Abstract:

ESDU 85041 discusses the problems met in thermal rating a vaporiser in terms of the flow patterns in boiling flow, the conditions for nucleate boiling, considerations of burn-out and dry-out, the use of mixtures, and the flow instabilities that can occur. Nine correlations for wet-wall boiling of a pure liquid were evaluated against over 3000 experimental points taken from the literature and the results tabulated. The most reliable prediction method is chosen and a graph shows its performance against experimental data for water, ethylene glycol and a number of refrigerants. A calculation procedure based on that correlation is provided, including checks on whether nucleate boiling or stratified flow exists. The calculation of the surface area required to reach a selected flow quality is also given. A practical worked example illustrates the use of the method. It applies to steam generators and to vaporisers for process fluids. Large water-tube boilers used in power generation are outside the scope, however.