Effect of Sintering Temperature Curve in Wick Manufactured for Loop Heat Pipe

Transcription

1 Effect of Sintering Temperature Curve in Wick Manufactured for Loop Heat Pipe Shen-Chun Wu, Chuo-Jeng Huang, Wun-Hong Yang, Jy-Cheng Chang and Chien-Chun Kung Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 Abstract This investigation examines the effect of the sintering temperature curve in manufactured nicke poder capiary structure (ick) for a oop heat pipe (LHP). The sintering temperature curve is composed of a region of increasing temperature; a region of constant temperature and a region of decining temperature. The most important region is that in hich the temperature increases, as an index in the stage in hich the temperature increases. The ick of nicke poder is manufactured in the stage of fixed sintering temperature and the time beteen the stage of constant temperature and the stage of faing temperature. When the sope of the curve in the region of increasing temperature is unity (equivaent to 10 /min), the structure of the ick is compete and the heat transfer performance is optima. The resut of experiment test demonstrates that the heat transfer performance is optima at 320W; the minima tota therma resistance is approximatey 0.18 C/W, and the heat fux is 17W/cm 2 ; the interna parameters of the ick are an effective pore radius of 3.1 µm, a permeabiity of m 2 and a porosity of 71%. Keyords Loop heat pipe (LHP), capiary structure (ick), sintered temperature curve. D I. INTRODUCTION EVELOPED and patented by Maidanik et a. [1], the oop heat pipe (LHP) has severa engineering appications, incuding the therma management of advanced space patforms and miitary spacecraft, as e as the cooing of eectrica and eectronic devices. An LHP is composed of an evaporator, ith a fine pored capiary structure (ick), and a condenser section that is connected to a separated vapor and iquid fo ines. It expoits atent heat of evaporation and condensation to transfer heat, and depends on the capiary pressure that is generated by the ick structure to circuate the orking fuid around the oop. Shen-Chun Wu Author is ith the Department of Aviation Mechanica Engineering, China University of Science And Technoogy, Taian, R.O.C (corresponding author to provide phone: ; e-mai: mimi1210@seed.net.t). Chuo-Jeng Huang Author is ith the Schoo of Defense Science Studies, Chung Cheng Institute of Technoogy, Nationa Defense University, Taian, R.O.C (e-mai: hcj631216@yahoo.com.t). Wun-Hong Yang Author is ith the Department of Aviation Mechanica Engineering, China University of Science And Technoogy, Taian, R.O.C(e-mai: j @yahoo.com.t). Jy-Cheng Chang Author is ith the Department of Mechanica, Energy and Aerospace Engineering, Chung Cheng Institute of Technoogy, Nationa Defense University, Taian, R.O.C (e-mai: changjc@ndu.edu.t). Chien-Chun Kung Author is ith the Department of Mechatronic, Energy and Aerospace Engineering Chung Cheng Institute of Technoogy, Nationa Defense University, Taian, R.O.C (e-mai: cckung@ndu.edu.t). Based on the principe of inverted menisci, the LHP can achieve a high heat transfer capacity, ong transport distance and o therma resistance, ith sef-adjustment. Researchers ordide have investigated various operating characteristics and the design architectures of LHPs [2-8], and have identified the features of these devices as high heat capacity, reiabiity of operation at adverse tits in a gravitationa fied and heat transfer over ong distances. Based on the above iterature, an LHP has a high heat transfer capacity, a arge transport distance, o therma resistance, and the capacity to sef-adjust. The key determinant of LHP performance is the capacity of the ick. The method by hich the ick is manufactured can infuence the heat transfer performance of the LHP. Unfortunatey, research on manufacturing a ick for use in an LHP is sti acking. Tracey [9] reported that the method of reguating sintering temperature and time can increase the porosity and strengthen the structure of the sintered nicke poder. Hoever, investigations