US3225553A - Method of shipping frozen food - Google Patents

Description

United States Patent 3,225,553 METHOD OF SHEPPING FROZEN FOOD Willard L. Morrison, Lake Forest, Ill., assignor to The Union Stock Yard and Transit Company of Chicago, Chicago, Ill., a corporation of Illinois No Drawing. Filed Jan. 21, 1963, Ser. No. 252,594 5 Claims. (Ci. 2-'76) This is a continuation-impart of my cop-ending application Serial No. 659,473, filed May 16, 1957, and entitled Method of Shipping Frozen Food, now abandoned.

My invention relates to improvements in method of shipping frozen foodstuffs and has for one object to provide a method for :greatly increasing the effectiveness of presently used means for shipping frozen foodstuffs in transit.

Another object of my invention is to greatly increase the effectiveness of the shipment of foodstuffs in refrigerator cars by rail and the like.

It is customary in connection with the shipment of frozen foods, for example, from California to the east coast, to charge the ice bunkers of refrigerator cars at a central point with ice and salt. The empty car is then discharged from the assembly point to the loading dock of the frozen food manufacturer. By the time the car reaches the dock, it has been to some extent precooled by cold air circulating in the car from the salt and ice bunker. Such circulation may be by gravity or by axle driven fan.

The solid ice in the bunker melts at substantially zero degrees F. and the temperature of the ice approaches that low point and so air currents somewhat above zero circulate through the car to cool the interior thereof. The temperature, of course, is never as low as zero. First, because the ice and salt mixture can only be at zero and second, because there is substantial heat infiltration through the insulation of the car and through air leakage because the car can never be gastight.

As a result, the frozen food at temperatures perhaps zero degrees F., perhaps above or perhaps below that point, is loaded into a car, the temperature of which even though it has been chilled is usually above the temperature of the foodstuff but, of course, far below ambient temperature. The loaded car is then returned to the assembly point. There because during its trip to the load ing dock and return, much of the salt and ice is melted away, the car is recharged with ice and salt and started on its way to the east. As the car travels and as the ice and salt melts, the amount of salted ice available as a coolant gradually decreases and so the effectiveness of the cooling in the car gradually decreases and the temperature of the contents gradually rise above zero. This is disadvantageous because it is a well known fact that the foodstuffs ought to be kept at zero or below. That is impossible because the ice and salt cannot provide a temperature below zero but can only provide a temperature substantially above it.

I propose, without any change in the equipment heretofore used, to first charge the bunker with the usual amount of ice and salt and immediately thereafter to discharge onto the bunker ice, liquid nitrogen at atmospheric pressure and so at substantially -320 F. The ice and salt at zero degrees F. will furnish the latent heat to vaporize this liquid nitrogen as the temperature of the ice drops to a point, depending upon the volume of liquid nitrogen discharged into the bunker.

As this liquid nitrogen evaporates, it will be immediately withdrawn from the car at a temperature little if any below the boiling point of liquid nitrogen at atmospheric pressure, namely '320 F. and the reliquefied nitrogen can again be used as a refrigerant.

Patented Dec. 28, 1965 There may be some rise in temperature of the gaseous nitrogen by heat exchange with the interior of the car and this will tend to assist the ice in the cooling function.

The car will then be forwarded with this superchilled salt and ice to the loading dock. The same air currents cooled by the ice will cool the interior of the car but under ordinary circumstances, the ice will not have time to rise in temperature to zero degrees, the melting point, so there will be no loss of salt and ice on the way to the loading dock but the car being chilled by a source of cold far below zero will be at a temperature also below zero.

When the car is then charged with frozen food at approximately zero, the food will be exposed to an atmosphere colder than itself and will either not rise in temperature and may usually fall somewhat in temperature on its way back to the distribution point.

If the amount of ice and the temperature to which it is reduced are properly selected, the ice will still be below zero when it gets back to. the central distribution point but will be at a temperature higher than the starting temperature.

At that point, since the destination of the car will then be known and since the approximate time of travel will then be known, all that is necessary is to add more liquid nitrogen to lower the bunker ice temperature down to the point at which it will reach destination either before the ice had melted or if longer time is required before the ice bunker can again be recharged.

The temperature of the foodstuffs will thus remain at zero or below for the major part of the trip and only toward the end of the trip when the ice has finally reached, if it does reach it, a temperature of zero degrees F. is the foodstuff exposed to a temperature above zero.

The specific heat of ice is in the order of .5. The specific heat of the foodstuffs is in the order of .383. Thus the ice furnishes a much more effective source of cold than does the foodstuffs itself and since the bunker area or bunker volume is only a small part of the car, it is easy to discharge the liquid nitrogen into the bunker and withdraw it before it has gained too much temperature above -320 P. so that the reliquefaction of the nitrogen after it has done its work is a practicable operation.

Under these circumstances, it might be suflicient merely to charge the bunker with salt and ice at the central point, then to ship it to the loading dock, fill it in the usual way and return it to the distribution point to start it on its way to destination. Under these circumstances, the ice bunker would be charged to replace that which was lost in transit to and from the loading dock and would then superchill the ice with liquid nitrogen but this would require two icings at the distribution point whereas in the first instance, the ice is chilled to the point where it will not melt before it returns to the distribution point, only one icing but two superchillings will be required. Which of the two alternatives is most economical would, of course, depend upon the circumstances of use, distances, time, etc.

