Exercise Estimate the requirements of steam and heat transfer surface, and the evaporating temperatures in each effect,...

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Mechanical Engineering

Exercise
Estimate the requirements of steam and heat transfer surface,and the evaporating temperatures in each effect, for a tripleeffect evaporator evaporating 500 kg h^-1 of a 10%solution up to a 30% solution. Steam is available at 200 kPa gaugeand the pressure in the evaporation space in the final effect is 60kPa absolute. Assume that the overall heat transfer coefficientsare 2270, 2000 and 1420 J m^-2 s^-1Â°C^-1 in the first, second and third effectsrespectively. Neglect sensible heat effects and assume noboiling-point elevation, and assume equal heat transfer in eacheffect.
Answer. A₁ = 2.4 m² =A₂ = A₃
Steam consumption: 0.35kg steam/kg water evaporated.
Note: Trial and error solution is not required here.

Answer & Explanation Solved by verified expert

4.4 Ratings (837 Votes)

Mass balance kg h1 Solids Liquids Total Feed 50 450 500 Product 50 117 167 Evaporation 333 Heat balance From steam tables the condensing temperature of steam at 200 kPa g is 134C and the latent heat is 2164 kJ kg 1 Evaporating temperature in final effect under pressure of 60 kPa abs is 86C as there is no boilingpoint rise See Answer

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