Heat transfer characteristics of plug flows with temperature-jump boundary conditions in parallel-plate channels and concentric annuli

• An analytical study on convective heat transfer of plug flows in parallel-plate channels and concentric annuli.
• The temperature-jump condition was included to represent the effect of rarefaction on plug flows.
• Closed form expressions were analytically derived for obtaining temperature distributions and Nusselt numbers.
• The results show that Nusselt number may increase or decrease depending on the major parameters.

In this study, heat transfer characteristics of plug flows in micro/nano scale were investigated by taking rarefaction effects into account. For this, thermal analysis of plug flows in parallel-plates and concentric annuli was performed for the constant heat flux condition at the walls, which were asymmetrically heated. First-order temperature-jump boundary condition was implemented at the wall assuming a gaseous plug flow, whereas its absence would correspond to either liquid plugs or plug flows at macro scale. Closed form expressions were analytically derived for obtaining temperature distributions and Nusselt numbers as a function of key parameters such as Knudsen number, Prandtl number, wall heat flux ratio, and annulus aspect ratio. The results show that Nusselt number may increase or decrease depending on the major parameters such as rarefaction, wall heat flux ratio and annulus aspect ratio.