Droplet dynamics in capillary parallel plate channel

Abstract

Sprays are more effective in dissipating heat compared to forced air convection. However, in heat exchangers, water films can block airflow through the fins during spray injection. This obstruction leads to a reduction in heat transfer and an increase in pressure drop. To address this issue, enhanced fins are essential to maintain a high heat transfer rate during spray cooling. Consequently, the study investigates the clogging processes related to the water films generated by sprays.

Numerical methods using the Volume Of Fluid (VOF) approach were employed to model the water–air interface of a droplet crossing a heat exchanger. The heat exchanger is modeled as a channel with two parallel plates as an embedded boundary. A variable-size droplet, representing an aggregate of spray droplets at the channel entry, is introduced and slides down the plates.

The outcome of the droplet penetration depends on factors such as the plate gap width, the droplet size, and the contact angle. In this context, overcoming an energy barrier is crucial for droplet penetration. The energy required, influenced by capillarity, makes hydrophobic surfaces challenging to penetrate. However, hydrophilic surfaces complicate droplet exit. Large droplets tend to break down into smaller ones during penetration. The crossing time, of similar magnitude for both hydrophobic and hydrophilic surfaces, depends mainly on the aspect ratio between the droplet diameter and the gap width. The drop break-up and the crossing time are thoroughly analyzed to identify the delicate balance of parameters essential for preventing channel clogging.