Adiabatic Conditions Research Articles

Application of a Numerical Simulation to the Estimation of Wind Loads on Photovoltaic Panels Installed Parallel to Sloped Roofs of Residential Houses

Many residential houses with sloped roofs are equipped with photovoltaic (PV) systems. In Japan, PV systems are generally designed based on JIS C 8955, which specifies wind force coefficients for designing PV panels. However, no specification is provided to the PV panels installed near the roof edges where high suctions are induced. When installing PV panels in such high-suction zones, we need to evaluate the wind loads on the PV panels appropriately, usually by performing a wind tunnel experiment. However, it is difficult to make wind tunnel models of PV panels with the same geometric scale as that for the building, e.g., 1/100, because the thickness of PV panels and the distance between PV panels and a roof are both several centimeters. Therefore, in the present paper a numerical simulation is applied to the estimation of pressures in the space between the lower surface of PV panels and the roof surface, called “layer pressures”, using the unsteady Bernoulli equation and the time histories of external pressure coefficients obtained from a wind tunnel experiment. An assumption of the weak compressibility of the air and an adiabatic condition is made for predicting the layer pressures from the flow speed through the gaps. The simulation method is validated by a wind tunnel experiment using a model of square-roof building.

Green Function Treatment of the Barocaloric Effect in Mn3GaN

Following our previous work on the magnetocaloric compounds FeMnAsxP[Formula: see text], we obtain thermomagnetic properties for the barocaloric antiperovskite Mn3GaN, which has been investigated in recent years in view of its thermal response under pressure cycling. Its structure displays canting of spins and a volume dilation in the antiferromagnetic (AFM) transition, related to magnetoelastic coupling. A random-phase-approximation (RPA) Green function theoretical treatment is applied to a two-exchange parameter Heisenberg model, and the canting of the spins orientation in the (111) planes of the structure is considered in the model. The observed first-order AFM phase transitions are reproduced by the introduction of a biquadratic spin term in the Hamiltonian, coupled to the volume dilation in the transition. The model is able to predict a greater stability for the canted spin structure as compared with conventional AFM, if the magnitudes of Mn magnetic moments in these structures are taken from the literature. The calculations of quantities of interest for barocaloric applications reproduce quite well the available data on temperature changes and latent heat under pressure cycling, at adiabatic and isothermal conditions, respectively.

Investigation of pyrolysis kinetics, mechanism and thermal stability of tert-butyl peroxy-2-ethyl hexanoate

Tert-butyl peroxy-2-ethyl hexanoate (TBPO), an important organic peroxide, is widely used as a polymerization initiator and curing agent in the chemical industry. Its thermal instability due to the presence of the peroxide bond may incur a decomposition reaction and cause further thermal runaway. The pyrolysis characteristics of TBPO were assessed by three advanced calorimetry techniques. The apparent activation energies under dynamic and adiabatic conditions were calculated, and critical thermal safety parameters were determined. The specific distribution of the pyrolysis products of TBPO were identified by combining thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) and gas chromatography/mass spectrometry (GC/MS), and the most likely pyrolysis mechanism was proposed. In addition, density functional theory (DFT) was used to evaluate the activation free energy and activation free enthalpy for each step of the pyrolysis process at the B3LYP/def2-TZVP calculation level, and kinetic calculations at different temperatures were performed by using the conventional transition state theory. The theoretical simulation results were found to be in good agreement with the experimental data. The findings of this study can provide a favorable reference to forestall thermal safety accidents in the actual storage, transportation, and operation of TBPO.

Limits of the adiabaticity assumption and conditions for improving laser focusing of atomic matter wave

AbstractThe adiabaticity assumption (AA) and the resulting concept of optical potential in the context of atom focusing with lasers were examined numerically for various experimentally controllable laser parameters. The Schrödinger equations for the atomic center‐of‐mass dynamics in a laser field were calculated using with or without the AA, and the results were compared. The validity of the AA was tested over a wide range of the Rabi frequency to detuning ratios and the optical potential depths. From the analysis, several specific guidelines were provided on choosing laser parameters that sustain the validity of the AA and improve atom focusing outcomes.

