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S S Mohapatra - One of the best experts on this subject based on the ideXlab platform.
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High Mass Flux spray quenching on an inclined surface a novel methodology for the attainment of enhanced uniform cooling with unaltered surface morphology in transition boiling regime
International Journal of Heat and Mass Transfer, 2019Co-Authors: A R Pati, Anita Panda, S S Mohapatra, Ajit Behera, Basudeb Munshi, Biswajit SahaAbstract:Abstract The main obligation in the successful implementation of ultra-fast cooling in a manufacturing process are: (1) significant minimization of film boiling effect, (2) achievement of unaltered surface morphology and (3) uniform cooling on the surface of the plate. The literature does not reveal any methodology, which depicts simultaneously enhancement, unaltered surface morphology and uniform cooling. Therefore, in the current work, an attempt has been made to develop an appropriate cooling process depicting all the aforesaid requirements. The cooling on an inclined condition of the plate mitigates the aforesaid requirements. The result reveals that the heat removal rate enhances (CHF from 1.21 MW/m2 to 1.46 MW/m2) due to augmentation of sweeping rate of vapor film from the hot surface as inclination angle increases from 0° to 30°. Further increase of the inclination from 30° to 60° decreases the cooling rate due to reduction of droplet velocity, residence time and the replacement rate of the vapor and liquid layers. The optimum inclination of the plate to achieve the maximum average surface heat Flux is 30°. In addition, the temperature distribution on the surface and across the thickness of the heat treated plate confirms uniform cooling. The SEM image and the EDS of the current heat treated metal is compared with the SEM images and EDS data of the metals cooled by potential coolants such as surfactant added water, NaCl added water and MgSO4 added water and the comparison clearly asserts unaltered surface morphology for the current case. The variation of the hardness on the surface and across the thickness clearly asserts the excellent shock absorbing characteristics.
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upward and downward facing High Mass Flux spray cooling with additives a novel technique to enhance the heat removal rate at High initial surface temperature
Heat and Mass Transfer, 2018Co-Authors: A R Pati, Aditya Kumar, S S MohapatraAbstract:The objective of the current work is to enhance the spray cooling by changing the orientation of the nozzle with different additives (acetone, methanol, ethanol, benzene, n-hexane, tween 20 and salt) in water. The experiments are carried out by upward, downward and both upward and downward facing sprays. The optimization result depicts that the spray produced by upward facing spray gives Higher heat Flux than the downward facing spray and also cooling by both the upward and downward facing spray simultaneously produces better result than the individual. Further experiments with both upward and downward facing spray by using different coolants reveal that in case of cooling by ethanol (500 ppm) + water mixture, the maximum enhancement of surface heat Flux (~2.57 MW/m2) and cooling rate (204 °C/s) is observed. However, the minimum surface heat Flux is achieved in case of methanol (100 ppm) + water due to Higher contact angle (710) among all the considered coolants.
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High Mass Flux air atomized spray with subcooled water a novel methodology to enhance the heat transfer rate in film boiling regime
International Journal of Heat and Mass Transfer, 2018Co-Authors: Anita Panda, A R Pati, S Pradhan, Biswajit Saha, Aditya Kumar, S S MohapatraAbstract:Abstract The main challenging tasks in the successful implementation of ultrafast cooling in the manufacturing process are significant reduction of Leidenfrost effect and achievement of unaltered surface morphology. The literature does not reveal any methodology depicting the aforesaid two characteristics and therefore, in the current work, an attempt has been made to develop a cooling process describing the above mentioned characteristics. In the proposed methodology, by using subcooled water as a coolant in case of High Mass Flux air atomized spray, the heat transfer rate is significantly enhanced without altering the surface morphology. The High Mass Flux subcooled water atomized spray augments the heat transfer rate by reducing the stability of the vapour film separating the coolant from the hot plate. The cooling ability of the subcooled water atomized spray is compared with the coolants, which depict significant enhancement, and the comparison confirms the suitability of the current process for the fast cooling operation. For the experimental investigation, air atomized spray cooling was conducted at 1000 °C initial surface temperature on a 6 mm thick AISI 304 steel plate by using subcooled water as a coolant. The surface heat Flux and surface temperatures are predicted by using the solution of inverse heat conduction problem (IHCP). For the understanding of heat transfer mechanism, the thermal properties, physical properties and spray properties at different conditions of air-atomized spray were analysed. The percentage of enhancement in initial heat Flux (qIHF) is found to be almost 60% of water temperature at 15 °C and this shows the appropriateness of the process for the fast cooling operations. The heat transfer analysis illustrates that the cooling rate achieved for water temperature of 15 °C is found to be almost three times of that corresponding to 50 °C. In addition to the above, the comparison of the morphologies between the heat-treated and the untreated substrate corroborates zero deposition of coolant after cooling. The effects of air flow rate and spray impingement density on the cooling rate are investigated. With the increasing airflow rate up to 30 m3/h, the heat transfer rate rises and thereafter, further increment declines the heat transfer rate.
