In the present study, the ice slurry refrigeration system with pre-cooling heat exchanger (ISSH) is studied experimentally to achieve the system performance, ice crystal formation time and the temperature of ice cryst...In the present study, the ice slurry refrigeration system with pre-cooling heat exchanger (ISSH) is studied experimentally to achieve the system performance, ice crystal formation time and the temperature of ice crystal formation. The operating parameters considered in this paper include the concentration of salt solution, suction pressure, discharge pressure and Energy Efficiency Ratio (EER). The result shows that the temperature of critical time of ice crystal formation decreases with the increasing concentration of salt solution and that the ice crystal formation time increases with the increasing concentration of salt solution. In the same concentration of salt solution, the ice crystal formation temperature of ISSH is lower than that of basic ice slurry refrigeration system (BISS), and the ice crystal formation time of ISSH is shorter than that of BISS. On the whole, the EER of ice slurry refrigeration system with pre-cooling heat exchanger is higher than that of basic ice slurry refrigeration system.展开更多
Various pre-cooling methods for‘Kyoho’grapes were selected,such as forced-air pre-cooling(FAPC),vacuum pre-cooling,natural convection pre-cooling(NCPC),electrolyzed water pre-cooling,cold water pre-cooling,and fluid...Various pre-cooling methods for‘Kyoho’grapes were selected,such as forced-air pre-cooling(FAPC),vacuum pre-cooling,natural convection pre-cooling(NCPC),electrolyzed water pre-cooling,cold water pre-cooling,and fluid ice pre-cooling.The aim of this study was to determine the most suitable pre-cooling method for grapes.The storage temperature of grapes was(4±0.5)℃ with a relative humidity of 85%,and physiological parameters were measured every 5 d.All pre-cooling methods,except for NCPC,were able to complete the pre-cooling process within 20 min.Interestingly,water and ice cooling methods were not suitable for pre-cooling grapes,probably due to microbial growth and damage to cellular tissue.In contrast,three groups of air pre-cooling methods were more effective in preserving freshness,the best of which was FAPC.It was found that FAPC inhibited grape weight loss,moisture loss,respiration rate,total viable count,malondialdehyde,and relative electrolyte leakage,while stimulating the activities of superoxide dismutase and phenylalanine ammonia-lyase.It also suppressed the activity of polyphenol oxidase.Additionally,in the FAPC group,optimal hardness,titratable acidity,and vitamin C content were observed.Among all the tested methods,FAPC demonstrated better efficacy in delaying the softening and senescence of‘Kyoho’grapes,thereby preserving fruit quality and nutritional content.展开更多
射流预冷技术是提高加力冲压双模态燃烧的涡轮基组合循环发动机(Turbine Based Combined Cycle,TBCC)涡轮模态上限,改善涡轮冲压过渡模态性能的有效方法,但是喷水会影响涡轮模态加力燃烧室的燃烧特性。本文利用数值计算的方法设计了合...射流预冷技术是提高加力冲压双模态燃烧的涡轮基组合循环发动机(Turbine Based Combined Cycle,TBCC)涡轮模态上限,改善涡轮冲压过渡模态性能的有效方法,但是喷水会影响涡轮模态加力燃烧室的燃烧特性。本文利用数值计算的方法设计了合适的喷嘴布置方案,在固定喷注点和点火点距离的条件下,研究了来流条件对于液滴蒸发性能的影响,并实验研究了喷水对于加力燃烧室稳态燃烧特性的影响。结果表明:来流温度是影响预冷段出口温度分布均匀性的关键因素,温度升高会导致出口温度分布的不均匀性增加;而来流速度则是影响出口总压分布均匀性的关键因素,随着来流速度的增加,总压分布的均匀性明显下降。喷水量0~5%内喷水不会对火焰的燃烧稳定性产生严重危害,而且适量喷水条件可显著改善火焰的燃烧稳定性。在本文的试验条件下,在高来流温度工况下(>800 K),1%喷水量增强了火焰的总释热量,改善了加力燃烧室内火焰燃烧的抗干扰能力,使得火焰表现出更强的稳健性。适量喷水可促进燃烧释热反应,提高了火焰的燃烧温度,改善了加力燃烧效率,有利于提升加力燃烧室的整体燃烧性能。展开更多
To achieve required indoor air quality,fresh air supply in buildings should meet relevant standards and regulations.However,the handling of fresh air introduced a cooling load that takes up a large portion of building...To achieve required indoor air quality,fresh air supply in buildings should meet relevant standards and regulations.However,the handling of fresh air introduced a cooling load that takes up a large portion of building energy consumption,especially in tropical and subtropical areas.A proper way should be employed to reduce the cooling load of fresh air.Radiative sky cooling,which is the process that an object cools itself by emitting thermal radiation to outer space without any energy input,is a cost-effective and eco-friendly technology.In this work,a fresh air pre-cooling system using radiative sky cooling is proposed to reduce fresh air cooling load.The system,consisting of filters,a radiative air-cooling system,an air handling unit(AHU),fans,etc.,is installed on the rooftop of the modeled building.Six cities in low-latitude areas are selected and investigated.Results show that with the radiative air-cooling system installed,annual cooling energy consumption of the modeled building can be reduced by around 10%in most cities.For arid areas,e.g.,Abu Dhabi,the system has even better performance with 19.34%annual cooling energy saving.展开更多
