Air Freight Temperature Controlled Device Using Liquid Nitrogen
1. An air freight unit load device (ULD) for an aircraft with a cargo bay, comprising:
- an enclosure withone or more cryogenic tanks;
a heat exchanger coupled to the one or more cryogenic tanksa Stirling engine having a cold sink coupled to the one or more cryogenic tanks;
a payload bay, isolated from the cargo environment, with a double wall and Vacuum Insulated Panels (VIPs) placed between the walls;
one or more valves coupling the cryogenic tanks, the heat exchanger, and the Stirling engine;
a controller coupled to the valves and one or more sensors to maintain temperature of the payload at a predetermined temperature setpoint, anda blowout panel attached to a side of the ULD,wherein the enclosure fits predetermined dimensions in an airplane cargo bay.
Systems and methods are disclosed for transporting products with an airplane by controlling temperature in a payload bay using cryogenic coolant and a heat exchanger to cool the payload bay and heat from a heater; recycling exhaust from the heat exchanger to power a Stirling engine; charging a storage device with power from the Stirling engine; housing the payload bay as part of a modular, stackable module in an aircraft bay for transportation; and venting exhaust gas to an exterior of the airplane.
- 1. An air freight unit load device (ULD) for an aircraft with a cargo bay, comprising:
an enclosure with one or more cryogenic tanks; a heat exchanger coupled to the one or more cryogenic tanks a Stirling engine having a cold sink coupled to the one or more cryogenic tanks; a payload bay, isolated from the cargo environment, with a double wall and Vacuum Insulated Panels (VIPs) placed between the walls; one or more valves coupling the cryogenic tanks, the heat exchanger, and the Stirling engine; a controller coupled to the valves and one or more sensors to maintain temperature of the payload at a predetermined temperature setpoint, and a blowout panel attached to a side of the ULD, wherein the enclosure fits predetermined dimensions in an airplane cargo bay.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- 14. A method for transporting products with an airplane, comprising:
controlling temperature in a payload bay using cryogenic coolant and a heat exchanger to cool the payload bay and heat from a heater; recycling exhaust from the heat exchanger to power a Stirling engine; charging a storage device with power from the Stirling engine; housing the payload bay as part of a modular, stackable module in an aircraft bay for transportation; and venting exhaust gas to an exterior of the airplane.
- View Dependent Claims (15, 16, 17, 18, 19, 20)
This application is a continuation in part of U.S. application Ser. No. 15/893,487, the content of which is incorporated by reference.
The present invention relates to temperature-controlled air freight type unit load devices (ULD).
The airline industry has been using Unit Load Devices (ULD) for decades. It allows a large quantity of cargo to be bundled into a single unit, saving ground crews time and effort. However, these units typically are not temperature controlled. Perishable items such as fruits and vegetables, fresh meats and fish, flowers, and plants typically will be damaged in flight without a temperature-controlled environment. The current temperature controlled ULDs require the inconvenience of replacing ice or dry ice, or being plugged into a power box for 6 hours per recharge.
In one aspect, systems and methods are disclosed for transporting products with an airplane by controlling the temperature in a ULD payload bay using cryogenic coolant and a heat exchanger to cool, and an electrical power source and heating element to heat the ULD payload bay; and providing electrical power to a storage device by means of a gas turbine generator and a Stirling engine; and housing the payload bay as part of a modular, stackable module in an aircraft bay for transportation.
Implementations of the above aspect may include one or more of the following: The system is powered by liquid nitrogen which heats or cools the payload bay as required to maintain a constant temperature for the customer'"'"'s product. Vacuum Insulated Panels (VIPs) thermally isolate the payload bay from the harsh, rapid, and extreme temperature changes typically experienced in airline cargo areas. The system is autonomous and can operate without additional power for up to 10 days. Refueling is accomplished with a cryogenic bulk tank or service truck. Sensors are deployed to report temperature to a remote computer for monitoring the temperature of the payload and shock encountered throughout the shipping duration, among others.
