Introduction:-
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Properties |
Unit |
Description |
Thermal conductivity /λ(lambda) |
W/m.K |
Thermal conductivity measures the ease with which heat can
travel through a material by conduction. The lower the figure, the better the
performance. |
Thermal resistance at 100mm |
K⋅m2/W |
Thermal Resistance is a figure that connects the Thermal
Conductivity of a material to its Width - providing a figure expressed in
resistance per unit area (m²K/W) A greater thickness means less heat flow and
so does a lower conductivity. Together these parameters form the thermal
resistance of the construction. A construction layer with a high Thermal
Resistance, is a good insulator; one with a low Thermal Resistance is a bad
insulator.The equation is Thermal Resistance (m²K/W) = Thickness (m) /
Conductivity (W/mK) |
Specific Heat Capacity |
J / (kg . K) |
The Specific Heat Capacity of a material is the amount of heat
needed to raise the temperature of 1kg of the material by 1K (or by 1oC) . A good insulator has a higher Specific Heat Capacity
because it takes time to absorb more heat before it actually heats up
(temperature rising) to transfer the heat. |
Thermal diffusivity |
m2/s |
Thermal Diffusivity measures the ability of a material to
conduct thermal energy relative to its ability to store thermal energy.
Thermal Diffusivity (mm2/s) = Thermal Conductivity / Density x Specific Heat
Capacity |
Embodied energy |
MJ/kg |
Embodied Carbon is usually considered as the amount of gases
released from usually fossil fuels and used to produce energy
expended between the extractions of raw material, via the manufacturing
process to the factory gates. |
Vapor permeable |
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Vapour Permeability is the extent to which a material permits
the passage of water through it. It is measured by the time rate of vapour
transmission through a unit area of flat material of unit thickness induced
by a unit vapour pressure difference between two specific surfaces, under
specified temperature and humidity conditions. |
Example:-
Pipe Insulation Thickness
Calculation |
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Tp |
Operating Temp. of fluid inside Pipe |
°C |
200 |
|
Dia. Of Pipe |
Mtr |
0.305 |
Rp |
Radius of Pipe |
Mtr |
0.152 |
N |
Length of Pipe |
Mtr |
|
Ti |
Max. Temp. allowed on the outside surface of insulation (
Typically 50 °C) |
°C |
50 |
k |
Thermal conductivity of Insulating material |
W/m.C |
0.035 |
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Q |
Total Heat transfer from pipe through insulating material |
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Fourier's equation for Heat conduction |
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Q = |
2πkN(Tp - Ti)/ In(Ri - Rp) |
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Q/N = |
Allowed Heat loss per Mtr of Pipe |
W/m |
80 |
|
(Tp - Ti) |
|
150 |
a |
In(Ri - Rp) = 2πk x (N/Q) x (Tp - Ti) |
|
0.413 |
Ri |
Radius of Insulation (Ri = Rp x ea ) |
Mtr |
0.230 |
|
Insulation Thickness = Ri - Rp |
Mtr |
0.078 |
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mm |
77.814 |
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