Thermodynamic Boundary Research Articles

Earth Air Tube Heat Exchanger Novel Way for Energy Saving

The demands of cooling energy & thermal comfort requirements are rapidly increasing day by day due to the global warming effect. The temperature of Tropical and Subtropical regions is as high as 50 ℃ in summer, and it is as low as below 10 ℃ in winter. So we may utilize the fact that the temperature of the earth at a depth of 2–3 m is constant throughout the year irrespective of the season, and that constant temperature is called earth undistributed temperature (EUT) so this may be utilized for heat rejection of air in the summer for cooling purpose (heat source) and heat addition of air in the winter for the heating purpose. The current setup is developed to explore the possibility of Earth Air Tube Heat Exchanger (EATHE) installation for heating and cooling in this region to curb the demand for energy Consumption. In the present research, a setup of Earth Air Tube Heat Exchanger (EATHE) is modelled in solid work and computational fluid dynamics software is used to analyse the performance of EATHE. The results are calculated by considering prominently two PVC and copper pipe materials, measurement of atmospheric temperature and inside temperature of soil at a depth of 6 feet in summer is done. Calculations of the amount of heat transfer and work input to the blower were done by applying suitable thermodynamic formulae and boundary condition. It has been found that a significant temperature drop has been found with the present Earth Air Tube Heat Exchanger (EATHE) modelled and proved to be very effective and novel technique which utilized geothermal energy to our advantage.

Improving solution availability and temporal consistency of an optimal-estimation physical retrieval for ground-based thermodynamic boundary layer profiling

Abstract. Thermodynamic profiles in the atmospheric boundary layer can be retrieved from ground-based passive remote sensing instruments like infrared spectrometers and microwave radiometers with optimal-estimation physical retrievals. With a high temporal resolution on the order of minutes, these thermodynamic profiles are a powerful tool to study the evolution of the boundary layer and to evaluate numerical models. In this study, we describe three recent modifications to the Tropospheric Remotely Observed Profiling via Optimal Estimation (TROPoe) retrieval framework, which improve the availability of valid solutions for different atmospheric conditions and increase the temporal consistency of the retrieved profiles. We present methods to enhance the availability of valid solutions retrieved from infrared spectrometers by preventing overfitting and by adding information from an additional spectral band in high-moisture environments. We show that the characterization of the uncertainty of the input and the choice of spectral infrared bands are crucial for retrieval performance. Since each profile is retrieved independently from the previous one, the time series of the thermodynamic variables contain random uncorrelated noise, which may hinder the study of diurnal cycles and temporal tendencies. By including a previous retrieved profile as input to the retrieval, we increase the temporal consistency between subsequent profiles without suppressing real mesoscale atmospheric variability. We demonstrate that these modifications work well at midlatitudes, polar and tropical sites, and for retrievals based on infrared spectrometer and microwave radiometer measurements.

Diverse kinetic pathways in shock-compressed phase transitions of a metallic single crystal

Diverse kinetic pathways in shock-compressed phase transitions of a metallic single crystal

Analytical Determination of Nusselt Numbers for Convective Heat Transfer Coefficients in Channel Macroporous Absorbers.

This article introduces a novel analytical equation for computing the Nusselt number within the macroporous structures of channel absorbers utilized in high-temperature solar receivers. The equation incorporates heat and mass transfer processes occurring within boundary layers as fluid flows through complex-shaped macroporous absorber channels. The importance of accounting for the length of the thermodynamic boundary layer within channel-type macroporous media when calculating heat transfer coefficients using the Nusselt equation is demonstrated. By incorporating proposed indicators of porosity and flow characteristics, this method significantly enhances the accuracy of heat transfer coefficient calculations for such media. Discrepancies observed in existing calculation relationships and experiments are attributed to the omission of certain proposed values in the Nusselt number for macroporous media. To address this, empirical coefficients for the Nusselt number are derived using statistical methods. The resulting semi-empirical equation is applied to macroporous absorbers in solar receivers. The findings enable more accurate predictions of future absorber characteristics, enhancing their efficiency. The derived equation is successfully validated against numerical data across various geometric structures of absorbers in concentrated solar power plants.

