Investigation for the Optimal Thermo Hydraulic Performance in Three Sides Artificially Roughened Solar Air Heaters

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1 Investigation fo the Optimal Themo Hydaulic Pefomance in Thee Sides Atificially Roughened Sola Ai Heates Ashwini Kuma 1, Auna Kuma Behua 2, Ravi Kuma 3 1 Assistant Pofesso, Depatment of Mechanical Engineeing, H.S.B.P.V.T s GOI, College of Engineeing- Paikama, Kasthi , India 2 Assistant Pofesso (S.), Depatment of Mechanical Engineeing, VIT Univesity, Velloe, India 3 Assistant Pofesso, Depatment of Mechanical Engineeing, RCE, Ramgadh, Jhakhand India 1 Coesponding autho s Tel: , aknitjs gmail. com Abstact Povision of atificial oughness on the absobe plate enhances heat tansfe ate in sola ai heates, which also esults in highe value of fiction facto and moe pumping powe equied. Based on the analysis (Pasad et al., 2015) fo optimization of themo hydaulic pefomance in thee sides atificially oughened sola ai heate, the pesent investigation deals with the esults on optimal themo hydaulic pefomance of such sola ai heates. The esults have been epesented in tems of the oughness Reynolds numbe, e +, an efficiency paamete L -1,which combines the effect of efficiency oughness paamete, C -1 and Stanton numbe oughness paamete, B -1, given byl -1 =C -1 B -1 and is equivalent to the themo hydaulic pefomance paamete. Results validate that the themo value of e opt , always coesponds to the optimal themo hydaulic pefomance fo such sola ai heates. It has been found that thee sides oughened sola ai heates ae themally and themo hydaulically supeio than those of one side oughened sola ai heates of Pasad and Saini, (1988) and Vema and Pasad, (2000) unde the same opeating conditions. Optimal themo hydaulic pefomance cuves have been pepaed to select the values of the oughness and flow paametes (p/e, e/d and Re), to design such sola ai heates to obtain optimal themo hydaulic pefomance. Keywods Relative oughness pitch (p/e), Relative oughness height (e/d), Stanton numbe oughness paamete (B -1 ), Efficiency oughness paamete (C -1 ), Efficiency paamete (L -1 ) and Roughness Reynolds numbe (e + ). NOMENCLATURE A C collecto aea, m 2 B sola ai heate duct height, m B -1 Stanton numbe oughness paamete, B -1 = G H -P t R M C -1 1 efficiency oughness paamete, C 2.5ln( e ) 5.5 RM C P specific heat at constant pessue of ai, KJ/KgK D hydaulic diamete of sola ai heate duct, m e oughness height, m e/d elative oughness height e + oughness Reynolds numbe, e e D f Re 2 e optimum value of e + opt f fiction facto f s fiction facto in smooth collecto f aveage fiction facto (Pasad et al., 2015) G H heat tansfe oughness function, G H =4.5(e+) 0.28 (P ) 0.57 g acceleation due to gavity, m/s 2 h convective heat tansfe coefficient, W/m 2 K K themal conductivity of G.I. sheet, W/mK l length of test section, m L collecto length, m L -1 efficiency paamete, L -1 = C -1 - B -1. m Nu Nu p p/e P P t mass flow ate, Kg/s Nusselt numbe aveage Nusselt numbe in thee sides oughened collecto pitch of oughness element, m elative oughness pitch Pandtl numbe tubulent Pandtl numbe Re Reynolds numbe R M momentum tansfe oughness function, R M = 0.95(p/e) 0.53 S Stanton numbe fo smooth collecto t S S t aveage Stanton numbe fo thee sides oughened collecto (Pasad et al., 2015) T 0 outlet tempeatue of ai, K inlet tempeatue of ai, K T i T p aveage plate tempeatue, K T f aveage fluid (ai) tempeatue, K fluid velocity in duct, m/s width of sola ai heate, m V W ρ ai density, Kg/m 3 ΔP pessue dop, N/m 2 3-Ø 3-phase Ƞ themo themo hydaulic efficiency paamete, I. INTRODUCTION themo 3 St St S f fs Atificial oughness has been found to enhance the ate of heat tansfe fom the collecto plate to the flowing fluid, which also esults in highe value of fiction facto and moe pumping powe equied. Atificial oughness utilized by (Pasad and Mullick, 1983) in a sola ai heate in the fom of small diamete wie enhanced heat tansfe coefficient. Fully 162

