Fins, deterioration

No other evidence of deterioration, such as corrosion, was apparent on either surface. The cracks are probably material defects. They may be laps or seams that were present on the external surface prior to the fin-rolling operation and were exaggerated during the rolling process. 

Unsealed products will be affected by low humidity of the air in the cooled space and may suffer dehydration. Conversely, some food products such as fresh meat will deteriorate in high humidities. Since the dewpoint of the air approaches the fm surface temperature of the evaporator (see also Chapter 24), the inside humidity is a function of the coil AT. That is to say, the colder the fin surface, the... 

Shellac is dark in colour, and is usually dyed black, red or brown. Its best known uses were as gramophone records. Another use was for American Union cases, which were small boxes used as folding picture frames (Fig. 13.1). They could be closed to preserve the silver nitrate coated glass photo des called Daguerreotypes, which deteriorate in the h t. Shellac was also used fin dressing table sets and for brooches. It is a britde material and can crack or chip. Shellac is compression moulded, and is still produced today. 

Fins are welded to pipe. Strong contact (between fins and pipe) does not deteriorate with cycling over time as compared to wrapped or unwelded thin fins, which lose heat transfer due to rising contact resistance. The heaters do not lose capacity with age. Fins are 1.5-mm thick. Liberal fin surface gives low watt density on heating surface. 

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