US2951642A - Heat-conducting system, especially for transport containers - Google Patents

Description

F. E. HAZARD Sept. 6, 1960 HEAT-CONDUCTING SYSTEM, ESPECIALLY FOR TRANSPORT CONTAINERS Filed Sept. 14, 1956 INVENTOR. F. E. HAZARD ATTORNEY HEAT-CONDUCTING SYSTEM, ESPECIALLY FOR TRANSPORT CONTAINERS This invention relates to a heat conducting system and more particularly to a novel heat-radiating pattern capable of integration with any refrigerating means or method for producing precise predetermined temperatures for achieving the safe transport of various types of fresh fruits and vegetables and other perishables.

It is known of course to refrigerate transport containers to protect and preserve produce and other commodities in transport against high ambients, as in warm climates, and it is also known to supply heat to containers as protection against low ambients during travel through low-temperature climates. In situations of this nature relatively substantial variations in temperature may occur in the container en route because of variations in ambient and/orloss of efiiciency of the refrigerating or heating system, resulting in serious damage to the shipment from over-refrigeration or over-heating. However, the basic problem is not one of simply refrigcrating or heating but of providing optimum temperatures for preserving top quality of the shipment and regulating ripening to a rate commensurate with delivery of the produce in condition to meet the demands of the market. Without proper control, such as aiforded by the present invention, shippers losses for spoilage and deterioration continue to increase and national food waste is aggravated. Added to these problems are those arising from the economical necessity of using a container for a variety of commodities at different times and the desire to achieve satisfactory results, according to one phase of the invention, by a system by which conventional transportable containers may be converted at small expense, thereby avoiding the imminent obsolescence of current equipment. Attempts to solve these problems by mechanical refrigeration incorporating a reverse cycle have been, in the main, commercially unfeasible because of initial cost and expensive maintenance.

It is a significant object of this invention to provide a pattern arrangement of heat-conducting means, preferably tubing or a conduit for heated liquid, so arranged as to balance the heat output throughout a critical zone, thus avoiding hot and cold spots. The pattern features such conduit as a plurality of serially connected sections of uniform volume arranged in pairs with one section of each pair alongside but reversely to or in counterflow relation with a section of different temperature so that the heat output of any pair substantially equals that of any other pair, at least in a critical zone. In a transport container, that zone will be a peripheral zone at the bottom of the lading, where it is most needed and from where it will be able to rise evenly. In the integration of this pattern with refrigeration methods, best results are obtained with railway cars or motor vehicle trailers having well known refrigeration equipment. In-the case of the railway cars, end bunkers for water ice or Dry Ice furnish the refrigeration. Mechanical refrigeration, brine,

etc. are not of course excluded. Of importance is the combination of the two to obtain the critical temperatures for purposes set out above and to be elaborated below in a description of a preferred embodiment of the invention, taken with the accompanying sheet of drawings wherein:

Figure 1 is an elevation, partly in section, of a con-- ventional end-bunker refrigerator car in which the present. invention has been embodied;

Figure 2 is a schematic view of the heat-radiating pattern; and

Figures 3 and 4 are representative sectional views of tubing employed for the conduit means.

The body 20 of the car shown in Figure 1 serves as a transport container having walls 22 which constitute marginal means surrounding or defining the floor or floor area 24 of the car, within all of which is the lading space 26. Each end of the car shown has an ice bunker 28 which is here representative of refrigeration means for abstracting heat from the space 26. It will be clear that other refrigerating means or methods may be used.

The car is equipped with a heating means 30 of the underslung type. Here again, variations may be indulged. The heating means chosen for purposes of illustration comprises a liquid-conducting coil, heated by any suitable fuel such as propane gas, characoal, etc. and this coil has a heated liquid output end 32 and a return end 34.

