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Abstract
An experimental study is performed to investigate condensation of superheated R134a and R437A inside a vertical tube. Experimental tests have been performed at the normal operating conditions found in a small power vapor compression refrigeration system. The experimental setup is described and the experimental procedure and data reduction method are explained. Experimental results of the condensation heat transfer coefficient are reported and discussed for different pressures, vapor mass flow rates, and vapor degrees of superheating. Different approximate methods to evaluate the condensate heat transfer coefficient of the zeotropic refrigerant mixture R437A are discussed. The experimental heat transfer coefficients are also compared with those obtained using different correlations; it is found that the values are well predicted with the Chen correlation.
Nomenclature
| A | = | surface area (m2) |
| cp | = | specific heat at constant pressure (J/kg-K) |
| D | = | diameter (m) |
| g | = | gravitational acceleration (m/s2) |
| h | = | specific enthalpy (J/kg) |
| k | = | thermal conductivity (W/m-K) |
| L | = | length (m) |
| = | condensation mass flux (kg/m2-s) | |
| = | mass flow rate (kg/s) | |
| N | = | number of components in the mixture |
| Nu | = | Nusselt number (–) |
| p | = | pressure (bar) |
| Pr | = | Prandtl number (–) |
| R | = | thermal resistance (K/W) |
| Re | = | Reynolds number (–) |
| T | = | temperature (°C, K) |
| U | = | overall heat transfer coefficient (W/m2-K) |
| = | heat power (W) | |
| = | volumetric flow rate (m3/s) | |
| = | power (W) | |
| xj | = | mass fraction of component j in liquid phase (–) |
| yj | = | mass fraction of component j in vapor phase (–) |
| zj | = | mass fraction of component j in the condensation flux (–) |
Greek symbols
| α | = | heat transfer coefficient (W/m2-K) |
| μ | = | dynamic viscosity (kg/m-s) |
| ρ | = | density (kg/m3) |
Subscript
| c | = | condensation |
| cond | = | condenser |
| cw | = | cooling water |
| e | = | external |
| elec | = | electrical |
| evap | = | evaporator |
| i | = | internal, interface |
| j | = | component index |
| k | = | section number |
| l | = | liquid |
| L | = | least volatile component |
| lm | = | logarithmic mean |
| M | = | most volatile component |
| ov | = | overall |
| r | = | refrigerant |
| t | = | total |
| trans | = | transitional |
| v | = | vapor |
| w | = | wall |
Superscript
| ¯ | = | average quantity |