SIMULATION ANALYSIS AND EXPERIMENTAL VALIDATION OF THERMO ELECTRIC GENERATOR BY DISCRETE RADIATION MODEL

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1 Internatonal Journal of Pure and Appled Mathematcs Volume 118 No , ISSN: (prnted verson); ISSN: (on-lne verson) url: do: /jpam.v Specal Issue jpam.eu SIMULATION ANALYSIS AND EXPERIMENTAL VALIDATION OF THERMO ELECTRIC GENERATOR BY DISCRETE RADIATION MODEL 1 N.Shanmugasundaram, 2 E.N. Ganesh, 3 S.Pradeep Kumar 1 Assocate Professor, Department of EEE 2 Dean, School of Engneerng 3 Assstant Professor, Department of EEE VELS Insttute of Scence, Technology & Advanced Studes, Pallavaram, Chenna shanmugam71.se@velsunv.ac.n, 2 dean.se@velsunv.ac.n 3 pradeep88.se@velsunv.ac.n Abstract: In ths study flow and heat transfer of flue gas and domestc heatng water n a fnned heat cell of a domestc wall hung boler was numercally nvestgated wth Fluent. Frstly, the heat cell was nvestgated and after that accordng to the temperature dstrbuton obtaned, thermoelectrc generator (TEG) locatons were chosen. Smulatons were performed usng dscrete ordnates radaton model. In addton, an expermental setup was nstalled to observe TEG performance Keywords: Heat Cell, Computatonal Flud Dynamcs, Fn, Heat Transfer 1. Introducton Snce the 1950s, the semconductor materal n varous techncal felds has been wdely appled and has developed very rapdly. Good thermoelectrc (TE) propertes of semconductor materals greatly mproved the effcency of the thermoelectrc effect, so that the thermoelectrc coolng and combned heat and power generaton has began to enter engneerng applcatons. Thermoelectrc unts embedded n heat exchangers by means of convertng ndustral waste heat nto electrcal power for local electrcal energy requrements. As a green envronmentally frendly energy converson technology, thermoelectrc power generaton technology s manly used n candle lamps, heat fans, thermoelectrc generators, feld generators, frewood generator, bo-fuel generator, vehcle exhaust waste heat generators, waste ncneraton generator system and boler heat generator system and a seres of other products and related felds. It can be seen from the lterature revew that both expermental and numercal nvestgatons have been done. Qu and Hayden developed a self-powered resdental heatng system usng thermoelectrc power generaton technology [1]. Qu and Hayden desgned, constructed and tested thermoelectrc modules where a full-sze prototype was ncorporated nto a gas-fred heatng boler [2]. Champer et al. have presented an expermental TE generator sutable for electrcty producton n multfuncton bomass stoves [3]. Thacheret al. tested a prototype automoble exhaust thermoelectrc generator (AETEG) nstalled n a 1999 GMC Serra pckup truck [4]. Masterbergen developed a thermoelectrc generator to convert a small amount of wasted heat nto electrcty [5]. Anatychuk et al. descrbed the development and testng of a TEG usng the exhaust heat of a 50-kW statonary desel power plant [6]. Maneewan and Chndaruksa consdered thermoelectrc power generaton from waste heat from a bomass drer [7]. Lertsattthanakorn nvestgated the feasblty of addng a thermoelectrc module to a stove s sde wall [8]. Belanger and Gosseln optmzed the desgn of a thermoelectrc generator sandwched n the wall of a cross flow heat exchanger [9]. Atk has done the thermal and electrcal modelng of a solar thermoelectrc generator [10]. Hsu et al. nvestgated a system to recover waste heat comprsed 24 TEG to convert heat from the exhaust ppe of an automoble to electrcal energy [11]. Yu and Zhao presented a numercal model to predct the performance of thermoelectrc generator wth the parallelplate heat exchanger [12]. A generator's effcency and output power are analytcally determned and compared to the expermental results. To demonstrate under constant temperature dfference, a heat exchanger effectveness of 0.5 s an optmal compromse between heat flux and temperature dfference for thermoelectrc power converson was confrmed n [13]. It can be seen from the lterature revew that many nvestgatons on TEG s usng waste heat were performed. In ths study, flow and heat transfer of flue gas and domestc heatng 435