In another aspect, cryogenic tanks are connected in parallel to a heat exchanger and a Stirling engine. Two solenoid valves determine the flow of liquid nitrogen through the heat exchanger for cooling and the Stirling engine for electric power. The solenoid valves are energized and opened by the controller and operate independently when there is a demand for cooling or a demand for recharging the deep cycle batteries. An additional source of electrical power is provided by a gas turbine generator that is powered by the exhaust from both the heat exchanger and the Stirling engine. A thermal sensor inside the payload bay communicates the current temperature to the controller. An electric heating element is placed in the same airflow path as the heat exchanger. A fan blows air through both the the heat exchanger for cooling and the electric heating element for heating. Storage devices such as deep cycle batteries are charged by a Stirling engine generator and a gas turbine generator to provide power for the electric heating element, fan, control electronics, data storage and telemetry. The ULD has an exhaust port and the exhaust nitrogen gas is vented outside the ULD. The gas may be vented directly into the cargo area or a hose may be used to vent the gas to a quick connect port that vents to the outside of the airplane.
In another aspect, when liquid nitrogen is prohibited during flight, the ULD can be precooled or preheated before takeoff. During flight, liquid nitrogen will not be stored, used, or exhausted by the ULD. The ULD will still maintain the setpoint, within a few degrees, without the use of coolant. This method of operation is referred to as “Passive Shipping”. Prior to flight the ULD is connected to a cryogenic bulk tank or service truck for coolant and to an electrical power source, such as a generator or AC outlet to recharge the deep cycle batteries and also supply power to the heating element when there is a demand for heat. The ULD is then operated in a cooling or heating capacity until the predetermined shipping setpoint is attained. The coolant and power are disconnected and the ULD is loaded into the cargo area of the airplane with no liquid nitrogen in the ULD cryogenic tanks. During flight, the ULD will maintain the setpoint temperature within a few degrees, because the ULD is extremely well insulated with state-of-the art Vacuum Insulated Panels that significantly reduces heat flow into or out of the ULD. When there is a demand for heat during Passive Shipping, the deep cycle batteries power the electric heating element. Without liquid nitrogen as a power source, the Stirling engine and gas turbine generator do not operate. Therefore the heating capability in Passive Shipping mode will be less than normal, but sufficient, to maintain the predetermined setpoint temperature to within a few degrees. After landing the ULD is again connected to a coolant and power source wherein cooling or heating resumes to bring the ULD exactly to the predetermined setpoint temperature. The cryogenic tanks in the ULD may also be refilled at this time for autonomous operation during transport to the final destination.
In another aspect, when the airline company not only restricts the use of liquid nitrogen but also restricts empty cryogenic tanks during flight, then the cryogenic tanks are removed from the ULD.
In another aspect, an alternative method of cooling is known as Direct Inject. The liquid nitrogen is sprayed into the payload bay. The design eliminates the heat exchanger and utilizes a tube with a multiplicity of nozzles. When there is a demand for cooling, the solenoid valve is energized, and the liquid nitrogen flows from the cryogenic tanks, through the solenoid valve, through the tube, and sprays through the nozzles and into the payload bay. The liquid nitrogen evaporates and provides extremely efficient cooling. The evaporated nitrogen gas increases the pressure of the payload bay, forcing the exhaust nitrogen gas through a vent pipe. But since the air in the cargo area of the airplane is continuously recycled with external air, oxygen depletion is not a significant concern. In certain aircraft, there may be a quick connect port that vents outside the airplane. The ULD vent hose is attached to that port, and the exhaust nitrogen vents outside the airplane, further reducing oxygen depletion concerns. The advantages of Direct Inject are faster and more efficient cooling. The disadvantages are extremely cold spots on product near the cryogenic spray and non-uniform distribution of cooling throughout the payload bay.
