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Pega Hrnjak - One of the best experts on this subject based on the ideXlab platform.
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effect of inclination on heat transfer and flow regimes in large flattened tube steam Condensers
Applied Thermal Engineering, 2019Co-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 used in air-cooled Condensers for power plants is presented. This is the fourth of a four-part group of papers. The first three parts (Kang et al., 2017; Davies et al., 2017, 2018) published in the same journal present the facility, pressure drop, void fraction, flow regime and heat transfer results, while this study presents the effects of inclination on heat transfer and flow regimes. The Condenser is a flattened steel tube with brazed aluminum fins. The full tube has dimensions 10.72 m × 214 mm × 18 mm. The Condenser tube is cut in half lengthwise and covered with a polycarbonate window to perform visualization simultaneously with the heat transfer measurements. The steam is condensed at atmospheric pressure, and cooled by air at a uniform velocity profile. The angle of inclination is varied from horizontal (0°) to 75° downward. Condenser performance is also predicted with a model. The majority of the Condenser is found to be in the stratified flow regime for all inclinations tested, with only a short annular section at the inlet of the Condenser. The tubes inclined greater than 60° are also found to have stratified-wavy flow near the Condenser outlet. Overall Condenser U is found to increase with increasing downward inclination angle of the Condenser, with a maximum increase of approximately 4% at 75° inclination. This improvement is found to be the result of improved drainage and increased void fraction near the Condenser outlet. Mean steam-side heat transfer coefficient 1 (HTC) is found to remain constant along the tube, and for the entire Condenser, with changes in tube inclination angle. Commonly-used inclined condensation HTC correlations are found to underpredict the magnitude of the experimentally-determined steam-side HTC.
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separation in Condensers as a way to improve efficiency
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Jun Li, Pega HrnjakAbstract:Abstract This paper introduces the concept of separation of two-phase flow in Condensers and discusses its possible application of enhancing the heat transfer performance by capitalizing on the high local heat transfer coefficient of vapor flow. The benefit of vapor–liquid refrigerant separation and the reason why it will improve the Condenser performance are explained. Numerical studies are performed on an R-134a microchannel Condenser. Model predicts that at the same mass flow rate, the exit temperature is lower by 1.3 K in the separation Condenser than in the baseline Condenser while the difference of pressure drop remains within 2%. 6.1% more flow rate of condensate is predicted in the separation Condenser as another comparison criterion. In addition, the trade-off between high quality and low mass flux for the vapor path downstream of the separation header is investigated by the model and results are presented. Modeling is conducted with pre-assumed separation efficiency in the header. The real value requires further investigation.
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experimental and numerical study on microchannel and round tube Condensers in a r410a residential air conditioning system
International Journal of Refrigeration-revue Internationale Du Froid, 2008Co-Authors: Chang Yong Park, Pega HrnjakAbstract:Abstract The effect of different type of Condensers on the performance of R410A residential air-conditioning systems was investigated in this study. Two R410A residential air-conditioning systems, one with a microchannel Condenser and the other with a round-tube Condenser, were examined experimentally, while the other components of the two systems were identical except the Condensers. Two Condensers had almost same package volumes. The two systems were operated in separate environmental chambers and their performance was measured in ARI A, B, and C conditions. Both the COP and cooling capacity of the system with the microchannel Condenser were higher than those for the round-tube Condenser in all test conditions. The refrigerant charge amount and the refrigerant pressure drop were measured; the results showed a reduction of charge and pressure drop in the microchannel Condenser. A numerical model for the microchannel Condenser was developed and its results were compared with the experiments. The model simulated the Condenser with consideration given to the non-uniform air distribution at the face of the Condenser and refrigerant distribution in the headers. The results showed that the effect of the air and refrigerant distribution was not a significant parameter in predicting the capacity of the microchannel Condenser experimentally examined in this study. Temperature contours, generated from the measured air exit temperatures, showed the refrigerant distribution in the microchannel Condenser indirectly. The temperature contours developed from the model results showed a relatively good agreement with the contours for measured air exit temperatures of the microchannel Condenser.
L J Yang - One of the best experts on this subject based on the ideXlab platform.
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trapezoidal array of air cooled Condensers to restrain the adverse impacts of ambient winds in a power plant
Applied Energy, 2012Co-Authors: L J Yang, M H Wang, Yanru YangAbstract:Ambient winds may deteriorate the thermo-flow performances of air-cooled Condensers, so it is of use to take measures against the adverse impacts of winds upon the air-cooled Condensers in a power plant. On the basis of a 2×600MW direct dry cooling power plant, a new trapezoidal array of air-cooled Condensers is proposed. The computational models of the air-side fluid and heat flows of the air-cooled Condensers in a trapezoidal array at various wind speeds and in various wind directions are developed, and the velocity and temperature fields are presented by using CFD simulations. The volumetric flow rate, inlet air temperature and heat rejection for different Condenser cells are obtained and compared with those of the current air-cooled Condensers in the rectangular array. The results show that the reversed flows arose in the upwind Condenser cells at high wind speeds disappear due to the trapezoidal array of air-cooled Condensers, resulting in a lowered inlet air temperature and an increased heat rejection of the upwind Condenser cells. The hot plume recirculation in the wind direction of 0° becomes very weak and only appears at one side near the main buildings. The thermo-flow performances are improved to a certain extent thanks to the trapezoidal array of air-cooled Condensers. It is recommended that air-cooled Condensers in a power plant take the form of trapezoidal array to restrain the adverse impacts of ambient winds.
