Stirling Engines With a Chemically Reactive Working Fluid—Some Thermodynamic Effects

1977 ◽  
Vol 99 (2) ◽  
pp. 284-287 ◽  
Author(s):  
M. M. Metwally ◽  
G. Walker
Keyword(s):  
Heat Pumps ◽  
Substantial Improvement ◽  
Regenerative Process ◽  
Operating Conditions ◽  
Working Fluid ◽  
Nitrogen Tetroxide ◽  
Specific Output ◽  
Stirling Engines ◽  
Compression And Expansion ◽  
Temperature Levels

Stirling engines operate on closed regenerative thermodynamic cycles with compression and expansion of the working fluids at different temperature levels. They may be used as prime movers, refrigerating machines, heat pumps, or pressure generators. Conventional machines use a gaseous working fluid, but substantial improvement in specific output may be gained with a partially reactive, condensing working fluid. The working fluid then consists of an inert gaseous carrier with a chemically reactive, condensing working fluid such as nitrogen tetroxide (N2O4). This may be liquid in the cold compression space and then evaporates and dissociates in the regenerative process to be in the elemental gaseous phase in the hot expansion space. The change of state of one component reduces the required compression work and has the effect of increasing the engine volume compression ratio with consequent benefit to the specific output. The results obtained using idealized theory show that an improvement may be gained in net cycle work of twice the output with a simple gaseous working fluid with no penalties in size, weight, or cost of the engine. The degree of improvement depends on the design and operating conditions of the engine. The effects of variation of some of these parameters are explored.

scholarly journals Experimental and Theoretical Analysis of a Linear Focus CPV/T System for Cogeneration Purposes

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2960 ◽  
Author(s):  
Carlo Renno
Keyword(s):  
Focal Length ◽  
Concentration Field ◽  
Operating Conditions ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Atmospheric Conditions ◽  
High Concentration ◽  
Environment Temperature ◽  
Temperature Levels ◽  
T System

The knowledge of the actual energy performances of a concentrating photovoltaic and thermal (CPV/T) system with a linear focus optics, allows to evaluate the possibility of adopting this type of system for cogeneration purposes. Hence, the main aim of this paper is the design, realization, setting and modeling of a linear focus CPV/T system in the high concentration field. An experimental linear focus CPV/T plant was created in order to determine its electrical and thermal performance under different working conditions in terms of environment temperature, sunny and cloudy conditions, focal length, etc. Moreover, a theoretical model of the linear focus CPV/T system was also studied. This model evaluates the temperatures of the working fluid that flows in the cooling circuit of the CPV/T system under several operating conditions. The temperatures of the triple junction (TJ) cells, experimentally evaluated referring to different solar radiation and atmospheric conditions, were considered as the input data for the model. The values of the fluid temperature, theoretically and experimentally determined, were thus compared with good agreement. The electrical production of the CPV/T system depends generally on the TJ cell characteristics and the concentration factor, while the thermal production is above all linked to the system configuration and the direct normal irradiance (DNI) values. Hence, in this paper the electric power obtained by the linear-focus CPV/T system was evaluated referring to the cogeneration applications, and it was verified if the TJ cell and the cooling fluid reach adequate temperature levels in this type of system, in order to match the electrical and the thermal loads of a user.

The Heat Transfer Performance of Porous Gas Turbine Blades

1968 ◽  
Vol 72 (696) ◽  
pp. 1087-1094 ◽  
Author(s):  
F. J. Bayley ◽  
A. B. Turner
Keyword(s):  
Gas Turbine ◽  
Turbine Blades ◽  
Engine Performance ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Specific Power ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet ◽  
Compression And Expansion

