Hasil untuk "Heat"

W. Large, S. Pond

P. Sorger, H. Pelham

Amjad E. Hamza, Mohammed S. Abdo, Bakri Younis et al.

This paper investigates qualitative properties of fractional delay differential equations formulated in terms of the Atangana–Baleanu–Caputo (ABC) fractional derivative of order <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1</mn><mo><</mo><mi>ϱ</mi><mo><</mo><mn>2</mn></mrow></semantics></math></inline-formula>. Three related problem settings are examined: equations with variable delay, the constant-delay case, and a multi-delay extension involving several discrete delay terms. For each formulation, sufficient conditions ensuring existence and uniqueness of solutions are established in both the supremum norm and an exponentially weighted Maksoud norm. The analysis is carried out using Banach’s fixed point theorem in conjunction with progressive contractions and suitable Lipschitz-type conditions. In addition, Ulam–Hyers (UH) and Ulam–Hyers–Rassias (UHR) stability results are derived, providing quantitative estimates on the sensitivity of solutions with respect to perturbations. To complement the theoretical findings, numerical examples are presented, one of which illustrates the behavior of approximate solutions for various fractional orders.

Xiaoping Wang, Liqiang Liang, Qingsong Song et al.

Traditional fluid network theory often underestimates pressure losses in complex pipe-bundle systems operating under vortex-dominated flow conditions, with deviations exceeding 20% in many cases. To address this limitation, this study proposes a vortex-based correction method. Three-dimensional simulations were performed on a multidirectional parallel pipe bundle to analyze vortex formation and to quantify the effects of fluid properties (viscosity and inlet velocity) and structural parameters (branch diameter, manifold cross-sectional ratio, and manifold arrangement) on pressure loss. To account for vortex-induced energy dissipation that is overlooked by conventional one-dimensional network models, an additional vortex-induced loss coefficient, α, is introduced to modify the pressure-loss formulation. Results indicate that higher viscosity, larger branch diameter, a higher manifold cross-sectional ratio, and a co-flow arrangement improve flow uniformity and prediction accuracy. Conversely, higher inlet velocities and counter-flow arrangements intensify vortex effects and increase prediction deviations. Least-squares fitting indicates that α ranges from 1.15 to 1.37. Implementation of the proposed correction reduces pressure-loss prediction errors to within 5%, demonstrating the method’s effectiveness and extending the applicability of fluid network theory to vortex-dominated flows.

Ahmed Abdulsahib, Dhirgham Alkhafaji, Ibrahim Albayati

Natural heat transfer is studied in a square enclosure containing a heat sink in the presence of a hybrid nanofluid (MWCNT and Fe3O4). The right wall is kept cool (Tc), while the left wall is hot (Th), and the upper wall and lower wall are thermally insulated. The study is carried out by making slots with different thicknesses (st = 0.01 and 0.02) and lengths (sh = 0.1 to 0.4) for each fin of the heat sink to increase heat transfer in the heat sink by using a Rayleigh number of 103 to 106 and a solid volume fraction (ϕ = 0.02). Also, internal circular cold bodies are added in the tip and between the fins with a diameter of 0.05 and different numbers (No = 2, 4, 6, 8, and 12). According to numerical results, the average Nusselt number increases with the Rayleigh number, slot thickness, and length. The optimal condition was slot thickness (st = 0.02) and length (sh = 0.4), which increased the average Nusselt number by 37.7% over solid fins. When cold circular internal bodies are present, an increase in the stream function and a better distribution of isotherm lines are generally observed. Nu increases by 62% when there are internal bodies at the tip of the fins (No = 6), 71.5% when there are internal bodies between the fins (No = 6), and 78% when there are internal bodies at the tip and between the fins (No = 12).

Hailong Lu, Nong Xiang, Zehua Qian et al.

