Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis

Transcription

1 Indian Journal of Science and Technology, Vol 9(13), DOI: /ijst/2016/v9i13/90566, April 2016 ISSN (Print) : ISSN (Online) : Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis M. Dev Anand 1*, G. Glan Devadhas 2, N. Prabhu 3 and T. Karthikeyan 4 1 Department of Mechanical Engineering, Noorul Islam Centre for Higher Education, Kumaracoil , Thuckalay, Kanyakumari District, Tamil Nadu, India; anandpmt@gmail.com 2 Department of Electronics and Instrumentation Engineering, Noorul Islam University, Kumaracoil , Thuckalay, Kanyakumari District, Tamil Nadu, India; glandeva@gmail.com 3 Department of Mechanical Engineering, Kottayam Institute of Technology and Science (KITS), Chengalam East, Pallickathodu, Kottayam , Kerala, India; prabhu72_jose@hotmail.com 4 Department of Mechanical Engineering, Saveetha Nagar, Thandalam, Chennai , Tamil Nadu, India; karthi.ngl09@gmail.com Abstract A ceramic monolith heat exchanger has been learnt for finding out heat transfer performance and effectiveness on computing numerically and ξ-ntu method. In entire domain computation numerically has been performed along with fluid region in rectangular ducts of exhaust gas side, ceramic core and rectangular duct fluid region in air side with the air exhaust in direction of cross flow. Additionally, the heat exchanger has been examined for estimating the functionality via ξ-ntu technique that is conventional along numerous Nusselt number links for rectangular duct flow for the literature. Based on the research, it has been performed on the ceramic heat exchangers and on the ceramic materials and the demand in utilizing the ceramic materials in heat exchangers. Then the recuperator is modeled by using GAMBIT and it is analyzed using FLUENT. The effectiveness and the heat transfer rate are also calculated. Then those outcomes have been assessed along the experimental data. By comparison of both functionality by computing numerically and the ξ-ntu technique, the efficiency by ξ-tu technique has been identified to be nearest to product by the numerical computation among the associative of 2.15% when Stephan s Nusselt number association has been adapted to the ξ-ntu technique within numerous connections. The total heat transfer and effectiveness by ξ-ntu method relative errors utilizing five Nusselt number correlations from literature have been lesser than 14.5% comparative to numerical computation. Associated to Nusselt number correlations, the entire heat transfer utilizing ξ-ntu technique with Stephan s correlation is highly nearest to numerical computation. For that reason, the exit temperature by ξ-ntu method with Stephan s correlation simulates within 1.2% of the relative error for exhaust exist temperature and 0.45% for the air exit temperature assessed against the numerical computation. Overall heat transfer coefficient s relative errors by ξ-ntu technique utilizing five Nusselt number correlations for the literature have been more than 17.5% to that on computing numerically. Keywords: Ceramic Recuperators, Cross Flow, Effectiveness, Heat Transfer, Pressure Drop 1. Introduction Devices which facilitate the heat exchange among two fluids at dissimilar temperature on holding them without each other mixing are known to be Heat exchangers. Heat exchangers have been usually utilized in practice in an extensive choice of applications, like heating and systems of air-conditioning in a household for chemical processing and production of power in huge plants. For example, in a car radiator, heat has been transferred from hot water which flows via the radiator tubes towards the air flowing via entirely spaced thin plates exteriorly hold to the tubes. Typically convection in every fluid and conduction gets associated by the heat transfer in a heat exchanger via *Author for correspondence

