Prediction of heat transfer coefficients, pressure drops and flow regimes in a natural circulation evaporator, with particular reference to entrance effects

• Main Author: Bakshi, Aamarjit Singh
• Published: University of Surrey 1973
• Subjects: 536
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.448693

The boiling of distilled water in a 9 ft long 2 in. I.D. copper single tube natural circulation evaporator was investigated with particular reference to entrance effects. Heat transfer coefficients and pressure drops were compared for with and without an entrance. The tube was divided into six sections and the heat transferred to each measured separately. Measurements included inlet velocities, heat fluxes, pressure drops and stream and wall temperatures. The heat transfer results from all the six sections were correlated by the following non-dimensional equations. With an entrance, hTFd/Kl = 0.38(Pr)0.6L (Re)0.35L (L/D) 0.06 (Q/GA)0.3 (/PD)-0.54 and without an entrance hTFd/Kl = 0.12 (Pr)0.6L (Re)0.28L (L/D)0.14 (Q/GA)0.27 (/PD)-0.65. The pressure drop results were correlated by the following equations. With an entrance, (PTP/L / PSPL/L) -- 1 = 1890 (Xo)0.81 and without an entrance, (PTP/L / PSPL/L) -1 = 649(Xo)0.45 by using a resistance probe technique, flow regimes during boiling were also investigated and graphs were produced for predicting the flow regimes. Throughout this work the terms "With and Without an entrance" refer to entrance effects.