Heat Problem Research Articles

Numerical modeling of heat and mass transfer processes in a capillary-porous body during contact drying

The problem of conductive (contact) drying of a capillary-porous body in a steam-air (gas) environment by heat transfer to the material during its contact with the heated surfaces of the material is considered. A system of significantly nonlinear differential equations of heat and mass transfer to describe such a process is obtained. To solve the formulated problem of heat and mass transfer (without taking into account deformability), the method of solving nonlinear boundary value problems is applied in the form of an iterative process, at each step of which a linear boundary value problem is solved. The results of the application of the method are verified based on the popular numerical scheme used. They agree well. A numerical experiment is conducted for materials of three types of porosity. The results are presented graphically and tabularly. The regularities of contact drying of capillary-porous materials in a steam-air environment are deduced.

Решение краевой задачи тепломассопереноса методом источников для условий лучистого обогрева почвы

The purpose of the research is to find, predict and regulate the temperature and humidity regime of the soil for the conditions of radiant heating of cultivation facilities using dark-type ceiling infrared emitters. A system of differential equations (in dimensional and dimensionless forms) is presented, reflecting the relationship of thermal and mass transfer processes in colloidal capillary-porous bodies in the case of surface radiant heating. A partial analytical solution of this system of differential equations for a semi-bounded body is considered with the exclusion of the phenomenon of thermal and thermal conductivity and period diffusion processes. On the example of milling peat, taking into account the initial data, the solution of the boundary value problem of heat and mass transfer by the method of sources is obtained, which is one-dimensional non-stationary fields of moisture content and temperature. It is established that under the given initial and boundary conditions, as well as taking into account the thermophysical properties of milling peat, the required moisture content will be achieved in six hours, the temperature in three hours. By adjusting the thermal power of the infrared radiation source, and, therefore, the intensity of moisture evaporation from the soil surface into the environment, it is possible to control the rate of heating and drying of the layer (for example, to determine the time or frequency of watering the soil). To clarify the values of moisture content and soil temperature by coordinate and over time, it seems expedient to consider analytical solutions that took into account not only basic, but also conjugate processes of heat and mass diffusion

Investigation of non-stationary thermal conductivity in a multilayer rubber-metal product during post-vulcanization cooling and before vulcanization

In this article, we considered the issues of obtaining analytical solutions to a non-stationary problem of heat and mass transfer for a multilayer elastomeric material. We determined the criteria influencing the temperature change process in the processed material. We have obtained a dependence that establishes a functional relationship between the primary heat transfer criteria and the temperature of the processed material. The dependence is the initial ratio in developing an engineering method for calculating an industrial installation.

Influence of polycrystalline diamond on silicon-based GaN material

Self-heating has become a limited factor for the performance improvement of GaN electronics. Growing polycrystalline diamond directly on GaN material to solve the heating problem of GaN devices has become one of the research highlights. Polycrystalline diamond on Si-based GaN material has the advantages of being close to the channel region and high heat dissipation efficiency. However, there is a problem that the thermal expansion mismatch between polycrystalline diamond and GaN material leads to the deterioration of electrical characteristics of GaN. In this work, we adopt microwave plasma chemical vapor deposition (MPCVD) method to grow polycrystalline diamond on 2-inch Si-based GaN material. The test results show that the polycrystalline diamond is uniform as a whole. The average thickness is in the range of 9–81 μm. With the thickness of polycrystalline diamond increasing, the XRD (002) diffraction peak FWHM increment and mobility loss gradually increase for the Si-based GaN material. Through laser cutting and acid etching, the Si-based GaN material is successfully stripped from the polycrystalline diamond. It is found that during the process of diamond growth at high temperature, hydrogen atoms etch the defect positions of the silicon nitride epitaxial layer, forming a hole area in the GaN, and the etching depth can reach the intrinsic GaN layer. During the process of cooling, a crack area is formed around the hole area. Raman characteristic peaks, full widths at half maximum of XRD (002) diffraction peaks, and electrical properties of the stripped Si-based GaN materials are all returned to their intrinsic states. The above results show that the thermal expansion mismatch between polycrystalline diamond and Si-based GaN introduces stress into GaN, which leads to lattice distortion of GaN lattice and the degradation of electrical property of GaN material. The degradation of GaN material is recoverable, but not destructive.