2 Internatonal Journal of Pure and Appled Mathematcs Specal Issue water n a fnned heat cell was nvestgated numercally by Fluent. After ths, smulatons were performed of an alternatve desgn for the heat cell wth TEG s. Ths was done accordng to the obtaned temperature dstrbutons. Also an expermental study was performed to acheve TEG performances. 2. Expermental and Numercal Model The expermental setup buld to measure TEG perfomances and the numercal model used n the smulatons of heat cell are shown n ths part. It can be seen from the fgure that a TEG s sandwched between two copper plates. The hot sde of TEG's was postoned on the heater whch was nsulated. On the cold sde of TEG a cold water tank was placed. A constant temperature water bath supples cold water to the tank and a crculaton was formed. The temperature on both the hot and cold sde of TEG s was measured usng T- type thermocouples and s acqured through a data logger. Usng these temperatures the power generated by the TEG was observed through performance curves of TEG's whch are gven by the supplers. be seen from the fgure. The flue gas channel s perpendcular to page and s flowng over the fnned water channels. Flue gas enters the flow secton wth 11 g/s mass flow rate and 1990 K temperature. Water enters wth 295 g/s mass flow rate and 333 K temperature. Materal of heat cell s alumnum and was modeled wth constant propertes. Convecton boundary condton were mplemented on the outer walls of heat cell to ar at 333 K. The flow was found to be turbulent so k-ω turbulence model was used to calculate the turbulence effects. There were also two models created where radaton s consdered and not consdered. For the smulatons where radaton was consdered, the dscrete ordnates model (DO) was used. Water was modeled wth constant propertes and flue gases were the combuston gases of natural gas and had a composton of of 7.7% CO2, 15.4% H2O, 4.0% O2 and 72.9% N2. Flue gases were modeled usng speces transport model n Fluent. Frstly, the smulatons were done for mesh ndependency and after that solutons are obtaned for velocty and temperature dstrbutons. The optmzed mesh number was found to be 5,403,407. TEG mounted heat cell s presented n Fgure 3. Sx TEG's were mplemented n the water channel of heat cell on the walls whch are n contact wth flue gases. Water enters the channel wth 333 K and 295 g/s mass flow rate at the secton where the frst TEG s mplemented and flows out at the sxth TEG. Flue gases enter from the top of the heat cell wth 1990 K and g/s mass flow rate. TEG s are mounted n the water channel on the walls wth contact to flue gases. TEG s were modeled as 40x40x4 mm (Thermonamc TEHP module) and heat conducton coeffcent was accepted as 2W/m.K. The flow was modeled as turbulent usng k-ω turbulence model and radaton was also calculated usng DO radaton model. Fgure 1. Schematc vew of expermental setup A. Numercal Model Numercal smulatons for the fnned heat cell were performed n the Fluent CFD code. The fnned heat cell used n the numercal smulatons of ths nvestgaton s presented n Fgure 2. Water nlet and outlet sectons can Fgure 2. Fnned Heat Cell 436

3 Internatonal Journal of Pure and Appled Mathematcs Specal Issue 4. Results and dscusson Fgure 3. TEG mounted heat cell 3. Governng Equatons and Data Reducton The governng equatons for three dmensonal, steady and ncompressble flow and heat transfer whch are the contnuty, turbulent momentum and energy equatons are solved va the Fluent program. Governng equatons are gven below. U U j ρu ρc U p = 0 (1) P = T = j + T [ k x U U j " " [ µ ( + ) ρu U j j ρc U T W = Q h -Q c = VI (4) Re = VD h / v (5) In these equatons, velocty, pressure and temperature are presented wth U, P and T, respectvely. Propertes whch are densty, specfc heat, conductvty and vscosty are presented wth ρ, cp, k and µ, respectvely. Accordng to the energy balance equatons, electrcal power can be obtaned from Eq. 4. In ths equaton, Qh and Qc shows the heat flux on the hot and cold surfaces, respectvely. V s the voltage and I s the current produced by each TEG. Reynolds number s calculated usng Eq. 5. In Eq. 5 v, Dh and ν show velocty, hydraulc dameter and knematc vscosty, respectvely. Usng Eq. 5. the Reynolds number for the water channel and flue gas channel was calculated as 8748 and 3279, respectvely. Ths shows that the flow s turbulent p " ] (3) (2) Results obtaned for the smulatons and expermental work done s presented n ths chapter. It was observed that the smulaton converged and the conservaton equatons were satsfed. The temperature contours obtaned perpendcular to the flow drecton of flue gases s presented n Fgure 4. The upper fgure shows the temperature dstrbuton on the fns and the lower one shows the temperature dstrbuton on the outlet secton. Ths result was obtaned for the smulaton wthout radaton. It can be seen that flue gases transfer ther heat to water and cools down. It was observed that flue gases are coolng down rapdly around the fns. The temperature dstrbuton on the outlet secton s very unform and shows that flue gases transfers ther heat effectvely to the water. The outlet temperature of flue gases was calculated as K. It was calculated that ncrease of water temperature along the channel was 19 K and had a value of 352 K at the outlet. Ths value was a satsfyng result, whch s very close to the real workng condtons, where the water outlet temperature s 353K.Temperature contour obtaned for the fnned heat cell parallel to the flue gases s presented n Fgure 5. It s observed that durng the flow of hot gases through the channel the temperature decreases rapdly on the fnned water channels. The velocty dstrbuton n the flue gas channel s presented n Fgure 6. The flow dstrbuton s n agreement wth the temperature contour obtaned before. An almost constant velocty dstrbuton was observed n the entrance regon of the channel. The velocty of flue gases rapdly decreases at the frst water channel and becomes nearly stagnant at the fnned channel. Smulatons performed wth radaton effects showed that hgher wall temperatures were acheved. The am was to observe the effects of radaton on heat transfer to the heat cell walls where TEG s wll be mplemented. Compared wth the results obtaned wthout radaton, lower temperatures for flue gases were observed. Especally, heat transfer to the walls occurred effectvely. It was observed that radaton effects decrease wth the decrease of flue gas temperature. However, due to hgher wall temperatures hgher outlet temperature for water was calculated and 360K was acheved, whch s stll a good result. It s seen that the results are meanngful and showed a good accuracy. After the smulatons for the fnned heat cell were completed, smulatons for the new heat cell wth TEG's mplemented were performed. The most mportant factor n ths part are temperature values on TEG surfaces. In ths analyss Thermonamc TEHP module was nvestgated. Maxmum hot sde temperature of ths module s 623K. Obtaned temperatures on the hot and cold sde of TEG s are presented n Fgure 6 437