2 Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis the wall splitting out both fluids. Heat transfer rate among both fluids in a heat exchanger at a location relies on temperature difference magnitude at that location that varies via the heat exchanger. In heat exchangers analysis, working with the logarithmic mean temperature difference LMTD, that is an equivalent mean temperature difference among both fluids for the complete heat exchanger is convenient. Q = UA LMTD The above equation is the fundamental equation for calculating the rate of heat transfer. High temperature heat exchangers seems to be necessary in numerous industrial systems for processing reasons or targeting for attaining greater efficiency whereas it is required in case of power plants. 1.1 Evolution of Ceramic Heat Exchangers Earlier to 1935 the world s metallurgical industries depend on ceramic heat exchangers and regenerators for providing greater temperature combustion air for furnace applications. Temperature of preheat air over 700 C have been necessary for producing greater flame temperatures due to the availability of coal deriving gaseous fuels were with calorific value at low range. Almost every ceramic heat exchanger utilized out of the short tube and tile type that pour out in operation and supposed to endure air pressures at low range. 1.2 Ceramic Heat Exchangers Hard, typically ionic or bonded covalently and might be amorphous or crystalline in structure are the ceramic materials. Presently ceramic CHEs are chiefly brought up by material replacement for existing CHEs parts with ceramic. Predominant parts preferred to be replaced are fins and tubes. Procedures for manufacturing comprise forming chief components out of raw materials, succeeding machining, joining, bonding, and assembling. Ceramic heat exchangers are generally categorized as; Monolithic Assembly. Non-Monolithic Assembly. In monolithic assembly, separated components are together bonded lastingly excluding internal joint, without any problem of sealing but concentrations of stress could shoot up beyond tremendous conditions to operate. Few predominant pros for ceramic materials compared to conventional metallic materials in compact heat exchanger construction are; It possesses tremendously elevated temperature stability. Low cost of material compared to traditional metallic materials. It has excellent corrosion resistance. At high range of operating temperatures it possesses greater fouling resistance and chemical erosion. Some of the ceramic materials and their temperature limits are tabulated in the below Table Selection of Heat Exchangers In most theoretical cases of heat transfer problem solving, we assume that the overall heat transfer coefficient U is invariable right through the heat exchanger and that the coefficients of convection heat transfer could be forecasted utilizing the convection correlations 1. On the other hand, certainty in the forecasted value of U could even cross 30 percent is the thing to be kept in mind. Therefore, it is natural with tendency of over designing the heat exchangers in the idea of avoiding disagreeable shock. Heat transfer improvement in heat exchangers is typically along with raising drop in pressure, in addition greater power in pumping. Hence, any rise from the improvement in heat transfer has to be weighed with respect to additional pressure drop cost. Engineers in industry frequently locate themselves in a place for selecting heat exchangers in accomplishing assure heat transfer tasks. Regularly, heating or cooling a specific fluid at a mass flow rate which is known and temperature to a preferred temperature. Hence, heat transfer rate in the potential heat exchanger is Q max = mcp(t in T out ) This contributes the heat transfer demand of the heat exchanger prior to have any thought regarding the Table 1. Typical ceramic materials and their temperature limits Material Temperature Limit Silicon Carbide (SiC) 1400 C Silicon Nitride (Si 3 N 4 ) 1900 C Alumina (Al 2 O 3 ) C Aluminium Nitride (AlN) 1300 C 2 Vol 9 (13) April Indian Journal of Science and Technology

