The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Zhiqiang Guan - One of the best experts on this subject based on the ideXlab platform.
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Development of small natural draft Dry Cooling Towers for geothermal power plants
2020Co-Authors: Yuanshen Lu, Zhiqiang Guan, Hal GurgenciAbstract:Current design methods for natural draft Dry Cooling Tower (NDDCT) do not include the crosswind effect which is unfavorable to the performance of Cooling Towers. This effect of the crosswind will be even more unfavorable to the performance of small Cooling Towers since the percentage of the disturbed free air flow is considerably higher than for large NDDCT. Therefore, the validity of the current design methods is questionable for small NDDCT design. Analytical and numerical modeling has been carried to investigate the performance of small NDDCT under different crosswind conditions. The smallest sizes of natural draft Cooling Towers were derived based on current design methods. The effect of various crosswinds on the performance of small Tower is demonstrated with a 3D CFD simulation. Preliminary results showed that the velocity and temperature distributions in the Tower have been significantly influenced by the crosswinds.
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Performance comparison of the crosswind effect on different size of natural draft Dry Cooling Towers
2020Co-Authors: Xiaoxiao Li, Hal Gurgenci, Zhiqiang GuanAbstract:Previous research have identified that the performance of the natural draft Dry Cooling Tower (NDDCT) is seriously influenced by the crosswind. For different size and different shape of the Cooling Towers, the crosswind effects are different. In order to better compare the crosswind effect on the different size of the Cooling Tower, this paper developed four different NDDCT models with the horizontal arranged air-cooled heat exchanger. The heights of the Towers are 20m, 60m, 100m and 140m with the same aspect ratio and same aircooled heat exchanger. The Cooling performance of these four Cooling Towers under crosswind condition were evaluated by the 3-D CFD models and the mechanism of the crosswind effect on the Cooling Tower was discussed.
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CFD simulations on small natural draft Dry Cooling Towers
2020Co-Authors: Yuanshen Lu, Zhiqiang Guan, Hal GurgenciAbstract:The natural draft Dry Cooling Tower (NDDCT) is believed to be the only cost-effective option for Cooling system of geothermal power plants proposed by Queensland Geothermal Energy Centre of Excellence (QGECE). By reviewing literatures related to the design of NDDCT, the effect of crosswind on the Cooling performance of NDDCT is not considered in contemporary design theories for Cooling Tower system. Practical operations on NDDCT showed that the crosswind larger than 1 m/s will have a profound effect on the performance and that cannot be neglected, especially for small size NDDCT. A study on the performance of a 15m-high natural draft Dry Cooling Tower under different crosswind conditions is presented in this paper. CFD models (both 2D and 3D) based on porous media have been established for numerical simulations of the air dynamics and heat transfer inside and outside the Cooling Tower. The CFD results have been validated by comparing the results under no crosswind condition with those obtained in theoretical calculations (1D model). 3D CFD simulations showed that the total Cooling capacity of the NDDCT is unfavourably affected by cross wind, and under certain conditions the heat rejection in the Cooling Tower can be reduced significantly. This trend matches the results of similar studies on large NDDCT found in open literatures well.
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Numerical simulation of solar enhanced natural draft Dry Cooling Towers
2020Co-Authors: Zhiqiang Guan, Hal GurgenciAbstract:Solar Enhanced Natural Draft Dry Cooling Tower is a new concept of hybrid Cooling, in which solar heat collection is added to traditional natural draft Dry Cooling Tower. Adding a solarheated space to further heat the air after it leaves the heat exchangers increases the temperature difference between the inside and outside of Tower, which leads to an increased air flow rate through the heat exchangers therefore better Cooling performance. A one-dimensional model has been developed to predict its Cooling performance by using MATLAB. The purpose of the present paper is to report on results of a detailed numerical analysis and to validate performance predictions from that onedimensional model. A three-dimensional numerical model of a Solar Enhanced Natural Draft Dry Cooling Tower was created using the CFD software FLUENT. Reasonably good agreement is found between these two models.
