Thermal Conductivity of Powder Material

THERMAL CONDUCTIVITY OF POWDER MATERIAL

Nusselt and others used the spherical shell method to determine the conductivity of poor conductors available in the form of powder or fibres i.e., sand, asbestos, cork, clay etc. The method can also be used to determine the conductivity of gases.

Nusselt's method - The arrangement of Nusselt's method is diagrammatically represented in fig. 1.11

The material B under test is packed into the space between two concentric hollow spheres, C and A, made of copper and aluminium of radii 15 cm and 7.5 cm

The spheres can be split into halves and reunited along a dividing line. An electrically heated body S is placed at the centre of the sphere inside A and electrical energy is supplied to it at a constant rate.

Temperatures θ₁, θ₂ are determined by thermocouples fitted in the material B. at different distances, say r = r₁ and r = r₂, from the centre and along or more radii.

If I be the current that flows in S under a potential difference E, then in the steady state the heat equivalent of electrical energy spent per second is

Q = EI/J…………………..(1)

With this value of Q in equation (1), we obtainи

Since all the quantities of Eqn.(2) are known, K can be readily evaluated

Note:

• In this experiment, the pressure at which K is determined must be recorded for the conductivities of powdered or fibrous solids always depend on the pressure applied.

Fenestration

It refers to the presence of openings in a building, most notably the doors and windows. 

Definition

Any opening in a building such as windows, doors, curtain walls and skylights which are designed to permit the passage of air, light, vehicles or people is called fenestration.

Fenestration System

There are various fenestration systems like glazing, windows, curtain walls, sloped glazing and external doors.

• Glazing (transparent): Glass is used for transmission of natural light into a building and weather shielding. This has led to glazing of majority of the new windows.

• Windows: Windows mainly use wooden frame, or metal windows (iron, steel and aluminium).

• Curtain walls: A curtain wall is any exterior wall that is attached to the building structure. It does not carry roof loads of the building.

• Sloped glazing: Skylights are used to provide interior day lighting through this sloped glazing.

• Exterior doors: These include entrance and exit doors.

• Emergency route: Escape route in case of fire in low rise buildings.

Main Components of Fenestration

Fenestration consists of 3 main components. They are

 (a) Glazing

(b) Framing

(c) Shading devices and screens

 (a) Glazing

It is a main part of fenestration that allows the light. It is usually made of glass or plastic.

(b) Framing

It is a material that holds the glazing in place. It is usually made of wood, metal, plastic or fiberglass.

 (c) Shading devices and screens

Shading is a provision used to avoid incident of light directly on the glazing.