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Chapter 1 - Introduction 2012 - Web

# Chapter 1 - Introduction 2012 - Web - WHAT IS HEAT TRANSFER...

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W HAT IS H EAT T RANSFER ? There are three principal laws upon which engineering studies are derived: Conservation of Mass (Mass Transfer, Reactor Design) Conservation of Momentum (Fluid Mechanics, Mass Transfer) Conservation of Energy (Thermodynamics, Heat Transfer )

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C ONSERVATION OF E NERGY Thermodynamics – the study of the transfer of work and energy between a system and its surroundings – in equilibrium Key thermodynamic functions (enthalpy, entropy) are state functions – neither rate or pathway influence values How we achieved equilibrium is not of concern in thermodynamics BUT is important for designing heating or cooling devices Heat Transfer – determination of the rate of energy transferred from one place to another resulting in a temperature change
E XAMPLE Consider a can of cola you want to cool down in a refrigerator. 20 o C How much heat needs to be removed from the can? THERMODYNAMICS If you leave it in the fridge, what will the temperature of the can be as a function of time? HEAT TRANSFER How long will it take to cool down? HEAT TRANSFER Surrounding Air, T = 4 o C REFRIGERATOR

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C OOLING THE C AN Question: How much heat needs to be transferred to cool the can? First Law of Thermodynamics Deals with the conservation of energy At steady state, we know between the system (can) and surroundings (refrigerator) We have a can ( closed system ), filled with 355 mL (~355g) of (mostly) water (+ 39 g of sugar!) Q: Sitting in the fridge, what kind of energy does the can possess? Potential energy? Kinetic energy? Other types of energy (like)? 0 E