LOW PRESSURE REFRIGERATION SYSTEM

Description

FIELD OF THE INVENTION

The present invention is in the field of low pressure refrigeration.

DISCUSSION OF RELATED ART

In ancient times, people used ice for cooling but ice transport remained difficult due to melting and slower transportation in the past. Therefore, closed-loop systems such as heat pumps became fashionable, but heat pumps require electrical connections or fossil fuel infrastructure. Evaporative cooling has also been popular but evaporative cooling requires a water supply. A variety of different thermal capacitance methods such as absorbing heat with melting wax provides a means for absorbing and dissipating heat.

SUMMARY OF THE INVENTION

It is well known that liquids like water usually boil under a vacuum. However, the present invention uses a counterintuitive method by providing a membrane to retain water vapor in a chamber while the water is being pumped under a vacuum. The membrane allows air to exit while retaining the water molecules. Thus, the membrane could be called an air permeable waterproof membrane. Alternatively, the water in the chamber can first be frozen in a refrigeration unit like a freezer and then capped with a waterproof membrane before vacuum application. The ice can maintain this state almost indefinitely. The operating pressure is close to a vacuum. By trapping liquid such as water in a vessel in a liquid gas membrane the liquid freezes when the vacuum is supplied.

A refrigeration system includes a vessel. The vessel is configured for a near zero vacuum pressure such as by having reinforced the sidewalls. An opening is formed on the vessel which is small relative to the volume of the vessel. A membrane fits over the opening. The membrane is configured to be gas permeable while retaining liquid molecules that are in a gas phase. A valve is mounted over the opening. A vacuum pump is connected to the valve. The vacuum pump is connected to a power source. A controller controls the operation of a vacuum pump. The controller has a memory for retaining data for optimizing vacuum pump operation.

The refrigeration system may also have a temperature sensor. The temperature sensor senses the temperature of the vessel. A pressure sensor is configured to sense the pressure of the vessel. An electrical sensor senses the electricity used by the vacuum pump. The refrigeration system has a pressure sensor mounted to the vessel valve or the valve. The vessel can be formed as a modular pod in the shape of a cylinder. A pod cylinder sleeve attachment can have pod cylinder heat fins and the pod cylinder attachment can have a cylindrical interface. The opening exposes a small surface area of a solid held within the vessel to sublimation. The small surface area is less than 10% of the total surface area of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the present invention showing a single pod a variety of different.

FIG. 2 is a diagram of the present invention showing charging and discharging of the thermal capacitance pods.

FIG. 3 is a side view diagram of the cylindrical pod receiving a heatsink with fins.

FIG. 4 is a top view diagram of the cylindrical pod receiving a heatsink with fins.

The following callout list of elements can be a useful guide and referencing the element numbers of the drawings.

20 Cap

• • 30 Valve
  • 31 Controller
  • 32 Temperature Sensor
  • 33 Pressure Sensor
  • 34 Electrical Sensor
  • 35 CPU
  • 36 Database
  • 40 Liquid Gas Membrane
  • 41 Vacuum
  • 42 Isolation Over The Opening To Vacuum
  • 43 Outlet
  • 44 Vessel
  • 45 Vessel Opening
  • 46 Vessel Side Wall Insulation
  • 50 Frozen Liquid
  • 51 Pod Cylinder
  • 52 Pod Cylinder Sleeve Attachment
  • 53 Pod Cylinder Heat Fins
  • 54 Pod Cylinder Attachment
  • 60 Refrigeration System
  • 61 Vacuum Chamber
  • 62 Vacuum Pump
  • 63 Vacuum Exhaust
  • 64 Cold Air Flow
  • 65 Cold Air Conduit
  • 66 Fan
  • 67 Cold Air Exit
  • 71 First Module Connection
  • 72 Second Module Connection
  • 73 Third Module Connection
  • 74 Fourth Module Connection
  • 81 First Valve
  • 82 Second Valve
  • 83 Third Valve
  • 84 Fourth Valve

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In this setup these vessels can be used in a ducting system to provide chilled air, or these vessels can be sealed and detached to provide cooling effects even after being separated from the main system because these containers are sealed and are under vacuum. The degree or final temperature met depends on the liquid used and the speed or rate where the vacuum reached while the liquid is freezing can change the freezing point of water by Clausius-Clapeyron equation as shown below.