Pyrite effects on the oxidation of in situ crude oil

As an enhanced oil recovery method, the air injection process (AIP) has been applied for decades. However, deviations are still being identified between laboratory tests and field applications. One possible reason for such deviations is the formation minerals of the crude oil reservoir. Some natural minerals are beneficial for the oxidation of hydrocarbons and may affect the AIP behavior. Herein, the accelerated-rate calorimetry (ARC) was adopted to study the crude oil oxidation when containing pyrite or iron oxide under adiabatic and high-pressure conditions. The temperature profiles and detailed kinetic data from the ARC tests were compared for the crude oil oxidation traits, with different ground mineral particles presented in the ARC vessel, to figure out the catalytic effects of iron minerals on the crude oil oxidation. Results indicate that iron oxide showed a catalytic effect on the high-temperature oxidation period of crude oil, whereas the pyrite could not generate enough iron oxides to catalyze crude oil oxidation under limited oxygen conditions. During the test, since pyrite oxidizes before the crude oil, the enthalpy from pyrite oxidation could benefit the onset of crude oil oxidation. Hence, this study could be beneficial for future AIP engineering design and AIP candidate reservoir screening.

Linear stability analysis of hypersonic boundary layers computed by a kinetic approach: a semi-infinite flat plate at $$\varvec{4.5\le \mathrm{M}_\infty \le 9}$$

Linear stability analysis is performed using a combination of two-dimensional Direct Simulation Monte Carlo (DSMC) method for the computation of the basic state and solution of the pertinent eigenvalue problem, as applied to the canonical boundary layer on a semi-infinite flat plate. Three different gases are monitored, namely nitrogen, argon and air, the latter as a mixture of 79\% Nitrogen and 21\% Oxygen at a range of free-stream Mach numbers corresponding to flight at an altitude of 55km. A neural network has been utilised to predict and smooth the raw DSMC data; the steady laminar profiles obtained are in very good agreement with those computed by (self-similar) boundary layer theory, under isothermal or adiabatic wall conditions, subject to the appropriate slip corrections computed in the DSMC method. The leading eigenmode results pertaining to the unsmoothed DSMC profiles are compared against those of the classic boundary layer theory. Small quantitative, but no significant qualitative differences between the results of the two classes of steady base flows have been found at all parameters examined. The frequencies of the leading eigenmodes at all conditions examined are practically identical, while perturbations corresponding to the DSMC profiles are found to be systematically more damped than their counterparts arising in the boundary layer at the conditions examined, when the correct velocity slip and temperature jump boundary conditions are imposed in the base flow profiles; by contrast, when the classic no-slip boundary conditions are used, less damped/more unstable profiles are obtained, which would lead the flow to earlier transition. On the other hand, the DSMC profiles smoothed by the neural network are marginally more stable than their unsmoothed counterparts.

Pressure-Tight and Non-stiff Volume Penalization for Compressible Flows

Embedding geometries in structured grids allows a simple treatment of complex objects in fluid simulations. Various methods for embedding geometries are available. The commonly used Brinkman-volume-penalization models geometries as porous media, and approximates a solid object in the limit of vanishing porosity. In its simplest form, the momentum equations are augmented by a term penalizing the fluid velocity, yielding good results in many applications. However, it induces numerical stiffness, especially if high-pressure gradients need to be balanced. Here, we focus on the effect of the reduced effective volume (commonly called porosity) of the porous medium. An approach is derived, which allows reducing the flux through objects to practically zero with little increase of numerical stiffness. Also, non-slip boundary conditions and adiabatic boundary conditions are easily constructed. The porosity terms allow keeping the skew symmetry of the underlying numerical scheme, by which the numerical stability is improved. Furthermore, very good conservation of mass and energy in the non-penalized domain can be achieved, for which the boundary smoothing introduces a small ambiguity in its definition. The scheme is tested for acoustic scenarios, for near incompressible and strongly compressible flows.

