The Experts below are selected from a list of 9780 Experts worldwide ranked by ideXlab platform
Yongping Yang - One of the best experts on this subject based on the ideXlab platform.
-
combined air cooled Condenser layout with in line configured finned tube bundles to improve cooling performance
Applied Thermal Engineering, 2019Co-Authors: Yanqiang Kong, Lijun Yang, Weijia Wang, Zhitao Zuo, Yongping YangAbstract:Abstract Air-Cooled Condensers (ACCs) are commonly arranged in the A-frame form to extend the heat transfer surface with some well-recognized design flaws that inhibit the cooling performance. For overcoming this geometric defect, the combined natural draft ACC is proposed with the horizontally in line arranged finned tube bundles inside the dry-cooling tower and vertically in line configured bundles outside the tower. A three dimensional CFD method with the realizable k-e model, radiator model and porous media model is developed and experimentally validated. The thermo-flow characteristics of the proposed ACC are analyzed and compared with two types of traditional ACCs. Besides, the effects of the platform heights from 5 m to 50 m are also investigated for the novel ACC layout. The results show that the new proposed ACC can endow with splendid cooling performance at the wind speeds lower than 9 m/s, especially in the absence of winds with the heat transfer rate increased by nearly 20% in comparison with two conventional ones. While at high wind speeds, the traditional ACC with vertically arranged heat exchanger bundles shows the highest cooling efficiency, thus is applicable to the regions with strong prevailing winds. Moreover, for the novel ACC, there exist the optimal platform heights of 15 m and 40 m at the low wind speeds and high wind speeds respectively, which can contribute to the optimal design of natural draft Air-Cooled Condenser in power plants.
-
circularly arranged air cooled Condensers to restrain adverse wind effects
Applied Thermal Engineering, 2017Co-Authors: Yanqiang Kong, Lijun Yang, Weijia Wang, Xianwei Huang, Yongping YangAbstract:Abstract Ambient winds may deteriorate the thermo-flow performances of Air-Cooled Condenser (ACC) due to its geometry defects to a certain extent. In this work, a novel circular array of ACCs is proposed to restrain the adverse wind effects. By means of CFD simulations, the air-side flow and heat transfer performances are investigated at various wind speeds in five characteristic wind directions (−45°, −90°, 0°, 45° and 90°). The cooling air variable fields, mass flow rate of axial flow fans and turbine back pressure are analyzed and compared with the conventional ACCs. The results show that, both the hot plume recirculation flows and reverse flows of the peripheral Condenser cells are greatly weakened for the proposed ACCs under wind conditions, leading to a much improved cooling efficiency. Besides in the wind direction of 90°, the cooling performance can be greatly improved, but in the wind direction of 0°, the proposed ACCs present an inappreciably inferior performance compared with the conventional ACCs. In the absence of winds, the circular array can also make the ACCs operate in a more energy efficient way. This work may contribute to the optimal design and energy efficient operation of Air-Cooled Condensers in power plants.
-
numerical simulation on flow and heat transfer of fin and tube heat exchanger with longitudinal vortex generators
International Journal of Thermal Sciences, 2015Co-Authors: Li Li, Xiaoze Du, Yuwen Zhang, Lijun Yang, Yongping YangAbstract:Abstract Fin-and-tube heat exchangers with plain fins are widely used in direct Air-Cooled Condenser system in the power plant, because of its relatively simple property compared to some other fins with variable cross-sectional area channel. In the present study, heat transfer performance and pressure drop for fin-and-tube heat exchanger with longitudinal vortex generators (LVGs) on the fin surface were numerically investigated. Rectangular and delta winglet pairs were punched/mounted on the fin surfaces to enhance the heat transfer of the air-side of the fin-and-tube heat exchangers. The results showed that the Nusselt numbers increased up to 20% for LVGs on plain fins comparing with plain fins channel without LVGs. The heat transfer enhancement by rectangular winglets was more significant than that of the delta winglets. The rectangular winglet with angle of attack of 25°showed the best overall performance than any other angles of attack in rectangular winglets configurations. Additionally, the delta winglet with angle of attack of 45° showed the best overall performance than the other angles of attack in delta winglets configurations.
