U.S. patent number 3,802,212 [Application Number 05/250,616] was granted by the patent office on 1974-04-09 for refrigeration apparatus.
This patent grant is currently assigned to General Cryogenics, Inc.. Invention is credited to Patrick S. Martin, Barron M. Moody.
United States Patent |
3,802,212 |
Martin , et al. |
April 9, 1974 |
REFRIGERATION APPARATUS
Abstract
Apparatus for refrigerating and heating comprising a source of
liquid nitrogen arranged to deliver nitrogen selectively through
coils of an evaporator or through heating apparatus and then
through coils of the evaporator such that nitrogen can be employed
for either cooling or heating a cargo compartment. Nitrogen gas
exhausted from coils of the evaporator is released to ambient
atmosphere outside of the compartment. Temperature sensors are
positioned for sensing the temperature of nitrogen gas exhausted to
atmosphere and to sense the temperature of air which has been drawn
across the evaporator coils. Control apparatus initiates a defrost
cycle to cause heated nitrogen vapor to be passed through
evaporator coils for defrosting the coils when ice accumulates
thereon in sufficient quantity to insulate the coils causing a
predetermined temperature differential between the exhaust gas and
air drawn across the evaporator coils.
Inventors: |
Martin; Patrick S. (Dallas,
TX), Moody; Barron M. (Dallas, TX) |
Assignee: |
General Cryogenics, Inc.
(Dallas, TX)
|
Family
ID: |
22948475 |
Appl.
No.: |
05/250,616 |
Filed: |
May 5, 1972 |
Current U.S.
Class: |
62/50.2; 62/80;
62/150; 62/156; 62/208; 62/407; 165/253; 62/53.2; 62/81; 62/151;
62/159; 62/275; 62/419 |
Current CPC
Class: |
F25D
29/001 (20130101); G05D 23/1919 (20130101); F25D
2400/30 (20130101) |
Current International
Class: |
F25D
29/00 (20060101); G05D 23/19 (20060101); F17c
007/02 () |
Field of
Search: |
;62/80,81,150,151,156,52,514,275,276 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wye; William J.
Attorney, Agent or Firm: Moore; Howard E. Crutsinger; Gerald
G.
Claims
Having described our invention, we claim:
1. A method of controlling the heat transfer rate through a wall of
a tube comprising the steps of: delivering coolant through the
tube; moving fluid in heat exchange relation with the tube; sensing
temperature of coolant exhausted from the tube; sensing temperature
of fluid which is passed in heat exchange relation to the tube; and
heating surfaces of the tube when a predetermined differential
between temperature of coolant exhausted and temperature of fluid
which has moved across the tube exists.
2. The method of claim 1 wherein the steps of sensing temperature
of coolant exhausted and sensing temperature of fluid are
accomplished by positioning a first temperature sensor in heat
exchange relation with coolant exhausted from the tube; positioning
a second temperature sensor in heat exchange relation with fluid
which is passed in heat exchange relation with the tube, said first
and second temperature sensors being connected in a resistance
bridge network adapted to initiate the steps of heating surfaces of
the tube and delivering coolant through the tube.
3. The method of claim 1 wherein the step of heating surfaces of
the tube comprises, heating a volume of coolant; and delivering the
heated coolant through the tube.
4. The method of claim 1 wherein the step of delivering coolant
through the tube comprises, delivering liquified cryogenic gas
through the tube.
5. The method of claim 4 wherein the cryogenic gas is nitrogen.
6. The method of claim 4 wherein the step of moving fluid in heat
exchange relation with the tube comprises, delivering liquified
cryogenic gas, which is circulated through the tube, through a
means for driving a fan disposed in driving relation with the
fluid.
7. A method of controlling apparatus to maintain temperature in a
compartment within limits comprising the steps of: moving coolant
through heat exchanger apparatus; moving fluid in heat exchange
relation with the heat exchanger apparatus; generating a first
signal representative of temperature of fluid in the compartment;
generating a second signal representative of temperature of coolant
exhausted from the heat exchanger apparatus; combining the first
and second signals to produce a control signal; delivering coolant
through the heat exchanger apparatus responsive to said control
signal when the magnitude thereof is less than a predetermined
value; and delivering heated fluid through the heat exchanger
apparatus responsive to a control signal exceeding a predetermined
value.