Lower hybrid wave (LHW) current drive plays a crucial role in sustaining steady-state (SS) discharges on the Experimental Advanced Superconducting Tokamak (EAST). Hotspots frequently form on the wave antenna and guard limiters during SS operations. Although both experimental and theoretical studies suggest that fast electrons could be responsible for these hotspots, the underlying mechanisms of fast electron generation under typical EAST operational parameters and their impact on the hotspots remain unresolved. In this work, particle-in-cell simulations are used to investigate the interactions between LHWs and electrons in front of the antenna, taking into account the realistic incident power spectra and localized field effects. The results show that, due to resonance overlap, fast electrons are produced through resonant interactions between electrons and LHW components with a high parallel refractive index ( N _∥ ). The velocity distribution function in velocity space is found to significantly depend on plasma parameters near the antenna, such as q _95 , electron temperature, and input power. These fast electrons notably enhance the sheath potential on the guard limiters and increase the heat flux to the wall.

Mohamed Awad Abd Allah, Ghada Khiralla, Hesham Elhariry

Abstract Refrigerated and frozen ready-to-eat cooked vegetables are becoming increasingly popular with consumers and catering services. Simulating digestion is essential for accurately assessing the nutritional value of ready-to-eat vegetables, as raw composition data alone may overestimate their health benefits. Therefore, this study evaluated the bioaccessibility of bioactive compounds in broccoli after heat treatment, storage, and in vitro gastrointestinal digestion. Fresh broccoli (FB) and heat-treated (boiled or steamed) broccoli were subjected to refrigerated (RBB, RSB) or frozen (FBB, FSB) storage. FB exhibited high phenol (610 mg GAE/100 g) and flavonoid (295 mg QE/100 g) contents. Thermal treatment significantly decreased the phenolic content to 503, 515, 368, and 393 mg GAE/100 g in RBB, RSB, FBB, and FSB, respectively. Total phenols, flavonoids, vitamin C, antioxidant capacity, dietary fibers, and phenolic profiles were analyzed before and after in vitro gastrointestinal digestion. After in vitro gastrointestinal digestion, phenol, flavonoid, and vitamin C contents decreased significantly compared to those after digestion with FB (DFB). No significant changes in total, soluble (SDF), or insoluble (IDF) dietary fiber were observed between heat-treated broccoli and FBs. However, in vitro, gastrointestinal digestion of FB decreased SDF from 1.84 to 1.59% and increased IDF from 1.02 to 1.3%. HPLC analysis revealed substantial phenolic compound losses after in vitro gastrointestinal digestion, ranging from 64.9% in DFB to 88% in DFBB. After digestion, the recovery of bioactive compounds decreased, particularly for vitamin C and phenolics. These findings emphasize the importance of simulating digestion when evaluating the nutritional value of processed vegetables, as relying solely on raw composition data may overestimate health-promoting compound intake. Therefore, dietary recommendations should consider cooking methods and the loss of bioactive substances during digestion. Further research is needed to gain deeper insights into the bioaccessibility of antioxidant compounds after the digestion of cooked and preserved vegetables.

D. R. Freitag, T. Mcfadden

R. Štěpán, V. Krutiš, R. Jelínek et al.

Currently, great emphasis is placed on the production of castings with complex shapes. The hybrid investment casting technology using 3D printed models offers new possibilities in the production of such complex and thin-walled castings. The motivation for this paper was to find a solution to the problem with ceramic shells cracking during the 3D model firing stage. The main factors affecting the shell cracking are the thermal expansion of the model and the shell material, and the newly considered pressure of the gas closed in the ceramic shell cavity. First, thermal analyses were performed of a commercial material used for 3D printing - Polymaker PolyCast™. The characteristics yielded by the measurements helped establish the glass transition temperature, the autoignition temperature and the behaviour of the gas produced by the model burning. Suitable experimental models in the shape of tetrahedrons were designed and used for a number of experiments. The tests confirmed that cracks only occur during shock firing in models printed by the FFF technology with 0% of infill. A solution suggested for further experiments is purposeful venting of the models. Practical testing of the optimization has also been performed. The last step was measurement of the heat transfer through the ceramic shell after being placed in the annealing furnace. There were temperature evolution profiles in the system model-ceramic shell obtained.