Experimental and theoretical study on water vapor isothermal adsorption-desorption characteristics of desiccant coated adsorber

Open air channels coated with porous desiccant are widely applied in solid desiccant cooling systems. In this study, the isothermal adsorption and desorption characteristics of silica gel coated single-channel adsorber were investigated. A modified LDF model considering air- and solid-side resistances was derived to evaluate the kinetics and estimate the total mass transfer rate for numerical modelling. Results show that the modified LDF model can well describe the dynamic behavior of isothermal dehumidification. A new numerical model predicting the mass transfer characteristics of dehumidification process was proposed and strictly validated. Parametric studies reveal that the moisture transfer strongly depends on kinetic constants, isotherm shapes and thermal boundaries. The higher kinetic constants, the larger adsorption/desorption rate and the faster equilibrium. It was found that neither too high nor too low shape factor R are conducive to improve dehumidification capacity. The isotherm with R=0.1 is considered as the optimum isotherm shape. With the transition of thermal boundary from ideal isothermal to adiabatic condition, the mass transfer performance decreases. The peak value of transient mass transfer rate of adsorption process under ideal isothermal boundary is almost twice and 2.6 times higher than these of the third type thermal boundary and adiabatic boundary, respectively.

Vibrational-Specific Model of Simultaneous and Relaxation Under Postshock Conditions

The present paper discusses the development of an aerothermochemistry model that can be efficiently coupled with fluid dynamics simulations and retains the accuracy of the quantum-mechanical and molecular dynamic principles from which it is derived. The present model allows simulations of thermochemical nonequilibrium in nitrogen without relying on the existence of a vibrational temperature. A series of verification tests suggest that the vibrational-specific master equation model is sufficiently accurate and computationally efficient when applied to the modeling of dissociating nitrogen flows under adiabatic conditions. Toward this end, a kinetic dataset describing vibrational energy transfer and dissociation in and collisions is obtained on a high-fidelity potential energy surface, and curve fit coefficients are reported. Validation against shock-tube data indicates that the inclusion of electronically excited and ionic species is potentially required when computing and comparing relaxation parameters with the experimental data derived from the radiative signatures of nitrogen shock flows.

Research on the decomposition kinetics and thermal hazards of aniline diazonium salt

Diazotization reaction, strong exothermic characteristics and thermal instability of diazonium salts make the production process high risk. To research thermal hazards of aniline diazonium salt, dynamic experiments are carried out by the differential scanning calorimeter (DSC) to obtain thermodynamic parameters. Moreover, the kinetic parameters are analyzed by Advanced Kinetics and Technology Solutions (AKTS) software. Finally, the GC-MS and UV spectrum are used to further study the decomposition mechanism of the aniline diazonium salt. The results indicate that aniline diazonium salt is very easy to decompose. When the heating rate is 2 K/min, the onset decomposition temperature is only 27.21 ℃ (Tonset). The apparent activation energy of the decomposition process calculated by Friedman and Ozawa methods are respectively 98-85 kJ/mol and 110-100 kJ/mol. Under the ideal adiabatic conditions (φ = 1), the initial temperatures of TMRad for 24 h is only 6.2 ℃ (TD24), which is predicted by the AKTS software. The decomposition process of aniline diazonium salt is inconsistent with a single reaction mechanism.

Unlocking the thermal safety evolution of lithium-ion batteries under shallow over-discharge

Shallow over-discharge has a significant impact on cell performance and thermal safety. This work comprehensively investigates the impact of shallow over-discharge on the heat generation upon discharging and thermal runaway behavior under adiabatic conditions, post-mortem characterization analysis is utilized to reveal the degradation mechanisms caused by shallow over-discharge. The solid electrolyte interface film decomposition and the copper plating are the primary degradation mechanisms during the shallow over-discharge process. Solid electrolyte interface film regeneration consumes active lithium and the electrolyte. The plated copper-containing substances tightly coating the secondary particles of the cathode severely hinders the intercalation of lithium ions. The shedding of the anode active materials causes the loss of the charge storage capability. These are the major causes for the cell capacity degradation. With the depth of over-discharge deepening, the severity of cell degradation increases, which makes the cell impedance increase. Therefore, as the depth of over-discharge deepens, the heat generation becomes more significant. Besides, the cell thermal stability decreases due to the reduced thermal stability of the regenerated solid electrolyte interface film. In addition, the maximum temperature of the over-discharged cell is lower than that of fresh cell, which is mainly caused by the loss of partial active materials.

