US20150034279A1

US20150034279A1 - Liquid nitrogen & carbon dioxide thermo vanes cold trap exchanger

Info

Publication number: US20150034279A1
Application number: US14/218,705
Authority: US
Inventors: James G. Davidson
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-03-18
Filing date: 2014-03-18
Publication date: 2015-02-05

Abstract

A cold trap heat exchanger with a horizontal and vertical arrangement of vaporization chambers, with vibration pads for vehicle use. Vaporization pipes each have a series of thermo vanes mounted on horizontal arranged pipes. This fluid controls the vaporization of the liquid fluid and surface area causing a liquid film on surface area varies of both tubes and pipes to occur, and this increases the facilitate refrigeration. The pneumatic chambers are filled with liquid N₂. These gases are controlled through regulated orifice for back pressure on gas turbines used to move atmosphere circuits across cold trap tubes and veins and flow through vanes for cooling control of designed areas and chambers in cooling application that may be required for cooling.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional application of U.S. Provisional Application No. 61/802/806, filed Mar. 18, 2013, entitled: LIQUID NITROGEN & CARBON DIOXIDE THERMO VANES COLD TRAP EXCHANGER AND, and claims the filing priority and benefit of the provisional application, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

This invention is to clean up the atmosphere and improve natural cycling for plant life.
A number of refrigerants and processes being used for refrigeration systems contribute pollution to the atmosphere. The present cryogenic process eliminates the release of Freon and other gases that are harmful to air and natural photon cycling.
After cooling with liquid nitrogen, the liquid nitrogen is transformed to a gas and the heat exchanger process is complete. This releases only pure nitrogen to the atmosphere. Nitrogen is clean and it accelerates nitrogen fixation for natural growth of nature's plants.
This invention relates to a liquid nitrogen thermo vane heat exchanger that is particularly well suited for refrigerated transportation storage containers.
Refrigerated trucks and other refrigerated transportation containers typically use conventional refrigerating systems operated by diesel engines. In such systems, a compressor operated by the diesel engine compresses a gaseous refrigerant until it is transformed into a liquid. The pressure on the liquid is then released through an expansion valve, and the refrigerant is passed through a heat exchanger, and this absorbs heat and chills the heat exchanger coils, thus cooling the container. While this system is in use widely, there are a number of drawbacks with this system.
Diesel engines are noisy, dirty and require fuel and need repairs from time to time. They also produce undesirable gaseous emissions. The refrigerating units themselves typically use fluro-chemical type compounds, which are an undesirable pollutant when released occasionally into the atmosphere. At present, no safety alarms are needed for this condition. The newest version uses a process known as Thermo Cycling. The process turns on or off the cooling unit when specific temperatures are reached. This process allows the food container atmosphere to maintain temperatures as low as 20 degrees. This process, along with the practice of running the devices at a higher average temperature, are methods employed to save on fuel costs, without losing safety of food.
A number of refrigerants and processes can be used for refrigeration systems. Liquid nitrogen is one such refrigerant. Liquid nitrogen vaporizes at a much lower temperature than the currently used gaseous refrigerant and thus provides a much colder refrigerant than the conventional gaseous refrigerant when released through a heat exchanger. Liquid nitrogen is available in pressurized containers and can be released through a thermo vane heat exchanger and then can provide power for gas turbines before being released to the atmosphere. Since nitrogen is a major component of air, the release of nitrogen poses no pollution threat.
It is an object of the present invention to provide a liquid nitrogen refrigeration system having improved and controlled cooling characteristics which is also useful in cold traps for a food processor.

SUMMARY OF THE INVENTION

A liquid nitrogen thermo vane heat exchanger comprises a vertical array of alternating vaporization chambers and pressure control chambers connected together in series. The vaporization chambers each have a plurality of thermo vanes mounted in exterior loops along the exterior of the chamber. The thermo vane tubes provide a controlled rate of vaporization of the liquid nitrogen and an increased exterior surface area to facilitate refrigeration.
In the present invention, the liquid nitrogen vane cooling exchanger comprises a plurality of separate heat exchanger chambers in the form of flat blades mounted in a vertically spaced relationship in a rack. The chambers having thermo vanes on the exterior are alternately positioned with adjacent chambers which are designed with deflector blades in the various chambers.
The thermo vanes are an important feature of the present invention. They provide a controlled rate of vaporization of the nitrogen while at the same time providing the equivalent of a cooling surface on the heat exchanger to provide added exterior surface area for improving the cooling capacity of the cold trap. Because of the small designed flat surface, liquid nitrogen in the thermo vane tubes cannot flash or boil turbulently in the tubes. Instead, the vanes have a controlling effect on liquid nitrogen that controls the vaporization of the liquid nitrogen. When the nitrogen can vaporize in thermo vanes by the process of film boiling under other conditions as well, when nitrogen vaporizes in thermo vanes by the process of film boiling, a thicker than normal layer of vapor or gas is formed at the wall of the vanes and this insulates the liquid nitrogen from the much warmer wall of the surface. This slows the vaporization rate of the nitrogen. At the same time, the vapor adjacent the walls flows in a laminar flow pattern to the outlet of the thermo vanes and then into the larger interior of the heat exchanger. The laminar flow improves the refrigeration effectiveness of the cold trap. In short, the thermo vanes provide an effective way of controlled vaporization of an otherwise very volatile liquid.
These and other features and advantages of the present invention are described below in connection with a detailed description of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a liquid nitrogen capillary heat exchanger constructed in accordance with the present invention.

