What is Relative Humidity?
Atmospheric air is a mixture of various gases and water vapour. The invisible water vapour in the air is called humidity. The amount of water that can be contained in a pound of air depends upon …… temperature of the air pressure of the air At a constant pressure, the warmer the air the amore water vapour it can retain. If air at a certain temperature has absorbed all the moisture it can hold at that temperature, it is said to be saturated. The amount of water present, or the degree of saturation is evaluated in terms of Relative Humidity or Saturation ratio. Hence, Relative Humidity is the actual water content in % of that of a saturated volume. When air is 50% saturated, it contains only one half the amount of water than it can contain at the same temperature and pressure. As the relative humidity approaches 100%, the air can take on less and less moisture and at 100% relative humidity, that air cannot hold more water. If air is saturated with water vapour at a given temperature,
Relative humidity is defined as the ratio of the water vapor pressure to the saturation vapor pressure at the prevailing ambient temperature, expressed as a percentage. In simpler terms, it is the measure of the amount of water vapor in the air compared to how much it can possibly hold at that temperature. For example, air at 20° C. can hold, at a maximum, about 17 grams of moisture per cubic meter of air. Air holding this much moisture would be considered “saturated” and would have a measure of 100% relative humidity. If the 20° C. air becomes drier to the point where it only contains 8.5 grams of moisture per cubic meter, then the air is holding only one-half, or 50% of its total capacity. The measure of the air then would be 50% RH. The capacity of air to hold water is heavily dependent on the temperature of the air. The warmer the air, the more moisture it can hold. Air at 30° C. can hold about 30 grams of moisture per cubic meter or about 75% more than it can hold at 20° C. Air at
Heat really needs no explanation. You may have difficulty defining it, but you’re certainly familiar with the experience of it. Relative humidity, on the other hand, does need explanation. Water is an extremely pervasive substance and can be found everywhere on the planet including in the air, where it’s held as vapour. The capacity of air to hold water-vapour varies according to the temperature of the air. The warmer the air, the more water-vapour it can hold. As the air cools down, its capacity to hold water will decrease. Relative humidity is a measure of the amount of the amount of water-vapour contained in air at a particular temperature. It is basically a comparison between: • the amount of water-vapour held in the air at any one time and at a particular temperature; and • the total amount of water-vapour which the air can hold at the same temperature, that is, the amount of water which will saturate the air at that temperature. Relative humidity is expressed as a percentage.
Many people notice that hot muggy days seem much warmer somehow than days with dry heat. One of the reasons for this is humidity, the amount of water the air holds. When the air holds more water, the basic act of perspiration or sweating is less efficient in cooling down the body. More water in the air means less water can evaporate from the skin, and most people will end up feeling warmer. Some of the ways that humidity is measured is by measuring absolute humidity, and relative humidity, which is often how people tell how “wet” a day will be. First, it’s important to understand that air can only hold a certain amount of water at any given time. This measurement is absolute humidity, and absolute humidity is dependent on the temperature of air. Under many circumstances, the actual air holds far less water than it technically could, so the term relative comes into play. When meteorologists discuss relative humidity they usually do so in percentage amounts, and this percentage is a rati
Air will always contain water vapour. At any given temperature there will be a saturation point at which no more moisture can be retained (any excess will condense). The Relative Humidity of air is the actual moisture content expressed as a percentage of this saturation content. The aim of using silica gel is to keep the Relative Humidity at levels below 50% of the saturation capacity. At these levels, corrosion and mould growth will not be promoted. Problems are often caused if the temperature drops as the saturation content of air at the new temperature becomes much lower.
