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IRJET- Performance Analysis of Automobile Radiator

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IRJET Journal
IRJET Journal

This document analyzes the performance of an automobile radiator at different air velocities. It begins with background on radiator design and operation. Assumptions are made to simplify the heat transfer analysis. Calculations are shown to determine the Nusselt number, heat transfer coefficient, fin efficiency, and overall heat transfer coefficient at varying air velocities and Reynolds numbers. Graphs illustrate trends such as Nusselt number and heat transfer coefficient increasing with Reynolds number. The analysis concludes that the radiator dimensions are suitable and cooling remains effective even at higher vehicle speeds, though fin efficiency decreases slightly with increasing Reynolds number.

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International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 98 Performance Analysis of Automobile Radiator Jeevananth P1, Prithivi Raaj S2, Theyagarajan S3, Vionth Kumar J4 1,2,3Student, Mechanical Engineering, BIT sathyamangalam, Tamil Nadu 4Asst.Professor, Mechanical Engineering, BIT sathyamangalam, Tamil Nadu ---------------------------------------------------------------------***---------------------------------------------------------------------- Abstract - An automobile radiator is a component of an automotive cooling system which plays a major role in transferring the heat fromthe enginepartstotheenvironment through its complex system and working. It is a type of cross flow heat exchanger which is designed to transfer the heat from the hot coolant coming from the engine to the air blown through it by the fan. A small segment of the radiator is analyzed for the various speed of the air striking the radiator as the vehicle moves from its rest position to a certain speed. The heat transfer processes takes placefromthecoolanttothe tubes then from the tubes to the air through the fins. After the analysis is carried out, the heat transfer coefficient of air and ethylene glycol is estimated and further overall heat transfer coefficient is calculated. Key Words: Automobile radiator, velocity, convection, fins, heat transfer coefficients. 1. INTRODUCTION An automobile travels at various ranges of velocities. The faster it travels, the more power engine needs to generate and hence the better the cooling process has to be. The coolant(ethylene glycol) coming from the engine passes through the tubes of the radiator where the heat transfer from the coolant to the surroundingtakesplacethroughheat transfer processes, mainly conductionandconvection.Thus, the velocity of the air striking the radiator becomes a crucial parameter during the cooling phenomenon throughthefins. Oliet et al. [1], studied different factors which influence radiator performance. It includes air and coolant flow, fin density and air inlet temperature. Yadav and Singh [2], in their studies also presented parametric study on automotive radiator. Thevariousparametersincludingmass flow rate of coolant, inlet coolant temperature; etc. are varied. Mazen Al- Amayreh[3],in his study, tested the thermal conductivities of ethylene glycol + water, diethylene glycol + water and triethylene glycol + water mixtures, measured at temperatures ranging from 25°C to 40°C and concentrations ranging from 25 wt. % glycol to 75 wt.% glycol. Trivedi and Vasava [4], illustrated the effect of Tube pitch for best configured radiator for optimum performance. Heat transfer increases as the surface area of the radiator assembly is increased. Chavan and Tasgaonkar [5], explained conventional radiator size is rectangular which is difficult for circular fan to cover whole surfacearea. It creates lower velocity zones at corners giving less heat transfer. Leong et all [6], described use of nanofluid based coolant in engine cooling system and its effect on cooling capacity. It is found that nano-fluid having higher thermal conductivity than base coolant like 50%/50% water and ethylene glycol. John Vetrovec [7], carried work on engine cooling system with heat load averaging capacity