Local Heat Sink Research Articles

HEAT TRANSFER ANALYSIS ON BASE OF HEAT SINK WITH UNIFORM HEAT GENERATION

The present work describes the important results of problem of combined conduction, convection and radiation from a rectangular heat sink base subjected to uniform internal heat generation in its base. The governing equations for temperature distribution within the base are obtained by a relevant energy balance between rate of heat generation, heat conducted, convected and radiated. The derived non-linear partial differential equations are converted into algebraic form using finite difference method with 2nd order accuracy. The obtained algebraic equations have been solved simultaneously by Gauss-siedel iterative method with stringent convergence criteria and a C code has been written for above purpose. The computational domain has been discretized uniformly in all directions. A grid convergence test has been carried out to optimize the size of element. A complete parametric study has been carried out to study the effect of material of heat sink, regime of convection and role of radiation on local temperature distribution and maximum heat sink base temperature. It has been observed that material with high conductivity decreases the local temperature gradient and thus the maximum temperature. The regime of convection has a great influence on maximum temperature of heat sink with 15K of drop in Tmax. for a change in flow regime from free convection to forced convection. A special study on exclusive role of convection on maximum temperature reveals that one should not ignore the role forced convection in heat dissipation. Key Words: Heat generation, Multimode heat transfer, Radiation

Constructal optimization of a rectangular non-uniform heat generation area with irregular high thermal conductivity material

Heat conduction models with three non-uniform heat generation conditions in a rectangular heat generation area (RHGA) are set up in this paper. Under given areas of the irregular high thermal conductivity material (HTCM) and RHGA, constructal optimization of the RHGA is conducted by changing the distribution of the HTCM and aspect ratio of the RHGA. The minimum dimensionless average temperature difference (DATD) of the RHGA is gained. It is found that the DATDs of the RHGA with linear heat generation distribution are abated by 82.43% and 82.65% after twice optimizations for boundary and central heat sinks, respectively. For the heat generation in one local area of the RHGA, the two decrements are 36.30% and 52.20%, respectively. For the heat generation in multiple local areas of the RHGA, the two decrements are 35.60% and 71.60%, respectively. The optimal structure of the RHGA with heat generation in multiple local areas and heat sink in the center exhibits the best cooling performance compared with the other models discussed in this paper. Moreover, the best cooling performance of the RHGA is at least augmented by 29.49% than those of the previous studies discussed in this paper.

A combined modelling approach to design test structures to study thermomigration in Cu interconnects

With the downscaling of microelectronic devices, thermal gradients become increasingly important, making thermomigration (TM) an important mass transport mechanism. We use a combination of thermal simulations using finite element (FE) methods and a 1D physics-based TM model to characterise and design test structures to study thermomigration in Cu interconnects. As the test structure, in order to locally heat a section of the Cu interconnect, we propose to add a W-heater below a classical electromigration (EM) test structure. Using experimentally calibrated FE thermal models, we study the temperature distribution and temperature gradients along the Cu interconnects for various configurations of the test structure. Subsequently, the 1D TM model is used to identify locations where the tensile stress would reach a critical stress, σcrit, which can lead to void nucleation induced by thermal gradients. By comparing different heater positions, we show that a higher thermal gradient is expected when the heater is positioned further away from the local heat sinks. Based on the outcome of the simulations, we propose a modified test structure where metal levels are inverted such that the Cu metal line is closer to the heater. Such structure shows a 4× increase in temperature gradient compared to the original structure, facilitating TM characterisation studies.

