VI CONGRESSO NACIONAL DE ENGENHARIA MECÂNICA VI NAIONAL CONGRESS OF MECHANICAL ENGINEERING 18 a 21 de agoto de 2010 Campina Grande Paraíba - Brail Augut 18 21, 2010 Campina Grande Paraíba Brazil HE USE OF FIBER WOOD AS EVAPORAIVE PAD PACKAGING MAERIAL hay Sthefanie do Santo, thayanto@yahoo.om.br Joé Rui Camargo, rui@unitau.br Univeridade de aubaté, Rua Daniel Danelli, /nº - Jardim Morumbi aubaté / SP CEP: 12060-440 Abtrat: Currently, the mot ued refrigeration ytem applied to air onditioning for human thermal omfort i the vapor ompreion ytem. However, other thermal ytem uh a the evaporative ooling ytem an be an eonomial alternative in many ae. hi paper preent the bai priniple of the diret evaporative ooling proe, the mathematial development of the equation of thermal exhange and the reult of experimental tet performed in the Air Conditioning Laboratory at the Univerity of aubate Mehanial Engineering Department.he main objetive of thi paper i to analyze the tehnial and eonomi viability of ue of natural fiber a evaporative ooling pakage material and new onfiguration aimed to energy aving and ue of natural reoure. Currently, the elluloe i the material ommerially ued and thi reearh tudie the ue of fiber wood a replaement material. It will be ontruted a everal range of panel thiknee, with different denitie and onduted laboratory tet with the rpoe of obtaining graph that repreent the oeffiient of performane (COP) a a funtion of flow rate and ompare the reult with thoe of the panel ommerially available. It onlude that the ue of fiber wood a evaporative pad material have a large potential to propitiate thermal omfort and an till be ued a an alternative to the evaporative pad atually available, when ompatible ot-benefit i preenting good thermal performane and a relation to an expeted one. Keyword: evaporative ooling, natural fiber, thermal omfort, evaporative panel 1. INRODUCION Evaporative ooling operate uing indued proee of heat and ma tranfer, where water and air are the working fluid. It onit, peifially, in water evaporation, indued by the paage of an air flow, thu dereaing the air temperature. When water evaporate into the air to be ooled, imultaneouly humidifying it, that i alled diret evaporative ooling (DEC) and the thermal proe i the adiabati aturation. he main harateriti of thi proe i the fat that it i more effiient when the temperature are higher, that mean, when more ooling i neeary for thermal omfort. It ha the additional attrativene of low energy onumption and eay maintenane. Due to ue total airflow renewal, it eliminate the reirulation flow and proliferation of fungi and bateria, a ontant problem in onventional air onditioning ytem. Due to it harateriti the evaporative ooling ytem i more effiient in plae where the limate i hot and dry but it an alo be ued under other limati ondition. Several author dediated their reearhe to the development of diret and indiret evaporative ooling ytem. Watt (1963) developed the firt eriou analye of diret and indiret evaporative ytem; Leung (1995) preent an experimental reearh of the fored onvetion between an air flow and an inner urfae of a horizontal ioele triangular dut; Halaz (1998) preented a general dimenionle mathematial model to deribe all evaporative ooling devie ued today; Camargo, Cardoo and ravelho (2000) developed a reearh where a thermal balane tudy for diret and indiret ooling ytem wa developed; Camargo and Ebinuma (2002) preented the priniple of operation for diret and indiret evaporative ooling ytem and the mathematial development of the equation of thermal exhange, allowing for the determination of heat tranfer onvetion oeffiient for primary and eondary air flow; Dai and Sumathy (2002) invetigated a ro-flow diret evaporative ooler, in whih the wet honeyomb paper ontitute the paking material and the reult indiate that there exit an optimum length of the air hannel and the performane an be improved by optimizing ome operation parameter; Liao and Chiu (2002) developed a ompat wind tunnel to imulate evaporative ooling pad-fan ytem and teted two alternative material; Al-Sulaiman (2002) evaluated the performane of three natural fiber (palm fiber, jute and luffa) to be ued a wetted pad in evaporative ooling; Camargo, Ebinuma and Silveira (2003) preent a thermoeonomi analyi method baed on the firt and