8. A method of controlling temperature in a compartment comprising
the steps of: circulating liquid nitrogen through a primary coil;
circulating nitrogen from the primary coil through a pneumatic
motor arranged to drive a fan; circulating nitrogen from the motor
through a secondary coil, said primary and secondary coils being
positioned such that the motor moves air thereacross; and
exhausting nitrogen from the secondary coil outside the
compartment.
9. The method of claim 8 with the addition of the step of, stopping
flow of liquid nitrogen to the primary coil when a predetermined
quantity of ice has formed on surfaces thereof; delivering liquid
nitrogen to a heating apparatus; directing heated nitrogen vapor
through the primary coils, through the motor, and through the
secondary coil for melting ice on surfaces thereof.
10. Temperature control apparatus comprising, a coil; means to
deliver fluid through said coil; means to move air across the coil;
first sensor means to sense temperature of air moving across the
coil; second sensor means to sense the temperature of fluid
exhausted from the coil; means to generate a signal when the
temperature of air drawn from across the coil exceeds the
temperature of fluid exhausted from said coil by a predetermined
temperature; and means energized by said signal to heat surfaces of
the coil to melt ice thereon.
11. The combination called for in claim 10 wherein the first and
second sensor means each comprises temperature-sensitive resistance
means positioned in heat exchange relation with the air and the
coolant, respectively; and wherein the means to generate a signal
comprises a resistance bridge network having the first and second
sensor means disposed therein such that the bridge becomes
unbalanced to generate a signal when the difference in temperature
of air drawn across the coil exceeds the temperature of fluid
exhausted from the coil by a predetermined amount.
12. The combination called for in claim 10 wherein the means
energized by said signal to heat surface of the coil comprises,
heater means; signal responsive valve means arranged to deliver
coolant to the heating device; and means to deliver heated coolant
from the heating device to the coil.
13. The combination called for in claim 10 wherein the means to
move air across the coil comprises, a fluid driven motor connected
in driving relation with impellar means; and means to direct fluid
from said coil through the motor.
14. The combination called for in claim 10 wherein the means to
deliver fluid through the coil comprises, a container; conduit
means connected between said container and the coil; and means in
said conduit means for controlling the flow of coolant
therethrough.
15. The combination called for in claim 14 wherein the container
comprises an outer shell; an inner shell disposed inside said outer
shell; said shells being spaced apart to form a vacuum chamber
between adjacent surfaces thereof; a first pipe segment extending
through the wall of the inner shell; a second pipe segment
extending through the wall of the outer shell, said first and
second pipe segments having ends terminating in spaced apart
relation in said vacuum chamber; and an insulated coupling arranged
to join ends of said first and second pipe segments, said coupling
being disposed in the vacuum chamber.
16. Apparatus to control temperature in a cargo compartment of a
trailer comprising, a source of liquefied cryogenic gas carried by
the trailer; an evaporator in the compartment; first conduit means
connecting the evaporator and the source of liquefied gas; a heat
exchanger; second conduit means connecting the heat exchanger with
the source of liquefied gas; a pneumatically operated motor driven
fan arranged to cause air in the compartment to circulate over
surfaces of the evaporator; flow control means having a first
position wherein the source of liquefied gas is connected with the
motor, and having a second position wherein the heat exchanger is
connected with the motor and the evaporator; a burner arranged to
heat said heat exchanger; a source of fuel; and supply conduit
means between said burner and said source of fuel.
17. The combination called for in claim 16 wherein the heat
exchanger comprises an outer coil of conduit and an inner coil of
conduit, said outer coil being positioned about said inner coil,
said inner coil having a central axis disposed transversely of a
central axis of said outer coil.
18. The combination called for in claim 16 with the addition of a
current responsive valve in said supply conduit means; a pilot
burner adjacent said burner; a fuel supply line between said source
of fuel and said pilot burner; heat sensitive switch means adjacent
said pilot burner; and electrical conductors between said switch
means and said current responsive valve to prevent opening of said
valve unless temperature adjacent said pilot burner exceeds a
predetermined temperature.
19. Apparatus to control temperature in a compartment comprising, a
source of liquefied cryogenic gas; a primary evaporator in the
compartment; first conduit means connecting the primary evaporator
and the source of liquefied gas; a pneumatically driven motor in
the compartment; second conduit means between said primary
evaporator and said motor; a secondary evaporator in said
compartment; third conduit means connecting said motor and said
secondary evaporator; a fan driven by said motor; and means
supporting said primary and secondary evaporators such that the fan
moves air across each of the evaporators.
