Mass atmospheric freeze drying

Di Matteo, P, Donsi, G. and Ferrari, G., The role of heat and mass transfer phenomena in atmospheric freeze-drying of foods in a fluidised bed, /. Food. Eng., 59 (2003) 267-275. 

Atmospheric freeze-drying of several foods, including mushrooms and carrots, was investigated in a fluidized bed of finely divided adsorbent that combined adsorption and fluidization, achieving improved heat and mass transfer and shorter drying time than vacuum drying [50,51]. Products could be dried economically using very simple equipment. 

Because of the internally controlled mass transfer, drying times for atmospheric freeze-drying are longer than for the vacuum freeze-drying. The difference in drying time increases with particle size (thickness). Thus, for 5-mm-thick particles, about 2 hours are needed to reduce the moisture content from 4 kg/kg to 2 kg/kg in the vacuum process, whereas 6 hours are required... 

A more detailed treatment of the application of ultrasound is provided in Chapter 8, along with a discussion of the principles of generation and transmission of ultrasound energy to the material to be treated. It is pointed out that power ultrasound can be used to assist both, liquid-solid processes, such as brine treatment, and drying. The acoustic field is shown to enhance, by a number of mechanisms, both, the external and the internal mass transfer when combined with hot air or atmospheric freeze drying of vegetables and fruits. The more porous the material, and the lower the permissible temperature and gas velocity, the higher is the intensification that can be reached by application of power ultrasound. 

Bantle, M., Eikevik, T. M., Griittner, A., 2010. Mass transfer in ultrasonic assisted atmospheric freeze-drying. Proceedings of 17th International Drying Symposium (IDS 2010), Magdeburg, pp. 763-768. 

Tab. 8.2 Identified effective diffusivity (De) and mass transfer coefficient (k) of different products during atmospheric freeze drying (—and 2ms ) with ultrasound (US ...

The material was first crushed under constant cooling with liquid nitrogen in a jaw crusher of which the parts in contact with the fish were made of PTFE or similar material. Subsequent grinding was done in a teflon ball mill under liquid nitrogen. The material was freeze-dried after grinding to obtain a moisture content of ca. 1% (loss of mass of approx. 80%) and was bottled under a dry air atmosphere 1200 bottles were filled each with 15 g of the freeze-dried material. This work is described in detail elsewhere [1,2]. 

Eor solution P-NMR analyses, samples of fine earth, washings and rock fragments from bulk, LAR and TAR of the 2C1 horizon were treated with 0.1 M NaOH solution (under N2 atmosphere, sofid/Uquid ratio, 1 10). After 24 h of shaking, the suspensions were centrifuged the supernatant was filtered at 0.45 pm, taken to pH < 4.0 (with 6 M HCl), and dialyzed at 100 Da molecular mass cut-off (Spectra/Por Biotec CE). The dialyzed extracts were freeze-dried and dissolved in 2 mL of 0.5 M NaOD. The P spectra were obtained using a 300-MHz NMR spectrometer (Varian VXR 300) operating at 121.4 MHz. 

A solution of 4.6 g (36 mmol) of pure 2.8d and 30 mg of dibenzoyl peroxide in 60 mL (rf dry toluene was heated for 24 h to 80 °C in a reaction vessel which was carefully liberated from water and oxygen (pump and freeze technique). After 8 and 16 h further portions of 30 mg of dibenzoyl peroxide were added in a nitrogen atmosphere. The solution was concentrated to 30 mL and poured slowly while stirring into 600 mL of cold ether (-30 °C). The precipitate was washed with ether and dried in vacuo at room temperature. The yield of the isolated polymer amounted to 2.76 g (60%). Above 165 °C the colorless material began to darken and to decompose. (Average molecular masses between 40000... 

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