The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the...The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96～1 06)ε 1j .展开更多
The dump diffuser is an important component in advanced annular combustor, and its performance affects greatly the fluid field and pressure loss of the combustor. This paper presents the characteristics of the total p...The dump diffuser is an important component in advanced annular combustor, and its performance affects greatly the fluid field and pressure loss of the combustor. This paper presents the characteristics of the total pressure loss. Experiments and numerical simulations, keeping the inlet March number of prediffuser constant ( Ma =0 20), are carried out to obtain the regularity of the total pressure loss. It varies with the relative dump gap ( δ =1 2～3 0)by changing the position of prediffuser and combustor liner, respectively. Research shows that there exists the minimum total pressure loss ( σ *=1 6%～1 75%) when relative dump gap δ is about 1 8.展开更多
Energy consumed by distribution valves causes an energy loss for the output energy of hydraulic breakers, which has a significant influence on its efficiency. A new type of distribution valve used for hydraulic breake...Energy consumed by distribution valves causes an energy loss for the output energy of hydraulic breakers, which has a significant influence on its efficiency. A new type of distribution valve used for hydraulic breakers, de- signed to reduce energy consumption, is analyzed on the basis of the operating principle and energy loss of the current distribution valve. The new distribution valve adopts a cone valve and the optimization technique of unequal open de- gree for the valve port. Theoretical calculations and analyses have proven that the new distribution valve can reduce en- ergy loss by 9.0127J, or energy consumption by 31%, during an impact cycle and the efficiency of the hydraulic breaker can be raised by 4.5%. It has the following characteristics: little leakage, little pressure loss and low energy consump- tion.展开更多
The interconnection of Embedded Generation （EG） in a distribution network would change the radiality of the convention power flows in the system. Instead of helping to reduce the system losses, it also improves the ...The interconnection of Embedded Generation （EG） in a distribution network would change the radiality of the convention power flows in the system. Instead of helping to reduce the system losses, it also improves the quality of the overall system network. However, improper allocation and sizing of its interconnection to the system could oppositely change those advantages. The total system may experience higher losses and instability. In this paper, a new technique to determine the optimal allocation of EG in distribution system by using Genetic Algorithm （GA） technique is proposed. The effectiveness of the technique is demonstrated using IEEE-69 bus distribution test system and simulated in MATLAB.展开更多
In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destructi...In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.展开更多
Thermal losses for a buried vertical thin plate can be expressed as a function of the assigned temperature distribution,the medium conductivity and the geometrical properties that describe the model. When the geometri...Thermal losses for a buried vertical thin plate can be expressed as a function of the assigned temperature distribution,the medium conductivity and the geometrical properties that describe the model. When the geometricalproperties reduce to one, the plate-ground thermal resistance can be expressed regardless of plate dimension, dependingonly on temperature distribution given at surface plate and its temperature difference with medium.展开更多
文摘The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96～1 06)ε 1j .
文摘The dump diffuser is an important component in advanced annular combustor, and its performance affects greatly the fluid field and pressure loss of the combustor. This paper presents the characteristics of the total pressure loss. Experiments and numerical simulations, keeping the inlet March number of prediffuser constant ( Ma =0 20), are carried out to obtain the regularity of the total pressure loss. It varies with the relative dump gap ( δ =1 2～3 0)by changing the position of prediffuser and combustor liner, respectively. Research shows that there exists the minimum total pressure loss ( σ *=1 6%～1 75%) when relative dump gap δ is about 1 8.
基金Project 50374071 supported by National Natural Science Foundation of China
文摘Energy consumed by distribution valves causes an energy loss for the output energy of hydraulic breakers, which has a significant influence on its efficiency. A new type of distribution valve used for hydraulic breakers, de- signed to reduce energy consumption, is analyzed on the basis of the operating principle and energy loss of the current distribution valve. The new distribution valve adopts a cone valve and the optimization technique of unequal open de- gree for the valve port. Theoretical calculations and analyses have proven that the new distribution valve can reduce en- ergy loss by 9.0127J, or energy consumption by 31%, during an impact cycle and the efficiency of the hydraulic breaker can be raised by 4.5%. It has the following characteristics: little leakage, little pressure loss and low energy consump- tion.
文摘The interconnection of Embedded Generation （EG） in a distribution network would change the radiality of the convention power flows in the system. Instead of helping to reduce the system losses, it also improves the quality of the overall system network. However, improper allocation and sizing of its interconnection to the system could oppositely change those advantages. The total system may experience higher losses and instability. In this paper, a new technique to determine the optimal allocation of EG in distribution system by using Genetic Algorithm （GA） technique is proposed. The effectiveness of the technique is demonstrated using IEEE-69 bus distribution test system and simulated in MATLAB.
基金supported by the National Basic Research Program of China(Grant No.2013CB228302)
文摘In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.
文摘Thermal losses for a buried vertical thin plate can be expressed as a function of the assigned temperature distribution,the medium conductivity and the geometrical properties that describe the model. When the geometricalproperties reduce to one, the plate-ground thermal resistance can be expressed regardless of plate dimension, dependingonly on temperature distribution given at surface plate and its temperature difference with medium.
