Heat Transfer Generation Research Articles

Simplified structural analysis of laminated glass panels during fire exposure

Due to their high aesthetic value, energy-efficient properties, and contribution to daylighting, the demand for using glass panels in modern buildings has considerably increased over the past decades. However, ordinary glass panels are highly susceptible to cracking during a fire because of the temperature difference between the part of the glass exposed to the fire and the part protected by the frame. Damage to the glass can allow additional oxygen intake, leading to the flashover phenomenon significantly increasing fire severity. Laminated glass is superior to ordinary glass in its impact resistance, sound insulation, and ability to maintain post-breakage integrity. This paper provides a simplified method to study the effect of temperature gradients on the cracking behaviour of laminated glass panels. The temperature of the unprotected portion of the glass panel is first estimated by evaluating the mid-thickness temperature using the general heat transfer equation. Then, equations developed based on a parametric study that utilized ABAQUS are proposed to estimate the exposed and unexposed surface temperatures. This step was followed by evaluating the temperature of the protected glass portion. Subsequently, a method based on strain-equilibrium principles was developed to predict the corresponding maximum thermal stress. Comparisons with experimental and numerical work by others validated the proposed method.

Discrete element method study of the mixing and heat transfer behaviour of a binary‐size granular system in a rotating drum

AbstractUnderstanding the internal solid motion and heat transfer behaviour within rotating drums is paramount for their design and operation across various industries. The discrete element method (DEM) is utilized to elucidate the general flow, mixing, and heat transfer characteristics of particles within rotating drums. Following model validation, this study delves into the mixing behaviour and heat transfer patterns of binary‐size particles in the rotating drum, while also assessing the impact of size ratio and rotating speed. The findings reveal that variations in particle size result in noticeable radial segregation, consequently affecting the heat transfer dynamics of solid phase within the system. Higher rotating speeds enhance mixing and dispersion of solid phase but lead to a decrease in the averaged particle temperature. Furthermore, the heat flux exhibits a negative correlation with particle size. Distinct heat transfer behaviours are observed among particles of different sizes in both active and passive areas, with larger particle size ratios exacerbating segregation, potentially impacting final product quality. In summary, these findings offer crucial insights into heat transfer phenomena in rotating drums, aiding in the design and operation of apparatus.

Assessment of the influence of flushing on the wear and morphological properties of the tool during electrical discharge machining

The present study is an integrated approach of experimental and simulation processes to investigate the influences of the flushing on the wear, textural feature, heat dissipation, tool-tip temperature, and elemental contents of the electrical discharge machining-tool. The general heat transfer equation in cylindrical coordinates is used to explain the thermal phenomenon through the tool, where the boundary conditions are influenced by convective interactions and dimensionless numbers. The inter-electrode flushing is considered a micro-channel flow, and the used model is conceptualized from “Hazen–Poiseuille observation.” It is observed that the adopted model has a prediction error of 8.503% and can accurately explain the thermal consequences of the process. The study reveals that tool wear is influenced by flushing velocity and flushing pressure. The tool-tip temperature reduces with the Reynolds number, and effectual expelling of the debris can be ensued with a flushing of a higher Reynolds number (Re). However, the increment of Re beyond 4500 provides rapid heat dissipation, which produces extensive residual stress and creates cracks on the surface.

Modeling of Non-stationary Heat Transfer of Floor Structures of Rooms with Artificial Ice

Statement of the problem. The purpose of the scientific article is to develop an adjusted methodology and program for calculating the non-stationary heat exchange of floor structures with artificial ice, taking into account the asymmetric radiation cooling of heat exchange surfaces to determine the time they reach the critical temperature. Results. An important characteristic of the adjusted technique is the use of the average coefficient of irradiation of the surfaces of the structure, as well as taking into account the displacement of the thermal center during its asymmetric heating. The technique takes into account the radiant component from the ice surface in the determining generalized heat transfer coefficient. Conclusions. The considered features make it possible to increase the accuracy of calculating the cooling time of the surface of the structure to critical values, which can be used to adjust the operating modes of microclimatic systems of rooms with artificial ice.