Objectives:In order to improve the prediction accuracy of forced-air pre-cooling for blueberries,a mathematical model of forced-air pre-cooling for blueberries based on the micro-cluster method was established.Materia...Objectives:In order to improve the prediction accuracy of forced-air pre-cooling for blueberries,a mathematical model of forced-air pre-cooling for blueberries based on the micro-cluster method was established.Materials and Methods:In order to determine the optimal micro-cluster model parameters suitable for forced air pre-cooling of blueberries,three factors controlling the micro-cluster geometry parameters were evaluated by 7/8 pre-cooling time,uniformity,and convective heat transfer coeffcient.Results:It was found that the optimal values of the number of micro-clusters(n3),the distance between individual units within a micro-cluster(a)and the distance between micro-clusters(c)were 3,0.75,and 0.2,respectively.Under these optimal values,the temperature error of the micro-cluster method remained below 1°C,achieving highly accurate temperature predictions during the blueberry pre-cooling process.The results showed that the micro-cluster method effectively solved the challenges of complex confguration,long simulation time,and low accuracy compared to the porous medium and equivalent sphere methods.Conclusion:Based on the above analysis,it can be concluded that the micro-cluster method provids a theoretical basis for optimizing forced-air pre-cooling processes and making informed control decisions.展开更多
冷冻熟面因口感好、方便等特点,发展潜力巨大。预冷是影响其品质的关键因素,为探究冷冻熟面在不同预冷方式处理的过程中品质特性的变化,选取了3种预冷方式:冰箱预冷(refrigerator pre-cooling,RPC)、冷水预冷(cold water pre-cooling,CW...冷冻熟面因口感好、方便等特点,发展潜力巨大。预冷是影响其品质的关键因素,为探究冷冻熟面在不同预冷方式处理的过程中品质特性的变化,选取了3种预冷方式:冰箱预冷(refrigerator pre-cooling,RPC)、冷水预冷(cold water pre-cooling,CWPC)、真空预冷(vacuum pre-cooling,VPC),4种预冷终温:20、15、10、5℃,对面条进行预冷。利用质构仪、傅里叶红外光谱仪、低场核磁等手段,探究不同预冷方式对冷冻熟面水分含量、质构特性、微观结构、蛋白质二级结构、水分分布等特性的影响规律。结果表明:RPC处理后的面条自由水含量增加,微观结构遭到破坏,面筋网络结构断裂,对面条品质产生负面影响;CWPC处理后的面条水分含量显著提升(P<0.05),在5℃升高至73.35%,预冷至20℃和15℃的面条有较好的拉伸特性和面筋网络结构,但随着预冷终温的降低,面条吸入更多的水分,形成了更多的冰晶,面条的品质特性有所下降;VPC处理后的面条水分含量显著(P<0.05)降低,在5℃时达到最低,与对照组相比下降了3.13%。VPC处理后的面条在硬度、弹性、黏性、咀嚼性上都存在下降趋势,蛋白质二级结构更有序,微观结构更连续、致密。因此,VPC对冷冻熟面的品质特性产生正面影响。研究结果为不同预冷方式在冷冻熟面产业中的应用提供了理论参考。展开更多
The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performan...The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser,thereby reducing the coefficient of performance.The experiments are performed on ACU with and without using an external cooling-water loop under different climate conditions.By using the experimental data,the systems’performances for both cases are evaluated based on the energy,exergy,and pressure drop analysis.Effects of several parameters,e.g.,ambient temperature,inlet water temperature,and water volume flow rate,on the energy and exergy performances of ACU systems are presented for the purpose of comparison.The outcomes display that the use of an external cooling water loop system has a significant impact on the system performance as compared to conventional ACU.The results display that the addition of an external cooling-water loop leads to a reduction in the compressor power consumption and to an increase in the coefficient of performance(COP)as compared to a normal ACU.The maximum reduction in compressor power consumption is obtained equal 37%at T_(w)=15℃and 11 L/min,whereas the maximum enhancement in COP is obtained equal 21.5%at T_(w)=30℃,11 L/min,and T_(amb)=45℃.The modified model shows an increase in exergy efficiency with the maximum enhancement of about 17%at T_(w)=30℃and 15.8 L/min.The use of an external cooling water loop leads to a reduction in the irreversibility process of the compressor,evaporator and expansion valve and to an increase in the condenser losses.The outcomes show that the pressure drop is reduced by using a cooling water loop as compared to a normal ACU,where the reduction becomes more evident with a reduction in water volume flow rate and inlet temperature.Finally,the present study reveals that the use of an external cooling water loop system leads to an improvement in the performance of ACUs.展开更多
文摘In the present study, the ice slurry refrigeration system with pre-cooling heat exchanger (ISSH) is studied experimentally to achieve the system performance, ice crystal formation time and the temperature of ice crystal formation. The operating parameters considered in this paper include the concentration of salt solution, suction pressure, discharge pressure and Energy Efficiency Ratio (EER). The result shows that the temperature of critical time of ice crystal formation decreases with the increasing concentration of salt solution and that the ice crystal formation time increases with the increasing concentration of salt solution. In the same concentration of salt solution, the ice crystal formation temperature of ISSH is lower than that of basic ice slurry refrigeration system (BISS), and the ice crystal formation time of ISSH is shorter than that of BISS. On the whole, the EER of ice slurry refrigeration system with pre-cooling heat exchanger is higher than that of basic ice slurry refrigeration system.