It is well known that the performance of the practical gas turbine cycle, in which compression and expansion are non-isentropic, is critically dependent upon the maximum temperature of the working fluid. In engines in which shaft-power is produced the thermal efficiency and the specific power output rise steadily as the turbine inlet temperature is increased. In jet engines, in which the gas turbine has so far found its greatest success, similar advantages of high temperature operation accrue, more particularly as aircraft speeds increase to utilise the higher resultant jet velocities. Even in high by-pass ratio engines, designed specifically to reduce jet efflux velocities for application to lower speed aircraft, overall engine performance responds very favourably to increased turbine inlet temperatures, in which, moreover, these more severe operating conditions apply continuously during flight, and not only at maximum power as with more conventional cycles.

scholarly journals Parametric Analysis of a Polygeneration System with CO2 Working Fluid

2021 ◽  
Vol 11 (7) ◽  
pp. 3215
Author(s):  
Evangelos Bellos ◽  
Christos Tzivanidis
Keyword(s):  
Heating Temperature ◽  
Operating Conditions ◽  
Critical Parameters ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Present System ◽  
High Heating ◽  
Pressure Medium ◽  
Polygeneration System ◽  
Temperature Levels

The objective of the present work is the investigation of a novel polygeneration system for power, refrigeration and heating production at two temperature levels. The present system uses CO2 as the working fluid, which is an environmentally friendly fluid. The total configuration is a combination of a transcritical refrigeration cycle coupled to a Brayton cycle with recompression, which is fed by a biomass boiler. The examined system, at nominal operating conditions, produces refrigeration at 5 °C, and heating at 45 °C and 80 °C. Additionally, the system can be converted into a trigeneration system where the two heating outputs are produced at the same temperature level. The system was studied parametrically by changing the following seven critical parameters: turbine inlet temperature, high pressure, medium pressure, heat exchanger effectiveness, refrigeration temperature, heat rejection temperature and high heating temperature. In nominal operating conditions, the system energy and exergy efficiencies were 78.07% and 26.29%, respectively. For a heat input of 100 kW, the net power production was 24.50 kW, the refrigeration production was 30.73 kW, while the low and high heating production was 9.24 kW and 13.60 kW, respectively. The analysis was conducted with a developed model in Engineering Equation Solver.

Temperature Transformation for High-Temperature Heat Pumps

1988 ◽  
Vol 110 (4) ◽  
pp. 652-657 ◽  
Author(s):  
R. Radermacher ◽  
L. A. Howe
Keyword(s):  
High Temperature ◽  
Heat Pump ◽  
Heat Pumps ◽  
Pure Component ◽  
Effect Of Temperature ◽  
Working Fluid ◽  
Fluid Mixture ◽  
Temperature Transformation ◽  
Temperature Levels ◽  
Very High

A heat pump cycle is introduced that allows heat pumping between two very high temperature levels, while the suction temperature of the working fluid vapor passing through the compressor is considerably lower. This effect of “Temperature Transformation” is achieved by using a working fluid mixture instead of a single pure component and by employing an unconventional cycle design. The proposed cycle allows the extension of heat pump applications to high temperature levels without encountering operating problems for conventional compressors. This cycle and its features are explained. Its performance has been calculated and the results are presented and discussed.

Design of a Centrifugal Turbo Compressor With the Working Fluid Water for the Operation in a Hybrid Sorption/Compression Heat Pump Cycle

2016 ◽  
Author(s):  
Thomas Eckert ◽  
Leo Dostal ◽  
Martin Helm ◽  
Christian Schweigler
Keyword(s):  
Heat Pump ◽  
High Speed ◽  
Fluid Dynamic ◽  
Pressure Ratio ◽  
Lithium Bromide ◽  
High Volume ◽  
Heat Pumps ◽  
Operating Conditions ◽  
Working Fluid ◽  
Turbo Compressor

In various applications the use of sorption chillers and heat pumps is limited by the available temperature level of the driving heat source or the heat sink for export of reject heat. These constraints can be overcome by integrating an efficient high-speed transonic turbo compressor into the internal cycle of a thermally driven water/lithium bromide absorption heat pump. The operation in a hybrid heat pump with the refrigerant water implies specific challenges for the design of the compressor: Saturation pressures in the sub-atmospheric range, low vapor density, high volume flows and a targeted pressure ratio of 3 result in high impeller tip speeds with machine Mach numbers close to 1. Here the authors present a theoretical design study based on a numerical simulation of a centrifugal compressor, targeted at the given operating conditions. Evaluation of the results is conducted with regard to the relevant thermodynamic and fluid mechanic figures. The optimization of the impeller geometry comprises both fluid dynamic behavior and structural stability.

