EXPERIMENTAL TECHNIQUES Chapter 12

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EXPERIMENTAL TECHNIQUESChapter 12

• KAI SIRÉN
• GUNNAR ROSÉN
• JÁNOS VAD
• PETER V. NIELSEN

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Contents of Chapter 12

• INTRODUCTION
• VISUALIZATION OF AIRFLOW AND CONTAMINANT
  DISPERSION
• Direct Observation of Aerosols Enhanced by
  Special Light
• Smoke Generation
• Flow Indicators
• Thermocamera Methods
• Graphical Presentation of Area Measurements
• Graphical Presentation of Measured Parameters in
  a Video
• References
• MEASUREMENT TECHNIQUES
• Introduction
• Measurement Planning
• Treatment of Measurement Uncertainties
• Dynamics of Measurements
• Temperature Measurement
• Air Humidity Measurement

• Pressure Difference Measurement
• Velocity Measurement
• Flow Rate Measurement
• Laser-Based Techniques (by Janos Vad)
• Nomenclature
• References
• SCALE-MODEL EXPERIMENTS
• Introduction
• Governing Equations and Dimensionless Numbers
• Similarity Principles and Conditions for Model
  Experiments
• Model Experiments in the Case of Fully Developed
  Turbulent Flow
• Model Experiments in Connection with the Local
  Ventilation in the Industrial Environment
• Labratory Experiments with General and Local
  Ventilation
• Using Similarity Principles in Planning
  Experiments
• References

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INTRODUCTION

• The use of experimental techniques is one method
  of designing, testing, and commissioning
  ventilation systems.
• A variety of complex problems are encountered in
  the wide field of industrial ventilation, the
  most common being the acceptability of airflow
  and temperature related to a new or rebuilt
  system.
• A complicated problem would be to experimentally
  investigate the influence of a hot oven on the
  airflow patterns in a large hall and how it
  influences the thermal conditions at the
  workplace.
• Ventilation engineers require answers to many
  difficult questions not only at the design stage,
  but at the commissioning and operating stage as
  well.

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INTRODUCTION

• The carrying out of visualization techniques or
  measurements is one approach to obtain answers to
  these questions.
• Computer simulation is another method that is now
  becoming a more exact science.
• A third, essential approach is to depend on
  experience and good engineering judgment.
• All the above methods may eventually lead to
  success however, the effort and cost of the work
  may differ considerably.
• This chapter describes the measurement and
  visualization techniques that can be applied in
  industrial ventilation problems.

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INTRODUCTION

• In planning experimental work, the following
  approach can be used
• Set goals What information is required as an
  output of the exercise?
• Select an experimental approach visualization,
  full-scale measurements, reduced-scale
  measurements
• Select measurement methods
• Ensure reliable analysis of results
• Select instruments
• Install and test the instrumentation
• Carry out the measurements
• Treat basic data to achieve the desired
  information

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FIGURE 12.4 Three examples of smoke sources
line, surface, and three-dimensional.
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FIGURE 12.7 Thermocamera picture visualizing
exposure to nitrous oxide during surgery (a)
without nitrous oxide in the breathing zone (b)
with nitrous oxide. (Picture from B. Ljungqvist.)
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Measurement Techniques

• In the wide field of industrial ventilation many
  factors require measurements to be carried out.
• One of the most common is the commissioning of a
  new or a renovated ventilation system. In this
  case the client has to see that the system works
  according to the specifications made with the
  consulting engineer, manufacturer, and
  contractor.
• Many other situations require quantitative
  information on ventilation and related systems,
  like
• The satisfactory functioning of a ventilation
  system,
• Troubleshooting in existing facilities,
• Testing the dynamics of subsystems, such as
  controls,
• Determining reasons for complaints,
• Checking on specified target values in a space,
• Carrying out an energy audit,
• Collecting data for renovation planning, and
• Collecting boundary values for a computational
  approach.

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Laser-Based Techniques

• In addition to their widespread use in research
  and development in fluid dynamics, laser-based
  techniques are also suited to experiments in
  industrial ventilation.
• The use of these advanced experimental methods is
  reasonable when their advantages in comparison
  with traditional measurement techniques
  counterbalance the significantly higher expenses
  of instrumentation.

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SCALE-MODEL EXPERIMENTS

• One of the methods used for the determination of
  airflow in large spaces is model experiments.
• This method is also useful in the study of local
  ventilation around a working area in the
  industrial environment.

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SCALE-MODEL EXPERIMENTS
Scale-model experiments have been used to study a
variety of ventilation problems as air movement
in a room, air movement around a building, energy
flow in a building, contaminant distribution at
an operators workplace, and smoke movement in a
building on fire.
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FIGURE 12.39 (a) Vortex exhaust at a concrete
element factory, (b) laboratory model of
the vortex exhaust, and (c) simplified model of
the exhaust.