Internatonal Journal of ChemTech search CODEN (USA): IJCRGG ISSN: 0974-4290 Vol.7, No., pp 202-20, 2014-2015 Heat transfer Effects for two dfferent mpellers usng Newtonan and Non-Newtonan fluds n an Agtated Vessel N.Fedal Castro 1*, B.Chtra 2, R.Pushpalatha 2,S.Sudala 3 1 Gmpex Pvt Lmted, Chenna, Inda 2 Department of Chemcal Engneerng, SSN College of Engneerng, Chenna, Inda. 3 Faculty of lluton Control & Envronmental Engneerng, ndcherry Unversty, Inda. Abstract: In many chemcal process ndustres, mxng and heat transfer n agtated vessel s an mportant operaton n both batch and contnuous process. Agtated vessels are generally used for processng lqud systems. In ths project work, the effect of mxng n heat transfer from jacket to bulk of lqud n an agtated vessel have been nvestgated both for Newtonan (water) and non-newtonan flud (Carboxy methyl cellulose soluton 5 and 1.5 weght % concentraton). The experments were conducted n an unbaffled dshed bottom vessel usng two dfferent mpellers separately, one s a four bladed paddle type mpeller havng a dameter of 314 m and the other type s V-shaped mpeller of dameter 0775 m. An emprcal correlaton s developed to calculate heat transfer coeffcent for both Newtonan and Non-Newtonan flud usng two dfferent mpellers. Investgaton also ncludes the comparson of power number for the mpellers. Keywords: Heat Transfer, mpeller, V shaped mpeller, Water, CMC, Agtated vessel. 1. Introducton and Expermental: The heatng or coolng of an agtated lqud mass n a vessel s a common ndustral practce. The rate of heat transfer s a functon of the physcal propertes of the agtated lqud and the heatng or coolng medum [1,,], the vessel geometry, the materal and thckness of the wall and the degree of agtaton. Heat transfer may take place by radaton, conducton or convecton [2,4,5,], or a combnaton of all three processes. Radaton occurs when energy, n the form of hgh frequency electromagnetc waves, s emtted from a heat source. Conducton s the transfer of energy between vbratng molecules, whch reman n a fxed poston relatve to each other. Convecton, both natural and forced, occurs between colldng molecules at dfferent degree of exctaton as they change poston and move throughout a lqud. Mxng has found wde applcaton n chemcal and bochemcal processng. Many agtated chemcal reactors and boreactors requre precse control of both mxng and heat transfer. Heat transfer n agtated vessels s mportant because flud temperature n the reactor s one of the most sgnfcant factors for controllng the outcome of chemcal and bochemcal processes. Usually, agtated vessels have a heat transfer surface, n the form of jacket or nternal cols, for addton or removal of heat. The ntensty of heat transfer durng mxng of flud depends on the type of agtator, the desgn of the vessel and condton of the process. The transfer of heat from the flud to the heat transfer area at the vessel wall can be characterzed by a flm heat transfer coeffcent. Mxng s perhaps the most unversal of all processng operatons. Both heat and mass transfer are greatly nfluenced by mxng [1]. In fact, mxng s an ntegral part of all chemcal processng. In spte of ths,
N.Fedal Castro et al /Int.J. ChemTech s.2014-2015,7(),pp 202-20. 203 mxng has proved ntractable to a rgd theoretcal analyss. Thus, n comparson wth the more theoretcally developed chemcal engneerng operatons, mxng s stll regarded as somethng of an art. The rotaton of an agtator n a confned lqud mass generates eddy currents [5]. These are formed as a result of velocty gradents wthn the lqud. A rotatng agtator produces hgh velocty lqud streams, whch move through the vessel. As the hgh velocty streams come nto contact wth stagnant or slower movng lqud, momentum transfer occurs. Low velocty lqud becomes entraned n faster movng streams, resultng n forced dffuson and lqud mxng s regarded as forced dffuson n a confned lqud mass. The degree of mxng wth n a system s a functon of two varables: (1) the magntude of eddy currents or turbulence formed and (2) the forces tendng to dampen ths formaton. The hgh the rato of appled to dampenng forces, the hgher s the degree of mxng. Ths relatonshp may be expressed by the well known rate equaton [3] Drvng force/resstance = flow or rate In ths case, Drvng force = the forces producng eddy currents or turbulence, sstance = the forces tendng to dampen the formaton of eddy currents or turbulence, Flow or rate = the degree of mxng. A hgh degree of mxng occurs when the entre lqud mass, confned n a vessel, s under turbulent flow condton. The quantty of mechancal energy