CFD Modeling and Experimental Study of the Vacuum Compression Process in the Production of Haylage from Fresh Alfalfa in a Flexible Air-Tight Container

Abstract

This study presents the results of experimental and computational fluid dynamics (CFD) modeling of vacuum compaction of partially dried alfalfa haylage in a flexible hermetic container. The objective was to increase the density of vacuum-packed haylage by flattening the plant material before compaction and to establish rational process parameters that avoid excessive release of plant juice. Laboratory experiments were performed using haylage with a moisture content of 50%. The flexible container was placed in a liquid medium to enable measurement of changes in container volume and haylage compaction. The true density of alfalfa stems at 50% moisture content was determined using a pycnometric method with kerosene as the immersion liquid for subsequent porosity calculations. A mathematical model of haylage compaction in a flexible container was developed to represent the effect of pressure during air removal. Numerical simulations were performed using the Reynolds-averaged Navier–Stokes (RANS) equations, the k-ω SST turbulence model, and the SIMPLE algorithm. The Volume of Fluid (VOF) method was used to describe the interaction between the gas phase and the plant material. Two pressure-application configurations were considered: pressure applied to the upper boundary only and pressure applied simultaneously to four boundaries. The results showed that flattening the haylage by passing it between squeezing rollers increased the compacted density by approximately 15–20% compared with the non-flattened material over the 40–80 kPa pressure range. Based on the experimental results, a vacuum level of 70–75 kPa is recommended for compacting pre-flattened haylage, providing substantial densification while avoiding excessive release of plant juice.