Evolution Of Average Temperature Research Articles

Exploring the impact of tube rotation on the melting performance of multi-tube latent heat storage systems: A numerical investigation

This study explores the impact of tube rotation on the melting performance of a multi-tube latent heat energy storage system through numerical analysis. The system involves a phase change material (PCM) contained within a tube, which absorbs heat from hot water flowing through a tube surrounding the PCM, as well as two tubes enveloped by the PCM. The investigation considers the angle between the line connecting the centers of the two inner tubes and the horizon (α = 0°, 45°, 90°, and 135°), along with the direction of rotation of inner tubes. Results are compared with data from scenarios involving only outer tube rotation and stationary systems. Temporal variations in temperature and liquid fraction contours, along with the temporal evolution of average temperature and average liquid fraction of PCM are presented. It was determined that for each α, the melting performance varied from best to worst across the system configurations as follows: the system with all three rotating tubes, the system with only the outer rotating tube, and the stationary system. The minimum time required to complete PCM melting for cases at α = 0°, 45°, 90°, and 135° is respectively 44.92 %, 42.11 %, 41.32 %, and 40.62 % less than that of the stationary system.

How to choose a model to address practical issues encountered during food transport in an insulated box equipped with phase change material

This article discusses the capabilities and the limitations of three validated models: lumped, zonal and Computational Fluid Dynamics (CFD), to solve several technical issues related to food transport in an insulated box with a Phase Change Material (PCM). The lumped model predicts the average temperature evolution and is suitable for investigating the effect of box design and operating conditions where the temperature heterogeneity is not the main concern. The zonal model depicts spatial temperature variations but requires some assumptions regarding airflow and heat transfer which are specific for a given product arrangement and PCM location. The CFD model gives the most extensive information on physical phenomena and temperature variations but involves a high computational cost that is inevitable. This study shows the possibility of combining these models with a quality model. Finally, the abilities/limitations of each model to solve certain practical issues are discussed.

Numerical and Experimental Analysis of the ZFC Heat Release from a YBCO Bulk and Validation of YBCO Thermal Parameters

This article presents results from a simple experimental methodology used to determine the amount of heat transferred from an yttrium barium copper oxide (YBCO) bulk to liquid nitrogen (LN2) and LN2 consumption during the process of zero-field cooling (ZFC). The thermal power can be determined from the YBCO bulk temperature variation, which is difficult to measure with accuracy. In this procedure, the thermal power from the YBCO bulk to LN2 is determined from the measured rate of LN2 evaporation, considering the LN2 latent heat. To reduce the influence of room temperature heating and make the LN2 mass variation depend as much as possible on the heat released from the YBCO bulk, a step transient from room temperature into the LN2 is performed. The precision of results is determined from the rate of LN2 evaporation due to room temperature heating with the bulk already cooled by ZFC. The temperature evolution at the bulk lateral surface where the heat transfer is higher is also measured. The results from experimental measurements are compared with 3D finite element analysis (FEA) numerical results. The obtained evolutions of the temperature and thermal power from the YBCO bulk are used to validate YBCO thermal parameters, such as thermal conductivity and specific heat capacity at constant pressure. The YBCO bulk equivalent heat capacity and thermal resistance are determined by analyzing the equivalent first-order thermal lumped parameter circuit based on the obtained evolutions in time of the YBCO temperature and heat transferred to the LN2. The characteristics of dependence of the YBCO thermal resistance and heat capacity with temperature are obtained by correlating their time evolutions with the bulk average temperature evolution in time. The YBCO-specific heat capacity at constant pressure is then calculated by dividing the obtained bulk heat capacity by the bulk mass. The YBCO thermal conductivity is calculated from the obtained thermal resistance considering an equivalent bulk section and length toward the main direction of heat flux.

Microwave pretreatment of biomass for conversion of lignocellulosic materials into renewable biofuels

For the conversion of lignocellulosic material into renewable biofuels the microwave pretreatment of raw material is a new and promising technology. This work presents a numerical simulation of microwave heating of materials derived from sugar cane, african palm and green algae in microwave domestic oven. The power absorption of biomasses is studied in cylindrical and spherical shapes, with volumes varying from 10−5 m3 to 100 × 10−5 m3, as function of humidity (from 20% to 80%). Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation when the humidity is varied. Penetration depth varied from 2 × 10−2 to 10 m and tanδ from 2 × 10−3 to 7 × 10−1 as function of humidity. Plots of electric field and temperature distribution inside the oven were done for sugar cane, palm oil and green algae for cylindrical and spherical samples for 30% and 65% of humidity in the samples. The coefficient of variation (COV) varied between 0.05 and 0.18. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (5K<ΔT<75K) and evolution of average temperature T‾ (300K<T‾<370K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient, that describes the usability of a specific lignocellulosic material in industry, varied between 0.3 and 10.0, was calculated for the biomasses shapes and sizes as function of power and humidity.