eond law of thermodynami and applied to an evaporative ooling ytem oupled to an adorption dehumidifier; Haan and Sirén (2003) invetigated the performane of two evaporatively heat exhanger operating under imilar ondition of air flow and inlet water temperature; Camargo, Ebinuma and Cardoo (2003) preent the bai priniple of the evaporative ooling proee for human thermal omfort and preent the mathematial development of the thermal exhange equation, allowing the determination of the effetivene of aturation. hi paper develop a mathematial model for diret evaporative ooling ytem and preent the experimental reult of the tet performed in a diret evaporative ooler that took plae in the Air Conditioning Laboratory at the Univerity of aubate, plaed in the ity of aubate, State of Sao Paulo, Brazil. 2. DIREC EVAPORAIVE COOLING he priniple underlying diret evaporative ooling i the onverion of enible heat to latent heat. Non-aturated air i ooled by heat and ma tranfer inreae by foring the movement of air through an enlarged liquid water urfae area for evaporation by utilizing blower or fan. Some of the enible heat of the air i tranferred to the water and beome latent heat by evaporating ome of the water. he latent heat follow the water vapor and diffue into the air (Watt and Brown, 1997). Figure (1) how a hemati diret evaporative ooling ytem, where water i running in a loop and the makeup water entering the ump to replae evaporated water mut be at the ame adiabati aturation temperature of the inoming air. In a DEC, the heat and ma tranferred between air and water dereae the air dry bulb temperature (DB) and inreae it humidity, keeping the enthalpy ontant (adiabati ooling) in an ideal proe. he minimum temperature that an be reahed i the thermodynami wet bulb temperature (WB) of the inoming air. he effetivene of thi ytem i defined a the rate between the real dereae of the DB and the maximum theoretial dereae that the DB ould have if the ooling were 100% effiient and the outlet air were aturated. Pratially, wet porou material or pad provide a large water urfae in whih the air moiture ontat i ahieved and the pad i wetted by dripping water onto the upper edge of vertially mounted pad. Figure 1. Shemati of evaporative pad for omfort 3. MAHEMAICAL MODEL In the tudy of the pyhometri proe dry air i onidered a a ingle ga haraterized by an average moleular ma equal to 28.9645. In thi work the humid air i onidered a a mixture of two gae: the dry air and water vapour. Conidering the humid air flow loe to a wet urfae, aording to Fig. (2), the heat tranfer will our if the urfae temperature i different from the draft temperature. If the abolute humidity (onentration) of the air loe the urfae w i different from the humidity of the draft w a ma tranfer will alo our. he elementary enible heat i Q h da ( ) (1)
he h oeffiient i determined from the Nuelt number (Nu) expreed a a funtion of the Reynold number (Re) and Prandtl number (Pr). In a imilar way the rate of water vapour tranfer dm V between the draft and the air loe to the urfae will be dm v h mda (w w ) (2) By analyi of the interfae air-liquid, the latent heat Q L i determined by the energy onervation law. QL Q Q hlv dm v (3) Rearranging Eq. (1), (2) and (3), the total differential heat flow i Q [h ( ) h h (w w)]da (4) w Lv m Equation (4) indiate that the total heat tranfer i the reult of a ombination of a portion originating from temperature differene and other portion originating from the differene of the abolute humiditie. hee two potential an be ombined by the Lewi relationhip o that the total heat flow will be expreed by a ingle potential that i the enthalpy differene between the air loe to the wet urfae and the air free urrent. Uing the peifi enthalpy of the mixture a the um of the individual enthalpie (Moreira, 1999) give h h (ha ha ) (wh v w h v ) (5) With