Page 217 - Design and Operation of Heat Exchangers and their Networks

206 Design and operation of heat exchangers and their networks

Example 5.1 Design a shell-and-tube heat exchanger
This example is taken from Shah and Sekulic (2003), Examples 8.3 and 9.4,
for rating calculation. We rewrite it here as a design problem.
Determine a TEMA E shell-and-tube heat exchanger with a fixed tube
sheet and one shell and two tube passes, which has the minimum total tube
length.
The tubes in the bundle are in 45degrees rotated square arrangement with
a tube pitch of s¼25mm, tube inside diameter of d i ¼16.6mm, and outside
diameter of d o ¼19mm. The thermal conductivity of the tube wall
λ w,t ¼111W/mK. The shell-side fluid is lubricating oil, and the tube-side
fluid is seawater with the salinity of 3.4%. Fouling factors for the oil
2
and water sides are R f,s ¼1.76 10 4 and R f,t ¼8.81 10 5 m K/W,
respectively. The oil has a mass flow rate of 36.3kg/s and shall be
cooled from 66°Cto60°C or lower. The inlet temperature and mass flow
rate of seawater are 32°C and 18.1kg/s, respectively. The area reserve
factor is 20%.
The specified geometric dimensions are provided as follows:

Number of sealing strip pairs N ss ¼1
Width of bypass lane δ tp ¼19mm
Number of tube passes N p ¼2
Number of pass partitions N tp ¼2

The following geometric dimensions with their initial values are to be
optimized:

Tube length L¼4.3m
Shell-side inside diameter d s ¼0.336m
Baffle cut l c ¼0.0867m
Central baffle spacing l bc ¼0.279m

The maximum allowable pressure drops are taken as the constraints
as follows:

Shell-side maximum pressure drop Δp s,max ¼0.6bar
Tube-side maximum pressure drop Δp t,max ¼0.18bar

Solution
(1) Calculation of fluid properties
The thermophysical properties of seawater can be calculated according to
Sharqawy et al. (2010) as follows: