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UBC Theses and Dissertations

Turbulent natural convection coupled with thermal radiation in a boundary layer Hood, Innes William


Turbulent natural convection coupled with thermal radiation in an absorbing gas, adjacent to a vertical heated plate has been studied. The results of a simplified theoretical model are compared with experimental data obtained using a heated vertical plate in a carbon dioxide and nitrogen gas mixture. The theoretical model assumes a gray, optically thin, nonscattering and infinite gas adjacent to a black, isothermal plate. In addition, the Boussinesq approximation was applied, using the velocity and temperature profiles of Eckert and Jackson. The momentum and energy equations were solved by an integral technique, with the radiation term modelled by two different methods: the mean beam length method; and an exponential kernal approximation. The experimental work consisted of obtaining the temperature and velocity profiles of a turbulent natural boundary layer at one location over a range of carbon dioxide and nitrogen gas compositions, and calculating and comparing the enthalpy flux for the different cases. Results are given in terms of a combined convective and radiative Nusselt number as a function of gas absorptivity. It was found that Eckert and Jackson's velocity profile did not predict the flow accurately. By modifying the profile to fit the data, good ageement between the theory and experiment was obtained.

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