-
heat transfer enhancement of wavy finned flat tube by punched longitudinal vortex generators
International Journal of Heat and Mass Transfer, 2014Co-Authors: Xiaoze Du, Lili Feng, Li Li, Lijun Yang, Yongping YangAbstract:Abstract Punched longitudinal vortex generators (LVGs) were employed to enhance air-side heat transfer on the wavy fin surface of flat tube used in direct Air-Cooled Condenser. The heat transfer enhancement of four types of the longitudinal vortex generators with different attack angles were compared by numerical simulations. It was found that the delta winglet pair with attack angle 25° could reach the greatest performance evaluation criteria (PEC) under the conditions of the inlet air flow velocity varied from 1 m/s to 5 m/s. The influences of locations on the wavy fin surface and the row number of the longitudinal vortex generators were also discussed. One delta winglet pairs at the middle of the wavy fin surface and the minimum row number, n = 1, with the average PEC is 1.23, has the best heat transfer performance of all conditions, which can be recommended for practical applications. Experimental study in wind tunnel with flow field visualization by Particle Image Velocimetry (PIV), as well as the numerical simulations verified that the delta winglet pairs can generate obvious longitudinal vortex pairs at the down-sweep zone, which can enhance the heat transfer between the cooling air flow and heated wall surface with acceptable pressure loss.
-
Heat load capability matching principle and its applications to anti-freezing of Air-Cooled Condenser
Applied Energy, 2014Co-Authors: Lijun Yang, Xiaoli Zhao, Yongping YangAbstract:Air-Cooled Condenser in power plants takes a risk of freezing in extremely cold days, so it is of benefit to the safe and economical operation of direct dry cooling system to propose the anti-freezing principles and take measures. On the basis of the heat load balance between the exhaust steam and cooling air, the heat load capacity matching principle for the anti-freezing of Air-Cooled Condenser is proposed with reference to the freezing point of water. By applying heat exchanger model to the finned tube bundles of Air-Cooled Condenser, the thermo-aerodynamic behavior of cooling air, the condensation of exhaust steam and the sensible heat rejection of condensate in a representative Air-Cooled Condenser cell are synchronously modeled and resolved. The correlations among the ambient temperature, flow rate of cooling air, exhaust steam flow rate and quality, and back pressure of turbine that prevent the Air-Cooled Condenser from freezing are discussed, and the anti-freezing flow rate of exhaust steam, back pressure of turbine and flow rate of axial flow fan are obtained. The results show that the anti-freezing flow rate of exhaust steam and back pressure both increase with decreasing the ambient temperature and increasing the flow rate of axial flow fan, from which derive the secure steam flow rate that can reduce the back pressure as much as possible to improve thermal efficiency. The anti-freezing fan flow rate increases with increasing the exhaust steam flow rate and ambient temperature, but varies little with back pressure. The increased steam quality will result in a higher heat load at the steam side, which allows a higher rotational speed of fan to be free of freezing for Air-Cooled Condenser. The application of heat load capacity matching principle to the anti-freezing of Air-Cooled Condenser contributes to the secure and optimal operation of dry cooling system in power plants.
Predrag Stojan Hrnjak - One of the best experts on this subject based on the ideXlab platform.
