Efficiency of heat engines presentation. Presentation "efficiency of heat engines"

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Block diagram of a heat engine

Heater Working fluid (gas) Refrigerator Q1 (heat) Q2 (heat) A’=Q1-Q2 (work)

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A physical quantity showing what proportion of the work performed by the engine is from the energy obtained during fuel combustion is called the efficiency factor of a thermal engine  = (A / Q) 100%

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Heat engine efficiency

 = A p/ Az  = Qp/ Qz  = Np/ Nz ALWAYS! 00% Why?  = (A / Q) 100%

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Characteristics of heat engines

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The use of heat engines and environmental problems

When burning fuel in heat engines, a large amount of oxygen is required. The combustion of various fuels consumes from 10 to 25% of the oxygen produced by green plants. Heat engines not only burn oxygen, but also emit equivalent amounts of carbon dioxide (carbon dioxide) into the atmosphere. Combustion of fuel in the furnaces of industrial enterprises and thermal power plants is almost never complete, therefore air pollution occurs with ash and soot flakes. Now all over the world, conventional power plants annually emit 200–250 million tons of ash and about 60 million tons of sulfur dioxide into the atmosphere. In addition to industry, transport also pollutes the air, primarily automobiles (residents of large cities are suffocating from the exhaust fumes of automobile engines).

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Where do you think most of the internal energy of heat engines is spent???? Are heat engines safe from an environmental point of view? You are right and this is clearly seen from the following data:

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– 1 ton of gasoline, when burned, emits 500–800 kilograms of harmful substances; – 5 billion tons of CO2 are emitted into the atmosphere annually; – one jet airliner consumes 45 tons of oxygen during a 5-hour flight; - over the past 25 years, the amount of carbon dioxide in the atmosphere has increased by 345 billion tons. - exhaust gases include 1200 components, including carbon monoxide, nitrogen oxides, hydrocarbons, aldehydes, metal oxides (the most harmful is lead oxide), soot, etc.

Ecological problems

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1. When solving the problem, one of the students received the answer that the efficiency of a heat engine is 200%. Did the student solve the problem correctly? Qualitative tasks: 2. The efficiency of the heat engine is 45%. What does this number mean? 3. Can the efficiency of a heat engine be equal to 1.8; 50; 4; 90; 100%?

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A challenge for biology lovers

There are about 600 muscles in the human body. If all the muscles of a person were tense, they would produce a force equal to approximately 25 tons. It is believed that under normal working conditions a person can develop a power of 70 - 80 W, but instantaneous energy release is possible in sports such as shot put or high jump . Observations have shown that when jumping high with simultaneous push-off with both legs, some men develop an average power of about 3700 W within 0.1 s, and women - 2600 W. The efficiency of human muscles is 20%. What does it mean? How much energy do muscles waste?

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1. A heat engine receives energy equal to 1000 J from the heater per cycle and transfers energy of 800 J to the refrigerator. What is the efficiency of a heat engine? 2. A heat engine receives energy equal to 1000 J from the heater per cycle and transfers energy of 700 J to the refrigerator. What is the efficiency of a heat engine?

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Carbon dioxide released during the operation of heat engines absorbs infrared radiation from the Earth's surface, which leads to an increase in atmospheric temperature by 0.05 degrees Celsius annually. This effect could create a threat of melting glaciers and a catastrophic rise in sea levels. Currently, about 5 billion tons of CO2 are emitted into the atmosphere annually. Environmental issues

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When heat engines operate, substances harmful to plants, animals and humans are continuously released into the atmosphere: nitrogen oxides, hydrocarbons, carbon monoxide. Oxygen consumption during fuel combustion reduces its content in the atmosphere. Nuclear power plants face the problem of disposing of hazardous radioactive waste. The use of steam turbines in power plants requires large areas for ponds to cool the exhaust steam. In our country, 200 km3 of water is required for this purpose.

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Nature conservation measures 1. Increasing the efficiency of treatment facilities. 2. Operation of vehicles with complete combustion of fuel in the internal combustion engine and minimal CO2 emissions into the atmosphere. 3. The use of fuel from a mixture of oxygen and hydrogen. 4. Construction of power plant complexes, primarily nuclear, with a closed water supply cycle.