The heat-conducting means designated in its entirety by the numeral 36, is a conduit or tubing pattern having an inlet end 38 connected to the heater output 32 and an outlet end 40 connected to the heater return 34. In the present instance, the pattern or means 36 is shown atop the floor or area 24 and is itself protected by a secondary fioor or rack 42, but these details are not material. Suffice it to note that the pattern, is juxtaposed relative to the floor means 24-42 and is at the bottom of the lading space 26. Interposed in the pattern, for reasons to appear below, is an expansion tank 44 (exaggerated in size for clarity), insulated at 46, and having conduit connections 48 and 50 connected serially into the pattern. These are also insulated as indicated at 52 and 54. The tank has a safety valve 56, which may be removed for the purpose of filling the liquid-containing system. Because of the insulation at 46, 52 and 54-, the temperature of the liquid, here water but not exclusively water, remains at a substantially high temperature and serves as a thermal flywheel.

Figures 3 and 4 show representative cross-sections of tubing, preferably aluminum, employed in the system. Figure 3 is the type appearing in the system operated according to the test runs to be outlined below.

In the test runs just referred to, the total length of tubing or conduit, of rectangular section 1 x 1 /2, was 192 feet, exclusive of the insulated connector portions 48 and 5% to the expansion tank 44. This afforded eighty square feet of heat-radiating surface with a K factor of 2.5. The tubing contained fifteen gallons of liquid exclusive of the tank 44 and conduit portions 45 and 50. The latter, added to the pattern 36, made a total of twenty-two gallons. The seven-gallon difference can be ignored for the present. The fifteen gallons of liquid (here water) in the pattern 36 weighed pounds.

Now, for purposes of comprehending the novel counter-flow feature by means of which the heat output .of the pattern is balanced throughout a critical peripheral zone in the container space 26, it is necessary to consider the pattern as made up of a plurality of serially .connected sections, here fifteen, each containing a gallon of liquid and each measuring 12.8 feet in length (19.2 feet divided by 15 gallons). These sections are numbered in Figure 2 from 1 to 15 and are schematically divided by the small triangles as shown. Section No. 1 is connected of course to the pattern inlet end 58 and leads to the expansion tank 44 via 48 and leaves the tank via 50 to connect serially to section No. 2. The latter is connected serially to section No. 3 and so on, so that sections Nos. 1 through part of 6 border the Walls 22 of the space 26.

It will be noted that section No. 6 is doubled bac upon itself at 58 and continues into section No. 7 and thence reversely or counter to sections Nos. 5, 4, 3 and 2, at which point the conduit again doubles back upon itself (at 60) so that sections Nos. 11 and 12 are parallel to but in counter-flow relation to sections Nos. 9 and 8. Again the conduit is doubled back upon itself at 62 and sections Nos. 13 and 14 are counter to and parallel with sections Nos. 7 and part of 6, whereupon the last section (No. 15) is doubled back upon itself at 64 to run alongside section No. 1 and back via the outlet end 40 to the heater return 34. Arrow-heads on the pattern indicate the direction of liquid flow.

A dotted rectangle 66 in Figure 2 represents the inner margins of a peripheral zone ZZZZ, bordered by the 'walls 22, throughout which the heat output is substantially constant. This zone is around or interiorly borders the walls 22 of the container, and the heat may rise evenly in the container, bearing in mind that uniform heat in this zone is important. Although the heat output Within the rectangle 66 (at C in the center of the space 26) is lower than in the peripheral zone ZZZZ, this is also significant because hot spots are avoided.

The foregoing may also be comprehended by considering the pattern 36 as having a peripheral or outer run or loop made up of sections Nos. 1, 2, 3, 4, and part of 6;' an intermediate loop made up of sections Nos. 6 (part), 7, 8, 9 and and an inner loop made up of sections Nos. :11, 12, 13 and 14 plus a terminal run made up of section No. 15. In other words, the peripheral loop has a return run including that portion of section No. 6 which borders the proximate wall 22, which return run approaches the inlet 38 and then reverses itself. Hence, part of section No. 6 is alongside another part thereof and the area heated by the whole of that section is but half that heated by two full-length sections (as sections Nos. 5 and 7), but the number of B.t.u. delivered per square inch or per square foot is identical with sections in the peripheral zone or area ZZZZ, which will more readily appear from the following.

