Hydride vapor phase epitaxy （HVPE） is utilized to grow nonpolar a-plane GaN layers on r-plane sapphire templates prepared by metal organic vapor phase epitaxy （MOVPE）. The surface morphology and microstructures of...Hydride vapor phase epitaxy （HVPE） is utilized to grow nonpolar a-plane GaN layers on r-plane sapphire templates prepared by metal organic vapor phase epitaxy （MOVPE）. The surface morphology and microstructures of the samples are characterized by atomic force microscopy. The full width at half maximum （FWHM） of the HVPE sample shows a W-shape and that of the MOVPE sample shows an M-shape plane with the degree of 0 in the high-resolution x-ray diffraction （HRXRD） results. The surface morphology attributes to this significant anisotropic. HRXRD reveals that there is a significant reduction in the FWHM, both on-axis and off-axis for HVPE GaN are compared with the MOVPE template. The decrease of the FWHM of E2 （high） Raman scat tering spectra further indicates the improvement of crystal quality after HVPE. By comparing the results of secondary- ion-mass spectroscope and photoluminescence spectrum of the samples grown by HVPE and MOVPE, we propose that C-involved defects are originally responsible for the yellow luminescence.展开更多
Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was unde...Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 61204006the Fundamental Research Funds for the Central Universities under Grant No 7214570101the National Key Science and Technology Special Project under Grant No 2008ZX01002-002
文摘Hydride vapor phase epitaxy （HVPE） is utilized to grow nonpolar a-plane GaN layers on r-plane sapphire templates prepared by metal organic vapor phase epitaxy （MOVPE）. The surface morphology and microstructures of the samples are characterized by atomic force microscopy. The full width at half maximum （FWHM） of the HVPE sample shows a W-shape and that of the MOVPE sample shows an M-shape plane with the degree of 0 in the high-resolution x-ray diffraction （HRXRD） results. The surface morphology attributes to this significant anisotropic. HRXRD reveals that there is a significant reduction in the FWHM, both on-axis and off-axis for HVPE GaN are compared with the MOVPE template. The decrease of the FWHM of E2 （high） Raman scat tering spectra further indicates the improvement of crystal quality after HVPE. By comparing the results of secondary- ion-mass spectroscope and photoluminescence spectrum of the samples grown by HVPE and MOVPE, we propose that C-involved defects are originally responsible for the yellow luminescence.
基金financial support from the National Natural Science Foundation of China under Grant No.51776201the National Science Foundation of Tianjin under Grant No.18JCQNJC07200。
文摘Film cooling combined with internal impingement cooling is one of the most effective technologies to protect the gas turbine vanes and blades from the hot gas. In this study, conjugate heat transfer CFD study was undertaken for a flat plate with combined film cooling and impingement cooling. An experiment on conjugate heat transfer of a flat plate with combined film and impingement cooling was performed to validate the code. Then the effects of several parameters including Biot number, blowing ratio, film hole shape and impingement hole diameter on the overall cooling effectiveness were numerically studied. The results show that for a specific combined cooling scheme and a given blowing ratio, the coolant potential can be reasonably allocated to the internal and the external cooling to achieve the overall cooling effectiveness. As the blowing ratio increases, the overall cooling effectiveness trends to reach a maximum value. For different film hole geometrical, the maximum values of the overall cooling effectiveness at high blowing ratio approximate to the same value. At a given mass flow rate of coolant, the increase of the impingement hole diameter leads to the reduction of the overall cooling effectiveness.
