Heat transfer of nonazeotropic mixtures in a falling film evaporator

The evaporative heat transfer coefficient for nonazeotropicmixtures of R12 and R114 has been studied in a falling filmheat exchanger. The main aim with the project has been tostudy how the heat transfer coefficient is influenced bythe additional mass transfer resistance that is introducedwhen a mixture is used instead of a pure refrigerant.The test apparatus consisted of one tube, which was heatedfrom the outside and with the refrigerant forming a fallingfilm on the inside. The heating was done by a liquidflowing in an annular space countercurrently to the fallingfilm.From the results it can be concluded that the heat transfercoefficients for the mixtures at surface evaporation conditions are between the corresponding ones for the pure refrigerants at given Re numbers. This indicates that theadditional mass transfer resistance when a mixture is usedis small in a falling film at such conditions. This isprobably due to the small film thickness.The heat transfer coefficients versus the heat flux werealso measured. Again, the values for the mixtures at agiven\u27heat flux fall between the corresponding for thetwo pure refrigerants, both at surface evaporation andnucleate boiling conditions