## Rationale for this lesson

Learn useful fluid mechanics knowledge.

Learn how engineers approach design.

Have fun ==> fire pistons are cool!

## The fire piston

Fire piston: A piston/cylinder that uses compression ignition to ignite paper or other materials.

Resources:

- Buy a fire piston at Amazon
- Many website explain how to build. Here is an explanation on YouTube
- You can find many other websites that give useful information.

Applications. The ideas of the fire piston show up in many engineered products. For example

- refrigeration system work based on expansion (cooling) and compression (heating) of fluids.
- diesel engines use compression ignition
- air compressors require cooling (because the compression of gas causes the gas to heat up).

## How Engineers Approach The Design Process

A smart person with no engineering training can easily design and build a FP.

An engineer would do everything a smart layperson would do, but would approach the problem

- apply a math model to predict what will happen; to understand cause and effect
- take data on the experiment (experimental validation)
- understanding ==> why, ….

## Math Modeling

Math model = one or more equations that can be used to predict or explain occurrences in the physical world.

Math model of a fire piston ==> 2 Eqns ==>

- IGL
- Eqn. for a polytropic process

Let's start building knowledge for math modeling

## Units for Pressure

pressure is ratio of normal force of a fluid to area at a point

3 categories of units

- force/area: Pa, psi, pst
- height of a fluid column
- atmospheric pressure: atm, bar

Pressure values to memorize

1 atm = 101.3 kPa = 1.013 bar = 14.7 psi = 10.3 m (33.9 ft) of water = 760 mm (29.92 in) of mercury

## How to convert from one pressure unit to another

## Gage Pressure, Absolute Pressure, and Vacuum Pressure

- p_abs = p_atm + p_gage (Eq. 3.3a)
- p_abs = p_atm - p_vacuum (3.3b)

## Why gas gets hot?

macroscopic description: explain w/o resorting to molecules

microscopic description: explain based on what the molecules are doing

## Temperature Units

Kelvin & Celsius

Ranking and Fahrenheit

## IGL

Resource: IGL NETMAD

## SWBOT

- list three categories of pressure
- covert pressure units
- convert between gage and absolute pressure
- explain what macroscopic and microscopic mean
- convert temperature units (K, deg-C, deg-F, Rankine)
- carry and cancel units using the ideal gas law
- define a mole, a lbm-mole, and a kg-mole
- define an ideal gas
- apply 3 forms of IGL in traditional and SI units
- apply the IGL to relevant calculations