Heat Transfer Enhancement with Different Square Jagged Twisted Tapes and CuO/water Nano fluid

Transcription

1 Internatonal Engneerng search Journal (IERJ) Specal Issue Page , 05, ISSN ISSN Heat Transfer Enhancement wth Dfferent Square Jagged Twsted Tapes and CuO/water Nano flud # Mr. Krshna S. Borate, # Prof. P.M. Khanwalkar, #3 Prof. V.N. Kapatkar Krshnakantk@redffmal.com pmkhanwalkar@snhgad.edu 3 vnkapatkar@snhgad.edu #3 Department of Mechancal Engneerng, Snhgad College of Engneerng, Pune, Inda. ABSTRACT Heat transfer & frcton factor characterstcs of CuO/water nano flud have been expermentally nvestgated. The nano flud was employed n crcular tube equpped wth square jagged copper twsted tape. The twst ratos of square jagged twsted tape was vared between 4, 6 and 7 by keepng the concentraton of nano flud constant at 0.% volume concentraton. The experments were performed n turbulent regme wth ynolds number spanned between 5400 and To evaluate heat transfer enhancement and the ncrease of frcton factor, the Nusselt number and frcton factor of base flud n the plan tube were employed as reference data. The obtaned results reveal that Nusselt number ncreases wth ncrease n ynolds number and decrease n twst rato. The smultaneous use of nano flud and square jagged twsted tape wth twst rato 4 shows ncrease n Nusselt number value by 87% however there s ncrease n frcton factor by only 3.4% as compared to the smooth tube values. Keywords heat transfer enhancement, nano flud, pressure drop, square jagged twsted tapes, turbulent regme, twst rato. ARTICLE INFO Artcle Hstory ceved :8 th November 05 ceved n revsed form : 9 th November 05 Accepted : st November, 05 Publshed onlne : nd November 05 I. INTRODUCTION Heat exchangers are wdely used n varous ndustral processes for heatng and coolng applcatons such as ar condtonng and refrgeraton systems, heat recovery processes food and dary processes, chemcal process plants etc. The major challenge n desgnng a heat exchanger s to make the equpment compact and acheve a hgh heat transfer rate usng mnmum pumpng power. Technques for heat transfer augmentaton are relevant to several engneerng applcatons. In recent years, the hgh cost of energy and materal has resulted n an ncreased effort amed at producng more effcent heat exchange equpment. Furthermore, sometmes there s a need for mnaturzaton of a heat exchanger n specfc applcatons, such as space applcaton, through an augmentaton of heat transfer. For example, a heat exchanger for an ocean thermal energy converson (OTEC) plant requres a heat transfer surface area of the order of 0000 m /MW []. Therefore, an ncrease n the effcency of the heat exchanger through an augmentaton technque may result n a consderable savng n the materal cost. Furthermore, as a heat exchanger becomes older, the resstance to heat transfer ncreases owng to foulng or scalng. These problems are more common for heat exchangers used n marne applcatons and n chemcal ndustres. In some specfc applcatons, such as heat exchangers dealng wth fluds of low thermal conductvty (gases and ols) and desalnaton plants, there s a need to ncrease the heat transfer rate. The heat transfer rate can be mproved by ntroducng a dsturbance n the flud flow thereby breakng the vscous and thermal boundary layer. However, n the process pumpng power may ncrease sgnfcantly and ultmately the pumpng cost becomes hgh. Therefore, to acheve a desred heat transfer rate n an exstng heat exchanger at an economc pumpng power, several technques have been proposed n recent years and are dscussed under the classfcaton secton. II. HEAT TRANSFER ENHANCEMENT SING VARIOUS SQUARE JAGGED TWISTED TAPE INSERTS AND NANO FLUID A. Present expermental work

