Some evaporative coolers may also serve as humidifiers in the heating season. Even in regions that are mostly arid, short periods of high humidity may prevent evaporative cooling from being an effective cooling strategy. An example of this event is the monsoon season in New Mexico and southern Arizona in July and August. In locations with moderate humidity there are many cost-effective uses for evaporative cooling, in addition to their widespread use in dry climates.
For example, industrial plants, commercial kitchens, laundries , dry cleaners , greenhouses , spot cooling loading docks, warehouses, factories, construction sites, athletic events, workshops, garages, and kennels and confinement farming poultry ranches, hog, and dairy often employ evaporative cooling. In highly humid climates, evaporative cooling may have little thermal comfort benefit beyond the increased ventilation and air movement it provides.
Other examples[ edit ] Trees transpire large amounts of water through pores in their leaves called stomata , and through this process of evaporative cooling, forests interact with climate at local and global scales. Several hot and dry regions throughout the world could potentially benefit from evaporative cooling, including North Africa, the Sahel region of Africa, the Horn of Africa, southern Africa, the Middle East, arid regions of South Asia, and Australia.
Benefits of evaporative cooling chambers for many rural communities in these regions include reduced post-harvest loss, less time spent traveling to the market, monetary savings, and increased availability of vegetables for consumption. The vapor above a reservoir of cryogenic liquid is pumped away, and the liquid continuously evaporates as long as the liquid's vapor pressure is significant.
Evaporative cooling of ordinary helium forms a 1-K pot , which can cool to at least 1. Evaporative cooling of helium-3 can provide temperatures below mK. These techniques can be used to make cryocoolers , or as components of lower-temperature cryostats such as dilution refrigerators. As the temperature decreases, the vapor pressure of the liquid also falls, and cooling becomes less effective.
This sets a lower limit to the temperature attainable with a given liquid. Evaporative cooling is also the last cooling step in order to reach the ultra-low temperatures required for Bose—Einstein condensation BEC.
Here, so-called forced evaporative cooling is used to selectively remove high-energetic "hot" atoms from an atom cloud until the remaining cloud is cooled below the BEC transition temperature. Although robotic spacecraft use thermal radiation almost exclusively, many manned spacecraft have short missions that permit open-cycle evaporative cooling.
Examples include the Space Shuttle , the Apollo command and service module CSM , lunar module and portable life support system. The Apollo spacecraft used sublimators , compact and largely passive devices that dump waste heat in water vapor steam that is vented to space.
The water expended is often available in surplus from the fuel cells used by many manned spacecraft to produce electricity. Designs[ edit ] Evaporative cooler illustration Most designs take advantage of the fact that water has one of the highest known enthalpy of vaporization latent heat of vaporization values of any common substance.
Because of this, evaporative coolers use only a fraction of the energy of vapor-compression or absorption air conditioning systems. Unfortunately, except in very dry climates, the single-stage direct cooler can increase relative humidity RH to a level that makes occupants uncomfortable.
Indirect and two-stage evaporative coolers keep the RH lower. Direct evaporative cooling[ edit ] Direct evaporative cooling Direct evaporative cooling open circuit is used to lower the temperature and increase the humidity of air by using latent heat of evaporation, changing liquid water to water vapor.
In this process, the energy in the air does not change. Warm dry air is changed to cool moist air. The heat of the outside air is used to evaporate water. The moist air has to be continually released to outside or else the air becomes saturated and evaporation stops. A mechanical direct evaporative cooler unit uses a fan to draw air through a wetted membrane, or pad, which provides a large surface area for the evaporation of water into the air.
Water is sprayed at the top of the pad so it can drip down into the membrane and continually keep the membrane saturated. Any excess water that drips out from the bottom of the membrane is collected in a pan and recirculated to the top. Single-stage direct evaporative coolers are typically small in size as they only consist of the membrane, water pump, and centrifugal fan. The mineral content of the municipal water supply will cause scaling on the membrane, which will lead to clogging over the life of the membrane.
Depending on this mineral content and the evaporation rate, regular cleaning and maintenance is required to ensure optimal performance. Generally, supply air from the single-stage evaporative cooler will need to be exhausted directly one-through flow because the high humidity of the supply air.
A few design solutions have been conceived to utilize the energy in the air, like directing the exhaust air through two sheets of double glazed windows, thus reducing the solar energy absorbed through the glazing.
The passive cooling tower design allows outside air to flow in through the top of a tower that is constructed within or next to the building. The outside air comes in contact with water inside the tower either through a wetted membrane or a mister. As water evaporates in the outside air, the air becomes cooler and less buoyant and creates a downward flow in the tower.
