Scholarly Works, Mechanical Engineering

Permanent URI for this collection

https://hdl.handle.net/10919/23262
Research articles, presentations, and other scholarship

Browse

Browsing Scholarly Works, Mechanical Engineering by Subject "09 Engineering"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Droplet Evaporation on Hot Micro-Structured Superhydrophobic Surfaces: Analysis of Evaporation from Droplet Cap and Base Surfaces
    Huang, Wenge; He, Xukun; Liu, Cong; Li, Xiaojie; Liu, Yahua; Collier, C. Patrick; Srijanto, Bernadeta R.; Liu, Jiansheng; Cheng, Jiangtao (Elsevier, 2022-04-01)
    In this study, evaporation of sessile water droplets on hot micro-structured superhydrophobic surfaces is experimentally and theoretically investigated. Water droplets of 4 µL are placed on micro-pillared silicon substrates with the substrate temperature heated up to 120°C. A comprehensive thermal circuit model is developed to analyze the effects of substrate roughness and substrate temperature on the sessile droplet evaporation. For the first time, two components of heat and mass transfer, i.e., one from the droplet cap surface and the other from the droplet base surface, during droplet evaporation are distinguished and systematically studied. As such, the evaporation heat transfer rates from both the droplet cap surface and the interstitial liquid-vapor interface between micropillars at the droplet base are calculated in various conditions. For droplet evaporation on the heated substrates in the range of 40°C – 80°C, the predicted droplet cap temperature matches well with the experimental results. During the constant contact radius mode of droplet evaporation, the decrease of evaporation rate from the droplet base contributes most to the continuously decreasing overall evaporation heat transfer rate, whereas the decrease of evaporation rate from the droplet cap surface is dominant in the constant contact angle mode. The influence of internal fluid flow is considered for droplet evaporation on substrates heated above 100°C, and an effective thermal conductivity is adopted as a correction factor to account for the effect of convection heat transfer inside the droplet. Temperature differences between the droplet base and the substrate base are estimated to be about 2°C, 5°C, 8°C, 13°C and 18°C for droplet evaporation on substrates heated at 40°C, 60°C, 80°C, 100°C, and 120°C, respectively, elucidating the delayed or depressed boiling of water droplets on a heated rough surface due to evaporative cooling.
  • Thumbnail Image
    The Effects of Torque Magnitude and Stiffness in Arm Guidance Through Joint Torque Feedback
    Kim, Hubert; Asbeck, Alan T. (IEEE, 2022-01-01)
    Joint torque feedback is a new and intuitive way of delivering kinesthetic feedback to a person or guiding them during motion tasks via wearable devices. In this study, we performed three experiments to understand how the elbow joint responds to guidance via small torques (<1 Nm).We first applied open-loop torque pulses to the elbow, and determined the magnitude and delay of the resulting arm motion. Second, we provided pulses of a desired position trajectory in combination with a torque proportional to the error between the joint's angle and the target angle. We compared the effects of different ratios between the error and applied torque, which is the torque stiffness. Finally, we investigated step inputs from one angle to another in conjunction with different torque stiffnesses. We found that open-loop extensional torques caused large elbow movements, independent of the torque magnitude or duration, while flexional torques caused arm motion proportional to both the magnitude and duration.With position pulses, the highest gain of 0.095 Nm/deg resulted in mean position errors of less than 10 degrees, while the lowest gain of 0.012 Nm/deg resulted in mean position errors of nearly 20 degrees. The higher gains caused the arm to move faster and required higher torques, likely due to masking. The arm had a bandwidth of close to 2 Hz, and step inputs resulted in larger mean errors during flexional motion (15.3 degrees for flexion vs. 9.0 degrees for extension).