using passive heat load accumulator. Salah et all [8], discussed about hydraulic actuated cooling system. Actuators can improve temperature tracking and reduce parasitic losses. Cengel [9], said that the common definition for cross flow heat exchanger is where both hot and cold fluid travel perpendicular to each other. Kishore [10], in his thesis dealt with enhancement of heat transfer for both laminar and turbulent flow conditions and derived the equations for Nusselt number and friction factor. Sarma et al. [11] in their article discussed the momentum effects and heat transfer induced effects in evaluating the correlations for heat transfer and friction factor. They said that the turbulence introduces the need for evaluating the momentum and thermal eddy diffusivities. K.Balanna andP.S.Kishoreintheir paper written about the evaluation of heat transfer and friction factor on wavy fin of an automotive radiator. 2.DESCRIPTIONANDWORKINGOFTHERADIATOR: LINE DIAGRAM OF HEAT TRANSFER THROUGH COOLING SYSTEM The radiator is part of the cooling system of the engine Automobile radiators utilize mostly a cross flow heat exchanger. The two working fluids are generally air and coolant. As the air flows through the radiator, the heat is transferred from the coolant to the air. The purpose of the air is to remove heat from the coolant, which causes the coolant to exit the radiator at a lower temperature than it entered at. Coolant is passed through engine, where it is absorb heat. The hot coolant is then feed into tank of the radiator. From tank of radiator, it is distributed across the radiator core through tubes to another tank on opposite side of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 99 much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The radiator acts as a heat exchanger, transferring excess heat from the engine’s coolant fluid into the air. The radiator is composed of tubes that carry the coolant fluid, a protective cap that’s actually a pressure valve anda tank oneachsideto catch the coolant fluid overflow. In addition, the tubes carrying the coolant fluid usually containa turbulator,which agitates the fluid inside. This way, the coolant fluid is mixed together, cooling all the fluid evenly, and not just cooling the fluid that touches the sides of the tubes. By creating turbulence inside the tubes, the fluid can be used more effectively. RADIATOR CORE GEOMETRY 1) Tube Radiator consists of circular tubes whose diameter is 0.59 cm (air side) and 0.56 cm (coolant side),numberoftubesare arranged in parallel as shown in Fig.1. The fluid circulates through the tubes which take out the heat from the engine cylinder. 2) Wavy Fin Continuous fins of thickness,madeofaluminum is taken 3) Upper and Lower Cover The upper and lower radiator covers are surrounded on top and bottom of radiator 3. THERMAL ANALYSIS OF THE PROBLEM: The performance parameters like heat transfer coefficient and efficiency are to be analyzed for different set ofvalues of velocity of the automobile (i.e., velocity of air) 3.1 ASSUMPTIONS: Heat transfer analysis of a radiator in an automobile radiatorin an automobile engine is done by considering the following assumptions. 1. The radiator operates under steady-state conditions that is constant flow rate and coolant temperatures at the inlet and within the radiator are independent of time. 2. There are no thermal energy sources and sinks in radiator walls or coolant. 3. Either there are no phase changes in the coolantstream flowing through the exchanger 4. The specific heats of ethylene glycol and air are constant throughout the radiator. 