Heat Source Configuration Research Articles

Identifying and assessing key parameters controlling heat transport in discrete rock fractures

Numerical modeling of heat transfer in low porosity fractured rock is challenging because of the complexity associated with the interactions between fractures, bedrock matrix, groundwater, and heat sources. Possible influential parameters include the heat source configuration, the thermal conductivity of the matrix, the velocity of the fluid, the thermal dispersivity in the fracture, and the aperture of the fracture. In this investigation we use factorial analysis (2K) to define which of the five parameters, or combinations thereof, significantly influence heat migration in a single fracture setting assuming a parallel plate condition. A 3-D numerical model based on the control-volume finite element method is used for the simulations. For the parameter ranges investigated, results indicate that the most influential factor controlling heat propagation in a single fracture setting is the velocity of the fluid in the fracture. The interaction between the thermal conductivity of the matrix and the velocity of the fluid, and between the thermal conductivity of the matrix and the aperture of the fracture, dominantly control the attenuation of the thermal front migration. Depending on the particular system, one or more of these parameters should be given better consideration during site characterization in fractured rock and in the compilation of site-specific models intended to predict heat propagation in fractured systems.

A parametric study on the effects of displacer-cylinder-circumferential-wall thermal conditions on the performance of a γ-type LTD Stirling engine

ABSTRACTRegarding a Stirling engine’s heat source and heat sink, most of the studies in the literature focus only on the magnitude of temperature difference between them. However, different Stirling engines adopt very different heat-source and heat-sink configurations. This study is aimed at understanding the effects of different displacer-cylinder-wall thermal conditions on engine performance using computational fluid dynamics (CFD). Results include p–V diagrams, heat flux distributions, temperature variations, and effects of three displacer-cylinder-wall parameters on indicated power and efficiency. It is found that the thermal conditions on the displacer-cylinder-circumferential wall (DCCW) impose significant effects on engine performance. Within the ranges of parameters investigated in this study, extending the coverage of heat source and heat sink on this wall improves up to 28% in indicated power at the cost of losing about 10% in efficiency, proving the significance of DCCW conditions on engine performance.

Study of weld formation in swing arc narrow gap vertical GMA welding by numerical modeling and experiment

A three-dimensional unified model is proposed to simulate the weld pool dynamic behavior in swing arc narrow gap vertical GMA welding with allowing for swing feature of arc heat source and joint configuration. Both the moving direction of arc and its inclination are considered by transformation of coordinate system. The model can simulate the weld pool sagging process reasonably. Based on the calculated and experimental results, the mechanism of weld formation in swing arc vertical-up welding is studied. The weld pool size and the peak temperature of liquid metal are reduced largely in the case of swing arc, which leads to the faster solidification of weld pool and is the major factor responsible for suppression of weld pool sagging. Meanwhile, upward component of arc force and the enhanced support force from solidified metal bulge benefits the weakness of downward flow of liquid metal. With increasing the swing frequency, weld cross section geometry tends to be symmetrical and weld bead surface becomes smoother. When the swing frequency is higher than 0.6 Hz, the satisfied weld formation can be obtained.

3D Defect Localization on Exothermic Faults within Multi-Layered Structures Using Lock-In Thermography: An Experimental and Numerical Approach.

Micro-electronic devices are increasingly incorporating miniature multi-layered integrated architectures. However, the localization of faults in three-dimensional structure remains challenging. This study involved the experimental and numerical estimation of the depth of a thermally active heating source buried in multi-layered silicon wafer architecture by using both phase information from an infrared microscopy and finite element simulation. Infrared images were acquired and real-time processed by a lock-in method. It is well known that the lock-in method can increasingly improve detection performance by enhancing the spatial and thermal resolution of measurements. Operational principle of the lock-in method is discussed, and it is represented that phase shift of the thermal emission from a silicon wafer stacked heat source chip (SSHSC) specimen can provide good metrics for the depth of the heat source buried in SSHSCs. Depth was also estimated by analyzing the transient thermal responses using the coupled electro-thermal simulations. Furthermore, the effects of the volumetric heat source configuration mimicking the 3D through silicon via integration package were investigated. Both the infrared microscopic imaging with the lock-in method and FE simulation were potentially useful for 3D isolation of exothermic faults and their depth estimation for multi-layered structures, especially in packaged semiconductors.

