The aim of the article is to compare two types of fly ash (from the fluidized and pulverized coal combustion process) as a filler for rigid polyurethane foam. Pulverized fly ash (PFA) is widely used in building materials, while fluidized fly ash (FFA) is not currently recycled, but landfilled. The produced rigid polyurethane foams were reinforced with 5 and 10% by weight addition of fly ash from two different types of boilers. The foaming process, physical properties, morphologies and thermal degradation were subject to comparative analysis. The research indicated that fly ash intensifies the reactions of foam synthesis, most commonly, polyurethane (PU) foam with an addition of 10% PFA. What is interesting is that both ashes can be used in PU foam technology as they do not cause deterioration of the physical parameters. As shown, the addition of filler affects the morphology and impairs the brittleness. Additionally, the use of fly ash from coal combustion in the technology of polyurethane materials complies with the guidelines of the circular economy stated in the European Union legislation. Partial replacement of petrochemical components with waste filler also reduces the total energy consumption in the production of PU composites.

The three-dimensional (3D) inverse solution to water spray cooling from 925 °C to room temperature of the AISI 309 steel plate has been presented. The finite element method with linear and nonlinear shape function has been employed in forward simulations of the plate temperature and in the inverse solutions. The forward finite element solvers have been first compared with the analytical solution to the plate cooling. The reduced finite element models have been compared with the reference model for plate cooling under variable in time and space heat transfer coefficient (HTC) and for the temperature-dependent thermophysical properties of steel. It has been shown that the reduced finite element model with only 216 degrees of freedom which utilizes nonlinear shape functions has given the inverse solution to the heat transfer at the cooled surface with the accuracy of 1.6%. The influence of the thermocouple location uncertainty and the temperature dependence of thermophysical properties have been tested in inverse solutions. The implementation of the reduced finite element heat conduction models and the function specification method in space and time have allowed to achieve the 3D inverse solution to the overall heat transfer at the cooled surface with the accuracy of 2%. The developed 3D inverse solution has been employed to the determination of the HTC distribution over the AISI 309 steel plate cooled by the water spray nozzle. The thermal characteristic of the full cone swirl spray nozzle has been developed.