Freezer with liquid cryogen refrigerant and method

1. A freezer for using liquid cryogen as a refrigerant comprising:

a) an inner vessel defining a storage chamber;

b) an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between;

c) a heat exchanger positioned in the storage chamber, said heat exchanger having an outlet and an inlet adapted to communicate with a supply of the liquid cryogen refrigerant so that the liquid cryogen refrigerant may flow through the heat exchanger to cool the storage chamber while being vaporized;

d) a purge line in communication with the outlet of the heat exchanger, said purge line including a purge outlet positioned adjacent to an exterior of the heat exchanger;

e) a purge valve positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger may be selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger;

f) an exhaust line in communication with the outlet of the heat exchanger and the purge line;

g) the exhaust line having an exhaust vent;

h) an exhaust valve positioned within the exhaust line;

i) a feed line in communication with the inlet of the heat exchanger and adapted to communicate with the supply of liquid cryogen;

j) as bypass line in communication with the feed line;

k) a bypass valve positioned in the bypass line;

l) a feed temperature sensor in communication with the feed line;

m) a purge gas temperature sensor in communication with the purge line;

n) an exhaust gas temperature sensor in communication with the exhaust line;

o) a chamber temperature sensor in communication with the storage chamber;

p) a controller in communication with the feed, purge gas, exhaust gas and chamber temperature sensors and the bypass, purge and exhaust valves, said controller programmed to:

i. open the bypass valve when a temperature of gas flowing through the feed line is higher than a temperature of the storage chamber;

ii. close the bypass valve when the temperature of gas flowing through the feed line is lower than the temperature of the storage chamber;

iii. open the purge valve and close the exhaust valve when a temperature of gas flowing through the purge line is greater than a minimum desired temperature of the storage chamber;

iv. close the purge valve and open the exhaust valve when the temperature of gas flowing through the purge line is lower than the minimum desired temperature of the storage chamber;

v. close the exhaust valve when a temperature of gas flowing through the exhaust line is lower than the minimum desired temperature of the storage chamber by a predetermined amount; and

vi. close all valves when a temperature of the storage chamber is less than the minimum desired temperature.

2. The freezer of claim 1 wherein the predetermined amount of p)v is approximately 10° C.

3. The freezer of claim 1 wherein the heat exchanger is a cooling coil.

4. The freezer of claim 1 wherein the purge outlet is positioned over the heat exchanger.

5. The freezer of claim 1 wherein the liquid cryogen refrigerant is liquid nitrogen.

6. The freezer of claim 1 wherein the insulation space is a vacuum insulation space.

7. The freezer of claim 1 further comprising an access opening formed through the inner vessel and the outer jacket and a lid for removably closing the access opening.

8. The freezer of claim 7 further comprising a rotating tray positioned within the storage chamber.

9. A freezer for using liquid cryogen as a refrigerant comprising:

a) an inner vessel defining a storage chamber;

b) an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between;

c) a heat exchanger positioned in the storage chamber, said heat exchanger having an outlet and an inlet adapted to communicate with a supply of the liquid cryogen refrigerant so that the liquid cryogen refrigerant may flow through the heat exchanger to cool the storage chamber while being vaporized;

d) a purge hue in communication with the outlet of the heat exchanger, said purge line including a purge outlet positioned adjacent to an exterior of the heat exchanger;

e) a purge valve positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger may be selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger;

f) an exhaust line in communication with the outlet of the heat exchanger and the purge line;

g) the exhaust line having an exhaust vent;

h) an exhaust valve positioned within the exhaust line;

i) a purge gas temperature sensor in communication with the purge line;

j) an exhaust gas temperature sensor in communication with the exhaust line;

k) a chamber temperature sensor in communication with the storage chamber;

l) a controller in communication with the purge gas, exhaust gas and chamber temperature sensors and the purge and exhaust valves, said controller programmed to:

i. open the purge valve and close the exhaust valve when a temperature of gas flowing through the purge line is greater than a minimum desired temperature of the storage chamber;

ii. close the purge valve and open the exhaust valve when the temperature of gas flowing through the purge line is lower than the minimum desired temperature of the storage chamber,

iii. close the exhaust valve when a temperature of gas flowing through the exhaust line is lower than the minimum desired temperature of the storage chamber by a predetermined amount; and

iv. close all valves when a temperature of the storage chamber is less than the minimum desired temperature.

10. The freezer of claim 9 wherein the predetermined amount of l)iii is approximately 10° C. to 20° C.

11. The freezer of claim 9 wherein the heat exchanger is a cooling coil.

12. The freezer of claim 9 wherein the purge outlet is positioned over the heat exchanger.

13. The freezer of claim 9 wherein the liquid cryogen refrigerant is liquid nitrogen.

14. The freezer of claim 9 wherein the insulation space is a vacuum insulation space.

15. The freezer of claim 9 further comprising an access opening formed through the inner vessel and the outer jacket and a lid for removably closing the access opening.

