Optimization of wall thickness and material for minimum heat losses


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Optimization of wall thickness and material for minimum heat losses

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME418OPTIMIZATION OF WALL THICKNESS AND MATERIAL FORMINIMUM HEAT LOSSES FOR INDUCTION FURNACE BY FEABhujbal Nitin B.1, Prof. S.B. Kumbhar21M. Tech student, Department of Mechanical Engineering RIT Sakharale,Sangli, Maharashtra, India,2Assistant professor, Department of mechanical Engineering RIT Sakharale,Sangli, Maharashtra, India.ABSTRACTInduction furnaces are most commonly used for melting of metals. Especially silicaramming mass is used as refractory material to prevent losses. Hence proper optimization isneeded in thickness. Increase in thickness plays an important role in effectiveness of thefurnace. As the thickness increases the heat losses goes on decreasing up to a certain limit.Optimum thickness reducing heat loss in furnace with economical cost is needed.This paper deals with optimization of wall thickness and material for minimum heatlosses during melting iron. Heat loss calculation requires thermal properties and physicalparameter. Calculations have been done for theoretical heat loss and temperature distributionwhich are later compared with actual values measured on existing furnace. There are hugelosses in the existing furnace hence we have concluded that optimization is necessary.ANSYS Software was used for optimization which gave more accurate results inminimum time consumption. Axi-symmetric type is used as the problem is symmetric aboutY- Axis. Finally we concluded that optimization in thickness of refractory material mayreduce 35% losses and optimization of thermal properties reduces 73% losses. Ultimately wecan reduce 70% losses by using proper thickness and material properties of refractory materialof induction furnace.Key words: Optimization, coreless induction furnace, Heat transfer coefficient, silicaramming mass, Refractory material.INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGAND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4, Issue 2, March - April (2013), pp. 418-428© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2013): 5.7731 (Calculated by GISI)www.jifactor.comIJMET© I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4191. INTRODUCTIONNow a day’s the increasing demand for electric power and the pursuit of itseconomical use, energy converters with higher and higher power have been developed andare being produced. In addition, the requirements of minimum electric power losses andenvironment protection have become extremely important, that is the minimization of theheat losses. Mostly there are heat losses by conduction, convection and radiation, and hencethe improvement in best refractory material and optimization in wall thickness of refractorymaterial [1] and [2] is needed.The optimization of the power equipment geometry is highly relevant today, andseveral studies have dealt with the heat loss problem.[3] The two basic designs of inductionfurnaces, the core type or channel furnace and the coreless, are certainly not new to theindustry. The Existing furnace is one of the largest commercial units that are capable ofmelting nearly 12 tons per hour with very high power densities of nearly 1800 kWh/tonwhich can melt a cold charge in 50 to 60 minutes [1].The main objective of this paper is to identify the problem related with the inductionfurnace and calculate heat losses through the side walls across the temperature distribution byusing analytical methods. Verification of analytical result is compared with actual measuredvalues on existing furnace and those are validated with APDL Ansys software. Model isprepared with existing dimensions in ANSYS software and is verified with the calculatedresults [4] and [5]. For minimum heat losses optimum changes in geometry of inductionfurnace and properties of wall material is done with ANSYS software. The purposes of thispaper are studying the influence of process parameters on the energy consumption andfinding the potential optimization of the refractory material of induction furnace.2. LITERATURE SURVEYProf. N. C. Mehta et.al. reviewed thermal fatigue analysis of Induction MeltingFurnaces that are highly used now- a-days for melting different kinds of materials. ANSYSsoftware was used for analysis of ramming mass. They have calculated stress distributionacross the refractory wall and concluded that critical stress can be reduced and life ofrefractory wall can be improved and the Refractory material loses its thermal propertieswithin 200-400 hours of lifetime.Hong-Seok Park and Xuan-Phuong Dang et.al. [4] Worked on Improving theefficiency of the manufacturing process like Optimization of the operating parameters of theinduction heating system, In addition, thermal insulation was proposed to reduce the heatlosses and concluded that energy efficiency can increase up to 6% and if the insulatingdevices are used to reduce the radiation and convection 4% of energy can be saved afteroptimization.M. M. Ahmed, M. Masoud et.al. [5] Reviewed the design of coreless inductionfurnaces for melting iron. The electrical parameters of the furnace such as number of turns ofcoil, inductance of the coil, resistance of the coil and the maximum flux density weredetermined based on transformer concept, comparison of the obtained design results with thecorresponding existing design results was done.