the hypothei that air and vapor are perfet gae it follow that h h ( ) h v (w w) (6) where the humid peifi heat i w (7) pa pv In the tandard environmental ondition C pa = 1006 J/kg.K and C pv = 1805 J/kg.K. herefore (h h) h v(w w) (8) Combining Eq. (4) and Eq. (8) give Q h da (h h) (w R Le w) (h Lv R Le h v ) (9) where R Le i the Lewi relationhip, a dimenionle number expreed a h R Le (10) h C m In the above dedution the denity of the humid air wa approximated by the denity of the dry air. aking the Lewi relationhip a being unitary, give h Lv h v h L. It i alo verified that the term w w h L i uually negligible in the preene of differene of the peifi enthalpie h h, o that only the firt term inide braket i ignifiant. In the ame way, the total heat flow i aued by the differene of peifi enthalpie of the air and of the aturated air loe to the wet urfae and i given by Q h da (h h) he enible heat tranferred i (11)
Q ma d (12) herefore by ombining Eq. (12) with Eq. (1) give h da ( ) ma d (13) whih an be integrated, reulting in 1 2 h A 1 exp (14) 1 m a he effetivene of a diret evaporative ooling equipment i defined a 1 1 2 (15) then h C A 1 exp (16) m a Analyzing Eq. (15) it i verified that an effetivene of 100% orrepond to air leaving the equipment at the wet bulb temperature of entrane. hi require a ombination of large area of heat tranfer and a high heat tranfer oeffiient and low ma flow. It i alo oberved that the effetivene i ontant if the ma flow i ontant ine it ontrol diretly and indiretly the value of the parameter on the Eq. (16). 4. EXPERIMENAL WORK Experiment were developed during the month from May/2009 to September/2009 in the Air Conditioning Laboratory at the Univerity of aubate Mehanial Engineering Department, loated in the ity of aubate (latitude S23º01 30, longitude E45º33 30 and altitude 580 m), State of São Paulo, Brazil. Performane tet were arried on an air onditioning devie by diret evaporative ooling. he evaporative devie wa intalled in a room of 6.50m x 5.30m x 2.90m and the following parameter were monitored: outdoor air humidity and temperature, evaporative ooler inlet air humidity and temperature, evaporative ooler outlet air humidity and temperature, water temperature inide the upplying tube, water temperature at the evaporative ooling reervoir, evaporative pad urfae temperature, evaporative ooler outlet air peed and the temperature and humidity inide the onditioned room. he air flow fan i ontrolled by a variable voltage tranformer Varikeld 220V. he air temperature and humidity are meaured with thermo-hygrometer model Intrutherm H-210. It i alo monitored the urrent and voltage in the eletri motor with multimeter. he air flow peed i meaured with digital hot wire thermo-anemometer model Intrutherm AFR-180. he auray harateriti of the meaurement intrument are preented in able 1. able 1. Charateriti of the meaurement intrument INSRUMEN MANUFACURER/MODEL RESOLUION/ACCURACY Variable voltage tranformer Varikeld 220V ± 2,5 V hermo-higrometer Intrutherm/H-210 1 o C / ± 0,05 % Multimeter Minipa/E 2052 0,0005V / ± 0,5% Multimeter Minipa/E 1552 0,005A / ± 0,5% Hot wire thermo-anemometer Intrutherm/AFR 180 0,1 m/ / ± 5% he material (traw, wood) wa plaed inide a panel made with wire meh with the following dimenion: 0.25 x 0.25 x 0.10 m. rial were arried out with filling denitie of 12.8 kg/m³, 19.2 kg/m³, 25.6 kg/m³, 32.0 kg/m³, and 38.4
kg/m³. During the tet, the air flow veloity wa varied between 0.5 m/ and 2.0 m/ for eah denity. able (2) preent the reult obtained. able 2. Cooling effetivene. Veloity (m/) Filling denity (kg/m 3 ) 12.8 19.2 25.6 32.0 38.4 0.5 0.698 0.730 0.740 0.760 0.847 1.0 0.670 0.680 0.688 0.732 0.834 1.5 0.649 0.655 0.680 0.702 0.825 2.0 0.638 0.645 0.667 0.680 0.816 Figure 2 how the experimental evaporative pad with the fiber wood a alternative for onventional elluloi. (a) (b) Figure 2. Evaporative pad ued: (a) onventional (elluloe); (b) experimental (fiber wood). Figure (3) how the graph of the performane of the traw ued a wood filler pad evaporative funtion of air peed at whih it wa ubmitted.
