Heat exchange in short microtubes and micro heat exchangers with low hydraulic losses

Abstract

 Miniaturization of heat exchangers opens up the way to a considerable increase of their volumetric characteristics. We examine the changes in heat transfer due to decreasing tube size and relative length. To get a higher overall thermal power, we have considered a “checkmate” design that allows to combine a number of micro cross-flow heat exchange modules. The requirement for low overall pumping power limits the pressure drop and also the minimal diameter of heat exchange tubes. An estimated volumetric heat transfer coefficient of a single symmetric air–air module of 50 mm³ volume (including supply channels) and 6 mm height is 4.3 MW/m³ K (at 260 Pa pressure drop, temperature difference of 5 K, pumping power comprising 4.3% of the thermal power, and micro tube size of 128×1200 μm). Micro machine-tools and assembly devices will allow fabrication of low-cost modules of this and smaller sizes and the ability to combine them into compact heat exchangers with high thermal power.