Freezing performance degradation

Regardless, structural alterations and water trapped in CCL described in Section 9.2.2 about effects of freezing-thaw cycles are also causes of performance degradations during cold start. However, they are emphasized during cold start as ice is produced in the core of the CCL and near the catalytic sites. Although an active area decrease is systematically observed by CV at the CCL, preponderance between ohmic, diffusion, and activation limitations is not clearly identified. 

In another, similar study, Mukundan et al. [260] performed 100 freeze-thaw cycles (from -40 to 80°C) with different types of CFPs and CCs. After 100 cycles, no obvious degradation was observed in the carbon cloth DL in fact, the performance of the fuel cell slightly improved. On the other hand, after 45 cycles, the CFPs showed significant breakage of the carbon fibers at the edges between the flow channels and the landing widths (or ribs). Thus, it was concluded that this breakage could potentially become a serious failure mechanism in PEM fuel cells when the system was started at subzero temperatures. 

Store purified anthocyanin extract at 4°C if subsequent analysis will be performed within 24 hr. Store sample for longer periods at -15°C or lower (preferably at -70°C) in a freeze-resistant container to minimize pigment degradation. 

If food samples need to be stored for later extraction, seal in a plastic bag and store up to 10 days at -20°C or lower to prevent isoflavone loss and degradation. Thaw the sample completely at room temperature immediately before extraction. If freeze drying is desired, perform after food samples have been prefrozen in a freeze-dry flask to -20°C or lower. 

Environmental and accelerated ageing tests were performed on the indoor dye modules described in Sect. 7.6 in order to detect failure mechanisms. Contrary to expectations, many modules survived humidity/freeze cycling tests (10 cycles, 85%, 20 h at 55°C per cycle) without major degradation, demonstrating the capability of the sealing concept (see Fig. 7.8). This was also true for temperature cycling (between —5 and 55°C). However, it has... 

There are, however, other ways in which conventional drying could, in principle, be performed at temperatures above Tg, without deleterious results. If a solution could be treated so that one or several components can undergo crystallisation, then the crystals formed would serve as a substitute for the subliming ice crystals and could mechanically protect the porous, amorphous matrix against structural collapse. The efficacy of this type of formulation for freeze-drying purposes has been demonstrated for the system water-sucrose-NaCl. " Its practical applications may, however, be limited to products where the bioactive component is not chemically degraded in the freeze-concentrate at temperatures above Tg. 

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