Characterization of parallel and opposed control dampers to observe the effect on thermal mixing of air streams in an air-cooling unit

Cold Aisle in data centers have characteristic operating conditions as per ASHRAE standards. Temperature and humidity must be maintained within a specified range for normal operation. Air cooled data centers need several methods of cooling to condition the air before reaching the IT equipment. Direct evaporative cooling, as the name infers, the hot air comes in direct contact with the chilled water as a result the temperature drops and humidity increases. Similarly, Indirect Evaporative cooling involves reducing the dry bulb temperature of the hot air. Sometimes both the methods are used when the air is dry and hot. To improve the efficiency in cooling, Air-side Economization or free cooling is used in areas where the weather is cold. The outside air and the return air from the datacenter mixes in a dedicated space to achieve a target operating temperature & humidity and sent to the cold aisle. This dedicated space is known as mixing chamber. The return air and the outside air is mixed in such a ratio using a set of dampers at the entrance of the mixing chamber. These dampers are of two types, parallel plate and opposed blade. These two types of dampers not only mix the air but also influences the mixing effectiveness of the air downstream. The objective of this paper is to study the various effects of thermal stratification, mixing effectiveness and pressure drop that occurs at the mixing chamber based on the two types of dampers at various positions/angles. Also, the underlying mechanics of mixing the air at different conditions is discussed. It is observed that opposed blade dampers are more effective in terms of mixing than parallel blade dampers based on the numerical study. Also, the mixing and thermal stratification is more effective when the dampers face the wall of the mixing chamber when they are operated.