Application of CFD in the industry


1. Introduction
2. CFD modeling of process-technological flows
3. Complex mesh generation for CFD
4. Flow visualization
5. Examples
Example 1: Flow simulation and residence times in UV-disinfection systems
Example 2: Hygienic design of flow installations in the food industry
Example 3: Heat exchanger
6. Final remarks

1. Introduction

Fluid flows play an important role in various equipment and processes in the industry. Flows of air or water are often used for cooling purposes. To localize regions of deficient cooling or to improve the cooling performance of an apparatus insight in the cooling flow pattern is necessary. In general, information about the structure of the flow in a process or an apparatus can be obtained from measurements in experimental test facilities or from flow visualization studies. Although these techniques have proven to be of great importance, there are also limitations and a full picture of the flow field is often hard to obtain in this way. Computational Fluid Dynamics, commonly abbreviated as CFD, is a technique to model fluid flow using a computer simulation. Due to the recent rapid grow of powerful computer resources and the development of general purpose CFD software packages CFD can nowadays be applied to solve industrial flow problems. Today, CFD has already proven to be a valuable tool to complement experimental findings in flow structure studies. In a computational simulation the flow structure is computed by solving the mathematical equations that govern the flow dynamics. The result is a complete description of the three-dimensional flow in the entire flow domain in terms of the velocity field and pressure distribution, including profiles of temperature variations, density and other related physical quantities. Today’s CFD codes include in their basic flow computations effects of heat and mass transfer and a range of physical and chemical models. These extensions are indispensable for application of CFD in process-technological flow problems.

2. CFD modeling of process-technological flows

Flows in process installations are usually very complex. Many processes deal with flows consisting of multiple phases or mixtures of several components and these flow properties have to be included in the numerical simulation. The motion of bubbles or droplets in a flow can be modeled by seeding the computed flow field with particles, which tracks are then traced as part of the solution of the flow computation. The mean time the particles spent in the flow domain provides the residence times of the droplets in the process. In mixing vessels the mixing of multi-component flows is modeled by introducing passive scalars for each flow component. These scalars are advected by the main flow and the scalar concentration is computed as part of the solution. The dispersion of these scalars in the flow is a measure for the mixing performance in the vessel. In heat exchangers, furnaces or cooling equipment a combination of effects of heat convection by the flowing medium and heat conduction in the solid material requires inclusion of the solid material properties in the computation of the temperature profile. The conjugate heat transfer between the fluid and the solid is based on a model for the thermal boundary layer along the solid surface. In fans and turbines a part of the flow geometry rotates while in engines the flow domain changes in time by the motion of pistons and valves. The time-variation of these flow geometries is programmed in the numerical simulation and the transient flow field is solved according to the geometrical variations.