基金supported by the Key Project in the Field of Agriculture by the Shanghai Municipal Commission of Science and Technology(No.23N31900100)the Shanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation(No.19DZ2284000).
文摘Various pre-cooling methods for‘Kyoho’grapes were selected,such as forced-air pre-cooling(FAPC),vacuum pre-cooling,natural convection pre-cooling(NCPC),electrolyzed water pre-cooling,cold water pre-cooling,and fluid ice pre-cooling.The aim of this study was to determine the most suitable pre-cooling method for grapes.The storage temperature of grapes was(4±0.5)℃ with a relative humidity of 85%,and physiological parameters were measured every 5 d.All pre-cooling methods,except for NCPC,were able to complete the pre-cooling process within 20 min.Interestingly,water and ice cooling methods were not suitable for pre-cooling grapes,probably due to microbial growth and damage to cellular tissue.In contrast,three groups of air pre-cooling methods were more effective in preserving freshness,the best of which was FAPC.It was found that FAPC inhibited grape weight loss,moisture loss,respiration rate,total viable count,malondialdehyde,and relative electrolyte leakage,while stimulating the activities of superoxide dismutase and phenylalanine ammonia-lyase.It also suppressed the activity of polyphenol oxidase.Additionally,in the FAPC group,optimal hardness,titratable acidity,and vitamin C content were observed.Among all the tested methods,FAPC demonstrated better efficacy in delaying the softening and senescence of‘Kyoho’grapes,thereby preserving fruit quality and nutritional content.
文摘射流预冷技术是提高加力冲压双模态燃烧的涡轮基组合循环发动机(Turbine Based Combined Cycle,TBCC)涡轮模态上限,改善涡轮冲压过渡模态性能的有效方法,但是喷水会影响涡轮模态加力燃烧室的燃烧特性。本文利用数值计算的方法设计了合适的喷嘴布置方案,在固定喷注点和点火点距离的条件下,研究了来流条件对于液滴蒸发性能的影响,并实验研究了喷水对于加力燃烧室稳态燃烧特性的影响。结果表明:来流温度是影响预冷段出口温度分布均匀性的关键因素,温度升高会导致出口温度分布的不均匀性增加;而来流速度则是影响出口总压分布均匀性的关键因素,随着来流速度的增加,总压分布的均匀性明显下降。喷水量0~5%内喷水不会对火焰的燃烧稳定性产生严重危害,而且适量喷水条件可显著改善火焰的燃烧稳定性。在本文的试验条件下,在高来流温度工况下(>800 K),1%喷水量增强了火焰的总释热量,改善了加力燃烧室内火焰燃烧的抗干扰能力,使得火焰表现出更强的稳健性。适量喷水可促进燃烧释热反应,提高了火焰的燃烧温度,改善了加力燃烧效率,有利于提升加力燃烧室的整体燃烧性能。
基金support from the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20200373).
文摘To achieve required indoor air quality,fresh air supply in buildings should meet relevant standards and regulations.However,the handling of fresh air introduced a cooling load that takes up a large portion of building energy consumption,especially in tropical and subtropical areas.A proper way should be employed to reduce the cooling load of fresh air.Radiative sky cooling,which is the process that an object cools itself by emitting thermal radiation to outer space without any energy input,is a cost-effective and eco-friendly technology.In this work,a fresh air pre-cooling system using radiative sky cooling is proposed to reduce fresh air cooling load.The system,consisting of filters,a radiative air-cooling system,an air handling unit(AHU),fans,etc.,is installed on the rooftop of the modeled building.Six cities in low-latitude areas are selected and investigated.Results show that with the radiative air-cooling system installed,annual cooling energy consumption of the modeled building can be reduced by around 10%in most cities.For arid areas,e.g.,Abu Dhabi,the system has even better performance with 19.34%annual cooling energy saving.
