Effect of inclined heat transfer rate on thermosyphon heat pipe under sound wave

Transcription

1 As. J. Energy Env. 2009, 10(04), Asian Jurnal n Energy and Envirnment ISSN Available nline at Research Article Effect f inclined heat transfer rate n thermsyphn heat pipe under sund wave Smpn Wngtm* and Tanngkiat Kiatsirirat Department f Mechanical Engineering, Faculty f Engineering, Chiang Mai University, Chiang Mai Thailand. *Authr t whm crrespndence shuld be addressed, w_smpn@htmail.cm This paper was riginally presented at the Internatinal Cnference n the Rle f Universities in Hands-On Educatin, Chiang Mai, Thailand, August Abstract This research studied the heat transfer rate enhancement f a thermsyphn heat pipe using sund wave t case evapratin prcess. The experiment was dne n a single thermsyphn with sund wave. The experimental set up was cmpsed f a bare cpper tube having m d and 0.45 m evapratr and cndenser sectins length. Inlet ht air temperature ranged between 50, 60, 70, 80 and 90 C and R-123 was the thermsyhpn wrking fluid. Filling fractin f the thermsyphn was 60, 70 and 80%. The sund wave generatr was installed at the evapratr sectin f each tube creating 70, 80, 90 and 100 Hz wave frequency and input pwer f 110 W. The results f this experiment shwed that a thermsyphn under sund wave culd increase the heat transfer rate by abut 67.65%, depending n the best case f a heat pipe at 15 degree incline, 70 C f ht water at evaprating sectin, with 100 Hz and a filling rati f 70% wrking fluid. Keywrds: energy, heat transfer cefficient, evapratr, cndenser, wrking fluid, Thailand Intrductin Thermsyphn heat pipe is a heat exchanger that is increasingly finding use in many industrial prcesses. This is because it prvides a higher heat transfer rate and is relatively simple t prduce. Thermsyphn heat pipes are cmprised f three majr parts, evaprating sectin, adiabatic sectin and cndensing sectin, as shwn in Figure 1. The evaprating sectin receives heat frm a high temperature surce and will transfrm the wrking fluid by biling t vapur. The vapur will then mve t the cndensing sectin at

2 As. J. Energy Env. 2009, 10(04), the tp, and then cndense t liquid t flw dwn t the evaprating sectin again in a cyclical prcess. Nrmally the heat transfer efficiency f a thermsyphn depends n the temperature f the heating surce. In cases where the surce has lw temperature, it is fund that the heat transfer prcess is insufficient. This is because it is difficult t bil the wrking fluid at lw temperature. The prblem can be slved by selecting the technique f vibrating the wrking fluid by using a sund wave in rder t actuate the wrking fluid inside the heat pipe t be turbulent, with subsequent n heat transfer. Buffer gas Heat Sink Cndenser Sectin Insulatin Adiabatic sectin Heat surce Evapratr Sectin Figure 1. Schematic f simple thermsyphn heat transfer. Oh et al [1], studied the effect f ultrasnic waves n heat transfer in changing phase prcess f wrking fluid. It was fund that the ultrasnic wave can increase the melting prcess by as much as 2.5 times cmpared t n ultrasnic prcess. Siriwichai [2], studied the incremental perfrmance f a thermsyphn heat pipe, including ultrasnics. Dimensins f the heat pipe were a diameter f m, 0.16 m in length f evaprating and cndensing sectin, the ht water temperature f C with 5 0 C f cl water, including an ultrasnic surce at the end f evaprating sectin. This research sets the frequency at 8-14 khz. It was fund that the heat pipe perfrmance increases 20-60%, depending upn wrking fluid and ht water temperature. The ptimum frequency was fund t be 8 khz. Techana [3], studied the perfrmance f biling inside a thermsyphn heat pipe that included an ultrasnic system. The research studied the psitin f the heat pipe in the vertical and incline by fcusing n the relatinship f cnvective heat transfer and inlet temperature f water at the evaprating sectin and the angle t level f heat pipe. The study used ht water and ht water as the heat exchange. The heat exchanger was made frm cpper withut any fins. Dimensins were mm inside diameter, 1.3 mm thickness, 1.2 m length, 0.5 m evaprating length and 0.2 m adiabatic length, with C ht water temperature. The wrking fluid was water with 50% filling f the evaprating sectin. The