Description
BACKGROUND OF INVENTION
Apparatus has been devised heretofore for spraying vapor of
cryogenic liquid through nozzles into an insulated compartment in
which food products are transported. One such spray system is
described in U. S. Pat. No. 3,525,235 which points out undesirable
characteristics of such systems including variations of several
degrees Fahrenheit in temperatures at various locations throughout
a compartment.
Spray type systems which discharge cryogenic gas, such as nitrogen,
into a refrigeration compartment have numerous inherent
characteristics which render the use thereof undesirable because of
the presence of the nitrogen enriched atmosphere within the
compartment. Meats exposed to the atmosphere often absorb the
nitrogen resulting in discoloration of the meat. Vegetable products
over a period of time wilt when deprived of oxygen.
The nitrogen gas deposited by a spray system must be removed from
the compartment before products can be unloaded therefrom since
workman cannot breathe the nitrogen enriched atmosphere. Such
evacuation of the atmosphere within the cargo compartment has
required excessive quantities of nitrogen to cool the fresh air
after a door has been opened to unload a portion of the cargo. The
fresh humid air also resulted in excessive frosting.
Refrigeration systems heretofore devised, wherein vapor from
cryogenic gas was directed through coils of an evaporator through
which air within a compartment was circulated by a fan, have been
generally commercially unacceptable because excessive quantities of
moisture collect on the evaporator coils forming ice, substantially
reducing the heat transfer rate from the coolant to the air drawn
across surfaces of the evaporator.
Refrigeration systems heretofore employed for cooling cargo
compartments in which food products were transported did not have
the capability of circulating heated air uniformly through the
compartment when the ambient temperature outside the compartment
was less than the minimum allowable temperature inside the
compartment. Consequently transporting vegetables, such as lettuce
and tomatoes, during winter months in northern portions of the
United States and Canada required the use of space heaters
positioned at various locations in the compartment to prevent
freeze damage.
SUMMARY OF INVENTION
We have developed apparatus for controlling temperature within a
mobile compartment wherein vapor delivered from a source of liquid
nitrogen or other suitable cryogenic gas, is directed through the
evaporator coils for cooling same and then directed through a
pneumatically operated motor for driving a fan to circulate air in
the compartment across surfaces of the evaporator coils. Nitrogen
vapor after passing through the evaporator coils and motor is
exhausted to atmosphere.
Temperature sensitive control apparatus is employed for regulating
the flow rate of nitrogen vapor through the evaporator coils. The
control apparatus is adapted to divert nitrogen through a
vaporizer, exposed to ambient temperature, and to direct vapor
therefrom through a heating apparatus. The vapor is heated to a
temperature of for example 1,000.degree. F. and is delivered
through the evaporator coils and the pneumatic motor to cause
heated air to be circulated through the storage compartment.
Temperature sensing apparatus is disposed within the system for
sensing the temperature differential between return air drawn from
across the evaporator coils and nitrogen vapor exhausted from the
evaporator coils and pneumatic motor to ambient atmosphere.
We have observed that the heat transfer rate through walls of the
evaporator coils is high so long as the temperature differential
between the exhaust coolant and air drawn across surfaces of the
evaporator coils is less than approximately 35.degree. F. However,
as ice begins to form on surfaces of the evaporator coils, the
coils become insulated reducing the heat transfer rate through the
walls thereof which requires defrosting if efficient operation is
to be maintained. Control apparatus is connected to the temperature
sensors such that heated nitrogen vapor is routed through the
evaporator coils and the pneumatic motor for defrosting same when
the temperature differential between return air and exhaust gas
exceeds a predetermined limit, for example 35.degree. F.
The defrost cycle is terminated by the control apparatus when the
temperature of the heated exhaust vapor and the temperature of the
return air, which has passed over surfaces of the evaporator coils,
are substantially equal.
A primary object of our invention is to provide refrigeration
apparatus particularly adapted to control temperature of a
compartment in any vehicle, such as a transport trailer, railroad
car, airplane or ship, which is self-contained and which utilizes
liquified gas to refrigerate, heat and defrost a compartment
without connection to an external source of power.
Another object of our invention is to provide refrigeration
apparatus utilizing liquified gas to provide high refrigeration
capacity without altering the normal oxygen content in the
compartment.
A further object of the invention is to provide refrigeration
apparatus which employs the expanding force of cryogenic gas to
drive a pneumatic motor to provide forced air circulation through a
compartment for providing even temperature control
therethrough.
