May 24, 2024
Shoaib Khanmohammadi

Shoaib Khanmohammadi

Academic rank: Associate professor
Address: Department of Mechanical Engineering, Kermanshah University of Technology, Kermanshah, Iran
Education: Ph.D in Mechanical Engineering
Phone: 0833-8305001
Faculty: Faculty of Engineering

Research

Title
Numerical study of a dimpled tube with conical turbulator using the first and second laws of thermodynamics
Type Article
Keywords
Heat transfer · Turbulator · Dimple · Pitch · Heat exchanger · First law · Second law
Researchers Shoaib Khanmohammadi، Ali Jahangiri، Faezeh Nazari، Neda Azimi

Abstract

The novelty of this numerical study is integrating strategy of dimpling the tube and using turbulators in the center of a tube under constant heat flux to improve heat transfer rate. This research focused on evaluating the effect of the geometric parameters in a dimpled tube equipped with a conical turbulator based on the first and second laws of thermodynamics. In CFD modeling, the uniform inlet velocity at the inlet of the dimpled tube, non-slip condition in the walls, and atmospheric pressure at the outlet of the dimpled tube, a uniform heat flux on the tube wall and an inlet temperature of 300 K are selected as boundary conditions. The effect of pitch (S) and number of dimples (N), Reynolds number (Re = in the range of 5000 to 20,000) and heat flux (3000, 5000, 10,000 W m−2) on entropy generation, Nusselt number and the pressure drop in a dimpled tube equipped with the turbulator was investigated. The results showed that increase in S reduces the Nusselt number, pressure drop and friction factor, but thermal entropy and friction entropy decrease and so the total entropy decreases. As the number of dimples increases, the Nusselt number increases, which has similar effect on the pressure drop and friction factor. Increase in the number of dimples leads to increase in the frictional and the overall entropy, but decrease in the thermal entropy. The results showed that in low Reynolds number, the share of thermal entropy generation is much higher than the friction entropy generation and as the Reynolds number increases the share of friction entropy generation in the total entropy generation increases. The maximum Nusselt number and friction factor are related to Re = 20,000, S = 14 mm and N = 4. Based on the obtained data from modeling, heat flux has not significant influence on heat transfer and pressure drop. The maximum thermal entropy and total entropy are at Re = 5000, S = 14 mm and N = 2, while the highest friction entropy is related to Re = 5000, S = 14 mm, N