Computational fluid dynamics calculations of high efficiency heat exchangers operating in laminar motion consisting of extruded plastic profiles with insert

The use of plastic-based materials is finding new applications in the heat exchangers sector: the very high values of heat exchange surface ratio per volume unit, the lightness of the products and the lower cost achievable with plastic material are the main advantages of resorting to their use (1),(2),(3). The object of this study is to analyze and validate in terms of CFD and thermodynamic analysis a solution for the realization of high efficiency counter-flow heat exchanger (HX) consisting of extruded alveolar/multi-wall polycarbonate profiles with inserts. Bundles composed of multiple channels are commonly produced to form alveolar/multi-wall polycarbonate products/panels; several extruded bundles can be assembled to obtain HX with large sections, making it possible to require shorter paths for the fluids and lower speed of the same, and therefore less pressure losses in pumping. A further characteristic of the HX analyzed is that, in order to obtain high values of thermal power per unit of volume, instead of resorting to pumping of fluids in turbulent motion, which is an ener-getically very expensive solution, this result is achieved thanks to the introduction, inside of the little channels that make up the extruded bundle, of filling profiles; those filling profiles produce a reduction in the passage thickness of the fluids and induce some positive effects on the nature of their motion: this leads to an enormous improvement of the value of the HX power per unit of surface. Six different CFD calculations were carried out with counterflows of 25 m3/h & BULL;m2 of water at inlet temperatures of 20 & DEG;C and 100 & DEG;C with square channels of 1 meter in length, 8 mm side and three different fillings, obtaining high volumetric heat transfer coefficient (in the cases examined up to 615 kW/m3 & BULL;K) and low pressure drops.