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

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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.