Heat-generating Devices Research Articles

Technological features of thick-film electric heating elements

The article deals with the technical parameters of thick-film heating elements, the peculiarities of their operation, as well as the scope of use in household and industrial heat-generating electrical devices.
 The world is constantly researching the possibility of developing heating elements without the aforementioned disadvantages of tube thermal elements, which allow more efficient use of consumed electricity, which leads to significant savings. A new type of heat to heat converter is proposed in this direction. The use of this converter - the heating element - in various industrial and household products can save up to 30% of electricity consumption.
 At the heart of the design of the heating element is a developed system of different properties of composite nanostructured materials - pastes. On the basis of this system of materials the technology of production of new heating elements with unique properties was created. The heating element is made by screen printing (silk screening) of special composite materials on a dielectric or metal substrate with their subsequent heat treatment. Dielectric, resistive, dielectric layers are sequentially applied to a flat substrate of any configuration, but can also be applied to cylindrical surfaces.
 Purposeful formation of a conductive structure in the resistive layers of thick-film heating elements and the ability to influence the properties of the nanoscale layer between the particles of the conductive phase allowed to create a group of materials, and on their basis, a series of heating elements with the properties of the technical intellect, environment. The technology for production of heating elements with self-regulation of parameters for wide values of supply voltage, thermal power, and specific heat dissipation power (surface heat flux density) has been developed.
 One of the significant advantages of the technology is the absence in the resistive paste of expensive and scarce precious metals and their compounds, which are part of similar pastes, offered by leading manufacturers in the world. Due to this, the cost of manufacturing such pastes is substantially lower than that of the world.

Synthesis of graphene encased alumina and its application as nanofluid for cooling of heat-generating electronic devices

Hybrid nanofluids were prepared using nanocomposites (G/Al2O3) with various graphene concentrations (5–50 wt%) to investigate the dispersion stability and the optimum concentration of graphene in nanocomposite (50/50 wt%). The thermophysical properties were studied as a function of particle loading (0–0.3 vol%) at the temperature range (20–70 °C). Results show that the thermal conductivity enhances to a maximum of 45% (±3%) compared to base fluid-DI water. The heat transfer performance was investigated by varying the Reynolds number (150–650) at nanofluid concentrations (0–0.2 vol%). The heat transfer coefficient and Nusselt number for 0.2 vol% were found to be higher than DI water by 51.73% (±2%) and 16% (±1.5%) respectively with a maximum rise in pressure drop of 5% (±0.5%). The enhancement in the thermal transport properties with a low penalty in pumping power requirement indicates the potential ability of (G/Al2O3) hybrid nanofluid in the cooling of heat-generating electronic systems.

Design, Fabrication, and Characterization of a Compact Hierarchical Manifold Microchannel Heat Sink Array for Two-Phase Cooling

High-heat-flux removal is critical for the next-generation electronic devices to reliably operate within their temperature limits. A large portion of the thermal resistance in a traditional chip package is caused by thermal resistances at interfaces between the device, heat spreaders, and the heat sink; embedding the heat sink directly into the heat-generating device can eliminate these interface resistances and drastically reduce the overall thermal resistance. Microfluidic cooling within the embedded heat sink improves the heat dissipation, with two-phase operation offering the potential for dissipation of very high heat fluxes while maintaining moderate chip temperatures. To enable multichip stacking and other heterogeneous packaging approaches, it is important to densely integrate all fluid flow paths into the device; volumetric heat dissipation emerges as a performance metric in this new heat sinking paradigm. In this paper, a compact hierarchical manifold microchannel design is presented that utilizes an integrated multilevel manifold distributor to feed coolant to an array of microchannel heat sinks. The flow features in the manifold layers and microchannels are fabricated in silicon wafers using deep reactive-ion etching. The heat source is simulated via Joule heating using thin-film platinum heaters. The on-chip spatial temperature measurements are made using four-wire resistance temperature detectors. The individual manifold layers and the microchannel-bearing wafers are diced and bonded into a sealed stack via thermocompression bonding using gold layers at the mating surfaces. Thermal and hydrodynamic testing is performed by pumping the dielectric fluid HFE-7100 through the device at a known flow rate, temperature, and pressure at different levels of chip heat input. A volumetric heat density of up to 2870 W/cm3 is dissipated at a chip temperature less than 112 °C and microchannel pressure drop less than 27 kPa. The overall pressure drop is governed by flowing through the manifold, rather than the microchannels, in this compact heat sink that occupies envelope of 5 mm $\times 5$ mm $\times2.3$ mm including all the functional flow features.

