Question

a shell and tube heat exchanger with four shells passes and eight tube passes uses 3kg/s of ethylene glycol in the shell to heat 1.5kg/s of water from 20 to 50 C.The glycol enters at 80c , and the overall heat transfer coefficient is 900W/m2C.Determine the area of the heat exchanger?

please slove it step by step .

Answer 1

Step 1: Calculation of rate of Heat transfer

Since all of the tube side data is available we will calculate the rate of heat transfer using this

Q = m*Cp*dT = 1.5*4.18*(50-20) = 188.1 KW = 188100 W

Step 2: Calculation of overall heat transfer coefficient

The overall heat transfer coefficeint is already given in the question

U = 900 W/m^2oC

Step 3: Calculation of Log mean temperature difference

We first need to find the outlet let temperature of glycol, for this we will make use of enthalpy balance

(m*Cp*dT)glycol = (m*Cp*dT)water

3*0.9*(80-T) =1.5*4.18*(50-20)

From above equation, The outlet temperature of glycol is 10.34 ^oC

Step 4: Calculation of Ft

Now as per data provided we hae 4 shell passes and 8 tube passes

From above equation and all the 4 temperatures ( 80,10.34,20,50)

Ft = 0.95

Step 5: Calculation of Area required for heat transfer

Q = U*A*FT*LMTD

188100 =  900 *A*0.95*17.95

A = 12.256 m²