A Novel Heat Generation Acquisition Method of Cylindrical Battery Based on Core and Surface Temperature Measurements

Abstract Heat generation measurements of the lithium-ion battery are crucial for the design of the battery thermal management system. Most previous works use the accelerating rate calorimeter (ARC) to test heat generation of batteries. However, utilizing ARC can only obtain heat generation of the battery operating under the adiabatic condition, deviating from common operation scenarios with heat dissipation. Besides, using ARC is difficult to measure heat generation of the high-rate operating battery because the battery temperature easily exceeds the maximum safety limit. To address these problems, we propose a novel method to obtain heat generation of cylindrical battery based on core and surface temperature measurements and select the 21700 cylindrical battery as the research object. Based on the method, total heat generation at 1 C discharge rate under the natural convection air cooling condition in the environmental chamber is about 3.2 kJ, and the average heat generation rate is about 0.9 W, while these two results measured by ARC are about 2.2 kJ and 0.6 W. This gap also reflects that different battery temperature histories have significant impacts on heat generation. In addition, using our approach, total heat generation at 2 C discharge rate measured in the environmental chamber is about 5.0 kJ, with the average heat generation rate being about 2.8 W. Heat generation results obtained by our method are approximate to the actual battery operation and have advantages in future applications.

ZrBDC-Based Functional Adsorbents for Small-Scale Methane Storage Systems

Metal-organic frameworks (MOF), potentially porous coordination structures, are envisioned for adsorption-based natural gas (ANG) storage, including mobile applications. The factors affecting the performance of the ANG system with a zirconium-based MOF with benzene dicarboxylic acid as a linker (ZrBDC) as an adsorbent were considered: textural properties of the adsorbent and thermal effect arising upon adsorption. The high-density ZrBDC-based pellets were prepared by mechanical compaction of the as-synthesized MOF powder at different pressures from 30 to 240 MPa at 298 K without a binder and mixed with polymer binders: polyvinyl alcohol (PVA) and carboxyl methylcellulose (CMC). The structural investigations revealed that the compaction of ZrBDC with PVA under 30 MPa was optimal to produce the ZrBDC-PVA adsorbent with more than a twofold increase in the packing density and the lowest degradation of the porous structure. The specific total and deliverable volumetric methane storage capacities of the ZrBDC-based adsorbents were evaluated from the experimental data on methane adsorption measured up to 10 MPa and within a temperature range from 253 to 333 K. It was measured experimentally that at 253 K, an 100 mL adsorption tank loaded with the ZrBDC-PVA pellets exhibited the deliverable methane storage capacity of 172 m3(NTP)/m3 when the pressure dropped from 10 to 0.1 MPa. The methane adsorption data for the ZrBDC powder and ZrBDC-PVA pellets were used to calculate the important thermodynamic characteristic of the ZrBDC/CH4 adsorption system—the differential molar isosteric heat of adsorption, which was used to evaluate the state thermodynamic functions: entropy, enthalpy, and heat capacity. The initial heats of methane adsorption in powdered ZrBDC evaluated from the experimental adsorption isosteres were found to be ~19.3 kJ/mol, and then these values in the ZrBDC/CH4 system decreased at different rates during adsorption. In contrast, the heat of methane adsorption onto the ZrBDC-PVA pellets increased from 19.4 kJ/mol to a maximum with a magnitude, width, and position depended on temperature, and then it fell. The behaviors of the thermodynamic state functions of the ZrBDC/CH4 adsorption system were interpreted as a variation in the state of adsorbed molecules determined by a ratio of CH4-CH4 and CH4-ZrBDC interactions. The heat of adsorption was used to calculate the temperature changes of the ANG systems loaded with ZrBDC powder and ZrBDC pellets during methane adsorption under adiabatic conditions; the maximum integrated heat of adsorption was found at 273 K. The maximum temperature changes of the ANG system with the ZrBDC materials during the adsorption (charging) process did not exceed 14 K that are much lower than those reported for the systems loaded with activated carbons. The results obtained are of direct relevance for designing the adsorption-based methane storage systems for the automotive industry, developing new gas-power robotics systems and uncrewed aerial vehicles.

