This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external ...This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external surface. Results indicate that external wall surface temperature and nearby air temperature vary with the change of orientation, height and season. In general, the external wall surface temperature is lower near the ground, and is higher near the roof, than nearby air temperature. But north wall surface temperature is mostly lower than nearby air temperature at the same height; south wall surface temperature during the daytime in December, and west wall surface temperature all day in August, is respectively higher than nearby air temperature. The heat fluxes into and out of external wall surfaces show the differences that exist in the various orientations, heights and seasons. In December, south wall surface at the lower sites emits heat and north wall surface at the higher sites absorbs heat. In April, all external wall surfaces, emit heat near the ground and absorb heat near the roof. In August, west wall surface all day emits heat, and other wall surfaces just show the commensurate behavior with that in April.展开更多
Internal and external wall surface temperatures (Tws) in April, August and December in Kunming, a city in low latitude plateau, were investigated. Results showed that the Tws in April were of the highest among the thr...Internal and external wall surface temperatures (Tws) in April, August and December in Kunming, a city in low latitude plateau, were investigated. Results showed that the Tws in April were of the highest among the three, followed by August and December. The Tws differences among walls with different orientation were higher in April and December when the weather tends to be sunny, and lower in August with more cloudy days in the time. In April and August, Tws of E-wall was the highest, followed by S- and N-wall. But in December Tws of S-wall might be sometimes higher than E one. Diurnal range of internal Tws was usually smaller than that of the external, with also a time lag for the occurrence of its maximum and minimum. The results can serve as a basis for further research on building microclimate and urban architecture designs. It also gives suggestions for similar studies in other areas.展开更多
The reported discrepancy between theory and experiment for external combustion Stirling engines is explained by the addition of thermal resistance of the combustion gasses to the standard Carnot model. In these cases,...The reported discrepancy between theory and experiment for external combustion Stirling engines is explained by the addition of thermal resistance of the combustion gasses to the standard Carnot model. In these cases, the Stirling engine ideal efficiency is not as is normally reported equal to the Carnot cycle efficiency but is significantly lower. A new equation for ideal Stirling engine efficiency when the heat is obtained through external combustion without pre-heating the air, is presented and results for various fuels tabulated. The results show that petrol and diesel, internal combustion engines (Otto cycle) have a higher ideal efficiency than the Stirling engine. When comparing thermoacoustic engines heated by wood, efficiency should not be quoted as a percentage of the Carnot efficiency, but against a figure 48% lower than Carnot. The effect is not seen with electrically heated rigs, solar or nuclear fission heated engines.展开更多
The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D bor...The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D borehole and total internal thermal resistance(R_(b,3D)and R_(a,3D))and analyze the impacts of parameters on the R_(b,3D)and R_(a,3D).Firstly,eight parameters affecting the R_(b,3D)and R_(a,3D),including the borehole diameter,pipe diameter,pipe-pipe distance,borehole depth,soil thermal conductivity,grout thermal conductivity,pipe thermal conductivity,and fluid velocity inside the pipe,were considered and an L-54 design matrix was generated.Then,the 3D numerical model,coupling with the four-resistance model,was proposed to calculate R_(b,3D)and R_(a,3D)for each case.After that,the response surface methodology was employed to obtain and verify the correlation of R_(b,3D)and R_(a,3D),which were compared with the existing resistance calculation methods.Lastly,analysis of variance was carried out to reveal parameters that have statistically significant impacts on the R_(b,3D)and R_(a,3D).Results show that the rationality and accuracy of the correlation of R_(b,3D)and R_(a,3D)can be verified by the determination coefficient and P value of regression model,as well as the P value of lack-of-fit.The existing resistance calculation methods are more or less inaccurate and the discrepancies in some cases can be up to 86.74%and 111.35%for the borehole and total internal thermal resistance.The pipe and grout thermal conductivity,pipe and borehole diameter,and the pipe-pipe distance can be seen as the significant contributory factors to the variation of R_(b,3D)and R_(a,3D).展开更多
文摘This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external surface. Results indicate that external wall surface temperature and nearby air temperature vary with the change of orientation, height and season. In general, the external wall surface temperature is lower near the ground, and is higher near the roof, than nearby air temperature. But north wall surface temperature is mostly lower than nearby air temperature at the same height; south wall surface temperature during the daytime in December, and west wall surface temperature all day in August, is respectively higher than nearby air temperature. The heat fluxes into and out of external wall surfaces show the differences that exist in the various orientations, heights and seasons. In December, south wall surface at the lower sites emits heat and north wall surface at the higher sites absorbs heat. In April, all external wall surfaces, emit heat near the ground and absorb heat near the roof. In August, west wall surface all day emits heat, and other wall surfaces just show the commensurate behavior with that in April.