A pilot project of TESS equipped with two models of encapsulation for nano-enhanced organic PCMs

ABSTRACT The unique thermal energy storage system (TESS) as an auxiliary system of solar water heater has a critical part to demonstration in preserving and efficiently utilizing energy, resolving demand-supply mismatches, and boosting the efficiency of energy systems. In this research, a suitable Nano enhanced-Composite Phase Change Material (NCPCM) was prepared to utilize in two model of metal cylinders. First of all, an experimental test for determination of melting point has been investigated by temperature variation test (TVT) method for NCPCM based on paraffin component. Then, two nanomaterial types (TiO2 and CuO) mixed at 50%/50% with two concentrations (0.6% and 0.12%) were dispersed with slack paraffin to provide a total of four experiments to compare the average temperature evolution and exergy efficiency. A theoretical framework for exergy analysis give away that use of nano composites in PCMs will improve efficiency rather than a single nanomaterial. However, to assess capability of this system to integrate with solar water heater, if there is no solar radiation limitation, NCPCM with 1.2% wt. will be a better choice with higher cylinders diameter (HD-Cylinders). Neverthless, for climates with limited time in storage energy, NCPCM with 1.2% wt. and lower cylinders diameter (LD-Cylinders) is our best suggestion for maximum efficiency that can be used during the peak solar energy period. Therefore, by considering NCPCM and integrating this novel study with solar technologies as a reliable heat source, outline is an excellent way for saving energy consumption in buildings at any remote area.

Numerical analysis of heat and mass transfer during hydrogen absorption in metal hydride beds with a novel peridynamic model

Numerical modelling and study of metal hydride bed with heat and mass transfer is a key to identify and predict the state of the storage device during absorption and desorption process. It is a great challenge to numerically study this problem considering cracks and volumetric expansion for conventional approaches due their limitations in treating discontinuities and large deformations. To effectively predict the hydrogen charging performance with the influences of cracks and volumetric expansion, a novel peridynamic (PD) model considering hydrogen absorption was proposed, which has not been used in most existing studies. The developed PD model was applied to simulate metal hydride reaction including depleted uranium (DU) and zirconium cobalt (ZrCo) in a thin-layer bed. The simulation results agreed well with both existing numerical solutions and experimental observations. The cracks were introduced to identify their influences on the performance of hydrogen absorption in a DU bed as a prototype. It is demonstrated that crack length and location had a significant influence on the absorption rate and average temperature evolution. With the increase in the crack length, the hydrogen absorption efficiency of the metal hydride bed (MHB) decreases dramatically due to the high bed temperature. The crack approaching the cooling boundary would greatly affect the temperature evolution, which causes the average H/M value to reach saturation later. Finally, the effects of the volumetric expansion were taken into consideration in the present PD model. Unlike ZrCo, the hydrogen kinetics performance would be overrated due to the neglection of the volumetric expansion in a DU bed.

Reduced model of plasma evolution in hydrogen discharge capillary plasmas.

A model describing the evolution of the average plasma temperature inside a discharge capillary device including Ohmic heating, heat loss to the capillary wall, and ionization and recombination effects is developed. Key to this approach is an analytic quasistatic description of the radial temperature variation which, under local thermal equilibrium conditions, allows the radial behavior of both the plasma temperature and the electron density to be specified directly from the average temperature evolution. In this way, the standard set of coupled partial differential equations for magnetohydrodynamic (MHD) simulations is replaced by a single ordinary differential equation, with a corresponding gain in simplicity and computational efficiency. The on-axis plasma temperature and electron density calculations are benchmarked against existing one-dimensional MHD simulations for hydrogen plasmas under a range of discharge conditions and initial gas pressures, and good agreement is demonstrated. The success of this simple model indicates that it can serve as a quick and easy tool for evaluating the plasma conditions in discharge capillary devices, particularly for computationally expensive applications such as simulating long-term plasma evolution, performing detailed input parameter scans, or for optimization using machine-learning techniques.

Heating of biomass in microwave household oven - A numerical study

To improve the efficiency of biomass heating by microwaves, this paper studied numerically the heating of wood, sugar cane bagasse, orange peel and palm oil in microwave domestic oven. The study focused in the evaluation of power absorption capability of the biomasses in cylindrical and sphere shapes. The Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation. Quantitatively, the power absorption capability and temperature distribution uniformity were, respectively, described by power absorption efficiency (PAE) (0.07 < PAE < 0.87) and the coefficient of variation (COV), varying between 0.01 and 0.14. Two dimensional plots of temperature evolution as function of time was used to determine the locations of the resonating peaks as function of peak number. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (1K<ΔT<102K) and evolution of average temperature T¯ (298K<T¯<343K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient (CEC), that describes the usability of a specific sample in industry, varied between 1 and 14, was calculated for the biomasses and shapes.

