Numerical simulation of fogging in a square duct — A data center perspective

Inlet Fogging has been utilized in gas turbine power augmentation, whereby water in the form of billions of droplets, created by using specially designed fogging nozzles is sprayed into the ambient air lowering its temperature (adiabatic cooling) with the corresponding increase in the turbine power output. This work via numerical simulation, attempts to study the application of fogging in a square duct in the context of data center air-side economizer cooling, using a commercial CFD code. The theoretical natural convection droplet evaporation model is considered to evaluate the numerical results. The range of the final dry bulb temperature and relative humidity known as target condition is decided initially to analyze the performance. It has been observed that once the initial and final states represented by dry bulb temperature and relative humidity (on a psychrometric chart) are fixed, the controlled variables i.e. nozzle operating pressure, duct inlet velocity, nozzle orientation play a significant role in shaping the performance of the fogging process. The study also reveals the impact of nozzle design on fogging. It is concluded that for a given range of uncontrolled variables i.e. ambient dry bulb temperature and ambient relative humidity, there exists a range of controlled variables which leads to optimized operation of the duct as whole improving uniformity and evaporation efficiency. It is suggested that the target condition mentioned in the above work, after carrying out preliminary climatic analysis for a suitable location, can be considered equivalent to the recommended range of dry-bulb temperature and relative humidity by ASHRAE for a specific data center class.