Analysis of heat transfer from a local heat source at cryogenic temperatures

Understanding the dispersion of heat around a cryogenic fluid tank, specifically the interaction between the cryogenic fluid and the tank wall is critical in the analysis of long duration cryogen storage in microgravity. The heat transfer interaction between a cryogenic storage tank and heat sources from external spacecraft structures is also one of the many factors that determine how much heat enters a tank. Recent flight experiments with two-phase fluids have indicated that local concentrations of heat input (also known as “hot spots”) can cause unwanted affects including local boiling. Computational fluid dynamic (CFD) models can provide a detailed assessment of the heat transfer occurring across a cryogenic storage system. However, CFD modeling takes time to construct and run. A simpler approach that can act as initial guidance for later CFD modeling analyzes external “hot spots” as point or finite heat sources. A radial, finite element network or a local direct solution can effectively estimate the heat spread across a cryogenic storage tank by calculating the temperature and heat load as a function of distance from the heat source. This calculation accounts for the convective heat transfer between the cryogenic fluid and storage tank surface. Similar approaches can be used to determine the effectiveness of cooling from a cryocooler as a finite, local heat sink. This approach allows for quick approximations of the thermal map across a cryogenic tank as well as sensitivity analysis under a wide range of design parameters including gravitational fields as implied through natural convection coefficients.

Two distinctly different modes of cooling high-temperature bodies in subcooled liquids

The paper sequentially substantiates an existence of the two distinct modes of film boiling during quenching the high-temperature bodies in subcooled liquids. Based on the vast investigations of film boiling regularities during cooling high-temperature metallic spheres in different subcooled liquids, the authors of the present paper revealed that among pure liquids, only in subcooled water there are the two distinctly different cooling regimes. According to the approximate physical model developed earlier (2018) by the authors, incipience of the micro-bubble boiling arises, if the local liquid/solid contacts occur between the surface roughness protrusions and the liquid crests of the wavy liquid/vapor interface. At such a contact, near a boundary of the three phases, a huge local heat sink (qev) acts. This heat sink is proportional to (σhlg/ν) and its value explains, in particular, why the fast cooling regime occurs in subcooled water at definite subcoolings, but never in cryogens or fluorocarbons. The model quantitatively predicts influence of the properties of a coolant and a cooled body on the incipience of the fast cooling regime. However, some issues remain open. The present paper considers the results of the numerical studies of a metallic body cooling under effect of the local heat sink qev. These studies shed light on some of these issues. The numerical simulation determines realistic values of a heat sink, a period of its action, and a size of the cooled area at the plane surface, which provide the conditions for spreading the wetted area at the surface of a cooled body. According to the simulation, the cooling process predictably occurs more rapidly for metals with lower thermal effusivity and for low-conductive and rather thick coating at the high-conductive metal. The strong effect of very thin low-conductive coatings from Teflon and silica exceeded expectation. At qev= 50 MW/m2 even 10-μm coating of the porous silica leads to the surface temperature drops larger 500 K during 0.01 s for the both basic metals studied. The results have confirmed that the local heat sink of high intensity, particularly at the modelled roughness protrusions, can provide the conditions of the liquid/wall contacts and spreading of the wetted area at the surface.

ВЛИЯНИЕ ТОПОЛОГИЧЕСКИХ ТЕПЛООТВОДЯЩИХ РЕШЕНИЙ НА ТЕМПЕРАТУРНЫЙ РЕЖИМ РАБОТЫ ЭРИ

In the modern world, both developers and engineers are more and more carefully approaching the study and calculation of the thermal conditions of electronic devices. This is a necessary measure, due to the tendency to increase the density of the arrangement of electronic radio products (ERI) on printed circuit boards (PCBs), to reduce sizes while increasing power, and also to increase the overall complexity of electronic devices. The use of local topological heat sink solutions (heat sink holes) allows you to reduce the temperature conditions of the ERI, but requires the use of a detailed mathematical model of the PCB in thermal calculations. The article discusses the use of such a model and its comparison withthe traditional approach

Trifluoroacetic Acid as a Theranostic Ablation Agent.

