Thermophysical Properties Of Fluids Research Articles

Thermocline Thermal Storage for Concentrated Solar Power Applications: Characterization of Novel Nitrate Salt Mixtures

Abstract Parabolic trough concentrated solar power (CSP) plants are particularly promising renewable sources of energy, whose easy integration with thermal energy storage (TES) systems allows to mitigate the intermittency of electricity generation. Currently, molten nitrates, with two tanks arrangement, are mainly used for sensible heat accumulation. To reduce costs and make the CSP storage systems more manageable, single tank configurations have been proposed, where the cold and hot fluids are stored in the same container and separated because of their density difference. The aim of the present work is to study the storage performances presented by two novel ternary and quaternary mixtures, proposed within the European project IN POWER. An experimental campaign was preliminarily performed to investigate the fluids thermo-physical properties, and the obtained values were utilized as input data to model the discharge phase in a thermocline tank. The simulation results were compared with the ones acquired considering two commercial materials, namely, solar salt and Hitec XL®. Overall, considering same temperature ranges, higher discharging times are obtained for the quaternary and ternary mixtures, with the ternary presenting a smaller thermocline thickness than the solar salt while this parameter is the same considering the quaternary and Hitec XL®.

Mixed convection and non-linear thermal radiative analysis for Carreau-Yasuda nanofluid in an endoscope

The understanding of flow behaviour of non-Newtonian fluids in the presence of nanoparticles is of great interest from an industrial point of view. Bulk addition of nano-sized particles in fluid enhance thermo-physical properties of fluid which is of crucial importance to industries such as medicine, agriculture, electronics etc. Current study discusses thermophoretic diffusion and Brownian motion in peristaltic flow of Carreau-Yasuda nanofluid in tube-like (endoscopic) structure. Unlike many existing studies, the nonlinear radiation effect in the presence of heat and mass transfer i.e., mixed convection is considered. Dissipation, Joule heating and heat source, sink effects are modelled. The governing mathematical problems are numerically solved. Non-dimensionalization is achieved via use of lubrication approach and streamline functions. Quantities like velocity, temperature, concentration, heat transfer rate and trapping are addressed. Observing effects of Weissenberg number (We = 0.1 − 0.3) on fluid flow conclude that velocity as well as the size of trapped bolus increases as We is increased. Heat transfer rate enhances as temperature ratio parameter (θ1 = 0.3 − 0.7) is increased.

Falling liquid films on a slippery substrate with variable fluid properties

We investigate the stability of a gravity-driven, thin, Newtonian liquid flowing on a uniformly heated slippery inclined plane. We construct a mathematical model of the flow that comprises the Navier–Stokes equation coupled with the equation of energy. While the rest of the boundary conditions are standard for thin-film problems, we apply a Navier slip boundary condition at the solid–liquid interface. We assume that the fluid thermophysical properties — density, dynamical viscosity, surface tension, and thermal diffusivity vary linearly with temperature as long as the change in temperature is small. In the analysis part, we follow the standard long-wave theory and construct a nonlinear evolution equation for the film thickness. This is followed by a linear and weakly nonlinear stability analysis. The linear analysis allows us to compute the critical Reynolds number of our problem and from this study, we conclude that the slippery substrate destabilizes the film flow. The weakly nonlinear stability analysis finds a finer description of various stable/unstable zones. Finally, we perform a numerical simulation of the evolution equation in a periodic domain using spectral methods. Our numerical results support the analytical predictions of the instability threshold using the linear and weakly nonlinear theories. The influence of the small Biot number is also investigated in presence of the slip length together with the variable fluid properties.