Simulation of ion temperature gradient mode in Chinese First Quasi-axisymmetric Stellarator

The Chinese First Quasi-axisymmetric Stellarator (CFQS) is now the only quasi-axisymmetric stellarator under construction in the world. In this work, ion temperature gradient (ITG) mode in CFQS is studied by using gyrokinetic Vlasov code GKV. The basic characteristics of the eletrtostatic ITG are separately given under the adiabatic condition and the non-adiabatic condition. There is a critical temperature gradient for ITG. The growth rate of ITG is proportional to the temperature gradient. Furthermore, the growth rate depends on not only the absolute value of density gradient, but also the plus or minus sign of the density gradient. The negative density gradient can strongly suppress the ITG. The kinetic electron can destabilize the ITG and the electron temperature gradient can also destabilize the ITG. For electromagnetic condition, the ITG modes can be suppressed by the finite plasma beta, and then a transition from ITG to Alfvenic ion temperature gradient mode/kinetic ballooning mode (AITG/KBM) comes into being. The maximum growth rate of KBM is linearly proportional to density gradient and temperature gradient when both gradients are large.

Propagation characteristics of (2 + 1) dimensional dust acoustic solitary waves in hot dusty plasma

The propagation characteristics of (2 + 1) dimensional nonlinear dust acoustic solitary wave in an unmagnetized hot dusty plasma composed of dust particles, electrons and nonthermal ions are studied in the paper. Firstly, the Kadomtsev-Petviashvili (KP) equation, which is used to describe the (2 + 1) dimensional nonlinear dust acoustic solitary wave, is derived by the reduced perturbation method, and the phase diagram and the Sagdeev potential equation of the system are obtained by using the traveling wave solution method. Then, the effects of different parameters in the hot dusty plasma system on the nonlinear coefficient, dispersion coefficient of the KP equation, system phase diagrams, Sagdeev potential function and the solitary wave solution in isothermal and adiabatic states are discussed by using numerical simulation and analysis method of mathematical software. Finally, the results show that the mass of dust particles, temperature, number density and distribution state of electrons and nonthermal ions have important effects on the amplitude, width and waveform of the nonlinear dust acoustic solitary wave under isothermal and adiabatic conditions.

Diurnal Cycle of Heating and Water Vapor in the Metropolitan Area of Porto in Portugal

In this work, it is investigated the Urban Heat Island (UHI) using conservative thermodynamic variables observed by surface weather stations on the Metropolitan Area of Porto (Oporto) in Portugal, under adiabatic conditions at the surface. These conditions are usually present and associated with the development of a mixture layer into the diurnal Convective Boundary Layer (CBL), which residual layer in the late afternoon defines the initial state for the development of the nocturnal UHI. Both the spatial structure and temporal variation of potential temperature and specific humidity were considered, along the hours and days of the year, from a statistical point of view, resulting in hourly climatology. Details of the hourly evolution of the meteorological variables on the Oporto surface are presented and discussed. Results show a seasonal variation of the potential temperature up to 17°C throughout the year, which is associated with horizontal thermal gradients that can control and trigger mesoscale circulations such as sea-land, urban and valley-mountain breezes.