HomeRadiology: Imaging CancerVol. 2, No. 1 Previous Research HighlightsFree AccessTrifluoroacetic Acid as a Theranostic Ablation AgentGary D. LukerGary D. LukerGary D. LukerPublished Online:Jan 31 2020https://doi.org/10.1148/rycan.2020204005MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In Take-Away Points■ Major Focus: To test efficacy of trifluoroacetic acid (TFA) for chemical ablation of liver tumors and optimize a fluorine 19 (19F) MRI sequence to detect TFA in tissue.■ Key Result: Real-time 19F MRI successfully detected TFA in porcine liver tissue, and histologic findings effectively verified coagulation and disruption of liver architecture.■ Impact: This study established an integrated imaging and therapy protocol to apply TFA as a theranostic agent for chemical ablation of solid tissue.Ablation methods encompass a wide range of minimally invasive techniques to destroy liver tumors, particularly smaller tumors in patients for whom surgery is not safe or feasible. Incomplete ablation remains a clinical challenge with residual tumor leading to local recurrence and potentially more aggressive disease. Although ablations most commonly use radiofrequency, laser, or other thermal methods, high-flow blood vessels can produce a local heat-sink effect that reduces peak temperatures of ablation and elimination of nearby tumors. Chemical ablations do not suffer from limitations of a local heat-sink, but agents used for chemical ablation may flow irregularly in tissue with associated off-target injury and systemic toxicities. To develop a theranostic agent for chemical ablation of liver tumors, the authors combined trifluoroacetic acid (TFA) as an ablation agent with fluorine 19 (19F) MRI. 19F MRI provides quantitative images with very minimal background signal, although low sensitivity typically requires millimolar concentrations of 19F to produce diagnostic quality images. Chemical ablation uses much higher concentrations, potentially overcoming sensitivity limits of 19F MRI. The investigators optimized a 19F MRI sequence to detect TFA in phantoms with signal-to-noise correlating directly with concentration. 19F MRI detected distribution and relative amounts of TFA used to ablate porcine liver tissue ex vivo, and histologic findings showed extensive damage to hepatocytes at concentrations of 0.5 mol/L TFA or higher. By developing a 19F MRI method to detect TFA in liver tissue, this research provides a new approach to optimize chemical ablation strategies and potentially a novel theranostic technique for future clinical translation.Highlighted ArticleEinstein SA, Thompson EA, Guo C, Whitley EM, Bankson JA, Cressman ENK. Application of trifluoroacetic acid as a theranostic agent for chemical ablation of solid tissue. J Vasc Interv Radiol 2020;31(1):169–175. doi: https://doi.org/10.1016/j.jvir.2019.05.002Highlighted ArticleEinstein SA, Thompson EA, Guo C, Whitley EM, Bankson JA, Cressman ENK. Application of trifluoroacetic acid as a theranostic agent for chemical ablation of solid tissue. J Vasc Interv Radiol 2020;31(1):169–175. doi: https://doi.org/10.1016/j.jvir.2019.05.002 Crossref, Medline, Google ScholarArticle HistoryPublished online: Jan 31 2020 FiguresReferencesRelatedDetailsRecommended Articles Colorectal Cancer Liver Metastases: Biopsy of the Ablation Zone and Margins Can Be Used to Predict Oncologic OutcomeRadiology2016Volume: 280Issue: 3pp. 949-959Combined Angio-CT Systems: A Roadmap Tool for Precision Therapy in Interventional OncologyRadiology: Imaging Cancer2021Volume: 3Issue: 5Hepatocellular Carcinoma: Intra-arterial Delivery of Doxorubicin-loaded Hollow Gold Nanospheres for Photothermal Ablation—Chemoembolization Therapy in RatsRadiology2016Volume: 281Issue: 2pp. 427-435Effects of Microwave Ablation on Arterial and Venous Vasculature after Treatment of Hepatocellular CarcinomaRadiology2016Volume: 281Issue: 2pp. 617-624Midterm Safety and Efficacy of Irreversible Electroporation of Malignant Liver Tumors Located Close to Major Portal or Hepatic VeinsRadiology2017Volume: 285Issue: 3pp. 1023-1031See More RSNA Education Exhibits Maximizing Procedural Success! A Trainee's Guide to Imaging Equipment in the IR SuiteDigital Posters2018The Emerging Role of Contrast-Enhanced Ultrasound in Oncological InterventionDigital Posters2018A Practical Guide of Locoregional Treatment for Patients with Hepatocellular CarcinomaDigital Posters2019 RSNA Case Collection Spindle cell lipomaRSNA Case Collection2022Extralobar Pulmonary Sequestration RSNA Case Collection2021Hepatic AdenomatosisRSNA Case Collection2021 Vol. 2, No. 1 Metrics Altmetric Score PDF download

