VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 27, through Friday, November 29. We will resume normal operations on Monday, December 2. Thank you for your patience.

Browsing by Author "Liu, Cong"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Convenient, Rapid and Accurate Measurement of SVOC Emission Characteristics in Experimental Chambers
    Liu, Cong; Liu, Zhe; Little, John C.; Zhang, Yinping (PLOS, 2013-08-28)
    Chamber tests are usually used to determine the source characteristics of semi-volatile organic compounds (SVOCs) which are critical to quantify indoor exposure to SVOCs. In contrast to volatile organic compounds (VOCs), the sorption effect of SVOCs to chamber surfaces usually needs to be considered due to the much higher surface/air partition coefficients, resulting in a long time to reach steady state, frequently on the order of months, and complicating the mathematical analysis of the resulting data. A chamber test is also complicated if the material-phase concentration is not constant. This study shows how to design a chamber to overcome these limitations. A dimensionless mass transfer analysis is used to specify conditions for (1) neglecting the SVOC sorption effect to chamber surfaces, (2) neglecting the convective mass transfer resistance at sorption surfaces if the sorption effect cannot be neglected, and (3) regarding the material-phase concentration in the source as constant. Several practical and quantifiable ways to improve chamber design are proposed. The approach is illustrated by analyzing available data from three different chambers in terms of the accuracy with which the model parameters can be determined and the time needed to conduct the chamber test. The results should greatly facilitate the design of chambers to characterize SVOC emissions and the resulting exposure.
  • 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
    Influences of Clay Brick Particles on the Performance of Cement Stabilized Recycled Aggregate as Pavement Base
    Miao, Yinghao; Yu, Weixiao; Hou, Yue; Liu, Cong; Wang, Linbing (MDPI, 2018-09-30)
    This paper presents an investigation on the influences of clay brick particles on the performance of cement stabilized recycled aggregate as pavement base. The comparative tests of unconfined compressive strength, compressive modulus of resilience, frost resistance, scouring resistance, drying shrinkage and temperature shrinkage of 6 kinds of mixtures with different coarse and fine clay brick particle contents were carried out. Test results showed that the unconfined compressive strength of cement stabilized recycled aggregate was compromised by the clay brick particles, especially the lateral strength. The coarse clay brick particles had little influence on the compressive resilience modulus of the mixture, while the fine clay brick particles could significantly increase it. The frost resistance of the mixture increased first and then slightly decreased with the increase of the content of coarse clay brick particle, while it increased with the increase of fine particle content. The scoured mass loss increased with the increase of coarse clay brick particle content. However, it is discovered that the fine clay brick particles had almost no influences on the scoured mass loss. The addition of both coarse and fine clay brick particles could decrease the drying shrinkage of the mixture at early construction stage. The temperature shrinkage performance of the mixture was not so sensitive to the addition of clay brick particles. Generally, the cement stabilized recycled aggregate with clay brick particles could meet the requirements of the pavement base in many cases but it needs to be optimized in application with consideration of the load and climate conditions.