Generalized solutions for time ψ-fractional heat equation

This paper focuses on the time fractional heat problem with the use of a new fractional derivative. Using Banach?s fixed point theorem and Laplace transforms, we give and prove the integral solution of the problem. In Colombeau?s algebra, The existence and uniqueness of the solution are demonstrated using the Gronwall lemma.

Novel solutions for the heat equations arising in the elliptic curves over the field of rational numbers

In this article we consider the solutions of the heat equations with use of the elliptic curves over the field of rational numbers. We propose the entire functions associated with the Hasse-Weil L-function. We show the conjectures that new functions have only real zeros in the entire function plane. The obtained results are proposed as new tool to describe the complex behaviors of the heat problems as well as number theory.

Thermal performance evaluation of a cool roof model in hot – dry climate

Roof is an essential component of the building envelope which is exposed direct solar radiation and contributes to the maximum load of the total cooling load of the building; and is an essential interface between the indoor and outdoor environments and to be strong enough to withstand all weather conditions; and it covered nearly 20–25% of overall urban surface areas. In the hot and summer seasons, the components of the building envelope must be designed to minimize the discomfort. Recently, many studies were revealed and showed that there can be different solutions to the excessive heat problem through the roof. But in Sudan, no significant research was conducted for cool roofs scenario, so more comprehensive experimental and simulation analyses need to be performed for different climatic zones to establish cool roof standards specific to the Sudan context in the future. The requirement of thermal comfort is a primary need in residential buildings located on hot-dry climates. The thermal performance of cool roof model will be analysed in terms of indoor temperature compared to Flat roof configuration of Reinforced Concrete (R.C), plaster, and cool paint roof for hot –dry climate, Indore, Khartoum state, Sudan. The study aims to assess the impact of the cool roof on the indoor temperature of buildings, on the other hand indicates that a cool roof performed better for indoor temperature profile and maintains a thermal comfort in buildings. Thermal performance modelling was undertaken for analysed in term of thermal performance of the cool roof. The cool roof technology is more useful and easy to implement in all residential buildings, both old or under construction to reduce indoor temperature.

Evaluating the effects of the analogical learning approach on eighth graders’ learning outcomes: the role of metacognition

Teaching with analogies is an important pedagogy that helps learners construct abstract conceptions through reasoning with something familiar. Heat concepts were chosen for this study because they have an intangible nature and involve complex mechanisms that often challenge school-aged learners. Learning this kind of complex concept with analogies involves complicated mental processes that could demand learners’ metacognitive abilities; yet, to date, the influence of metacognition has been left unexamined. This study therefore investigated how metacognition differentially affected adolescents’ processes and outcomes of analogical learning about abstract heat concepts. Eighty-three eighth graders participated in the study and attended two units of Teaching-With-Analogies on specific heat and heat transfer. This study adopted a mixed-method approach along with within-group comparisons. Among them, eight individuals from each of the high-, moderate- and low-metacognitive groups were interviewed to explore the utilized metacognitive activities and their relation with the ability to reason with analogies. The quantitative findings revealed that analogies benefited the moderate metacognitive learners, and yet did not alter the conceptual understanding of the high and low metacognitive cohorts. A unique explanatory power of metacognition was also observed on the learners’ post conceptual understanding, in addition to on their prior knowledge. Verbal process data illustrated that metacognitive abilities substantially influenced every stage of solving heat problems with analogies. The differential outcomes of the analogical learning approach were explained by in-depth case analyses considering the use of prior knowledge and the absence of metacognition during analogical reasoning. Metacognitive characteristics of the dynamic analogy-inferring process for different metacognitive groups were synthesized. The associated implications for the analogical learning approach and accommodations for adolescents of different levels of metacognition are also discussed.