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enhancement of heat removal rate of High Mass Flux spray cooling by sea water
Experimental Thermal and Fluid Science, 2017Co-Authors: A R Pati, Basudeb Munshi, A P Behera, S S MohapatraAbstract:Abstract The main obligation in achieving High cooling rates in case of spray cooling at High surface temperature is the occurrence of film boiling phenomenon. Although the High Mass Flux spray reduces the film boiling affect, still, the heat transfer rate is not significant and hence, this process needs to be enhanced. In the absence of any information on the heat transfer augmentation technique, the present work deals with the enhancement of High Mass Flux spray cooling at very High initial plate temperature by using sea water. The sea water spray cooling process increases the heat removal rate by creating High heat transfer area for the droplet evaporation and by reducing the vapour pressure of vapour film on the hot plate. The cooling ability of the sea water spray is compared with the coolants (salt added water, surfactant added water and surfactant and salt added water) which partially depict the properties of sea water. For the experimental investigation, spray cooling was conducted at 900 °C initial surface temperature on a 6 mm thick AISI 304 steel plate (100 × 100 mm) by using sea water and also aforesaid coolants at different concentrations. The surface heat Flux and surface temperature have been predicted using the solution of the Inverse Heat Conduction Problem (IHCP). For the understanding of heat transfer mechanism, the properties of coolants (contact angle, thermal conductivity, density, specific heat and Mass diffusivity) at different concentrations and spray behaviour (droplet diameter, spray pressure, droplet velocity and spray impingement density) at different flow rates were measured. The physical properties of the coolant reveal that the contact angle decreases with the increasing salt concentration up to 0.1 M and further increment in salt concentration enhances the contact angle. From the thermal properties of the coolant, it is observed that thermal diffusivity in sea water is Higher than salt added water. The sea water spray cooling asserts that the heat removal rate increases with the increasing percentage of sea water in the mixture of seawater and pure water due to the salt deposition on the hot surface. However, the achieved heat removal rate is lower than that of salt added water due to the comparatively less amount of salt deposition in case of sea water spray. Furthermore, the combined effect of the salt deposition and lowering of vapour pressure in vapour film phenomena produce better heat removal rate than the pure water and surfactant and salt added water. In comparison between sea water and surfactant added water spray cooling, the former produces Higher heat removal rate because of the dominance of salt deposition phenomenon over the lowering of contact angle property. In case of sea water spray, the achieved critical heat Flux (1.55 MW/m 2 ) is 1.3 times that of pure water (1.2 MW/m 2 ); moreover, the enhanced critical heat Flux is obtained at 170 °C Higher surface temperatures. In addition to the above, the enhancement by NaCl added water spray is almost 1.6 times that of pure water. Due to the above mentioned favourable conditions for the fast cooling, the maximum cooling rates of 115 °C/s and 135 °C/s are achieved with sea water and NaCl added water sprays, respectively.
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enhancement of heat transfer rate of High Mass Flux spray cooling by ethanol water and ethanol tween20 water solution at very High initial surface temperature
International Journal of Heat and Mass Transfer, 2017Co-Authors: N H Bhatt, A R Pati, Aditya Kumar, Basudeb Munshi, R Raj, Priya Varshney, D Chouhan, S S MohapatraAbstract:•Obligations in achieving High cooling rates by spray cooling are overcome.•Heat removal is enhanced by spray cooling with coolants-ethanol and tween20 in water.•Achieved CHF with Tween 20-ethanol-water mixture is 1.6 times Higher than pure water.•Maximum obtained cooling rate is 141°C/s in case of ethanol-water-Tween 20 mixture.
