Abstract ：

Aiming at the high-efficiency OTEC application, a 30 kW radial-inflow turbine using ammonia was constructed via the one-dimensional design. In addition, a 3D CFD simulation was carried out to research the turbine performance. Furthermore, the effects of blade tip clearance on the flow characteristic in turbine were elucidated and the turbine performance under the off-design conditions was examined. It is indicated that the performance of the designed turbine is satisfactory with a theoretical isentropic efficiency of 85.2% under the design condition. The leakage flow encounters the scraping flow after leaving the tip clearance, forming the vortexes in the cross-section of the flow passage, which decreases the turbine efficiency, and the best ratio of blade tip clearance to inlet blade height is suggested to be 0.04–0.06. When the rotational speeds deviated from the design value, the vortexes appear in the flow passage of the turbine, resulting in non-negligible impact loss of blade and the consequent efficiency reduction. At the design rotational speed, the turbine shows a good adaptability to the inlet temperature variations with the inlet temperature varying from T0 = 296K to T0 = 304K. When the inlet pressure increases, the rotational speed corresponding to the maximum efficiency is also increased. © 2022 Elsevier Ltd

Keyword ：

Ammonia Computational fluid dynamics Energy conversion efficiency Energy efficiency Thermal energy Turbine components Turbomachine blades Vortex flow

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Abstract ：

This paper numerically qualifies the effect of rib orientation on heat transfer and flow performances of mist/steam in square channels with inclined ribs. Four types of rib orientations are investigated. The study is conducted in contrast to steam with Reynolds number ranged from 10,000 to 60,000. Secondary flow patterns and droplet trajectories are analyzed to reveal the underlying reasons bringing about heat transfer enhancement due to mist/steam. The results indicate that rib orientation greatly determines secondary flow pattern in channels, and the distribution of secondary flow triggered by N type ribs is opposite to that by P type ribs. Such secondary flow forces droplets at different locations to assemble near different side walls. The places where water drops gather in a large quantity provide splendid heat transfer enhancement. And this effect gets more obvious at higher Reynolds number. For mist/steam, both heat transfer coefficient and overall heat transfer performance in the first passage are remarkably stronger than that in the second one. In general, NN channels and PP channels filled with mist/steam have the best heat transfer performance among the investigated cases. © 2020 Elsevier Ltd

Keyword ：

Drops Flow patterns Heat transfer coefficients Heat transfer performance Reynolds number Secondary flow

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Abstract ：

This study numerically examines the effect of actual gas turbine operating conditions on heat transfer characteristics in a ribbed passage with mist/steam cooling. A 60 degrees ribbed passage with aspect ratio of 1/1 was investigated at Reynolds number of 300,000, and steam cooling was used to provide a contrast. Three main factors were considered: coolant temperature, operating pressure, and wall heat flux density. The heat transfer enhancement mechanism of mist/steam cooling was explored, and the results showed that the heat transfer performance of mist/steam cooling was superior to steam cooling. When the coolant temperature varied from 300 to 500 degrees C, the average Nusselt number of mist/steam cooling decreased by 26.6%, and the heat transfer enhancement ratio dropped from 15% to 10%. As operating pressure increased, the heat transfer performance factor of mist/steam firstly increased and then decreased. At an operating pressure of 1.5 MPa, the heat transfer achieved its optimal performance, and the heat transfer enhancement ratio achieved its maximum value of 15.9%. Larger wall heat flux density provided less heat transfer enhancement. When the heat flux density increased from 100,000 to 300,000 Wm(-2), the average Nusselt number of mist/steam cooling decreased by 13.8%, while the heat transfer enhancement ratio decreased from 25.3% to 12.6%.

Keyword ：

heat transfer enhancement internal cooling channel mist numerical simulation steam cooling

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Abstract ：

A numerical investigation of frost growth on a cold flat surface was presented based on two-dimensional Lattice Boltzmann model. This model has been validated to have less prediction error by past experiments. According to the results, it is shown that average frost density appears different at an increasing rate at different frosting stages. In addition, cold surface temperature has great influence on frost growth parameters such as frost crystal deposition mass, frost deposition rate, and frost crystal volume fraction. It was found that the frost crystal deposition mass, frost crystal volume, and the deposition rate first increase rapidly, then gradually slow down, finally remaining unchanged while the cold surface temperature decreases. The further away from the cold surface, the more sparser the frost layer structure becomes due to the smaller frost crystal volume fraction. © 2018 MDPI AG. All Rights Reserved.