requred to extend turbulence throughout a lqud mass depends upon (1) Vessel geometry (2) Agtator geometry and (3) The physcal propertes of the lqud(s) beng mxed. Lqud vscosty affects the flow created by a rotatng agtator []. Vscosty s the property of a lqud to resst flow or a change n shape through nternal forces and molecular attracton. The more vscous a lqud, the greater s the quantty of energy requred to produce a desred state of flow. Low vscosty lqud show lttle resstance to flow and therefore requre relatvely small amounts of energy per unt volume for a condton of mxng to occur. Hgh vscosty lquds dampen the mechancal energy transmtted from a rotatng agtator and requre relatvely large quanttes of power per unt volume to reach a state of flow great enough for adequate mxng to occur. The objectves of ths present project work are () () () (v) Estmaton of heat transfer coeffcent for Newtonan flud usng four bladed paddle and V type mpeller. Estmaton of heat transfer coeffcent for Non- Newtonan flud usng four bladed paddle and V type mpeller. To propose a correlaton to the calculaton of heat transfer coeffcent for both Newtonan and Non- Newtonan fluds usng four bladed paddle and V type mpeller. Calculaton of power number for Newtonan and Non-Newtonan fluds usng four bladed paddle and V type mpeller. 2. Expermental Work: In ths experment, heat transfer and power consumpton are found out for both Newtonan and non- Newtonan fluds mxed n an unbaffled jacketed dshed bottom vessel. Ths experment s performed for two dfferent types of agtators. The agtators used are standard four bladed paddle type and V type mpeller. The lqud s heated by supplyng steam nto the jacket. The steam s suppled to mantan constant heatng medum. The condensaton of steam results n heatng the lqud. The steam s obtaned from the boler and the capacty of the boler s about 200 kg/h and a pressure range of kg/cm 2. The pressure s reduced consderably by adjustng the valves and fnally the steam pressure s mantaned at about 1 to 3 kg/cm 2 and t s ndcated by the pressure gauge.
N.Fedal Castro et al /Int.J. ChemTech s.2014-2015,7(),pp 202-20. 204 2.1 Expermental Setup: The apparatus consst of jacketed vessel made up of stanless steel and s provded wth steam nlet equpped wth globe valve for adjustng the steam flow rate and steam pressure s ndcated by the pressure gauge. Vent valves and dran valves are provded n the vessel for steam and condensate outlet respectvely. Ths vessel s supported by mld steel angle frame stand. Condensate collector s attached at the bottom of the vessel and the amount of condensate n the condenser s ndcated drectly by the glass tube ndcator. The dmensons of the apparatus are gven n the fgure. The mpeller s mounted on the shaft that s drven by varable speed motor located at the top. Motor s supported by a stand separately. Speed of the mpeller can be adjusted by a knob. Fg 2.1: Expermental Set up of Agtate vessel Whle loadng the lqud nsde the vessel, the level of the lqud should not exceed certan level. The level s chosen n such a manner that whle runnng the agtator, the water should not over flow from the vessel. Twenty one lters of lqud s taken for every analyss. Temperature s measured usng mercury thermometer. Thermometers are placed n dfferent locatons nsde the vessel both radally and axally and the average temperature s taken nto account. For some specal cases, long steam thermometers are also used. The wall temperature s not much concerned due to lack of temperature sensng devce. wer requred for the agtaton s measured usng wattmeter. A separate connecton s made from the motor to the wattmeter. The wattmeter used s n the range of 70 watt, so the power s measured wthn ths range. The speed of the agtator s measured usng the tachometer. The dgtal sensor arrangement dsplays the speed of the agtator. The perfecton of the sensor was verfed by conductng many trals wth dfferent agtator speeds and the readngs were noted usng tachometer. In a vessel contanng an agtated lqud, heat transfer s brought about prmarly through conducton and forced convecton. The resstance, or flm, theory convenently descrbes ths process. 3. sults and Dscussons: The effect of mxng n heat transfer was analyzed usng two dfferent mpellers n an unbaffled dshed bottomed vessel. The nsde heat transfer coeffcent s calculated usng the overall heat transfer coeffcent and steam sde heat transfer coeffcent. The ndvdual nsde heat transfer coeffcent s estmated for both Newtonan flud (water) and Non-Newtonan flud (CMC 5% and 1.5 % concentratons).
