Research Article EXPERIMENTAL STUDY OF HEAT TRANSFER CHARACTERISTICS OF STAINLESS STEEL FIBROUS FLOW INSULATOR

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1 Tansactions of the TSME (16) Vol. 4, No. 2, Jounal of seach and Applications in Mechanical Engineeing Copyight 16 by TSME ISSN pint DOI: /jame seach Aticle EXPERIMENTAL STUDY OF HEAT TRANSFER CHARACTERISTICS OF STAINLESS STEEL FIBROUS FLOW INSULATOR P. Khantikomol* M. Polsonkam T. Poowadin newable Enegy Technology Laboatoy (RTER) Depatment of Mechanical Engineeing, Faculty of Engineeing and Achitectue, Rajamangala Univesity of Technology Isan, 744 Suanaai Road, Muang, Nakhonatchasima, 3, Thailand ABSTRACT: Flow insulation is the eduction of heat tansfe of flowing fluid moving though the objects. The mateials chosen fo flow insulation is the poous mateial, which the fluid can flow though it and ecove the heat fom the flowing fluid leading to educe the tempeatue of the fluid. The pesent eseach aticle aims to popose the heat tansfe chaacteistics of the stainless steel fibous mateial as the flow insulato. The stainless steel fibous plate (poous plate) having diamete 1 mm, thickness 1, 15,, 25, and 3 mm, and poosities.9292,.9469, and.9646 wee examined. In the expeiment, ynolds numbe 1-25 and the inlet ai tempeatues o C wee vaied flowing though the poous media nomally. The tempeatue change along the test tube, tempeatue dop acoss the poous plate, and the heat ecovey efficiency wee poposed. Obviously, the tempeatue dop acoss the poous plate and the themal efficiency of the poous plate incease with the inlet gas tempeatue due to the effect of adiation heat tansfe mode. The inceasing of poosity, which decease the heat tansfe aea, leads to decease both of tempeatue dop and themal efficiency. It could conclude that the fibous poous mateial could be a good flow insulato at low velocity, high inlet fluid tempeatue and low poosity. Keywods: Flow insulato, Themal efficiency, Fibous mateial, Heat tansfe, ynolds numbe 1. INTRODUCTION Ove pass two decades, heat tansfe in the poous media has been studied both expeiment and theoy analysis. Due to the poous having high aeas fo heat tansfe, theefoe it have high heat tansfe coefficient at the suface. Many high tempeatue facilities wee done by the high poosity poous mateial, fo example, a gaseous coe nuclea eacto, plasma, combustion bune [1-3] and high tempeatue heat exchange [4]. This application can be done by using a multiphase medium consisting of fluid phase (gas) and paticulate phase (solid) [5-8] of the poous media. Owing to the advantage of the poous media on high efficiency heat tansfe, the enegy of the flowing fluid flow though the poous element was ecoveed leading to the tempeatue diffeent between the upsteam and the downsteam side. This so call novel concept was called flow insulation due to the poous could act the same behavio as themal insulato. In 1982s, Echigo [9] has pesented placing high poosity poous mateial nomal to the gas flow diection in an exhaust duct. It was found that the high tempeatue exhaust gas was geatly educed owing to the enegy was * Coesponding autho: P. Khantikomol addess: peecha@muti.ac.th 148 /Volume 4(2), 16 Tansactions of the TSME: JRAME

2 tansfeed to the poous mateial by convection heat tansfe leading to decease its tempeatue moe than 1 o C fo only 15 mm thickness. When the poous eceive the themal enegy, the poous emits the themal adiation into both upsteam and downsteam side. In 9s, Viskanta [1] was poposed about the high poosity poous mateial and its application. He has been showed the advantage of high poosity poous mateials that could emit, absob, and adiate the themal adiation due to it has a lage of suface fo heat tansfe. Seveal eseaches [11-18] wee studied both numeically and expeimentally, they illustated the ecoveing themal enegy fom flowing fluid using the poous mateials which involve with the flow insulation concept. Khantikomol et al. [19-] has been poposed the numeical and expeimental study on the flow