Abstract:

ESDU 90001 gives methods for calculating the heat transfer coefficient in the post dry-out region (that is when the critical heat flux is exceeded and the liquid no longer wets the tube walls) for upward flow in vertical tubes. The methods are restricted to high quality flow (that is when a large proportion of the fluid is vapour) and a test for the applicability of the methods is included. Two different methods are given, one for steam/water flows and one for other fluids. Detailed step-by-step calculation procedures are set out in both cases for the determination of either the wall temperature when the tube is subjected to known heat flux (for example, when electrically heated) or the heat flux when the tube is heated to a known temperature, and all four cases are illustrated by worked example calculations. The accuracy of the methods is discussed. For steam/water the method is stated to provide a root mean square error on wall temperature of about 10 per cent by comparison of predictions with some 2000 experimental values for which the ranges of the variables are also given. The root mean square error on heat transfer coefficient was about 20 per cent. Results in the case of the method for other fluids were about the same, but were only tested against 350 experimental points for four fluids. The ranges of the experimental data are again included. A method of taking account of radiation is also provided. ESDU 86032 and ESDU 88001 give procedures for predicting the critical heat flux in heated tubes with vertical upwards flow and horizontal flow respectively. ESDU 85041 gives a method of predicting heat transfer rates in saturated wet-wall boiling.