4 Internatonal Journal of Pure and Appled Mathematcs Specal Issue Fgure 4 (a). Temperature contour on fnned heat cell Fgure 6 (b). Velocty vectors of flue gases Fgure 4. (b). Temperature contour on fnned heat cell. Fgure 5. Temperature contours parallel to flue gases Fgure 6 (a). Velocty vectors of flue gases It was seen that the hghest temperatures occurred on the ffth and sxth TEG s. Ths was explaned wth the fact that water heats up through the channel and the coolng effect on cold sde degrades. Due to the same reason the temperature dstrbuton was not symmetrcal on the TEG s. However, the temperature dstrbutons on the thrd and fourth TEG are almost symmetrcal. Also the lowest temperature values are obtaned on these two TEG s. Ths s due to the coolng effect of water from two sdes of TEG s. Hot and cold surface temperatures obtaned from the smulaton are n the operatng temperature range of TEG s. After the temperature contours on TEG s were nvestgated, the temperatures on hot and cold sdes of TEG s were calculated. The temperature dfference and accordng to these temperatures power output of each TEG was also obtaned from the suppler s catalog values. The results are presented n Table 1. The temperature on hot sde and cold sde s shown wth Th and Tc, respectvely. Temperature dfference between hot and cold sde s shown wth T and the power output accordng to ths temperature s presented wth P. The power output of each TEG s obtaned usng the supplers catalog data. Mean values were also calculated. It s seen that the calculated temperatures are n agreement wth the temperature contours. All hot sde temperatures are n the workng range of TEG s. The mean outpup power of TEG s was calculated as 3.26 W, whch overall supples approxmately 20 W of power. Ths s a good result for an alternatve desgn of heat cell, but has to be mproved to be a self-powered resdental heatng system. Expermental results were also obtaned and were n agreement wth the numercal results. Tests were done to measure the performances of Thermonamc modules under dfferent workng condtons were measured. It was amed to create the same temperature ranges on the hot and cold sdes of TEG s to nvestgate the power output of each module under the same workng condtons wth the numercal model. 438