5. The fluid flow rate is uniformly distributed through the radiator on each fluid side in each pass. No flow stratification, flow bypassing or flow leakages occur in any stream 6. Kinetic energy and potential energy changes are negligible 3.2 HYDRAULIC DIAMETER: The hydraulic diameter must be used because it is a non- circular cross section. The hydraulic diameter can then be used to estimate the Reynolds number. The equation for the hydraulic diameter calls for the wetted perimeter of the tubes. However, the difference in the outer and inner tube dimensions is so negligible that the outer perimeter is used for convenience. Hydraulic diameter, Dhyd = 4Atube Ptube Where Atube = Area of the radiator tube Ptube = Perimeter of the radiator tube 3.3 NUSSELT NUMBER The Nusselt number was found for a rectangular cross section for fully developed laminar flow. The ratio of width over height of the tube is used. Nueg = 0.023 × Re0.8 × Pr0.4 (2) Where, Dhyd x ρ x v Reg = _______________________ μ Reg = Reynolds number of ethylene glycol Preg = Prandtl number of ethylene glycol EXTERNAL FLOW OF AIR The air flows from the fan across the radiator tubes and through the fins utilizing convective heat transfer. In reality, the flow of air over the tubes will be slightly different due to the fluid flowing around the first tube before reaching the second tube, so calculating the heat transfer coefficient would be very difficult. To simplify the calculations, the flow is assumed to be the same over both tubes. Also, because the height to width ratio of the tubes is so small, the air will be assumed to be flowing on both sides of a flat plate. (1)
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 100 3.4 VELOCITY Qair Vair = _____________________________________ (3) Aradiator – Ntube Htube Lradiator Here, Qair = Total air volumetric flow rate Aradiator = Area of the radiator Ntube = Number of tubes Htube = Height of the tube Lradiator = Length of the radiator 3.5 REYNOLDS NUMBER Vair Wfin Reair = __________________ (4) νair Here, Vair = Velocity of air WFIN = Width of the fin νair = Kinematic viscosity of air 3.6 NUSSELT NUMBER Looking at the geometry of the tubes, it can be assumed that the flow of air is similar to parallel flow over a flat plate. Since the flow never reaches the critical Reynolds number for a flat plate, Re = 0.5x10⁶, it is said to be laminar for the entire process. 1 1 2 3 Nuair = .664 Reair Prair (5) Where Reair = Reynolds number of air Prair = Prandtl number of air 3.7 CONVECTIVE HEAT TRANSFER COEFFICIENT Nuair x kair FOR AIR FLOW hair = _______________________ (6) Wtube Where, Nuair = Nusselt number of air kair = Thermal conductivity of air Wtube = Width of thetube 3.8 FIN DIMENSIONS AND EFFICIENCY The geometry of the fins on the radiator is sinusoidal. The troughs of the fins touch the lower adjacent tube and the peaks of the fins touch the upper adjacent tube. The heat from the tubes emanates through the fins. Thefinsandtubes are then cooled by the air from the fan, which is traveling across the radiator. To simplify the geometry for the ease of calculations, the fins are assumed to be straight instead of sinusoidal. This is a minor transition in geometry since the shape and position of the actual fins are so close to the straight configuration. The following formulas are given below to calculate the fin efficiency tanh ⁡(m Lc ) ɳfin = _______________ m Lc Where, Lc = Characterstic length of the fin 4. RESULTS AND DISCUSSIONS: Graphs are drawn between different parameters from the values that we derive from the calculations 4.1 NUSSELT NUMBER OF AIR vs REYNOLDS NUMBER OF THE The graph is plotted between Nusselt number on Y-axis and Reynolds number of air on X-axis. The graph clearly shows that as the Reynolds number of the air increases the Nusselt number also increases Reynolds number of air 100000500000 200 150 100 50 0
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 101 4.2 HEAT TRANSFER COEFFICIENT OF AIR vs VELOCITY OF AIR In the graph, Heat transfer coefficient of air (W/m2k) is plotted against velocity of air (kmph). 4.3 EFFICIENCY OF THE FINS vs. REYNOLDS NUMBER OF THE AIR The graph shows the variation of efficiency of the fins with the Reynolds number of the air that strikes the radiator at different velocities. When an automobile travels at a very faster rate, huge amount of heat is generated in the engine and its parts. The fins used in the radiator play a crucial role in helping the radiator to dissipate the heat. As we can see from the graph with increase in Reynolds number the efficiency of the fins decreases, but the decrement is very small and it is still very useful for the cooling of the radiator. 