1. Why does the number of circuits affect coil capacity?
The number of circuits defines the effective path length of the refrigerant.
Fewer circuits → longer path per circuit → higher pressure drop.
More circuits → shorter paths → lower pressure drop.
For two-phase fluids, these pressure drops directly influence coil performance.
2. What happens with single-phase fluids (e.g., water)?
With single-phase fluids, pressure drops increase with velocity but do not affect thermal capacity.
The only impact is the need for a more powerful pump to maintain the flow rate.
Secondary effects may include:
pipe erosion at very high velocities,
higher pumping costs.
3. What changes with two-phase fluids (refrigerants)?
For two-phase fluids, pressure drop shifts the evaporation or condensation pressure, thus altering the heat exchange temperature.
This results in:
reduced cooling/heating capacity,
higher sensitivity in evaporators (even small pressure drops → significant temperature variations).
4. Why is the evaporator more sensitive to pressure drop than the condenser?
From the pressure–enthalpy diagram:
in condensation: a Δp of ~34 kPa corresponds to about 1°C,
in evaporation: the same Δp can correspond to about 4°C.
Therefore, pressure drops penalize evaporators much more strongly.
5. What is “glide” in refrigerants?
Glide is the temperature difference between the start and end of phase change at nearly constant pressure (typical of blends).
High glide → more complex performance behavior, larger variations in capacity.
Simulation software often uses mean values to simplify calculations.
6. What is the practical impact of the number of circuits?
Too few circuits → long paths, high pressure drops, large Δp → reduced capacity (especially in evaporation).
Too many circuits → short paths, low velocity → reduced turbulence and poorer heat transfer.
The goal is to find an optimal circuiting that balances pressure drop, velocity, and heat transfer coefficient.