Ebullioscopic investigation of the boiling of large volumes of liquids

Abstract

Boiling is the phase transformation of liquid into vapor, which develops on the heating surface and is accompanied by simultaneous transfer of heat and mass. The greatest number of scientific studies in the world are devoted to the boiling of liquids used as working media and heat-transfer media. Despite copious scientific-technical information, the boiling process is still not well understood, as a result of which many difficulties are encountered in selecting optimal thermal loads and determining the coefficient of heat transfer from the heating surface to the boiling liquid.Let us examine the development of scientific-research studies in the field of the boiling of liquids. In 1934, Nuldyama observed a minimum and maximum on the boiling curve for a large volume of liquid [1]; this marked the beginning of brisk development of scientific-research work both in our country and abroad. Among the first studies, we should make note of Farber and Scorah's research [2], as a result of which it was established that the relationship between the specific heat load q and the temperature differential At has boundaries of nucleate and film boiling (Fig. 1). The curve showing the development of nucleate boiling increases, and for water, the critical load reaches the maximum when At = 25"C. A further increase in the temperature differential above At= results in the formation of so-called film boiling and a reduction in heat transfer, i.e., to rational utilization of the heat conducted to the heating surface. In similar experiments on the boiling of liquids, Jakob [3] defined the boundaries of the film boiling of liquids more precisely.Based on many experiments, Fa-uzhflin [4] developed a working relationship between the coefficient of heat transfer (~ and the critical heat load q=, and the temperature differential and effective pressure [4]. Kichigin and Tobilevich [5] propose working relationships between the critical specific heat flux and the temperature differential, as well as the critical coefficient of heat transfer (x~ under different boiling regimes for large volumes of water. Kutateladze [6], who indicated a relationship between the coefficient of convective heat transfer and the specific heat load and pointed out that nucleate boiling is terminated when ~ = 30.I03 W/(m2-K) on arrainlng a thermal load q --8.3-105 W/m e, was extremely original in his investigation of the boring of water and aqueous solutions.Studies [7][8][9][10][11][12][13], which have made a significant contribution to the theory of boiling, have been conducted and published within a short period of time. The following equations were recommended for thermal calculations of the coefficient of convective heat exchange during the nucleate boiling of liquids under an effective pressure of from 0.1 to 0.5 MPa:(1)where A = 3 and At = 38.7 are the exponential coefficients for water when P/Per = 0.18 MPa. Practice has demonstrated, however, that use of Eqs. (I) and (2) for calculation of the coefficient of convective heat exchange of organic liquids yiel...