The need to humidify an environment is determined by a number of factors:
The presence of hygroscopic material (capable of absorbing moisture from the air)
The presence of static electricity
The importance of well-being and comfort
1. Hygroscopic materials
If a piece of wood in equilibrium with the moisture content in the outside air is brought into a
heated room with a lower humidity, the wood will start to release part of its moisture to the dry air in the room. As the wood releases its moisture, it will contract, leading to the formation of cracks or deformations. The same damage can be seen in paper, fabrics, some plastics, wax, fruit and vegetables and other materials that have the property to absorb or release moisture Hygroscopic is the term given to materials whose cells absorb moisture, leading to a variation in their dimensions. This is different from hydrophilic absorption, in which case the water is absorbed into the cells of the material with NO consequent variation in dimensions. Hygroscopic materials tend to reach equilibrium with the surrounding environment. It is therefore the variation in the dimensions of the materials, due to the change in relative humidity, that affects the workability of the materials and the production processes
even more significantly than the temperature.
The protection of hygroscopic material can be guaranteed only by the stability of the environment they are situated in. This objective can be achieved by dehumidification when the air becomes too moist, and humidification when the air is too dry.
hygroscopic: term given to a substance or body capable of absorbing the moisture in the air and that consequently changes its dimensions
hydrophilic: term given to a substance or body capable of absorbing the moisture in the air without changing its dimensions
PRINTING
The paper reaches the printing facilities in the form of reels, conditioned in the paper mill with a certain quantity of moisture and packaged in impermeable material so as to ensure that such moisture is maintained. As soon as the packaging is removed, if the air in the environment is drier, the paper starts to lose moisture and its cells contract, or alternatively, if the air in the environment is more humid, it starts to absorb moisture. A reel of paper may vary in size by a number of centimetres, in both width and length. When the reel of paper is placed in the printing press and unwound, it quickly loses moisture. These variations, which may also occur in a very short period, can cause problems, above all when printing with a number of different colours. One of the solutions is to adjust the rollers so as to compensate for this error, however if the humidity varies too quickly, frequent adjustments are required, with consequent loss of paper and time and decreases in production speed.
The stabilisation of the ambient conditions, thanks to appropriate humidity control, ensures that the dimensions of the paper remain constant and that the printing process will be faster, limiting downtime during production.
WOODWORKING
During the humidification or dehumidification process, wood expands or contracts, causing cracks, breakages, shrinkages and deformations. When drying, wood absorbs the solvent of the finishes, taking on a granulose and matt appearance. Similarly, the glued joints are unstable, as the wood absorbs the solvent of the glue before the glue has the chance to polymerise. In this case too, the stabilisation of the environmental conditions allows the wood to maintain the same dimensions throughout the entire process, ensuring better results.
polymerisation: the reaction that occurs between many molecules of a monomer to form larger molecules (polymers)
TEXTILE INDUSTRY
If the textile fibres are dry when they are run through the looms, they become fragile and break, leading to stoppages, downtime and a slowing down of production. In addition, the fibres that break release fluff into the air, often causing a worsening of the air quality. Appropriate humidification reduces the breakage of the fibres, the quantity of dust in the air and at the same time speeds up the operation of the looms.
OFFICES
Dry air in the winter increases the level of dust present in the air.
With correct humidification, the quality of the air can be improved, reducing the concentration of dust due to a decreased fragmentation of fibres, as well as the increased tendency of particles to agglomerate and therefore be more effectively filtered.
HI TECH MICROCHIP MANUFACTURING
Chips are becoming increasingly smaller, and the distances are now measured in Angstroms. For this reason, even a slight variation in the dimensions of a silicon wafer during the photographic masking process causes unacceptable misalignments and the consequent malfunction of the components.
Angstrom: unit of measure of length equal to 10-10 m. wafer: thin layer of semiconductor material making up the basic element for the construction of a diode or a transistor photographic masking: procedure used during printing to modify the effects of the contrast using slides or duplicates of the negative
MUSEUMS
The correct stabilisation of the environment is essential for preserving expensive works or art over time. If the canvas were to constantly change dimensions, the paintings, the size of which on the other hand remains unaltered, would be irreversibly damaged; in addition, the works made from wood and on parchment would be destroyed in a brief time if the dryness of the surrounding environment started to make them deteriorate.
DEFENCE
At Boeing, McDonnell Douglas, Hughes Aircraft and Lockheed, humidity control is considered of the maximum importance for the new stealth technology. The paint used is very sensitive to ambient humidity and if it polymerises incorrectly due to an environment that is too dry it will crumble, leaving the metal exposed to the reflection of the radar waves.
stealth technology: for purely military requirements, in 1975 the "Advanced
Project Division" of Lockheed-California started work on the design that lead to the creation of the first two prototypes of planes
that are invisible to radar, given the code bane: "Have
Blue". Since then a series of models have been designed using so-called stealth technology, with different characteristics from ordinary fighter planes.
The principle by which the plane is invisible to radar is based on a series of characteristics that act in unison. The outer surface of the stealth plane is covered by a layer of special paint that has the capacity to absorb most of the radar waves, including on the transparent cockpit.
FOOD PROCESSING
Meats maintain their red colour without the addition of nitrates if they are preserved in suitable containers and appropriately humidified cold stores. If fruit or vegetables lose too much moisture, the cells of the vegetables dry out irreversibly. For this reason it is important for the foodstuffs to be humidified from the moment they reach the store to when they are purchased by the consumer.
2. Static electricity
Static electricity is reduced significantly when the relative humidity is maintained above 35%. There are many sectors of industry that are especially sensitive to this problem.
COMPUTER ROOMS
The poor control of the humidity in a computer room involves the potential accumulation of static electricity, which when discharged may delete memories and damage electronic components. If the air is too dry, for example, the high speed printers may generate electrostatic charges when driving the paper.
PRINTING
In the printing process, as well as the hygroscopic variations in the paper, the problem of electrostatic discharges may also arise. The solvents contained in the printing presses may catch fire if the electrostatic discharges inflame the vapour. In addition, the printing presses may generate electrostatic charges when driving the paper (a newspaper press may generate up to 2,000,000 volts when driving the paper).
PHOTOGRAPHY
Most photographic laboratories feature humidity control systems to prevent the accumulation of charges on the films. This phenomenon is of special significance in relation to X-ray films in hospitals.
3. Well-being and comfort
In today's complex society, well-being and comfort have assumed crucial importance. Correct humidification, as well as a reduction in the amount of dust in suspension, ensures that the people present in closed rooms can breathe correctly, without problems deriving from the dryness of the upper airways. In addition, the reduction of cutaneous evaporation resulting from correct humidification reduces the feeling of cold and consequently allows the temperature of the room to be kept lower, saving on heating bills and limiting the dispersion of heat between the inside and the outside of the building.
upper airways: this refers to the external respiration organs (nose, mouth, throat)