3 M. Dev Anand, G. Glan Devadhas, N. Prabhu and T. Karthikeyan heat exchanger itself. An engineer over viewing heat exchanger manufacturers catalog was besieged by means of type and quantity of willingly accessible off-the-shelf heat exchangers. Appropriate choices rely on numerous factors Heat Transfer Rate One of a highly significant quantity in choice of a heat exchanger is potential to transfer heat at a particular rate in the idea of achieving the targeted change in fluid temperature at the mentioned mass flow rate Cost Budgetary restrictions typically participates a significant role in choice of heat exchangers, excluding for few particular cases where money is no object. An off-theshelf heat exchanger possesses an appropriate advantage of cost over those made to order. On the other hand, in few cases, no heat exchangers that exist would do, and it might be essential for undertaking the costly and time-consuming job of designing and manufacturing a heat exchanger from scratch for suiting the need which is frequently the case on making the heat exchanger an integral part of the overall device to be manufactured. Heat exchanger operation and maintenance costs are moreover significant deliberation in estimating entire cost Pumping Power In a heat exchanger, both fluids seem to be typically required to flow via pumps or fans which devour electrical power. Annual electricity cost is associated with the pumps and fans operation could be estimated from where the power of pumping is the wholesome electrical power frenzied by the pumps and fans motors. operating cost = ( Pumping Power,kW) (Hours of P enetration, h Size and Weight PriceofElectricity, Rupees kwh Usually, slighter and lighter the heat exchanger, far improved it is which particularly in aerospace and automotive industries, where weight and size necessities are highly stringent. Additionally, a superior heat exchanger typically takes a costlier price tag. For the heat exchanger, available space in a few scenarios restricts tubes length which could be used Type Heat exchanger type could be chosen relies principally on the fluids type involved, the weight and size restrictions, and any phase modify processes presence. For example, a heat exchanger is appropriate in cooling a liquid by a gas if the area of surface on the gas side is numerous times on the liquid side. Moreover, a plate or shell-and-tube heat exchanger is highly appropriate in cooling a liquid by an additional liquid Materials Materials utilized in heat exchanger construction might be a significant deliberation in choice of heat exchangers. For example, structural and thermal stress possessions might not be preferred at pressures below 15 bar or temperatures less than 150 C. However these influences are considered chiefly higher than 70bar or 550 C and critically restrict the satisfactory heat exchanger materials. Variation of temperature of 50 C or more among the tubes and the shell would most likely create issues associated with differential thermal expansion and requirements to be measured. With regard to corrosive fluids, we might choose expensive corrosion-resistant materials namely stainless steel or even titanium if we are unwilling in replacing low-cost heat exchangers repeatedly Other Considerations Occurrence of additional thought in choice of heat exchangers which might or may not be significant, relying on the application. For example, existing as leak-tight is a significant consideration on toxic or luxurious fluids were associated. Low maintenance cost, Ease of servicing and reliability and safety are few other significant considerations in the process of selection. Calmness is one of the most important thought in the choice of liquid-to-air heat exchangers utilized in heating and air-conditioning applications. Comprehensive discussions with regard to the requirement off high temperature heat exchangers and the evolution of ceramic heat exchangers have been illustrated in this section. Factors considered for the selection of heat exchanger were also discussed. The main focus is to identify the various practical application of the ceramic heat exchanger. In 1 stated that heat resistant material is required in constructing high temperature heat exchangers. They judged the ceramic monolith heat exchanger performance, calculating Vol 9 (13) April Indian Journal of Science and Technology 3

