Experimental and numerical study on heat transfer and flow characteristics in the shell side of helically coiled trilobal tube heat exchanger

Heat transfer and flow characteristics in the shell side of helically coiled trilobal tube (HCTT) heat exchanger are investigated by experiment and a 3D numerical simulation. Compared to experimental tests and existing empirical formulas, calculated results indicate that the shell-side fluid of HCTT heat exchanger shows a strong ability to rotate and to disturb the boundary layer. In addition, the circumferential and radial velocities near the tube wall are improved, and the velocity vector exhibits a good synergy with temperature gradient. Nusselt number (Nu) increases and friction factor (f) decreases in shell side of HCTT as the Reynolds number increases. Under the same condition, the augmentation on heat transfer performance of HCTT is about 1.16-1.36 times compared with the helically coiled plain tube (HCPT), while friction factor sharply increases 0.96-1.10 times. The performance evaluation criterion (PEC) could be up to 1.32. The Field synergy number of HCTT based on the field synergy principle (FSP) is much higher than that of HCPT and helically coiled elliptical tube (HCET), which indicates effective improvement of flow and heat transfer by HCTT. The correlation equations in the shell side of HCTT heat exchanger are in conformity with the orthogonal experimental design points.