Thermal stability of hexamethyldisiloxane (MM) as a working fluid for organic Rankine cycle

Organic Rankine Cycle (ORC) systems are increasingly gaining relevance in the renewable and sustainable energy scenario. Recently our research group published a manuscript identifying a new type of thermodynamic cycle entitled Buoyancy Organic Rankine Cycle (BORC) [J. Schoenmaker, J.F.Q. Rey, K.R. Pirota, Renew. Energy 36, 999 (2011)]. In this work we present two main contributions. First, we propose a refined thermodynamic model for BORC systems accounting for the specific heat of the working fluid. Considering the refined model, the efficiencies for Pentane and Dichloromethane at temperatures up to 100 °C were estimated to be 17.2%. Second, we show a proof of concept BORC system using a 3 m tall, 0.062 m diameter polycarbonate tube as a column-fluid reservoir. We used water as a column fluid. The thermal stability and uniformity throughout the tube has been carefully simulated and verified experimentally. After the thermal parameters of the water column have been fully characterized, we developed a test body to allow an adequate assessment of the BORC-system's efficiency. We obtained 0.84% efficiency for 43.8 °C working temperature. This corresponds to 35% of the Carnot efficiency calculated for the same temperature difference. Limitations of the model and the apparatus are put into perspective, pointing directions for further developments of BORC systems.

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Component-Oriented Modeling of a Micro-Scale Organic Rankine Cycle System for Waste Heat Recovery Applications

Applied Sciences ◽

10.3390/app11051984 ◽

2021 ◽

Vol 11 (5) ◽

pp. 1984

Author(s):

Ramin Moradi ◽

Emanuele Habib ◽

Enrico Bocci ◽

Luca Cioccolanti

Keyword(s):

Electric Power ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Waste Heat ◽

Organic Rankine Cycle ◽

Rankine Cycle ◽

Operating Conditions ◽

Working Fluid ◽

Pump Efficiency ◽

Micro Scale

Organic Rankine cycle (ORC) systems are some of the most suitable technologies to produce electricity from low-temperature waste heat. In this study, a non-regenerative, micro-scale ORC system was tested in off-design conditions using R134a as the working fluid. The experimental data were then used to tune the semi-empirical models of the main components of the system. Eventually, the models were used in a component-oriented system solver to map the system electric performance at varying operating conditions. The analysis highlighted the non-negligible impact of the plunger pump on the system performance Indeed, the experimental results showed that the low pump efficiency in the investigated operating range can lead to negative net electric power in some working conditions. For most data points, the expander and the pump isentropic efficiencies are found in the approximate ranges of 35% to 55% and 17% to 34%, respectively. Furthermore, the maximum net electric power was about 200 W with a net electric efficiency of about 1.2%, thus also stressing the importance of a proper selection of the pump for waste heat recovery applications.

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Organic Rankine cycle for turboprop engine application

The Aeronautical Journal ◽

10.1017/aer.2021.32 ◽

2021 ◽

pp. 1-21

Author(s):

G.E. Pateropoulos ◽

T.G. Efstathiadis ◽

A.I. Kalfas

Keyword(s):

Waste Heat ◽

Organic Rankine Cycle ◽

Weight Ratio ◽

Rankine Cycle ◽

Aircraft Engine ◽

Working Fluid ◽

Engine Fuel ◽

Exhaust Gases ◽

Waste Heat Recovery System ◽

Turboprop Engine

ABSTRACT The potential to recover waste heat from the exhaust gases of a turboprop engine and produce useful work through an Organic Rankine Cycle (ORC) is investigated. A thermodynamic analysis of the engine’s Brayton cycle is derived to determine the heat source available for exploitation. The aim is to use the aircraft engine fuel as the working fluid of the organic Rankine cycle in order to reduce the extra weight of the waste heat recovery system and keep the thrust-to-weight ratio as high as possible. A surrogate fuel with thermophysical properties similar to aviation gas turbine fuel is used for the ORC simulation. The evaporator design as well as the weight minimisation and safety of the suggested application are the most crucial aspects determining the feasibility of the proposed concept. The results show that there is potential in the exhaust gases to produce up to 50kW of power, corresponding to a 10.1% improvement of the overall thermal efficiency of the engine.

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Theoretical and experimental investigation of an organic Rankine cycle for a waste heat recovery system

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/09576509jpe725 ◽

2009 ◽

Vol 223 (5) ◽

pp. 523-533 ◽

Cited By ~ 47

Author(s):

W Gu ◽

Y Weng ◽

Y Wang ◽

B Zheng

Keyword(s):

Heat Source ◽

Entropy Generation ◽

Waste Heat ◽

Organic Rankine Cycle ◽

Rankine Cycle ◽

Entropy Generation Rate ◽

Working Fluid ◽

Total Entropy ◽

Waste Heat Recovery System ◽

Cycle Efficiency

This article describes and evaluates an organic Rankine cycle (ORC) for a waste heat recovery system by both theoretical and experimental studies. Theoretical analysis of several working fluids shows that cycle efficiency is very sensitive to evaporating pressure, but insensitive to expander inlet temperature. Second law analysis was carried out using R600a as a working fluid and a flow of hot air as a heat source, which is not isothermal, along the evaporator. The result discloses that the evaporator's internal and external entropy generation is the main source of total entropy generation. The effect of the heat source temperature, evaporating pressure, and evaporator size on the entropy generation rate is also presented. The obtained useful power is directly linked to the total entropy generation rate according to the Gouy—Stodola theorem. The ORC testing system was established and operated using R600a as a working fluid and hot water as a heat source. The maximum cycle efficiency of the testing system is 5.2 per cent, and the testing result also proves that cycle efficiency is insensitive to heat source temperature, but sensitive to evaporating pressure. The entropy result also shows that internal and external entropy of the evaporator is the main source of total entropy generation.

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