Thermodynamics Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Thermodynamics flashcards as text
What does the Zeroth Law of Thermodynamics establish?
Answer: If two bodies are in thermal equilibrium with a third, they are in equilibrium with each other
The Zeroth Law is the basis for temperature measurement — it defines thermal equilibrium between bodies.
In heat transfer, which mode involves the movement of a fluid (liquid or gas) carrying thermal energy from one place to another?
Answer: Convection
Convection transfers heat through fluid movement, which is the primary mechanism in forced-air HVAC systems.
What is the specific heat of water (BTU/lb·°F), a value commonly used in hydronic HVAC calculations?
Answer: 1.0
Water has a specific heat of 1.0 BTU/lb·°F, meaning 1 BTU raises 1 pound of water by 1°F.
An HVAC technician measures 10°F of superheat at the evaporator outlet. This reading indicates:
Answer: The refrigerant is fully vaporized with 10°F above saturation
10°F superheat means the vapor exiting the evaporator is 10°F warmer than the saturation temperature at that pressure.
The First Law of Thermodynamics, applied to a refrigeration system, means that:
Answer: The total energy entering equals energy leaving plus any change in stored energy
The First Law is energy conservation: energy in equals energy out plus changes in stored energy, governing all HVAC energy balances.
What property describes how much a substance resists temperature change when heat is added?
Answer: Specific heat capacity
Specific heat capacity (c) defines how much energy is needed to raise 1 unit mass by 1 degree of temperature.
Which refrigerant state is found between the expansion valve and the evaporator inlet in a properly operating system?
Answer: Saturated mixture (liquid-vapor)
After expansion, the refrigerant is a low-pressure liquid-vapor mixture entering the evaporator to absorb heat.