Telemark Cryogenics 3600 - Page 60

Telemark Cryogenics Microprocessor Based Cryochillers
Page
60
of
63
Revision 1.0.7 October 2018
Model
Suggested
cryo-surface
Sustainable H
2
O pumping
speed (30% de-rating)
1200 0.798 M
2
65,000 l/s
1800 0.997 M
2
100,000 l/s
1800 EXT 0.997 M
2
100,000 l/s
2400 1.197 M
2
135,000 l/s
3000 1.596 M
2
165,000 l/s
3600 1.995 M
2
200,000 l/s
Note: The above performance figures are for units running
with a 60Hz mains frequency.
The value for the sustainable pumping speed represents a 30% reduction to
account for factors such as proximity of system components reducing
conductance and the accumulation of ice reducing heat transfer. The de-
rating is subjective and unique to each installation and process.
Since the pumping action is a function of temperature the cryo-surface must
be designed to minimise heat gains from sources of external heat. In a perfect
system all of the heat load placed on the unit would come from the
condensation of water. Internal heat from the mass of the coil also must be
removed before the system is capable of pumping therefore a design which
uses a thermally conductive material of low mass should be selected.
 The construction of ideal cryogenic surface
 Appropriate surface area for system
 Copper or Stainless steel construction
 Thin Wall
 Large surface area volume ratio
 Internal volume of not less than 0.4 Litres
 A pressure drop between the inlet and outlet of less then 0.3 bar or
equivalent to 40M 12.5mm (1/2”) smooth tubing.
 Capable of handling a pressure of 17 bar (250PSIG)over a temperature
range of +160°C to -160°C
 Simple to clean – coating processes often create large amounts of
powdery deposits which reduce the efficiency of the cyrochiller.
The most common form of cryo-surface is Stainless 304. The simplest (but
perhaps most expensive) to work is 12mm (1/2”) refrigeration grade copper
tubing - the only significant limitation or consequence of using a thicker wall
tubing would be the thermal mass is usually high, resulting in slowing the rate
of cooling significantly.
Table 15 Maximum recommended coil surfaces and theoretical pumping speed for
water vapour at
–
105
o
c coil average temperature