The Effect of Linear Change of Tube Diameter on Subcooled Flow Boiling and CHF

Document Type: Original Article


Department of Mechanical Engineering, University of Hormozgan, BandarAbbas, Iran


One of the essential industry problems is the flow boiling, which reaching to the CHF condition can lead to the temperature jumping and damaging to the systems. In the present study, the effects of a uniform change in tube diameter on subcooled flow boiling and critical heat flux (CHF) investigated numerically. The Euler-Euler model has been used to investigate the relationship between the two liquid and vapor phases. The ANSYS Fluent code used for simulation. According to the results, a linear increase in tube diameter leads to enhance vapor volume fraction adjacent to the tube wall, as compared to a regular tube with a fixed-diameter, which leads to raising the tube wall temperature due to the low value of the heat transfer coefficient. At critical heat flux (CHF) conditions, where the tube wall temperature is much higher than that in subcooled flow boiling, an increase in tube diameter may lead to higher tube wall temperature before the temperature jump, as compared to the post-jump temperature of a tube with a constant diameter. The best approach for decreasing the tube wall temperature was found to be a linear decrease in tube diameter. For the tube diameter change angles of θ < - 0.0383°, tube wall temperature exhibited a decreasing trend from the inlet of the tube to its end.