Research of near-wall thermodynamic state for indoor airflow over the vertical heating unit using TIV/PIV/RTD

Abstract

Up to now, few studies focus on thermodynamic state including the velocity and temperature of the air near heating unit. The thermodynamic state of the airflow over an indoor heating unit has a significant influence on indoor thermal comfort and energy consumption. This study analyzed the thermal and dynamic state of the near-wall airflow over the heating unit. The thermal state was measured using resistance thermal detectors (RTDs). The near-wall airflow fields were measured by particle image velocimetry (PIV) and thermal image velocimetry(TIV). The performance of TIV in natural and mixed convection was evaluated by comparing the TIV and PIV measurement results. Under natural convection, the velocity shows vertical variation and the spatial difference changes more pronounced with the increase of heating temperature. Under mixed convection, the near-wall temperature changes uniform and the velocity exhibits a decreasing trend with the increase of height. Through the spectrum analysis of the temperature, it is found that the velocity measured by TIV is close to the velocity near the boundary layer to some content. The positions of the near-surface velocity measured by TIV are not fixed in all cases and change with the change of the boundary layer. The findings in this study can provide a convenient and feasible flow field measurement method suitable for actual space scale. This method can predict the effect of heating terminal units on indoor airflow and thermal environment, so as to optimize the form and arrangement of the heating terminal units, and improve heating efficiency and occupants’ thermal comfort.