The Effect of Liquid Hydrocarbon Stream Recirculation on the Efficiency of Heat Exchange in a Shell-and-tube Unit

Studying the efficiency of heat exchange in shell-and-tube units is among the key objectives in process engineering. An experimental setup was developed to investigate the effect of raw material stream recirculation on the heat exchange process in tubular heat exchangers. The setup consists of a shell with a length of L = 1 m and a shell diameter of D = 76 mm, containing n = 7 tubes, each with an inner diameter of d = 15 mm. The diameter of the main stream pipe is dₐ = 20 mm, and the diameter of the recirculation stream pipe is d _r = 10 mm. The raw material feed rate is 10 L/min, with an initial temperature of t₀ = 20°C. The influence of recirculation ratios ranging from 5–30% on the hydrodynamic regimes of the flow and the effect of changes in the thermal-physical properties of heat carriers on the heat exchange process was studied. It was found that increasing the oil recirculation ratio up to 30% leads to a temperature increase at the outlet of the oil stream by up to 16°C, and for the gas condensate stream by up to 18°C. Recirculating up to 30% of the hot stream back into the initial stream improved the hydrodynamic regime due to a 1.36% increase in density and a 25.4% decrease in kinematic viscosity of the primary gas condensate stream, and a 1.06% increase in density and 28.1% decrease in viscosity for the oil stream. As a result, the heat transfer coefficient α₂ increased by 5.49% during oil heating and by 6.38% for gas condensate, while the overall heat transfer coefficient K of the process rose by 14%.