.3 mm, 0.4 mm, and 0.5 mm. The measurements were done with two resonators with length of 0.8 m and 1.0 m, with air at atmospheric pressure and room temperature, correspond to thermal penetration depths (δκ) of 0.26 mm and 0.29 mm, respectively. It was found that there is an optimum porosity which gives the largest temperature decreases, and there is a tendency that the optimum porosity shifts to a larger value and the temperature decrease become larger when we used a stack with thinner plates. On the other hand, the study on the dependence of the temperature decrease on the plate thickness and the plate spacing reveals more useful information than that on the stack porosity itself. We found that stack with thinner plates tends to give larger temperature decrease, and the plate spacing of around 4δκ leads to the largest temperature decrease.

Influence of parameter on the performance of a standing-wave thermoacoustic prime mover

The standing-wave thermoacoustic prime mover is a device to convert heat into work in the form of sound. It is one of the most potential applications for a thermoacoustic prime mover to utilize low-grade heat source to drive a refrigerator or electrodynamic linear alternator. Low efficiency of the device becomes interesting to be studied; it is because of no optimum heat exchange between the channel wall and the working gas that occur in the stack. The stack is the main part of the thermoacoustic prime mover in where the thermoacoustic energy conversion process takes place. The ωτ parameter is regarded as a nondimensional parameter determining the efficiency of the heat exchange in the stack and it depends on the hydraulic radius of the stack. This experiment was carried out by changing the hydraulic radius of the stack to control the value of ωτ. The stack was made of a pile stainless steel wire mesh because it is easier to vary the hydraulic radius than another kind of stack. The length of the resonator...

Influence of resonator length on the performance of standing wave thermoacoustic prime mover

A research on the influence of resonator length on the performance of a standing wave thermoacoustic prime mover has been conducted. The thermoacoustic prime mover consists of an electric heater, a resonator tube filled with atmospheric air, and a stack. The stack was made of stainless steel wire mesh screens with mesh number of #14. The stack had a length of 5u2005cm and placed 13u2005cm from resonator hot-end. The resonator tube was made of stainless steel pipe with 6.8u2005cm inner diameter. The electric heater which has a maximum power capability of 299u2005W was attached to the hot side of the stack. We varied the resonator length from 105u2005cm until 205u2005cm. It was found that the thermoacoustic prime mover with a resonator length of 155u2005cm generated the sound with the smallest onset temperature difference and shortest time to reach the onset condition, those are 252 °C and 401 s, respectively. Also, the prime mover with a resonator length of 105u2005cm produced the highest frequency that is 174u2005Hz. On the other hand, by using resonator length of 180u2005cm, the prime mover generated the highest pressure amplitude of 0.0041u2005MPa, and the thermoacoustic device delivered the highest acoustic power of 2.8u2005W and efficiency of 0.9%.

Simulation on Solar Energy Collection to Power a Thermoacoustic Prime Mover Using Pressurized Hot Steam

It has been performed a simple simulation and calculation on solar energy collection which is used indirectly to power a thermoacoustic prime mover by producing pressurized hot steam which would supply thermal energy to the prime mover via sealed-off hot heat exchangers. The solar energy collection took place in Yogyakarta City - Indonesia where the average energy of solar global radiation of 4.8 kWh/m2 /day (17.3MJ/m2 /day) is available around the year. The calculation including the amount of the remaining heat stored, steam pressure, and steam temperature for various areas of the collector unit (Fresnel lens) and volume of water, were done as a function of time for several days. We found that appropriate combinations of lens area and water volume would enable us to operate the thermoacoustic prime mover continuously all day and night.Copyright

Study on the Looped-Type Thermoacoustic Prime Mover for the High Efficient and Practical System( The 14th National Symposium on Power and Energy System)

A thermoacoustic prime mover, due to its simple structure, would serve as very desirable systems because it can be driven with the waste heat such as an exhaust gas from engines, and with heat from the nature such as sunlight and a geothermal heat. The advantages of this prime mover are the flexibility for various heat sources as an external engine and a possibility as the cost effective system due to simple structure. On the other hand, the energy conversion from waste heats to more effective energy such as motion energy or electric energy is desired in the automotive area because of demands of improvement of fuel efficiency. In this research, our interests focused on the performance improvement of looped-type thermoacoustic prime mover by varying stack configuration, inserting membrane to cut off the DC flow and adopting equipment of phase adjustment between pressure and velocity of gas oscillation. The experimental setup we use here is operated under the condition of a 4.2m loop length, the working fluid is argon, the 75Hz operating frequency and stacked screen mesh as a stack configuration. To improve the total thermal efficiency, various efforts have been made experimentally to grasp the optimization of stack structure which plays an important role to energy conversion. Finally, discussions on the future application of prime mover aiming to utilize the waste energy of exhaust gas are made and, by installing a membrane of natural rubber inside the tube, the acoustic intensity has increased by 20%.

Fundamental study of a thermoacoustic refrigerator

Nowadays there are demands on the refrigerator which will be used under maintenance‐free condition. In particular, it is hoped that the thermoacoustic refrigerator will be used in artificial satellites, air conditioners, and so forth because of its simplicity and high reliability. This refrigerator has no mechanical parts in its system which cause friction loss and is similar in its refrigeration process to the basic‐type pulse tube refrigerator. In this paper, a thermoacoustic refrigerator has been manufactured and its performance is discussed both experimentally and analytically. In experiments investigating the basic performance of this refrigerator, the stacks (which correspond to the regenerator of the pulse tube) of both the stainless‐steel parallel plate and the ceramic capillary tube were installed in the resonance tube of quarter‐wavelength. The temperature profiles were measured 50 mm apart along the tube. From experimental results, a COP of 0.334 has been obtained. In addition, the theoretical ...