Three-dimensional Steady-state Heat Transfer Research Articles

Experimental and Numerical Study of Newly Assembled Lightweight Radiant Floor Heating System

In this study, the heating capacity of a new prefabricated assembled hot water radiant modular heating system made from a recycled waste building masonry structure is investigated through experimental and numerical simulation methods. The heating capacity of the system in different working conditions (a water supply temperature of 48 °C, 51 °C, 56 °C, and 61 °C; a flow rate of 0.49 m3/h, 0.35 m3/h, and 0.21 m3/h) is analyzed and verified. A three-dimensional steady-state heat transfer numerical model of the floor heat transfer of the module is established, and the accuracy of the model is verified through the measured results to investigate the heating capacity of this system under different water supply temperatures, flow rates and coil spacings. The results show that the new prefabricated hot water radiant module heating system has a 0.9 °C higher air temperature and 2.1 °C higher average floor surface temperature than the traditional wet floor radiant heating system under the same experimental conditions, and the response time is 44% shorter. The water supply temperature can significantly change the heating capacity of the system, while the water supply flow rate has little effect on the system. The established three-dimensional steady-state numerical model can be in good agreement with the measured results. This study can provide an experimental and theoretical basis for the design and application of such systems.

Insulation performance evaluation of stone-finished exterior insulation systems with insulation frames for green remodeling of concrete exterior walls

This study aimed to evaluate the thermal bridge reduction effect of insulation frames applied to a stone-finished exterior insulation system, which is commonly used in green remodeling projects. The insulation performance of the exterior walls and the energy performance of the building in a baseline case in which an existing steel pipe frame was applied were compared with those in cases alt 1 and alt 2, which included application of double- and single-wired truss-shaped insulation frames, respectively. First, a three-dimensional steady-state heat transfer simulation was conducted for the exterior wall-floor joint of the model building, and the effective U-factor was obtained. Next, mock-ups were constructed and the U-factor was tested to verify the insulation performance of cases alt 1 and alt 2. The heat loss decreased as the effective U-factors of alt 1 and alt 2 decreased by 19.0 % and 19.7 %, respectively, compared to the baseline case, according to the heat transfer simulations. In the mock-up test, the U-factors of alt 1 and alt 2 were similar to design U-factor, indicating almost no heat loss caused by the thermal bridges. Notably, the U-factor of alt 2 was 2.4 % lower than that of alt 1. Finally the energy performance of the entire building was compared through dynamic building energy simulations by reflecting the thermal bridging effect. The annual heating and cooling energy use of alt 1 and alt 2 were 2.5 % and 2.6 % lower than those of the baseline case, respectively, confirming the energy-saving effect of reducing thermal bridges.

A new set of explicit solutions for postbuckling behaviour of anisotropic shear deformable laminated cylindrical shells with general imperfection distribution and thermal loading

Thermal postbuckling analysis is presented for shear-deformable anisotropic laminated cylindrical shell with general imperfection distribution under several typical temperature fields are analyzed, including uniform temperature, tent-like linear distribution, axial and circumferential quadratic parabolic temperature fields over the shell surface and through the shell thickness. On this basis, the general temperature distribution can be obtained based on the three-dimensional steady-state heat transfer equation. At the same time, based on the high order shear deformation theory including anisotropic coupling effect, geometrically nonlinear large deflection displacement-strain relationship, the general initial geometric imperfections obtained by measurement and analytical means are introduced, and the thermal buckling equilibrium differential equation of anisotropic shear deformable laminated cylindrical shell with initial imperfections is established. A two-step perturbation-Galerkin integral method is used to obtain explicit solutions for the path development direction of post-thermal buckling equilibrium. The results of parameter analysis show that the material properties and temperature dependence, temperature distribution, lay-up and geometric parameters such as radius-to-thickness ratio have important effects on the thermal buckling load and postbuckling equilibrium path. The present method provides an effective theoretical prediction and analysis method for the design of the carrying capacity of submarine pipelines.

Insulation Performance Comparison of Curtain Wall Systems with Existing Pipe Frames and Truss-Shaped Insulation Frames

The purpose of this study was to compare insulation performance between a base case that applied the existing steel pipe frame and an alternative case that reduced thermal bridging by applying a truss-shaped insulation frame (TIF) to a back frame type curtain wall. Insulation performance was compared by obtaining the effective U-factor and the lowest indoor surface temperature through a three-dimensional steady-state heat transfer simulation. In addition, mock-up tests were performed to compare the U-factors of the base case and alternative case. The simulation results showed that the effective U-factor of the alternative case was 36% lower than in the base case, a significant heat loss reduction. The lowest indoor surface temperature of the alternative case was 0.5 °C higher than in the base case, showing that the surface condensation risk also decreased. In the mock-up test results, the alternative case U-factor was 33% lower than in the base case, confirming the associated large heat loss reduction. For the base case, both the effective U-factor by simulation and the U-factor by the mock-up test were much higher than the design U-factor according to the Korean Design Standard, which neglects thermal bridging, indicating a significantly increased heat loss caused by this factor. For the alternative case, however, both U-factors were similar to the design U-factor.

