What type of heat transfer is carried out by the transfer of matter. Heat transfer - what is it? Types, methods, calculation of heat transfer
Heat exchange between two media occurs through a solid wall separating them or through the interface between them.
Heat can only transfer from a body with a higher temperature to a body with a lower temperature.
Heat exchange always proceeds in such a way that a decrease in the internal energy of some bodies is always accompanied by the same increase in the internal energy of other bodies participating in the heat exchange.
Thermal conductivity
Thermal conductivity is a type of heat transfer in which there is a direct transfer of energy from particles (molecules, atoms) of a more heated part of the body to particles of its less heated part.
Thermal conductivity is not accompanied by the transfer of matter! It should be remembered that during thermal conductivity the substance itself does not move along the body, only energy is transferred.
The thermal conductivity of different substances is different.
You can conduct the following experiment - take a glass of hot water and put spoons made of various materials (aluminum, cupronickel, steel, wood and plastic) in it. After 3 minutes, see if the spoons are heated equally? Analyze the result
The table shows that metals have the highest thermal conductivity, Moreover, different metals have different thermal conductivities.
Liquids have lower thermal conductivity than solids, and gases have lower thermal conductivity than liquids.
Let's consider an experiment with the thermal conductivity of liquids. If you put ice at the bottom of a barrel of water and heat the top layer of water with a boiler. Then the water at the surface will soon boil, but the ice below will not melt. This is explained by the fact that in liquids the molecules are located at greater distances from each other than in solids.
Hair, feathers, paper, cork and other porous bodies also have poor thermal conductivity. This is due to the fact that air is contained between the fibers of these substances. Vacuum (space freed from air) has the lowest thermal conductivity. This is explained by the fact that thermal conductivity is the transfer of energy from one part of the body to another, which occurs during the interaction of molecules or other particles. In a space where there are no particles, thermal conduction cannot occur.
Metals - solids - liquids - gases
Weakening of thermal conductivity
If there is a need to protect the body from cooling or heating, then substances with low thermal conductivity are used. So, the handles of the faucets on the radiator are made of plastic, and handles for pots are also made of a similar alloy. Houses are built from logs or porous bricks, which have poor thermal conductivity, which means they protect the premises from cooling.
Currently, in many regions, buildings have begun to be built on stilts. In this case, heat is transferred only by thermal conductivity from the foundation to the pile and further from the pile to the soil. Piles are made of durable solid material, and inside they are filled with kerosene. In summer, the pile conducts heat from top to bottom poorly, because the liquid has low thermal conductivity. In winter, the pile, due to convection of the liquid inside it, will, on the contrary, contribute to additional cooling of the soil.
on this topic "Types of heat transfer."
I-option.
№ 1. Which method of heat transfer is the heating of solids based on?
№ 2. What type of heat transfer is accompanied by the transfer of matter?
A. Thermal conductivity. B. Convection. B. Radiation.
№ 3. Which of the following substances has the highest thermal conductivity?
A. Fur. B. Tree. V. Steel.
№ 4. Which of the following substances has the lowest thermal conductivity?
A. Sawdust. B. Lead. B. Copper.
№ 5. In which pan will the liquid in it cool faster?
A. 1.
B. 2.
B. The liquid will cool faster if you put
ice on the side.
№ 6. Name a possible method of heat transfer between bodies separated by an airless
space.
A. Thermal conductivity. B. Convection. B. Radiation.
8th grade. Independent work
on this topic "Types of heat transfer."
Option II.
№ 1. In what way does heat transfer occur in liquids?
A. Thermal conductivity. B. Convection. B. Radiation.
№ 2. What types of heat transfer are not accompanied by the transfer of matter?
A. Convection and thermal conductivity. B. Radiation and convection. B. Thermal conductivity and radiation.
№ 3. Which of the following substances has the lowest thermal conductivity?
A. Air. B. Cast iron. B. Aluminum.
№ 4. Which of the following substances has good thermal conductivity?
A. Straw. B. Cotton wool. B. Iron.
№ 5. In which kettle will boiling water cool faster?
A. 1.
B. 2.
№ 6. In what cases can heat transfer occur by convection?
A. In the sand. B. In the air. V. In the stone.
№ 7. A metal handle will feel colder to the touch than a wooden door at temperatures...