N.Fedal Castro et al /Int.J. ChemTech s.2014-2015,7(),pp 202-20. 205 The overall heat transfer coeffcent was calculated usng the graph drawn between ln(t s T) and tme and the steam sde heat transfer coeffcent s calculated usng the Nusselt s equaton. The power number for Newtonan flud (water) and Non-Newtonan flud (CMC 5% and 1.5% concentratons) s estmated for dfferent speeds. The values of ndvdual heat transfer coeffcents, power number and ynold s number are gven below. 9 y = 9592x +.2505 ln h 7 5 4 3 y = 3923x + 3.342 Vshaped Lnear () Lnear (Vshaped) 2 1 0 4.4439099 4.040245 4.9739 ln N Fg 3.1 Heat Transfer Correlaton for Newtonan (water) flud Heat transfer correlaton 5.2 ln h 5.1 5 4.9 4. 4.7 4. 4.5 4.4 y = 122x + 4.904 y = 1729x + 4.417 4.24495242 4.320235 4.700403 ln N Lnear () Lnear () Fg 3.2 Heat Transfer Correlaton for Non- Newtonan (CMC 5%) flud Heat Transfer correlaton y = 09x + 5.9 ln h 5. 5. 5.4 5.2 5 4. 4. 4.4 y = 1931x + 4.7954 4.320235 4.700403 ln N v Shaped Lnear () Lnear (v Shaped) Fg 3.3 Heat Transfer Correlaton for Non- Newtonan (CMC 1.5%) flud
N.Fedal Castro et al /Int.J. ChemTech s.2014-2015,7(),pp 202-20. 20 wer number correlaton 11 15 y = 12x + 23 ln N 9.5 9.5 y = 022x +.91 PAddle Lnear (PAddle) Lnear () -.522492 -.4904494 -.5319172 ln P Fg 3.4 wer number correlaton for Newtonan (water) flud wer Number Vs ynolds number ln N 1 14 12 4 2 0 y = 22x + 13.007 y = 27x + 7.49-4.90275279-4.5751134-4.49141501-4.425351759-4.24959547 ln P Lnear () Lnear () Fg 3.5 wer number correlaton for Non- Newtonan (CMC 5 %) flud wer Number Vs ynolds number 1 14 y = 157x + 14.72 ln N 12 4 2 0-5.0437514-4.3740545 ln P y = 2929x +.517 Lnear () Lnear () Fg 3. wer number correlaton for Non-Newtonan (CMC 1.5%) flud 4. Concluson: Heat transfer from jacketed wall to the bulk of the lqud n dshed bottomed unbaffled vessel for both Newtonan and Non-Newtonan fluds (water and carboxy methyl cellulose) were calculated usng overall heat transfer coeffcent, steam sde heat transfer coeffcent and resstance factor for two dfferent mpellers.
N.Fedal Castro et al /Int.J. ChemTech s.2014-2015,7(),pp 202-20. 207 A generalzed correlaton for heat transfer coeffcent was found for Newtonan and Non-Newtonan fluds usng two dfferent mpellers. Ths was obtaned by plottng a graph between ln h and ln N. We obtaned the followng results from the expermental work. For Newtonan flud (water) usng, Four bladed paddle type mpeller h.342( ) 3927 = 3 N V-shaped mpeller h.2505 = N ( ) 9592 For Non-Newtonan flud (5% CMC) usng, Four bladed paddle type mpeller h.4017( ) 1729 = 4 N V-shaped mpeller h.904 = 4 N ( ) 123 For Non-Newtonan flud (1.5% CMC) usng, Four bladed paddle type mpeller h.9( ) 09 = 5 N V-shaped mpeller h.7954 = 4 N ( ) 1931 wer number was also calculated for Newtonan and Non-Newtonan fluds usng two dfferent mpellers. A generalzed correlaton was found for power number by plottng a graph between ln (wer number) and Ln( ynolds number). We obtaned the followng results. For Newtonan flud (water) usng, Four bladed paddle type mpeller N.91( ) 022 = N V-shaped mpeller N.023 = N ( ) 12 For Non-Newtonan flud (5% CMC) usng, Four bladed paddle type mpeller N.49( ) 27 = 7 N V-shaped mpeller N.007 = 13 N ( ) 22 For Non-Newtonan flud (1.5% CMC) usng, Four bladed paddle type mpeller N.517( ) 292 = N V-shaped mpeller N.72 = 14 N ( ) 157 Ths experment confrms that the mpeller was effectve n mxng and wth ncrease n mxng effect heat transfer coeffcent enhances. From the expermental work usng paddle type mpeller and V shaped mpeller we conclude that V type mpeller was effectve n mxng both Newtonan and Non-Newtonan fluds wth least power consumpton.
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