Local Single- and Two-Phase Heat Transfer from an Impinging Cross-Shaped Jet

Local single- and two-phase heat transfer distributions are measured under a confined impinging jet issuing from a cross-shaped orifice. Spatially resolved temperature maps and convection coefficients resulting from the impinging flow are obtained via infrared imaging of a thin-foil heat source. The cooling patterns in single- and two-phase operation are explained by an accompanying numerical investigation of the fluid flow issuing from the orifice; computed velocity magnitudes and turbulence intensities are presented. In single-phase operation, the coolest surface temperatures correspond to areas with high liquid velocities. High velocities and developing turbulence are also shown to increase convective heat transfer along the diagonal outflow directions from the impinging jet. During two-phase transport, boiling preferentially begins in regions of low velocity, providing enhanced heat transfer in the areas least affected by the impingement. The cross-shaped orifice achieves local heat transfer coefficients that exceed the stagnation-point value of a circular jet of equivalent open orifice area by up to 1.5 times, while resulting in an increased pressure drop only 1.1 times higher than that of the circular jet

Boiling Heat Transfer from an Array of Round Jets with Hybrid Surface Enhancements

The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5x5 array of jets, each 0.75mm in diameter, is compared to that of a single 3.75mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates

Area-scalable high-heat-flux dissipation at low thermal resistance using a capillary-fed two-layer evaporator wick

A two-layer sintered porous evaporator wick for use in vapor chambers is shown to offer very high performance in passive high-heat-flux dissipation over large areas at a low thermal resistance. The two-layer wick has an upper cap layer dedicated to capillary liquid feeding of a thin base layer below that supports boiling. An array of vertical posts bridges these two layers for liquid feeding, while vents in the cap layer provide an unimpeded pathway for vapor removal from the base wick. The two-layer wick is fabricated using a combination of sintering and laser machining processes. The thermal resistance of the wicks during boiling is characterized in a saturated environment that replicates the capillary-fed working conditions of a vapor chamber evaporator. Thermal characterization tests are first performed using conventional single-layer evaporator wicks to analyze the effect of sintered particle size on capillaryfed boiling of water. Of the particle size ranges tested, wicks sintered from 180 to 212 micrometer-diameter particles provided the best combination of high dryout heat flux and a low boiling resistance. A two-layer evaporator wick comprising particles of this optimal size and a 15 x 15 array of liquid feeding posts yielded a maximum heat flux dissipation of 485 W/cm2 over a 1 cm2 heat input area while also maintaining a low thermal resistance of only ~0.052 K/W. The thermal performance of the two-layer wick is compared against various hybrid and biporous evaporator wicks previously investigated in the literature. While previous wick designs are typically restricted to small areas and low power levels or high surface superheats when dissipating such heat fluxes, the unique area-scalability of the two-layer wick design allows it to achieve an unprecedented combination of high total power and low-thermal-resistance heat dissipation over larger areas than were previously possible

The Role of Vapor Venting and Liquid Feeding on the Dryout Limit of Two-Layer Evaporator Wicks

Vapor chambers developed for high-heat-flux operation require advanced evaporator wick designs that can sustain capillary flow when boiling occurs over the heater region. A two-layer evaporator wick inte- grates a thin base wick layer that is supplied with liquid from a thick cap layer through an array of ver- tical feeding posts distributed over the heated area. This design allows boiling to occur within the thin base layer, while separating the incoming liquid feeding and outgoing vapor venting pathways. In our prior work, boiling in two-layer wicks was experimentally demonstrated to provide high-heat-flux dissi- pation over larger heater areas and at low thermal resistance. The current study experimentally explores the effect of two-layer wick design parameters, specifically the dimensions that alter the area available for liquid feeding and vapor venting, on the thermal performance and dryout limit of the wick, using water as the working fluid. Four different two-layer wick designs are fabricated over a 1 cm 2 evaporator area by sintering 180–212 μm copper particles. Increasing the vapor-venting area from 7% to 16% of the total evaporator area yielded a significant increase in the dryout limit, from 315 W/cm 2 to 405 W/cm 2 . Increasing the liquid-feeding area using wider posts increased the dryout limit further. Finally, a paramet- rically optimized design with fewer but larger posts and vents resulted in better performance compared to a design with denser features. With this two-layer wick design, we demonstrate an extremely high dryout limit of 512 W/cm 2 over the large 1 cm 2 heated area at a thermal resistance of 0.08 K/W

