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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com A New Method for Prediction of Local Heat Flux on Membrane Waterwall with Rifled Tubes of Subcritical Boilers Sankar G Engineer, Bharat Heavy Electricals Ltd., Tiruchirappalli, Tamil Nadu, India. E-mail: [email protected] Chandrasekhara Rao A Deputy General Manager, Bharat Heavy Electricals Ltd., Tiruchirappalli, Tamil Nadu, India. E-mail: [email protected] Kartikeyan V R Engineer, Bharat Heavy Electricals Ltd., Tiruchirappalli, Tamil Nadu, India. E-mail: [email protected] Seshadri P S Addl. General Manager, Bharat Heavy Electricals Ltd., Tiruchirapalli, Tamil Nadu, India. E-mail: [email protected] Balasubramanian K R Assistant Professor, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India. E-mail: [email protected] the powerplant. A furnace model capable of predicting heat flux based on the specified operating parameters will be able to mitigate this problem. A thoroughly validated model with a set of experimental results will be an effective tool in the determination of boiler furnace heat flux for a variety of operating variables. A review of heat flux measurement techniques adopted by various researchers resulted in a conclusion that, the use of chordal thermocouples for measurement of tube crown temperature and then arriving at the surface absorbed heat flux by using heat transfer equations is a more viable solution. In that direction, an attempt has been made to develop a new method to calculate the applied local outside heat flux (Q/Ao) of the membrane waterwall of boiler with rifled tubing. An inverse heat conduction problem was solved using an iterative procedure. ‘Predicted’ temperatures required for the inverse problem were artificially generated by solving a direct heat conduction problem using ANSYS-FLUENT software. The calculated Q/Ao is compared with that of the Q/Ao used for generation of ‘predicted’ temperatures. Abstract A simplified procedure for prediction of local heat flux on the membrane waterwall rifled tubes of a sub-critical boiler is presented which requires the measurement of metal temperature at the tube crown using a chordal thermocouple. An inverse problem of heat conduction was solved using an iterative procedure to calculate the outside heat absorption rate from conduction and convection related heat transfer equations. The temperature distribution over the cross-section of the tube was found using ANSYS-FLUENT software for different range of values of outside heat flux, inside heat transfer coefficient and operating pressures. ‘Predicted’ temperatures obtained from the solution of direct heat conduction problem has been used to solve for the outside heat flux. Keywords: Heat flux measurement, Furnace modelling and heat flux prediction, Heat flux distribution, Indian-coal fired boilers, Inverse heat conduction problem Introduction A boiler furnace is an enclosure of tubes carrying water/steam. Tube failures are imminent when there is excessive heating due to reduction of flow in the furnace wall or due to a sudden increase in incident heat flux.. Judicious selection of waterwall tube thickness is required to avoid these failures. Moreover, the fluid pressure drop in the furnace wall is also affected by the thickness of the tube. Hence arriving at an optimum thickness is required to achieve a trade-off between pressure drop and metal temperatures. This requires a lucid understanding of heat flux profile in the furnace, especially for boilers firing high ash Indian coal. Heat flux and temperature are to be measured for a large permutation of operating variables like furnace size, operating load, water wall flow, type of coal fired, and ash deposition for a complete understanding of the absorption phenomenon. But a large scale experimentation requires meticulous planning and a sufficiently large number of measurements which will lead to the temporary shutdown of Literature review Previous work done by researchers in the areas of furnace modeling, heat flux prediction, heat flux measurement techniques and effect of ash deposit on thermal performance are discussed in the forthcoming section. A. Furnace modeling S. Rajaram and K. U. Abraham [1] described an iterative procedure for the calculation of furnace heat flux from measured metal temperatures using finite-difference equations formulated using the procedure given by Adams and Rogers [2] and solving the same using relaxation technique to obtain the relationship between outside heat flux and total temperature drop. Martins et al. [3, 4] worked on a hemispherical radiation heat flux meter to measure the difference between hemispherical radiation heat flux and convective heat flux and 1273 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com experimentally verified the same for measuring totalhemispherical radiation with the range of heat flux 40-150 kW/m2. Yuh-Long Hwang and John R. Howell [5] calibrated a furnace model based on PCGC-3 code developed by Brigham Young University using measurements of local gas temperature distributions, local radiative and total wall heat flux distributions, and stack NOX. Modeling of the effect of ash deposition is discussed by many authors [6-15], [25]. The models included the effects of ash formation, growth rate and particle sticking on heat transfer. Various other authors [16-24] have also worked on developing a numerical model for predicting furnace performance parameters like gas temperatures and heat flux pattern. A few authors [26-28] have attempted thermal-hydraulic modelling of boiler wherein the waterwall of the boiler is treated as a flow network containing series and parallel loops, pressure grids and connecting tubes and a mathematical model is developed based on mass, momentum and energy conservation of the above said components. Mathematical model for studying performance of CFB boiler was developed by [29, 30]. But, very few research articles are available on accurate prediction of heat flux for high ash coal fired boilers especially in super-critical range. Hence, a research involving prediction of heat flux for high ash coal fired boilers and validation of the same will be of high importance in arriving at optimum boiler design. transfer and surrounding atmosphere like ash deposition is satisfied by tubular instruments. The EPRI report [34] throws light on two of the currently manufactured sensors namely Applied Synergistics' Heat flux sensor and Chordal thermocouples. Chordal thermocouples are widely used in heat flux evaluation by measuring tube wall temperatures where holes are drilled along the chords of a tube wall and the thermocouple wire is installed through these holes. Measurement of heat flux has been widely used in the boiler industry for monitoring of ash deposition on water wall tubes and the development of smart soot blowing system as discussed in [36], [37], [41-44], [55-63]. Optimization of soot-blowing is the end requirement in many of these researches. The measurement techniques discussed are also based on deriving heat flux from basic conduction principle by measuring temperature at two different points. Various authors have used different locations for measurement. Since only an indication of ash fouling is required, none of the above techniques explained above will result in an accurate measurement of heat flux. Hence, there is a need to develop a technique concerning the application of understanding the heat flux variation in the furnace waterwall. This requires measurement of heat flux either directly or temperature using chordal thermocouple placed on the tube crown. However, the latter area needs to be explored further. Direct heat conduction problem B. Heat flux measurement techniques Different techniques available for measurement of heat flux are outlined by various researchers [31-34]. The authors explain regarding heat flux measuring devices using two major principles viz. radial disk principle and guarded cylinder technique. Even though the radial disk principle is easy to use, the method does not always guarantee an accurate measurement of heat flux since it is mounted on the surface of the tube. This is because, the measurement depends on the heat flux on the top and bottom surface of the device. Any change in the varied operating conditions mainly due to ash deposition will lead to a considerably erroneous indication of heat flux. The guarded cylinder technique