NUMERICAL STUDY OF FLOW AND HEAT TRANSFER CHARACTERISTICS IN SHELL-AND-PLATE HEAT EXCHANGERS

The shell-and-plate heat exchanger is a completely welded heat exchanger that combines the best features of a shell-and-tube heat exchanger with a plate heat exchanger. The flow between the circular corrugated plates behaves as a first expanding then converging flow, leading to the intricate nature of flow structures, flow resistance, and phase-change heat transfer. The present paper numerically investigates the flow behaviors and heat transfer characteristics in the channel between the circular corrugated plates of 0.2 m in diameter, 0.0022 in corrugation depth, and 75° in corrugation angle. In the simulation, the gas velocity ranges from 0.25-6.00 m/s while the liquid velocity from 0.01-0.20 m/s. The wall is set as adiabatic and constant temperature condition of 350 K, respectively. For the single-phase flow, a longitudinal spiral flow along the main flow direction is formed, and the local velocity at the edge of the circular plate is generally higher and more turbulent than that in the central area. Additionally, the increase of Reynolds number leads to a more significant pressure drop but an apparent heat transfer enhancement. Based on the analysis of the friction factor and Nusselt number with Reynolds number, the empirical correlations for predicting the flow resistance and heat transfer characteristics in the channel are proposed. For the two-phase flow, we employed the VOF model to investigate the distribution of the phases in the downward flows. Compared with the experimental data, the numerical results are demonstrated to provide an accurate analysis of the phases distribution, particularly in the cross section of the channel. Accordingly, the flow patterns in the downward two-phase flows are identified as bubbly flow, slug flow, film flow, and churn flow. Based on the variation of the averaged void fraction, the film flow can be identified as α > 0.8 while bubbly flow as α < 0.5. Additionally, the void fraction in the cross section of the flow channel along the flow direction is analyzed in detail. Since the effect of the expansion and contraction of structures will go away with an increase in the gas mass flow rate, it can be anticipated that the effect of uniform distribution is more prominent for slug flow and is negligible for film flow.

Modeling and Analysis of Heat Transfer and Fluid Flow Mechanisms in Nanofluid Filled Enclosures Irradiated from Below

Radiation driven transport mechanisms are ubiquitous in many natural flows and industrial processes. To mimic and to better understand these processes, recently, radiatively heated nanofluid filled enclosures have been extensively researched. The present work is essentially a determining step in quantifying and understanding the transport mechanisms involved in such enclosures. In particular, a two dimensional square nanofluid filled enclosure irradiated from the bottom has been investigated in laminar flow situation. Effects of nanofluid optical depth, inclination angle of the enclosure, incident flux, and boundary conditions (adiabatic and isothermal) have been investigated. Moreover, the temperature and flow fields have been carefully analyzed in the situation ranging from volumetric to mixed to surface absorption modes. Under adiabatic boundary conditions, steady state is unconditionally achieved irrespective of the incident flux magnitude (varied between 5Wm-2 to 50Wm-2), enclosure inclination angle (varied between 0 to 60 degrees) and mode of absorption (surface, mixed or volumetric). However, in case of isothermal boundaries; onset of natural convection and its transition into transient regime is significantly impacted by the mode of absorption and the enclosure inclination angle.

Numerical Study of Radiation and Fuel–Air Unmixedness on the Performance of a Dry Low NOx Combustor

Abstract The development of gas turbine combustors is expected to consider the effects of radiation heat transfer in modeling. However, this is not always the case in many studies that neglect this for adiabatic conditions. The effect of radiation is substantiated here, concerning the impact on the performance, mainly the emissions. Also, the fuel–air unmixedness (mixing quality) influenced by the combustor design and operational settings has been investigated with regard to the emissions. The work was conducted with a Mitsubishi-type dry low NOx combustor developed and validated against experimental data. This 3D computational fluid dynamics study was implemented using Reynolds-averaged Navier Stokes simulation and the radiative transfer equation model. It shows that NO, CO, and combustor outlet temperature reduce when the radiative effect is considered. The reductions are 17.6% and below 1% for the others, respectively. Thus, indicating a significant effect on NO. For unmixedness across the combustor in a non-reacting simulation, the mixing quality shows a direct relationship with the turbulence kinetic energy (TKE) in the reacting case. The most significant improvements in unmixedness are shown around the main burner. Also, the baseload shows better mixing, higher TKE, and lower emissions (particularly NO) at the combustor outlet, compared to part-load.

Application of the CALPHAD Approach to Adiabatic Conditions: Combustion Synthesis in the Ni-Al System

Application of the CALPHAD Approach to Adiabatic Conditions: Combustion Synthesis in the Ni-Al System