4 Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis pressure drop and heat transfer by numerical computation and the ε-ntu technique. In 2 predicted that the thermal hydraulic performances of compact surface heat exchangers are strongly influenced by their geometry and flow configurations. A novel fin configuration for high temperature ceramic Plate-Fin Heat Exchanger (PFHE) was brought up utilizing the three-dimensional Computational Fluid Dynamics (CFD) FLUENT code. In 3 numerically investigated the lateral fin profiles effect on stress functionality of finned tubes internally in a greater temperature heat exchanger using ANSYS software. Three types of lateral fin profiles, specifically S-shape, Z-shape and V-shape have been learnt and assessed. In 4 stated ceramic materials are the preferable natural alternative for the High Temperature Heat Exchanger (HTHE). Current research contributed one thermodynamic research of one EFGT (Externally Fired Gas Turbine) with one briefed model for the ceramic heat exchanger. In 5 stated that there exists a possible requirement for heat exchangers competent of sustaining elevated temperatures, classically greater than 800 C, for utilization in thermal power plants. In implementing EFGT (Externally Fired Gas Turbines) cycles, these heat exchangers are utilized. Data for finned heat exchangers flat tubes. In 6 researched the effect of honeycomb ceramic on heat extraction numerically on the fundamental of experimental authentication of mathematical model. In 7 calculated the influence of temperature at inlet and rib height on the fluid flow and heat transfer functioning of the ribbed channel within the high temperature heat exchanger have been illustrated. Inlet temperature keeps changing from 850ºK to 1250ºK and the ratio of rib height to channel height keeps changing from to In 8 brought up a model to calculate the thermal performance of a heat recovery unit made-up from an alumina honeycomb matrix and a technique for the discretization of the energy equations required for developing estimating algorithm to design and size packed in heat recovery units. In 9 developed the thought of producing a superior geometry for a heat exchanger by taking the extruded 2D honeycomb structure as a basis from a receiver system that targets at relocating heat from strenuous radiation to an air circuit feeding the steam turbine boiler. In 10 designed, fabricated and evaluated a ceramic counter-flow micro-channel heat exchanger. This work informs the model-based design and assessment of functionality of experiment of an all-ceramic compact counter-flow micro-channel heat exchanger. Ceramic materials facilitate operation at greater-temperature which could go beyond the ability of equivalent metal heat exchangers. In 11 investigated a novel bayonet tube high temperature heat exchanger with fins on its inner and outer region. In the environment of elevated temperature like production of hydrogen, much elevated temperature reactor and externally fired associated cycle utilizes this. In 12 investigated numerically a compact SiC heat exchanger performance for a broad choice of thermal media, helium gas, flow rates and liquid LiPb for its development. Numerical model utilized depend on test module of heat exchanger brought up earlier. Among the extent of experiment, the heat quantity which is transferred from greater temperature liquid LiPb to helium gas and coefficients of overall heat transfer achieved numerically conform to the experimental outcomes. In 13 tested and simulated a ceramic micro heat exchangers manufactured for usage in chemical and thermal process engineering. Ceramic microstructure devices in form of cross-flow and counter flow micro-channel heat exchangers have been considered. Performances of such heat exchangers were examined involving water as a test fluid with greatest amount of flow rates of 120kg/ h 14 have projected a novel ceramic heat exchanger with high temperature plate-fin depend on the Offset Strip Fin design for application of heat exchanger requiring tremendous operation temperatures namely power generation field or heat recovery. In 15 proposed a honeycomb monolith structures comprise of materials that are highly thermal conductive as an impressive catalysts supporting improved heat transfer properties. The work has been focused on the performance of heat transfer of structures that are conductive monolith wrapped up into tubes of heat exchanger. In 16 developed a finite element model for thermal analysis of a ceramic heat exchanger tube under axial non-uniform convective heat transfer coefficient. He studied the distribution of temperature for steady-state heat transfer and the thermal stresses simulated by variations in temperature in a Silicon Carbide (SiC) ceramic tube of equipment of heat transfer. A comprehensive discussion on the literature review associated with work is available in this section. Numerous practical 4 Vol 9 (13) April Indian Journal of Science and Technology

