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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]

• Fluid flow and thermal performances of PHE are investigated experimentally. • The effectiveness and NTU of PHE are improved with increasing Rr. • Pressure drop and pumping power are increased by increasing Rr. • SHR is improved with increasing surface roughness particularly at low Reynolds number. • Empirical correlations are proposed to predict SHR as a function of Rr and Re. In the present paper, an experimental study of the effectiveness and pumping power of plate heat exchanger (PHE) with rough surface was performed. The experiments were developed for different values of relative roughness, Rr, of 2.6 * 10−4 (smooth surface), 3.4 * 10−4, 7.5 * 10−4 and 9.8 * 10−4 for Reynolds number, Re, varied from 500 to 5000. The average heat transfer rate, Q avg , hence the effectiveness of PHE, ε , and number of transfer units, NTU , as well as pressure drop, Δp , consequently pumping power, P, and specfic heat rate, SHR, were estimated. The results show that Q avg and NTU are enhanced with increasing Rr ; while, they are decreased with increasing Re. At Re = 5000, the effectiveness of PHE with relative roughness of 3.4 * 10−4, 7.5 * 10−4 and 9.8 * 10−4 is greater than that of the smooth surface by 11.5%, 16.6% and 18.6%, respectively. Furthermore, Δp and P are increased by increasing Rr and Re. Moreover, at Re = 500, SHR is enhanced with increasing Rr and its improvements compared with the smooth surface are 39.5%, 23.4% and 6.9% for Rr of 3.4 * 10−4, 7.5 * 10−4 and 9.8 * 10−4, respectively. In addition, empirical correlations are proposed to estimate SHR as a function of Rr and Re with a standard deviation of 5.1%. [ABSTRACT FROM AUTHOR]