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College of Science & Engineering > Department of Mechanical Engineering

Compressed Air Approach for Wind Energy Storage



Research: Fluid Dynamics of Sprays and Droplets on Surfaces



The storage efficiency can be improved through the optimization of :
I.  Spray Properties
II. Injection Method

A research team led by Professor Eric Loth from the University of Virginia is analyzing the optimization methods.


In order to keep the liquid piston isothermal during its operating cycle, droplets are sprayed into the piston chamber which in turn provides a large total surface area for heat transfer. The heat transfer rate is directly proportional to the total surface area and therefore our research focuses on keeping the maximum of number droplets aloft.

A summary of the liquid piston stages are shown below:

Spray CoolingSpray Cooling 2

Results and Ongoing Research:

A. Droplets

As the droplets are sprayed into the liquid piston, there are two types of droplet interaction:
I.  Interaction between droplets and side walls
II. Interaction between droplets

The typical Weber and Reynolds number regime for the liquid piston is shown below. Droplets tend to coalesce into bigger droplets in this regime, which would reduce the total available surface area for heat transfer.

We-Re RegimeSuperhydrophobic

However, having a super-hydrophobic coated surface promotes bounce (or even break-up) which is a desirable quality of the spraying. It is clearly seen that the water droplet coalesces (or liquid film) in the case of an aluminum surface.

Further research is being conducted into analyzing the droplet behavior in high pressure environment (up to 500 psi) and different spray nozzles and configurations.

B. Injection Methods

Different injection methods could also have varying effect on the efficiency of the liquid piston as shown below.


Initial analysis was conducted by considering direct and pre-mixed injection. Other types of injection methods and nozzle configurations are currently being studied.

In addition to that, simulation efforts are being undertaken to analyze the droplet and spray physics. A 2D simulation is shown as above.

Future work includes a full 3D simulation incorporating collision & break-up models and droplet heat transfer model during compression and expansion stage of the liquid piston.

  Contacts: Prof. Perry Y Li
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