Predicting Thermochemical Equilibria with Interacting Defects: Sr1−xCexMnO3−δ Alloys for Water Splitting

Solar thermochemical hydrogen is one of the few potential routes towards direct fuel production from renewable energy sources, but the thermodynamic boundary conditions for efficient and economic energy conversion are challenging. Success or failure of a given oxide working material depends on the subtle balance between enthalpy and entropy contributions in the redox processes. Developing a mechanistic understanding of the behavior of materials on the basis of atomistic models and first-principles calculations is an important part of advancing the technology. One challenge is to quantitatively predict thermochemical equilibria at high concentrations when the redox-active defects start to interact with each other, thereby impeding the formation of additional defects. This problem is of more general importance to applications that rely on high levels of off-stoichiometry or doping, including, for example, batteries, thermoelectrics, and ceramic fuel cells. To account for such repulsive defect interactions, we introduce a statistical mechanics approach, defining an expression for the free energy of defect interaction based on limited sampling of defect configurations in density functional theory supercell calculations. The parameterization of this energy contribution as a function of defect concentration and temperature allows on-the-fly simulation of thermochemical equilibria. The approach consistently incorporates finite temperature effects by including the leading contributions to the temperature-dependent free energy for the case at hand, i.e., the ideal gas and configurational enthalpies and entropies. We demonstrate the capability and utility of the approach by simulating the water splitting redox processes for Sr1−xCexMnO3−δ alloys. Published by the American Physical Society 2024

Temperature effects on noise radiated by concrete railway structures

Temperature effects on noise radiated by concrete railway structures

Linear modeling analysis of the heat balance of the transmission line in high frequency critical ice melting state

Abstract The icing of transmission lines can cause many problems such as increased line load, unbalanced tension, and galloping, posing a serious threat to the reliable operation of the power system. Therefore, linear modeling analysis of the heat balance under a high-frequency critical ice melting state of transmission lines is studied. The thermal conduction states of melting, heating, twisting, rotating melting, and ice layer detachment of ice melting conductors are analyzed. Based on the heat conduction process of thermal melting of ice on transmission lines, a simplified calculation formula for thermal melting ice time is derived to calculate times for heating, ice layer torsion, and air gap increase. At the same time, based on the law of conservation of energy, thermodynamic boundary conditions for iced conductors were established and corresponding physical models were constructed. Based on this model, we conduct a linear modeling of the heat balance in the melting state in order to provide a more accurate prediction of temperature distribution. The experimental results show that there is a negative correlation between environmental temperature and critical melting current, and the melting time decreases with the increase of environmental temperature.

Investigation of non-ideal effects in compressible boundary layers of dense vapors through direct numerical simulations

In this work, we present an investigation about the sources of dissipation in adiabatic boundary layers of non-ideal compressible fluid flows. Direct numerical simulations (DNS) of transitional, zero-pressure gradient boundary layer flows are performed for two fluids characterized by different complexity of the fluid molecules, namely, “air” and siloxane MM. Different sets of thermodynamic free-stream boundary conditions are selected to evaluate the influence of the fluid state on both the frictional loss and the dissipation mechanisms. The thermophysical properties of siloxane MM are calculated with a state-of-the-art equation of state. Results show that the dissipation due to both time-mean strain field, irreversible heat transfer, and turbulent dissipation differs significantly depending on both the molecular complexity of the fluid and its thermodynamic state. The dissipation coefficient calculated from the DNS results is then compared against the one obtained using a reduced-order model (ROM), which solves the two-dimensional boundary layer flow equations for an arbitrary fluid [M. Pini and C. De Servi, “Entropy generation in laminar boundary layers of non-ideal fluid flows,” in 2nd International Seminar on Non-Ideal Compressible Fluid Dynamics for Propulsion and Power (Springer, 2020), pp. 104–117]. Results from both the DNS and the ROM show that low values of the overall dissipation are observed in the case of fluids made of simple molecules, e.g., air, and if the fluid is at a thermodynamic state in the proximity of that of the vapor–liquid critical point.