-
thermo hydraulic model for steam condensation in a large inclined flattened tube air cooled Condenser
Applied Thermal Engineering, 2019Co-Authors: William A Davies, Predrag Stojan HrnjakAbstract:Abstract A thermo-hydraulic model for calculating capacity, heat transfer coefficient and void fraction of an inclined Air-Cooled steam Condenser is presented. The Condenser tube has an elongated-slot cross-section, with inner dimensions of 214 × 16 mm. The model was developed for a 10.7 m-long tube, and validated by comparison with experiments in a 5.7 m-long tube. The model is for downward inclination angles from 0 to 90°, with co-current vapor and condensate flow. The cooling air is in cross flow. This model is developed based on existing models for inclined, stratified-flow condensation. These have been adapted to the flattened-tube Air-Cooled Condenser geometry and conditions. The model couples both air- and steam-side behavior in order to accurately resolve the variations in heat transfer coefficients, temperatures, and heat flux. On the steam side, the model is for stratified flow, and separates the flow into two sections: a falling film along the wall, and an axially-flowing condensate river along the tube bottom. The axially-flowing condensate river is modeled using open-channel-flow theory. On the air side, heat transfer coefficient is determined from a combination of empirical correlation and CFD. The model and experimental results show agreement within 5% for capacity and 20% for void fraction for all tube inclinations.
William A Davies - One of the best experts on this subject based on the ideXlab platform.
-
local heat transfer coefficient during stratified flow in large flattened tube steam Condensers with non uniform heat flux and wall temperature
International Journal of Heat and Mass Transfer, 2020Co-Authors: William A Davies, Pega HrnjakAbstract:Abstract Steam condensation heat transfer coefficient (HTC) in a large, flattened tube with non-uniform heat flux and wall temperature, and variable inclination angle is determined experimentally. The Condenser tube is that typically used in an Air-Cooled Condenser for power plants. The steel tube has an elongated-slot cross section with inner dimensions of 216 × 16 mm. Water vapor and liquid flow co-currently through a 5.7 m long Air-Cooled conditioning section, followed by a 0.12 m long water-cooled test section. The long conditioning section creates conditions in the test section that mimic the conditions in an operating Condenser – allowing for the realistic development of flow regime and void fraction. HTC is then determined in the water-cooled section. The water-cooled section is designed as a crossflow heat exchanger to match the temperature and heat flux conditions of an Air-Cooled Condenser. Visualization sections at the tube inlet and outlet allow determination of flow regime and void fraction. The flow is found to be stratified for all conditions. Tube inclination angle is varied from 0 to 38° downwards. Inlet quality in the water-cooled section ranges from 0 to 0.74. HTC is found to increase by more than 400% along the Condenser height. In addition, inclination angle, wall-steam temperature difference, inlet water-steam temperature difference, water temperature glide and vapor quality are all found to affect the condensation HTC.
-
thermo hydraulic model for steam condensation in a large inclined flattened tube air cooled Condenser
Applied Thermal Engineering, 2019Co-Authors: William A Davies, Predrag Stojan HrnjakAbstract:Abstract A thermo-hydraulic model for calculating capacity, heat transfer coefficient and void fraction of an inclined Air-Cooled steam Condenser is presented. The Condenser tube has an elongated-slot cross-section, with inner dimensions of 214 × 16 mm. The model was developed for a 10.7 m-long tube, and validated by comparison with experiments in a 5.7 m-long tube. The model is for downward inclination angles from 0 to 90°, with co-current vapor and condensate flow. The cooling air is in cross flow. This model is developed based on existing models for inclined, stratified-flow condensation. These have been adapted to the flattened-tube Air-Cooled Condenser geometry and conditions. The model couples both air- and steam-side behavior in order to accurately resolve the variations in heat transfer coefficients, temperatures, and heat flux. On the steam side, the model is for stratified flow, and separates the flow into two sections: a falling film along the wall, and an axially-flowing condensate river along the tube bottom. The axially-flowing condensate river is modeled using open-channel-flow theory. On the air side, heat transfer coefficient is determined from a combination of empirical correlation and CFD. The model and experimental results show agreement within 5% for capacity and 20% for void fraction for all tube inclinations.