A critical re-examination of Reynolds analogy for micro-convective flow

The present research numerically investigates the validity of the Reynolds analogy for micro-convective water flow between Stanton number (St) and Fanning friction factor (ff), taking into account combined fluid properties variations such as temperature-dependent density, viscosity, and thermal conductivity. The Reynolds analogy is suggested to be valid when St increases for thermophysical fluid properties (TFP) with a decrease in ff. This analogy, therefore, helps to find the flow regime that increases heat transfer while shear stress decreases for TFP. Hence, the Reynolds analogy for TFP helps to design and improve the performance of the different devices, including micro-scale heat exchangers for electronics cooling, internal cooling passages of turbine airfoils, and many biomedical devices. Three modified non-dimensional parameters (ΠSρT, ΠSμT, and ΠSkT) appear from the non-dimensionalization of the governing conservation equations. Using dimensional analysis, the dependence of the friction factor on these parameters is examined.

A Volume-of-Fluid Heat Pipe Model Resolving Pressure Discontinuities at the Wick-Vapor Interface

Heat pipes are passive cooling devices which play an increasingly important role in a vast field of cooling solutions for technologies like electric machines or consumer electronics. Simulations that reliably predict the heat pipe’s performance and operational limits are the key for optimizing cooling efficiency. In this paper, a novel Volume-of-Fluid model is presented which resolves temperature and pressure discontinuities at the wick-vapor interface. The flow resistance in the wick structure is modeled using momentum sources based on the Darcy-Forchheimer formulation. Additional momentum sources perpendicular to the phase boundary account for capillary forces and ultimately lead to distinct pressure regimes in the wick and vapor flow. Evaporation and condensation are modeled using a data set which takes wick microstructure effects into account and is based on statistic rate theory. The involved thermophysical fluid properties are obtained from a model by the International Association for the Properties of Water and Steam depending on temperature and pressure. Eventually, the simulation approach is validated against experimental and numerical data from literature. The final model enables thermal engineers to predict dry-out conditions and to optimize the capillary structure and heat pipe geometry. Furthermore, this paper reveals a methodical error in the state-of-the-art simulation approach which leads to a significant underestimation of mass flow and pressure drop.

Searching for Sustainable Refrigerants by Bridging Molecular Modeling with Machine Learning.

We present here a novel integrated approach employing machine learning algorithms for predicting thermophysical properties of fluids. The approach allows obtaining molecular parameters to be used in the polar soft-statistical associating fluid theory (SAFT) equation of state using molecular descriptors obtained from the conductor-like screening model for real solvents (COSMO-RS). The procedure is used for modeling 18 refrigerants including hydrofluorocarbons, hydrofluoroolefins, and hydrochlorofluoroolefins. The training dataset included six inputs obtained from COSMO-RS and five outputs from polar soft-SAFT parameters, with the accurate algorithm training ensured by its high statistical accuracy. The predicted molecular parameters were used in polar soft-SAFT for evaluating the thermophysical properties of the refrigerants such as density, vapor pressure, heat capacity, enthalpy of vaporization, and speed of sound. Predictions provided a good level of accuracy (AADs = 1.3–10.5%) compared to experimental data, and within a similar level of accuracy using parameters obtained from standard fitting procedures. Moreover, the predicted parameters provided a comparable level of predictive accuracy to parameters obtained from standard procedure when extended to modeling selected binary mixtures. The proposed approach enables bridging the gap in the data of thermodynamic properties of low global warming potential refrigerants, which hinders their technical evaluation and hence their final application.

Velocity modeling of supercritical pore fluids through porous media under reservoir conditions with applications for petroleum secondary migration and carbon sequestration plumes

