Predictive correlations for heat transfer characteristics of oil-water horizontal pipe flow-an experimental study

This paper presents convective heat transfer characteristics of liquid-liquid horizontal pipe flow. Experiments are carried out in a stainless-steel pipe of diameter 1.59 cm with L/D ratio of 377. Three different oils with varying properties (viscosity: 630 mPa-s, 202 mPa-s and 1.95 mPa-s and density: 919 kg/m3, 901 kg/m3 and 790 kg/m3 respectively) are employed as oil phase and the other fluid phase being water. The experiments are conducted for four oil-water flow patterns-stratified flow, stratified flow with droplets at the interface, dispersed oil-in-water and dispersed water-in-oil with fluid fractions ranging 0 to 1 at different fluid velocities. A constant temperature heat supply, using jacketed hot water flowing over the test pipe, is maintained. The analysis of heat transfer experiments indicates that the heat transfer process in liquid-liquid flow depends on the same dimensionless terms, the Reynolds number and the Prandtl number, that signifies single-phase flow heat transfer. Accordingly, it is found that the established and existing single-phase heat transfer correlations, modified according to flow regime, flow pattern and fluid flow and thermal properties, are also applicable for liquid-liquid flow. The heat transfer in liquid-liquid flow found to be influenced by the fluid fraction. Effectively, for stratified flow, the heat transfer in the liquid-liquid flow is the sum of heat transfer of the individual fluid phases. However, for dispersed flow, the presence of additional fluid phase is incorporated by employing the effective Reynolds number and effective Prandtl number. Using this methodology, more than 85% of stratified flow and 92% of dispersed flow heat transfer characteristics are predicted within +/- 20% of experimental data.