A Structural Model for Air Flow in Flexible PUR Foams
N.C. Hilyard, P. Collier- Organic Chemistry
- Polymers and Plastics
A new structural model based on the two term fluid flow equation of Gent and Rusch is described. The classical theory of flow through porous packed beds is used to relate the permeability and flow inertia coefficients to the average cell diameter, the tortuosity of the flow path and a skin friction coefficient. The model is used to predict how air flow is influenced by compression of the cellular matrix. Results of laboratory investigations are presented and compared with the model. For the most part good agreement is obtained for compressions up to about 60%. It is shown that the permeability is governed by cell size and the flow inertia parameter is governed by cell size, tortuosity and a roughness parameter. It is concluded from data obtained from crushed and uncrushed foams that the roughness parameter is strongly associated with cell membrane density. It is proposed that the experimental procedure can be used to quantify separately the effects of cell size and cell membranes.