Numerical model for matching of coiled adiabatic capillary tubes in a split air conditioner using HCFC22 and HC290

The present work presents a simple model for matching coiled capillary tubes and the refrigerant charge in a split air conditioner when the other components are fixed. The system model is composed of sub-models for the key components, i.e., a lumped model for the compressor, zone models for the condenser and the evaporator, and a four flow region distributed model for the coiled adiabatic capillary tube in series with the liquid tube. The C-M-N method is employed to calculate the friction factors in the coiled capillary tube. HCFC22 and HC290 are used for the simulations. The comparison of the model prediction with experimental data shows the errors are less than ±5% except for the mass flow rate with a maximum deviation of 8.63%. The results confirm that both the cooling capacity and input power are slightly reduced when HCFC22 is replaced by HC290 with the coiled capillary tube and refrigerant charge matched to the HC290 refrigerant. The results also show that when coil diameter is reduced from 0.3 m to 0.04 m, the capillary tube length is reduced by about 10% for both HCFC22 and HC290. This model can be used to design components for small air conditioning systems using HCFC22 and HC290.