A still further object of our invention is to provide a
refrigeration apparatus, having a cryogenic evaporator coil,
adapted to be triggered to a defrost cycle when the temperature
differential between gas exhausted from the evaporator coil and
return air drawn across surfaces of the evaporator exceeds a first
predetermined limit and which is triggered back into a cooling
cycle when the temperature differential reaches a second
predetermined limit.
A further object of our invention is to provide refrigeration
apparatus for transport vehicles having a minimum number of moving
parts to provide a reliable system requiring minimum
maintenance.
A still further object of the invention is to provide a
refrigeration system for transport vehicles having high cooling
capacity which occupies minimum space within the cargo
compartment.
Other and further objects of our invention will become apparent by
reference to the detailed description hereinafter following and to
the drawings annexed hereto.
DESCRIPTION OF DRAWING
Drawings of a preferred embodiment of our invention are annexed
hereto so that the invention will be better and more fully
understood, in which:
FIG. I is a side elevational view of a transport vehicle having
refrigeration apparatus installed thereon:
FIG. II is a cross-sectional view taken substantially along line
II--II of FIG. I;
FIG. III is a schematic diagram of the refrigeration apparatus;
FIG. IV is a partially sectionalized elevational view of a storage
vessel for cryogenic gas;
FIG. V is an end view of the tank illustrated in FIG. IV;
FIG. VI is a cross-sectional view taken substantially along line
VI--VI in FIG. V;
FIG. VII is a plan view of heat exchanger coils;
FIG. VIII is a side elevational view of the heat exchanger coils;
and
FIG. IX is a diagrammatic illustration of the sensor arrangement
employed for triggering the defrost cycle.
Numeral references are employed to designate like parts throughout
the various figures of the drawing.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIGS. I and II of the drawing, the numeral 1 generally
designates a transport vehicle having a cargo compartment 2
disposed therein. The vehicle 1 may assume any desired
configuration having top and bottom walls 3 and 4 connected across
and upper and lower ends of side walls 5 and 6 and end walls 8 and
9 forming an insulated area on the inside thereof.
As will be hereinafter more fully described, one or more sources 10
and 11 of liquified cryogenic gas are provided for delivering
coolant to an evaporator 12. In the particular embodiment of the
invention illustrated in FIG. II, the evaporator 12 is secured to
an upper portion of front end wall 8 of the transport and is
arranged to force cooled air through a plurality of air ducts
14a-14f of varying lengths such that cooled air is distributed
uniformly throughout the compartment 2.
The source of cryogenic gas 10 and 11 is connected through a
vaporizer 15, preferably disposed outside the refrigerated cargo
area 2, to a heating device 16. Heated vapor from heating device 16
is delivered through coils of evaporator 12 for defrosting same and
for causing heating air to be delivered through the cargo
compartment.
As will be hereinafter more fully explained, a container 18 houses
apparatus employed for controlling the flow of both hot and cold
vapor through coils of evaporator 12 and an indicator 20 is
connected to suitable temperature sensing means inside cargo
compartment 2 for providing a visual indication of the temperature
therein.
Referring to FIG. III of the drawing, the source of cryogenic gas
10 preferably comprises an insulated container having an outer
shell 22 and an inner shell 24 spaced by a vacuum chamber 23, as
will be hereafter more fully described in the description relating
to FIGS. IV, V and VI of the drawing.
Container 10 contains liquid nitrogen 30 and the volume of
container 10 above the liquid nitrogen is filled with nitrogen
vapor. An insulated tube 32 is arranged to deliver liquid nitrogen
through flow control valve 34 to a line 36 communicating with
branch lines 38 and 40.
Branch line 38 is connected through valve 42 and line 44 with
primary coils 46 of evaporator 12.
The flow passage through valve 42 is controlled by suitable
actuating means 43 connected to a valve element in the body of the
valve. Actuator 43 is preferably pneumatically operated having a
movable element disposed therein such that a change in fluid
pressure delivered thereto through line 50 causes the movable
element to move thereby shifting the valve element for controlling
flow through valve 42. Line 50 is connected through a three-way
solenoid actuated valve 52 and line 54 to pneumatic temperature
controller 56.
Temperature controller 56 is of conventional design comprising a
capillary type temperature sensor 56a connected through line 56b to
control apparatus of the controller 56. Pressurized fluid is
delivered from controller 56 through solenoid actuated valve 43a to
line 54 so long as sensor 56a is maintained at a temperature higher
than that set on a thermostat in the controller. Controller 56
preferably has a visual indicator associated therewith to indicate
the temperature of air in the cargo compartment 2. Controller 56
preferably has temperature recording apparatus associated therewith
(not shown) for plotting temperature in relation to time. Such
instruments are commercially available from the Partlow Corporation
of New Hartford, N. Y..
