This paper reports experimental results on two kinds of atmospheric Stirling engines that were designed and manufactured using a pin-fin array heat exchanger for the heater and cooler (abbreviated to “pin-fin Stirling engine” hereafter). The first one is a large β type pin-fin Stirling engine with a 1.7-liter displacement volume and power piston volume. The heater consists of an aluminum circular disk with a diameter of 270mm and with large-scale pin-fin arrays carved into the surface. The maximum output reached 91W at a temperature difference of 330K, which is 36% of the scheduled value and 68% of the Kolin's cubic power law. The maximum thermal efficiency was estimated 4.2%. The second engine is an α type pin-fin Stirling engine. Glass syringes were used for the piston-cylinder system and the Ross-yoke mechanism was used for the crank mechanism. By changing temperature difference, the characteristic of output torque in the large range was measured with a precision torque detector.

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In order to improve the specific power of piston-cylinder type machinery, there is a point in capacity or power where an advantage accrues with increasing number of piston-cylinder assemblies. In the case of Stirling machinery where primary energy is transferred across the casing wall of the machine, this consideration is even more important. This is due primarily to the difference in scaling of basic power and the required heat transfer. Heat transfer is found to be progressively limited as the size of the machine increases. Multiple cylinder machines tend to preserve the surface area to volume ratio at more favorable levels. In addition, the spring effect of the working gas in the so-called alpha configuration is often sufficient to provide a high frequency resonance point that improves the specific power. There are a number of possible multiple cylinder configurations. The simplest is an opposed pair of piston-displacer machines (beta configuration). A three-cylinder machine requires stepped pistons to obtain proper volume phase relationships. Four to six cylinder configurations are also possible. A small demonstrator inline four cylinder alpha machine has been built to demonstrate both cooling operation and power generation. Data from this machine verifies theoretical expectations and is used to extrapolate the performance of future machines. Vibration levels are discussed and it is argued that some multiple cylinder machines have no linear component to the casing vibration but may have a nutating couple. Example applications are discussed ranging from general purpose coolers, computer cooling, exhaust heat power extraction and some high power engines.

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Small-scale biomass CHP (combined heat and power) plants are in demand for environmental reasons - particularly systems fueled by wood waste, which are simple to operate and require no maintenance while having high thermal efficiency similar to oil-fired units. A 55kWe Stirling engine CHP system, combined with a simplified biomass combustion process that uses pulverized wood powder has been developed to meet these requirements. Wood powder of less than 500 μm was mainly used in these tests, and a combustion chamber length of 3 m was applied. Under these conditions, the air ratio can be reduced to 1.1 without increasing CO emissions by less than 10 ppm, and with combustion efficiency of 99.9%. Under the same conditions, NOx emissions are estimated to be less than 120 ppm (on the basis of 6% O₂). Wood powder was confirmed to have excellent properties as a fuel for Stirling engines. The 55 kWe Stirling engine performance test was carried out to optimize the operating condition of wood powder burners. The status of Stirling engine operation at a full load with 55 kWe was stable, and start-up and shut -down operations were easy to perform. Operational status was evaluated as being excellent, except for an ash fouling problem in the Stirling engine heater tubes. Ash fouling characteristics were considered in the final stage of the demonstration test. This paper summarizes the wood powder combustion test and Stirling engine performance test. Furthermore, the ash fouling data is shown and the mechanism of ash fouling in heater tubes is discussed.

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A test model of a free piston Stirling engine (FPSE) converter was developed as a heat-to-electricity power converter for a demonstration of solar heat energy utilization at the Japan Aerospace Exploration Agency, for future aerospace applications. The target performance of the converter was 200 W electrical power output and 20% overall efficiency. A bench test of the converter was conducted to evaluate performance. The converter showed good performance as expected. In addition, the characteristics of the FPSE were investigated. Based on these achievements, prototype models of the FPSE for household use were designed and tested as part of a project supported by the New Energy and Industrial Technology Development Organization.

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Two different analytical models were developed on water type Stirling engine. One is the resonance model which qualitatively clarifies the relationship between performance and resonance tube length, and the other is the heat transfer model considering heat transfer between working gas and the tube walls of heating and cooling units. These analyses and experiments were carried out changing the resonance tube length variously, then it was confirmed that the resonance tube length which maximizes the water column amplitude of the power piston agrees well and the oscillations of water columns at that resonance tube length also agrees. In addition, a series of analysis using the heat transfer model was carried out with changing cross sectional area of the resonance tube, loss factors of the elbows, heat transfer area of heating and cooling unit, and pressure of working gas. By this numerical investigation, the effect on the resonance tube length and the work at the length in which these parameters maximize the amplitude of power piston water column was clarified.