Somchai Wongwises - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the modeling of condensation heat transfer coefficients in High Mass Flux region of refrigerant hfc 134a inside the vertical smooth tube in annular flow regime
Heat Transfer Engineering, 2011Co-Authors: Ahmet Selim Dalkilic, Somchai WongwisesAbstract:This article presents an experimental investigation on the co-current downward condensation of R134a in a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. Condensation experiments are done at Mass Fluxes varying between 260 and 515 kg/m2-s. The condensing temperatures are 40°C and 50°C; heat Fluxes are between 10.16 and 66.61 kW/m2. The quality of the refrigerant in the test section is calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section is directly measured by a differential pressure transducer. The average experimental heat transfer coefficient of the refrigerant is calculated by applying an energy balance based on the energy transferred from the test section. The average predicted heat transfer coefficient of the refrigerant is determined by means of the model of Kosky and Staub, and Von Karman universal velocity distribution correlations using different interfacial shear stress equations valid for...
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experimental analysis for the determination of the convective heat transfer coefficient by measuring pressure drop directly during annular condensation flow of r134a in a vertical smooth tube
International Journal of Heat and Mass Transfer, 2011Co-Authors: Ahmet Selim Dalkilic, Ismail Teke, Somchai WongwisesAbstract:Abstract This study investigated the direct relationship between the measured condensation pressure drop and convective heat transfer coefficient of R134a flowing downward inside a vertical smooth copper tube having an inner diameter of 8.1 mm and a length of 500 mm during annular flow. R134a and water were used as working fluids on the tube side and annular side of a double tube heat exchanger, respectively. Condensation experiments were performed at Mass Fluxes of 260, 300, 340, 400, 456 and 515 kg m −2 s −1 in the High Mass Flux region of R134a. The condensing temperatures were around 40 and 50 °C; the heat Fluxes were between 10.16 and 66.61 kW m −2 . Paliwoda’s analysis, which focused mainly on the determination of the two-phase flow factor and two-phase length of evaporators and condensers, was adapted to the in-tube condensation phenomena in the test section to determine the condensation heat transfer coefficient, heat Flux, two-phase length and pressure drop experimentally by means of a large number of data points obtained under various experimental conditions.
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an investigation of a model of the flow pattern transition mechanism in relation to the identification of annular flow of r134a in a vertical tube using various void fraction models and flow regime maps
Experimental Thermal and Fluid Science, 2010Co-Authors: Ahmet Selim Dalkilic, Somchai WongwisesAbstract:In the present study, new experimental data are presented for literature on the prediction of film thickness and identification of flow regime during the co-current downward condensation in a vertical smooth copper tube having an inner diameter of 8.1 mm and a length of 500 mm. R134a and water are used as working fluids in the tube side and annular side of a double tube heat exchanger, respectively. Condensation experiments are done at Mass Fluxes of 300 and 515 kg m{sup -2} s{sup -1}. The condensing temperatures are between 40 and 50 C; heat Fluxes are between 12.65 and 66.61 kW m{sup -2}. The average experimental heat transfer coefficient of the refrigerant HFC-134a is calculated by applying an energy balance based on the energy transferred from the test section. A mathematical model by Barnea et al. based on the momentum balance of liquid and vapor phases is used to determine the condensation film thickness of R134a. The comparative film thickness values are determined indirectly using relevant measured data together with various void fraction models and correlations reported in the open literature. The effects of heat Flux, Mass Flux, and condensation temperature on the film thickness and condensation heat transfer coefficientmore » are also discussed for the laminar and turbulent flow conditions. There is a good agreement between the film thickness results obtained from the theoretical model and those obtained from six of 35 void fraction models in the High Mass Flux region of R134a. In spite of their different valid conditions, six well-known flow regime maps from the literature are found to be predictive for the annular flow conditions in the test tube in spite of their different operating conditions. (author)« less
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comparison of frictional pressure drop models during annular flow condensation of r600a in a horizontal tube at low Mass Flux and of r134a in a vertical tube at High Mass Flux
International Journal of Heat and Mass Transfer, 2010Co-Authors: Ahmet Selim Dalkilic, Ozden Agra, Ismail Teke, Somchai WongwisesAbstract:Abstract This study compares well-known two-phase pressure drop models with the experimental results of a condensation pressure drop of (i) R600a in a 1 m long horizontal smooth copper tube with an inner diameter of 4 mm, outer diameter of 6 mm and (ii) R134a in a 0.5 m vertical smooth copper tube with an inner diameter of 8.1 mm and outer diameter of 9.52 mm. Different vapour qualities (0.45–0.9 for R600a and 0.7–0.95 for R134a), various Mass Fluxes (75–115 kg m −2 s −1 for R600a and 300–400 for R134a kg m −2 s −1 ) and different condensing temperatures (30–43 °C for R600a and 40–50 °C for R134a) were tested under annular flow conditions. The quality of the refrigerant in the test section was calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section was directly measured with a differential pressure transducer. The most agreeable correlations of various available options were then identified according to the results of analysis during annular flow regime.