4.4 OVERALL HEAT TRANSFER COEFFICIENT vs REYNOLDS NUMBER OF AIR A graph is plotted between overall heat transfer coefficient and Reynolds number on. From the graph, it is seen clearly that the value of overall heat transfer coefficientincreases as the Reynolds number increases. Overall heat transfer coefficient depends upon the heat transfer coefficient of the air and the coolant used (ethylene glycol). 5. CONCLUSIONS Heat transfer analysis of an automobile radiator is done for the range of 15 kmph to 75 kmph speed of the air striking the radiator with ethylene glycol as coolant and conclusions obtained are as follows: 1. Nusselt number of the air is calculated, as the Reynolds number of the air increases, the value of Nusselt number increases from 69 % to 125 %. 2. The heat transfer coefficient values areincreasedby 125 % when the velocity of the air striking the radiator changes. 3. It is also observed that, at higher velocity of air striking the radiator, the Reynoldsnumberishigher and as a result of it the efficiency of the fins is reduced slightly. Efficiency of the fins reduces by 6.1% when the Reynolds number changes from 14000 to 71000. 4. Overall heat transfer coefficient is the function of the heat transfer coefficient of the air as well as the coolant used (ethylene glycol). As the Reynolds number increases from 14000 to 71000, there is 91 % increase in the overall heat transfer coefficient. 5. When engines run at high values of rpm to increase the speed of the vehicle, the heat generated in the parts of the engine also increasesdrastically.Hence, at higher speed the cooling process should also be effective in order to dissipate the heat to the atmosphere. It can concluded by this analysis that, even at higher speed the given dimensioned radiator with given number of fins attached to it works properly with slight compromise in the decrease in efficiency of the fins used in the radiator. 6. NOMENCLATURE L Lemgth, m H Height, m W Width, m D Diameter, m A Cross-sectional area, m2 P Perimeter, m V Velocity, m/s Q Volumetric flow rate, m3/s N Number Re Reynolds number h Convective heat transfer coefficient, W/m2-K Nu Nusselt number k Thermal conductivity, W/m-K Pr Prandtl number m Coefficient for calculating efficiency UA Overall heat transfer coefficient Reynolds number 20000 40000 60000 800000 96 94 92 90 88 150 100 50 0 0 20000 40000 60000 80000 Reynolds number of air Overallheattransfer coeffecient
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 102 6.1 GREEK SYMBOLS μ Dynamic viscosity ν Kinematic viscosity ɳ Efficiency 6.2 SUFFIXES eg Ethylene glycol f Fin b Base hyd Hydraulic rad Radiator REFERENCES 1. C. Oliet, A. Oliva, J. Castro, C.D. Pe rezSegarra, ―Parametric Studies on Automotive Radiators‖, Applied Thermal Engineering, 27,2007 2. JP Yadav and Bharat Raj Singh, ―Study on Performance Evaluation of Automotive Radiator‖, S- JPSET : ISSN : 2229-7111, Vol. 2, Issue 2, 2011 3. Mazen Al-Amayreh, ―Experimental Study of Thermal Conductivity of Ethylene Glycol Water Mixtures‖, European Journal of Scientific Research, Vol.44 No.2, 2011 4. P. K. Trivedi, N. B. Vasava, ―Effect of Variation in Pitch of Tube on Heat Transfer Rate in Automobile Radiator by CFD Analysis‖, International Journal of Engineering and Advanced Technology (IJEAT)ISSN: 2249 –8958, Volume-1, Issue-6, 2012 5. Prof. D. K. Chavan, Prof. Dr. G. S. Tasgaonkar, ―Thermal Optimization of Fan Assisted Heat Exchanger (Radiator) by Design Improvements‖, International Journal of Modern Engineering Research (IJMER),Vol.1, Issue 1, 2011 6. K.Y. Leong, R. Saidur, S.N. Kazi, A.H. Mamun, ―Performance Investigation of an Automotive Car Radiator Operated with Nanofluid-Based Coolants (Nanofluid as a Coolant in a Radiator)‖, AppliedThermal Engineering,30,2010 7. John Vetrovec, ―Engine Cooling System with a Heat Load Averaging Capability‖, SAE International, 2008 8. M.H. Salah, P.M.Frick, J.R.Wagner, D.M.Dawson, ―Hydraulic Actuated Automotive Cooling Systems— Nonlinear Control and Test‖, Control Engineering Practice, 17, 2009 9. Y.A.Cengel, Heat Transfer , Tata Mcgraw- Hill publications, New Delhi, 2011 10. P.S. Kishore, Experimental and theoretical studies of convective momentum and heat transferintubes with twisted tape inserts, Ph.D. Thesis, Andhra University,Visakhapatnam, India, 2001. 11. P.K.Sarma, C.Kedarnath, V.Dharma Rao, P.S.Kishore, T.Subrahmanyam and A.E.Bergles, ―Evaluation of Momentum and Thermal Eddy Diffusivities for Turbulent Flow in Tubes‖, Published in International Journal of Heat and Mass Transfer, Vol.53, Issues 5-6, pp. 1237- 1242, Feb., 2010. 12. Evaluation of Heat Transfer and Friction Factor on Wavy Fin Automotive Radiator (IJSRD/Vol. 3/Issue 08/2015/037)