Heat transfer characteristics of R134a flow boiling in a microfin tube under typical ORC pressures based on comparison with a smooth tube

The experimental investigation on the flow boiling heat transfer of an organic working fluid under typical organic Rankine cycle (ORC) operating conditions is insufficient, which directly affects the performance of the ORC system. In this paper, the flow boiling characteristics of R134a in a horizontal microfin tube were experimentally investigated in the reduced pressure range 0.6 ∼ 0.9. The general convection heat transfer characteristics of R134a flow boiling, along with the effects of heat flux, mass flux, pressure, and rewetting conditions, were investigated in a microfin tube and compared with that in a smooth tube. Results show that the main flow regime in the microfin tube under typical ORC operating pressures is the stratified flow with dry-out occurring at the top surface. The microfin effectively enhances the heat transfer and restrains the wall temperature separation through inducing strong helical flow due to buoyancy and centrifugal forces. With the heat flux increasing, the micro-fin strengthens the nucleate boiling by enhancing the vaporization cores, leading to more pronounced heat transfer enhancement compared with that in the smooth tube. The heat transfer on the bottom surface shows almost negligible sensitivity to variations in mass flux. However, in regions of high vapor quality, an increase in mass flux results in higher heat transfer coefficients on the top surface. Due to the interaction between intensified nucleate boiling and weakened gas convection when pressure is increased, it slightly affects the heat transfer coefficient. Unlike the smooth tube, the rewetting in the microfin tube can be maintained within a larger range of vapor quality due to the spiral flow caused by the micro-fin.

THERMAL ANALYSIS OF STEEL PIPE

This study is based on the general heat transfer between two pipe joints. Three sample tubes are used in this study. A different connection method is treated Arc welding method is used to connect pipes. Two identical pipe sections are joined together. In this study, the thermal conditions of heat transfer between the pipes are determined using Ansys software. Key Words: Welding, Pipe, Heat Transfer, Temperature...

Heat transfer study and optimization of nanofluid triangular cavity with a pentagonal barrier by finite element approach and RSM

Nowadays, several engineering applications and academic investigations have demonstrated the significance of heat transfers in general and mixed convection heat transfer (MCHT) in particular in cavities containing obstacles. This study's main goal is to analyze the MCHT of a nanofluid in a triangular cavity with a pentagonal barrier using magneto hydrodynamics (MHD). The cavity's-oriented walls are continuous cold temperature, whereas the bottom wall of the triangle and all pentagonal obstacle walls are kept at a constant high temperature. For solving governing equations, we utilized the Galerkin's finite element approach. Four dimensionless factors, Richardson number (0.01 ≤ Ri ≤ 5), Reynolds number (10 ≤ Re ≤ 50), Buoyancy ratio (0.01 ≤ Br ≤ 10) and Hartmann number (0 ≤ Ha ≤20) are examined for their effects on streamlines, isotherms, concentration, velocity, and the Nusselt number. Also, with the help of Taguchi method and Response Surface Method (RSM) the optimization of the studied dimensionless parameters has been done. The optimum values of Ri, Re, Ha and Br are obtained 4.95, 30.49,18.35 and 0.05 respectively. Ultimately, a correlation has been extracted for obtaining the optimum average Nusselt number (Nu) in mentioned cavity.

Entropy generation and natural convection analyses in a non-darcy porous square cavity with thermal radiation and viscous dissipation

This study investigates the phenomena of fluid flows, general heat transfer and entropy generation on transient natural convection in a square cavity occupied with a saturated non-Darcy porous medium with dissipation effects and thermal radiation. The governing equations for the fluid flows and heat transfer, with corresponding boundary and initial conditions in the porous system are solved with the use of the alternate direct implicit method (ADI). The impact of the dimensionless parameters on the flow and thermal effect including entropy generation, with the fluid structure interaction cases are discussed. The following ranges have been used for simulations for the relevant dimensionless parameters: Grashof Number (103≤Gr≤107), Rayleigh number (103≤Ra≤106), Eckert number (0≤Ec≤5×10-5), the Forschheimer resistance (0≤Γ,γ≤10), radiation parameter (0≤Rd≤5) and Prandtl number (0≤Pr≤10). The present numerical work, compared with previously published work are made, and excellent agreement is discovered. According to the simulation results, the top right wall and base of the heated wall are where entropy is being generated most. Furthermore, as the Forschheimer resistance increases the flow rate, the heat transfer, and entropy production reduce. As Pr decreases at Ra=105 the buoyancy force takes control of the flow fields when the porous medium’s resistance weakens. As a result, the fluid flow becomes stronger.

