HEAT-TRANSFER FROM A PLATE COOLED BY A WATER FILM WITH COUNTERCURRENTAIR-FLOW

An experimental program at the University of Pisa provides specific da ta for the evaluation of heat and mass transfer by falling film evapor ation. The problem is addressed primarily because of its relevance to the study of the behavior of passive containment cooling systems in si mplified pressurized wafer reactors. In these plants, after an acciden t that releases vapor from the primary circuit, the steel containment envelope is cooled either by an ascending stream of air in natural cir culation or by the combination of airflow and falling film evaporation . To qualify models for the prediction of the heat transfer capabiliti es in postulated accident conditions, researchers have built an experi mental facility consisting of a flat heated plate with wafer sprays an d a fan to simulate a countercurrent air stream. The range of relevant parameters to be investigated has been determined on the basis of int egral calculations performed for the AP600 reactor containment. The fa cility has enabled the collection of data that confirm the adequacy of the classical heat and mass transfer analogy in predicting evaporatio n phenomena. Further developments in the research are needed to confir m the first results and to extend the experimental database by conside ring more subtle aspects of the phenomenon such as the characteristics of surface waviness of the water film and its effect on heat transfer .