High-Performance and Lightweight Thermal Management Devices by 3D Printing and Assembly of Continuous Carbon Nanotube Sheets.

Free-standing carbon nanotube films or buckypaper can provide a significant platform to develop practical applications of nanocarbon materials. For this research, buckypaper with high thermal conductivity (20 W/m K) and large surface area (350 m2/g) was mass produced in-house to investigate for use in lightweight thermal management devices. Floating catalyst chemical vapor deposition carbon nanotube sheets were also studied in this work. We introduced two manufacturing techniques to use the sheets for heat dissipation: (1) printing conductive composite ink on the sheets to make lightweight thermal devices, such as heat sinks and (2) assembling the sheets directly into 3D structures that were mounted on the back of heat-generating devices. These manufacturing techniques resulted in extremely lightweight, high-performance heat dissipation devices compared with other heat sink materials.

Energy saving and optimum insulation thicknesses in building upgrading

Heat pumps are classified as ecologically friendly heat-generating devices and are one of the most suitable solutions for improving energy efficiency in buildings. Systems based on such solutions replace conventional sources very well. Household sector is one of the major energy consumers, where energy is used mainly for space heating and providing hot water. To increase renewable energy consumption levels, it is necessary to take decisive actions aimed at energy modernization of existing buildings. Particular emphasis must be put on the use of renewable energy sources. A wide selection of insulation materials is available on the market, however proper technologies are required to apply those materials, especially for historical buildings. Therefore, while planning investment, a question must be answered what type of material should be used, and what costs that will generate. The paper presents simple methodology for calculating the optimal insulation thickness so that the costs of the thermo-modernization would be covered by savings in heating expenses, when bank loan for the project is available at fixed interest rate.

PARAMETERIZATION OF ACTUATING ELEMENTS OF PUMPING ELECTROMECHANICAL CONVERTERS

[For the English abstract and full text of the article please see the attached PDF-File (English version follows Russian version)].ABSTRACT The question of validity of the choice of an actuating element of heat-generating pumping devices with blade structures is considered. These devices are characterized by low hydraulic resistance of a working channel, absence of support and sealing parts, a wide range of design modifications of increased efficiency. Their feature is that the supporting element is not the traditional shaft, but the outer surface of the actuating element. The article shows what parameters of the elements used ensure modeling and control of heat transfer processes. Keywords: transport power system, heat-generating transfer device, actuating element, parameters, 3D model, independent control.

Testing the Design of Technical Solutions for Liquid Hydrocarbon Wastes Fire Disposal

The relevance of the work is caused by the need to develop the environmentally friendly heat-generating devices for disposal liquid technological wastes. The main aim of the research is to optimize the constructive implementation of technical solutions for disposal liquid hydrocarbon wastes. Using the software package «Ansys Multiphysics» the authors have simulated the combustion front at various flow conditions and measured reaction rate, temperature and components concentrations in the combustion zone. The results of the investigation have shown that the proposed technical solution has a number of features.