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IRJET- Performance Analysis of Automobile Radiator

  • 1. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 98 Performance Analysis of Automobile Radiator Jeevananth P1, Prithivi Raaj S2, Theyagarajan S3, Vionth Kumar J4 1,2,3Student, Mechanical Engineering, BIT sathyamangalam, Tamil Nadu 4Asst.Professor, Mechanical Engineering, BIT sathyamangalam, Tamil Nadu ---------------------------------------------------------------------***---------------------------------------------------------------------- Abstract - An automobile radiator is a component of an automotive cooling system which plays a major role in transferring the heat fromthe enginepartstotheenvironment through its complex system and working. It is a type of cross flow heat exchanger which is designed to transfer the heat from the hot coolant coming from the engine to the air blown through it by the fan. A small segment of the radiator is analyzed for the various speed of the air striking the radiator as the vehicle moves from its rest position to a certain speed. The heat transfer processes takes placefromthecoolanttothe tubes then from the tubes to the air through the fins. After the analysis is carried out, the heat transfer coefficient of air and ethylene glycol is estimated and further overall heat transfer coefficient is calculated. Key Words: Automobile radiator, velocity, convection, fins, heat transfer coefficients. 1. INTRODUCTION An automobile travels at various ranges of velocities. The faster it travels, the more power engine needs to generate and hence the better the cooling process has to be. The coolant(ethylene glycol) coming from the engine passes through the tubes of the radiator where the heat transfer from the coolant to the surroundingtakesplacethroughheat transfer processes, mainly conductionandconvection.Thus, the velocity of the air striking the radiator becomes a crucial parameter during the cooling phenomenon throughthefins. Oliet et al. [1], studied different factors which influence radiator performance. It includes air and coolant flow, fin density and air inlet temperature. Yadav and Singh [2], in their studies also presented parametric study on automotive radiator. Thevariousparametersincludingmass flow rate of coolant, inlet coolant temperature; etc. are varied. Mazen Al- Amayreh[3],in his study, tested the thermal conductivities of ethylene glycol + water, diethylene glycol + water and triethylene glycol + water mixtures, measured at temperatures ranging from 25°C to 40°C and concentrations ranging from 25 wt. % glycol to 75 wt.% glycol. Trivedi and Vasava [4], illustrated the effect of Tube pitch for best configured radiator for optimum performance. Heat transfer increases as the surface area of the radiator assembly is increased. Chavan and Tasgaonkar [5], explained conventional radiator size is rectangular which is difficult for circular fan to cover whole surfacearea. It creates lower velocity zones at corners giving less heat transfer. Leong et all [6], described use of nanofluid based coolant in engine cooling system and its effect on cooling capacity. It is found that nano-fluid having higher thermal conductivity than base coolant like 50%/50% water and ethylene glycol. John Vetrovec [7], carried work on engine cooling system with heat load averaging capacity using passive heat load accumulator. Salah et all [8], discussed about hydraulic actuated cooling system. Actuators can improve temperature tracking and reduce parasitic losses. Cengel [9], said that the common definition for cross flow heat exchanger is where both hot and cold fluid travel perpendicular to each other. Kishore [10], in his thesis dealt with enhancement of heat transfer for both laminar and turbulent flow conditions and derived the equations for Nusselt number and friction factor. Sarma et al. [11] in their article discussed the momentum effects and heat transfer induced effects in evaluating the correlations for heat transfer and friction factor. They said that the turbulence introduces the need for evaluating the momentum and thermal eddy diffusivities. K.Balanna andP.S.Kishoreintheir paper written about the evaluation of heat transfer and friction factor on wavy fin of an automotive radiator. 