Effect of microwave post-process heat treatment on the microstructure of wire-arc additively manufactured Mg alloy

Effect of microwave post-process heat treatment on the microstructure of wire-arc additively manufactured Mg alloy

Physical Phenomena Governing Mineral Morphogenesis in Molluscan Nacre.

Mollusks, as well as many other living organisms, have the ability to shape mineral crystals into unconventional morphologies and to assemble them into complex functional mineral-organic structures, an observation that inspired tremendous research efforts in scientific and technological domains. Despite these, a biochemical toolkit that accounts for the formation of the vast variety of the observed mineral morphologies cannot be identified yet. Herein, phase-field modeling of molluscan nacre formation, an intensively studied biomineralization process, is used to identify key physical parameters that govern mineral morphogenesis. Manipulating such parameters, various nacre properties ranging from the morphology of a single mineral building block to that of the entire nacreous assembly are reproduced. The results support the hypothesis that the control over mineral morphogenesis in mineralized tissues happens via regulating the physico-chemical environment, in which biomineralization occurs: the organic content manipulates the geometric and thermodynamic boundary conditions, which in turn, determine the process of growth and the form of the biomineral phase. The approach developed here has the potential of providing explicit guidelines for the morphogenetic control of synthetically formed composite materials.

Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions

Article Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions Jian Li 1, Lulu Li 1, Rujie Xiao 1, Yuanfei Liang 1, Shuyi Qiu 2, and Xuesong Li 2,* 1 SAIC GM Wuling Automobile Co., Ltd., 18 Hexi Rd, Liunan District, Liuzhou 545001, China 2 School of Mechanical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China * Correspondence: xuesonl@sjtu.edu.cn Received: 12 June 2023 Accepted: 9 August 2023 Published: 28 August 2023 Abstract: Gasoline direct injection (GDI) is the most common and advanced fuel supply strategy for gasoline engines. The fuel atomization quality and fuel/air mix degree determine the subsequent combustion efficiency and emissions. However, the engine works in complex conditions which have numerous thermodynamic boundary conditions, and the characteristics of fuel atomization also change accordingly. It is necessary to clarify the influence of various thermodynamic conditions on the GDI spray. In this work, three different types of optics diagnostic methods were utilized to capture the macroscopic and microscopic characteristics of a commercial GDI injector spray under various thermodynamic boundary conditions. Specifically, Mie-scattering photography was employed to get the macroscopic parameters; planar Mie-scattering photography was utilized to get the spray pattern; phase Doppler interferometry (PDI) was used to get the microscopic characteristic, i.e., the droplet size distributions. It is found from this study that higher injection pressure, lower ambient pressure, and lower ambient temperature would lead to longer penetration and larger plume width. Lower ambient pressure and higher ambient temperature would cause a smaller spray pattern. Higher injection pressure, lower ambient pressure, and higher ambient temperature would result in smaller droplet sizes.

A four-parameter generalized van der Waals equation of state: theoretical determination of thermodynamic stability boundary and vapor–liquid equilibrium of vanadium, niobium and tantalum

ABSTRACT A new four-parameter generalized van der Waals equation of state is proposed. The criteria for the applicability of the proposed equation of state in describing the thermodynamic properties of substances have been formulated. The generalized van der Waals equation of state is found to be applicable to vanadium, niobium and tantalum. To validate the generalized van der Waals equation of state, the spinodal, ideal tensile strength, thermodynamic limit of superheat and binodal of vanadium, niobium and tantalum have been determined. The obtained results agree with that of Filippov correlation and other equations of state. Using the obtained spinodal, the binodal of vanadium, niobium and tantalum has been determined.

