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Unformatted text preview: qwertyuiopasdfghjklzxcvbnmqwertyui opasdfghjklzxcvbnmqwertyuiopasdfgh jklzxcvbnmqwertyuiopasdfghjklzxcvb nmqwertyuiopasdfghjklzxcvbnmqwer tyuiopasdfghjklzxcvbnmqwertyuiopas dfghjklzxcvbnmqwertyuiopasdfghjklzx cvbnmqwertyuiopasdfghjklzxcvbnmq wertyuiopasdfghjklzxcvbnmqwertyuio pasdfghjklzxcvbnmqwertyuiopasdfghj klzxcvbnmqwertyuiopasdfghjklzxcvbn mqwertyuiopasdfghjklzxcvbnmqwerty uiopasdfghjklzxcvbnmqwertyuiopasdf ghjklzxcvbnmqwertyuiopasdfghjklzxc vbnmqwertyuiopasdfghjklzxcvbnmrty uiopasdfghjklzxcvbnmqwertyuiopasdf ghjklzxcvbnmqwertyuiopasdfghjklzxc Heat Transfer Model Chemical Engineering 157 3/13/2008 Yuria Anaga 2 ABSTRACT Previously conducted heat transfer experiment is modeled by using Comsol Multiphysics program version 3.5. Contour plots of velocity field, axial velocity, radial velocity, and temperature profile for different air flow rates (4 SCFM, 3 SCFM, 2 SCFM, and 1 SCFM) are generated to compare the trends among the plots. Axial and radial velocity plots show that axial velocity dominates at the region where the air flows in while radial velocity dominates at the region near the solid surface. Temperature profile plots show that higher air speed gives higher temperature gradient and thus gives higher driving force for heat to transfer. Temperature as a function of axial position plot is generated by using Microsoft Excel to compare the temperature inside the brass rod obtained from the experiment and model. The experimental data give lower temperature than the modeled data due to some experimental limitations and model errors. Furthermore, momentum and thermal boundary layers are generated graphically from radial velocity and temperature surface plots versus arc length. The model shows that higher air speed will give thinner boundary layer. By using Comsol, the validity of no slip and zero heat flux can be justified. The model shows that changing the no slip condition to slip and zero heat flux to total convective heat flux does not significantly change the data. So, those assumptions are valid. The assumption of no heat loss used in the experimental data calculation is also justified by using energy balance. Boundary integration feature from Comsol shows that the quantity of heat in is bigger than heat out. So, there must be some heat loss during the experiment. Moreover, the model estimates the heat transfer coefficients for different air flow rates. For 4 SCFM, 3 SCFM, 2 SCFM, and 1 SCFM, the experiment gave 188.78 W/(m 2 K), 169.14 W/(m 2 K), 145.85 W/(m 2 K), and 118.50 W/(m 2 K) respectively while the model gives 71.78 W/(m 2 K), 61.71 W/(m 2 K), 50.18 W/(m 2 K), and 36.45 W/(m 2 K) respectively. The differences may be caused by some experimental errors and limitations. The trend shows that higher air speed will give higher heat transfer coefficient and thus thinner thermal and momentum boundary layers. The heat transfer coefficients found are correlated by using standard Nusselt number. The constant, C 2 , found from the experiment is...
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- Spring '11