ASSESSMENT OF A HEAT

EXCHANGER INLET NOZZLE FLOW

USING ANSYS-CFX®

Delvonei Alves de Andrade, Gabriel Angelo,

Gerson Fainer and Edvaldo Angelo

PRESENTATION TOPICS

• Company Overview;

• Problem Description;

• Methodology;

• Goals;

• Results;

• Conclusion and next steps.

COMPANY OVERVIEW

• IPEN – Nuclear and Energy Research Institute – National

Nuclear Energy Commission CNEN - autarchy, associated to

the University of São Paulo – USP for educational purposes

• Federal agency of the Ministry of Science and Technology.

• Founded in 1956 - main purpose - research and development

in the fields of nuclear energy and its applications.

• Located at the campus of USP - São Paulo

• Over 1.000 employees - 40% qualification at master or doctor

level.

• IPEN is recognized as a national leader institution in research

and development in the areas of radiopharmaceuticals,

industrial applications of radiation, basic nuclear research,

nuclear reactor operation and nuclear applications, materials

science and technology, laser technology and applications.

COMPANY OVERVIEW

• R&D - Educational activity - Program of

Excellence - Grade 6 by the Federal Government

Evaluation institution – CAPES.

• This program started at 1976 and has awarded

458 Ph.D. degrees and 937 master degrees since

them. The actual graduate enrollment is around

400 students.

• IPEN has a rigorous program of radiological

control and nuclear safety. This program

comprises personal and environmental monitoring

and radiological emergency assistance.

PROBLEM DESCRIPTION

• IEA-R1 heat exchanger is of the type shell-and-tube, STHE, with one-pass shell and

one-pass tube in countercurrent flow. Its total length is 7 meters. It was commissioned

in 2009.

• Operational characteristics: Mass flow rate is 188 kg/s and operational average

pressure is 5x105 Pa. Temperature difference, is about 6.5 ºC. IEA-R1 heat

exchanger is projected to remove 5,015 kW which is the maximum power for the

reactor primary circuit.

PROBLEM DESCRIPTION

• Inlet and outlet nozzles for the hot and cold fluid and stationary-head channel can

be observed. For the IEA-R1 STHE hot fluid is injected in the inlet nozzle into the

shell passing through the baffles and tube bundle towards the outlet nozzle. Cold

fluid removes the hot fluid heat and flows into the tube bundle in countercurrent

flow.

PROBLEM DESCRIPTION

• The problem consists in numerically solving the heat exchange inlet nozzle with

its annular region and tube bundle.

METHODOLOGY

• Design-Modeler and CFX-Mesh were used for the construction of the geometry and

mesh generation, respectively, in the Workbench environment. A tridimensional model

was developed using the finite volume method applied to a tetrahedral non structured

mesh. Inflation layers were considered for the annular region.

• The equations considered are the mass conservation and momentum equation. k - e

model is considered for turbulence.

• Operation fluid is water in stationary regime. Due to the small temperature variation in

the inlet section, for this analysis flow is considered isothermal at 45 ºC.

• A volumetric element generation shows a degree of complexity. It is related to the fact

that some elements present aspect ratio of 100:1. It is illustrated when one compares

the shell diameter to the small tube diameter in the tube bundle. So that, the

computational domain comes to a size as to test the computer system limits.

METHODOLOGY

• Mesh dependency was studied and verified using Stern, F. at al. and Wilson, R. V. at al.

approach. The methodology considers, for the same boundary condition, an increase of the

mesh density using predefined ratios. This procedure must be performed in such a way that

property variation or small variations are not present. When this condition is satisfied the

solution is independent of the mesh. A mesh of approximately 28 million elements was

generated.

• In order to avoid turbulence behaviors as swirl, an increment of the outlet dimension of the

heat exchanger model was included.

• At first it is assumed an average velocity of 2.07 m/s for the inlet nozzle, which is based on

the mass flux. Pressure at the outlet of the heat exchanger is equal to the operation

pressure.

• Convergence criterion is controlled by setting the maximum residues to 0.0001 for all

variables.

METHODOLOGY

• Results of this preliminary analysis were used to initiate the final resolution. In this case the

operation pressure was set as the pressure at the inlet nozzle and mass flux was set as the

boundary condition at the outlet. It guarantees variations of velocity at the inlet nozzle and

variations of pressure at the heat exchanger outlet.

• Non slip condition is applied to all other surfaces.

GOALS

• CFX training task;

• Comparison between the simplified and this model;

• Better understanding of the heat exchanger inlet nozzle flow

dynamics.

RESULTS

• Pressure contour for the simplified and this model

RESULTS

• Velocity contour for the simplified and this model

RESULTS

• Streamlines for the simplified and this model

RESULTS

• Velocity vectors for the simplified and this model

Conclusions

• CFX showed to be a very useful CFD tool;

• New limits to our department computer systems were

established;

• A CFX model for the IEA-R1 reactor heat exchanger inlet

nozzle was created;

• The mathematical model results for the pressure field,

velocity field, streamlines and vectors showed consistency.

Next steps

• Investigation of other turbulence models;

• New model with an equivalent geometry in order to solve the

problem for the whole heat exchanger.