A single effect vacuum evaporator has 100 tubes of $25 \mathrm{~mm}$ diameter. One thousand $\mathrm{kg}$ feed of milk per hour with $15 \%$ TS is concentrated to $20 \%$ TS in the evaporator. Film heat transfer coefficients on either sides of the tube are 5000 and $800 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$. Thermal conductivity of 1.5 $\mathrm{mm}$ thick SS tubes is $15 \mathrm{~W} \mathrm{~m}^{-1} \mathrm{~K}^{-1}$. Latent heat of vapourization under vacuum is $2309 \mathrm{~kJ} \mathrm{~kg}^{-1}$. For $10^{\circ} \mathrm{C}$ temperature difference across the tube wall, the height of each tube, in $\mathrm{m}$ is

(A) 1.36

(B) 2.13

(C) 2.56

(D) 3.17

A single effect vacuum evaporator has 100 tubes of $25 \mathrm{~mm}$ diameter. One thousand $\mathrm{kg}$ feed of milk per hour with $15 \%$ TS is concentrated to $20 \%$ TS in the evaporator. Film heat transfer coefficients on either sides of the tube are 5000 and $800 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$. Thermal conductivity of 1.5 $\mathrm{mm}$ thick SS tubes is $15 \mathrm{~W} \mathrm{~m}^{-1} \mathrm{~K}^{-1}$. Latent heat of vapourization under vacuum is $2309 \mathrm{~kJ} \mathrm{~kg}^{-1}$. For $10^{\circ} \mathrm{C}$ temperature difference across the tube wall, the height of each tube, in $\mathrm{m}$ is

(A) 1.36

(B) 2.13

(C) 2.56

(D) 3.17

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