This paper presents a method based on riblet surfaces. Its advantage lies in that it is more with testing methods using instruments such as a the Spalding formula for testing drag-reduction on convenient and yields mo...This paper presents a method based on riblet surfaces. Its advantage lies in that it is more with testing methods using instruments such as a the Spalding formula for testing drag-reduction on convenient and yields more precise data compared scale. With this method, data is obtained from the velocity distribution within the inner layer, nearest the riblet surface. Precision of measurement of the velocity distribution is the key factor affecting the precision of the testing.展开更多
Wind microturbines typically have rotor diameters of 2 m or less. This paper presents theoretical expressions that can be used to determine the aerodynamic performance of wind microturbines. A commercially-available t...Wind microturbines typically have rotor diameters of 2 m or less. This paper presents theoretical expressions that can be used to determine the aerodynamic performance of wind microturbines. A commercially-available three-bladed microturbine was tested at the outlet plane of a wind tunnel. The cross-section dimensions of the wind tunnel jet are 2.5 m （horizontal） x 1.5 m （vertical）. The tested microturbine has a diameter of 1.2 m, and it generates a maximum power output of about 300 W. The paper provides the wind tunnel test methodology that was used to determine the mean and fluctuating forces generated by the aforementioned wind microturbine. Both the static and dynamic responses of the turbine were measured, and results from this testing are presented in this paper. These results enable the trends and predictions of the theoretical expressions to be compared with wind tunnel measurements. It is shown that, for this particular microturbine, the behaviours of these test measurements are consistent with the expected theoretical predictions.展开更多
System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are les...System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.展开更多
In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a vari...In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a variety of transformers are studied, and the applicable scope of the conversion formula is discussed emphatically, combined with the test results are analyzed of transformer insulation resistance value to temperature and oiliness and dielectric loss tangent to temperature and oiliness, and puts forward suggestions on how to improve the insulation performance of transformer.展开更多
基金Supported by National Natural Science Foundation (50835009 and 10672136)Science and Technology Innovation Foundation of NWPU(2008KJ02012)
文摘This paper presents a method based on riblet surfaces. Its advantage lies in that it is more with testing methods using instruments such as a the Spalding formula for testing drag-reduction on convenient and yields more precise data compared scale. With this method, data is obtained from the velocity distribution within the inner layer, nearest the riblet surface. Precision of measurement of the velocity distribution is the key factor affecting the precision of the testing.
文摘Wind microturbines typically have rotor diameters of 2 m or less. This paper presents theoretical expressions that can be used to determine the aerodynamic performance of wind microturbines. A commercially-available three-bladed microturbine was tested at the outlet plane of a wind tunnel. The cross-section dimensions of the wind tunnel jet are 2.5 m （horizontal） x 1.5 m （vertical）. The tested microturbine has a diameter of 1.2 m, and it generates a maximum power output of about 300 W. The paper provides the wind tunnel test methodology that was used to determine the mean and fluctuating forces generated by the aforementioned wind microturbine. Both the static and dynamic responses of the turbine were measured, and results from this testing are presented in this paper. These results enable the trends and predictions of the theoretical expressions to be compared with wind tunnel measurements. It is shown that, for this particular microturbine, the behaviours of these test measurements are consistent with the expected theoretical predictions.
文摘System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.
文摘In view of long-term transformer insulation resistance and dielectric loss measurement, measurement and according to the national standard formula conversion values are not completely consistent, in this paper, a variety of transformers are studied, and the applicable scope of the conversion formula is discussed emphatically, combined with the test results are analyzed of transformer insulation resistance value to temperature and oiliness and dielectric loss tangent to temperature and oiliness, and puts forward suggestions on how to improve the insulation performance of transformer.
