Studies of two-phase flow patterns and their transitions during condensation have gained increasing interest because heat transfer characteristics are strongly dependent on flow patterns.Therefore,it is very important...Studies of two-phase flow patterns and their transitions during condensation have gained increasing interest because heat transfer characteristics are strongly dependent on flow patterns.Therefore,it is very important to know flow pattern inside a condenser at certain flow conditions and hence to develop heat transfer correlations consistent with the prevailing heat transfer mechanism in each flow pattern. The condensation heat transfer for R134a in two kinds of in-tube three-dimensional (3-D) microfin tubes with different geometries is investigated experimentally.In the range of experimental conditions,six distinguishable flow patterns (annular flow,semi-annular flow,stratified flow,wavy flow,slug flow and plug flow) are recorded by a video camera.The obtained results show that the flow regime transition criterion between annular flow and stratified-wavy flow decreases from Fr equal to 7 to Fr equal to 2 in the Soliman flow regime map.In stratified-wavy flow regime,the average heat transfer coefficients h of the two kinds of in-tube 3-D microfin tubes increase as mass flux increases and the number of microfins in 3-D microfin tube is not the controlling factor of condensation heat transfer performance.The regressed condensation heat transfer correlation from the experimental data of stratified-wavy flow regime is obtained.The disparity of the experimental data is within the limits of ±22%.Combined with the criteria of flow pattern transitions,the correlations can be used for the design of condenser of 3-D microfin tubes.展开更多
For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grid...For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grids are used in middle additional areas. An algebra method is used to produce the initial grids in each area. And the girds are optimized by elliptical differential equation method. Then C-O-H zonal patched grids around multi-element airfoils are produced automatically and efficiently. A time accurate finite-volume integration method is used to solve the compressible laminar and turbulent Navier-Stokes (N-S) equations on the grids. Computational results prove the method to be effective.展开更多
We enhance a robust parallel finite element model for coasts and estuaries cases with the use of N-Best refinement algorithms,in multilevel partitioning scheme.Graph partitioning is an important step to construct the ...We enhance a robust parallel finite element model for coasts and estuaries cases with the use of N-Best refinement algorithms,in multilevel partitioning scheme.Graph partitioning is an important step to construct the parallel model,in which computation speed is a big concern.The partitioning strategy includes the division of the research domain into several semi-equal-sized sub-domains,minimizing the sum weight of edges between different sub-domains.Multilevel schemes for graph partitioning are divided into three phases:coarsening,partitioning,and uncoarsening.In the uncoarsening phase,many refinement algorithms have been proposed previously,such as KL,Greedy,and Boundary refinements.In this study,we propose an N-Best refinement algorithm and show its advantages in our case study of Xiamen Bay.Compared with original partitioning algorithm in previous models,the N-Best algorithm can speed up the computation by 1.9 times,and the simulation results are in a good match with the in-situ data.展开更多
To investigate the effects of various erosion control measures on mountain floods, a case study was conducted in Censhui River South Branch Watershed using scenario analysis and soil conservation service （SCS） metho...To investigate the effects of various erosion control measures on mountain floods, a case study was conducted in Censhui River South Branch Watershed using scenario analysis and soil conservation service （SCS） methods. A distributed hydrological model was developed, and watershed parameters were determined based on satellite imagery, digital terrain models, digital maps and field investigations. Two types of erosion control measures were investigated： the variation of vegetation covers and the change of cultivation techniques. Seven scenarios were considered for the test watershed. The results show： （1） while the de-vegetation results in the increase of peak discharge, the improve of vegetation covers decreases peak discharge at watershed scale; （2） by both improving vegetation cover and enhancing terrace-cultivation technology, the peak discharge is reduced and the peak flow arrival time is delayed; （3） attention should be attached to both early warning system and measures changing the underlying surface and conveyance systems.展开更多
文摘Studies of two-phase flow patterns and their transitions during condensation have gained increasing interest because heat transfer characteristics are strongly dependent on flow patterns.Therefore,it is very important to know flow pattern inside a condenser at certain flow conditions and hence to develop heat transfer correlations consistent with the prevailing heat transfer mechanism in each flow pattern. The condensation heat transfer for R134a in two kinds of in-tube three-dimensional (3-D) microfin tubes with different geometries is investigated experimentally.In the range of experimental conditions,six distinguishable flow patterns (annular flow,semi-annular flow,stratified flow,wavy flow,slug flow and plug flow) are recorded by a video camera.The obtained results show that the flow regime transition criterion between annular flow and stratified-wavy flow decreases from Fr equal to 7 to Fr equal to 2 in the Soliman flow regime map.In stratified-wavy flow regime,the average heat transfer coefficients h of the two kinds of in-tube 3-D microfin tubes increase as mass flux increases and the number of microfins in 3-D microfin tube is not the controlling factor of condensation heat transfer performance.The regressed condensation heat transfer correlation from the experimental data of stratified-wavy flow regime is obtained.The disparity of the experimental data is within the limits of ±22%.Combined with the criteria of flow pattern transitions,the correlations can be used for the design of condenser of 3-D microfin tubes.
文摘For a complex flow about multi-element airfoils a mixed grid method is set up. C-type grids are produced on each element′s body and in their wakes at first, O-type grids are given in the outmost area, and H-type grids are used in middle additional areas. An algebra method is used to produce the initial grids in each area. And the girds are optimized by elliptical differential equation method. Then C-O-H zonal patched grids around multi-element airfoils are produced automatically and efficiently. A time accurate finite-volume integration method is used to solve the compressible laminar and turbulent Navier-Stokes (N-S) equations on the grids. Computational results prove the method to be effective.
基金Supported by the National Natural Science Foundation of China (Nos. 40406005,41076001,40440420596)
文摘We enhance a robust parallel finite element model for coasts and estuaries cases with the use of N-Best refinement algorithms,in multilevel partitioning scheme.Graph partitioning is an important step to construct the parallel model,in which computation speed is a big concern.The partitioning strategy includes the division of the research domain into several semi-equal-sized sub-domains,minimizing the sum weight of edges between different sub-domains.Multilevel schemes for graph partitioning are divided into three phases:coarsening,partitioning,and uncoarsening.In the uncoarsening phase,many refinement algorithms have been proposed previously,such as KL,Greedy,and Boundary refinements.In this study,we propose an N-Best refinement algorithm and show its advantages in our case study of Xiamen Bay.Compared with original partitioning algorithm in previous models,the N-Best algorithm can speed up the computation by 1.9 times,and the simulation results are in a good match with the in-situ data.
文摘To investigate the effects of various erosion control measures on mountain floods, a case study was conducted in Censhui River South Branch Watershed using scenario analysis and soil conservation service （SCS） methods. A distributed hydrological model was developed, and watershed parameters were determined based on satellite imagery, digital terrain models, digital maps and field investigations. Two types of erosion control measures were investigated： the variation of vegetation covers and the change of cultivation techniques. Seven scenarios were considered for the test watershed. The results show： （1） while the de-vegetation results in the increase of peak discharge, the improve of vegetation covers decreases peak discharge at watershed scale; （2） by both improving vegetation cover and enhancing terrace-cultivation technology, the peak discharge is reduced and the peak flow arrival time is delayed; （3） attention should be attached to both early warning system and measures changing the underlying surface and conveyance systems.