FIG. 2 is a front elevational view of the capillary heat exchanger.

FIG. 3 is an end view of one of the chambers taken along lines 3-3 of FIG. 2.

FIG. 4 is a perspective view showing a cooling tube with capillary tubes employing the capillary tube covering fins of the present invention, with only one representation capillary tube set and cover being shown.

FIG. 5, consisting of FIGS. 5 a 5 b and 5 c are schematic diagrams of alternate embodiments of the capillary tube heat exchange of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The basic construction of the heat exchanger of the present invention is similar to the heat exchanger disclosed in applicant's U.S. Pat. No. 5,582,015, which is incorporated herein by reference and described below.
Referring to the drawings and more particularly FIG. 1, a heat exchanger 10 in which the present invention is employed comprises a series of heat exchanger chambers 12, 14 spaced vertically apart in alternating arrangement in a support rack 16. Support rack 16 comprises a pair of spaced vertical support members 18 positioned at each end of the rack and interconnected by cross-members 20 and longitudinal members 21. A base 22 is connected at the bottom of the support members and extends outwardly from each side thereof in order to provide support for the rack.
Chambers 12 and 14 are substantially the same in construction, with the exception that chambers 12 have a series of capillary tubes 24 and 26 spaced along the longitudinal length of each chamber. Chambers 12 desirably are copper pipes 28 having a four and one-half inch O.D. and a wall thickness of ¼ inches. The pipes in the preferred embodiment are about 56 inches long. Caps 30 are removably fitted on the ends of the pipes by welded ends on the pipes and on the interior of the caps or by such suitable fasteners. A pressure tight fit is essential. The pipes are mounted in the rack with the end caps 30 resting on cross-members 20 of the rack and with flexible metal bands 32 extending from the cross-member one side of the cap over the top of each cap and then down into attachment with the cross-member on the other side of the cap. The bands are held in place by removable fasteners.
While the pipes for chambers 12 and 14 are substantially the same, with the exception of the capillary tubes 32, for convention, the pipe for chamber 12 will be referred to as pipe 28 and the pipe for chamber 14 will be referred to as pipe 29.
Referring to the construction of chamber 12, pipe 28 includes a series of small openings one-quarter inch in diameter at four separate angularly spaced locations at each of 51 axial positions along the pipe, with each series of openings preferably being spaced axially apart by a distance of one inch. The first three inches at each end of the pipe has no openings. As shown in FIG. 3, the openings in pipe 28 comprise a horizontal opening 36 at the left hand side of the pipe, an opening 38 positioned downwardly therefrom by an angle of 45 degrees, an opening 40 positioned downwardly form opening 36 a distance of 78 degrees, and an opening 42 positioned upwardly to the right from a vertical position by a distance of 35 degrees. Capillary tubes 24 and 26, which are about nine inches long, form elongated loops as shown and are fitted and welded into these openings. Each capillary tube is formed of copper and preferably has a one-quarter inch O.D. and a one-sixteenth ( 1/16) inch I.D. The capillary tubes extend all the way through the walls of the pipes so that the interior of the capillary tubes is in communication with the interior of the pipes. All chambers 12 are of substantially the same construction.