One-dimensional collision carts computer model and its design ideas for productive experiential learning

We develop an Easy Java Simulation (EJS) model for students to experience the physics of idealized one-dimensional collision carts. The physics model is described and simulated by both continuous dynamics and discrete transition during collision. In the field of designing computer simulations, we discuss briefly three pedagogical considerations such as 1) consistent simulation world view with pen paper representation, 2) data table, scientific graphs and symbolic mathematical representations for ease of data collection and multiple representational visualizations and 3) game for simple concept testing that can further support learning. We also suggest using physical world setup to be augmented complimentary with simulation while highlighting three advantages of real collision carts equipment like tacit 3D experience, random errors in measurement and conceptual significance of conservation of momentum applied to just before and after collision. General feedback from the students has been relatively positive, and we hope teachers will find the simulation useful in their own classes. 2015 Resources added: http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/46-one-dimension-collision-js-model http://iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/195-elastic-collisionComment: 6 pages, 8 figures, 1 table, 1 L. K. Wee, Physics Education 47 (3), 301 (2012); ISSN 0031-912

Head and Neck Cancer Primary Tumor Auto Segmentation Using Model Ensembling of Deep Learning in PET/CT Images

Auto-segmentation of primary tumors in oropharyngeal cancer using PET/CT images is an unmet need that has the potential to improve radiation oncology workflows. In this study, we develop a series of deep learning models based on a 3D Residual Unet (ResUnet) architecture that can segment oropharyngeal tumors with high performance as demonstrated through internal and external validation of large-scale datasets (training size = 224 patients, testing size = 101 patients) as part of the 2021 HECKTOR Challenge. Specifically, we leverage ResUNet models with either 256 or 512 bottleneck layer channels that demonstrate internal validation (10-fold cross-validation) mean Dice similarity coefficient (DSC) up to 0.771 and median 95% Hausdorff distance (95% HD) as low as 2.919 mm. We employ label fusion ensemble approaches, including Simultaneous Truth and Performance Level Estimation (STAPLE) and a voxel-level threshold approach based on majority voting (AVERAGE), to generate consensus segmentations on the test data by combining the segmentations produced through different trained cross-validation models. We demonstrate that our best performing ensembling approach (256 channels AVERAGE) achieves a mean DSC of 0.770 and median 95% HD of 3.143 mm through independent external validation on the test set. Our DSC and 95% HD test results are within 0.01 and 0.06 mm of the top ranked model in the competition, respectively. Concordance of internal and external validation results suggests our models are robust and can generalize well to unseen PET/CT data. We advocate that ResUNet models coupled to label fusion ensembling approaches are promising candidates for PET/CT oropharyngeal primary tumors auto-segmentation. Future investigations should target the ideal combination of channel combinations and label fusion strategies to maximize segmentation performance.</p

Associations of Hair Dye and Relaxer Use with Breast Tumor Clinicopathologic Features: Findings from the Women’s Circle of Health Study

Background Building upon our earlier findings of significant associations between hair dye and relaxer use with increased breast cancer risk, we evaluated associations of select characteristics of use with breast tumor clinicopathology. Methods Using multivariable-adjusted models we examined the associations of interest in a case-only study of 2998 women with breast cancer, overall and stratified by race and estrogen receptor (ER) status, addressing multiple comparisons using Bonferroni correction. Results Compared to salon application of permanent hair dye, home kit and combination application (both salon and home kit application) were associated with increased odds of poorly differentiated tumors in the overall sample. This association was consistent among Black (home kit: OR 2.22, 95 % CI: 1.21–5.00; combination: OR 2.46, 95 % CI: 1.21–5.00), but not White women, and among ER+ (home kit: OR 1.47, 95 % CI: 0.82–2.63; combination: OR 2.98, 95 % CI: 1.62–5.49) but not ER-cases. Combination application of relaxers was associated with increased odds of tumors \u3e2.0 cm vs. \u3c1.0 cm (OR = 1.82, 95 % CI: 1.23–2.69). Longer duration and earlier use of relaxers and combination application of permanent hair dyes and relaxers were associated with breast tumor features including higher tumor grade and larger tumor size, which often denote more aggressive phenotypes, although the findings did not maintain significance with Bonferroni correction. Conclusions These novel data support reported associations between hair dye and relaxer use with breast cancer, showing for the first time, associations with breast tumor clinicopathologic features. Improved hair product exposure measurement is essential for fully understanding the impact of these environmental exposure with breast cancer and to guide risk reduction strategies in the future