» Measuring Humidity and Technological Applications
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Measuring Humidity and Technological Applications

It is not the heat but the humidity that matters. Humidity is the term used to describe the quality of air in relationship to the amount of water it can retain before the air becomes saturated. At saturation, water in its gaseous – more correctly, vapourous – state condenses to its liquid state.

In order to establish a baseline measurement, absolute humidity was defined as the maximum amount of water vapour that can be supported by air before it must condense to a liquid. Due to confusion in terminology, the British have established a standard – BS 1339 – that suggests the term “absolute humidity” be replaced with the more accurate and descriptive term “volumetric humidity.” This term transcends the units of measurement; of which there are several, including some hybrid forms that mix English and Metric measurements.

Because volume is directly proportional to pressure and inversely proportional to temperature, absolute or volumetric humidity is an inconvenient method of defining humidity. Relative humidity is able to account for variances caused by pressure and temperature and it is the most commonly encountered term. Technically, relative humidity is defined as the ratio of the amount of water vapour present to the maximum possible amount of water vapour before the air is saturated. It is expressed as a percentage. A relative humidity of 50% describes air that is at half of its saturation potential. At 100% RH, water condenses to its liquid form and because of its relative mass, falls out of the air in the presence of gravity.

There are a number of devices and technologies used to determine and measure humidity. Humidity sensors detect the presence of humidity and humidity indicators typically quantify the degree of humidity present or humidity level. Humidity charts, tables and graphs are useful for predictive analysis. Mathematics can derive and express humidity measurements in terms that can be easily manipulated for calculation. For example, to convert from an English unit measurements to Metric units.

Humidity control is achieved by a number of methods, however, in automated humidity control systems, humidity sensors – such as humidistats – are used to start and stop dehumidification processes based on the degree of humidity present.

Humidity control is dependent on the application and environment. In some cases, always-on humidity control is required; in other cases, controlling humidity to fall into a certain pre-determined range is desirable. Sometimes, humidity is simply inconvenient – as in the weather. In many industrial process applications, humidity is generally an enemy to be eliminated. Conversely, in some storage applications, humidity is desirable to prevent over-drying, as in fine wood furniture storage, preserving paintings in museums, and similar tasks. Complete elimination of humidity is essential for long-term storage of metallic components, such as mothballed weapons.

The measure of humidity is an engineering task, part of the science of psychrometrics called hygrometry. Please note: this term is often confused with hydrometry. While they are related, there is a distinction. When discussing humidity, the former describes the amount of water in the air and the latter term describes water alone.

Desiccant dehumidification is being used for preservation, pharma, food processing, eletrical & electronics.

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