Nanofluid Heat transfer in a Double Pipe Heat Exchanger (Validation)
The present problem validates the article “Heat transfer enhancement of nanofluids in a double pipe heat exchanger with louvered strip inserts“ applying CFD simulation, using ANSYS Fluent software.
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The present problem simulates the heat transfer inside a double pipe heat exchanger that has a Louvre strip inside it, using ANSYS Fluent software. The simulation process is based on the data in the reference article [Heat transfer enhancement of nanofluids in a double pipe heat exchanger with louvered strip inserts] and the results are compared and validated with the results in the article. The model is related to a double pipe heat exchanger, in the interior of which, a strip is placed in a louvered manner connected to the inner pipe with certain angles and distances.
In the present model, the angle of each of the diagonal strips is equal to 30 degrees and the distance between the two strips is equal to 60 mm, which are connected to the body of the inner tube of the heat exchanger. The fluid flowing inside this pipe is nanofluid with a Reynolds number equals 30,000, and as a result, according to the Reynolds equation, assuming the diameter of the outer tube as the characteristic length, the inlet nanofluid flow velocity is 1.537279 m.s-1. Also, the inlet nanofluid flow temperature to the pipe is equal to 293 K.
The wall of the heat exchanger consists of three parts, in the middle of which, there is an inner tube with a Louvre tape attached to it, and also the outer tube wall is under heat flux. Thus, the wall of the outer tube in the middle part of the heat exchanger under the thermal boundary condition of constant heat flux is equal to 200000 W.m-2; While the Louvre strip connected to the inner tube as well as the outer wall of the tube are thermally insulated at the beginning and end of the heat exchanger.
The purpose of this work is to investigate the amount of Nusselt number on the outer tube wall in the middle of the heat exchanger and under constant heat flux.
Double Pipe Heat Exchanger Geometry & Mesh
The present model is designed in two dimensions using Design Modeler software. The model includes a double pipe heat exchanger; Thus, the diameter of the inner tube in the middle of the heat exchanger is equal to 0.001 m and the diameter of the outer tube is equal to 0.0196 m. Also, the length of the outer tube is equal to 1.5 m and the length of the inner tube is equal to 0.5 m. Louvre strips are attached to the body of the inner tube of the converter, which has an angle of 30 degrees and the distance between the two strips is 0.06 m.
The meshing of the model has been done using ANSYS Meshing software and the mesh type is structured. The element number is 296880. The following figure shows the mesh.
Nanofluid CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is steady.
- The gravity effect on the fluid is ignored.
The following table represents a summary of the defining steps of the problem and its solution:
|near wall treatment||standard wall functions|
|velocity magnitude||1.537972 m.s-1|
|gauge pressure||0 Pascal|
|wall motion||stationary wall|
|heat flux||200000 W.m-2|
|louvered strips Wall||Wall|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|momentum||second order upwind|
|turbulent kinetic energy||second order upwind|
|turbulent dissipation rate||second order upwind|
|energy||second order upwind|
|gauge pressure||0 pascal|
Paper Validation Results
At the end of the solution process, the value of the Nusselt number is obtained on the outer tube wall of the heat exchanger which is under constant heat flux. This value is obtained when the value of the Reynolds number is equal to 300,000 and the angle of the Louvre strips is 30 degrees and the distance between the two Louvre strips is 60 mm. Calculating the value of the Nusselt number requires the correct reference values.
So that in the present model, the characteristic length is equal to the diameter of the outer tube of the heat exchanger, ie 0.0196 m, and the reference temperature is equal to the temperature of the fluid bulk temperature inside the tube, which is equivalent to 293 K. The comparison of the results of the present work with the results of the article and the validation of the results have been done using the diagram of Figure 6-A of the reference article.
|Re||Nusselt number @ paper||Nusselt number @ present work|
Finally, two-dimensional contours related to pressure, temperature and velocity, as well as two-dimensional pathlines are obtained.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.