Effects of micro heat pipe (MHP) cross-sections and orientations on its thermal performance are experimentally investigated in this study. Tests are conducted using five different cross-sections (circular, semicircular, elliptical, semi-elliptical and rectangular) of micro heat pipes having same hydraulic diameter of 3 mm placed at three different inclination angles (0 o , 45 o , 90 o ), where water is used as the working fluid. Evaporator section of the MHP is heated by an electric heater and the condenser section is cooled by circulation of water in an annular space between condenser section and the water jacket. Temperatures at different locations of the MHP are measured using five calibrated K type thermocouples. Heat supply is varied using a voltage regulator which is measured by a precision ammeter and a voltmeter. It is found that thermal performance tends to deteriorate as the MHP is flattened. Thus among all cross-sections of MHP, circular one exhibits the best thermal performance in terms of heat flux dissipation followed by semi-elliptical, semi-circular, elliptical and rectangular cross-sections. Moreover, its heat transfer capability also decreases with decreasing of its inclination angle. Finally, a correlation is developed which covers all the experimental data within +7%.

Experimental study of natural convection heat transfer across air layers bounded by a lower hot rectangular and a square corrugated plates to an upper cold flat plate has been carried out. The surroundings of this space are adiabatic. The effect of the angle of inclination, the aspect ratio, the temperature potential and the Rayleigh number on average heat transfer coefficients are investigated within a range of 0°<0'Z-75 °, 2.33<_A<6.33, 10°

This work describes an experimental investigation into the effects of surface geometry variations on heat transfer performance in forced flow boiling. Ribs of rectangular cross section were machined on flat stainless steel test specimens of 1.60 mm thickness. The height of the ribs was kept constant at 0.50 mm and a number of test specimens with rib width varying from 0.50 mm to 2.0 mm and rib spacing ranging from 0.50 mm to 3.5 mm were produced. In order to maintain a constant microsurface roughness of 0.7 μm over the entire test specimen, all test surfaces were subjected to vequa-blasting after machining. Precautions were taken to ensure that aging of the heat transfer surface had been established so that the data recorded were reproducible. Experimental data are reported for water at atmospheric pressure with flow velocities of 0.20 m/s to 1.40 m/s. Inlet subcoolings were varied from 5°C to 30°C. The results for the longitudinal ribbed surfaces (LRS) were compared with those for the transverse rectangular ribbed surfaces (TRS) and both sets of data were compared with the heat transfer performance of an optimum flat roughened surface.

An experimental study is conducted to investigate the heat transfer augmentation in developing turbulent flow through a ribbed square duct. The duct is made of 16mm thick bakelite sheet. The bottom surface of the ribbed wall having rib pitch to height ratio of 10 is heated by passing a c current to the heater placed under it. The uniform heating is controlled using a digital temperature controller and a variac. The results of ribbed duct are compared with the results of a smooth duct under the same experimental conditions. It is observed that the heat transfer augmentation in ribbed duct is better than that of the smooth duct. At Re=5.0 10 × 4 , the mean temperature of air flowing through the ribbed duct increases by 2.45 percent over the smooth duct, whereas in the ribbed duct Nusselt number increases by 15.14 percent than that of the smooth duct with a 6 percent increase in pressure drop .

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