Study of In line Tube Bundle Heat Transfer to Downward Foam Flow

Transcription

1 Proceedins o the 5th IASME/WSEAS Int. Conerence on Heat Transer, Thermal Enineerin and Environment, Athens, Greece, Auust 25-27, Study o In line Tube Bundle Heat Transer to Downward Foam Flow J. GYLYS, T. ZDANKUS and A. INGILERTAS Enery Technoloy Institute Kaunas University o Technoloy Kaunas, K. Donelaicio 2, LT LITHUANIA jonas.ylys@ktu.lt S. SINKUNAS and M. BABILAS Department o Thermal and Nuclear Enery Kaunas University o Technoloy Kaunas, K. Donelaicio 2, LT LITHUANIA Abstract: An experimental investiation o heat transer rom the in line tube bundle to the two phase oam low was perormed. Statically stable as liquid oam low was used as a coolant. Investiation was perormed on the experimental laboratory set up consistin o the oam enerator, an experimental channel and tube bundle. Reularities o the heat transer o the tube bundle to the downward oam low under the 18 deree turn were analysed in the work. Heat transer character o rontal and urther tubes to downward oam low is dierent in comparison with the one phase coolant low. Ater the turn, local void raction o the oam is less on the inner side o the oam low. Thereore heat transer intensity o the inner side line tubes is hiher than or other tubes o the bundle. Results o the investiation were eneralized by criterion equation, which can be used or calculation and desin o the statically stable as liquid oam heat exchaners with the in line tube bundles. Key-Words: heat transer, oam low, downward low, in line tube bundle, experimental channel. 1 Introduction Smaller coolant mass low rate, relatively lare heat transer rate, low enery consumption required or coolant delivery to heat transer place may be achieved by usae o two phase as liquid oam low as a coolant [1, 2]. Characteristics o one as liquid oam type statically stable oam showed its perect availability or this purpose [1]. Tube bundles o dierent types and eometry are used in heat exchaners and sinle phase coolants such as water or air usually are used or heat and mass transer process in industrial heat exchaners. Thereore heat transer o dierent tube bundles to one phase luids was investiated enouh [3, 4], but there is no suicient data concernin heated suraces heat transer to the statically stable oam low yet. Thereore problems arise when oam systems and heat exchaners are desined. In our previous works heat transer o alone circular surace tube, and such tubes line to upward statically stable oam low was investiated [1]. Next experimental series with staered (spacin between centres o the tubes across the bundle was s 1 =.7 m and spacin alon the bundle was s 2 =.175 m) and in line (s 1 = s 2 =.3 m) tube bundles in upward and downward oam low were ollowed [5, 6, 7]. Presently the heat transer o the in line tube bundle (s 1 =.3 m, s 2 =.6 m) to vertical downward ater 18 deree turnin oam low was investiated experimentally. It was determined a dependency o tubes heat transer intensity on low velocity and oam volumetric void raction. Apart o that, inluence o tube position in the bundle on heat transer intensity was investiated also. The structure o oam is one o the actors which inluences on the heat transer intensity o the tubes to the oam low. When oam low is passin throuh the bundle o tubes oam bubbles are intermixed, some bubbles collapsed or divided into smaller bubbles. In order to observe visually the vertical downward oam low crossin the tube bundles, the walls o the experimental channel were made rom transparent material. Results o investiations were eneralized usin relationship between Nusselt and Reynolds numbers and volumetric void raction o oam. The obtained eneralized equation can be used or the desinin o oam heat exchaners and heat transer intensity s calculations o the in line tube bundle.

