scholarly journals Thermodynamic Analysis of Irreversible Desiccant Systems

Entropy ◽  
2018 ◽  
Vol 20 (8) ◽  
pp. 595 ◽  
Author(s):  
Niccolò Giannetti ◽  
Seiichi Yamaguchi ◽  
Andrea Rocchetti ◽  
Kiyoshi Saito
Keyword(s):  
Control Volume ◽  
Ideal Gas ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Specific System ◽  
Equilibrium Relationship ◽  
Working Medium ◽  
Vapour Mixture ◽  
Energy Balances ◽  
Relationship Of

A new general thermodynamic mapping of desiccant systems’ performance is conducted to estimate the potentiality and determine the proper application field of the technology. This targets certain room conditions and given outdoor temperature and humidity prior to the selection of the specific desiccant material and technical details of the system configuration. This allows the choice of the operative state of the system to be independent from the limitations of the specific design and working fluid. An expression of the entropy balance suitable for describing the operability of a desiccant system at steady state is obtained by applying a control volume approach, defining sensible and latent effectiveness parameters, and assuming ideal gas behaviour of the air-vapour mixture. This formulation, together with mass and energy balances, is used to conduct a general screening of the system performance. The theoretical advantage and limitation of desiccant dehumidification air conditioning, maximum efficiency for given conditions constraints, least irreversible configuration for a given operative target, and characteristics of the system for a target efficiency can be obtained from this thermodynamic mapping. Once the thermo-physical properties and the thermodynamic equilibrium relationship of the liquid desiccant mixture or solid coating material are known, this method can be applied to a specific technical case to select the most appropriate working medium and guide the specific system design to achieve the target performance.

Development of Prototype Pump Using a Vibrating Pipe With a Valve

1994 ◽  
Vol 116 (4) ◽  
pp. 741-745 ◽  
Author(s):  
Hiroyuki Hashimoto ◽  
Hirokuni Hiyama ◽  
Rokuro Sato
Keyword(s):  
Maximum Flow ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Maximum Pressure ◽  
Electromagnetic Excitation ◽  
Durability Test ◽  
Current Frequency ◽  
Working Medium ◽  
One Year ◽  
Chemical Pump

Tests were conducted on a prototype pump which has an extremely simple structure and excellent controllability. Its structural and hydrodynamic features are different from those of previous conventional reciprocating pumps. The pump structure constitutes a leak-proof short vibrating pipe equipped with a nonreturn valve on the edge of its outlet. The authors developed a prototype pump which uses a 25 mm diameter vibration pipe and an electromagnetic excitation device. The pump performance, intentionally changed by adjusting the coil voltage or the coil current frequency, featured a maximum pressure of approximately 1.0 bars, a maximum flow rate of approximately 40 liters per minute, and a maximum efficiency of approximately 30 percent. Results of both a one-year test run, using water as the working medium, and a three-month durability test, using concentrated nitric acid as the working fluid, assuming application as a chemical pump, indicated favorable results.

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.

A Numerical Study of Unsteady Natural Convection in a Rectangular Enclosure: The Effect of Compressibility

2004 ◽  
Author(s):  
K. M. Akyuzlu ◽  
Y. Pavri ◽  
A. Antoniou
Keyword(s):  
Mathematical Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Vertical Wall ◽  
Ideal Gas ◽  
Working Fluid ◽  
Two Dimensional ◽  
Algebraic Equations ◽  
Rectangular Enclosure ◽  
Circulation Patterns

A two-dimensional, mathematical model is adopted to investigate the development of buoyancy driven circulation patterns and temperature contours inside a rectangular enclosure filled with a compressible fluid (Pr=1.0). One of the vertical walls of the enclosure is kept at a higher temperature then the opposing vertical wall. The top and the bottom of the enclosure are assumed insulated. The physics based mathematical model for this problem consists of conservation of mass, momentum (two-dimensional Navier-Stokes equations) and energy equations for the enclosed fluid subjected to appropriate boundary conditions. The working fluid is assumed to be compressible through a simple ideal gas relation. The governing equations are discretized using second order accurate central differencing for spatial derivatives and first order forward finite differencing for time derivatives where the computation domain is represented by a uniform orthogonal mesh. The resulting nonlinear equations are then linearized using Newton’s linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns (primitive variables) of the problem. A numerical experiment is carried out for a benchmark case (driven cavity flow) to verify the accuracy of the proposed solution procedure. Numerical experiments are then carried out using the proposed compressible flow model to simulate the development of the buoyancy driven circulation patterns for Rayleigh numbers between 103 and 105. Finally, an attempt is made to determine the effect of compressibility of the working fluid by comparing the results of the proposed model to that of models that use incompressible flow assumptions together with Boussinesq approximation.