M. Pettine, S. Imbeah, J. Rathbun et al.

Abstract Juno has allowed clear, high‐resolution imaging of Io's polar volcanoes using the Jovian Infrared Auroral Mapper (JIRAM) instrument. We have used data from JIRAM's M‐band (4.78 μm) imager from 11 Juno orbits to construct a global map of volcanic flux. This map provides short‐term insight into the spatial distribution of volcanoes and the ways in which high‐ and low‐latitude volcanoes differ. Using spherical harmonic analysis, we quantitatively compare our volcanic flux map to the surface heat flow distribution expected from models of Io's tidal heat deposition (summarized in de Kleer, Park, et al. (2019, https://doi.org/10.26206/d4wc‐6v82). Our observations confirm previously detected systems of bright volcanoes at high latitudes. Our study finds that both poles are comparably active and that the observed flux distribution is inconsistent with an asthenospheric heating model, although the south pole is viewed too infrequently to establish reliable trends.

Baohu Han, Xingjun Ju, Lei Zhang et al.

Bearing is the core component of high-speed rotating machinery. However, the lubricating oil plays an important role in reducing the temperature and the collision between components. It can improve the performance of the bearing under high-speed rotation. Therefore, based on the theory of oil-air two-phase flow, this paper establishes a numerical analysis flow-heat model of ball bearing under different oil supply. At the same time, the vibration is calculated. The influence of internal oil-air field and thermal characteristics on vibration is analyzed. The results show that the volume of oil is not uniformly distributed in the bearing chamber. The oil gradually decreases from the outer ring to the inner ring. It is mainly concentrated on the oil-air inlet. With the increasing of oil supply speed, the temperature of the bearing decreases firstly and then increases, and there is an optimal oil supply speed. The inner ring vibration velocity is basically similar to the temperature trend. Meanwhile, the lowest temperature is mainly concentrated near the oil-air inlet. The maximum error between simulation results and experimental results is 11.37%. Finally, the reliability of the simulation analysis is verified by the temperature and vibration experiment. It provides some theoretical support for the optimization of oil-air lubrication parameters of angular contact ball bearings.

A. D. Chaudhari, P. Bhupathi, V. V. Joshi

This paper explores the potential of a cylindrical enclosure with vent holes to create and maintain the desired thermal environment for indoor farming. Different thermal zones can be made in a single room when such enclosures are used in multiple numbers in a single room. A comparative analysis of twelve different air cooling/heating configurations was conducted. Each cylindrical enclosure is air-filled, with two heat sinks facing each other and vent holes in the top and bottom surfaces. Six configurations had heat sinks oriented vertically, and the other six had heat sinks inclined at 45°. These configurations (vertical and inclined heat sinks) have been studied for different heat sink temperatures and sidewall heat flux conditions. The numerical simulations were conducted using ANSYS-Fluent. The studies have shown that different thermal environments can be created inside the enclosure, and cooling can be achieved with sufficient air exchange through vent holes. The instabilities due to buoyancy-driven flow are found to be necessary for air exchange through vent holes. Validation studies have shown that the heat flux from the sidewall should be considered, even if it is an excellent thermal insulator.

Shuchi Goyal, Divya Thirumal, Jaya Rana et al.

Therapeutic tools in the biomedical field are increasingly utilizing nanoparticles (NPs) with a small size and large surface area. Chitosan (CS), a biotic polymeric carbohydrate found in shellfish, is a promising carrier for these diagnostic systems due to its biocompatibility, low toxic effects, and diverse shapes. CS-NPs are therapeutic transporters with properties such as bionomical, pH, and heat sensitivity, increased homogeneity, and potential to pass through the brain. These nanomaterials can detect and cure pathological conditions using curative instruments. CS-NPs slow down the movement and growth of anti-inflammatory colonies while encouraging the growth of cells causing inflammation. They could provide active substances for treating various medical conditions, such as auto-immune deformities, hyperglycemia, hypersensitivity, and cancer. Scientific resources are dedicated to improving the efficacy of CS-NP active agent compositions. Recent discoveries highlight the medicinal implications of CS-NPs preparations for drug delivery in managing severe inflammatory aberrations.

Eunice B. Yuwono, Yvonne M. Stokes, Hayden Tronnolone et al.

