Isentropic Fluid Research Articles

Global weak solutions to the Vlasov–Poisson–Fokker–Planck–Navier–Stokes system

We consider the compressible Vlasov–Poisson–Fokker–Planck–Navier–Stokes system in a three‐dimensional bounded domain with nonhomogeneous Dirichlet boundary conditions. The system describes the evolution of charged particles ensemble dispersed in an isentropic fluid. For the adiabatic coefficient , we establish the global existence of weak solutions to this system with arbitrary large initial and boundary data.

Motion of a rigid body in a compressible fluid with Navier-slip boundary condition

In this work, we study the motion of a rigid body in a bounded domain which is filled with a compressible isentropic fluid. We consider the Navier-slip boundary condition at the interface as well as at the boundary of the domain. This is the first mathematical analysis of a compressible fluid-rigid body system where Navier-slip boundary conditions are considered. We prove existence of a weak solution of the fluid-structure system up to collision.

Energy and Exergy-Based Screening of Various Refrigerants, Hydrocarbons and Siloxanes for the Optimization of Biomass Boiler–Organic Rankine Cycle (BB–ORC) Heat and Power Cogeneration Plants

The cogeneration of power and heat was investigated for Biomass Boiler–Organic Rankine Cycle (BB–ORC) plants with the characteristics of typical units, such as the 1 MWel Turboden ORC 10 CHP. The thermodynamic analysis of the ORC unit was undertaken considering forty-two (42) dry and isentropic candidate pure working fluids. Only subcritical Rankine cycles were considered, and the pinch point temperature differences for the evaporation and condensation heat exchangers were kept constant at 10 °C in all cases. The study provides an original and unique screening of almost all pure working fluids that are considered appropriate in the literature under the same operation and optimization conditions and compiles them into a single reference. In its conclusions, the study provides useful fluid selection and design guidelines, which may be easily followed depending on the optimization objective of the ORC designer or operator. In general, hydrocarbons are found to lie in the optimum middle range of the fluid spectrum, between the siloxanes that maximize the production of mechanical power and the refrigerants that maximize the production of heat. Specific hydrocarbon fluids, such as cyclopentane, heptane, hexane, benzene, and toluene, are found as rational options for maximum mechanical efficiency when operating with practically feasible condensation pressures between 10 and 200 kPa. At condensation pressures below 10 kPa, ethylbenzene, o-xylene, m-xylene, p-xylene, and nonane are also found to be feasible options. Finally, cyclopentane, hexane, and MM (hexamethyldisiloxane) are selected as the most appropriate options for cogeneration plants aiming simultaneously at high mechanical power and maximum temperature water production.

Performance parameters assessment of a pneumatic engine for low capacity commercial vehicles

In the present work, the performance evaluation of a low capacity pneumatic engine is shown, through modeling and simulation in order to identify the feasibility of its application in commercial vehicles for short distances. For the modeling of the pneumatic engine, a comprehensive approach has been used that includes the compressed air supply pipe, the cylinder compression - expansion chamber, and the intake and exhaust valves. The compressed air supply system is modeled using compressible fluid flow models. The fluid flow is considered adiabatic represented by the model known as Fanno flow (or non-isentropic) and it is assumed to be in a steady state. The flow in the opening and exhaust valves are evaluated as adiabatic and isentropic fluid, using a divergent - convergent compressible fluid model. The simulation results show that the feeding pressure and the pipe diameter have a great influence on the motor power. Also, the compression ratio has been found to have strong influence on the overall system efficiency. On the other hand, the simulations show that the initial pressure of the piston does not have a great influence on performance indicators, such as power or efficiency. However, from the results found in this work, it can be seen that the model and all the results obtained in this work can be used to design and generate an optimization model that describes a pneumatic engine proposed for commercial vehicles of low capacity and short distances.

Jeotermal ısı kaynaklı Organik Rankine Çevriminde kuru ve izantropik akışkanların çevresel etkilerinin ve termodinamik performanslarının karşılaştırılması

Organic Rankine Cycle (ORC) is an electricity generation system in which organic fluid is used instead of water in the low temperature range. ORC is used in power plants to use waste heat to generate electricity. In this study, thermophysical, environmental and thermodynamic performance comparisons of the ORC model were made using dry and isentropic fluids. Within the scope of geothermal applications, the heat source temperature was determined as 110 °C. The effect of changing the evaporation temperature between 65-100 °C on system performance was determined. As performance parameters, pump work, turbine work, input heat, irreversibility values, thermal efficiency and exergy efficiency have been determined for ORC. Thermodynamic analysis was performed using Engineering Equation Solver (EES). As a result of this study, it was observed that the highest values in terms of turbine work and thermal efficiency with R601 fluid were 54.72 kJ/kg and 11.34%, respectively, and 32.84 kJ/kg and 11.91% with R141b fluid, respectively. A fluid that performs best from dry and isentropic fluids has been proposed for ORC.

