Electro-Thermal Modeling of Power IGBT Module Cooled by A Heat Pipe Cooling System

This paper deals with the development of an electro-thermal model of an Insulated Gate Bipolar Transistor (IGBT) with a water-cooled heat pipe cooling system. Firstly, a thermal model of the heat pipe cooling system is proposed. Then, an electro-thermal model of the IGBT is developed to predict the junction temperature variations in transient operation. The thermal model of the IGBT is determined on the base of the thermal-capacitance lumped method. The electrical model of the IGBT is developed by considering the effect of the junction temperature on its static electrical parameters. Finally, the electro-thermal model is considered in a boost converter application. The model predictions show the effectiveness of the heat pipe cooling system for different commutation frequencies. It is proved that the heat pipe cooling system can keep the junction temperature of the IGBT at values allowing safe operation.

Asymmetric Supercapacitors: Optical and Thermal Effects When Active Carbon Electrodes Are Embedded with Nano-Scale Semiconductor Dots

Optical and thermal effects in asymmetric supercapacitors, whose active-carbon (AC) electrodes were embedded with nano-Si (n-Si) quantum dots (QD), are reported. We describe two structures: (1) p-n-like, obtained by using a polyethylimine (PEI) binder for the “n” electrode and a polyvinylpyrrolidone (PVP) binder for the “p” electrode; (2) a single component binder—poly(methyl methacrylate) (PMMA). In general, AC appears black to the naked eye and one may assume that it indiscriminately absorbs all light spectra. However, on top of a flat lossy spectrum, AC (from two manufacturers) exhibited two distinct absorption bands: one in the blue (~400 nm) and the other one in the near IR (~840 nm). The n-Si material accentuated the absorption in the blue and bleached the IR absorption. Both bands contributed to capacitance increase: (a) when using aqueous solution and a PMMA binder, the optical-related increased capacitance was 20% for low n-Si concentration and more than 100% for a high-concentration dose; (b) when using ion liquid (IL) electrolyte, the large, thermal capacitance increase (of ca. 40%) was comparable to the optical effect (of ca. 42%) and hence was assigned as an optically induced thermal effect. The experimental data point to an optically induced capacitance increase even in the absence of the n-Si dots. Overall, the experimental data suggest intriguing possibilities for optically controlled supercapacitors.

Thermal Behavior of Teeth During Restoration Procedure With Composite: Experimental Tests and Numerical Simulation

Different thermal mechanisms influence the tooth temperature during the reconstruction practice of tooth restoration: conduction in the hard tissues and their thermal capacitance, heat generation by composite curing, irradiation of the surface from the LED lamp, convection, and conduction to the environment. All these phenomena were considered into a numerical (finite difference, FD) model to simulate the temperature trend in a tooth during reconstruction with a resin composite addition, and results compared with experiments on cylindrical sample with a cavity filled with resin. Results demonstrate that all the phenomena have been sufficiently accurately described, and the way to apply the model to real teeth is recognized.

Experimental Characterization of Heat Transfer and Thermal Energy Storage Capability Using Swirling Two-Phase Flow in the Package Integrated Cyclone COoler (PICCO)

The increasing demand for high power density wide-bandgap power electronics has propelled heat transfer research leading to a constant increase in the thermal performance of cold plates and heat sinks. Most of this research has focused on reducing thermal resistance of the package which can have a detrimental effect on transient thermal performance if thermal capacitance is reduced. In order to provide both a low thermal resistance and a higher thermal capacitance integrated into the package and near the thermal junction, a new cold plate called the Package Integrated Cyclone COoler (PICCO) was developed. GE Research and the US Army Research Lab collaborated to explore and validate the potential of this concept. The PICCO coldplate, which is enabled by 3D printing, establishes a swirling coolant flow field to remove heat. The swirling flow is anticipated to significantly aid in vapor removal from the surface and hence allow for the fluid to provide thermal capacitance through two-phase heat transfer efficiently. This paper describes the experiment design and development for thermal storage and cooling performance characterization of PICCO. The test rig includes a high-pressure capability gear pump moving fluid first through a Coriolis flowmeter and then through PICCO, where the fluid is accelerated in the cyclone and heated by miniaturized ceramic heaters, simulating SiC power electronics. The coolant releases the accumulated enthalpy to a plate-fin heat exchanger that is connected to a chiller. Several absolute and differential pressure transducers and thermocouples monitor the state of FC-72. The experiments will provide empirical transfer functions characterizing the PICCO pressure drop, heat transfer coefficient, critical heat flux and thermal energy storage capability.