2 developed tubulent flow in a sola ai heate duct with small diamete potusion wie on the collecto plate has been analyzed by Pasad and Saini, (1988, 1991). Gupta et al., (1997), used continuous ibs at an inclination of 60 0 to the ai flow diection and found that the opeating flow ate deceases with the incease in elative oughness height. By using chamfeed ib oughness on the absobe plate, Kawa et al., (1999) found that at low flow ate, the sola ai heate having highe elative oughness height yields a bette pefomance. Pasad, (2013) and Pasad et al., (2014) have investigated fo fully developed tubulent flow in atificially oughened sola ai heate fo heat tansfe and fiction facto. Pasad et al., (2014) analyzed fo the effect of oughness and flow paametes on heat tansfe fo fully developed tubulent flow in thee sides atificially oughened sola ai heates. As the enactment of ate of heat tansfe is attempted by poviding atificially oughness, it always goes with an incement of pessue dop and the moe pumping powe is equied. So, thee is a need to optimize the system paametes to maximize heat tansfe while keeping fiction losses as low as possible. Analysis fo the optimal themo hydaulic pefomance of ough sufaces (cicula tube with ibs) to heat exchange design was made by Webb and Ecket, (1971)., coveing a wide ange of the values of heat tansfe suface aea (A), oveall heat conductance (k) and flow fiction powe (p), to obtain the conclusion that the value of paamete, oughness Reynolds numbe, e + =20, gives the optimal themo hydaulic pefomance. Fo optimal themo hydaulic pefomance of cicula tube oughened suface with ibs, (Lewis, 1975a, b); aived at the conclusion that the value of the oughness Reynolds numbe e + =20, coesponds to the optimal themo hydaulic condition. Sheiff and Gumbley, (1966) has studied fo annulus with wie type oughness and found the value of oughness Reynolds numbe, e + = 35, fo the optimum condition. Pasad and Saini, (1991) obtained a paticula set of values of oughness and flow paametes to give the value of oughness Reynolds numbe, e + = 24, fo optimum themo hydaulic condition.optimal themo hydaulic pefomance of sola ai heates has been investigated by Vema and Pasad, (2000), fo the maximum heat tansfe and minimum pessue dop to aive at the conclusion that the value of e + =24 coesponds to the optimal themo hydaulic pefomance. Mittal and Vashney, (2005) has woked on optimal themo hydaulic pefomance of wie mesh packed sola heate. Second law optimization of sola ai heate having chamfeed ib goove as a oughness element has been analyzed by Layek et al., (2007). Kamae and Tikeka, (2008) has optimized the themo hydaulic pefomance of sola ai heate which is integated with metal ib as oughness element. Yadav and Bhagoia, (2014) has analyzed fo the optimization of themo hydaulic pefomance computationally using ANSYS FLUENT, as was found to be 2.11 at e/d =0.042 and p/e =7.14 fo equilateal tiangula ib section at Re = Pasad et al., (2015) has analyzed fo the optimization of themo hydaulic pefomance in thee sides atificially oughened sola ai heate and found that, fo a paticula set of values of oughness and flow paametes, oughness Reynolds numbe, e + = 23, always coesponds to the optimized condition. The diffeent values of optimal oughness Reynolds numbe, e opt, found in liteatue of diffeent oughness geometies and ange of values of oughness and flow paametes fo fully developed tubulent flow have been summaized in Table 1. TABLE 1. Value of e opt fo diffeent oughness geometies fo fully developed tubulent flow Sl No. Refeences Roughness geomety type p/e e/d Re e opt 1. Sheiff and Gumley (1966) Annulus with wies Webb and Ecket (1972) Rectangula Lewis (1975a, 1975b) Cicula tubes with ibs Pasad and Saini (1991) Rectangula duct with thin wies on one side Pasad et al., (2015) Rectangula duct with thin wies on thee sides The pesent investigation is aimed at to develop the thee sides atificially oughened sola ai heate duct system fo investigation unde actual outdoo conditions coveing a wide ange of opeational paametes to confim fo the optimal themo hydaulic pefomance condition of e opt =23, (Pasad et al., 2015). II. INVESTIGATION The expeimental set-up consists of two ectangula sola ai heate ducts of simila size, thee sides oughened and the smooth one. Fig. 1(a) shows the fou sided smooth duct and Fig. 1(b) shows the pesent duct model with thee sided oughened and one side smooth suface. Cicula wie of diffeent diametes has been povided on the absobe plate at vaying pitches to seve as an atificial oughness element. Fig. 2(a) shows typically the oughened top absobe plate with povision of atificial oughness elements on it and Fig. 2(b) shows typically a side absobe plate with atificial oughness elements on it. The expeimental set-up fo investigation consists of the two simila size ectangula sola ai heate ducts of high aspect atio (W>>B) as shown in Fig. 3(a). Both the ducts ae having thee sides glass coves. The total length of the ducts consists of bell-mounted enty sections fo flow stabilization and test sections. Mass flow ate was vaied by contolling the blowe speed by means of an (3- Ø) auto vaiac. Flange-tape oifice-metes measued the flow ates in both the sola ai heates (oughened and smooth). Since both the sola ai heate ducts ae simila in dimensions and ae connected to a single blowe to un simultaneously, mass flow ate fo a paticula un fo both the sola ai heates measued by mean of two sepaate flange tape oifice-metes happened to be the same. Multi-tube manometes wee used to 163

