fɔːɹ ɪntˈɜːnəl flˈoʊz ðɪs mˈeɪ tˈeɪk ðə vˈæljuː ʌvðɪ ˈɪnlɪt dˈʌkt ɔːɹ pˈaɪp wˈɪtθ ɔːɹ daɪˈæmɪɾɚ ɔːɹ ðə haɪdɹˈɔːlɪk daɪˈæmɪɾɚ.
For internal flows this may take the value of the inlet duct (or pipe) width (or diameter) or the hydraulic diameter.