Heat Extraction Capability Research Articles

Thermal analysis and characterization of the effect of substrate thinning on the peformances of GaN‐based light emitting diodes

AbstractWe report the effect of substrate thickness on the optical and thermal characteristics of InGaN/GaN light emitting diodes (LEDs), operating at λ ∼ 450 nm, with different mesa sizes. For various mesa sizes with different substrate thicknesses, the junction temperature (Tj) is measured as a function of injection current by the forward voltage method and the characteristic temperature is also investigated by measuring the temperature‐dependent electroluminescence spectrum. Based on the experimentally determined heat source density, the junction temperature, heat flux, and thermal resistance (Rth) are calculated theoretically by using a three‐dimensional anisotropic heat dissipation model. The use of a thin substrate thickness of 150 µm effectively improves the heat extraction capability due to the shorter heat transfer path length. For 150 µm (443 µm) thick substrate, the Tj value of LEDs is experimentally estimated as 307.7 K (322.6 K), 311.6 K (329.5 K), and 323 K (355.9 K) under an injection current of 80 mA for 450 × 450, 400 × 400, and 300 × 300 µm2, respectively. At a high injection current of 400 mA, the Tj of 450 × 450 µm2 LED with 150 µm thick substrate is reduced by ∼25.7% compared to that of LED with 443 µm substrate thickness, indicating a value of Tj = 384.5 K. The Rth value is decreased for larger mesa size and thinner substrate thickness, resulting in Rth < 30 K/W for 450 × 450 µm2 LED with 150 µm thick substrate. The theoretically calculated Rth values indicate a good agreement with the experimentally measured data.

The Thermal Resistance of Solder Joints in High Brightness Light Emitting Diode (HB LED) Packages

We present a framework to calculate the thermal resistance of Au-Sn eutectic solder joint (Rth, Au-Sn joint) in high brightness light emitting diode (HB LED) packages whose heat extraction capability controls the optical efficiency and reliability of HB LEDs. Using the transient thermal measurement combined with the structure function based analytical method and the finite element method, we find that the thermal conductivity (k) of the thin solder joint becomes significantly smaller than the Au-Sn alloy after joining; hence, Rth, Au-Sn joint constitutes a large portion of the total Rth of the package (Rth PKG).

Effect of Nozzle Configuration on Cooling of a Hot Moving Steel Plate

The objective of this study is to develop an experimental database for modelling boiling heat transfer that occurs during run-out table cooling. Experiments have been carried out on a pilot scale run-out table with an emphasis on the effect of nozzle configuration on the overall heat extraction rate. The heat extraction capability of an individual nozzle is generally determined by the surface temperature of the to-be-impinged and surrounding areas of the steel plate to be cooled. Nozzle arrangements of subsequent jet lines with respect to hot and cold regions developed by prior jet line impingement is crucial inmaintaining uniform and efficient cooling of the hot plate or strip. Results from a series of tests are presented and discussed to examine quantitatively heat extraction for a moving steel plate as a function of nozzle configuration.

Thermodynamic analysis of an existing coal-fired power plant for district heating/cooling application

In a conventional coal-fired power plant, which is only designed for electricity generation, 2/3 of fuel energy is wasted through stack gases and cooling water of condensers. This waste energy could be recovered by trigeneration; modifying the plants in order to meet district heating/cooling demand of their locations. In this paper, thermodynamical analysis of trigeneration conversion of a public coal-fired power plant, which is designed only for electricity generation, has been carried out. Waste heat potentials and other heat extraction capabilities have been evaluated. Best effective steam extraction point for district heating/cooling system; have been identified by conducting energetic and exergetic performance analyses. Analyses results revealed that the low-pressure turbine inlet stage is the most convenient point for steam extraction for the plant analyzed.

Heat transfer in a 155 mm compound gun barrel with full length integral midwall cooling channels

When firing, large amounts of heat flow into the gun bore surfaces and result in wear and erosion of the gun bore. Moreover, the chamber surface temperature will reach the cook-off temperature of propellant during long sustained firing, which will impact on user safety and facilities. For large-caliber gun, a serious limitation on the weapon’s availability for action is imposed with high-energy propellants used and firing rates increasing. An effective method for solving this problem is to adopt barrel liquid-cooling technique. In this paper, heat transfer in a 155 mm midwall cooled compound gun barrel was analyzed theoretically. For the reference, heat transfer in a naturally cooled monobloc gun barrel was also discussed. Finite element analysis (FEA) method was employed to validate the results obtained by theoretical analyses. The present study showed: (1) natural air cooling is ineffective for transferring the heat out of the barrel because the combined convection and radiation heat transfer coefficient is relatively small; (2) forced midwall cooling has great heat extraction capability and is able to keep the chamber temperature below the cook-off temperature by increasing the heat transfer coefficient; (3) an optimal flow rate should be selected to balance the cooling efficiency and the pressure loss.

