Vapour-pressure deficit the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa. In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature. Unlike relative humidity, vapour-pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation. To compute the VPD, we need the ambient (greenhouse) air
Mercury vapour turbine Mercury vapour turbine A mercury vapour turbine is a form of heat engine that uses mercury to drive the thermal cycle. A mercury vapour turbine has been used in conjunction with a steam turbine for generating electricity. This example of combined cycle generation does not seem to have been widely adopted, probably because of high capital cost and the obvious toxic hazard if the mercury leaked into the environment. The mercury cycle offers an efficiency increase compared to a steam-only cycle because energy can be injected into the Rankine cycle at higher temperature. Metallurgical developments have allowed steam-only plants to