New approach for the optimization of pass-schedules in open-die forging

Open-die forging is an incremental forming process, which is mainly used for the production of large parts with high requirements regarding the mechanical properties and reliability of the forged parts. Finite element analysis (FEA) is able to simulate open die forging sequences. It is therefore very suitable to confirm, whether a selected schedule will be successful in terms of reaching the desired geometry and internal product quality. However, it is comparably slow and therefore not suitable for early process design, when out of an almost infinite number of potential sequences of strokes, an appropriate pass schedule needs to be designed. This is today usually achieved by pass schedule planning software, which takes into account volume constancy, empirical spread behavior and average temperature evolution. However, they do not account for product quality characteristics like microstructure and voids closure. In this paper recently developed fast models, which are able to calculate the temperature, equivalent strain and microstructure evolution along the core fibre of a forged workpiece are coupled with an optimization algorithm to allow automatic pass schedule layout and optimization. Different cost functions are evaluated regarding their impact on the resulting properties of the workpiece. The results indicate that for an overall optimization of open-die forging processes different phenomena and influencing parameters need to be considered, since all of these parameters have a significant influence on the resulting properties such as equivalent strain, temperature and grain size of the ingot.

Experimental Investigation on Rate Dependence of Thermomechanical Response in Superelastic NiTi Shape Memory Alloy

In this paper, we focus on thermomechanical response of superelastic NiTi SMA at different strain rates under uniaxial loading. In situ digital image correlation method is applied to measure the local strain of the specimen. The evolution of the transformation bands is tracked by a CCD camera and the temperature field is recorded by an infrared camera. We show that there exists a strong link among strain rate, average temperature evolution, and the mechanical behavior of the material. It is also observed in the experiments that with the increase in strain rate, the deformation modes of the material transform from localization modes to homogenous modes.

VERIFICATION OF CORONAL LOOP DIAGNOSTICS USING REALISTIC THREE-DIMENSIONAL HYDRODYNAMIC MODELS

Many different techniques have been used to characterize the plasma in the solar corona: density-sensitive spectral line ratios are used to infer the density, the evolution of coronal structures in different passbands is used to infer the temperature evolution, and the simultaneous intensities measured in multiple passbands are used to determine the emission measure distributions. All these analysis techniques assume that the intensity of the structures can be isolated through background subtraction. In this paper, we use simulated observations from a three-dimensional hydrodynamic simulation of a coronal active region to verify these diagnostics. The density and temperature from the simulation are used to generate images in several passbands and spectral lines. We identify loop structures in the simulated images and calculate the background. We then determine the density, temperature, and emission measure distribution as a function of time from the observations and compare these with the true temperature and density of the loop. We find that the overall characteristics of the temperature, density, and emission measure are recovered by the analysis methods, but the details are not. For instance, the emission measure curves calculated from the simulated observations are much broader than the true emission measure distribution, though the average temperature evolution is similar. These differences are due, in part, to a limitation of the analysis methods, but also to inadequate background subtraction.

Numerical simulations of convection in crystal‐bearing magmas: A case study of the magmatic system at Erebus, Antarctica

The sustained heat and gas output from Erebus volcano reflects a regime of magma convection that we investigate here using a bi‐phase (melt and crystals), fluid dynamical model. Following validity and verification tests of the model, we carried out four single‐phase and three bi‐phase numerical 30‐year‐ simulations, in an idealized 2D geometry representing a lava lake cooled from above and a reservoir heated from below that are linked by a 4‐to‐10–m‐diameter conduit. We tested the effects of crystals on convection while changing conduit size and the system boundaries from closed to open. Neglecting crystal settling yields only a limited number of features, i.e., (i) the formation of a central instability, (ii) the average temperature evolution, and (iii) the average velocity range of the surface flow motion. Bi‐phase simulations show that while crystals are quite efficiently transported by the liquid phase a small decoupling reflecting their large size (5 cm) results in settling. This leads to more complex circulation patterns and enhances the vigor of fluid motion. A sufficiently large conduit sustains convection and retains 6 and 20% of crystals in suspension, for a closed and open system, respectively. Model outputs do not yet correspond well with field observations of Erebus lava lake (e.g., real surface velocities are much faster than those modeled), suggesting that exsolved volatiles are an important source of buoyancy.

Coupling fluid flow, heat transfer and thermal denaturation-aggregation of beta-lactoglobulin using an Eulerian/Lagrangian approach

The transformation of liquid food product under heat treatment is often represented by considering average temperature evolution along the exchanger and by assuming plug-flow. Our aim is to demonstrate that thermal denaturation-aggregation of whey proteins can be more realistically represented by taking into account the different dynamical and thermal histories associated with fluid parcels which progress more or less quickly, far or close to the heating wall, inside the processing unit. A numerical approach is proposed for evaluating the thermal denaturation-aggregation of whey proteins, combining computational fluid dynamics and the population balance equation. The approach is illustrated by the evolution of a suspension of beta-lactoglobulin. Fluid flow and heat transfer are solved through the finite element method in the Eulerian frame, while product transformation is evaluated along representative Lagrangian trajectories. Outlet bulk results show that the product reaches a higher level of transformation than in assuming plug-flow and radially-independent temperature.

Transient thermal characterization of micro/submicroscale polyacrylonitrile wires

In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive. In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted. Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their thermal diffusivities (around 1.53×10-7 m2/s), which are slightly smaller than the bulk value.