TED-AJ03-196 EFFECT OF NON-CONDENSABLE GAS ON EXPERIMENTAL VALUE OF CONDENSATION COEFFICIENT
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概要
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Effect of the non-condensable gas on the condensation process at the liquid-vapor interface is analyzed by using the Direct Simulation Monte Carlo (DSMC) method. The motivation of the study is concerned with a disagreement between experimental measurements and molecular dynamics (MD) study on the condensation coefficient of water. Most of experiments have resulted in smaller values of the condensation coefficient of water, while the MD simulations give us values close to unity. In the experiments to obtain the condensation coefficient the condensation heat transfer coefficients were measured under lower pressure conditions than the atmospheric pressure, it is difficult to remove perfectly the non-condensable gas inside the experimental apparatus. On the other hand, the MD simulations have been conducted for pure systems. The presence of non-condensing gas increases the interface resistance and reduces the estimated value of the condensation coefficient. We consider this is a reason we have the discrepancy. In the DSMC simulation, air molecule is considered as the non-condensable gas in a one-dimensional condensing flow of water vapor. The simulation domain has 120 times of mean free path and molar density of non-condensable gas is set in the range from 0.1% to 2%. The surface temperature is set at 300K. We use a value of unity as the condensation coefficient of water and obtain the mass transfer rate from the DSMC analysis. Then, the estimation of the condensation coefficient has been done based on Labuntsov's equation in a similar way to the experimental method. Also, we have concentration distribution of non-condensable gas as well as temperature profiles. The simulation results show that the condensing flow causes an accumulation of the non-condensing gas in the vicinity of the liquid surface that increases the resistance and reduces the condensation teat transfer rate. Even if the concentration of the non-condensing gas is low in the bulk phase, the non-condensing gas is much accumulated at the interface. The present paper indicates the possibility of low values of the experimental condensation coefficient is due to the existence of non-condensable gases.[figure]
- 一般社団法人日本機械学会の論文
著者
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Tsuruta Takaharu
Department Of Mechanical Engineering Kyushu Institute Of Technology
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NAKA Yurika
Teijin Ltd. Iwakuni Medical Factory
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