does not have this limitation, but it is difficult to implement owing to requirement of high manufacturing accuracies. According to Taler et al. [35], three types of heat flux measurement devices can be used broadly in boiler water-walls: (1) portable heat flux meters inserted in inspection ports (2) Gardon type heat flux meters welded to the section of boiler tubes (3) tubular type instruments placed between two adjacent boiler tubes. A device named fluxprobe [37] was designed for measuring values of incident radiation flux primarily in membrane walls with an accuracy of +5%. Gardon type heat flux meters have been the subject of research of many researchers [38-45]. These are heat flux measuring devices welded to the surface of the boiler tube. They predominantly work on radial disc principle. Since these devices are mounted to the surface of the waterwall tube, the effect of non-uniform ash deposition on the measuring device and the tube leads to inaccuracies in the computed values of heat flux. Tubular type instruments have been explored by [33], [35], [46-54]. The requirement that the heat flux instrument used for measuring absorbed heat flux should represent the boiler tube as closely as possible in terms of both radiant heat A linear direct heat conduction problem was formulated and solved using ANSYS-FLUENT code to obtain the temperature distribution across the cross section of the boiler tube. The following assumptions were made in the analysis. Heat transfer coefficient on the inner surface of the boiler tube (h i) does not vary along the circumference of the tube. Rear side of the boiler tube is thermally insulated. Thermal conductivity (k) of the tube material is constant (40. 5 W/mK). Heat flux distribution on the outer surface is dependent on the view factor computed using equations (1) and (2). Effect of ash deposition is neglected. Analysis was performed using ANSYS-FLUENT code for the following conditions: Operating pressure (PDRUM) range: 120 bar to 160 bar Outside heat flux (Q/Ao): 220, 000 to 355, 000 W/m2 Inside heat transfer coefficient (h i): 46, 000 to 55, 000 W/m2K A. View factor determination Radiation heat transfer between surfaces depends on the orientation of those surfaces relative to each other in addition to their temperatures, emissivity and transmissivity of the medium in between them. Effect of view factor on radiation incident on tube outer surface was considered using the procedure furnished by Ganapathy [67] as depicted in Fig. 1. The following set of equations have been adopted separately for view factor (ψ) on fin and tube View factor on tube outer surface= 1274 (1+ cos ϕ) 2 (1) International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com View factor on fin outer surface= ( cos ϕ1 + cos ϕ2 ) 2 (2) View factor variation on tube & fin outer surface 1.2 For the purpose of computation of view factor at a point on the tube surface, the angle (φ) between the tangents to the particular tube of interest and to its adjacent tube to the corresponding point is found out. Relation between the view factor of the boiler tube at the particular point of interest and the angle subtended by the line connecting the point from the center of the tube with the horizontal was arrived. Similarly for the fin, a relation between the view factor of the tube-fin at the particular point of interest and the distance between that point and the vertical axis of the tube. The above relations were coded into ANSYS-FLUENT for analysis [68]. The view factor variation on the outer surface of the tube and fin as a function of curve length is shown in Fig. 2 View factor 1 0.8 0.6 0.4 0.2 0 0 0.01 0.02 0.03 0.04 0.05 Curve length (m) Figure 2: View factor variation on tube and fin outer surface B. Solution procedure After computing the view factor as mentioned previously, the direct heat conduction problem was solved using ANSYSFLUENT code. Tube temperature distribution is expressed by the following heat conduction equation: k ∇2T = 0 (3) The boundary condition at the tube outside surface may be expressed as: k ∂T | ∂r (r= ro) = q̇ m (4) The absorbed outside surface heat flux (q̇ m ) as a function of Q applied heat flux (A ) and view factor (ψ) is expressed in the 0 form