Insulators-ceramics-refractory and abrasive material, Mechanical Engineering

Insulators

Thermal insulators are essential in industrial practices, domestic and equipment appliances. That type of materials is basically those that do not have free electrons in their structure and heat conduction in only because of lattice vibration in form of elastic waves. Those elastic vibrations are affected via impurity atoms and defects like grain boundaries, dislocations and vacancies. The interference among elastic waves and defects causes also anisotropy of heat conductivity. This is easy to know that in crystalline materials the interference will reduce along with decreasing temperature along with consequent increase in thermal conductivity as in figure of Schematic Variation of Thermal Conductivity. Such interferences do not exist in amorphous materials like plastics and glasses and their thermal conductivity therefore, increases with increasing temperature. Following figure of Thermal Conductivity as Functions of Temperature shows variation of thermal conductivity of some solids utilized at high temperatures. The normal insulating materials are mixtures of cellular, granular of fibrous bodies along with voids filled through air. Airs being a bad thermal conductor, such porous materials are good insulator.

                                                              1673_insulator.png

                                                  Figure: Schematic Variation of Thermal Conductivity

The insulating materials are separated in four groups. Low temperature insulators are for employ up to 10oC. Porous polymeric materials might carry gases that freeze in pores to create vacuum. Vacuum is greatly better insulator because it terminates elastic wave. Such insulators are utilized for cryogenic applications. Building insulators are utilized in the range of 10oC to 150oC. Such are generally wood and plastics. Industrial insulators form the group that is utilized between 150oC to 315oC. Bricks, concrete are primarily utilized in this range but are often more insulated by minerals, slag wools, glasses and various inorganic powders filled between sheets. High temperature insulators are such group which is utilized above 315oC. Porous ceramic bricks for refractory and ceramic powders are utilized as insulators at such temperatures. Insulating bricks can't sustain flames directly but firebricks can withstand flame.

                                                                791_Insulators.png

                                                      Figure: Thermal Conductivity as Functions of Temperature

Posted Date: 2/27/2013 1:44:07 AM | Location : United States







Related Discussions:- Insulators-ceramics-refractory and abrasive material, Assignment Help, Ask Question on Insulators-ceramics-refractory and abrasive material, Get Answer, Expert's Help, Insulators-ceramics-refractory and abrasive material Discussions

Write discussion on Insulators-ceramics-refractory and abrasive material
Your posts are moderated
Related Questions
Q. Show Maximum Allowable Working Pressure? The MAWP to be marked on the Section VIII nameplate is defined as the maximum gauge pressure permissible at the top of a completed v

Draw schematic diagram of a position control system using armature controlled DC Servo motor. Graph the signal flow graph and hence calculate the closed loop transfer function.

#wHAT WILL BE THE PULLEY CRITERIA TO DECIDE THE RPM

triangle law of forces

Copper-Nickel Alloys Complete solubility arises between nickel and copper. All alloys have same microstructure and may be cold or hot worked. Cupro-nickel also termed as Ge

Importance of stresses in shaft: What is  importance of stresses in shaft ? Sol.: In shaft the following significant stresses occur. 1. A maximum shear stress occurs on

case study for factors affecting process design decisions

Can you give me the Prove of the bending Equation M/I=E/R=σ/Y

Matter, Particle and Weight: Sol: Matter: Matter is anything which occupies space and have some mass, offers resistance to any stress, for example Iron, stone, air, Water.

State elongation of a conical bar due to its self weight?