Simulation Blowing Agent Performance, Cell Morphology, and Cell Pressure in Rigid Polyurethane Foams

A series of over 30 differential equations were solved to model experimental data on urethane foam formation. Methyl formate and C5-C6 hydrocarbons were used as physical blowing agents, and water was used as a chemical blowing agent. The rate of evaporation of the physical blowing agents was estimated using an overall mass-transfer coefficient times the difference in activity in the gas phase inside the bubbles and in the resin walls of the bubbles. The rate of CO2 diffusion was expressed as the overall mass-transfer coefficient times the rate of CO2 generation. The overall mass-transfer coefficient was found to decrease to near zero as the gel point of the resin was approached. Only one fitted parameter was used for the overall mass-transfer calculation for all blowing agents. The simulation results for foam height agree with the experimental data. Bubble growth and bubble pressure were simulated for the first time as compared to the available literature.