Design of Anisotropic Thermal Conductivity in Multilayer Printed Circuit Boards

The design of anisotropic thermal conductivity in multilayer printed circuit boards (PCB) is studied, where the flow of heat is manipulated through the informed layout of circuit board electrothermal traces. Three representative circuit board configurations are considered to illustrate the basic method. A baseline circuit board (Configuration 1) comprising a heat-generating device in thermal communication with a heat sensitive device by the way of a standard electrical trace connection is studied first to characterize heat flow due to conduction and convection. Building off of this baseline structure, the thermal management advantages and disadvantages of a closed heat shield for anisotropic PCB thermal conductivity are explored using the second circuit board (Configuration 2). The design of the third multilayer circuit board (Configuration 3) with optimized anisotropic PCB thermal conductivity for enhanced heat flow control is simultaneously explored. It is experimentally shown that, for PCBs subject to free convection and power densities on the order of 1–10 W/cm2, the design technique allows for noticeable (−10 °C) reduction in the temperature of the heat sensitive device without a significant (<3 °C) increase in the heat-generating device temperature. The experimental heat transfer results are verified through simulations that further confirm and explain the functionality and limitations of the heat flow control concept. The effect of Joule heating is also investigated numerically. A conceptual framework for electrothermal codesign of multilayer PCBs with integrated heat flow control and more device-dense packaging is proposed.

Validation of Numerically Simulated Tissue Temperatures During Transcutaneous Recharge of Neurostimulation Systems.

A research study combining numerical simulation and animal-model experiments has been performed to assess the ability of simulation to accurately calculate temperatures within living tissue during the recharge of a neuromodulation system (Restore Ultra device, Medtronic Neuromodulation, Minneapolis, MN, USA). The experiments were carried out on a sheep with the neuromodulation implant set to depths of 0.6 cm and 2.1 cm. Temperatures were recorded on the surfaces of the implant and on the sheep skin. Finite element simulations were carried out to determine the degree to which the simulations and experiments match. Additional calculations were performed for an intermediate implant depth. It was found that there was excellent agreement between the simulations and the animal model for both depths. It is shown that numerical simulation using the Pennes bioheat equation is capable of predicting temperature increases within living tissues when implanted heat-generating devices are in use. The device used in the present study does not give rise to temperatures which cause concern of thermal injury or safety. The study was performed for aligned antenna and implant.

Measurement of Steady-State CHF in Horizontal Channels for Low-Pressure, Low-Flow Conditions

Experimental investigations on critical heat flux (CHF) are mostly on vertical channels involving high mass fluxes and high system pressures. Reported studies on CHF in horizontal flow channels under low-pressure, low-flow (LPLF) conditions are limited. Understanding CHF is essential in the design and operation of heat exchangers and heat-generating devices including fuel channels of nuclear reactors. The present work investigates CHF in horizontal tubes for low steady flow at atmospheric pressure conditions. Appearance of a “red hot” spot on the test section is considered to be the occurrence of critical heat flux condition in this study. Present data could not be predicted using the reported method of applying a correction factor for the vertical lookup table data. A correlation using the experimental data is developed incorporating the fluid-to-fluid modeling parameters for the prediction of CHF in horizontal channels under LPLF conditions. Numerical study using thermal hydraulic system code RELAP5 suggests liquid film dryout as the mechanism of CHF occurrence in the present investigations.

Thermoelectric Self-Cooling System to Protect Solar Collectors from Overheating

Solar collectors for water heating have spread rapidly in recent years, as their use saves significant amounts of fuel and electricity. One of the main problems with these systems is overheating of the internal fluid, which takes place when an enormous amount of heat is collected but the demand for hot water is low, resulting in high-pressure, high-temperature conditions that damage some of the components. Nowadays, most such systems include either static or dynamic dissipators that remove excess heat. This paper presents a thermoelectric self-cooling system designed to dissipate excess heat from a solar-collector system and prevent overheating of the internal fluid. Thermoelectric self-cooling (TSC) is a novel thermoelectric application, proven to enhance the cooling of any heat-generating device without electricity consumption. This paper presents the design and computational study of a TSC system, pointing out that the most important parameters are the thermal resistances of the heat exchangers, and that their reduction significantly improves the performance of the thermoelectric system. The final design outperforms currently used static and dynamic dissipators, increasing the heat transfer coefficient by more than 50% and requiring no electricity, representing a promising alternative to prevent overheating of solar collectors.

