Jet impingement can be particularly effective for removing
high heat fluxes from local hotspots. Two-phase jet
impingement cooling combines the advantages of both
the nucleate boiling heat transfer with the single-phase
sensible cooling. This study investigates two-phase confined
jet impingement cooling of local, laser-generated hotspots
in a 100 nm thick Hafnium (Hf) thin film on glass. The
jet/nozzle diameter is ∼1.2 mm and the normal distance
between the nozzle outlet and the heated surface is ∼3.2
mm. The jet coolants studied are FC 72, Novec 7200, and
Ethanol with jet nozzle outlet Reynolds numbers ranging
from 250 to 5000. The hotspot area is ∼0.06 mm2 and the
applied hotspot-to-jet heat fluxes range from 20 W/cm2 to
350 W/cm2. This heat flux range facilitates studies of both
the single-phase and two-phase heat transport mechanisms
for heat fluxes up to critical heat flux (CHF). The temporal
evolution of the temperature distribution of the laser-heated
surface is measured using infrared (IR) thermometry. This
study focuses on the stagnation point heat transfer - i.e.,
the jet potential core is co-aligned with the hotspot center.
For ethanol, the CHF is ∼315 W/cm2 at Re ∼ 1338 with a
corresponding heat transfer coefficient of h ∼ 102 kW/m2·K.
For FC 72, the CHF is ∼94 W/cm2 at Re ∼ 5000 with a
corresponding h ∼ 56 kW/m2·K. And for Novec 7200, the
CHF is ∼108 W/cm2 at Re ∼ 4600 with a corresponding
h ∼ 50 kW/m2·K.
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Hotspot Cooling Performance of a Submerged Water Jet via Infrared Thermometry
Liquid jet impingement is one of the most effective methods for dissipating local hotpot heat fluxes in microelectronics. Due to its normal incident flow-field, jet impingement cooling can achieve heat transfer coefficients (HTCs) approaching ≈1 MW/m 2 ·K due to its ability to thin the local thermal boundary layer in the stagnation region. This experimental study presents HTC data for water jet impingement cooling of a laser heated Hafnium (Hf) thin-film on glass. A laser diode induces local hotspots for either a steady- or pulsed-laser operation mode. The hotspots have areas ranging within 0.04 mm 2 to 0.2 mm 2 and heat fluxes up to ≈3.5 MW/m 2 . A submerged jet impingement configuration is pursued with an inlet jet diameter of ~1.2 mm, jet nozzle to hotspot/surface distance of ~3.2 mm, and the jet Reynolds Number of ~2004. The HTCs are measured using infrared (IR) thermometry using a 1.5-5 μm spectral resolution FLIR camera. Also investigated is the spatial dependence of the HTC relative to the offset between jet/wall stagnation point and the center of the local hotspot. For example, for impinging jets that are co-aligned with the hotspot center, HTCs of ~650 kW/m 2 ·K and ~470 kW/m 2 ·K are measured for steady and pulsed-modulated laser heating (respectively), whereas, for offsets beyond ~6 mm (x/D >5), the measured HTCs are <; 100 kW/m 2 ·K.
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- Award ID(s):
- 1653396
- NSF-PAR ID:
- 10433056
- Date Published:
- Journal Name:
- 2020 19th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)
- Page Range / eLocation ID:
- 166 to 172
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Jet impingement can be particularly effective for removing high heat fluxes from local hotspots. Two-phase jet impingement cooling combines the advantage of both the nucleate boiling heat transfer with the single-phase sensible cooling. This study investigates two-phase submerged jet impingement cooling of local hotspots generated by a diode laser in a 100 nm thick Hafnium (Hf) thin-film on glass. The jet/nozzle diameter is ∼1.2 mm and the normal distance between the nozzle outlet and the heated surface is ∼3.2 mm. Novec 7100 is used as the coolant and the Reynolds numbers at the jet nozzle outlet range from 250 to 5000. The hotspot area is ∼ 0.06 mm2 and the applied hotspot-to-jet heat flux ranges from 20 W/cm2 to 220 W/cm2. This heat flux range facilitates studies of both the single-phase and two-phase heat transport mechanisms for heat fluxes up to critical heat flux (CHF). The temporal evolution of the temperature distribution of the laser heated surface is measured using infrared (IR) thermometry. This study also investigates the nucleate boiling regime as a function of the distance between the hotspot center and the jet stagnation point. For example, when the hotspot center and the jet are co-aligned (x/D = 0), the CHF is found to be ∼ 177 W/cm2 at Re ∼ 5000 with a corresponding heat transfer coefficient of ∼58 kW/m2.K. While the CHF is ∼ 130 W/cm2 at Re ∼ 5000 with a jet-to-hotspot offset of x/D ≈ 4.2.