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wind effect on the thermo flow performances and its decay characteristics for air cooled Condensers in a power plant
International Journal of Thermal Sciences, 2012Co-Authors: L J Yang, Yanru YangAbstract:Abstract Ambient wind plays important roles in the thermo-flow performances of air-cooled Condensers, but the wind effect mainly imposes on the upwind and bilateral Condenser cells and will decay immediately. It is of benefit to the design and operation optimization of air-cooled Condensers in a power plant to investigate the wind effect and its decay characteristics. On the basis of a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flows for the air-cooled Condensers at various ambient wind speeds and directions are set up. The velocity and temperature fields are presented and the volumetric flow rate, inlet air temperature and heat rejection for different Condenser cells are obtained by using CFD simulation. The results show that the reversed flows happened in the upwind Condenser cells lead to the high inlet air temperature, worsening the cooling capability of air at high wind speeds. Due to the combined behavior of hot plume discharge and ambient wind, the wind effect decays rapidly along the wind direction. At the wind direction of 90°, the deficiencies of the thermo-flow performances of air-cooled Condensers are mainly resulted from the flow rate decrease of the upwind Condenser cells, not the hot plume recirculation. The hot plume recirculation flows play adverse roles in deteriorating the performances of air-cooled Condensers at the wind direction of 0°.
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space characteristics of the thermal performance for air cooled Condensers at ambient winds
International Journal of Heat and Mass Transfer, 2011Co-Authors: L J Yang, Yang YangAbstract:Abstract Ambient winds may lead to poor fan performance, exhaust air recirculation and mal-distribution of the air across the tube bundles of the air-cooled Condensers in a power plant. Investigations of the impacts of the ambient winds on the air-cooled Condensers are key area of focus. Based on a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flow in the air-cooled Condensers at various ambient wind speeds and directions are set up by introducing the radiator model to the fin-tube bundles. The volumetric flow rate, inlet air temperature and heat rejection for different air-cooled Condensers as a whole, Condenser cells and fin-tube bundles are obtained by using CFD simulation. The results show that the thermo-flow performances for the air-cooled Condenser as a whole, Condenser cells and heat exchanger bundles vary widely in space. The thermal performances of the air-cooled Condensers, Condenser cells and fin-tube bundles at the downstream are generally superior to those at the upwind. It is of use for the upwind fan regulations and the A-frame Condenser cell geometric optimization to investigate the space characteristics of the thermal performance for the air-cooled Condensers in a power plant.
Yanru Yang - One of the best experts on this subject based on the ideXlab platform.
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trapezoidal array of air cooled Condensers to restrain the adverse impacts of ambient winds in a power plant
Applied Energy, 2012Co-Authors: L J Yang, M H Wang, Yanru YangAbstract:Ambient winds may deteriorate the thermo-flow performances of air-cooled Condensers, so it is of use to take measures against the adverse impacts of winds upon the air-cooled Condensers in a power plant. On the basis of a 2×600MW direct dry cooling power plant, a new trapezoidal array of air-cooled Condensers is proposed. The computational models of the air-side fluid and heat flows of the air-cooled Condensers in a trapezoidal array at various wind speeds and in various wind directions are developed, and the velocity and temperature fields are presented by using CFD simulations. The volumetric flow rate, inlet air temperature and heat rejection for different Condenser cells are obtained and compared with those of the current air-cooled Condensers in the rectangular array. The results show that the reversed flows arose in the upwind Condenser cells at high wind speeds disappear due to the trapezoidal array of air-cooled Condensers, resulting in a lowered inlet air temperature and an increased heat rejection of the upwind Condenser cells. The hot plume recirculation in the wind direction of 0° becomes very weak and only appears at one side near the main buildings. The thermo-flow performances are improved to a certain extent thanks to the trapezoidal array of air-cooled Condensers. It is recommended that air-cooled Condensers in a power plant take the form of trapezoidal array to restrain the adverse impacts of ambient winds.