2.DESCRIPTIONANDWORKINGOFTHERADIATOR: LINE DIAGRAM OF HEAT TRANSFER THROUGH COOLING SYSTEM The radiator is part of the cooling system of the engine Automobile radiators utilize mostly a cross flow heat exchanger. The two working fluids are generally air and coolant. As the air flows through the radiator, the heat is transferred from the coolant to the air. The purpose of the air is to remove heat from the coolant, which causes the coolant to exit the radiator at a lower temperature than it entered at. Coolant is passed through engine, where it is absorb heat. The hot coolant is then feed into tank of the radiator. From tank of radiator, it is distributed across the radiator core through tubes to another tank on opposite side of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers
  • 2. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 99 much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The radiator acts as a heat exchanger, transferring excess heat from the engine’s coolant fluid into the air. The radiator is composed of tubes that carry the coolant fluid, a protective cap that’s actually a pressure valve anda tank oneachsideto catch the coolant fluid overflow. In addition, the tubes carrying the coolant fluid usually containa turbulator,which agitates the fluid inside. This way, the coolant fluid is mixed together, cooling all the fluid evenly, and not just cooling the fluid that touches the sides of the tubes. By creating turbulence inside the tubes, the fluid can be used more effectively. RADIATOR CORE GEOMETRY 1) Tube Radiator consists of circular tubes whose diameter is 0.59 cm (air side) and 0.56 cm (coolant side),numberoftubesare arranged in parallel as shown in Fig.1. The fluid circulates through the tubes which take out the heat from the engine cylinder. 2) Wavy Fin Continuous fins of thickness,madeofaluminum is taken 3) Upper and Lower Cover The upper and lower radiator covers are surrounded on top and bottom of radiator 3. THERMAL ANALYSIS OF THE PROBLEM: The performance parameters like heat transfer coefficient and efficiency are to be analyzed for different set ofvalues of velocity of the automobile (i.e., velocity of air) 3.1 ASSUMPTIONS: Heat transfer analysis of a radiator in an automobile radiatorin an automobile engine is done by considering the following assumptions. 1. The radiator operates under steady-state conditions that is constant flow rate and coolant temperatures at the inlet and within the radiator are independent of time. 2. There are no thermal energy sources and sinks in radiator walls or coolant. 3. Either there are no phase changes in the coolantstream flowing through the exchanger 4. The specific heats of ethylene glycol and air are constant throughout the radiator. 5. The fluid flow rate is uniformly distributed through the radiator on each fluid side in each pass. No flow stratification, flow bypassing or flow leakages occur in any stream 6. Kinetic energy and potential energy changes are negligible 3.2 HYDRAULIC DIAMETER: The hydraulic diameter must be used because it is a non- circular cross section. The hydraulic diameter can then be used to estimate the Reynolds number. The equation for the hydraulic diameter calls for the wetted perimeter of the tubes. However, the difference in the outer and inner tube dimensions is so negligible that the outer perimeter is used for convenience. Hydraulic diameter, Dhyd = 4Atube Ptube Where Atube = Area of the radiator tube Ptube = Perimeter of the radiator tube 3.3 NUSSELT NUMBER The Nusselt number was found for a rectangular cross section for fully developed laminar flow. The ratio of width over height of the tube is used. Nueg = 0.023 × Re0.8 × Pr0.4 (2) Where, Dhyd x ρ x v Reg = _______________________ μ Reg = Reynolds number of ethylene glycol Preg = Prandtl number of ethylene glycol EXTERNAL FLOW OF AIR The air flows from the fan across the radiator tubes and through the fins utilizing convective heat transfer. In reality, the flow of air over the tubes will be slightly different due to the fluid flowing around the first tube before reaching the second tube, so calculating the heat transfer coefficient would be very difficult. To simplify the calculations, the flow is assumed to be the same over both tubes. Also, because the height to width ratio of the tubes is so small, the air will be assumed to be flowing on both sides of a flat plate. (1)
  • 3. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 100 3.4 VELOCITY Qair Vair = _____________________________________ (3) Aradiator – Ntube Htube Lradiator Here, Qair = Total air volumetric flow rate Aradiator = Area of the radiator Ntube = Number of tubes Htube = Height of the tube Lradiator = Length of the radiator 3.5 REYNOLDS NUMBER Vair Wfin Reair = __________________ (4) νair Here, Vair = Velocity of air WFIN = Width of the fin νair = Kinematic viscosity of air 3.6 NUSSELT NUMBER Looking at the geometry of the tubes, it can be assumed that the flow of air is similar to parallel flow over a flat plate. Since the flow never reaches the critical Reynolds number for a flat plate, Re = 0.5x10⁶, it is said to be laminar for the entire process. 1 1 2 3 Nuair = .664 Reair Prair (5) Where Reair = Reynolds number of air Prair = Prandtl number of air 3.7 CONVECTIVE HEAT TRANSFER COEFFICIENT Nuair x kair FOR AIR FLOW hair = _______________________ (6) Wtube Where, Nuair = Nusselt number of air kair = Thermal conductivity of air Wtube = Width of thetube 3.8 FIN DIMENSIONS AND EFFICIENCY The geometry of the fins on the radiator is sinusoidal. The troughs of the fins touch the lower adjacent tube and the peaks of the fins touch the upper adjacent tube. The heat from the tubes emanates through the fins. Thefinsandtubes are then cooled by the air from the fan, which is traveling across the radiator. To simplify the geometry for the ease of calculations, the fins are assumed to be straight instead of sinusoidal. This is a minor transition in geometry since the shape and position of the actual fins are so close to the straight configuration. The following formulas are given below to calculate the fin efficiency tanh ⁡(m Lc ) ɳfin = _______________ m Lc Where, Lc = Characterstic length of the fin 4. RESULTS AND DISCUSSIONS: Graphs are drawn between different parameters from the values that we derive from the calculations 4.1 NUSSELT NUMBER OF AIR vs REYNOLDS NUMBER OF THE The graph is plotted between Nusselt number on Y-axis and Reynolds number of air on X-axis. The graph clearly shows that as the Reynolds number of the air increases the Nusselt number also increases Reynolds number of air 100000500000 200 150 100 50 0
  • 4. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 101 4.2 HEAT TRANSFER COEFFICIENT OF AIR vs VELOCITY OF AIR In the graph, Heat transfer coefficient of air (W/m2k) is plotted against velocity of air (kmph). 4.3 EFFICIENCY OF THE FINS vs. REYNOLDS NUMBER OF THE AIR The graph shows the variation of efficiency of the fins with the Reynolds number of the air that strikes the radiator at different velocities. When an automobile travels at a very faster rate, huge amount of heat is generated in the engine and its parts. The fins used in the radiator play a crucial role in helping the radiator to dissipate the heat. As we can see from the graph with increase in Reynolds number the efficiency of the fins decreases, but the decrement is very small and it is still very useful for the cooling of the radiator. 4.4 OVERALL HEAT TRANSFER COEFFICIENT vs REYNOLDS NUMBER OF AIR A graph is plotted between overall heat transfer coefficient and Reynolds number on. From the graph, it is seen clearly that the value of overall heat transfer coefficientincreases as the Reynolds number increases. Overall heat transfer coefficient depends upon the heat transfer coefficient of the air and the coolant used (ethylene glycol). 