Effect of heat-source geometry on distribution and deposition of particulates in a ventilated chamber

To investigate the effect of near-wall heat-source shape on particulate motion, the particulate distribution and deposition in a ventilated chamber with different heat-source configurations were numerically modeled. Using the discrete random walk model of the Lagrangian method, the trajectories of 3200 mono-disperse particulates ranging from 1 to 10μm with a density of 1400kg/m3 were tracked. Airflow pattern, temperature fields, the distribution of particulate concentrations, and deposition patterns are calculated and presented. The results show that the shape of a near-wall heat source has an influence on the airflow as well as the temperature field in the chamber and hence affects the particulate distribution and deposition.

Experimental study on the performance characteristics of a cylindrical heat pipe having a screen wick subject to multiple heat sources

In a simple model to predict heat pipe performance, uniform thermal loads are assumed over heat transfer surfaces. The validity of the simple model is limited in many application areas such as electronics cooling and space thermal control, where a heat pipe is often subject to multiple, unequal thermal loads. This study aims to experimentally identify the performance of a cylindrical heat pipe under various multiple heat source configurations and thus to quantitatively estimate the deviation from a heat pipe under uniform conditions. The model heat pipe was 9.53mm in diameter and 0.6m in length, with a 0.4m evaporator. The working fluid and the container wall were water and copper, respectively, and a wire mesh screen was inserted as a capillary structure. The fluid charge ratios tested were 100% and 120% based on the wick void volume. The heat pipe was in gravity-assisted mode with an inclination angle of 45° to extend the range of thermal input. Five small heaters were installed in the evaporator with equal spacing, and the power inputs were controlled individually. Three different thermal load configurations were imposed: equal, increasing and decreasing distributions toward the condenser. The results were compared from the viewpoints of thermal resistance and effective thermal conductance. The thermal resistance of the heat pipe with a 100% fluid charge exhibited excellent values from 0.16K/W (at 50W) to 0.03K/W (at 300W) for a uniform heat load. However, those with multiple thermal loads resulted in almost a 100% increase for the lower thermal load, and up to a 40% increase for the higher thermal loads, depending on the configuration. The behavior of the heat pipe with a fluid charge of 120% exhibited little difference. The results herein can be employed to estimate the performance deviation of a heat pipe due to thermal load distribution.

Investigation of dimensional and heat source effects in Lock-In Thermography applications in semiconductor packages

Lock-In Thermography (LIT) is a powerful non-contact and non-destructive investigating technique that has recently emerged in the semiconductor industry. The current LIT applications interpret LIT data using the semi-infinite models. However, semiconductor package has finite geometry with convective heat transfer on surface. This paper studies the accuracy of the interpretation of LIT data based on the commonly used semi-infinite models. The effects of finite dimensions, heat source configuration, convective heat transfer coefficient, thickness of material, thermal diffusivity of material, and lock-in frequency are examined. Furthermore, the effects of heat source’s shape and location, as well as the problems involving non-homogeneous materials are also investigated. It has been found that the errors in phase shift estimate using semi-infinite models may occur at lower lock-in frequency with high diffusivity material and thinner specimen. When multiple materials are involved with various scenarios of heat source locations, the phase shift may decrease with the lock-in frequency, as observed in experiment. Finite element transient heat conduction analysis is a useful tool to derive the actual z-depth of heat source based on the phase shift data from experiment.