In the fabrication of optical fibres, the viscosity of the glass varies dramatically with temperature so that heat transfer plays an important role in the deformation of the fibre geometry. Surprisingly, for quasi-steady drawing, with measurement of pulling tension, the applied heat can be adjusted to control the tension and temperature modelling is not needed. However, when pulling tension is not measured, a coupled heat and fluid flow model is needed to determine the inputs required for a desired output. In the fast process of drawing a preform to a fibre, heat advection dominates conduction so that heat conduction may be neglected. By contrast, in the slow process of extruding a preform, heat conduction is important. This means that solving the coupled flow and temperature modelling is essential for prediction of preform geometry. In this paper we derive such a model that incorporates heat conduction for the extensional flow of fibres. The dramatic variations in viscosity with temperature means that this problem is extremely challenging to solve via standard numerical techniques and we therefore develop a novel finite-difference numerical solution method that proves to be highly robust. We use this method to show that conduction significantly affects the size of internal holes at the exit of the device.

T. Uttal, J. Curry, M. Mcphee et al.

Y. Povstenko

H. Takebayashi, M. Moriyama

Miroslav Variny, Marianna Kšiňanová, Patrik Furda

Trigeneration provides an effective means of power, heat, and cold production on site. Proper design and well-managed operation of such units can bring in substantial savings in consumed primary energy as well as in the amount of greenhouse gases released to the atmosphere, compared to separate production of all three media. The studied sub-MW-sized trigeneration unit comprises an internal combustion engine combined with an absorption chiller and a heat management system, delivering all three media to a nearby industrial facility. A mathematical model is developed based on available design and process data, a profit function is set up, and the subsequent sensitivity analysis of economic parameters is realized. The lowered efficiency of summer operation is analyzed, and a suitable solution is proposed, with an estimated total investment cost of EUR 114,000 and an anticipated simple payback period less than 2 years.

Miaoling Liang, Xing Yuan, Wenyan Wang

The GRAPES (Global/Regional Assimilation and Prediction System) global medium-range forecast system (GRAPES_GFS) is a new generation numerical weather forecast model developed by the China Meteorological Administration (CMA). However, the forecasts of surface latent heat fluxes and surface air temperature have systematic biases, which affect the forecasts of atmospheric dynamics by modifying the lower boundary conditions and degrading the application of GRAPES_GFS since the 2 m air temperature is one of the key components of weather forecast products. Here, we add a soil resistance term to reduce soil evaporation, which ultimately reduces the positive forecast bias of the land surface latent heat flux. We also reduce the positive forecast bias of the ocean surface latent heat flux by considering the effect of salinity in the calculation of the ocean surface vapor pressure and by adjusting the parameterizations of roughness length for the exchanges in momentum, heat, and moisture between the ocean surface and atmosphere. Moreover, we modify the parameterization of the roughness length for the exchanges in heat and moisture between the land surface and atmosphere to reduce the cold bias of the nighttime 2 m air temperature forecast over areas with lower vegetation height. We also consider the supercooled soil water to reduce the warm forecast bias of the 2 m air temperature over northern China during winter. These modified parameterizations are incorporated into the GRAPES_GFS and show good performance based on a set of evaluation experiments. This paper highlights the importance of the representations of the land/ocean surface and boundary layer processes in the forecasting of surface heat fluxes and 2 m air temperature.

Susumu Nakayama, Masaki Shiomi

This study investigates the enhancement of blue afterglow emission from ZrO2:Ti heat treatment at 1500 °C in air with raw ZrO2 containing 1000 ppm TiO2. The afterglow time of KZrB4O8.5, which was melt heat-treated with ZrO2:Ti heat-treated at 1500 °C, K2CO3, and H3BO3 at 1300 °C in air, was extended by approximately 2.5 times. XRD analysis of ZrO2:Ti revealed only monoclinic peaks, while that of KZrB4O8.5 with a glass-ceramic composition displayed monoclinic peaks and a halo. In the XPS analysis of ZrO2:Ti and KZrB4O8.5 with a glass-ceramic composition, the presence of Zr4+ and a small amount of Zr3+ was observed, while that of Zr2+ could not be confirmed. SEM observations revealed that ZrO2:Ti was composed of uniformly sized grains of approximately 0.5 μm size, whereas KZrB4O8.5 with a glass-ceramic composition exhibited coarsened grains of approximately 10 μm size. The afterglow decay curves of KZrB2O5.5, KZrB3O7.0, KZrB5O10.0, and KZrB6O11.5 with a glass-ceramic composition with varying B content in KZrB4O8.5 with a glass-ceramic composition were measured, and based on the results obtained, the afterglow time increased with an increase in the coarse grain size.