Vol. 2(5), 10, 91-9 THERMAL PERFORMANCE OF A TWO PHASE CLOSED THERMOSYPHON USING AQUEOUS SOLUTION M. KARTHIKEYAN 1, S. VAIDYANATHAN 2, B. SIVARAMAN 1 Lecturer (Senior Scale) in Mechanical Engineering, Annamalai University, Annamalai Nagar 02, TamilNadu, India. Ph: +91 98 246 2 Reader in Mechanical Engineering, Annamalai University, Annamalai Nagar 02, Tamil Nadu, India. ABSTRACT The thermal performance of an inclined two phase closed thermosyphon with different working fluid has been investigated experimentally in this paper. Distilled water and an aqueous solution that has a positive gradient of surface tension with temperature are used as the working fluid. A copper thermosyphon with a length of 0 mm long, an inner diameter of 17 mm and an outer diameter of 19 mm was employed. Each thermosyphon was charged with % of the working fluid and was tested with an evaporator length of 0 mm and condenser length of 4 mm. The thermosyphon was tested for various inclinations of 45, and to the horizontal. Flow rate of 0.08Kg/min, 0.1 Kg/min and 0.12 Kg/min and heat input of W, W and W were taken as input parameters. The thermal performance of aqueous solution charged two phase closed thermosyphon was out performed the distilled water in both heat transfer and temperature distribution. Keywords: Two phase closed thermosyphon, heat transfer coefficient, aqueous solution 1. INTRODUCTION Two phase closed thermosyphon also known as wickless heat pipes is an effective heat transfer device. It is a vertically oriented wickless heat pipe with a liquid pool at the bottom. It consists of an evacuated closed pipe filled with a certain amount of suitable working fluid. The two phase closed thermosyphon is divided into three main sections namely the evaporator section, adiabatic section and condenser section. When heat is added on the evaporator section, the working fluid inside the pipe vapourize and carries heat from the heat source to the condenser section, where heat is transferred to the heat sink. The condensate working fluid returns to the evaporator section by gravity force only. Hence, the condenser section of the pipe must be located above the evaporator section. Due to the large latent heat transfer associated with the phase change processes, a large quantity of heat can be transferred from the evaporator section to the condenser section with a relatively small temperature difference. The important advantage of a two phase closed thermosyphon is that its critical heat flux is 1.2 1.5 times greater than the heat pipe [6]. Thermosyphons offer many advantages in electronics cooling, chemical engineering, waste heat recovery, power generation, air conditioning systems, water heater and solar collectors. [2,4,5,9,12,14]. Negishi and Sawada [7] experimentally studied the heat transfer performance of an inclined two phase closed thermosyphon. They used water and ethanol as working fluids, and found that highest heat transfer rates are obtained when the filling ratio is between 25% and % for water and % and 75% for ethanol and the inclination angle is between o and o for water and more than 5 o for ethanol. Amornkitbumrung et al. [] studied the effect of the inclination angle on the heat transfer rate of a two phase closed thermosyphon using a copper water thermosyphon. They studied that the highest heat transfer rate occurred at 22.5 o with a filling ratio of 0%. Payakaruk et al [8] investigated the heat transfer characteristics of copper thermosyphons with 7.5, 11.1 and 25.4 mm inner diameter and water, ethanol, R-22, R- 12 and R-14 as working fluids. They found that the optimum inclination angle for water is between o and o. Terdtoon et. al [10] investigated the effect of the aspect ratio and Bond number on the heat transfer characteristics of an inclined two phase closed thermosyphon and found that the optimum inclination angle for water is between o and o from a horizontal axis. Wang and Ma [11] studied condensation heat transfer inside vertical and inclined ISSN: 0975-5462 91
