This study presents the results of experimental studies on the thermal conductivity of specimens made from selected pure polymer filaments manufactured with the use of FFF 3D-printing technology. The tested samples were made of polylactic acid (PLA), polyethylene terephthalate glycol (PET-G), and acrylonitrile butadiene styrene (ABS). In particular, the effects of the infill patterns and infill density on the tested samples were examined in order to characterize the influence of these parameters on the materials’ effective thermal conductivity. Honeycomb and grid infill patterns of the tested samples with infill densities of 40%, 60%, 80%, and 100% were examined. The influence of temperature on thermal conductivity was studied as well. Thermal conductivity was measured using the guarded heat flow method, according to the ASTM E1530 standard within the defined temperature ranges of 20–60 °C for ABS and PET-G and 20–50 °C for PLA material. Samples of the tested materials were manufactured with the use of the Fused Filament Fabrication method (FFF), and filaments with a uniform black color were used. The obtained results were analyzed in terms of thermal conductivity variation after samples’ infill pattern and infill density modifications, which provides extended thermal property characterization of the polymeric filaments adopted for 3D printing.

The paper discusses and presents the application of the Wilson plot method to the variety of issues related to convective heat transfer. The Wilson plot is a remarkable calculation procedure, which enables the analysis and estimation of convection heat transfer coefficient on the basis of experimental measurements of heat exchanger thermal and flow parameters and the evaluation of corresponding correlation equations. The main facility of the Wilson method is that the heat transfer coefficient can be obtained without the requirement of determining the surface temperature. Much attention was paid to clarify the concept of the standard, original Wilson method as well as its modified versions. The issue was presented in the form of the latest literature review, which featured the investigation of convection coefficients obtained by the Wilson method in the following cases: the flow of nanofluids, refrigerants and other working media in conventional and mini/micro channels and micro-tubes as well as heat transfer under boiling/condensation conditions. The validity of the method utilization has been presented and its future prospects have been specified