Pool boiling of pure fluids and mixtures on plain and enhanced surfaces

• Main Author: Tarrad, Ali Hussain
• Published: Heriot-Watt University 1991
• Subjects: 660; Chemical engineering
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280740

The thesis contains a comprehensive literature survey of the important aspects of the boiling heat transfer process. The effect of different parameters on the performance of the heating element is reviewed in detail which includes the heating surface condition and pressure. The fundamentals of bubble growth rate and departure parameters, diameter and time, are reviewed and discussed. An experimental investigation of pool boiling on an electrically heated horizontal 90% copper:10% nickel 19 mm o.d and 56 mm long tube is described. Boiling heat transfer coefficients were obtained for four enhanced surfaces and compared to those of a plain tube in the heat flux range 5-60 kW /m2 at atmospheric pressure. Three integrally formed tube surfaces, Turbo-B, 19 FPI Gewa-TX and 19 FPI Low Finned and one sintered porous surface, High Flux, were used in the tests. The boiling pure liquids were water, ethanol, n-pentane and R113. The plain tube was tested with p-xylene in addition to these liquids in the heat flux range 5-50 kW /m2. The te~ts were carried out on two types of mixtures, the wide boiling range n-pentane/tetradecene mixture and the narrow boiling range ethanol/water mixture. Qualitative and quantitative information gained from the mass of data obtained in this investigation together with some unreported phenomenon accompanying the boiling process are reported. Longitudinal temperature variation in the tube section was measured in the tests. This was achieved by locating four thermocouples in three different longitudinal positions in the tube section. A numerical finite difference analysis was employed to predict the temperature distribution in the tube section using apxxxvi propriate boundary conditions. The model failed to predict the exact measured temperature variation in the tube section. However, the temperature profile was predicted well. A new approach to prediction of bubble growth rate in pure liquids and binary mixt,ures is developed. This technique is considered a new application for the numerical moving boundary problems in the polar coordinates and including the convection effect produced from the density difference between the vapour and liquid phases. The analysis employs the boundary conditions at the vapour /liquid interface to trace the motion of the bubble wall together with any associated variables. The mass and/or energy equations were solved for the liquid domain in the vicinity of the bubble wall. Good agreement between the calculated bubble growth rate in pure liquids and that of other investigators was obtained . The prediction of mixture growth rate is lower than that of existing correlations.