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Heat transfer augmentation and opimisation in a solar enhanced natural draft Dry Cooling Tower
2020Co-Authors: Mostafa Odabaee, Zhiqiang Guan, Mohsen Modir Shanechi, K. HoomanAbstract:Different heat transfer surface extension techniques are considered in order to improve the performance of an air-cooled heat exchanger and an optimisation process on a Solar Enhanced Natural Draft Dry Cooling Tower (SENDDCT) is conducted by Queensland Geothermal Energy Centre of Excellence (QGECE), as the air-cooled condenser of a geothermal power plant. The conventional method of extending the heat transfer area by means of fins is compared with a modern technique being the application of a thin metal foam layer to the outer surface of the tube. Aiming at maximizing the heat transfer enhancement and minimizing the total pressure drop, different tube bundle arrangements are numerical investigated by ANSYS-Fluent where the number of rows and tube spacing are systematically changed. An optimum design ispresented for an existing Tower to be equipped with solar panels to afterheat the air leaving the heat exchanger bundles arranged vertically around the Tower skirt.
Hal Gurgenci - One of the best experts on this subject based on the ideXlab platform.
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Development of small natural draft Dry Cooling Towers for geothermal power plants
2020Co-Authors: Yuanshen Lu, Zhiqiang Guan, Hal GurgenciAbstract:Current design methods for natural draft Dry Cooling Tower (NDDCT) do not include the crosswind effect which is unfavorable to the performance of Cooling Towers. This effect of the crosswind will be even more unfavorable to the performance of small Cooling Towers since the percentage of the disturbed free air flow is considerably higher than for large NDDCT. Therefore, the validity of the current design methods is questionable for small NDDCT design. Analytical and numerical modeling has been carried to investigate the performance of small NDDCT under different crosswind conditions. The smallest sizes of natural draft Cooling Towers were derived based on current design methods. The effect of various crosswinds on the performance of small Tower is demonstrated with a 3D CFD simulation. Preliminary results showed that the velocity and temperature distributions in the Tower have been significantly influenced by the crosswinds.
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Performance comparison of the crosswind effect on different size of natural draft Dry Cooling Towers
2020Co-Authors: Xiaoxiao Li, Hal Gurgenci, Zhiqiang GuanAbstract:Previous research have identified that the performance of the natural draft Dry Cooling Tower (NDDCT) is seriously influenced by the crosswind. For different size and different shape of the Cooling Towers, the crosswind effects are different. In order to better compare the crosswind effect on the different size of the Cooling Tower, this paper developed four different NDDCT models with the horizontal arranged air-cooled heat exchanger. The heights of the Towers are 20m, 60m, 100m and 140m with the same aspect ratio and same aircooled heat exchanger. The Cooling performance of these four Cooling Towers under crosswind condition were evaluated by the 3-D CFD models and the mechanism of the crosswind effect on the Cooling Tower was discussed.
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CFD simulations on small natural draft Dry Cooling Towers
2020Co-Authors: Yuanshen Lu, Zhiqiang Guan, Hal GurgenciAbstract:The natural draft Dry Cooling Tower (NDDCT) is believed to be the only cost-effective option for Cooling system of geothermal power plants proposed by Queensland Geothermal Energy Centre of Excellence (QGECE). By reviewing literatures related to the design of NDDCT, the effect of crosswind on the Cooling performance of NDDCT is not considered in contemporary design theories for Cooling Tower system. Practical operations on NDDCT showed that the crosswind larger than 1 m/s will have a profound effect on the performance and that cannot be neglected, especially for small size NDDCT. A study on the performance of a 15m-high natural draft Dry Cooling Tower under different crosswind conditions is presented in this paper. CFD models (both 2D and 3D) based on porous media have been established for numerical simulations of the air dynamics and heat transfer inside and outside the Cooling Tower. The CFD results have been validated by comparing the results under no crosswind condition with those obtained in theoretical calculations (1D model). 3D CFD simulations showed that the total Cooling capacity of the NDDCT is unfavourably affected by cross wind, and under certain conditions the heat rejection in the Cooling Tower can be reduced significantly. This trend matches the results of similar studies on large NDDCT found in open literatures well.