Unsteady natural convection heat transfer in a nanofluid-filled square cavity with various heat source conditions

Steady and unsteady natural convection heat transfer in a nanofluid-filled square enclosure cavity with various heat source configurations at the bottom were numerically studied using a characteristic-based split scheme finite element method. A wide range of Rayleigh numbers [Formula: see text], solid volume fractions of nanoparticles [Formula: see text], the lengths [Formula: see text], and locations [Formula: see text] of heat sources as well as different types of nanoparticles were considered. Results showed that addition of nanoparticles into the base fluid leads to evident enhancement of heat transfer, particularly at low Rayleigh numbers and that cooling performance is strongly influenced by thermo-physical properties of the nanoparticles. Temporal development of thermal layer in a nanofluid-filled cavity was demonstrated from initial to steady stage through unsteady analysis. We found that the maximum temperature and the average Nusselt number started to oscillate, which is a typical characteristics of high Rayleigh number flow, at higher Rayleigh number in nanofluid than in pure water.

パルス電流波形による溶込み形状の制御

Conventional selection of welding conditions has a high dependence over the experience of the welder. Since the effect of process parameter on the penetration has not been grasped quantitatively when the target groove configuration and a welding position change, selection of welding conditions has to be performed each time. Moreover, there is the necessity of cutting and observing a cross-section in the penetration shape check to select optimal conditions, and it requires much time. Therefore, the demand to predicting and controlling penetration shape is increasing. In this research, the relation of an output waveform formation parameter, arc phenomena, and penetration shape is estimated for the controlling of the penetration shape change by a current pulse waveform. As a result, it becomes clear that a large factor in the penetration shape change is a Droplet Transfer Mode. Then, the possibility of penetration shape control is found. Moreover, the above-mentioned relation is incorporated into the conventional penetration shape simulation model and the validity of a simple heat source model which imitates change of the Droplet Transfer Mode as change of heat source configuration is evaluated.

Optimal Distribution of Discrete Heat Sources Under Natural Convection Using ANN–GA Based Technique

Experiments have been conducted from five protruding rectangular discrete heat sources (aluminum) of non-identical sizes arranged at different positions on a substrate board (Bakelite), under natural convection, to determine their optimal configuration. A substrate board is designed for conducting experiments on multiple configurations of heat sources using the same board. A heuristic non-dimensional geometric parameter, λ, is defined for the purpose of identifying the optimal configuration for which the maximum temperature excess among the five heat sources of a configuration is the minimum, among all possible configurations. The maximum temperature excess is found to decrease with λ, so the configuration with highest λ is deemed to be the optimal one. The effect of surface radiation on the heat transfer rate from the heat sources is studied by painting their surfaces with black paint of high emissivity, which reduces their temperature by as much as 15%. An empirical correlation is developed for the non-dimensional maximum temperature excess (θ) in terms of λ, taking into account the effect of radiation. To minimize the error between the temperatures obtained by prediction (correlation) and experiment, and to determine the global optimal configuration of heat sources more rigorously, an artificial neural network (ANN) is trained using the experimental data, which then powers the genetic algorithm (GA) code.

Analytical models of heat conduction in fractured rocks

Discrete fracture network models routinely rely on analytical solutions to estimate heat transfer in fractured rocks. We develop analytical models for advective and conductive heat transfer in a fracture surrounded by an infinite matrix. These models account for longitudinal and transverse diffusion in the matrix, a two‐way coupling between heat transfer in the fracture and matrix, and an arbitrary configuration of heat sources. This is in contrast to the existing analytical solutions that restrict matrix conduction to the direction perpendicular to the fracture. We demonstrate that longitudinal thermal diffusivity in the matrix is a critical parameter that determines the impact of local heat sources on fluid temperature in the fracture. By neglecting longitudinal conduction in the matrix, the classical models significantly overestimate both fracture temperature and time‐to‐equilibrium. We also identify the fracture‐matrix Péclet number, defined as the ratio of advection timescale in the fracture to diffusion timescale in the matrix, as a key parameter that determines the efficiency of geothermal systems. Our analytical models provide an easy‐to‐use tool for parametric sensitivity analysis, benchmark studies, geothermal site evaluation, and parameter identification.