5 Internatonal Journal of Pure and Appled Mathematcs Specal Issue Table 1. Temperature values on TEG s. TEG T h T c T P(W) Mean Results were n agreement wth the numercal results and nearly the same power outputs were obtaned. So the numercal results were valdated and due to these results a prototype was manufactured and the TEG s were mplemented. Expermental study s ongong and t s amed to have power outputs whch are n agreement wth the foregong results 5. Conclusons CFD smulatons of a domestc wall hung boler heat cell were performed and presented n ths nvestgaton. The effects of radaton on the heat transfer especally on the walls were examned usng DO radaton model. After completng the smulatons for the present heat cell, desgn studes were performed for new heat cell desgn wth TEG s mplemented. Very close results were obtaned to the real workng condtons from the CFD smulatons. Due to fns, flue gases ext the flow channel slower, thereby heat transfer to water s more effcently. Water outlet temperature was calculated as 79 C whch s very close to the real workng condtons. Although, flow and heat transfer smulatons of heat cell were approprate and n agreement wth real workng condtons, temperature dfferences on walls could not be observed. So, radaton effects were mplemented. Sgnfcant temperature dstrbutons on walls were observed and ths gave an opnon on the new desgn of the heat cell, ncludng TEG s. The same approaches were used for the desgn of the new heat cell and TEG s were mplemented on t. Smulaton results were approprate. Investgaton of surface temperature of hot and cold sdes of TEG s was done and t was seen that the temperatures were n the workng range of TEG s. The results showed that ths approach could be used for the new heat cell. Although work done on new deas about heat cell desgn and TEG mplementaton are stll gong on. References [1] K. Qu, A. C. S. Hayden, Development of a thermoelectrc self-powered resdental heatng system, J. of Power Sources, 2008, Vol. 180, pp [2] K. Qu, A. C. S. Hayden, Development of Thermoelectrc Self-Powered Heatng Equpment, J. of Electronc Materals, 2011, Vol. 40, No. 5, pp [3] D. Champer, J. P. Bedecarrats, T. Kousksou, M. Rvaletto, F. Strub, P. Pgnolet, Study of a TE generator ncorporated n a multfuncton wood stove, Energy, 2011, Vol. 36, pp [4] E. F. Thacher, B. T. Helenbrook, M. A. Karr, C. J. Rchter, Testng of an automoble exhaust thermoelectrc generator n a lght truck, Proceedngs of the Insttuton of Mechancal Engneers, Part D: Journal of Automoble Engneerng, 2007, Vol. 221, pp [5] D. Masterbergen, Development and Optmzaton of a stove powered thermoelectrc generator, Ph.D. Thess, Colorado State Unversty Department of Mechancal Engneerng, Fort Collns Colorado, [6] I.Anatychuk, Y. Y. Rozver, D. D. Velchuk, Thermoelectrc Generator for a Statonary Desel Plant, J. of Electronc Materals, 2011, Vol. 40, No. 5, pp [7] S. Maneewan, S. Chndaruksa, Thermoelectrc Power Generaton System Usng Waste Heat From Bomass Dryng, J. of Electronc Materals, 2009, Vol. 38, No. 7, pp [8] Lertsattthanakorn, C., Electrcal performance analyss and economc evaluaton of combned bomass cook stove thermoelectrc (BITE) generator, Bosource Technology, 2007, Vol. 98, pp [9] Belanger, S., Gosseln, L., Thermoelectrc generator sandwched n a crossflow heat exchanger wth optmal connectvty between modules, Energy Converson and Management, 2011, Vol. 52, pp [10] Atk, K., Numercal Smulaton of a Solar Thermoelectrc Generator, Energy Sources, Part A, 2011, Vol. 33, pp [11] Hsu, C. T., Yao, D. J., Yu, B., Applcaton Of Thermoelectrc Waste Heat Recovery From Automobles, proceedngs Of The Asme nd Mcro/Nanoscale Heat & Mass Transfer Internatonal Conference, Shangha, Chna. 439

6 Internatonal Journal of Pure and Appled Mathematcs Specal Issue [12] Yu, J., Zhao, H., A numercal model for thermoelectrc generator wth the parallel-plate heat exchanger, Journal of Power Sources, 2007, Vol. 172, pp [13] Érc V. Sempels; Frédérc J and Lesage Optmal Thermal Condtons for Maxmum Power Generaton When Operatng Thermoelectrc Lqud-to Lqud Generators" IEEE Transactons on Components, Packagng and Manufacturng Technology, Volume: 7, Issue: 6, Year: [14] T. Padmaprya and V. Samnadan, Inter-cell Load Balancng technque for mult-class traffc n MIMO-LTE-A Networks, Internatonal Journal of Electrcal, Electroncs and Data Communcaton (IJEEDC), ISSN: , vol.3, no.8, pp , Aug [15] S.V.Mankanthan and K.Baskaran Low Cost VLSI Desgn Implementaton of Sortng Network for ACSFD n Wreless Sensor Network, CT Internatonal Journal of Programmable Devce Crcuts and Systems,Prnt: ISSN X & Onlne: ISSN , Issue : November 2011, PDCS [16] Rajesh, M., and J. M. Gnanasekar. "Path observaton-based physcal routng protocol for wreless ad hoc networks." Internatonal Journal of Wreless and Moble Computng 11.3 (2016):

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