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Numerical simulation of solar enhanced natural draft Dry Cooling Towers
2020Co-Authors: Zhiqiang Guan, Hal GurgenciAbstract:Solar Enhanced Natural Draft Dry Cooling Tower is a new concept of hybrid Cooling, in which solar heat collection is added to traditional natural draft Dry Cooling Tower. Adding a solarheated space to further heat the air after it leaves the heat exchangers increases the temperature difference between the inside and outside of Tower, which leads to an increased air flow rate through the heat exchangers therefore better Cooling performance. A one-dimensional model has been developed to predict its Cooling performance by using MATLAB. The purpose of the present paper is to report on results of a detailed numerical analysis and to validate performance predictions from that onedimensional model. A three-dimensional numerical model of a Solar Enhanced Natural Draft Dry Cooling Tower was created using the CFD software FLUENT. Reasonably good agreement is found between these two models.
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spray Cooling system design and optimization for Cooling performance enhancement of natural draft Dry Cooling Tower in concentrated solar power plants
Energy, 2019Co-Authors: Zhiqiang Guan, Hal Gurgenci, Jianyong Wang, Peixin Dong, K. HoomanAbstract:Abstract In concentrated solar power (CSP) plants built in Dry and arid areas, natural draft Dry Cooling Tower (NDDCT) are commonly employed to dissipate waste heat into the atmosphere. The Cooling performance of NDDCT mainly depends on the induced air flow caused by the buoyancy effect. However, the high ambient temperature in summers reduce the Cooling efficiency of Dry Cooling Towers and cause significant power loss for CSP plants. To address this problem, spray Cooling system utilizing water evaporation was developed to pre-cool the inlet hot air. Different designs of spray Cooling systems were proposed and tested on a 20 m high experimental Tower. Experimental data were collected to evaluate the performance of the spray Cooling system. To our knowledge, this is the world's first attempt to practice spray Cooling on a full-scale natural draft Dry Cooling Tower. This study confirms the feasibility and effectiveness of employing spray Cooling for Cooling performance enhancement of NDDCT. With the goal of maximal Cooling effect with least water consumption, the optimal design was proposed, which consists of 3 upward injections at the low level (Height = 2 m), 2 counterflow injections at the middle level (H = 3 m) and 3 counterflow injections at the high level (H = 4 m). The Cooling capacity of NDDCT increases from 789 kW to 841.73 kW, as the result of an intensified natural convection. Moreover, in the spray zone, the presence of a low-temperature area is featured by high relative humidity (70%–80%). The intensified natural convection caused by pre-cooled air and the presence of high vapour concentration are attributed to spray evaporation, which confirms the necessity to introduce the spray Cooling system.
Xiaoxiao Li - One of the best experts on this subject based on the ideXlab platform.
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Performance comparison of the crosswind effect on different size of natural draft Dry Cooling Towers
2020Co-Authors: Xiaoxiao Li, Hal Gurgenci, Zhiqiang GuanAbstract:Previous research have identified that the performance of the natural draft Dry Cooling Tower (NDDCT) is seriously influenced by the crosswind. For different size and different shape of the Cooling Towers, the crosswind effects are different. In order to better compare the crosswind effect on the different size of the Cooling Tower, this paper developed four different NDDCT models with the horizontal arranged air-cooled heat exchanger. The heights of the Towers are 20m, 60m, 100m and 140m with the same aspect ratio and same aircooled heat exchanger. The Cooling performance of these four Cooling Towers under crosswind condition were evaluated by the 3-D CFD models and the mechanism of the crosswind effect on the Cooling Tower was discussed.
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study of flue gas emission and improvement measure in a natural draft Dry Cooling Tower with flue gas injection under unfavorable working conditions
Atmospheric Pollution Research, 2020Co-Authors: Guangjun Yang, Xiaoxiao Li, Li Ding, Wenxin Tian, Zhen Xu, Zhigang Wang, Jingxin Xu, Sheng WangAbstract:Abstract In this paper, we observed that flue gas from a natural draft Dry-Cooling Tower (NDDCT) with flue gas injection could not be discharged smoothly under unfavorable working conditions (e.g., when the louvers are closed in winter), which may have caused severe corrosion on the inner shell of the Cooling Tower. In light of this issue, we proposed an improvement measure. On the basis of the computational fluid dynamics (CFD) method, we established a numerical model for NDDCT with flue gas injection to predict the flow field and pollutant diffusion. We simulated flue gas emissions for a NDDCT with flue gas injection under normal and unfavorable working conditions. The results showed that the air mass flow rate and heat rejection of the Cooling Tower decreased significantly, and the air flow in the Cooling Tower became disorganized when the louvers were closed under unfavorable working condition. Compared with normal working conditions, the pollutant concentration on the inner shell of the Cooling Tower increased by 1.5 times under unfavorable working conditions. After increasing the height of flue gas outlet, the pollutant concentration on the inner shell of the Cooling Tower decreased obviously.