Keyword ：

Cold surface Crystal deposition Frost growth Lattice boltzmann Lattice Boltzmann method Numerical investigations Prediction errors Two-dimensional lattices

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Abstract ：

A two-dimensional Lattice Boltzmann model was established to study the dynamic physical process of frost growth on a cold flat surface. It is verified that the theoretical results are in good agreement with the experiment data with better accuracy. The frost morphology is explored by showing two-dimension density distribution with different cold surface temperatures. The results also include dynamic characteristics of frost properties such as thickness, deposition weight, volume fraction, density, temperature. According to the results, it is found that the nearer it is from the cold flat plate, the larger of frost crystal volume fraction and density are. The frost surface temperature increases rapidly at the early period of frosting and then increases gradually towards the triple point temperature of the water. The frost internal temperatures rise in a linear tendency with the frost thickness and decrease at the same frost layer location with frost growth. Super-saturation degree of moist air has non-negligible effect on frost growth parameters such as frost thickness, frost crystal deposition mass, frost deposition rate and frost crystal volume fraction. © 2018

Keyword ：

Cold surface Density distributions Dynamic characteristics Frost growth Internal temperature Lattice boltzmann Triple point temperatures Two-dimensional lattices

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Abstract ：

Internal steam cooling used in the vane can not only reduce the consumption of high-pressure air but also improve the overall turbine cycle efficiency. The present paper presents a research on a turbine vane with complicated cooling structure. The vane was cooled by a combination of steam and air, which was achieved by (1) cooling the leading edge with four rows of cooling air film holes; (2) cooling the middle chord area with two internal cooling steam ribbed channels; (3) cooling the trailing edge with a row of cooling air jet holes. The temperature and the static pressure were measured by the thermocouples and pressure taps located on the vane middle section. The coolant temperature and the coolant flow were then adjusted to obtain the cooling effectiveness to assess the vane cooling performance in different cooling conditions. The results of this study confirm that (1) when the test vane is applied to the advanced duplex-medium combined cooling, surface temperature can be even, accompanied with a small thermal stress as well as a high cooling effectiveness (the average cooling effectiveness was over 0.68), which implies that a satisfactory cooling performance has been achieved; (2) film cooling used at the leading edge can shift the stagnation point downstream and produce some flow losses, which, however, does not significantly affect the entire flow field of the vane passages; (3) the best cooling effect on the vane surface is in the middle chord area with internal steam cooling and its worst is on the pressure side near the trailing edge; (4) in improving cooling performance, increasing the steam flow rate is the most effective, enhancing the coolant pressure the next, and lowering the coolant temperature the least; (5) in lowering the overall vane surface temperature, lowering the coolant temperature is the most effective, increasing the steam flow rate the next, and enhancing the coolant pressure the least. (C) 2014 Elsevier Ltd. All rights reserved.

Keyword ：

Cooling coefficient Film cooling Gas turbine Heat transfer Steam cooling

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Abstract ：

The present experiment compares the heat transfer and friction characteristics in steam cooled and air cooled rectangular channels (simulating a gas turbine blade cooling passage) with two opposite rib-roughened walls. The Reynolds number (Re) whose length scale is the hydraulic diameter of the passage is set within the range of 10000-60000. The channel length is 1000 mm. The pitch-to-rib height ratio, the channel aspect ratio and the channel blockage ratio is 10, 0.5 and 0.047, respectively. It is found that the average Nu, the average friction coefficient, and the heat transfer performance of both steam and air in the ribbed channels show almost the same change trend with the increase of Re. Under the same test conditions, the average Nu of steam is 30.2% higher than that of air, the average friction coefficient is 18.4% higher, and the heat transfer performances of steam on the ribbed and the smooth walls are 8.4% and 7.3% higher than those of air, respectively. In addition, semi-empirical correlations for the two test channels are developed, which can predict the Nu under the given test condition. The correlations can be used in the design of the internal cooling passage of new generation steamcooled gas turbine blade/vane.

