Constructed by a solar chimney power plant(SCPP)and a honeycomb photocatalytic reactor(HPCR),the system can remove non-CO_(2)greenhouse gases on a large scale.A mesoscopic-scale fluid flow heat transfer model of the p...Constructed by a solar chimney power plant(SCPP)and a honeycomb photocatalytic reactor(HPCR),the system can remove non-CO_(2)greenhouse gases on a large scale.A mesoscopic-scale fluid flow heat transfer model of the photocatalytic reaction region within the SCPP-HPCR system has been established based on the Lattice Boltzmann method(LBM).Multiple distribution functions have been introduced to simulate the distribution of flow,temperature,and concentration of the photocatalytic region.The performance of photocatalytic methane in the SCPP-HPCR system has been analyzed under the influence of different operating and structural parameters.The results show that increasing the inlet methane flow rate can improve the efficiency of photocatalytic and purification rate of CH4,and lead to the increase in carbon dioxide generation rate.When the solar radiation Gr=857 W/m^(2) and the inlet flow rate Q_(p)=750 mL/min,the photocatalytic efficiency can reach 30.67%.Furthermore,decreasing the aperture size results in enhanced photocatalytic efficiency,purification rate of CH4,and equivalent CO_(2)reduction rate.When the inlet flow rate Q_(p)=1000 mL/min and the aperture size Dp=0.5 mm,the photocatalytic efficiency can reach 40.23%.Conversely,an increase in the temperature leads to a slight decrease in all evaluated criteria,and the highest photocatalytic efficiency is 24.79%at a temperature of 298 K.These findings provide valuable insights and guidance for subsequent simulation studies on a more microscopic scale.展开更多
The methane concentration in the atmosphere is far lower than that of carbon dioxide,but it is more potent,accounting for 30%of the global greenhouse effect.Although removing atmospheric methane would be an effective ...The methane concentration in the atmosphere is far lower than that of carbon dioxide,but it is more potent,accounting for 30%of the global greenhouse effect.Although removing atmospheric methane would be an effective way to mitigate climate change,no practical methods have been identified.The enhancement of the oxidative capacity of ecosystems to remove atmospheric methane is a green approach.This paper presents the novel concept of utilizing a solar chimney power plant(SCPP)associated with a solar pond to remove atmospheric methane.In the proposed system,the production of both hydroxyl radicals from ozone photolysis and chlorine atoms from converting Fe(Ⅲ)to Fe(Ⅱ)under optimized conditions degrades the atmospheric methane.The results reveal that a 200 MW SCPP associated with a solar pond could eliminate 0.22 million tons of atmospheric methane per year.The construction of 5400 systems worldwide could remove 1.19 billion tons of atmospheric methane per year,achieving the climate goal of a temperature rise of less than 2℃this century.The devices require an investment of about 3.5748×10^(12)EUR.Although the proposal seems a promising way to mitigate the effects of a warming climate,a comprehensive model must be developed to evaluate its feasibility.展开更多
The application of thermal diodes,which allow heat to flow more readily in one direction than the other,is an important way to reduce energy consumption in buildings and enhance the battery heat dissipation of electri...The application of thermal diodes,which allow heat to flow more readily in one direction than the other,is an important way to reduce energy consumption in buildings and enhance the battery heat dissipation of electric vehicles.Depending on various factors including the specific design,materials used,and operating conditions,the convective thermal diode can exhibit the best thermal rectification effect in intended applications compared to the other thermal diodes.In this study,a novel convective thermal diode with a wick was proposed based on the phase change heat transfer mechanism.This design takes advantage of both capillary forces provided by the wick and gravity to achieve enhanced unidirectional heat transfer performance for the designed convective thermal diode.The effect of the filling liquid ratio on the thermal performance of the thermal diode was experimentally investigated,which was in good agreement with the theoretical analysis.The research findings showed that with an optimal liquid filling ratio of 140%,the thermal diode with a wick can achieve a better thermal rectification ratio when subjected to a lower heating power,and the maximum thermal rectification ratio of 21.76 was experimentally achieved when the heating power of the thermal diode was 40 W.展开更多
