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Freezing of Foods
Published in Susanta Kumar Das, Madhusweta Das, Fundamentals and Operations in Food Process Engineering, 2019
Susanta Kumar Das, Madhusweta Das
The cooling curve for pure water is shown in Figure 11.3. Temperature of food (T) with removal of heat (q) is plotted. Three stages in the cooling curve of pure water are observed: (1) removal of sensible heat of the liquid water from the initial temperature to the freezing point, (2) removal of latent heat of fusion during the phase change of water to ice when the temperature remains constant at this freezing point till whole liquid water turn to ice and (3) removal of sensible heat from freezing point to final temperature. The decrease in temperature during stage 1 is almost linear for a particular rate of heat removal. In stage 2, the formation of ice crystal starts after a small supercooling of liquid water below its normal freezing point (0°C). This supercooling initiates formation of ice nuclei (aggregates of small number of water molecules) upon which ice crystal grows (homogeneous nucleation). This aggregation of water molecules may occur on the small particles present. This is called heterogeneous nucleation. After completion of freezing of the whole mass, temperature of the frozen material starts decreasing linearly with further removal of heat.
Sea Ice Bacteria: Reciprocal Interactions of the Organisms and their Environment
Published in Rita A. Horner, Sea Ice Biota, 1985
Freezing nuclei are defined as particles capable of nucleating ice in supercooled water. If no distinction is made between freezing and deposition the nuclei are referred to as ice nuclei.15 Ice nuclei, both from terrestrial and marine sources, have been studied by atmospheric scientists for their role in precipitation processes (rain, snow, hail, and fog). Biotic and abiotic ice nuclei have been reported.36–38
Introduction to the A&WMA 2023 Critical Review: Environmental sampling for disease surveillance: Recent advances and recommendations for best practice
Published in Journal of the Air & Waste Management Association, 2023
Bioaerosols form a complex mixture of particulate matter (PM) with chemical aerosols (e.g., inorganic and organic components) (Jahne et al. 2015) which impact the atmospheric chemistry and physics. They can influence the global climate system and precipitation through different mechanisms such as scattering and absorbing radiation (Després et al. 2012), cloud micro physical processes by acting as ice nuclei (Vali et al. 1976), and cloud condensation nuclei (Fröhlich-Nowoisky et al. 2016). The dispersion and transport of bioaerosols through atmospheric long distances movement (Maki et al. 2019; Meola, Lazzaro, and Zeyer 2015; Peter et al. 2014) also generate an increase in diversity of genetic poll with the potential of the evolvement and alteration of the ecosystem’s dynamic (Burrows et al. 2009).
Simultaneous measurement of methylamine in size-segregated aerosols and the gas phase
Published in Tellus B: Chemical and Physical Meteorology, 2021
Organic nitrogen compounds in the particulate WSON fraction have not been sufficiently identified, but amines and amino acids have been considered to be important components of the WSON fraction (Zhang and Anastasio, 2003; Ge et al., 2011). Previous studies have pointed out that the amines are much more effective than ammonia in terms of new particle formation processes (Barsanti et al., 2009; Smith et al., 2010; Zhang et al., 2012; Yao et al., 2018). Compared to ammonia, amines more preferentially react with sulfuric acid and contribute to new particle formation processes in the atmosphere (Yu et al., 2012; Zollner et al., 2012; Almeida et al., 2013; Berndt et al., 2014). The new particle formation by amines would have significant impacts on the global climate (Lee et al., 2019). The increase in the aerosol number in the atmosphere can affect the global climate through direct and indirect effects (IPCC, 2001; Boucher et al., 2013; Levy et al., 2013); the aerosols directly scatter and absorb sunlight and contribute to the cloud droplet formation through their ice nuclei and cloud condensation nuclei activities.
A review of microfluidic concepts and applications for atmospheric aerosol science
Published in Aerosol Science and Technology, 2018
Andrew R. Metcalf, Shweta Narayan, Cari S. Dutcher
Because of the small size of microfluidic devices, thermal equilibrium driven by a temperature-controlled microscope stage is possible. Recent studies use microfluidic devices to generate water droplets which are then collected in a trap array and transferred to a cryostage to observe freezing events which characterize the presence of ice nuclei particles within those droplets (Riechers et al. 2013; Reicher et al. 2017). A multi-zone, custom-built cold stage (see Figure 3a) has been used to homogeneously freeze water droplets near −40°C (Stan et al. 2009). Thermoelectric temperature control devices, such as Peltier elements, can be conveniently incorporated into multi-layer lab-on-a-chip devices (Erickson and Li 2004). An embedded electric heater can induce surface tension gradients which precisely control the size of daughter droplets formed during parent droplet breakup in a bifurcated channel (Ting et al. 2006). Temperature-dependent interfacial tension measurements based on droplet deformation have been performed by integrating microheaters into a conventional contraction-expansion device (Lee et al. 2017). Temperature-induced surface tension gradients can also be generated using lasers, and the resulting thermo-capillary effects can be harnessed to block droplet motion, leading to merging of droplets (Baroud et al. 2007).