Heat Technology Ch 10.4 8th

Heat TechnologyChapter 10 Section 4

Objectives:

•Analyze several kinds of heating systems

•Describe how a heat engine works

•Explain how a refrigerator keeps food cold

•List some effects of heat technology and the environment

It’s a Fact!

•Heating, cooling, and breathing can produce hazardous waste gases and vapors

•An adequate ventilation system provides about 280L to 850L of outside air per min. for each person in a room

Important names in history…

•James Watt (modern steam engine)

•Rudolf Diesel & Gottlieb Daimler (internal combustion engines – 2 and 4-cycle engines)

•Karl Benz (patented internal combustion engines) – credited with Daimler for building the first automobile

Examples of Heat Technology:

•Heater in your home

•Automobiles

•Refrigerators

•Air conditioners

http://images.clipartof.com/small/33820-Clipart-Illustration-Of-A-Handy-Penguin-Mascot-Cartoon-Character-Wearing-A-Tool-Belt-And-Standing-By-An-Air-Conditioning-Unit.jpg

Heating Systems:

•Many homes and buildings have a central heating system that controls the temperature of every room

•There are several different kinds…

Hot Water Heating:•The high specific heat of water makes it

useful for heating systems

•Hot water heaters raise the temperature of water

•Heated water is pumped through pipes that lead to radiators in each room

•The water returns to the heater to be heated again

Warm Air Heating:• Air cannot hold as much thermal energy as water can

• Air is heated by burning fuel (natural gas) in a furnace

• The air travels through ducts to different rooms

• Cool air sinks and enters vents near the floor

• A fan forces the cooler air into the furnace to be heated again

• Air filters clean the air

Heating & Insulation:

•Heat can escape quickly. How do you create a system that is not wasteful?

•Insulation: a material that reduces the transfer of thermal energy; used in walls, ceilings, floors

•Fiberglass insulation

http://1.bp.blogspot.com/_0vuJZhliRZA/SZgriXsZ5oI/AAAAAAAABuU/NG_85S96pgQ/s400/E78869.jpg

It’s a Fact!

•Earth receives enough energy from the sun in 1 minute to meet the planet’s energy demands for an entire year!!

Solar Heating:•Passive solar heating: no moving parts; relies

on the building’s structural design & materials

•Active solar heating: has moving parts; pumps and fans distribute the sun’s energy

Solar Home Design:

http://www.hotwaterheaters.us/hot-water-heater-648.jpg

Heat Engines:

•Automobiles work because of heat

•Heat engine: a machine that transforms heat into mechanical energy, or work

•Fuel combines with oxygen in a chemical change that releases thermal energy: combustion

External Combustion Engines:

•Heat engines that burn fuel outside the engine

•Fuel is burned to release thermal energy that can be used to do work

•Ex: simple steam engine▫Steam drives pistons or turbines to

generate electrical energy from thermal energy

External Combustion Engine:

http://cr4.globalspec.com/PostImages/200712/Engine_stirling_ani_AA3E93E2-9BB0-FA90-5188B53F7C419C55.gif

Internal Combustion Engines:

•Heat engines that burn fuel inside the engine

•Fuel used is gasoline in a 6-cylinder car engine (burned inside the cylinders)

Internal Combustion Engines:

•A series of steps in burning fuel:1. Intake stroke: gas and air enter cylinder2. Compression stroke: crankshaft turns and

pushes piston up compressing the fuel mixture

3. Power stroke: spark plug uses electrical energy to ignite the compressed fuel mixture, piston moves down

4. Exhaust stroke: crankshaft turns and piston is forced back up, pushing gasses out of the cylinder

Internal Combustion Engine:

http://blog.thetechnonaut.com/wp-content/uploads/2007/10/4-stroke-engine.gif

Cooling Systems:

•Transfers thermal energy from a warm area to an area outside

•Thermal energy naturally goes from an area of higher temperature to an area of lower temperature

•Air conditioners need to do work to move warm air to a warmer area

Cooling & Energy:

•Most cooling systems require electrical energy to do the work

•Electrical energy is used by a device called a compressor (compresses the refrigerant)

•The refrigerant is a gas that has a boiling point below room temperature, it condenses easily

How a refrigerator works…

http://www.solarpowerwindenergy.org/wp-content/uploads/2009/06/refregiratorparts.jpg

Heat Technology & Thermal Pollution:•All systems transfer heat to the environment

•Negative effect of excess thermal energy: thermal pollution (excessive heating of a body of water)

•Thermal “waste” energy

•Dangerous for organisms that live in the water

Quick Quiz:

•You can cool the kitchen by leaving the refrigerator door open. (T/F)

•Refrigeration is possible because of energy absorbed and released during changes in state (T/F)

•A radiator heats a room by heating the air, which circulates in convection currents (T/F)