Studies on Helical Coil Heat Exchanger

Transcription

1 P IJISET - Internatinal Jurnal f Innvative Science, Engineering & Technlgy, Vl. Issue 1, January Studies n Helical Cil Heat Exchanger 1 4 G.V.S.K. ReddyP P*, K.Rama Krishna RajuP P*, J. Divya LakshmiP P*, P. DileepP P*, K.V.R MuryP *(Department f Chemical Engineering, M.V.G.R Cllege f Engineering, Vizianagaram * P kristnarama@yah.cm) 5 P*. ABSTRACT The present wrk is mainly fcused n e behavir f helical cil heat transfer equipment by subjecting t varius prcess cnditins. These variatins usually are e alteratins in e speed f e impeller, heat energy prvided t e ba liquid and ereby changing e temperature f at liquid, and e vlumetric flw rate f e clant at is being circulated inside e helical cil. The variatins mentined abve are used fr every arbitrarily chsen different type f impeller in cmbinatrial fashin f pre-fixed impeller speeds (RPM) and vlumetric flw rates. The effect f system behavir is als characterized fr tw different ba liquids such as Water and Mtr Oil, by circulating clant being Water. The results are analyzed in rder t calculate e Heat Transfer Cefficients in e abve mentined b e cases experimentally frm e data generated. The analysis is fllwed by cnclusins and pssible explanatin f e equipment behavir. Keywrds Helical cil, Water, Mtr Oil, Heat Transfer Cefficient, Impeller I. INTRODUCTION Heat transfer in e prcess industries is an essential unit peratin. Almst all f e prcess emplys e transfer f heat energy in ne way r e er. Fr e prcess heat transfer t take place, e equipment r e cmprising unit part f e entire prcess shuld be able t remve r add heat frm a certain surce by cnductin, cnvectin r radiatin mdes f heat transfer. These heat transfer entities are knwn as Heat Exchangers. Depending n e requirements at hand e heat transfer is directed. Heat is remved frm ht substances r heat can be added t a cld substance as per e demands f e prcess at is being carried ut. One such heat exchange apparatus at is chsen fr study is Helical Cil Heat Exchanger. Cil heat exchangers are used fr heating and cling fluids in a variety f industries. Cils are cmmnly used in chemical reactrs, agitated vessels and strage tanks t heat and cl materials ranging frm chemicals t dairy prducts, vegetable and fruit juices and prcess ils. They are used fr heat recvery frm waste liqurs, vaprs and gases. Tube cils affrd ne f e cheapest means f btaining heat transfer surface. They are usually made by rlling lengs f cpper, steel r ally tubing int helixes r duble helical cils in which e inlet and exit are cnveniently lcated side by side. Helical cils f eier type are frequently installed in vertical cylindrical vessels wi r wiut an agitatr, alugh free space is prvided between e cils and e vessel wall fr circulatin. When such cils are used wi mechanical agitatin, e vertical axis f e agitatr usually crrespnds t e vertical axis f e cylinder. Duble helical cils may be installed in shells wi e cil cnnectins passing rugh e shell r shell cvers. Such an apparatus is similar t a tubular exchanger, alugh limited t smaller surfaces. Curved cils can be classified int se wi a cnstant curvature and wi a variable curvature. The frmer is referred t as helices and e latter curved pipes as spirals. The rlling f e cils, particularly wi diameters abve ne inch requires a special winding technique t prevent e tube frm flattening int an elliptical crss sectin, since distrtin reduces e flw area. Cmpared t e relatively simple case f steady flw in a straight tube, e flw in a curved tube is s exceptinally cmplicated at even e details f e mean flw are nt yet knwn. Here in is prject wrk e steady state peratin f helical cil heat exchange equipment is adpted. The verall behavir and perfrmance f such apparatus is determined in e steady state batch peratin. 65