Computational methods to characterize secondary migration in porous media traditionally rely on fluid transport equations with assumptions of time invariance, such as flow-path modeling of buoyancy vectors, statistical percolation algorithms, capillary pressure curves, or a form of Darcy’s law, which presumes instantaneous fluid transport. However, in petroleum systems modeling, the timeframe of secondary migration from source to reservoir is important to quantify in relation to other geologic factors, such as the timing of petroleum generation, fault movement, and seal formation. In addition, quantifying migration velocities enables an estimation of the distance a plume of geologically sequestered carbon dioxide travels over time, as well as the identification of low-permeability strata appropriate for long-term containment. This study introduces a method to quantify transport velocities of supercritical fluids in low-permeability lithologies for a broad range of rock and fluid properties likely encountered in the sedimentary sequence. A time-dependent form of Darcy’s law for pressure-driven viscous flow through homogeneous isotropic porous media was used to model flow velocities within a carrier bed. Thermodynamic equations of state were used to determine thermophysical properties of supercritical pore fluids under reservoir pressures ranging from 0 MPa to 200 MPa (0–29,000 psi) to constrain the momentum equations. Three case studies were examined that (1) estimated fluid flow velocities of methane within the low-permeability Upper Jurassic Haynesville Formation, (2) defined permeability-based flow units to evaluate saline formations for long-term geologic carbon sequestration, and (3) calculated the migration distance of carbon dioxide plumes at the Decatur, Illinois injection and sequestration project.

Thermo-physical properties of fluid and gases near a solar rough rotating disk

A numerical study is assumed to analyze the small-scale influence of surface roughness near the boundary layer region of a heated rotating disk. To calculate the shear thickening and thinning behavior, we evaluate the base flow profiles and also examined the surface roughness by imposing the wall partial slip boundary conditions with radial and azimuthal anisotropic and isotropic roughness. Thermo-physical properties are adopted to study the following phenomena. Moreover, the impact of thermo-physical characteristics and solar radiation near the disk are also considered. For the transformation of governing PDEs into resultant ODEs, we consider a von Kàrmàn similarity transformation and then numerical solutions are achieved via shooting method (Runge–Kutta Fehlberg and Newton Raphson). The numerical results concerned with the base flow profiles are given physically interpreted through tables and graphs. The shear thickening and shear thinning base flow profiles are shown here. Correlations in term of velocity, temperature, and concentration are plotted graphically. The comparison of literature with present work is also presented here.

A versatile interferometric technique for probing the thermophysical properties of complex fluids

Laser-induced thermocapillary deformation of liquid surfaces has emerged as a promising tool to precisely characterize the thermophysical properties of pure fluids. However, challenges arise for nanofluid (NF) and soft bio-fluid systems where the direct interaction of the laser generates an intriguing interplay between heating, momentum, and scattering forces which can even damage soft biofluids. Here, we report a versatile, pump-probe-based, rapid, and non-contact interferometric technique that resolves interface dynamics of complex fluids with the precision of ~1 nm in thick-film and 150 pm in thin-film regimes below the thermal limit without the use of lock-in or modulated beams. We characterize the thermophysical properties of complex NF in three exclusively different types of configurations. First, when the NF is heated from the bottom through an opaque substrate, we demonstrate that our methodology permits the measurement of thermophysical properties (viscosity, surface tension, and diffusivity) of complex NF and biofluids. Second, in a top illumination configuration, we show a precise characterization of NF by quantitively isolating the competing forces, taking advantage of the different time scales of these forces. Third, we show the measurement of NF confined in a metal cavity, in which the transient thermoelastic deformation of the metal surface provides the properties of the NF as well as thermo-mechanical properties of the metal. Our results reveal how the dissipative nature of the heatwave allows us to investigate thick-film dynamics in the thin-film regime, thereby suggesting a general approach for precision measurements of complex NFs, biofluids, and optofluidic devices.

Generalized Nusselt Number Correlation for Binary Hybrid Nano-Oils as Heat Transfer Fluid in Solar Thermal Systems

