Cork insulation; a complete illustrated textbook on cork insulation ...

STRUCTURAL SUGGESTIONS 201
Temperature aflFects the growth of living organisms, both vege-
table and animal, and, when below the temperature level best suited
to this growth, or development, has the effect of slowing them up,
rendering them dormant or destroying them entirely; depending upon
the decreasing temperature to which they are subjected; therefore, in
the case of vegetables or fruit products, their life span is increased,
and, in respect to attack from the outside, they are again protected
by the dormant condition of their enemies.
Animal products, which are dead substances, can only be preserved
by the prevention of changes due to attack by living organisms,
either contained in but not a part of them, or by attack from the
outside; again, as in the case of the vegetable kingdom, these enemies
are rendered less active as the temperature decreases.
Our problem may then be divided into two parts. The first is to
determine the correct temperature and relative humidity of the air,
for each particular product; and this division may best be left in the
hands of scientists, who have the proper knowledge and apparatus for
making scientific tests and determinations for solution. The second
involves the application of the conditions first found, and naturally
leads to the designing engineer, with the co-operation of the scientist,
in providing such construction, apparatus and operation as will secure
the correct temperature and air conditions.
Having been instructed regarding the proper temperatures and
relative humidity, how shall we proceed to secure them?
Temperature.
We shall first consider temperature. It is self-evident that if a
product is to be held at a certain specified temperature, it is the temperature
of the product and not necessarily the temperature of the
room which is important.
This being the case, how are we to insure the temperature of
the product? In answer to this, it is necessary to consider the trans-
fer of heat. Heat must be taken from the goods and delivered into
the refrigerant, which is circulating through the refrigerating coils,
and this heat can only be transferred in two ways—by conduction, or
by convection.
Heat transfer by conduction through air is a slow process, and
altogether out of consideration for practical results; therefore, transfer
by convection is the only practical method, and this involves a
definite air movement, and the rapidity with which the heat is transferred
is in direct proportion to the rapidity of the air movement
through the goods, to and over the refrigerating coils and back to the
goods.
There are two methods of circulating air, one way being to take
advantage of what is called natural circulation, that is, air movement
in a vertical direction, due to the difference in temperature, or specific
gravity, which method is slow, uncertain, and with little power to