2 IJISET - Internatinal Jurnal f Innvative Science, Engineering & Technlgy, Vl. Issue 1, January 16. The variatins in e n. f mechanisms emplyed fr carrying ut e prcess invlves e changes in RPMs f e impellers, flw rates f e clants and ba liquids at different reference temperatures. This enables e sufficient difference exhibitin in e perfrmance and at e pint f time where all e values becme fixed i.e., when system attains steady state e desired functining and predictins can be btained frm e generated data. The batch peratin is ften chsen raer an cntinuus peratin because f e feasibility f study at certain cnditins intact all e way during e curse f e experimental prcedure. Cil Inlet Impeller Helix Cil Frmatin Cil Outlet II. EXPERIMENTAL SETUP.1: Helical Cil Heat Transfer Equipment The apparatus as shwn in e figure abve is equipped wi a helical cil hused inside e vessel. The ends f e cil are prvided wi grves fr checking e inlet and utlet clant temperature respectively. The vessel is attached t e stand bearing e mtr rig and e cntrl system. This system huses e dimmerstat fr invking variatins in e temperatures and changes in e impeller speeds. The ermstat is inserted int e ba vessel fr temperature regulatin at desired ranges. The apparatus has ne valve at e bttm fr draining e ba liquid. The mtr directly abve e vessel is fitted wi an impeller shaft and e mtr RPM is cntrlled by aut transfrmer cnnected in series wi an ammeter..: Materials f Cnstructin The material used fr e cnstructin f ba vessel is stainless steel. The helical cil is made up f cpper, which is a knwn fr its lw resistance t heat flw. The impellers used fr experimentatin are als f stainless steel make. Irn shaft is used fr impeller hlding purpses. Fig. 1. Sketch f Helical cil heat exchanger..: Specificatins Material f cnstructin f e ba vessel: Stainless steel Diameter f e vessel : cm Capacity f ba : 5 Liters Internal diameter f e cil: 9.6 mm External Diameter f e cil: 1.5 mm Cil Diameter: mm Number f cil turns: 7 Pwer f e Heating element: KW Mtr : ¼ HP cnnected t aut transfrmer (fr variable speed) Paddle, Mixer and Mincer grinder blade fr agitatin Thermmeters: -11P PC III. Ba Liquid SYSTEM OF CHOICE The chice f system at is being used in e experiment is purely speculative. Depending n e resurces e system is adpted. Water which is easily available in surplus is chsen t be e primary cmpnent. Mtr il is chsen t e 66

3 IJISET - Internatinal Jurnal f Innvative Science, Engineering & Technlgy, Vl. Issue 1, January er cmpnent, attributing t its substantial cntrast in viscsity when cmpared t water. The Overall heat transfer cefficient, U (W/m.K) 6 4 Overall heat transfer cefficient, U (W/m.K) Reynlds number (N Re ) Reynlds number (N Re ) Overall heat transfer cefficient, U (W/m.K) Overall heat transfer cefficient, U (W/m.K) 4 6 Reynlds number (N Re ) 4 6 Reynlds number (N Re ) Fig.. Graphs drawn between verall heat transfer cefficient, URR (W/mP P.K) and Reynlds number (NRReR) fr paddle at different temperatures i.e., 4P PC (Tp left), 5P PC (Tp right), 6P PC (Bttm left), 7P PC (Bttm right) wi varying speed. 5 Overall heat transfer cefficient, U (W/m.K) Overall heat transfer cefficient, U (W/m.K) Reynlds number (N Re ) Reynlds number (N Re ) Fig.. Graphs drawn between verall heat transfer cefficient,urr (W/mP P.K) and Reynlds number (NRReR) fr paddle (left) and mixer blade (right) at 4P PC temperature wi varying speed. 67