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experimental investigation of heat transfer coefficient of r134a during condensation in vertical downward flow at High Mass Flux in a smooth tube
International Communications in Heat and Mass Transfer, 2009Co-Authors: Ahmet Selim Dalkilic, Suriyan Laohalertdecha, Somchai WongwisesAbstract:article i nfo Available online 23 July 2009 The two-phase heat transfer coefficients of pure HFC-134a condensing inside a smooth tube-in-tube heat exchanger are experimentally investigated. The test section is a 0.5 m long double tube with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is constructed from smooth copper tubing of 9.52 mm outer diameter and 8.1 mm inner diameter. The test runs are performed at average saturation condensing temperatures between 40-50 °C. The Mass Fluxes are between 260 and 515 kg m −2 s −1 and the heat Fluxes are between 11.3 and 55.3 kW m −2 . The quality of the refrigerant in the test section is calculated using the temperature and pressure obtained from the experiment. The average heat transfer coefficient of the refrigerant is determined by applying an energy balance based on the energy transferred from the test section. The effects of heat Flux, Mass Flux and condensation temperature on the heat transfer coefficients are also discussed. Eleven well-known correlations for annular flow are compared to each other using a large amount of data obtained from various experimental conditions. A new correlation for the condensation heat transfer coefficient is proposed for practical applications.
Ahmet Selim Dalkilic - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the modeling of condensation heat transfer coefficients in High Mass Flux region of refrigerant hfc 134a inside the vertical smooth tube in annular flow regime
Heat Transfer Engineering, 2011Co-Authors: Ahmet Selim Dalkilic, Somchai WongwisesAbstract:This article presents an experimental investigation on the co-current downward condensation of R134a in a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. Condensation experiments are done at Mass Fluxes varying between 260 and 515 kg/m2-s. The condensing temperatures are 40°C and 50°C; heat Fluxes are between 10.16 and 66.61 kW/m2. The quality of the refrigerant in the test section is calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section is directly measured by a differential pressure transducer. The average experimental heat transfer coefficient of the refrigerant is calculated by applying an energy balance based on the energy transferred from the test section. The average predicted heat transfer coefficient of the refrigerant is determined by means of the model of Kosky and Staub, and Von Karman universal velocity distribution correlations using different interfacial shear stress equations valid for...
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experimental analysis for the determination of the convective heat transfer coefficient by measuring pressure drop directly during annular condensation flow of r134a in a vertical smooth tube
International Journal of Heat and Mass Transfer, 2011Co-Authors: Ahmet Selim Dalkilic, Ismail Teke, Somchai WongwisesAbstract:Abstract This study investigated the direct relationship between the measured condensation pressure drop and convective heat transfer coefficient of R134a flowing downward inside a vertical smooth copper tube having an inner diameter of 8.1 mm and a length of 500 mm during annular flow. R134a and water were used as working fluids on the tube side and annular side of a double tube heat exchanger, respectively. Condensation experiments were performed at Mass Fluxes of 260, 300, 340, 400, 456 and 515 kg m −2 s −1 in the High Mass Flux region of R134a. The condensing temperatures were around 40 and 50 °C; the heat Fluxes were between 10.16 and 66.61 kW m −2 . Paliwoda’s analysis, which focused mainly on the determination of the two-phase flow factor and two-phase length of evaporators and condensers, was adapted to the in-tube condensation phenomena in the test section to determine the condensation heat transfer coefficient, heat Flux, two-phase length and pressure drop experimentally by means of a large number of data points obtained under various experimental conditions.