2 Proceedins o the 5th IASME/WSEAS Int. Conerence on Heat Transer, Thermal Enineerin and Environment, Athens, Greece, Auust 25-27, Experimental Set up The in line tube bundle consisted o ive vertical rows with three tubes in each. Spacin between centres o the tubes across the experimental channel was s 1 =.3 m and spacin alon the channel was s 2 =.6 m. A schematic view o the experimental channel with tube bundles is shown in the Fi. 1. External diameter o all the tubes was equal to.2 m. An electrically heated tube calorimeter had an external diameter equal to.2 m also. Durin the experiments calorimeter was placed instead o one tube o the bundle. An electric current value o heated tube was measured by an ammeter and voltae by a voltmeter. Temperature o the calorimeter surace was measured by eiht calibrated thermocouples: six o them were placed around the central part o the tube and two o them were placed in both sides o the tube at a distance o 5 mm rom the central part. Temperature o the oam low was measured by two calibrated thermocouples: one in ront o the bundle and one behind it. s 1 Cross section o the experimental channel had dimensions.14 x.14 m; heiht o it was 1.8 m. Radius o the channel turnin (R) was equal to.17 m. Statically stable oam low was used or an experimental investiation. This type o as liquid oam was enerated rom water solution o deterents. Concentration o deterents was kept constant and was equal to.5%. Foam low was produced durin as and liquid contact on the riddle, which was installed at the bottom o the experimental channel. Liquid was delivered rom the reservoir to the riddle rom the upper side; as was supplied to the riddle rom below. Measurement accuracies or lows, temperatures and heat luxes were o rane correspondinly 1.5%,.15.2% and.6 6.%. 3 Methodoloy Durin the experimental investiation a relationship was obtained between Nusselt number (heat transer intensity) rom one side and oam low volumetric void raction β and as low Reynolds number Re rom the other side: ( β, ) Nu =. (1) Re D1 D2 D3 E1 E2 E3 F1 F2 F3 s2 d Nusselt number was computed by ormula Nu hd =, (2) λ where λ is the thermal conductivity o the statically stable oam low, W/(mK), computed by the equation βλ - ( β) l λ = + 1 λ. (3) An averae heat transer coeicient was calculated as Foam Fi. 1. In line tube bundle in oam low The experimental set up consisted o the ollowin main parts: experimental channel, tube bundle, as and liquid control valves, as and liquid low meters, liquid storae reservoir, liquid level control reservoir, air an, electric current transormer and stabilizer [5, 6, 7]. qw h=. (4) T Gas Reynolds number o oam low was computed by ormula Re Gd =. (5) Aν

3 Proceedins o the 5th IASME/WSEAS Int. Conerence on Heat Transer, Thermal Enineerin and Environment, Athens, Greece, Auust 25-27, Foam low volumetric void raction can be expressed by the equation G β =. (6) G + G l It is known [5] that there are our main reimes o the statically stable oam low in the vertical channel o rectanular cross section: Laminar low reime Re = ; Transition low reime Re = 15; Turbulent low reime Re =15 19; Emulsion low reime Re >19. Experiments were perormed within Reynolds number diapason or as (Re ): (laminar low reime) and oam volumetric void raction (β):.998. Foam low as velocity was chaned rom.14 to.32 m/s. Heat transer coeicient (h) varied rom to W/(m 2 K). 4 Results Statically stably oam initially moved vertically upward, then made 18 deree and R=.17 m radius turnin and moved downward crossin the in line tube bundle. The main three parameters o oam low inluence on heat transer intensity o dierent tubes o the bundle: oam structure, distribution o local low velocity and distribution o local oam void raction across and alon the experimental channel. Foam structure can be characterized by diameter o the oam bubble (d b ). This parameter depends not only on the oam volumetric void raction (β), but on the oam low eneration conditions as well. Larer size bubbles oam low is enerated i the eedin as rate G and accordinly the Re is low. Diameter o the oam bubbles is d b =15±2 mm or the volumetric void raction o oam β=.998 and Re =19. Diameter o oam bubbles or drier (β=.997) oam low is equal to 1±1.5 mm and