To solve the issues of non-uniform heating,low heat transfer performance and high temperature in the absorber tube(AT)of parabolic trough receiver(PTR),a PTR with annular sector inserts(A-S-PTR)is proposed and its num...To solve the issues of non-uniform heating,low heat transfer performance and high temperature in the absorber tube(AT)of parabolic trough receiver(PTR),a PTR with annular sector inserts(A-S-PTR)is proposed and its numerical study is carried out in detail.The effects of the annular sector's parameters on the PTR's performance are comprehensively investigated,and the optimal parameters of the annular sector are obtained by multi-objective optimization based on the NSGA-Ⅱalgorithm.The optimal parameter combination of the A-S-PTR areα_(1opt)=30.878°,β_(1opt)=49.636°,r_(1opt)=7.47 mm andθ_(1opt)=17.449°.Lastly,the performances of the optimal A-S-PTR under various operational scenarios are analyzed in detail.Results indicate that the flow field structure of the A-S-PTR is similar to that of the PTR optimized by exergy destruction minimization,specifically,two pairs of longitudinal vortices that are symmetrically distributed in the AT's lower part.The annular sector can guide the high-temperature fluid near the AT to mix with the fluid in the core region,thus accelerating heat transfer.As a result,when compared with the conventional PTR,the maximum wall temperature of the AT's inner wall and the heat loss for the optimal AS-PTR are reduced by 23.7%and 72.6%,respectively,and the thermal efficiency is increased by 3.25%.This research provides guidelines for the designs of more effective PTRs.展开更多
Because of the important role of the absorption heat pump in low-grade thermal energy utilization,this paper extends it to micro domain and performs a finite-time thermodynamic modelling for a three-heat-reservoir(THR...Because of the important role of the absorption heat pump in low-grade thermal energy utilization,this paper extends it to micro domain and performs a finite-time thermodynamic modelling for a three-heat-reservoir(THR)thermal Brownian heat pump with heat transfer effect by using an equivalent combined cycle method,which was applied for macro endoreversible THR heat pumps.The working principle and energy transformation rule are studied,and the coefficient of performance(COP)and heating load are derived.With a fixed overall thermal conductance of three heat exchangers,the maximal heating load is determined by optimizing thermal conductance distributions among three heat exchangers and barrier height,and the optimal working temperatures are also obtained.The impact of external heat transfer is elucidated to show the difference between this model and a non-equilibrium thermodynamic one.Results indicate that external heat transfer determines the energy transformation directly,and performance characteristics are closer to reality when external heat transfer is considered.The heating load has a maximal value about thermal conductance allocation ratios.About half the overall heat exchanger inventory needs to be assigned to the heat exchanger of the heating space for maximal heating load.When the cycle is with only heat transfer effect,the net particle numbers are zero,and the cycle fails to pump heat.The research results are expected to offer an idea for thermodynamic optimization and design of micro THR thermal Brownian heat pump devices.展开更多
This paper establishes an irreversible DualMiller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Mil...This paper establishes an irreversible DualMiller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal popt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P,η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P,η and E are derived. The relationships among P,η, E and compression ratio (ε) are obtained by numerical examples. The effects of ρ and rM on P,η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P,η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twicemaximum efficiency, and a twice-maximum ecological fiinction, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2% of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in rj compared to choosing as the optimization objective.展开更多
In finite-time thermodynamic analyses for various gas turbine cycles,there are two common models:one is closed-cycle model with thermal conductance optimization of heat exchangers,and another is open-cycle model with ...In finite-time thermodynamic analyses for various gas turbine cycles,there are two common models:one is closed-cycle model with thermal conductance optimization of heat exchangers,and another is open-cycle model with optimization of pressure drop(PD)distributions.Both of optimization also with searching optimal compressor pressure ratio(PR).This paper focuses on an open-cycle model.A two-shaft open-cycle gas turbine power plant(OCGTPP)is modeled in this paper.Expressions of power output(PP)and thermal conversion efficiency(TCE)are deduced,and these performances are optimized by varying the relative PD and compressor PR.The results show that there exist the optimal values(0.32 and 14.0)of PD and PR which lead to double maximum dimensionless PP(1.75).There also exists an optimal value(0.38)of area allocation ratio which leads to maximum TCE(0.37).Moreover,the performances of three types of gas turbine cycles,such as one-shaft and two-shaft ones,are compared.When the relative pressure drop at the compressor inlet is small,the TCE of third cycle is the biggest one;when this pressure drop is large,the PP of second cycle is the biggest one.The results herein can be applied to guide the preliminary designs of OCGTPPs.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52206108 and 52171317)the Natural Science Foundation of Hubei Province(Grant No.2022CFB677)the Graduate Innovative Fund of Wuhan Institute of Technology(Grant No.CX2023254)。