Influence of Imperfections in the Working Media on Diesel Engine Indicator Process: Part 2 — Results

1998 ◽  
Author(s):  
Stanislav N. Danov ◽  
Ashwani K. Gupta
Keyword(s):  
Mathematical Model ◽  
Diesel Engine ◽  
High Pressures ◽  
Combustion Process ◽  
Ideal Gas ◽  
Working Medium ◽  
High Pressures And Temperatures ◽  
Specific Heat Capacities ◽  
Working Media ◽  
The Mathematical Model

Abstract In the companion Part 1 of this two-part series paper several improvements to the mathematical model of the energy conversion processes, taking place in a diesel engine cylinder, have been proposed. Analytical mathematical dependencies between thermal parameters (pressure, temperature, volume) and caloric parameters (internal energy, enthalpy, specific heat capacities) have been obtained. These equations have been used to provide an improved mathematical model of diesel engine indicator process. The model is based on the first law of thermodynamics, by taking into account imperfections in the working media which appear when working under high pressures and temperatures. The numerical solution of the simultaneous differential equations is obtained by Runge-Kutta type method. The results show that there are significant differences between the values calculated by equations for ideal gas and real gas under conditions of high pressures and temperatures. These equations are then used to solve the desired practical problem in two different two-stroke turbo-charged engines (8DKRN 74/160 and Sulzer-RLB66). The numerical experiments show that if the pressure is above 8 to 9 MPa, the working medium imperfections must be taken into consideration. The mathematical model presented here can also be used to model combustion process of other thermal engines, such as advanced gas turbine engines and rockets.

Small Scale Supercritical CO2 Radial Inflow Turbine Meanline Design Considerations

2018 ◽  
Author(s):  
Tina Unglaube ◽  
Hsiao-Wei D. Chiang
Keyword(s):  
High Velocity ◽  
Gas Turbines ◽  
Velocity Ratio ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Working Fluid ◽  
Small Scale ◽  
Optimum Velocity ◽  
Set Up ◽  
Very High

In recent years closed loop supercritical carbon dioxide Brayton cycles have drawn the attention of many researchers as they are characterized by a higher theoretic efficiency and smaller turbomachinery size compared to the conventional steam Rankine cycle for power generation. Currently, first prototypes of this emerging technology are under development and thus small scale sCO2 turbomachinery needs to be developed. However, the design of sCO2 turbines faces several new challenges, such as the very high rotational speed and the high power density. Thus, the eligibility of well-established radial inflow gas turbine design principles has to be reviewed regarding their suitability for sCO2 turbines. Therefore, this work reviews different suggestion for optimum velocity ratios for gas turbines and aims to re-establish it for sCO2 turbines. A mean line design procedure is developed to obtain the geometric dimensions for small scale sCO2 radial inflow turbines. By varying the specific speed and the velocity ratio, different turbine configurations are set up. They are compared numerically by means of CFD analysis to conclude on optimum design parameters with regard to maximum total-to-static efficiency. Six sets of simulations with different specific speeds between 0.15 and 0.52 are set up. Higher specific speeds could not be analyzed, as they require very high rotational speeds (more than 140k RPM) for small scale sCO2 turbines (up to 150kWe). For each set of simulations, the velocity ratio that effectuates maximum efficiency is identified and compared to the optimum parameters recommended for radial inflow turbines using subcritical air as the working fluid. It is found that the values for optimum velocity ratios suggested by Rohlik (1968) are rather far away from the optimum values indicated by the conducted simulations. However, the optimum values suggested by Aungier (2005), although also established for subcritical gas turbines, show an approximate agreement with the simulation results for sCO2 turbines. Though, this agreement should be studied for a wider range of specific speeds and a finer resolution of velocity ratios. Furthermore, for high specific speeds in combination with high velocity ratios, the pressure drop of the designed turbines is too high, so that the outlet pressure is beyond the critical point. For low specific speeds in combination with low velocity ratios, the power output of the designed turbines becomes very small. Geometrically, turbines with low specific speeds and high velocity ratios are characterized by very small blade heights, turbines with high specific speeds and small velocity ratios by very small diameters.

