13.1 Insulating Material Properties, Types and Thickness calculation

 

Introduction:-

 Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials.

 Properties of Thermal Insulating material:-

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		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.

Pipe Insulation Thickness Calculation

Example:-

Pipe Insulation Thickness Calculation
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
Q	Total Heat transfer from pipe through insulating material
	Fourier's equation for Heat conduction
Q =	2πkN(Tp - Ti)/ In(Ri - Rp)
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
		mm	77.814