Discrete Heat Sources Research Articles

ИСПОЛЬЗОВАНИЕ ОБМЕННОЙ ЭНЕРГИИ В ФОРМИРОВАНИИ ТЕПЛОВОГО СОСТОЯНИЯ ОРГАНИЗМА КРУПНОГО РОГАТОГО СКОТА

Scientific advances in biological sciences make it possible to significantly increase the energy efficiency of productive livestock. For life, as the highest form of existence of matter, thermal energy is of particular importance. It does not only connect the actions and interactions of all types of matter, it creates order from the chaotic movements of discrete heat sources, determining the measure of irreversible energy dissipation (entropy) and the change gradient of metabolic processes, “outflow and inflow of energy”, the state of saturation and deficiency of nutrients in the body. Metabolic energy is the energy of nutrients entering the tissues and cells of the body from the digestive tract. In the process of intracellular metabolism, substances are converted into new compounds, energy is released and accumulated. Approximately half of the energy is used in the electrochemical reactions of the synthesis of substances inherent in this organism. Heredity, age, environment, condition of animals influence their quantity and quality. The second half of the energy generated in the basic metabolism is “dissipated” and released into the internal and external environment. This part of the energy, in the thermoregulation process, provides isothermal state of the body of animals. Thermal homeostasis, the range of fluctuations in body temperature within the physiological norm is a significant part of the metabolic energy consumption. The article presents results of studying such consumptions when adapting to feeding factors and changes of weather conditions of cattle of different age and productivity.

Natural convection from discrete reactions on the bottom wall of an enclosure

Natural convection resulting from discrete reactive heat sources on the bottom wall of an enclosure is investigated. The rest of the bottom wall apart from the heat sources, the top wall, and the vertical walls are kept at the surrounding temperature. The remarkable findings, which have not been reported in any study, are that the flow field and temperature distribution are quite distinct depending on the odd and even number of reactive heat sources on the bottom wall. For odd numbers of heat sources, the vortices have a quite sharp corner near the center of the middle source and the base of the thermal plume is in the middle heat source. Contrary to this, for even numbers of reactive heat sources, the vortices have a blunt corner near the middle two heat sources and it seems that the thermal plume evolves from the coalescence of the middle two heat sources. Whatever the number of heat sources, for increasing the Rayleigh number, the maximum value of the stream function increases and the maximum temperature decreases. However, both of them are increased for higher values of the Frank–Kamenetskii number. It is also observed that the heat loss to the environment through the walls of the enclosure is stronger with the increase in the Rayleigh number and Frank–Kamenetskii number.

Numerical Investigation of Rayleigh–Benard Natural Convection and Entropy Generation in a Cubic Cavity With Discrete Heat Sources

Abstract Three-dimensional (3D) natural convection with isothermal discrete heat sources in a cubical cavity has been carefully studied using the 3D vector potential–vorticity formulation. Based on the finite volume method, the governing equations are solved with a homemade computational code (written in Fortran). Assuming that all cavity vertical walls are adiabatic, the upper wall of the cavity is kept at a cold temperature. However, in the bottom face, heat sources are placed under different configurations. The size of the discrete sources, their positions, and their numbers are varied for different Rayleigh numbers. The Prandtl number is fixed at 0.71. Three-dimensional distribution of the temperature iso-surfaces, the heat transfer rate, and entropy generation is evaluated. It is found that heat transfer and entropy generation are strongly affected by the arrangement of the discrete heated sources. In conclusion, the heat transfer rate is maximized, and the entropy generation is minimized for the inline arrangement of more than two heaters compared to the diagonal one.

