There are differences between open cooling towers and closed cooling towers in multiple aspects, as follows:
Cooling principle:
Open cooling tower: by spraying the circulating water on the glass fiber and other fillers in the form of spray, the water and air are fully contacted for heat exchange. The heat exchange process includes sensible heat transfer and latent heat transfer. On the one hand, the heat of water is directly transferred to the air, causing the air temperature to rise. On the other hand, water evaporates into water vapor, absorbing a large amount of heat and achieving cooling of water. The fan drives the circulation of airflow inside the tower, carrying the hot air flow exchanged with water out of the tower.
Closed cooling tower: There are two cycles, namely internal circulation and external circulation. Internal circulation is a closed circulation system formed by connecting with the object equipment that needs cooling, and the circulating medium is usually soft water, etc. The internal circulation medium carries the heat from the target equipment to the cooling tower. The external circulation is carried out in the cooling tower, and heat is exchanged and dissipated through heat exchangers (such as copper tube surface coolers) inside the cooling tower, without contact with the internal circulation water phase.
Cooling medium:
Open cooling tower: In principle, it can only cool water because its cooling medium comes into direct contact with air, and other media may undergo chemical reactions or be contaminated with air, so its application range is relatively narrow.
Closed cooling tower: It can directly cool various media, such as water, oil, alcohol, quenching solution, salt water, and chemical solution. Due to its closed-loop operation, it is not affected by external air and can adapt to a variety of cooling media with different properties.
Cooling temperature:
Open cooling tower: usually can only cool water below 65 ℃, which largely depends on the material and performance of its packing and other components. If the water temperature is too high, it may cause problems such as deformation and aging of the packing, affecting the cooling effect and equipment life.
Closed cooling tower: It can cool high-temperature media and has better adaptability for some industrial production processes or equipment cooling needs with higher temperatures.
Equipment structure:
Open cooling tower: The structure is relatively simple, mainly composed of tower body, packing, water distributor, fan and other components. The tower body is usually made of fiberglass material, which has a certain degree of corrosion resistance. Filler is an important heat dissipation component, which increases the contact area between water and air and improves the cooling effect.
Closed cooling tower: The structure is relatively complex, including not only tower body, fan and other components, but also heat exchangers, spray pumps, water collection tanks, etc. The heat exchanger is its core component, used to achieve heat exchange between internal and external circulation.
Operation and maintenance:
Open cooling tower: The operation and maintenance costs are relatively high. Due to the direct exposure of circulating water to the air, it is prone to pollution and requires regular water quality treatment, such as adding disinfectants, descaling agents, etc. Moreover, water will continue to be lost during the evaporation process, and a large amount of water needs to be replenished regularly. In addition, fillers are prone to clogging and scaling, requiring regular cleaning or replacement, and require a significant amount of maintenance work.
Closed cooling tower: Low operation and maintenance costs. Circulating fluid operates in a closed manner, without being contaminated, evaporated, or concentrated. There is no need to replenish water or add chemicals, and only regular checks on the operating status of the equipment are required, such as checking the operation of fans and pumps, cleaning heat exchangers, etc. Daily management is relatively convenient, and the lifespan of the equipment is also relatively long.
Energy saving effect:
Open cooling tower: relatively poor energy-saving effect. The evaporation rate of water is relatively high, and the fan needs to continuously carry the hot air flow out of the tower, consuming a lot of electricity. Moreover, due to the evaporation loss of water, it is necessary to constantly replenish new water, which increases the consumption of water resources.
Closed cooling tower: The float rate and evaporation rate are much lower than those of open cooling towers, and the energy-saving effect is better. In environments with lower temperatures, automatic control can be used to reduce the operation of fans and spray pumps, further reducing energy consumption.
Environmental friendliness:
Open cooling tower: unable to operate dry, water evaporation will produce a large amount of water mist, which may have a certain impact on the surrounding environment. Moreover, if the cooling medium contains harmful substances, they may be discharged into the air with water mist, causing pollution to the environment.
Closed cooling tower: It can operate dry without breeding various bacteria, especially suitable for occasions with air purification needs, and is often used in areas with water shortage and dryness. When the fluid is volatile, toxic, or irritating, using a closed cooling tower can avoid environmental pollution.
Security:
Open cooling tower: When the cooling medium is volatile, toxic, or irritating solution, using an open cooling tower poses a safety hazard because these media may evaporate into the air, posing a health hazard to the operators.
Closed cooling tower: When the fluid is volatile or toxic, irritating solution, a closed circulation system is used, which will not pollute the environment and has higher safety.
Purchase cost:
Open cooling tower: The purchase cost is relatively low, its structure is simple, and the manufacturing process is relatively easy, so the equipment price is relatively cheap.
Closed cooling tower: The purchase cost is relatively high, generally 3-5 times higher than that of open cooling tower. Its structure is complex, and the manufacturing process requirements for core components such as heat exchangers are high, so the price of the equipment is relatively expensive.