3 measue the pessue dop, while themocouples measued the ai and plate tempeatues. Intensity of sola adiation was measued by a pyanomete. Themocouple aangement fo the top plate tempeatue measuement and digital themomete fo ai tempeatue measuement inside the ducts ae shown in Fig. 3 (a), while Fig. 3 (b) shows the themocouple aangements fo top and side absobe plates of the ducts. Test data wee obtained on clea sky days between 10 AM to 2 PM duing the months of Apil and May. A wide ange of expeimental data fo 75 numbe of test uns fo 15 numbe of oughened absobe plates wee collected simultaneously with the smooth one. The oughness and flow paametes wee selected so as to yield the value of the oughness Reynolds numbe, e +, in the ange of Table 2 shows the ange of oughness and flow paametes investigated, while Table 3 shows the detailed values of oughness paametes used in the espective 15 numbe of oughened absobe plates. 164

4 TABLE 2. Range of paametes Sl. No Investigated paametes Range of paametes 1. Mass flow ate (Kg/s) Reynolds numbe, Re Roughness height 0.6 mm 1.1 mm 4. Roughness pitch 6 mm 30 mm 5. Relative oughness pitch, p/e Relative oughness height, e/d Roughness Reynolds numbe, e

5 Table 3 shows the details of oughness and flow paametes used fo the investigation. Plate Numbe TABLE 3. Detail of oughness paametes Roughness Relative pitch, p oughness (mm) height, e/d Roughness height, e (mm) Relative oughness pitch, p/e Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no Plate no III. RESULTS AND DISCUSSIONS The methodology adopted to find out the themo hydaulic esults have been caied out in a simila way as those of Lewis (1975a, b); Pasad and Saini (1991) and Pasad et al., (2015). The themo hydaulic pefomance equation Eq. (1) fo thee sides oughened sola ai heate as unde: has been used to wok out fo the vaious values of the esults togethe with the following Eqs. (2) to (5) as unde: (1) (2) (3) Futhe Eq. (1) witten by Eqs. (6) and (7) (6) Whee, (4) (5) (7) (8) (9) (10) and togethe with the following espective Eqs. (11) & (12) fo thee sides oughened sola ai heate (Pasad et al., 2015) and well known Eqs. (13) & (14) fo smooth sola ai heate ae used to wok out fo the values of the paametes B -1, C -1, and L -1. (11) (12) (13) (14) Table 4 epesents the values of the paametes B -1 and C -1, while Table 5 shows the values of the paamete L -1 =(B -1 C - 1 ), fo vaying values of elative oughness pitch and oughness Reynolds numbe at a given value of elative oughness height. Based on the values of paametes in Table- 4 & 5, Figs. 4, 5 & 6 have been dawn fo compaison of the efficiency paametes B -1, C -1, and L -1. It could be seen fom these figues that the expeimental values of these paametes compae well with those of the analytical values. TABLE 4. B -1 and C -1 fo the vaying values of p/e at vaying values of e + e + p/e = 10 B -1 C -1 p/e = 15 B -1 C -1 p/e = 20 B -1 C -1 p/e = 25 B -1 C -1 p/e = 30 B -1 C TABLE 5. Efficiency paamete L -1 as a function of e + and p/e p/e = 10 p/e = 15 p/e = 20 p/e = 25 p/e = 30 e + L -1 e + L -1 e + L -1 e + L -1 e + L

6 e/d = Re = Analytical values Expeimental values p/e = 10 p/e = 15 p/e = 20 p/e = 25 B -1 = G H -P t R M p/e = e e/ D f / 2 Re Fig.4 Compaision of B -1 fo vaying values of p/e ed = Re = Analytical values Expeimental values p/e = 10 p/e = 15 C -1 = 2.5 ln(e + ) R M p/e = 20 p/e = 25 p/e = e e/ D f / 2 Re Fig.5 Compaision of C -1 fo vaying values of p/e 167

7 L -1 L -1 = C -1 - B -1 Intenational Reseach Jounal of Advanced Engineeing and Science e/d = Re = Analytical values Expeimental values p/e=10 p/e-15 p/e=20 p/e=25 p/e= e e/ D f / 2 Re Fig.6 Compaision of efficiency paamete L -1 fo vaying values of p/e e + opt =23.12 e/d = Re= e + = 8.29 e + = e + = e + = e + = e + = e + = p/e Fig.7 Efficiency paamete L -1 as a fuction of p/e and e + 168