or the driest (β=) oam low d b =5±1 mm at the same conditions (Re =19). Increase o G inluences on eneration o oam low with smaller bubbles (size o the bubble is about times lower), thereore oam low becomes more homoenous and heat transer process intensiies. Liquid drainae process inluences on the distribution o the oam local void raction and accordinly on heat transer intensity o the tubes. Liquid drainae rom oam phenomena depends on ravity and capillary [8, 9]. In a vertical direction these orces are actin toether. In a horizontal direction inluence o ravity orces is neliible and inluence o capillary orces is dominatin. Inluence o electrostatic and molecular orces on drainae is insiniicant [8]. Gravity orces act alon the upward and downward oam low. While oam low makes a turn the ravity orces act across and alon the oam low. Liquid drains down rom the upper channel wall and local void raction increases (oam becomes drier) here as well. Ater the turn, local void raction o oam is less (oam is wetter) on the inner let side o the cross section (tubes D, Fi. 1). The low velocity distribution in cross section o the channel transorms ater turn too. Heat transer intensity o the irst tubes o the in line bundle to downward wettest (β=) oam low is shown in Fi. 2. Increasin oam low as Reynolds number (Re ) rom 19 to 44, heat transer intensity ( ) o the tube D1 increases twice (rom 75 to 1486), that o the tube E1 increases by 2.6 times (rom 46 to 158), and that o the tube F1 increases by 3 times (rom 256 to 757) or oam volumetric void raction β=. When Re =44, the heat transer intensity o the tube D1 is by 1.4 times more than that o the tube E1 and twice more than that o the tube F Re Fi. 2. Heat transer o the irst tubes D1, E1 and F1 to downward oam low, β= Heat transer intensity o the irst tubes o the in line bundle to downward driest (β=.998) oam low is shown in Fi. 3. Heat transer intensity ( ) o the tube D1 increases by 1.8 times (rom 431 to 768), that o the tube E1 increases twice (rom 31 to 614), and that o the tube F1 increases by 1.9 times (rom 253 to 475) or Re =19 44 and β=.998. Heat transer intensity o the tube D1 is twice better to the wettest (β=) oam low in comparison with the heat transer o the same tube to the driest (β=.998) oam low. The same or the tube F1 is by 1.4 times better to the wettest (β=) oam low in comparison with the heat

4 Proceedins o the 5th IASME/WSEAS Int. Conerence on Heat Transer, Thermal Enineerin and Environment, Athens, Greece, Auust 25-27, 7 17 transer o the same tube to the driest (β=.998) oam low Re Fi. 3. Heat transer o the irst tubes D1, E1 and F1 to downward oam low, β=.998 Increasin oam low as Reynolds number (Re ) rom 19 to 44, heat transer intensity ( ) o the tube D3 increases twice (rom 778 to 1566), that o the tube E3 increases by 2.3 times (rom 468 to 161), and that o the tube F3 increases by 2.7 times (rom 252 to 687) or oam volumetric void raction β= (Fi. 4). In one phase low case heat transer intensity o the rontal tubes is equal to about 6% o the third tubes heat transer intensity [3]. It is dierent in two phase oam low case. Heat transer intensity o the tube D3 is only by 3% better than that o the tube D1 or Re =19 44 and β=. Heat transer intensity o the tube E3 is by 3% better than that o the tube E1 and heat transer intensity o the tube F3 is by 1% better than that o the tube F1 or the same conditions Re Fi. 4. Heat transer o the third tubes D3, E3 and F3 to downward oam low, β= Heat transer intensity o the third tubes o the in line bundle to downward driest (β=.998) oam low is shown in Fi. 5. Heat transer intensity o the tube D3 increases by 1.6 times (rom 415 to 668), that o the tube E3 increases by 1.8 times (rom 32 to 584), and that o the tube F3 increases by 1.8 times (rom 252 to 462) or Re =19 44 and β= Re Fi. 5. Heat transer o the third tubes D3, E3 and F3 to downward oam low, β=.998 Heat transer intensity o the irst tubes is better than that o the third tubes to the driest (β=.998) oam low. Heat transer intensity o the tube D1 is by 8% better than that o the tube D3 or Re =19 44 and β=.998. Heat transer intensity o the tube E1 is by 3% better than that o the tube E3 and heat transer intensity o the tube F1 is by 6% better than that o the tube F3 or the same conditions Re Fi. 6. Averae heat transer o the tubes o the in line bundle to downward vertical oam low: β=,.997 and.998 An averae heat transer rate was calculated in order to analyze the experimental results o in line tube bundle. An averae heat transer intensity o the