4 IJISET - Internatinal Jurnal f Innvative Science, Engineering & Technlgy, Vl. Issue 1, January 16. clant at is used f remving e heat frm e ba liquids (Water & Mtr il) is als water. The abve chices are replaced wi any alternative type f flwing materials subjected t e limitatins f e apparatus..1: System Prperties System 1: Water Water The system 1 is assumed like water acting like ba liquid as well as a clant. The prperties mentined belw are at ambient temperature. Density f water (ρ) = kg/mp Viscsity f water (μ) = 1P Pa.s Thermal cnductivity f water (K) =.65 W/m K Specific heat capacity (Cp) = 4.18 kj/kg K System : Mtr Oil Water The system is assumed like Mtr il is e ba liquid and water as clant. The prperties mentined belw are at ambient temperature. Density f Mtr Oil (ρ) = 876 kg/mp Thermal cnductivity f Mtr Oil (K) =.145 W/m K Specific heat capacity (Cp) = kj/kg K IV. - EXPERIMENTAL PROCEDURE After e initial trail run f e experiment is dne, e ba vessel is filled wi e ba liquid f chice i.e., Water r Mtr Oil till all e cils inside e vessels are submerged. Heat input is given t e ba liquid using e dimmerstat prvided, by turning e knb t a desired value f temperature, say 4 P PC. Allw e ba liquid t gain temperature gradually. Using e aut transfrmer put e mtr int mtin by fixing a value f rtatin n e scale. This mtr rtatin allws e impeller t turn inside e liquid. The inlet f e cil is prvided wi clant stream and e vlumetric flw rate is regulated as per e need. Using a stpwatch and a measuring jar e flw rate f e liquid is measured. Wait till e steady state is reached. Measure e temperature values f e inlet and utlet clant streams at e respective prvisins prvided as shwn in e fig.1. Take ntes f e ba, inlet and utlet temperatures. Als measure e RPM f e mtr using a Tachmeter. Carry ut e experiment at different temperatures wi different pre fixed flw rates using chsen impeller. Repeat e experiment wi different impellers mentined earlier at se pre fixed flw rates and temperatures. The entire prcess is carried ut wi different ba liquid i.e., Mtr Oil. V. RESULTS & DISCUSSIONS Frm e abve pltted graphs i.e., Fig. and Fig. between Overall Heat Transfer Cefficient and Reynlds Number it can be asserted at e verall heat transfer cefficient varies wi change in speed f impeller and e flw rate f e clant. As frm e Water-Water system graphs at different pre chsen temperatures i.e., 4P PC, 5P PC, 6P PC, 7P PC using different impellers it can be understd at e heat transfer cefficient attains higher magnitudes wi e impeller speed increments and gradual raise in temperature. The speed f impeller has n direct cnsequence n e lcal inner heat transfer cefficient. The variatin inside e cil in e H.T. C. is due t e secndary flw existence at e curves f e cil which regulates e effective heat transfer. But in e case f Oil-Water system e verall heat transfer cefficient values are nt greatly prmted in cmparisn wi water as ba liquid. This might be due t e cnstrained impeller impact n e high viscus ba and lesser turbulence which will be hurdle fr e heat transfer t be mre prductive. 68

5 P P P IJISET - Internatinal Jurnal f Innvative Science, Engineering & Technlgy, Vl. Issue 1, January 16. The prperty depend functin like heat transfer cefficient is sensitive twards varius features f e chsen ba liquid. In is case water which has higher ermal cnductivity, heat capacity and lwer viscsity will be a gd medium fr better heat transfer mechanism. In cntrast Mtr Oil is highly viscus and has lwer ermal cnductivity. The impeller speed has effect ver e film ickness frmatin ver e slid-fluid interface. S uter lcal heat transfer cefficient is effected by e RPM wi which impeller is rtating. The difference btained in e readings at same cnditins can be attributed t e ful frmatin inside e cil and n e uter surface. The irregular flw cnditins can als have certain measure f effect n e verall utcme. Assuming e liberty f taking cnstant values fr speed, vlumetric flw and e ambient temperature, e experimentatin yield is acceptable wi quarter f an errr and deviatin frm its riginal behavir. Inherent defects like impeller pitch, cil curvature, ermstat effective temperature regulatin and shaft lad n e mtr are negligible. furer study at different speeds which are intermediate t e riginal nes is dne. Helical cil heat exchangers are nt studied extensively s ere is gap fr any frward cmments n e effects f Reynlds number in tube side and cnsequent changes due t secndary flw. Hence fr higher flw rates als e study is suppsed t be dne. REFERENCES Jurnal Papers: [1] J.S. Jayakumar, Experimental and CFD Estimatin f Heat Transfer in Helically Ciled Heat Exchangers. [] G.S. Aravind, Natural Cnvective Heat Transfer in Helical Ciled Heat Exchanger, Jurnal f e Institutin f Engineers (India): Chemical Engineering Divisin, Sep, Vl. 84, p.5-7. Bks: [] R.K. Sinntt, Chemical Engineering Design (Vlume VI, 4P Editin, Elsevier). VI. CONCLUSIONS [4] J.O. Malney, Perry s chemical Engineers Handbk (8P Editin, McGraw-Hill). As per e expected values, e deviatins are appreciably lw. In Water-Water system e heat transfer is mre effectively dne in cmparisn wi Oil-water system. [5] M.L. Warren, Unit peratins f Chemical Engineering (7P Editin, McGraw-Hill). The Overall Heat Transfer Cefficient U as expected increases wi Reynlds Number NRReR. As e flw rates increases e mlecular mvement increases s e film ickness reduces due t turbulence creatin. The crrectin factrs are t be assciated t e existing crrelatins t accunt fr deviated behavir f e apparatus. The variatins f fall and raise in e H. T. C values frm e graphs and bservatins ntes at e predictable values are yet t arrive nly if 69