Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

Chapter 4: Heat and Work Heat, Work & First Law: A Review Temperature & Heat Heat Transfer Principles

Heat, Work & First Law: A Review E = Q + W = KE + PE + TE + other forms – Other forms refer to chemical & electrical energy Heat is transfer of energy between two bodies as a result of a temperature difference

Heat, Work & First Law: A Review Units for heat – Joules(J) – calorie(cal) – British Thermal Unit (Btu) Heat is not contained in a body but is manifest only as the interaction of that body with its environment

Heat, Work & First Law: A Review First Law Thermodynamics ΔE = Q + W = Δ(KE + PE + TE)

Temperature & Heat Temperature is a property of an object; specifically the average kinetic energy of the atoms or molecules of that object. Three Temperature Scales – Celsius – Farenheit – Kelvin K = C + 273

Temperature & Heat Specific Heat of a substance is amount of heat added or removed per unit mass per degree of temperature increase or decrease Q = mcΔT – Metric System: Units are J/kg C – English System:Units are Btu/lb F

Temperature & Heat Absorption or liberation of Heat are sometimes accompanied by change of phase – Three phases of matter (solid, liquid, gas) – Heat of Vaporization(liquid -> gas) – Heat of Fusion(solid -> liquid) Heating & Cooling Curves

Example Problem 4.1 How much heat, in Btu, is required to raise the temperature of 4 gallons of water from 60 F to 100 F? (Note: 1 gallon of water weighs 8.3 lbs) Answer: 1328 Btu

Example Problem 4.2 How much heat is required to bring 1 liter (1 kg) of water to a boil from 20 C? How much heat is required to boil away this much water? Express your answers in kilojoules. Answers:334 kJ and 2260 kJ Total Energy for Entire Process2594 kJ

Heat Transfer Principles Heat flows from one object to another only when there is a temperature difference between the objects Heat flows from a hot object to a cold object

Heat Transfer Principles Three ways heat flows from hot object to a cold object – Conduction – Convection – Radiation

Heat Transfer Principles Conduction involves heat transfer arising from molecular collisions from hot object to colder object m/watch?v=- UcBRveX_78 m/watch?v=- UcBRveX_78

Heat Transfer Principles Rate Heat Transfer by Conduction

Heat Transfer Principles A = surface area (thickness) material T1 & T2 = Temperatures on either side of material k = thermal conductivity of material Units:Btu/hr orJ/s (Watts)

Heat Transfer Principles Convection involves heat transfer through a fluid medium by the motion of the gas or liquid. m/watch?v=ovSMAujQb z4 m/watch?v=ovSMAujQb z4

Heat Transfer Principles Radiation is heat transfer that does not involve a medium. Heat emitted by object as waves moving at speed of light Electromagnetic Radiation

Heat Transfer Principles Amplitude – height of wave Frequency – no. waves pass point /unit time Wavelength – distance between wave heights c = νλ c = speed of light ν = frequencyλ = wavelength

Example Problem What is the wavelength of electromagnetic radiation emitted from a radio station broadcasting at 1500 kHz? Answer200 m