Type your question here A counterflow, concentric tube heat exchanger used for e

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A counterflow, concentric tube heat exchanger used for engine cooling has been in<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

service for an extended period of time. The heat transfer surface area of the exchanger

is 5 m2, and the design value of the overall heat transfer coefficient is 38 W/m2-K. During

a test run, engine oil flowing at 0.1 kg/s is cooled from 110 oC to 66 oC by water

supplied at a temperature of 25 oC and a flow rate of 0.2 kg/s.

1. Determine whether fouling has occurred during the service period. If so,

calculate the fouling factor, Rf%u201D (m2-K/W).

Explanation / Answer

A = 5 m2

U = 38 W/m2-K

mass flow rate of oil = 0.1kg/s

mass flow rate of water = 0.2 kg/s

Change in temp of oil = 44 C

Change in temp of water = 41 C

Rd = 1 / Ud - 1 / U   

where

Rd = fouling factor - or unit thermal resistance of the deposit (m2K/W)

Ud = thermal conductance of heat exchanger after fouling (W/m2K)

U = thermal conductance of clean heat exchanger (W/m2K)

A*U*(Th-Tc) = m1*C1*(T1'-T1) = m2*C2*(T2-T1')

5*U'*(110-25) = 0.1*4.18*1000*(41)=40.324 W/m2-K

Rd = 1/38 - 1/40.324 = 1.5*10^-3 = 0.0015

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