Design of single and two phase modeled nanofluid CPU cooler and their numerical analysis

AbstractThe heating problems in electronic devices have become even more significant with the development of technology and the rapid increase in areas of use. In cases where passive cooling and active cooling processes are not sufficient to improve overheating in electronic devices, high temperature generation is prevented by liquid cooling if convenient. The effect of nanofluid use on heat transfer to improve the thermal performance of liquid cooling systems was examined with computational fluid dynamics from numerical methods in this research. For different cooler designs, both single‐phase and multiphase modeling methods were utilized in fluid modeling in the research involving forced convection and heat transfer in laminar and turbulent flow. The mathematical models utilized were validated on different experimental and numerical researches. The single‐phase modeling was conducted for pure H2O, 1% Al2O3, 5% Al2O3 nanofluids at different Reynolds numbers. The analyzes were conducted at different Reynolds values and the increase in Reynolds value decreases the maximum temperature value at the output. In the multiphase modeling method, the nanofluid Al2O3 is defined and modelled as a separate phase suspended in different sizes into the base fluid H2O. The use of nanofluid increased the thermal conductivity in both methods compared to the use of pure H2O. At the same time, the use of nanofluids at 5% concentration gave better results than 1% concentration. As the temperature distributions are examined, the Mixture model, one of the single‐phase and multiphase modeling methods, presents very similar distributions. The effect of nanofluids on thermal performance varies depending on many parameters. A significant one is the size of the suspended nanoparticle. Different particle sizes, 20, 30, and 40 nm, were investigated in both Mixture and Eulerian modeling approaches in this research. Two different design coolers were utilized in the researches. In these designs, the flow is distributed in parallel and serpentine. The flow distribution and pressure drop also had an effect on thermal performance. The temperatures were read lower in the serpentine block, which provides a more regular flow distribution.

Propagating and Stationary Bright Knots in the Quiet Sun

The question of what heats the solar chromosphere and corona remains one of the most important puzzles in solar physics and astrophysics. Up to now, two mechanisms are considered to work in heating the chromosphere and corona: magnetic reconnection and wave (turbulent flow) dissipation. But it is still not understood which mechanism is dominant. To solve the heating problem, one important topic at this stage is that we should understand how much energy is contributing from the two mechanisms respectively to the heating. In the quiet Sun, the thermal energy signal is observed as brightenings. Here we report two kinds of bright knots with a total of 3605 in the chromosphere of the quiet Sun, using the data from the New Vacuum Solar Telescope at Yunnan Observatories. The first kind of 1537 bright knots, which is first detected in chromospheric fibrils where waves and their dissipation are ubiquitous, propagates along these fibrils with velocities from 5 to 69 km s−1. The second kind of 2068 knots keeps stationary, and always appears at the footpoints of these fibrils where network magnetic fields exist, suggesting that magnetic reconnection locally produces these stationary knots. Based on the observations of thousands of bright knots, we display the different distribution patterns of the two kinds of bright knots in the quiet Sun, and deduce that half of the energy for heating the chromosphere is supplied by wave dissipation, and the other half by magnetic reconnection.