In one test, water ice formed at 4° C. and another example water ice reached much colder temperatures down to −70° C. at 700 mTorr. A variety of different vacuum rates will work for freezing water including flash freezing under a sudden vacuum. A stable vessel is maintained under vacuum so that sublimation is dependent on the temperature of the ice at the exit point of the vessel, a narrow-nosed exit point at the top of the vessel would also work to maximize these different vacuum effects on water and other fluids. Retaining water with a watertight gas membrane 40 above the ice prevents water vapor from escaping both during the vacuum pull and preventing the sublimated water vapor from escaping. In this closed system then a heat load can be added to the base of the chamber. It would seem the ice on the outer wall might melt but cannot melt due to the vacuum effect and the exit port, however since the load is high the ice on the outer surfaces if they melt and form water, the vacuum effect would then freeze again at the same temperature that is required by the vacuum. It is preferred to use the Hertz-Knudsen equation to note that there is a rate of sublimation where the colder the ice, the lower the sublimation.

In other tests, experiments indicated that below freezing temperatures were reached after pulling low vacuum levels at high rates. For example, if it takes 30 seconds to reach 700 mtorr the test could obtain very cold temperatures like −70° C. but if we take minutes to obtain that vacuum level we get to only −10 to −20° C. Thus, pulling a fast vacuum has a stronger result.

After water is frozen under vacuum, the water is very stable as ice due to the vacuum. In a closed system even a simple enclosed system like a non-insulated test tube where only the top or the ice in a test tube need be insulated to keep the liquid in the rest of the tube frozen due to sublimation limitations under a vacuum.

A controller can calculate the rate of sublimation of water ice at different temperatures under vacuum conditions with a preprogrammed equation such as the Hertz-Knudsen equation or the mass transfer equation.

As seen in FIG. 1, the vessels can be formed as pods such as detestable nonisolated cold pods which may only be partially insulated. The vacuum 41 can be a 760 torr vacuum. The valve 30 can have a cap 20 for capping the valve stem. The liquid gas membrane 40 can be mounted at the outlet 43. The outlet 43 is mounted to the vessel 44. A thermal isolation 42 such as an insulated gasket is mounted over the opening to the vacuum such as by being mounted to the outlet 43. The thermal isolation 42 can be formed as a tube connected to nipple of vessel 44. Thermal isolation 42 is mounted over the vessel opening 45. The vessel optionally has vessel side wall insulation 46. The opening exposes a small surface area of a solid held within the vessel to sublimation. The small surface area is less than 10% of the total surface area of the vessel.

The system used to freeze the ice in these pods can be made according to the diagram of FIG. 1. Pods can be frozen and can be set up to also create cold air by convective heat transfer where warm air is blown across cold surfaces. In the case of this system the vacuum pump would rarely come on once the vacuums are established, and the vessels become frozen. So here we get refrigeration for some time until the vacuum subsides or the sublimation of all the ice occurs but even then, we are limiting it with the mechanical design having a small port for exposing only a small surface area to sublimation. The pod preferably includes a temperature sensor 32 and a pressure sensor 33.

As seen in FIG. 2, a system view of the present invention is used to obtain the vacuum condition. In the case where the frozen pods are removed if properly sealed under the same vacuum levels as above say 700 mtorr then these units can be kept cold by the vacuum and sent out to the beach or into a delivery vehicle or to transport anything cold or to be sent to communities who need refrigeration but don't have power or means or part of a remote missionary or nonprofit makeshift medical hospital may receive these cold pods. The temperature sensor 32 and pressure sensor 33 can provide data to the controller 31. The controller 31 may have a CPU 35 and a database 36. Optionally, an electrical sensor 34 such as a current or voltage sensor can provide information on electrical usage of the motor in the vacuum pump. The electrical sensor 34 can send electrical usage data to the controller 31 so that the controller 31 can intelligently manage electrical use of the motor. The motor of the vacuum pump 62 is preferably controlled by the controller 31.

