Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions
Abstract
:1. Introduction
2. Thermophysical Properties of sCO2
3. Materials and Methods
3.1. Geometrical Model
3.2. Numerical Model and Boundary Conditions
3.3. Turbulence Model
3.4. Mesh Independence Test
4. Results
4.1. Data Processing
4.2. Heat Transfer
4.2.1. Nusselt Number Empirical Correlations
4.2.2. Thermophysical Characteristics of sCO2 in Tube Heat Exchanger
4.2.3. Temperature and Velocity Profiles
4.3. Friction Factor
5. Discussion
6. Conclusions
- Numerical simulations confirmed that increasing the flow rate of supercritical CO2 and cooling water significantly improves the heat transfer efficiency in the tube-in-tube condenser;
- The overall heat transfer coefficient U exceeded 4500 W/m2 K at the highest analyzed flow rates, which confirms the high efficiency of the system;
- The Nusselt number and heat transfer coefficient increase nonlinearly with the increase in the Reynolds number and flow velocity;
- Friction factor tests showed that increasing water velocity leads to a decrease in CO2 flow resistance for the same Reynolds number;
- The results of the work indicate that optimizing the difference in CO2 and water flow velocities is crucial for obtaining high cooling efficiency;
- The developed methodology and results can be used to design compact, ecological cooling systems using CO2.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Nomenclature
As | average area of the tube [m2]; |
Cp,b | average heat capaticy at bulk [J/kgK] |
Cp,w | average heat capacity at wall [J/kgK] |
average heat capacity [J/kgK] | |
D | diameter [m] |
ft | friction factor [-] |
f | theoretical friction factor [-] |
h | heat transfer coefficient [W/m2K] |
L | length [m] |
LMTD | Logarithmic Mean Temperature Difference |
Nu | Nusselt number [-] |
Δp | pressure drop [Pa] |
Pr | Prandtl number [-] |
Prb | Prandtl number at bulk [-] |
Q | refrigeration power [W] |
q | wall heat flux [W/m2] |
Re | Reynolds number [-] |
Reb | Reynolds number at bulk [-] |
Tb | average bulk temperature [K] |
Tc,in | inlet temperature of cold fluid [K] |
Tc,out | outlet temperature of cold fluid [K] |
Th,in | inlet temperature of hot fluid [K] |
Th,out | outlet temperature of hot fluid [K] |
Tw | average wall temperature [K] |
TKE | thermal kinetic energy [m2/s2] |
U | heat transfer coefficient [W/m2K] |
u | velocity [m/s] |
uav | average velocity [m/s] |
Greek symbols: | |
δ | characteristic dimension [m] |
λ | thermal conductivity [W/mK] |
λb | average bulk thermal conductivity [W/mK] |
λw | average wall thermal conductivity [W/mK] |
μ | dynamic viscosity [Pa*s] |
ν | kinematic viscosity [m2/s] |
ρ | density [kg/m3] |
ρb | average bulk density [kg/m3] |
ρf | average film density [kg/m3] |
ρw | average wall density [kg/m3] |
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Domain | Boundary Condition | Parameter | Value |
---|---|---|---|
sCO2 (fluid domain) Reference pressure 10 MPa | Inlet | Temperature | 353 K |
Velocity | 1, 2, 3, 4, 5, 6, 7, 8 m/s | ||
Outlet | Average static pressure | 0 Pa | |
Copper (solid domain) | Domain Interface 1 | ||
Domain Interface 2 | |||
sCO2 (fluid domain) | Inlet | Temperature | 293 K |
Velocity | 0.5, 1, 1.5, 2 m/s | ||
Outlet | Average static pressure | 0 Pa |
Mesh | A | B | C | D | E | F | G | H | I |
---|---|---|---|---|---|---|---|---|---|
Number of nodes | 3.14 × 105 | 3.66 × 105 | 4.77 × 105 | 6.06 × 105 | 8.29 × 105 | 9.91 × 105 | 1.12 × 106 | 1.32 × 106 | 1.49 × 106 |
Average y+ | 6.81 | 5.73 | 4.69 | 3.34 | 2.27 | 1.90 | 1.52 | 1.26 | 1.09 |
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Szymczak, P.; Jasiński, P.B.; Łęcki, M. Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions. Energies 2025, 18, 2992. https://doi.org/10.3390/en18112992
Szymczak P, Jasiński PB, Łęcki M. Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions. Energies. 2025; 18(11):2992. https://doi.org/10.3390/en18112992
Chicago/Turabian StyleSzymczak, Piotr, Piotr Bogusław Jasiński, and Marcin Łęcki. 2025. "Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions" Energies 18, no. 11: 2992. https://doi.org/10.3390/en18112992
APA StyleSzymczak, P., Jasiński, P. B., & Łęcki, M. (2025). Numerical Study of the Condenser of a Small CO2 Refrigeration Unit Operating Under Supercritical Conditions. Energies, 18(11), 2992. https://doi.org/10.3390/en18112992