Experimental Methods for Engineers: Introduction to Experimentation and Design, Lecture notes of Aerospace Engineering

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Experimental Methods for

Engineers

Introduction (Chapter 1)

By Mohsen Soori

Why experiments are so important?

• When was the last time that you run the experiment?
• Running experiment is really important. We do it all the time. Whether when we are making food, or trying to find the shortest distance on the map. We are also running experiment in our family and friends or even in our Colleagues at work.

The importance of this course

• Experimentation is so important in all phases of engineering
• There is a very definite need for the engineer to be familiar with methods of measurement
• As well as analysis techniques for interpreting experimental data.

Development of experimental techniques

• Experimental techniques have changed quite rapidly with the development of electronic devices for sensing primary physical parameters and for controlling process variables. In many instances more precision is now possible in the measurement of basic physical quantities through the use of these new devices.

Clinical Thermometer

Resistance measuring instrument

Design of experiments (example)

• Absolute zero :
• Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0.
• Ideal gas equation:
• PV=nRT

QUESTION? How many gas variables do we have ??

Design of experiments

• First design: the absolute zero is defined by means of an isochoric process (constant volume), conducted with a set amount of air closed in a regular jar.
• Second design: the absolute zero is determined by means of an isobaric process (constant pressure) with air closed in a flask.

T =

𝑃𝑃 𝑛𝑛𝑛𝑛 V

T =

𝑉𝑉 𝑛𝑛𝑛𝑛 P

Data Analysis

Finally, to analyze the data, the experimental engineer must have a combination of

into the physical principles of the processes being investigated and a knowledge of the limitations of

the data.

Research involves a combination of analytical and experimental work. The theoretician strives to explain or predict the results of experiments on the basis of analytical models which are in accordance with fundamental physical principles that have been well established over the years.

The data analysis process:

1. Define Your Questions
2. Set Clear Measurement Priorities

A) Decide What To Measure

B) Decide How To Measure It

3. Collect Data
4. Analyze Data
5. Interpret Results