Two-phase model for mixed convection and flow enhancement of a nanofluid in an inclined channel patterned with heated slip stripes

PurposeThe purpose of this study is to analyze the heat transfer and flow enhancement of an Al2O3-water nanofluid filling an inclined channel whose lower wall is embedded with periodically placed discrete hydrophobic heat sources. Formation of a thin depletion layer of low viscosity over each hydrophobic heated patch leads to the velocity slip and temperature jump condition at the interface of the hydrophobic patch.Design/methodology/approachThe mixed convection of the nanofluid is analysed based on the two-phase non-homogeneous model. The governing equations are solved numerically through a control volume approach. A periodic boundary condition is adopted along the longitudinal direction of the modulated channel. A velocity slip and temperature jump condition are imposed along with the hydrophobic heated stripes. The paper has validated the present non-homogeneous model with existing experimental and numerical results for particular cases. The impact of temperature jump condition and slip velocity on the flow and thermal field of the nanofluid in mixed convection is analysed for a wide range of governing parameters, namely, Reynolds number (50 ≤ Re ≤ 150), Grashof number (), nanoparticle bulk volume fraction (5), nanoparticle diameter () and the angle of inclination ().FindingsThe presence of the thin depletion layer above the heated stripes reduces the heat transfer and augments the volume flow rate. Consideration of the nanofluid as a coolant enhances the rate of heat transfer, as well as the entropy generation and friction factor compared to the clear fluid. However, the rate of increment in heat transfer suppresses by a significant margin of the loss due to enhanced entropy generation and friction factor. Heat transfer performance of the channel diminishes as the channel inclination angle with the horizontal is increased. The paper has also compared the non-homogeneous model with the corresponding homogeneous model. In the non-homogeneous formulation, the nanoparticle distribution is directly affected by the slip conditions by virtue of the no-normal flux of nanoparticles on the slip planes. For this, the slip stripes augment the impact of nanoparticle volume fraction compared to the no-slip case.Originality/valueThis paper finds that the periodically arranged hydrophobic heat sources on the lower wall of the channel create a significant augmentation in the volume flow rate, which may be crucial to augment the transport process in mini- or micro-channels. This type of configuration has not been addressed in the existing literature.

Natural convection and wall radiation in a cubical cavity with different discrete heat source configurations: Geometric parameters effect

The heat transfer by natural convection and wall radiation in filled air partially heated 3-D cavity is a problem related to different practical situations. In this study, the effects of several geometric parameters (form, orientation, size, position) of a discreet heat source on the flow structure and heat transfer characteristics are discussed for a wide range of the Rayleigh number 103≤Ra≤107 and the different wall-emissivities 0≤ε≤1. The heater is maintained at a high-temperature and positioned on a given vertical or horizontal passive wall of the enclosure. The right vertical surface of the cavity is completely isothermal at a fixed cold temperature. Flow and thermal fields were exhibited using of velocity vectors (or streamlines) and isotherms, respectively. The local and average Nusselt numbers were also presented. A numerical procedure based on both the finite volume and the discrete ordinate methods are used to solve the governing equations. It is found that the rate of heat transfer is not so sensitive to the form and the orientation of the discreet heat source. On the other hand, the position and the size of the heater are found to play a significant role in the global Nusselt number.

Enhancement of Mixed Convection in a Channel with Discrete Heat Sources by Using a Highly Conducting Porous Medium.(Dept.M)

Enhancement of Mixed Convection in a Channel with Discrete Heat Sources by Using a Highly Conducting Porous Medium.(Dept.M)

