Air-impingement cooling of boiled eggs: Analysis of flow visualization and heat transfer

摘要

Production of ready-to-eat boiled eggs is a rapidly expanding process. Cooling of the boiled eggs, before peeling, is therefore a significant part of the production. Use of water immersion for cooling purposes is traditional way to accomplish a faster cooling process. However, the utilization of water brings the waste water problem with itself, and there also might be a cross-contamination problem after a longer use. Since the air-impingement processes are to produce higher heat fluxes over the product surface, cooling of boiled eggs by a slot air (24℃) impingement system (H/D of 3-jet exit to object distance over hydraulic diameter of the jet, Reynolds number of ≈7000) was investigated in this study. Continuity, conservation of momentum and conservation of energy equations were solved using Fluent 6.0 (Lebanon, NH). In order to model the turbulent air flow, the k-ε turbulence model was applied. The model results were validated by comparing them with the experimental flow (the particle image velocimetry-PIV data) and temperature data (obtained at different locations of the egg). Different cooling conditions (0℃ impinged air and 0℃ water-for immersion type of cooling) were also simulated, and the results were compared with each other to show the effectiveness of the air-impingement systems. The results of this study showed the potential of air-impingement systems for an effective use in cooling of boiled eggs. However, it would also be valuable to show the effects of different impingement parameters (e.g., H/D, d/D, different nozzle arrangements and effects of higher Reynolds numbers) to compare the results with different cooling systems (e.g., use of spray water).