Energy: Thermal

Objectives

Learn the formula for calculating Heat Energy Evaluate social, economic, and

environmental issues related to thermal energy

Learn the differences in heat transfer. Conduction, Convection, Radiation

Energy (Thermal): Main Ideas Work and thermal energy are often related. When mechanical, fluid or

electrical work is done, part of the work turns into heat energy. Heat energy can also be used to do work (steam engines and internal combustion engines).

There is a direct relationship between heat energy and mechanical energy. This relationship is called “the mechanical equivalent of heat”.

Heat energy always moves from hot objects to cold objects. The heat gained or lost by an object can be calculated using the formula, H = mcΔT

Heat moves from hot objects to cold objects in three processes: conduction, convection and radiation.

Heat energy losses prevent 100% efficiency in useful energy conversions.

When mechanical work is done (measured in Joules), some of this work is used to overcome resistance. This produces heat energy which is measured in BTUs or Calories. There is a direct conversion from mechanical work to heat energy which is referred to as the mechanical equivalent of heat.

Mechanical Energy ExpendedMechanical Equivalent of Heat = Heat Energy Produced when all

mechanical energy goes into heat energy

Processes for transferring Heat Energy

Conduction: Heat energy is transferred from a hot region to a cooler region by vibrating molecules or atoms.

Convection: An air mass or volume of fluid is used as a medium by which heat energy is transferred.

Radiation: Movement of heat energy by electromagnetic waves. Radiation may be visible (red hot piece of steel), or invisible (infrared radiation from the sun).

Heat energy gained or lost

Heat Energy Applications

Current ProjectsIvanpah, California

Using Solar Energy for Heat

Societal Context:Millions of people get sick every year from drinking contaminated water.An estimated 1.5 billion people get diarrhea because of bad water and from that 2 million deaths occur. Billions of people worldwide don’t have access to clean water that we enjoy, and infrastructure doesn’t exist to allow access to clean water.

Making use of Solar Energy

These populations do however have plenty of sun, that can be used for free energy. Solar ovens can not only cook food, but can kill harmful microbes that cause illness and death.

Water Pasteurization

Louis Pasteur discovered the science of killing harmful pathogens and we know it now as pasteurization; the killing of disease-causing contaminants in food.

Practice Problem

How much heat energy is required to pasteurize 1 Liter of water that is originally 10˚C?

specific heat of water (c) = 4.186 J/g•˚C

water pasteurization = 65˚C

formula: H=mc∆T

H=(1000g)(4.186J/g•˚C)(55˚C)

H=230,230 Joules

Practice Problem

How much heat energy is required to heat a can of chili (3.06kg) from 21˚C to boiling point (100˚C) c of chili is 5.128 J/g•˚C

H=mc∆T

H=(3060g)(5.128 J/g•˚C)(79˚C)

H=1,239,642.72Joules

H=1.239MJ

Solar Oven Challenge

Engage in cooperative learning to create a solar oven that can pasteurize water and cook food

Create an oven that is inexpensive to build and that can be easily transported and stored

Conduct experiments that test the effectiveness of your constructed oven

Divide into teams

Get into teams of 3-4 people Read the instruction packet Timeline: 2 full class days to construct. Should be finished by next weekend. Use RTI

if more time is needed School-wide Physics Class Potluck April 16

during lunch You can conduct research to help you find a

good oven design, so you don’t have to start from scratch