-
method for evaluating the effect of inclination on the performance of large flattened tube steam Condensers with visualization of flow regimes
Applied Thermal Engineering, 2018Co-Authors: William A Davies, Pega Hrnjak, Yu Kang, Anthony M JacobiAbstract:Abstract An experimental study of convective steam condensation inside a large, inclined, flattened-tube Air-Cooled Condenser for power plants is presented. This is the second of a four-part group of papers. The first part presents pressure drop and visualization results, while this study presents the experimental method along with heat transfer results. Follow-up papers present further heat transfer results and the effect of inclination. The Condenser in this study is steel with brazed aluminum fins. The Condenser measures 10.72 m in length, with a cross section of 214 mm × 16 mm. The Condenser tube was cut in half lengthwise and covered with a polycarbonate viewing window in order to provide visualization access simultaneously with the heat transfer measurements. Inlet steam mass flux ranged from 6.2 to 9.5 kg m−2 s−1, and Condenser capacity varied from 25 to 31 kW. The angle of inclination was varied from horizontal to 75° downward. The experiments were performed with a uniform fin-face velocity of crossflowing air at 2.2 m/s. Condenser capacity was found to increase linearly with increasing downward inclination angle of the Condenser, at a rate of 0.041% per degree of inclination below horizontal. This improvement was found to be the result of improved drainage and increased void fraction near the Condenser outlet.
Pega Hrnjak - One of the best experts on this subject based on the ideXlab platform.
-
local heat transfer coefficient during stratified flow in large flattened tube steam Condensers with non uniform heat flux and wall temperature
International Journal of Heat and Mass Transfer, 2020Co-Authors: William A Davies, Pega HrnjakAbstract:Abstract Steam condensation heat transfer coefficient (HTC) in a large, flattened tube with non-uniform heat flux and wall temperature, and variable inclination angle is determined experimentally. The Condenser tube is that typically used in an Air-Cooled Condenser for power plants. The steel tube has an elongated-slot cross section with inner dimensions of 216 × 16 mm. Water vapor and liquid flow co-currently through a 5.7 m long Air-Cooled conditioning section, followed by a 0.12 m long water-cooled test section. The long conditioning section creates conditions in the test section that mimic the conditions in an operating Condenser – allowing for the realistic development of flow regime and void fraction. HTC is then determined in the water-cooled section. The water-cooled section is designed as a crossflow heat exchanger to match the temperature and heat flux conditions of an Air-Cooled Condenser. Visualization sections at the tube inlet and outlet allow determination of flow regime and void fraction. The flow is found to be stratified for all conditions. Tube inclination angle is varied from 0 to 38° downwards. Inlet quality in the water-cooled section ranges from 0 to 0.74. HTC is found to increase by more than 400% along the Condenser height. In addition, inclination angle, wall-steam temperature difference, inlet water-steam temperature difference, water temperature glide and vapor quality are all found to affect the condensation HTC.
-
method for evaluating the effect of inclination on the performance of large flattened tube steam Condensers with visualization of flow regimes
Applied Thermal Engineering, 2018Co-Authors: William A Davies, Pega Hrnjak, Yu Kang, Anthony M JacobiAbstract:Abstract An experimental study of convective steam condensation inside a large, inclined, flattened-tube Air-Cooled Condenser for power plants is presented. This is the second of a four-part group of papers. The first part presents pressure drop and visualization results, while this study presents the experimental method along with heat transfer results. Follow-up papers present further heat transfer results and the effect of inclination. The Condenser in this study is steel with brazed aluminum fins. The Condenser measures 10.72 m in length, with a cross section of 214 mm × 16 mm. The Condenser tube was cut in half lengthwise and covered with a polycarbonate viewing window in order to provide visualization access simultaneously with the heat transfer measurements. Inlet steam mass flux ranged from 6.2 to 9.5 kg m−2 s−1, and Condenser capacity varied from 25 to 31 kW. The angle of inclination was varied from horizontal to 75° downward. The experiments were performed with a uniform fin-face velocity of crossflowing air at 2.2 m/s. Condenser capacity was found to increase linearly with increasing downward inclination angle of the Condenser, at a rate of 0.041% per degree of inclination below horizontal. This improvement was found to be the result of improved drainage and increased void fraction near the Condenser outlet.