文摘To solve the issues of non-uniform heating,low heat transfer performance and high temperature in the absorber tube(AT)of parabolic trough receiver(PTR),a PTR with annular sector inserts(A-S-PTR)is proposed and its numerical study is carried out in detail.The effects of the annular sector's parameters on the PTR's performance are comprehensively investigated,and the optimal parameters of the annular sector are obtained by multi-objective optimization based on the NSGA-Ⅱalgorithm.The optimal parameter combination of the A-S-PTR areα_(1opt)=30.878°,β_(1opt)=49.636°,r_(1opt)=7.47 mm andθ_(1opt)=17.449°.Lastly,the performances of the optimal A-S-PTR under various operational scenarios are analyzed in detail.Results indicate that the flow field structure of the A-S-PTR is similar to that of the PTR optimized by exergy destruction minimization,specifically,two pairs of longitudinal vortices that are symmetrically distributed in the AT's lower part.The annular sector can guide the high-temperature fluid near the AT to mix with the fluid in the core region,thus accelerating heat transfer.As a result,when compared with the conventional PTR,the maximum wall temperature of the AT's inner wall and the heat loss for the optimal AS-PTR are reduced by 23.7%and 72.6%,respectively,and the thermal efficiency is increased by 3.25%.This research provides guidelines for the designs of more effective PTRs.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171317,51779262).
文摘Because of the important role of the absorption heat pump in low-grade thermal energy utilization,this paper extends it to micro domain and performs a finite-time thermodynamic modelling for a three-heat-reservoir(THR)thermal Brownian heat pump with heat transfer effect by using an equivalent combined cycle method,which was applied for macro endoreversible THR heat pumps.The working principle and energy transformation rule are studied,and the coefficient of performance(COP)and heating load are derived.With a fixed overall thermal conductance of three heat exchangers,the maximal heating load is determined by optimizing thermal conductance distributions among three heat exchangers and barrier height,and the optimal working temperatures are also obtained.The impact of external heat transfer is elucidated to show the difference between this model and a non-equilibrium thermodynamic one.Results indicate that external heat transfer determines the energy transformation directly,and performance characteristics are closer to reality when external heat transfer is considered.The heating load has a maximal value about thermal conductance allocation ratios.About half the overall heat exchanger inventory needs to be assigned to the heat exchanger of the heating space for maximal heating load.When the cycle is with only heat transfer effect,the net particle numbers are zero,and the cycle fails to pump heat.The research results are expected to offer an idea for thermodynamic optimization and design of micro THR thermal Brownian heat pump devices.
基金This paper was supported by the National Natural Science Foundation of China (Grant No. 51576207).
文摘This paper establishes an irreversible DualMiller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal popt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P,η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P,η and E are derived. The relationships among P,η, E and compression ratio (ε) are obtained by numerical examples. The effects of ρ and rM on P,η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P,η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twicemaximum efficiency, and a twice-maximum ecological fiinction, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2% of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in rj compared to choosing as the optimization objective.
基金supported by the National Natural Science Foundation of China(Project Nos.52171317 and 51779262).The authors wish to thank the reviewers for their careful,unbiased and constructive suggestions,which led to this revised manuscript.
文摘In finite-time thermodynamic analyses for various gas turbine cycles,there are two common models:one is closed-cycle model with thermal conductance optimization of heat exchangers,and another is open-cycle model with optimization of pressure drop(PD)distributions.Both of optimization also with searching optimal compressor pressure ratio(PR).This paper focuses on an open-cycle model.A two-shaft open-cycle gas turbine power plant(OCGTPP)is modeled in this paper.Expressions of power output(PP)and thermal conversion efficiency(TCE)are deduced,and these performances are optimized by varying the relative PD and compressor PR.The results show that there exist the optimal values(0.32 and 14.0)of PD and PR which lead to double maximum dimensionless PP(1.75).There also exists an optimal value(0.38)of area allocation ratio which leads to maximum TCE(0.37).Moreover,the performances of three types of gas turbine cycles,such as one-shaft and two-shaft ones,are compared.When the relative pressure drop at the compressor inlet is small,the TCE of third cycle is the biggest one;when this pressure drop is large,the PP of second cycle is the biggest one.The results herein can be applied to guide the preliminary designs of OCGTPPs.
