Velocity Measurements in Two Natural Convection Air Flows Using a Laser Velocimeter

Abstract

Velocities in two laminar free convection air flow fields were measured using a laser velocimeter. Velocities were first measured in the boundary layer around a heated vertical flat plate and results compare within two percent of theoretical and previous experimental (streak photography) data. Second, velocities were measured throughout a two-dimensional triangular enclosure, which consisted of two isothermal side walls (one heated and one cooled), an insulated bottom, and glass end plates. Enclosure data are compared to simple inclined isothermal plate data and are also presented so that the flow patterns can be observed.

Periodically Forced Natural Convection Through the Roof of an Attic-Shaped Building

“…A comparison study is performed by Ridouane et al (2005) where the authors compare their numerical results produced for two different boundary conditions, (a) cold base and hot inclined walls (b) hot base and cold inclined walls with the experimental results obtained by Flack (1980;1979). A good agreement has been obtained between the numerical predictions and the experimental measurements of Nusselt number.…”

“…The author also reported the critical Rayleigh numbers of the transition from laminar to turbulent regimes. Kent (2009a) has also investigated the natural convection in an attic space for two different boundary conditions similar to Flack (1980;1979). The author observed that for top heating and bottom cooling case the flow is dominated by pure conduction and remains stable for higher Rayleigh numbers considered.…”

“…This may due to the fact that the flow structure in the attics subject to the daytime condition is relatively simple. The flow visualization experiments of Flack (1979) showed that the daytime flow remained stable and laminar for all the tested Rayleigh numbers (up to about 5 × 10 6 ). Akinsete & Coleman (1982) numerically simulated the attic space with hot upper sloping wall and cooled base.…”

“…A small number of publications are devoted to laminar natural convection in two dimensional isosceles triangular cavities in the vast literature on convection heat transfer. The temperature and flow patterns, local wall heat fluxes and mean heat flux were measured experimentally by Flack (1980;1979) in isosceles triangular cavities with three different aspect ratios. The cavities, filled with air, were heated/cooled from the base and cooled/heated from the sloping walls covering a wide range of Rayleigh numbers.…”

“…The Rayleigh number for the periodic boundary condition has been defined based on the maximum temperature difference between the inclined surface and the bottom over a cycle as Ra = 2gβT A h 3 κν Three aspect ratios 0.2, 0.5 and 1.0, four Rayleigh numbers, 1.5 × 10 6 ,7.2× 10 5 ,1.5× 10 4 ,and 1.5 × 10 3 , and a fixed Prandtl number 0.72 are considered in the present investigation. Based on the experimental observations of Flack (1979), which reported the critical Rayleigh number for the flow to become turbulent, we have chosen the maximum Rayleigh number, Ra = 1.5 × 10 6 so that the flow stays in the laminar regime. It is understood that in real situations the Rayleigh number may be much higher than this and an appropriate turbulence model should be applied.…”