The ambient temperature (which could as well have been container temperature) remained constant at 88 F. during the test period, a factor contributing materially to the absolute accuracy of the results recorded.

During the test runs the temperature of the circulating liquid (water was used for accurate test calculations) entering the circulating system was constant at 164-166 F. and the temperature of the liquid leaving the system was constant at 107110 F.

The constant fall -in temperature of the liquid was, therefore, 56 F. As exactly fifteen gallons weighing 125 pounds were in the tube pattern at all times, 466.66 B.t.u. per gallon were delivered while passing through the 192 feet of the tube pattern, or 7000 B.t.u. during the 48 minutes required for each gallon to pass through the 192 feet of the tube pattern, flowing at the rate of 8750 B.t.u. per hour.

From the above it may be concluded that if a constant temperature of 44 F. (as an example) were maintained in an insulated container (railway car or trailer body) and the temperature entering this tube pattern were 164 F., thus maintaining a constant initial temperature difference of 120 F., instead of the initial temperature difference of 76 R, which existed during the running of the above tests, the fifteen (15) gallons in the tube pattern would pass through the 192 feet of tubing in 30 .minutes, instead of 48 minutes, and would deliver 8400 4 B.t.u. during that 30 minute periodflowing at the rate of 16,800 B.t.u. per hour.

This pattern provides more than enough heat radiating surface to assure delivery of the maximum heat producing capacity of the heater; the balanced counter-flow feature providing uniform delivery of heat units throughout the floor area and in each section of the floor-area (no hot spots-no cold spots); delivery of all heat at the bottom of the lading space where it is most needed and from where it will be able to rise evenly.

To recapitulate:

192 linear feet ofrectangular 1" x 1 /2 tubing in pattern.

square feet of heat radiating surface on tubing.

2.5 K factor used.

12.8 linear feet of tubing in each section as shown.

1 gallon liquid contained in tubing of each section.

15 gallons liquid contained in 192 feet of tubing, comprising pattern-15 sections.

22 gallons liquid in entire system, including expansion tank, etc.

88 F. ambient temperature.

125 pounds of liquid in 192 linear feet of 15 sections of patternl5 gallons 8.33 pounds to gallon.

183 pounds of liquid in entire system-22 gallons 8.33

lbs. to gallon. (Seven gallons in expansion tank.) 3.2 minutes time required for liquid to pass through 12.8 feet section. 48 minutes time required for :15 gallons of liquid to pass through 192 feet of tubing .in pattern in this instance.

5.33 square feet heat radiating surface on each 12.8 foot section of tubing-this multiplied by K factor of 2.5 equals 13,325 B.t.u. per degree F. temperature difference per hour. Therefore, temperature difference at any point multiplied by 13.325 will give number of B.t.u. per hour radiated at that point.

This may be further clarified in tabular form as follows:

A B C D E F Liquid Temper- Poten- Poten- Temperature Tempertie] in tial in Section ature Diflerature B.t.u. B.t.u. F.) ence Drop per hr. per 3.2

minutes Cglumn B represents temperatures at beginning and end of successive see 0115.

Column C is difference between Column B temperature and ambient (here 88 F.).

Column D represents temperature drop between ends of sections; e.g. 76.00 minus 69.52 equals 6.48.

Column E is Column CX13.325.

Column F is Column E divided by 18.75;

This gives a heat distribution characteristic as follows:

By comparing the section numbers shown on the drawing with the above, a clear understanding of how evenly and uniformly heat is distributed and, in proportion, where needed, can be quickly acquired.

The principle of counter-flow is illustrated by noting that the tubing of one section will deliver B.t.u. in compensating proportion to the tubing of the section paralleling it. This is accomplished to such balance that there is barely 4 B.t.u. difference between the greatest number of B.t.u. delivered in one area as compared to the smallest number delivered in any other areas extending in from the sides and ends of the car body for a distance of 2 /2 feet-a total of 190 sq. feet-embracing sections 1-15, 3-9, 4-8, 5-7 and single section 6.