Vol. 2(5), 10, 91-9 thermosyphons and concluded that the inclination angle of a thermosyphon has a notable influence on the condensation coefficient and the optimum inclination angle varies from o to o with filling ratio. Zhang [1] promoted the use of working fluids for heat pipe systems like dilute alcohol solutions (range between 0.0005 and 0.008 moles per litre) which exhibit a non-linear dependence of the surface tension with temperature and a positive gradient with increasing temperature in a suitable range of temperatures and concentrations. At low concentration, the aqueous solutions behave like positive binary mixtures [1]. 2. EXPERIMENTAL SETUP To study the thermal performance of a two phase closed thermosyphon, an experimental setup has been designed. The schematic of the experimental test is shown in the Figure 1. The parameters and the ranges of two phase closed thermosyphon and limitation of thermosyphon are tabulated in Table 1 and 2 respectively. Figure 1. The experimental set up The thermosyphon under the study has 0 mm long of 19 mm outer diameter and 17 mm inner diameter made of copper tube. The length of the evaporator section is 0 mm, adiabatic section is 1 mm and condenser section is 4 mm. Distilled water and aqueous solution of n-butanol (1x10 - moles/litre) were used as the working fluid. Five thermocouples are provided in the thermosyphon to measure the vapour temperature, evaporator temperature, one thermocouple is provided to measure adiabatic temperature, three thermocouples are provided to measure condenser temperature and two thermocouples are provided to measure water inlet temperature and water outlet temperature. Copper constantan thermocouples (T Type) are used to measure the temperature. The flow rate of cooling water was regulated by a rotameter. Electric heater which supplies heat respect to the evaporator section was made of nickel-chrome wire with a power of 0 W. Thermocouples were connected to the digital temperature indicator to measure the corresponding temperatures. Auto transformer was used to vary the heat input. Before charging the pipe, it was cleaned thoroughly to remove the grease or oil from the inner surface. A vacuum pump was used to eliminate any non condensable gases from the thermosyphon. Finally, the pipe was charged with the working fluid to make it ready for the experiment. A series of experiments were performed for inclination angle of 45, and with flow rate of 0.08 Kg/min, 0.1 Kg/min and 0.12 Kg/min and heat input of W, W and W for a filling ratio of %. ISSN: 0975-5462 914
Vol. 2(5), 10, 91-9 Table 1: Parameters and the ranges of thermosyphon Parameters Range Inner diameter of the pipe 17 mm Outer diameter of the pipe 19 mm Total length of the pipe 0 mm Length of evaporator section 0 mm Length of adiabatic section 1 mm Length of condenser section 4 mm Working fluid Distilled water, aqueous solution Inclination angle 45,, Charging ratio % Heat input W, W, W Table 2: Limitation of thermosyphon Sonic Limit Boiling Limit Counter current flow Limit 4677.68 W 1241.48 W 2516.08 W. RESULTS AND DISCUSSION.1 Temperature distribution along the thermosyphon Fig. 2 to 10 shows distance Vs surface temperature along the thermosyphon. When heat input increases, the surface temperature of distilled water and aqueous solution used in the thermosyphon increases. The surface temperature of thermosyphon with aqueous solution is higher than the distilled water..2 Effect of thermosyphon efficiency Fig 11 to 1 shows the heat input Vs efficiency of thermosyphon for various heat input and flow rates for both distilled water and aqueous solution. The efficiency of thermosyphon gives better results for aqueous solution than the distilled water for all inclinations, heat input and flow rates. For vertical position of thermosyphon, the efficiency is higher than the other inclination. The lower inclination reduces the efficiency due to the obstruction of vapour with condensate return from the condenser. The efficiency is higher for W heat input than the W and W heat inputs. 110 0 0 water - W water - W water - W aqueous - W aqueous - W aqueous - W Fig 2 : Flowrate 0.08Kg/min inclination 45 water - W water - W aqueous - W water - W aqueous - W aqueous - W Fig : Flowrate 0.08Kg/min inclination ISSN: 0975-5462 915