The Role of Internal Irreversibilities in the Performance and Stability of Power Plant Models Working at Maximum ϵ-Ecological Function

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Gabriel Valencia-Ortega ◽  
Sergio Levario-Medina ◽  
Marco Antonio Barranco-Jiménez
Keyword(s):  
Power Plants ◽  
Heat Engine ◽  
Combined Cycle ◽  
Ecological Function ◽  
Operating Conditions ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Engine Model ◽  
Improved Stability ◽  
The Stability

Abstract The proposal of models that account for the irreversibilities within the core engine has been the topic of interest to quantify the useful energy available during its conversion. In this work, we analyze the energetic optimization and stability (local and global) of three power plants, nuclear, combined-cycle, and simple-cycle ones, by means of the Curzon–Ahlborn heat engine model which considers a linear heat transfer law. The internal irreversibilities of the working fluid measured through the r-parameter are associated with the so-called “uncompensated Clausius heat.” In addition, the generalization of the ecological function is used to find operating conditions in three different zones, which allows to carry out a numerical analysis focused on the stability of power plants in each operation zone. We noted that not all power plants reveal stability in all the operation zones when irreversibilities are considered through the r-parameter on real-world power plants. However, an improved stability is shown in the zone limited by the maximum power output and maximum efficiency regimes.

scholarly journals Time–energy uncertainty principle for irreversible heat engines

2020 ◽  
Vol 378 (2170) ◽  
pp. 20190171 ◽  
Author(s):  
Rudolf Hanel ◽  
Petr Jizba
Keyword(s):  
Uncertainty Principle ◽  
Nonequilibrium Thermodynamics ◽  
Real Life ◽  
Ideal Gas ◽  
Irreversible Processes ◽  
Bohr Radius ◽  
Heat Engines ◽  
Working Medium ◽  
Semi Empirical ◽  
The Ideal

Even though irreversibility is one of the major hallmarks of any real-life process, an actual understanding of irreversible processes remains still mostly semi-empirical. In this paper, we formulate a thermodynamic uncertainty principle for irreversible heat engines operating with an ideal gas as a working medium. In particular, we show that the time needed to run through such an irreversible cycle multiplied by the irreversible work lost in the cycle is bounded from below by an irreducible and process-dependent constant that has the dimension of an action. The constant in question depends on a typical scale of the process and becomes comparable to Planck’s constant at the length scale of the order Bohr radius, i.e. the scale that corresponds to the smallest distance on which the ideal gas paradigm realistically applies. This article is part of the theme issue ‘Fundamental aspects of nonequilibrium thermodynamics’.

Biomass combined cycles based on externally fired gas turbines and organic Rankine expanders

2011 ◽  
Vol 225 (8) ◽  
pp. 1066-1075 ◽  
Author(s):  
C M Invernizzi ◽  
P Iora ◽  
R Sandrini
Keyword(s):  
Gas Turbines ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Combined Cycle ◽  
Economic Feasibility ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Inlet Temperature ◽  
System A ◽  
Combined Cycles

This article investigates the possibility to enhance the performance of a biomass organic Rankine cycle (ORC) plant by adding an externally fired gas turbine (EFGT), yielding a combined EFGT + ORC system. A typical ORC configuration is first modelled and validated on data available from an existing unit 1.5 MW reference plant. Then, different working fluids belonging to the methyl-substituted benzene series and linear methylpolysiloxanes have been evaluated for the ORC section on the basis of both thermodynamics considerations and design issues of the regenerator and the turbine. Results of the simulations of the combined cycle (CC) referred to a furnace size of about unit 9 MW, assuming a maximum GT inlet temperature of 800 °C, show a maximum efficiency of 23 per cent, obtained in the case where toluene is adopted as a working fluid for the bottoming section. This value is about 4 points per cent higher than the efficiency of the corresponding simple ORC. Finally, to conclude, some preliminary considerations are given regarding the techno-economic feasibility of the combined configuration, suggesting the need of a further investigation on the possible technological solution for the furnace which represents the main uncertainty in the resulting costs of the CC.