Boundary Control of Embedded Heaters for Uniform Bondline Temperatures During Composite Joining

This paper investigates an out-of-autoclave (OoA), embedded-resistive heating method to precisely control the bondline temperature when curing high strength adhesives for joining composite adherends. A challenge with OoA methods is that nonuniform heat loss, e.g., due to substructures that act as local heat sinks, can lead to nonuniform temperatures in the bondline, which in turn, can result in uneven curing, residual stresses, and potentially weak joints. The main contribution of this work is to apply a voltage pattern at the boundary of the embedded heater to control the distribution of the electrical power at the interior bondline, and thereby reduce temperature variations. Additionally, this work devises an empirical model (that can be applied when material parameters and models are not readily available) to predict the desired power generation, and to design the embedded heater and voltage pattern that minimizes the bondline temperature variation. The technique is demonstrated experimentally for bonding a single-lap joint, and the maximum temperature variation in the bond area was reduced by five times from 31.6 °C to 6.0 °C.

Local cooling, plasma reheating and thermal pinching induced by single aerosol droplets injected into an inductively coupled plasma

The injection of a single micrometer-sized droplet into an analytical inductively coupled plasma (ICP) perturbs the plasma and involves three sequential effects: local cooling, thermal pinching and plasma reheating. Time-resolved two-dimensional monochromatic imaging of the load-coil region of an ICP was used to monitor this sequence of plasma perturbations. When a microdroplet enters the plasma, it acts as a local heat sink and cools the nearby plasma region. The cooling effect is considered local, although the cooling volume can be large and extends 6mm from the physical location of the vaporizing droplet. The liberated hydrogen, from decomposition of water, causes a thermal pinch effect by increasing the thermal conductivity of the bulk plasma and accelerating heat loss at the plasma periphery. As a response to the heat loss, the plasma shrinks in size, which increases its power density. Plasma shrinkage starts around the same time when the microdroplet enters the plasma and lasts at least 2ms after the droplet leaves the load-coil region. Once the vaporizing droplet passes through a particular plasma volume, that volume is reheated to an even higher temperature than under steady-state conditions. Because of the opposing effects of plasma cooling and reheating, the plasma conditions are different upstream (downward) and downstream (upward) from a vaporizing droplet — cooling dominates the downstream region whereas reheating controls in the upstream domain. The boundary between the local cooling and reheating zones is sharp and is only ~1mm thick. The reheating effect persists a relatively long time in the plasma, at least up to 4ms after the droplet moves out of the load-coil region. The restoration of plasma equilibrium after the perturbation induced by microdroplet injection is slow. Microdroplet injection also induces a momentary change in plasma impedance, and the impedance change was found to correlate qualitatively with the different stages of plasma perturbation.

Conjugate Heat Transfer in a Closed Volume with the Local Heat Sources and Non-Uniform Heat Dissipation on the Boundaries of Heat Conducting Walls

Is solved the problem of heat transfer in the closed volume, limited by heat-conducting walls, with the local source of heat emission and the heterogeneous conditions of heat sink on the outer boundaries of solution area. The problem of convective heat transfer is solved with using a system of differential Navier-Stokes equations in the Boussinesq approximation. The simulation of turbulent flow conditions of heated air is carried out within the framework to k -e model. On the basis the analysis of the obtained temperature field and the contour lines of stream functions is made conclusion about the essential transiency of the process in question. The obtained values of temperatures and speeds in different sections of region illustrate turbulence of the process. Are investigated laws governing the formation of temperature fields in closed areas with a local heat emission source under the conditions of intensive local heat sink into environment and accumulation of heat in the enclosing constructions.

