The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

Pumped heat electricity storage (PHES) has the advantages of a high energy density and high efficiency and is especially suitable for large-scale energy storage. The performance of PHES has attracted much attention which has been studied mostly based on steady thermodynamics, whereas the transient characteristic of the real energy storage process of PHES cannot be presented. In this paper, a transient analysis method for the PHES system coupling dynamics, heat transfer, and thermodynamics is proposed. Judging with the round trip efficiency and the stability of delivery power, the energy storage behavior of a 10 MW/4 h PHES system is studied with argon and helium as the working gas. The influencing factors such as the pressure ratio, polytropic efficiency, particle diameters, structure of thermal energy storage reservoirs are also analyzed. The results obtained indicate that, mainly owing to a small resistance loss, helium with a round-trip efficiency of 56.9% has an overwhelming advantage over argon with an efficiency of 39.3%. Furthermore, the increases in the pressure ratio and isentropic efficiencies improve the energy storage performance considerably. There also exit optimal values of the delivery compression ratio, particle sizes, length-to-diameter ratios of the reservoirs, and discharging durations corresponding to the maximum round-trip efficiency and preferable discharging power stability. The above can provide a basis for the optimal design and operation of the Joule–Brayton based PHES.

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Cyclic transient behavior of the Joule–Brayton based pumped heat electricity storage: Modeling and analysis

This paper reviews progress reported in the open literature of the use of expanders to recover expansion power to improve the energy efficiency of vapour compression refrigeration systems. Pioneering works in the field are first discussed, and then a variety of expander mechanisms, including reciprocating piston, rolling piston, rotary vane, scroll, screw and turbine are reviewed together with their reported performance. Most of the reported works have been for transcritical CO2 refrigeration systems, which have reported improvements in the coefficient of performance (COP) of up to 30%. In a non-CO2 system, the maximum reported increase in the COP was 10%. The maximum reported expander efficiency (i.e. the ratio of measured power to the power available from an isentropic expansion) was 83%, obtained with a scroll expander in a CO2 refrigeration cycle. Other expander issues including heat transfer, expansion process, internal leakage, irreversibility, control strategies, installation issues and economic analysis are also reviewed. It is noted that there are a limited number of studies in these areas. Finally, challenges and recommendations for future research in the area of refrigeration expander technology is presented.

A review on expanders and their performance in vapour compression refrigeration systems

Due to the high variability of weather-dependent renewable energy resources, electrical energy storage systems have received much attention. In this field, one of the most promising technologies is compressed-air energy storage (CAES). In this article, the concept and classification of CAES are reviewed, and the cycle efficiency and effective energy are analyzed in detail to enhance the current understanding of CAES. Furthermore, the importance of the real-gas properties of air is discussed. Related research on adiabatic CAES and isothermal CAES is also presented.Due to the high variability of weather-dependent renewable energy resources, electrical energy storage systems have received much attention. In this field, one of the most promising technologies is compressed-air energy storage (CAES). In this article, the concept and classification of CAES are reviewed, and the cycle efficiency and effective energy are analyzed in detail to enhance the current understanding of CAES. Furthermore, the importance of the real-gas properties of air is discussed. Related research on adiabatic CAES and isothermal CAES is also presented.

A review of compressed-air energy storage

An experimental study on the design of counter-rotating axial-ﬂowfans was carried out. The fans were designed using an inversemethod. In particular, the system is designed to have a pure axialdischarge ﬂow. The counter-rotating fans operate in a ducted-ﬂowconﬁguration and the overall performances are measured in a nor-malized test bench. The rotation rate of each fan is independentlycontrolled. The relative axial spacing between fans can vary from17% to 310%. The results show that the efﬁciency is stronglyincreased compared to a conventional rotor or to a rotor-statorstage. The effects of varying the rotation rates ratio on the overallperformances are studied and show that the system has a very ﬂexi-ble use, with a large patch of high efﬁcient operating points in theparameter space. The increase of axial spacing causes only a smalldecrease of the efﬁciency. [DOI: 10.1115/1.4007591]

Design and Experimental Validation of a Ducted Counter-Rotating Axial-Flow Fans System

The invention provides a compressed air electric power energy storage system achieving hydraulic and pneumatic coupling According to the compressed air electric power energy storage system, in the electric valley period, a compressor unit compresses air into a constant-pressure air storage device, liquid in the constant voltage air storage device is compressed into a variable-pressure air storage device through a liquid pump, and accordingly electric energy is converted to air and liquid internal energy for storage; in the electric peak period, heat of high-pressure air in the constant-pressure air storage device is absorbed through a heater, an expansion machine drives an electric generator to generate electricity, high-pressure fluid in the variable-pressure air storage device drives a hydraulic motor generator set to generate electricity, and the fluid is injected into the constant-pressure air storage device to keep constant pressure of the constant-pressure air storage device The energy storage period of the compressed air electric power energy storage system is not limited, and the compressed air electric power energy storage system is suitable for power sources of various types and environmentally friendly, and has wide use prospects

Compressed air electric power energy storage system

It is a common practice to use closed impeller in radial inflow turbine against the flow leakage from tip clearance of impellers, especially in small volume flow condition. It utilizes labyrinths between the shroud and the case to abate the higher pressure leakage. Experimental and computational investigations of shroud clearance flow in a radial inflow turbine with labyrinth seals are presented in this paper. Compared with the result without leakage, numerical computation result including the leakage of labyrinth seals agrees better with that of the experiment result, which indicates that the leakage of labyrinth seals cannot be neglected. Several geometrical arrangements with a series of different clearance of labyrinth seals are investigated experimentally and numerically, and the dimensionless shroud clearance is of 0%, 0.6%, 1.2%, 1.8%, 2.7%, 3.6%. Finally, the character of flow and loss is analyzed by computational fluid dynamics (CFD) tools. The results indicate that the labyrinth seal flow has no effect on the main flow passage and mainly causes different leakage mass flow.

Experimental and Numerical investigation of closed Radial-Inflow Turbine with Labyrinth Seals

Effect of blade tip leakage flow on erosion of a radial inflow turbine for compressed air energy storage system

Compressed air in supercritical compressed air energy storage system expand from supercritical to atmospheric conditions at lower inlet temperature (<500 K) to generate MW scale power. Therefore, a...

Flow characteristic of a multistage radial turbine for supercritical compressed air energy storage system

In present study, the effect of back cavity in a radial inflow turbine is investigated numerically. The size effect of labyrinth seal clearance is revealed. The performances of radial turbine with back cavity at different total expansion ratio are also investigated. Results illustrate that the clearance variation of original labyrinth seal in back cavity has limited effect on the leakage flow and the isentropic efficiency. The existence of back cavity reduces the isentropic efficiency at every total expansion ratio, and a maximum isentropic efficiency reduction of 1.5% is obtained when total expansion ratio is 2.89. To control the rotor‐back cavity coupling flow loss, a “rotor‐back cavity seal” is also proposed, and the isentropic efficiency of radial turbine is significantly improved at different total expansion ratio.

Flow analysis and performance improvement of a radial inflow turbine with back cavity under variable operation condition of compressed air energy storage

Zhu Yangli

Papers

Compressed air electric power energy storage system

Experimental and Numerical investigation of closed Radial-Inflow Turbine with Labyrinth Seals

Effect of blade tip leakage flow on erosion of a radial inflow turbine for compressed air energy storage system

Flow characteristic of a multistage radial turbine for supercritical compressed air energy storage system

Flow analysis and performance improvement of a radial inflow turbine with back cavity under variable operation condition of compressed air energy storage