October 7, 2023

Mist cooling system effects on dry and wet bulb temperature

The maximum delta temperature (ΔT) achieved by mist cooling depends on various factors, including the initial dry bulb temperature, relative humidity, and the type of misting system used. To understand this, it's essential to distinguish between dry bulb temperature and wet bulb temperature:

Dry Bulb Temperature (DBT): This is the standard temperature measurement that we commonly use and is the air temperature typically reported by weather forecasts. It represents the actual temperature of the air.

Wet Bulb Temperature (WBT): WBT is the temperature registered by a thermometer covered with a wet cloth exposed to moving air. It is lower than the dry bulb temperature because the evaporating water cools the air. WBT is a crucial factor when assessing the cooling potential of misting systems.

The maximum ΔT achieved by mist cooling is related to the difference between the initial dry bulb temperature (DBT_initial) and the final wet bulb temperature (WBT_final) of the air after it has been cooled by the misting system. The maximum ΔT occurs when the air is cooled to its wet bulb temperature.

Here's a simplified example to illustrate:

Initial Dry Bulb Temperature (DBT_initial): Let's say the initial dry bulb temperature is 95°F (35°C).

Relative Humidity (RH): The maximum cooling effect is achieved in dry or low-humidity conditions. The lower the relative humidity, the closer the wet bulb temperature is to the dry bulb temperature. For this example, let's assume a low RH of 20%.

Wet Bulb Temperature (WBT_final): Using a psychrometric chart or calculator, you can estimate the final wet bulb temperature after mist cooling. In low-humidity conditions, mist cooling can approach the wet bulb temperature. In this example, it might cool the air down to around 75°F (24°C) based on the psychrometric chart.

Maximum ΔT = DBT_initial - WBT_final
Maximum ΔT = 95°F - 75°F = 20°F (11°C)

So, in this scenario, the mist cooling system achieved a maximum ΔT of 20°F (11°C) by cooling the air from its initial dry bulb temperature to its final wet bulb temperature.

It's important to note that the actual cooling effect can vary based on factors like the quality and size of the misting system, airflow, and ambient conditions. Additionally, higher relative humidity levels will result in a smaller ΔT because the wet bulb temperature is closer to the dry bulb temperature in humid conditions.

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