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A double pipe counter flow heat exchanger transfers heat between two water streams. Tube side water at 19 litre/s is heated frim 10°C to 38°C. Shell side water at 25 litre/s is entering at 46°C Assume constant properties of water, density is 1000 kg/m3 and specific heat is 4186 J/kgK. The LMTD (in °C) is ____.
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- 11.0206 °C
- 11.06 °C
- 11.0 °C
- None of these
Correct Option: A
Given: ṁh = 25 L/S; Th,i = 46°C, Th,o =?
ṁc = 19 L/S; Tc,i = 10°C, Tc,o = 38°C
ρ = 1000 kg/m33, C = 4186 J/kg.k
Energy balance, ṁc = C(Tc,o – Tc,i) = mn C(Th,i – Th,o)
19 (38 – 10) = 25 (46 – Th,o)
Th,o = 24.72 °C
| LMTD = | ln | |||
| θ2 | ||||
θ1 = Th,i – Tc,o = 46 – 38 = 8 °C
θ2 = Th,o – Tc,i = 24.72 – 10 = 14.72
| LMTD = | = 11.0206°C | ln | |||
| 14.72 | |||||
