Evaluation of the differences of process variables in vertical and horizontal configurations of High Pressure Thermal (HPT) processing systems through numerical modelling

• Vertical and horizontal models for High Pressure (Thermal) Processing are reported.
• Temperature performance and uniformity are different for the two configurations.
• Temperature is more uniform, and lower on average, for the horizontal case.
• Most industrial processes take place in horizontally oriented HP systems.
• Models available in the public domain to date are predominantly for vertical HP systems.

High Pressure Thermal (HPT) processing of foods is a preservation technology which can potentially satisfy consumer demand for high-quality products better than classical thermal processing. Numerical modelling can be used to predict locally specified temperature profiles arising during HPT processing, which is very important in order to ensure microbiological food safety and quality. To date nearly all of the models developed and published on prediction of temperature and flow distribution are based on vertically oriented HPT units. However, because of the increase of horizontal units in industry, and the lack of published work on horizontal models, it was seen important to bridge this research gap in order to advance the technology further. In this work a horizontal model was developed by adapting a previously validated vertical one. It was shown that the temperature performance and uniformity is different for the two configurations, indicating that the research conducted on vertical systems is not directly transferable to horizontal systems in HPT processing.Industrial relevanceHigh Pressure Processing in combination with elevated temperatures can not only inactivate vegetative microorganisms but at appropriate temperature levels also pressure resistant microbial spores. It has been suggested that there are synergistic effects allowing inactivation of the spores of pathogenic and spoilage organisms at reduced times or lower temperatures. Therefore, and because the required temperatures can be achieved faster due to volumetric compression heating, quality attributes, such as colour, texture and nutrients, can be retained better than in conventional thermal processing.To date, most of the studies reported in the public domain were conducted in lab- and pilot-scale vertical systems; however, the equipment available commercially is largely in horizontal orientation to facilitate easier loading and unloading and, therefore, improving process flow.Scaling up from lab or pilot scale to commercial scale is difficult enough even when the vessel orientation remains the same; changing the orientation from vertical to horizontal during scale up introduces a further degree of complexity.As this study has shown, temperature magnitude and uniformity are significantly different, even when the scale remains unchanged.Therefore, this research is essential for transferring the scientific studies on High Pressure Thermal processing to date into industrial scale horizontal processing and the models will be of great assistance to determine appropriate insulation strategies and process conditions to achieve the required outcome, i.e., food safety, quality and shelf life of the processed food products.