Boiling heat transfer and critical heat flux in pool boiling of ammonia-water mixture

在氨质量浓度C=0.5~1，较高压力P=0.7~1.5 Mpa，较低压力P=0.1~0.7 Mpa，在0~0.3范围内，测量了氨水混合物的池沸腾换热系数。根据热流密度的不同，换热特性可分为三个部分，即低、高和第二瞬时热流区。在本研究中，换热系数被处理在高瞬时热流区和第二瞬时热流区两个区域。与纯液体相比，在C=0.1~0.9的质量浓度范围内，换热系数显著降低。但换热比氨的换热大0.97倍左右。将实测的换热系数与已有的几个关联式进行比较，发现没有一个关联式能很好地预测换热系数。因此，通过对Stephan和Korner关联式的修正，提出了一种新的关联式，因为它们的关联性呈现出相似的趋势。关联式可以用如下形式给出：h=1/B((1-C)/h_1+C/h_2)，其中B=1+A_0|y_1-(1-C)|(0.88+0.12P)，hi=di(P/P_S)^n(fξQ)^b/R，i=1和2是西川和藤田给出的每种纯液体的换热系数。Y_1的值是水蒸气的MSS浓度。用上述关联式可以很好地预测换热系数，与表中列出的值相吻合。

Heat transfer coefficient has been measured during pool boiling of ammonia-water mixture at a ammonia mass concentration ranging from C=0.5 to 1 at a higher pressure of P=0.7 to 1.5 MPa and from 0 to 0.3 at a lower pressure of 0.1 to 0.7 MPa. The characteristics of heat transfer can be categorized into three parts depending on heat fluxes such as low, high and second transient heat flux regions. In the present study, the heat transfer coefficients are treated in the two regions of high and second transient heat flux regions. The heat transfer coefficients dramatically decrease in the mass concentration ranging from C=0.1 to 0.9 compared with those for both the pure liquid. However, the heat transfer is found to become around range of 0.97 larger than that for ammonia. On comparison of the measured heat transfer coefficients and several existing correlations, it is found that no correlation can predict the heat transfer coefficients well. Therefore, a new correlation is proposed by revising the Stephan and Korner correlation, since their correlation shows a similar trend. The correlation can be given in the following form :h=1/B ((1-C)/h_1+C/h_2)where B=1+A_0|y_1-(1-C)|(0.88+0.12P), and h_i=d_i(P/P_s)^n(fξq)^b/R of i=1 and 2 are heat transfer coefficients for each pure liquid given by Nishikawa and Fujita. The value of y_1 is mss concentration of water vaporThe heat transfer coefficients can be predicted well by the above correlation with the value listed in Table.