With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modem advanced cooling technologies. In this work, t...With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modem advanced cooling technologies. In this work, the combination of dimples, impinging jets and microchannel heat sink was proposed to improve the heat transfer performance on a cooling surface with a constant heat flux 500 W/cm2. A mathematical model was ad- vanced for numerically analyzing the fluid flow and heat transfer characteristics of a microchannel heat sink with impinging jets and dimples （MHSIJD）, and the velocity distribution, pressure drop, and thermal performance of MI-ISIJD were analyzed by varying the radii of dimples. The results showed that the combination of dimples and MHSIJ can achieve excellent heat transfer performance; for the MHSIJD model in this work, the maximum and average temperatures can be as low as 320 K and 305 K, respectively when mass flow rate is 30 g/s; when dimple radius is larger than 0.195 mm, both the heat transfer coefficient and the overall performance h/AP of MHSIJD are higher than those of MHSIJ.展开更多
Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation o...Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation on a linear Fresnel reflector was investigated.The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer,scanning electron microscope,and X-ray diffractometer.The results showed that the dust density on the mirror increased,and the relative reflectivity decreased with an increase in the dust accumulation time.During 48 days of dust accumulation,the average relative reflectivity decreased 9.4%for a 1 g/m^(2)increase in the dust density.Additionally,the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle.The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation.The main component of the dust particles in the test area was SiO_(2),and the particle size range of the dust was 0.9 um to 87µm.According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror,a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed.The predicted results deviated about 1%from the test results.展开更多
Dust accumulation is one of the reasons for the performance degradation of concentrating photovoltaic and thermal(CPV/T) systems due to the deposition of dust particles with different compositions, shapes, sizes, and ...Dust accumulation is one of the reasons for the performance degradation of concentrating photovoltaic and thermal(CPV/T) systems due to the deposition of dust particles with different compositions, shapes, sizes, and masses. In this work, an optical model was developed to investigate the influence of the particle size, diameter, shape, and deposition density on the light concentration efficiency, using the Monte Carlo raytracing(MCRT) method in the Tracepro software. The triangular particles had a larger influence on the light ray deflection and energy flux degradation than the circular and square particles. An average increase in the dust density of 1 g/m^(2) decreased the light concentration efficiency of particles with sizes smaller than 50 μm and 60 μm by 3.31% and 3.26%, respectively. Furthermore, the effect of the incidence angle on the light concentration efficiency was considered at an angle less than 2°.展开更多
The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxe...The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design.展开更多
In this paper,a one-dimensional thermodynamic model was developed to evaluate the device-level performance of thermoelectric cooler(TEC)with the Thomson effect,contact resistance,gap heat leakage,heat sink,and heat lo...In this paper,a one-dimensional thermodynamic model was developed to evaluate the device-level performance of thermoelectric cooler(TEC)with the Thomson effect,contact resistance,gap heat leakage,heat sink,and heat load taken into account.The model was generalized and simplified by introducing dimensionless parameters.Experimental measurements showed good agreement with analytical results.The parametric analysis indicated that the influence of the Thomson effect on cooling capacity continued to expand with increasing current,while the effect on COP hardly changed with current.Low thermal contact resistance was beneficial to obtain lower hot-junction temperature,which can even reduce 2 K compared with the electrical contact resistance in the case study.The gap heat leakage was a negative factor affecting the cooling performance.When the thermal resistance of the heat sink was small,the negative effect of heat leakage on performance would be further enlarged.The enhancement of heat load temperature would increase the cooling power of the TEC.For example,an increase of 5 K in heat load can increase the cooling capacity by about 4%.However,once the current exceeded the optimum value,the raising effect on the cooling power would be weakened.The research can provide an analytical approach for the designer to perform trade studies to optimize the TEC system.展开更多
