自然对流条件下冰水界面换热系数的试验研究

Determination of heat transfer coefficient on water-ice interface under free convection condition

在冰脊的固结过程中,由于接触面积与温差的大幅提升,冰水之间的换热强度显著增强。本文通过浸没试验对自然对流条件下冰水间的换热系数进行了研究。在试验过程中,对试样内部的温度分布与体积变化分别用温度梯度测试系统与数字图像进行测量。为研究初始条件对换热系数的影响,分别采用不同初始温度与厚度的试样在瞬态热传导的环境下进行测试。试验结果表明,换热系数与表面温差呈指数增长,且在本文试验条件下的变化区间为0.3~175 W/(m2·K)。试样的初始温度及厚度并不是影响换热系数的直接因素,而其根本因素为流-固界面的边界层状态。在自然对流状态下流体的驱动条件是热胀效应,即当边界层存在温度差时,虽然外界并不存在扰动流体状态的因素,但由于液体自身温差引起的密度差进而驱动流体运动并影响了换热系数。随着边界层温度梯度的增加,边界层的影响区域扩大,从而导致了较高的换热系数。

In ice ridges consolidation,the convective heat flux becomes critical due to the larger contact areas and surface temperature differences compared with those from level ice.In this paper,a submerging experiment was designed to determine the heat transfer coefficient（h）between fresh ice and fresh water in a free convection.A thermistor string was used to measure temperature changes while ice growth was recorded by photograph.To study the factors,the tests were carried out on different ice thickness（4.9 cm to 20.5 cm）and initial temperatures（-20℃and-32℃）.The result shows that the h exponential increased with temperature difference from 0.3 W/（m^2·K）to 175 W/（m^2·K）.On the other hand,the variation of initial thickness and temperature was not a direct influence on h.For convective heat transfer,the boundary layer condition is central for understanding the convection between ice surface and water flowing past it.From the governing equation,the water flow in a free convection is caused by density difference,which is driven by the thermal expansion.A large temperature difference between surface and environmental water creates a thicker boundary layer,which leads to a higher h.