Figure 3. Effetivene of traw wood in funtion of the air veloity 5. CONCLUSIONS he reult obtained, it an be aid that the traw wood have great potential to be ued a an alternative to fill the evaporative pad. Analyzing graphially their performane through the effetive veloity. Note that the higher the denity of the filling (kg/m³), the better effetivene of ooling. It appear that while the pad at a veloity between 0.5 and 2.0 m/ the effetivene range from 0.847 to 0.816, whih how that the ue of traw and wood filler pad i feaible evaporative. 6. ACKNOWLEDGEMENS he author aknowledge the finanial upport of he National Counil for Sientifi and ehnologial Development (CNPq), Brazil, Pro. 303301/2006-6 and Univerity of aubate (PIC). 7. REFERENCES Al-Sulaiman, F., 2002, Evaluation of the Performane of Loal Fiber in Evaporative Cooling. Energy Converion & Management, Elevier Siene Ltd., p. 2267-2273. Camargo, J.R., Cardoo, S., ravelho, J.S., 2000, Condiionamento de Ar por Refriamento Evaporativo, Proeeding of the 9º Congreo Chileno de Ingenieria Meânia, IV Congreo Naional de Energia, COCIM-CONAE 2000, Valparaio, Chile, (in Portuguee). Camargo, J.R., Ebinuma, C.D., 2002, A Mathematial Model for Diret and Indiret Evaporative Cooling Air Conditioning Sytem, Proeeding of the 9th Brazilian Congre of hermal Engineering and Siene, ENCI2002, UFPB, João Peoa, PB, paper CI02-0855. Camargo, J.R, Ebinuma, C.D., Cardoo, S., 2003, A Mathematial Model for Diret Evaporative Cooling Air Conditioning Sytem, hermal Engineering, nº 4, Brazil, p. 30-34. Camargo J.R, Ebinuma, C.D., Silveira, J.L., 2003, hermoeonomi Analyi of an Evaporative Deiant Air Conditioning Sytem, Applied hermal Engineering 23, p. 1537-2549. Dai, Y.J., Sumathy, K., 2002, heoretial Study on a Cro-flow Diret Evaporative Cooler Uing Honeyomb Paper a Paking Material, Applied hermal Engineering, Elevier Siene Ltd, p.1417-1430. Halaz, B.A., 1998, A General Mathematial Model of Evaporative Cooling Devie, Rev. Gén. herm. Elevier, Pari, Frane, vol.37, p. 245-255. Haan, A., Sirén, K., 2003, Performane Invetigation of Plain and Finned ube Evaporatively Cooled Heat Exhanger, Applied hermal Engineering, Elevier Siene Ltd., p. 325-340. Leung, C.W., 1995, Fored onvetion inide horizontal ioele triangular dut, I MehE Conferene ranation, Mehanial Engineering Publiation Ltd., London, p. 117-121.
Liao, C., Chiu K., 2002, Wind unnel Modeling the Sytem Performane of Alternative Evaporative Cooling Pad in aiwan Region, Building and Environment. Elevier Siene Ltd., p. 177-187. Moreira, J.R.S., 1999, Fundamento e Apliaçõe da Pirometria, RPA Editorial Ltda, São Paulo, (in Portuguee). Watt, J.R., 1963, Evaporative Air Conditioning, Ed. he Indutrial Pre, New York, 300p. Watt, J.R., Brown, W.K., 1997, Evaporative Air Conditioning Handbook, 3ª ed., he Fairmont Pre, In., Lilburn, GA, 507 p. 8. RESPONSIBILIY NOICE he author() i (are) the only reponible for the printed material inluded in thi paper.