Investigation on inlet obstruction in transitional flow regime: Heat transfer augmentation and pressure drop analysis

Abstract

Thermohydraulic characteristics of air as the working medium in a circular heated channel fitted with inlet obstruction (ribbed prism) at the inlet is carried out experimentally for transitional flow regime. The ribbed prism is fabricated using aluminum metal. Three non-dimensional parameters clearance ratio (C = 0.4, 0.5 and 0.6) and pitch ratio (e = 0.12, 0.15 and 0.16) were investigated. The Reynolds number (Nu) varied from 500 to 7036 to cover all the flow regimes. Experiments were conducted at two constant heat fluxes of 0.5 kW/m2 and 1 kW/m2. It was found that start and end of transitional flow regime was influenced by insertion of the inlet obstruction at the inlet of the test section. With placement of prism in the channel, the boundaries of transition changes when compared with the plain channel. It is observed that transition starts early and also end early to the transition limit of plain channel. Heat flux shows significant influence on the onset and termination of the transition. At higher heat flux the transition starts later and terminates later when compared with the lower heat flux conditions. For the case of C = 0.6 and e = 0.16, the transition begins Re = 1648 and ends at Re = 3387 for 1 kw/m2 heat flux. The transition of 0.5 kW/m2 of heat flux for C = 0.6 and e = 0.16 begins at Re = 1554 and ends at Re = 3321. Correlations were also developed for predicting the Nusselt number and friction factor and the results are useful to design solar thermal systems and heat exchangers.