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Jacques Yves Cousteau: “Nature used to frighten man, but now man frightens nature.”

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1. Does a simple mechanism give a benefit in work? Justify the answer. 2. Contents of the “Golden Rule” of mechanics. 3. What is the relationship between the paths traveled by the points of application of forces on the lever and these forces? 4.What are simple mechanisms used for? 5. In what way do they lose when using a lever that gives a gain in strength? Repetition:

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6. How many times do they lose on the way, using a movable block to lift loads? 7. Specify the formulas for calculation: Power A = F*S Work V = S / t Speed ​​P = F / S Density p = m / v Pressure N = A / t

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Study plan for the topic: “Efficiency of mechanisms.”

1.What are simple mechanisms used for? 2. The concept of useful and complete work and their comparison. 3. The concept of mechanism efficiency, its comparison with 100%. 4.Ways to increase efficiency.

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Simple mechanisms are used for...

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The concept of useful and complete work. The loader pours apples for processing into juice from the baskets into the back of the car. A full job is loading apples. It consists of lifting the apples themselves and lifting the baskets. The work of lifting the apples themselves is useful, but lifting the baskets is useless, because they need to be lowered or thrown down.

Yes. The energy of the burnt gunpowder is converted into the mechanical energy of the projectile. 4. Can the human body be classified as a heat engine? Yes 5. Why are internal combustion engines not used in submarines for scuba diving? Under water, for the operation of an internal combustion engine, air is needed, but there is none there, or it is necessary to take liquefied air, but this is unprofitable and complicates the process. 6. Does the temperature of the steam in the turbine change? Yes, it is decreasing. 7. Are all heat engines equally cost-effective? No, not all, there are more economical ones, for example a diesel engine.

Work on lifting a load using an inclined plane, height h and length ℓ.

F Useful work A p = F *h = m *q *h But at the same time we overcome the force of friction, the force of gravity of other devices, and do additional work. The work expended is greater than the useful work Az > A p. Useful work is only a part of the total work.

To characterize the efficiency of a heat engine in converting internal energy into mechanical energy, the coefficient of performance (COP) of the heat engine is introduced. It is denoted by the letter η

The characteristic of the mechanism that determines what proportion of the useful work is the total work is called efficiency.

A n Az 100% Can the efficiency be equal to 100%, > 100%? Justify the answer. How to increase efficiency? Reduce the mass of moving parts, reduce friction in parts. Efficiency =

Coefficient (from Latin coefficientis) is usually a constant or known value - a multiplier for a variable or known value.

Solving problems for calculating efficiency.

Determine the efficiency of devices and mechanisms in the following situations: 1. The barrel is rolled along an inclined platform, applying a force of 240 N. The mass of the barrel is 100 kg, the length of the platform is 5 m, the height of the platform is 1 m. 2. A bucket of sand weighing 200 N is lifted using a stationary block to a height of 10 m, acting on a rope with a force of 250 N.

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Simple mechanisms Mechanism - from the Greek word - tool, structure. Machine - from the Latin word machina - structure. Block - from the English word block - part of a lifting mechanism in the form of a wheel with a groove around its circumference. Devices used to convert force are called simple mechanisms

Simple mechanisms An inclined plane is used to move heavy objects to a higher level without lifting them directly. ramps, escalators, ordinary stairs, conveyors. If you need to lift a load to a height, it is always easier to use a gentle slope than a steep one: the steeper the slope, the easier it is to do this job.

Arm of force The shortest distance between the fulcrum and the straight line along which the force acts on the lever is called the arm of force Arm of force F 2 Arm of force F 1 Arm of force F 2 To find the arm of force, from the fulcrum, lower a perpendicular to the line of action of the force Support point Line of action forces Perpendicular

Conditions for equilibrium of a lever A lever is in equilibrium when the forces acting on it are inversely proportional to the arms of these forces l 2 = 2 F 2 = 3 l 1 = 3 F 1 = 2 This rule was established by Archimedes. According to legend, he exclaimed: “Give me a point of support and I will lift the Earth.”