In another aspect, a blowout panel is attached to the ULD. The blowout panel consists of a hollow box approximately 2 feet square, wherein the exterior side of the blowout panel is exposed to the interior environment of the aircraft. The interior side of the blowout panel consists of two parts, one of which is an unmoving frame while the other is a panel that is attached to guide poles. The panel fits within the unmoving frame in such a way as to make the two parts airtight. Springs around the guide poles provide force so as to keep the panel sealed against the unmoving frame. The blowout panel is made of stainless steel and filled with a Vacuum Insulated Panel, making it thermally equivalent with the typical surface of the ULD. In the unlikely event of a pressure drop inside the airplane, the blowout panel will experience a force arising from the pressure difference between the interior of the ULD and the interior of the aircraft. This pressure difference will create a force against the blowout panel, greater and opposite to that of the springs. This force will cause the panel to push away from the unmoving frame, allowing the interior pressure of the ULD to rapidly equalize with the interior pressure of the aircraft. In the event of decompression of the aircraft, the air inside the cargo area may drop as much as 10 PSI in one second. This large instantaneous pressure drop equates to 1,440 pounds per square foot, and this pressure difference between the air outside and inside the ULD can cause the ULD to behave like a bomb and explode. However, the blowout panel counteracts this by rapidly equalizing the pressures within and without the ULD, effectively eliminating the risk of the ULD exploding. After decompression is complete, the blowout panel will return to its closed and sealed state, thus allowing for normal operation to recommence without significant temperature losses from the decompression.
In another aspect, one or more load cells are placed such that they support the weight of the liquid nitrogen tanks. Blocks are welded above and below the load cells to limit the load cell travel during high shock landings and takeoffs. The load cells enable the accurate reading of the volume of liquid nitrogen in liquid nitrogen tanks.
In another aspect, one or more LN2 tanks are positioned within the ULD in a horizontal fashion. The ULD payload bay geometrical configuration doesn'"'"'t allow for LN2 tanks to be placed vertically within, thus horizontally placed tanks are required. Due to the horizontal configuration of the LN2 tanks, the liquid nitrogen within may move around in such a way as to expose gaseous nitrogen to the liquid nitrogen outlet. Baffles are placed within the LN2 tank to partially restrict liquid flow and maintain liquid nitrogen around the liquid nitrogen outlet.
In another aspect, large fans and large heat exchangers are positioned within the ULD such that a large surface area of the heat exchanger is exposed to the payload bay and the fans draw air flow through the heat exchanger and into the payload bay. The rapid cooling of products is sometimes necessary, especially when the ULD will not be actively cooling during a large portion of time with product within it, such as when the aircraft it is on is in flight. The large heat exchangers allow for a large surface area to be exposed to the payload bay atmosphere. Cooling of the payload bay occurs through conduction, or the transfer of thermal energy from one substance to another by direct contact. The large surface area allows for more conduction to occur, or in other words for quicker cooling to occur. The large fans create air flow through the heat exchangers, causing convection to occur. Convection is conduction with added air flow, and is typically much more effective at transferring heat than conduction alone. The combination of large fans and large heat exchangers allow for extremely fast cooling of the payload bay. This enables the ULD to rapidly freeze or cool product prior to transport, without having to freeze or cool product during transit.
In another aspect, fiberglass beams are used in place of steel or similar beams to provide structural support. Fiberglass is much lighter compared to steel or similar beams. This is important for air transport because the weight of an object being transported directly influences how much money it costs to transport it, much more so than other methods of transportation. The fiberglass beams also act as thermal breaks, stopping the transfer of heat from the interior of the aircraft to the payload bay of the ULD. While fiberglass isn'"'"'t as insulating as vacuum-insulated paneling, it is much more insulated then steel or comparable materials. Thus, fiberglass is the best material with consideration being given for cost, insulation properties, and specific weight.
In another aspect, safety valves are designed with several components whose purposes are to prevent the valves from failing in the open condition. Within an LN2 tank, the nitrogen will slowly warm up within. This increase in thermal temperature will cause a larger percentage of the nitrogen mass to be in the gaseous phase, which has a much higher specific volume than liquid nitrogen. When some of the liquid nitrogen within the tank phase changes to a gas, it will increase the pressure of the contents. This will increase indefinitely without further measures being taken. A safety valve is a component that maintains the pressure of a tank below a certain value. An LN2 tank with a safety valve will cycle through a pressure lower than the pressure of the safety valve, steadily increase to a pressure above that of the safety valve, and then drop as LN2 is vented from the tank through the safety valve. If this venting process takes a relatively long time, the venting LN2 will freeze any water vapor near the safety valve, causing the safety valve to freeze in an open position. This safety valve failure would cause all the LN2 within the LN2 to eventually evaporate and exit through the failed safety valve into the ULD, causing a potentially hazardous environment. The resulting drop in pressure of the LN2 tank would also render the cooling system inefficient. The safety valves are designed to have an extended length of copper tubing between the tank and safety valve. This tubing will enable to LN2 to warm up for a longer time before reaching the safety valve, maintaining a warmer safety valve. The copper tubing may have cooling fins along its length to aid in further warming up of the LN2 flowing through the tubing. An electrical heater is also attached to the safety valve, close to the valve'"'"'s moving parts. This prevents the safety valve from freezing and sticking in the open position.