Problems and Issues for Tokamak Long-Pulse Operation: Major Progress on Tore Supra

During winter 2001–2002, the Tore Supra tokamak went through a major upgrade to provide a heat extraction capability of 25 MW in steady state (composants internes et limiteur project). In the new configuration, the operational domain has experienced a rapid extension. Indeed, discharges of more than 4 min have been performed with a world-record-breaking discharge accounting for 0.75 GJ of injected/extracted energy. Stationary discharges with fully noninductively driven current are performed routinely (typical parameters: plasma current, 0.52 MA; toroidal magnetic field, 4 T; lower hybrid power, ~3 MW, electron line density, 2.5 × 1019 m–2), limited in duration by the original lower hybrid current drive (LHCD) system. Ion cyclotron waves [ion cyclotron resonance heating (ICRH)] have been coupled to plasma for 1 min in combination with LHCD in a higher-density scenario (Greenwald fraction of 0.8, 0.11 GJ of injected ICRH power for 0.42 GJ total injected power) and with a substantial fraction of bootstrap current (15 to 20%). Electron cyclotron current drive experiments are also carried out: A new world record of electron cyclotron injected energy has been established in a single electron cyclotron resonance heating pulse of 32 s (25 MJ). In these discharges, stable central electron temperature oscillations sometimes appear, probably due to the interplay between heat transport and current drive. Density profile peaking is observed despite the absence of toroidal electric field, suggesting the existence of a turbulent inward pinch. Finally, particle balance analyses indicate that the in-vessel deuterium inventory never reaches saturation. Many carbon deposits and flakes have been found in the inner vessel, possibly playing a role in the fuel retention.

Progress Toward Steady-State Operation on Tore Supra

Important technological and physics issues related to steady-state operation required for next step are being examined on Tore Supra, after a major upgrade of internal components in order to increase the heat extraction capability to 25 MW for 1000 s. Here, we show first experimental results, where all the plasma facing components were actively cooled during pulses exceeding four minutes, with reactor-relevant heat load. New physics was observed in non-inductively driven plasmas, including a stationary peaked radial profile of the plasma density generated by an anomalous inward pinch; and a regime characterized by sinusoidal oscillations of central electron temperature, governed by non-linear coupling between heat transport and plasma current analogous to a predator-prey mechanism.

Recent developments in steady-state physics and technology of tokamaks in Cadarache

Operation of Tore Supra has resumed after a major upgrade of internal components in order to increase the heat extraction capability to 25 MW for 1000 s and address long-pulse research at the level of power density flowing through the last closed flux surface relevant for the next step. This overview highlights first the related technology developments: industrial realization and tests with plasma of about 600 limiter components made of some 12 000 actively cooled CFC tiles. World record breaking discharges with a coupled (and extracted) energy of 0.74 GJ have been obtained, with durations exceeding 4 min, limited only by the long-pulse capability of the heating and current drive systems. Particle balance analysis shows that the in-vessel deuterium inventory never reached saturation. For the same plasma parameters, the in-vessel inventory is reduced by a factor of ≈2 when efficient supersonic gas injection is used. New physics is observed when the loop voltage vanishes for long times: the density remains peaked in spite of the absence of the Ware pinch effect, and, independently, the response to additional heating becomes dominated by a complex interplay between transport and current drive. The contributions of the EURATOM-CEA Association to fusion energy research also include new developments in the field of plasma-facing components, negative ion beam injection (1000 s H− source and SINGAP acceleration to 1 MeV) and superconductors (cable in conduit concept, connections, testing). Finally, European studies for Cadarache as a site for ITER conclude that all ITER technical requirements are met.

Experimental Investigation on a Novel Four-bed Adsorption Chiller

A prototype multi-bed regenerative adsorption chiller with a novel four-bed operation mode has been designed, fabricated and tested. The rating tests are conducted under assorted ARI coolant, using a purpose-built rating. The 4.bed design exhibits superior heat extraction capability from the heat source as its slave-first-then-master arrangement permits individual bed to maximize energy utilization in a batch cycle. Overall system performance of chiller is evaluated for various adsorption-desorption cycle and switching time at assorted coolant inlet temperatures. For fair comparison, the 4-bed chiller is also compared with that of a two-bed mode at the same working conditions.

Design and Analysis: Thermal Emulator Cubes for Opto-Electronic Stacked Processor

3D finite element modeling of thermal emulator cube and its composition consisting of composite stack of multi-layer chip are developed. Thermal analysis of the Multi-Chip Module consisting of 16 alternate layers Si processor and heat sink layers with Si spacers and AlN ceramic cap is undertaken. The various alternatives for design of the emulator cubes such as thermal cube floating in free-space, thermal cube-on-substrate, thermal cube-on-flex cable with a continuous joint of solder and thermal cube embedded in rectangular Si-spacer are investigated for their heat extraction capability. Thermal modeling of a composite structural unit stack of chip offers first hand information as to the operating performance of the entire thermal emulator cube to be used in the construction of buffer cube. The scientific understanding of the mode of heat transfer of the emulator cube, heat extraction of the various heat sink materials, ceramic and the metallic substrates are investigated. A thin sheet of ceramic (AlN) substrate is at least three times more effective in extraction of heat than thick block of steel under similar conditions. The homogeneous and heterogeneous nature of the composite structure of thermal emulator in heat transfer is analyzed. The primary and secondary hotspots in thermal cubes with AlN heat sink are found in thermal simulations. The mode of heat transfer advances normal to lateral and transverse directions of stacking from the central core of the cube towards the outward face. The sharp corners of the cube typically exhibit edge convection due to chilling effect. Buffer-on-flex cable is modeled with a continuous solder joint and its further improvement with alternate hinges of solder joints and micro-channels is proposed for enhanced heat transfer analysis. The embedded emulator cubes are developed for thermal analysis of the optical layers on top of buffer. The optical layers with an interconnection of solder joints on top of the embedded emulator cubes coupled with micro-channels and hinged solder joints will be used for further enhanced heat transfer and higher dissipation of heat 1∼3W/layer resulting in efficient and cost effective thermal management technique.