Dehumidifier With DPM Model, CFD Simulation ANSYS Fluent Training

Description

Dehumidifier With DPM Model Description

The present simulation is about a dehumidifier via ANSYS Fluent. A dehumidifier is an air conditioning device that reduces and maintains the level of humidity in the air. This device is used to increase the health and thermal comfort of the people in the environment, eliminate the musty odor, and prevent mildew growth by removing water from humid air.

This project uses moisture absorption by surfaces to dehumidify the air. A chamber is designed where several rows of plates are placed inside the barrier as flow barriers. The presence of these barriers causes the humid airflow to pass through a winding path and constantly contact different plates, thus trapping the moisture in the air by these plates.

In this study, humid airflow is assumed to be a combination of airflow as a continuous medium and injection of many water particles as a discrete medium. Therefore, the discrete phase model (DPM) is used, and an injection is defined.

The use of the discrete phase model causes the solution approach to change from Eulerian-Eulerian to Eulerian-Lagrangian. In this modeling, a continuous airflow with a velocity of 0.05 m/s and a temperature of 373.15 K enters the chamber and collides with 21 plates perpendicular to the flow path. Simultaneously, the water flow is sprayed in a discrete environment from the nine holes of the chamber inlet to the continuous airflow.

Water injection is defined as inert particles with a diameter of 0.0001 m and a mass flow rate of 1e-5 kg/s, and a velocity of 0.05 m/s. Also, the behavior of discrete particles in contact with the surface of the plates is defined as a trap so that the discrete particles are separated from the continuous airflow and dehumidification results.

Geometry & Mesh

The present geometry is designed in a 3D model via Design Modeler. The computational zone is the interior of a dehumidifier. Inside the chamber, 21 rows of plates are designed as obstacles perpendicular to the fluid flow path.

Ten plates are connected to the upper level of the chamber, and eleven plates are connected to the lower level of the chamber and are placed in the middle with one arrangement. The air inlet is from the chamber’s left side, and nine separate vents are defined as the center for spraying water with discrete particles.

The mesh of the present model has been done via ANSYS Meshing. Mesh is done unstructured, and the number of production cells equals 2863327.

Set-up & Solution

Assumptions used in this simulation:

• pressure-based solver is used.
• The present simulation is steady.
• The effect of gravity on the model is ignored.

 

Models
Viscous		k-epsilon
	k-epsilon model	realizable
	near-wall treatment	standard wall function
Discrete Phase		On
	interaction	interaction with continuous phase
Injection		On
	injection type	surface
	particle type	inert
	diameter	0.0001 m
	velocity	0.05 m.s-1
	total flow rate	1e-5 kg.s-1
Energy		On
Boundary conditions
Inlet		Velocity Inlet
	velocity magnitude	0.05 m.s-1
	temperature	373.15 K
	discrete phase BC type	escape
Outlet		Pressure Outlet
	gauge pressure	0 Pascal
	discrete phase BC type	escape
Plates		Wall
	wall motion	stationary wall
	heat flux	0 W.m-2
	discrete phase BC type	trap
Methods
Pressure-Velocity Coupling		SIMPLE
	pressure	second-order
	momentum	first-order upwind
	turbulent kinetic energy	first-order upwind
	turbulent dissipation rate	first-order upwind
	energy	first-order upwind
Initialization
Initialization methods		Standard
	gauge pressure	0 Pascal
	temperature in chamber	373.15 K
	temperature	373.15 K

Dehumidifier With DPM Model Results

After calculation, 2D and 3D contours related to velocity, pressure, pressure gradient, and DPM concentration are obtained. The particle tracks based on residence time are also shown. The results show that the fluid flow passes through a tortuous path through the space between the plates and is in constant contact with the surface of the plates.

These contacts cause discrete water particles in the air to be trapped by these plates in the space between the plates. Thus, the dehumidification process of moist air is done correctly by trapping water droplets. The results show that the 175 tracked water particles are all trapped by the plates.