Boiling inside a Nanotube CFD Simulation Training

Description

Boiling inside a Nanotube CFD Simulation by ANSYS Fluent, Training

The present problem simulates the boiling process inside a nanotube using ANSYS Fluent software.

A nanotube is a tube that is made at the nano-scale by nano-particles. This type of tube’s diameter can be about a few nanometers, While its length can reach several millimeters.

This simulation assumes that the water saturation temperature is 383.15 K; at this temperature, a phase change from liquid water to water vapor occurs.

The water stream enters the pipe at a speed of 1e-5 and a temperature of 373.15 K, and since this water stream is close to the saturation temperature, it can be said that it is ready for the boiling process.

The present model is designed in two dimensions using Design Modeler software. The model is a nanotube drawn in two dimensions due to its symmetrical geometric structure and reduced computational cost.

This pipe is of nanotube type and has a length of 0.00005 m and a radius equal to 0.00000015 m.

We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is structured. The element number is 100000.

Boiling Methodology

It is assumed that the pipe wall has a constant heat flux boundary condition equal to 100,000,000 W/m2 and can transfer this heat to water flow through the pipe. The water flow reaches the temperature above saturation by receiving heat from the pipe body and is in a superheated state.

As a result, when the water temperature reaches saturation temperature, the water turns into water vapor. Therefore, in the present simulation, a multiphase model is used; its primary phase is liquid water, and its second phase is water vapor. To define the multiphase model, the Eulerian model is used.

This model is the most complex multiphase model and can solve a set of momentum and energy equations for each phase separately. Since this modeling is supposed to deal with the boiling process, the Eulerian multiphase model should be used, and the boiling model option should be activated.

Also, to define the phase conversion process from liquid to gas, a mass transfer with a saturation temperature of 383.15 K must be specified.

Boiling Conclusion

At the end of the solution process, two-dimensional parameters related to pressure, water vapor velocity, water vapor temperature, water vapor volume fraction, and mass transfer rate from water to vapor (boiling) are obtained.

As the pictures show, water flow under the heat caused by the heat flux applied to the pipe wall increases with temperature. After reaching the defined saturation temperature, it turns into steam, or the so-called boiling process occurs.