Basic principle of water cooling

10-04-2019

Basic principle of water cooling


The phenomenon that the hot water is lowered by the cooling device to the water temperature is often encountered in daily life. If a cup of boiling water is used to pour boiling water into two cups, the water temperature will decrease. This is to make the water form a water film layer or water droplets, increase the contact area between hot water and air, and increase the evaporation and heat dissipation of water. The cooling rate of the water thus turns the boiling water into warm water relatively quickly. Another example is when swimming in the summer, just coming out of the water, it is very cold when it is blown by the wind. This is also caused by the evaporation of water from the body and the removal of a lot of heat. The cooling of water is actually a combination of three processes: evaporative heat dissipation, contact heat dissipation and radiation heat dissipation. Evaporative heat dissipation and contact heat dissipation are the main ones, and the radiation heat dissipation is small.


Why use water to cool equipment or products

There are a lot of gases and various liquids in nature. Why use water to cool equipment or products? There are three reasons for this:

1. The specific heat of water is 1kcal/(kg·°C), which means that the temperature of 1kg water is increased or decreased by 1°C, and 1000cal (1kcal) of heat can be absorbed or released. When 1kg H2O is used to cool the equipment or product, the water temperature rises by 5 °C, which theoretically absorbs 5000 calories of the equipment or product.

2. The price of water is relatively cheap. Generally speaking, as long as the pump water cost and water purification treatment fee of the water are raised, the water is not only cheaper but also relatively more abundant than other liquids and gases.

3. The vaporization heat of water is large: at 0 ° C, the heat of vaporization of 1 kg of water is 59,713 kcal. What is vaporization heat? That is to say, the heat absorbed by 1 kg of 0 ° C water when it becomes 0 ° C of water vapor is called heat of vaporization. So what is the significance of vaporization heat? That is to say, water of 1kg0 °C, which evaporates 1% of water (1% of 1kg) can lower the temperature of 1kg water by 6 °C. The specific heat and vaporization heat of water and alcohol and other liquids are shown in Table 4-1. It can be seen that the specific heat of water and the heat of vaporization are the largest, and the effect of water cooling is best.

Water is used to cool the production equipment and products, so that the temperature of the production equipment and products is lowered, and the heat is transferred to the water to raise the temperature of the water. This process is to conduct heat dissipation.

In the process of cooling water in the cooling tower, water is formed into small water droplets or extremely thin water film, expanding the contact area of water and air and prolonging the contact time, which is to enhance the evaporation and evaporation of water and take away a large amount of heat in the water. Therefore, the process of cooling water in the cooling tower is a process of conducting heat dissipation and evaporating heat.

The air can hold a certain amount of water vapor. When there is less water vapor in the air, the climate is very dry and the weather is good. When there is a lot of water vapor in the air, it will feel very humid. When there is a lot of water vapor in the air, it will appear. Very small dew point. This indicates that the air can receive water vapor, and that there is a limit to the air receiving water vapor. When a small dew point appears in the air, it indicates that the water vapor received by the air is "full" and can no longer be accepted, that is, the water in the air. The vapor reaches saturation and is called saturated water vapor.

During the cooling process, as long as the water vapor in the air has not reached saturation, the hot water surface will continuously emit water vapor and run into the air when it is in direct contact with the air. During the process of turning into water vapor in the water molecules on the hot water surface, heat is absorbed from the water to cool the water.


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