Graduate Thesis Or Dissertation
 

The effect of entrance configuration on local heat transfer coefficients in subsonic diffusers

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jm214r85p

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  • The effects of round, square, and reentrant entrances on flow regimes and local heat transfer coefficients were determined using a symmetrical, plane-wall two-dimensional, subsonic air diffuser with one of the diverging walls heated and maintained isothermal. Flow and heat transfer studies were made at total divergence angles ranging from 0 to 45 degrees, at diffuser wall length to throat ratios ranging from 6 to 18, and at Reynolds numbers based on throat velocity and throat width ranging from approximately 40,000 to 300,000. Flow studies were made using wool-yarn tufts and a smoke generator. Flow regimes developed were: no "appreciable" separation, large transitory stall, and fully-developed two-dimensional stall. Velocity measurements were made for fully-developed two-dimensional stall. Steady-state heat transfer measurements were obtained with 23 electrically heated spot heaters mounted in the isothermal wall. Only one of the diffuser walls was heated to an isothermal condition. The other walls and the diffuser entrance sections were adiabatic. Results indicated that the total divergence angle, the ratio of wall length to throat width, and inlet turbulence level had the greatest effect on establishment of flow regimes. Flow patterns were found to be in general agreement with those observed by Waitman, Reneau, and Kline. Heat transfer results for round entrances agreed substantially with those of VanSant. Heat transfer rates for all entrances tested were greatest when the angle of divergence was 0 degrees. When the angle was increased, the heat transfer rates decreased. For the configurations tested, heat transfer rates were greater for reentrant than square entrances. Heat transfer rates from square entranced diffusers were equal to or slightly greater than those with round entrances depending on the flow regime.
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