Thermodynamic and heat transfer models for refueling hydrogen vehicles: Formulation, validation and application

Compression is currently the preferred storage technology for hydrogen vehicles due to its quick refueling process and relatively simple design. However, the temperature rise associated with fast filling must be controlled to ensure its safe operation. This article discusses general heat transfer models based on the mass and energy balance equations for the refueling process of the compressed hydrogen storage tank. Depending on the way of treating the geometric structure of the storage tank, three general lumped parameter models of single-zone (hydrogen), dual-zone (hydrogen and tank wall) and triple-zone (hydrogen, tank wall liner and shell) are built. The general single-zone and dual-zone models are reduced to some special cases which have been published. Under adiabatic and diathermic conditions, four models, including single-zone, dual-zone single-temperature (hydrogen temperature), dual-zone dual-temperature (hydrogen and tank wall temperatures) and triple-zone triple-temperature (hydrogen, tank wall liner and tank wall shell temperatures), are implemented using Matlab/Simulink™ to simulate the hydrogen refueling process under corresponding conditions. Analytical solutions of single-zone and dual-zone lumped parameter models are derived. The temperature rises of the compressed hydrogen storage tank are described by comparing the analytical solution with the numerical solution. The proposed general models were applied to estimate the final hydrogen temperature and mass, the SOC, the refueling time, and the precooling hydrogen temperature, reviewed and summarized in this article. The analytical solutions of the heat transfer during hydrogen refueling can provide theoretical guidance for improving the refueling efficiency and enhancing refueling safety.

Методика расчета тепловлагопереноса в специальной защитной обуви пожарного-спасателя

Разработана методика расчета тепловлагопереноса в специальной защитной обуви пожарного-спасателя, которая позволяет учесть терморегуляционные механизмы в стопе для оценки комфортности обуви, изготовленной из определенных пакетов материалов и эксплуатируемой в широком диапазоне внешних воздействий, как по тепловым и влажностным факторам, так и в зависимости от уровня активности (тяжести выполняемой работы) пожарного-спасателя. Для определения безопасной работы в специальной защитной обуви необходима оценка степени деструкции кожи (степень ожога). The article describes the solution of the problem of non-stationary heat transfer in the «foot – footwear – environment» system for multilayer flat, cylindrical or spherical materials and non-stationary heat transfer from the outer surface of the special protective footwear to firefighter's foot. The well-known biothermal equation and the generalized heat transfer equation are used as the basis for the model of heat and moisture transfer in boot materials, taking into account sweating on the human skin surface. It is possible to get data on the thermal state of the foot under various conditions by solving these equations with appropriate coefficients and boundary conditions: zero heat flow in the center of the foot and convective environmental conditions on the surface of the last layer of porous shoe material. Modeling for three cases of human activity: resting state, walking with a speed of 4.8 km/h, light work (in the office room) under the same environmental conditions was carried out. The obtained results showed that the model of heat and moisture transfer in protective boots, taking into account thermoregulatory processes in the foot, can be used to predict the functionality of the materials for the bottom and top of the boots in terms of the skin burns likelihood. The method for calculating heat and moisture transfer in special protective boots for a firefighter-rescuer has been developed, based on the simulation, which includes: - construction of a geometric image of a model of protective boots; - determination of the firefighter-rescuer operating mode; - selection of material packages for the details of the boot top and bottom. An indication of the thermophysical, structural, geometric characteristics of the materials allows, using the selected climatic conditions and the firefighter-rescuer operating mode, to establish the initial and boundary conditions for solving the basic system of heat and moisture transfer equations. The solution of the system of equations with the boundary and initial conditions makes it possible to assess the comfort of boots, as well as the rate of destruction of the skin under intense thermal effects (the probability of burns of varying degrees). Based on this analysis, further optimization of the boots design can be carried out by choosing different material packages or evaluating the thermal effect under various external influences.