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In this paper the working mechanism of Stirling engine is studied from the standpoint of thermoacoustic framework. The work flux measurement is performed in a glass tube equipped with/without a regenerator-heat exchanger assembly. An atmospheric pressure air confined in the tube is periodically perturbed by two speakers at the same frequency (=48Hz) but out of phase. It is experimentally demonstrated that the phasing of two pistons in the Stirling engine (alpha arrangement type) plays the role in creating a steady work flux from the compression piston to the expansion piston, whereas a differentially heated regenerator in the engine operates as a power amplifier for the traveling wave propagating up the temperature gradient.

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In order to understand thermoacoustic phenomena from a point of view of thermodynamics, oscillating pressure, velocity and temperature were measured in the tube having a temperature gradient. By converting the measured Eulerian quantities to the Lagrangian quantities associated with a given gas parcel, we determined the local energy conversion rate per unit volume and time. The obtained data demonstrate the validity of the thermodynamic approach to thermoacoustic phenomena.

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Apart from double acting type engines, Stirling engines have either 2 pistons in 2 cylinders or 2 pistons in a single cylinder. Typically, the heater, regenerator and cooler are installed between the 2 pistons. The pulse tube engine, on the other hand, consists of a single piston in a single cylinder, a pulse tube, a heater, a regenerator, a cooler and a second cooler. For this paper, a simple prototype engine that uses air at normal atmospheric pressure as the working gas was fabricated. The oscillating velocity of the working gas in the pulse tube was measured using LDV, and the work flow emitting out of the pulse tube was observed. In addition, the effect of inserting heat storage material in the pulse tube on shaft power and indicated power was examined experimentally. A dramatic increase in the shaft power was achieved.

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When a traveling acoustic wave propagates through a regenerator, the gas in the regenerator undergoes the Stirling thermodynamic cycle, and thus, the energy conversion between heat flux and acoustic power takes place. A cooler that utilizes this energy conversion is called as a traveling-wave thermoacoustic cooler. Swift et al. [The Journal of the Acoustical Society of America, 105, 711 (1998)] have proposed a new traveling wave thermoacoustic cooler that is equipped with a looped tube. This paper describes a numerical method to estimate the performance of this thermoacoustic cooler and shows a comparison between the estimated and experimentally obtained performances.

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The Fuji Electric Group has established main technologies with high reliability for use in Stirling cryocoolers for space satellite systems. For commercial applications, we also have developed and started selling a miniature pulse tube cryocooler from 2W to 3W at 70K with 100W electric power input. In the development of a new compressor, we introduce a moving magnet to a driving system to achieve greater compactness and higher efficiency in place of the moving coil that had about 70% efficiency. In addition, we adopted a coaxial pulse tube as an expander for compactness. This development is aimed at cooling a high-temperature superconductive (HTS) device in a wireless telecommunication system. The compressor requires total compression work of 75W with 90% efficiency for longer than 50,000 hours. Preliminary tests of each part of a moving magnet linear motor and a coaxial pulse tube have been completed. In the next phase, we have made a first-stage prototype compressor used by the new linear motor, and we have tested the new machine. Here we describe each test and combination test results of the cryocooler.

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Cryosurgical system utilizing liquid nitrogen and argon gas as cryogens has been used for the treatment of malignant tumors. Those devices fail to cool the tissues to the low temperatures that completely destroy the bulky tumors. It is of course difficult for the low power cooling devices using Peltier effect, to destroy the large tumors. Therefore adjunctive treatment such as hyperthermia treatment is needed to intensify the tissue destruction. Actually, hyperthermia has been clinically used to destroy tumors, but it is unclear that the hyperthermia enhances the tissue injury in cryosurgery because there have been few studies of the combination use of hyperthermia and cryosurgery. The purposes of this study are to produce the cryosurgery-hyperthermia treatment system utilizing Peltier device and Stirling cooler and to evaluate the effects of hyperthermia treatment immediately after thawing in cryosurgery onto the living normal liver tissue of mouse. In the no-load running test of our system, the minimum temperature of the cryoprobe reached -74.0 degrees C in 30 minutes. The findings of the stained tissues suggested that the combination treatment of both was effective to destroy the tissue and the higher temperature applied immediately after freezing and thawing in cryosurgery might reinforce the tissue destruction.

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