Overall and Stage Characteristics of Axial-flow Compressors

1950 ◽  
Vol 163 (1) ◽  
pp. 235-248 ◽  
Author(s):  
A. R. Howell ◽  
R. P. Bonham
Keyword(s):  
Axial Flow ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Test Results ◽  
Analytical Treatment ◽  
Axial Compressors ◽  
Simplified Method ◽  
Mass Flows ◽  
The Individual ◽  
Lengthy Process

Axial compressors, particularly near design conditions are, on the whole, amenable to analytical treatment, and usually a good estimate of their performance can be made before they are run. Away from the design points, the performances are conveniently thought of in terms of the overall characteristics of pressure-rises, temperature-rises, and efficiencies plotted against mass-flows. For these performance estimations the aerodynamicists must have knowledge of the stage and overall characteristics of previous compressors and of methods of predicting such characteristics. Obtaining the overall characteristics from a stage-by-stage calculation is a lengthy process, but, fortunately, simplified methods can often be used. In this lecture we have indicated some of the methods that are employed to obtain and predict the overall characteristics and their associated stage characteristics. Reference is made to test-results from various National Gas Turbine Establishment research compressors, one of which uses water instead of air as the working fluid, and also to published information on other compressors. The importance of blade and test errors on performance and analysis work is also emphasized. In our simplified method of analysis and prediction of overall characteristics we have reduced the individual overall characteristics at each speed to what are, in effect, mean stage characteristics plotted relative to their maximum-efficiency-point conditions. Then the maximum-efficiency-point conditions at the different speeds are plotted and considered separately.

A Sensitivity Analysis for Effective Use of CO2 for Heat Mining in Geothermal Reservoirs

2015 ◽  
Author(s):  
Ana Laura Soto-Sánchez ◽  
Carlos Rubio-Maya ◽  
Alicia Aguilar Corona ◽  
Oscar Chávez
Keyword(s):  
Carbon Dioxide ◽  
Sensitivity Analysis ◽  
Power Plants ◽  
Control Volume ◽  
Working Fluid ◽  
Unusual Behavior ◽  
Geothermal Heat ◽  
Geothermal Reservoirs ◽  
Linear Behavior ◽  
Better Than

Carbon dioxide (CO2) emitted from various sources, mainly fossil fuel power plants, is considered responsible of the global warming effect. Many processes and techniques are still under research for CO2 capture and sequestration. On the other hand, it is proposed that the geothermal heat be mined from geothermal reservoirs using captured CO2. In this sense, some theoretical studies show feasibility of using supercritical carbon dioxide (sCO2) as a heat mining media in such geothermal reservoirs. In this work, it is carried out a set of numerical simulations to determine the most effective distance between injection and production wells for extracting geothermal energy utilizing sCO2 (Water is used for comparison). In the study, the permeability is considered in the range of 0.5 mD to 3.5 mD, with the aim of determining also the critical point in which sCO2 works better than water (H2O) as a working fluid. The remaining properties such as volume, density and other thermal properties remain fixed. Afterwards, it is constructed a numerical model which is implemented in TOUGH2 and PETRASIM 5 software to simulate the cases established. In the model, it is considered a simplified control volume, i.e. only one well for injection and one for production, assuming a constant flow rate at the inlet and at the outlet, meaning that sequestration is not taken into account. A length of 300 meter is defined for reservoir thickness, considering also a pressure and temperature of 100 bar and 200 °C, respectively. The energy mined is estimated for a period of twenty-five years. As typically, the sensitivity analysis is performed by varying only one property and keeping the remaining properties constant, isolating in this way the effect of such variable. Results show that for small permeabilities H2O works better than sCO2, but it is possible to assure that for permeabilities greater than 1 mD, sCO2 presents more advantages as extracting heat media instead of water. Both, H2O and sCO2 show a linear behavior. A deep analysis is necessary to carry out, because results shows that sCO2 works better in an intermediate zone (greater than 200 meter length, but smaller than 800 meter length). An unusual behavior is presented when the distances between the wells are varied; water shows a linear behavior increasing monotonically, while sCO2 shows a nonlinear behavior for some distances sCO2 works better. As expected, the more the distance, the greater the amount of the energy mined due to the volume related with each one of the distances.

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