Pneumatic temperature controller 56 is connected through line 58,
pressure regulator 60 and line 62 to an upper portion of nitrogen
tank 10 such that nitrogen vapor is delivered therethrough.
During a cooling cycle liquid nitrogen passes through branch line
38, valve 42, and line 44 to the coils of evaporator 12.
For defrosting coils of evaporator 12, liquid nitrogen passes
through branch line 40 to vaporizer 64 which is exposed to ambient
atmosphere outside of the cargo compartment 2 to provide sufficient
heating to cause the nitrogen to vaporize. Vapor from vaporizer 64
passes through line 66 and solenoid actuated valve 68 to the
heating device generally designated by numeral 16. Heated vapor
passing from heating device 16 passes through line 70 to vaporizer
12 as will be hereinafter more fully described.
The heating device 16 comprises a burner 72 and a pilot light 74
connected through lines 73 and 75, respectively, to valve 76. A
suitable fuel, such as propane, is delivered through line 78 from
tank 80.
A conventional pilot generator 82 is connected through conductors
83 and 84 to the coil 85a of thermostatically controlled pilot
single pole double throw relay 85 having a pole 85b and contacts
85c and 85d. Pilot generator 82 and pilot relay 85 are safety
devices adapted to prevent opening of valve 76 for releasing fuel
from burner 72 unless pilot light 72 has been previously ignited.
If pilot generator 82 is heated by pilot 74 current is generated
maintaining coil 85a of relay 85 in an energized condition causing
a circuit to be broken through pole 85b and contact 85c.
An electrical ignition system is provided comprising an igniter
plug 86 connected through plug wire 87 to an igniter system 88.
The igniter system 88 comprises an induction coil and a vibrator
which is arranged to periodically make and break the primary
circuit. The igniter system is connected through line 160 to a
source of low voltage electricity as will be hereinafter more fully
explained.
Line 160 is connected to the primary of the induction coil through
an automatic switch which is actuated by the vibrator. When the
vibrator opens the circuit, the induction coil generates a high
voltage, delivered through plug wire 87, which is sufficient to
cause a spark momentarily to jump the static spark points of
igniter plug 86 for igniting fuel delivered through burner 72.
A heat sensitive switch 69, adapted to close when temperature is
more than, for example, 200.degree. F and to open when temperature
is less than 190.degree. F, is positioned adjacent burner 72.
Switch 69 is disposed in the energizing circuit connected with
solenoid actuated valve 68 through which vapor is delivered to the
heating device 16. It should be readily apparent that switch 69
prevents actuation of valve 68 to an open position unless burner 74
has been ignited for heating vapor passing through heating device
16.
Heated vapor delivered from heating device 16 passes through line
70 to line 44 communicating with the entrance end of primary coils
46 of evaporator 12. Line 70 also communicates through solenoid
actuated valve 90 with line 92 which is connected to the intake
passage of a pneumatic motor 94. The outlet passage of motor 94 is
connected through a line 96 to secondary coils 48 of evaporator 12,
said secondary coils being connected through line 98 to muffler 100
through which nitrogen vapor is exhausted to atmosphere outside the
cargo compartment 2 of the vehicle.
Heating device 16 has coils 15 and 15' as illustrated in FIGS. VII
and VIII which are preferably arranged such that the axes thereof
are disposed perpendicularly. The outer coil 15 has an inlet end
15a, connected through valve 68 to pipe 66 and vaporizer 64, and an
outlet end 15b adapted to connect with the inlet end 15a' of the
inner coil 15'. Inner coil 15' has a discharge end 15b' connected
to pipe 70 which delivers heated vapor to evaporator 12.
Heat from burner 72 is transferred through walls of coils 15 and
15' for heating nitrogen vapor flowing therethrough. Vapor
discharged from coil 15' is preferably heated to a temperature of
approximately b1,000.degree. F. providing a high heating capacity
while expending a relatively small volume of liquid nitrogen. The
volume of the heated vapor is approximately 600 times the volume of
liquid nitrogen delivered to vaporizer 64 from tank 10.