Graphene-mediated electrospray cooling for discrete heat sources in microslits

Efficient and targeted cooling of small discrete heat sources located in a confined gap, such as a microslit, is challenging. In this study, we demonstrate by using electrospray technique, the charged droplets can be effectively transported within a microslit – consisting of a top substrate and a bottom substrate – and subsequently deposited on the heated spots located within it; up to approximately 28% cooling enhancement can be obtained, and, increases to approximately 67% cooling enhancement when the surface of the heated electrode (representing a heated spot) is coated with graphene nanoplatelets (GNPs), which can be attributed to the fast water permeation. Specifically, two heated electrodes are located within the microslit – one on the top substrate (top electrode) and one on the bottom substrate (bottom electrode) – and induced convection within the microslit. We observe that majority of the charged droplets are dragged by the convection and deposited mostly on the top heated electrode, indicating that near the heated electrodes, drag force exerted on the charged droplets is significant. Interestingly, by applying the GNPs coating only on one heated electrode, for the positively charged droplets, we observe a reduction in the cooling enhancement when the top electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface repels the positively charged droplets. On the other hand, for negatively charged droplets, we observe a reduction in cooling enhancement when the bottom electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface attracts the negatively charged droplets. These findings are crucial for the design of an effective cooling system, particularly for the targeted cooling of small heat sources within microslit.

Thermal Performance of an Axially Grooved Heat Pipe Subjected to Multiple Heating Sources

An experiment of axial temperature test for a heat pipe subjected to discrete heating sources is performed for deep understanding of the thermal characteristics of axial dovetail grooved heat pipe during the unsteady and steady state. The influences of heating length, heating source position, source configurations and incline angle on the temperature profiles, heat transfer limit of the heat pipe under single heating source and multiple heating sources are examined and analyzed. As can be seen from the experiment results, the heating source shows a pivotal role in the transient characteristics of the dovetail grooved heat pipe. The heated zone of the heat pipe shows higher temperature level than that of the non-heated zone, and there is a sharp temperature variation at the transition region of the heating zone and non-heating zone. When heat is imposed at the front end of heat pipe, a dramatic increase of temperature appears soon after the heating power has reached its heat transport limitation. And this limitation can still be increased when the heating source is imposed close to the cooling section as the distance between the heating source and the cooling section decreases. Increase of heating length narrows the gap of the temperature between evaporator section and condenser section, and hence lead to lower thermal resistance, higher thermal conductivity, and superior heat transport performance. Owing to the gravity assistance on the backflow fluid in microgrooves, better thermal performance can be observed when the heat pipe works under incline state than that under horizontal state.

Multi-objective optimization of mixed convection air cooling in an inclined channel with discrete heat sources

In this paper, a multi-objective optimization of mixed convection air-cooling of two identical discrete heat sources mounted in an inclined channel is conducted to obtain the optimal design parameters, using Response Surface Methodology (RSM) and desirability function approach. Reynolds number (Re), inclination of the channel (r) and the width of the discrete heat source (b) are selected as the input parameters. The computational simulations are done for different Reynolds numbers (25-Re-250), inclination angles of the channel (0o-r-360o) and the width of the heat source (5-b-10 mm). A central composite design (CCD), which comes under the RSM approach, with design parameters was used for analysis of variance (ANOVA). A second-order regression models were developed to correlate the design parameters (Re, r and b) with mean Nusselt number (Nu) and maximum temperature (TMax). The optimum values of design parameters produce the lowest value of maximum temperature (TMax) with a higher mean Nusselt number (Nu) are Reynolds number (Re)=209.94, inclination angle of the channel (r)=330o and heat source width (b)=5.13 mm.

Role of gradients and vortexes on suitable location of discrete heat sources on a sinusoidal-wall microchannel

The idea of using the compact device with higher heat transfer potential has encouraged researchers to use microchannels. Creating sinusoidal walls is a technique leading to better effectiveness and smaller size. In this study, the effects of discrete heat sources location on heat transfer and pressure drop are investigated, using graphene nanoplatelets/water inside a sinusoidal microchannel. For this, discrete heat sources are installed in a smooth microchannel (layout A) and compared with two sinusoidal-wall microchannels. In layouts B and C, the heating sources are installed above the convergent/diverging sections, respectively. Since the velocity and temperature gradients are higher in the converging region, the heat exchange and pressure drop for layout B are greater than other ones. In other words, installing heating sources in these regions with high-temperature gradient has a more obvious positive efficacy on heat exchange. For the best layout (B), although the heat exchange compared to the base layout (A) is 37.5% higher, the pressure drop and entropy generation are higher by 79% and 35.2%, respectively. By introducing a new figure of merit (FOM), it is found that layout B is in the desirable zone.

