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Polyalkylene Glycols
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
One potential disadvantage of PAGs is their affinity for water. The levels of water absorbed are dictated by the polymer structure. Simplistically, polymers with a high ethylene oxide content will absorb more water than those with a lower ethylene oxide content. Hygroscopicity is a concern since in severe cases it can lead to the formation of ice crystals in the fluid which can block capillaries in the compressor. For these reasons, refrigeration lubricants are dried to very low water levels. But it is important to understand that at the very low levels of water in refrigeration lubricants, typically 400–800 ppm, the water is effectively inert since the PAG polymer acts as a polymeric sponge absorbing the water via hydrogen bonding within its structure. Specifications on maximum water levels are usually set at 1000 ppm.
Air Analysis
Published in Pradyot Patnaik, Handbook of Environmental Analysis, 2017
The concentration of pollutants in air is generally expressed as mg/m3 of air. This unit is used to express the concentrations for all kinds of analytes including organic compounds, metal ions, inorganic anions, and particulate matter. Another unit is ppm, which is often used to express concentrations of a specific compound. Conversion of ppm to mg/m3 is as follows: 1ppm=(Molecular weight of the compound22.4)mg/m3at STPwhere STP is the standard temperature and pressure which is 273°K and 1 atm (760 Torr), respectively. The molar volume at STP is 22.4 L.
Environmental Analysis
Published in Connie Kelly Tang, Lei Zhang, Principles and Practices of Transportation Planning and Engineering, 2021
Parts per million, known as ppm, is one of the most commonly used measurement units in air quality analysis. PPM may have a unit of volume/volume or mole/mole. For example, 6 ppm means 6 volumes of a substance in 1 million volumes of total air or 6 moles of a substance in 1 million moles of total air. Occasionally, units such as g/m3 or µg/m3 are used. Given that different compounds have different molecular weighs, mass/volume unit specification requires additional conditions such as air pressure and temperature. For the above reason, the mass volume unit is used neither often nor widely.
Molecular scale insights from NMR studies of hybrid systems formed via doping silver QDs in 6CHBT liquid crystal: a quantitative investigation of their optoelectronic properties
Published in Liquid Crystals, 2023
Archana Kumari Singh, Satya Pal Singh
Here, through experimentation, we find chemical shift (δ), also known as the location on the plot at which the nuclei absorb. In the theoretical approach, we got shielding (ppm) using Gaussian 9 software, i.e. structural characteristics of the molecule got affected by the precise magnitude of the magnetic field experienced by a single nucleus. Three primary characteristics electronegativity, the magnetic anisotropy of the π systems, and hydrogen bonding have an impact on the shielding of the nucleus. Parts per million (ppm) is a commonly used expression to denote the scale. The scale is known as the delta scale. Chemical shift (δ) is given by
Pollutant and heat removal of a small fire in a cinema hall by different ventilation systems
Published in Chemical Engineering Communications, 2023
Mostafa Ramezani, Amir Mohammad Jadidi, Roohollah Rafee
The permissible concentration of carbon monoxide in indoor space is 50 ppm. Higher concentrations lead to death in a short period (Building protection against fire1990). The allowable concentration of carbon dioxide in indoor air for a long time is 10,000 ppm and higher values can cause death (Hashemi and Khoshzad 2007). According to Figures 4–6, it is clear that in this volume of fire, the concentration of toxic gases in the environment is not enough to harm the people present at the scene. However, it is important to note that ventilation systems performed very well in the extraction of these pollutants and prevented them from aggregating more.
Graphene-based optical fiber ammonia gas sensor
Published in Instrumentation Science & Technology, 2018
Yong Zhao, Shu-Yuan Zhang, Gao-Feng Wen, Zi-Xiong Han
The results and analysis of gas measurements are provided in this section. Parts-per-million by volume (ppm) was used as unit for measuring the gas concentrations. The diameter and length of the down-taper waist are 16 and 400 µm; the diameter and length of the up-taper waist are 187.5 and 280 µm. At room temperature (25°C), the change of reflectance spectra of the 10 µm graphene-wrapped fiber at ammonia concentrations of 0, 100, 200, and 300 ppm are shown in Figures 10 and 11.