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An experimental investigation is performed to study the effect of the inclination angle of air jets on heat transfer from a horizontal surface. A pair of inclined circular jets issuing from the straight pipes of length to diameter ratio of 40 is considered. The inclination angles of 0°, 10°, 20°, 30° 45°, and 60° are selected while the Reynolds number is varied from 10,000 to 40,000 based on a jet exit diameter. Jets to impingement plate distance (L/D) as well as the spacing distance (S/D) are changed from 2 to 8. The results of the temperature contours as well as the Nusselt number contours are illustrated to study the characteristics of heat transfer from a flat surface cooled by a pair of oblique jets. The experimental results show that the maximum magnitude of average heat transfer coefficient is achieved in the range of inclination angle from 10° to 20°. Empirical correlations are presented to predict the value of average Nusselt number as a function of Re , Pr , and θ. Moreover, a comparison between the values of average Nusslet number of the present study and those available in the literature is carried out. [ABSTRACT FROM AUTHOR]

In this study, experimental investigation has been conducted on fluid flow and heat transfer of rough mini-channels with rectangular cross sections. The mini-channel considered consists of twelve identical rectangular channels with 4 mm width, 8 mm height, and 80 mm length. Air is employed as the working fluid with Reynolds number varied from 1500 to 5000. Four mini-channels were examined with different values of relative surface roughness ( ɛ ) 1.6 ∗ 10 −4 , 3.45 ∗ 10 −4 , 6.15 ∗ 10 −4 , and 10.5 ∗ 10 −4 . The friction factor ( f ), average Nusselt number ( Nu ), pressure drop penalty factor ( E f ), heat transfer enhancement factor ( E hn ), and universal evaluation parameter (PEC) were evaluated to study fluid flow and heat transfer of rough mini-channels with rectangular cross sections. The results showed that increasing the Reynolds number ( Re ) of air passing through the rectangular rough mini-channel, increases the average Nusselt number ( Nu ) and the pressure drop penalty factor ( E f ), while decreasing the friction factor ( f ) and the heat transfer enhancement factor ( E hn ) which, has a great effect on the universal evaluation parameter (PEC) rather than the pressure drop penalty factor ( E f ). Moreover, a correlation of the relative surface roughness ( ε ) and the universal evaluation parameter (PEC) was obtained. [ABSTRACT FROM AUTHOR]