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4203. STUDY OF EXISTING FURNACEA. GeometryThe coreless induction furnace consists generally a Crucible, inductor coil, shell,cooling system and tilting Mechanism. The crucible is formed from refractory material.This crucible holds the charge material and subsequently the melt.Fig.1. The geometry of the furnaceThe choice of refractory material depends on the type of charge, i.e. acidic, basicor neutral. The durability of the crucible depends on the grain size, ramming technique,charge analysis and rate of heating and cooling the furnace [4]. The geometric shape likewidth, height of each material of the Furnace is shown in fig.1B. Analytical studyFurnace has generally heat losses by conduction, convection and radiation. Heatloss can be calculated from several methods, but apart from those methods we mustjustify proper method for more accurate results. Here it is determined that heat conductionthrough composite cylinder for calculations of heat losses and temperature distributionfrom furnace is proper method [7] and it gives us accurate results. Sometimesassumptions can be required for calculations of heat losses.Mathematical calculation needs temperature at inner and outer wall of the furnace,thermal conductivity of each material. Therefore it required to measure temperatures andphysical dimensions by using proper instruments. Thermal properties have taken in toaccount for calculation as they are also important to find out results. Measuredtemperature have presented in table1.Table1. Temperature distribution in existing induction furnaceNotation Content Temperature °CTi Inner wall temperature 1500To Ambient temperature 40Tw Outer wall temperature 40 to 75Twi Inlet water temperature 25 to 35Two Outlet temperature of water 40 to 75
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME421Following are measured geometrical dimensions on existing furnace and the properties ofmaterial at 1500°C have presented in table2.Table 2.Dimensions and properties of existing furnace:Material Dimensions in mm ThermalPropertiesUnitsDiameter ThicknessCoil corecement1550 10 K = 1.39 w/m 0Ch = 30 W/m2 0CMicasil 1530 3.5 K = 0.12 w/m 0CRamming mass 1200 160 K = 11 w/m 0Ch = 200 W/m2 0C4. HEAT LOSS CALCULATION:Heat loss can be calculated by referring electrical circuit for steady state condition ofcomposite cylinder [7]. From given data in table1 and table2 we can calculate conduction,convection and radiation losses with temperature distribution.A. Heat loss calculation1. Calculation of resistance R = ln (r2/r1) / 2πLkTotal resistance ∑R = R1+R2+R32. Conduction losses Q = (Ti – To) / ∑R3. Radiation losses Q = ε A σ (Ti4– To4)4. Convection losses Q = h A (Ti – To)5. Total heat losses from furnace Q = Q convection + Q radiation + Q conduction6. Total heat flux = Heat generated / 2πrlQ = Total heat loss from furnace in W =To, Ti = Temperatures at outlet and inlet in °CK = Thermal conductivity of material of wall in w/m °Ch = Heat transfer coefficient from outer surface of wall in W/m2 °Cb = Thickness of wall in mmɛ = Emissivity of red hot body = 0.43A = C/S area of the furnaceσ = Stefan Boltzmann constant = 5.669 x e-8Table 3. Calculated heat loss and temperature distribution is shown in following tableHeat loss kwh TotallosskwhTemperature °CConductionConvectionRadiation T1 T2 T3 T4309 297 140 746 1500 435 265 76B. Comparison between Actual and analytical resultsTo verify the design results, a comparison between total heat loss and temperaturedistribution of calculated results and actual results of induction furnace were carried out,which are tabulated below in table 4. From this table it can be seen that the analytical valuesare close to the actual ones.
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME422Table 4. Verification of calculated value with actual valueMethod Temperature °C Heat loss kwhT1 T2 T3 T4Actual Value 1500 - - 76 720Analytical value 1500 436 265 72 746Table indicates that there are very huge losses in furnaces. So there is potential toreduce heat losses with optimization of geometry and properties of refractory material. Ifthese losses of 746 kwh are considered economically then there will be huge losses.Economic rate is 7.28 Rs/unit, so per year directly crores of rupees is going to be wastedwith the power losses.5. MODELING IN SOFTWAREThe accurate analysis of Induction melting furnace refractory wall is done for findingout temperature distribution, heat flow [1]. These conditions include initial and boundaryconditions, material properties and assumptions (if required).5.1 Analysis of existing model of furnaceBased on drawing and dimensions a model of existing furnace is developed usingAPDL Ansys. Problem is symmetric about Y-Axis so for better result and accuracy we canachieve with Axi-symmetric condition. Analysis is done with static thermal analysis becauseof its actual measurement and parameter which is collected at steady state[6]. We have donethree kinds of meshing i.e. course, normal and fine meshing [1]. Then we had selected normalmesh density which gave 25806 nodes and 25181 elements. In FEA, Axi-symmetricmodeling of furnace geometry with the three materials with APDL Ansys for Static thermalanalysis is carried out. All materials were modeled by quad mesh types with smart size 1 forall areas.PLANE55 can be used as a plane element or as an axisymmetric ring element with a2-D thermal conduction capability. The element has four nodes with a single degree offreedom, temperature, at each node. The element is applicable to a 2-D, steady-state ortransient thermal analysis. The element can also compensate for mass transport heat flowfrom a constant velocity field.5.2 Boundary conditionTo solve this heat transfer problem of induction melting furnace wall, the followinginitial and boundary conditions, material properties are made:Ambient Temperature is 40 °C.Apply heat convection over the inner and outer wall.The boundary conditions are introduced into module ANSYS by Choosing thestatic mode of analysis. First of all define the physical dimensions of material andthen thermal properties. At boundary condition the convection at inner and outer wallof the furnace should be applied.
