Refrideration Flashcards
What is the relationship between viscosity and temperature in fluids?
Viscosity in all fluids varies with temperature.
How is the viscosity of steam and water listed in the tables?
As dynamic viscosity, μ [kg·m⁻¹·s⁻¹] on page 10.
How can you calculate density from specific volume?
Invert the specific volume [m³·kg⁻¹] to get density.
How is kinematic viscosity (ν) calculated?
Divide dynamic viscosity (μ) by density. Units: [m²·s⁻¹].
What is a heat pump?
A thermodynamic machine using work to move heat from low to high temperature.
How is a refrigerator related to a heat pump?
It’s a heat pump where the goal is extracting heat from a low-temp source.
What is the coefficient of performance (COP) of a heat pump?
COP = Useful heat transferred / Work done to transfer heat.
What does a heat pump do using a fluid?
It drives a fluid to transfer heat from a cool place to a hot one by applying work.
What are the four components of a heat pump cycle?
- Throttle, 2. Evaporator, 3. Compressor, 4. Condenser.
What does the compressor do?
Moves refrigerant from low to high pressure.
What does the condenser do?
Rejects heat to the surroundings and condenses vapour into liquid.
What does the throttle do?
Reduces refrigerant pressure to drop its saturation temperature.
What does the evaporator do?
Absorbs heat from surroundings to evaporate the refrigerant.
How does the condenser heat exchanger work?
Condenses superheated vapour to liquid by releasing heat.
Why must T_sat in the condenser be above the hot reservoir temp?
To ensure heat transfer out of the vapour.
What happens in the throttle valve?
Reduces pressure without heat or work, using SFEE: Q̇ + Ẇ = ṁΔh.
Why does enthalpy stay constant through a throttle?
Because Q̇ and Ẇ are zero in a well-insulated, short throttle.
What happens in the evaporator?
Liquid heats to T_sat and evaporates, gaining slight superheat at the end.