of the following equation: q̇ m = Q A0 ψ (5) The boundary condition at the tube inside surface may be expressed as a convection boundary condition: A) Estimation of View For Tube -k ∂T | ∂r (r= ri ) = hi (Tf – Ti) (6) The above direct heat conduction problem was solved using ANSYS-FLUENT software with the following mesh configuration: Tetrahedral mesh with 2751077 elements, 524163 nodes C. Grid independence study A grid independence study was carried out with the grids as shown in Fig. 3. The values of temperature at the thermocouple location points for the three grids are tabulated in Table 1. As it can be noted, the variation in temperature is very low across the three types of grids. For generating the temperatures mentioned in the Table 1, heat flux of 2, 50, 000 W/m2, inside heat transfer coefficient of 54, 000 W/m2 K and a fluid temperature of 363 °C was used. B) Estimation of View Factor for Fin Figure 1: View factor estimation for membrane wall tubes [67] 1275 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com Figure 5: Temperature distribution across the tube circumference and fin Inverse heat conduction problem A. Analytical Procedure for inverse heat conduction problem The iterative procedure for computation of boiler tube outside surface heat flux (Q/Ao) is discussed. The tube material, outside diameter (Do), major inside diameter (Dmajor), minor inside diameter (Dminor) and the thermocouple installation diameter (Dc) are the known physical dimensions as shown in Fig. 6. Figure 3: Division of geometrical model of tube into elements (a) Hexahedral mesh with 77410 elements, 53100 nodes (b) Tetrahedral mesh with 334028 elements, 68314 nodes (c) Tetrahedral mesh with 2751287 elements, 524218 nodes Table 1: Temperature at measuring points computed for different meshes in Fig. 3 Sl. No. 1 2 3 Temperature (°C) 400. 98 401. 21 401. 55 Mesh type 3 (a) 3 (b) 3 (c) D. Results Total surface heat flux i. e Applied local outside heat flux (Q/Ao) variation across the tube and fin surface for a sample case (P=120 bar, Q/Ao = 2, 80, 000 W/m2 and hi = 51, 000 W/m2 K) is shown in Fig. 4. The effect of view factor on the tube and fin is clearly visible. The temperature distribution in the tube is shown in Fig. 5. Figure 6: Schematic representation of the tube and thermocouple location In the sub-critical operating range, it is appropriate to take the saturation temperature as the bulk fluid temperature (T f) and assume the region of operation in nucleate boiling regime. An initial assumption for tube inside surface temperature (T i) and inside heat transfer coefficient (h i) is required for further computations. Average metal temperature (Tav) is computed using one-dimensional heat conduction equation as given by Cengel [64] with the temperature dependence of thermal conductivity, heat generation and unsteady terms neglected. 1 ∂ r ∂r Figure 4: Heat flux variation across the tube circumference and fin (r k ∂T ∂r ) +ġ = ρ Cp ∂T ∂t (7) The tube metal thermal conductivity (k) is computed based on average temperature in case of non-linear heat conduction 1276 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com problem and is constant in case of linear heat conduction problem. From the known values of thermal conductivity and temperature difference between outside and inside metal temperatures, inside surface heat flux (Q/Ai) is calculated based on heat conduction equation given below: ∂T =- k | ∂r (r= ri ) (8) Further, the film temperature drop (ΔTsat) is calculated using Jens-Lottes equation as suggested in [65] using inside surface heat flux (Q/Ai) and drum pressure (PDRUM). ΔTsat = 60 ( e 1/4 Q⁄Ai ⁄ 6) 10 PDRUM ⁄ 900 Jens-Lottes (9) Thom et. al Computed outside surface heat lux (W/m2) Q Ai B. Results Since both the equations, (9) and (10) are used to calculate the film temperature drop, outside heat flux (Q/Ao), computed using both the equations are compared in Fig. 8. The data shown is for the case with a pressure of 120 bar corresponding to the 'predicted' temperatures obtained from solving the direct heat conduction problem. It is clear that usage of Jens-Lottes equation (Eq. 9) leads to a higher value of computed heat flux for the same 'predicted’ temperature when compared to Thom et al. equation (Eq. 10). 