5 M. Dev Anand, G. Glan Devadhas, N. Prabhu and T. Karthikeyan applications of ceramic heat exchanger was spotted out and researched. 2. Work Description This section defines the problem, ultimate objective and scope of the current work. It also discuss about the methodology followed in the work. 2.1 Statement of Problem Practically every heat exchanger is a possible candidate to enhance heat transfer. On the other hand, every potential application has to test for seeing when enhanced heat transfer is feasible or practicable. Parameters performances of the heat exchanger are effectiveness, rate of heat transfer, and drop in pressure and those are greatly influenced by surface area of heat transfer, heat exchanger material s heat conducting capability, flow properties and the alteration in stream temperatures. In the literature ceramic heat exchanger made up of Silicon Carbide (SiC) was analysed. Necessary condition of the ceramic material for this application type is highly thermal conductive, resistance to corrosion, coefficient of low thermal expansion and chemical erosion resistance. 2.2 Objectives To do comparative theoretical analysis on performance of a ceramic heat exchanger using Silicon carbide (SiC) with Aluminum Nitride (AlN) ceramic material. To conduct a theoretical investigation on the enhancement of performance parameters like heat transfer rate, drop in pressure and effectiveness of a ceramic monolithic heat exchanger by rising the heat transfer surface area by providing extended surfaces and by changing the flow patterns. In order to validate the theoretical analysis a numerical computations has to be executed using ANSYS FLUENT software. 2.3 Scope The ultimate target of the work is enhancement of the performance parameters of the heat exchanger such as heat transfer rate, effectiveness and drop in pressure. In current work, the way of approach to attain this high performance is one by trying with alternate ceramic material which has higher thermal conductivity than the existing ceramic material under function. 2.4 Methodology The work presented here starts with a study on potential of ceramic and ceramic matrix composites in high temperature applications from literature is shown in Figure Selected Application Recovered heat might be utilized for generating electricity in SOFC/GT hybrid power generating systems together with gas turbines and HRU (Heat Recovery System) 6, as detailed in Figure 2. A hybrid recuperators was preferred for utilization in those power systems. Figure Figure Flow Chart of Present Work Methodology. Figure 2. Figure 2. System. Schematic of SOFC/GT Hybrid Power Generating Vol 9 (13) April Indian Journal of Science and Technology 5

6 Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis The area focused for the work is only the ceramic monolith core shown in the Figure Design of Ceramic Heat Exchanger Core The ceramic recuperators comprise of a rectangular hot exhaust and cold air passages with the exhaust and air passing in the cross-flow direction devoid of each other mixing Figure 4. In which the hot exhaust gas from Solid oxide fuel cell flows along the vertical axis and it transfers heat to the compressed air coming out from the compressor in the gas turbine circuit. The total dimensions of the prototype model considered for analysis were mm Material Selection Primary features/benefits of few of the technical ceramics were discussed below: Aluminum Oxide (Al O ). 2 3 Zirconium Oxide (ZrO ). 2 Fused Silica (SiO ). 2 Figure Three Pass Recuperators. Figure Design of Ceramic Heat Exchanger Core. Titanium Diboride (TiB ). 2 Boron Carbide (B C). 4 Silicon Carbide (SiC). Tungsten Carbide (WC). Aluminum Nitride (AlN). Boron Nitride (BN). Silicon Nitride (Si N ). 