As best illustrated in FIGS. IV, V and VI, tank 10, comprising
inner and outer shells 22 and 24 separated by evacuated space 23,
has pipes extending through the walls thereof. Liquid nitrogen
flows into and out of tank 10 through tube 10a connected to line 32
communicating with evaporator 12 and vaporizer 64. Vapor passes
through tube 10b to temperature controller 56. A vacuum line 10c is
sealed after space 23 has been evacuated.
Lines 10a, 10b and 10c are preferably constructed of stainless
steel or other suitable material. To prevent heat transfer from the
tubes, some of which are exposed to ambient temperature, each of
said tubes is segmented (FIG. VI) and a coupling 10d joins segments
10b' and 10b". Coupling 10d is constructed of polyvinyl chloride or
other suitable heat insulator material and is positioned in vacuum
chamber 23 between inner and outer shells 22 and 24. Thus, coupling
10d interrupts the heat conductive path along walls of segments
10b' and 10b" of tube 10b.
Pneumatic motor 94 has a shaft 102 on which a fan blade 104 is
mounted such that the flow of nitrogen vapor through pneumatic
motor 94 causes fan blade 104 to rotate causing air within the
cargo compartment 2 of vehicle 1 to pass across the primary coils
46 and the secondary coils 48 of evaporator 12.
Shaft 102 has a pulley 106 secured thereto about which a belt 108,
in driving engagement with a pulley 110 on an alternator, extends.
Alternator 112 is a standard AC generator of the type normally used
in present day modern automobiles such as the Delco "DELCOTRON,"
the Ford "Autolite" and alternators manufactured by Motorola and
Leech-Neville. The alternator 112 is connected to be driven by the
pneumatic motor 94 and has a field terminal, an output terminal and
a neutral terminal.
Alternator 112 is connected with a voltage regulator 120 which
serves to regulate the voltage and current. Regulator 120 has a
field terminal connected to line 114, and an output terminal
connected through line 122, rectifier 124 and line 126 to line 153,
as will be hereinafter described for maintaining battery 140 in a
charged condition.
The control system illustrated in FIG. III generally comprises
double pole-double throw relays R1, R2, and R3 actuated by signals
delivered from temperature controller 56 and defrost controller
128.
When thermostat 56t of temperature controller 56 calls for cooling,
indicator light G is illuminated and valve 52 is held open.
When defrost controller 128 calls for defrosting, indicator light A
is illuminated and the coils of relays R1 and R2 are energized to
turn on the burner 72, to permit opening of valve 68, and to open
valve 43.
During heat and defrost cycles valve 43 is closed because line 50
is vented through valve 52.
Defrost controller 128 comprises a resistance bridge network
arranged for energizing or de-energizing a relay which controls
apparatus for triggering and terminating a defrost cycle.
The resistance bridge network of defrost controller 128 includes a
first thermistor 136 mounted in vapor exhaust line 98 through which
nitrogen vapor is exhausted to atmosphere. Thermistor 136 is a
temperature-sensitive resistance, the resistance of which varies
with temperature.
A second thermistor 138 is disposed inside cargo compartment 2 and
is positioned such that air drawn across coils 46 and 48 of
evaporator 12 flows across thermistor 138 when returning to the
cargo compartment 2.
Thermistor 136 is connected through lines 136a and 136b to defrost
controller 128 and thermistor 138 is connected thereto through
lines 138a and 138b.
Thermistors 136 and 138 are connected in a resistance bridge
network such that when the resistance of thermistor 136 increases
more than the resistance of thermistor 138, because ice has formed
on coils 46 and 48 of evaporator 12, the resistance bridge will
become unbalanced. Current then energizes the coil 128a of the
relay connected across the bridge network, causing the flow of
liquid nitrogen to evaporator 12 to be stopped and causing heated
nitrogen vapor to flow therethrough melting ice from the surface
thereof.
It should be apparent that temperature sensor devices such as
silicon diodes and thermocouples may be employed in lieu of
thermistors 136 and 138 for sensing temperature and that changes in
voltage or current may be employed to trigger defrost controller
128. It should be further apparent to persons skilled in the art
that defrost controller 128 may include other and further devices
for detecting an unbalanced condition in the bridge network. For
example, we contemplate employment of a differential integrated
circuit amplifier to detect the unbalance and to feed an output
voltage to a phase-controlled pulse generator which delivers
trigger pulses to a triac and, thus, controls current through lines
173 and 174 to initiate and terminate defrost cycles.
Current for actuating the control apparatus and the heating
apparatus is delivered from battery 140 having a negative terminal
connected to ground and a positive terminal connected through a
fuse 141 and conductor 142 to an ammeter 143. The ammeter 143 is
connected through line 116 to alternator 112 and through a line 144
to terminals 145a and 145b of a double pole-double throw main power
switch 145.