Utilization of Expansion Work in Transcritical CO2 Heat Pumps in Combined Heating and Cooling

2008 ◽  
Author(s):  
Nikola Stosic ◽  
Ian K. Smith
Keyword(s):  
Control Strategies ◽  
Industrial Process ◽  
Power Input ◽  
Heat Pumps ◽  
Operating Conditions ◽  
Hot Water ◽  
Design Parameters ◽  
Working Fluid ◽  
Heating And Cooling ◽  
Twin Screw

The use of CO2 as a refrigerant in transcritical vapour compression cycles has significant advantages, for systems which require simultaneous heating and cooling at approximately equal rates. However, then need for a compressor, to operate across high pressure differences, and the large throttle losses associated with these pressure differences have limited its use. This paper describes a study carried out to evaluate the efficiency gains and cost benefits possible from such a system when a twin screw machine is used to both compress and expand the working fluid in a single unit. It also shows the values of the critical design parameters required to optimise the system’s potential advantages when used in larger combined heating and cooling systems in industrial process and heat generation plants. The results show that recovery of work from the expansion process improves the COP by 15 to 20%. For the design conditions specified in this paper, this implies that the expander is worth fitting if it can be installed for a cost of less than approximately €750/kW of shaft power input. Thus, depending on the operating conditions, transcritical CO2 heat pumps using a compressor-expander can produce hot water at 90°C with a COP of approximately 6, with thermal outputs of up to 1.5 MW. This could be extended with simple control strategies up to outputs of 10 MW.

Performance Evaluation of Asymmetric CPC-PVT Collectors Connected in Series

2017 ◽  
Author(s):  
M. T. Nitsas ◽  
I. P. Koronaki
Keyword(s):  
Open Circuit ◽  
Operating Conditions ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Solar Collectors ◽  
In Series ◽  
Reflector Geometry ◽  
Temperature Levels ◽  
Useful Heat ◽  
Fundamental Equations

In this study, a series of thermal-photovoltaic collectors with hybrid reflector geometry and flat plate receiver is investigated experimentally and analytically through fundamental equations regarding solar collectors. The series of five compound parabolic thermophotovoltaic collectors are located in Athens, Greece and the experiments took place in June at open circuit state, i.e. the collectors were not electrically connected. The developed model combines optical and thermal analysis. The main objective of this study is to determine the thermal and the exergetic performance of the collectors under various operating conditions. For these reasons, the developed model is validated with the respective experimental data and afterwards, the solar collector model is examined parametrically for different tilt angles. The experiments are performed with water as heat transfer fluid and for low temperature levels up to 60°C. The final results proved that the investigated solar collectors are able to produce about 2.8 kW useful heat for low working fluid mass flow rates exhibiting at the same time an exergetic efficiency of nearly 1.4%. Also, the results of the developed model showed that the maximization of the produced thermal energy during summer occurs at a tilt angle of 10°.

Analysis of Real-Gas and Matrix-Conduction Effects in Cyclic Cryogenic Regenerators

1973 ◽  
Vol 95 (2) ◽  
pp. 199-205 ◽  
Author(s):  
M. F. Modest ◽  
C. L. Tien
Keyword(s):  
Numerical Solutions ◽  
Operating Conditions ◽  
Physical Parameters ◽  
Governing Equations ◽  
Real Gas ◽  
The Matrix ◽  
Compression And Expansion ◽  
Temperature Levels ◽  
The One ◽  
Gas Conduction