The thin-film thermoelectric cooler(TEC)is a promising solid-state heat pump that can remove the high local heat flux of chips utilizing the Peltier effect.When an electric current pulse is applied to the thin-film TE...The thin-film thermoelectric cooler(TEC)is a promising solid-state heat pump that can remove the high local heat flux of chips utilizing the Peltier effect.When an electric current pulse is applied to the thin-film TEC,the TEC can achieve an instantaneous lower temperature compared to that created by a steady current.In this paper,we developed a novel strategy to reduce the peak temperature of the chip working under dynamic power,thus making the semiconductor chip operate reliably and efficiently.A three-dimensional numerical model was built to study the transient cooling performance of the thin-film TEC on chips.The effects of parameters,such as the current pulse,the heat flux,the thermoelement length,the number of thermoelements,and the contact resistance on the performance of the thin-film TEC,were investigated.The results showed that when a current pulse of 0.6 A was applied to the thin-film TEC before the peak power of the chip,the peak temperature of the chip was reduced by more than 10℃,making the thin-film thermoelectric cooler a promising technology for the temperature control of modern chips with high peak powers.展开更多
基金supported by the National Key Research and Development Plan(Grant No.2019YFE0197500)the European Commission H2020Marie Curie Research and Innovation Staff Exchange(RISE)award(Grant No.871998)the National Natural Science Foundation of China(Grant Nos.52278123 and 52208124)。
文摘Constructed by a solar chimney power plant(SCPP)and a honeycomb photocatalytic reactor(HPCR),the system can remove non-CO_(2)greenhouse gases on a large scale.A mesoscopic-scale fluid flow heat transfer model of the photocatalytic reaction region within the SCPP-HPCR system has been established based on the Lattice Boltzmann method(LBM).Multiple distribution functions have been introduced to simulate the distribution of flow,temperature,and concentration of the photocatalytic region.The performance of photocatalytic methane in the SCPP-HPCR system has been analyzed under the influence of different operating and structural parameters.The results show that increasing the inlet methane flow rate can improve the efficiency of photocatalytic and purification rate of CH4,and lead to the increase in carbon dioxide generation rate.When the solar radiation Gr=857 W/m^(2) and the inlet flow rate Q_(p)=750 mL/min,the photocatalytic efficiency can reach 30.67%.Furthermore,decreasing the aperture size results in enhanced photocatalytic efficiency,purification rate of CH4,and equivalent CO_(2)reduction rate.When the inlet flow rate Q_(p)=1000 mL/min and the aperture size Dp=0.5 mm,the photocatalytic efficiency can reach 40.23%.Conversely,an increase in the temperature leads to a slight decrease in all evaluated criteria,and the highest photocatalytic efficiency is 24.79%at a temperature of 298 K.These findings provide valuable insights and guidance for subsequent simulation studies on a more microscopic scale.
基金supported by the National Natural Science Foundation of China(Grant No.52278123)the National Key R&D Program of China(Grant No.2019YFE0197500)the European Commission H2020 Marie Curie Research and Innovation Staff Exchange(RISE)award(Grant No.871998)。
文摘The methane concentration in the atmosphere is far lower than that of carbon dioxide,but it is more potent,accounting for 30%of the global greenhouse effect.Although removing atmospheric methane would be an effective way to mitigate climate change,no practical methods have been identified.The enhancement of the oxidative capacity of ecosystems to remove atmospheric methane is a green approach.This paper presents the novel concept of utilizing a solar chimney power plant(SCPP)associated with a solar pond to remove atmospheric methane.In the proposed system,the production of both hydroxyl radicals from ozone photolysis and chlorine atoms from converting Fe(Ⅲ)to Fe(Ⅱ)under optimized conditions degrades the atmospheric methane.The results reveal that a 200 MW SCPP associated with a solar pond could eliminate 0.22 million tons of atmospheric methane per year.The construction of 5400 systems worldwide could remove 1.19 billion tons of atmospheric methane per year,achieving the climate goal of a temperature rise of less than 2℃this century.The devices require an investment of about 3.5748×10^(12)EUR.Although the proposal seems a promising way to mitigate the effects of a warming climate,a comprehensive model must be developed to evaluate its feasibility.
