Experimental Study on Thermal Behavior of a Stainless Steel-Di Water Flat Plate Heat Pipe

World Applied Sciences Journal 16 (10): 1393-1397, 01 ISSN 1818-495 IDOSI Publications, 01 Experimental Study on Thermal Behavior of a Stainless Steel-Di Water Flat Plate Heat Pipe 1 3 S.M. Rassoulinejad-Mousavi, S. Porkhial, M. Layeghi, B. Nikaeen and H. Samanipour 1 Young Researchers Club, Karaj branch, Islamic Azad University, Karaj, Iran Department of Mechanical Engineering, Karaj Branch, Islamic Azad University, Karaj, Iran 3 Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran Abstract: Thermal performance of a stainless steel-di water flat plate heat pipe (FPHP) is investigated experimentally. The heat pipe walls are made of stainless steel plate. Also DI-water and stainless steel mesh screen are utilized as working fluid and wick structure respectively. Experiments are conducted with various input heat fluxes in order to study thermal performance of the FPHP. The results show that thermal resistance increases with time and stays constant at the steady state condition. Furthermore, it is found that time of reaching to the steady-state condition decreases by increasing the heat flux. Moreover, it has been concluded that temperature distribution on the FPHP walls is rather uniform. Key words: Experimental study Stainless steel DI water Flat plate heat pipe INTRODUCTION porous wick of the evaporator section creates the main thermal resistance resulting in the largest temperature Flat-plate heat pipes (FPHPs) are effective heat drop, that affects the performance of the heat pipe. transfer devices in many industrial applications. They are Furthermore, they obtained an empirical correlation for the special types of heat pipes which can usually transfer time constant in terms of input heat flux (q). In their work higher amounts of heat fluxes with respect to cylindrical a correlation for the maximum temperature rise and heat pipes. A FPHP consist of three main part namely, maximum temperature difference within the FPHP are also container, working fluid and wick structure which is a investigated. porous media. For more information about porous media Kikuchi et al. [16] had performed experiments on an an interested reader can refer to [1-5]. As FPHPs have electro hydrodynamic flat plate heat pipe. The heat pipe suitable thermal characteristics, flat-plate heat pipes are was 100 cm in length and 10 cm in width. Two Freon 111 used in many applications including cooling of high and 113 were used as working fluid. Their results showed power semiconductor chips and cooling of electronic that Freon 11 was superior to Freon 113 from the point of equipments, spacecraft radiator segments and thermal view of thermal transport. management in the irradiation facility for Boron Neutron Basiulis et al. [6] carried out experiments to find out Capture Therapy (BNCT) [6-14]. They can also be used as the performance of flat plate heat pipes for cooling printed a constant temperature surface along with a heater in wiring boards. Thomson et al. [4] investigated the some specific applications such as chemical heat application of FPHPs in the cooling of high power treatment processes in wood industries. amplifiers for communication satellites. A comprehensive experimental study has been Boukhanouf et al. [1] experimentally investigated performed by Vafai et al. [15] on a copper- DO flat plate the performance of a flat-plate heat pipe using an IR heat pipe. The heat pipe was 190.50 mm in length (L), thermal imaging camera. Steady-state and transient 139.70 mm in width and thickness of 34.93 mm. They temperature distribution of the evaporator surface of the Concluded that the temperature along the heat pipe wall FPHP have been measured using a single heat source with surfaces is quite uniform and also indicated that the varied heat flux inputs. Corresponding Author: S.M. Rassoulinejad-Mousavi, Young Researchers Club, Karaj branch, Islamic Azad University, Karaj, Iran. 1393

