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.

This study presents an experimental and numerical investigation of the sealing performance of welded joints in flexible polyethylene containers subjected to external pressure during vacuum compaction of forage material. The objective was to improve the reliability of welded seams under vacuum gauge pressures of up to 75 kPa. A three-dimensional transient heat-conduction model was developed to investigate the thermal behavior of polyethylene film during heat sealing. The governing heat-conduction equation was solved using ANSYS Fluent based on the finite volume method, employing a pressure-based transient solver and first-order implicit time discretization. Temperature distributions and their temporal evolution, T(t), were determined at selected locations within the film. The strength of welded joints in thin polyethylene films subjected to pressure loading of up to 75 kPa was experimentally evaluated as a function of weld-seam width and clamping force at a selected heat-sealing temperature of 175 °C. High-density polyethylene film (PE-180) with a thickness of 200 μm was used to carry out research specimens measuring 100 × 100 mm. The experimental results were analyzed using a design-of-experiments approach, and a regression equation was developed to describe the dependence of welded-joint strength on seam width and clamping force. The combined numerical and experimental findings provide a basis for selecting appropriate heat-sealing parameters to enhance the reliability of welded seams at the neck of flexible polyethylene containers subjected to vacuum-induced loading.