Design of heat exchanger

can you guide me? my procedure is correct or not

1.Q=m cp dT

2.m1 cp1 dT =m2 cp2 dT

3.Finding U(h) AND ^T

4.A= Q/ U*^T

For finding no.of tubes

5. Flow rate = AREA* VELOCITY

by assumption, average velocity =0.9 m/sec....... will find area.

6.for 5/8 OD i will get no.of tubes n*pi*d2/4 = area

For finding length,

7. surface area = 2*pi*r*h* n

will find h value- length of the tube...

for reducing length i will use correction factor in area formula.

THEN will continue MECHANICAL DESIGN.

HERE I have doubt in

1. HOW TO ASSUME VELOCITY FOR PROPER HEAT TRANSFER.

2.PRESSURE DROP IN CALCULATION AND EFFECTIVE LENGTH OF HEAT EXCHANGER...

3.ANY OTHER METHOD FOR THERMAL DESIGN...

4.FINDING SHELL SIDE HEAT TRANSFER COEFFICIENT...