基金Key project from the Natural Science Foundation of China (59836250)
文摘Internal and external wall surface temperatures (Tws) in April, August and December in Kunming, a city in low latitude plateau, were investigated. Results showed that the Tws in April were of the highest among the three, followed by August and December. The Tws differences among walls with different orientation were higher in April and December when the weather tends to be sunny, and lower in August with more cloudy days in the time. In April and August, Tws of E-wall was the highest, followed by S- and N-wall. But in December Tws of S-wall might be sometimes higher than E one. Diurnal range of internal Tws was usually smaller than that of the external, with also a time lag for the occurrence of its maximum and minimum. The results can serve as a basis for further research on building microclimate and urban architecture designs. It also gives suggestions for similar studies in other areas.
文摘The reported discrepancy between theory and experiment for external combustion Stirling engines is explained by the addition of thermal resistance of the combustion gasses to the standard Carnot model. In these cases, the Stirling engine ideal efficiency is not as is normally reported equal to the Carnot cycle efficiency but is significantly lower. A new equation for ideal Stirling engine efficiency when the heat is obtained through external combustion without pre-heating the air, is presented and results for various fuels tabulated. The results show that petrol and diesel, internal combustion engines (Otto cycle) have a higher ideal efficiency than the Stirling engine. When comparing thermoacoustic engines heated by wood, efficiency should not be quoted as a percentage of the Carnot efficiency, but against a figure 48% lower than Carnot. The effect is not seen with electrically heated rigs, solar or nuclear fission heated engines.
基金This work was supported by the National Natural Science Foundation of China(No.51708551).
文摘The borehole and total internal thermal resistance are both significant parameters in evaluating the thermal performance of the ground source heat pump.This study aimed to obtain the accurate correlation of the 3D borehole and total internal thermal resistance(R_(b,3D)and R_(a,3D))and analyze the impacts of parameters on the R_(b,3D)and R_(a,3D).Firstly,eight parameters affecting the R_(b,3D)and R_(a,3D),including the borehole diameter,pipe diameter,pipe-pipe distance,borehole depth,soil thermal conductivity,grout thermal conductivity,pipe thermal conductivity,and fluid velocity inside the pipe,were considered and an L-54 design matrix was generated.Then,the 3D numerical model,coupling with the four-resistance model,was proposed to calculate R_(b,3D)and R_(a,3D)for each case.After that,the response surface methodology was employed to obtain and verify the correlation of R_(b,3D)and R_(a,3D),which were compared with the existing resistance calculation methods.Lastly,analysis of variance was carried out to reveal parameters that have statistically significant impacts on the R_(b,3D)and R_(a,3D).Results show that the rationality and accuracy of the correlation of R_(b,3D)and R_(a,3D)can be verified by the determination coefficient and P value of regression model,as well as the P value of lack-of-fit.The existing resistance calculation methods are more or less inaccurate and the discrepancies in some cases can be up to 86.74%and 111.35%for the borehole and total internal thermal resistance.The pipe and grout thermal conductivity,pipe and borehole diameter,and the pipe-pipe distance can be seen as the significant contributory factors to the variation of R_(b,3D)and R_(a,3D).