3 4 After going through those ceramic materials it is decided to choose Aluminium Nitride (AlN) ceramic material for analysis since it has high thermal conductivity when compared to other ceramic materials and also has good corrosion resistance. Some of the properties of silicon carbide and aluminum nitride are computed in the Table Theoretical Analysis 3.1 Overall Heat Transfer Coefficient (U) 1 U= 1 X A + + air h k η ta h air Additionally, η t is the total surface effectiveness of a fin. Kays and Crawford correlation, gas gas (1) K h= Nu (2) Dh ( ) Nu = / α / α / α / α4 2/ α 5 (3) Sieder-Tate correlation, Nu =1.86(RePrDh/L)0.33( µ f/ µ w) 014. (4) Stephan correlation, 086(ReprDh/ L) 133. Nu = Pr(ReDh/L) Shah and London Correlation, Table (RePrDh/L). 033 Nu= (RePrDh/ L) (5) (6) Property Comparison between SiC and AlN Properties Silicon Carbide (SiC) Aluminium Nitride (AlN) Density (kg/m 3 ) Specific Heat (J/kg K) Thermal Conductivity (W/m 2 K) Vol 9 (13) April Indian Journal of Science and Technology

7 M. Dev Anand, G. Glan Devadhas, N. Prabhu and T. Karthikeyan 3.2 ε-ntu Method NTU0.22 e = 1 exp [exp( CNTU0.78)-1] (7) C 3.3 Pressure Drop Pcore = f 1 ρmv2m(l/dh) 2 (8) Here f= 64 because the flow in this paper was preferred to be Re laminar. 3.4 Ceramic Core Analysis Reynolds numbers as per mass flow rates are illustrated in Table 3. The obtained value from the theoretical analysis of the ceramic heat exchanger is listed in the Tables 4. First the correlations are used for analyzing the heat exchanger using silicon carbide material. The obtained values are listed corresponding to the Reynolds number in Tables 5 7. Similarly the values of overall heat transfer coefficient, effectiveness and heat transfer rate for the ceramic heat exchanger using aluminum nitride material are calculated. Table 3. Number Mass Flow rate according to Reynolds Air Side Exhaust Side Re. No m air (kg/s) Re. No m gas (kg/s) Table 4. Based on Kays and Crawford Nusselt Number Correlation Re.No U (W/m 2 K) ε- NTU Q (W) Table 5. Based on Sieder-Tate Nusselt Number Correlation Re.No U (W/m 2 K) ε- NTU Q (W) Table 6. Based on Stephan Nusselt Number Correlation Re.No U (W/m 2 K) ε- NTU Q (W) Table 7. Based on Shah and London Nusselt Number Correlation Re.No U (W/m 2 K) ε- NTU Q (W) Results and Discussions The performance of the ceramic monolith heat exchanger is analyzed using Silicon Carbide and Aluminum Nitride ceramic materials and the results are discussed. 4.1 Analysis of the Heat Exchanger with SiC First the heat exchanger is analyzed using silicon carbide material and the heat exchanger performance using Aluminum Nitride was compared. The following Figures 5 to 14 shows the variation in coefficient of overall heat transfer, effectiveness and heat transfer rate with respect to Reynolds number by means of a variety of Nusselt number correlations. The overall heat transfer coefficient estimated using Kays and Crawford Nusselt number correlations was W/m 2 K. For Sieder-Tate correlations the overall heat transfer coefficient varied from W/m 2 K. Vol 9 (13) April Indian Journal of Science and Technology 7

8 Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis Figure 5. Figure 5. (SiC). Comparison of Overall Heat Transfer Coefficient Figure 9. Figure 9. Comparison of Effectiveness (AlN). Figure 6. Figure 6. Comparison of Effectiveness (SiC). Figure 10. Figure 10. Comparison of Heat Transfer Rate (AlN). Figure 7. Figure 7. Comparison of Heat Transfer Rate (SiC). Figure 11. Comparison of Overall Heat Transfer Coefficient of AlN with SiC. Figure 8. Figure 8. (AlN). Comparison of Overall Heat Transfer Coefficient Figure Comparison of Effectiveness of AlN with SiC. 8 Vol 9 (13) April Indian Journal of Science and Technology