Nanoprecipitation through solvent-shifting using rapid mixing: Dispelling the Ouzo boundary to reach large solute concentrations

The addition of a non-solvent to a solute in good solvent solution leads to nanoprecipitation, which is the spontaneous formation of nanodomains. Yet, increasing solute concentration usually leads to the formation of macrodomains that quickly separate into a bulk phase, which is a severe process limitation. The corresponding concentration threshold, often termed as the Ouzo boundary, remains a mystery that could find its origin in the complex interplay between nanoprecipitation and mixing. We performed a systematic investigation of nanoprecipitation thermodynamics and kinetics as well as its interplay with mixing hydrodynamics for the hexadecane-acetone-water system, in the presence of the non-ionic C16EO8 surfactant. The binodal curve and its underlying tie-lines were obtained using Raman spectroscopy, allowing the computation of the spinodal curve. Kinetics were probed using a continuous flow setup that combines two sequential rapid mixers. The impact of mixing efficiency was probed systematically by varying the oil concentration for respectively slow and rapid mixing, while the uncoupling from mixing and nanoprecipitation was quantified by modifying systematically the flow rate in a continuous flow approach. We elucidate the nature of the Ouzo boundary that marks the maximal solute concentration leading to nanoobjects. Rather than a thermodynamic boundary, as evidenced by its uncorrelation to the spinodal curve, it results from the coupling of nanoprecipitation and mixing when both processes occur within the same time range, leading to heterogeneous conditions and the escape of some objects to the macroscale. Increasing the solute concentration speeds up nanoprecipitation and thus requires increasingly faster mixing times to uncouple both processes. Accordingly, if the mixing efficiency is large enough, it is possible to dispel the Ouzo boundary and reach very large solute concentrations. Implementing rapid mixing strategies in continuous flow approaches is thus the solution to overcome the most stringent condition of nanoprecipitation and open the way to scale-up, while also providing efficient means to probe its fast mechanism. Overall, the simultaneous control of hydrodynamics and physical chemistry is thus key to boost up the Ouzo effect.

A Rapid, Open-Source CCT Predictor for Low-Alloy Steels, and Its Application to Compositionally Heterogeneous Material

The ability to predict transformation behaviour during steel processing, such as primary heat treatments or welding, is extremely beneficial for tailoring microstructures and properties to a desired application. In this work, a model for predicting the continuous cooling transformation (CCT) behaviour of low-alloy steels is developed, using semi-empirical expressions for isothermal transformation behaviour. Coupling these expressions with Scheil’s additivity rule for converting isothermal to non-isothermal behaviour, continuous cooling behaviour can be predicted. The proposed model adds novel modifications to the Li model in order to improve CCT predictions through the addition of a carbon-partitioning model, thermodynamic boundary conditions, and a Koistinen–Marburger expression for martensitic behaviour. These modifications expanded predictions to include characteristic CCT behaviour, such as transformation suppression, and an estimation of the final constituent fractions. The proposed model has been shown to improve CCT predictions for EN3B, EN8, and SA-540 B24 steels by better reflecting experimental measurements. The proposed model was also adapted into a more complex simulation that considers the chemical heterogeneity of the examined SA-540 material, showing a further improvement to CCT predictions and demonstrating the versatility of the model. The model is rapid and open source.

Simulation Study on Sunshine Temperature Field of a Concrete Box Girder of the Cable-Stayed Bridge

This paper investigates the distribution of the sunshine temperature field in bridge structures. To implement thermodynamic boundary conditions on the structure under the influence of sunshine, this study utilized the FILM and DFLUX subroutines provided by ABAQUS. Based on this method, the sunshine temperature field of the concrete box girder of a cable-stayed bridge was analyzed. The results showed that the simulated temperature values were in good agreement with the measured values. The temperature difference between the internal and external surfaces of the box girder under the influence of sunshine was significant, with the maximum negative temperature difference appearing around 6:00 a.m. and the maximum positive temperature difference appearing around 2:00 p.m. The temperature gradient of the box girder section calculated by the method presented a C-shaped distribution pattern, which differs from the double-line distribution pattern specified in the current “General Specifications for Design of Highway Bridges and Culverts” in China (JTG D60-2015). Furthermore, a sensitivity analysis of thermal parameters using the proposed simulation method for the sunshine temperature field of the concrete box girder was conducted, and the results indicated that the solar radiation absorption coefficient had a significant impact on the temperature field. A 30% increase or decrease in the solar radiation absorption coefficient caused the maximum temperature change on the surface of the structure to exceed 10 °C. This paper provides an accurate simulation of the sunshine temperature field of the concrete box girder of a cable-stayed bridge, and the research results are significant for controlling bridge alignment and stress state during the construction period, ensuring the reasonable initial operating state of the bridge, and enhancing the sustainability of the structure.