The economic performance of combined heat and power from biogas produced from manure in Sweden – A comparison of different CHP technologies

Interest in the generation of biogas from agricultural residues is increasing rapidly due to its climate benefits. In this study, an evaluation of the economic feasibility of various technologies, also on different scales, for the production of combined heat and power from manure-based biogas in Sweden is presented. The overall conclusion is that such production is not profitable under current conditions. Thus, the gap between the calculated biogas production cost and the acceptable cost for break-even must be bridged by, for example, different policy instruments. In general, efficiency of scale favors large-scale plants compared to individual farm-scale ones. However, a large, centralized biogas plant, using manure from numerous farms, is not always more cost efficient than a large, farm-scale plant treating manure from a few neighboring farms. The utilization of the produced heat, electricity prices, and political incentives, all have a significant impact on the economic outcome, whereas the value of the digestate as fertilizer is currently having a minor impact. Utilization of heat is, however, often limited by the lack of local heat sinks, in which case the implementation of a biogas process operating under thermophilic conditions could increase the profitability due to a more efficient utilization of reactor volume by using more process heat. The results from this study could be utilized by policy makers when implementing policy instruments considering biogas production from manure as well as companies involved in production and utilization of biogas.

Improving a process's efficiency by exploiting heat pockets in its heat exchange network

On the grand composite curve of a heat exchange network, a heat pocket exists when a local heat source above the pinch point or a local heat sink below the pinch point appears. In this paper, heat recovery in the heat pocket is presented by combining the pinch technology and exergy analysis. When the heat pocket is big, hot streams in the pocket can be used to generate a higher level utility, and the cold streams in the pocket can be heated by a lower level utility. In this way, exergy loss can be reduced, and the process's efficiency can be improved. The heat exchange network of a hydrogen production process is used as a case study. The energy performance of the heat exchange network can be further improved by recovering the heat in the heat pocket, compared with the scheme based only on pinch technology.

Diagnostics and Modeling of Heat Transfer in High-Enthalpy Gas Flows with Local Heat Sources and Sinks

The use of the laser Raman scattering method is considered for the diagnostics of a near-wall high-enthalpy boundary layer on the surface of ablating materials with a view of detecting volumetric-spatial zones of fast gas-phase chemical reactions of exo- and endothermic types between the ablation vapor and gas components of the main strean. Based on the experimental data, a rational mathematical model is suggested which takes into account the influence of the zones on the character of combined heat transfer, with simultaneous presence of heat conduction and radiation.

How to apply a discrete vessel model in thermal simulationswhen only incomplete vessel data are available

For accurate predictions of the temperature distribution during hyperthermiatreatment a thermal model should incorporate the individual impact of discretevessels. In clinical practice not all vessels can be reconstructedindividually. This paper investigates five possible strategies to model thethermal impact of these missing vessels.A tissue volume with a detailed, realistic, counter-current discretevasculature is heated and the steady-state temperature distribution iscalculated using our DIscrete VAsculature (DIVA) thermal model. To mimicincomplete discrete vasculatures the full tree is gradually stripped, that is,the number of discretely described vessels is reduced in four steps until nodiscrete vessels are left.At each strip level the steady state temperature distribution is calculatedfor five different strategies to model the missing vessels. The strategies alluse a local or global heat sink model in addition to the discrete vasculature.The resulting temperature distributions are compared with the full treesimulation.With increasing strip level the correspondence with the full tree simulationdeteriorated for all strategies. An optimal strategy was found to model themissing vessels depending on the available angiographic data. It was alsofound that simulations with a decreased number of discrete vessels, or novessels at all, yield temperatures which are too high. Theoretically this can becompensated by increasing the thermal conductivity; finding the optimal valueis done empirically.