At the bottom of the tower, an outlet allows the cooler air into the interior. Similar to mechanical evaporative coolers, towers can be an attractive low-energy solution for hot and dry climate as they only require a water pump to raise water to the top of the tower. For arid climates with a great wet-bulb depression, cooling towers can provide enough cooling during summer design conditions to be net zero.
The cooled moist air from the direct evaporative cooling process never comes in direct contact with the conditioned supply air. The moist air stream is released outside or used to cool other external devices such as solar cells which are more efficient if kept cool. One indirect cooler manufacturer uses the so-called Maisotsenko cycle which employs an iterative multi-step heat exchanger that can reduce the temperature of product air to below the wet-bulb temperature, and can approach the dew point.
Still, the relatively dry air resulting from indirect evaporative cooling allows inhabitants' perspiration to evaporate more easily, increasing the relative effectiveness of this technique. Indirect Cooling is an effective strategy for hot-humid climates that cannot afford to increase the moisture content of the supply air due to indoor air quality and human thermal comfort concerns.
The following graphs describe the process of direct and indirect evaporative cooling with the changes in temperature, moisture content, and relative humidity of the air. Passive indirect evaporative cooling strategies are rare because this strategy involves an architectural element to act as a heat exchanger for example a roof.
This element can be sprayed with water and cooled through the evaporation of the water on this element. These strategies are rare due to the high use of water, which also introduces the risk of water intrusion and compromising building structure.
Two-stage evaporative cooling, or indirect-direct[ edit ] In the first stage of a two-stage cooler, warm air is pre-cooled indirectly without adding humidity by passing inside a heat exchanger that is cooled by evaporation on the outside.
In the direct stage, the pre-cooled air passes through a water-soaked pad and picks up humidity as it cools. Since the air supply is pre-cooled in the first stage, less humidity is transferred in the direct stage, to reach the desired cooling temperatures.
Materials[ edit ] Traditionally, evaporative cooler pads consist of excelsior aspen wood fiber inside a containment net, but more modern materials, such as some plastics and melamine paper, are entering use as cooler-pad media. Modern rigid media, commonly 8" or 12" thick, adds more moisture, and thus cools air more than typically much thinner aspen media. From the installed water meters,[ original research? Sunlight may, however, degrade some media, in addition to heating up other elements of the evaporative cooling design.
Therefore, shading is advisable in most applications. Mechanical systems[ edit ] Apart from fans used in mechanical evaporative cooling, pumps are the only other piece of mechanical equipment required for the evaporative cooling process in both mechanical and passive applications. Pumps can be used for either recirculating the water to the wet media pad or providing water at very high pressure to a mister system for a passive cooling tower.
Pump specifications will vary depending on evaporation rates and media pad area. Otherwise, pressure develops and the fan or blower in the system is unable to push much air through the media and into the air-conditioned area.
The evaporative system cannot function without exhausting the continuous supply of air from the air-conditioned area to the outside. By optimizing the placement of the cooled-air inlet, along with the layout of the house passages, related doors, and room windows, the system can be used most effectively to direct the cooled air to the required areas.
A well-designed layout can effectively scavenge and expel the hot air from desired areas without the need for an above-ceiling ducted venting system. Continuous airflow is essential, so the exhaust windows or vents must not restrict the volume and passage of air being introduced by the evaporative cooling machine. One must also be mindful of the outside wind direction, as, for example, a strong hot southerly wind will slow or restrict the exhausted air from a south-facing window.
The effective cooling of water depends upon the dry bulb temperature and wet bulb temperature, size, height of the cooling tower and velocity of air. The project deals with the performance study and analysis of induced draft cooling tower, which is one of the deciding factors used for increasing the power plant efficiency also modelling and analysis of flow using software. A cooling tower is an enclosed device for the evaporative cooling of water by contact with the air.
Cooling tower is a heat rejection device. Common application includes cooling the circulating water used in oil refineries, petrochemical, and other chemical plants, thermal power stations and HVAC system for cooling buildings.
The primary task of a cooling tower is to reject heat into the atmosphere. Hot water from Condenser is sent to the cooling tower. The water exits the cooling tower and is sent back to the boiler or together units for further process. In cooling towers, air is passed concurrently or counter currently with water. The heat gained by air is the heat lost by water. The efficiency of cooling tower depends on air and water flow rates and operating temperatures.
In the chemical industries, utilities play an important role in plant operations. Two types of utilities are used in industries. Cooling utilities and heating utilities. Cold water is required for condenser, heat exchangers, reactors and other cooling purposes. Hot utilities include steam and other hot liquid used for heating in heat exchangers and to maintain reaction conditions.
