INTRODUCTION This Item is intended for use in conjunction with the ESDU Data Items on two-phase flow pressure gradients which present statistically evaluated and corrected correlations. The solution of two-phase flow pressure change and related problems generally involves the integration of locally evaluated pressure gradients. For a general solution and to take advantage of the correlations that are optimised for local conditions@ these integrals must be evaluated numerically. However@ there exists in the literature a number of methods that produce rapid solutions to specific problems by employing@ for example@ pre-integrated forms of correlations giving pressure gradients in straight pipes. The reliability of these treatments depends on the applicability of the simplifying assumptions that inevitably have to be incorporated into the integrals@ e.g. constant fluid properties and constant heat flux@ as well as the accuracy of the pressure gradient correlations themselves. Although it is especially suitable for use with the existing Data Items on two-phase flow@ this Item allows other data on pressure losses in two-phase flow to be employed. Its calculation procedures@ which may be found in Sections 7 to 9@ have been devised for use both with hand-held calculators and computers. However@ where they are used frequently@ it is recommended that interactive computer programs be written. For this reason@ the procedures are presented in a modular form that allows simple programming and enables options to be added at later stages. Three basic problems are solved by the detailed procedures in Sections 7 to 9 and Sections 3@ 4 and 5 show how most two-phase problems can be reduced to one of these. They are as follows: (i) in Section 3@ the calculation of the pressure change in a system of known geometry carrying a known mass flow rate with known heat transfer distribution@ (ii) in Section 4@ the calculation of the mass flow rate in a system of known geometry with known inlet and exit pressures and known heat transfer distribution@ (iii) in Section 5@ the calculation of the inside diameter of a constant bore system of known length@ carrying a known mass flow rate and having specified inlet and exit pressures. Section 6 gives information on common difficulties in two-phase flow@ namely instability and choking@ and the detailed calculation procedures@ given in Sections 7 to 9@ are followed by three worked examples in Section 10.
ESDU 78018-1978 history
1978ESDU 78018-1978 GUIDE TO CALCULATION PROCEDURES FOR SOLVING TYPICAL PROBLEMS RELATED TO PRESSURE DROP IN TWO-PHASE FLOW