A playground for compressible natural convection with a nearly uniform density

In the quest to understand the basic universal features of compressible convection, one would like to disentangle genuine consequences of compression from spatial variations of transport properties. For instance, one may choose to consider a fluid with uniform dynamic viscosity, but, then, compressible effects will generate a density gradient and consequently the kinematic viscosity will not be uniform. In the present work, we consider a very peculiar equation of state, whereby entropy is solely dependent on density, so that a nearly isentropic fluid domain is nearly isochoric. Within this class of equations of state, there is a thermal adiabatic gradient and a key property of compressible convection is still present, namely its capacity to viscously dissipate a large fraction of the thermal energy involved, of the order of the well-named dissipation number. In the anelastic approximation, under the assumption of an infinite Prandtl number, the number of governing parameters can be brought down to two, the Rayleigh number and the dissipation number. This framework is proposed as a playground for compressible convection, an opportunity to extend the vast corpus of theoretical analyses on the Oberbeck–Boussinesq equations regarding stability, bifurcations or the determination of upper bounds for the turbulent heat transfer. Here, in a two-dimensional geometry, we concentrate on the structure of numerical solutions. For all Rayleigh numbers, a change in the vertical temperature profile is observed in the range of dissipation number between $0$ and less than $0.4$ , associated with the weakening of ascending plumes. For larger dissipation numbers, the heat flux dependence on this number is found to be well predicted by Malkus's model of critical layers. For dissipation numbers of order unity, and large Rayleigh numbers, dissipation becomes related to the entropy heat flux at each depth, so that the vertical dissipation profile can be predicted, and so does the total ratio of dissipation to convective heat flux.

Comparative Study of Rankine Cycle Power Generation using Water and Organic Fluids in Saturated and Superheated States

The Rankine cycle is an electricity generation system that uses water or organic fluids as high-grade or low-grade heat sources, respectively. In this paper, we present the results of our study of Rankine-cycle power generation in which we compared water and organic fluids (toluene and n-nonane) as working fluids in saturated and superheated states. We analyzed the energy and exergy of the Rankine cycle in a saturated vapor state at 300 °C and superheated states at 400 °C and 500 °C (the pressure remained the same as that at 300 °C), and assumed a constant heat input for all states. In the energy analysis, we determined the mass flow rate, heat rejection, work input of the pump, work generated by the turbine, net work output, and thermal efficiency. In the exergy analysis, we determined the exergy input, exergy loss, exergy destruction at the pump and the turbine, and the exergetic efficiency. The results show that water, categorized as a wet fluid, obtains a better performance with respect to both analyses in saturated and superheated states than toluene and n-nonane, which are categorized as isentropic and dry fluids, respectively. The water realizes a higher performance in the superheated than in the saturated state, whereas the performances of toluene and n-nonane are poorer in the superheated than in the saturated state.

On port-Hamiltonian formulations of 3-dimensional compressible Newtonian fluids

In this manuscript, a general formulation of 3-dimensional compressible fluids based on the port-Hamiltonian framework is presented, both for isentropic and non-isentropic assumptions, describing the energy flux between the mechanical, chemical, and thermal domains, with an explicit characterization of the first and the second law of thermodynamics. For isentropic fluids, the conversion of kinetic energy into heat by viscous friction is considered as energy dissipation associated with the rotation and compression of the fluid. A dissipative port-Hamiltonian formulation is derived for this class of fluids, including vorticity boundary conditions in the port variables. For non-isentropic fluids, we consider a fluid mixture with multiple chemical reactions. To describe the energy fluxes, we propose a pseudo port-Hamiltonian formulation, which includes the rate of irreversible entropy creation by heat flux, chemical reaction, diffusion of matter, and viscous friction.

Linear stability analysis of the homogeneous Couette flow in a 2D isentropic compressible fluid

In this paper, we study the linear stability properties of perturbations around the homogeneous Couette flow for a 2D isentropic compressible fluid in the domain mathbb {T}times mathbb {R}. In the inviscid case there is a generic Lyapunov type instability for the density and the irrotational component of the velocity field. More precisely, we prove that their L^2 norm grows as t^{1/2} and this confirms previous observations in the physics literature. On the contrary, the solenoidal component of the velocity field experiences inviscid damping, namely it decays to zero even in the absence of viscosity. For a viscous compressible fluid, we show that the perturbations may have a transient growth of order nu ^{-1/6} (with nu ^{-1} being proportional to the Reynolds number) on a time-scale nu ^{-1/3}, after which it decays exponentially fast. This phenomenon is also called enhanced dissipation and our result appears to be the first to detect this mechanism for a compressible flow, where an exponential decay for the density is not a priori trivial given the absence of dissipation in the continuity equation.

