Experimental and numerical study of transient heat transfer for forced convection flow of helium gas over a twisted plate

Abstract

This study was conducted to investigate the transient heat transfer process between the solid surface and the coolant (helium gas) in Very High Temperature Reactor (VHTR). Forced convection transient heat transfer for helium gas flowing over a twisted plate was experimentally and theoretically studied. The heat generation rate of the twisted plate was increased with a function of Q = Q0exp(t/τ)(where t is time, τ is period). Experiment was carried out at various periods ranged from 35 ms to 14 s and gas temperature of 303 K under 500 kPa. The flow velocities ranged from 4 m/s to 10 m/s. Platinum plates with a thickness of 0.1 mm and width of 4 mm were used as the test heaters. The plate was 180° twisted with a pitch of 20 mm. Based on the experimental data, it was found that the average heat transfer coefficient approaches the quasi-steady-state value when the dimensionless period τ* (τ* = τU/L, U is flow velocity, and L is effective length) is larger than about 300 and it becomes higher when τ* is small. Three dimensional numerical study were conducted and the results of three typical turbulence models were compared with experimental data. Numerical simulation results were obtained for average surface temperature difference, heat flux and heat transfer coefficient of the twisted plate and showed reasonable agreement with experimental data. Based on the numerical simulation, mechanism of local heat transfer coefficient distribution was clarified. A comparison of the twisted plate and flat plate was conducted to show the difference in heat transfer coefficient distribution.

Keywords

• transient heat transfer
• forced convection
• twisted plate
• exponentially increasing heat generation
• numerical simulation