基金supported by the National Natural Science Foundation of China(Grant No.52208124)Hubei Provincial Key Research and Design Project(Grant No.2020BAB129)Scientific Research Foundation of Wuhan University of Technology(Grant No.40120237 and 40120551)。
文摘The application of thermal diodes,which allow heat to flow more readily in one direction than the other,is an important way to reduce energy consumption in buildings and enhance the battery heat dissipation of electric vehicles.Depending on various factors including the specific design,materials used,and operating conditions,the convective thermal diode can exhibit the best thermal rectification effect in intended applications compared to the other thermal diodes.In this study,a novel convective thermal diode with a wick was proposed based on the phase change heat transfer mechanism.This design takes advantage of both capillary forces provided by the wick and gravity to achieve enhanced unidirectional heat transfer performance for the designed convective thermal diode.The effect of the filling liquid ratio on the thermal performance of the thermal diode was experimentally investigated,which was in good agreement with the theoretical analysis.The research findings showed that with an optimal liquid filling ratio of 140%,the thermal diode with a wick can achieve a better thermal rectification ratio when subjected to a lower heating power,and the maximum thermal rectification ratio of 21.76 was experimentally achieved when the heating power of the thermal diode was 40 W.
基金financially supported by the National Natural Science Foundation of China(Grant No.51778511)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFA029)the Key Project of ESI Discipline Development of Wuhan University of Technology(WUT Grant No.2017001)
文摘With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modem advanced cooling technologies. In this work, the combination of dimples, impinging jets and microchannel heat sink was proposed to improve the heat transfer performance on a cooling surface with a constant heat flux 500 W/cm2. A mathematical model was ad- vanced for numerically analyzing the fluid flow and heat transfer characteristics of a microchannel heat sink with impinging jets and dimples （MHSIJD）, and the velocity distribution, pressure drop, and thermal performance of MI-ISIJD were analyzed by varying the radii of dimples. The results showed that the combination of dimples and MHSIJ can achieve excellent heat transfer performance; for the MHSIJD model in this work, the maximum and average temperatures can be as low as 320 K and 305 K, respectively when mass flow rate is 30 g/s; when dimple radius is larger than 0.195 mm, both the heat transfer coefficient and the overall performance h/AP of MHSIJD are higher than those of MHSIJ.
基金This research was supported by the National Natural Science Foundation of China(NO.51766012)the Inner Mongolia Graduate Research and Innovation Project in 2019(NO.B20191126Z)+1 种基金the Inner Mongolia Science and Technology Major Project in 2019,the Inner Mongolia Financial Innovation Funding Project in 2017,the Inner Mongolia Natural Science Foundation of china(No.2019MS05025)the Fundamental Research Funds for the Central Universities(WUT Grant No.2019IVB082).
文摘Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation on a linear Fresnel reflector was investigated.The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer,scanning electron microscope,and X-ray diffractometer.The results showed that the dust density on the mirror increased,and the relative reflectivity decreased with an increase in the dust accumulation time.During 48 days of dust accumulation,the average relative reflectivity decreased 9.4%for a 1 g/m^(2)increase in the dust density.Additionally,the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle.The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation.The main component of the dust particles in the test area was SiO_(2),and the particle size range of the dust was 0.9 um to 87µm.According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror,a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed.The predicted results deviated about 1%from the test results.