360000 Alternatively, Thom et al. equation [66] has also been used. ΔTsat = 72 ( e 1/2 Q⁄Ai ⁄ 6) 10 PDRUM ⁄ 1260 320000 (10) The above calculated value of film temperature drop (ΔT sat) is used to calculate new values Ti and hi. This iterative procedure is repeated until specified tolerance limits are achieved. The outside surface heat flux (Q/Ao) is calculated from inside surface heat flux (Q/Ai) after correcting suitably for circumferential heat flow. The temperature obtained at the thermocouple measuring point at the tube crown after solving the direct heat conduction problem is termed as 'predicted' temperature. From the predicted temperature, the outside heat flux (Q/Ao) is computed by the procedure described above. A flow chart depicting the suggested calculation procedure is shown in Fig. 7. 280000 240000 200000 355 360 365 370 375 380 Predicted themocouple temperature (°C) 385 Figure 8: Heat flux calculation: Comparison between heat flux calculated Jens-Lottes and Thom equations Fig. 9 shows the comparison between actual values of outside heat flux (Q/Ao) used for generating the predicted temperatures and the computed values of (Q/Ao) arrived by solving the inverse heat conduction problem using the 'predicted' temperatures. The values are shown for 120 bar operating pressure. It can be seen that the calculated heat flux matches closely with that of the actual heat flux. Thom et. al Actual Computed outside surface heat lux (W/m2) Jens-Lottes 360000 320000 280000 240000 200000 350 360 370 380 390 Predicted themocouple temperature (°C) Figure 9: Heat flux calculation: Comparison with actual values Figure 7: Flow chart for calculation of heat flux 1277 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com The uncertainties (95% confidence interval) for predicted heat flux through the iterative procedure is given in the Table 2 below. From the table, it can be inferred that at 120 bar, Jens Lottes correlation has a lesser uncertainty. At operating pressures higher than 120 bar Thom’s correlation can be used for better accuracy. with rifled tube configuration. It has been found that, outside heat flux in the membrane waterwall of a boiler can be computed with reasonable accuracy with the measurement of only one temperature at the tube crown for lower sub-critical pressures. Acknowledgement Table 2: Uncertainties (95 % confidence interval) for predicted heat flux Operating pressure (bar) Uncertainties in heat flux calculated using Jens-Lottes equation (W/m2 ) 120 140 160 ±9704 ±12820 ±19364 The authors wish to thank the management of Bharat Heavy Electricals Limited for having granted permission to publish this paper. Uncertainties in heat flux calculated using Thom equation (W/m2 ) ±10679 ±6231 ±10801 List of symbols and abbreviations B Fin width (m) Cp Specific heat of tube material (kJ / (kg K)) Dc Thermocouple installation diameter (m) Dmajor Major inside diameter of waterwall tube (m) Dminor Minor inside diameter of waterwall tube (m) Do Outside diameter of waterwall tube (m) The calculation procedure was used to compute the outside heat flux for the parameters specified by Duda and Taler [49] which are specified below: Outside radius: 0. 03 m Inside radius: 0. 025 m Thermocouple location radius: 0. 029 m Thermal conductivity: 40. 5 W/ mK Fluid temperature: 318. 2 ˚C ‘Measured’ temperature: 349. 17 ˚C ġ Rate of heat generation (W/m3) hi Inside heat transfer coefficient (W/ (m2 K)) k Thermal conductivity of the tube material q̇ m Absorbed outside surface heat flux (W/ m2) Table 3 shows the comparison of calculated values of outside heat flux with that of the values obtained in [49]. The calculated values are closer to that of values furnished in [49] Q/Ao Applied local outside surface heat flux (W/ (W/ (m K)) PDRUM Eq. (9) and Eq. (10) m2) Q/Ai 1 2 Parameter Outside heat flux (W/m2) Inside heat transfer coefficient (W/ m2 K) Taler and Duda [49] 220135. 3 37105. 5 JensLottes equation Thom equation 221302. 2 219792. 6 37443. 8 38622. 