Effects of solid particle thermal conductivity on heat storage performance of heat storage bed

The thermal properties of particles are important parameters that directly affect the heat storage performance of the solid particle heat storage bed. This paper reports the effects of solid particle thermal conductivity on heat storage performance of heat storage bed. A three-dimensional steady-state heat transfer model of heat storage bed with a single vacancy was established using ANSYS 19.0. The effects of thermal conductivity of particles were studied. With the increase in thermal conductivity of particles, the effect of the vacancy on heat storage particle bed heat transfer performance increases, the affected area size increases, so the heat storage and release performance of heat storage bed decreases. With the increase of thermal conductivity of particles from 0.5 W/ (m·K) to 50 W/ (m·K), the size of the affected region increased from 0.61 times of particle size to 1.82 times of particle size in the direction perpendicular to the heat transfer, and the size of the affected region increased from 1.61 times of particle size to 3.91 times of particle size in upstream of the direction parallel to the heat transfer. At the same time, the size of the affected region increased from 1.69 times of particle size to 3.93 times of particle size in downstream of the direction parallel to the heat transfer. It can provide a basis for improving the thermal resistance theory.

Effect of the single vacancy in particle pile on heat transfer performance of particle pile

This paper reports the effect of a single vacancy on heat transfer of particle pile. A three-dimensional steady-state heat transfer model of particle pile with a single vacancy was established. The effects on the temperature distribution, heat transfer mode and heat flux characteristics of the particle pile were studied. In the area close to the vacancy, the particle temperature distribution is significantly affected, and the average temperature line is significantly deformed. The heat conduction between particles along the Y-direction is the dominant heat transfer mode around the vacancy. Compared with a particle pile without vacancy, the total heat flux at the hot wall decreases by 0.63% and the apparent thermal resistance of the particle pile increases by 0.71%. The size of the region affected by a vacancy on heat transfer was determined. At the X-direction, the size of the region affected by a vacancy is 1.79 times of particle size. Upstream position of vacancy at the Y-direction, the size of the region is 4.03 times of particle size. Downstream position of vacancy at the Y-direction, the size of the region is 3.81 times of particle size. The research results can be used to improve the thermal resistance network theory.

Probing torque, traverse force and tool durability in friction stir welding of aluminum alloys

A coupled theoretical and experimental study was undertaken to examine the impact of plate thickness, alloy strength and processing conditions on the susceptibility of tool failure in friction stir welding of AA7075 and AA7039. A three-dimensional steady-state heat transfer model was used to compute the temperature field in tool and workpiece alloy. The torque and traverse force, and the mechanical stresses on the tool were estimated analytically and validated with the corresponding experimentally measured results for a range of processing conditions. The propensity of the tool to failure was assessed by a durability factor, which was estimated as a ratio of tool material strength at the computed peak temperature and the resultant mechanical stress on the tool probe. The results showed that rise in welding speed, alloy strength and plate thickness could lead to increased mechanical stresses on tool probe, reduced durability factor and enhanced susceptibility of tool failure. The overall methodology was used successfully to provide the underlying basis for two reported practical examples of tool failures in friction stir welding.

3-D numerical study of the effect of Reynolds number and baffle angle on heat transfer and pressure drop of turbulent flow of air through rectangular duct of very small height

Summary Present article illustrates a computational study of three-dimensional steady state heat transfer and high turbulent flow characteristics through a rectangular duct with constant heat fluxed upper wall and single rectangular cross-sectioned baffle insertion at different angles. RNG k–ɛ model along with standard wall function based computations has been accomplished applying the finite volume method, and SIMPLE algorithm has been executed for solving the governing equations. For a Reynolds number, Re of 10,000 to 50,000, Prandtl Number, Pr of 0.707 and baffle angle, α of 30°, 60°, 90°, 120°, 150°, computational studies are executed, centred onto the hydraulic diameter, D h , test section and hydrodynamic entry length of the duct. Flow field has been solved using Ansys Fluent 14.0 software. Study exposes that baffled rectangular duct has a higher average Nusselt number, Nu and Darcy friction factor, f compared to a smooth rectangular duct. Nu as well as f are found to be maximum at 90° baffle angle. Results illustrate that both α and Re play a significant role in heat transfer as well as flow characteristics and also effects TEF. The correctness of the results attained in this study is corroborated by comparing the results with those existing in the literature for smooth rectangular duct within a precision of ±2% for f and ±4% for Nu .