Cooling towers are used to cool the water for its various applications. The used water from various applications at higher temperature can be cooled and reused.
Various types of cooling towers include Natural draft, induced draft and forced draft cooling towers. Various researchers have carried out studies and investigation on various aspects of cooling tower which influence the effectiveness and working of cooling tower. Figure 1. Frame and casing: Most towers have structural frames that support the exterior enclosures casings , motors, fans, and other components. With some smaller designs, such as some glass fiber units, the casing may essentially be the frame.
Fill: Most towers employ fills made of plastic or wood to facilitate heat transfer by maximizing water and air contact. Fill can either be splash or film type. With splash fill, water falls over successive layers of horizontal splash bars, continuously breaking into smaller droplets, while also wetting the fill surface. Plastic splash fill promotes better heat transfer than the wood splash fill.
Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in contact with the air. These surfaces may be flat, corrugated, honeycombed, or other patterns. The film type of fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill. Cold water basin: The cold water basin, located at or near the bottom of the tower, receives the cooled water that flows down through the tower and fill.
The basin usually has a sump or low point for the cold water discharge connection. In many tower designs, the cold water basin is beneath the entire fill. In some forced draft counter flow design, however, the water at the bottom of the fill is channelled to a perimeter trough that functions as the cold water basin. Propeller fans are mounted beneath the fill to blow the air up through the tower.
With this design, the tower is mounted on legs, providing easy access to the fans and their motors. Drift eliminators: These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere. Air inlet: This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower—cross flow design— or be located low on the side or the bottom of counter flow designs.
Louvers: Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow into the fill and retain the water within the tower. Many counter flow tower designs do not require louvers. Nozzles: These provide the water sprays to wet the fill.
Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface.
Two-stage evaporative cooling, or indirect-direct[ edit ] In the first stage of a two-stage cooler, warm air is pre-cooled indirectly without adding humidity by passing inside a heat exchanger that is cooled by evaporation on the outside. It is always best to have the downwind windows open, while the upwind windows are closed. In the chemical industries, utilities play an important role in plant operations. Generally, supply air from the single-stage evaporative cooler will need to be exhausted directly one-through flow because the high humidity of the supply air. Cooling towers can often be found on large buildings or on industrial sites. The inlet air louvers may be glass fibre, the fill may be plastic, and the cold water basin may be steel.
At the bottom of the tower, an outlet allows the cooler air into the interior. Similar to mechanical evaporative coolers, towers can be an attractive low-energy solution for hot and dry climate as they only require a water pump to raise water to the top of the tower. Digital Thermometer: 2 Digital thermometer are used to detect the inlet water temperature to the cooling tower and outlet water temperature out of the cooling tower. The cooling units can be mounted on the roof down draft, or downflow or exterior walls or windows side draft, or horizontal flow of buildings.
A fan having non-automatic adjustable pitch blades permits the same fan to be used over a wide range of kW with the fan adjusted to deliver the desired air flow at the lowest power consumption. Drift eliminators: These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere. If the basin was not of wood, it likely was of concrete. Passive indirect evaporative cooling strategies are rare because this strategy involves an architectural element to act as a heat exchanger for example a roof. The water exits the cooling tower and is sent back to the boiler or together units for further process.
Direct evaporative cooling[ edit ] Direct evaporative cooling Direct evaporative cooling open circuit is used to lower the temperature and increase the humidity of air by using latent heat of evaporation, changing liquid water to water vapor. Once the wet bulb temperature and the dry bulb temperature are identified, the cooling performance or leaving air temperature of the cooler may be determined. Small portable battery-powered misting fans, consisting of an electric fan and a hand-operated water spray pump, are sold as novelty items. Cunningham and T.
Plastic splash fill promotes better heat transfer than the wood splash fill. In cooling towers, air is passed concurrently or counter currently with water.
If the basin was not of wood, it likely was of concrete. Centrifugal fans are often fabricated from galvanized steel. Continuous airflow is essential, so the exhaust windows or vents must not restrict the volume and passage of air being introduced by the evaporative cooling machine. Benefits of evaporative cooling chambers for many rural communities in these regions include reduced post-harvest loss, less time spent traveling to the market, monetary savings, and increased availability of vegetables for consumption. In many tower designs, the cold water basin is beneath the entire fill.
The used water from various applications at higher temperature can be cooled and reused. Digital Thermometer: 2 Digital thermometer are used to detect the inlet water temperature to the cooling tower and outlet water temperature out of the cooling tower.
Vapor-compression refrigeration uses evaporative cooling, but the evaporated vapor is within a sealed system, and is then compressed ready to evaporate again, using energy to do so.