3 Inside surface heat flux (W/ m2) or (Btu / (hr ft2)) in Eq. (9) and Eq. (10) Table 3: Comparison of results with Duda and Taler paper [49] Sl. No. Drum operating pressure (bar) or (psi (a)) in r radius of the waterwall tube (m) ro Outside radius of waterwall tube (m) ri Inside radius of waterwall tube (m) T Temperature of waterwall tube (°C) Tav Average wall temperature of the tube (°C) Tc Temperature measured by chordal thermocouple (°C) Tf Bulk fluid temperature (°C) Ti Inside surface temperature of waterwall tube (°C) Conclusion ΔTsat The sizing of a furnace necessitates an extensive study of heat flux distribution in the furnace both along the height of the furnace and laterally (along the width and depth). Measuring the metal temperature using a chordal thermocouple inserted into a hole drilled at the crown of the waterwall tube and then computing the absorbed heat flux is a more viable and simple method for sub-critical boilers in the operating pressure range of 120-160 bar. An iterative procedure for calculation of heat flux from the measured metal temperatures has been proposed and validated for the membrane waterwall of sub-critical boiler Film temperature drop (°C) or (°F) Eq. (5) and Eq. (6), ΔTsat = (Tf – Ti) Greek Symbols θ, ϕ, ϕ1 and ϕ2 Angles as shown in Fig. 1 1278 ρ Density of tube material (kg/m3) ψ View factor International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com and cleaning, Greece, pp. 150-155. [15] Adams, Bradley et al., 2013, "Ash Deposition Modeling Incorporating Mineral Matter Transformations Applied to Coal and Biomass Co-firing", AFRC Industrial Combustion Symposium. [16] Adam, E. J. and Marchetti, J. L., 1999, "Dynamic simulation of large boilers with natural recirculation", Computers and Chemical Engineering, 23, pp. 10311040. [17] Yamomoto, Kenji et al., 2000, "Development of Computer Program for Combustion Analysis in Pulverized Coal-fired Boilers" Hitachi Review, Electric Power and Energy Technologies, 49, pp. 76-80. [18] Xu, M., Azevedo, J. L. T. and Carvalho, M. G., 2001, "Modeling of a front wall fired utility boiler for different operating conditions", Comput. Methods Appl. Mech. Engrg., 190, pp. 3581-3590. [19] Xu, M., Azevedo, J. L. T. and Carvalho, M. G., 2001, "Modeling of the combustion process and NOx emission in a utility boiler", Fuel, 79, pp. 1611-1619. [20] Kouprianov, V. I., 2001, "Modeling of thermal characteristics for a furnace of a 500 MW boiler fired with high-ash coal", Energy, 26, pp. 839–853. [21] Yin, Chungen et al., 2002, "Investigation of the flow, combustion, heat-transfer and emissions from a 609 MW utility tangentially fired pulverized-coal boiler", Fuel, 81, pp. 997-1006. [22] Diez, Luis I, Cortes, Cristobal and Campo, Antonio, 2005, "Modeling of pulverized coal boilers: review and validation of on-line simulation technique", Applied Thermal Engineering, 25, pp. 1516–1533. [23] Vuthaluru, R. and Vuthaluru H. B., 2006, "Modelling of a wall fired furnace for different operating conditions using FLUENT" Fuel Processing Technology, 87, pp. 633–639. [24] Mohammad, Hadi Bordbar and Hyppanen, Timo, 2007, "Modeling of Radiation Heat Transfer in a Boiler Furnace", Adv. Studies Theor. Phys., 1, pp. 571 – 584. [25] Yu, M., Chernetskii, A., Alekhnovich, N. and Dekterev A. A., 2012, "A Mathematical Model of Slagging of the Furnace of the Pulverized_Coal_Firing Boiler", Thermal Engineering, 59, pp. 610–618. [26] Tucakovic, Dragan R. et al., 2007, "Thermal–hydraulic analysis of a steam boiler with rifled evaporating tubes", Applied Thermal Engineering, 27, pp. 509–519. [27] Pan, Jie et al., 2009, "Mathematical modeling and thermal-hydraulic analysis of vertical water wall in an ultra-supercritical boiler", Applied Thermal Engineering, 29, pp. 2500–2507. [28] Pan, Jie et al., 2012, "Thermal-hydraulic analysis of a 600 MW supercritical CFB boiler with low mass flux", Applied Thermal Engineering, 32, pp. 41-48. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Rajaram, S. and Abraham, K. U., 1984, “Determination of boiler furnace heat flux”, Technical Notes, Intl. Journal of Heat Mass Transfer, 27 (11), pp. 2161-2166. Adams, J. A. and Rogers, D. F., 1973, Computer-aided Heat Transfer Analysis, New York. : Mc-Graw Hill, pp. 119-153. Martins, N., Carvalho, M. G., Afgan, N. H. and Leontiev, A. I., 1995, “A new instrument for radiation flux heat measurement-Analysis and parameter selection”, Heat recovery systems and CHP, 15 (8), pp. 787-796. Martins, N., Carvalho, M. G., Afgan, N. H. and Leontiev, A. I., 1998, “Experimental verification and calibration of the blow-off heat flux sensor”, Applied Thermal Engineering, 18 (6), pp. 481-489. Hwang, Yuh-Long and Howell, John R., 2002, “Local Furnace Data and Modeling Comparison for a 600-MWe Coal-Fired Utility Boiler”, Transactions of the ASME, 124, pp. 56-66. Wang, Huafeng and Harb, John N., 1997, “Modeling of ash deposition in large-scale combustion facilities burning pulverized coal”, Prog Energy Combust Sci, 23, pp. 267-282. Litchford, Ron J. and San-Mou Jeng., 1991, “Efficient Statistical Transport Model for Turbulent Particle Dispersion in Sprays”, AIAA Journal, 29 (9), pp. 14431551. Litchford, Ron J. and San-Mou Jeng., 1992, “Statistical Modeling of turbulent dilute combusting sprays”AIAA Journal, 30 (10), pp. 2549-2552. Richards, G. H., Slater, P. N. and Harb, J. N., 1993, "Simulation of Ash Deposit Growth in a Pulverized Coal-Fired Pilot Scale Reactor", Energy & Fuels, 7, pp. 774-781. Fan, J. R., Zha, X. D., Sun, P and Cen, K. F., 2001, "Simulation of ash deposit in a pulverized coal-fired boiler", Fuel, 80, pp. 645-654. Wall, T. F et al., 1995, "The character of ash deposits and thermal performance of furnaces", Fuel Processing Technology, 44, pp. 143-153. Rezaei, H. R., et al., 2000, "Thermal conductivity of coal ash and slags and models used", Fuel, 79, pp. 16971710. Zbogar, A., Frandsen, F. J., Jensen, P. A. and Glarborg, P., 2005, "Heat transfer in ash deposits: A modelling tool-box", Progress in Energy and Combustion Science, 31, pp. 371-421. Ots, A., 2011, "Thermophysical properties on ash deposit on boiler heat exchange surfaces", Proceedings of International Conference on Heat Exchanger fouling 1279 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com [29] Zhang, R., Yang, H., Hu, N., Lu, J. and Wu, Y., 2013, "Experimental investigation and model validation of the heat flux profile in a 300MW CFB boiler", Powder Technology, 246, pp. 31-40. [30] Chinsuwan, Anusorn., Dutta, Animesh and Jansalad, Nadnalin, 2014, “Prediction of the heat flux profile on the furnace wall of circulating fluidized bed boilers”, Journal of the Energy Institute. 87, pp. 314-320. [31] Marner, W. J. and Henslee, S. P., 1984, “A survey of gas-side fouling measuring devices”, US Department of Energy, 3. 2-3. 8. [32] Arai, Norio., Matsunami, Aritaka and Churchill, Stuart W., 1996, “A review of measurements on heat flux density applicable to the field of combustion”, Experimental thermal and fluid science, 12, pp. 452-460. [33] Taler, Jan and Taler, Dawid, 2012, “Measurement of heat flux and heat transfer coefficient in heat flux process”, In: Cirimele G, D’Elia M, Heat flux: processes, measurement techniques and applications, Nova Science publishers, pp. 1-103. [34] Sensors for furnace ash deposition measurement on boiler tubes: Technology Review: 1000409, EPRI Palo Alto, CA, 2000. [35] Taler, Jan. et al., 2009, “Identification of local heat flux to membrane water-walls in steam boilers”, Fuel, 88, pp. 305-311. [36] Neal S. B. H. C and Northover, E. W., 1980, “The measurement of radiant heat flux in large boiler furnaces-I: Problems of ash deposition relating to heat flux”, International Journal of Heat and Mass Transfer, 23, pp. 1015–1021. [37] Neal S. B. H. C., Northover, E. W and Preece, R. J., 1980, “The measurement of radiant heat flux in large boiler furnaces –II Development of flux measuring instruments”, International Journal of Heat and Mass Transfer, 23, pp. 1023–1031. [38] Northover E. W and Hitchcock J. A., 1967, “A heat flux meter for use in boiler furnace”, Journal of Scientific Instruments, 44, pp. 371-374. [39] Semenovker, I. E. and Gendelev V. G., 1970, “A heat flux meter for use in waterwall tubes”, Thermal Engineering, 17, pp. 96-100. [40] Nosov, B. N. and Ivanov N. V., 1984, “An investigation of local heat fluxes in the furnace waterwalls of oncethrough boilers within a wide range of load”, Thermal Engineering, 31 (3), pp. 46-48. [41] Wynnyckyj, John R., Rhodes, Edward and Chambers, Allan K., 1983, “Furnace wall ash monitoring system”, US Patent No. 4408568. [42] Wynnyckyj, John R., Rhodes, Edward and Chambers, Allan K., 1985, “Furnace