An off grid refrigeration system 60 can operate on remote power such as solar or wind energy during periods of energy availability. When energy is available, the excess energy can operate a vacuum pump 62 which exhausts a vacuum exhaust 63. The vacuum pump 62 draws down a vacuum chamber 61. The vacuum chamber 61 is connected to the four pods at a first module connection 71, a second module connection 72, a third module connection 73, and a fourth module connection 74. The user may open a first valve 81, a second valve 82, a third valve 83, and a fourth valve 84. A fan 66 generates a cold air flow 64 in a cold air conduit 65. The cold air conduit can be a part of a central cooling system or exhausted to the room. The cold air conduit can be a part of a split air system. For example, a vacuum pump 62 is on the exterior of the building and the vacuum chamber 61 is on the interior of the building. Thus, the vacuum pump 62 can operate as an energy input for a cooling system.

The pods allow for a cooling capacitance such as if the sun goes down on a photovoltaic operated cooling system, then the vacuum pump ceases to operate at night but the cold air flow 64 can continue to cool the cold air conduit 65 and provide cold air through the cold air exit 67. The fan 66 can force air through the cold air conduit 65 or the system can rely on natural convection.

The controller preferably contains reference questions input into a CPU or microprocessor having a nonvolatile RAM memory. The actual rate that describes the relationship between pressure and freezing point of water is preferably the Clausius-Clapeyron equation which is preferably input into the controller for controlling the vacuum pump: as ln(P2/P1)=ΔHvap/R*(1/T1−1/T2) where, P1 and T1 represent the initial pressure and temperature, P2 and T2 represent the final pressure and temperature, ΔHvap is the enthalpy of vaporization of water, and R is the gas constant. However, it's important to note that this equation is typically used to calculate the vapor pressure of water at different temperatures, rather than specifically the freezing point. The freezing point is the temperature at which the vapor pressure of a substance equals the pressure exerted on it, so the Clausius-Clapeyron equation can indirectly provide information about the freezing point by determining the vapor pressure. Still, such an equation can provide an estimate for the controller.

The Hertz-Knudsen equation is also preferably input into the controller for controlling the vacuum pump. The Hertz-Knudsen equation describes the rate of sublimation or evaporation of a solid or liquid in a vacuum as a function of temperature, pressure, and other factors. It is given by: R=C*A*P*sqrt ((2*π*M)/(R*T)) where:

• • R=rate of sublimation (mass per unit time)
  • C=a constant that depends on the properties of the substance
  • A=surface area of the ice exposed to the vacuum
  • P=pressure of the vapor in the vacuum chamber
  • M=molar mass of the vapor
  • R=ideal gas constant
  • T=temperature in Kelvin

Various phase diagrams can be stored in the controller for calculating the state of the vessels. A review of various phase diagrams shows that the present invention is not only limited to water as most liquids can eventually freeze under certain vacuum conditions.

The present invention collects information on change of water temperature under vacuum through sensors such as a pressure sensor and a temperature sensor. The pressure sensor and temperature sensor are connected to the controller and the controller can sense if water ice is more densely packed when colder and may be able to find new freezing point of water by continuously collecting data. By varying the vacuum rate, the controller can keep data of the vacuum rates relative to the other pressure and temperature data. The controller can include a processor and database such as if needed for optimizing use of energy when vacuum pumping. The controller can also have a current sensor which would determine the optimal energy efficiency vacuum pump rate. By optimizing using the pressure, temperature and vacuum pump current sensor, the present invention can optimize and maximize usable vacuum energy such as if the vacuum is powered by solar power for example. The present invention thus stores a renewable energy source such as wind or solar power in the form of a cold vessel.

As seen in FIG. 3, each pod 44 can be formed as a cylinder with a heatsink sleeve fitting over the cylinder to improve convective, and radiative heat transfer. A pod cylinder 51 can have a pod cylinder sleeve attachment 52 that has pod cylinder heat fins 53. The pod cylinder attachment 54 can have a cylindrical interface. Optionally, thermal grease can improve heat transfer.