№ 7. The metal handle and the wooden door will feel equally warm to the touch when
temperature...
A. above body temperature. B. below body temperature. B. equal to body temperature.
№ 8. In what direction does air move in the atmosphere on a hot summer day (see figure)?
A. ABCD .
B. ADCB .
№ 9. What happens to a body’s temperature if it absorbs as much energy as it emits?
№ 10. Which glass is more likely to remain intact when pouring boiling water?
A. 1.
B. 2.
№ 8. The upper part of the test tube with ice was placed in the flame. Will the ice melt at the bottom?
test tubes?
A. It will melt.
B. Will not melt.
№ 9. What happens to a body’s temperature if it absorbs more energy than it emits?
A. The body heats up. B. The body cools. B. Body temperature does not change.
№ 10. When comparing the thermal conductivity of metals, copper and steel were chosen for the experiment
rods to which buttons are attached with plasticine. Which rod has more
thermal conductivity?
A. Steel.
B. Copper.
8th grade. Independent work
on this topic "Types of heat transfer."
ANSWERS
1
2
3
4
5
6
7
8
9
10
I-option
Option II
Any 7 tasks – “3”
Any 8 tasks – “4”
Any 9 tasks – “5”
1. convection only;
2. thermal conductivity only;
3. radiation only
What is thermal motion?
1. ordered movement of a large number of molecules;
2. continuous random movement of a large number of molecules;
3. rectilinear movement of an individual molecule.
17. Which of the following is the definition of internal energy?
1. the energy that a body possesses as a result of its movement;
2. energy, which is determined by the position of interacting bodies or parts of the same body;
3. the energy of movement and interaction of particles that make up the body.
What physical quantities does the internal energy of a body depend on?
1. on the mass and speed of the body;
2. on height above the ground and speed;
3. on temperature and body weight.
In what state of matter does convection proceed faster (under the same conditions)?
1. in liquid;
2. in solid;
3. in gaseous form.
What kind of motion of molecules and atoms in the solid state is called thermal?
1. random movement of particles in all possible directions at different speeds;
2. random movement of particles in all possible directions with the same speeds at the same temperature;
3. ordered movement of particles with a speed proportional to temperature;
4. oscillatory movement of particles in different directions around certain equilibrium positions.
In which of the following cases is energy transferred to the body mainly by thermal conductivity?
1. from the heated Earth by the upper layer of the atmosphere;
2. a person warming himself by the fire;
3. from a hot iron to ironed linen;
4. a person warming up by running.
17. The basis of the structure of biological membranes is:
1. layer of proteins;
2. carbohydrates;
3. double layer of phospholipids;
4. amino acids;
5. DNA double helix.
18. For the occurrence of a transmembrane potential difference it is necessary and sufficient:
1. the presence of selective membrane permeability;
2. difference in ion concentrations on both sides of the membrane;
3. the presence of selective permeability and differences in ion concentrations on both sides of the membrane;
4. emergence of autowave processes;
5. increased permeability for ions.
Active transport of ions is carried out due to. . .
1. energy of hydrolysis of macroergic bonds of ATP;
2. processes of ion diffusion through membranes;
3. transfer of ions through the membrane with the participation of carrier molecules;
4. lateral diffusion of molecules in the membrane;
5. electrodiffusion of ions.
Nernst's equation for the resting potential shows that. . .
1. resting potential arises as a result of active transport;
2. the transfer of ions is determined by the unevenness of their distribution (concentration gradient) and the influence of the electric field (electric potential gradient);
3. the main role in the occurrence of the resting potential belongs to potassium ions;
4. membranes have selective permeability;
5. The coefficient of permeability of substances through the membrane is determined by their mobility.
Provided that the membrane is permeable only to potassium ions, the Goldman-Hodgkin-Katz equation is transformed into the equation. . .
1. Nernst for potassium ions;
2. Nernst for sodium ions;
3. Fika for diffusion of potassium ions.
22.What transmembrane redistribution of K⁺ and Na⁺ ions is characteristic of the initial moment of development of the action potential?
1. active penetration of K⁺ ions into the cell;
2. active penetration of Na⁺ ions into the cell;
3. active release of K⁺ ions from the cell;
4. active release of Na⁺ ions from the cell.
