Hydrogen energy and fuel cell technology are critical clean energy roads to pursue carbon neutrality. The proton exchange membrane fuel cell (PEMFC) has a wide range of commercial application prospects due to its simple structure, easy portability, and quick start-up. However, the cost and durability of the PEMFC system are the main barriers to commercial applications of fuel cell vehicles. In this paper, the core hydrogen recirculation components of fuel cell vehicles, including mechanical hydrogen pumps, ejectors, and gas–water separators, are reviewed in order to understand the problems and challenges in the simulation, design, and application of these components. The types and working characteristics of mechanical pumps used in PEMFC systems are summarized. Furthermore, corresponding design suggestions are given based on the analysis of the design challenges of the mechanical hydrogen pump. The research on structural design and optimization of ejectors for adapting wide power ranges of PEMFC systems is analyzed. The design principle and difficulty of the gas–water separator are summarized, and its application in the system is discussed. In final, the integration and control of hydrogen recirculation components controlled cooperatively to ensure the stable pressure and hydrogen supply of the fuel cell under dynamic loads are reviewed. 

A review of key components of hydrogen recirculation subsystem for fuel cell vehicles

Large-scale heat pumps can contribute towards the decarbonisation of district heating systems and industrial processes. Unidentified faults can have a negative impact on the availability, performance and maintenance costs of heat pump systems. This study provides a description of faults related to the operation of 53 heat pumps based on a vapour compression cycle. Faults were characterized according to potential causes, mitigation or prevention implications as well as detection and diagnosis methods. Faults in the compressor, evaporator and source heat exchanger were more recurrent than in other components of large-scale heat pumps. Overall, the most common faults were fouling of heat exchangers and refrigerant leakage. Faults related to negative impacts like system shutdown, performance reduction and release of refrigerant into the environment, were mainly described to be originated in the compressor. Several directions for future research were identified, which included developing specific fault detection and diagnosis methods for large-scale heat pump applications, proposing methods to detect and diagnose multiple and simultaneous faults, and integrating performance degradation monitoring with fault detection and diagnosis. 

A review of common faults in large-scale heat pumps

In recent years, noise problems have been taken as an important issue with the demanding of better life quality by human beings. Applications of Helmholtz resonators on eliminating noises can be widely seen in pipelines, jet engines, tailpipes and mufflers, or even in electronic equipment. On the other hand, the beautiful sound made by organ pipes and musical instruments are based on the concept of resonator as well. As a result, we can see the potential of taking advantages of sound to different applications. For instance, players of the musical instrument can easily overcome learning barriers by decreasing the difficulty of driving musical resonators, engineers can create specific sounds by exploiting the Helmholtz resonator, etc. In this study, we explore various driving conditions by means of air jet to drive the resonator in different locations and angles first. Then, the performance difference between mouthpieces and blowers is compared. Finally, suitable conditions of guiding mouthpieces and blowers are obtained. Accordingly, experiments show several key results: (a) The thicker of the resonator wall, the louder sound it can create; (b) Higher sound intensities and more consistent frequency values can be obtained nearby the orifice of the resonator than other places; (c) With modified blowers and mouthpieces, resonators are much easier to be driven.

Helmholtz resonator 在不同驅動方式下之聲音特性

Currently, a scroll compressor is used in many industrial fields; hence, research on its reliability is important. The major loading type during operation is pressure. However, unexpected contact between scroll compressors typically occurs, and thus, the severe loading condition should be considered. To consider this condition, the study modified the scroll compressor’s structure to a C-type specimen. The study applied cyclic axial load in the specimen. The main objective of the study is to define a proper fatigue life method for the aluminium scroll compressor and proper finite element method (FEM) modeling. To define the method, the study included a case study for various parameters, such as mean stress effects. Furthermore, a crack propagation study is presented. In the study, the Darveaux method that considers the Bauschinger effect of ductile material is used. It is expected that the consideration of the parameters can help define the fatigue life assessment of an aluminium scroll compressor.

Assessment of fatigue lifetime and characterization of fatigue crack behavior of aluminium scroll compressor using C-specimen

The electric scroll compressor is driven by a built-in electric motor that rotates the scroll disk. It is known for its simple structure, adjustability, and high efficiency, making it highly promising for various applications. This paper reviews the current application and research status of electric scroll compressors. It covers topics such as the optimal design of scroll compressor profiles, scroll disk leakage sealing, and computer simulation optimization design methods. Additionally, the progress and development trends of vapor-injection scroll compressors (SCVIs) are discussed. This paper also presents the latest research progress on the application of the new refrigerant CO2 in electric scroll compressors, along with its latest applications that align with sustainable development requirements. Finally, this paper concludes with recommendations for the application of electric scroll compressors and suggests future directions for research.