Saturated/subcooled flow boiling heat transfer inside micro/mini-channels: A new prediction correlation and experiment evaluation

In this study, a new general heat transfer correlation was developed for predicting the saturated/subcooled flow boiling heat transfer coefficient in micro/mini-channels. The collected database included 4250 data points, which covered eleven different working fluids. These included deionized water, new electronic fluorinated solutions, and refrigerants, among others. The temperature range of the experimental operation was from 0 to 100 °C with a saturated pressure of 101 to 775 kPa. The hydraulic diameter of micro/mini-channels varied from 0.1 to 3 mm, and the liquid sub-cooling was between 0 and 80 K. The database included various operation conditions, such as mass flux, heat flux, vapor quality, and reduced pressure. The liquid and vapor Reynolds numbers were calculated based on the hydraulic diameter. Six existing flow boiling heat transfer correlations were employed to evaluate the present data points in micro/mini-channels. However, it was observed that these correlations were unable to predict the present data points accurately due to high liquid sub-cooling and heat flux. Therefore, a new prediction correlation based on the present database was developed by dividing flow boiling into three stages, including subcooled boiling, developed nucleate boiling and nucleate boiling deterioration. This new prediction model can predict more than 80% of data points within ±30% error band.

Research Progress on Convective Heat Transfer Characteristics of Supercritical Fluids in Curved Tube

Because of their compact structure, ease of processing and higher heat transfer coefficient, curved-tube heat exchangers are widely applied in various industry applications, such as nuclear power systems, solar-powered engineering, aircraft engine cooling systems and refrigeration and cryogenic systems. Accurate knowledge about the heat transfer characteristics of the supercritical fluids in the tube is critical to the design and optimization of a curved-tube heat exchanger. The available literature indicates that the flow of supercritical fluids flowing in curved tubes affected by the dual effects of the buoyancy force and centrifugal force is more complex compared to straight tubes. Therefore, to obtain insight into their unique characteristics and further research progress, this paper presents a comprehensive review of available experimental and numerical research works on fluids at supercritical pressure flowing in curved tubes. Overall, the secondary flow caused by the curvature enhances the heat transfer and delays the heat transfer deterioration, but it also causes a non-uniform heat transfer distribution along the circumferential direction, and the strengthening performance of the curved tube is damaged. Compared with the more mature theories regarding straight tubes, the flow structure, the coupling mechanism of buoyancy and centrifugal force, and the general heat transfer correlation of supercritical fluids in a curved tube still urgently need to be further studied. Most importantly, studies on the suppression of heat transfer oscillations and heat transfer inhomogeneities specific to curved tubes are scarce. Considering the current status and shortcomings of existing studies, some study topics for supercritical fluids in a curved tube are proposed.

Study of the Effect of the Reduced Pressure on a Mechanistic Heat Transfer Model for Flow Boiling of CO2 in Macroscale and Microscale Tubes

The effect of the reduced pressure on flow boiling of CO2 in macroscale- and microscale-tubes was analyzed in this paper. First, flow boiling heat transfer at high and low reduced pressures were simulated using a general mechanistic heat transfer model for flow boiling CO2 to analyze the heat transfer mechanisms. Then, the simulated heat transfer coefficients were compared to an experimental database at the reduced pressure from 0.1332 to 0.9082 (the corresponding saturation temperature from -40.6 to 26.77 °C), the tube diameter from 0.529 to 9.52 mm, the heat flux from 2 to 72 kW/m2 and the mass flux from 100 to 1500 kg/m2s. The model predicts 81.3% of the data before the dryout inception within ±30% while it only predicts 21% of data in the dryout and mist flow regimes within ±30%. The poor prediction of the heat transfer in these two regimes are because the model does not capture the dryout inception and completion. Furthermore, the heat transfer mechanisms are discussed from the standpoint of the flow regime variations and unstable flow boiling phenomena in macroscale and microscale tubes. It is recommended that the model should be improved by considering the mechanisms at low and high reduced pressures.

