VISUALIZATION OF AIRFLOW AND CONTAMINANT DISPERSION
Clean air and many air contaminants are under normal conditions invisible. It is, however, often desired to actually see the movement of air or the emission and transport of contaminants in order to ensure good air quality. Methods aimed at the visualization of airflow, contaminants emission to the air, and their transportation out in the workplace and to the breathing zone of the worker are therefore important tools for designers of industrial ventilation systems.
The main purpose with flow visualization is to make the airflow field or the emission and transport of air contaminants visible and thereby possible to study. In technical terms, flow visualization gives possibilities to study airflow field and contaminant dispersion and changes in it depending on general changes in geometry, boundary conditions, inlet and exhaust airflow, etc. It is
Also used to study airflow field and contaminant dispersion in the near field of a potentially exposed worker and how it changes depending on the behavior and position of the worker, or to collect an overview of airflow patterns before more detailed measurements are performed. In its simplest application it is used for checking that the ventilation system is working, e. g., that an airflow really is coming out of an inlet air unit.
The purpose of visualization of contaminant dispersion is to study the concentration of the substance of interest in a special point, area, or volume as a function of parameters of interest for the reduction of that concentration. One such point of special interest is in the breathing zone of a worker.
The reasons for using airflow or contaminant dispersion visualization techniques may be divided into purely technical and pedagogical, both with the purpose to give a base for the design and proper use of a contaminant control technology for workplaces with a good air quality.
The technical reasons for using visualization techniques are obvious. The designers of the ventilation have a great interest in studying how the airflow in a factory hall around a certain process or machine is distributed, to see if the design of a local ventilation unit is successful. The designer also needs to know in what way, in this context, disturbing factors such as heat sources, physical obstacles, or the presence and movements of a worker may affect the efficiency of the ventilation system.
The pedagogical background for using visualization methods is the fact that proper use and maintenance of industrial ventilation in most situations are dependent on persons without the deep knowledge about air and contaminant transport phenomena that can be expected from the designer of the systems. There are numerous examples of well designed industrial ventilation systems not fulfilling their original function due to a lack of knowledge regarding how to take advantage of and maintain the system in the most effective way. Knowledge of some basic qualities of the system and important air transport phenomena among the staff that is supposed to use and take advantage of the ventilation system is therefore fundamental to reach desired goals. This is of special importance when local ventilation systems are used, since the efficiency of the system very often is dependent on the behavior of the worker. Visualization techniques have thereby proved to be an effective tool to give basic knowledge of interest in this context.
To involve the staff in a change process, of which the installation or improvement of a ventilation system is one example, is also of vital importance for a successful result. Their knowledge of how the work is or may be done in an effective way, combined with the knowledge of the ventilation expert, increases the chance for an effective and durable solution of an air quality problem. Visualization methods have thereby proved to be effective both to communicate important knowledge and to motivate the staff to take part in the process.1
In this chapter the most common and/or well-evaluated techniques for the visualization of airflow and contaminant dispersion are described. The strategy for its use as a pedagogic tool is not included; this can be found elsewhere.1 To separate the different methods according to either airflow or contaminant dispersion studies is meaningless and not always possible. For example, smoke may many times be used for both purposes. The emitted smoke acts like a substitute for the contaminant in question and visualizes its dispersion to, e. g., the
Breathing zone of the worker at the same time as it enables the airflow patterns in the area to be studied. The two different purposes behind the use of the visualization methods have therefore not been explicitly separated.
To document by video or photography what is being u’.udhzc. J is often very useful. This makes it possible to analyze more carefully \ h. u has been documented. It is not possible to see all details the first time and me joint analysis of the results by all involved persons will many times bt ‘valuable.
There are of course a number of methods that can be classitic d a. methods for the visualization of airflow and contaminant dispersion, f his thjprer describes some of these that are useful for designers of industrial imitation. Methods that not are presented in more detail here are, for example, to fill small soap bubbles or ordinary balloons with helium in order to study the airflow field in large rooms. A large number of textbooks focus on flow usual — izarion. The research in this area can also be followed in The fourth!! of H<ni> Visualization and Image Processing.-
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