Correlating equations for laminar and turbulent free convection from a vertical plate

Studies of mixed convection in vertical tubes

Characteristics of a turbulent natural convection boundary layer along a vertical flat plate

Measurement and simulation of flow rate in a water-in-glass evacuated tube solar water heater

The impetus of this paper is to analyse numerically and experimentally the flow and heat transfer characteristics of buoyancy-driven air convection behind photovoltaic panels. Both convection and radiation heat exchanges are considered as the heat transfer mechanisms by which the thermal energy is transferred into the air. Numerical and experimental results are obtained for a channel of 7.0 m in height and the channel walls are separated by a distance of 0.23 m. In the experiment heat is supplied to the air gap from heating foil attached to one of the vertical walls. Different input heat fluxes and emissivity of the bounding surfaces are considered in order to show their effect on the heat transfer across the air layer. Detailed studies of the flow and thermal fields in the air are presented in order to explore the thermal behaviour of the air in the channel. Velocity and temperature profiles of the outlet air and the surface temperature of the heated and insulated wall is presented. The numerical results agreed well with the experimental measurements.

Flow and heat transfer in the air gap behind photovoltaic panels

An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014 ; i.e., fully developed turbulent flow occurs by Ra* = 104 . This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014 . For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.

C. K. Liu

Papers

An Experimental Study of Turbulent Natural Convection Boundary Layers