Conditions for the equilibrium of a lever Equilibrium of a rigid body under the action of three forces. For a non-rotating body to be in equilibrium, it is necessary that the resultant of all forces applied to the body be equal to zero. When calculating the resultant, all forces are reduced to one point C

Applying the balance of a lever to a block Fixed block M = F2r = P2r does not give a gain in work serves only to change the direction of the force Movable block M = F r = Pr/2 F = P/2 gives a gain in force by 2 times Fixed block with during operation, does not change the position of the rotation axis. The moving block moves during operation. Arm of force l = 2r Arm of force l = r

By combining a certain number of movable and stationary blocks, you can get a significant gain in force. Fixed block. Movable block. Gain in force by 2 times. Fixed blocks. Movable blocks. Gain in force by 4 times. If there is a simple pulley combination of a group of movable and fixed blocks, then the gain in traction force is even, and in more complex designs arbitrary

Efficiency of a mechanism One or another mechanism is ultimately needed to perform work. Useful work A p is the work we need. The work spent on lifting always turns out to be more useful Work to overcome the force of gravity: A = mgh When lifting a load, we overcome the force of gravity of the rope, the force of friction, the force of gravity of other devices. The characteristic of the mechanism, which determines what proportion of useful work makes up the total work, is called the efficiency factor

A selection of tasks on kinematics (from the tasks of the State Academy of Sciences). Let's consider the tasks:

GIA Which of the simple mechanisms can give a greater gain in operation: a lever, an inclined plane or a movable block? 1) lever 2) inclined plane 3) movable block 4) not a single simple mechanism gives a gain in work

The GIA Lever gives a gain of 5 times in strength. What is the gain or loss in distance? 1. winning 5 times 2. neither winning nor losing 3. losing 5 times 4. winning or losing depending on the speed of movement

Unified State Exam-2002 A3. The lever is acted upon by two forces, the arms of which are equal to 0.1 m and 0.3 m. The force acting on the short arm is equal to 3 N. What should the force acting on the long arm be equal to for the lever to be in equilibrium? 1.1 N 2.6 N 3.9 N 4.12 N F 1 d 1 = F 2 d 2 3 N 0.1 m = F 2 0.3 m

Unified State Exam 2003 A4. The figure shows a thin weightless rod to which forces F 1 = 100 N and F 2 = 300 N are applied at points 1 and 3. At what point should the axis of rotation be located for the rod to be in equilibrium? The axis of rotation is fixed

2005 A4 (DEMO). The load A of the well crane (see figure) balances the weight of the bucket, equal to 100 N. (Consider the lever weightless.) The weight of the load is 1.20 N 2.25 N N N

2008 A5 (DEMO). When performing laboratory work, the student set an inclined plane at an angle of 60 to the table surface. The length of the plane is 0.6 m. The moment of gravity of a block of mass 0.1 kg relative to point O when it passes the middle of the inclined plane is 1.0.15 N m 2.0.30 N m 3.0.45 N m 4.0.60 N m

Literature 1.Gutnik, E.M., Physics. 7th grade. Textbook for secondary schools / E. M. Gutnik, A. V. Peryshkin. - M.: Bustard, – 302 p. 2.Zorin, N.I. GIA Physics. Training tasks: 9th grade / N.I. Zorin. – M.: Eksmo, – 112 p. – (State (final) certification (in a new form). 3. Kabardin, O.F. Physics. 9th grade: a collection of test tasks to prepare for the final certification for the primary school course / O.F. Kabardin. – M.: Bustard, - 219 pp.; 4. Inclined plane. Cool physics for the curious. /[Electronic resource]// 5. Cool physics for the curious./[Electronic resource]// Power. Physics /[Electronic resource]// html html 7. Units of work / Unified collection of digital educational resources / [Electronic resource] / 95ff c9a66/5_1. Federal Institute of Pedagogical Measurements (KIM) Physics GIA / /[Electronic resource]// Federal Institute of Pedagogical Measurements (KIM) Physics Unified State Examination //[Electronic resource]//