Vol. 2(5), 10, 91-9 0 0 water - W water - W water - W aqueous - W aqueous - W aqueous - W water - W water - W water - W aqueous - W aqueous - W aqueous - W Fig 4 : Flowrate 0.08Kg/min inclination Fig 7 : Flowrate 0.1Kg/min inclination 0 water - W water - W aqueous - W water - W aqueous - W aqueous - W Fig 5 : Flowrate 0.1Kg/min inclination 45 0 water - W water - W water - W aqueous - W aqueous - W aqueous - W Fig 8 : Flowrate 0.12Kg/min inclination 45 0 water - W water - W water - W aqueous - W aqueous - W aqueous - W Fig 6 : Flowrate 0.1Kg/min inclination 0 water - W water - W water - W aqueous - W aqueous - W aqueous - W Fig 9 : Flowrate 0.12Kg/min inclination ISSN: 0975-5462 916
Vol. 2(5), 10, 91-9 Temperature in Degree C 0 water - W water - W aqueous - W water - W aqueous - W aqueous - W Efficiency % 0 Heat input in Watt w ater 0.08Kg/min w ater 0.1Kg/min w ater 0.12Kg/min aqueous 0.08Kg/min aqueous 0.1Kg/min aqueous 0.12Kg/min Fig 10 : Flowrate 0.12Kg/min inclination Fig 11 : Efficiency for 45 o inclination Efficiency % Efficiency % 1 0 Heat input in Watt water 0.08Kg/min aqueous 0.08Kg/min water 0.1Kg/min water 0.12Kg/min aqueous 0.1Kg/min aqueous 0.12Kg/min 0 water 0.08Kg/min water 0.1Kg/min water 0.12Kg/min Heat input in Watt aqueous 0.08Kg/min aqueous 0.1Kg/min aqueous 0.12Kg/min Fig 12 : Efficiency for o inclination Fig 1 : Efficiency for o inclination 4. CONCLUSION The effect of various flow rate, various heat input and inclination angle for both distilled water and aqueous solution on thermal performance of two phase closed thermosyphon has been investigated under normal operating conditions experimentally. Based on the results, the thermosyphon charged with aqueous solution has the maximum thermal performance than compared to thermosyphon charged with distilled water. 5. REFERENCES 1. Abe Y, About self rewetting fluids possibility as a new working fluid, Thermal Science Engg 8(4), (0). 2. Akbarzadeh A, Johnson P, Nguyen T, Mochizuki M, Mashiko M, Sauciuc I, Kusaba S and Suzuki H, Formulation and Analysis of the heat pipe turbine for production of power from renewable sources, Applied thermal Engineering, vo.21, pp. 1551-156, (01).. Amornkitbamrung M, Wangnippanto S and Kiatsirirote T, Performance studies on evaporation and condensation of a thermosyphon heat pipe, Proc 6 th ASEAN Conference of Energy Technology, 28-29 August, Bangkok, Thailand, pp 27-4, (1995). 4. Dunn P D, Reay D A, Heat pipes, Fourth Edition, Pergamon Press, 1994 5. Faghri A, Heat pipe science and Technology, Taylor and Francis, London, 1995 6. Imura H., Sasaguchi K., and Kozai H., Critical Heat flux in a closed two phase thermosyphon, Int. J. of heat and Mass Transfer, vo.26, no.8, pp.11-18, (198). 7. Negishi K and Sawada T, Heat transfer performance of an inclined two phase closed thermosyphon, Int. Journal of Heat and Mass Transfer, vol 26, no.8, pp. 17-121, (198). 8. Payakaruk T, Terdtoon P and Ritthidech S, Correlations to predict heat transfer characteristics of an inclined closed thermosyphon at normal operating conditions, Applied Thermal Engineering, vol, pp 781-7, (00). 9. Peterson G P, An Introduction to heat pipe, Wiley and Sons, 1994 10. Terdtoon P, Ritthidech S and Shiraishi M, Effect of aspect ratio and bond number on an inclined closed two phase thermosyphon at normal operating condition, Proc 5 th International Heat pipe symposium, 17- November, Melbourne, Australia, pp 261-266, (1996). 11. Wang J C Y and Ma Y Condensation heat transfer inside vertical and inclined thermosyphons, Journal of Heat transfer, vol 11, pp 777-7, August (1991). 12. Xiao P W, Johnson P and Akbarzadeh A, Application of Heat pipe heat exchanger to humidity control in air-conditioning systems, Applied thermal Engineering, vo.17, pp. 561-568, (1997). 1. Zhang N, Innovative heat pipe systems using a new working fluid, Int. Comm. Heat and Mass Transfer, vol. 28, no.8, pp 1025-10, (01). ISSN: 0975-5462 917
Vol. 2(5), 10, 91-9 14. Zuo Z J, Fale J E, Gement N J and Goryca M L, Heat pipe radiator analysis, design and manufacturing, Proc. 10 th International heat pipe conf, 21-25 September, Stuttgart, Germany, Session C-8, pp 1-11, (1997). ISSN: 0975-5462 9