The main power switch 145 has an off position wherein pole 145e is
disconnected from contacts 145a and 145b, a "cool only" position
wherein pole 145e engages contact 145a, and a "cool and heat"
position wherein pole 145e engages contact 145b. In the "cool and
heat" position pole 145f of main switch 145 engages contact 145d
allowing a circuit to be completed through contact 56 Rc of relay
56r of temperature controller 56 to the coil of relay R1 as will be
hereinafter more fully explained. When the switch 145 is in the
"cool only" position the contact 56 Rc of temperature controller 56
is isolated from the control system.
Pole 145e of the main switch 145 is connected through line 146 and
line 147 to the pole 56Ra of the relay in temperature controller
56.
Pole 145e of main switch 145 is connected through line 146, line
148 and line 149 to terminal 150 of defrost controller 128.
Terminal 150 of defrost controller 128 is connected to pole 128b of
the relay in the defrost controller and is connected to lines 136b
and 138b connected to the thermistors 136 and 138, respectively, in
a bridge network.
Pole 145e of main switch 145 is connected through conductors 146,
148 and 151 to the pole R1a of relay R1.
The pole 145e of main switch 145 is connected through conductors
146 and 152 to the pole R2b of relay R2, and through conductors 146
and 153 to the pole 85b of pilot relay 85.
From the foregoing it should be readily apparent that when pole
145e of main switch 145 engages the contact 145a or 145b the
positive terminal of battery 140 is connected to pole 85b of pilot
relay 85, to pole R2b of relay R2, to pole R1a of relay R1, to pole
128b of defrost controller 128, and to pole 56Ra of temperature
controller 56.
Remaining parts of the electrical control system will be
hereinafter described in conjunction with the operation
thereof.
OPERATION
The operation and function of the apparatus hereinbefore described
is as follows:
Poles 145e and 145f of main power switch 145 are moved to the "cool
and heat" position for energizing the control circuit.
If the thermostat 56t of temperature controller 56 is calling for a
cooling cycle, electrical current is directed from the positive
terminal of battery 140 to pole 56Ra of temperature controller 56,
as hereinbefore described, and through contact 56Rb of the relay of
temperature controller 56, conductor 170, contact R3c and pole R3a
of relay R3, and conductor 173 to lamp G to provide visual
indication that cooling is required.
Unless a defrost cycle has been initiated, the positive terminal of
battery 140 is connected through pole 128b of the relay in defrost
controller 128 to contact 128d, and through line 172 to the coil of
solenoid actuated valve 52, holding valve 52 open permitting flow
of nitrogen vapor therethrough. Vapor from container 10 passes
through line 62, regulator 60, line 58, valve 43a, line 54, valve
52 and line 50 to pressurize actuator 43 for maintaining valve 42
in an open position.
Liquid nitrogen then flows through line 32, valve 34, line 36,
branch line 38, valve 42 and line 44 into the primary coils 46 of
evaporator 12. The liquid nitrogen is at a temperature of
approximately -320.degree. F, and as heat is absorbed through the
walls of primary coils 46 air adjacent thereto is cooled. Nitrogen
from primary coils 46 passes through line 92 for driving pneumatic
motor 94 causing fan 104 to circulate air across the primary and
secondary coils. Nitrogen exhausted from motor 94 passes through
line 96 to secondary coils 48 to absorb as much heat as possible
before being exhausted through line 98 across thermistor 136 to
ambient atmosphere through muffler 100.
It should be readily apparent that no nitrogen passes into the
cargo compartment of the vehicle.
As ice forms on coils 46 and 48 of the evaporator 12, the rate of
heat transfer through walls of the coils is reduced. When the
temperature of air moving across the coils of the evaporator 12
reaches a predetermined temperature, for example, 28.degree. F,
above the temperature of nitrogen discharged across thermistor 136,
the resistance bridge network in defrost controller 128 becomes
unbalanced energizing the coil 128a, causing pole 128b to move out
of engagement with contact 128d and into engagement with contact
128c.
When the circuit through contact 128d is broken, the flow of
current through conductor 172 and the coil of solenoid actuated
valve 52 is stopped causing valve 52 to shift to a position
stopping the flow of liquid nitrogen therethrough and causing line
50 connected to actuator 43 to be vented to atmosphere. This closes
valve 42 stopping the flow of liquid nitrogen to coils of
evaporator 12.
