In order to improve the design efficiency of capillary tubes, capillary tube models have been developed. Yilmaz and U¨nal presented a general approximate analytic equation for the design of adiabatic capillary tubes. In this work, the Yilmaz-U¨nal equation was analyzed in detail and some problems were found. Consequently, a modified general equation was developed and verified by theoretical and experimental data.

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