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME423Results of existing induction furnace with the APDL Ansys softwareA. Temperature distribution curve B. Heat flowC. Nodal Thermal flux vector sum D. Element thermal flux vector sumIf we go for very fine meshing or very course meshing accuracy is not obtained. Sonormal mesh density is selected which will give closer value to actual value. Thus mesh density isfound. It was found that meshing does not affect temperature distribution but affected the heatflow and heat flux.5.3 Verification with the analytical resultsIt is needed to verify analytical and software results. Once verification is done we canoptimize the geometry and properties for to minimum heat losses from the induction furnace.Table 5 shows the verification of analytical and software results.Table 5 Analytical and software Result verificationMethod Temperature 0C Heat flow KwhT2 T3 T4Software 436 191 68.92 756.22Analytical 436 265 76 746The verified values of calculated results by using software are closer to actual measured values.6. OPTIMIZATION OF GEOMETRICAL PARAMETER:Induction heating is a complex electromagnetic and heat transfer process because of thetemperature dependency of electromagnetic, electrical, and thermal properties of material as wellas skin effect. The temperature profile of the heated work piece and the energy consumption are
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME424complicated functions and depend on characteristics of the power supply. So it reduces with theoptimum geometry of refractory material.Table 6. Optimum geometrical parameterMaterial Ramming mass Micasil Coil core cement Heat loss kwh Temperature0CThickness in mm 165 3.5 10 757 66.70Thickness in mm 170 3.5 10 649 66.63Thickness in mm 175 3.5 10 478 66.67Thickness in mm 180 3.5 10 493 66.65Thickness in mm 185 3.5 10 506 65.30Results with optimum geometry analyzed in APDL ANSYS softwareA. Temperature distribution curve B. Heat flowC. Nodal thermal flux vector sum D. Elemental thermal flux vector sumOptimization of geometrical parameter is effective to reduce the heat losses, andreduces 35% losses from furnace.Total heat loss calculated with the optimum geometry is 477 kwh. So we have saved260 kwh with 175 mm optimum thickness of the ramming mass.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4257. OPTIMIZATION OF MATERIAL PROPERTIES:Optimization of the geometrical parameter is reducing heat losses up to certain limit,but this is not sufficient because of its huge losses.Table 7 Optimum thermal propertiesAnalysis has done with material optimization of induction furnace. Following are theOptimum result with taking optimum properties drawn in table 7 and with the optimumgeometry.A. Temperature distribution B. Heat flowC. Nodal thermal flux vector sum D. Element thermal flux vector sumMaterial RammingmassMicasil Coil corecementHeat losskwhTemperature0CThermalconductivityw/m 0C3 0.12 1.39 204 433.5 0.12 1.39 226 44.124 0.12 1.39 254 45.594.5 0.12 1.39 273 46.565 0.12 1.39 298 48.105.5 0.12 1.39 316 49.156 0.12 1.39 337 50.85
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME426This analysis shows that, optimization of geometrical parameter as well as materialproperties may help to reduce thermal losses and temperature distribution. With the optimumproperties of ramming mass total losses from furnace are 204 kwh. As compare to thegeometrical optimization, properties optimization is more effective to reduce heat losses fromfurnace and it saves 542 kwh. Ultimately we can reduce 70% losses.Table 8. Result of optimum property and geometryMaterial Optimum Geometry Optimum PropertiesRamming mass 175 mm 3 w/m 0CMicasil 3.5 mm 0.12 w/m0CCoil core cement 10 mm 1.39 w/m 0CHeat flow 477 kwh 271e3 KwhTFVsumNodal 69e3 Kwh 31e3 Kwhelement 73.12 Kwh 33.4e3 KwhThese conditions constitute the initial conditions of our simulation. After having fixedthese parameters8. RESULTS AND DISCUSSIONSFollowing graph shows the effect of optimum geometry on heat losses andtemperature distribution for induction furnace. Effect of increasing in thickness ofrefractory material is reduced heat losses and temperature distribution with 175mmthickness. Following graph shows its behavior against thickness fig 2.Fig 2. Heat loss and temperature distribution profile for optimum thickness ofrefractoryFollowing graph shows the effect of optimum material properties on the heat lossesand temperature distribution for induction furnace. Optimum thermal conductivity has a greateffect in reduction of losses and it reduces temperature distribution. Increasing thermalconductivity affects on temperature and losses from furnace, so it must be as lower aspossible. Fig 3 shows the effect of thermal conductivity on losses and temperaturedistribution of furnace.