When the car has reached its destination and has been unloaded, having had the benefit of the superchill effect during its travel with frozen goods, even though there is no nitrogen reliquefaction or liquid nitrogen supply at destination, the use of the nitrogen to superchill the ice has not in any way interfered with the normal usefulness of the refrigerator car under usual salt and ice conditions so my method can easily be superposed on the usual ice cooled refrigerator car without any change whatever in that car, with the mere addition of a source of liquid nitrogen, preferably accompanied by the reliquefaction of the gaseficd nitrogen.

When the cold dry icebecause when below zero it does not melt and so is dryhas finally risen to zero degrees F., then and then only does the chemical salt ice action come into play and one thing that the superchilling effect of the liquid nitrogen accomplishes is a delay of the start of the chemical reaction of salt and ice. So I propose to use the salt and ice first as a storage for cold without any chemical reaction or any change of the material except a rise in temperature and later as a supply of cold resulting from the melting of the ice and salt.

When the ice in the bunker has been cooled below the melting point zero degrees F. and is dry because it is not melting, it will, of course, pick up somevmoisture from the ambient air or from the air in the car because vapor migration moves toward the cold spot. This may result in some slight expansion in weight and volume of the ice but as the ice temperature rises and as long as the ice temperature is below that of the air surrounding it this sitnation will prevail but as soon as the ice reaches zero and begins to melt, water runs off the ice and the volume or weight of the ice will then commence to decrease.

In my invention under ordinary circumstances, I will not rely on the cooling elfect of the ice and salt, as above zero degrees F. My solution of the problem will be entirely effective provided the car reaches destination with the food and the ice at the same temperature in the order of zero degrees The presence of the salt and the ice serves as a safety device if the trip takes too long or the temperature to which the car is exposed is inordinately high and if the temperature of the ice rises to and above zero, then I still will have the additional protection available until the ice is all melted but this protection is a protection which still involves an undesirable though perhaps not fatal rise in the temperature of the contents of the car.

Instead of liquid nitrogen I may use other inert liquefied .gases having an extremely low boiling point temperature at atmospheric pressure, such as liquefied air.

I claim:

1. In the method of shipping perishable products in a transport having a storage space of large capacity for housing the perishable products and ice bunkers alongside said storage space but separate and apart therefrom for refrigeration of air circulated through the storage space, the steps of filling said ice bunkers with ice, and contactingsaid ice with a liquefied gas selected from the group consisting of air and nitrogen having a boiling point at atmospheric pressure of less than 300 F. to superfreeze the ice to temperatures below freezing.

2. In the method of shipping perishable products in a transport having a storage space of large capacity for housing the perishable product-s and ice bunkers alongside said storage space for refrigeration of air circulated through the said storage space, the steps of filling the ice bunkers with ice and salt, and applying a liquefied gas selected from the group consisting of liquefied air and liquefied nitrogen to the ice in the ice bunkers to superfreeze the ice to temperatures substantially below freezing.

=3. The method of shipping perishable products in a transport having a storage space of large capacity for housing the perishable products and ice bunkers alongside said storage space for refrigeration of air circulated through the said storage space, the steps of filling the ice bunkers with ice, treating the ice in the ice bunkers with liquid nitrogen until the temperature of the ice has been reduced to far below freezing.

4. The method as claimed in claim 3, in which the ice in the ice bunkers is treated with the liquefied nitrogen before the storage space is filled with the perishable product.

5. The method as claimed in claim 3, in which the ice in the ice bunkers is treated with liquefied nitrogen after the storage space has been filled with the perishable product.

References Cited by the Examiner UNITED STATES PATENTS 2,337,600 12/1943 Harris 6276 2,353,909 7/1944 Lager 6262 2,479,821 8/ 1949 Deutsch 62--62 2,479,840 8/ 1949 Johnson 6262 2,501,141 3/1950 Plummer 6262 2,5 02,527 4/ 1950 McFarlan 62-67 2,516,166 7/1950 Wiczer 62l 2,784,567 3/1957 Reynolds 6263 EDWARD J. MICHAEL, Primary Examiner.

Claims (1)

1. IN THE METHOD OF SHIPPING PERISHABLE PRODUCTS IN A TRANSPORT HAVING A STORAGE SPACE OF LARGE CAPACITY FOR HOUSING THE PERISHABLE PRODUCTS AND ICE BUNKERS ALONGSIDE SAID STORAGE SPACE BUT SEPARATE AND APART THEREFROM FOR REFRIGERATION OF AIR CIRCULATED THROUGH THE STORAGE SPACE, THE STEPS OF FILLING SAID ICE BUNKERS WITH ICE, AND CONTACTING SAID ICE WITH A LIQUEFIED GAS SELECTED FROM THE GROUP CONSISTING OF AIR AND NITROGEN HAVING A BOILING POINT AT ATMOSPHERIC PRESSURE OF LESS THAN -300*F. TO SUPERFREEZE THE ICE TO TEMPRATURES BELOW FREEZING.