Dynamic model for simulation of thermoelectric self cooling applications

Thermoelectric self-cooling systems hold good prospects for the future, since they improve the cooling of any heat-generating device without electricity consumption. The potential number of applications seems to be enormous, hence the necessity of a specific model to simulate this type of thermoelectric application.This paper presents a computational model for thermoelectric self-cooling applications, capable of simulating both the steady and the transient state of the whole system. Supported by fluid-dynamics software and based on the implicit finite differences, the model solves the system of equations composed of the Fourier's law and the thermoelectric effects Seebeck, Peltier, Joule and Thomson, including temperature-dependant properties. Furthermore, the model architecture allows the inclusion of new analytical expressions and/or procedures in order to simulate any component with higher accuracy or include more complex ones.Statistical studies indicate ±12% of maximum deviation between experimental and simulated values of the main outputs. Furthermore, the model simulates the performance of the system under abruptly changing conditions.In conclusion, the computational model turns out to be a powerful tool that will play a key role in the design and development of thermoelectric self-cooling applications.

Achieving hemostasis in dermatology - Part 1: Preoperative, intraoperative, and postoperative management

As dermatological procedures continue to become increasingly complex, improved methods and tools to achieve appropriate hemostasis become necessary. The methods for achieving adequate hemostasis are variable and depend greatly on the type of procedure performed and the unique characteristics of the individual patient. In Part 1 of this review, we discuss the preoperative, intraoperative, and postoperative management of patients undergoing dermatologic surgery. We address oral medications and supplements that affect hemostasis, hemostatic anesthesia, and intraoperative interventions such as suture ligation and heat-generating cautery devices. In Part 2 of this review, we will discuss topical hemostats. The authors conducted an extensive literature review using the following keywords: “hemostasis,” “dermatology,” “dermatological surgery,” “dermatologic sutures,” “electrosurgery,” “hemostatic anesthesia,” and “laser surgery.” Sources for this article were identified by searching the English literature in the Pubmed database for the time period from 1940 to March 2012. A thorough bibliography search was also conducted and key references were examined.

Field test with Stirling engine micro-combined heat and power units in residential buildings

The Institute for Energy Economy and Application Technology (IfE), together with the Energie Südbayern (ESB), the local gas supplier in southern Bavaria, are responsible for a field measurement campaign of four gas fired Stirling engine micro-combined heat and power units. These units and the measurement equipment were installed in four different single family houses at the end of 2009. After monitoring over 1 year, it can be said that the Stirling engine micro-combined heat and power units are capable in supplying small residential buildings with thermal and electric power. The data evaluation shows the micro-combined heat and power-units work with a steady-state efficiency above 90%. The main goals of this field test, besides the verification of the Stirling engine’s efficiency, are an analysis of the complete system’s overall energy performance. Therefore, a detailed examination of not only the heat-consuming devices, space heating and the domestic hot water system, but also the examination of heat-generating devices, the Stirling engine and the auxiliary burner were made. The implementation of heat demand curves helps to assess not only the steady state, but also the yearly performances of each micro-combined heat and power units. For a future integration of micro-combined heat and power units into a smart grid, they have to be predictable. Hence, a detailed analysis was taken onto the electricity generation curves at different ambient temperatures and its hourly behaviour. Lastly, for the economic evaluation, the onsite consumption characteristics were considered in depth.

On the problem of determining speed-torque characteristics of thermal electromechanical converters

The main energy characteristics of electromagnetic, thermal, and hydraulic processes in heat-generating devices are considered.

Achieving Hemostasis in the Surgical Field

Hemostatic mechanisms are an integral part of the human physiology. Traditionally divided into intrinsic and extrinsic arms, the coagulation cascade converges, through the interactions of many different factors, at a common element-thrombin. As a consequence, a number of different agents have been developed to supplement this common, critical step to aid surgical hemostasis. Intraoperative interventions most commonly include sutures and heat-generating cautery devices; however, these methods are sometimes insufficient or inappropriate for a specific procedure or anatomic location, leading to the development of other adjunctive therapies, including topical hemostats. Topical hemostatic agents generally act as active, passive, and combinations therapies, depending on their individual composition and mode of action. We provide a brief review of the normal coagulation cascade, including critical points, followed by a discussion of surgical strategies and adjuctive therapies used to achieve surgical hemostasis and concluding with a discussion of topical thrombins.

