Condensation inside a Shell and Tube Condenser

Description

Condensation inside a Shell and Tube Condenser CFD Simulation, ANSYS Fluent Training

The present problem simulates the condensation process inside a shell and tube condenser using ANSYS Fluent software.

The process of condensation means the conversion of a fluid from a gaseous phase to a liquid phase; This means that when the liquid vapor reaches a saturation temperature, it turns into a liquid. The heat that causes a phase change between a liquid and a gas is called latent heat.

The saturation temperature for the condensation process occurrence is 46 ºC, and the time-frequency coefficient of this mass transfer is defined as 0.1.

In this modeling, the condensation occurs inside a shell and tube condenser. Thus, the flow of cooling water flows through the condenser pipes (tube) with a flow rate of 5 kg/s and a temperature of 20 ºC.

The flow of water vapor inside the shell’s interior with a speed of 10 m/s and in the saturation temperature is equivalent to 46 ºC.

Therefore, saturated steam undergoes a condensation process due to contact with the outer surface of the inner cold pipes, and its temperature drops to a temperature below the saturation temperature. As a result, liquid water is produced.

The present model is designed in three dimensions using Design Modeler software. The model is a shell & tube type condenser heat exchanger designed horizontally. A shell with two baffles is designed to carry hot water, and four rows of pipes are placed inside the shell to carry cold water.

Due to the symmetrical structure of the heat exchanger, the model is semi-drawn. We carry out the model’s meshing using ANSYS Meshing software. The mesh type is unstructured. The element number is 342486.

Condensation Methodology

In this simulation, the vapor stream of saturated water is converted to liquid water at saturation temperature. Since two different phases occur in the solution process, it is necessary to define a multiphase flow.

For this simulation, a multiphase mixture model is used; Because the two phases of liquid water and water vapor are thoroughly mixed together. Also, to define condensation, a Mass Transfer in the form of evaporation-condensation must be defined.

Condensation Conclusion

At the end of the solution process, two-dimensional and three-dimensional contours related to pressure, velocity, temperature, water vapor volume fraction, liquid water volume fraction, and mass transfer rate between water and steam or condensation are obtained.

After contact with the cold water pipes and heat transfer between the shell and the cold pipes, the contours show that the hot steam stream undergoes a temperature drop, and its temperature drops below the saturation temperature.

As a result, this process causes the phase change process, water vapor condensation, and water production in the condenser.