Research Papers: Gas Turbines: Heat Transfer

The Application of Rotary Vane Expanders in Organic Rankine Cycle Systems—Thermodynamic Description and Experimental Results

[+] Author and Article Information
Zbigniew Gnutek

e-mail: zbigniew.gnutek@pwr.wroc.pl

Piotr Kolasiński

e-mail: piotr.kolasinski@pwr.wroc.pl
Department of Thermodynamics,
Wrocław University of Technology,
Institute of Heat Engineering
and Fluid Mechanics,

Wybrzeże Wyspiańskiego 27,
Wrocław 50-354, Poland

Contributed by the IC Engine Division of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received February 27, 2012; final manuscript received January 28, 2013; published online May 20, 2013. Assoc. Editor: Piero Colonna.

J. Eng. Gas Turbines Power 135(6), 061901 (May 20, 2013) (10 pages) Paper No: GTP-12-1049; doi: 10.1115/1.4023534 History: Received February 27, 2012; Revised January 28, 2013

Small (10–100 kW) and micro (0.5–10 kW) Organic Rankine Cycle (ORC) power systems are nowadays considered for local and domestic power generation. Especially interesting are micropower applications for heat recovery from dispersed low potential (85–150 °C) waste and renewable heat sources. Designing and implementing an ORC system dedicated to energy recovery from such a source is difficult. A proper working fluid must be selected together with a suitable expander. Volumetric machines can be adopted as a turbine alternative in small-capacity applications under development, like, e.g., domestic cogeneration. Scroll and screw expanders are a common choice. However, scroll and screw expanders are complicated and expensive. Vane expanders are mechanically simple, commercially available and cheap. This paper documents a study providing the preliminary analysis of the possibility of employing vane-expanders in mini-ORC systems. The main objective of this research was therefore a comprehensive analysis of the use of a vane expander for continuous operation with a low-boiling working fluid. A test-stand was designed and set up starting from system models based on thermodynamic analysis. Then, a series of experiments was performed using the test-stand. Results of these experiments are presented here, together with a model of multivane expanders and a thermodynamic-based method to select the working fluid. The analysis presented in this paper indicates that multivane expanders are a cheap and mechanically simple alternative to other expansion devices proposed for small-capacity ORC systems.

Copyright © 2013 by ASME
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Fig. 1

The relationship between the operational frequency and the working chamber size for volumetric machines [9]. The volume of working chambers in different machine types was recalculated to the volume of the sphere with radius ru. The ru numerical value is presented on a graph with the corresponding machine operational frequency. 1—rotary-blower for coke-oven gas, 2—diesel engine, 3—aircraft model engine, 4—piston vacuum pump, 5—large piston marine engine, 6—small screw compressor, 7—refrigerating piston compressor, 8—rotary multivane compressor, 9—vane pneumatic engine, 10—slow-speed piston steam engine, 11—piston motorbike engine, 12—Wankel engine.

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Fig. 2

The simplified scheme of the multivane expander [17]

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Fig. 3

The comparison between the ideal and the real multivane expander thermodynamic cycles in the p-V plane [17,18]. (a) ideal cycle, (b) real cycle.

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Fig. 4

The relationship σ = f(αe2, z) for κ = 1.4 [17]

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Fig. 5

The relationship between P¯ and αe2 for κ = 1.4 [17]

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Fig. 6

The ORC system with multistage expansion

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Fig. 7

The heat source isobaric cooling curves [26]

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Fig. 8

The isobaric cooling of the heat source in T-s diagram [26]

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Fig. 9

The thermal characteristic of the heat source (histogram) [26]

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Fig. 10

The process of isentropic working fluid expansion in the ORC system [26]

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Fig. 11

The w = f(THS) diagram [26]

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Fig. 12

Ws = f(σ) diagram [26], referred to the heat source whose temperature profile in the T-s diagram is depicted in Fig. 9

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Fig. 13

The simplified scheme of the ORC system utilizing a vane expander at the Research Laboratory of the Department of Thermodynamics at the Wrocław University of Technology 1—gas central eating boiler, 2—evaporator, 3—working fluid pump, 4—working fluid reservoir, 5—plate condenser, 6—multivane expanders with generators

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Fig. 14

The general view of the ORC system whose scheme is presented in Fig. 13

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Fig. 15

The variation of the ORC system efficiency during the experiment. The drop in efficiency at τ = 150 is due to the closing of the vapor inlet to the first vane expander.

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Fig. 16

The relation between the system efficiency and working fluid mass flow

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Fig. 17

The variation of the expander power output




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