of the reguation of sintering temperature and time are acking. Based on the above discussion, the main objective of this investigation is to study the reguation of the sintering temperature curve of the manufactured ick. Wu et a. [10] suggested a fixed sintering time of 45 min and a constant temperature of 600. This investigation aso studies the effect of the sope of the sintering temperature curve of a fabricated ick. Finay, a heat transfer performance test is performed in an LHP. A. Wick fabrication II. EXPERIMENTAL METHOD An LHP is composed of an evaporator section, a condenser section, vapor and iquid ines, and a compensation chamber (Fig. 1). The evaporator is equipped ith a specia ick and joined to a compensation chamber, hich receives the orking fuid that is dispaced from the vapor ine and the condenser during the start-up and from the condenser during the operation of the device. By definition of its function, the LHP is a heat-transfer device that operates in a cosed evaporation-condensation cyce, using capiary forces to pump a orking fuid. 495 schoar.aset.org/1999.8/4824

2 important is the region of increasing temperature, hich is cosey reated to the mutua bonding of poder partices. Based on the effect of the sintering process in various stages of sintering, the sintering temperature curve at fixed temperature and time is anticipated. This investigation is to study the reguation of the sintering temperature curve of the manufactured ick. Fig. 1 LHP Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 To study the effect of reguating the sintering temperature curve of a manufactured ick, various icks are fabricated from pure Icon type 255 nicke poder ith a partice size of µm, as in Tracey [11]. The nicke poder is then eighed and a stainess stee mod is fied by hammering. After the sintering temperature curve is reguated, the ick is sintered in (a high-temperature air sintering oven. Fooing sintering, the mod is stripped off, yieding a ick of nicke poder (Fig. 2). Fig. 2 Wick manufacture B. Sintering Temperature Curve Reguating the parameters of the manufacturing process of a ick is rather difficut. Hence, in this investigation, the ick parameters are determined form the reguative sintering temperature curve. The sintering temperature curve is determined by sintering temperature and time. Based on the experimenta experience of the authors, various sintering temperature curves can be obtained. The sintering temperature curve is composed of (1) a region of increasing temperature, (2) a region of constant temperature, (3) a region of faing temperature. The sintering temperature curve obtained herein is simiar to that obtained by Wu et a. [10] (Fig. 3). The most Fig. 3 Typica temperature curve To sho the sensitivity that reguated of increased temperature curve sope hich in transition temperature coordinates is constricted 10 times. Therefore, the temperature change is 10 /min. Hoever, based on the experimenta experience of the authors and the range of quaity of the ick on hich the therma test can be conducted, the sope of the rising temperature curve is 0.7 (equivaent to 7 /min) to 1.3 (equivaent to 13 /min) (Fig. 3). As the sope of the temperature curve increases, the rate of increase in temperature increases, arrived specified temperature in a short time. When the sope of the temperature curve is 0.7 (equivaent to 7 /min), the ick is too dense to be usabe. When the sope of the temperature curve is 1.3 (equivaent to 13 /min), the ick is too oose to be used. This investigation examines the sope of rising temperature curve from type II to VI. Tabe 1 presents the durations of the increase in temperature for various curve sopes. TABLE I DURATION OF INCREASE IN TEMPERATURE type sope time I II III IV 1 60 V VI VII To study the effect of the sope of the curve of the increase in temperature on the performance in LHP, icks are manufactured ith various sopes to test their heat transfer 496 schoar.aset.org/1999.8/4824