Heat transfer correlation for film boiling during quenching of micro-structured surfaces

This work investigates the separate effects of liquid subcooling, substrate material, and surface micro-structure on the film boiling characteristics. A quenching facility was constructed to conduct vertical quenching experiments using rods with various substrate materials and surface morphologies. The surface morphology is characterized using field emission scanning electron microscopy (FESEM). Stainless steel, zirconium, and Inconel-600 rods are used with a diameter of 9.5 mm that simulates the size of fuel rods in commercial nuclear reactors. Other Inconel-600 rods with different porosity percentages are used to study the effect of fouling on the quenching behavior. The surface temperature and wall heat flux at the surface are deducted from the temperatures measured by the thermocouples embedded inside the rods using an inverse heat conduction code, from which the heat transfer coefficient and Nusselt number are calculated. The data are used to develop a generalized heat transfer correlations that includes the effects of liquid subcooling and substrate materials. It predicted the data within ±40% error band. The results also suggest that the heat transfer coefficient increases gradually as the sample cools down and in higher subcooled pools. Moreover, the variation in the substrate material shows a significant effect on the heat transfer characteristics. However, the surface micro-structure impact on the film boiling regime is negligible.

Shape optimization of a thermal insulation problem

We study a shape optimization problem involving a solid Ksubset {mathbb {R}}^n that is maintained at constant temperature and is enveloped by a layer of insulating material Omega which obeys a generalized boundary heat transfer law. We minimize the energy of such configurations among all (K,Omega ) with prescribed measure for K and Omega , and no topological or geometrical constraints. In the convection case (corresponding to Robin boundary conditions on partial Omega ) we obtain a full description of minimizers, while for general heat transfer conditions, we prove the existence and regularity of solutions and give a partial description of minimizers.

Bending and free vibration analyses of multi-directional functionally graded plates in thermal environment: A three-dimensional Isogeometric Analysis approach

This study presents a three-dimensional numerical approach to analyze the bending and free vibration behavior of multi-directional functionally-graded plates under the effect of thermal environment. The effective material properties are temperature dependent and the temperature field within the plate’s volume are determined directly based on a generalized heat transfer equation. The governing equations for static bending and free vibration analyses are developed based on the three-dimensional elasticity theory. The Isogeometric Analysis approach is utilized to discretize the weak forms of heat transfer equation, static bending equation and free vibration equation. A iterative scheme is proposed to heat transfer problems with material being dependent on temperature. Rectangular and circular plates are investigated to validate the efficiency of Isogeometric Analysis approach on modeling and analyzing aspects. Various numerical examples are also presented to validate the accuracy of the proposed approach and investigate the influences of material variation profiles, thickness ratios, temperature rise, and boundary conditions on thermal responses of the plates.

General heat transfer correlations for supercritical carbon dioxide heated in vertical tubes for upward and downward flows

Supercritical CO2 is a promising working fluid for many industrial applications. To improve the performances of relevant components and systems, the prediction of the heat transfer of supercritical CO2 is an important research topic. General explicit heat transfer correlations of supercritical CO2 for upward and downward flows heated in circular tubes were established using the genetic programming (GP) method. A total of 12720 experimental data points from 22 publications were collected to develop the models. The data included hydraulic diameter from 0.0992 to 22 mm, bulk temperature from -6.0 to 134.5°C, pressure from 7.44 to 10.50 MPa, mass flux from 50 to 4834 kg•(m2•s)−1, heat flux from 2.9 to 748 kW•m−2 and wall temperature from 6.4 to 368.2°C. The database was divided into four parts according to the flow direction and the relationship between the bulk temperature and the pseudo-critical temperature. The developed correlations considered various non-dimensional parameters as the independent variables to reflect the effects of supercritical properties, flow acceleration and buoyancy on the heat transfer. The results showed that the proposed correlations had excellent accuracy with a mean absolute relative error (MARE) of 20.10% based on prediction with the iterated wall temperature. The developed correlations outperformed the existing correlations in the literature. Compared to other correlations, the trend analysis indicated that these newly developed correlations could appropriately present the physics sense when the condition parameters varied.