2 Internatonal Engneerng search Journal (IERJ) Specal Issue Page , 05, ISSN The expermental study on passve heat transfer augmentaton usng square jagged copper twsted tape nserts for no. of twsts wth nano flud were carred on n a sngle phase flow heat exchanger havng the specfcatons as lsted below- I. PAGE STYLE Fg. Photographc vew of expermental set up for forced convecton. B. Expermental Set up Expermental set up conssts of test secton havng tube n tube heat exchanger. Insde tube s of Copper and outsde tube s of Stanless Steel. Four thermocouples are connected to the test secton, two at the nlet and two at the outlet of hot and cold water respectvely. Two rotameters are connected at nlet of cold and hot water to measure the flow rates. Also control valves and bypass valves are provded at nlet of both the rotameters. Two centrfugal pumps are used to crculate the cold and hot water. Two tanks are used for storng the hot water and cold water. Electrc heater s attached to the hot water tank havng capacty of 500watt. To measure the pressure dfference between nlet and outlet of test secton of hot flud nverted U-tube manometer s used. Dfferent twsted tape nserts are used along wth CuOnano flud. 4. Start cold water pump 5. Adjust flow rate of cold water at 00 LPH 6. Start hot water pump 7. Adjust flow rate of hot water at 00 LPH and keep t constant 8. The temperatures wll keep on rsng contnuously. When steady state s reached, note all the temperatures (T to T4) 9. Now Adjust flow rate of hot water at 00 LPH 0. The temperatures wll keep on rsng contnuously. When steady state s reached, note all the temperatures (T to T4). peat step 9 and 0 for hot water flow rates at 300,400,500,600,700,800 and 900 LPH. Now use the nano flud wth nserts. 3. Fll the hot water tank wth prepared CuOnano flud. 4. Start nano flud pump. 5. peat step nos. 7,8,9,0. 6. Swtch off pumps, water heater and temperature dsplay. D. Specfcatons of Inserts Materal : Copper. Wdth of twsted tape = mm. Twst rato = 7, 6, 4. Length of nsert = 00cm v. Thckness of nserts = 3mm E. Specfcatons of CuO Nano Partcle. Average partcle sze =<80nm. Purty =>99%. Content of CuO =>99% v. Appearance = Black powder. Fg.3 Photographc vew of CuO nanopartcles. Fg. Schematc dagram of forced convecton set up C. Expermental Procedure. fer to the Fg. and make all the cable connecton carefully.. Swtch ON the water heater wat untl water temperature reaches 70C 3. Swtch on temperature dsplay

3 Internatonal Engneerng search Journal (IERJ) Specal Issue Page , 05, ISSN Q c = m c C pc (T c -T c ) Fg.4 Copper square jagged Twsted tape (y/w=7). 4) Average heat transfer Q avg. = Q h Q c 5) Overall heat transfer coeffcent Qavg. = U A s Tm a) Surface area of tube A s = d L b) Logarthmc mean temperature dfference T m = T T T ln T T = T h T c T = T h T c 6) Nusselt Number of cold water flowng throughthe annular space. Nuo = 0.03(R eo ) 0.8 (P r ) 0.3 o U od h D h = D - d o Contnuty equaton m c = A o U o Fg.5 Copper square jagged Twsted tape (y/w=6). Fg.6 Copper square jagged Twsted tape (y/w=4). III. DATA REDUCTION ) Propertes of water a) Propertes of hot water calculated at mean bulk temperature. Th Th T bh = b) Propertes of cold water T bc = Tc Tc ) Heat gven by hot water Q h = m h C ph (T h -T h ) 7) Heat transfer coeffcent of cold water flowng through the annular space. Nu o = h o D h K h o = Nu o K D h 8) Heat transfer coeffcent of hot water flowng through the tube. U h h o h = U ho 9) Expermental Nusselt Number of hot water flowng through the tube. Nu = h d K 0) Theoretcal Nusselt Number of hot water flowng through the tube (Dttus-Boelterequaton). Nu = 0.03(R e ) 0.8 (P r ) 0.3 ) Expermental Frcton Factor () P =ƍgh flu () P= d gdh f LU ) Theoretcal Frcton Factor 3) Heat gven by cold water

