Flow patterns and heat transfer coefficients using a rotational diffuser coupled with a radiant floor cooling

Abstract

In this research, we explore the characteristics of an HVAC system consisting of a rotational floor diffuser with an underfloor plenum, coupled with a radiant floor cooling. Numerical simulations are performed using two different meshes. Firstly, we solve the diffuser outflow entering into the room by means of a very detailed mesh.Secondly, the whole room with the radiant floor using as input the flow obtained from the former diffuser mesh. Besides, we analyze the flow visualizations that emerge near the rotational diffuser, and we demonstrate that there are two different regimes depending on the flow rate: (i) displacement ventilation that works as a radial flow, and (ii) a vertical jet with a very active mixing process for low or high flow rates, respectively. We calculate the Nusselt number versus the Reynolds number and collapse into a linear fit with different slopes below and above the Reynolds number 16,000, a limit that coincides with the previously observed change in flow patterns. Therefore, the type of flow patterns created near the diffuser only affect the level of heat transfer, but not its linear dependence. Finally, we propose another non-linear general adjustment of the Nusselt number as a function not only of Reynolds number but of the temperature ratios for all cases considered (isothermal and non-isothermal). This last non-linear regression model shows us that only inertia controls heat transfer and independence on the temperature ratio for Reynolds numbers lower than 16,000.