3 As. J. Energy Env. 2009, 10(04), ultrasnic system was set at the bttm f the heat pipe at the evaprating sectin with 8, 10 and 14 khz. It was fund that the ultrasnic wave culd increase the cnvective heat transfer cefficient at the evaprating sectin t 370% at ht water inlet temperature C. Hwever, at increasing water temperature it was fund that the heat pipe perfrmance with n ultrasnic was the same as using ultrasnic. In the case f a heat pipe set t an incline, it was fund that perfrmance was the highest when set at a 30 0 incline. Frm the previus research [4, 5, 6], there has t date been n knwn study f thermsyphn heat pipe perfrmance with sund waves and the heat pipe set t incline at varying degrees, and is thus the purpse f this research. Our study can als be applied t the case f slar water heating which uses a heat pipe. T14 T1 T2 T15 T4 T4 Cling Jacket Cld bath T5 T6 F P adiabatic T13 Cntrl valve T17 T7 T8 Thermsyphn T18 T9 T10 Ht Jacket Ht bath T11 T12 F P Functin generatr amplifier tranducsr T16 Cntrl valve Figure 2. Heat transfer experimental set-up f thermsyphn heat pipe including sund wave system. Methdlgy Installatin Figure 2 shws the experiment set-up fr the study f heat transfer characteristics f a thermsyphn heat pipe that includes an ultrasnic system. The thermsyphn is made frm cpper tubes with a diameter f m, 1.3 mm thickness, 1 m length, evaprating sectin 04.5 m in length, 0.1 m adiabatic sectin with wrking fluid filling 80% f the evaprating sectin. Thermcuples, type K, are used t measure the temperature with 18 pints [7]. They are the inlet and utlet water f bth evaprating and cndensing sectins, uter wall temperature f heat pipe at bth evaprating and cndensing sectins, and inside heat pipe temperature f bth evaprating and cndensing sectins with 3 pints fr each spt. ROtameter is used t measure the inlet flw rate f the water in the range 1-10 l/min.

4 As. J. Energy Env. 2009, 10(04), with 0.01 l/min in errr. The heat surce cnsists f a stainless vessel with dimensins 50 x 50 x 45 cm, including 6 sets f 1 kw heaters and sund wave surce with a high pwer f 110 watts that generates a wave f 40 khz. Heat Transfer Analysis Heat transfer rate f the thermsyphn can be determined frm heat transfer at the cndensing sectin: Q = mcp & ( T T ) c sc,ut sc,in (1) In the case f adiabatic prcess, the heat transfer rate at the cndensing sectin will be equal t the heat transfer rate at evaprating sectin as per the equatin: Q c = Q e (2) Z 3 Z 4 Z 1 Z 2 Figure 3. Heat Circuit Resistance. Frm the heat circuit resistance as shwn in Figure 3, the heat transfer rate at the evaprating sectin will be: Where, Te Tei Qe = Z + Z 1 2 D 0 ln Di Z1 = 2π K L cpper e (3) (4) S that the heat transfer cefficient at the evaprating sectin can be calculated frm:

5 As. J. Energy Env. 2009, 10(04), Z h T T = Z e ei 2 1 Qe ei 1 = Z A 2 ei (5) (6) Results and Discussin Figure 4 shws the case f thermsyphn heat transfer at 15 0 incline and 80 0 C ht water at the evaprating sectin and 80 Hz sund wave. The results shw that the heat transfer resistance value inside the pipe is the lwest. 0 Hz Hz Hz Hz Hz 15 heat transfer resistance (K/W) Hz 15 0 Hz inlet temperature f ht water( 0 c) Figure 4. Relatinship between heat transfer resistance inside the pipe and water temperature inlet t evapratin with sund wave at 0, 70, 80, 90, and 100 Hz, respectively. At 15 0 incline f heat pipe the filling rate f wrking fluid is 70%. Figure 5 shws the case f thermsyphn heat transfer with 15 0 incline, 80 0 C ht water inlet and 80 Hz f sund wave. The results shw that the cnvective heat transfer cefficient inside the pipe is the highest.

