Determination of heat transfer intensity between free streaming water film and rigid surface using thermography

Transcription

1 IV Conferencia Panamericana de END Buenos Aires Octubre 2007 Determination of eat transfer intensity between free ing water film and rigid surface using termograpy Ivanka Boras and Srecko Svaic Faculty of Mecanical Engineering and Naval Arcitecture Ivana Lucica 5, Zagreb, Croatia ivanka.boras@fsb.r Mirela Susa Department of Electrical and Computer Engineering Université Laval, Quebec, G1K7P4, Canada Abstract Te goal of te researc was to find te relation for determining te eat transfer coefficient between a free ing water film and metal corrugated surface. Te relation between relevant parameters wic determine te eat transfer coefficient as been obtained by means of Wilson-plot metod using data from te measurement. 1. Introduction Te open plate eat excanger (OPHE) consists of two plates welded togeter so tat one is flowing between plates and anoter one over te outer surface of upper plate. Te aim of suc eat excanger design is to enable te eat excange between outer wic could be waste dirty water and inner. Te OPHE are often used for eat recovery purposes in laundries, paper industries etc. Te main problem in termodynamical calculation of suc type of eat excanger is determination of te eat transfer coefficient on outer side. Because te plates are always inclined to te orizontal plane and outer surface is corrugated to ensure better eat transfer te standard relations for flat plate could not be used. Te paper presents te results of te researc done on te one plate of OPHE wit te aim to find te relation for eat transfer coefficient between ing film and plate. Te IR termograpy was used for measurements of temperature distribution on water film ing over te outer plate surface 2. Te problem Te open plate eat excanger is aimed for eat excange between ot waste water and cold fres water. Waste water flows over te outer (upper) side of te OPHE plate in free and fres water flows inside, between te plates. OPHE are used in te case wen waste water contents particles or coagulants. Te advantage of

2 suc design is easy cleaning of te plates and module design wic enables enlargement of te unit. Te upper side of OPHE plate is corrugated to improve te eat excange between te free of waste water and te plate. Te OPHE plates are inclined (5 º) to orizontal plane to ensure te free ing by means of gravity. Wile te equations for calculating te eat transfer coefficient inside te plates could be found in literature, te relation for te calculation of eat transfer coefficient on te outer side became a problem. Te goal of te researc was to find te relation for te eat transfer coefficient on te outer side of te OPHE plate. Te single plate of OPHE used in experiment is sown in figure 1 and te detail of corrugated upper surface in figure 2. Figure 1. Te plate of te eat excanger 3. Te experimental rig Figure 2. Te features of upper plate Te experimental rig consists of single OPHE plate placed on a frame wit up and down container (see figure 3). Te ot waste water enters te up container and overflow on te plate. After passing te plate te water enters te down container. Te fres water s in counter flow between te plates. IV Conferencia Panamericana de END Buenos Aires Octubre

3 Figure 3. Experimental rig Te mass flow of waste (ot) and fres (cold) water are measured by weiging wile te temperatures are measured by termocouples (see figure 4). Beside te termocouples te surface temperature distribution of ot water ing over te plate was recorded by IR camera. All measurements were done in stationary state. Hot inlet Hot outlet Cold outlet Cold inlet Figure 4. Positions of termocouples and directions of ot and cold water 4. Measurements Te measurements were carried out wit mass flow of 0,1; 0,2; 0,3 and 0,4 kg/s for ot and 0,1 and 0,2 kg/s for cold. Some of te results are presented in table 1 and te related termograms are sown in figure 5. IV Conferencia Panamericana de END Buenos Aires Octubre

4 4.1 Te results of measurement using termocouples Table 1. Te results of measurement using termocouples Measurement No Hot Cold Mass flow [kg/min] 12,58 6,31 Inlet temperature [ C] 25,67 12,57 Outlet temperature [ C] 19,59 21,93 Mass flow [kg/min] 5,03 12,48 Inlet temperature [ C] 43,54 13,47 Outlet temperature [ C] 15,31 23,65 Mass flow [kg/min] 12 12,14 Inlet temperature [ C] 27,29 13,72 Outlet temperature [ C] 18,23 21,21 Mass flow [kg/min] 24,5 12,25 Inlet temperature [ C] 21,90 15,11 Outlet temperature [ C] 19,07 19, Te results of measurement using infrared camera a) Measurement No.1 IV Conferencia Panamericana de END Buenos Aires Octubre

