REF UNIT 21 Flashcards
(21.2) What is the normal temperature range for high temperature application for refrigeration?
47F to 60F
(21.2) What products are commonly stored in high temp refrigeration applications?
flowers and candy
(21.2) What is the normal temperature range for medium temperature application for refrigeration?
28F to 40F
(21.2) What products are commonly stored in a medium temp refrigeration application?
eggs, lettuce, tomato (stuff in a domestic refrigerator really).
(21.2) What is the normal temperature range for low temperature application for refrigeration?
below freezing to -20F
(21.2) What products are commonly stored in a low temp refrigeration application.
frozen shit.
(21.7) What material evaporators used when cooling acidic products?
stainless steel, even though it doesn’t conduct heat as well as copper.
(21.7) Between what 2 states does the best heat exchange occur?
2 liquids
(21.7) Define film factor
the relationship between the medium giving up heat and the evaporator itself.
(21.8) What are stamped evaporators?
an evaporator with a stamped surface, increasing surface area
(21.8) What are the evaporators with fins called?
finned-tube evaporators. They are the most common air-refrigerant evaporators today.
(21.8) Why are finned-tube evaporators more prone to frost accumulation?
because the fins act as more surface area for the moisture to freeze.
(21.8) Why are multiple circuits used in evaporators?
reduces pressure drop
(21.8) What does FPI stand for?
fins per inch
(21.9) How is an evaporator’s capacity rated?
in BTUs/hr
(21.11) What is a flooded evaporator?
evaporators where instead of the end of the evaporator having vapor, it is still liquid. This improves system efficiency.
(21.11) What metering device do flooded evaporators usually use?
float-type metering device.
(21.11) What is a dry-type or direct expansion evaporator?
basically what we’ve been learning.
(21.13) What is the term for a coil that isn’t receiving enough refrigerant.
starved.
(21.14) What is hot pulldown?
when the refrigerated box temperature gets very high, so the metering device feeds the evaporator more refrigerant.
(21.14) What is the term for a coil that is receiving too much refrigerant?
flooded
(21.18) Where does condensate meant for defrost go once it passes the evaporator?
into the accumulator. dense vapors rise out. Without accumulator, it will flood compressor, causingoil foaming, causing bearing washout.
(21.18) What is used to prevent wet compression in a compressor?
a thermistor at the discharge line.
(21.19)
EVAPORATOR EFFICIENCY CONTROLLER
