Chemistry

Mass and heat transport

Mass and heat transport



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Construction of the energy-saving house

The energy-saving house was developed to study the processes of heat and energy transfer and to demonstrate the possibilities of remote control. The incident sunlight is converted into electricity and heat by means of a solar cell and solar collector. Various consumers are operated with the electricity and the heat circuit heats the interior of the house. Now make yourself familiar with the structure of the energy-saving house.

All temperature and energy flows in the house can be monitored and controlled with the help of a browser. At the same time, the application demonstrates the principle of remote control and remote monitoring.


1 666714 8 Cartridge burner DIN version />
1 666715 8 Gas cartridge />
Tripod material
  • Email: [email protected]
  • Tel .: 02233/604 430
    Mon-Thu 7:45 a.m. - 12:00 p.m. and 12:30 p.m. - 3:00 p.m.
    Fri. 7:45 a.m.-12: 00 p.m. and 12:30 p.m.-2: 30 p.m.

Online service portal
Do you have any questions or suggestions about our devices, products, tests or equipment or our software? Do you need spare parts? FORM

Repair service
Would you like to register a repair? FORM


Direction of heat conduction

Heat conduction takes place in a body only when areas of different temperatures are present. The heat is always transferred from areas of higher temperature to areas of lower temperature (Fig. 2). If a body is left to its own devices, the temperature will gradually equalize. The heat transferred through a body depends on

  • of the substance of which the body is made,
  • from the cross-sectional area of ​​the body,
  • on the temperature difference,
  • the length of the body,
  • from the time.

Objectives: enumerate and name phase transitions, explain and calculate phase transitions,
Explain the triple point and critical point using a phase diagram.

There are 6 transition phases + plasma.

What are physical states?

States of aggregation are the states of a substance. [In PowerPoint: aggregare (Latin): to accumulate]
Which physical state is present depends on the properties of the substance, the temperature, the volume and the ambient pressure. A phase diagram is used to represent temperature and pressure. With a p-V-T, the pressure, volume and temperature. The triple point is the point at which all three phases are in equilibrium. At the critical point, the visible separation between the liquid and gaseous phases disappears because their densities are the same here.

How do you differentiate between the states?

Fixed: highest density (the particles occupy fixed positions, the particles are very close to one another, there are strong forces of attraction between the particles, the particles move slightly (little)), retains shape and volume, difficult to deform, difficult to split, difficult to compress ( reduce without loss of material), solid (symbol: s). Particles are arranged.

Fluid: adapts to its surroundings, easily deformable, easily divisible, difficult to compress, the particles do not occupy fixed positions, they can move against each other, the particles lie close to each other, the distances between the particles are greater than in a solid, the forces of attraction between the Particles are weaker than in a solid. Particles change their arrangement constantly due to the movement, liquid (symbol: l).

Gaseous: takes up all available space, easily compressible, large distances between the particles, the particles are free to move, they move with great speed, the distances between the particles are very large, the forces of attraction between the particles are low. No arrangement due to the movement of the particles, gaseous (symbol: g).

The following transitions are possible through the supply of heat (heating):

  • evaporate (transition from liquid to gaseous)
  • melt (transition from solid to liquid)
  • sublimate (transition from solid to gaseous).

The following transitions are possible through heat extraction (cooling):

  • condense (transition from gaseous to liquid)
  • solidify (transition from liquid to solid)
  • resublimate (transition from gaseous to solid).

Melt

When atoms protrude sufficient kinetic energy through the supply of heat, the bond between the atoms is broken. The substance melts because the atoms are no longer bound to the crystal lattice. The temperature as well as the amount of heat depend on the substance. The heat of fusion (or enthalpy of fusion) is the amount of heat required to melt a substance.
(e.g. melting ice)

Freeze

A substance solidifies when the substance reaches its freezing point. At its solidification temperature, a substance changes from the liquid to the solid state of aggregation. This gives off heat. Melting temperature and solidification temperature are the same.

Change in volume during melting and solidification

Most substances expand when they melt and contract when they solidify. Water expands when it solidifies and contracts when it melts.

Evaporation

Evaporation occurs when an atom or molecule overcomes the binding force. This happens when:

  • the kinetic energy due to collisions is not evenly distributed - & gt evaporation,
  • Heat energy is supplied. The particles move faster and overcome the interaction & # 8211 & gt boil.

The temperature (boiling point) & the amount of heat are dependent on the substance as well as the pressure. The heat of vaporization (or enthalpy of vaporization) is the amount of heat required to vaporize a substance.

A liquid evaporates until it reaches the saturation vapor pressure (= the same number of molecules evaporate as they condense back in the liquid). The saturation vapor depends on the substance and the temperature. The boiling point is the temperature at which the vapor pressure equals the ambient pressure. The boiling point depends on the pressure.

Condense

A substance changes from the gaseous to the liquid state of aggregation at its condensation temperature. In doing so, heat has to be withdrawn from him. The boiling temperature and condensation temperature are the same.

Volume change during evaporation and liquefaction:

The substances expand when they evaporate and contract when they liquefy.

