Condensation heat transfer of binary refrigerant mixtures of R22 and R114 inside a horizontal tube with internal spiral grooves

An experimental study of the condensation of pure and mixed refrigerants of R22 and R114 inside a spirally grooved horizontal copper tube has been carried out. A double-tube counterflow condenser in the pressure range 3–21 bar and at a mass flow-rate 26–70 kg h⁻¹ was used. The axial distributions of refrigerant, tube wall and cooling water temperatures, wall heat flux density and vapour quality are shown graphically. The variation of tube wall temperature around the circumference of the tube is also shown. The local Nusselt number depends on the molar fraction, whereas the average Nusselt number can be correlated by an equation which is modified from a previously established equation for pure refrigerants inside a horizontal smooth tube. The frictional pressure drop evaluated is correlated well by the Lockhart-Martinelli parameters and is independent of the concentration of the mixture.