基金supported by the Natural Science Foundation of Shandong Province,China(No.ZR2021QC186)the China Postdoctoral Science Foundation(No.2023M743923).
文摘Objectives:In order to improve the prediction accuracy of forced-air pre-cooling for blueberries,a mathematical model of forced-air pre-cooling for blueberries based on the micro-cluster method was established.Materials and Methods:In order to determine the optimal micro-cluster model parameters suitable for forced air pre-cooling of blueberries,three factors controlling the micro-cluster geometry parameters were evaluated by 7/8 pre-cooling time,uniformity,and convective heat transfer coeffcient.Results:It was found that the optimal values of the number of micro-clusters(n3),the distance between individual units within a micro-cluster(a)and the distance between micro-clusters(c)were 3,0.75,and 0.2,respectively.Under these optimal values,the temperature error of the micro-cluster method remained below 1°C,achieving highly accurate temperature predictions during the blueberry pre-cooling process.The results showed that the micro-cluster method effectively solved the challenges of complex confguration,long simulation time,and low accuracy compared to the porous medium and equivalent sphere methods.Conclusion:Based on the above analysis,it can be concluded that the micro-cluster method provids a theoretical basis for optimizing forced-air pre-cooling processes and making informed control decisions.
文摘冷冻熟面因口感好、方便等特点,发展潜力巨大。预冷是影响其品质的关键因素,为探究冷冻熟面在不同预冷方式处理的过程中品质特性的变化,选取了3种预冷方式:冰箱预冷(refrigerator pre-cooling,RPC)、冷水预冷(cold water pre-cooling,CWPC)、真空预冷(vacuum pre-cooling,VPC),4种预冷终温:20、15、10、5℃,对面条进行预冷。利用质构仪、傅里叶红外光谱仪、低场核磁等手段,探究不同预冷方式对冷冻熟面水分含量、质构特性、微观结构、蛋白质二级结构、水分分布等特性的影响规律。结果表明:RPC处理后的面条自由水含量增加,微观结构遭到破坏,面筋网络结构断裂,对面条品质产生负面影响;CWPC处理后的面条水分含量显著提升(P<0.05),在5℃升高至73.35%,预冷至20℃和15℃的面条有较好的拉伸特性和面筋网络结构,但随着预冷终温的降低,面条吸入更多的水分,形成了更多的冰晶,面条的品质特性有所下降;VPC处理后的面条水分含量显著(P<0.05)降低,在5℃时达到最低,与对照组相比下降了3.13%。VPC处理后的面条在硬度、弹性、黏性、咀嚼性上都存在下降趋势,蛋白质二级结构更有序,微观结构更连续、致密。因此,VPC对冷冻熟面的品质特性产生正面影响。研究结果为不同预冷方式在冷冻熟面产业中的应用提供了理论参考。
文摘The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser,thereby reducing the coefficient of performance.The experiments are performed on ACU with and without using an external cooling-water loop under different climate conditions.By using the experimental data,the systems’performances for both cases are evaluated based on the energy,exergy,and pressure drop analysis.Effects of several parameters,e.g.,ambient temperature,inlet water temperature,and water volume flow rate,on the energy and exergy performances of ACU systems are presented for the purpose of comparison.The outcomes display that the use of an external cooling water loop system has a significant impact on the system performance as compared to conventional ACU.The results display that the addition of an external cooling-water loop leads to a reduction in the compressor power consumption and to an increase in the coefficient of performance(COP)as compared to a normal ACU.The maximum reduction in compressor power consumption is obtained equal 37%at T_(w)=15℃and 11 L/min,whereas the maximum enhancement in COP is obtained equal 21.5%at T_(w)=30℃,11 L/min,and T_(amb)=45℃.The modified model shows an increase in exergy efficiency with the maximum enhancement of about 17%at T_(w)=30℃and 15.8 L/min.The use of an external cooling water loop leads to a reduction in the irreversibility process of the compressor,evaporator and expansion valve and to an increase in the condenser losses.The outcomes show that the pressure drop is reduced by using a cooling water loop as compared to a normal ACU,where the reduction becomes more evident with a reduction in water volume flow rate and inlet temperature.Finally,the present study reveals that the use of an external cooling water loop system leads to an improvement in the performance of ACUs.
