An official website of the United States government
Electronic components, especially the CPUs/GPUs used in data centers are concentrated heat-generating sources. Their large Thermal Design Power (TDP), small die area and confined packaging make their thermal management a unique challenge. While conventional single-phase cooling methods fail to dissipate such large amounts of heat efficiently, recently developed two-phase cooling systems also lack the holistic approach of combining efficient boiling and condensation mechanisms. It is hypothesized that subcooled boiling with submerged condensation and reduced saturation pressure will result in high-heat flux dissipation while maintaining low surface temperatures. The novel boiling chamber presented in this work is demonstrated in a compact configuration that fits in a 1U/2U server rack by combining submerged condensation with subcooled pool boiling. The boiling chamber is filled with 13% and 40% fill ratio of water and Novec-7000 and experimentally investigated on a thermal test vehicle. Results show that the boiling chamber dissipates about 400 W of heat with a surface temperature of less than 80 °C using Novec-7000 working fluid. When tested with water, the device dissipated more than 750 W of heat (heat flux ≈ 67 W/cm2) with a surface temperature of less than 90 °C. Though the surface temperature rose to 120°C, further testing shows the device to dissipate more than 1 kW from a 34.5 × 32 mm2 plain copper chip. High-speed images identify submerged condensation and small diameters of vapor bubbles. Further enhancements can be achieved by implementing enhanced boiling and condensation surfaces. Lastly, a guide to design considerations and future work is provided to unlock the greater performance potential of the novel boiling chamber.
more »
« less
An experimental study on high-pressure pulsed sprays for efficient management of high heat fluxes for moderate area devices
This work showcases an experimental sub-saturation spray cooling setup for a range of heat fluxes from 0.93 W/cm 2 to 4.66 W/cm 2 . The system consists of a 12” Aluminum square heat source unit with 28 embedded 1800 W cartridge heaters. An external high-pressure air tank provides the system with spraying pressures ranging from 500 to 3000 Psi. User-defined control algorithms command four piezoelectric actuated injectors allowing for the manipulation of the spray frequency, duration, duty cycle, and coordination between multiple piezo-injectors. Thus far, experiments in the horizontal configuration have shown that at 60°C, surface temperatures for all heat fluxes prove difficult to control. At 90°C, however, successful results show that heat fluxes of 1.86 W/cm 2 and 2.79 W/cm 2 are sustainable. Conducting experiments at aggressive power loads and surface temperatures significantly below saturation intro-duce spray-pooling, coolant pools which inhibit the evaporation rate, significantly diminishing the spray cooling efficiency. To counteract this effect, additional experiments were performed in a vertical configuration to avoid the pooling of non-evaporated coolant and enhance the heat transfer through the falling film. The results show surface temperature control for 60°C and 90°C within 6°C of the average surface temperature for heat fluxes up to 0.93 W/cm 2 and 3.72 W/cm 2 , respectively.
more »
« less
- Award ID(s):
- 2032764
- PAR ID:
- 10474047
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 979-8-3503-2166-1
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Location:
- Orlando, FL, USA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The demand for flexible microelectronics has increased significantly within the last decade. This study investigates the cooling performance of flexible pulsating heat pipes (PHPs) made from acrylic with a bend radius of ≈300 mm. The fabricated devices support two-phase, pulsating fluid flow inside the rectangular microchannels. Both water and ethanol are used as coolants, where local hot spots are generated by cobalt-alloy foil heaters inside the flexible PHPs. The PHP's dissipate the heat generated to the environment via copper condensers with controlled setpoint temperatures. Based on a heater surface area of ≈1.5 cm 2 and a condenser setpoint temperature of 25°C, the maximum heat flux observed for sustained and repeatable cooling with water and ethanol was 8 W /cm 2 . These heat fluxes correlate well with other PHP studies with similar heater power loads, channel geometries, and coolants.more » « less
-
Controlled but explosive growth in vaporization rates is made feasible by ultrasonic acoustothermal heating of the microlayers associated with microscale nucleating bubbles within the microstructured boiling surface/region of a millimeter-scale heat exchanger (HX). The HX is 5 cm long and has a 1 cm × 5 mm rectangular cross section that uses saturated partial flow-boiling operations of HFE-7000. Experiments use layers of woven copper mesh to form a microstructured boiling surface/region and its nano/microscale amplitude ultrasonic (~1-6 MHz) and sonic (< 2 kHz, typically) vibrations induced by a pair of very thin ultrasonic piezoelectric-transducers (termed piezos) that are placed and actuated from outside the heat-sink. The ultrasonic frequencies are for substructural microvibrations whereas the lower sonic frequencies are for suitable resonant structural microvibrations that assist in bubble removal and liquid filling processes. The flow and the piezos' actuation control allow an approximately 5-fold increase in heat transfer coefficient value, going from about 9000 W/m2-°C associated with microstructured no-piezos cases to 50,000 W/ m2-°C at a representative heat flux of about 25 W/cm2. The partial boiling approach is enabled by one inlet and two exit ports. Further, significant increases to current critical heat flux values (~70 W/cm2) are possible and are being reported elsewhere. The electrical energy consumed (in W) for generating nano/micrometer amplitude vibrations is a small percentage (currently < 3%, eventually < 1% by design) of the total heat removed (in W), which is a heat removal rate of 125 W for the case reported here.more » « less
-
This paper focuses on two-phase flow boiling of dielectric coolant HFE 7000 inside a copper multi-microchannel heat sink for high heat flux chip applications. The heat sink is composed of parallel microchannels, 200 μm wide, 2500 μm high, and 20 mm long, with 200-μm-thick fins separating the channels. The copper heat sink consists of almost 100 channels connected by a longitude groove with a nearly trapezoidal cross section. Coolant impinges down to the base at the groove and then goes along the microchannels. A copper block heater arrangement was used to mimic a computer chip with a footprint of 1”x1” (6.45 cm2). The base heat flux was varied from 7.75 W/cm2 to 96.1 W/cm2 and the mass flux from 547.6 to 958.4 kg/m2s, at a nominal saturation temperature of 54 °C. Heat transfer coefficients as high as 57.5 kW/m2K were reached, keeping the base temperature under 66 °C with a maximum of 21.9 kPa of pressure drop, for inlet subcooling of 5 degree and a coolant flow rate of 958.4 kg/m2. Effects of inner diameter of tubing on thermal performance and pressure drop are also discussed. It was observed that an increase of tubing inner diameter by 60 % can result in increase of heat transfer coefficient by 47.8 % and reduction in pressure drop by 63 %.more » « less
-
Advancements in electronic device fabrication with increasing integration levels have resulted in very high device densities. This has led to higher power dissipation and heat fluxes, increasing integrated circuit (IC) operating temperature. High and nonuniform heat generation degrades device and system performance. Therefore, thermal management to keep ICs within prescribed temperature limits is an important challenge for reliable and economic performance. Cooling techniques, including liquid coolants and air conditioning (AC), have been utilized to remove heat at the package and system level. However, these techniques must overcome high thermal impedances and require complex integration, while global cooling is generally wasteful, inefficient, and expensive. To improve thermal management, we have developed Si microthermoelectric coolers (μTECs) with areas as small 1E−5 cm^2 that can be integrated on -chip near local hot spots using the standard fabrication processes. While Si μTECs cannot achieve low base temperatures, they can actively pump relatively high heat fluxes directly to a heat sink, thus reducing local temperature increases and allowing targeted rather than global waste heat removal. We demonstrate μTECs that can pump up to 43 W/cm^2 of locally generated excess heat with no increase in chip temperature.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/ITherm55368.2023.10177517
