Condensed milk with $25\%$ solids is produced by evaporating milk in an evaporator with stainless steel tubes $32$ mm in diameter and $6$ m long. Evaporation occurs at $60\backslash$deg C$,$ boiling point of milk at $2\mathrm{.}7$ psia. Steam at $70\backslash$deg C is used. The milk is fed at $40$ kg$/$h per tube at $60\backslash$deg C$.$ Estimate the internal heat transfer coefficient hi and the global heat transfer coefficient U and the tube evaporation rate. The following data is available:

For unconcentrated milk:

m$=0\mathrm{.}94$ cP$,$ r$=1010$ kg$/$m$3,$ k$=0\mathrm{.}62$ W$/$mK and l$=2357$ J$/$g

and for concentrated milk with $25\%$ solids:

m$=1\mathrm{.}6$ cP$,$ r$=1030$ kg$/$m$3,$ k$=0\mathrm{.}55$ W$/$mK and l$=2357$ J$/$gYou can consider that the film T for steam is $70\backslash$deg C and for milk it is $60\backslash$deg C$.$ Considering that it is a falling film evaporator, the heat transfer coefficients of the liquid side are very similar to those obtained for film condensation on vertical surfaces.