-
microchannel heat exchangers for charge minimization in air cooled ammonia Condensers and chillers
International Journal of Refrigeration-revue Internationale Du Froid, 2008Co-Authors: Pega Hrnjak, Andy D LitchAbstract:Abstract This paper presents experimental results from a prototype ammonia chiller with an Air-Cooled Condenser and a plate evaporator. The main objectives were charge reduction and compactness of the system. The charge is reduced to 20 g/kW (2.5 oz/Ton). This is lower than any currently available Air-Cooled ammonia chiller on the market. The major contribution comes from use of microchannel aluminum tubes. Two aluminum Condensers were evaluated in the chiller: one with a parallel tube arrangement between headers and “microchannel” tubes (hydraulic diameter Dh = 0.7 mm), and the other with a single serpentine “macrochannel” tube (Dh = 4.06 mm). The performances of the chiller and Condensers are compared based on various criteria to other available ammonia chillers. This prototype was made and examined in the Air Conditioning and Refrigeration Center in 1998, at the University of Illinois at Urbana-Champaign.
Lijun Yang - One of the best experts on this subject based on the ideXlab platform.
-
combined air cooled Condenser layout with in line configured finned tube bundles to improve cooling performance
Applied Thermal Engineering, 2019Co-Authors: Yanqiang Kong, Lijun Yang, Weijia Wang, Zhitao Zuo, Yongping YangAbstract:Abstract Air-Cooled Condensers (ACCs) are commonly arranged in the A-frame form to extend the heat transfer surface with some well-recognized design flaws that inhibit the cooling performance. For overcoming this geometric defect, the combined natural draft ACC is proposed with the horizontally in line arranged finned tube bundles inside the dry-cooling tower and vertically in line configured bundles outside the tower. A three dimensional CFD method with the realizable k-e model, radiator model and porous media model is developed and experimentally validated. The thermo-flow characteristics of the proposed ACC are analyzed and compared with two types of traditional ACCs. Besides, the effects of the platform heights from 5 m to 50 m are also investigated for the novel ACC layout. The results show that the new proposed ACC can endow with splendid cooling performance at the wind speeds lower than 9 m/s, especially in the absence of winds with the heat transfer rate increased by nearly 20% in comparison with two conventional ones. While at high wind speeds, the traditional ACC with vertically arranged heat exchanger bundles shows the highest cooling efficiency, thus is applicable to the regions with strong prevailing winds. Moreover, for the novel ACC, there exist the optimal platform heights of 15 m and 40 m at the low wind speeds and high wind speeds respectively, which can contribute to the optimal design of natural draft Air-Cooled Condenser in power plants.
-
circularly arranged air cooled Condensers to restrain adverse wind effects
Applied Thermal Engineering, 2017Co-Authors: Yanqiang Kong, Lijun Yang, Weijia Wang, Xianwei Huang, Yongping YangAbstract:Abstract Ambient winds may deteriorate the thermo-flow performances of Air-Cooled Condenser (ACC) due to its geometry defects to a certain extent. In this work, a novel circular array of ACCs is proposed to restrain the adverse wind effects. By means of CFD simulations, the air-side flow and heat transfer performances are investigated at various wind speeds in five characteristic wind directions (−45°, −90°, 0°, 45° and 90°). The cooling air variable fields, mass flow rate of axial flow fans and turbine back pressure are analyzed and compared with the conventional ACCs. The results show that, both the hot plume recirculation flows and reverse flows of the peripheral Condenser cells are greatly weakened for the proposed ACCs under wind conditions, leading to a much improved cooling efficiency. Besides in the wind direction of 90°, the cooling performance can be greatly improved, but in the wind direction of 0°, the proposed ACCs present an inappreciably inferior performance compared with the conventional ACCs. In the absence of winds, the circular array can also make the ACCs operate in a more energy efficient way. This work may contribute to the optimal design and energy efficient operation of Air-Cooled Condensers in power plants.
