Experimental investigation of micro heat pipes of different cross-sections having same hydraulic diameter

Abstract

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%.

Study of Two-Metal (Cu-Ag) Micro Heat Pipe of Square Cross Section Using Different Liquids of Low Boiling Point

“…Then the Variac is connected with the AC power source to produce controlled heat by the heater. The power range is chosen from 2W to 16W producing heat flux ranging 3.1 kW/m 2 to 24.7 kW/m 2 simulating the generated heat in a laptop computer processor and similar electronic equipment [6]. It can be noted, before wrapping the heater coil, its red-hot power limit is checked and found to be 24W.…”

“…Authors here disagree with Annamalai that there should be no reason to windup the heater coil densely in the middle of the evaporator rather wrapping must be uniformly done so the produced heat flux remains constant throughout the evaporator. Based on this work and the work of Sakib [6] and Sreenivasa [4], the working fluid should be filled only equal to or less than the empty space (vapor core) of the evaporator of the heat pipe. However, a lot more space in the heat pipe is still vacant to travel during operation.…”

“…That's why we notice the temperature rise at point T 2, hence this end of the evaporator act as a super heater. Regarding the rise of temperature in the evaporator, a comparative relationship between the fluids in the TMMHP and in the SMMHP [6] is shown in Figure 13 (ac). The trend for temperature rise for all the hydrocarbons is quite similar throughout the heat pipe.…”

“…398 W/m-K for copper and 429 W/m-K for silver) for variable heat conductivity has been selected by the author Iqbal [8] in his doctoral thesis. Out of four TMMHP cross sections, Iqbal and Akhanda [9] found the triangular one enhances the heat transfer coefficient by two and a half times from that one produced by SMMHP [6]. Moreover, because of its geometry, the pressure gradient of the working fluid will also be variable in the respected TMMHP sub-sections.…”

“…Akhanda et al [5] tested an air cooled condenser to investigate the thermal performance of MHPs charged with different fluids and oriented a different inclinations. Sakib Lutful Mahmood [6] at Islamic University of Technology (IUT), OIC has performed tests on different cross sections of MHP of the same hydraulic diameter charged with water at different inclinations. It was found that the best heat transfer coefficient at the circular cross section was at an angle of 90 o .…”