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Ambient Pressure

The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Yu-cheng Chang – 1st expert on this subject based on the ideXlab platform

  • preparation of monolithic silica aerogel of low thermal conductivity by Ambient Pressure drying
    Journal of the American Ceramic Society, 2007
    Co-Authors: Tso Fu Chang, Shih Yuan Lu, Yu-cheng Chang

    Abstract:

    Monolithic silica aerogels with thermal conductivity as low as 0.036 W·(m·K)−1 and porosity as high as 97% were successfully prepared by Ambient Pressure drying through a multiple modification approach. This approach may replace the more costly and dangerous operation of supercritical drying. The tetraethoxysilane (TEOS)-derived wet gel was made hydrophobic with multiple treatments of trimethylchlorosilane and dried under Ambient Pressure. The multiple treatments were found to be necessary to achieve sufficient modification of the wet gel for reduction in drying-induced surface tension force to maintain product integrity and high porosity. Comparisons in nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy for surface bonding and contact angle measurement for hydrophobicity between the no, single, and multiple surface modification (MSM) samples were conducted to reveal the difference in the extent of the resulting surface modification. In conclusion, the MSM procedure reduced the volume shrinkage, increased the monolithicity and porosity, and lowered the thermal conductivity of the resulting aerogels.

  • Preparation of monolithic silica aerogel of low thermal conductivity by Ambient Pressure drying
    Journal of the American Ceramic Society, 2007
    Co-Authors: Te Yu Wei, Tso Fu Chang, Shih Yuan Lu, Yu-cheng Chang

    Abstract:

    Monolithic silica aerogels with thermal conductivity as low as 0.036 W center dot(m center dot K)(-1) and porosity as high as 97% were successfully prepared by Ambient Pressure drying through a multiple modification approach. This approach may replace the more costly and dangerous operation of supercritical drying. The tetraethoxysilane (TEOS)-derived wet gel was made hydrophobic with multiple treatments of trimethylchlorosilane and dried under Ambient Pressure. The multiple treatments were found to be necessary to achieve sufficient modification of the wet gel for reduction in drying-induced surface tension force to maintain product integrity and high porosity. Comparisons in nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy for surface bonding and contact angle measurement for hydrophobicity between the no, single, and multiple surface modification (MSM) samples were conducted to reveal the difference in the extent of the resulting surface modification. In conclusion, the MSM procedure reduced the volume shrinkage, increased the monolithicity and porosity, and lowered the thermal conductivity of the resulting aerogels.

Ljubinko Kondic – 2nd expert on this subject based on the ideXlab platform

  • Dependence of single-bubble sonoluminescence on Ambient Pressure
    Ultrasonics, 2000
    Co-Authors: J.d.n. Cheeke, Ljubinko Kondic

    Abstract:

    Abstract Kondic et al.’s theory makes several specific predictions on the dependence of single-bubble sonoluminescence (SBSL) on Ambient Pressure. We have carried out experiments to verify these predictions for air bubbles in a water–glycerine mixture at about 17.5 kHz. The results show an increase in SBSL with reduced Ambient Pressure down to a critical value below which SBSL is extinguished. The results are all in good agreement with Kondic et al.’s theory and are also compatible with the dissociation hypothesis of Lohse et al.

  • Ambient Pressure EFFECT ON SINGLE-BUBBLE SONOLUMINESCENCE
    Physical Review Letters, 1999
    Co-Authors: J.d.n. Cheeke, Ljubinko Kondic

    Abstract:

    We report the first results on the influence of Ambient Pressure on single bubble sonoluminescence.The equilibrium radius as well as the maximum radius of the bubble increased as the Ambient Pressureover the liquid head was decreased. The number of photons emitted during a sonoluminescence pulseincreased linearly with a decrease of Ambient Pressure. These results are in good agreement with thetheory of the Ambient Pressure effect [L. Kondic et al., Phys. Rev. E 57, R32 (1998)] and with therecent dissociation hypothesis.