9 M. Dev Anand, G. Glan Devadhas, N. Prabhu and T. Karthikeyan Figure Figure Comparison of Heat Transfer Rate of AlN with SiC. Figure Variation of Pressure Drop with Reynolds Number. Also for Stephan correlation it varied from W/m 2 K and for Shah and London the overall heat transfer coefficient varied from W/m 2 K. The effectiveness calculated using Kays and Crawford Nusselt number correlations varied from For Sieder-Tate correlations the effectiveness varied from Also for Stephan correlation it varied from and for Shah and London the effectiveness varied from The heat transfer rate calculated using Kays and Crawford Nusselt number correlations varied from W. For Sieder-Tate correlations the heat transfer rate varied from W. Also for Stephan correlation it varied from W and for Shah and London the heat transfer rate varied from W. 4.2 Analysis of the Heat Exchanger with AlN Same heat exchanger performance under same operating has been analyzed using Aluminum Nitride ceramic material. Coefficient of overall heat transfer estimated using Kays and Crawford Nusselt number correlations was W/m 2 K. For Sieder-Tate correlations the overall heat transfer coefficient varied from W/m 2 K. Also for Stephan correlation it varied from W/m 2 K and for Shah and London the overall heat transfer coefficient varied from W/m 2 K. The effectiveness calculated using Kays and Crawford Nusselt number correlations varied from For Sieder-Tate correlations the effectiveness varied from Also for Stephan correlation it varied from and for Shah and London the effectiveness varied from The heat transfer rate calculated using Kays and Crawford Nusselt number correlations varied from W. For Sieder-Tate correlations the heat transfer rate varied from W. Also for Stephan correlation it varied from W and for Shah and London the heat transfer rate varied from W. 4.3 Performance Comparison of the Heat Exchanger with SiC And AlN Finally the performance parameters of the Aluminum Nitride heat exchanger were compared with silicon nitride heat exchanger. The Aluminum Nitride heat exchanger showed enhanced performance such as improved coefficient of overall heat transfer of the system, also improved effectiveness and heat transfer. The main reason for selecting Aluminum Nitride as heat exchanger material is due to its higher thermal conductivity, its increased corrosion resistance and higher temperature with standing capacity. Coefficient of overall heat transfer of the heat exchanger utilizing Aluminum Nitride (AlN) material has increased by 4.55% when compared to Silicon Carbide (SiC) material. The effectiveness of the heat exchanger using Aluminum Nitride (AlN) material has increased by 3% when compared to Silicon carbide (SiC) material. Heat transfer rate of the heat exchanger utilizing Aluminum Nitride (AlN) material has increased by 4.5-5% when compared to Silicon Carbide (SiC) material. Pressure drop of both the heat exchangers was same at the considered operating conditions since the pressure does not depend greatly on the material property. The calculated pressure drop varied from Pa. 5. Conclusion In current research, the ceramic monolith heat exchanger performance was compared using silicon carbide and Aluminum Nitride as the heat exchanger material. The Vol 9 (13) April Indian Journal of Science and Technology 9

10 Ceramic Monolith Heat Exchanger - A Theoretical Study and Performance Analysis theoretical calculations have been executed for the hot exhaust gas, cold air and ceramic core areas in a ceramic heat exchanger measuring C. Total heat transfer rates and effectiveness as estimated for silicon carbide material were compared with those calculated for Aluminum Nitride material. The calculations have been executed utilizing a ε-ntu method considering numerous Nusselt number correlations taken off from the literature. Coefficient of OHT of the CHE utilizing AlN as the heat exchanger material increased by 4.5 5% when compared to SiC material.effectiveness of the CHE using AlN as the heat exchanger material was increased by 3% when compared to SiC material. Total heat transfer rate of the CHE using AlN as the heat exchanger material was increased by 3% when compared to SiC material. In future, a theoretical investigation will be carried out for the same CHE by increasing the heat transfer area by proving extended surfaces in the cold stream region. Also a validation procedure will be executed by numerical computation using ANSYS-FLUENT software. 6. References 1. Paeng JG, Yoon YH, Kim KH, Yoon KS. Theoretical and Numerical Analyses of a Ceramic Monolith Heat Exchanger. Journal of Mechanical Science and Technology. 2010; 24(7): Nagarajan V, Chen Y, Wang Q, Ma T. Hydraulic and Thermal Performances of a Novel Configuration of High Temperature Ceramic Plate-Fin Heat Exchanger. Applied Energy. 