Multiphase Flows

Condensation on micro-nano textured surfaces:

Condensation is a natural phenomenon that occurs when the substrate temperature goes below the dew point temperature. It has already been established that the dropwise condensation (DWC) is more efficient than the filmwise mode of condensation (FWC) for pure vapor. This is due to the higher heat transfer coefficient observed during DWC. Dropwise condensation of water vapor on solid surfaces is an enduring research topic due to the widespread applications. Dropwise condensation on surfaces has been investigated through experiments, numerical as well as theoretical modeling. Researchers are still searching for the durable dropwise condensing surfaces, as most of the surfaces either not durable or not scalable to the industrial scale. Besides the search for the durable dropwise condensing surfaces, researchers are interested in further improvement of the heat transfer coefficient during condensation. Micro-nano textured surfaces, lubricant impregnated surfaces, physically and chemically patterned surfaces have been used to demonstrate the further improvement of DWC heat transfer coefficient. The main bottleneck of dropwise condensation is the faster droplet removal. In our group, we work on the fast and effective technique of droplet removal from a surface for sustained dropwise condensation in the presence of non-condensable gases.

 For details see:

  1. Mahapatra et al., Key design and operating parameters for enhancing dropwise condensation through wettability patterning, International Journal of Heat and Mass Transfer, (2016), 92, 877–883

Jet impingement cooling

Wettability-patterning approach is used to divert an orthogonally-impinging laminar water jet onto a pre-determined portion of the target surface. Diverging wettable tracks on a superhydrophobic background provide the means to re-direct the impinging jet and enable spatially-selective cooling on the heated surface. By comparing with other jet impingement cooling approaches, our approach provides roughly four times more efficient cooling. Multiple hot spot cooling is also possible using a single jet to feed two different tracks by minimally displacing or splitting the impinging jet.

 For details see:

  1. Koukoravas et al., Wettability-confined liquid-film convective cooling: Parameter study, International Journal of Heat and Mass Transfer, (2018) 126, 667-676.
  2. Koukoravas et al., Spatially-selective cooling by liquid jet impinging orthogonally on a wettability-patterned surface, International Journal of Heat and Mass Transfer, (2016) 95, 142-152.

Granular Flows

The mixing of dense solid particles is important in many engineering applications. The discrete element modeling (DEM) approach was used to model the mixing of polydisperse elastic particles in Newtonian fluid. The granular slurry was driven by a belt moving at constant velocity in a square cavity. Size segregation and energy requirement for different types of polydisperse particles were identified.

 

 For details see:

  1. Mahapatra et al., The effect of size distribution mixing of wet granular materials in a belt-driven enclosure, Granular Matter, (2016), 8, 1-12

Particle-liquid interaction

Interaction of molten metals (particles) with coolant (water) is very important for severe accident study of a nuclear reactor, geological research and many engineering applications. Eulerian-Eulerian based modeling approach was used to develop a multiphase CFD code to capture the interaction of high-temperature particles with water. Distribution of the particles in the domain was captured and subsequently, the phase change of water was modeled considering film boiling. 

 For details see:

  1. Mahapatra et al., Heat transfer partitioning model of film boiling of particle cluster in a liquid pool: Implementation in a CFD code, Heat and Mass Transfer, (2015), 51 (8), 1149-1166
  2. Mahapatra et al., Analysis of Entropy Generation during Convective Quenching of cluster of balls, Numerical Heat Transfer: Part A, (2014), 66 (6), 689-711
  3. Mahapatra et al., Hydrodynamic and thermal interactions of a cluster of solid particles in a pool of liquid of different Prandtl numbers using two-fluid model, Heat and Mass Transfer, (2013), 49 (11), 1659-1679