Influence of Thermal Bridges on the Insulation Performance of Curtain Wall Panel Systems

AbstrctThermal insulation plays a key role in saving energy consumed by buildings. To obtain a high level of insulation performance, repeated thermal bridges should be minimized. These bridges may cause a substantial heat loss through the building envelope. Recently, the application of curtain walls has been rapidly increasing. However, thermal bridges frequently occur in the non-vision panel system in which the insulation materials are installed because of the numerous metal members passing through the insulation layer. The aim of this study was to analyze the influence of thermal bridges on the insulation performance of curtain wall panels in terms of the energy performance and internal surface condensation risk. A three-dimensional steady state heat transfer simulation was performed for four types of panel systems: insulation-joined metal sheet, insulation-separated metal sheet, bracket-fixed metal panel and screw-fixed metal panel. The heat loss, effective U-value, lowest internal surface temperature and lowest temperature factor of each panel system with and without thermal bridges were calculated and compared.

실측실험과 3차원 정상상태 열전달 해석을 통한 발열유리의 온도 및 전열량 분석

실측실험과 3차원 정상상태 열전달 해석을 통한 발열유리의 온도 및 전열량 분석

Optical, spectral, and thermal characteristics of InGaN/GaN green flip-chip light-emitting diodes

We reported the temperature-dependent device characteristics of InGaN/GaN green flip-chip light-emitting diodes (large chip size of 1125×1125μm2) on patterned sapphire substrate. Through the experiments in the temperature range of 298–358K, optical, electrical, and spectral properties were measured and analyzed. At 350mA and 298K, the optical output power of 56.2mW, forward voltage of 3.26V, and emission peak wavelength of 503.6nm were obtained. The characteristic temperature was also estimated at an injection current of 350mA under pulsed mode, indicating a value of 1019K. The junction temperature was experimentally measured by the forward voltage method. For comparison with theoretically calculated results, three-dimensional steady-state heat transfer model based on finite element method was employed. The thermal resistance (∼12.76K/W) extracted from the experimental results exhibited a similar value with the simulated result (~14.22K/W).

Prediction of solidification behaviour of weld pool through modelling of heat transfer and fluid flow during gas tungsten arc welding of commercial pure aluminium

A mathematical model is developed to assess the solidification behaviour of the weld pools. To do so, during gas tungsten arc welding of commercial pure aluminium, equations of conversation of mass, energy and momentum are numerically solved considering three-dimensional steady state heat transfer and fluid flow conditions. The weld pool geometry, weld thermal cycles and various solidification parameters are calculated using temperature and velocity fields acquiring from the utilised model. The solidification behaviour of the weld pool at the weld centreline and the fusion line is then studied using the solidification parameters including temperature gradient G, solidification rate R and the combined forms G/R and GR. In order to verify the predictions, welding experiments are performed and geometry of the weld fusion zone is measured. The calculated geometry of the weld fusion zone is found to be in good agreement with the corresponding experimental result. The predictions show that the cooling rate GR increases toward the centreline while the other solidification parameter G/R shows a different behaviour. In addition, it is found that under the employed welding conditions, as the welding speed increases temperature gradients both at the weld centreline and at the fusion line are reduced.

Permeable Porosity and Thermal Conductivity of Construction Materials

Water permeable porosities and thermal conductivity of ceramic construction materials have been experimentally determined in this work. The samples were selected so as to obtain a wide variation in their apparent porosity. To study the influence of porosity on thermal conductivity, thermal conductivities of all the samples were measured in oven dried and water saturated conditions. A model relating porosity with thermal conductivity of these materials is proposed. In the model, two types of pores are hypothesized, namely; enclosed pores and enclosing pores. The three-dimensional steady-state heat transfer through unit cells containing each of the two types of pores, is solved to evaluate their effective thermal conductivity. By using the law of mixture for the random distribution of the type of pores, an equation combining the conductivities of the two cells is framed to get overall effective thermal conductivity of the material, in both dry and saturated states. The experimentally determined values of thermal conductivities reported in literature for some bricks are then compared with those predicted through this model.

Modeling of three-dimensional steady state non-linear heat transfer in CANDU nuclear fuel

Modeling and analysis of three-dimensional steady-state heat transfer in a CANDU6 1 1 CANadian Deuterium and Uranium and trademark of Atomic Energy of Canada Ltd. nuclear fuel rod are presented in this paper. A special three-dimensional finite element, developed through combining the nine-node two-dimensional isoparametric finite element and the Fourier series, is employed to model the temperature distribution in the pellets and the sheath. To achieve high accuracy and a high convergence rate, the temperature-dependent thermal conductivity matrices of UO 2 and Zircaloy are allowed to vary with spatial coordinates in the same manner as temperature within a finite element. The non-linear algebraic equations of nodal temperatures are formulated using the Galerkin method and solved using the iteration approach. A computer code, fuel3d, which contains the finite element modeling and solution schemes described in this paper, was developed for heat transfer analysis of nuclear fuel rods. Numerical simulation results obtained using fuel3d have shown excellent agreement with other independent solutions.