The Rankine, Kelvin, and Celsius scales are all used for thermodynamic measurements, but they have different applications and contexts. Here are some key differences and considerations for each scale:
Rankine scale (°R): The Rankine scale is an absolute temperature scale that uses the same degree increment as the Fahrenheit scale but starts at absolute zero, where the theoretical lowest temperature is 0°R. The Rankine scale is primarily used in engineering applications in the United States, particularly in the field of mechanical engineering. It is less commonly used in scientific research and international contexts.
Kelvin scale (K): The Kelvin scale is also an absolute temperature scale, starting at absolute zero (0 K) and using the same degree increment as the Celsius scale (1 K = 1°C). The Kelvin scale is widely used in scientific research, international standards, and most branches of science and engineering. It is the preferred scale for most thermodynamic calculations and equations because of its direct relationship with the ideal gas law and other fundamental thermodynamic principles.
Celsius scale (°C): The Celsius scale is a relative temperature scale that is widely used for everyday temperature measurements. It is based on the melting and boiling points of water, where 0°C is the freezing point and 100°C is the boiling point at standard atmospheric pressure. The Celsius scale is commonly used for weather forecasts, household temperature measurements, and general discussions of temperature. It is also utilized in scientific research and engineering applications, particularly in countries that predominantly use the metric system.
In terms of which scale to use when, the Kelvin scale is generally recommended for most thermodynamic calculations and scientific research due to its alignment with fundamental thermodynamic principles. It simplifies mathematical relationships and avoids the negative temperature values found in Celsius and Rankine scales. The Celsius scale is useful for everyday temperature discussions and contexts where relative temperature differences are more relevant than absolute values.
Ultimately, the choice of temperature scale depends on the specific application, context, and conventions used in a particular field or region. It's important to understand the requirements and preferences of the target audience or the scientific community in which the measurements or calculations will be communicated or utilized.