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positive impact of a Tower inlet cover on natural draft Dry Cooling Towers under crosswind conditions
Applied Thermal Engineering, 2018Co-Authors: Mengqi Hu, Xiaoxiao Li, Zihao MiAbstract:Abstract This study proposes a Tower inlet cover to improve the performance of the small natural draft Dry Cooling Tower (NDDCT) under crosswind conditions. CFD analyses are performed on a small NDDCT with Tower inlet covers of different lengths, and the CFD model is validated against experimental results. The air temperature, air pressure, air flow and heat flux fields are presented, and the thermal performance for each heat exchanger and the NDDCT are obtained using CFD simulations. The CFD simulation results show that the high-pressure zone around the Tower side wall, formed by the crosswind, causes the decrease in air flow through the Tower and the deterioration in Tower performance with a crosswind. The Tower inlet cover can improve the Tower performance in crosswinds by increasing the air flow of the heat exchangers. Tower inlet covers with lengths of 1.5 m, 3 m and 4.5 m improve the Tower heat load by 40–65%, 70–130% and 85–230%, respectively, when the crosswind increases from 4 m/s to 12 m/s.
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preliminary analysis of direct and indirect heat rejection systems for a small sco2 brayton cycle using an existing natural draft Dry Cooling Tower
Journal of Energy Engineering-asce, 2018Co-Authors: Xurong Wang, Xiaoxiao Li, Zhiqiang GuanAbstract:AbstractThe supercritical carbon dioxide (sCO2) Brayton cycle has been the focus of much research in recent years because of its high efficiency and compactness. One of the key issues is the heat r...
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investigations on the influence of nozzle arrangement on the pre Cooling effect for the natural draft Dry Cooling Tower
Applied Thermal Engineering, 2018Co-Authors: Zhiqiang Guan, K. Hooman, Hal Gurgenci, Xiaoxiao LiAbstract:Abstract Natural draft Dry Cooling Tower (NDDCT), with little water usage, is a primary choice for power plants in dried regions. However, the increased ambient temperature during summer days decreases the Cooling performance of NDDCT. Inlet air pre-Cooling is used to alleviate the Tower deterioration by making use of water evaporation to remove excess heat from inlet air. To achieve the maximal Cooling effect, the injection heights, radial distances and injection directions of employed nozzle LNN1.5 were studied based on the CFD results. The study shows that lower nozzle placement can cool the central part of the radiator while the higher one cools the middle part. Additionally, the increasing extended length can boost the evaporation process of generated spray. Moreover, the upward and co-flow injections have poorer performance than the downward and counter-flow injections. Furthermore, an introduction of wall cover changes the flow field and drives the pre-cooled air flow through the edge of radiator. Since the wall cover reduces the blockage caused by the near-wall vortex the resultant low-temperature region move outwardly.
Fengqi Si - One of the best experts on this subject based on the ideXlab platform.
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internal flow reconstruction strategies to improve both thermo flow performance and flue gas diffusion characteristic of the integrated Dry Cooling Tower and stack system
Applied Thermal Engineering, 2020Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract The interaction between thermo-flow performance and flue gas injection in an integrated Dry-Cooling Tower and stack system was revealed. Flue gas injection slightly increases the ventilation and heat rejection of the Tower, and rear radiators are protected due to the blocking effect of the desulfurizer and stack. Both the swirl and downwind deflection of internal rising airflows contribute to the chaotic diffusion of flue gas. Two internal flow reconstruction strategies were proposed. One works in the stage of inflow air mixing, and the other works in the following stage of airflow rising. Numerical results show that the former strategy performs better on Tower performance improvement, since the latter one causes a decline of Tower ventilation at low wind speed. Both the two strategies have evident superiority in controlling gas diffusion inside the Tower, especially at the medium wind speed of 10 m/s, the chaos of internal rising airflows reduces remarkably, and the contact area between flue gas and inner Tower shell reduces over 85%. Thanks to the mitigation of plume downwash after flow reconstruction, diffusion passage of flue gas in the atmosphere is uplifted, and the reduction of contact area between flue gas and outer Tower shell reaches 40%.
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study on the effects of apex angle of the delta type radiator on thermo flow performance of natural draft Dry Cooling Tower
International Journal of Heat and Mass Transfer, 2020Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract A numerical model was established to reveal the effects of apex angle of the vertical arranged delta-type radiators on thermo-flow performance of natural draft Dry Cooling Tower. When radiator number is fixed, a large apex angle along with the corresponding long Tower base diameter contribute to Tower performance improvement. The wide apex angle slightly mitigates air inflow deviation at radiator’s inlet and draws in more fresh air. The long base diameter alleviates the adverse impacts of internal vortex formed after air inflow convergence on heat transfer of the downstream radiators. The maximum increment of Cooling capacity of the Tower 15.6% is achieved under the medium wind speed of 8 m/s as apex angel increases from 48° to 60°. As wind speed further increases, sideward and leeward radiators suffer a sharp performance decline, and their performances achieve much smaller enhancement brought by apex angle increase, compared with windward radiators. So downwind deflection of internal rising airflows is more severe under a larger apex angle. When Tower base diameter is fixed, larger apex angle results in fewer radiators. Although Cooling capacity of the entire Tower drops under this strategy, the greater heat dissipation capacity of windward radiators under a larger apex angle would gradually make up the defect of fewer radiators as wind speed increases. However, using larger apex angle but fewer radiators causes an aggravated air inflow rate imbalance among the radiators, which accelerates performance degradations of leeward radiators.
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quantitative research of spray Cooling effects on thermo flow performance of the large scale Dry Cooling Tower with an integrated numerical model
International Journal of Heat and Mass Transfer, 2019Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract An integrated model with a coupling procedure was developed to combine the dynamics of spray injections and natural draft of the Dry Cooling Tower. By the integrated model, the interaction was clearly revealed that pre-Cooling slightly reduces the buoyancy and ventilation of the Tower while enhancing heat transfer, but velocity decrease of inflow air in turn promotes droplet evaporation and enhances spray Cooling effects. Under an example pre-Cooling system, the calculated inflow air temperature drop is about 6.6% larger than that obtained by the traditional model which neglected this interaction. Moreover, spray Cooling effects on Tower performance were directly quantified by the integrated model, and the Tower achieved 6.94% heat dissipation improvement and 2.75% ventilation decrease. According to streamlines, effective air inflow area of the Tower gradually shrinks, which promotes the formations of interferences among the injections and severely impedes the evaporation process. Especially near the inlet of the radiator, evaporation rate hardly grows, and it gets worse under the case of more nozzles. The larger droplet size and the lower droplet velocity under a smaller spray pressure are adverse to droplet evaporation, and spray Cooling makes little sense at low air temperature and especially high air humidity. The proposed integrated model is a powerful tool for spray Cooling research and optimization for the Dry Cooling Tower and some other large-scale objects.
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utilization of partial through flow Tower shell to cope with the excess Cooling capacity of Dry Cooling Tower in extremely cold days with crosswind
International Journal of Thermal Sciences, 2019Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract During low ambient temperature periods, the huge heat transfer temperature difference would result in an excess Cooling capacity of the natural draft Dry Cooling Tower. So low Cooling water temperature and back pressure can be easily achieved in cold days due to the unavoidable air leakage in practical operation, and the excess Cooling capacity is a great threat to the safe operation of the indirect Dry Cooling system. To cope with that problem, a novel partial through-flow Tower shell is proposed. By numerical simulation of the Tower, aerodynamic fields in and around the Tower were presented, and Cooling water temperature drop was exported as well. It was found that thermal performance of the Tower would get enhanced by crosswind under the air leakage condition, but that can be counteracted by the proposed partial through-flow Tower shell. The through-flow Tower shell is effective to reduce air inflow rate and Cooling capacity of the Tower, and increase back pressure and Cooling water temperature after the coupling of the Tower and condenser. Compared with the sideward or leeward through-flow Tower shell, the windward through-flow Tower shell would provide a much larger feasible region for safe operation of the system, and achieve the maximum anti-freezing result at the moderate wind speed. At the fairly high wind speed, the sideward through-flow Tower shell would bring the adverse effect, while the other two forms are still active, although their anti-freezing effects degrade a bit in this condition.
