Mango pulp at an initial temperature of 25 °C and a moisture content of 70 % (wb) is to be dried into leather to a final moisture content of 10 % (wb) using hot air at 95 °C. The latent heat of vaporization of water at 95 °C and at standard atmospheric pressure is 2250 kJ·kg⁻¹. Considering the specific heat of mango pulp as 3.8 kJ·kg⁻¹·°C⁻¹, the energy required for drying per kg of mango pulp, in kJ, is __________. (Rounded off to 1 decimal place)
Official Answer Key:
1764.0 to 1768.0
Step-by-Step Solution & Explanation
Basis: 1 kg of mango pulp as fed.
Step 1 — solids balance to find the water removed.
Initial: water = 0.70 kg, solids = 0.30 kg
Final product at 10 % (wb) contains the same 0.30 kg solids as 90 % of its mass:
Product mass = 0.30/0.90 = 0.3333 kg
Water evaporated = 1.0 − 0.3333 = 0.6667 kg
Step 2 — sensible heat to raise the pulp from 25 °C to the drying temperature 95 °C:
Q_sensible = m c ΔT = 1 × 3.8 × (95 − 25) = 266 kJ
Step 3 — latent heat to vaporise the water removed:
Q_latent = 0.6667 × 2250 = 1500 kJ
Step 4 — total energy:
Q = 266 + 1500 = 1766.0 kJ per kg of mango pulp
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.