Heat Transfer Analysis of Flat Heat Pipe With Enhanced Microchannel Shape

Flat heat pipe has many excellent characteristics such as high thermal conductivity, reversibility of heat flow direction and so on. In this paper, a flat heat pipe model with multiple microchannels is established, and the effects of different microchannel shapes and different materials on the heat transfer efficiency of flat heat pipe are studied. Then, based on the general rectangular and inverted trapezoidal microchannel shape, the enhancement is carried out. That is to fill a number of materials in the bottom of the microchannel to change the bottom shape of the microchannel. In the steady-state thermal simulation of flat heat pipe, the axial temperature of the flat heat pipe with enhanced microchannel shape is lower than that of the flat heat pipe with general microchannel, which shows that the enhanced microchannel shape is helpful to the heat dissipation of flat heat pipe. The fluid simulation results show that the enhanced rectangular microchannel shape can accelerate the flow velocity of working fluid. Therefore, the flat heat pipe with enhanced microchannel shape has better heat transfer performance. In order to obtain the local temperature of flat heat pipe quickly, the transient analytical solution is provided. In this paper, the temperature field calculated by using transient analytical solution is compared with that simulated by COMSOL. The results show that the maximum error between the results of discrete heat source model and continuous heat source model calculated by transient solution and COMSOL simulation results is less than 2%.

ГЕНЕЗИС ИСПОЛЬЗОВАНИЯ ОБМЕННОЙ ЭНЕРГИИ В ЛАКТАЦИОННОЙ ФУНКЦИИ КОРОВ РАЗНОГО ВОЗРАСТА И ПРОДУКТИВНОСТИ

The formation and development of lactation function as an integral process of reproduction concerns all systems of the whole organism. The influence of heredity and expression of a trait under the influence of the environment determines the individuality and synergy of traits that determine milk productivity. Thermal conductivity, intracellular cyclosis, membrane potential, neuro-hormonal signals, blood and lymph are the main ways of communication and mutual influence of these signs. The nutrition system is most important for lactation function. Nutrients divided during digestion into amino acids, monosaccharides, fatty acids, and other elementary parts are delivered to the breast cells, where they become a substrate for the enzymatic synthesis of milk. Circadian changes in life processes and, first of all, feed intake reactions determine the circadian frequency of feed intake and the intake of nutrients into the organism. This affects the concentration of the intracellular substrate, the activity of enzymes and the thermal state of the whole organism. For life, as the highest form of existence of matter, thermal energy is particularly important. It not only connects the actions and interactions of all types of matter, it creates order from the chaotic movements of discrete heat sources, determining the measure of irreversible energy dissipation, entropy, and the gradient of changes in the metabolic processes of “outflow and inflow of energy”, the state of saturation and nutrient deficiency. The article is based on convergence, biophysical, ethological and animal sciences. Using the Joule as a single estimate of energy consumption and work performed (milk production) increases the scientific reliability of the research.

Natural convection heat transfer from discrete heat sources mounted in rectangular enclosure surrounded by a single-phase liquid coolant (Dept.M)

In the present work, natural convection heat transfer from discrete heat sources mounted in rectangular enclosure using liquid coolant is investigated. Heat transfer from discrete heaters is non-uniform and should be accounted for by applying the averaging techniques. The averaged two-dimensional governing equations along with the standard k-e model and wall function are solved using the SIMPLE algorithm. The effects of the e cooling fluid type water and dielectrics oil, the different heat flux and time on heat transfer are investigated. The results are compared with experimental measurements. Results show that water gives a good cooling effect compared with dielectrics oil. Maximum heat transfer occurs at the heater leading and side edges. The heater surface temperature is highest at the top-row heaters. Results show also good agreement between the theoretical and experimental measurements.