Histologic Comparison of Canine Skin Biopsies Collected Using Monopolar Electrosurgery, CO2 Laser, Radiowave Radiosurgery, Skin Biopsy Punch, and Scalpel

To compare the histologic appearance of canine skin biopsies collected by use of a scalpel, skin biopsy punch, monopolar electrosurgery, CO2 laser, and radio wave radiosurgery in fully rectified wave form (RWRS). Experimental, randomized design. Healthy adult grayhounds (n=4). Skin biopsies were collected using 5 techniques. Cut margins of biopsy specimens and adjacent peripheral skin were evaluated using light microscopy to compare penetration of the dermis by tissue carbonization (char). No char occurred in skin specimens collected by biopsy punch and scalpel. Char penetration occurred in all specimens collected by electrosurgery, CO2 laser, and RWRS. Mean char penetration in skin biopsies collected by RWRS (0.158 mm) was significantly less than for monopolar electrosurgery (0.223 mm) and CO2 laser (0.215 mm). Mean char penetration in adjacent peripheral skin surrounding biopsies collected by RWRS (0.171 mm) was significantly less than monopolar electrosurgery (0.255 mm) but not less than CO2 laser (0.215 mm, P<.07). RWRS (blended waves in cut-coagulate mode) caused less lateral thermal damage to canine skin biopsies than monopolar electrosurgery and CO2 laser and less lateral thermal injury to peripheral skin than monopolar electrosurgery. Excision of canine skin biopsies with heat-generating devices may not allow reliable histologic interpretation, particularly when assessing margins of small biopsy specimens. RWRS may be less traumatic to canine skin than monopolar electrosurgery and CO2 laser when used to make incisions.

Advanced Thermal Interface Materials

ABSTRACTThermal interface materials (TIMs) are used to dissipate thermal energy from a heat-generating device to a heat sink via conduction. The growing power density of the electronic device demands next-generation high thermal conductivity and/or low thermal resistance TIMs. This paper discusses the current state-of-art TIM solutions, particularly fusible particles for improved thermal conductivity. The paper will address the benefits and limitations of this approach, and describe a system with unique filler morphology. Thermal resistance and diffusivity/conductivity characterization techniques are also discussed.

Sensitivity analysis of one-dimensional heat transfer in tissue with temperature-dependent perfusion.

Design criteria for implantable heat-generating devices such as the total artificial heart require the determination of safe thresholds for chronic heating. This involves in-vivo experiments in which tissue temperature distributions are obtained in response to known heat sources. Prior to experimental studies, simulation using a mathematical model can help optimize the design of experiments. In this paper, a theoretical analysis of heat transfer is presented that describes the dynamic, one-dimensional distribution of temperature from a heated surface. Loss of heat by perfusion is represented by temperature-independent and temperature-dependent terms that can reflect changes in local control of blood flow. Model simulations using physiologically appropriate parameter values indicate that the temperature elevation profile caused by a heated surface adjacent to tissue may extend several centimeters into the tissue. Furthermore, sensitivity analysis indicates the conditions under which temperature profiles are sensitive to changes in thermal diffusivity and perfusion parameters. This information provides the basis for estimation of model parameters in different tissues and for prediction of the thermal responses of these tissues.

Numerical investigation of natural convection in a vertical slot with two heat source elements

Numerical modeling of natural convection air cooling of two heat-generating devices in an upright open-top slot has been considered. The heat sources are located on a vertical substrate of finite thermal conductivity, and the effect of different substrate material on the heat transfer performance has been quantified. The influence of the heat generation rate and the separation distance between the sources has been investigated. It has been shown that wall conduction is important, and for substrates with a finite thermal conductivity, it is essential that the conjugate analysis is employed.