Abstract The turbulent flow of binary hybrid nano-oils is investigated and Nusselt number correlation is developed for futuristic concentrated solar thermal application. Available Nusselt number correlations for water-based hybrid nanofluids are nanoparticle-specific property correlations dependent and substantially over-predict the values for hybrid nano-oils. Therefore, a generalized Nusselt number correlation for turbulent flow of water and oil-based binary hybrid nanofluids is deduced using the separation approach. Dissimilar to the available correlations, the developed correlation needs only the thermophysical properties of base fluid and nanoparticles. It is valid for the Reynolds number range 10,000–30,000 and the Prandtl number range 0.5–2000. It is found that the proposed correlation predicts the published experimental values for different hybrid nanofluids mostly within ±10–20%. Computational fluid dynamics simulation is also performed for turbulent flow of different hybrid nano-oils to assess the developed correlation. The comparative assessment also confirms that the developed correlation predicts the numerical values for hybrid nano-oils within ±10–20%. The deduced Nusselt number correlation will be useful for a realistic heat transfer analysis with different water or oil-based hybrid nanofluids. The need for experiments with different hybrid nano-oils is realized for further improvement.

Influence of vapor generator design on thermodynamic and techno-economic performances of transcritical organic Rankine cycle

Transcritical organic Rankine cycle is of great potential in converting low-grade heat into electricity. Due to sharp variations in fluid thermophysical properties, accurate design of vapor generator in transcritical cycle remains challenging. This work aims to investigate the influence of vapor generator design on both component and system levels. Vapor generator employing supercritical R134a or R1234yf was designed by two models. One is more accurate and the other is more commonly used but may be less accurate. A multi-factor evaluation method was developed to comprehensively analyze the system thermo-economic performance. Results show that two design models led to a difference up to 36% in the size of vapor generator Avapor, but only 1% change in system electricity production cost (EPC). The increase of turbine inlet temperature caused a 10% change in Avapor, while the change with operating pressure was only 1%. In the case of multi-objective optimization, two designs gave 16%∼36% deviation in Avapor and less than 2.5% changes in four performance indicators, but differences in their optimal operating conditions caused 2%∼8% deviations between design condition and the assumed real condition. Quite consistent results were obtained for two working fluids, and a linear correlation was found between uncertainties in Avapor and EPC.

Thermal resistance modeling of flat plate pulsating heat pipes

Flat plate pulsating heat pipes (FP-PHP) represent a future technology, enabling a more efficient thermal management of high heat flux devices. Whereas established thermal resistance models exist for wicked heat pipes, there are no such comprehensive models for pulsating heat pipes. In this paper, a conduction-based approach for pseudo-steady heat transfer is presented which can be used for 3D thermal simulations. For the calculation of the internal thermal resistance, multi-fluid correlations for flow boiling and condensation are utilized. A saturated homogenized state in-channel is assumed which allows the temperature-dependent determination of thermophysical fluid properties. A good agreement for the external temperature field was achieved compared to two independent experiments. The simulations show a significant sensitivity to the condenser conditions. Interestingly no adiabatic zone exists along the channels. Furthermore, it is shown that consideration of thermal spreading effects is key for the interpretation of the overall thermal resistance, effective heat fluxes and the design of optimal FP-PHPs.

The role of enthalpy and activation energy on thermophysical properties of third grade fluid near a magnetized radioactive irregular wavy surface

The present article communicates mathematical and theoretical study of three dimensional mixed convection flow of an electrical conducting third grade fluid flow near a non-uniform irregular wavy surface. The flow field is incorporated with an applied magnetic field. Heat and mass transfer characteristics are scrutinized with combined impact of enthalpy change along with energy activation and non-linear thermal radiation. The prime structure of differential equations is achieved in momentum, energy, magnetic and concentration forms. We defined some new dimensionless functions which transformed non-linear PDEs into dimensionless ODEs. Lobatto(iiiA) formula based technique Bvp4c is used for graphical and numerical solution of governing equations. Features of different dimensionless parameters are studied for velocity, concentration, magnetic and energy distributions by using graphical approach. Skin friction coefficients, rate of heat and mass fluxes are calculated by changing the values of some dimensionless parameters. Comparative study of Nusselt number with previous published results are demonstrated to investigate the accuracy of current problem. Final outcome justifies that better agreement is achieved with existing published work.