Performance analysis and optimisation of a reheat organic Rankine cycle

ABSTRACT A reheat Organic Rankine Cycle (ORC) is investigated to recuperate a low-grade heat source using six different organic working fluids (WFs). The results indicate that wet fluids produce more power output compared to dry and isentropic fluids. The reheat pressures of the selected WFs were optimised to maximise the exergy efficiency and minimise the total UA. Reheat pressure ranges of 27–48% and 45–54% of the evaporation pressure were obtained, for ORCs with and without IHE, respectively. A maximum of 49.1% exergetic efficiency is achieved by the addition of IHE: a 13.6% improvement compared to the ORC without IHE. Finally, the results indicate that R236ea and propyne are the best WFs for the ORC with and without IHE, respectively.

Thermodynamic efficiency of trilateral flash cycle, organic Rankine cycle and partially evaporated organic Rankine cycle

Emerging and promising ways of utilizing any heat sources from geothermal, solar, combustion, and industrial waste heat may be the application of power plants that are operating according to conventional Rankine cycle (RC), organic Rankine cycle (ORC), trilateral flash cycle (TFC) employing different types of expansion (i.e., volumetric expanders or turbine). In this paper, the studies about partially evaporated ORC (PE-ORC) was carried out; furthermore, it reports on novel results related to the comparison of thermodynamic efficiency of TFC, ORC and PE-ORC. These results were obtained by modelling the system operations computed with MATLAB and the thermal properties library taken from CoolProp and REFPROP. The calculation was based on selected different types of working fluid classified by A, C, Z, M, N points (conventionally categorized by dry, wet, and isentropic working fluids) and the upper-lower operating temperature. The obtained results explain a new point of view on the efficiency of TFC, ORC and PE-ORC plants, that in some of the conditions (i.e., one can find certain combinations of working fluid quality, maximal and minimal cycle temperature), the efficiency of PE-ORCs outperforms TFC and ORC. It means that at certain temperature ranges and conditions when starting the expansion step from a partially evaporated state, it may be recommended to improve the performance of the cycle. It seems that obtained results offer new insight to scientists and engineers in designing the thermal power plant working under a subcritical cycle with high-temperature heat sources or a low-temperature heat sinks employing the selection of working fluids and different types of expanders.

Analytical model for thermal efficiency of organic Rankine cycles, considering superheating, heat recovery, pump and expander efficiencies

This article proposes a new analytical model that calculates the thermal efficiency of subcritical Organic Rankine Cycles (ORCs) and integrates the main cycle components and parameters in a single analytical solution accounting the effect of turbine and pump isentropic efficiencies, heat recuperation, superheating, fluid type, and hot and cold reservoir temperatures. Previous analytical models for ORCs covered neither heat recuperation, nor pump isentropic efficiency, which are important features for improving the cycle thermal efficiency. The analytical solution was compared with numerical solutions of ORCs for 22 fluids, and the model showed highly accurate for wet and isentropic fluids. The highest percentage divergences were verified for both dry fluids of heavier molecular weight and evaporation temperatures close to the fluid́s critical temperature. The model can be applied to most fluids and for the main operation conditions of ORC applications.

Machine learning prediction of ORC performance based on properties of working fluid

In order to develop machine learning methods for performance prediction of basic ORC (BORC) and regenerative ORC (RORC), thermodynamic properties of working fluids are used to separately model thermodynamic processes including compression, expansion, evaporation and regeneration by artificial neural network (ANN), based on REFPROP calculation data of 106 working fluids. These properties include critical temperature, critical pressure, acentric factor and ideal gas heat capacity. Other cycle performances can be derived from the predictions of established ANNs. Furthermore, for RORC, considering that dry or isentropic working fluid is usually preferred, vapor slope of temperature-entropy saturation curve is modeled by ANN to determine the working fluid behavior. Meanwhile, for ensuring occurrence of heat exchange in regenerator, temperature difference between outlets of turbine and pump is modeled to judge whether temperature difference is larger than the assumed pinch point temperature difference. Based on the obtained predictions for BORC, average absolute deviations (AADs) of net work and thermal efficiency are 1.3928% and 1.5461%, respectively. As for RORC, AADs of vapor slope, temperature difference, net work and thermal efficiency are 2.3659%, 1.2020% 1.8277% and 2.1047%, respectively. Based on the above models, cycle performances of BORC and RORC can be accurately predicted from thermodynamic properties of any working fluid.

