Flow induced vibration of tube bank structures, could has the harmful effects on a system. In the... more Flow induced vibration of tube bank structures, could has the harmful effects on a system. In the current work vibration of cantilever tube in the present of fluid flow is investigated. For this purpose the cantilever tube modeled as a simple mass-spring system. The numerical results are compared with Blevins and Coughran works (J. Fluids eng., vol.131, 2009), for reduced velocity between 5 and 8, the mass ratio of 5.02 and the structural damping ratio of 0.05. Numerical results predict the range of reduced velocity, which the amplitude of vibrations raises, but, the upper branch of amplitude is in lower values than in experimental. Finally variation of amplitude, L C and D C versus time, and vortex shedding are plotted.
The extreme spray water mass flow rate deviation was observed to occur in the middle temperature ... more The extreme spray water mass flow rate deviation was observed to occur in the middle temperature superheater of Sahand 2 Â 325 MW Power Plant utility boiler, which severely affected its economic performance and safe operation. Boilers operating in these conditions led to failure in superheater tubes at the same place for two consecutive times in a three year span. Thus, the failure analysis of superheater tubes by investigating the visual inspection, chemical, scale and creep analysis was carried out. The brittle failure occurred in the superheater tubes after the fuel was changed from natural gas to heavy oil. Failure analysis showed that tubes were suffering from long term overheating which was instigated by high spray water flow rate. In order to rectify the boiler operating conditions, some modifications were applied in the boiler unit 1 and operating parameters on this boiler were compared with boiler unit 2. The results showed that the 8.33% reduction in heating surface area corresponds to 52.84 and 17.80% reduction in spray water mass flow rate for capacities equal to 300 and 260 MW, respectively.
In this study, an inverse algorithm based on the Artificial Neural Networks and the Sequential Fu... more In this study, an inverse algorithm based on the Artificial Neural Networks and the Sequential Function Specification method was successfully applied for estimation of the heat flux absorbed by the locomotive brake disc. The three dimensional direct problem involving turbulent, unsteady and conjugate heat transfer boundary condition is numerically solved for known values of 47 different heat fluxes, and temperature histories of 18 different locations inside the brake disc were obtained. The braking process is experimentally simulated and the experimental data are used to verify the simulation results. Then 39 simulated heat fluxes are utilized to train the ANN and 8 remaining are used to test it. Results showed the ability of the ANN in accurate heat flux estimation. Furthermore, the consequence of changing the number and the locations of temperature sensors on the accuracy of the estimated results has been considered. Finally, the effect of noise on the exact temperature on the heat flux estimation has been investigated.
The main aim of this work is devoted to numerical optimization of fin-pin arrangement in the doub... more The main aim of this work is devoted to numerical optimization of fin-pin arrangement in the double pipe heat exchanger. For this reason, heat exchanger which is used by Sahiti et al. was studied as an initial geometry. Since they did not consider the fin-pin arrangement effects, modification of their model by changing the fin arranges and using the Brent's optimization algorithm based on the thermodynamically design concept, would be useful. In this work by minimizing the entropy generation in constant heat duty per length and constant fins diameters Dand changing the pin's longitudinal (SL) and transversal (ST) distances, better results have beenachieved. Results showed that, in all conditions entropy generation number decreased and consequently leads to reduction in pumping power and manufacturing costs.
Keywords: Brake disc Thermal stress Locomotive The frictional heat generated during braking appli... more Keywords: Brake disc Thermal stress Locomotive The frictional heat generated during braking application can cause several negative effects on the brake system such as brake fade, premature wear, thermal cracks and disk thickness variation. It is then important to determine with precision, the temperature field and thermal stresses of the brake disc. In this study, thermal stress analyses on a ventilated locomotive wheel-mounted brake disc R920K with a three-dimensional model for two cases (the first case considers braking to a standstill; the second case considers braking on a hill and maintaining a constant speed) were investigated. The rate of braking heat generation is calculated using the assumption of uniform pressure distribution at the contact area. Then, thermal stress analyses for each case were performed. Finally, we have found that the maximum thermal stresses occur in the case with an emergency braking in the beginning of the braking process. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i c h m t Please cite this article as: B. Ghadimi, et al., 3D investigation of thermal stresses in a locomotive ventilated brake disc based on a conjugate thermofluid coupling, Int. Commun. Heat Mass Transf. (2013), http://dx.
In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticl... more In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticle mixtures is investigated. The experimental setup was prepared with a smooth horizontal tube as a test section with the length and diameter of 9.5 and 103 mm, respectively, and pure R-600a was applied for evaluating the heat transfer enhancement. Six mixtures containing 1% weight fraction of R-600a/oil with different concentrations of CuO nanoparticles including 0.0, 0.5, 1.0, 1.5, 2.0 and 5.0% weight fraction of R-600a/oil/nanoparticle were used in our study. The mass velocity per cross area was considered at the range of 50-700 kg/m 2 s for low vapor quality (ϕ b 0.25). The results showed that the convective boiling heat transfer coefficient will be increased by increasing the mass fraction of nanoparticles up to 2%, while by increasing the mass fraction of nanoparticles up to 5% the heat transfer coefficient will be reduced.
h i g h l i g h t s < At each time step the local HTC was calculated, and used for disc thermal a... more h i g h l i g h t s < At each time step the local HTC was calculated, and used for disc thermal analysis. < Numerical results compare well with experimental data. < Lagging effect renders no cooling at the beginning of the braking. < Disc surface temperatures increased with increasing braking time, and then decreased.