Sublimation

When a low pressure and a high temperature arise, the phase transition from the solid to the gaseous state can occur. Sublimation is the amount of energy required to completely break the bond in the solid. Sublimation is the transition from a solid to a gaseous state without the substance becoming liquid beforehand. On frosty days, a layer of ice slowly recedes on roads and after a few days the road is dry. This is also an example of sublimation.

Resublimation (deposition)

Resublimation is the transition from the gaseous to the solid state without the substance becoming liquid beforehand (e.g. ripe)

Liquids and solids

cohesion: The bonding force between particles of the same substance. (e.g. surface tension)

adhesion: The binding force between particles from the other substance (e.g. capillarity)

There are phase transitions between the states of aggregation, which take place when heat is absorbed or released. The temperature of the substance does not change in the process. (This heat is called latent heat). The applied heat is used to break the attractive force between the particles. When the bond is created, the energy is released as heat.


Calculation of the heat transferred

Under the condition that the heat conduction takes place in a substance and that there is a constant temperature difference between two areas (Fig. 2), the calculation of the transferred heat can be done with the following equation:

Q = λ ⋅ A ⋅ t ⋅ Δ ϑ l Q heat transferred through the substance λ thermal conductivity of the substance A cross-sectional area t time of heat conduction l length Δ ϑ temperature difference

The thermal conductivity is a material constant. Depending on the value of these material constants, a distinction is made between good heat conductors and bad heat conductors.

All metals, especially silver, copper, gold and aluminum, are good heat conductors. Almost all plastics, wood, water, glass and, above all, air are poor heat conductors. That is why materials are used as insulation materials in which a lot of air is trapped (e.g. styrofoam, glass wool). The poor thermal conductivity of water can be demonstrated in a simple experiment (Fig. 3). Water is filled into a test tube. The upper part of the test tube is held over a flame. After a short time, the water begins to boil at the point in question. Due to the poor thermal conductivity of the water, you only feel a slight warming on your fingers.


Momentum, mass and heat transport through the interface of spherical particles †

Lecture at the 10th Tutzing Symposium of D ECHEMA, “Interface phenomena between two fluid phases” ︁, from March 12th to 15th, 1973.

Abstract

The steady mass and heat transport is characterized by the transition from creeping flow to boundary layer flow as the Reynolds number increases. In the case of solid balls, the vortex movement in the separation area also creates a boundary layer character on the back of the ball. The mass transfer equation communicated agrees well with the measured values. It also takes into account the influence of the degree of turbulence in the external flow, which considerably increases the mass transfer. When the air flows around spherical bubbles, the conditions for the mass transfer are completely different. As the Reynolds number increases, the laws for potential flow are approached. The laws communicated only apply to spherical bubbles. Above its validity limit, which was specified, the bubble loses its spherical shape and experiences stochastic changes in shape. The unsteady mass transport through the boundary surface of a sphere, taking into account a stationary convective component, is discussed using an example. For very short and for very long times, the convective part loses its importance for transient transport.


Chemical bond experiment

Pupils should examine three unknown substances and assign one substance each to a chemical bond (metal bond, ionic bond and atomic bond).

For this purpose, three investigations of the material properties (conductivity, solubility, increase in conductivity in water) are carried out in the student experiment. The results are recorded in a table and evaluated.

Chemistry members have experimental instructions including a table for recording (one A4 page), a compact version (two tasks on one A4 page, recording in the chemistry notebook), a solution expectation and an information sheet for chemistry teachers in the formats Word, Writer and PDF available as a master copy.

Please log in to see the download links (chemistry membership).

Keywords: iron filings (Fe), table salt, sodium chloride, NaCl, sugar

Friedrich Saurer 23:01 at the March 25, 2017 permalink | Login to write a comment Tags: teacher lecture (20), thermodynamics (10), heat conduction (2), heat transport (3), heat transfer (4)


a) The transport of energy from the heating plate via the saucepan to the liquid in it is primarily effected by conduction. Both the plate and the saucepan are made of metal. Metals are very good conductors of heat. Energy is transported within the liquid mainly by convection.

b) The base of the saucepan and hotplate should be level in order to avoid good heat-insulating "air cushions". It is ideal if the base and hotplate have the same diameter. If the diameter of the hotplate is larger than that of the pot, unnecessary energy is transferred from the hotplate to the air in the room.

c) When the saucepan is covered, the escape of heated air is partially prevented. The rising water vapor condenses on the lid. In this way, the condensation energy benefits the cooking process.

d) The use of bare metal pots reduces the losses due to heat radiation.


1 666714 8 Cartridge burner DIN version />
1 666715 8 Gas cartridge />
Tripod material
  • Email: [email protected]
  • Tel .: 02233/604 430
    Mon-Thu 7:45 a.m. - 12:00 p.m. and 12:30 p.m. - 3:00 p.m.
    Fri. 7:45 a.m.-12: 00 p.m. and 12:30 p.m.-2: 30 p.m.