Keyword ：

Friction characteristics Gas turbine Heat transfer characteristics Rectangular channel Steam-cooled

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Abstract ：

Advanced cooling technology is a key measure of thermal protection for turbine blades, and raising inlet gas temperature of gas turbines. Using steam as a coolant in the internal cooling channels of turbine blade can significantly reduce the consumption of air drawn from the compressors and the closed circuits convective steam cooling can help to avoid the mixing loss between the mainstream and the cooling air so as to raise the overall efficiency of gas turbine. In this study, cooling performance comparison between the steam and air is conducted on a test blade with five smooth radial convective cooling channels. The temperature and static pressure on the surface of the mid-span of the test blade are measured and the cooling performance of the blade under different cooling conditions is evaluated. Results show that the middle region of the test blade has the highest cooling effectiveness, and then the leading edge follows. The cooling effectiveness at the trailing edge is the lowest. At the same mass flow rate, the averaged cooling effectiveness of steam cooling is higher than air by about 0.12. To obtain a similar cooling performance, the consumption of cooling steam is only 40.82% of the cooling air. In conclusion, steam cooling can achieve a better cooling performance than air, and improvements of cooling structure for the trailing edge is required for steam-cooling application in the given configuration. (C) 2014 Elsevier Inc. All rights reserved.

Keyword ：

Cooling efficiency Gas turbine Internal cooling Steam cooling

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Abstract ：

Supersonic gas flow entraining solid particles changed the direction after passing through an oblique shock wave, but the solid particles maintained original movement direction due to their large inertia. So the solid particles will depart from the gas phase flow. A three-dimensional numerical simulation of gas and solid separation in supersonic flow was carried out by using ANSYS CFX software based on Euler-Lagrange model. The influence of inlet total temperature of particle-entrained gas on gas-solid two-phase flow field and the track of solid particles of different sizes was analyzed in detail. The simulation result shows that the separation efficiency of particle with diameter of 10μm is 79.09% when the total temperature of inlet particleentrained gas is 873.15K. When the total temperature of inlet particle-entrained gas is 1000K and 1100K, the separation efficiency of the particle with the same diameter will be 80.3% and 80.9% respectively. As the total temperature increases from 873.15K to 1000K and 1100K, the corresponding separation efficiency is 56.3%, 58.5%, 59.9% for the particle with diameter of 5 μm and 88.9%, 89.4%, 89.7% for the particle with diameter of 20μm. The total pressure loss of particle-entrained gas at the total temperature of 873.15K varies from 27KPa to 39KPa, which changes with the diameter of particle. The total pressure loss of particleentrained gas increases very little when the total temperature increases.

Keyword ：

Oblique shock waves Pressure loss Separation efficiency Supersonic gas Total temperatures

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Abstract ：

An experimental study of heat transfer characteristics in steam-cooled rectangular channels with two opposite rib-roughened walls for Reynolds number (Re) in the range of 10,000-80,000 was conducted. To simulate the actual geometry and heat transfer structure of turbine blade/vane internal cooling passage, each of the test channels was made by welding four stainless steel plates. The pitch-to-rib height ratio pie was kept at 10 and the channel length L was kept at 1000 mm. The channel aspect ratios (W/H) were 0.25, 0.5 and 1, respectively. The channel blockage ratios were 0.047 for W/H = 1, 0.5 and 0.078 for W/H = 0.25. We have found that the average Nusselt number (Nu) for the channel with alpha = 45 degrees is about 15-25 percent higher than that for the channel with alpha = 60 degrees. For the channels with W/H = 0.5 or 1, the average Nu decreases along the rib axes because of the rib-induced secondary flow that moves from the left-hand side to the right-hand side. In addition, based on the heat transfer results, we have developed the semi-empirical correlations for the two test channels with the highest and the lowest heat transfer. The correlations can be used in the design of the internal cooling passage of new-generation steam-cooled gas turbine blade/vane. (C) 2012 Elsevier Ltd. All rights reserved.

Keyword ：

Gas turbine Heat transfer characteristics Rectangular channel Steam-cooled

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