When an electrical circuit is completed through contact 128c of
defrost controller 128, current flows through conductor 173 and
conductor 174 to illuminate lamp A indicating that a defrost cycle
has been initiated. Current flows from conductor 174 through
conductor 175 to energize the coil of solenoid actuated valve 90
for opening valve 90.
Current is also directed through contact 128c, conductor 173,
conductor 176, and conductor 177 for energizing the coil of relay
R3. Current then flows from conductor 176 through contact R3f, pole
R3b of relay R3, and conductor 178 to pole R2a. If pilot light 74
is burning, pilot generator 82 will maintain the coil 85a of pilot
relay 85 in an energized condition which maintains the coil of
relay R2 in a non-energized condition.
Current from the pole R2a of relay R2 thus passes through contact
R2c and conductor 165 to energize the coil of relay R1. When the
coil of relay R1 is energized current from pole R1a, connected to
the positive terminal of battery 140 as hereinbefore described,
passes through contact R1d and conductor 179 to heat sensitive
switch 69. When the heat sensitive switch 69 is heated to a
temperature, for example 200.degree. F. the circuit is completed
therethrough connecting current through conductor 180 to the coil
of solenoid actuated valve 68 causing valve 68 to open.
When the coil of relay R1 is energized, the circuit is completed
from pole R1b through contact R1f and through conductors 181 and
182 opening valve 76 causing fuel to flow from container 80 through
line 78, valve 76, and line 73 to burner 72 for heating the coils
15 and 15' of heating device 16.
Heated vapor flow through conduit 70, valve 90, and line 92 to
motor 94 for melting any ice on the surface thereof. Heated gas
also flows from conduit 70 through conduit 44 to primary coils 46
of evaporator 12. Vapor discharged from motor 94 passes through the
secondary coils 48 and is exhausted to atmosphere.
When the temprature differential between sensors 136 and 138
reaches a predetermined limit, for example when the temperatures
are substantially equal the defrost controller 128 causes current
to flow through 128a switching the pole 128b out of engagement with
contact 128c, de-energizing the coils of relays R1 and R3 and
de-energizing the coil of solenoid actuated valve 52. When such
occurs the burner is turned off, valve 68 is closed stopping the
flow of nitrogen vapor to heating device 16, solenoid actuated
valve 90 is closed blocking the bypass directly to motor 94.
As pole 128b of defrost controller 128 moves into engagement with
contact 128d the coil of solenoid actuated valve 52 becomes
energized opening said valve which causes valve 42 to be opened
permitting flow of liquid nitrogen to the primary primary coils 46
of the evaporator 12.
It should be appreciated that the intense heat of vapor delivered
from the heating device 16 results in very rapid melting of ice on
surfaces of the coils 46 and 48 of evaporator 12 and on the
surfaces of motor 94. Although motor 94 is running during the
defrost cycle, the defrost cycle is so short that the cargo
compartment is not heated appreciably.
When the thermostat 56t in temperature controller 56 calls for a
heating cycle, a switch in the thermostat 56t is closed energizing
the coil of relay 56R causing pole 56Ra to move out of engagement
with contact 56Rb into engagement with contact 56Rc, and energizing
the coil of solenoid actuated valve 43a causing valve 43a to
close.
When pole 56Ra of temperature controller 56 engages contact 56Rc,
current is directed through a conductor 185 through pole 145f of
main power switch 145 through contact 145b, and through conductor
186 to illuminate lamp R. Current is also directed from contact
145d to main power switch 145 through conductor 187, contact R3e
and pole R3b of relay R3, and through conductor 178 to pole R2a of
relay R2 for energizing the coil of relay R1 to light the burner
72, and to direct nitrogen vapor through valve 68, as hereinbefore
described in the discussion related to the defrost cycle.
From the foregoing it should be readily apparent that we have
developed apparatus employing liquid nitrogen, or other suitable
cryogenic material, for cooling, heating and defrosting. The
control system is self-sustained, being energized by a battery 140
which is maintained in a charged condition by alternator 112 driven
by motor 94 which is driven by the flow of nitrogen
therethrough.
The system is completely automatic employing thermostat control
means to initiate cooling and heating cycles and employing means
for sensing a temperature differential between air in the cargo
compartment and nitrogen vapor discharged from the evaporator coils
for initiating and terminating defrost cycles.
It should be appreciated that other and further embodiments of our
invention may be devised without departing from the basic concept
of the invention.
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