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The theory behind heat transfer
Plate heat exchangers

Inside view

Heat transfer theory

	 2	 Heat transfer theory

The natural laws of physics always
allow the driving energy in a system to
flow until equilibrium is reached. Heat
leaves the warmer body or the hottest
fluid, as long as there is a temperature
difference, and will be transferred to the
cold medium.

Heat transfer theory
Heat can be transferred by three
­ ethods.

A heat exchanger follows this principle
in its endeavour to reach equalisation.
With a plate type heat exchanger, the
heat penetrates the surface, which
separates the hot medium from the
cold one very easily. It is therefore
possible to heat or cool fluids or gases
which have minimal energy levels.
The theory of heat transfer from one
media to another, or from one fluid to
another, is determined by several basic

• Conduction – Energy is transferred
between solids or stationary fluids by
the movement of atoms or molecules.

•	 Heat will always be transferred from
a hot medium to a cold medium.

b) Forced convection, where the movement of the media depends entirely or
partly upon the results of an outside
influence. One example of this is a
pump causing movement in a fluid.


Heat exchangers
Heat transfer theory
Heat exchanger types

	 4	 Calculation method

Temperature program
Heat load
Logarithmic mean temperature
Thermal length
Flow rate
Pressure drop
Specific heat
Overall heat transfer coefficient
Calculation method
Construction materials
Pressure and temperature
Fouling and fouling factors

	 8	 Product range
	 9	 Applications

Heat exchanger selection
Heat exchanger selection
Heat exchanger selection

	 0	 Plate heat exchanger

Plate heat exchanger components
Brazed plate heat exchangers
Fusion-bonded plate heat

	 1	 Assembly
11		 Installation

•	 There must always be a temperature
difference between the media.

• Radiation – Energy is transferred by
electromag­ etic radiation. One example
is the heating of the earth by the sun.

• Convection – Energy is transferred by mixing part of a medium with
another part.
a) Natural convection, where the movement of the media depends entirely
upon density difference, and temperature differences are evened out.

•	 The heat lost by the hot medium is
equal to the amount of heat gained by
the cold medium, except for losses to
the surroundings.
Heat exchang...