6 As. J. Energy Env. 2009, 10(04), Hz Hz Hz Hz Hz 15 heat transfer cefficient (W/m 2 K) Hz Hz inlet temperature f ht water( 0 c) Figure 5. Relatinship between heat transfer rate inside the pipe and water temperature inlet t evapratin with sund wave at 0, 70, 80, 90 and 100 Hz, respectively. At 15 0 incline f heat pipe the filling rate f wrking fluid is 70%. Figure 6 shws the case f thermsyphn heat transfer with 15 0 incline, 90 0 C ht water inlet and 100 Hz sund wave. The results shw that the heat transfer rate inside the pipe is the highest. 0 Hz Hz Hz Hz Hz 15 heat transfer rate (W) Hz 15 0 Hz inlet temperature f ht water( 0 c) Figure 6. Relatinship between heat transfer rate inside the pipe and water temperature inlet t evapratin with sund wave at 0, 70, 80, 90 and 100 Hz, respectively. At 15 0 incline f heat pipe the filling rate f wrking fluid is 70%. Cnclusin The experimental results shw that in the case f thermsyphn heat pipe at 15 0 incline, 80 0 C ht water inlet at evaprating sectin and 80 Hz sund wave, the heat transfer

7 As. J. Energy Env. 2009, 10(04), resistance is K/W. In the case f thermsyphn heat pipe at 15 0 incline, 70 0 C ht water inlet at evaprating sectin and 80 Hz sund wave it is shwn that the cnvective heat transfer cefficient can be increased t 48.51%. Finally, in the case f thermsyphn heat pipe at 15 0 incline, 80 0 C ht water inlet at evaprating sectin and 100 Hz sund wave it is shwn that the heat transfer rate is 67.65%. This experiment and the calculatins are part f nging research. The results shw that heat transfer in a thermsyphn can be enhanced using sund waves. This research can be applied t the heat transfer enhancement f a thermsyphn flat-plat slar cllectr by applying the sund waves. References 1. Oh, Y.K., Park, S.H. and Ch, Y.I. (2002). A Study f the Effect f Ultrasnic Vibratins n Phase-Change Heat Transfer. Internatinal Jurnal f Heat and Mass Transfer, Vl. 45, pp Siriwichai, Sirisak (2007). Heat transfer enhancement f thermsyphn heat pipe heat- exchanger by ultrasnic wave, Department f Mechanical Engineering, Faculty f Engineering, Chiang Mai University (in Thai). 3. Techana, Thammann (2008). Effect f inclinatin angle n perfrmance f thermsyphn heat pipe perating under utrasnic wave, Department f Mechanical Engineering, Faculty f Engineering, Chiang Mai University (in Thai). 4. Kim, H.T., Kim, Y.G. and Kang, B.H. (2004). Enhancement f Natural Cnvectin and Pl Biling Heat Transfer via Ultrasnic Vibratin. Internatinal Jurnal f Heat and Mass Transfer, Vl. 47, pp Nuntaphan. A., Tiansuwan. J. and Kiatsirirat, T. (2001). Heat Transfer Cefficients f Thermsyphn Heat Pipe at Medium Operating Temperature, Bangkk: King Mngkut s University f Technlgy Thnburi. 6. Nuntaphan. A., Tiansuwan. J. and Kiatsirirat, T. (2002). Enhancement f Heat Transprt in Thermsyphn air preheater at high temperature with binary wrking Fluid:A case study f TEG-water, Applied Thermal Engineering, pp Engineering Data Science Unit N (1983). Heat Pipe-Perfrmance Enhancement f Tw-Phase Clsed Thermsyphn, ESDU Int. Plc., Lndn, UK.