Linear compressor has no crank mechanism compared with conventional reciprocating compressor. This allows higher efficiency, oil-free operation, lower cost and smaller size when linear compressors are used for vapour compression refrigeration (VCR) system. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency. This paper presents a review of linear compressors for refrigeration system. Different designs and modelling of linear compressors for both domestic refrigeration and electronics cooling (miniature VCR system) are discussed. Key characteristics of linear compressor are also described, including motor type, compressor loss, piston sensing and control, piston drift and resonance. The challenges associated with the linear compressors are also discussed to provide a comprehensive review of the technology for research and development in future.

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A review of linear compressors for refrigeration

https://tsukuba.repo.nii.ac.jp/?action=repository_action_common_download&item_id=27685&item_no=1&attribute_id=17&file_no=1

Design of a cryogenic CO2 capture system based on Stirling coolers

AC losses in power transmission cables composed of coated conductors could be potentially small. A strategy to approach their potentially small AC loss was studied. AC losses in mono-layer conductors for cables were calculated numerically in order to show the principle for AC loss reduction: use of narrower coated conductors and/or decrease in space between conductors reduce the magnetic field component perpendicular to the wide face of coated conductors, and they are effective for AC loss reduction. This principle was confirmed experimentally by using short mono-layer conductors. Based on the principle, 1 kArms-class three-layer conductors were fabricated, and AC loss of 0.054 W/m at 1 kArms was achieved in a three-layer conductor whose outer diameter is 19.6 mm. The influence of a magnetic substrate on the AC losses in a single coated conductor and a mono-layer conductor for a cable was studied numerically.

AC Loss Reduction of Superconducting Power Transmission Cables Composed of Coated Conductors

This paper presents experimental and numerical results of the dynamic characteristic and COP of a linear compressor in a refrigeration system using R600 refrigerant. The numerical analysis consists of a model and a simulation that includes the linear compressor. In this study, the dynamic characteristic of the natural frequency of the linear compressor is validated by comparing the simulation results with the experimental results. To investigate the effect of system resonance on the performance of linear compressor, COP is evaluated under evaporator pressure in the range of 48.3–63.2 kPa abs, and condenser pressure in the range of 439.0–573.3 kPa abs. Based on the results, the system resonance at the TDC was varied within a range of 3% under the test conditions. COP and its sensitivity were found to vary within 3% according to the operating frequency of the system ranging from 48.5 to 51.5 Hz.

An experimental and numerical study on dynamic characteristic of linear compressor in refrigeration system

Study on static and dynamic characteristics of moving magnet linear compressors.

A study on the linear compressor characteristics of the Stirling cryocooler

The effect of operating parameters in the Stirling cryocooler

HTS power cables appear to be the replacement and retrofitting of underground cable in urban areas and HTS power cable offers a number of technical and economic merits compared to normal conductor cable system. A 3 phase 22.9 kV, 50 MVA class HTS power cable system have been developed by Korea Electrotechnology Research Institute (KERI), LS Cable Ltd. and Korea Institute of Machinery and Materials (KIMM) that is one of 21st century frontier project in Korea. The 30 m long cable with 3 cores in 1 cryostat has been manufactured and installed to conduct long-term reliability test. The HTS power cable consists of two layers of phase conductor and two layers of shield used Ag/Bi-2223 tapes and polypropylene laminated paper is used in LN2 as electrical insulation. A HTS power cable has been tested with DC and rated current and voltage in pressurized liquid nitrogen. The evaluation results clarify good performance of HTS cable and these results prove that the HTS power cable has the basic electrical properties for 22.9 kV HTS power cable. This paper describes the results of developmental the 30 m, 3 phase, 22.9 kV, 50 MVA HTS power cable in Korea

Design and Experimental Results of a 3 Phase 30 m HTS Power Cable

A high temperature superconducting power cable requires forced flow cooling. Liquid nitrogen is circulated by a pump and cooled down by a subcooling system. Typical operating temperature range is expected to be between 65 K and 80 K. The circulating liquid nitrogen is subcooled by liquid nitrogen boiling on the shell side of a subcooler heat exchanger, and then it cools the HTS cable. The HTS power cable needs sufficient cooling to overcome its low temperature heat loading. This loading typically comes in two forms. One is heat leak from the surroundings and the other is internal heat generation, i.e., AC loss. This paper describes performance tests of the cooling system. Heat exchanging performance of the subcooler, pressure drop between supply and return lines, and heat transfer coefficient of a former are examined for the performance test.

Performance tests of high temperature superconducting power cable cooling system

This paper describes the thermal response of a high-temperature superconducting (HTS) wire model to instantaneous heat generation in a pressurized liquid nitrogen chamber for an HTS fault current limiter. A dc impulse power input to a stainless steel strip is adopted to simulate the quench state of the HTS wire. The test sample is submerged in the liquid nitrogen, which maintains a 77 K temperature with operating pressures of 101, 250, 400, and 600 kPa. Three different levels of dc current are supplied to the test sample during 50 ms for each operating condition. The boiling phenomena are captured with a high-speed camera and the surface temperature of the sample strip is measured to investigate the recovery process. From the captured video, the suppression of bubble generation is clearly observed as increasing operating pressure, especially for the lower heat flux condition. From the measurement of temperature, temperature rise of sample strip during heat generation decreases with increasing operating pressure except for the higher heat flux. For the recovery process, increasing operating pressure delays the recovery of the sample strip, but recovery time is within a few seconds for all cases.

Deuk-Yong Koh

Papers

A study on the linear compressor characteristics of the Stirling cryocooler

The effect of operating parameters in the Stirling cryocooler

Design and Experimental Results of a 3 Phase 30 m HTS Power Cable

Performance tests of high temperature superconducting power cable cooling system

Study on Thermal Response to Instantaneous Heat Generation in LN2 Chamber for HTS-FCL