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Linear compressor
Linear compressor
Linear compressor
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A linear compressor is a gas compressor where the piston moves along a linear track to minimize friction and reduce energy loss during conversion of motion. This technology has been successfully used in cryogenic applications which must be oil-less. The suspension spring can be flexure type or coil type. An oil-free valved linear compressor enables the design of compact heat exchangers.[1] Linear compressors work similarly to a solenoid: by using a spring-loaded piston with an electromagnet connected to AC through a diode. The spring-loaded piston is the only moving part, and it is placed in the center of the electromagnet. During the positive cycle of the AC, the diode allows energy to pass through the electromagnet, generating a magnetic field that moves the piston backwards, compressing the spring, and generating suction. During the negative cycle of the AC, the diode blocks current flow to the electromagnet, letting the spring uncompress, moving the piston forward, and compressing the refrigerant. The compressed refrigerant is then released by a valve.

History

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A number of patents for linear compressors powered by free-piston engines were issued in the 20th century, including:

The first market introduction of a linear compressor to compress refrigerant in a refrigerator was in 2001.[3]

Valved linear compressor

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The single piston linear compressor uses dynamic counterbalancing, where an auxiliary movable mass is flexibly attached to a movable piston assembly and to the stationary compressor casing using auxiliary mechanical springs with zero vibration export at minimum electrical power and current consumed by the motor.[4] It is used in cryogenics.[4] Linear compressors are used as they have fewer mechanical losses.[5]

Linear compressors are made by LG and used in LG and Kenmore refrigerators. Linear compressors were also announced by Embraco.[6][7] Compressors of this type have less noise, and are more energy efficient than conventional refrigerator compressors. The Embraco linear compressors are also claimed to be oil-free. In the 2010s and 2020s, multiple lawsuits in the United States alleged that the LG compressors had a high rate of failure or lack of expected cooling. As of 2024, there were settlements[8] and ongoing cases.[9]

See also

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References

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Linear compressor

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from Grokipedia
A linear compressor is a positive displacement gas that drives a in straight-line using a , without the need for a or rotary-to-linear conversion mechanisms typical of conventional reciprocating compressors. This design incorporates mechanical springs to suspend the and motor assembly, enabling operation at the system's resonant frequency for optimal efficiency. Key components include the (often moving-magnet or moving-coil type), , reed valves for gas flow control, and a compression chamber, with the entire unit typically housed in a low-pressure vessel to contain vibrations and . By minimizing friction through direct drive and contactless elements, linear compressors achieve mechanical efficiencies exceeding 95% and isentropic efficiencies over 82%, making them suitable for applications requiring precise capacity modulation, such as and . The operating principle relies on electromagnetic forces generated by the to induce oscillatory motion in the , synchronized with from the springs to amplify stroke amplitude while reducing power consumption. Gas intake occurs through suction reed valves during the piston's outward stroke, followed by compression and discharge via exhaust valves on the inward stroke; advanced models account for leakage flows and using conservation equations for , , and . This resonant operation allows for variable capacity control—ranging from 10% to 100% of swept volume—via inverter-driven adjustment, contrasting with fixed-speed rotary compressors. Notable variants include oil-free designs for clean gas handling and dual-piston configurations to balance forces and mitigate vibrations. Linear compressors excel in energy efficiency, with up to 20% improvement over traditional types due to eliminated mechanical losses and enhanced in oil-free environments, though they require sophisticated to manage electromagnetic and resonant forces. However, in commercial household refrigeration applications, such as those using LG's linear inverter compressors, reliability issues including premature failures have been reported, leading to lawsuits as of 2025. Their compact size (e.g., 147 mm diameter, 300 mm height) and low noise (around 67 dBA) make them ideal for appliances, in cooling such as prototypes for devices like laptops, systems, and medical cryocoolers. Challenges include sensitivity to manufacturing tolerances in spring stiffness and the need for active control systems to optimize performance across load variations. Overall, these compressors represent a shift toward more sustainable refrigeration technologies, particularly with refrigerants like or R-134a.

Fundamentals

Definition and Components

A linear compressor is a type of gas compressor in which the moves in a straight linear path along a single axis, driven directly by a to eliminate the need for rotary components and thereby reduce and mechanical losses. This design enables oil-free operation, as the absence of a and connecting rods minimizes wear points that typically require in conventional systems. The primary components of a linear compressor include a piston that reciprocates within a cylinder, typically featuring minimal radial clearance of 10-20 microns to maintain sealing without oil. The linear motor, often a voice coil type with a moving coil and fixed permanent magnets or a moving magnet type with fixed coils, provides direct axial drive to the piston. Flexure springs or bellows guide the piston's motion while preventing lateral contact with the cylinder walls, and reed or ring valves manage gas intake and discharge in valved designs. In contrast to traditional reciprocating compressors, which rely on a to convert rotational motion into linear reciprocation, linear compressors achieve direct electromagnetic drive, simplifying the and enhancing through reduced mechanical complexity. Typical materials for the and include aluminum alloys, often with hard-anodized surfaces or coatings for low-friction performance in oil-free environments, or for added durability in high-pressure applications. Many linear compressors are designed for resonant operation to optimize energy transfer, though this is achieved through the integrated spring-mass system.

Operating Principles

The linear compressor operates through the of a within a , directly driven by electromagnetic forces generated by an integrated , which eliminates the need for a and converts into mechanical reciprocation. This setup produces a sinusoidal displacement that approximates , particularly under resonant conditions, where the oscillates back and forth along the axis. To achieve high , the linear compressor is designed for resonant operation, where the driving of the is tuned to match the 's , minimizing the electrical input required to sustain the piston's . The fnf_n is determined by the spring-mass dynamics of the and given by fn=12πkm,f_n = \frac{1}{2\pi} \sqrt{\frac{k}{m}},
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