5 Proceedins o the 5th IASME/WSEAS Int. Conerence on Heat Transer, Thermal Enineerin and Environment, Athens, Greece, Auust 25-27, tubes o the in line bundle to downward vertical oam low is shown in Fi. 6. Chanin Re rom 19 to 44, an averae heat transer intensity o the tubes increases by 2.4 times or β=; by 2.1 times or β=.997, and by 1.8 times or β=.998. Experimental results o investiation o heat transer o the in line tube bundle to downward ater 18 turnin statically stable oam low were eneralized by criterion equation usin dependence between Nusselt number and as Reynolds Re number. This dependence within the interval 19<Re <44 or the in line tube bundle (s 1 =.3 and s 2 =.6 m) in downward oam low with the volumetric void raction β=,.997, and.998 can be expressed as ollows: n m Nu = cβ Re. (7) On averae, or entire let (D) side line o the in line tube bundle in the downward oam low: c=19.8, n=347, m=13(1.3 β). On averae, or entire middle (E) line o the in line tube bundle in the downward oam low: c=5.8, n=123, m=249.5(1.1 β). On averae, or entire riht (F) side line o the in line tube bundle in the downward oam low: c=47, n=1422, m=28.2(1.1 β) and on averae, or the whole in line tube bundle (s 1 =.3 and s 2 =.6 m) in the downward oam low c=22.4, n=675, m=167.8(1.2 β). 5 Conclusions Heat transer rom in line tube bundle to laminar downward ater 18 deree turnin oam low was investiated experimentally. Three main parameters o oam low inluence on heat transer intensity o dierent tubes o the tube bundles: oam structure, distribution o local low velocity and distribution o local oam void raction across and alon the experimental channel. Heat transer intensity o the let (D) side line tubes is hiher than that o the middle (E) and riht (F) side line tubes. Heat transer intensity o the third tubes is better than that o the irst tubes to the wettest (β=) oam low. It is dierent with driest (β=.998) oam low. Heat transer intensity o the irst tubes is better than that o the third tubes in that case. Results o investiation were eneralized by criterion equations, which can be used or the calculation and desin o the statically stable oam heat exchaners with in line tube bundles. Nomenclature: A cross section area o exper. channel, m 2 ; c, n, m coeicients; d external diameter o tube, m; G volumetric low rate, m 3 /s; Nu Nusselt number; q heat lux density, W/m 2 ; Re Reynolds number; T temperature, K; h averae heat transer coeicient, W/(m 2 K); β volumetric void raction; λ thermal conductivity, W/(m K); ν kinematic viscosity (m 2 /s). Indexes: oam; as; w wall o heated tube. Reerences: [1] J. Gylys, Hydrodynamics and Heat Transer under the Cellular Foam Systems, Technoloija, Kaunas, [2] J. Gylys, S. Sinkunas, T. Zdankus, Analysis o tube bundle heat transer to vertical oam low, Enenharia Termica, Vol.4, No. 2, 5, pp [3] A. Zukauskas, Convectional Heat Transer in Heat Exchaners, Nauka, Moscow, [4] G. F. Hewitt, Heat exchaner desin handbook 2, York, Beell House, 2. [5] J. Gylys, M. Jakubcionis, S. Sinkunas, T. Zdankus, Analysis o staered tube bank heat transer in cross oam low, 1st International Conerence on Heat Transer, Fluid Mechanics and Thermodynamics, South Arica, vol. 1, part 2, 2, pp [6] J. Gylys, S. Sinkunas and T. Zdankus, Experimental Study o Staered Tube Bundle Heat Transer in Foam Flow, 5th International Symposium on Multiphase Flow, Heat Mass Transer and Enery Conversion, Xi an, China, 5, p. [1 6]. [7] J. Gylys, V. Giedraitis, S. Sinkunas, T. Zdankus and M. Gylys, Study o in-line tube bundle heat transer in upward vertical oam low, Enery: production, distribution and conservation ASME conerence, Milan, Italy, 6, pp [8] V. Tichomirov, Foams. Theory and Practice o Foam Generation and Destruction, Chimija, Moscow, [9] B. Fournel, H. Lemonnier, J. Pouvreau, Foam Drainae Characterization by Usin Impedance Methods, 3rd Int. Symp. on Two Phase Flow Modellin and Experimentation, Pisa, Italy, 4, p. [1 7].