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the adoption of windbreak wall partially rotating to improve thermo flow performance of natural draft Dry Cooling Tower under crosswind
International Journal of Thermal Sciences, 2018Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract To reduce the adverse effect of crosswind on thermo-flow performance of the natural draft Dry Cooling Tower (NDDCT), a novel type of external flat windbreak walls is introduced. Taking the prevailing wind direction as the symmetry axis, windbreak wall arranged at each flank of the Tower is divided into three rotatable columns according to the size of the researched NDDCT, with the rotating angle equal to air inflow deviation angle of nearest Cooling delta. Subsequently, using the steady model and half Tower simulations after comparison, effects of various combinations of the rotatable columns were revealed based on the analysis of velocity and temperature fields in and around the Tower. At the general wind speeds, wall form of only middle column rotating contributes the largest performance improvement to the Tower, which is over 17% at wind speed of 8 m/s, nearly 2.5% larger than that brought by the traditional radial walls. Meanwhile, it was found that outlet water temperatures of the next three Cooling deltas at the back of inner column get increased under the optimal wall form. To overcome this problem, porous walls were tested to be applicable, but without overwhelming superiority, compared to the solid walls. In addition, when crosswind gradually deviates from the specified prevailing wind direction, wall form of only middle column rotating is still superior to the traditional radial walls, especially at a small crosswind deviation angle, but the difference between the benefits brought by the two wall forms to the Tower is decreasing.
Junshan Wang - One of the best experts on this subject based on the ideXlab platform.
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internal flow reconstruction strategies to improve both thermo flow performance and flue gas diffusion characteristic of the integrated Dry Cooling Tower and stack system
Applied Thermal Engineering, 2020Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract The interaction between thermo-flow performance and flue gas injection in an integrated Dry-Cooling Tower and stack system was revealed. Flue gas injection slightly increases the ventilation and heat rejection of the Tower, and rear radiators are protected due to the blocking effect of the desulfurizer and stack. Both the swirl and downwind deflection of internal rising airflows contribute to the chaotic diffusion of flue gas. Two internal flow reconstruction strategies were proposed. One works in the stage of inflow air mixing, and the other works in the following stage of airflow rising. Numerical results show that the former strategy performs better on Tower performance improvement, since the latter one causes a decline of Tower ventilation at low wind speed. Both the two strategies have evident superiority in controlling gas diffusion inside the Tower, especially at the medium wind speed of 10 m/s, the chaos of internal rising airflows reduces remarkably, and the contact area between flue gas and inner Tower shell reduces over 85%. Thanks to the mitigation of plume downwash after flow reconstruction, diffusion passage of flue gas in the atmosphere is uplifted, and the reduction of contact area between flue gas and outer Tower shell reaches 40%.
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study on the effects of apex angle of the delta type radiator on thermo flow performance of natural draft Dry Cooling Tower
International Journal of Heat and Mass Transfer, 2020Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract A numerical model was established to reveal the effects of apex angle of the vertical arranged delta-type radiators on thermo-flow performance of natural draft Dry Cooling Tower. When radiator number is fixed, a large apex angle along with the corresponding long Tower base diameter contribute to Tower performance improvement. The wide apex angle slightly mitigates air inflow deviation at radiator’s inlet and draws in more fresh air. The long base diameter alleviates the adverse impacts of internal vortex formed after air inflow convergence on heat transfer of the downstream radiators. The maximum increment of Cooling capacity of the Tower 15.6% is achieved under the medium wind speed of 8 m/s as apex angel increases from 48° to 60°. As wind speed further increases, sideward and leeward radiators suffer a sharp performance decline, and their performances achieve much smaller enhancement brought by apex angle increase, compared with windward radiators. So downwind deflection of internal rising airflows is more severe under a larger apex angle. When Tower base diameter is fixed, larger apex angle results in fewer radiators. Although Cooling capacity of the entire Tower drops under this strategy, the greater heat dissipation capacity of windward radiators under a larger apex angle would gradually make up the defect of fewer radiators as wind speed increases. However, using larger apex angle but fewer radiators causes an aggravated air inflow rate imbalance among the radiators, which accelerates performance degradations of leeward radiators.
