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A well-mixed vessel contains 1000 kg of liquid initially at 30°C, which must be heated to 120°C. The heating is done using immersed coils with a surface area of 1.2 m², through which steam condenses at 150°C. Given the overall heat transfer coefficient to the liquid is 1500 W/m²·°C, and the liquid's specific heat capacity is 4 kJ/kg·°C, calculate the time required for the liquid to reach the target temperature. Assume heat losses to the environment are negligible.

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Subject
Chemical Heat Transferchemical-engineering › heat-transfer-chemical-engineering
Published
3 Mar 2019
Last updated
28 May 2026

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Explanation

To determine the heating time, calculate the heat needed to raise the liquid's temperature, then divide by the rate of heat transfer through the coils. The heat required is Q = mass × specific heat × temperature change = 1000 × 4000 × (120 - 30) = 360,000,000 J. The heat transfer rate is Q̇ = U × A × ΔTlm, where ΔTlm is the log mean temperature difference between steam and liquid. Using these values, the time taken is approximately 51 minutes.

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