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Solar Thermal Power
Published in D. Yogi Goswami, Principles of Solar Engineering, 2023
Free-piston arrangement is an innovative way to realize the Stirling cycle. In this arrangement, the power piston is not connected physically to an output shaft. The piston bounces between the working gas space and a spring (usually a gas spring). The displacer is also usually free to bounce. This configuration is called the Beale free-piston Stirling engine after its inventor, William Beale (Stine 2004). Since a free-piston Stirling engine has only two moving parts, it offers the potential of simplicity, low cost, and reliability. Moreover, if the power piston is made magnetic, it can generate current in the stationary conducting coil around the engine as it moves. This is the principle of the free-piston/linear alternator in which the output from the engine is electricity. Figure 8.29 shows a schematic of a free-piston Stirling engine with a linear alternator.
Stirling Engines
Published in D. Yogi Goswami, Frank Kreith, Energy Conversion, 2017
In a kinematic engine, the power piston is connected to the output shaft by a connecting rod crankshaft arrangement. Free-piston arrangement is an innovative way to realize the Stirling cycle. In this arrangement, the power piston is not connected physically to an output shaft. The piston bounces between the working gas space and a spring (usually a gas spring). The displacer is also usually free to bounce. This configuration is called the Beale free-piston Stirling engine after its inventor, William Beale [2]. Since a free-piston Stirling engine has only two moving parts, it offers the potential of simplicity, low cost, and reliability. Moreover, if the power piston is made magnetic, it can generate current in the stationary conducting coil around the engine as it moves. This is the principle of the free piston/linear alternator in which the output from the engine is electricity.
Parametric analysis on the critical oscillation point of a free piston Stirling engine with a nonlinear load
Published in International Journal of Green Energy, 2023
Pengfan Chen, Changshuang Zhi, Wenhao Ding, Chao Zhu, Yingwen Liu
K11 represents the total effect of the blade spring and the gas spring in compression and expansion spaces on the displacer. K12 represents the gas spring effect in compression space on the displacer, which is caused by the power piston’s oscillation. K21 represents the gas spring effect in compression space on the power piston, which is caused by the displacer’s oscillation. K22 represents the total effect of the blade spring and the gas spring in compression space on the power piston. It is observed that the gas spring stiffness is related to the average pressure, as well as the temperature in expansion and compression spaces. The nonlinear dynamic matrix function given by Equation (22) is numerically solved by the Runge-Kutta algorithm in MATLAB, the displacement, velocity, pressure and operating frequency can be obtained.
Effect of displacer on performance of Stirling-type pulse tube refrigerator with work recovery
Published in Science and Technology for the Built Environment, 2021
Pu Zheng, Xi Chen, Yangping Zeng, Weidong Wu, Yinong Wu
From the previous studies, there are two kinds of pneumatic displacer-type SPTRs, according to the situation of whether the displacer has a rod or not. For the rod displacer type, the rod has two functions. One is to supply additional driving force for the pneumatic displacer, and the other is to provide gas spring stiffness. The mechanical spring supporting the displacer rod is set in the backpressure space instead of working space (auxiliary compression space or expansion space). For the rodless displacer type, a much larger mechanical spring stiffness is required to achieve good phase relations in the regenerator (Wang et al. 2015). Several pieces of flexure springs directly support the displacer in the working space, which leads to a large void volume. Moreover, it is difficult to directly measure the displacement of the rodless displacer without influencing the internal gas flow. Compared with the rodless displacer type, the rod displacer type has more parameters to be designed, especially the displacer rod diameter. Although some researchers (Guo, Lin, and Zhu 2020; Zhu and Nogawa 2010) have conducted analysis about the effect of rod displacer parameters on the performance, they only focus on the regenerator phase angles without considering the work recovery effectiveness. The high efficiency is related to the phase relations at both ends of the regenerator for the conventional SPTR. However, the work recovery effectiveness, which is a unique attribute of the work recovery SPTR, should be given more attention.
The effects of a passive exoskeleton on muscle activity and metabolic cost of energy
Published in Advanced Robotics, 2020
Wei Wei, Wei Wang, Zhicheng Qu, Jihua Gu, Xichuan Lin, Chunfeng Yue
In this study, a passive exoskeleton called MeBot-EXO was used as presented in Figure 3. This exoskeleton consists of three types of parts: one belt, two hip joints and two upper leg pads. On both sides of the body, there is a gas spring that provides assistant force when human bending forward and lifting things. Meanwhile, the gas springs will not be compressed when users are in normal walking. The exoskeleton is intended to transfer forces from the lower back to the abdomen and leg pads. The mechanical structure in this paper utilizes torso angle to determine when to provide a restoring torque, which in turn creates a disconnect between lifting and walking. The main body of the device is made of aluminum alloy and nylon material, which meets the requirements of structural strength and weight. The total weight of the exoskeleton is 2.5 kg. The joints of this device are connected in the form of hinges and have two degrees of freedom. The size of the gas spring is 800 N, it is equivalent to offsetting the upper body weight of the human body in the case of a human weighted 60 kg. The material of leg pads is ABS, so that there is larger friction between leg pads and thigh.