Online service portal
Do you have any questions or suggestions about our devices, products, tests or equipment or our software? Do you need spare parts? FORM

Repair service
Would you like to register a repair? FORM


Objectives: enumerate and name phase transitions, explain and calculate phase transitions,
Explain the triple point and critical point using a phase diagram.

There are 6 transition phases + plasma.

What are physical states?

States of aggregation are the states of a substance. [In PowerPoint: aggregare (Latin): to accumulate]
Which physical state is present depends on the properties of the substance, the temperature, the volume and the ambient pressure. A phase diagram is used to represent temperature and pressure. With a p-V-T, the pressure, volume and temperature. The triple point is the point at which all three phases are in equilibrium. At the critical point, the visible separation between the liquid and gaseous phases disappears because their densities are the same here.

How do you differentiate between the states?

Fixed: Highest density (the particles occupy fixed positions, the particles are very close to each other, there are strong forces of attraction between the particles, the particles move slightly (little)), retains shape and volume, difficult to deform, difficult to divide, difficult to compress ( reduce without loss of material), solid (symbol: s). Particles are arranged.

Fluid: adapts to its surroundings, easily deformable, easily divisible, difficult to compress, the particles do not occupy fixed positions, they can move against each other, the particles lie close to each other, the distances between the particles are greater than in a solid, the forces of attraction between the Particles are weaker than in a solid. Particles change their arrangement constantly due to the movement, liquid (symbol: l).

Gaseous: takes up all available space, easily compressible, large distances between the particles, the particles are free to move, they move with great speed, the distances between the particles are very large, the forces of attraction between the particles are low. No arrangement due to the movement of the particles, gaseous (symbol: g).

The following transitions are possible through the supply of heat (heating):

  • evaporate (transition from liquid to gaseous)
  • melt (transition from solid to liquid)
  • sublimate (transition from solid to gaseous).

The following transitions are possible through heat extraction (cooling):

  • condense (transition from gaseous to liquid)
  • solidify (transition from liquid to solid)
  • resublimate (transition from gaseous to solid).

Melt

When atoms protrude sufficient kinetic energy through the supply of heat, the bond between the atoms breaks. The substance melts because the atoms are no longer bound to the crystal lattice. The temperature as well as the amount of heat depend on the substance. The heat of fusion (or enthalpy of fusion) is the amount of heat required to melt a substance.
(e.g. melting ice)

Freeze

A substance solidifies when the substance reaches its freezing point. At its solidification temperature, a substance changes from the liquid to the solid state of aggregation. This gives off heat. Melting temperature and solidification temperature are the same.

Change in volume during melting and solidification

Most substances expand when they melt and contract when they solidify. Water expands when it solidifies and contracts when it melts.

Evaporation

Evaporation occurs when an atom or molecule overcomes the binding force. This happens when:

  • the kinetic energy due to collisions is not evenly distributed - & gt evaporation,
  • Heat energy is supplied. The particles move faster and overcome the interaction & # 8211 & gt boil.

The temperature (boiling point) & the amount of heat are dependent on the substance as well as the pressure. The heat of vaporization (or enthalpy of vaporization) is the amount of heat required to vaporize a substance.

A liquid evaporates until it reaches the saturation vapor pressure (= the same number of molecules evaporate as they condense back in the liquid). The saturation vapor depends on the substance and the temperature. The boiling point is the temperature at which the vapor pressure equals the ambient pressure. The boiling point depends on the pressure.

Condense

A substance changes from the gaseous to the liquid state of aggregation at its condensation temperature. In doing so, heat has to be withdrawn from him. The boiling temperature and condensation temperature are the same.

Volume change during evaporation and liquefaction:

The substances expand when they evaporate and contract when they liquefy.

Sublimation

When a low pressure and a high temperature arise, the phase transition from the solid to the gaseous state can occur. Sublimation is the amount of energy required to completely break the bond in the solid. Sublimation is the transition from a solid to a gaseous state without the substance becoming liquid beforehand. On frosty days, a layer of ice on roads slowly recedes and after a few days the road is dry. This is also an example of sublimation.

Resublimation (deposition)

Resublimation is the transition from the gaseous to the solid state without the substance becoming liquid beforehand (e.g. ripe)

Liquids and solids

cohesion: The bonding force between particles of the same substance. (e.g. surface tension)

adhesion: The binding force between particles from the other substance (e.g. capillarity)

There are phase transitions between the states of aggregation, which take place when heat is absorbed or released. The temperature of the substance does not change in the process. (This heat is called latent heat). The applied heat is used to break the attractive force between the particles. When the bond is created, the energy is released as heat.


Direction of heat conduction

Heat conduction takes place in a body only when areas of different temperatures are present. The heat is always transferred from areas of higher temperature to areas of lower temperature (Fig. 2). If a body is left to its own devices, the temperature will gradually equalize. The heat transferred through a body depends on

  • of the substance of which the body is made,
  • from the cross-sectional area of ​​the body,
  • on the temperature difference,
  • the length of the body,
  • from the time.


Video: Overall Heat Transfer Coefficient - - Heat u0026 Mass Transfer in Tamil (August 2022).