In another aspect, the ULD is equipped with a GPS tracker to enable constant remote tracking and a wireless datalogger to enable remote datalogging. Some types of highly valuable biomedical products require stringent environmental controls to maintain a high level of quality. It is highly desirable that when transporting such materials there is a means to track and monitor it. The GPS tracker and wireless datalogger enables this.
Advantages of the temperature controlled ULD invention may include one or more of the following: The system provides a temperature controlled environment to protect perishable products throughout the duration of airline flights and longer. The system provides cooling or heating for a large ULD and can maintain a constant internal temperature in the cargo area temperature environment that ranges from 50 deg C. on runways to −40 deg C. at flight altitudes. The ULD only requires a refill of liquid nitrogen once a week, which takes about 15 minutes. The system is easy to use, and the liquid nitrogen can be filled by the normal procedure used to fill cryogenic tanks in the field. There are no 6 hour power hookups or replacing ice or dry ice.
Turning now to the figures, in one embodiment,
In one embodiment, the liquid nitrogen temperature controlled device has the capability of cooling or heating the payload bay 19 and maintaining the predetermined setpoint temperature to within +/−2 deg C. in an air cargo compartment environment ranging from −40 to 50 deg C. for 10, 20, 30 or 90 days. Longer durations are possible with larger cryogenic tanks and deep cycle batteries.
In another embodiment, the controller 6 receives input from a thermal sensor 5, compares that temperature to a predetermined setpoint temperature and utilizes a Proportional Integral Derivative (PID) module that accurately maintains the payload bay 19 temperature.
In another embodiment, Operational data is recorded and stored in a data recorder and transmitter 7. Through telemetry a remote receiver monitors the operational data.
Cooling the payload bay 19 is accomplished as follows: When the payload bay 19 temperature is higher than the predetermined setpoint temperature, the controller 6 calls for cooling. The controller 6 communicates with and opens solenoid valve 17, which causes liquid nitrogen to flow from the cryogenic tanks 1 into and through the heat exchanger 2. The liquid nitrogen temperature as it enters the heat exchanger 2 is approximately −196 deg C., immediately providing substantial cooling in the heat exchanger 2. A fan 4 moves the air 18 through the heat exchanger 2 and throughout the payload bay 19 to ensure the customer product receives ample and uniform cooling by convection.
Heating the payload bay 19 is accomplished as follows: When the payload bay 19 temperature is colder than the predetermined setpoint, the controller 6 calls for heat. The controller 6 communicates with and energizes the electric heating element 3. The fan 4 moves the air 18 through the electric heating element 3 and throughout the payload bay 19 to ensure the customer product receives ample and uniform heating by convection.
Power is derived from the Stirling engine 11 as follows: The controller 6 detects the deep cycle battery voltage is below a preset threshold and opens solenoid valve 14 causing liquid nitrogen to flow from the cryogenic tanks 1 through the Stirling engine cold sink 13. The efficiency and power of a Stirling engine 11 is determined mainly by the temperature difference between the cold sink and the heat sink. Since the liquid nitrogen temperature entering the cold sink 13 is approximately −196 deg C. and the ambient temperature, the hot sink, is always warmer than −40 deg C., the temperature difference between the cold sink and the hot sink will always be greater than 156 deg C., thus providing the Stirling engine 12 sufficient energy to rotate a generator 12 that is connected directly to a Stirling engine 11. Generator 12 then recharges deep cycle batteries 7.
