Gas Dynamics of the Temperature-Determined Stirling Cycle

1981 ◽  
Vol 23 (4) ◽  
pp. 207-216 ◽  
Author(s):  
A. J. Organ
Keyword(s):  
Angular Speed ◽  
Momentum Equation ◽  
Operating Conditions ◽  
Working Fluid ◽  
Gradient Term ◽  
Unexpected Finding ◽  
State Variables ◽  
Frictional Drag ◽  
Stirling Cycle ◽  
In Series

The Stirling cycle machine is modelled as a number of sections of duct in series, some tapered, some parallel. The working fluid assumes the temperature of the adjacent metal wall. Flow is defined by two conservation equations (mass and momentum) and the equation of state, p = ρRT. Friction is taken into account by using the steady-state correlation between friction factor, local instantaneous Reynolds number, and local hydraulic radius. The formulation permits frictional drag and frictional reheating to interact more or less as they do during operation of a Stirling cycle machine at high rotational speeds. The equations are converted to characteristic form and solved numerically with pressure, p, and velocity, u, as state variables rather than the more usual a (acoustic speed) and u. This formulation paves the way for a full characteristics solution incorporating the energy equation but avoiding the entropy gradient term ∂s/∂x which is inappropriate to conditions within the Stirling machine. The paper includes a Mach-line net plotted by computer for the first revolutions of the crankshaft after start-up. Indicator diagrams are presented corresponding to different angular speeds. It is found that the indicator diagram for the compression space is not greatly affected by angular speed, while that for the expansion space changes from positive, via figure-of-eight to negative over a relatively narrow speed range. An attempt is made to explain this unexpected finding in terms of the momentum equation for constant area flow with a severe temperature gradient. A comparison is included between the computed results and those predicted for the same operating conditions by the Schmidt isothermal analysis.

Design and Evaluation of MEMS-Based Stirling Cycle Micro-Refrigeration System

2011 ◽  
Author(s):  
Dongzhi Guo ◽  
Jingsheng Gao ◽  
Alan J. H. McGaughey ◽  
Matthew Moran ◽  
Suresh Santhanam ◽  
...  
Keyword(s):  
Volume Ratio ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Heat Extraction ◽  
Dead Volume ◽  
Working Fluid ◽  
Phase Lag ◽  
Refrigeration System ◽  
Cold Side ◽  
Stirling Cycle

A Stirling cycle micro-refrigeration system composed of arrays of silicon MEMS cooling elements has been designed and evaluated thermodynamically. The cooling elements are each 5 mm-long, 2.25 mm-wide, have a thickness of 300 μm, and are fabricated in a stacked array on a silicon wafer. A 0.5 mm-long regenerator is placed between the compression (hot side) and expansion (cold side) diaphragms. The diaphragms are 2.25 mm circles driven electrostatically. Helium is the working fluid, pressurized at 2 bar and sealed in the system. Under operating conditions, the hot and cold diaphragms oscillate sinusoidally 90° out of phase such that heat is extracted to the expansion space and released from the compression space. The bulk silicon substrate on which the device is grown is etched with “zipping” shaped chambers under the diaphragms. The silicon enables efficient heat transfer between the gas and heat source/sink as well as reduces the dead volume of the system, thus enhancing the cooling capacity. In addition, the “zipping” shaped substrates reduce the voltage required to actuate the diaphragms. An array of vertical silicon pillars in the regenerator serves as a thermal capacitor transferring heat to and from the working gas during a cycle. In operation, the push-pull motion of the diaphragm makes a 300 μm stroke and actuates at a frequency of 2 kHz. Parametric study of the design shows the effects of phase lag, swept volume ratio between the hot space and cold space, and dead volume ratio on cooling capacity. At TH = 313.15 K and TC = 288.15 K and assuming a perfect regenerator, the thermodynamic optimization analysis gives a heat extraction rate of 0.22 W per element and cooling capacity of 30 W/cm2 for the stacked system. Evaluation of the stacked system shows that the COP will reach 6.3 if the expansion work from the cold side is recovered electrostatically and used to drive the hot side diaphragm.

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°.

