Introduction to Energy Management

Week 2 Heat, Temperature and Pressure Basics

After completing this week, you will be able to:  Define heat and its units of measurements  Define conduction, convection and radiation  Apply specific, sensible and latent heat concepts  Compare temperature scales  Compare gauge pressures and atmospheric pressures Heat, Temperature and Pressure Basics

Heat Basics  Flows from sources of higher temperature  Flows to sources of lower temperature  Entropy  Calories  Btus  Absolute zero Heat, Temperature and Pressure Basics

Absolute Zero Thought to have no movement Scientists are rethinking the concept and found that there is movement Superconductor researchers are interested in electrical currents at absolute zero The possibility of zero loss magnetic fields across coils exists Sustainability science at work in the lab

Sustainable Transportation Systems Extend the conversation about the possibility of electromagnetic-repulsive-levitation transportation systems What new and innovative solutions might exist over the next 10 years to reduce the need for fossil fuels? Write a 3 page paper about what a scientific discovery that is being investigated now in energy

Heat Transfer  One or a combination of the following:  Conduction – requires physical contact between surfaces  Convection – Conduction plus fluid motion  Radiation – heat generated by electromagnetic waves Heat, Temperature and Pressure Basics

Specific Heat  Measures heat storage capacity of a substance  Specific heat of water is 1.0  Specific heat of air is 0.24 Heat, Temperature and Pressure Basics

Sensible Heat  Can be measured with a thermometer  Sensible heat is denoted Qs  Changes in sensible heat are denoted ΔT  Qs = ΔT x Weight of water x Specific heat Heat, Temperature and Pressure Basics

Example  Changing the temperature of 1 gallon of water from 140 to 160 degrees F.  Qs = ΔT x Weight of water x Specific heat  Qs = ( ) x 8.34 lb/gal x 1.0  Qs = Btu/gal Heat, Temperature and Pressure Basics

Example 2  Changing the temperature of 1000 gallons of water from 50 to 200 degrees F.  Qs = ΔT x Weight of water x Specific heat  Qs = (50-200) x (8.34 x lb/gal x 1000  Qs = ? Heat, Temperature and Pressure Basics

Latent Heat  Causes a change of state of a substance  No temperature change takes place  Latent heat of fusion  Latent heat of vaporization Heat, Temperature and Pressure Basics

It takes more energy to change the state of a substance From ice to water From water to steam Each substance requires a specific amount of Btu to change its state

Heat Content – Total heat contained in a substance Temperature – Thermal state of matter Review of Measuring Heat Change – Thermometers  Fahrenheit scale  Celsius scale Heat, Temperature and Pressure Basics

Converting between Fahrenheit and Celsius  ºF = 9/5 (ºC) + 32º  ºC = 5/9 (ºF – 32º) Example 2-2  Convert 77ºF to Celsius degrees  ºC = 5/9 (77ºF – 32º)  ºC = 5/9 (45º) = 25ºC Heat, Temperature and Pressure Basics

Absolute Temperature Scales  Rankine scale Water boils at 672º Water freezes at 492º  Kelvin scale Water boils at 373º Water freezes at 273º Heat, Temperature and Pressure Basics

Dry Bulb Thermometers  Measure only sensible heat content Wet bulb Thermometers  Water soaked wicks  Measure the latent heat content of air  Moisture from wick evaporates Heat, Temperature and Pressure Basics

Pressure  Atmospheric pressure Pressure above the Earth at a specific location  Elevation pressure Height above a specified level  Mechanical pressure Created by pumps Heat, Temperature and Pressure Basics

Measuring Pressure  Barometers Mercury barometer 29.92" Hg at sea level  Manometers Inches of Mercury ("Hg) Inches Water Gauge (WG) Heat, Temperature and Pressure Basics

Types of Manometers  Inclined manometer  Magnehelic mechanical manometer Standard air pressure gauge Bourdon tube gauge Metal diaphragm gauge Heat, Temperature and Pressure Basics

Gauge Pressure Gauges  Do not take atmospheric pressures into account  Pounds per square inch gauge (psig) Absolute Pressure Gauges  Take the atmospheric pressure into account  Read both atmospheric and medium pressure  Pounds per square inch absolute (psia) Heat, Temperature and Pressure Basics