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quantitative research of spray Cooling effects on thermo flow performance of the large scale Dry Cooling Tower with an integrated numerical model
International Journal of Heat and Mass Transfer, 2019Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract An integrated model with a coupling procedure was developed to combine the dynamics of spray injections and natural draft of the Dry Cooling Tower. By the integrated model, the interaction was clearly revealed that pre-Cooling slightly reduces the buoyancy and ventilation of the Tower while enhancing heat transfer, but velocity decrease of inflow air in turn promotes droplet evaporation and enhances spray Cooling effects. Under an example pre-Cooling system, the calculated inflow air temperature drop is about 6.6% larger than that obtained by the traditional model which neglected this interaction. Moreover, spray Cooling effects on Tower performance were directly quantified by the integrated model, and the Tower achieved 6.94% heat dissipation improvement and 2.75% ventilation decrease. According to streamlines, effective air inflow area of the Tower gradually shrinks, which promotes the formations of interferences among the injections and severely impedes the evaporation process. Especially near the inlet of the radiator, evaporation rate hardly grows, and it gets worse under the case of more nozzles. The larger droplet size and the lower droplet velocity under a smaller spray pressure are adverse to droplet evaporation, and spray Cooling makes little sense at low air temperature and especially high air humidity. The proposed integrated model is a powerful tool for spray Cooling research and optimization for the Dry Cooling Tower and some other large-scale objects.
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utilization of partial through flow Tower shell to cope with the excess Cooling capacity of Dry Cooling Tower in extremely cold days with crosswind
International Journal of Thermal Sciences, 2019Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract During low ambient temperature periods, the huge heat transfer temperature difference would result in an excess Cooling capacity of the natural draft Dry Cooling Tower. So low Cooling water temperature and back pressure can be easily achieved in cold days due to the unavoidable air leakage in practical operation, and the excess Cooling capacity is a great threat to the safe operation of the indirect Dry Cooling system. To cope with that problem, a novel partial through-flow Tower shell is proposed. By numerical simulation of the Tower, aerodynamic fields in and around the Tower were presented, and Cooling water temperature drop was exported as well. It was found that thermal performance of the Tower would get enhanced by crosswind under the air leakage condition, but that can be counteracted by the proposed partial through-flow Tower shell. The through-flow Tower shell is effective to reduce air inflow rate and Cooling capacity of the Tower, and increase back pressure and Cooling water temperature after the coupling of the Tower and condenser. Compared with the sideward or leeward through-flow Tower shell, the windward through-flow Tower shell would provide a much larger feasible region for safe operation of the system, and achieve the maximum anti-freezing result at the moderate wind speed. At the fairly high wind speed, the sideward through-flow Tower shell would bring the adverse effect, while the other two forms are still active, although their anti-freezing effects degrade a bit in this condition.
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the adoption of windbreak wall partially rotating to improve thermo flow performance of natural draft Dry Cooling Tower under crosswind
International Journal of Thermal Sciences, 2018Co-Authors: Fengqi Si, Junshan WangAbstract:Abstract To reduce the adverse effect of crosswind on thermo-flow performance of the natural draft Dry Cooling Tower (NDDCT), a novel type of external flat windbreak walls is introduced. Taking the prevailing wind direction as the symmetry axis, windbreak wall arranged at each flank of the Tower is divided into three rotatable columns according to the size of the researched NDDCT, with the rotating angle equal to air inflow deviation angle of nearest Cooling delta. Subsequently, using the steady model and half Tower simulations after comparison, effects of various combinations of the rotatable columns were revealed based on the analysis of velocity and temperature fields in and around the Tower. At the general wind speeds, wall form of only middle column rotating contributes the largest performance improvement to the Tower, which is over 17% at wind speed of 8 m/s, nearly 2.5% larger than that brought by the traditional radial walls. Meanwhile, it was found that outlet water temperatures of the next three Cooling deltas at the back of inner column get increased under the optimal wall form. To overcome this problem, porous walls were tested to be applicable, but without overwhelming superiority, compared to the solid walls. In addition, when crosswind gradually deviates from the specified prevailing wind direction, wall form of only middle column rotating is still superior to the traditional radial walls, especially at a small crosswind deviation angle, but the difference between the benefits brought by the two wall forms to the Tower is decreasing.