-
Anti-Freezing Mechanism Analysis of a Finned Flat Tube in an Air-Cooled Condenser
MDPI AG, 2017Co-Authors: Yonghong Guo, Tongrui Cheng, Lijun YangAbstract:In cold winter weather, the Air-Cooled Condensers (ACCs) face serious freezing risks, especially with part load of the power generating unit. Therefore, it is of benefit to investigate the heat transfer process between the turbine exhaust steam and cooling air, by which the freezing mechanism of the finned tube bundles can be revealed. In this work, the flow and heat transfer models of the cooling air coupling with the circulating water, are developed and numerically simulated for the anti-freezing analysis on basis of the finned tube bundles of the Condenser cell. The local air-side heat transfer coefficient, condensate film development, and non-condensable gas development are obtained and analyzed in detail. The results show that, the most freezing risk happens at the fin base due to the highest air-side cooling capacity, besides the windward velocity, ambient temperature and turbine back pressure all determine the freezing risk with the constant inlet flow rate of the non-condensable gas. Furthermore, increasing fin thickness and decreasing fan rotating speed are the most effective anti-freezing measures. Additionally, increasing turbine back pressure can also be adopted to avoid ACC freezing, however the adjustment of outlet steam-air flow is not recommended
-
numerical simulation on flow and heat transfer of fin and tube heat exchanger with longitudinal vortex generators
International Journal of Thermal Sciences, 2015Co-Authors: Li Li, Xiaoze Du, Yuwen Zhang, Lijun Yang, Yongping YangAbstract:Abstract Fin-and-tube heat exchangers with plain fins are widely used in direct Air-Cooled Condenser system in the power plant, because of its relatively simple property compared to some other fins with variable cross-sectional area channel. In the present study, heat transfer performance and pressure drop for fin-and-tube heat exchanger with longitudinal vortex generators (LVGs) on the fin surface were numerically investigated. Rectangular and delta winglet pairs were punched/mounted on the fin surfaces to enhance the heat transfer of the air-side of the fin-and-tube heat exchangers. The results showed that the Nusselt numbers increased up to 20% for LVGs on plain fins comparing with plain fins channel without LVGs. The heat transfer enhancement by rectangular winglets was more significant than that of the delta winglets. The rectangular winglet with angle of attack of 25°showed the best overall performance than any other angles of attack in rectangular winglets configurations. Additionally, the delta winglet with angle of attack of 45° showed the best overall performance than the other angles of attack in delta winglets configurations.
-
heat transfer enhancement of wavy finned flat tube by punched longitudinal vortex generators
International Journal of Heat and Mass Transfer, 2014Co-Authors: Xiaoze Du, Lili Feng, Li Li, Lijun Yang, Yongping YangAbstract:Abstract Punched longitudinal vortex generators (LVGs) were employed to enhance air-side heat transfer on the wavy fin surface of flat tube used in direct Air-Cooled Condenser. The heat transfer enhancement of four types of the longitudinal vortex generators with different attack angles were compared by numerical simulations. It was found that the delta winglet pair with attack angle 25° could reach the greatest performance evaluation criteria (PEC) under the conditions of the inlet air flow velocity varied from 1 m/s to 5 m/s. The influences of locations on the wavy fin surface and the row number of the longitudinal vortex generators were also discussed. One delta winglet pairs at the middle of the wavy fin surface and the minimum row number, n = 1, with the average PEC is 1.23, has the best heat transfer performance of all conditions, which can be recommended for practical applications. Experimental study in wind tunnel with flow field visualization by Particle Image Velocimetry (PIV), as well as the numerical simulations verified that the delta winglet pairs can generate obvious longitudinal vortex pairs at the down-sweep zone, which can enhance the heat transfer between the cooling air flow and heated wall surface with acceptable pressure loss.