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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Vapor density is a physical characteristic that affects the travel of vapor; it is the weight of a vapor compared to the weight of air. Vapor density is usually determined in the reference books by dividing the molecular weight of a compound by 29, which is the assumed molecular weight of air. Air is given a weight value of 1, which is used to compare the vapor density of a material. If the vapor of a material has a density greater than 1, it is considered heavier than air. Heavier-than-air vapor will lie low to the ground and collect in confined spaces and basements. This can cause problems because many ignition sources are in basements, such as hot water heaters and furnace pilot lights. If the vapor density is less than 1, the vapor is considered to be lighter than air, so it will move up and travel farther from the spill.
Environmental Fate and Transport of Solvent-Stabilizer Compounds
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
Thomas K.G. Mohr, James Hatton
The rate of evaporation of a chemical from dry soil is a function of soil, chemical, and air temperatures, wind speed, air turbulence and surface roughness, air humidity, solar radiation, and the relevant properties of the chemical, including total mass released, molecular weight, vapor pressure, vapor density, and diffusivity in air (Mackay et al., 1993; Thibodeaux, 1996). In particular, vapor pressure describes the concentration of a chemical as its partial pressure in the gas phase in air above a liquid sample, usually measured at 20°C or 25°C and reported in pressure units (e.g., mm Hg). Vapor density is the mass per unit volume of a chemical in the vapor phase at a fixed temperature, usually expressed as a ratio to air density. Vapors heavier than air are reported as a multiple of air density and measured at 25°C (e.g., perchloroethylene, vapor density = 5.7). Diffusion is the average rate of migration of a chemical in air in response to temperature, pressure, and concentration gradients exclusive of any chemical movement in response to advection. The air diffusion constant is sometimes called air diffusivity, often denoted as Da (expressed in units of cm2/s). Temperature affects the air diffusion constant, which affects the volatilization rate.
Pool Boiling
Published in Neil E. Todreas, Mujid S. Kazimi, Nuclear Systems Volume I, 2021
Neil E. Todreas, Mujid S. Kazimi
As evident from Figure 12.10, the water critical heat flux seems to have a peak value at a pressure near 6.4 MPa. At low pressure, the effect of an increase in pressure is mainly to increase the vapor density, thus reducing the velocity and/or the flow area of the vapor for a given heat flux. Therefore, more vaporization is possible before the vapor flux reaches such a magnitude as to prevent the liquid from reaching the surface. On the other hand, because the heat of vaporization of water decreases with pressure, the heat flux associated with this critical vapor flux for fluidization starts to decrease at high pressures, when the relative changes in the vapor density with pressure become smaller.
Exergy and energy analysis of low GWP refrigerants in the perspective of replacement of HFC-134a in a home refrigerator
Published in International Journal of Ambient Energy, 2022
Mohammad Hasheer Shaik, Srinivas Kolla, Bala Prasad Katuru
Mass flow rate of the refrigerant Vs Evaporator temperature is depicted in Figure 3 for different refrigerants considered in this analysis at a condenser temperature of 25°C and 45°C. Volumetric efficiency, geometrical dimensions of a compressor and the specific volume at the entry conditions of a compressor are the parameters which influences the mass flow rate of the refrigerant. The mass flow rate of refrigerants HFO-1234Ze (E), R152, R290 was lower than that of the refrigerant HFC-134 by approximately 26%, 23% and 55% at the evaporator temperature range between −20°C to 10°C. From the plot, it is clearly indicated that maximum mass flow rate requirement is seen for the refrigerant HFO-1234yf among all the refrigerants used, while the refrigerant HC-600a has the minimum mass flow rate requirement as compared to the refrigerant HFC-134a in these operating conditions. The reason for this trend is that, the vapour density of HC-600a refrigerant has the minimum value and the refrigerant HFO-1234yf has higher vapour density among all the refrigerants considered. For all refrigerants, condenser temperature does not show any effect on the mass flow rate.
Study of Falling Condensate Droplets on Parallelepiped Solid Surface Using Hybrid 3D MRT-LBM
Published in International Journal of Computational Fluid Dynamics, 2022
Salaheddine Channouf, Mohammed Jami
is the inter-particle force acting on solid-fluid which is calculated as (Channouf, Jami, and Mezrhab 2022a) is a switch function that is equal to 1 on the solid node and 0 on the fluid node. is the pseudopotential function that adjusts the degree of wetting on the surface, it depends on the density value as Note that, is the density of the solid surface ranging from the vapour density to the liquid density . The choice of the value of the coexisting densities will be detailed in the validation part.
How well does the Tang-Toennies potential represent the thermodynamic properties of argon?
Published in Molecular Physics, 2022
Isabel Nitzke, Sven Pohl, Monika Thol, Roland Span, Jadran Vrabec
While deviations of the vapour pressure for the LJ model reach almost 5% at low temperatures, for TT they do not exceed 2.5% and are slightly lower over the entire temperature range. As expected, deviations of the saturated vapour density are in accordance with this observation. Concerning the liquid density, both models perform rather similar with deviations below 1%. The differences only increase upon the approach to the critical point, which is for argon at 150.7 K and 4.86 MPa according to Tegeler et al. [23]. Deviations of the homogenous density mostly remain below 5%. For the TT potential, they cover are broader strip in the liquid region but are more centred around the critical point. For the speed of sound, deviations of LJ and TT differ noticeably. For the TT potential, they are spread over a wider area such that different isotherms become visible.