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Enhancement of heat transfer due to bubbles passing through a narrow vertical rectangular channel and its upper limit

气泡通过狭窄垂直矩形通道的传热强化及其上限

基本信息

批准号：
62550160
负责人：
MONDE Masanori
金额：
$ 1.15万
依托单位：
Saga University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62550160/
关键词：
Phase Change Boiling Enhancement of Heat Transfer Natural Conyection 自然対流垂直流路自然流動

项目摘要

In order to elucidate the mechanism of enhancement of heat transfer due to bubbles passing through a narrow vertical channel, an experiment has been carried out by two different procedures: one is that an artificial bubble is employed to control the period and the length of the bubble and the other is that bubbles naturally generated on the several heated surface mounted in the narrow vertical channel are used. The experimental range is as follows: for the artificial bubble, the bubble length is l = 10, 20, and 30 mm, the period is from T_o = 0.033 to 1.0 sec, the clearance of the channel is from S = 2 to 7 mm, water, R113, and ethanol is used as working fluid, and the system pressure is atmospheric pressure and for the natural bubble, the number of the heated surface are 3 or 5, the heat flux is from q_w = 10^3 to 7 x 10^4 w/m^2, the clearance is S = 1, 2, and 4 mm, and water, R113, and R12 are employed as working fluid, and the pressure is form p = 1 to 20 bar.The following experimental results are obtained:1. The enhancement of the heat transfer strongly depends on the bubble length and the effectiveness of the enhancement is increased as its length becomes large.2. The upper limit of the enhancement would be determined as a function of ROO<aT>_o/ and , where a is thermal diffusivity, is the thickness of the liquid film created by the bubble when it passes over the heated surface and is the time during which the heated surface is covered with the bubble.3. On the basis of the experimental result, an theoretical analysis is made to predict the characteristic of the enhancement and it can predict the experimental result fairly well.

为了阐明气泡通过竖直窄缝通道强化传热的机理，采用了两种不同的实验方法：一种是利用人工气泡控制气泡的周期和长度，另一种是利用在竖直窄缝通道内的几个受热面上自然产生的气泡。实验范围如下：对于人工气泡，气泡长度为l = 10、20和30 mm，周期为T_0 = 0.033 ~ 1.0 sec，通道间隙为S = 2 ~ 7 mm，工作流体为水、R113和乙醇，系统压力为大气压;对于天然气泡，加热面数为3或5，热流密度为q_w = 10^3 ~ 7 × 10^4W/m^2，间隙为S = 1、2和4 mm，工质为水、R113和R12，压力为p = 1 ~ 20 bar。气泡的长度对强化传热有很大的影响，随着气泡长度的增大，强化传热效果增强.增强的上限将被确定为R 00 <aT>- 0/f的函数，并且其中a是热扩散率，是当气泡经过加热表面时由气泡产生的液膜的厚度，并且是加热表面被气泡覆盖的时间。在实验结果的基础上，对增强特性进行了理论分析，并对实验结果进行了较好的预测。