Wound-up phase turbulence in the Complex Ginzburg-Landau equation

We consider phase turbulent regimes with nonzero winding number in the one-dimensional Complex Ginzburg-Landau equation. We find that phase turbulent states with winding number larger than a critical one are only transients and decay to states within a range of allowed winding numbers. The analogy with the Eckhaus instability for non-turbulent waves is stressed. The transition from phase to defect turbulence is interpreted as an ergodicity breaking transition which occurs when the range of allowed winding numbers vanishes. We explain the states reached at long times in terms of three basic states, namely quasiperiodic states, frozen turbulence states, and riding turbulence states. Justification and some insight into them is obtained from an analysis of a phase equation for nonzero winding number: rigidly moving solutions of this equation, which correspond to quasiperiodic and frozen turbulence states, are understood in terms of periodic and chaotic solutions of an associated system of ordinary differential equations. A short report of some of our results has been published in [Montagne et al., Phys. Rev. Lett. 77, 267 (1996)].Comment: 22 pages, 15 figures included. Uses subfigure.sty (included) and epsf.tex (not included). Related research in http://www.imedea.uib.es/Nonlinea

Evaporative Spray Cooling Of Power Electronics Using High Temperature Coolant

A pressure atomized evaporative spray cooling nozzle array was used to thermally manage the power electronics of a 3 phase inverter module. The module tested was a COTS module manufactured by Semikron, Inc., and has a maximum DC power input of 180 kW (450 VDC and 400 A) with 25°C coolant. However, the standard heat sink that the module uses is a single phase liquid heat sink and when 100°C coolant is used (as in automotive applications), the maximum module power is de-rated to 45 kW so that the IGBT chips will not overheat. The module tested here incorporated a custom heat sink that allowed for the use of spray cooling nozzles, which were designed and developed by RTI. The spray liquid was a 50/50 mixture of water and propylene glycol (WPG) at a temperature of 100°C. The sprays impinged directly onto the bottom surface of the DBC boards to which the power electronics were mounted. This arrangement, combined with the high heat transfer coefficient of evaporative spray cooling, greatly reduced the thermal resistance of the power electronics material stack up, but did so without directly wetting the electronics. The results of this work were that the unique evaporative spray cooling nozzle design and patented electronics interface design allowed the module to be run to full power while keeping the IGBT junction temperatures acceptable, despite the high coolant temperature. The junction temperatures of the IGBT\u27s were measured by electrically insulated type T thermocouples placed on top of the devices, and the thermocouple readings at the full load were within several degrees of one another. Consistent and uniform junction temperatures are an important factor in long term device reliability. For the standard heat sink, which uses single phase liquid cooling, the pressure drop and flow rate required for maximum heat removal would be 17 psi and 5.3 GPM. For the pressure atomizer spray nozzles, the module would require a pressure drop and flow rate of 40 psi and only 2.7 GPM. ©2008 IEEE

Enabling Much Higher Power Densities In Aerospace Power Electronics With High Temperature Evaporative Spray Cooling