Pipes 29 have no capillary tubes attached to the outside thereof but can be filled with a heat transmissive particulate material, preferably copper filings 31. The copper filings improve the heat transfer in the interior of the pipe and also serve to slow down the flow of refrigerant through the pipe so as to maximize heat transferring the interior of the pipe and also serve to slow down the flow of refrigerant through the pipe so as to maximize heat transfer. It is desirable to have the flow of refrigerant through the system be slow enough that the amount of heat that the refrigerant can absorb from the exterior environment is maximized and the back pressure caused by vaporization is controlled.
As shown in FIG. 2, all of the chambers are connected in series, starting from the first chamber at the bottom of the rack (the numbers of the chambers and tubes in serial order from bottom to the top being indicated in parenthesis after the number of the chamber or tube) to the last chamber or ninth chamber at the top of the rack. Pipe 28(1) has an inlet 44 at the left hand end (FIG. 2), which is connected through an inlet orifice valve 46 to a conduit 48 leading upwardly thorough relief valve 49 to a suitable source of liquid nitrogen, which is maintained under pressure in a conventional pressurized tank 51 of the type that can be purchased commercially from any number of vendors. The right hand end of pipe 2891) is connected through openings in the end cap to a larger pipe 50 and a smaller pipe 52 leading upwardly to corresponding openings in the right hand end cap of pipe 29(2). Pipe 50 has a three-quarter inch O.D. and pipe 52 has a one-quarter inch O.D. As shown in FIG. 2, the level of liquid nitrogen 54 in pipe 28(1) covers the bottom of the pipe and does not fill the entire pipe. And inlet 56 of pipe 50 extends inwardly into the interior of pipe 28(1) and then downwardly under the surface of the liquid nitrogen 11 in the pipe, so that pipe 50 will be filled with liquid. The smaller pipe 52 is in communication with the vapor portion of the interior of pipe 28(1) and conveys vapor into the next adjacent pipe. Pipe 52 enters the end cape of pipe 29(2) in an opening 33 on the left hand side of the end cap on the horizontal axis, while pipe 50 enters the pipe at an opening 35 at the axis (FIG. 4).
On the left hand side of pipe 29(2), a large pipe 58 corresponding with pipe 50 exits pipe 29(2) and extends upwardly to the left hand end of 29(3), with the pipe exiting from the axis of the pipe and entering in the axis of the next adjacent pipe. A smaller pipe 60 exits from an opening 62 on the right hand side of the end cap at the horizontal axis and extends upwardly into an opening 64 in the upper portion of the end cap on the vertical axis.
All of the pipes in the heat exchanger are connected in the same way, so that liquid nitrogen enters the heat exchanger in the left hand end of the lowermost pipe for level control, extends backwardly and forwardly through each of the pipes as it moves upwardly through the heat exchanger, and then exits from an outlet opening 66 at the right hand end of the uppermost pipe 2999). The movement of the liquid and the gas through the heat exchangers is caused by the vapor pressure of nitrogen as it evaporates in the system.
Pressure gauges 70(1)-70(9) are mounted on the respective pipes 28 or 29 (1)-(9) in order to monitor the pressure in each of the pipes. Since back pressure is a critical factor in this system, it is important to maintain proper pressure in each of the pipes. In addition, a pressure valve 72 is connected to outlet 66 of the heat exchanger. This sets the threshold pressure for release of nitrogen.
The desired pressures in each of the pipes, as indicated by the pressure gauges and the pressure at the outlet pressure valve 72 are set forth in the following table.


