Free piston expander-linear generator used for organic Rankine cycle waste heat recovery system

Hou, Xiaochen; Zhang, Hongguang; Yu, Fei; Liu, Hongda; Yang, Fubin; Xu, Yonghong; Tian, Yaming; Li, Gaosheng

doi:10.1016/j.apenergy.2017.09.024

Cited by 52 publications

(24 citation statements)

References 51 publications

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“…Prior efforts recorded in literature have made progress on design and operation of thermal harvesters on several fronts -different working fluids (steam, helium, and air) have been considered [14,15,17,18] -different boiler and superheater designs for miniature length scales have been proposed [19,20] -new lumped parameter-based and numerical-based models of the free piston expander (FPE) have been developed [16,21]. Many efforts are specific to low temperature waste-heat harvesting and multiple have resulted in real prototypes across different length scales [22,23,14,15,16,18]. More recent prototype development has included low grade energy use in ORCstyle free piston expanders with real devices characterized by several groups [14,15,16].…”

Section: Introductionmentioning

confidence: 99%

“…Many efforts are specific to low temperature waste-heat harvesting and multiple have resulted in real prototypes across different length scales [22,23,14,15,16,18]. More recent prototype development has included low grade energy use in ORCstyle free piston expanders with real devices characterized by several groups [14,15,16]. In these works, a linear electric generator was also incorporated for real-world demonstration of power output.…”

Section: Introductionmentioning

confidence: 99%

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Design and performance of a miniature free piston expander

Burugupally

Weiss

2019

Energy

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The availability of free thermal energy provide an opportunity for power generation at miniature length scales (millimeter). Though free piston based expanders at macro length scales (centimeter and above) are found to be suitable for heat energy harvesting, their implementation at miniature scales are plagued by significant parasitic losses, yielding low thermal efficiencies. Through physics-based models we investigate the behavior and performance of a miniature free piston expander that operates on an open cycle. Here, we explore the design space of the free piston expander with an objective to achieve an efficiency of at least 15%. Three observations are reported that contribute to higher efficiency operation: (1) a higher injection pressure;(2) an optimum nondimensionalized duration of injection time of 1.5; and (3) softer springs, lower loads, and heavier pistons. A sample calculation showed that a centimeter-sized expander can generate an output power of 2.24 W at 18% efficiency. We observe that both the performance parameters of the expander, namely efficiency and output power are sensitive to injection pressure of the working fluid compared to the time duration of the working fluid injection. Our study reveals that the miniature free piston expander is promising for low temperature waste-heat harvesting.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Design and performance of a miniature free piston expander

Burugupally

Weiss

2019

Energy

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“…Specifically, the linear motion of the FPE allows coupling with a linear alternator for electricity generation similar to the work by Refs. [8,15,16]. Moreover, multiple boiler-expander units can be placed on waste heat sources where larger power output is necessary; whereas, single units can produce milli-Watt scale power for low power applications.…”

Section: Introductionmentioning

confidence: 99%

“…However, a proper choice of the working fluid is necessary for the optimal performance of the FPE. Different fluids (pure and mixtures), such as R-123 and R245fa, are being investi- gated as potential candidates [8,15] due to a negative slope on the saturated vapor curve -hence called dry fluids-that enables superheating and expansion at a lower pressure while remaining 100% vapor. This enables a greater output work from the FPE without the deleterious effects of condensed working fluids.…”

Section: Introductionmentioning

confidence: 99%

The effect of working fluid properties on the performance of a miniature free piston expander for waste heat harvesting

Burugupally

Weiss

Depcik

2019

Applied Thermal Engineering

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Power generation from waste heat sources at the miniature length scales may be generated by using phase change working fluids (liquid-to-vapor) in a traditional boiler-expander-condenser-pump system. This paper builds on our prior work of boiler and expander design by investigating the effects of working fluid properties on an expander unit based on a Free Piston (FPE) architecture. Here, using first principles, a lumped-parameter model of the FPE is derived by idealizing the FPE as a linear spring-mass-damper system. Moreover, a linear-generator model is incorporated to study the effects on useful power output from the FPE directly. As a result, insight into the thermodynamic processes within the FPE are detailed and general recommendations for working fluid selection are established. They include: (1) to achieve a higher FPE efficiency, it is desirable for a working fluid to have high specific heat ratio, and (2) a peak output voltage of about 20 V AC and peak output power of around 2 W can be generated by coupling a centimeter-scale electromagnetic energy converter to the FPE. Overall, this effort shows the promise of reliable miniature thermal power generation from low temperature waste heat sources.

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“…In some cases, it requires a superheater, a recuperator, or other auxiliary units [7]. Also, the type of expander in use depends on the fluid properties [8][9][10][11], but this problem is not addressed in this paper.…”

Section: Introductionmentioning

confidence: 99%

A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle

2019

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One of the most crucial challenges of sustainable development is the use of low-temperature heat sources (60–200 °C), such as thermal solar, geothermal, biomass, or waste heat, for electricity production. Since conventional water-based thermodynamic cycles are not suitable in this temperature range or at least operate with very low efficiency, other working fluids need to be applied. Organic Rankine Cycle (ORC) uses organic working fluids, which results in higher thermal efficiency for low-temperature heat sources. Traditionally, new working fluids are found using a trial-and-error procedure through experience among chemically similar materials. This approach, however, carries a high risk of excluding the ideal working fluid. Therefore, a new method and a simple rule of thumb—based on a correlation related to molar isochoric specific heat capacity of saturated vapor states—were developed. With the application of this thumb rule, novel isentropic and dry working fluids can be found applicable for given low-temperature heat sources. Additionally, the importance of molar quantities—usually ignored by energy engineers—was demonstrated.

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Free piston expander-linear generator used for organic Rankine cycle waste heat recovery system

Cited by 52 publications

References 51 publications

Design and performance of a miniature free piston expander

Design and performance of a miniature free piston expander

The effect of working fluid properties on the performance of a miniature free piston expander for waste heat harvesting

A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle

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