Neural network approach to response surface development for reaction model optimization and uncertainty minimization

Neural network approach to response surface development for reaction model optimization and uncertainty minimization

Design, optimization and thermodynamic analysis of SCO2 Brayton cycle system for FHR

Design, optimization and thermodynamic analysis of SCO2 Brayton cycle system for FHR

Impact of thermodynamic hypotheses on the calculation of the quantity of CO2 stored in a saline aquifer

The aim of this paper is to study the impact of thermodynamics models on the CO2 storage capacity of an aquifer, by using modelling and simulation of transport phenomena in porous media. The aquifer is represented here by a simplified three phase isothermal non-reacting medium composed by an inert solid phase and two binary (CO2 and H2O) fluid phases. The mathematical description is classically developed by the volume averaging method. For each phase, the conservation equations of mass, momentum and energy alongside thermodynamic laws and boundary conditions are first written. They are then integrated over a representative elementary volume in order to establish the description at the local scale. In a thermodynamic point of view, two kinds of models have been implemented and compared. The first one assumes that the gas and liquid phases are ideal. On the contrary, in the second approach, non-ideal thermodynamics is taken into account by calculating an activity coefficient (γ-φ approach) for the liquid phase and a fugacity coefficient (PengRobinson approach) for the gas phase. Results show, among other things, that the amount of CO2 dissolved in the liquid phase is significantly reduced with the non-ideal approach compared to the ideal case. These results highlight the interest of considering non-ideal phases in more complex models.

Pre-ignition phenomena in the tension field between operating agents and thermodynamic boundary conditions

Against the background of EU legislation with regard to CO2 emissions, a development trend towards higher geometric compression is emerging for gasoline engines. In principle, this leads – especially in combination with high mean pressure at low engine speed – to a higher pre-ignition tendency, well known as low speed pre-ignition (LSPI). The worldwide use of engine families with different fuel and oil quality represents an additional challenge, which has to be ensured within the scope of series development. IAV has extensive expertise and methodical approaches to minimize the risk of pre-ignition starting in the preliminary development through to series application and to avoid engine damage in the field. The definition and phenomenology of pre-ignition are presented. The presentation highlighted thermodynamic aspects as well as influences from operating agents and engine design. By using the IAV enthalpy approach, it is possible to evaluate designed engines objectively. This knowledge can also be used in the development of new engines concepts. Finally, a test method is presented which is used for the final assurance of the operational stability even in the case of stochastically occurring pre-ignition.

TWO-COMPONENT STATISTICAL MODEL OF A NUCLEAR FIREBALL IN THE COOLING STAGE (FREEZEOUT)

The saddle point method is applied to the statistical integral of the Grand Canonical Ensemble for the cases of one-component and two-component van der Waals gas. This made it possible to obtain the state equation and corrections to the pressure and density of the final statistical system. These contributions, taking into account the realistic effective potential, make it possible to take into account the finite dimensions of the system and, as expected, can be used, in particular, in the case of a nuclear fireball that occurs in high-energy nucleus-nucleus collisions. The corrections depending on the size of the system were compared with the corresponding fluctuations. These corrections become insignificant at the thermodynamic boundary, where, according to statistical physics, the difference between the observed thermodynamic quantities obtained in different statistical ensembles disappears. Taking into account modern estimates of the sizes of mesons and nucleons, as well as realistic estimates for the potentials of their effective interactions, formulas for pressure with a transparent nonrelativistic constraint are obtained. It is expected that they can be used to analyze experimental data on the quantitative characteristics of the yield of particles of various types in the final state from the final stages of the freezeout and to determine the critical parameters of the system in high-energy nucleus-nucleus collisions.