The one-dimensional governing equations for the thermal performance of cryogenic regenerators are developed and simplified by neglecting gas conduction and pressure drop along the matrix. The present formulation includes the effects of matrix conduction and real-gas behavior, which can be quite important in actual situations but were neglected in all previous analyses. The time dependence of the governing equations is eliminated by integration over the compression and expansion periods. Numerical solutions of the resulting time-independent equations are presented for various values of physical parameters and temperature levels. Comparison with the corresponding cases neglecting real-gas and matrix-conduction effects demonstrates the significant nature of these effects for many operating conditions.

scholarly journals Large Eddy Simulations of Strongly Non-Ideal Compressible Flows through a Transonic Cascade

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 772
Author(s):  
Jean-Christophe Hoarau ◽  
Paola Cinnella ◽  
Xavier Gloerfelt
Keyword(s):  
Compressible Flows ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Organic Rankine Cycle ◽  
Ideal Gas ◽  
Operating Conditions ◽  
Large Eddy Simulations ◽  
Working Fluid ◽  
Viscous Effects ◽  
Large Eddy

Transonic flows of a molecularly complex organic fluid through a stator cascade were investigated by means of large eddy simulations (LESs). The selected configuration was considered as representative of the high-pressure stages of high-temperature Organic Rankine Cycle (ORC) axial turbines, which may exhibit significant non-ideal gas effects. A heavy fluorocarbon, perhydrophenanthrene (PP11), was selected as the working fluid to exacerbate deviations from the ideal flow behavior. The LESs were carried out at various operating conditions (pressure ratio and total conditions at inlet), and their influence on compressibility and viscous effects is discussed. The complex thermodynamic behavior of the fluid generates highly non-ideal shock systems at the blade trailing edge. These are shown to undergo complex interactions with the transitional viscous boundary layers and wakes, with an impact on the loss mechanisms and predicted loss coefficients compared to lower-fidelity models relying on the Reynolds-averaged Navier–Stokes (RANS) equations.

scholarly journals Identification of Existing Challenges and Future Trends for the Utilization of Ammonia-Water Absorption–Compression Heat Pumps at High Temperature Operation

2021 ◽  
Vol 11 (10) ◽  
pp. 4635
Author(s):  
Marcel Ulrich Ahrens ◽  
Maximilian Loth ◽  
Ignat Tolstorebrov ◽  
Armin Hafner ◽  
Stephan Kabelac ◽  
...  
Keyword(s):  
High Temperature ◽  
Water Absorption ◽  
Industrial Sector ◽  
Heat Pumps ◽  
Working Fluid ◽  
Large Temperature ◽  
Future Trends ◽  
Ammonia Water ◽  
Starting Point ◽  
High Temperature Operation

Decarbonization of the industrial sector is one of the most important keys to reducing global warming. Energy demands and associated emissions in the industrial sector are continuously increasing. The utilization of high temperature heat pumps (HTHPs) operating with natural fluids presents an environmentally friendly solution with great potential to increase energy efficiency and reduce emissions in industrial processes. Ammonia-water absorption–compression heat pumps (ACHPs) combine the technologies of an absorption and vapor compression heat pump using a zeotropic mixture of ammonia and water as working fluid. The given characteristics, such as the ability to achieve high sink temperatures with comparably large temperature lifts and high coefficient of performance (COP) make the ACHP interesting for utilization in various industrial high temperature applications. This work reviews the state of technology and identifies existing challenges based on conducted experimental investigations. In this context, 23 references with capacities ranging from 1.4 kW to 4500 kW are evaluated, achieving sink outlet temperatures from 45 °C to 115 °C and COPs from 1.4 to 11.3. Existing challenges are identified for the compressor concerning discharge temperature and lubrication, for the absorber and desorber design for operation and liquid–vapor mixing and distribution and the choice of solution pump. Recent developments and promising solutions are then highlighted and presented in a comprehensive overview. Finally, future trends for further studies are discussed. The purpose of this study is to serve as a starting point for further research by connecting theoretical approaches, possible solutions and experimental results as a resource for further developments of ammonia-water ACHP systems at high temperature operation.

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