What is the sign of the potential difference between the inner and outer surfaces of cell membranes at rest?
1. positive;
2. negative;
3. the potential difference is zero.
What ions contribute to the creation of the resting potential of cell membranes?
1. Na⁺ and Cl - ions;
2. K⁺ ions
3. Ca 2+, K⁺ and Cl - ions;
4. K⁺, Na⁺ and Ca 2+ ions.
25. The presence of capacitive properties in biological membranes is confirmed by the fact that:
1. the current strength is ahead of the applied voltage in phase;
2. the current is out of phase with the applied voltage;
3. The current is in phase with the applied voltage.
26. Indicate the correct statements:
1) The diffusion of charged particles through a membrane obeys the Fick equation.
2) The diffusion of charged particles through the membrane obeys the Nernst equation;
3) The diffusion of uncharged particles through the membrane obeys the Nernst equation.
27. Indicate the correct statements:
1) The membrane permeability coefficient for potassium ions is higher than for sodium or chlorine ions when a resting potential is generated on the cell membrane.
2) When an action potential occurs, the permeability coefficient of the membrane for sodium ions has the highest value.
3) When an action potential occurs, the membrane permeability coefficient for chlorine ions has the highest value.
28. Indicate the correct statements:
1) The Goldman-Hodgkin-Katz equation describes the occurrence of only the resting potential, but not the action potential.
2) The Goldman-Hodgkin-Katz equation describes the occurrence of only the action potential, but not the resting potential.
3) The Goldman-Hodgkin-Katz equation describes the occurrence of a transmembrane potential difference across membranes both in the case of the generation of resting potentials and action potentials.
Let the ratio of the concentrations of potassium ions on opposite sides of the membrane be equal to 10 and the membrane is selectively permeable to potassium. The resulting transmembrane potential difference is 60 mV. What will be the potential difference if we replace potassium ions with calcium ions in the same concentrations and make the membrane selectively permeable to calcium?
30. At rest, the cell membrane:
1.impermeable to Na⁺ and K⁺ ions;
2. permeable to Na⁺ ions 25 times more than for K⁺ ions;
3. permeable to K⁺ ions 25 times more than for Na⁺ ions;
4.equally permeable to Na⁺ and K⁺ ions.
31. Na⁺ - K⁺ pump transfers:
1. 3 K⁺ outside, 2 Na⁺ inside the cell;
2. 3 Na⁺ inside the cell, 2 K⁺ outside;
3. 3 Na⁺ outside, 2 K⁺ inside the cell;
4. 3 K⁺ inside the cell, 2 Na⁺ outside.
32. The Fick equation describes:
1. passive transport;
2. transport of non-electrolytes;
3. ion transport;
4. active transport.
33. For the occurrence of a transmembrane potential difference, it is necessary and sufficient to fulfill the following two conditions:
1) the membrane must contain integral proteins;
2) the membrane must contain surface proteins;
3) there must be selective permeability of ions through the membrane;
4) the concentrations of ions on both sides of the membrane must be different;
1. Methods for studying membrane permeability:
A. Osmotic method
B. Calorimetric method
C. Indicator method
D. Electron microscopic method
E. Radioisotope method
F. Conductivity Measurement Method
2. The concept of transport includes:
A. The ability of the membrane to pass a given substance
B. Method of penetration of a substance through a membrane
C. Kinetics of substance penetration through the membrane
3. Transport carried out against the gradient with the expenditure of macroerg energy is called:
A. Active
B. Passive
C. Electrogenic
4. Active mode of transport differs from passive mode:
A. Direction relative to the concentration gradient
B. Energy use
C. Type of transferred ions
5. The transfer of two ions in opposite directions by an ion transport system is called:
A. Uniport
B. Simport
C. Antiport
6. Simple diffusion is:
7. Facilitated diffusion is:
A. The process of spontaneous penetration of a substance through a membrane along a concentration gradient
B. The process of spontaneous penetration of a substance through a membrane against a concentration gradient
C. The process of penetration of a substance through a membrane along a concentration gradient with the participation of a carrier protein
8. The kinetics of the process of diffusion of a substance through the cell membrane is described:
A. The Collender-Berlund equation
B. Fick's equation
C. Bernoulli's equation
9. The kinetics of the facilitated diffusion process is described by the equation:
B. Collender-Berlund
