Investigation and measurement of crude oil heat transfer coefficient in forced convection and subcooled flow boiling heat transfer

In this study, forced convection and subcooled flow boiling heat transfer coefficients of crude oil from southern oil fields of Iran were experimentally measured under different operating conditions. Despite the little data available on the heat transfer coefficient of crude oil at different operating conditions, there is an urgent need for precise and sufficient information about the status and mechanism of crude oil heat transfer for design and economic optimization of equipment such as crude oil preheaters in production units and oil refineries. The experiments were carried out in a constant heat flux heat exchanger heated by an electric heater equipped with adjustable heat flux in the range of 40-90 kW m(-2). Firstly, in order to ensure the quality of obtained data, the heat transfer coefficients of distilled water were measured and compared with the available literature data. The experimental results indicated that the heat transfer coefficient of crude oil is relatively 31% less than that of distilled water; so, the ability of crude oil in heat transfer is less than distilled water, and the temperature of the heated surface in the crude oil experiment is higher than that of distilled water. Furthermore, enhancement of fluid flow rate and heat flux increases the heat transfer coefficient. It is very difficult to distinguish the transition from forced convective heat transfer to boiling of crude oil by enhancement of heat flux. For this purpose, (T-w-T-b) was plotted against heat flux, and the obtained results indicated that the subcooled flow boiling of crude oil starts in the range of 41.9-51.3 kW m(-2). Finally, the convective heat transfer coefficients were correlated in dimensionless Nusselt form as a function of dimensionless numbers Re and Pr.