Numerical study of natural convection in an enclosure with discrete heat sources on one of its vertical walls

In this study, natural convection in a fluid-filled rectangular enclosure is analyzed using COMSOL? commercial software. The fluid in which natural convection takes place is a dielectric liquid called FC-75. Attached to one of the vertical walls of the enclosure is an array of rectangular protrusions, each representing computer chips mounted on a printed circuit board. The nominal power consumed by each chip is assumed to be 0.35, 1.07, 1.65, and 2.35 W. This corresponds exactly to the values used in the experiments, which were performed once by the author of this study. The results of the experiment and the numerical study are shown as Nusselt numbers vs. Rayleigh numbers, both being the most important dimensionless parameters of natural convection. A comparison of the results has shown that COM-SOL? can achieve reliable results in similar problems, eliminating the need to build expensive experimental set-ups and spending time conducting experiments. The simulation results are aimed to be used in similar designs of electronic circuits in confined spaces.

Numerical investigation of heat transfer from heat sources placed in a horizontal rectangular channel

In this study, three dimensional mixed convection heat transfer from discrete heat sources placed in a horizontal rectangular channel has been investigated numerically. 8x4 flush-mounted discrete heat sources were mounted on the lower and upper surfaces of the channel. Air is used as working fluid (Pr0.7). The heaters at the bottom and at the top wall were kept at a constant heat flux. Side walls, upper and lower walls are insulated and considered adiabatic. Nusselt number distributions and the effect of the Grashof number (5.8x106≤ Gr* ≤ 2.3x107) and Reynolds number (150 ≤ Re ≤ 971) on the buoyancy-driven secondary flow have been investigated. Distributions of velocity vectors and temperature contours have been determined by the numerical method, and the results have been presented in detail. Governing equations were solved by the control volume method using suitable boundary conditions. The numerical parametric study was made for aspect ratio of AR=8, at various Reynolds and Grashof numbers.

Constructal design of heat sources with different heat generation rates for the hot spot mitigation

This work aims to determine the optimum heat generation ratio among discrete heat sources generating different amounts of heat in order to mitigate the hot spot. Six different heat generation ratios are considered by following the constructal design method. For comparison, the average and total heat sources’ heat generation rates are kept equal for every examined cases. Meanwhile, Reynolds number ranges from 792 to 3962. All the three heat transfer mechanisms are taken into account with an integrated approach to calculate precisely the dimensionless global conductance of the IC pack. Three dimensional simulations are done with ANSYS Fluent while measuring surface temperatures in experiments. The output parameters of the study are the surface and hot spot temperatures, Nusselt number and dimensionless global conductance change with Reynolds number and heat generation ratio. It is disclosed that relative decreasing heat generation rates are convenient for hot spot mitigation.

3D study of convection-radiation heat transfer of electronic chip inside enclosure cooled by heat sink

Three-dimensional study of convection-radiation heat transfer of a discrete heat source (chip) inside an enclosure cooled by rectangular finned heat sink is studied. Conduction heat transfer through the enclosure walls and radiation exchange between these walls are considered. Convection heat transfer on the outer surfaces of the enclosure to the ambient is considered. A complete three-dimensional mathematical model of the physical system is presented and solved numerically by using finite difference method and programmed inside MATLAB software and validated by using an experimental work. Results show good agreement between the numerical and experimental results in case of considering radiation. The impact of the enclosure aspect ratio and chip power on its cooling and heat transfer and fluid flow inside the enclosure is investigated. The results indicate that in an enclosed electronic device, the impact of the radiation is important in the thermal analysis when the natural convection cooling is presented. At chip heat flux of 5 kW/m2, neglecting radiation impact rises chip temperature by about 20%. The minimum chip temperature is obtained at an aspect ratio of 1.25. Increasing the chip heat flux and aspect ratio reduces the airflow eddies inside the enclosure. At chip heat flux of 1.25 and 5 kW/m2, radiation Nusselt number represents about 17.8 and 19.7% of the total Nusselt number, respectively.

