Browsing by Author "Bello, Aliyu Abdulhammeed"

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    Experimentation and modelling of microwave-assisted spray drying of pineapple juice
    (Universiti Teknologi Malaysia, 2018) Bello, Aliyu Abdulhammeed
    Microwave spray drying (MWSD) is a novel intensified process for producing heat sensitive powder at low temperatures using a hybrid microwave and heating energy. The process offers benefits of producing thermolabile powders like fruit juice with reduced stickiness and other operational problems associated with high temperature conditions without affecting the product yield and quality. These benefits would be maximized if transport phenomena and electromagnetic mechanisms on droplet drying kinetics can be modelled so that studies on process dynamics can be carried out prior to detailed design of the proposed system. This thesis proposes a mathematical model of a spray drying process, taking pineapple juice as a case study. The model that was based on conventional spray drying was then extended into a coupled electromagnetic, energy and mass transfer model. The microwave propagating fields were incorporated using Maxwell’s electromagnetic equations, formulated as a finite difference time domain solution with perfect boundaries. Both models were validated with laboratory experiments, designed based on two microwave power intensities (0.2 kW and 0.4 kW), three feed solids compositions (20 %, 30 % and 40 %) and three different inlet air temperatures (105 °C, 110 °C and 115 °C). Spray dried powders for the same feed composition at different temperatures (130 °C, 140 °C and 150 °C) were also examined. Results obtained showed that the MWSD process was able to produce fruit powder with moisture content of up to 10 % lower than those produced by the conventional spray drying process. The spray dried powders also had higher solubilities as well as higher bulk and tapped densities. Model validation with experimental results on powder moisture content showed good agreement with errors between 0.7 % to 7 %, and 1 % to 5.25 % for the MWSD and spray drying models respectively. Simulation results indicated that the MWSD moisture evaporation rates were 100 % higher than conventional spray drying during the falling stage. The evaporation rate increased with increasing droplet size and microwave power. The microwave electric field intensity increased in a similar way and varied with spatial positions. Droplet surface and average temperatures were respectively 20% and 15% cooler under MWSD conditions. The developed models provide valuable insights into the MWSD energy and mass transport mechanisms and lay a sound basis to support the development of energy efficient spray drying process.