3 Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 performance. The externa diameter, interna diameter and ength of the ick are 12.5mm, 9mm, and 60mm, respectivey. Tabe 1 shos the externa dimensions of the proposed LHP system. TABLE II LHP SYSTEM PARAMETERS Evaporator Liquid ine Length 40 mm Length 580 mm Materia Auminum Compensation chamber Vapor ine Length 118 mm Length 470 mm Working fuid Condenser Ammonia Heat oad 50~350(W) Length 800 mm Operating temperature 10~85 ( ) C. Evauation of Interna Parameters of Wick The interna parameters of a sintered ick are reated to its heat transfer performance. The most important interna parameter is determined by evauating the quaity of the sintered ick test pieces. The three main parameters that must be evauated in the evauation of a ick are permeabiity ( K ), maximum effective pore radius (γ ), and porosity (ε ). These parameters are given by Eqs. (1), (2), and (3). Equations (1), (2), and (3) are not described in detai because of imitations of space. Figure 3 presents the device for measuring the interna parameters of a ick. This device is designed and manufactured according to the aforementioned equations and ASTME [12]. Fig. 4 Device for measuring interna parameters of ick K ( D D ) = µ mɺ 2πρ P L n (1) r = 2 σ P (2) ( W W ) ( W / M ) ε = (3) t o i D. Test of Heat Transfer Performance of LHP The performance of a icks as tested in an amost ambient environment, ith the condenser sink temperature maintained at 10 ± 2 using a ater cooer. A heater, connected to a poer suppy, is adopted to simuate the heat source during the operation of the LHP. The evaporator on the LHP may impose a heat oad and generate an initia poer of 50W. The evaporator does not stop operating unti either the temperature approaches 85 or drying occurs. Thermocoupe measurements ere made and transferred to a computer through a data acquisition device. Additionay, the K-type thermocoupe (ith a measurement error of ± 0.2 ) is caibrated, and the variation of its measured temperature in the experiment is monitored cosey. Based on an anaysis of error, Kine and McCintock [13] estimated the overa therma resistance in Eq. (4) (ith an error of ± 5.24%), the permeabiity in Eq. (1) (ith an error of ± 2.62%), the effective pore radius in Eq. (2) (ith an error of ± 6.9%) and the porosity in Eq. (3) (ith an error of ± 3.9%). ( ) R = T T Q (4) tota e c Fig. 5 Device for therma testing of LHP III. RESULTS AND DISCUSSION A. Effect of sintering temperature curve on performance of ick Tabe II shos the interna parameters of the ick. A ick that is ooser cannot be formed hen the sope of the curve of increase in temperature is 1.3 (equivaent to 13 /min). The ranges tested by Maidanik [6] ere an effective pore radius of 0.7 ~ 10 µm, porosity of 60 ~ 75% and permeabiity of 0.2 ~ m 2. The most important interna parameter is permeabiity. 497 schoar.aset.org/1999.8/4824

4 Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 TABLE III INTERNAL PARAMETERS OF WICK Sope ε (%) γ (µm) K (m ) 0.7 dense oose To investigate the effect of the sope of the curve of the increase in temperature on the ick, hich interna parameters of the ick are evauated. The permeabiity of interna parameters is as an index. In Fig. 6, as the sope of the curve of the increase in temperature increases, the permeabiity increases. When the sope of the increase in temperature is unity (equivaent to 10 /min), the ick performance is better. When the sope of the curve of the increase in temperature is ess than 0.8 (equivaent to 8 /min), a ong sintering time is required, making the ick dense, affecting performance. When the sope of the curve of the increase in temperature exceeds 1.2 (equivaent to 12 /min), the required sintering time is short, making the ick oose, affecting performance. Accordingy, the resuts obtained using the ick that as manufactured for LHP ithin reveaed three zones of the curve of the increase in temperature. The three zones are (i) a dense zone (ith a sope of ess than 0.9), (ii) a good zone (ith a sope of beteen 1 to 1.1), and (iii) a oose zone (ith a sope of more than 1.2). When the sope of the