Transitional natural convection flow and heat transfer in an open channel

The work presented here is an experimental study on natural convection flows in a differentially heated open channel configuration. The applications concern the free cooling of both the photovoltaic components integrated within the building envelope (double-skin configuration) and the building itself. Particular focus is given to the identification of integration configurations favorable to both heat transfer on the rear side of components and buoyancy enhancement. The test section consists of a vertical channel with two walls composed of different heating modules. In the present investigation the thermal configuration considers one wall heated uniformly while the other is not heated. We focus on the kinematic characteristics of the flow and convective heat transfer at the heated wall. A PIV system allows investigating the mean velocity field and velocity fluctuations at different levels of the channel height. The experimental procedure allows inferring the wall surface temperature, local heat transfer coefficient and local and average Nusselt numbers. The experimental evidence shows that the flow is neither really turbulent nor purely laminar for the range of Rayleigh numbers considered. Although the average characteristics of the flow seem perfectly consistent with the results obtained, changes of behavior seem to occur intermittently. ► We study experimentally transitional natural convection flow in a vertical channel. ► We focus on the kinematic characteristics of the flow and wall heat transfer rates. ► Performed under UHF conditions, the assumption of an intermittent flow is favored. ► The flow exhibits a high sensitivity to the ambient conditions. ► The identified flow mechanisms suggest a possible control of the wall heat transfer.