4 Internatonal Engneerng search Journal (IERJ) Specal Issue Page , 05, ISSN f ) Performance evaluaton crtera PEC Nu) Nu p f f 3 p 0.33 IV. RESULT & DISCUSSION The accuracy wth whch the Nusselt number and frcton factor could be evaluated expermentally wth the use of present expermental set up was determned by conductng prelmnary experments wth plan tube. The results are compared wth standard emprcal relatonshps and prevous research work for turbulent flow. The purpose was to check the relablty of the apparatus. A. Expermental and theoretcal heat transfer results for smooth tube Fg. 7 shows the relaton between ynolds number v/s. Nusseltnumber. The curve shows that Nusselt number s a functon of ynolds number. The values are n close agreement wth the Dttus-Boelter equaton wth a maxmum varaton of 0 % C. Comparson of "Plan Tube" and "Tubes wth varous twsted tapes Fg. 9 shows the relaton between Nussult number and ynolds number for plan tube and tube wth varous nserts. The fgure concludes that the Nusselt number s functon of ynolds number. Nusselt number ncreases wth ncrease n ynolds number. Hence, convectve heat transfer rate s more wth hgher ynolds number. Further, t can be concluded that, twsted tapes wth lower twst rato gves hghest Nusselt number for a partcular ynolds number. Heat transfer rate s better wth twsted tapes of lower twst rato. S c atterplot of m ultple v arables agans t R e g. 9 ynolds number S preads v/s. heet 0v Nussult * 0c number plot for N u_c uo = * log0 (x ) N u C uo (y /w =7 ) = * log0 (x ) Y=7,6,4, CuO, water N u_c uo (y /w =6) = * log0(x ) N u_c uo (y /w =4) = * log0(x ) N u_w ater = * log0(x ) Fg. 9 ynolds number v/s. Nussult number plot for Y=7,6,4, CuO, water. N u _C u O N u C uo (y /w =7) N u _C u O (y /w =6 ) N u _C u O (y /w =4 ) N u _w a te r S c atterplot of m ultple v arables agans t R e S preadsheet 0v * 0c N u_e x pt. = * log0 (x ) N u_th. = * log0 (x ) Fg. 0 shows the relaton between frcton factor and ynolds number for plan tube and tube wth varous nserts. The fgure concludes that the frcton s mnmum for a plan tube. Wth decrease n twst rato, the frcton factor goes on ncreasng for a partcular ynolds number N u _E x pt. N u _Th. Fg.7 ynolds number v/s. Nusselt number for plan tube. B. Expermental and Theoretcal Frcton Factor sults for Smooth Tube. Fg. 8 shows the relaton between ynolds number v/s. frcton factors for turbulent flow n a plan tube. The results obtaned are n close wth theoretcal values. Ths proves that the expermental test rg s valdated and further expermentaton can be carred out. S c atterplot of m ultple v arables agans t R e Fg.0 ynolds number v/s. Frcton factor plot for Y=7,6,4,CuO, water S preads heet3 0v * 0c f_e xpt. = * ex p(-.9869e -5* x ) f_th. = * ex p(-.08e -5* x ) The curves are very steep for lesser values of ynolds number. Ths s due to the fact that, for lower values of ynolds number, the vscous force domnates the nerta force. For lower ynolds number, less than 6000, the curves are more leanng and the frcton factor s comparatvely hgh f_e xpt. f_th. V.CONCLUSION Fg. 8 ynolds number v/s. Frcton factor plot for plan tube. Expermental nvestgaton of heat transfer and frcton factor characterstcs of crcular tube ftted wth full-length square jagged twsted tape nserts and CuOnano flud of dfferent twst ratos have been presented. Calculatons and