Effects of concave curvature on the formation and propagation of capillary wave induced by electrowetting-on-dielectric

Capillary-wave propellers (CWPs) based on the phenomenon of electrowetting-on-dielectric (EWOD) have shown great potential for floating-object propulsion, heat-transfer enhancement, and fluid thermophysical property measurement. However, the small amplitude of the EWOD-induced capillary-wave limits the performance of the CWP in practical applications. Herein, a CWP with a concave curvature is proposed to enlarge the capillary-wave amplitude. The formation and propagation of the capillary wave are visualized by using a high-speed camera and a free-surface synthetic schlieren method. The wave amplitude and wave propagation are modeled theoretically. The effects of the concave curvature and the frequency of the electrical signal are investigated, and the results show that the concave curvature increases the wave amplitude, velocity vector, and wave intensity as compared with flat EWOD units. In addition, the results show that 20 Hz electrical signals are favorable for pursuing large wave energy density. The underlying mechanism for increasing the wave energy via concave CWPs is revealed experimentally and explained theoretically. The proposed concave CWP is helpful for increasing the propulsion speed of small-scale floating objects and is promising for improving the performance of CWPs in other applications.

The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications

This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces.

Experimental investigations on nucleate pool boiling over micro-finned cylindrical surfaces

The nucleate pool boiling heat transfer over micro-finned cylindrical surfaces has application in the heat exchangers used in thermal power plants and chemical industries. The estimation of boiling heat transfer coefficient is an important parameter in the design of two-phase heat exchangers using micro-finned cylindrical surfaces. In the present work, related experimental investigations on four micro-finned cylindrical surfaces with different surface geometry using refrigerant R-141b at atmospheric pressure are conducted to determine the boiling heat transfer coefficient over micro-finned cylindrical surfaces. A correlation is developed by dimensional analysis wherein the effects of geometrical parameters, operating pressure and thermo-physical properties of fluids are taken into consideration and dimensional analysis conducted using Buckingham π-theorem. The correlation developed utilizes experimental data obtained over the present study as well as from previous studies by various researchers including experimental data for water over different micro-finned cylindrical surfaces at 1 bar by Mehta and Kandlikar, experimental data for R123 at 0.97 bar by Saidi et al. and experimental data for R134a over micro-finned cylindrical surface at 6.1 bar, 8.1 bar, 10.1 bar and 12.2 bar by Rocha et al. The heat flux ranging from 5 to 1100 kW/m2 are considered for the analysis. The data points have been compared with the proposed correlation and the absolute average deviation of the whole data set was obtained as 13.43% with root mean square deviation of 0.0273. All the predicted values were within ±15% of the experimental values of the boiling heat transfer coefficient.

Effect of multi-walled carbon nanotube on thermophysical properties of polyester and mineral oil

In the past few decades, multi-walled carbon nanotubes (MWCNT) have been used to increase the efficiency of thermal systems. Many nanofluids were synthesized using MWCNT, using which the thermophysical properties of normal fluid have enhanced. Out of these fluids, polyester oil (POE) and mineral oil (MO) are the oils that are used in the refrigeration sector. In this paper, MWCNT has been used to increase the thermophysical properties of these two oils. Two different types of nanoparticle concentrations of 0.05 wt% and 0.1 wt% MWCNT have been used. The thermal conductivity and viscosity of both these types of concentrations have been measured theoretically and experimentally. In theoretical evaluation, the Hamilton model is used for the evaluation of thermal conductivity and the Brinkman model to evaluate the viscosity. The investigation concluded that the thermophysical properties of POE and mineral oil increases through MWCNT nanoparticles dispersion. The result obtained from the theoretical model and experimentation was observed to followed a similar pattern. Out of the two oils, the highest thermal conductivity was gained by using 0.1 wt% MWCNT with POE oil. The thermal conductivity of POE oil increased by 1.09 W/mk and that of mineral oil increased by 0.91 W/mk. Also, the viscosity of POE increased by 26.4 % and that of mineral Oil by 24.4 % by using 0.1 wt% of MWCNT. The optimal concentration of MWCNT is utilized to avoid agglomeration. It is observed that up to 0.1 wt% of MWCNT nanoparticle concentration, no sedimentation or agglomeration was observed in POE and MO based nanosuspensions.

