Heat Recovery in Counter and Cross Flow Plate Heat Exchangers, Paper Numerical Validation

Heat Recovery in Counter and Cross Flow Plate Heat Exchangers, Paper Numerical Validation, CFD Simulation by ANSYS Fluent

The present problem is an ANSYS Fluent software CFD simulation of a cross-flow heat exchanger plate panel.

This simulation is based on the data in the reference article “Numerical model and effectiveness correlations for a run-around heat recovery system with combined counter and cross-flow exchangers,” The results are compared and validated with the results in the paper.

This heat exchanger consists of two special flow channels; In this way, the airflow flows from one side of the panel’s central panel, and the solution flows from the other side but in the opposite direction to the airflow.

This panel generally belongs to one of the two panels in the closed cycle of solution and airflow. The fluids used in the present model include air and ethylene glycol (CH2OH), although their thermophysical properties are manually defined in the Fluent.

Ethylene glycol is a colorless, odorless, low volatility, low viscosity material whose properties are temperature-dependent polynomials. Also, since hot and cold flows are not integrated into this heat exchanger, there is no need to use a multiphase flow module, and on the other hand, a separating plate is used as an interface.

CFD Methodology

The geometry of the present model is designed in three dimensions using Design Modeler software.

The meshing has been done using ANSYS Meshing software, and the mesh type is structured. The element number is 155000. The cells near the wall boundaries are smaller and more accurate.

Exterior walls also act as insulation.

Heat Recovery in Counter and Cross Flow Plate Heat Exchangers Conclusion

The solution fluid in the model has a temperature higher than the airflow; therefore, the purpose of the problem is to cool the hot air flow outlet. The general purpose of the present problem is to study the fluid behavior and heat transfer of the flows and investigate the heat exchanger’s performance efficiency.

At the end of the simulation process, the efficiency of the heat exchanger is calculated, compared, and validated with the value obtained in the reference paper. This comparison and validation are based on the values ​​in the diagram in Figure 11 of the article.

This diagram shows the changes in the heat exchanger efficiency (Ԑ) in the ratio xi / x0. This ratio xi / x0 is defined as the ratio of the liquid flow inlet length to the heat exchanger’s total length. According to the modeled geometry of the present numerical simulation, the value of this ratio in the current work is 0.1.

The relationships in the paper are used to calculate the heat exchanger efficiency. The amount of air and liquid inlet temperature was defined in the boundary conditions.

The outlet temperature of the air and fluid was obtained. It should be noted that the heat transfer from the cold fluid to the hot fluid during the simulation process equals the heat transfer from the hot fluid to the cold fluid.

	Present simulation	Paper result
Effectiveness based on xi/x0	0.665	0.716

Also, according to the relations and calculations mentioned above, the ratio of the heat capacity of the liquid to the air can be calculated. According to the diagram in Figure 19, the efficiency of the heat exchanger can be obtained in the amount of the mentioned ratio and be compared with the calculated efficiency according to the above relations.

	Present simulation	Paper result
Effectiveness based on CL/CA	0.665	0.580

Also, two-dimensional contours related to temperature, pressure and velocity have been obtained in two sections, X-Z and Y-Z, and two-dimensional path lines.