"The Efficiency of Heat Engines" Utilization of Internal Energy PPT Courseware 2

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"The Efficiency of Heat Engines" Utilization of Internal Energy PPT Courseware 2

1. Calorific value of fuel

Want to discuss

Do different fuels have the same heat release capabilities? How do we compare which one of them has the stronger ability to release heat?

The combustion of fuel is a chemical reaction. During the combustion process, the chemical energy stored in the fuel is released and converted into internal energy.

Experience tells us that when coal and dry firewood of equal quality are fully burned, coal releases much more heat than firewood. We use the concept of calorific value to express the ability of fuel to release heat.

1. calorific value

(1) Definition

The ratio of the heat released by complete combustion of a certain fuel to its mass is called the calorific value of the fuel.

(2) Physical meaning

The calorific value is numerically equal to the heat released by the complete combustion of 1 kg of a certain fuel.

(3) Unit

International unit: joule per kilogram; symbol: J/kg.

The unit of gaseous fuel: joule per cubic meter; symbol: J/m3.

Calorific value unit: J/kg, (J/m3)

P139The calorific value of some fuels.

Charcoal: 3.4×107J/kg

Physical meaning: The heat released when 1 kilogram of charcoal is completely burned is 3.4×107J

Gas: 3.9×107J/m3

Physical meaning: The heat released when 1 cubic meter of gas is completely burned is 3.9×107J

According to the calorific value table, calculate how many joules of heat are released by the complete combustion of 10 tons of hydrogen?

The calorific value of hydrogen is 1.4×108 J/kg

Released heat Q = calorific value × mass = 1.4 × 108 J/kg × 10 × 103 kg = 1.4 × 1012 J

Calculate again, if dry firewood is completely burned to obtain these calories, how many tons of dry firewood will be needed?

The calorific value of dry firewood is 1.2×107 J/kg

2. Efficiency of heat engine

think about it

Can fuel be completely burned in an internal combustion engine? Where does the energy released by fuel combustion go?

1. The ratio of the part of energy used to do useful work to the energy released by complete combustion of the fuel is called the efficiency of the heat engine.

2. Improve thermal engine efficiency, save energy and reduce pollution

(1) The efficiency of the heat engine is an important indicator of the performance of the heat engine.

(2) Ways to improve efficiency

Improve fuel utilization and ensure full combustion of fuel;

Improve heat engines and reduce various energy losses;

Harness the energy of exhaust gas.

practice

1. Regarding the calorific value of fuel, which of the following statements is correctly understood ( )

A. The calorific value of a fuel is directly proportional to the heat released when the fuel burns

B． Fuel has no calorific value when it is not burned

C. For a certain fuel, its calorific value is a certain value, which has nothing to do with the quality of the fuel and the heat released by the combustion of the fuel.

D. Fuel that burns easily must have a high calorific value

2. It is known that the calorific value of dry firewood is 1.2×107 J/kg. How much heat can be released by complete combustion of 0.7 kg of dry firewood? Assuming that all the heat is absorbed by the water, how many kilograms of water can increase the temperature from 20 ℃ to 70 ℃? It is known that the specific heat capacity of water is 4.2×103 J/(kg·℃).

3. Regarding the efficiency of heat engines, which of the following statements is correct: ( )

A. The higher the efficiency of the heat engine, that is, the more useful work the heat engine does

B． The higher the efficiency of the heat engine, the greater the power of the heat engine

C. To improve the efficiency of thermal engines, it is necessary to minimize various energy losses and ensure good fluidity.

D. Improve the efficiency of heat engines, which is beneficial to environmental protection and emission reduction

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For more information about the PPT courseware "Utilization of Internal Energy and the Efficiency of Heat Engines", please click on the Utilization of Internal Energy ppt Efficiency of Heat Engines ppt tag.

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Update Time: 2024-11-20

This template belongs to Physics courseware People's Education Edition Ninth Grade Physics Complete Book industry PPT template

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