Jiuyang Yu

Numerical Simulation on Flow and Heat Transfer at Shell-Side of Flat-Tube Heat Exchangers

The fluid flow and heat transfer of the shell-side in one type of flat-tube heat exchangers (FHE) were studied through numerical simulation and experimental methods. In the numerical simulation, hot/cold air was set as working fluid, and the standard k-ɛ turbulence model supplemented by boundary conditions was used, and also the control volume method was used to the discrete control equations. Compared with the same type of circular-tube heat exchangers (CHE), the numerical simulation results show that the pressure drop at the shell-side of FHE decreases by 12%–20%, and heat transfer coefficient increases by about 24%. The coefficient of integral performance Nu/ζ 0.29 has an increment of 22%–34%. Under the same conditions, the experimental results of temperature and the overall pressure drop show that the deviation percentage with those of numerical simulation are less than 8% and 25%, respectively. Both results verify that the heat transfer efficiency and flow resistance characteristics of FHEs are superior to that of CHEs.

Numerical Analysis on Convection Heat Transfer of Pulsating Flow in a Corrugated Tube

Heat transfer enhancement of corrugated tube in Laminar flow was studied using CFD. Numerical calculation performed with grids of increasing density confirms that the grids are independent. In order to get the optimal numerical calculation the boundary layer was refined. The final grid consisted of 146,000 computational cells. The fluid inlet was defined as a velocity inlet with a sinuaoidal pulasating flow input. The outlet was modeled as a pressure-outlet. By numerical simulation, the distribution of velocity and temperature of the corrugated tube of different conditions in different Reynolds number (380–1900) of steady flow, and the vibration frequency (50–200HZ)and the vibration amplitude of sinusoidal (0.1–0.9) pulsating flow is analysed, thus the characteristics of distribution of velocity and temperature are demonstrated. The simulation result indicates that by comparing with the steady flow, the pulsating flow increases the heat transfer efficiency of the corrugated tube in Laminar flow by 83% for most. The enhancement is due to the pulsating flow increating vortex. The vortex result in increasrs disturbance, decreasing the thermal boundary layer thickness, enhancing heat transfer of the corrugated tube. The result also shows that enhancement of heat transfer coefficient inceases as the velocity rises in a certain range, and it also increases as the frequency rises before reaching the peak point and then decreases as the vibration frequency rises in a certain range. Under the condition of none-backflow, the velocity of increasing enhancement of heat transfer coefficient becomes slower and slower as the vibration amplitude rises. In our study, the best dimensionless pulsating frequencies of the corrugated tube are 100∼200 Hz and the amplitudes are 0.4∼0.6, when condition that the Reynolds number is ranged from 380 to 1900.Copyright