curve of the increase in temperature is 1.3 (equivaent to 13 /min), the ick is so oose hich cannot be formed. Fig. 6 Reationship beteen sope of curve of increase in temperature and permeabiity B. Anaysis of heat transfer performance A icks are set into the LHP to test their heat transfer performance, and thereby determine ho the sope of the curve of the increase in temperature affects that performance. The heat oad is eectronicay cooed, hich process is simuated using a heat sink at 10 in an evaporator hose temperature is imited to 85 (at a room temperature of 20 ). Therma testing systems are normay operated a 20 times atmospheric pressure. Figure 7 pots the reationship beteen the evaporator temperature (on vertica axis) and the heat oad (on horizonta axis). When the heat source is connected to the evaporator, the temperature of the evaporator increases. At a permissibe temperature of 85, the high heat oad corresponds to favorabe heat transfer performance. The heat transfer performance of the ick in the LHP varies ith the sope of the curve of the increase in temperature. This sope is transformed into an index in the manufacture of the ick. As the sope increases, the rate of increase of temperature increases, but the oosening of the ick detrimentay affects performance, mainy because a higher sope corresponds to a shorter required sintering time, and therefore a eaker mutua bonding among poder partices, finay to an extent so great that the ick cannot even be formed. As the sope decreases, the rate of increase of temperature decreases, and the increasing density of the ick affects performance, primariy because a shorter sope corresponds to the need for a onger sintering time, and therefore a stronger mutua bonding of poder partices, and a denser ick. At a sope of 0.9 (equivaent to 9 /min), the optima heat oad is about 320W (as dispayed in Fig. 8). Fig. 7 Reationship beteen evaporator temperature and heat oad Figure 8 pots the reationship beteen the tota therma resistance of the system (as a function of the heat oad. The icks are manufactured ith curves of the increase of temperature ith various sopes, and these are used in LHPs, hose operating mode is consistent the same as that of a traditiona LHP. As the heat oad increases, the therma resistance decines. A oer therma resistance corresponds to a greater heat transfer performance. A heat oad of around 150W causes a shift from the zone of variabe therma resistance into the zone of constant therma resistance. The change in the therma resistance is responsibe for the change in the sope of 498 schoar.aset.org/1999.8/4824

5 Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 the curve of the increase in temperature, making the ick ooser or denser, affecting the heat transfer performance in the LHP. The resuts indicate that the heat transfer performance is optima at a sope of unity (equivaent to 10 /min), and the optima therma resistance is approximatey 0.18 /W. The therma test as carried out at a heat transfer of 320W, a tota therma resistance of 0.18 /W and a heat fux of 17W/cm 2 ; the interna parameters of the ick ere an effective pore radius of 3.1 µm, a permeabiity of m 2 and a porosity of 71%. Fig. 8 Reationship beteen therma resistance and heat oad C. Sintered temperature curve From the ick capacity and the resuts of the therma test, the optima sope of the sintering temperature curve is unity (equivaent to 10 /min). The stages of the sintering temperature curve are one of increasing temperature, one of constant temperature and one of faing temperature (Fig. 9). The stage of increasing temperature invoves a quantity of 600 and a duration of 60 min, respectivey. The stage of constant temperature invoves a sintering temperature of 600 and duration of 45 min. The stage of faing temperature invoves a sintering temperature of 30 and duration of 495 min. IV. CONCLUSION This investigation examined the effect of changes in the sope of the curve of increasing temperature in the manufacture of icks for LHPs by therma testing. The fooing concusions are dran. 