The heat source layout optimization using deep learning surrogate modeling

In practical engineering, the layout optimization technique driven by the thermal performance is faced with a severe computational burden when directly integrating the numerical analysis tool of temperature simulation into the optimization loop. To alleviate this difficulty, this paper presents a novel deep learning surrogate-assisted heat source layout optimization method. First, two sampling strategies, namely the random sampling strategy and the evolving sampling strategy, are proposed to produce diversified training data. Then, regarding mapping between the layout and the corresponding temperature field as an image-to-image regression task, the feature pyramid network (FPN), a kind of deep neural network, is trained to learn the inherent laws, which plays as a surrogate model to evaluate the thermal performance of the domain with respect to different input layouts accurately and efficiently. Finally, the neighborhood search-based layout optimization (NSLO) algorithm is proposed and combined with the FPN surrogate to solve discrete heat source layout optimization problems. A typical two-dimensional heat conduction optimization problem is investigated to demonstrate the feasibility and effectiveness of the proposed deep learning surrogate-assisted layout optimization framework.

Thermal stack airflows inside the solar chimney with discrete heat sources: Reversal flow regime defined by chimney inclination and thermal Rayleigh number

Present work numerically and theoretically investigates the fluid flow and heat transfer in an inclined solar chimney induced by thermal buoyancy within a range of thermal Rayleigh numbers (Ra) and chimney inclination angles (α). Transport paths of fluid and heat were visualized by streamlines and heatlines, respectively. Backflow could be observed in the solar chimney when Ra increases beyond a certain value, and it directly paralyses the ventilation of the chimney. Numerical results further demonstrate that the larger the inclination angle α is, the smaller the corresponding critical Ra number of the reverse flow occurs at the glass side is. The larger the inclination angle α is, the greater Nusselt (Nu) value of the absorber wall is, while its increment rate decreases gradually with the increase of the inclination angle α, when thermal Ra is maintained. As α varies from 30° to 90°, corresponding critical Ra for reversal flows gradually decreases; furthermore, these critical values obtained by the theoretical solutions were higher than those from simulation. Volume flow rates increase positively with Ra when α is no more than 30°; however, they increase initially and then decline with Ra when α is no less than 45°. In order to enhance ventilation performance, a solar chimney flush attached with discrete heating sources on the glazing wall is proposed. The numerical results indicated that modified inclined solar chimney with discrete heating sources could enhancing its ventilation performance by preventing reverse flow occurring in the channel. Our investigations also showed that the optimal inclination angle for maximum volume flow rate heavily depends on Ra. This research could provide necessary technical support and guidance for solar energy utilization and building energy conservation through air channel in building envelopes.

A simple direct heating thermal immersed boundary-lattice Boltzmann method for its application in incompressible flow

A simple direct heating thermal immersed boundary-lattice Boltzmann method for buoyancy-driven incompressible flow with complex geometry boundaries is developed to simulate natural convection with curved boundary. In the newly developed method, both Dirichlet and Neumann boundary conditions in macroscopic equation are deduced into a novel mesoscopic discrete heat source. The mesoscopic discrete heat source consists of simplified explicit discrete heat source scheme which reduces the computational complexities and is introduced into lattice Boltzmann equation for temperature field, which extends the idea of the previous direct forcing IB-LBM. Both isothermal boundary condition (i.e. Dirichlet boundary condition) and constant heat flux boundary condition (i.e. Neumann boundary condition) are considered in our simulations. The efficiency and accuracy of the present method are demonstrated by simulating both two dimensional and three dimensional thermal flow with curved boundaries. Numerical results indicate that the efficiency and accuracy of the present method are well consistent with experimental and the other numerical results. The present method has also been successfully applied to three dimensional simulations of natural convection in a thin annulus with adiabatic wall at both vertical sides.