Effects of air vents on the flow of reacting polyurethane foam in a refrigerator cavity

Abstract

The transport equations for momentum, enthalpy, and chemical species are solved to simulate the reactive flow of polyurethane foam in a refrigerator cavity. The chemical reactions are described by a mechanism with four reactions and eight species. The numerical findings are also supported by dimensional arguments, which lead to important design attributes. Results prove that the model can be used not only to predict the flow features during the expansion of a multi-component foam, but also to determine the locations and the size of the air vents to avoid air bubbles trapped during the solidification process. It appears that the distribution of the vent holes must be evenly balanced around the cabinet cavity, where the larger holes must be located at positions far from the injector. To prevent the formation of large air voids, which cannot reach the vent holes by the action of gravity, there must be additional holes located on the lower surfaces of the cavity to purge the air trapped. K E Y W O R D S computational fluid dynamics, injection molding, multi-component flow, polyurethane foams, reactive flow

Effects of composition and temperature of initial mixture on the formation and properties of polyurethane foam

“…The viscosity is a very important property of practical interest as far as filling process in a real engineering geometry is concerned. Recent computational fluid dynamic simulations show that the filling process is very dependent on viscosity and affects the design parameters such that the square of the size of the venting holes (the area of the holes) changes proportionally with the local viscosity and the length of the flow path and inversely with the local velocity. Furthermore, the spatial frequency of venting holes is correlated inversely with the viscosity.…”

Mejora de los Procesos de Producción en una Empresa Fabricadora de Electrodomésticos de Línea Blanca Mediante la Metodología Lean Six Sigma

“…Por lo tanto, la solución propuesta de acuerdo a estudios realizados [32] es perforar zonas estratégicas del gabinete para formar pequeños agujeros donde el aire pueda escapar. Estos agujeros de ventilación deben estar lo más alejado posible del punto de inyección de espuma y lo más cercano a las áreas donde se espera que pueda producirse una acumulación de aire, ya que dirigirán el flujo de la espuma de poliuretano hacia la zona en la que están ubicados.…”

“…Cabe resaltar que es el diámetro del orificio, es la distancia entre el punto de inyección y el agujero, es la velocidad del fluido y es la viscosidad cinemática. Luego de todo lo expuesto, se propone la siguiente distribución y tamaño de agujeros en un gabinete estándar similar al de la empresa [32] [33]. Los orificios más grandes permiten una salida de aire más acelerada que en las zonas en las que se colocan varios agujeros pequeños juntos entre sí.…”

Numerical simulation of mold filling water blown polyurethane foams: Effects of sequential pour

“…1–7 Many of the current models used are calibrated to experimental foaming data, however the challenge of predicting where flow fronts merge, and hence where vents should be placed to remove entrapped air, is still a major challenge. 8 An injection mold simulation by Rao et al. tracked the appearance of knit lines from bifurcated flows and found they appeared earlier and in different locations than experimental results.…”