Basic of conduction, Conduction through a slab, Conduction of heat transfer through Hollow Cylinder

1. Presentation
On
Applied Thermal &
Hydraulic Engineering
Submitted by:
Gohel Vishal (140123109003) / Electrical Engg. / B-3
Submitted To:
Aditya singh
(2140907)
GA N D H IN A GA R IN STITU TE OF
TEC H N OLOGY

2. Basic of conduction
Conduction through a slab
Conduction of heat transfer through
Hollow Cylinder
FLOW OF PRESETATION

3. BASIC OF CONDUCTION

4.  In the simplest of terms, the discipline of heat transfer is concerned
with only two things
1. Temperature
– Temperature represents the amount of thermal energy
available
2. Flow of heat
– whereas heat flow represents the movement of thermal
energy from place to place.
 On a microscopic scale, thermal energy is related to the kinetic
energy of molecules.
 The greater a material's temperature, the greater the thermal
agitation of its constituent molecules
BASIC OF CONDUCTION

5. Heat Transfer Mechanisms
Conduction
– Regions with greater molecular kinetic energy will pass
their thermal energy to regions with less molecular energy
through direct molecular collisions, a process known as
conduction
Convection
Convection is the movement of a physical quantity (for
example heat) because of the movement of the matter.

6. • Radiation
• All materials radiate thermal energy in amounts
determined by their temperature, where the
energy is carried by photons of light in the
infrared and visible portions of the
electromagnetic spectrum.
• When temperatures are uniform, the radioactive
flux between objects is in equilibrium and no net
thermal energy is exchanged.
• The balance is upset when temperatures are not
uniform, and thermal energy is transported from
surfaces of higher to surfaces of lower
temperature.

7. • If a slab of material, as shown in Fig. 5.1, has two faces at different
temperatures T1 and T2 heat will flow from the face at the higher
temperature T1 to the other face at the lower temperature T2.
» Figure 5.1. Heat conduction through a slab
Conduction through a slab

8. • The rate of heat transfer is given by Fourier's equation:
• dQ/dt = kA DT/Dx = kA dT/dx
• Under steady temperature conditions dQ/dt =
constant, which may be called q: and so q = kA dT/dx
• but dT/dx, the rate of change of temperature per unit
length of path, is given by (T1 - T2)/x where x is the
thickness of the slab,
• so q = kA(T1 - T2)/x
• or q = kA DT/x = (k/x) A
DT (5.2)
• This may be regarded as the basic equation for simple
heat conduction. It can be used to calculate the rate of
heat transfer through a uniform wall if the temperature
difference across it and the thermal conductivity of the
wall material are known.

9. Conduction of heat transfer through
hollow cylinder
• For radial geometry of a
hollow cylinder,
following equation
expresses the heat
transfer rate.
• N = length of the hollow cylinder
• T1 and T2 are inner and outer wall temperature of the
hollow