Application of RW Drying for better Quality Retention

Mylar is a polyethylene terephthalate . The amount of energy conducted and radiated from the Mylar layer change according to the temperature of the heating source, the thickness of the flim, the thickness of the product and the humidity of the product. RW™ is a powerful tool that allows for the Refractance Window Dryer dehydration of fruit using temperatures of 95 °C and provides a 50% reduction in drying time. A slurry of liquid product is evenly applied to the top surface of a continuous sheet of transparent plastic. This impervious conveyor belt floats on a surface of hot water (210° F / 99° C or less).
Sun-dried sample has significantly (αw. The aw of all samples was well in acceptable levels . In the Refractance Window Drying system, the high-moisture product is placed on a thin plastic film and the material is dried by heating the film layer from below with hot water circulation. The thin plastic film layer creates a ‘window’ in the system in which allow heat and mass transfer from hot water to moist material.

In case of aromatic compounds, sample analysis showed that RW-dried strawberry purees had less esters and alcohols and more heat-induced ketones and aldehydes. Total drying time was about 4 minutes . Refractance Window™ drying uses circulating water at atmospheric pressure to carry heat to the product to be dried. Moist product is applied to the upper surface of an infrared-transparent, plastic conveyer belt that floats on the surface of the heated, circulating water. This water is continuously re-circulated and re-heated, so as to maintain temperature as heat energy is transferred to the product. Three different heat transfers occur in the Refractance Window Drying system during drying as conduction, convection and radiation.
Novel drying techniques emerging as outcome of laboratory-based research may yet prove to have a positive impact on the food industry in terms of scalability, energy efficiency, cost and end-product quality. Refractance window drying is one such technique that gained a lot of attention in recent years, owing to the numerous benefits it claims. The technique involves drying purees and liquids placed over a thin infrared transparent film that essentially forms a ‘window’ through which drying occurs.
The heat energy then radiates from the wanter, primarily through evaporation. Water sorption behavior and thermal analysis of freeze-dried, Refractance Window-dried and hot-air dried açaí juice. LWT-Food Science and Technology, 48, pp.75-81. It can be suitable for drying microbial cultures with acceptable viability and other bioactive compounds, as the product can be dried at a lower temperature (not exceeding 30°C). Comparison of energy consumption of RW with other selected dryers (C. I. Nindo & Tang, 2007).

Because the foods are only briefly exposed to non-damaging temperatures and are never subjected to pressure or shear force, the dried food retains all the nutritional attributes of its fresh, raw-food equivalent. The mylar film temperature was observed to be approx. 10 °C less than that of the water bath and kernel surface temperature was also 10 °C less than the temperature of the film. Kernels were placed on the surface of the film. All the experiments were done in triplicates and data was reported by ANOVA using IBM SPSS statistic 26 software.
The current review outlines the state-of-the-art of various modelling techniques for drying technologies, explores the unresolved bottlenecks in technology development, and provides new avenues for more innovative and sustainable drying technologies. First, the drying mechanism and novel drying technologies are explained. Then, various modelling methods are summarised.

She said the RW method of drying can be used with a wide range of food and beverage products including fruit, vegetables, eggs, cocoa mix, tea, coffee, meat, fish and poultry. Because the RW drying process maintains the temperature of the raw material far below the temperature of the water circulating beneath the conveyor belt, its precious nutrients are protected from oxidization. Overall energy efficiency of spray, freeze and RW dryers (Baeghbali et al., 2016). Evaluation of energy efficiency and quality retention for the Refractance Window TM drying systemResearch ReportWashington State UniversityPullman WA. & Chiewchan, N. Effects of acid pretreatments on some physicochemical properties of carrot undergoing hot air drying.
Ponkham K., Meeso N., Soponronnarit S., Siriamornpun S. Modeling of combined far-infrared radiation and air drying of a ring shaped-pineapple with/without shrinkage. Senadeera W., Bhandari B.R., Young G., Wijesinghe Y. Influence of shapes of selected vegetable materials on drying kinetics during fluidized bed drying. Karanthanos V.T., Belessiotis V.G. Application of a thin-layer  equation to drying data of fresh and semi-dried fruits. Akinola A.A., Talabi O.G., Ezeorah S.N. Effective moisture diffusivity and activation energy estimation of cucumber fruit slices using a Refractance WindowTM dryer.
Natural convection resulted in a higher average temperature at the different points of samples, while forced convection caused lower temperatures during the drying process. Drying curves also showed that the lowest moisture kinetics were obtained in samples dried with natural-convection, while the samples dried with forced-convection showed the highest moisture loss values. RW drying system uses circulating water at 90 to 95°C as a means to convey thermal energy to materials to be dehydrated . As the product does not have direct contact with the heat transfer medium during RW drying, no cross-contamination occurs (Moses, Norton, Alagusundaram, & Tiwari, 2014). Evaporation capacity up to 10 kg m−2 h−1 shows that RW is a very efficient drying process (Zotarelli, Carciofi, & Laurindo, 2015). Refractance Window is a new film drying method and it is characterized by maintaining a relatively low temperature inside the food and by requiring shorter process times (C. I. Nindo, Sun, Wang, Tang, & Powers, 2003).