Experimental Study of Steam Injection into a Water Stream for Milk Sterilization
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RESEARCH PAPER
Experimental Study of Steam Injection into a Water Stream for Milk Sterilization Ali Esmaeeli1 · Mohammad Passandideh‑Fard1 Received: 31 December 2018 / Accepted: 23 September 2020 © Shiraz University 2020
Abstract Steam injection into milk stream is a frugal method for milk sterilization. In this paper, the steam injection into a steady liquid water stream (instead of milk stream) is experimentally investigated. A transparent mixing chamber is fabricated using which the variations in steam condensation process are photographed by a high-speed camera. The length of the steam plume in water is determined using image processing of the still images of the phenomenon. The factors affecting the quality of steam condensation are studied. Increasing the chamber pressure reduces the steam plume length which in turn improves the quality of direct contact condensation. Decreasing the liquid water flow rate has an adverse effect on the phenomenon where the steam plume length is increased. It is also found that injecting the steam in a multi-stage configuration results in a reduction of the steam plume length, thereby, improving the condensation process. Keywords Direct contact condensation · Image processing · Milk sterilization · Steam plume
1 Introduction Today, a large number of dairy products require long-term preservation to prevent the spoilage and prolong their shelf life time. In some cases, this time may increase up to 6 months. Consequently, the application of thermal processes to these types of foods with the aim of achieving a high shelf life time is necessary. An instance of such processes is the sterilization of milk to prolong its shelf life in room temperature(Mortazavi 2006). In sterilization, a great deal of heat is transferred to the product to rise its temperature to a certain level, thereby, inactivating microbes, spores and enzymes (Shafafi Shafafi 2000). The most common method of continuous sterilization is the use of ultra-high temperature (UHT) treatment. For milk UHT sterilization, the temperature and pressure must be held at 150 °C and 3.5 bar, respectively, for a duration of 4 s. The heated milk then enters an expansion chamber where it is flash cooled. In this method, the product is mixed with the steam to reach the sterilization temperature. As a result, the steam is condensed, transferring the latent heat of vaporization to milk. * Mohammad Passandideh‑Fard [email protected] 1
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Azadi Square, Mashhad, Iran
There are two ways to mix the steam: one is injecting the liquid product (milk) in a chamber filled with steam. The second method, considered in this paper, is injecting the steam in the liquid stream(Lewis and Neil 2000). Figure 1 shows a schematic illustration of the continuous sterilization of milk by a direct contact condensation process. First, the raw milk is preheated in a heat exchanger after which it is mixed in a mixing chamber with the steam supplied by a boiler. The direct contact condensatio
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