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Planar Laser Induced Fluorescence (PLIF) has been demonstrated to investigate a round jet impinging on a flat surface. Detailed thermal field distributions have been obtained near the flat target surface to characterize the wall jet development ensuing from the stagnation point. While PLIF has been demonstrated for combustion applications to measure concentration gradients within a mixture, its application for temperature field measurements is less established. Therefore, the technique was applied to a simple, cylindrical impinging jet. The jet Reynolds number varied with Rejet = 5,000 – 15,000 while the jet – to – target surface spacing varied from H / D = 4 – 10. The cooling jet (Tjet ~ 300 K) impinged on a flat, heated surface. The PLIF technique was able to capture the free jet structure and jet development along the target surface. With a short impingement length (H / D = 4), the potential core of the jet strikes the target surface. The thermal gradients captured during the experiments demonstrate the fully turbulent nature of the impinging jet with H / D = 10. The thermal boundary development along the target surface is clearly captured using this fluorescence method. The near wall temperature gradients acquired with the PLIF method have been used to calculate heat transfer coefficients on the heated surface, and these values compare favorably to those measured using a well-established steady state, heat transfer method. The PLIF technique has been demonstrated for this fundamental impingement setup, and it has proven to be applicable to more complex heat transfer and cooling applications.more » « less
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Transient heat fluxes in cutting-edge computing systems, electromagnetic switches, and diode-pumped lasers can exceed 50 MW/m2, which is nearly the heat flux radiated by the Sun. To manage extreme thermal loads, the State-of-the-Art is to boil and evaporate liquid coolants on micro- and nano-structured heat sinks. This work demonstrates the application of laser-scanning fluorescence thermography to identify the spatiotemporal limits of local, transient hot-spot cooling with impinging pulsed micro-jets and sprays. The laser-scanning fluorescence thermography measurements are based on the fluorescence of PS microspheres and quantum-dot thin-films deposited on FTO-glass heater substrates. The fluorescence-based thermometers are subsequently coated with either Hafnium (Hf) or Titanium (Ti) metal thin-films, serving as both protective coatings and the heater surfaces at near critical heat flux conditions. This work also discusses the fabrication procedure of the fluorescence heater/thermometers with micro-mesh heater surfaces and the corresponding pulsed-jet-boiling data via IR thermography.more » « less
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Abstract Nanoparticle heating due to laser irradiation is of great interest in electronic, aerospace, and biomedical applications. This paper presents a coupled electromagnetic-heat transfer model to predict the temperature distribution of multilayer copper nanoparticle packings on a glass substrate. It is shown that heat transfer within the nanoparticle packing is dominated by the interfacial thermal conductance between particles when the interfacial thermal conductance constant, GIC, is greater than 20 MW/m2K, but that for lower GIC values, thermal conduction through the air around the nanoparticles can also play a role in the overall heat transfer within the nanoparticle system. The coupled model is used to simulate heat transfer in a copper nanoparticle packing used in a typical microscale selective laser sintering (μ-SLS) process with an experimentally measured particle size distribution and layer thickness. The simulations predict that the nanoparticles will reach a temperature of 730 ± 3 K for a laser irradiation of 2.6 kW/cm2 and 1304 ± 23 K for a laser irradiation of 6 kW/cm2. These results are in good agreement with the experimentally observed laser-induced sintering and melting thresholds for copper nanoparticle packing on glass substrates.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/ITherm45881.2020.9190595
