If you do not know the flow rate of the other fluid, assume it with the desired value. So, You can now know the heat load Q = m Cp dT (using conditions of the cold fluid) and then You can calculate the mass flow rate for Saline water by applying energy balance. Then you can calculate N where m =N rAu

Also, with using LMTD, you can assume U as 1200 or 1300, then from the calculated Q = m Cp dT (using conditions of the cold fluid), calculate tubes surface area, from which you can get N

From the two methods, select the larger N, and repeat calculations to get the required mass flow rate of Saline water.

For more safety, multiply the obtained value by 1.1

Regards

What is the type and flow rate of the other fluid????

If you do not know the flow rate of the other fluid, assume it with the desired value. So, You can now know the heat load Q = m Cp dT (using conditions of the cold fluid) and then You can calculate the mass flow rate for Saline water by applying energy balance. Then you can calculate N where m =N rAu

Also, with using LMTD, you can assume U as 1200 or 1300, then from the calculated Q = m Cp dT (using conditions of the cold fluid), calculate tubes surface area, from which you can get N

From the two methods, select the larger N, and repeat calculations to get the required mass flow rate of Saline water.

For more safety, multiply the obtained value by 1.1

Regards

One fluid is stationary while other is moving

I stand to be corrected but arnt the 2 fluids supposed to be flowing( hence flow rates are present in the calculations) Mahesh

Is it necessary to balance the energy (Qh=Qc)?

If we balance and calculated the mass flow rate then obtained pressure drop is more thereby we need to decrease the mass flow rate to decrease pressure drop.

Having known, Th1, Tc1,, Tc2, LMTD, di, do and L, Here could be the steps to determine mass flow rates of both fluids: (1). Determine Th2 from the equation, assuming counter flow, LMTD = [(Th1 - Tc2) - (Th2, -Tc1)]/ loge ((Th1 - Tc2)/ (Th2, -Tc1)), (2). Overall heat transfer coefficient (U) is estimated by taking two heat transfer coefficients for saline water and other fluid from tables in data book. and estimating as appropriately as 1/U = 1/h(saline water) + 1/h(another fluid). (3). Using the equations, UA/(mccpc) = (Tc2- Tc1)/LMTD and UA/(mhcph) = (Th1- Th2)/LMTD , where A is surface area, 3.1417 do L , mc mh, cpc, cph are mass flow rates and specific heats of cold and hot fluids 9determined by temperatures of fluid at bulk temperatures from data book, mass flow rates can be determined. (4).Heat transfer (Q) = mccpc (Tc2- Tc1) can be determined. (5). After getting, Q, number of tubes (N) is estimated by, Q = U N A LMTD, where A represents for single tube.