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME427Fig 3. Heat loss and temperature distribution profile for optimum properties ofrefractory9. CONCLUSIONIn this paper, the analysis of static thermal behavior of the induction furnace ispresented. The optimization plays an important role to reduce losses and provides a goodtemperature distribution profile.The analysis result shows that, temperature field and heat flow in the process ofmelting decreases. The thermal flux vector sum at nodal and element of the furnace increases.Nowadays, the industrial sector is rapidly growing and produces the high quality metalproducts, electric induction furnaces are great tools for the melting metals and castingapplications. In electric induction furnaces, the optimization is an essential part to preventpower losses and heat distribution from outer wall which may damage the induction coil. So,the extensive emphasis of optimum properties and geometry should be considered to be moreefficient and effective rather than the present geometry. Finally, the general trend studied onthe furnace is that the optimization of ramming mass of electric melting furnace in foundrysectors is an important role for reducing losses.Regarding the calculated results, we can say that they are commonly found in theliterature investigations. It would be interesting to solve the problem in static thermal analysiswith Ansys software. There is need to validate analytical calculation with software results.So from above results we can reduce 73% losses from properties optimization and 35 % bygeometrical optimization. Finally optimum geometry and properties of ramming mass canreduce total 70 % losses with optimum thickness and properties of material of inductionfurnace.REFERENCES1. Prof. N. C. Mehta, Mr. Akash D. Raiyani, Vikas R. Gondalia“ Thermal FatigueAnalysis of Induction Melting Furnace Wall for silica ramming mass”, InternationalJournal of Emerging Technology and Advanced Engineering Website: www.ijetae.com(ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 2, February2013).2. Laszlo Koller, Balazs Novak, “Ridged surface for reducing eddy-current losses inferromagnetic shielding”, Electr Eng (2009) 91:117–124, DOI 10.1007/s00202-009-0124-z.
  11. 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4283. K. C. Bala, “Design Analysis of an Electric Induction Furnace for Melting AluminumScrap” Mechanical Engineering Department, Federal University of Technology Minna,Niger State, Nigeria AU J.T. 9(2): 83-88 (Oct. 2005).4. Hong-Seok Park and Xuan-Phuong Dang, “Optimization of the In-line InductionHeating Process for Hot Forging in Terms of Saving Operating Energy” Internationaljournal of precision engineering and manufacturing vol. 13, no. 7, pp. 1085-10935. M. M. Ahmed, M. Masoud and A. M. El-Sharkawy, “design of a coreless inductionfurnace for melting iron” international conference on communication, computer andpower (icccp09) muscat, february 15-18, 2009.6. Kalinchak, V. I. Sadkovskii, and S. G. Orlovskaya, “Influence of internal response onthe critical conditions of heat and mass transfer of carbon particles” Journal ofEngineering Physics and Thermophysics, Vol. 71, No. 5,1998.7. Maung Thant Zin Win, “design and construction of an induction furnace coolingsystem”, (October, 2003) to the Department of Mechanical Engineering in partialfulfilment of the requirements for the degree of Ph.D. (Mechanical Engineering).8. Prof. D.S. Pavaskar, Prof. S.H. choudhari, “Heat transfer” thirteen edition 5th july 2006Nishant prakashan pune.9. Cherian Paul and Parvathy Venugopal, “Modelling of Interfacial Heat TransferCoefficient and Experimental Verification for Gravity Die Casting of AluminiumAlloys”, International Journal of Mechanical Engineering & Technology (IJMET),Volume 1, Issue 1, 2010, pp. 253 - 274, ISSN Print: 0976 – 6340, ISSN Online: 0976 –6359.10. Dr P.Ravinder Reddy, Dr K.Srihari and Dr S. Raji Reddy, “Combined Heat and MassTransfer in Mhd Three-Dimensional Porous Flow with Periodic Permeability & HeatAbsorption”, International Journal of Mechanical Engineering & Technology (IJMET),Volume 3, Issue 2, 2012, pp. 573 - 593, ISSN Print: 0976 – 6340, ISSN Online: 0976 –6359.