基金supported by the National Natural Science Foundation of China(No.51766012)the Natural Science Foundation of Inner Mongolia(No.2019MS05025)+1 种基金the Inner Mongolia Science and Technology Major Project(No.2019ZD014)the Key Project of the ESI Discipline Development of Wuhan University of Technology(WUT Grant No.2017001)。
文摘Dust accumulation is one of the reasons for the performance degradation of concentrating photovoltaic and thermal(CPV/T) systems due to the deposition of dust particles with different compositions, shapes, sizes, and masses. In this work, an optical model was developed to investigate the influence of the particle size, diameter, shape, and deposition density on the light concentration efficiency, using the Monte Carlo raytracing(MCRT) method in the Tracepro software. The triangular particles had a larger influence on the light ray deflection and energy flux degradation than the circular and square particles. An average increase in the dust density of 1 g/m^(2) decreased the light concentration efficiency of particles with sizes smaller than 50 μm and 60 μm by 3.31% and 3.26%, respectively. Furthermore, the effect of the incidence angle on the light concentration efficiency was considered at an angle less than 2°.
基金financially supported by the National Natural Science Foundation of China(Grant No.51778511)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFA029)the Key Project of ESI Discipline Development of Wuhan University of Technology(WUT Grant No.2017001)
文摘The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design.
基金financially supported by the National Natural Science Foundation of China(NSFC)(Grant No.52106032)the Science Challenge Program(Grant No.TZ2018003)+2 种基金the National Natural Science Foundation of China(Grant No.51778511)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFA029)the Key Project of ESI Discipline Development of Wuhan University of Technology(WUT Grant No.2017001)。
文摘In this paper,a one-dimensional thermodynamic model was developed to evaluate the device-level performance of thermoelectric cooler(TEC)with the Thomson effect,contact resistance,gap heat leakage,heat sink,and heat load taken into account.The model was generalized and simplified by introducing dimensionless parameters.Experimental measurements showed good agreement with analytical results.The parametric analysis indicated that the influence of the Thomson effect on cooling capacity continued to expand with increasing current,while the effect on COP hardly changed with current.Low thermal contact resistance was beneficial to obtain lower hot-junction temperature,which can even reduce 2 K compared with the electrical contact resistance in the case study.The gap heat leakage was a negative factor affecting the cooling performance.When the thermal resistance of the heat sink was small,the negative effect of heat leakage on performance would be further enlarged.The enhancement of heat load temperature would increase the cooling power of the TEC.For example,an increase of 5 K in heat load can increase the cooling capacity by about 4%.However,once the current exceeded the optimum value,the raising effect on the cooling power would be weakened.The research can provide an analytical approach for the designer to perform trade studies to optimize the TEC system.
基金the National Natural Science Foundation of China(Grant No.51778511)Natural Science Foundation of Hubei Province(Grant No.2018CFA029)+3 种基金Key Research and Design Projects of Hubei Province(Grant No.2020BAB129)Key Project of ESI Discipline Development of Wuhan University of Technology(Grant No.2017001)Scientific Research Foundation of Wuhan University of Technology(Nos.40120237 and 40120551)the Fundamental Research Funds for the Central Universities(WUT:2021IVA037)。
文摘The thin-film thermoelectric cooler(TEC)is a promising solid-state heat pump that can remove the high local heat flux of chips utilizing the Peltier effect.When an electric current pulse is applied to the thin-film TEC,the TEC can achieve an instantaneous lower temperature compared to that created by a steady current.In this paper,we developed a novel strategy to reduce the peak temperature of the chip working under dynamic power,thus making the semiconductor chip operate reliably and efficiently.A three-dimensional numerical model was built to study the transient cooling performance of the thin-film TEC on chips.The effects of parameters,such as the current pulse,the heat flux,the thermoelement length,the number of thermoelements,and the contact resistance on the performance of the thin-film TEC,were investigated.The results showed that when a current pulse of 0.6 A was applied to the thin-film TEC before the peak power of the chip,the peak temperature of the chip was reduced by more than 10℃,making the thin-film thermoelectric cooler a promising technology for the temperature control of modern chips with high peak powers.