C. Michaelisa-Menten
10. Mechanisms of water penetration through the cell membrane:
A. Through pores formed by integral proteins
B. Through structural defects in the membrane - kinks
C. By dissolution in the lipid bilayer
11. Osmosis is the movement of water through a membrane:
12. Oncotic pressure is:
A. Osmotic pressure inside the cell
B. Protein-mediated component of osmotic pressure
C. Osmotic pressure in malignant tumor cells
13. Filtration is the movement of water through a membrane:
A. To an area of lower hydrostatic pressure
B. To an area of lower concentration of dissolved substances
C. To an area of higher concentration of dissolved substances
14. Cell membranes perform the following functions:
A. Compartmentation
B. Receptor
C. Transport
D. Conduction of nerve impulses
E. Muscle contraction
F. Intercellular interactions
15. The composition of biomembranes includes:
C. Glycoproteins
16. Membrane lipids are represented by the following classes:
A. Phospholipills
B. Glycoproteins
C. Glycolipids
D. Steroids
17. Lipid molecules are:
A. Hydrophobic compounds
B. Hydrophilic compounds
C. Amphiphilic compounds
18. Phase transitions in the membrane occur between the following states:
A. Gel – sol
B. Gel - liquid phase
C. Liquid crystal - gel
19. Based on their location in the membrane, proteins are divided into:
A. Peripheral
B. Integral
C. Enzymatic
D. Semi-integral
E. Monotopic
20. Membrane proteins make up the following functional groups (indicate the wrong answer):
A. Enzymatic
B. Cytoskeletal proteins
C. Contractiles
D. Receptors
21. Lipids can modify the structure of membrane proteins:
A. Secondary
B. Tertiary
C. Quaternary
22. A mosaic membrane model was proposed by:
A. Singer and Nicholson
B. Danieli and Devson
C. Warburg and Nigilein
D. Gorter and Grendel
23. Modern ideas about the structure of membranes correspond to:
A. Lipid bilayer model
B. Mosaic model
C. Unitary model
Heat transfer is a way of changing the internal energy of a body when transferring energy from one part of the body to another or from one body to another without doing work. There are the following types of heat transfer: thermal conductivity, convection and radiation.
Thermal conductivity
Thermal conductivity is the process of transferring energy from one body to another or from one part of a body to another due to the thermal movement of particles. It is important that during thermal conduction there is no movement of matter; energy is transferred from one body to another or from one part of the body to another.
Different substances have different thermal conductivities. If you put a piece of ice at the bottom of a test tube filled with water and place its upper end over the flame of an alcohol lamp, then after a while the water in the upper part of the test tube will boil, but the ice will not melt. Consequently, water, like all liquids, has poor thermal conductivity.
Gases have even poorer thermal conductivity. Let's take a test tube containing nothing but air, and place it over the flame of an alcohol lamp. A finger placed in a test tube will not feel any heat. Consequently, air and other gases have poor thermal conductivity.
Metals are good conductors of heat, while highly rarefied gases are the worst. This is explained by the peculiarities of their structure. Molecules of gases are located at distances from each other that are greater than molecules of solids, and collide much less frequently. Therefore, the transfer of energy from one molecules to others in gases does not occur as intensely as in solids. The thermal conductivity of a liquid is intermediate between the thermal conductivity of gases and solids.
Convection
As is known, gases and liquids conduct heat poorly. At the same time, the air is heated from steam heating batteries. This occurs due to a type of thermal conductivity called convection.
If a pinwheel made of paper is placed over a heat source, the pinwheel will begin to rotate. This happens because the heated, less dense layers of air rise upward under the action of the buoyant force, and the colder ones move down and take their place, which leads to the rotation of the turntable.
Convection- a type of heat transfer in which energy is transferred through layers of liquid or gas. Convection is associated with the transfer of matter, so it can only occur in liquids and gases; Convection does not occur in solids.
Radiation
The third type of heat transfer is radiation. If you bring your hand to the coil of an electric stove plugged in, to a burning light bulb, to a heated iron, to a radiator, etc., you can clearly feel the heat.
