Modeling Boiling Phenomena using User Defined Functions in FLUENT, Slides of Physics

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Presentation Layout

Introduction Literature Review Methodology Code Implementation Analysis and Results Discussion Conclusion, Recommendation and Future Work 2

Introduction (cont.)

This study will lead to the modeling of complete steam generators and boilers. The modeling of boiling phenomenon in such equipment will improve the design and trouble shoot faults in the existing equipment. Different test cases were simulated to validate the code. 4

Boiler

A boiler or steam generator is a device used to create steam by applying heat energy to water. It incorporates a source of heat in order to burn the fuel and generate heat. The heat is then transferred to water to make steam. The higher the furnace temperature is, the faster the steam will produce. 5

Mass Transfer

Mass transfer is the transfer of mass from high concentration to low concentration. The driving force for mass transfer is the heat input or removal which causes the phase change from liquid to gas or gas to liquid. 7

Multiphase Flow

Multiphase flow is a generalization of the modeling used in two-phase flow to cases where the two phases are not chemically related (e.g. dusty gases or water and air) or where more than two phases are present (e.g. in modeling of propagating steam explosions). Each of the phases is considered to have a separately defined volume fraction (the sum of which is unity), and velocity field. Two-phase flow is a particular example of multiphase flow. 8

Boiling (cont.)

Boiling occurs in three characteristic stages, which are

1. Nucleate,
2. Transition &
3. Film boiling. These stages generally take place from low to high surface temperatures, respectively. 10

Boiling (cont.)

11 The boiling curve

“Multidimensional modeling of two-phase flow

and heat transfer” (Michael Z. Podowski)

13 Calculated temperature contours in boiling

(cont.)

14 Calculated void fraction contours in boiling

(cont.)

16 Calculated vapor velocity contours in boiling

“CFD modeling of subcooled boiling - Concept,

validation and application to fuel assembly

design” (Eckhard Krepper et. al.)

17 Calculated distributions of temperature in the channel

(cont.)

19 Measured vs. calculated averaged void fraction, averaged temperature, axis temperature and wall temperature

Methodology

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