5. CONCLUSIONS Heat transfer analysis of an automobile radiator is done for the range of 15 kmph to 75 kmph speed of the air striking the radiator with ethylene glycol as coolant and conclusions obtained are as follows: 1. Nusselt number of the air is calculated, as the Reynolds number of the air increases, the value of Nusselt number increases from 69 % to 125 %. 2. The heat transfer coefficient values areincreasedby 125 % when the velocity of the air striking the radiator changes. 3. It is also observed that, at higher velocity of air striking the radiator, the Reynoldsnumberishigher and as a result of it the efficiency of the fins is reduced slightly. Efficiency of the fins reduces by 6.1% when the Reynolds number changes from 14000 to 71000. 4. Overall heat transfer coefficient is the function of the heat transfer coefficient of the air as well as the coolant used (ethylene glycol). As the Reynolds number increases from 14000 to 71000, there is 91 % increase in the overall heat transfer coefficient. 5. When engines run at high values of rpm to increase the speed of the vehicle, the heat generated in the parts of the engine also increasesdrastically.Hence, at higher speed the cooling process should also be effective in order to dissipate the heat to the atmosphere. It can concluded by this analysis that, even at higher speed the given dimensioned radiator with given number of fins attached to it works properly with slight compromise in the decrease in efficiency of the fins used in the radiator. 6. NOMENCLATURE L Lemgth, m H Height, m W Width, m D Diameter, m A Cross-sectional area, m2 P Perimeter, m V Velocity, m/s Q Volumetric flow rate, m3/s N Number Re Reynolds number h Convective heat transfer coefficient, W/m2-K Nu Nusselt number k Thermal conductivity, W/m-K Pr Prandtl number m Coefficient for calculating efficiency UA Overall heat transfer coefficient Reynolds number 20000 40000 60000 800000 96 94 92 90 88 150 100 50 0 0 20000 40000 60000 80000 Reynolds number of air Overallheattransfer coeffecient
  • 5. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 102 6.1 GREEK SYMBOLS μ Dynamic viscosity ν Kinematic viscosity ɳ Efficiency 6.2 SUFFIXES eg Ethylene glycol f Fin b Base hyd Hydraulic rad Radiator REFERENCES 1. C. Oliet, A. Oliva, J. Castro, C.D. Pe rezSegarra, ―Parametric Studies on Automotive Radiators‖, Applied Thermal Engineering, 27,2007 2. JP Yadav and Bharat Raj Singh, ―Study on Performance Evaluation of Automotive Radiator‖, S- JPSET : ISSN : 2229-7111, Vol. 2, Issue 2, 2011 3. Mazen Al-Amayreh, ―Experimental Study of Thermal Conductivity of Ethylene Glycol Water Mixtures‖, European Journal of Scientific Research, Vol.44 No.2, 2011 4. P. K. Trivedi, N. B. Vasava, ―Effect of Variation in Pitch of Tube on Heat Transfer Rate in Automobile Radiator by CFD Analysis‖, International Journal of Engineering and Advanced Technology (IJEAT)ISSN: 2249 –8958, Volume-1, Issue-6, 2012 5. Prof. D. K. Chavan, Prof. Dr. G. S. Tasgaonkar, ―Thermal Optimization of Fan Assisted Heat Exchanger (Radiator) by Design Improvements‖, International Journal of Modern Engineering Research (IJMER),Vol.1, Issue 1, 2011 6. K.Y. Leong, R. Saidur, S.N. Kazi, A.H. Mamun, ―Performance Investigation of an Automotive Car Radiator Operated with Nanofluid-Based Coolants (Nanofluid as a Coolant in a Radiator)‖, AppliedThermal Engineering,30,2010 7. John Vetrovec, ―Engine Cooling System with a Heat Load Averaging Capability‖, SAE International, 2008 8. M.H. Salah, P.M.Frick, J.R.Wagner, D.M.Dawson, ―Hydraulic Actuated Automotive Cooling Systems— Nonlinear Control and Test‖, Control Engineering Practice, 17, 2009 9. Y.A.Cengel, Heat Transfer , Tata Mcgraw- Hill publications, New Delhi, 2011 10. P.S. Kishore, Experimental and theoretical studies of convective momentum and heat transferintubes with twisted tape inserts, Ph.D. Thesis, Andhra University,Visakhapatnam, India, 2001. 11. P.K.Sarma, C.Kedarnath, V.Dharma Rao, P.S.Kishore, T.Subrahmanyam and A.E.Bergles, ―Evaluation of Momentum and Thermal Eddy Diffusivities for Turbulent Flow in Tubes‖, Published in International Journal of Heat and Mass Transfer, Vol.53, Issues 5-6, pp. 1237- 1242, Feb., 2010. 12. Evaluation of Heat Transfer and Friction Factor on Wavy Fin Automotive Radiator (IJSRD/Vol. 3/Issue 08/2015/037)