Flow induced vibration of tube bank structures, could has the harmful effects on a system. In the... more Flow induced vibration of tube bank structures, could has the harmful effects on a system. In the current work vibration of cantilever tube in the present of fluid flow is investigated. For this purpose the cantilever tube modeled as a simple mass-spring system. The numerical results are compared with Blevins and Coughran works (J. Fluids eng., vol.131, 2009), for reduced velocity between 5 and 8, the mass ratio of 5.02 and the structural damping ratio of 0.05. Numerical results predict the range of reduced velocity, which the amplitude of vibrations raises, but, the upper branch of amplitude is in lower values than in experimental. Finally variation of amplitude, L C and D C versus time, and vortex shedding are plotted.
The extreme spray water mass flow rate deviation was observed to occur in the middle temperature ... more The extreme spray water mass flow rate deviation was observed to occur in the middle temperature superheater of Sahand 2 Â 325 MW Power Plant utility boiler, which severely affected its economic performance and safe operation. Boilers operating in these conditions led to failure in superheater tubes at the same place for two consecutive times in a three year span. Thus, the failure analysis of superheater tubes by investigating the visual inspection, chemical, scale and creep analysis was carried out. The brittle failure occurred in the superheater tubes after the fuel was changed from natural gas to heavy oil. Failure analysis showed that tubes were suffering from long term overheating which was instigated by high spray water flow rate. In order to rectify the boiler operating conditions, some modifications were applied in the boiler unit 1 and operating parameters on this boiler were compared with boiler unit 2. The results showed that the 8.33% reduction in heating surface area corresponds to 52.84 and 17.80% reduction in spray water mass flow rate for capacities equal to 300 and 260 MW, respectively.
In this study, an inverse algorithm based on the Artificial Neural Networks and the Sequential Fu... more In this study, an inverse algorithm based on the Artificial Neural Networks and the Sequential Function Specification method was successfully applied for estimation of the heat flux absorbed by the locomotive brake disc. The three dimensional direct problem involving turbulent, unsteady and conjugate heat transfer boundary condition is numerically solved for known values of 47 different heat fluxes, and temperature histories of 18 different locations inside the brake disc were obtained. The braking process is experimentally simulated and the experimental data are used to verify the simulation results. Then 39 simulated heat fluxes are utilized to train the ANN and 8 remaining are used to test it. Results showed the ability of the ANN in accurate heat flux estimation. Furthermore, the consequence of changing the number and the locations of temperature sensors on the accuracy of the estimated results has been considered. Finally, the effect of noise on the exact temperature on the heat flux estimation has been investigated.
The main aim of this work is devoted to numerical optimization of fin-pin arrangement in the doub... more The main aim of this work is devoted to numerical optimization of fin-pin arrangement in the double pipe heat exchanger. For this reason, heat exchanger which is used by Sahiti et al. was studied as an initial geometry. Since they did not consider the fin-pin arrangement effects, modification of their model by changing the fin arranges and using the Brent's optimization algorithm based on the thermodynamically design concept, would be useful. In this work by minimizing the entropy generation in constant heat duty per length and constant fins diameters Dand changing the pin's longitudinal (SL) and transversal (ST) distances, better results have beenachieved. Results showed that, in all conditions entropy generation number decreased and consequently leads to reduction in pumping power and manufacturing costs.
Keywords: Brake disc Thermal stress Locomotive The frictional heat generated during braking appli... more Keywords: Brake disc Thermal stress Locomotive The frictional heat generated during braking application can cause several negative effects on the brake system such as brake fade, premature wear, thermal cracks and disk thickness variation. It is then important to determine with precision, the temperature field and thermal stresses of the brake disc. In this study, thermal stress analyses on a ventilated locomotive wheel-mounted brake disc R920K with a three-dimensional model for two cases (the first case considers braking to a standstill; the second case considers braking on a hill and maintaining a constant speed) were investigated. The rate of braking heat generation is calculated using the assumption of uniform pressure distribution at the contact area. Then, thermal stress analyses for each case were performed. Finally, we have found that the maximum thermal stresses occur in the case with an emergency braking in the beginning of the braking process. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / i c h m t Please cite this article as: B. Ghadimi, et al., 3D investigation of thermal stresses in a locomotive ventilated brake disc based on a conjugate thermofluid coupling, Int. Commun. Heat Mass Transf. (2013), http://dx.
In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticl... more In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticle mixtures is investigated. The experimental setup was prepared with a smooth horizontal tube as a test section with the length and diameter of 9.5 and 103 mm, respectively, and pure R-600a was applied for evaluating the heat transfer enhancement. Six mixtures containing 1% weight fraction of R-600a/oil with different concentrations of CuO nanoparticles including 0.0, 0.5, 1.0, 1.5, 2.0 and 5.0% weight fraction of R-600a/oil/nanoparticle were used in our study. The mass velocity per cross area was considered at the range of 50-700 kg/m 2 s for low vapor quality (ϕ b 0.25). The results showed that the convective boiling heat transfer coefficient will be increased by increasing the mass fraction of nanoparticles up to 2%, while by increasing the mass fraction of nanoparticles up to 5% the heat transfer coefficient will be reduced.
h i g h l i g h t s < At each time step the local HTC was calculated, and used for disc thermal a... more h i g h l i g h t s < At each time step the local HTC was calculated, and used for disc thermal analysis. < Numerical results compare well with experimental data. < Lagging effect renders no cooling at the beginning of the braking. < Disc surface temperatures increased with increasing braking time, and then decreased.
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