8 e/d= Re= p/e=20 (Analytical values) p/e=15 (Analytical values) p/e=10 (Analytical values) p/e=20 (Expeimental values) p/e=15 (Expeimental values) p/e=10 (Expeimental values) 65 themo p/e=20 p/e=15 p/e= e e/ D f / 2 Re Fig.8 Efficiency vesus Roughness Reynolds numbe Table-6 Themo hydaulic pefomance at e/d= and Re= e + p/e =10 p/e =15 p/e =20 Ƞ themo (%) Ƞ themo (%) Ƞ themo (%) Re= e/d p/e Fig.9.1 Optimal themo hydaulic pefomance cuve fo thee sides atificially oughened sola ai heate 169

9 0.030 e/d Re= p/e Fig.9.2 Optimal themo hydaulic pefomance cuve fo thee sides atificially oughened sola ai heate e/d Re= p/e Fig.9.3 Optimal themo hydaulic pefomance cuve fo thee sides atificially oughened sola ai heate Fig. 7 has been dawn based on the values of the paamete L -1 (shown in Table 5) vesus p/e fo vaying values of e +, anging fom 8.29 to It could be seen that the efficiency paamete L -1 attain the maximum value when, and theefoe, e opt 23, gives the 170

10 optimal themo hydaulic pefomance condition. Fig. 8 has been dawn fo actual values of the optimal themo hydaulic pefomance, woked out by using Eqs. (1) to (5) and the analytical values woked out by using Eqs. (11) to (14). This figue shows a good ageement with the actual and analytical values fo the optimal themo hydaulic pefomance paamete e opt 23. It can theefoe, concluded be that e 23, gives the set of values of the oughness and flow opt paametes p/e, e/d and Re to esult in the optimal themo hydaulic pefomance in thee sides oughened sola ai heates. It has been aleady discussed by authos (Pasad et al., 2014) that thee sides oughened sola ai heates pefom bette than one side oughened sola ai heates (Pasad and Saini, 1988) with espect to heat tansfe and in authos pevious wok (Pasad et al., 2015) it has been discussed that thee sides oughened sola ai heates pefom bette with espect to optimal themo hydaulic pefomance as compaed to one side oughened sola ai heates. As such optimal themo hydaulic pefomance cuves of (Pasad et al., 2015) ae valid to povide fo the set of values of p/e, e/d and Re in thee sides oughened sola ai heates fo even bette yield with espect to optimal themo hydaulic pefomance and have been shown in Figs. 9.1 to 9.3. Fom Fig. 8, it could also be seen that fo the optimum oughness Reynolds numbe value e opt 23, value of optimal themo hydaulic pefomance inceases with inceasing values of the elative oughness pitch, p/e, fo a given value of elative oughness height, e/d, which has been shown in Table-6. This is because of the fact that fo a given value of e/d, the ate of incease of heat tansfe is moe than that of fiction facto fo inceasing values of p/e. Fig. 8 also shows the values of at e fo p/e = 10, 15, 20, which themo ae maximum, confiming that e opt 23, gives the optimal themo hydaulic pefomance. IV. CONCLUSIONS On the basis of the esults and discussions of the pesent investigation the following conclusions have been dawn:- 1. Investigation fo themo hydaulic pefomance of thee sides atificially oughened sola ai heates have been caied out. 2. An optimization paamete e +, which combines the effect of flow and oughness paametes, witten as f e e Re, has been consideed. D 2 3. The themo hydaulic pefomance paamete St 3 StS themo, has been consideed. f f S 4. Results validate that the optimal value of e opt 23, coesponds to the optimal themo hydaulic pefomance in such sola ai heates. 5. The value of optimal themo hydaulic pefomance in such sola ai heates inceases with inceasing values of elative oughness pitch, p/e, fo a given value of elative oughness height, e/d. 6. The values of optimal themo hydaulic pefomance have been found to be 78.81%, 76.12% and 74.61%, fo p/e equal to 20, 15 and 10 espectively at a given value of e/d equal to Thee sides oughened sola ai heates ae even supeio to one side oughened sola ai heate with espect to optimal themo hydaulic pefomance unde the same opeating condition of mass flow ate and intensity of sola adiation. 8. The optimal themo hydaulic pefomance cuves ae valid fo the design of such sola ai heates to give optimal themo hydaulic pefomance. REFERENCES [1] B. N. Pasad, Ashwini Kuma, and K. D. P. Singh, Optimization of themo hydaulic pefomance in thee sides atificially oughened sola ai heates, Sol. Enegy, vol. 111, pp , [2] Ashwini Kuma, B. N. Pasad, and K. D. P. Singh, Pefomance chaacteistics of thee sides glass coveed smooth sola ai heates, Tansylvanian Review, vol. 24, issue 11, pp , [3] Ashwini Kuma and Mahmood Alam, A eview on compaative study of themal pefomance of atificially oughened sola ai heates, Int. 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