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an investigation of a model of the flow pattern transition mechanism in relation to the identification of annular flow of r134a in a vertical tube using various void fraction models and flow regime maps
Experimental Thermal and Fluid Science, 2010Co-Authors: Ahmet Selim Dalkilic, Somchai WongwisesAbstract:In the present study, new experimental data are presented for literature on the prediction of film thickness and identification of flow regime during the co-current downward condensation in a vertical smooth copper tube having an inner diameter of 8.1 mm and a length of 500 mm. R134a and water are used as working fluids in the tube side and annular side of a double tube heat exchanger, respectively. Condensation experiments are done at Mass Fluxes of 300 and 515 kg m{sup -2} s{sup -1}. The condensing temperatures are between 40 and 50 C; heat Fluxes are between 12.65 and 66.61 kW m{sup -2}. The average experimental heat transfer coefficient of the refrigerant HFC-134a is calculated by applying an energy balance based on the energy transferred from the test section. A mathematical model by Barnea et al. based on the momentum balance of liquid and vapor phases is used to determine the condensation film thickness of R134a. The comparative film thickness values are determined indirectly using relevant measured data together with various void fraction models and correlations reported in the open literature. The effects of heat Flux, Mass Flux, and condensation temperature on the film thickness and condensation heat transfer coefficientmore » are also discussed for the laminar and turbulent flow conditions. There is a good agreement between the film thickness results obtained from the theoretical model and those obtained from six of 35 void fraction models in the High Mass Flux region of R134a. In spite of their different valid conditions, six well-known flow regime maps from the literature are found to be predictive for the annular flow conditions in the test tube in spite of their different operating conditions. (author)« less
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comparison of frictional pressure drop models during annular flow condensation of r600a in a horizontal tube at low Mass Flux and of r134a in a vertical tube at High Mass Flux
International Journal of Heat and Mass Transfer, 2010Co-Authors: Ahmet Selim Dalkilic, Ozden Agra, Ismail Teke, Somchai WongwisesAbstract:Abstract This study compares well-known two-phase pressure drop models with the experimental results of a condensation pressure drop of (i) R600a in a 1 m long horizontal smooth copper tube with an inner diameter of 4 mm, outer diameter of 6 mm and (ii) R134a in a 0.5 m vertical smooth copper tube with an inner diameter of 8.1 mm and outer diameter of 9.52 mm. Different vapour qualities (0.45–0.9 for R600a and 0.7–0.95 for R134a), various Mass Fluxes (75–115 kg m −2 s −1 for R600a and 300–400 for R134a kg m −2 s −1 ) and different condensing temperatures (30–43 °C for R600a and 40–50 °C for R134a) were tested under annular flow conditions. The quality of the refrigerant in the test section was calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section was directly measured with a differential pressure transducer. The most agreeable correlations of various available options were then identified according to the results of analysis during annular flow regime.
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experimental investigation of heat transfer coefficient of r134a during condensation in vertical downward flow at High Mass Flux in a smooth tube
International Communications in Heat and Mass Transfer, 2009Co-Authors: Ahmet Selim Dalkilic, Suriyan Laohalertdecha, Somchai WongwisesAbstract:article i nfo Available online 23 July 2009 The two-phase heat transfer coefficients of pure HFC-134a condensing inside a smooth tube-in-tube heat exchanger are experimentally investigated. The test section is a 0.5 m long double tube with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is constructed from smooth copper tubing of 9.52 mm outer diameter and 8.1 mm inner diameter. The test runs are performed at average saturation condensing temperatures between 40-50 °C. The Mass Fluxes are between 260 and 515 kg m −2 s −1 and the heat Fluxes are between 11.3 and 55.3 kW m −2 . The quality of the refrigerant in the test section is calculated using the temperature and pressure obtained from the experiment. The average heat transfer coefficient of the refrigerant is determined by applying an energy balance based on the energy transferred from the test section. The effects of heat Flux, Mass Flux and condensation temperature on the heat transfer coefficients are also discussed. Eleven well-known correlations for annular flow are compared to each other using a large amount of data obtained from various experimental conditions. A new correlation for the condensation heat transfer coefficient is proposed for practical applications.
A R Pati - One of the best experts on this subject based on the ideXlab platform.