Flow Development in a Channel Having a Longitudinally Moving Wall

1970 ◽  
Vol 37 (2) ◽  
pp. 498-507
Author(s):  
H. S. Yu ◽  
E. M. Sparrow
Keyword(s):  
Pressure Distribution ◽  
Fluid Velocity ◽  
Momentum Equation ◽  
Operating Conditions ◽  
Working Fluid ◽  
Channel One ◽  
Moving Wall ◽  
Flow Development ◽  
Linearized Model ◽  
Plate Channel

The problem of laminar flow development in a parallel-plate channel having one moving wall is investigated both analytically and experimentally. In the first phase, an analytical solution for the velocity field is derived by employing a linearized model of the momentum equation. Numerical results are obtained which cover the entire range of operating conditions corresponding to fully forward-moving (i.e., nonreverse) flows. Results for the axial pressure distribution and for the drag force on the moving wall are also presented. The experiments were performed in a channel, one of whose walls was the surface of a rotating cylinder. Air was the working fluid. The operating conditions of the experiment covered the range from uw/u¯ = 0 to 1.5 (uw = velocity of the moving wall, u¯ = mean fluid velocity). Measurements were made of the pressure distribution along the length of the channel. The agreement between the experimental and analytical results was found to be very good, thereby lending support to the analytical model.

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 Sensitivity Analysis of OTEC-CC-MX-1 kWe Plant Prototype

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2585
Author(s):  
Jessica Guadalupe Tobal-Cupul ◽  
Estela Cerezo-Acevedo ◽  
Yair Yosias Arriola-Gil ◽  
Hector Fernando Gomez-Garcia ◽  
Victor Manuel Romero-Medina
Keyword(s):  
Sensitivity Analysis ◽  
Experimental Tests ◽  
Caribbean Sea ◽  
Ocean Model ◽  
Operating Conditions ◽  
Working Fluid ◽  
Ocean Energy ◽  
Mexican Caribbean ◽  
Water Temperature Data ◽  
Mass Flows

The Mexican Caribbean Sea has potential zones for Ocean Thermal Energy Conversion (OTEC) implementation. Universidad del Caribe and Instituto de Ciencias del Mar y Limnologia, with the support of the Mexican Centre of Innovation in Ocean Energy, designed and constructed a prototype OTEC plant (OTEC-CC-MX-1 kWe), which is the first initiative in Mexico for exploitation of this type of renewable energy. This paper presents a sensitivity analysis whose objective was to know, before carrying out the experimental tests, the behavior of OTEC-CC-MX-1 kWe regarding temperature differences, as well as the non-possible operating conditions, which allows us to assess possible modifications in the prototype installation. An algorithm was developed to obtain the inlet and outlet temperatures of the water and working fluid in the heat exchangers using the monthly surface and deep-water temperature data from the Hybrid Coordinate Ocean Model and Geographically Weighted Regression Temperature Model for the Mexican Caribbean Sea. With these temperatures, the following were analyzed: fluctuation of thermal efficiency, mass flows of R-152a and water and power production. By analyzing the results, we verified maximum and minimum mass flows of water and R-152a to produce 1 kWe during a typical year in the Mexican Caribbean Sea and the conditions when the production of electricity is not possible for OTEC-CC-MX-1 kWe.

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

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.

scholarly journals Determination of synchronous generator nonlinear model parameters based on power rejection tests using a gradient optimization algorithm

2017 ◽  
Vol 65 (4) ◽  
pp. 479-488 ◽  
Author(s):  
A. Boboń ◽  
A. Nocoń ◽  
S. Paszek ◽  
P. Pruski
Keyword(s):  
Parameter Estimation ◽  
Objective Function ◽  
Optimization Algorithm ◽  
Least Squares Method ◽  
Synchronous Generator ◽  
Operating Conditions ◽  
Model Parameters ◽  
State Variables ◽  
Starting Point ◽  
Gradient Optimization

AbstractThe paper presents a method for determining electromagnetic parameters of different synchronous generator models based on dynamic waveforms measured at power rejection. Such a test can be performed safely under normal operating conditions of a generator working in a power plant. A generator model was investigated, expressed by reactances and time constants of steady, transient, and subtransient state in the d and q axes, as well as the circuit models (type (3,3) and (2,2)) expressed by resistances and inductances of stator, excitation, and equivalent rotor damping circuits windings. All these models approximately take into account the influence of magnetic core saturation. The least squares method was used for parameter estimation. There was minimized the objective function defined as the mean square error between the measured waveforms and the waveforms calculated based on the mathematical models. A method of determining the initial values of those state variables which also depend on the searched parameters is presented. To minimize the objective function, a gradient optimization algorithm finding local minima for a selected starting point was used. To get closer to the global minimum, calculations were repeated many times, taking into account the inequality constraints for the searched parameters. The paper presents the parameter estimation results and a comparison of the waveforms measured and calculated based on the final parameters for 200 MW and 50 MW turbogenerators.

scholarly journals A Novel Hybrid LDC Converter Topology for the Integrated On-Board Charger of Electric Vehicles