insulation system using open-cellula poous mateial. They indicated that the upsteam adiation tempeatue stongly affected the quantity of the gas tempeatue dop acoss the poous plate. Accoding to the liteatue, it seems that the high poosity poous mateial is significant to the flow insulation system. Howeve, it has not found any infomation about the fibous mateial as flow insulato. In the pesent wok, the heat tansfe chaacteistics of the flow insulation system using the stainless steel fibous mateial as high poosity poous mateial is poposed. The stainless steel fibous is pepaed into the poous plate with 1, 15,, 25, and 3 mm thickness. Thee poosities ae examined. Heat tansfe chaacteistics ae pesented in tems of heat ecovey, tempeatue dop and the tempeatue pofile. 2. EXPERIMENTAL SETUP In the pesent expeimental study, the stainless steel fibous mateial was examined to be the flow insulato. The fibous mateial was pepaed as flat plate with five thickness as 1, 15,, 25, and 3 mm. Each thickness having thee poosities as.9292,.9469, and.9646 wee tested. The expeimental appaatus diagam was shown in fig.1. The expeimental appaatus was made of the steel tube with 1 mm inne diamete. The tube was insulated by the ceamic fibe both inne and oute side. Theefoe, the expeimental tube had the inne diamete 1 mm. An ai was used to be a woking fluid blew by the blowe though the electic heate contolled by the PID tempeatue contolle. The single poous plate was placed nomally to the hot ai flow at the top of the expeimental tube which was distance 3 mm fom the electic heate. The ai tempeatues in font of the poous plate wee vaied fom o C and volume flow ate 6-12 m 3 /h. Type K-themocouples wee used to measue the tempeatues of the flowing ai at inlet of the heate (T 1 ), outlet of the heate (T 2 ), inlet of the poous plate (T 3 ) and out of the poous plate ( ). Moeove, the ambient tempeatue was also measued duing the expeiment. Poous plates Type-K themocouples Themal insulato Electical heate T T 2 3 Flow mete T1 T Data logge Blowe Fig. 1. The schematic diagam of the expeimental appaatus. Tansactions of the TSME: JRAME 16, Volume 4(2) / 149

3 D = 1 mm h = 1, 15,, 25, 3 mm h =.9292,.9469,.9646 Fig. 2. The examined poous plate made of stainless steel fibous mateial. 3. DATA PROCESSING In the pesent study, the heat tansfe chaacteistics was done unde the exchange of heat between the fluid and the solid element of the poous mateial (fibous). The tempeatue distibution along the test section, the tempeatue dop acoss the poous plates ( T ), the heat ate ecovey of the poous fom the hot gas ( Q poous ), and the themal efficiency of the flow insulato ( T ) wee conducted. The flow condition (ynolds numbe, ), the inlet tempeatue of hot gas (T in ), the poosity ( ), poous thickness wee consideed as the independent paametes. In this section, the elative equations would be descibed. The based on the tube diamete is given by VD /. (1) Whee, is the ambient ai density (1.225 kg/m 3 5 ), is the atmospheic absolute viscosity ( Pa s ), V is the aveage hot ai velocity (m/s), and D is the duct diamete (m). In the pesent expeiment, the wall of the tube with themal insulato is assumed as the adiabatic wall. Theefoe, the gas tempeatue diffeence occued acoss the poous plate is due to the exchange enegy between the gas and solid phase (poous plate). The ai flowing though the test tube was assumed to be a unifom flow. The pesent wok was done unde the lamina flow condition due to the fluid flow was athe low. The data was done unde the steady state. The ecovey enegy of the poous plate was equal to the heat loss of the ai by convection to the solid element of poous mateial, which can be expessed as follow: ecovey p in out Q mc T T. (2) The ecovey efficiency ( ) of the flow insulato can be evaluated by the atio of ecovey heat ( ) input enegy ( Q input ), which was expessed in equation (3). Q and the poous Qpoous T T Q T T input (3) Whee, T is ambient tempeatue (3 o C). 4. RESULTS AND DISCUSSION 4.1 Tempeatue distibution in test section The stainless steel fibous mateial (poous mateial) used in the pesent wok have the same element dimensions of width and thickness. Theefoe, the aea of heat tansfe depend on the amount (mass) of the mateial. In the same volume of the poous, the poosity decease with inceasing the mass of the fibous. It could explain that the aea of heat tansfe inceases with deceasing poosity. 15 /Volume 4(2), 16 Tansactions of the TSME: JRAME