World Appl. Sci. J., 16 (10): 1393-1397, 01 For performance comparison, the experimental measurements have also been carried out on an identical flat plate heat pipe with a defect and on a solid copper block of similar dimensions. It has been shown that temperature excursion on the surface of the fully functioning flat plate heat pipe is less than 3 C for operating temperatures up to 90 C and heat flux inputs ranging from 4 to 40 W/cm. Furthermore, the thermal spreading resistance of the flat plate heat pipe has been found to be about 40 times smaller than that of the solid copper block and flat plate heat pipe with a defect. Xuan et al. [13] examined the transient behavior of flat plate heat pipes with applied heat flux ranging from about 10 W/cm to 16 W/cm and achieved operating temperatures of about 63 C. Chien et al. [14] studied evaporation resistance on porous surfaces in flat heat pipes. Koito et al. [15] performed an experimental and numerical analysis of heat transfer in FPHPs with a single axisymmetric heat source. In the present work, an experimental investigation is conducted to describe the thermal treatment of a stainless steel-di water flat plate heat pipe in different heat fluxes. Fig. 1: Experimental system: (a) experimental setup and (b) location of the embedded thermocouples Experimental Set Up: Flat plate heat pipe which is studied RESULTS AND DISCUSSION in this work is 00 mm in length, 00 mm in width with thickness of 30 mm. The heat pipe walls were made of The results consist of three parts. First the transient mm thick stainless steel plate. DI-water was selected as thermal behaviour of the heat pipe is investigated. working fluid. Also stainless steel Mesh screen Then, the effect of input heat flux on the time of (900 pores per inch) utilized for wick structure. The wick reaching to the steady-state condition is thickness is 1.7 mm, with porosity of 0.73. A flexible heater described. Afterwards, the wall temperature with length of 100 mm and width of 00 mm was used as distribution for different values of time in different heat a unit heat source. The heater was attached on the centre fluxes is studied. of top outside surface of the heat pipe. In addition the Figure shows the transient temperature response other side of the heater was insulated with asbestos to for different values of heat flux. It can be seen that prevent heat loss. Input power was controlled by an temperature difference between the condenser Ac power supply and its value was measured by a sections and the surfaces next to the evaporator Lutron DW-6060 wattmeter. An insulate frame was used increases with time. Also it is clear form the Figure to cover around of FPHP and prevent heat loss through that, with increasing time thermal resistance the edges. A table has also employed for installation of increases and become constant at the steady state heat pipe on four rods to a certain height so as not to condition. Furthermore, the figure exemplifies that affect the free air convection over the condenser surface. increasing the heat flux increases the wall Fourteen PT-100 thermocouples with accuracy ± C were temperature. attached to measure temperature of outside surface of the Figure 3 demonstrates the effect of input heat flux evaporator and condenser sections, as shown in Figure 1. value on time to reach the steady-state condition. It must be noticed that the thermocouple at L=0 is It is obvious that with increasing the heat flux the attached at the edge and does not show the temperature steady-state condition is achieved faster. It is due to of the surface under the heater while displays the increasing the rate of liquid evaporation and vapor temperature of the wall edge across the heater. condensation in the heat pipe. 1394

World Appl. Sci. J., 16 (10): 1393-1397, 01 Fig. : Transient temperature response of the heat pipe Fig. 3: Influence of heat flux on time of reaching to steady-state condition 1395

World Appl. Sci. J., 16 (10): 1393-1397, 01 Fig. 4: Temperature distributions along the heat pipe surface In Figure 4 the wall temperature distribution is illustrated for different times. It is shown that the temperature distribution is rather uniform in the surfaces of the heat pipe. Thus, it can be concluded that the evaporation of liquid, condensation in vapor region and liquid pumping to evaporator section by the wick structure is good. CONCLUSION An experimental study is conducted to investigate the thermal performance of the stainless steel-di water FPHP. The experiments are done in three different heat fluxes and Transient temperature response of the heat pipe is obtained. Base on the results of this study, the following conclusion can be drawn: Thermal resistance increase with increasing the time and becomes constant at the steady state condition. The time of reaching to the steady-state condition decreases with increasing input heat flux. Temperature distribution is rather uniform and maximum temperature differences between condenser sections and surfaces next to the evaporator in heat fluxes 91.5, 6850 and 11800 w/m are: 3, 6.1 and 14.9 C respectively. REFERENCES 1. Rassoulinejad-Mousavi, S.M. and S. Abbasbandy, 011. Analysis of Forced Convection in a Circular Tube Filled Witha Darcy-Brinkman-Forchheimer Porous Medium Using Spectral Homotopy Analysis Method, J. Fluids Eng-Trans ASME, 133(10): 10107-(1-9). 1396

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