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wind effect on the thermo flow performances and its decay characteristics for air cooled Condensers in a power plant
International Journal of Thermal Sciences, 2012Co-Authors: L J Yang, Yanru YangAbstract:Abstract Ambient wind plays important roles in the thermo-flow performances of air-cooled Condensers, but the wind effect mainly imposes on the upwind and bilateral Condenser cells and will decay immediately. It is of benefit to the design and operation optimization of air-cooled Condensers in a power plant to investigate the wind effect and its decay characteristics. On the basis of a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flows for the air-cooled Condensers at various ambient wind speeds and directions are set up. The velocity and temperature fields are presented and the volumetric flow rate, inlet air temperature and heat rejection for different Condenser cells are obtained by using CFD simulation. The results show that the reversed flows happened in the upwind Condenser cells lead to the high inlet air temperature, worsening the cooling capability of air at high wind speeds. Due to the combined behavior of hot plume discharge and ambient wind, the wind effect decays rapidly along the wind direction. At the wind direction of 90°, the deficiencies of the thermo-flow performances of air-cooled Condensers are mainly resulted from the flow rate decrease of the upwind Condenser cells, not the hot plume recirculation. The hot plume recirculation flows play adverse roles in deteriorating the performances of air-cooled Condensers at the wind direction of 0°.
Cedric Briens - One of the best experts on this subject based on the ideXlab platform.
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fractional condensation of bio oil vapors produced from birch bark pyrolysis
Separation and Purification Technology, 2014Co-Authors: Akhil Tumbalam Gooty, Cedric Briens, Franco BerrutiAbstract:The bio-oil vapors produced from the pyrolysis of birch bark have been fractionated using a series of three Condensers maintained at different temperatures. The temperatures of the Condensers have been optimized in order to separate the water present in the bio-oil vapor stream from the organic phases and, consequently, increase the quality and the stability of the bio-oil. The Condenser train consisted of an electrostatic precipitator-cum-Condenser (C–ESP) installed between two cyclonic Condensers. As a result of the high efficiency of the fractional condensation system, the water content of the fractionated bio-oil was reduced to be less than 1 wt%. The effect of pyrolysis temperature on the fractionated bio-oil yield and characteristics is also reported.
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kraft lignin pyrolysis and fractional condensation of its bio oil vapors
Journal of Analytical and Applied Pyrolysis, 2014Co-Authors: Akhil Tumbalam Gooty, Franco Berruti, Cedric BriensAbstract:Abstract Kraft lignin has been pyrolyzed in a modified bubbling bed reactor coupled with an internal stirrer, and the resulting bio-oil vapors have been fractionated using a series of three Condensers maintained at different temperatures. The temperatures of the Condensers have been optimized in order to selectively separate most of the water present in the bio-oil vapor stream and increase the quality of the remaining bio-oil. The Condenser train comprised of an electrostatic precipitator-cum-Condenser (C-ESP) installed between two cyclonic Condensers. The fractionated bio-oil was found to be rich in phenolic compounds with a water content of less than 1 wt%. The effect of pyrolysis temperature on the fractionated bio-oil yield and characteristics is also discussed.
Zeyi Xiao - One of the best experts on this subject based on the ideXlab platform.
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ethanol fermentation coupled with pervaporation by energy efficient mechanical vapor compression
Energy Procedia, 2017Co-Authors: Zeyi XiaoAbstract:Abstract Ethanol production could be enhanced with ethanol removal in situ from the broth, during the experiments of ethanol fermentation coupled with pervaporation by mechanical vapor compression. The yeast cell could continuously grow for long time with cell density of 38 g/L obtained. The byproducts accumulation in the broth led to the culture deterioration of the fermentation and became the main inhibitor against the cell growth. The total flux of the polydimethylsiloxane (PDMS) membrane was in the range of 350 g/m 2 /h and 600 g/m 2 /h. At the downstream of the membrane, part of the permeate vapor under the vacuum condition before the inlet of the vacuum pump was condensed at the first Condenser by the running water at the room temperature and the non-condensed vapor enriched with ethanol was compressed to the atmospheric pressure and pumped into the second Condenser by the vacuum pump. The vapor in the second Condenser was easily condensed into a liquid by air at room temperature since the pressure was increased. Ethanol concentration of over 50wt% could be obtained in the second Condenser, which could greatly reduce the amount of the waste water treatment. Recovery of the permeate vapor heat would be achieved by the use of mechanical vapor compression heat pump, which could evidently save energy.
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energy efficient of ethanol recovery in pervaporation membrane bioreactor with mechanical vapor compression eliminating the cold traps
Bioresource Technology, 2016Co-Authors: Zeyi XiaoAbstract:An energy efficient pervaporation membrane bioreactor with mechanical vapor compression was developed for ethanol recovery during the process of fermentation coupled with pervaporation. Part of the permeate vapor at the membrane downstream under the vacuum condition was condensed by running water at the first Condenser and the non-condensed vapor enriched with ethanol was compressed to the atmospheric pressure and pumped into the second Condenser, where the vapor was easily condensed into a liquid by air. Three runs of fermentation-pervaporation experiment have been carried out lasting for 192h, 264h and 360h respectively. Complete vapor recovery validated the novel pervaporation membrane bioreactor. The total flux of the polydimethylsiloxane (PDMS) membrane was in the range of 350gm(-2)h(-1) and 600gm(-2)h(-1). Compared with the traditional cold traps condensation, mechanical vapor compression behaved a dominant energy saving feature.