16. The freezer of claim 15 further comprising a rotating tray positioned within the storage chamber.

17. A freezer comprising:

a) an inner vessel defining a storage chamber;

b) an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between;

c) a supply of liquid cryogen refrigerant;

d) a heat exchanger positioned in the storage chamber, said heat exchanger having an outlet and an inlet in communication with the supply of the liquid cryogen refrigerant so that the liquid cryogen refrigerant selectively flows through the heat exchanger to cool the storage chamber while being vaporized;

e) a purge line in communication with the outlet of the heat exchanger, said purge line including a purge outlet positioned adjacent to an exterior of the heat exchanger; and

f) a purge valve positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger is selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger;

g) an exhaust line in communication with the outlet of the heat exchanger and the purge line;

h) the exhaust line having an exhaust vent;

i) an exhaust valve positioned within the exhaust line;

j) a feed line in communication with the inlet of the heat exchanger and the supply of liquid cryogen;

k) a bypass line in communication with the feed line;

l) a bypass valve positioned in the bypass line;

m) a feed temperature sensor in communication with the feed line;

n) a purge gas temperature sensor in communication with the purge line;

o) an exhaust gas temperature sensor in communication with the exhaust line;

p) a chamber temperature sensor in communication with the storage chamber;

q) a controller in communication with the feed, purge gas, exhaust gas and chamber temperature sensors and the bypass, purge and exhaust valves, said controller programmed to:

i. open the bypass valve when a temperature of gas flowing through the feed line is higher than a temperature of the storage chamber;

ii. close the bypass valve when the temperature of gas flowing through the feed line is lower than the temperature of the storage chamber;

iii. open the purge valve and close the exhaust valve when a temperature of gas flowing through the purge line is greater than a minimum desired temperature of the storage chamber;

iv. close the purge valve and open the exhaust valve when the temperature of gas flowing through the purge line is lower than the minimum desired temperature of the storage chamber;

v. close the exhaust valve when a temperature of gas flowing through the exhaust line is lower than the minimum desired temperature of the storage chamber by a predetermined amount; and

vi. close all valves when a temperature of the storage chamber is less than the minimum desired temperature.

18. The freezer of claim 17 wherein the predetermined amount of q)v is approximately 10° C. to 20° C.

19. The freezer of claim 17 wherein the supply of liquid cryogen refrigerant includes a pressurized container containing the liquid cryogen refrigerant.

20. The freezer of claim 17 wherein the supply of liquid cryogen refrigerant includes a container containing the liquid cryogen and a pump in circuit between the container and the heat exchanger inlet.

21. A freezer comprising:

a) an inner vessel defining a storage chamber;

b) an outer jacket generally surrounding the inner vessel so that an insulation space is defined there between;

c) a supply of liquid cryogen refrigerant;

d) a heat exchanger positioned in the storage chamber, said heat exchanger having an outlet and an inlet in communication with the supply of the liquid cryogen refrigerant so that the liquid cryogen refrigerant selectively flows through the heat exchanger to cool the storage chamber while being vaporized;

e) a purge line in communication with the outlet of the heat exchanger, said purge line including a purge outlet positioned adjacent to an exterior of the heat exchanger;

f) a purge valve positioned within the purge line so that the vaporized liquid cryogen from the heat exchanger is selectively directed to the exterior of the heat exchanger to reduce ice formation on the heat exchanger;

g) an exhaust line in communication with the outlet of the heat exchanger and the purge line;

h) the exhaust line having an exhaust vent;

i) an exhaust valve positioned within the exhaust line;

j) a purge gas temperature sensor in communication with the purge line;

k) an exhaust gas temperature sensor in communication with the exhaust line;

l) a chamber temperature sensor in communication with the storage chamber;

m) a controller in communication with the purge gas, exhaust gas and chamber temperature sensors and the purge and exhaust valves, said controller programmed to:

i. open the purge valve and close the exhaust valve when a temperature of gas flowing through the purge line is greater than a minimum desired temperature of the storage chamber;

ii. close the purge valve and open the exhaust valve when the temperature of gas flowing through the purge line is lower than the minimum desired temperature of the storage chamber;

iii. close the exhaust valve when a temperature of gas flowing through the exhaust line is lower than the minimum desired temperature of the storage chamber by a predetermined amount; and

iv. close all valves when a temperature of the storage chamber is less than the minimum desired temperature.

22. The freezer of claim 21 wherein the predetermined amount of m)iii is approximately 10° C.