Experiments also show that black bodies absorb and emit energy well, while white or shiny bodies emit and absorb it poorly. They reflect energy well. Therefore, it is understandable why people wear light-colored clothes in the summer, and why they prefer to paint houses in the south white.
By radiation, energy is transferred from the Sun to the Earth. Since the space between the Sun and the Earth is a vacuum (the height of the Earth’s atmosphere is much less than the distance from it to the Sun), energy cannot be transferred either by convection or by thermal conduction. Thus, the transfer of energy by radiation does not require the presence of any medium; this heat transfer can also be carried out in a vacuum.
Lesson summary “Types of heat transfer: thermal conductivity, convection, radiation.”
SUBJECT : repetition of the topic “Types of heat transfer”
LESSON OBJECTIVES:
1. Review the material covered on the topic.
2. Check the knowledge acquired on the topic.
3. Learn, with the help of acquired knowledge, to explain various physical phenomena occurring in nature, everyday life and technology.
LESSON PLAN.
I. Organizational moment.
II. Repetition of covered material.
We have completed our study of the topic “Types of Heat Transfer”. We learned that heat transfer plays a huge role in nature, everyday life and technology, so a person needs to have a good understanding of this topic in order to correctly and profitably apply this knowledge in our daily lives. It is for this purpose that today we will once again talk about different types of heat transfer.
Let's first review the basic concepts of the topic.
(LAUNCH PRESENTATION)
Let's Remember (students can use the workbook to answer questions about basic concepts)
1. What is heat transfer? (questions are duplicated on the screen using a presentation).
2. What types of heat transfer do you know?
3. What is thermal conductivity?
4. Is thermal conductivity the same for different bodies?
5. Which bodies have the largest?
6. What has the lowest thermal conductivity?
7. Where is thermal conduction not possible? Why?
8. What is convection?
9. What is radiation?
III.Well, now let’s try to answer questions related to the manifestations of different types of thermal conductivity in nature, everyday life and technology.
1. Hot tea is poured into a cup. What type of heat transfer occurs between the tea and the walls of the cup?
2. Why do we burn our lips when we drink hot tea from a metal mug, but not when we drink from a porcelain mug?
3. Why are vents placed at the top of the window?
4. Two identical sized kettles were filled with water and the water was heated to a boil. Which kettle will cool the water faster, white or black?
5. Why the expression “a fur coat keeps you warm”
isn't it right?
IV.We thoroughly repeated the theme "Types of heat transfer." Now let's check how well you have mastered the material. To do this, you will answer the test questions.
TEST.
1. How is energy transferred from the Sun to the Earth?
a) thermal conductivity; b) radiation;
c) convection; d) work.
a) so that they are not damaged; b) so that they do not interfere; c) so that the water in them does not freeze;
d) so that sunlight does not fall on them.
3. In which direction does the wind blow on a hot summer day at the seashore?
a) from sea to land; b) from land to sea;
c) from west to east d) from east to west.
4.What types of heat transfer are taken into account when creating a thermos?
a) thermal conductivity and radiation; b) radiation and convection;
c) thermal conductivity; d) convection.
5. Why is the basement the coldest place in the house?
a) because it’s dark there; b) because it is close to the ground; c) warm air does not penetrate there;
d) cold air falls there due to convection.
6.Why is the frost worse on clear winter nights than on cloudy days?
a) because it is dark at night; b) because clouds transfer their energy to the earth; c) in cloudless weather, energy is more easily radiated into space and the earth cools faster;
d) there is no correct answer.
7.What type of heat transfer is accompanied by the transfer of matter?
a) thermal conductivity; b) radiation;
c) thermal conductivity and radiation; d) convection.
8.Why are heating radiators usually placed under windows?
a) to make it easier to wash them;
b) so that the cold air from the window falls down and, when heated, rises;
c) to fill the space under the windowsill;
d) there are no correct answers.
9. How is food heated in a microwave oven?
a) radiation; b) work; c) thermal conductivity; d) convection;
10. Which of the following substances has the lowest thermal conductivity?
a) silver; b) air; c) water; d) tree.
V.Peer review of the test.
ANSWERS TO THE TEST
EVALUATION OF ANSWER.
Correct Answers Score
less than 5 rating is not given
VI.Summing up the lesson.
