Sayed Hossein Ganjiani, Alireza Hossein Nezhad,
Volume 16, Issue 9 (11-2016)
Abstract
In this work the effect of carbon nanotube length on the nanofluidic energy absorption system is investigated by using molecular dynamic simulation. For this purpose, four rigid armchair carbon nanotubes (8,8), (10,10), (12,12) and (14,14), and six lengths (5.0 nm, 6.0 nm, 7.0 nm, 8.0 nm, 9.0 nm and 10.0 nm ) for each one are studied. Results of simulations show that the surface of carbon nanotube is frictionless in all length and diameters, causing water molecules defiltrated from carbon nanotubes after applying the loading-unloading cycle on the system. Contact angle which represents hydrophobic intensity of carbon nanotube is decreased averagely 4 and 2 % by increasing length and diameter of carbon nanotube, respectively; therefore, infiltration pressure of water molecules through carbon nanotube is decreased averagely 30 and 15 %, respectively. Moreover, the mass and size of carbon nanotube increase by increasing length and diameter of carbon nanotube, leading to the reduction of energy absorption density and efficiency. Also, density of water molecules in carbon nanotube unlike the bulk of liquid phase is non uniform, decreases in the first and second shells, and increases along the distance between them by increasing length of carbon nanotube.
A. Yousefi, A. Hossein Nezhad,
Volume 20, Issue 2 (February 2020)
Abstract
In the present work, the effects of fin pitch, transverse pitch, longitudinal pitch and the number of the longitudinal pitch in a plate-fin flat tube heat exchanger were studied. The fluid flow was assumed laminar, steady, and incompressible. Continuity, momentum, and energy equations for fluid flow and conduction equation for fin were solved, using the finite volume method. Dimensionless results showed that increasing the fin pitch causes to increase of the j-Coulburn coefficient by 132.68% and reduces the friction coefficient rate by 13.35%. Also, increasing transverse tube pitch causes to increase of j coefficient by 203.83% and reduces 24.22% of the f coefficient. By increasing longitudinal tube pitch, j and f coefficients are reduced 84% and 32%, respectively. Dimensional results showed that by increasing fin pitch, heat transfer is reduced 2.2% and thermal performance is increased by 75%. Increasing transverse tube pitch causes to increase heat transfer and thermal performance about 341% and 255%, respectively. Increasing longitudinal tube pitches result in decreasing the heat transfer and thermal performance about 71% and 79%, respectively. Increasing the number of longitudinal tube pitches, N, causes to increase of the heat transfer rate, but for N>28, no sensible increase in heat transfer rate is observed therefore, N>28 is not recommended. Maximum thermal performance is achieved at N=5 and for N>5 thermal performance is decreased.