Power is derived from the gas turbine generator 16 as follows: When there is liquid nitrogen flowing from the cryogenic tanks 1 through the heat exchanger 2, or the Stirling engine cold sink 13, or both 2 & 13, the nitrogen gas evaporates as it absorbs heat and expands to 700 times the original liquid volume. Gas expansion is ideal for powering the gas turbine generator 16. Whenever there is a demand for cooling or a demand for operating the Stirling engine, expanded nitrogen gas flows through the gas turbine generator 16 and it delivers energy to recharge deep cycle batteries 10.
The payload bay 19 has double walls. Vacuum Insulated Panels (VIPs) 20 are placed between the walls to substantially reduce payload bay 19 thermal losses.
The payload bay 19 is box shaped with 4 doors for easy access to the contents of the payload bay. The entire thermal system is located in the two opposing sides of the ULD shown in
Now referring to
In the event of an immediate depressurization of the aircraft interior, or the immediate exterior of the ULD, the pressure from the payload bay 19 suddenly becomes much higher than the pressure on the exterior of the ULD. The ULD is not designed as a pressure vessel and could behave like a bomb from the sudden pressure gradient, if not for the blowout panel 29. When the force resulting from the pressure within the payload bay 19 reaches past a certain level, the blowout panel 29 will immediately act as a pressure equalizer, eliminating any potential explosive behavior from the ULD.
The one or more springs 38 that fit over the guide rails 37 and guide poles 36 provide a spring force by pushing against the exterior side 30 and the sliding panel 33. Since the exterior side 30 is part of the frame 32 and does not move, the sliding panel 33 is pushed firmly against the hole 34. In the event of a depressurization of the immediate exterior of the ULD, the pressure within the payload bay 19 becomes greater than that of the pressure without the payload bay 19. The resulting force will overpower the spring force from the one or more springs 38 and push the sliding panel 33 along the guide poles 36 and create a substantial pathway for air to escape the payload bay 19, allowing for the rapid pressure equalization from within and without the payload bay 19.
Now referring to
One or more load cell units 39 support the full weight of the cryogenic tanks 1, with the full weight of the cryogenic tanks being supported by the cantilevers formed by the load cells 40. During high-shock landings, high-shock take-offs, and turbulent flight of aircraft, the upper guard 41 and lower guard 42 prevent the load cell 40 from deflecting outside operational limits.
Now referring to
One or more baffles 44 are placed within the LN2 tanks 43. The baffles 44 are positioned so that they partially block liquid flow during periods of acceleration, ensuring that the LN2 outlet 45 is always sufficiently covered, enabling the LN2 tanks 43 to provide a steady and continuous supply of liquid nitrogen 46.
The LN2 tanks 43, should they not have baffles, when tilted left or right will be at more risk to move the liquid nitrogen 46 in such a way as to expose the LN2 outlet 45 to gaseous liquid nitrogen. LN2 tanks 43, with baffles, shield the LN2 outlet 45 more efficiently from gaseous liquid nitrogen during periods of abrupt changes of motion.
Now referring to
Now referring to
Now referring to
Now referring to
Now referring to
Heat gains are minimized in the cryogenic plumbing by using stainless steel sheet metal surrounding the cryogenic piping that is vacuum sealed. These assemblies are referred to as Vacuum Jacketed Piping. Fittings for input and output connection in the assembly are configured and welded or bayoneted with cryogenic connectors in place. Preferably, the connection between the Vacuum Jacketed Piping is done with a bayonet connector that uses thermal contraction/expansion mechanisms. The contraction/expansion provides a mechanical connection for sections of Vacuum Jacketed Piping with a low heat gain connection. The bayonets are constructed of stainless steel with the nosepiece of the male bayonet being made from a dissimilar material such as the polymer INVAR36 to prevent mechanical seizing. A secondary o-ring seal is used at the flange of each bayonet half to provide a seal in which a gas trap is formed between the close tolerance fitting sections of the bayonet assembly. This gas trap is formed using the initial cryogen flow which is vaporized and forms a high pressure impedance for the lower pressure liquid, thus forming a frost free connection with lowered heat gain to the cryogenic flow.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.