Synthesis and thermophysical properties of functionalized graphene quantum dots for enhancing heat transfer of conventional fluid

For the past few years, graphene quantum dots have been utilized in versatile applications due to their ultra-small size, non-toxicity, high heat transfer capacity, water solubility, and biocompatibility. In the presented work, the graphene quantum dots (GQD) is utilized to improve the thermophysical properties of conventional heat transfer fluid. In this research, the polyalkyline glycol (PAG) has been used as a conventional heat transfer fluid. The graphene quantum dots have been synthesized using hydrothermal method and further functionalized for the proper dispersion in PAG. The novel nanofluid has been synthesized using functionalized graphene quantum (FGQD) with based fluid as PAG. The FGQD-PAG nanofluid is synthesized with very lower concentrations of 100 ppm, 200 ppm, and 500 ppm. In order to investigate heat transfer capacity, each concentration of nanofluid has been investigated for thermal conductivity and viscosity. The experimental result shows that 500 ppm of FGQD-PAG lubricant improves the thermal conductivity by 2 W/mk. Also, the optimal viscosity for the nanofluid is observed with 100 ppm of FGQD-PAG based nanofluid. Further, it is observed that the use of graphene quantum dots with PAG base fluid is stable and does not require any use of surfactant for the dispersion. From this research, the problem of aggregation, agglomeration and precipitation occurring due to vander waal force has been addressed and is resolved by covalent surface modification. Thus, it is concluded that the graphene quantum dots can be effectively utilized in industrial applications where energy conservation is required.

Optimal design of radial inflow turbine for ocean thermal energy conversion based on the installation angle of nozzle blade

Ocean Thermal Energy Conversion (OTEC), as a new type of renewable energy, has huge development potential. Turbine is the most critical component in the ocean thermal energy conversion system, which directly determines the performance and energy conversion efficiency of the system. Therefore, the optimal design of turbines is very important to improve the efficiency of ocean thermal energy conversion. Based on the full consideration of the small temperature difference application characteristics of ocean thermal energy conversion and the special thermophysical properties of organic working fluids, this paper designs an ammonia working centripetal turbine with a power of 100 kW for OTEC applications, and then analyzes the effect of different geometric parameters on turbine performance. At the same time, the key parameters of the turbine are optimized based on full three-dimensional CFD numerical simulation analysis. It's shown that the nozzle blade installation angle has a very important impact on the performance of the turbine. Through optimization, when the nozzle blade installation angle reaches 30.5°, the efficiency is 91.77%, which is 6.25% points higher than the design value. The internal flow field performance is the best without obvious shock wave and reverse vortex phenomenon, which further improves the efficiency of the turbine and improves the internal flow.

The thin film flow of Al2O3 nanofluid particle over an unsteady stretching surface

This work emphasizes the thermophysical properties of base fluid with different-shaped Al2O3 particles in the heat transfer of an unsteady thin film flow over a stretching layer. The study is performed under convective boundary conditions. A system of Partial Differential Equations (PDEs) is formed through detailed mathematical modeling. Using an appropriate set of similarity transformations, PDEs’ system is transformed into a set of nonlinear ordinary differential equations (ODE). The system of ordinary differential equations is solved in MATLAB using BVP4C. The graphical simulations analyze the impact of multi-shape Al2O3 nanoparticles and other physically significant related parameters such as Prandtl, Eckert and biot-numbers on the flow and heat transfer characteristics. In addition, the coefficient of skin friction and Nusselt number are measured and tabulated numerically for discussion. The study shows that Al2O3 nanoparticles have a high flow and heat transfer rate in a platelet form. Moreover, the temperature profile increases by growing the volume-fraction parameter and the biot-number, but the reverse pattern is found only for the slip parameter. The study is in excellent agreement with existing literature for a limited number of cases.