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HEAT and COMBUSTION:

HEAT and COMBUSTION By, Sameer D. Devidas

HEAT :

HEAT

HISTORY OF HEAT:

HISTORY OF HEAT In ancient times it was discovered that light and heat are different. Joseph Black was the first to give explanation to Heat. Lavoisier was then to formalize heat-fluid concept; into what he called the ‘CALORIFIC THEORY’. In 1798, Benjamin Thompson observed that mechanical motion tended to produce heat.

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In 1849, James Prescott Joule confirmed and declared that work could be converted into heat. In 1915, Nusselt published his pioneering paper: The Basic Laws of Heat Transfer.

What is Heat?:

What is Heat ? Heat is the energy transferred from an object at a higher temperature to an object at a lower temperature. Energy in the form of heat always flows from hot to cold. Measured in JOULES (J).

How is Heat produced?:

How is Heat produced? The movement of particles/molecules produces heat Particles move about more and take up more room if heated – this is why things expand if heated

SOURCES OF HEAT:

SOURCES OF HEAT

Heat Transfer:

Heat Transfer Heat always moves from a warmer place to a cooler place. Hot objects in a cooler room will cool to room temperature. e.g.: tea, coffee Cold objects in a warmer room will heat up to room temperature. e.g.: butter, ice.

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Heat a. The flow of thermal energy from one object to another. b. Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler Cup gets cooler while hand gets warmer

Forms of Heat Transfer:

Forms of Heat Transfer 3 types Conduction Convection Radiation

Conduction:

Conduction Conduction heat transfer is the flowing of heat energy from a high-temperature object to a lower-temperature object.

Conduction:

Conduction Transfer of heat is through a SOLID by being passed from one particle to the next Particles at the warm end move fast er and this then causes the next particles to move faster and so on. In this way heat in an object travels from: the HOT end the COLD end

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COLDER END HOTTER END

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THE PARTICLES GAIN ENERGY AND STARTS VIBRATING VIGOROUSLY.

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PARTICLES COLLIDE WITH EACH OTHER PASSING THE HEAT TO OTHER PARTICLES.

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Electrons Atoms

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THE MOLECULES GAIN ENERGY AND STARTS VIBRATING VIGOROUSLY.

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Heat passes faster due to the electrons which are moving around . “METALS ARE AMAZING AT CONDUCTING”

EXAMPLES OF CONDUCTION:

EXAMPLES OF CONDUCTION

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HOT END COLD END

Conductors / Insulators:

Conductors / Insulators If a substance easily allows heat to move through it, we can say it is a good conductor of heat. e.g: most metals If a substance does not allow heat to pass through it easily we can say it is an Insulator . E.g: wood, plastic, glass.

Refrences:

Refrences ^Lavoisier Reflections on Phlogiston 1: “ Against Phlogiston Theory” , Foundation Of Chemistry,137-151. Adiutori , E.F., The New Heat Transfer, p 1-11. Transfer of Heat

Convection:

Convection The particles in a liquid or a gas when you heat them. The Particles spread out and become less dense. A liquid or gas. HEAT

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GAS PARTICLES

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The particles near the fire gains energy and starts moving faster.

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The particles near the fire gains energy.

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The particles gain energy and become less dense and they move upwards.

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The more dense particles move downwards near the source of heat and starts gaining energy and they in turn become less dense.

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This process goes no continuing: the more dense particles move near the source of heat and the less dense particles move upwards. This take place in circular manner giving rise to the CONVENTIONAL CURRENT.

Convection:

Convection It is the way in which particles in a GAS or LIQUID move upwards , carrying heat with them

EXAMPLES OF CONVECTION:

EXAMPLES OF CONVECTION

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When water is boiled, the water moves in roughly circular patterns because of convection. This motion is due to density differences that result from temperature differences. The motion is called a convection current . 33

Convection:

Convection Where is the cooling compartment put in a fridge? Cooling compartment It is put at the top, because cool air sinks, so it cools the food on the way down. It is warm er at the bottom, so this warmer air rises and a convection current is set up.

Radiation:

Radiation Radiation is the transfer of energy by electromagnetic waves. Examples of EM waves: visible light, microwaves, infrared light When radiation is emitted from one object and then absorbed by another, the result is the transfer of heat. Radiation can travel through empty space.

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RADIATION

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How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ? RADIATION

EXAMPLES OF RADIATION:

EXAMPLES OF RADIATION

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Unit 2 Lesson 3 Thermal Energy and Heat Practical Uses of Radiation Copyright © Houghton Mifflin Harcourt Publishing Company A solar cooker is a device that cooks food using mirrors that concentrate radiation from the sun. In parts of the world that are far from electricity and clean water, solar cookers are a cheap and portable way to sterilize water for drinking. Many people like to use solar cookers because they do not require any fuel and do not release harmful emissions . 42

TRANSFERE OF HEAT BY ALL THE THREE PROCESSES ; CONDUCTION, CONVECTION AND RADIATION.:

TRANSFERE OF HEAT BY ALL THE THREE PROCESSES ; CONDUCTION , CONVECTION AND RADIATION .

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