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This paper reports on the acoustic streaming in a looped-tube thermoacoustic prime mover equipped with an asymmetric constriction called a jet pump. The time-averaged mass flow velocity was determined using visualization methods and using acoustic field measurements. It was demonstrated that the magnitude and the direction of the velocity were dependent on the orientation of the jet pump. From the observed velocities, we estimated the heat carried away from the hot heat exchanger by the mass flow. It was shown that the heat loss was decreased from 30 W to 6.5 W by reversing the orientation of the jet pump, when the input heat power supplied to the prime mover was 100 W. The influence of the acoustic streaming was also studied from the cooling temperature of the looped-tube cooler.

Swelling characteristics of three kinds of single coal particles heated with a well-characterized CO2 laser were directly observed and quantitatively evaluated by combined application of a high-speed video camera with an image analysis system. The results are as follows:  (1) The interval time between swelling and shrinking of bubbles of coking coal particles (Blue Creek, Goonyella) could be used to express the ease of reforming bubbles after bursting and the growth of the bubbles before bursting. The distribution of the interval time of coking coals depends on laser intensity, particle size, and coal properties. (2) For the high-volatile weak coking coal (Witbank), there is no formation of bubbles during heating and the maximum swelling ratio is much smaller than that of coking coals. (3) The maximum swelling ratio and final swelling ratio evaluated with the relative projection area decrease with the increasing of laser intensity (or temperature and heating rate) and particle size. (4) There is a monotonously increasing relationship between the maximum relative projection area and the maximum Gieseler fluidity for all three kinds of coal, although the maximum relative projection area increases with increasing laser intensity. This result suggests that the relative projection area of coal particles on heating can be used for evaluating both the swelling and fluidity properties of coals. (5) The present results suggest a possibility that the “surface tension” of bubble film of the coking coal on heating seems to be attainable from the calculation of the rupture pressure of bubbles.

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A CO 2 laser controlled well by specially designed double shutters was used to heat uniformly dispersed coal particles in nitrogen. The temperatures of the coal particles were measured using a highly accurate multiplepoint, two-color temperature measurement system. The average performance and characteristics of three kinds of coals with different volatile content were carefully investigated at various experimental conditions. The conclusions are as follows: (1) the proximate volatile matter content, particle size, and laser intensity are the three most important factors in the devolatilization process of coal particles under the laser heating condition;(2) the devolatilization processes can be separated into two parts by the proximate volatile matter contents of three coals, which suggests that two devolatilization schemes exist in each coal; (3) the effect of laser intensities on the devolatilization processes indicates that the devolatilization process cannot be well-characterized by only laser intensity; (4) the existence of cross points in the curves of weight loss and particle temperatures among the samples with different sizes are one of the important features of laser heating, which is distinctively different from other heating methods; (5) the variation in V/V 0 values of all three kinds of coals with particle temperatures exponentially depends on coal particle temperatures, and can be expressed as V/V 0 ) 9.0 × 10 -4 exp(5.3 × 10 -3 T p ) with R 2 ) 0.8833; (6) the change in V/V 0 of W coal with different particle sizes is highly dependent on particle temperatures and can be expressed as V/V 0 ) 1.3 × 10 -3 exp(5.2 × 10 -3 T p ) with R 2 ) 0.9169; (7) a comprehensive expression, which includes volatile matter content, in situ energy density per surface area of coal particle, final particle temperature, and in situ particle properties, such as swelling, shrinking, emissivity, etc., should be further investigated.