4 Figues 3 shows the effect of the inlet hot ai tempeatue (T 3 ), ynolds numbe (), the thickness of poous plate, and the poosity to the tempeatues distibution along the test tube. The esults indicated that the tempeatue decease with inceasing the inlet hot ai tempeatue as shown in fig.3 (a). It eveals that the inlet ai tempeatue affect to the tempeatue pofiles at the upsteam of the poous plate extemely owing to the adiation heat tansfe acts as the impotance ole at high tempeatue. Obviously, the ynolds numbe is moe effect to the tempeatue pofile than those of thickness and the poosity (fig.3 (b)). In consideation of the effect of the poous plate thickness to the tempeatue pofiles along the test tube. The tempeatue pofiles along the test tube at the insulated section (upsteam side) somewhat simila. But at the downsteam side, the tempeatue athe high decease with the poous thickness due to a lage of heat tansfe aea as illustated in fig 3 (c). In consideation of the influence of the poosity to the tempeatue pofiles shown in fig. 3 (d), the tempeatue at the upsteam side quite simila of the case of poous thickness. At the same thickness, howeve, the deceasing tempeatue along the poous plate was high accoding to the deceasing poosity due to the aea of heat tansfe inceases with deceasing poosity. It could conclude that inceasing to the inlet hot ai tempeatue, the poous thickness, and the poosity significantly influence to the tempeatue pofile along the poous plate especially at the poous plate owing to the change of heat tansfe aea. T f ( o C) Inlet Heate Insulato Poous Exit Thickness 1 mm Poosity Inlet tempeatue (T 3 ) 35 o C 4 o C 45 o C 5 o C 55 o C T f ( o C) Inlet Heate Insulate Poous Exit Thickness 1 mm Poosity.9292 Inlet tempeatue (T 3 ) 5 o C ynolds numbe () T T T T T 1 T 2 T 3 Measuement Station T 1 T 2 T 3 Measuement Station (a) Effect of inlet tempeatue (b) Effect of ynolds numbe T f ( o C) Inlet Heate Insulate Poous Exit Poosity ( ) T 3 = 5 o C T f ( o C) Inlet Heate Insulate Poous Exit Thickness 1 mm = 1152 T 3 = 5 o C Poosity T T T x o =1 mm T T 1 T 2 T 3 Measuement Station (c) Effect of poous plate thickness T 1 T 2 T 3 Measuement Station (d) Effect of poosity Fig. 3. Tempeatue distibution in the test section. Tansactions of the TSME: JRAME 16, Volume 4(2) / 151

5 4.2 Tempeatue dop The tempeatue dop acoss the poous plate ( T ) is the main paamete of themal insulato popety. It means that the mateial keep highe tempeatue dop is bette themal insulato. Fig. 4 indicates the tempeatue dop acoss the poous plate. The expeimental esults eveal the effect of seveal paametes, which wee the inlet hot ai tempeatue, ynolds numbe, the poous plate thickness and the poosities, to the tempeatue dop due to the heat ecovey by the poous media. Highe tempeatue dop of the hot ai flowing though the poous plate depicted the high heat exchange between the hot ai and the solid element of the poous. The expeimental esults evealed that the tempeatue dop acoss the poous plate (flow insulato) incease with the inlet hot ai tempeatue owing to the poous plate could act as the good adiation absobing and emitting themal adiation at high tempeatue (fig.4 (a)). While the tempeatue dop decease with ynolds numbe ( VD tube / ) due to the heat cay by the ai element is highe than the heat tansfe fom the hot ai to the poous element by convection. These easons veify the esults that the tempeatue dop acoss the poous plate could be high at low fluid velocity and high inlet hot ai tempeatue. In consideation of the effect of the poous thickness (fig.4 (b)) and the poosities (fig.4 (c)), it indicated that the tempeatue dop ( T ) incease with the poous thickness but decease with the poosity due to the eason of heat tansfe aea. Although the lage thickness effect to the pessue dop of the fluid flow acoss the poous plate but it is not significant fo the high poosity poous mateial. Theefoe, the amount of enegy tansfe fom the high tempeatue ai to the solid phase of poous element by convection heat tansfe could incease with the thickness (inceasing heat tansfe aea) while the poous could convet the enegy to heat adiation and emits to the upsteam egion leading to lage tempeatue dop C Thickness mm Poosity.9292 Inlet tempeatue (T 3 ) 35 o C 4 o C 45 o C 5 o C 55 o C C Poosity.9292 Inlet tempeatue (T 3 ) 5 o C (a) Effect of ynolds numbe and inlet tempeatue C Thickness mm Inlet tempeatue 5 o C Poosity ( C (b) Effect of ynolds numbe and thickness Inlet tempeatue (T 3 ) 5 o C = 1152 Poosity (c) Effect of ynolds numbe and poosity (d) Effect of thickness and poosity Fig. 4. Tempeatue dop acoss the poous plate. 152 /Volume 4(2), 16 Tansactions of the TSME: JRAME

6 4.3 Heat ecovey efficiency The heat ecovey efficiency ( ) of the flow insulato defined as the atio of enegy ecovey fom the flowing fluid of the poous media accoding to the equation (2). The expeimental esults have been indicated in fig. 5. The esults depicted that the heat ecovey efficiency decease with inceasing ynolds numbe () and poosities ( ), and incease with the inlet tempeatue (T3) and the poous thickness. Notice, the tendency of the heat ecovey efficiency is same as the tempeatue dop acoss the poous plate. Consideation the effect of the poous thickness to the heat ecovey efficiency, the optimum of the thickness fo the pesent flow insulato was 25 mm, which ecove the highest enegy of all conditions. 4 3 Thickness 1 mm Poosity.9292 Inlet tempeatue (T3) 35 o C 4 o C 45 o C 5 o C 55 o C 4 3 Inlet tempeatue(t 3 ) 5 o C Poosity (a) Effect of ynolds numbe and the inlet tempeatue (b) Effect of ynolds numbe and thickness Inlet tempeatue(t 3 ) 5 O C Thickness 1 mm Poosity Inlet tempeatue(t 3 ) 5 O C = 1152 Poosity (c) Effect of ynolds numbe and poosity (d) Effect of thickness and poosity Fig. 5. Heat ecovey efficiency. 5. CONCLUSIONS The pesent study conducted about the heat tansfe of flowing fluid moving though the poous plate, the examined as the flow insulato. The expeiment was done unde the conditions accoding to the heat tansfe chaacteistics of the poous media. The heat exchange between the hot ai and the solid element of the poous was poposed in tem of heat ecovey. Many independent paametes wee investigated which could conclude as follow. 1. The inlet hot ai tempeatue in font of the poous plate athe affect to incease the tempeatue pofile along the test duct, the tempeatue dop acoss the poous plate, and the ecovey efficiency due to the effect of adiation heat tansfe that plays an impotant ole in high tempeatue. Tansactions of the TSME: JRAME 16, Volume 4(2) / 153

7 2. In consideation of the effect of the flow velocity of the fluid (ynolds numbe), the expeimental esults indicated that the tempeatue pofile along the test duct, the tempeatue dop acoss the poous plate, and the ecovey efficiency decease with inceasing the ynolds numbe due to deceasing the atio of the amount of heat tansfe by mass of the fluid and the heat tansfe by convection to the poous element. 3. The tempeatue dop and the heat ecovey efficiency incease with the poous thickness until about 25 mm. Theefoe, the optimum thickness condition fo the stainless steel fibous mateial plate was 25 mm thickness. 4. Although the aea of heat tansfe of the poous plate at low poosity incease but the fluid does not easy flow acoss the poous plate due to the poosity of the stainless steel fibous mateial decease with inceasing the amount of mass. Theefoe, the tempeatue dop and heat ecovey incease with decease the poosity. 