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Index for evaluating the effect of cooling damp curtain

2020-04-08

Cooling efficiency is evaluationCooling wet curtainThe important index of cooling effect, its calculation formula is as follows:η =(Tdb-Ti)/(Tdb-Twb)x 100

among them:η—Cooling efficiency(%);Tdb—Air dry bulb temperature before cooling(℃);Twb—Air wet bulb temperature before cooling(℃);Ti —Dry air temperature after cooling(℃).

It can be seen from the formula that what affects the cooling efficiency is the temperature of the air wet and dry bulbs before cooling, which usually refers to the outdoor air parameters. The second is the temperature of the dry air bulb after cooling, that is, the temperature of the cold air entering the room. The parameters that affect the indoor temperature are relatively complex, such as the structure of the wet curtain, the water distribution of the wet curtain paper, the water temperature, and the wind speed of the curtain.

The outdoor high-temperature air passes through the water-containing wet curtain and exchanges heat and moisture with water. The heat exchange is divided into latent heat and sensible heat exchange, and the heat exchange basically comes from latent heat exchange.

Latent heat exchange, the evaporation of water releases latent heat of vaporization. Due to the pressure difference between the partial pressure of water vapor on the surface of the water and the air, an evaporation phenomenon occurs under the effect of pressure, taking away the heat in the air. The air entering the wet curtain paper is dry air with low wet bulb temperature. There is a concentration difference of water molecules and a pressure difference of kinetic energy between the water and the air. When the fan is running, under the effect of static pressure, the water molecules continuously flow into the air Evaporates and absorbs heat from high-temperature air. The amount of water evaporation is positively related to the pressure difference of the saturated water, that is, the drier the air, the higher the temperature, the greater the temperature drop of the wet curtain, the better the effect. But as the water temperature rises, evaporation will intensify, the heat taken away by the water will increase, and the effect of cooling the wet curtain will be better.

Sensible heat exchange, the factor that affects the sensible heat exchange is the temperature difference, that is, the temperature difference between the main air and the boundary layer air. In principle, the lower the water temperature, the larger the temperature difference from the main air, the greater the heat exchange, and the air is over wet The greater the temperature drop. Due to the large air volume, the amount of water on the surface of the wet curtain is small, and the air flow rate is fast, the heat exchange between cold water and air is very small, accounting for a small part of the air cooling amount, and the temperature of the pump water pumping has little effect on the air cooling.

The cooling process of the air passing through the cooling curtain is an enthalpy cooling process. In general, the air decreases after passing the curtain1 ℃, The humidity will increase4% ~ 5%Left and right, the specific changes need to check the enthalpy chart.

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