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Forced Convection Heat Transfer in Circular Meso-Tubes
Lofty H. Rabie, Hesham M. Mostafa, Gamal I. Sultan and M.A. El-Booz

Convection heat transfer of water flow inside a circular meso-channel was investigated experimentally. To perform this experimental study, an experimental test rig was designed and constructed. Test section was shell and tube heat exchanger. It consists of seven meso-scale circular tubes surrounded by a saturated steam to perform its outer surface at constant temperature. Water flows inside these tubes in steady flow and pulsating flow. The ranges tested for pulsation frequencies are 0.5 Hz to 5 Hz and Reynolds number is of 200 to 5000. Four values of inner diameters was tested in this study; 0.25, 0.35, 0.52 and 0.7 mm. Experimental measurements for mass flow rate, temperature, pressure, pressure drop and pulsation frequency are taken to perform the required analysis. Therefore, the average value of convection heat transfer coefficient and friction factor for different operating parameters are computed.

The experimental results show that, the friction factor in the studied operating range decreases as Reynolds number increases but its values are deviated from those reported in conventional tubes due to the small dimensions of the meso-tubes. The friction factor decreases with decreasing tube diameter. Also, Nusselt number increases with increasing Reynolds number for pulsating flow and steady flow. For pulsating flow, Nusselt number takes lower values than steady flow for the same conditions in the studied operating ranges.

Comparison between the obtained experimental results with the previous data and the classical correlations for conventional tubes was done and the disagreement among the researchers was still. Two empirical correlations for both friction factor and Nusselt number were obtained in the range of the studied operating parameters.

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