FUNDAMENTAL STUDIES ON ICE ABRASIVE JETS

研究对象冰磨料射流有望成为下一阶段的先进磨料射流。然而。由于对超高冷却速度冷却水滴的结冰机理缺乏基本认识，这些射流的研制一直没有取得成功。利用液化天然气(LNG)返回气相制取冰粒的冷热是本研究的目标之一。本研究的目的是通过数值模拟和实验技术来阐明水滴的结冰机理，特别是在传热工程方面。(I)作为研究的第一步，利用数值模拟的结果讨论了水滴的凝固时间。环状物质(低温气态下11OK为CH4，21K为H2)、物质与水滴的相对速度(0~200m/S)、水滴直径(0.001~2.0 mm)(INT…)的影响更重要的是，在277.15K)下，用球体内非定常热传导的精确解对液滴的温度变化进行了理论研究。结果表明：(1)冻结温度，即水滴直径越大、相对速度越小，各尺寸水滴的过冷临界温度越大。(2)液滴在低温气体中的临界冻结时间受液滴直径的影响大于液滴的相对速度，在氢气中比在甲烷中的临界冻结时间短。(3)液滴直径越大，液滴冻结的临界飞行距离越长，液滴相对速度越小，液滴冻结的临界飞行距离越短。在较短的临界飞行距离下，H_2比CH_4更有效。(2)用几乎相同的模型讨论了液滴在CH_4、N_2和H_2中的凝固时间。(1)结果表明：(1)水滴在液化气体中的凝固时间比在各种气体中的凝固时间短；(2)提高水滴的相对速度不利于冰粒的生长。较少

OBJECT OF STUDIES Ice abrasive jets are expected as a next stage advanced abrasive jet. However. the development of the jets have been not succeeded, because of lack of basic knowledge of ice growth mechanisms of water droplet cooled with super-higher cooling velocities. Utilization of cold heat from LNG (Liquified Natural Gas) at which is returned to gaseous phase for making ice particles is one of the target of this study. The objective of this study is to clarify the ice growth mechanisms of water droplets by numerical simulations and exper imental techniques with special reference to heat transfer engineering.(I) Solidification times of the water droplet are discussed using results of numerical simulations as a first step of the research. The influences of the circumferential substance (CH_4 in 11OK and H_2 in 21K in cryogenic gaseous state), relative velocity (0 to 200m/s) between the substance and the water droplet, and particle diameter (0.001 to 2.0mm) of the water droplet (int … More ially in 277.15K) on thetemperature change of the droplet are using exact solution of unsteady heat conduction in sphere investigated theoretically. The following are summarized as the results ; (1) Freezing temperature, that is, critical limits of supercooling temperatures of each size of the water droplet is larger for larger droplet diameter and smaller relative velocities of the water droplet. (2) Critical freezing time of the water droplets in the cryogenic gases is more affected by the droplet diameter than the relative velocity of the droplet, and is shorter for H_2 than for CH_4. (3) Critical flight distance of the droplets to freeze them is longer for larger droplet diameter and is shorter for smaller relative velocity of the droplet. And H_2 is more effective for shorter critical flight distance than CH_4.(II) Solidification times of the water droplet in liquified CH_4, N_2 and H_2 are discussed using almost the same model. (1) The following are summarized as the results ; (I) Solidification times of the water droplet in liquified gases are more shorter than that in each gas.(2) Increase of the relative velocity of the droplet is not effective for growth of the ice particles.EXPERIMENT An observation apparatus for the ice growth is developing. Less