  • Experimental observations of the effect of Ambient Pressure on single‐bubble sonoluminescence
    Journal of the Acoustical Society of America, 1999
    Co-Authors: J.d.n. Cheeke, Ljubinko Kondic

    Abstract:

    The experimental observations of the influence of Ambient Pressure on single‐bubble sonoluminescence will be presented. In the SBSL regime as the Ambient Pressure was decreased only about 10%, the SL intensity increased significantly as predicted [L. Kondic, C. Yuan, and C. K. Chan, Phys. Rev. E 57(1), R32–R35 (1998)]. There was an increase of about five times in SL intensity as the Ambient Pressure was decreased by about 10%–12%, at constant driving acoustic Pressure. This increment continued until a certain value of the Ambient Pressure, below which the bubble became unstable and vanished. The equilibrium radius and the maximum radius of the SBSL bubble both incerased with decrease of Ambient Pressure. This observation provides valuable insight into the mass flow mechanism between the bubble and the liquid, and gives the first direct confirmation of ‘‘argon bubble hypothesis.’’ [Work supported by NSERC and Concordia Seagram Fund for Innovative Research.]

Jie Ji – 3rd expert on this subject based on the ideXlab platform

  • Effects of Ambient Pressure on smoke movement and temperature distribution in inclined tunnel fires
    International Journal of Thermal Sciences, 2019
    Co-Authors: Jie Ji, Zhiyong Wang, Long Ding, Longxing Yu

    Abstract:

    Abstract A series of simulations with regard to inclined road tunnel were conducted to investigate the effect of Ambient Pressure on smoke movement and temperature distribution. The tunnel slope and Ambient Pressure were systematically changed. When a fire breaks out in an inclined tunnel, the thermal buoyancy induced by smoke temperature difference will induce an airflow through the tunnel due to the stack effect. The induced longitudinal airflow is a key factor in inclined tunnel fires. Under the combined effect of induced longitudinal airflow and Ambient Pressure, the smoke movement and temperature distribution pattern are presented firstly. Then the variation of induced longitudinal airflow velocity with tunnel slope and Ambient Pressure is explained. Finally, taking the tunnel slope, the Ambient Pressure and the velocity of resulted induced longitudinal airflow into account, a correlation predicting the maximum smoke excess temperature beneath the ceiling is proposed. Moreover, the correlation agrees well with previous experimental results at normal Pressure. The results can provide an engineering reference for tunnel structural fire protection, smoke control and safe evacuation in inclined tunnels at different Ambient Pressures.

  • effects of Ambient Pressure on transport characteristics of thermal driven smoke flow in a tunnel
    International Journal of Thermal Sciences, 2018
    Co-Authors: Jie Ji

    Abstract:

    Abstract Thermal-driven smoke flow is the greatest threat to the trapped people in tunnels, and the basic understanding of the smoke transport characteristics is necessary for the engineering applications of smoke control and exhausting system. However, most of the previous studies only focused on the smoke transport at normal Pressure. As a matter of fact, the Ambient Pressure decreases with the increasing of the altitude, and the influence of different Ambient Pressures on the transport characteristics of thermal-driven smoke has been rarely considered before. This paper presents an investigation on the effect of Ambient Pressure on the smoke transport characteristics in a tunnel. A series of fire simulations were conducted in a full scale road tunnel with Ambient Pressure ranged from 100 kPa to 50 kPa and the heat release rate (HRR) varied from 3 MW to 15 MW. The smoke mass transport along the tunnel for different conditions is analyzed, and results show that for a certain HRR, the smoke mass flow rate decreases with reduced Ambient Pressure due to the decreased air density and the weakening of air entrainment strength. Based on the dimensional analysis, a quantitative model to predict the average smoke mass flow rate in the tunnel is proposed considering both Ambient Pressure and HRR. Moreover, the credibility of the predictive model is validated by comparing with a wide range of experimental results from both full scale and reduced scale experiments at different Pressures.