Browsing by Author "Alijani, Hossein"

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Open Access
Effect of design and operating parameters on the thermal performance of aluminum flat grooved heat pipes
(Elsevier, 2018-03-05) Alijani, Hossein; Çetin, Barbaros; Akkuş, Y.; Dursunkaya, Z.
Four aluminum flat grooved heat pipes with groove widths of 0.2, 0.4, 0.8 and 1:6 mm are fabricated and the effect of filling ratio on the thermal performance is experimentally studied for four different heat flux values of 2.1, 3.2, 4.2 and 5:3W=cm2. An optimum filling ratio corresponding to each heat flux is determined where the heat pipe has the best thermal performance. Thermal performance of the heat pipes are evaluated using three indicators; (i) the temperature difference between the heat source and heat sink surfaces, (ii) the temperature difference between the peak system temperature and the temperature of the cooling ambient and (iii) heat pipe effectiveness defined as a temperature difference ratio under dry and operating conditions. A flow and evaporative mass scaling model is developed to interpret the experimental findings. Experimental results reveal that at the optimum point the heat pipe with the 0:4 mm groove width has the best thermal performance, and the heat pipe with the smallest 0:2 mm groove operates under dryout conditions even for the lowest heat flux, the reason of which is discussed based on interpretation of underlying phase change physics. Experiments reveal the existence of two operating regimes; with and without dryout in the grooves. Although higher heat loads can be carried under dryout conditions, a limit exists for the maximum heat flux where the pipe operates without the onset of dryout for a specific groove density.
Open Access
Experimental thermal performance characterization of flat grooved heat pipes
(Taylor and Francis, 2019) Alijani, Hossein; Çetin, Barbaros; Akkuş, Y.; Dursunkaya, Z.
The thermal characterization of aluminum flat grooved heat pipes is performed experimentally for different groove dimensions. Three heat pipes with groove widths of 0.2 mm, 0.4 mm, and 1.5 mm are used in the experiments. The effect of the amount of the working fluid is extensively studied for each groove width. The results reveal that, although all three succeed in dissipating the heat input through the phase change of the working fluid by continuous evaporation and condensation, the effectiveness of the heat transfer increases with reduced groove width. Furthermore, it is observed that there exists an optimum operating point, where the temperature difference between the heating and cooling sections is at a minimum, and the magnitude of this temperature difference is a strong function of the groove width. To the best of the authors’ knowledge, the combined effects of groove dimensions and the amount of the working fluid, from fully flooded to dry, is reported for the first time for aluminum flat grooved heat pipes.