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What is Thermodynamics ?

By Edited Aug 21, 2015 0 0

What is Thermodynamics? - An overview and Introduction into Thermodynamics

Heat Loss and Equilibrium

Hello, In this article I'm going to explain a little about Thermodynamics.Thermodynamics by definition is: The study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, pressure, and volume.

That's a pretty lengthy definition, so I'm going to break that down into what you need to know in order to use thermodynamics to evaluate systems. The first thing you need to understand about Thermodynamics are the four laws of thermodynamic systems that are always true and cannot be broken when working with these systems.

  • The zeroth law of thermodynamics states that when two systems with different temperatures exchange heat with eachother, they will cool to equal temperature and are then said to be in equilibrium with eachother.
  • The first law of thermodynamics states that energy can never be created nor destroyed, only converted. It also specifies that heat transfer is a form of energy conversion.
  • The second law of thermodynamics is complicated to say the least. To summerize, the second law dictates that the amount of usuable energy in a system is gradually decreasing and the amount of entropy, or unusable energy in a system, is gradually increasing. Another way to think of this is to think of the sun bonding hydrogen to make helium. The more the stars in the universe bond hydrogen, the less hydrogen there is in the universe. This law usually doesn't apply as much to smaller systems, but is an important concept to remember when talking about the universe.
  • The third law of thermodynamics is much simpler and states that there is no such thing as zero thermal energy being left in a system. As you approach zero energy in a system, there is always a smaller amount of thermal energy in that system that can't be taken away.

Ok, now that we know the Laws of Thermodynamics, I'm breifly going to highlight some major equations used to solve Thermdynamic systems.

Variables

P= Rate of heat transer, Q= Energy transfer, Δt= Difference in time, k= Thermal conductivity, A= Area of thermal conductivity, L= Thickness, ΔT= Difference in temperature, S= 5.6696 x 10-8 W/m2 K4 (Stefan's constant), U= Thermal transmittance (U-factor), R= Resistance to heat flow (R-value), e= emissivity (a constant), Cp= specific heat capacity of the material (a constant).

Equations

  • Q= m x Cp x ΔT - used to find how much heat was lost or given between two systems
  • P= Q/ Δt -used to find the rate of energy transfer between two systems
  • P= k x A x (ΔT/L) -Commonly used to find the rate of heat loss through windows or insulators
  • Pnet = S x A x e x (T4-T4) -used to find the total energy lost or gained over a period of time
  • U-value= Q/(A x ΔT) -used to find U-value (thermal transmittance)
  • U= 1/R -alternate way to find U-value

That's all for this article, I hope these explainations help you!

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