5 Internatonal Engneerng search Journal (IERJ) Specal Issue Page , 05, ISSN curve fttng s done and correlatons are obtaned. The results showed that there was an apprecable enhancement n heat transfer and that the heat transfer s more wth lesser twst rato. Maxmum ncrease n Nu for nano flud was found to be 43 %. Maxmum ncrease n Nu for twsted tape wth y/w = 7 and nano flud was found to be 66 %. Maxmum ncrease n Nu for twsted tape wth y/w = 6 and nano flud was found to be 78%. Maxmum ncrease n Nu for twsted tape wth y/w = 4 and nano flud was found to be 87%. Frcton factor s ncreased by 9 % wth nano flud. Frcton factor s ncreased by 4 % wth y/w=7 &nano flud. Frcton factor s ncreased by 9 % wth y/w=6 and nano flud. Frcton factor s ncreased by 3 % wth y/w=4 and nano flud. It s concluded that Nusselt number ncreased by 87% whle frcton factor ncreases by 3% so wth less pumpng power more heat transfer can acheved REFERENCES [] Hseh and Huang, Expermental studes for heat transfer and pressure drop of lamnar flow n horzontal tubes wth/wthout longtudnal nserts, 000. [] S. Lu, M. Sakr, A compressve revew on passve heat transfer enhancements n ppe exchangers, 03, [3] KhwanchtWongcharee, Smth Eamsa- ard Enhancement of heat transfer usng CuO/water nanoflud and twsted tape wth alternate axs, 0, [4] S. Suresh, M. Chandrasekar, S. Chandra Sekhar, Expermental studes on heat transfer and frcton factor characterstcs of CuO/water nanoflud under turbulent flow n a helcally dmpled tube, 0, [5] Mlad Tajk Jamal-Abad, AmrhossenZamzaman, MazarDehghan, Expermental studes on the heat transfer and pressure drop characterstcs of Cu water and Al water nanofluds n a spral col, 03, 06-. [6] S. Suresh, K.P. Venktaraj, P. Selvakumar, M. Chandrasekar, A comparson of thermal characterstcs of AlO3/water and CuO/water nanofluds n transton flow through a straght crcular duct ftted wth helcal screw tape nserts, 0, [7] KhwanchtWongcharee, Smth Eamsa-ard, Heat transfer enhancement by usng CuO/water nanoflud n corrugated tube equpped wth twsted tape, 0, [8] M. Chandrasekara, S. Sureshb, T. Senthlkumar, Mechansms proposed through expermental nvestgatons on thermophyscal propertes and forced convectve heat transfer characterstcs of varous nanofluds A revew, 0, [9] S. Eamsa-ard, K. Wongcharee, Sngle-phase heat transfer of CuO/water nanofluds n mcro-fn tube equpped wth dual twsted-tapes, 0, [0] Sarma, Heat transfer coeffcents wth twsted tape nserts, 003. [] ParsonNaphon, Effect of col-wre nsert on heat transfer enhancement and pressure drop of the horzontal concentrc tube, Internatonal Communcatons n Heat and Mass Transfer 33 (006) ,006. [] Manglk R.M and Bergles A.E, 99, Heat transfer enhancement and pressure drop n vscous lqud flows n sothermal tubes wth twsted-tape nserts, Heat and Mass Transfer, Vol. 7, No. 4, pp [3] Manglk R.M and Bergles A.E, Applcaton of twsted tape nserts n tubular heat exchangers,heat and Mass Transfer, Vol. 7, No. 4, pp [4] Chang S.W, Yang T.L, Lou J.S, 007. Heat transfer and pressure drop n tube wth broken twsted tape nsert, Expermental Thermal and Flud Scence, Vol. 3, No., pp [5] Saha S.KandMallck D. N., September 005. Heat transfer and pressure drop characterstcs of lamnar flow n rectangular and square plan ducts and ducts wth twsted-tape nserts, Transactons of the ASME, Vol. 7. [6] Svashanmugam, P. and Suresh, S. Expermental studes on heat transfer and frcton factor characterstcs of turbulent flow through a crcular tube ftted wth regularly spaced helcal screw tape nserts, Advances n Energy search, 006, [7] SbelGunes, VeyselOzceyhan, OrhanBuyukalaca, Heat transfer enhancement n a tube wth equlateral trangle cross sectoned coled wre nserts, Expermental Thermal and Flud Scence 34 (00) [8] Rahm.M, Shabanan S.R., Alsaraf A.A., 009. Expermental and CFD studes on heat transfer and frcton factor characterstcsof a tube equpped wth modfed twsted tape nserts, Chemcal Engneerng and Processng, Vol. 48, pp [9] Chang S.W., Jan Y.J, Lou J.S., 007. Turbulent heat transfer and pressure drop n tube ftted wth serrated twsted tape, Internatonal Journal of Thermal Scences, Vol. 46, No. 5, pp