6. ACKNOWLEDGEMENT The authos acknowledge Rajamangala Univesity of Technology Isan who suppoted the fund fo the pesent eseach and suppoted the place and necessay eseach equipment. NOMENCLATURE Cp D m specific heat at constant pessue, J/kg.K tube diamete, m mass flow ate, kg/s Q heat ate, W ynolds numbe T tempeatue, o C V velocity, m/s ρ fluid density, kg/m 3 absolute viscosity, Pa.s Subscipts 1 in font of the heate 2 out of the heate 3 in font of the poous plate 4 out of the poous plate f fluid (ai) ecovey poous poous plate ambient REFERENCES [1] Golombock, M., Petheo, A, Shivill, L. C. and Small, L. M., Suface combustion in metal fibe bunes, Combust. Sci. and Tech., Vol. 77, 1991, pp [2] Hanamua, K. and Echigo, R., An analysis of flame stabilization mechanism in adiation bunes, Wame-und Sttoffubetagung, Vol. 26, 1991, pp [3] Hanamua, K., Echigo, R. and Zhdanok, S. A., Supeadiabatic combustion in a poous medium, Int. J. Heat Mass Tansf., Vol. 16, 1993, pp [4] Jugjai, S. and Chuenchit, C., A Study of enegy convesion by a poous combusto-heat exchange with cyclic flow evesal combustion, Int. Enegy J., Vol. 2, No. 2, 1, pp [5] Echigo, R., and Hasegawa, S., Radiative heat tansfe by flowing multiphase medium-pat I. An analysis on heat tansfe of lamina flow between paallel flat plates, J. Heat Mass Tansfe, Vol.15, 1972, pp [6] Echigo, R., Hasegawa, S. and Tamehio, H., Radiative heat tansfe by flowing multiphase medium-pat II. An analysis on heat tansfe of lamina flow in an entance egion of cicula tube, J. Heat Mass Tansfe, Vol.15, 1972, pp /Volume 4(2), 16 Tansactions of the TSME: JRAME

8 [7] Tamehio, H., Echigo, R. and Hasegawa, S., Radiative heat tansfe by flowing multiphase medium-pat II. An analysis on heat tansfe of tubulent flow in a cicula tube, Int. J. Heat Mass Tansfe, Vol.16, 1973, pp [8] Hasegawa, S., Echigo, R., and Shimizu, A., Convective and Radiative Heat Tansfe of Flowing Gaseoussolid Suspensions: in Handbook of Heat and Mass Tansfe, Heat Tansfe Opeation, Gulf Publishing Company, Vol.1,1986, pp [9] Echigo, R., Effective Enegy Convesion Method between Gas Enthalpy and Themal Radiation and Application to Industial Funaces. Poc.7th Int. Heat Tansfe Conf. Vol. 6, 1982, pp [1] Viskanta, R., Oveview of adiative tansfe in cellula poous mateials, in: Poc. ASME 9 Heat Tansfe Summe Conf., July 19-23, San Fancisco, CA, 9. [11] Wang, K. Y. and Tien, C. L., Themal insulation in flow system: Combined adiation and convection though a poous segment. ASME. J. Heat Tansfe Vol.16, 1984, pp [12] Khantikomol, P., Saito, S. and Yokomine, T., Study of Multilaye Flow Insulation utilizing Open-Cellula Poous Plates. Poc. Int. Conf. Powe Engineeing (ICOPE-9), Vol. 3, 9, pp [13] Khantikomol, P. and Kamiuto, K., Combined Foced-Convection and Radiation Heat Tansfe in an Open- Cellula Poous Plate. Poc. of Int. Conf. on Themal and Fluids Engineeing (The 7th JSME-KSME), 8. [14] Kamiuto, K., Study of Dul nev s Model fo the Themal and Radiative Popeties of Open-Cellula Poous Mateials. JSME Int. J., Seies B Vol.4, 1977, pp [15] Kamiuto, K., Combined conductive and adiative heat tansfe though open-cellula poous plates. JSME Int. J., Seies B Vol.43,, pp [16] Kamiuto, K., Modeling of elementay tanspot pocesses and composite heat tansfe in open-cellula poous mateials. Tends in Heat, Mass & Momentum Tansfe, Vol.5, 1999, pp [17] Kamiuto, K., Saito, S. and Ito, K., Numeical model fo combined conductive and adiative heat tansfe in annula packed beds. Numeical Heat Tansfe Pat A, Vol. 23, 1993, pp [18] Kamiuto,K. and Yee, S. S., Heat tansfe coelations fo open-cellula poous mateials, Int. Communi. Heat Mass Tansfe, Vol.32 No.7, 5, pp [19] Khantikomol, P. and Kamiuto, K., Design consideations of poous gas enthalpy-adiation convetes fo exhaust-heat ecovey systems. J. Themal Science and Technology, Vol. 3 No.2, 8, pp [] Khantikomol, P., Saito, S., Kamiuto, K. and Yokomine, T., Study on single laye flow insulation utilizing NiC open-cellula poous plate, Intenational Communications in Heat and Mass Tansfe, Vol. 37, 1, pp Tansactions of the TSME: JRAME 16, Volume 4(2) / 155