Quantities and units of heat
1Key Takeaways
This standard specifies the names and symbols of thermal quantities and units; where appropriate, conversion factors are given. This standard applies to all fields of science and technology.
2Expert Interpretation
An in-depth interpretation of the national standard GB 3102.4-93 "Thermal Quantities and Units", covering the definitions and unit specifications of core concepts such as thermodynamic temperature, thermal conductivity, and heat transfer coefficient, and providing the background for standard formulation, technology evolution analysis, and implementation recommendations.
Standard Overview and Background
GB 3102.4-93 is an important part of the "Quantity and Unit" series of national standards. It is equivalent to the international standard ISO 31-4:1992 and systematically standardizes the definition of quantity and unit in the field of thermal science. This standard was implemented on July 1, 1994, replacing the 1986 version of the standard. Its technical content reflects the latest requirements of the 1990 International Temperature Scale (ITS-90).
Core Concept Analysis
| Physical Quantity | Symbol | SI Unit | Definition Points |
|---|---|---|---|
| Thermodynamic Temperature | T,(Θ) | Kelvin (K) | Basic quantity, definition based on the triple point of water (273.16K) |
| Celsius Temperature | t,θ | Degrees Celsius (℃) | t=TT0, T0=273.15K |
| Thermal conductivity | λ,(κ) | W/(m·K) | Key parameter to characterize the thermal conductivity of materials |
Technology Evolution Analysis
The standard places special emphasis on the technological development of temperature measurement:
- The 1990 International Temperature Scale (ITS-90) replaced the 1968 version and expanded the measurement range to above 0.65K
- Clearly distinguish the symbol system of thermodynamic temperature (T) and international Kelvin temperature (T90)
- Abolish non-standard temperature interval expressions such as "degree" and "deg"
Implementation Recommendations
- Temperature symbol usage standards: A space must be left before the Celsius temperature symbol "℃"
- Preferably use the single symbol system recommended by the standard and avoid using alternative symbols
- Pay attention to the distinction in thermal calculations:
- Heat capacity (process-related quantity) and specific heat capacity (material property)
- Different application scenarios of heat transfer coefficient K and surface heat transfer coefficient h
Appendix content description
The standard appendix lists the conversion relationship of imperial units in detail, including:
| Imperial units | SI conversion | Application areas |
|---|---|---|
| British thermal unit (Btu) | 1 Btu = 1 055.056 J | Traditional heating engineering |
| Rankine degree (°R) | 1 °R = 5/9 K | Anglo-American thermodynamic calculation |