A power electronics module was equipped with an evaporative spray cooling nozzle assembly that served to remove waste heat from the silicon devices. The spray cooling nozzle assembly took the place of the standard heat sink, which uses single phase convection. The purpose of this work was to test the ability of spray cooling to enable higher power density in power electronics with high temperature coolant, and to be an effective and lightweight system level solution to the thermal management needs of aerospace vehicles. The spray cooling work done here was with 95 °C water, and this data is compared to 100 °C water/propylene glycol spray cooling data from a previous paper so as to compare the spray cooling performance of a single component liquid to that of a binary liquid such as WPG. The module used during this work was a COTS module manufactured by Semikron, Inc., with a maximum DC power input of 180 kW (450 VDC and 400 A). With single phase convective cooling, the coolant must be kept at 25 °C in order to prevent the insulated gate bipolar transistor (IGBT) die temperatures from exceeding acceptable limits at full power. If the coolant temperature is higher (100 °C, for example) the module power rating is reduced by a factor of 4 to 45 kW. Due to the high heat transfer coefficient of the evaporative spray cooling nozzles, the module was run at full load while maintaining satisfactory die temperatures even with the coolant at high temperature. The temperatures of the IGBT dies were measured by electrically insulated type T thermocouples that were placed on the die surfaces by Semikron during the manufacturing process. It was found that water spray cooling yielded IGBT device temperatures about 10 °C lower than WPG did, and both offer a substantial improvement over single phase convective cooling. The ability to cool power electronics with high temperature coolant means that a large ΔT is available for heat rejection to ambient conditions, which translates into a small and lightweight condenser. This higher coolant temperature also means it is possible to reject heat to warm ambient air. Also, the use of lower coolant flow rates enables the use of a smaller and lighter liquid pump. These factors, combined with the higher power density achieved, mean that evaporative spray cooling has significant potential to yield a lightweight thermal management system for aerospace applications. Copyright © 2008 SAE International

Thermal Management Of Power Inverter Modules At High Fluxes Via Two-Phase Spray Cooling

A spray cooling system was developed and tested for thermal management of power inverter modules utilized in automotive applications. The system featured an array of 1 × 2 pressure atomized nozzles that used 88°C boiling point antifreeze coolant with 0.15-l/min.cm 2 liquid flow rate and 145-kPa pressure drop. A 2-cm 2 simulated device, having two kinds of enhanced spray surface with microscale structures, reached up to 400-W/cm 2 heat flux with as low as 14°C surface superheat. These experimental results demonstrated the capability of greatly reducing the overall thermal resistance of the inverter modules that are commonly cooled with single-phase convective systems. The long-term reliability of the spray cooling was assessed with 2000 h of testing time. Performance of the presented system proved the spray cooling of power electronics as an attractive option that enables high power densities while maintaining acceptable and uniform device temperatures. In addition, due to the use of high temperature coolant at low flow rates, the spray cooling offers a compact and efficient system design. © 2011-2012 IEEE

Spray Cooling Of Power Electronics Using High Temperature Coolant And Enhanced Surface

A spray cooling system was developed and tested for thermal management of power inverter modules utilized in automotive applications. System featured an array of 1×2 pressure atomized nozzles that used 90 °C antifreeze coolant with 0.15 L/min-cm2liquid flow rate and 145 kPa pressure drop. Two cm2 simulated device, having an enhanced spray surface with micro scale structures, reached up to 400 W/cm2 heat flux with only 14 °C surface superheat. These experimental results demonstrated the capability of greatly reducing the overall thermal resistance of the inverter modules that are commonly cooled with single phase convective systems. Performance of the presented system proved the spray cooling of power electronics as an attractive option that enables high power densities while maintaining satisfactory and uniform device temperatures. In addition, due to the use of high temperature coolant at low flow rates, spray cooling offers compact and efficient system design. ©2009 IEEE

Spray Cooling With Ammonia On Micro-Structured Surfaces

Experiments were performed to investigate spray cooling enhancement on micro-structured surfaces. Surface modification techniques were utilized to obtain micro-scale indentations and protrusions on the heater surfaces. A smooth surface was also tested to have baseline data for comparison. Tests were conducted in a closed loop system with ammonia using RTI\u27s vapor atomized spray nozzles. Thick film resistors, simulating heat source, were mounted onto 1cm x 2cm heaters and heat fluxes up to 500 W/cm2 (well below critical heat flux (CHF) limit) were removed. Two nozzles each spraying 1 cm2 of heater area used 96 ml/cm2-min (9.7 gal/in2-hr) liquid and 13.8 ml/cm2-s (11.3 ft3/in2-hr) vapor flow rate with only 48 kPa (7 psi) pressure drop. Results for micro-structured surfaces with protrusions and indentations offered significant performance enhancement of 115% and 52% increase in heat transfer coefficient over smooth surface respectively. ©2008 IEEE