Simulation and Optimization of a Planar-Type Micro-Hotplate with Si3N4-SiO2 Transverse Composite Dielectric Layer and Annular Heater.

Micro-hotplates (MHPs) have become widely used basic structures in many micro sensors and actuators. Based on the analysis of the general heat transfer model, we propose a new MHP design based on a transversal composite dielectric layer, consisting of different heat transfer materials. Two general proven materials with different thermal conductivity, Si3N4 and SiO2, are chosen to form the composite dielectric layer. An annular heater is designed with a plurality of concentric rings connected with each other. The relationship between MHP performance and its geometrical parameters, including temperature distribution and uniformity, thermal deformation, and power dissipation, has been fully investigated using COMSOL simulation. The results demonstrate that the new planar MHP of 2 μm thick with a Si3N4-SiO2 composite dielectric layer and annular heater can reach 300 °C at a power of 35.2 mW with a mechanical deformation of 0.132 μm, at a large heating area of about 0.5 mm2. The introduction of the composite dielectric layer effectively reduces the lateral heat conduction loss and alleviates the mechanical deformation of the planar MHP compared with a single SiO2 dielectric layer or Si3N4 dielectric layer.

Solar parabolic dish collector for concentrated solar thermal systems: a review and recommendations.

Energy demand in the present scenario is rising to meet the increasing demands of energy usage. On the other hand, the use for renewable energy sources now becomes essential to mitigate the climate change as well as to reduce gradual depletion of fossil fuels. Among these renewable energy sources, solar energy particularly solar thermal systems have phenomenal scope in present and future research. In solar thermal systems, concentrators are used to extract the energy from solar irradiation and convert it into useful form. Among different types of solar concentrators, the parabolic dish solar concentrator is preferred as it has high efficiency, high power density, low maintenance, and potential for long durability. In this paper, a detailed review has been carried out on the design parameters like focal length, concentration ratio, and rim angle of the parabolic dish solar concentrator system for achieving higher overall efficiency. The effects of different geometrical shapes of receivers on the overall heat transfer rates are discussed in this paper. Conical shaped receiver is having high overall optical and thermal efficiency comparing with other shapes of receivers. This study also shows that how the thermal performance of the receiver gets enhanced by 10-13% using nanofluids in place of general heat transfer fluids. The paper highlights different models using ray-tracing method for estimation and evaluation of the solar irradiation distribution on the receiver surface. The empirical relations for the design of parabolic dish solar concentrator system are derived for estimating overall concentrator efficiency and heat available at the receiver are given in this review. From the literature, the thermal performance of the receiver affecting the overall performance of the system is observed. Thermal losses due to geometrical properties and ordination of the receiver are explained in the observation section.

О НАДЕЖНОСТИ ОЦЕНКИ ТЕПЛОВОГО РЕЖИМА ПОДЗЕМНОГО ОБЪЕКТА ХРАНЕНИЯ ОТРАБОТАВШЕГО ЯДЕРНОГО ТОПЛИВА НА БАЗЕ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ

The results of checking the reliability of a previously performed assessment of the thermal mode of an underground facility for long-term storage of spent nuclear fuel in a variant of an integrated reinforced concrete structure on three calculation grids (Coarse, Normal, Fine) are presented. The test was performed on a previously developed three-dimensional computer model in the COMSOL program. The mathematical basis of the model is following: continuity equation, Navier-Stokes equations averaged by Reynolds, standard turbulence model and general heat transfer equation. The consideration of mixed convection conditions was implemented in the "incompressible ideal gas" approximation. It was shown that when using computational grids with high resolution (Normal, Fine), some characteristics may be predicted. They are: temperature increase inside the built-in structure and at the boundary "rock mass - built-in structure" no more than 1°C; a significant change in the structure of the spatial distribution of temperature and an increase in maximum temperatures by about 1°C on the surface of the built-in structure. The duration of calculations in variants with small grids increased approximately 3.4 (Normal) and 7.7 (Fine) times, respectively