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3603
Author(s):  
Vu-Hai Nam ◽  
Duong-Van Tinh ◽  
Woojin Choi
Keyword(s):  
Low Voltage ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Battery Charger ◽  
Forward Converter ◽  
Vehicle To Grid ◽  
Circulating Current ◽  
In Series ◽  
Converter Topology ◽  
Output Capacitor

Recently, the integrated On-Board Charger (OBC) combining an OBC converter with a Low-Voltage DC/DC Converter (LDC) has been considered to reduce the size, weight and cost of DC-DC converters in the EV system. This paper proposes a new integrated OBC converter with V2G (Vehicle-to-Grid) and auxiliary battery charge functions. In the proposed integrated OBC converter, the OBC converter is composed of a bidirectional full-bridge converter with an active clamp circuit and a hybrid LDC converter with a Phase-Shift Full-Bridge (PSFB) converter and a forward converter. ZVS for all primary switches and nearly ZCS for the lagging switches can be achieved for all the operating conditions. In the secondary side of the proposed LDC converter, an additional circuit composed of a capacitor and two diodes is employed to clamp the oscillation voltage across rectifier diodes and to eliminate the circulating current. Since the output capacitor of the forward converter is connected in series with the output capacitor of the auxiliary battery charger, the energy from the propulsion battery can be delivered to the auxiliary battery during the freewheeling interval and it helps reduce the current ripple of the output inductor, leading to a smaller volume of the output inductor. A 1 kW prototype converter is implemented to verify the performance of the proposed topology. The maximum efficiency of the proposed converter achieved by the experiments is 96%.

A Parametric Examination of the Factors Affecting the Performance of a Diffusion Absorption Refrigeration System

2021 ◽  
pp. 1-38
Author(s):  
Noman Yousuf ◽  
Timothy Anderson ◽  
Roy Nates
Keyword(s):  
Waste Heat ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Low Grade ◽  
Absorption Refrigeration ◽  
Factors Affecting ◽  
Thermally Driven ◽  
Mass Flowrate ◽  
Diffusion Absorption

Abstract Despite being identified nearly a century ago, the diffusion absorption refrigeration (DAR) cycle has received relatively little attention. One of the strongest attractions of the DAR cycle lies in the fact that it is thermally driven and does not require high value work. This makes it a prime candidate for harnessing low grade heat from solar collectors, or the waste heat from stationary generators, to produce cooling. However, to realize the benefits of the DAR cycle, there is a need to develop an improved understanding of how design parameters influence its performance. In this vein, this work developed a new parametric model that can be used to examine the performance of the DAR cycle for a range of operating conditions. The results showed that the cycle's performance was particularly sensitive to several factors: the rate of heat added and the temperature of the generator, the effectiveness of the gas and solution heat exchangers, the mass flowrate of the refrigerant and the type of the working fluid. It was shown that can deliver good performance at low generator temperatures if the refrigerant mass fraction in the strong solution is made as high as possible. Moreover, it was shown that a H2O-LiBr working pair could be useful for achieving cooling at low generator temperatures.

Preliminarily Design of Supercritical CO2 Compression Test System

2021 ◽  
Author(s):  
Geng Teng ◽  
Laijie Chen ◽  
Xin Shen ◽  
Hua Ouyang ◽  
Yubo Zhu ◽  
...  
Keyword(s):  
Simulation Model ◽  
Compression Test ◽  
Thermodynamic Model ◽  
Supercritical Co2 ◽  
Operating Performance ◽  
Test System ◽  
Operating Conditions ◽  
Working Fluid ◽  
Stable Operation ◽  
Test Loop

Abstract The centrifugal compressor is the core component of the supercritical carbon dioxide (SCO2) power cycle. It is essential to carry out component-level experimental research on it and test the working characteristics of the compressor and its auxiliary equipment. Building an accurate closed-loop simulation model of closed SCO2 compression loop is a necessary preparation for selecting loop key parameters and establishing system control strategy, which is also an important prerequisite for the stable operation of compressor under test parameters. In this paper, the thermodynamic model of compressor, pre-cooler, orifice plate and other components in supercritical CO2 compression test system is studied, and the simulation model of compression test system is established. Moreover, based on the system enthalpy equations and physical property model of real gas, the compressor, pre-cooler and other components in the test loop are preliminarily designed by using the thermodynamic model of components. Since the operating conditions are in the vicinity of the critical point, when the operating conditions change slightly, the physical properties of the working fluid will change significantly, which might have a greater impact on the operating performance of the system. So the operating performance and the parameter changes of key nodes in the test loop under different operating conditions are calculated, which will provide theoretical guidance for the construction of subsequent experimental loops.

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