	70(1)	24.7 psig
	70(2)	23.2 psig
	70(3)	22.9 psig
	70(4)	21.4 psig
	70(5)	21.3 psig
	70(6)	15.1 psig
	70(7)	12.9 psig
	70(8)	7.5 psig
	70(9)	5.2 psig

In addition to the inclusion of copper filings in tubes 29, it is desirable to include a desiccant to remove moisture from the gas. An aluminum silicate gel, which has the appearance of small pellets works fine for this purpose.
The tubes 28 do not have the desiccant or copper filings in them but instead are provided with the capillary tubes on the exterior portions of them. The capillary tubes are extremely important features of the present invention. They provide a controlled rate of vaporization of the nitrogen while at the same time providing added exterior surface area for improving the cooling capacity of the heat exchanger. Because of the small diameter of the capillary tubes, liquid nitrogen in the capillary tubes cannot flash or boil turbulently in the tubes. Instead, the capillary tubes have a controlling effect on liquid nitrogen that controls the vaporization of the liquid nitrogen. The nitrogen vaporizes in the capillary tube by a phenomenon known as film boiling. While liquid nitrogen vaporizes by film boiling under other conditions as well, when nitrogen vaporizes in a capillary tube by the process of film boiling, a thicker than normal layer of vapor or gas is formed at the wall of the capillary tube, thus insulating the liquid nitrogen from the much warmer wall of the capillary tube. This slows the vaporization rate of the nitrogen. At the same time, the vapor adjacent the walls flows in a laminar flow pattern to the outlet of the capillary tube and then into the larger interior of the pipe. The laminar flow improves the refrigerating effectiveness of the heat exchanger. In short, the capillary tubes provide an effective way of controlled vaporization of an otherwise very volatile liquid.
In accordance with the present invention, the construction of the foregoing capillary tube heat exchanger is modified to give the heat exchanger substantially enhanced heat transfer characteristics. In the present invention, the capillary tube loops 24 and 26 are covered with hollow covers or fins 100, shown in FIGS. 4 and 5. Each fin 100 is formed of a heat transmissive material, such as a metal. Copper or other metal with good heat transmission properties is desirable. A somewhat elastic material can be desirable. Fin 100 is a flat, hollow member having spaced sides 104 and 106 and edges 108 joining the sides. The sides may have a rounded outer contour to conform with the rounded outer contours of the capillary tube loops being encased. As shown, a single fin desirably covers both capillary tube loops located at approximately the same axial position on the cooling tube. Separate fins could be used for each loop, but a single fin provides a larger heat transfer surface and is therefore preferred. The fins may be formed of a flexible material that can be deflected somewhat in order to fit the fins over the capillary tube loops.
The dimensions of the fins corresponds with the dimensions of the capillary tube loops. Desirably, the fins are shaped and the interior sides are spaced apart by a distance sufficient to permit the fin to be inserted over the capillary tube loops with the fin being in at least loose general contact with the loops when installed.
When the fins are thus installed and in contact with the capillary tubes, the area of the effective cooling surface provided by the capillary tubes is dramatically increased without losing any of the benefits achieved by the narrow size of the capillary tubes. With the construction of the present invention, the effective area of the cooling surface can be increased by as much as 88%. This can result in dramatically decreased cooling tubes for a refrigerator truck. In the refrigerated truck industry, it is desired to be able to drop the refrigerative temperature to −20 degrees in twenty minutes. In one test, a cooling system without cooling fins was able to reduce the temperature only to −18 degrees in this time. With the fins, the temperature was reduced to as low as −40 degrees. While these results are merely exemplary of limited testing, they do reflect that the cooling fins provide a significant improvement in the cooling capabilities of a nitrogen refrigeration system in a truck cooler.
Heat Exchanger Specifications. The specification of a heat exchange construction in accordance with the present invention are as follows.


Height	94″
Width	72″
Depth	72.5″ for thermo vanes, the entire length of trailer
Weight (empty)	750 lbs.
Weight (operational)	785 lbs.
BTU's (in operation)	48,000
Operation pressure	20-30 psi (gauged)
Static Pressure	0
Barometric Pressure	1009 HPA
Humidity	Varies with product
Temp. Control Range	−30° to +170° F.
Dew Point	Varies with product
Material	Copper and Stainless Steel
Gs Type	Liquid Nitrogen

A fuel tank for storage and supply of liquid Nitrogen can have the following specifications:


	Overall Length	75″
	Diameter	26′
	Capacity	100 gal.
	Operating Pressure	20-30 psi (gauged)
	Static Pressure	20-30 psi (gauged)
	Weight (empty)	405 lbs.
	Weight (full)	1195 lbs.

One advantage to the use of this cryogenic process for refrigerating vehicles is that gas turbines are running off the exhaust of the fuel source and generating electric power to run electric strip heaters when heat is required for vehicle trailers or storage. As well as the turbines that run the fans of the circulation systems and are released to the atmosphere with 100% heat recovery as well the exhaust from the fans that give cooling efficiency of 100%. Using cooling fins attached to thermo vanes cryogenic activity and heat transfer that is more efficient than existing cooling devices.
The outlet of thermo vane collectors support the pneumatic supply for control valves and temperatures controls, with 15 psig regulator before exit of system.

Claims

What is claimed is:

1. In a liquid Nitrogen capillary tube refrigerative system wherein liquid Nitrogen is passed through a cooling tube having a plurality of capillary tube loops mounted on an exterior side of the cooling tube and wherein the capillary tube loops are in fluid communication with the interior of the cooling tubes, the improvement wherein the capillary tube loops are enclosed in heat transmissive fins that contact outer surfaces of the capillary tubes and have sides that extend across the loops, the fins increasing the heat dissipation surface of the capillary tube heat exchanger and increasing the efficiency of the liquid Nitrogen heat exchanger.

2. A capillary tube heat exchanger as in claim 1 wherein the cooling tube has at least two capillary tube loops at different radial positions at approximately the same axial position on the cooling tube and the fins include a single fin that covers both loops and provides an increased cooling surface representing the entire area between the loops as well as the area inside the individual loops.