Drum Sludge Drying Equipment Energy Dissipation Factor Analysis

Drum sludge drying equipment is used widely both at home and abroad, and the energy consumption is the key factor of measuring sludge drying equipment. Based on the basis of study of drum sludge drying equipment energy consumption, this paper conducts a comprehensive analysis of drum sludge drying equipment energy consumption factor, and points out that the drum sludge drying equipment energy consumption mainly depends on heat source and drying system configuration, aims to provide reference and research for drum sludge drying equipment.

Constructal placement of unequal heat sources on a plate cooled by laminar forced convection

The present study deals with the influence that the size of adiabatic spacing in an array of heat sources exerts on the heat transfer performance. This issue plays a significant role in controlling the thermal boundary layer development in order to enhance the convective heat transfer along a plate. Constructal theory was systematically applied to determine the optimal configuration of heat sources in the array. The global objective is either to minimize the ‘hot spot’ temperature of the plate or to maximize the rate of heat transfer. Two thermal boundary conditions for the heat sources are employed: constant heat flux condition or constant temperature. Analytical solutions were determined for several length sizes of heat sources without imposing the common simplifying assumptions that were considered in similar studies. In this work, the optimization was first carried out for a problem with no attached constraint on how to distribute the heat sources for a fixed plate length. It was shown that in the first case, the ‘hot spot’ temperature was reduced by 11% for two optimized-size heat sources with uniform heat flux articulated with optimum adiabatic spacing. Additionally, for two heat sources with uniform temperature, a level of maximum heat transfer enhancement of 7.7% was achieved.

Numerical study of the lock-up phenomenon of human exhaled droplets under a displacement ventilated room

This paper adopts an Eulerian-Lagrangian approach to investigate the lock-up phenomenon (or trap phenomenon) of human exhaled droplets in a typical office room under displacement ventilation (DV). A particle-source-in-cell (PSI-C) scheme is used to correlate the concentration with the Lagrangian particle trajectories in computational cells. Respiratory droplets with sizes of 0.8 μm, 5 μm and 16 μm are released from a numerical thermal manikin (NTM). The influence factors including indoor temperature gradient, heat source configuration and exhalation modes are studied. It is found that large temperature gradient would result in trap phenomenon of small exhaled droplets (smaller than 5 μm). The intensive heat source near the NTM could help to transport the small droplets to the upper zone and decrease the concentration level in the trapped zone. Both nose-exhaled and mouth-exhaled small droplets would be trapped at the breathing height when temperature gradient is sufficiently high. However, the trap height of the droplets from mouth is a little bit higher. Because of large gravitational force, it is difficult for the thermal plume to carry 16 μm respiratory droplets to the upper zone.

Effect of heat source configuration on the result quality of numerical calculation of welding-induced distortion

The results of numerical welding simulations strongly depend on its temperature field. In the present paper, the temperature field of a pulsed gas metal arc weld of structural steel S355J2+N (ASTM A572 Gr. 50) with a thickness of 5 mm is experimentally and numerically investigated. In the case of temperature field validation, volumetric Gauss and double-ellipsoid Goldak heat sources are applied. Additionally, different heat source configurations, including adaptations of thermal conductivity, are analyzed regarding their influence on the calculation of welding-induced distortion. The investigations clarify the influence of heat source configurations on the calculated results, thus, contribute to an improved prediction of welding-induced distortion.

Configuration of heat sources or sinks in a finite volume

This work documents the design method of allocating channels that serve as heat sources or heat sinks in a conducting body. First, we develop a numerical model to find the optimum channel spacing for specified properties of the surrounding medium, the time scale of the heat transfer process, and the dimensions of the configuration. Second, we show with scale analysis that the optimal spacing (S/D) must equal τ1/2 in an order of magnitude sense, where τ is the dimensionless time scale of the process. This conclusion holds for the two heat transfer histories that were considered, exponential and top hat. We extend the method to a packing of channels of two sizes (diameters and heat source strengths). The optimal spacings and packing density obey the scaling rule determined for packing sources of a single size.