Contact cooling of the skin

Skin precooling can be used to reduce epidermal thermal damage in laser procedures (such as hair removal) where the target structures are located up to several millimetres below the skin surface. We have developed and experimentally verified a computational model that describes contact precooling of a multilayered skin structure prior to laser irradiation. The skin surface is assumed to be brought into thermal contact with a cold plate made of material with a high thermal conductivity. The approximate analytical solution for the skin temperature is obtained by considering the plate as a local heat sink. The time evolution of temperature (in both the skin and the plate) is simulated numerically to yield the optimal cooling parameters. To experimentally verify the numerical results of the model, we performed direct measurements of skin temperature for contact cooling with a sapphire plate held at several different temperatures in the range +10 to C.

Comparison of temperature distributions in interstitial hyperthermia: experiments in bovine tongues versus generic simulations

Temperature distributions resulting from hyperthermia treatments on isolated perfused bovine tongues were compared with simulations by a treatment planning system. The aim was to test whether the discrete vessel model used for the treatment planning is able to predict correct generic temperature distributions. Tongues were heated with the multielectrode current source interstitial hyperthermia treatment (MECS IHT) system, while the steady-state temperature distribution was mapped by scanning 10 thermocouples along paths perpendicular to the interstitial implant. For simulations a tongue was defined with generic discrete vasculature and an electrode implant analogue to the experiments. To model vascular generations not described discretely, a local heatsink was implemented at the end of each terminating branch. The discretely modelled vasculature showed itself on the temperature distributions in two ways. Individual vessels caused very local, sharp wells in the tracked temperature profiles. In the presence of large vessels a collective behaviour was also seen, i.e. a regional lowering of temperature. Both phenomena can be recognized in the experimentally obtained temperature distributions too. Predicting correct generic temperature distributions is feasible with the discrete vessel model used.

Modelling of surface temperature measurement errors in vertical natural convection cooled channels

This paper describes a methodology and numerical procedure for calculation of surface temperature measurement errors in buoyant channel flow applied to the case of surface-mounted thermocouples. Heat transfer calculations within the channel are based on initial measurement information and performed via a marching numerical procedure. The results of these calculations are in turn utilized for the determination of surface measurement errors modelled with emphasis on the thermocouple-induced local heat sink and convective stray losses. The influence of measurement location and channel width on the surface measurement error is numerically investigated for a group of air-cooled channels with results presented in graphical form.

Initial conditions implied by [formula omitted] solidification of a sphere with capillarity and interfacial kinetics

We explore the initial conditions implied by t 1 2 growth ofa spherical crystal solidifying from a pure, undercooled melt, including the effects of both capillarity and interface kinetics, and relate our findings to initial conditions that would be expected on the basis of classical nucleation theory. For crystal sizes near the nucleation radius, the calculated temperature profiles show a cold region ahead of the advancing interface that is even more undercooled than the undercooled bath. This cold region acts as a local heat sink that compensates for the reduced growth speed that would otherwise result from capillarity and kinetics, leading to precisely the same t 1 2 growth law that would have been obtained had both capillarity and kinetics been neglected. We submit that this t 1 2 solution should not be taken seriously in the context of the classical theory of nucleation of a crystal from an isothermal melt.

An Evaporating Ethanol Meniscus—Part II: Analytical Studies

A model of capillary flow heat transfer is used to analyze the data obtained in Part I. The results indicate that fluid flow resulting from a change in the meniscus profile replenishes the liquid evaporated in a stationary evaporating meniscus. Local evaporative heat fluxes can be very high near the interline region of a finite contact angle meniscus. Therefore, a small stationary evaporating meniscus can be used as a very effective local heat sink.

Thermal deformation vector for a bilinear temperature distribution in an anisotropic quadrilateral membrane element

AbstractThis paper presents a thermal‐structural deformation vector for an anisotropic quadrilateral membrane element. The elastic properties of the element are based on linear stress assumptions and were developed by Robinson1. A general bilinear temperature field within the element is chosen in order to obtain a thermal deformation capability for the element commensurate with its elastic capability. A pseudo shear term is developed to account for part of the thermal deformation. The element is suitable for finite element analysis of advanced aircraft structures under elevated temperature environments and is particularly well suited for analysis of regions with severe temperature gradients such as occur in the vicinity of local heat sources and sinks. An example problem is included to demonstrate the behaviour of the element.