The four sections-1144 and 12-13-furnishing heat to the 90 sq. feet area in the center of the car body deliver only about one-half the number of B.t.u. in any given period as do the sections furnishing heat to the 190 sq. foot areas around the edge. This is in proper ratio to the relative requirements for uniform heat distribution throughout the floor area; to prevent hot spots in the center where the lading prevents heat flow upward; and to assure ample heat flow around the sides and ends of the lading.

As far as is known, this is the first time that any heating system for transport vehicles has been designed to provide adequate and balanced heating for the protection of perishables in transit. means the most important feature of this achievement. For this enables the heating system at long last to be integrated with the refrigerating method-any refrigerating methodto provide the precise predetermined temperature required for each specific fruit, vegetable or other perishable product, making possible the conversion of the current fleet of end-bunker water-iced cars into the most perfect container for the transportation of fresh fruits and produce yet conceived.

Variations in detail will readily occur to those versed in the an, as will other features and objects not categorically enumerated, all of which may be achieved without departure from the spirit and scope of the invention.

What is claimed is:

1. A liquid conducting system for a generally flat area defined by peripheral edge means and including a central zone relatively remotely surrounded by said edge means, comprising: a conduit of heat-radiating material having an inlet adjacent to the peripheral edge means and connected thereat to a source of liquid at a substantially constant temperature and an outlet for discharging But this is not by any liquid, said conduit being arranged in a heat-radiating pattern generally parallel throughout to said area and including an outer loop beginning at said inlet and lying inwardly of and relatively closely following the peripheral edge means and continuing as a return portion lying along part of said edge means and closely approaching said inlet so that said outer loop lies in relatively remote surrounding relation to said central zone for conducting main liquid flow about said edge means, said conduit immediately continuing from said return portion as a doubled-back portion closely inwardly of said return portion to run immediately counter to said return portion and continuing thence at least in part as a counterflow loop including a run of substantial length continued from said doubled back portion and lying next inwardly, counter to and proximate to said outer loop and of substantially similar length as said outer loop so that said run of sub stantial length lies outwardly of said central zone, and said counterfiow loop including in addition to said second loop run, an extension in the form of a third loop next inwardly of and paralleling said run so as to lie at least in part in said central zone and disposed reversely as respects said run to conduct liquid in a flow path counter to the flow in said second loop.

2. A heat-conducting system of the class described, comprising: a heat flow conductor having an input end connectible to a source of heat at a selected substantially constant temperature, said conductor being arranged in a heat-radiating pattern including an outer substantially closed outer loop beginning at said input end and returning toward and closely adjacent to said input end to afford a main heat flow portion, said conductor where returning toward the input end having a portion doubled back inwardly upon itself adjacent to said input end and continuing immediately counter to and next inwardly of said outer loop as a counter run of substantial length retracing an outer loop portion also of substantial length and said conductor extending thence at least in part in the form of a second loop run reversed relative to and generally coplanar with the outer loop and inwardly of and paralleling said outer loop, and counter run including an extension of said second loop run in the form of a third loop having a run next inwardly of, generally coplanar with and paralleling said second loop run and said third loop being disposed reversely as respects said second loop run to conduct heat in a flow path counter to the flow in said second loop run.

References Cited in the file of this patent UNITED STATES PATENTS R6. 21,674 Niven Dec. 24, 1940 707,361 Searle Aug. 19, 1902 1,404,901 Schreiber Jan. 31, 1922 1,562,229 Grindrod Nov. 17, 1925 2,181,742 Rumpf Nov. 28, 1939 2,265,536 McFarlane Dec. 9, 1941 2,762,570 Zimmermann Sept. 11, 1956 FOREIGN PATENTS 63,543 France Apr. 13, 1955

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