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

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 °C) 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 κ–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 °C impinged air and 0 °C 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).