Key Technologies and Application of Electric Scroll Compressors: A Review

Noise control of a two-stage screw refrigeration compressor

The invention discloses a double-motor driven double-rolling piston compressor structure and a control method thereof; the compressor structure comprises two cylinders which are independently driven by two motors, wherein a suction orifice of the first-stage cylinder is directly connected with an air intake pipeline; an exhaust orifice of the first-stage cylinder is connected with an exhaust pipeline through a first electromagnetic valve; the suction orifice of the second-stage cylinder is connected with the air intake pipeline through a third electromagnetic valve; a second electromagnetic valve is arranged between the exhaust orifice of the first-stage cylinder and the suction orifice of the second-stage cylinder; the exhaust orifice of the second-stage cylinder is directly connected with the exhaust pipeline; the two motors are connected with an inverter for controlling the rotating speed, and the electromagnetic valves are connected with a controller. By selectively controlling theseries and parallel connection of the two cylinders autonomously, the large pressure ratio is achieved in series connection, and the large flow rate is achieved in parallel connection. The two motorscan be controlled by a frequency converter to achieve the frequency conversion, and the stepless variable flow and the voltage ratio regulation are implemented.

Double-motor driven double-rolling piston compressor structure and control method thereof

The invention relates to a quasi-elliptic rolling piston and a rolling piston compressor. The quasi-elliptic rolling piston has a profile formed by combining a plurality of molded lines; the center ofmass coincides with a main shaft; a piston body is concentric with a cylinder; compared with a circular rolling piston, the quasi-elliptic rolling piston has a greater radius of curvature at a contact point with the cylinder, the up-and-down motion rate of a sliding sheet can be reduced in the exhaust process, and the friction angles between the quasi-elliptic rolling piston and the cylinder andbetween the quasi-elliptic rolling piston and the sliding sheet can be reduced; and the radiuses of curvature of the molded lines of various portions at the combined and connected parts are the same.The rolling piston compressor comprises the cylinder; the piston is arranged in a cavity of the cylinder; the piston is fixedly connected with the main shaft and driven to make rotary motion by the main shaft; the sliding sheet capable of being in close contact with the piston all the time is arranged on the inner wall of a cavity of the cylinder; the sliding vane is supported by a sliding sheet spring; an air inlet hole and an exhaust hole are formed in cylinder end covers at the two ends of a casing; and an exhaust valve is arranged on the exhaust hole. Friction and leakage of the piston canbe reduced, and the size and mass of the piston are increased.

Quasi-elliptic rolling piston and rolling piston compressor

The invention discloses a thermoelectric conversion device based on a hydrogen ion concentration difference battery. The device comprises a hydrogen ion concentration difference battery for ionizing hydrogen to generate a current and a heat exchanger for heating gas in the hydrogen ion concentration difference battery, wherein the hydrogen ion concentration difference battery comprises a proton exchange film and negative and positive electrodes arranged on two sides of the proton exchange film, hydrogen is introduced into a positive electrode to generate ionization reaction to generate 2e and 2H , inert gas is introduced into a negative electrode, ionized H reaches the negative electrode through the proton exchange film, ionized e reaches the negative electrode from the positiveelectrode through an external circuit, hydrogen is regenerated in the negative electrode, and the current used by a power supply and consumption device is generated in the external circuit. The device is advantaged in that the heat exchanger is used for heating to improve a proton passing rate of the proton exchange film, so discharge efficiency is improved, the hydrogen is not consumed in the whole reaction, but the current is generated in the external circuit, compared with a traditional waste heat power generation system, the device is advantaged in that the device is efficient, free of pollution, low in noise and the like.

Thermoelectric conversion device based on hydrogen ion concentration difference battery

The invention discloses a three motor driven single-screw compressor control method. The method includes the following steps that firstly, a screw rod is arranged in a machine shell, two star wheels are symmetrically arranged on the two sides of the screw rod, the screw rod and the two star wheels are independently connected with three motors through couplers correspondingly, the rotating speeds of the three motors are controlled through frequency converters, and the frequency converters are connected with a controller; and secondly, rotating speed sensors are used for measuring the real-timerotating speed of the three motors, rotating speed signals of the three rotating speed sensors are analyzed through the controller, the rotating speed is set in the controller, the difference value ofthe rotating speed signals of the three motors is analyzed according to the controller, increasing or decreasing of the frequency of the frequency converters is controlled according to difference value signals, then the rotating speeds of the three motors are controlled, and synchronous rotation of the three motors is achieved. By means of the three motor driven single-screw compressor control method, flow of a single-screw compressor can be adjusted, stepless variable-flow adjustment is achieved, the compression ratio of the single-screw compressor can also be changed, the control process issimple and convenient, and the control effect is reliable.

Three motor driven single-screw compressor control method

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