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High Mass Flux spray quenching on an inclined surface a novel methodology for the attainment of enhanced uniform cooling with unaltered surface morphology in transition boiling regime
International Journal of Heat and Mass Transfer, 2019Co-Authors: A R Pati, Anita Panda, S S Mohapatra, Ajit Behera, Basudeb Munshi, Biswajit SahaAbstract:Abstract The main obligation in the successful implementation of ultra-fast cooling in a manufacturing process are: (1) significant minimization of film boiling effect, (2) achievement of unaltered surface morphology and (3) uniform cooling on the surface of the plate. The literature does not reveal any methodology, which depicts simultaneously enhancement, unaltered surface morphology and uniform cooling. Therefore, in the current work, an attempt has been made to develop an appropriate cooling process depicting all the aforesaid requirements. The cooling on an inclined condition of the plate mitigates the aforesaid requirements. The result reveals that the heat removal rate enhances (CHF from 1.21 MW/m2 to 1.46 MW/m2) due to augmentation of sweeping rate of vapor film from the hot surface as inclination angle increases from 0° to 30°. Further increase of the inclination from 30° to 60° decreases the cooling rate due to reduction of droplet velocity, residence time and the replacement rate of the vapor and liquid layers. The optimum inclination of the plate to achieve the maximum average surface heat Flux is 30°. In addition, the temperature distribution on the surface and across the thickness of the heat treated plate confirms uniform cooling. The SEM image and the EDS of the current heat treated metal is compared with the SEM images and EDS data of the metals cooled by potential coolants such as surfactant added water, NaCl added water and MgSO4 added water and the comparison clearly asserts unaltered surface morphology for the current case. The variation of the hardness on the surface and across the thickness clearly asserts the excellent shock absorbing characteristics.
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upward and downward facing High Mass Flux spray cooling with additives a novel technique to enhance the heat removal rate at High initial surface temperature
Heat and Mass Transfer, 2018Co-Authors: A R Pati, Aditya Kumar, S S MohapatraAbstract:The objective of the current work is to enhance the spray cooling by changing the orientation of the nozzle with different additives (acetone, methanol, ethanol, benzene, n-hexane, tween 20 and salt) in water. The experiments are carried out by upward, downward and both upward and downward facing sprays. The optimization result depicts that the spray produced by upward facing spray gives Higher heat Flux than the downward facing spray and also cooling by both the upward and downward facing spray simultaneously produces better result than the individual. Further experiments with both upward and downward facing spray by using different coolants reveal that in case of cooling by ethanol (500 ppm) + water mixture, the maximum enhancement of surface heat Flux (~2.57 MW/m2) and cooling rate (204 °C/s) is observed. However, the minimum surface heat Flux is achieved in case of methanol (100 ppm) + water due to Higher contact angle (710) among all the considered coolants.
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High Mass Flux air atomized spray with subcooled water a novel methodology to enhance the heat transfer rate in film boiling regime
International Journal of Heat and Mass Transfer, 2018Co-Authors: Anita Panda, A R Pati, S Pradhan, Biswajit Saha, Aditya Kumar, S S MohapatraAbstract:Abstract The main challenging tasks in the successful implementation of ultrafast cooling in the manufacturing process are significant reduction of Leidenfrost effect and achievement of unaltered surface morphology. The literature does not reveal any methodology depicting the aforesaid two characteristics and therefore, in the current work, an attempt has been made to develop a cooling process describing the above mentioned characteristics. In the proposed methodology, by using subcooled water as a coolant in case of High Mass Flux air atomized spray, the heat transfer rate is significantly enhanced without altering the surface morphology. The High Mass Flux subcooled water atomized spray augments the heat transfer rate by reducing the stability of the vapour film separating the coolant from the hot plate. The cooling ability of the subcooled water atomized spray is compared with the coolants, which depict significant enhancement, and the comparison confirms the suitability of the current process for the fast cooling operation. For the experimental investigation, air atomized spray cooling was conducted at 1000 °C initial surface temperature on a 6 mm thick AISI 304 steel plate by using subcooled water as a coolant. The surface heat Flux and surface temperatures are predicted by using the solution of inverse heat conduction problem (IHCP). For the understanding of heat transfer mechanism, the thermal properties, physical properties and spray properties at different conditions of air-atomized spray were analysed. The percentage of enhancement in initial heat Flux (qIHF) is found to be almost 60% of water temperature at 15 °C and this shows the appropriateness of the process for the fast cooling operations. The heat transfer analysis illustrates that the cooling rate achieved for water temperature of 15 °C is found to be almost three times of that corresponding to 50 °C. In addition to the above, the comparison of the morphologies between the heat-treated and the untreated substrate corroborates zero deposition of coolant after cooling. The effects of air flow rate and spray impingement density on the cooling rate are investigated. With the increasing airflow rate up to 30 m3/h, the heat transfer rate rises and thereafter, further increment declines the heat transfer rate.
