Effect of Pressure
At temperatures below 300 °C water is fairly incompressible, which means that pressure has little effect on the physical properties of water, provided it is sufficient to maintain liquid state. This pressure is given by the saturated vapour pressure, and can be looked up in steam tables, or calculated. As a guide, the saturated vapour pressure at 121 °C is 200 kPa, 150 °C is 470 kPa, and 200 °C is 1,550 kPa. The critical point is 21.7 MPa at a temperature of 374 °C, above which water is supercritical rather than superheated. Above about 300 °C, water starts to behave as a near-critical liquid, and physical properties such as density start to change more significantly with pressure. However, higher pressures increase the rate of extractions using superheated water below 300 °C. This could be due to effects on the substrate, particularly plant materials, rather than affecting water properties.
Read more about this topic: Superheated Water
Famous quotes containing the words effect of, effect and/or pressure:
“The effect of a good government is to make life more valuable; of a bad one, to make it less valuable.”
—Henry David Thoreau (1817–1862)
“It has never been in my power to sustain ... I can pass swiftly from one effect to another, but I cannot fix one, and dwell on it, with that superb concentration which seems to me the special attribute of the tragic actress.”
—Ellen Terry (1847–1928)
“Much of the pressure contemporary parents feel with respect to dressing children in designer clothes, teaching young children academics, and giving them instruction in sports derives directly from our need to use our children to impress others with our economic surplus. We find “good” rather than real reasons for letting our children go along with the crowd.”
—David Elkind (20th century)