1. A curve of sintering temperature for nicke poder manufactured ick is obtained. The curve consists of a region of increasing temperature, a region of constant temperature and a region of faing temperature. The densities of the icks that ere manufactured at various points on the curve fe into three zones. The three zones ere (i) a dense zone, (ii) a good zone, and (iii) a oose zone. 2. In the stage of the curve of the increase in temperature in hich its sope increases, the optima capabiity of ick is sope unity (equivaent to 10 /min). From the test resuts, the interna parameters of the ick are an effective pore radius of 3.1 µm, a permeabiity of m 2 and a porosity of 71%. 3. The resuts of the therma test of the ick for LHP indicate that the heat transfer performance is optima at 320W; the minimum tota therma resistance is about 0.18 C/W, and the heat fux is 17W/cm 2. NOMENCLATURE D o D L i externa diameter of porous materia interna diameter of porous materia ength of ick mɺ ratio of fo of fuid mass to fo of fuid time P capiary force in ick Q input Watt R tota tota therma resistance of LHP T T e c W t W σ ρ surface temperature of evaporator temperature of therma sink eight of ick infused ith test fuid net eight of ick surface tension coefficient of fuid density of fuid µ viscosity coefficient of fuid ACKNOWLEDGMENT The authors oud ike to thank the Nationa Science Counci of the Repubic of China, Taian, for financiay supporting this research under Contract No. NSC: E Ted Knoy is appreciated for his editoria assistance. Fig. 9 Sintering Temperature Curve 499 schoar.aset.org/1999.8/4824

6 Internationa Science Index, Mechanica and Mechatronics Engineering Vo:6, No:2, 2012 aset.org/pubication/4824 REFERENCES [1] Maidanik, Y. F., Vershinin, S. V., Khoodov, V. F. and Dogirev, J. E., Heat Transfer Apparatus, US Patent, No , [2] Wof, D. A., Ernst, D. M., and Phiips, A. L., Loop Heat Pipes-Their Performance and Potentia, SAE Paper, No , [3] Gernert, N. J., Badassarre, G. J. and Gottschich, J. M., Fine pore oop heat pipe ick structure deveopment, SAE Paper, No , [4] Cheung, K. H., Hoang, T. T., Ku. J. and Kaya, T., Therma Performance and Operationa Characteristics of Loop Heat Pipe (NRL LHP), SAE Paper, No , [5] Kaya T. and Jentung Ku, Therma Operationa Characteristics of a Sma-Loop Heat Pipe, J. Thermophys. Heat tr., Vo.17 No.4, 2003, pp [6] Maidanik, Y. F., Loop Heat Pipes-revie, App. Therm. Eng., Vo.25, No.5-6, 2005, pp [7] Li, J., Zou, Y., Cheng, L., Singh, R. and Akbarzadeh A., Effect of fabricating parameters on properties of sintered porous icks for oop heat pipe, Poder Technoogy, Vo.204 No.2-3, 2010, pp [8] Tang, Y., Zhou, R., Lu, L. and Xie, Z., Anti-Gravity Loop-Shaped Heat Pipe ith Graded Pore-Size Wick, App. Therm. Eng., In Press, Accepted Manuscript, [9] Tracey, V. A., Effect of sintering conditions on structure and strength of porous nicke, Poder Metaurgy, No. 2, 1979, pp [10] Wu, S. C., Huang, C. J., Wei, K. H. and Chen, Y. M., Enhanced performance of monoporous ick appications at Loop Heat Pipe by experimenta design, App. Therm. Eng., (2011) Submitted. [11] Tracey, V. A., Pressing and Sintering of Nicke Poders, Internationa Journa of Poder Metaurgy and Poder Technoogy, Vo.20, 1984, pp [12] ASTM E128-61, Standard test method for maximum pore diameter and permeabiity of rigid porous fiters for aboratory use. [13] Kine, S. J. and McCintock, F. A., Describing Uncertainties in Singe Sampe Experiments, Mechanica Engineering, Vo.75, 1953, pp.3-8. Shen-Chun Wu received his bacheor degree from Chung Cheng Institute of Technoogy in 1989 R.O.C. Air Force Academy and Ph. D. degree from Nationa Taian University in Afterards, he joined the Dept. of Mechanica Engineering of Chung Cheng Institute of Technoogy as an assistant professor. He as promoted to associate professor in In August 2009, He transferred to China University of Science and Technoogy to be an associate professor. His research areas incude ne energy technoogies, eectronics cooing. E-mai: mimi1210@seed.net.t 500 schoar.aset.org/1999.8/4824