VACUUM INSULATION PANELS

Vacuum Insulation Panels



Vacuum Insulation Panels

Introduction

The pupose of this study is to expand the boundaries of our knowledge by exploring some relevant facts and figures relating to the determination of Thermal Conductivity for Vacuum Insulation panels(VIPs) in Laboratory Researchers have taken specific measures for improving the quality of insulation associated with the use of evacuated material. It is known that the thermal conductivity of different materials can be significantly reduced when they are placed in a vacuum. In many works to ensure a high thermal resistance of building envelopes is invited to use the hollow vacuum insulation panels (Thorsell, 2006, pp. 251-256).

In the next section we will examine heat transfer mechanisms in Vacuum Insulation Panels, and also analyze the standards procedures for Hot Box Testing.

Determination of Thermal Conductivity for Vacuum Insulation panels(VIPs) in Laboratory

To understand the high insulating properties of vacuum insulation, it is necessary to recall the mechanisms of heat transfer. The main mechanism of heat transfer in solids - is the thermal conductivity. When heated, one end of a metal rod heat flux moves toward its other end.

By conduction, heat can be transported through gases. In this fast warm molecular gas layer are faced with slow molecules, neighbouring the cold layer. As a result, the heat fluxes. The gases from the lungs of the molecules (hydrogen) conduct heat better than the heavy gas (nitrogen).

By convection, heat transfer is carried out only in gases and liquids, and is based on the fact that by heating the gas, its density decreases. Non-uniform heating of the lighter layers is lifted, the heavy fall. The vertical heat flux associated with this movement is usually much greater than the flow associated with the thermal conductivity.

Radiation is the mechanism of heat transfer by electromagnetic waves. In this way, the sun is warming the earth's surface. Body's ability to absorb and emit electromagnetic waves is determined by its atomic structure (Mukhopadhyaya, 2006, pp. 9-15).

Vacuum technology eliminates all three mechanisms of heat transfer. Dewar flask or thermos is well-known example of vacuum insulation. In the space between the double walls of the Dewar creates a deep vacuum of the order of 10 -2 Pa. Because of this, heat transfer due to convection and conduction, is almost completely eliminated, and extremely low thermal conductivity - 10 -3 -10 -4 W / (m • K). The need to create a high vacuum greatly limits the choice of the shape of the vessel and structural materials. Since the depressurization of the vessel could cause a thermal insulation wall it must be absolutely gas-and waterproof. In order to reduce radiative heat transfer between the walls of the Dewar list of materials is limited to metal and glass with a metallic coating (Mukhopadhyaya, 2006, pp. 9-15).

Guarded Hot Box

Guarded hot-plates and heat flow meter apparatus are designed to measure the thermal conduct of isotropic, homogeneous materials. ASTM Standard c-Ill (ASTM 1993) . which prescribes the standard test method for guarded-hot-plate apparatus, states that testing of inhomogeneous ...