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Computational modeling and simulation
In this study six baffles are placed along the shell in alternating orientations with cut
facing up, cut facing down, cut facing up again etc., in order to create flow paths across the tube
bundle. The geometric model is optimized by varying the baffle inclination angle i. e., 0°, 10°,
and 20°. The computational modeling involves pre-processing, solving and post- processing.
The geometry modeling of shell and tube heat exchanger is explained below.
Geometry modeling
The model is designed according to TEMA (Tubular Exchanger Manufacturers Asso-
ciation) Standards Gaddis (2007), using Pro/E Wildfire-5 software as shown in fig. 1. Design
parameters and fixed geometric parameters have been taken similar to Ozden et al. [4], as indi-
cated in tab. 1.The 3-D model is then discretized in ICEM CFD. In order to capture both the thermal
and velocity boundary layers the entire model is discretized using hexahedral mesh elements
which are accurate and involve less computation effort. Fine control on the hexahedral mesh
near the wall surface allows capturing the boundary layer gradient accurately. The entire geome-
try is pided into three fluid domains Fluid_Inlet, Fluid_Shell, and Fluid_Outlet, and six solid
domains namely Solid_Baffle1 to Solid_Baffle6 for six baffles, respectively. The heat
exchanger is discretized into solid and fluid domains in order to have better control over the
number of nodes.
The fluid mesh is made finer then solid mesh for simulating conjugate heat transfer
phenomenon. The three fluid domains are as shown in fig. 2. The first cell height in the fluid do-
main from the tube surface is maintained at 100 microns to capture the velocity and thermal
boundary layers. The discretized model is checked for quality and is found to have a minimum
angle of 18° and min determinant of 4.12. Once the meshes are checked for free of errors and
minimum required quality it is exported to ANSYS CFX pre-processor.
Governing equations
The 3-D flow through the shell-and-tube heat exchanger has been simulated by solv-
ing the appropriate governing equations, eq. (1) to eq. (5). viz. conservation ofmass,momentum
and energy using ANSYS CFX code. Turbulence is taken care by shear stress transport (SST)
k-wmodel of closure which has a blending function that supports Standard k-w near the wall and
Standard k-e elsewhere.In ANSYS CFX pre-processor, the various fluid and solid domains are defined. The
details of the domains created with the corresponding fluid-solid & fluid-fluid interfaces are
provided in tab. 2, respectively. The flow in this study is turbulent, hence SST k-w turbulence
model is chosen. The boundary conditions are specified in ANSYS CFX pre-processor and then
the file is exported to the ANSYS CFX. The same procedure is adopted for the other twomodels.
Validation
Simulation results are obtained for different mass flow rates of shell side fluid ranging
from0.5 kg/s, 1 kg/s, and 2 kg/s. The simulated results for 0.5 kg/s fluid flow rate formodel with
0° baffle inclination angle are validated with the data available in [4]. It is found that the exit
temperature at the shell outlet is matching with the literature results and the deviation between
the two is less than 1%.
The simulation results for 0.5 kg/s mass flow rate formodels with 0°, 10°, and 20° baf-
fle inclination are obtained. It is seen that the temperature gradually increases from 300 K at the
inlet to 340 K at the outlet of the shell side. The average temperature at the outlet surface is
nearly 323 K for all the three models. There is no much variation of temperature for all the three
cases considered.
The maximumpressure for models with 0°, 10° and 20° baffle inclinations are 94 .43,