A novel working fluid selection and waste heat recovery by an exergoeconomic approach for a geothermally sourced ORC system

A novel working fluid selection methodology is proposed for organic Rankine cycles (ORCs) coupled with low-grade geothermal sources by employing an existing dataset of an operating binary geothermal plant that works with n-pentane. Thermodynamic and thermoeconomic aspects of power production are combined to evaluate 29 different single-component working fluid candidates from different chemical branches in four-step elimination methodology. In terms of working fluid classification from physical point of view, results indicate that there is a direct relationship between vapor expansion ratio (VER) and net work output for dry working fluids. On the other hand, it is shown that isentropic fluids behave differently from dry fluids. Based on the proposed methodology, R113 is selected as a new working fluid for the existing plant instead of n-pentane. Results indicate that by applying the proposed methodology, it is possible to increase first and second law efficiencies of plant 0.59% and 3.18%, respectively, while reducing the levelized electrical cost (LEC) around 11% in comparison to base plant outputs with n-pentane. Furthermore, a case study is presented in addition the plant level analysis by implementing a hypothetical waste heat recovery cycle, configurated with proposed methodology, in order to reduce exergy losses originating from brine re-injection. It is shown that it may be possible to further reduce the LEC around 1% and increase the overall efficiencies 0.1% for the first law and 0.26% for the second law. However, it is necessary to be deliberate about these final results since they also demonstrate the sensitivity of LEC to the increases in second law efficiency rather than levelized capital investments.

Thermodynamic comparison of modified Rankine cycle configurations for LNG cold energy recovery under different working conditions

In this study, we present the evaluation of two modified single-stage Rankine cycles (RC) and two two-stage RCs to provide a guidance for configuration selection under different working conditions. Moreover, a regenerative-reheat RC, which is the combination of the modified single-stage RCs, is proposed to utilize the cold energy of liquefied natural gas (LNG) and the thermal energy of low grade heat. The key parameters of these five configurations using eight working fluids are optimized with exergy efficiency as the optimization objective. The results show that the modified single-stage RCs are usually better than the two-stage RCs since they have simpler configurations with similar or higher efficiencies. The regenerative-reheat RC performs even better under most working conditions and it achieves the maximum efficiency of 24.57% by using ethane as the working fluid under the heat source temperature of 180 °C and the pipeline pressure of 3 MPa. The addition of direct expansion cycle can improve the exergy efficiencies of most fluids and configurations under lower pipeline pressures. However, the improvements decrease greatly for fluids with low normal boiling point temperatures (NBPTs) and especially under higher pipeline pressures. As to the fluid selection, high critical temperature and low NBPT are both important for reheat RC and parallel two-stage RC. NBPT weights more than critical temperature for regenerative RC and regenerative-reheat RC. Besides, wet working fluids are more suitable for reheat RC while dry and isentropic fluids are more suitable for regenerative RC and regenerative-reheat RC. The optimal regenerative ratio and reheat pressure ratio vary with different working fluids and working conditions. Lower reheat pressure ratio usually leads to higher regenerative ratio.

Stability of the planar rarefaction wave to three-dimensional Navier–Stokes–Korteweg equations of compressible fluids

This study is concerned with the large time behaviour of the three-dimensional isentropic compressible Navier–Stokes–Korteweg equations, which are used to model viscous and compressible fluids with internal capillarity. Based on the fact that the rarefaction wave is nonlinearly stable to the one-dimensional isentropic compressible Navier–Stokes–Korteweg equations, the planar rarefaction wave to the three-dimensional isentropic compressible Navier–Stokes–Korteweg equations is first constructed. Then it is shown that the planar rarefaction wave is asymptotically stable in the case that the initial data are a suitably small perturbation of the planar rarefaction wave and the strength of the rarefaction wave is small. The proof is based on the delicate energy method. The result indicate that the planar rarefaction wave of the inviscid Euler system is stable for the three-dimensional isentropic compressible fluids with physical viscosities and internal capillarity.

Evaluation and selection of dry and isentropic working fluids based on their pump performance in small-scale organic Rankine cycle

• A trapezoid model used to represent the power consumption of pump is established. • The perfection of Organic Rankine Cycle relative to the Carnot cycle is analyzed. • The deviation between the real and ideal gas behavior is obtained. • The optimal condensation temperature of each working fluids is determined. • Their suitable pump types are determined. The circulation pump is an important element limiting the development of small-scale Organic Rankine Cycle system which may have a negative efficiency when the power consumption of the pump is considered and if a suitable pump that corresponds to the working fluid is not properly selected. Based on the consideration mentioned above, in this paper, a trapezoid used to represent the power consumption of the pump and a triangle used to represent the degree of subcooling of the working fluid are defined. Using these two models, the perfection of Organic Rankine Cycle at the optimal condensation temperature relative to the Carnot cycle within the same temperature limitation is analyzed when 69 dry and isentropic working fluids are used in Organic Rankine Cycle. The deviation between the real and ideal gas behavior of each working fluid is also obtained. On this basis, the optimal condensation temperature of each dry and isentropic working fluid is determined. Moreover, the applicability of each organic working fluid in Organic Rankine Cycle is discussed from the viewpoint of pump performance. 36 working fluids are suitable and 33 ones not suitable for the application in small-scale Organic Rankine Cycle system. Suitable pump types corresponding to applicable organic working fluids are also analyzed and determined. The graphic method proposed in this paper and the findings about pump performance can provide reference for the operation of practical Organic Rankine Cycle.

Global weak solutions for a Vlasov–Fokker–Planck/Navier–Stokes system with nonhomogeneous boundary data

In this paper, we consider a kinetic-fluid model with nonhomogeneous Dirichlet boundary data in a 3D bounded domain. This model consists of a Vlasov–Fokker–Planck equation coupled with the compressible Navier–Stokes equations via a friction force. We establish the global existence of weak solutions to it for the isentropic fluid (adiabatic coefficient $$\gamma > \frac{3}{2}$$ ) with large initial data, and large velocity and density at the inflow boundary.

Effects of working fluid type on powertrain performance and turbine design using experimental data of a 7.25ℓ heavy-duty diesel engine

This paper outlines a comparative assessment of the effects of various fluid types on the performance of powertrain performance (i.e. heavy-duty diesel engine + organic Rankine cycle) and the design of the radial inflow turbine. The considered organic fluids are R123 (dry), R21 (wet) and R141b (isentropic). The exhaust gas of a 7.25ℓ heavy duty diesel engine is utilized as the system heat source. The powertrain system, including the radial inflow turbine, is analyzed under superheated conditions and near saturated vapor curve, at various operating conditions. Surprisingly, wet fluids offer attractive cycle performance in the superheated region (12.65% on average) followed by isentropic fluids (12% on average). Near the saturated vapor curve, isentropic fluids are found to present best cycle performance (13.77% on average) while wet fluids offer the lowest (10.90% on average). However, wet fluids present a compact turbine design and best isentropic efficiency with an average value of 82% in the superheated region. Near the saturated vapor curve, isentropic and dry fluids offer relatively lower turbine efficiencies (80.9% and 80.3 on average) while wet fluids result in two-phase condition at the turbine exit which results in poor turbine performance (63.30% on average). Moreover, R141b shows best improvements of engine power and BSFC with values of 11.18% and 10%, respectively, at 1 kg/s. Compared to R123 and R141b, R21 improved the engine power and BSFC by at least 7.86% and 7.63% under superheated conditions.

Effect of working fluids on the performance of phase change material storage based direct vapor generation solar organic Rankine cycle system

Working fluids can play a critical role in the working of an organic Rankine cycle system. A direct vapor generation solar organic Rankine cycle embedded with phase change material storage is analyzed in this study. The system comprised of an array of evacuated flat plate collectors, phase change material based thermal storage, expander, condenser, and organic working fluid pump. The storage tank model is modeled using a finite difference method in MATLAB programming environment while the 1D model of ORC system is used to evaluate the system performance. After a careful screen, 12 dry and isentropic working fluids were selected and their impact on the performance of the heat storage tank and the overall system is evaluated. The results show that the system efficiencies increase and decrease with the increment and decrement in the critical temperature of the working fluid. Moreover, the rise and fall of working fluid temperature, phase change material temperature, and the quantity of energy stored and released generally increase with an increase in the critical temperature of the working fluid. At the evaporation temperature of 10 °C higher and lower than the melting point temperature of the phase change material, Benzene has achieved the highest system efficiencies of 10.7% & 10.4% during charging and discharging mode, respectively. However, the maximum the rise and fall of working fluid temperature, phase change material temperature, and the quantity of energy stored and released during charging and discharging mode is attained by Heptane which is found to be 5.35 °C & 7.34 °C, 0.48 °C & 0.44 °C and 13.81 MJ & 23.04 MJ, respectively. Heptane has shown overall best performance among the selected working fluids and found to be feasible for phase change material storage based direct vapor generation solar ORC system.