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enhancement of heat removal rate of High Mass Flux spray cooling by sea water
Experimental Thermal and Fluid Science, 2017Co-Authors: A R Pati, Basudeb Munshi, A P Behera, S S MohapatraAbstract:Abstract The main obligation in achieving High cooling rates in case of spray cooling at High surface temperature is the occurrence of film boiling phenomenon. Although the High Mass Flux spray reduces the film boiling affect, still, the heat transfer rate is not significant and hence, this process needs to be enhanced. In the absence of any information on the heat transfer augmentation technique, the present work deals with the enhancement of High Mass Flux spray cooling at very High initial plate temperature by using sea water. The sea water spray cooling process increases the heat removal rate by creating High heat transfer area for the droplet evaporation and by reducing the vapour pressure of vapour film on the hot plate. The cooling ability of the sea water spray is compared with the coolants (salt added water, surfactant added water and surfactant and salt added water) which partially depict the properties of sea water. For the experimental investigation, spray cooling was conducted at 900 °C initial surface temperature on a 6 mm thick AISI 304 steel plate (100 × 100 mm) by using sea water and also aforesaid coolants at different concentrations. The surface heat Flux and surface temperature have been predicted using the solution of the Inverse Heat Conduction Problem (IHCP). For the understanding of heat transfer mechanism, the properties of coolants (contact angle, thermal conductivity, density, specific heat and Mass diffusivity) at different concentrations and spray behaviour (droplet diameter, spray pressure, droplet velocity and spray impingement density) at different flow rates were measured. The physical properties of the coolant reveal that the contact angle decreases with the increasing salt concentration up to 0.1 M and further increment in salt concentration enhances the contact angle. From the thermal properties of the coolant, it is observed that thermal diffusivity in sea water is Higher than salt added water. The sea water spray cooling asserts that the heat removal rate increases with the increasing percentage of sea water in the mixture of seawater and pure water due to the salt deposition on the hot surface. However, the achieved heat removal rate is lower than that of salt added water due to the comparatively less amount of salt deposition in case of sea water spray. Furthermore, the combined effect of the salt deposition and lowering of vapour pressure in vapour film phenomena produce better heat removal rate than the pure water and surfactant and salt added water. In comparison between sea water and surfactant added water spray cooling, the former produces Higher heat removal rate because of the dominance of salt deposition phenomenon over the lowering of contact angle property. In case of sea water spray, the achieved critical heat Flux (1.55 MW/m 2 ) is 1.3 times that of pure water (1.2 MW/m 2 ); moreover, the enhanced critical heat Flux is obtained at 170 °C Higher surface temperatures. In addition to the above, the enhancement by NaCl added water spray is almost 1.6 times that of pure water. Due to the above mentioned favourable conditions for the fast cooling, the maximum cooling rates of 115 °C/s and 135 °C/s are achieved with sea water and NaCl added water sprays, respectively.
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enhancement of heat transfer rate of High Mass Flux spray cooling by ethanol water and ethanol tween20 water solution at very High initial surface temperature
International Journal of Heat and Mass Transfer, 2017Co-Authors: N H Bhatt, A R Pati, Aditya Kumar, Basudeb Munshi, R Raj, Priya Varshney, D Chouhan, S S MohapatraAbstract:•Obligations in achieving High cooling rates by spray cooling are overcome.•Heat removal is enhanced by spray cooling with coolants-ethanol and tween20 in water.•Achieved CHF with Tween 20-ethanol-water mixture is 1.6 times Higher than pure water.•Maximum obtained cooling rate is 141°C/s in case of ethanol-water-Tween 20 mixture.
Aditya Kumar - One of the best experts on this subject based on the ideXlab platform.
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upward and downward facing High Mass Flux spray cooling with additives a novel technique to enhance the heat removal rate at High initial surface temperature
Heat and Mass Transfer, 2018Co-Authors: A R Pati, Aditya Kumar, S S MohapatraAbstract:The objective of the current work is to enhance the spray cooling by changing the orientation of the nozzle with different additives (acetone, methanol, ethanol, benzene, n-hexane, tween 20 and salt) in water. The experiments are carried out by upward, downward and both upward and downward facing sprays. The optimization result depicts that the spray produced by upward facing spray gives Higher heat Flux than the downward facing spray and also cooling by both the upward and downward facing spray simultaneously produces better result than the individual. Further experiments with both upward and downward facing spray by using different coolants reveal that in case of cooling by ethanol (500 ppm) + water mixture, the maximum enhancement of surface heat Flux (~2.57 MW/m2) and cooling rate (204 °C/s) is observed. However, the minimum surface heat Flux is achieved in case of methanol (100 ppm) + water due to Higher contact angle (710) among all the considered coolants.
