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Helium is one of the best coolants in closed Brayton cycle power plants as it has superior transport properties; however, the main shortcoming is its compression, which is very difficult to achieve. It leads to a higher number of compressor stages, means bigger mass and big size of the compressor, which create dynamic issues in a compressor of the power conversion unit. All the helium compressors ever constructed have a very high number of stages such as Oberhausen II type 50 MW and JAEA 300 MW, high and low pressure compressors have 25 and 35 stages respectively. In this paper thermodynamic traits of mixing helium with an inert gas xenon were presented. Helium xenon mixture up to the molecular weight of <40 g/mol not only increases heat transfer coefficient but also significantly increase the loading of the compressor. A 7% higher heat transfer coefficient can be achieved with 15 g/mol helium xenon mixture. Therefore, a 15 g/mol helium xenon mixture compressor was designed and its performance analysis conducted using Ansys CFX. It is found that the use of 15 g/mol helium xenon mixture greatly increases the blade loading, which gives a higher total outlet pressure ratio. The obtained results indicated that only 18.75% stages of helium xenon compressor can generate requisite outlet pressure. Hence, the use of helium xenon over pure helium is advantageous as it reduces size and cost of turbo compressor of HTGR power plant. • He-Xe gas mixture 15 g/mol MW has 7% higher heat transfer coefficient than He. • 81.3% lesser stages achieved desired pressure in He-Xe compressor. • Compressor of HTGR working on CBC reduced to 3 against 16 stages. • Stall margin of He-Xe compressor is reduced compare to He compressor. [ABSTRACT FROM AUTHOR]

In the present study, numerical simulation of wet compression in a transonic single stage compressor (NASA stage 35) was performed. Thermodynamic processes, heat and mass transfer that greatly influenced the water droplets in the wet compression of the gas turbine compressor were also studied. The results show that, injecting substantial amount of water droplets at the compressor inlet, fully evaporated inside the rotating blade rows, raises the amount of mass flow rates and lower the compression work which greatly influence the compressor performance and maximize its efficiency. Evaporation of water droplets decreases the temperature in front of the rotor blade position, which boosts the moisture content in the air and the formation of vapor. Combination of these factors changes the thermodynamics properties of the fluids, thus, accelerates the convective heat and mass transfer of the mixture. The convective heat between water droplets and compressed air is the primary factor for cooling in the compressor channel and helps to overcome the flow loss caused by water injection and improve the performance and efficiency of the compressor. The overall efficiency of the wet compression process growths to an average of 84%, roughly, 2 percent above the dry and experimental values of 82%. [ABSTRACT FROM AUTHOR]

Closed Brayton cycle power plant with High Temperature Gas-cooled Reactor is one of the most promising solutions for reduction in carbon emission. Helium is being used as a coolant in power conversion unit of these power plants. The output power of these systems is regulated by varying the density of helium in the power conversion unit in such a way that the compressor is required to operate over a wide range of Reynolds numbers. In this paper, the vortices structure in conventional and highly loaded helium compressor cascade are analyzed at low Reynolds numbers. Accordingly, the evolution mechanism of vortex structure in the highly loaded helium compressor cascade was studied and validated by experiments. It is concluded that with the decrease in Reynolds number, the vortex size and total pressure loss coefficient increase gradually. The loss weight factor of the passage vortex (PV) and concentrated shedding vortex (CSV) in the highly loaded helium compressor cascade increases by 262 % and 53.8 %, respectively, in comparison with the conventional compressor cascade. • The highly loaded design method for helium compressors was used to improve the compression performance of the working fluid. • The vortices structure in conventional and highly loaded helium compressor cascade are analyzed at different Reynolds numbers. • The relationship between the loss and the vortex structure was established from the loss weight factor. • Experiments with highly loaded helium compressor cascade were conducted with the substitute working medium. [ABSTRACT FROM AUTHOR]

• The application background of helium compressor is introduced. • The theoretical research of helium compressor is reviewed. • The challenges and potential breakthroughs were highlighted. The power conversion unit of a high-temperature gas-cooled reactor (HTGR) could be a closed Brayton cycle power plant with helium as the working fluid. The helium compressor is the main component of such a power conversion unit, and its performance has significant effects on the power output and cycle efficiency. However, helium is difficult to compress owing to its thermo-physical properties, making the helium compressor design challenging. This paper provides a review of the studies and applications of helium compressors. The background of the helium compressor is introduced, the theoretical studies on helium compressors are reviewed and the development of the helium compressor is discussed. Based on the review, the helium compressor future challenges and potential breakthroughs in different aspects are highlighted. The results show that helium compressor development requires a special design technique which takes the thermo-physical properties of helium into consideration and advanced technologies suitable for helium compressor should focus on development. [ABSTRACT FROM AUTHOR]

The highly loaded design method of helium compressors can effectively solve the compression problem of helium in high-temperature gas-cooled reactors. However, the reduction in blade height and the increase in transverse pressure gradient lead to more leakage flow problems at the tip clearance. This study aims to develop a deeper understanding of the tip leakage flow physics and its influence on the loss mechanism. The tip leakage loss characteristics and loss mechanisms in a highly loaded helium compressor are analyzed by numerical simulation to provide the necessary knowledge for optimizing the blade tip aerothermal design. Five different blades are designed with different loading conditions and analyzed with five different blade tip clearances. The sensitivity of the aerothermal performance on tip clearance scales in the highly loaded helium compressor rotor is also analyzed. Based on the results and analysis, a new loss model is developed, which can be fully utilized to predict the tip clearance loss in highly loaded helium compressors. The deviations between the predicted values and CFD values can be less than 3%. [ABSTRACT FROM AUTHOR]

The highly loaded design method of helium compressor can effectively resolve the problem of helium compression in high temperature gas cooled reactor (HTGR). However, the alteration in design method has led to the variation of its characteristics at the same speed. In order to resolve this issue, in this paper, a three-dimensional, multi-passage unsteady numerical analysis is conducted to develop the understanding of the performance of a 1.5 stages highly loaded helium compressor. At first, the influence of the highly loaded design method on the unsteady flow of helium compressor is analyzed at the design point. Then, the instability characteristics of highly loaded helium compressor are studied by analyzing the flow field near stall point. Finally, the main factors causing the instability of highly loaded helium compressor are discussed. The result shows that radial separation which is caused by the inverse pressure gradient at the stator root is the main factor causing instability in highly loaded helium compressor. Image 1 [ABSTRACT FROM AUTHOR]

In this paper a novel casing treatment structure i.e. leading edge suspended groove shroud end wall structure is proposed in order to reduce the tip clearance losses in highly loaded helium compressor. The highly loaded design method of helium compressor can effectively resolve the problem of helium compression in high temperature gas cooled reactor (HTGR) plants. However, smaller blade height and increase in blade loading cause higher tip clearance leakage losses. The result shows that the leading edge suspended groove shroud structure in highly loaded helium compressor rotor effectively controls the formation of the tip clearance leakage flow and reduces the tip clearance leakage loss. 30° groove slope minimizes the total clearance losses close to blade tip. Moreover, It increases the efficiency of the highly loaded helium compressor by 0.4% at 1 mm tip clearance gap. • The influence of shroud end wall structure on the leakage flow is analyzed. • The working methodology of the suspended groove clearance is discussed. • The advantages and disadvantages of shroud end wall structures are compared. [ABSTRACT FROM AUTHOR]