5 b) Measurement No. 2 c) Measurement No.3 IV Conferencia Panamericana de END Buenos Aires Octubre

6 d) Measurement No.4 Figure 5. Termograms and referent temperatures Table 2. Te results of measurement; te termocouples were used for cold and infrared camera for ot Measurement No Hot Cold Mass flow [kg/min] 12,58 6,31 Inlet temperature [ C] 25,1 12,57 Outlet temperature [ C] 20,3 21,93 Mass flow [kg/min] 5,03 12,48 Inlet temperature [ C] 40,1 13,47 Outlet temperature [ C] 15,9 23,65 Mass flow [kg/min] 12 12,14 Inlet temperature [ C] 27,3 13,72 Outlet temperature [ C] 19,0 21,21 Mass flow [kg/min] 24,5 12,25 Inlet temperature [ C] 21,8 15,11 Outlet temperature [ C] 19,5 19,61 Te eat excanged between te s is calculated using relations: - for ot ( ϑ ϑ ) Φ = q c kw...(1) i o IV Conferencia Panamericana de END Buenos Aires Octubre

7 - for cold c c ( ϑ ϑ ) Φ = q c kw...(2) oc ic Table 3. Te results of calculation of te eat fluxes Measurement No. Φ c Φ termocouples Φ IR kw kw kw cold ot 1 4,119 5,327 4,21 2 8,861 9,883 8,49 3 6,343 7,580 6,68 4 3,845 4,843 3,92 It can be seen tat, using recordings by infrared camera (for ot water) a fair accordance was obtained between eat fluxes calculated for ot water and cold water, respectively. Using recordings obtained by termocouples (for ot water) te differences between eat fluxes were more empasized. 5. Calculation of eat transfer coefficients By means of overall eat transfer coefficients, calculated from measurement, and eat transfer coefficient for cold using Eq. (3), te eat transfer coefficient for ot as been determined using Eq. (4). 0,8 0,4 λ α c = 0,022 Re Pr...(3) d 1 α wall k λwall α c ekv 1 δ 1 =...(4) Using Wilson-plot metod te relation Eq. (5) for determination of eat transfer coefficient of outer can be found using data from measurements: α 0,74 1/ 3 λ = 0,524 Re Pr...(5) L Calculating te eat transfer coefficient using Eq. (5) for ot and comparing tem wit tose obtained from measurement it can be seen tat good mutual correspondence is obtained (see table 4). IV Conferencia Panamericana de END Buenos Aires Octubre

8 Table 4. Te comparison of eat transfer coefficients for ot, measurement and Eq.(5) Measurement No. α from measurement α calculated Eq.(5) W/m 2 K W/m 2 K ,7 2866, ,4 2286, ,5 2832, ,8 3376,5 6. Conclusion In te paper te application of IR termograpy in determination of eat transfer intensity as been described. Te specific profile of eat excanger's surface required an investigation for new relations for calculation of eat transfer coefficients. Te results obtained using Eq. (5) for calculation eat transfer coefficients on ot water side indicated a good correspondence wit te measurement's result. References 1. D. P. Almond, P. M. Patel, Pototermal Science and Tecnique, London, Capman & Hall, S. V. Patankar, Numerical Heat Transfer and Fluid Flow, Hemispere Publising Corporation, Mc Grow-Hill Book Co, Wasington, Gerald C. Holst, Common sense approac to termal imaging, SPIE Optical Engeenering Press, Bellingam, Wasington, USA, M. Necati Ozisik, Heat transfer: A Basic Approac, McGraw-Hill Companies, 1984 IV Conferencia Panamericana de END Buenos Aires Octubre