Thermodynamics, Railroading and Linear Expansion

My last post entertained briefly the First Law of Thermodynamics.  Such a concept permeates most all systems including what is often referred to as a closed system.  Within a closed system, matter can not cross a set boundary - enter or leave.  Most textbooks refer only to energy as being able to cross the set boundary within a closed system.  We demonstrated from earlier posts that work and energy were in fact synonomous, and as such, we can include work as being able to cross the set boundary of the system; this validates both th qualitative and quantitative definitions of the law: 1.  conservation of energy; 2.  delta U= Q-W - change in internal energy is equal to energy/heat added to the system minus the work done on the system.  Let's discuss why most solids expand when energy/heat is added.

As a child, I can remember my grandmother running hot water over the lids of jars to help open them.  This practice is based on the concept of linear expansion.  When energy/heat is added to most solids the molecules of the material speed up their interactions, push outward and the solid expands.  Quantitatively, and from a linear perspective, this is given by delta L = «a»L delta T - change in length is equal to the coefficient of linear expansion times the original length times the change in temperature. This «a» or coefficient of linear expansion will almost always be given in a stated problem.  For a good list of coefficients of this type you can go to www.engineeringtoolbox.com and search for coefficient of linear expansion for materials.  Here is a railroad example.

You are reviewing some specifications on a newly constructed railroad.  As you are examining the 12 meter long rails, you notice there is 2.5  millimeter gap between the rails. The coefficient of linear expansion for the steel used in the rail is 1.2*10^-5 C^-1; the units for coefficient of linear expansion are 1/C or C^-1. You check the almanac and find that the normal temperature can increase as much as 50 degrees Celsius on a hot day.  Did the chief engineer wisely design the rail system or should he retake high school physics?

Next time, we will.check the answer to this and tackle some other thermodynamic issues with rail transport.

www.engineeringtoolbox.com

Clearcutting Controversy

Here is a link to an interesting article from Clemson University which discusses the controversy surrounding clearcutting.  As with most pursuits of humankind, rarely if ever can we deal in absolutes.

http://www.clemson.edu/extfor/timber_production/fortp19.htm

Tree Identification

Tree identification will be an important part our project.  I have chosen to link  to a business named Industrial Timber and Lumber.  This group has several locations.  Yet, what pulled me to them was that they have two major sawmill operations in Vinton County, Ohio only about 45 minutes from my home, and a huge kiln drying operation in Marlington, WV.  I believe this is close to Elkins, WV.  I plan on visiting the sawmills
inthe next few days and hope we can stop at the Marlington location during our trip. 

Their site offers great deal of information on various species.  This includes tree identification by leaf, charted information about relative working properties for each wood, sample grade photos, and an overview of each species.  Incidently, information about each location's production offers some good insight into the productivity of our region. 

http://www.itlcorp.com/Species.aspx

First Law of Thermodynamics and Steam Locomotives

Recently, we have discussed work and energy concepts.  Let us now build upon those concepts within a basic steam locomotive.

We know from previous posts that there is more than one way to define work.  I am going to now offer another definition.  Work equals force times distance - W=Fd, is our most common definition. We also know this is equal to a change in energy.  Yet, if we consider pressure is equal to force divided by area - P=F/A, a common concept learned at least by middle school.  An easy manipulation tells us that F=PA.  Substituting this into our equation yields work equals pressure times area times distance - W=PAd.  But, area times distance is a definition of volume.  So work is equal to pressure times a change in volume - W=PdeltaV.  This concept of changing volume at constant pressure to move a piston is precisely the mechanism behind basic steam locomotive operation and owes its origination to the 1st Law of Thermodynamics;  the change in the internal energy of a system is equal to the heat added to a system minus the work done on the system - delta U=Q- W.

Our locomotive burns coal or oil to heat water. The water eventually changes to high pressure steam which increases its volume and expands pushing a piston within a cylnder.  This explains why locomotives must take on water periodically as its water supply is constantly be turned to steam.  The piston is connected to a rod apparatus which connects to coupling rods which move the wheels.  Incidently, the steam exaust is simply released by a valve under great pressure which accounts for the "choo choo choo choo" we hear and, the piston returns to its original position ready to be pushed again by pressure and volume expansion.

We now should begin to recognize some basic relationships among work, energy, power, and force with a locomotive.