Foreword

TCVN 9312:2012 is completely equivalent to ISO 9251:1987.

TCVN 9312:2012 was converted from TCXDVN 300:1987 (ISO 7345:1987) according to the regulation at Clause 1, Article 69 of the Law on Standards and Technical Regulations and Point a), Clause 1, Article 7 of the Decree No. 127/2007/ND-CP detailing the implementation of some articles of the Law on Standards and Technical Regulations.

TCVN 9312:2012 was compiled by the Institute of Architecture, Urban and Rural Planning, proposed by the Ministry of Construction, appraised by the Directorate for Standards, Metrology and Quality, and announced by the Ministry of Science and Technology.

1. Scope

This standard defines the terms used in the field of thermal insulation to describe heat transfer conditions and properties of materials.

2. Heat transfer conditions

2.1. Steady state

Heat transfer condition when all relevant parameters do not change over time.

2.2. Non-steady state

Heat transfer condition when relevant parameters vary over time.

2.3. Periodic state

Non-steady state in which the values of the relevant parameters repeat after equal time intervals regardless of the initial conditions.

2.4. Transient state

Non-steady state in which the values of the relevant parameters gradually change from the initial state to the steady state or periodic state.

2.5. Heat transfer

The transmission of energy by thermal conduction, convection or radiation, or a combination of all the above modes.

3. Properties of materials

3.1. Porosity, x

The total volume of voids in a porous material divided by the total volume of the material.

NOTE: The porosity of a material can be determined by the following formula:

Where:

ρ: The apparent density of the material;
ρ_s: The density of the solid part of the material;
ρ_g: The density of the air in the voids of the material.

The apparent density of the material is determined by experimental methods.

3.2. Local porosity, ξ_P

The porosity at point P located in a part of the material with a volume small compared to the total volume but large enough to calculate a meaningful average value.

3.3. Porous medium

A heterogeneous medium consisting of voids and solid parts distributed evenly.

Porous media can be classified according to their geometric structure as specified from 3.3.1 to 3.3.4.

3.3.1. Fibrous porous medium

A medium formed by continuous gaseous elements located between solid elements whose length is the predominant dimension.

3.3.2. Granular loose fill medium

A medium formed by continuous gaseous elements located between solid elements of irregular shape and no predominant dimension.

3.3.3. Cellular porous medium

A medium formed by continuous solid parts separated by air-filled voids of nearly spherical shape.

3.3.4. Interconnected porous medium

A medium formed by continuous solid parts encompassing voids that are interconnected internally, creating continuous gaseous elements.

3.4. Homogeneous porous medium

A medium in which the local porosity does not depend on the position of the calculation point.

3.5. Homogeneous medium

A medium in which the relevant properties depend on the position within the medium itself, and may depend on parameters such as time, direction, or temperature, etc.

3.6. Heterogeneous medium

A medium in which the relevant properties depend on the position of the observation points within the medium itself.

3.7. (Mass) density, ρ

Mass divided by volume.

NOTES:

1) For porous materials and granular materials, the density of the solid part and the density of the bulk can be determined.

2) According to ISO 31, density is denoted by “ρ”, with the unit of measurement being kilograms per cubic meter (kg/m³).

3.8. Isotropic medium

A medium in which the relevant properties do not depend on direction but may be a function of the position of the observation points within the medium or a function varying with time, temperature, etc.

3.9. Anisotropic medium

A medium in which the relevant properties are a function of direction.

3.10. Stable medium

A medium in which the relevant properties do not depend on time, but may be a function varying with coordinates, direction, temperature, etc.

REFERENCES

ISO 31¹⁾, Quantities and units

ISO 31 has been replaced by ISO 80000