wall ash deposit fluent phase change monitoring system”, US Patent No. 4514096. [43] Chambers A. K., Wynnyckyj, J. R. and Rhodes, E., 1981, “Development of a monitoring system for ash deposits on boiler tube surfaces”, The Canadian Journal of Chemical Engineering, 59, pp. 230-235. [44] Chambers A. K., Wynnyckyj, J. R. and Rhodes, E., 1981, “A furnace wall ash monitoring system for coal fired boilers”, ASME journal of Engineering for Power, 103, pp. 532-538. [45] Wynnyckyj, John R. and Rhodes, Edward., 1986, “Heat flux meter”, US Patent No. 4607961. [46] Taler, J., 1990, “Measurement of heat flux to steam boiler membrane water walls”, VGB Kraftwerkstechnik, 70, pp. 540–546. [47] Taler, J., 1992, “A method of determining local heat flux in boiler furnaces”, Int J Heat Mass Transfer, 35, pp. 1625–1634. [48] Taler, Jan et al., 2008, “Measurement of local heat flux to membrane water walls in steam boilers”, International Conference on engineering optimization, Rio de Janeiro: Brazil. [49] Duda, Piotr and Taler, Jan, 2009, “A new method for identification of thermal boundary conditions in waterwall tubes of boiler furnaces”, International Journal of Heat and Mass Transfer, 52, pp. 1517-1524. [50] Taler, Jan., Taler, Dawid and Kowal, Andrzej, 2011, “Measurements of absorbed heat flux and water-side heat transfer coefficient in water wall tubes”, Archives of thermodynamics – De Gruyter, 32 (1), pp. 77-88. [51] Taler, Jan., Taler, Dawid., Sobota, Tomasz and Dzierwa, Piotr., 2011, “New technique of the local heat flux measurement in combustion chambers of steam boilers”, Archives of thermodynamics – De Gruyter, 32 (3), pp. 103-116. [52] Taler, Jan and Taler, Dawid., 2012, “An Overview of Heat Transfer Phenomena”, InTech, ISBN 978-953-510827-6, pp. 3-34. [53] Taler, Jan., Taler, Dawid and Ludowski, Pawel., 2014, “Measurements of local heat flux to membrane water walls of combustion chambers”, Fuel, 115, pp. 70-83. [54] Johannes Van Den Ende, Cornelis Jan Van Den Bos, Manfred Frach and Stephan Simon, 2007, “Heat flux measuring device for pressure pipes”, US Patent No. 7249885. [55] Valero, A and Cortes, C., 1996, “Ash fouling in coalfired utility boilers: Monitoring and optimization of onload cleaning”, Prog Energy Combust Sci, 22, pp. 189– 200. [56] Bueters, Kees A. and Andersen, Mark S., 1984, “Soot blower system”, US Patent No. 4488516. [57] Brajuskovic, Branislav., Matovic, Miodrag and Afgan, Naim., 1991, “A heat flux meter for ash deposit monitoring systems-I: Ash deposit prevention”, Int. J. 1280 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 2 (2016) pp 1273-1281 © Research India Publications. http://www.ripublication.com Heat Mass Transfer, 34 (9), pp. 2291-2301. [58] Brajuskovic, Branislav and Afgan, Naim., 1991, “A heat flux meter for ash deposit monitoring systems-II: Clean heat flux meter characteristics”, Int. J. Heat Mass Transfer, 34 (9), pp. 2303-2315. [59] Paist., A., Poobus, A. and Tiikma, T., 2002, “Probes for measuring heat transfer parameters and fouling intensity in boilers”, Fuel, 81, pp. 1811-1818. [60] Melvin John Albrecht and Scott Edward Hawk., 2002, “Attachable heat flux measuring device”, US Patent 6485174 [61] Breen, Bernard P and Schrecengost, Robert A., 2005, “Method of monitoring heat flux and controlling corrosion of furnace wall tubes”, US Patent No. 6848373 B2. [62] Teruel E., Cortes, C., Die, L. I. and Arauzo, I., 2005, “Monitoring and prediction of fouling in coal-fired utility boilers using neural networks”, Chem Eng Sci, 60, pp. 5035–5048. [63] Bella, O., Cortes, C. and Valero, A., “Intelligent Soot blowing system for coal-fired utility boilers”, CIRCE, Spain. [64] Cengel, Yunus A., Heat Transfer – A Practical Approach, Second Edition, pp. 70. [65] Jens, W. H. and Lottes, P. A., 1951, “Analysis of heat transfer, burnout, pressure drop and density data for high-pressure water”, Argonne National Laboratory, pp. 15. [66] Tong, L. S. and Tang, Y. S., 1997, Boiling Heat Transfer and Two-Phase Flow, 2nd Edition, Washington, DC. : Taylor and Francis Publishers, pp. 257. [67] Ganapathy, V., 2014, Steam Generators and Waste Heat Boilers: For Process and Plant Engineers, CRC Press, pp. 61-63. [68] Ansys Fluent 12. 0 UDF Manual, April 2009. 1281