"THERMOELASTIC DISPLACEMENT AND TEMPERATURE RISE IN A HALF-SPACE DUE TO A STEADY-STATE HEAT FLUX "

Due to model complexity, classical contact mechanics theory assumes isothermal contact processes, involving bodies with uniform temperatures and no heat transmitted or generated through or near the contact interface. This paper addresses the problem of frictional heating in non-conforming or rough contacts by investigating the thermoelastic behaviour of asperities. The heat generated in a sliding contact by interfacial friction leads to thermoelastic distortion of the contact surface, further modifying contact parameters such as pressure, gap or temperature. The thermal expansion of the contacting bodies must therefore be accounted for when solving the contact problem. The thermoelastic displacement is computed with the aid of the half-space theory and of fundamental solutions for point sources of heat located at the free surface, derived in the literature of heat conduction in solids. The linearity of conduction equations encourages the use of superposition principle in the same way as for the elastic displacement. As the thermoelastic displacement is expressed mathematically as a convolution product, methods derived in contact mechanics for elastic displacement calculation are adapted to the heat conduction equations. The influence coefficients needed to efficiently compute the convolution products are derived, and the Discrete Convolution Fast Fourier Transform technique is applied to improve the algorithm computational efficiency. A similar method is then advanced for the temperature rise on the contact interface due to arbitrary heat input. The predictions of the newly advanced computer programs are tested against existing closed-form solutions for uniform circular or ring heat sources, and a good agreement is found.

Design of an Innovative Wireless Left Ventricular Assist Device Driven by either Extracorporeal Magnets or an Intracorporeal Battery Pack.

This study aimed to design a new wireless left ventricular assist device (LVAD) that solved the driveline problem of current LVADs and the heat problem of the transcutaneous energy transfer system (TETS). Our new wireless LVAD consisted of two blood pumps capable of driving using extracorporeal magnets and an intracorporeal battery pack. When one pump was driven, the other pump was stopped. The battery pack was wirelessly and slowly charged using TETS with low-power transmission, whereas the magnetic pump was driven wirelessly by extracorporeal magnets. We demonstrated the feasibility of our system in a bench-top durability test for 7 days. The distance between the extracorporeal magnets and the magnetic pump was 27.5 mm. Our LVAD system had steadily provided sufficient pressure and flow volume (approximately 108 mmHg and 5.0 L/min, respectively) to the test loop for 7 days. Although loss of synchronism occurred once during the test, it recovered within a few minutes. The results demonstrate the feasibility of the proposed wireless LVAD system. Further technical improvements are required in our system, such as downsizing the electric devices inside the body, to conduct an in vivo test for the next step.

There is More Than Just One “Corona” That Can Kill Us All

When most people hear the phrase "space exploration", they imagine preparing the colonisation of Mars, studying distant planets, searching for alien life or studying exotic black holes. Many times, however, mankind tends to leap before looking and focus on the exotic and the interesting instead of that which might not seem that special to most of us, but which which can be crucial for our survival. This way, many major and important issues in astrophysics - and sciences in general - can become overlooked and take very long to resolve. One such major issue in astrophysics is the behaviour of our closest star, the Sun. While we generally assume that we have a good idea about the most significant processes in the solar interior acting as its main energy source, our attempts at explaining the dynamics and structure of the solar atmosphere (the so-called corona) are still merely an educated guesswork at best. Due to several of the magnetohydrodynamic processes which we do not yet fully understand, the temperature of the solar atmosphere is very high compared to the layers underneath and reaches millions of Kelvins. Since this is where the major mass ejections occur, some of which might be directed towards the Earth causing geomagnetic storms, it is crucial that we start not only to fully understand these processes, but also to be able to accurately predict their outcomes. As will be shown in this text however, it is not only our limited understanding of the physics which prevents us from doing that; it is also the lack of computational resources. This paper firstly briefly discusses the basic physics behind the behaviour of the solar coronal plasma. Afterwards, it discusses the coronal heating problem in more detail and finally, it outlines the major challenges we currently face which seem to prevent us from efficient simulation and complete understanding of the behaviour of our closest star.