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High Mass Flux air atomized spray with subcooled water a novel methodology to enhance the heat transfer rate in film boiling regime
International Journal of Heat and Mass Transfer, 2018Co-Authors: Anita Panda, A R Pati, S Pradhan, Biswajit Saha, Aditya Kumar, S S MohapatraAbstract:Abstract The main challenging tasks in the successful implementation of ultrafast cooling in the manufacturing process are significant reduction of Leidenfrost effect and achievement of unaltered surface morphology. The literature does not reveal any methodology depicting the aforesaid two characteristics and therefore, in the current work, an attempt has been made to develop a cooling process describing the above mentioned characteristics. In the proposed methodology, by using subcooled water as a coolant in case of High Mass Flux air atomized spray, the heat transfer rate is significantly enhanced without altering the surface morphology. The High Mass Flux subcooled water atomized spray augments the heat transfer rate by reducing the stability of the vapour film separating the coolant from the hot plate. The cooling ability of the subcooled water atomized spray is compared with the coolants, which depict significant enhancement, and the comparison confirms the suitability of the current process for the fast cooling operation. For the experimental investigation, air atomized spray cooling was conducted at 1000 °C initial surface temperature on a 6 mm thick AISI 304 steel plate by using subcooled water as a coolant. The surface heat Flux and surface temperatures are predicted by using the solution of inverse heat conduction problem (IHCP). For the understanding of heat transfer mechanism, the thermal properties, physical properties and spray properties at different conditions of air-atomized spray were analysed. The percentage of enhancement in initial heat Flux (qIHF) is found to be almost 60% of water temperature at 15 °C and this shows the appropriateness of the process for the fast cooling operations. The heat transfer analysis illustrates that the cooling rate achieved for water temperature of 15 °C is found to be almost three times of that corresponding to 50 °C. In addition to the above, the comparison of the morphologies between the heat-treated and the untreated substrate corroborates zero deposition of coolant after cooling. The effects of air flow rate and spray impingement density on the cooling rate are investigated. With the increasing airflow rate up to 30 m3/h, the heat transfer rate rises and thereafter, further increment declines the heat transfer rate.
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enhancement of heat transfer rate of High Mass Flux spray cooling by ethanol water and ethanol tween20 water solution at very High initial surface temperature
International Journal of Heat and Mass Transfer, 2017Co-Authors: N H Bhatt, A R Pati, Aditya Kumar, Basudeb Munshi, R Raj, Priya Varshney, D Chouhan, S S MohapatraAbstract:•Obligations in achieving High cooling rates by spray cooling are overcome.•Heat removal is enhanced by spray cooling with coolants-ethanol and tween20 in water.•Achieved CHF with Tween 20-ethanol-water mixture is 1.6 times Higher than pure water.•Maximum obtained cooling rate is 141°C/s in case of ethanol-water-Tween 20 mixture.
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High Mass Flux spray cooling with additives of low specific heat and surface tension a novel process to enhance the heat removal rate
Applied Thermal Engineering, 2017Co-Authors: N H Bhatt, A R Pati, Aditya Kumar, Ajit Behera, Basudeb Munshi, S S MohapatraAbstract:Abstract High Mass Flux spray cooling is a good replacement of conventional cooling methods such as jet cooling and laminar cooling in metallurgical industries. However, the cooling rates obtained in spray cooling are still not sufficient for the production of High tensile strength and moderate hardenability steel. The challenging task in the conventional spray cooling is the elimination of film boiling phenomenon. The solution to such difficulties is the use of High Mass Flux spray which generates High momentum droplets that penetrates the vapour film and almost excludes the film boiling affect. Along with the aforesaid advantage, the High Mass Flux spray also creates low residence time that leads to incomplete evaporation and as a consequence, the obtained heat transfer rate is not significant. Hence, the heat removal rate needs to be further enhanced. This can be achieved by increasing the heat transfer area and lowering the sensible heating time. So, in the current work, coolants of low specific heat and surface tension are prepared by separately mixing water with benzene, acetone and n -hexane in different combinations to see the effects of specific heat and surface tension on heat transfer rate. The substrate used was a square AISI 304 steel plate (100 × 100 × 6 mm). The surface temperatures and heat Fluxes were calculated by using INTEMP software. Before experimentation, the Mass Flux and nozzle to plate distance were optimised. The result shows significant augmentation of heat removal rate with an increment in critical heat Flux of 40, 30 and 20% with acetone, n -hexane and benzene, respectively. Moreover, mathematical correlations are developed using Design Expert software to determine the heat transfer coefficient at different properties of coolants.