Optimal configuration of discrete heat sources in a vertical duct under conjugate mixed convection using artificial neural networks

This paper reports the results of a numerical investigation of the problem of finding the optimum configuration for five discrete heat sources, mounted on a wall of a three-dimensional vertical duct under mixed convection heat transfer, using artificial neural networks (ANN). The objective is to locate the positions for the five heat sources in such a way that the maximum temperature of any of the heat sources in a given configuration is a minimum. The three-dimensional governing equations of mass, momentum and energy equations for the fluid flow and the energy equation for the solid regime have been solved by using FLUENT 6.3 and a database of temperature versus configuration was generated. The temperature database developed from CFD simulations is used to train the neural network. The trained neural network predicts the temperature of the heat sources very accurately and much faster than the CFD software. With the use of this network, an exhaustive search for all possible configurations was done that resulted in a global optimum for the problem.

Real time temperature estimation of heat sources in integrated circuits with remote temperature sensors

This paper presents a theoretical study of the possibility to carry out real time estimation of power dissipated in electronic integrated circuits based on remote temperature sensor measurements. Due to the damping of the thermal response, the considered inverse problem is ill-posed; hence special attention has to be paid to the estimation process in order to assure the robustness of the obtained results. First, the authors focused on the issue of the proper placement of the temperature sensors for a given heat source configuration. Once the optimal locations of the sensors were determined, the problem of the estimation of the power dissipated in the heat sources was studied in detail. The tests were carried out for the computer generated input data with several noise levels. For the estimation the function specification algorithm with different number of temperature sensors and variable number of averaged measurements was considered. For all the presented thermal simulations as well as for the generation of the test input data, the authors used their own three-dimensional thermal solver employing the Green's function solution of the heat equation. The numerical experiments served as an indication for the design of a real test integrated circuit.

Experimental natural convection on vertical surfaces for building integrated photovoltaic (BIPV) applications

An experimental study on natural convection in an open channel is carried out in order to investigate the effect of the geometrical configuration of heat sources on the heat transfer behaviour. To this aim, a series of vertical heaters are cooled by natural convection of air flowing between two parallel walls. The objective of the work is to investigate the physical mechanisms which influence the thermal behaviour of a double-skin photovoltaic (PV) facade. This results in a better understanding of the related phenomena and infers useful engineering information for controlling the energy transfers from the environment to the PV surfaces and from the PV surfaces to the building. Furthermore increasing the heat transfer rate from the PV surfaces increases the conversion efficiency of the PV modules since they operate better as their temperature is lower. The test section consists in a double vertical wall, 2 m high, and each wall is constituted by 10 different heating modules 0.2 m high. The heater arrangement simulates, at a reduced scale, the presence of a series of vertical PV modules. The heat flux at the wall ranges from 75 to 200 W/m 2. In this study, the heated section is 1.6 m in height, preceded by an adiabatic of 0.4 m in height. Different heating configurations are analyzed, including the uniform heating mode and two different configurations of non uniform, alternate heating. The experimental procedure allows the wall surface temperature, local heat transfer coefficient and local and average Nusselt numbers to be inferred. The experimental evidences show that the proper selection of the separating distance and heating configuration can noticeably decrease the surface temperatures and hence enhance the conversion efficiency of PV modules.

Estimation of thermal resistance distributions for die-attach testing in microelectronics

In the present study, a steady-state inverse heat conduction problem is solved by using the conjugate gradient method to estimate the two-dimensional thermal resistance distribution of die-attach materials. The thermal performance of such interface materials is crucial for reliability issues in microelectronics. The spatial distribution of the thermal resistance is obtained from temperature measurements on the upper face of a semiconductor chip. Numerical experiments are performed by simulating infrared thermography measurements. The heat source configuration on the semiconductor chip and the measurement errors are investigated. Finally, the inverse algorithm is improved to decrease the computation time of the identification and to determine the refinement level of the searched distribution.