Evaluation of combined heat and mass transfer in hydromagnetic micropolar flow along a stretching sheet when viscous dissipation and chemical reaction is present

In this study, the problem of heat and mass transfer in the hydromagnetic flow of a micropolar fluid through a stretching sheet with an existence of viscous dissipation and chemical reaction. By using MATLAB inbuilt bvp4c approach, we are able to numerically solve the converted equations for the flow regime. The influence of key factors on the velocities, microrotations, temperatures, and concentration functions has been analyzed. The magnetic field has been measured and found to The micropolar factor has the reverse impact on all functions excluding temperature, whereas the microrotational parameter slows things down and raises temperature and concentration function. When the Eckert number increases, the temperature rises and the concentration falls with enhanced values of Schmidt number.

SULIS: A coronal magnetism explorer for ESA’s Voyage 2050

Magnetism dominates the structure and dynamics of the solar corona. To understand the true nature of the solar corona and the long-standing coronal heating problem requires measuring the vector magnetic field of the corona at a sufficiently high resolution (spatially and temporally) across a large Field-of-View (FOV). Despite the importance of the magnetic field in the physics of the corona and despite the tremendous progress made recently in the remote sensing of solar magnetic fields, reliable measurements of the coronal magnetic field strength and orientation do not exist. This is largely due to the weakness of coronal magnetic fields, previously estimated to be on the order of 1-10 G, and the difficulty associated with observing the extremely faint solar corona emission. With the Solar cUbesats for Linked Imaging Spectro-polarimetry (SULIS) mission, we plan to finally observe, in detail and over the long-term, uninterrupted measurements of the coronal magnetic vector field using a new and very affordable instrument design concept. This will be profoundly important in the study of local atmospheric coronal heating processes, as well as in measuring the nature of magnetic clouds, in particular, within geoeffective Earth-bound Coronal Mass Ejections (CMEs) for more accurate forecasting of severe space weather activity.

Study on aerodynamic force and aerothermal effect of two-dimensional wedge wave rider with different passivation shape of the head

With the rapid development of space technology, hypersonic vehicles flying at altitudes of 20-100 km near space are showing more and more important application value, and how to solve the serious aerodynamic heating problem caused by hypersonic vehicles in the process of flight is the focus of current research. In this paper, the simplified two-dimensional wedge-shaped waveride is treated with the passivation leading edge by the Computational Fluid Dynamics (CFD) method, and the aerodynamic and aerothermal properties of the hypersonic continuous flow basin are numerically simulated. The flow field structure of the model is analyzed, and the law of heat-resistant rise is revealed. The research contents mainly include the characteristics of body head heat flux and body lift-drag ratio under different passivation shapes. Within the research scope: 1. The larger the passivation radius, the more effective it is to reduce the head heat flux. When the passivation radius is 2 mm, the reduction is about 82.5%. 2. The larger the passivation radius, the more serious the lift-drag ratio reduction. When the passivation radius is 2mm, the maximum reduction is about 72.4%; 3. The four passivation leading edge modes have the best thermal protection effect when the passivation radius R is the same, and the lift-drag ratio of the Bezier curve passivation leading edge mode is the largest.

Study of a low-frequency wireless charging system crossing the metal Dewar wall of a high-temperature superconducting magnet

Using a wireless charging method to charge high-temperature superconducting (HTS) magnets is a way to solve the existing problem of high leakage heat introduced by charging through current leads. However, the available studies on charging HTS magnets using wireless charging methods rarely involve the role of a Dewar in the charging process. Nowadays, most HTS magnets use a metal Dewar because of the high requirements of the Dewar for gas tightness and mechanical strength. How to charge the HTS magnets wirelessly through the metal walls of the Dewar is an issue that needs to be addressed. In response to the above concerns, taking into account the role of the metal Dewar, a low-frequency wireless charging system with an isolation transformer as the core is proposed in this paper, where the primary coil of the transformer is a copper coil, installed on the outside of the Dewar. The secondary coil is a superconducting coil, installed on the inside of the Dewar. A theoretical model of the proposed wireless charging system is developed, and the prototype is fabricated based on the theoretical model. Both numerical and experimental methods were used to study the operational characteristics of the prototype, and the experimental results proved the validity of the theoretical model and the numerical model in this paper. Experimental results show that the proposed wireless charging system can charge an 8.5 mH HTS magnet with a current of 48.58 A over a 6 cm transmission distance, where the 6 cm gap includes a 1.6 mm thick metal wall. The results in this paper can provide new ideas for research work on charging HTS magnets wirelessly through a metal Dewar.

