The group Ⅲ nitrides are an important class of materials with aplications in UV and visible optoelectronics,high temperature electronics,cold cathodes and solar blind detectors.In recent years,with the realisation of...The group Ⅲ nitrides are an important class of materials with aplications in UV and visible optoelectronics,high temperature electronics,cold cathodes and solar blind detectors.In recent years,with the realisation of nitride based LEDs,the use of GaN IED has the potential to compete with 1raditional filament and discharge lamps,for the provision of white lighting,and there has been an explosion of interest in the MOCVD growth of GaN based materials with an increasing focus on large area multiwafer reactors and wafer uniforrmity.This paper will review the design philosophy and characteristics of close-coupled showerhead reactors,relating these to the requirements of group Ⅲ-nitride growth,and will present a selection of data resulting from the operation of such equipment.These results suggest that the close coupled showerhead style of reactor is very suitable for the growth of GaN based structures in both research and production environments.展开更多
As the interaction between the combustor and the turbine in the aero-engine continues to increase,the film cooling design considering the combustor swirling outflow has become the research focus.The swirling inflow an...As the interaction between the combustor and the turbine in the aero-engine continues to increase,the film cooling design considering the combustor swirling outflow has become the research focus.The swirling inflow and high-temperature gas first affect the vane leading edge(LE).However,no practical improved solution for the LE cooling design has been proposed considering the combustor swirling outflow.In this paper,the improved scheme of showerhead cooling is carried out around the two ways of adopting the laid-back-fan-shaped hole and reducing the coolant outflow angle.The film cooling effectiveness(η) and the coolant flow state are obtained by PSP(pressure-sensitive-paint) and numerical simulation methods,respectively.The research results show that the swirling inflow increases the film distribution inhomogeneity by imposing the radial pressure gradient on the vane to make the film excessively gather in some positions.The showerhead film cooling adopts the laid-back-fan-shaped hole to reduce the momentum when the coolant flows out.Although this cooling scheme improves the film attachment and increases the surface-averaged film cooling effectiveness(η_(sur)) by as much as15.4%,the film distribution inhomogeneity increases.After reducing the coolant outlet angle,the wall-tangential velocity of the coolant increases,and the wall-normal velocity decreases.Under the swirl intake condition,both ηand the film distribution uniformity are significantly increased,and the growth of η_(sur) is up to 16.5%.This paper investigates two improved schemes to improve the showerhead cooling under the swirl intake condition to provide a reference for the vane cooling design.展开更多
The mass transport process in a showerhead MOCVD reactor is mathematically analyzed.The mathematical analysis shows that the vertical component velocity of a point over the substrate is only dependent on vertical dist...The mass transport process in a showerhead MOCVD reactor is mathematically analyzed.The mathematical analysis shows that the vertical component velocity of a point over the substrate is only dependent on vertical distance and is independent of radial distance.The boundary layer thickness in stagnation flow is independent of the radial position too.Due to the above features,the flow field suitable for film growth can be obtained.The ceiling height of the reactor has important effects on residence time and the mass transport process.The showerhead MOCVD reactor has a short residence time and diffusion plays an important role in axial transport,while both diffusion and convection are important in radial transport.展开更多
文摘The group Ⅲ nitrides are an important class of materials with aplications in UV and visible optoelectronics,high temperature electronics,cold cathodes and solar blind detectors.In recent years,with the realisation of nitride based LEDs,the use of GaN IED has the potential to compete with 1raditional filament and discharge lamps,for the provision of white lighting,and there has been an explosion of interest in the MOCVD growth of GaN based materials with an increasing focus on large area multiwafer reactors and wafer uniforrmity.This paper will review the design philosophy and characteristics of close-coupled showerhead reactors,relating these to the requirements of group Ⅲ-nitride growth,and will present a selection of data resulting from the operation of such equipment.These results suggest that the close coupled showerhead style of reactor is very suitable for the growth of GaN based structures in both research and production environments.
基金financial support from the National Natural Science Foundation of China (Grant No.U2241268)the Natural Science Foundation of Hunan Province (Grant No.2021JJ40646)+1 种基金the National Science and Technology Major Project(Grant No.J2019-Ⅲ-0019-0063)the Innovation Capacity Support Plan in Shaanxi Province of China (Grant No.2023-CX-TD-19)。
文摘As the interaction between the combustor and the turbine in the aero-engine continues to increase,the film cooling design considering the combustor swirling outflow has become the research focus.The swirling inflow and high-temperature gas first affect the vane leading edge(LE).However,no practical improved solution for the LE cooling design has been proposed considering the combustor swirling outflow.In this paper,the improved scheme of showerhead cooling is carried out around the two ways of adopting the laid-back-fan-shaped hole and reducing the coolant outflow angle.The film cooling effectiveness(η) and the coolant flow state are obtained by PSP(pressure-sensitive-paint) and numerical simulation methods,respectively.The research results show that the swirling inflow increases the film distribution inhomogeneity by imposing the radial pressure gradient on the vane to make the film excessively gather in some positions.The showerhead film cooling adopts the laid-back-fan-shaped hole to reduce the momentum when the coolant flows out.Although this cooling scheme improves the film attachment and increases the surface-averaged film cooling effectiveness(η_(sur)) by as much as15.4%,the film distribution inhomogeneity increases.After reducing the coolant outlet angle,the wall-tangential velocity of the coolant increases,and the wall-normal velocity decreases.Under the swirl intake condition,both ηand the film distribution uniformity are significantly increased,and the growth of η_(sur) is up to 16.5%.This paper investigates two improved schemes to improve the showerhead cooling under the swirl intake condition to provide a reference for the vane cooling design.
文摘The mass transport process in a showerhead MOCVD reactor is mathematically analyzed.The mathematical analysis shows that the vertical component velocity of a point over the substrate is only dependent on vertical distance and is independent of radial distance.The boundary layer thickness in stagnation flow is independent of the radial position too.Due to the above features,the flow field suitable for film growth can be obtained.The ceiling height of the reactor has important effects on residence time and the mass transport process.The showerhead MOCVD reactor has a short residence time and diffusion plays an important role in axial transport,while both diffusion and convection are important in radial transport.
