Molecular Dynamics Simulation Of Water Heat Transport In Nanochannles Affected By Applied Electric Field

When water is confined in nanopores,nanotubes or nanochannels,it is called nanoconfined water.Due to the limitation of nanoscale and significant interfacial influence,the kinetic and thermal transport characteristics are obviously different from those at macroscopic scale.It has been found that the electric field effect affects the heat transport of nanoconfined water.In this paper,molecular dynamics method is used to study the differences of water heat transport characteristics in the nanochannel under the action of uniform electric field parallel to or perpendicular to the solid-liquid interface,which provides guidance for the heat transfer of microelectronic devices.When a uniform electric field parallel or perpendicular to the solid-liquid interface is applied,the dipole moment orientations of water molecules in the nanochannel are rearranged along the direction of the electric field,resulting in significant differences in the thermal transport characteristics of water in the main area and the Interfacial thermal resistance of the solid-liquid interface.The results show that the thermal conductivity of nanoconfined water is0.780 W·m^-1·K^-1 without field strength.When the electric field parallel to the solid-liquid interface E_x=2,4 V·nm^-1 is applied to the nanochannel,the thermal conductivity of the nanoconfined water is 0.759 and 0.755 W·m^-1·K^-1,compared with no electric field,the thermal conductivity of the nanoconfined water is reduced by 2.69%and 6.28%,respectively.This is because the thermal motion of water molecules is inhibited by electric field force,which weakens the heat transfer ability of water molecules.When the electric field of E_x=6 V·nm^-1and 8 V·nm^-1 is applied,the thermal conductivity is 1.177 and 1.193 W·m^-1·K^-1,the thermal conductivity of nanoconfined water increases by 50.86%and 52.99%,respectively,because the water molecules are electrically frozen into ice crystal structure.The heat transfer mode changes from thermal diffusion of water molecules to vibration between solids,resulting in a significant increase in the thermal conductivity of nanoconfined water.When electric fields perpendicular to the solid-liquid interface E_z=3,6,9,12 V·nm^-1 are applied to the nanochannel,the thermal conductivity of nanoconfined water was 0.744,0.703,0.668,0.691 W·m^-1·K^-1,respectively.Compared with no electric field,the thermal conductivity of nanoconfined water decreased by4.62%,9.87%,14.36%and 11.41%,respectively.When E_z=15 V·nm^-1 is applied,the thermal conductivity is 1.205 W·m^-1·K^-1,and the thermal conductivity of nanconfined water is increased by 54.49%.The electric field parallel to the solid-liquid interface makes it easier for water molecules to freeze electrically because the first layer of water molecules at the solid-liquid interface does not need to be destroyed.With the increase of the field intensity,the matching degree of copper atoms and oxygen atoms at the interface changes,resulting in a monotonically decreasing Kapitza length at the heat source and an monotonically increasing Kapitaz length at the cold source.The size of the nanochannel affects the binding degree of the solid wall to the water molecules in the channel,leading to the differences in the heat transport characteristics of nanoconfined water.In this paper,the model of 12,14,16,18,20 nm nanochannel was constructed to study the influence of nanochannel size on water heat transport.The results show that with the increase of channel size,the thermal motion of water molecules is gradually weakened by the binding degree of solid wall,resulting in the increase of thermal conductivity of nanoconfined water by 10.61%,20.85%,22.19%and 33.74%,respectively.The uniform electric field was applied to 12,14 and 16 nm nanochannels to study the influence of the size of nanochannels on the water heat transport.The results show that the thermal conductivity of nanoconfined water increases with the increase of channel size under the same field intensity.And the longer the channel,the more easily the water molecules in the nanochannel are frozen by electricity.The variation law of Kapitza length at hot and cold source ends of nanochannels with different sizes is the same.