Nonstationary Heat Transfer in Graphene-Modified Hydrogels

In this study, we investigate the emergence of convective flows in graphene-modified hydrogels experiencing phase transition and determine the thermophysical characteristics of such systems; the results are compared with numerical simulation data. We analyze the effect of graphene on the heat-transfer properties of hydrogel materials as applied to 3D bioprinting technologies. Using holographic interferometry, gradient calorimetry, and resulting temperature dependences of refractive indices, we have developed the computational complex for calculating the thermophysical parameters of hydrogel materials with graphene admixtures. It has been established that even insignificant concentrations of graphene admixture substantially affects the thermophysical properties. It is also shown that a graphene admixture reduces the viscosity of hydrogel samples, which is measured by the Höppler viscometer. Using the experimentally obtained thermophysical and rheological properties of hydrogels with graphene and the results of numerical simulation, we have calculated the Rayleigh numbers for the corresponding convective heat-exchange modes in the experimental cells with a hydrogel. The Rayleigh number (Ra) demonstrates substantial differences in the heat transfer of the material and its convective properties that depend on the viscosity, density, thermal conductivity, and other parameters of the system. In our case, the variations of the Rayleigh number indicate the difference in the thermal and hydrodynamic properties of different hydrogels with graphene.