Predictions of Heat Transfer and Flow Circulations in Differentially Heated Liquid Columns With Applications to Low-Pressure Evaporators

Abstract

Numerical computations are presented for the temperature and velocity distributions of two differentially heated liquid columns with liquor depths of 0.1 m and 2.215 m respectively. The temperatures in the liquid columns vary considerably with respect to position for pure conduction, free convection and nucleate boiling cases using 1D thermal resistance networks. In the thermal resistance networks the solutions are not sensitive to the type of condensing and boiling heat transfer coefficients used. However these networks are limited and give no indication of velocity distributions occurring within the liquor. To alleviate this issue, 2D axisymmetric and 3D CFD simulations of the test rigs have been performed. The axisymmetric conditions of the 2D simulations produce unphysical solutions; however the full 3D simulations do not exhibit these behaviours. There is reasonable agreement for the predicted temperatures, heat fluxes and heat transfer coefficients when comparing the boiling case of the 1D thermal resistance networks and the CFD simulations. This work was undertaken by the University of Leeds and National Nuclear Laboratory Ltd as part of our on-going support of Sellafield Ltd's operations. The work was funded by the EPSRC, National Nuclear Laboratory Ltd and Sellafield Ltd/NDA through an EPSRC CASE award.