Power Optimization of a Modified Closed Binary Brayton Cycle with Two Isothermal Heating Processes and Coupled to Variable-Temperature Reservoirs

A modified closed binary Brayton cycle model with variable isothermal pressure drop ratios is established by using finite time thermodynamics in this paper. A topping cycle, a bottoming cycle, two isothermal heating processes and variable-temperature reservoirs are included in the new model. The topping cycle is composed of a compressor, a regular combustion chamber, a converging combustion chamber, a turbine and a precooler. The bottoming cycle is composed of a compressor, an ordinary regenerator, an isothermal regenerator, a turbine and a precooler. The heat conductance distributions among the six heat exchangers are optimized with dimensionless power output as optimization objective. The results show that the double maximum dimensionless power output increases first and then tends to be unchanged while the inlet temperature ratios of the regular combustion chamber and the converging combustion chamber increase. There also exist optimal thermal capacitance rate matchings among the working fluid and heat reservoirs, leading to the optimal maximum dimensionless power output.

Comparison and Implementation of Thermally Massive Wall and Roof Models for Use in Simplified Building Energy Models

An increasing trend in building energy simulations is to use simplified models to reduce simulation time, evaluate different model configurations, and analyze for energy consumption across different constructions and weather climates. Simplified models tend to share some common benefits such as ease of calibration and reduced setup and operation time. All of which allows for shorter time and simpler program to evaluate different situations or systems. Some of these simplified models ignore thermal capacitance within walls and roofs; removing thermal capacitance can decrease simulation time but may alter loading due to ignoring the delay between when exterior surfaces receive loading and when the load is transferred to the interior. While this simplification is sometimes useful, it often overlooks the delay that occurs between the external wall heating and that heat being transferred to the interior. This paper will explore alternative methods for evaluating conduction loads in opaque surfaces for use in building energy models. Specifically, a differential equation conduction method with numerical integration, closed form solution, and forward difference calculation. These methods will be evaluated for how different conduction simulation techniques can be used in different situations to provide a potential increase in accuracy for simplified models while simultaneously reducing computational loads. Understanding the physics of dynamic envelope loading can change how much energy a building uses and when room conditioning needs to occur.

On the Reproducibility of Thermal Measurements and of Related Thermal Metrics in Static and Transient Tests of Power Devices

Traditionally the thermal behavior of power devices is characterized by temperature measurements at the junction and at accessible external points. In large modules composed of thin chips and materials of high thermal conductivity the shape and distribution of the heat trajectories are influenced by the external boundary represented by the cooling mount. This causes mediocre repeatability of the characteristic RthJC junction to case thermal resistance even in measurements at the same laboratory and causes very poor reproducibility among sites using dissimilar instrumentation. The Transient Dual Interface Methodology (TDIM) is based on the comparison of measured structure functions. With this method high repeatability can be achieved although introducing severe changes into the measurement environment is the essence of this test scheme. There is a systematic difference between thermal data measured with TDIM method and that measured with temperature probes, but we found that this difference was smaller than the scatter of the latter method. For checking production stability, we propose the use of a structure function-based Rth@Cth thermal metric, which is the thermal resistance value reached at the thermal capacitance belonging to the mass of the package base. This metric condenses the consistency of internal structural elements into a single number.