2013; 113: Zeng M, Ma T, Sunden B, Trabia M B, Wang Q. Effect of Lateral Fin Profiles on Stress Performance of Internally Finned Tubes in a High Temperature Heat Exchanger. Applied Thermal Engineering. 2013; 50(1): De Mello PEB, Monteiro DB. Thermodynamic Study of an EFGT (Externally Fired Gas Turbine) Cycle with One Detailed Model for the Ceramic Heat Exchanger. Energy. 2012; 45(1): Monteiro DB, de Mello PEB. Thermal Performance and Pressure Drop in a Ceramic Heat Exchanger Evaluated Using CFD Simulations. Energy. 2012; 45(1): Gao Z, Liu Y, Gao Z. Heat Extraction Characteristic of Embedded Heat Exchanger in Honeycomb Ceramic Packed Bed. International Communications in Heat and Mass Transfer. 2012; 39(10): Maa T, Wang Q-W, Zeng M, Chen Y-T, Liu Y, Nagarajan V. Study on Heat Transfer and Pressure Drop Performances of Ribbed Channel in the High Temperature Heat Exchanger. Applied Energy. 2012; 99: Cadavid Y, Amell A, Cadavid F. Heat Transfer Model in Recuperative Compact Heat Exchanger Type Honeycomb: Experimental and Numerical Analysis. Applied Thermal Engineering. 2013; 57(1 2): Fend T, Volker W, Miebach R, Smirnova O, Gonsior D, Schollgen D, Rietbrock P. Experimental Investigation of Compact Silicon Carbide Heat Exchangers for High Temperatures. International Journal of Heat and Mass Transfer. 2011; 54(19 20): Kee RJ, Almand BB, Blasi JM, Rosen BL, Hartmann M, Sullivan NP, Zhu H, Manerbino AR, Menzer S, Grover Coors W, Martin JL. The Design, Fabrication, and Evaluation of a Ceramic Counter-Flow Micro Channel Heat Exchanger. Applied Thermal Engineering. 2011; 31(11 12): Ji Y, Ma T, Zeng M, Zhu H, Wang Q. Investigation of a Novel Bayonet Tube High Temperature Heat Exchanger with Inner and Outer fins. International Journal of Hydrogen Energy. 2011; 36(5): Takeuchia Y, Park C, Noborio K, Yamamoto Y, Konishi S. Heat Transfer in SiC Compact Heat Exchanger. Fusion Engineering and Design. 2010; 85(7 9): Alm B, Imke U, Knitter R, Schygulla U, Zimmermann S. Testing and Simulation of Ceramic Micro Heat Exchangers. Chemical Engineering Journal. 2008; 135S(1): Schulte-Fischedick J, Dreissigacker V, Tamme R. An Innovative Ceramic High temperature Plate-Fin Heat Exchanger for EFCC Processes. Applied Thermal Engineering. 2007; 27(8 9): Boger T, Heibel AK. Heat Transfer in Conductive Monolith Structures. Chemical Engineering Science. 2005; 60(7): Islamoglu Y. FEM for Thermal Analysis of Ceramic Heat Exchanger Tube under Axial Non-Uniform Convective Heat Transfer Coefficient. Materials and Design. 2004; 25(6): Appendix 1 Calculation 1) Total Flow Area, Air Side At = (W H) Number of Channels = = m 2 Exhaust Side at = (W H) Number of Channels = = m 2 2) Hydraulic Diameter, Dh = 4A/P = (4 ( ))/(2 ( )) = m 2 3) Velocity, Air side Va = m/ρa = /( ) = m/s 10 Vol 9 (13) April Indian Journal of Science and Technology

11 M. Dev Anand, G. Glan Devadhas, N. Prabhu and T. Karthikeyan Exhaust Side Va = m/ρa = / ( ) = m/s 4) Reynolds Number (Re.No.) Air Side, Re.No. = ρvd h /µ = ( )/ ( ) = Exhaust Side, Re.No. = ρvd h /µ = ( )/( ) = ) Nusselt Number and Convective Heat Transfer Coefficient: Air Side, Kays and Crawford Correlation, Nu = 8.235( α (α (α (α 4-2 α 5 )))) Aspect Ratio, α = (0.052/0.0065) = 8 Nu = 8.235( ( ( ( )))) Nu = 6.7 h air = Nu k/d h = 6.7 ( ) = W/m 2 K Sieder-Tate correlation, Nu = 1.86(RePrD h L) 0.33 (μ f μ w ) 0.14 Nu = 1.86(( ) 0.335) 0.33 ( ) 0.14 Nu = h air = Nu k/d h = ( ) = W/m 2 K Stephan Correlation, Nu = (RePrD h L) 1.33 /( Pr (ReD h L) 0.83 ) Nu = (( ) 0.335) 1.33 / ( (( ) 0.335) 0.83 ) Nu = 5.68 h Air = Nu k/d h = 5.68 ( ) = W/m 2 K Shah and London Correlation, Nu = (RePrD h L) Nu = (( ) 0.335) Nu = h air = Nu k/d h = ( ) = W/m 2 K 6) Overall Heat Transfer Coefficient: U = 1/(1/h air + X/k + A air /(η t A gas h gas )) = 1/(1/ / /( )) U = 22.78W/m 2 K 7) Effectiveness (NTU- Method): NTU = (UA C min ) = (( )/4.441) = C = C min /C ma x = 4.441/4.516 = ε = 1-exp {NTU 0.22 /C [exp( CNTU 0.78 ) 1]} 100% ε = 1 exp {0.995»0.22»/0.984 [exp ( ) 1]} 100% ε = 47% 8) Total Heat Transfer Rate: q = ε C»min» (T»gas_in»-T air_in ) q = ( ) q = W Appendix 2 Fluid Properties Air Side Mean Temperature 630( C) Exhaust Side Mean Temperature 786( C) ρ (kg/m 3 ) µ (Ns/m 2 ) Pr C p (J/kgK) k (W/mK) Vol 9 (13) April Indian Journal of Science and Technology 11