Rod mangle rotation patterns for adjustable magnetic field generation

The use of adjustable magnetic field sources is becoming an indispensable necessity in numerous applications. In particular, permanent magnet assemblies, such as the rod mangle design, avoid the large power consumption and Joule heating problems present in electromagnets. In this work, we present a systematic 2D study of rod mangle configurations with different number of rods. We observe that the magnetic field homogeneity increases with the number of used rods and, for a sufficiently large number, the behavior of the assembly is similar to that of a perfect Halbach. Generally, the rotation of only one rod changes the direction and decreases the homogeneity and magnitude of the magnetic field. Nevertheless, the impact of such rotation reduces with the increase of the number of rods in the system. We also study how different rotation patterns influence the generated magnetic field and demonstrate how one can: (i) reduce the magnetic field magnitude rotating its direction; (ii) reduce the magnetic field magnitude keeping its direction constant; (iii) invert the magnetic field direction, after being reduced; or (iv) rotate the magnetic field direction keeping its magnitude constant. These results are similar to those obtained by a nested Halbach. In addition to the low cost, the results show that the mangle system is highly versatile, can be easily manipulated and, consequently, has a large application potential. The magnetic model was successfully validated with experimental systems of three and four rods.

Combined Heat and Power Dispatch Problem Using Comprehensive Learning Wavelet-Mutated Slime Mould Algorithm

In this article, bio-inspired metaheuristic evolutionary algorithm named as a comprehensive learning wavelet-mutated slime mould algorithm is proposed for finding the optimal solution of combined heat and power dispatch problem with non-linear and discontinuous constraints such as valve point loading effect and prohibited operating zones in thermal only units. The proposed algorithm is based on the behavior of slimes and their reproduction stages. The wavelet mutation was introduced to help to adapt individuals to avoid local minimia. The comprehensive learning method is employed in wavelet mutated slime mould to handle the dimensional complexity that arises during the construction of new slime mould positions from parent slimes by learning from the experiences of more than one sources. Proposed hybrid slime mould algorithm which speeds up the searchability of solutions and hence enhances its robustness. Four different tests are performed and the obtained test solutions by the application of the proposed algorithm are compared with other reported solutions in the literature, in terms of generation cost and convergence speed in the CHPED problem. The obtained results are statistically verified on the Wilcoxon test.

Thermal comfort and energy conservation of a four-sided enclosed local heating device in a cold environment

It has been proven that local heating can satisfy the thermal comfort needs of people with low energy consumption. Previous research on local heating equipment has been conducted in artificial climate chambers rather than in naturally conditioned buildings. In this study, a four-sided enclosed local heating device was developed, and experiments were conducted to investigate the thermal comfort and corresponding energy consumption when 20 subjects (half male and half female) used this device in a naturally conditioned environment in winter (12–16 °C). The experimental results indicated that the overall thermal responses of the subjects stabilized after the local heating device was used for 15 min, which significantly improved the overall thermal responses of the subjects (p < 0.01); furthermore, female subjects preferred a warmer environment. The upper limbs and shanks had the most intense cold sensations in the upper and lower body, respectively. Compared with the condition without local heating, the difference in body temperature of the shank was significant (p < 0.01). In addition, the total heating power of the equipment was related to the number of heating plates turned on. The fitting results indicated that the thermoneutral temperatures when three and four heating plates were turned on were 15.7 °C and 13.5 °C, respectively. The study results contributed to providing a reference for solving heating problems in areas where there were no central-heating facilities.