WO2002095305A1

WO2002095305A1 - Method and apparatus for cooling perishable goods

Info

Publication number: WO2002095305A1
Application number: PCT/EP2001/005904
Authority: WO
Inventors: Rolf Blomgren; Martin Starzmann
Original assignee: Mast I Göteborg Ab
Priority date: 2001-05-22
Filing date: 2001-05-22
Publication date: 2002-11-28

Abstract

Method and apparatus for cooling perishable goods in a compartment (18). The apparatus comprises a cooling arrangement and a length of plastic piping (34) associated with the cooling arrangement. The length of plastic piping is intended to pass through at least a portion of the compartment (18) to thereby allow a heat transporting medium flowing through the length of plastic piping to absorb heat from the compartment. The length of piping has a wall (38) with an inner surface (40) and an outer surface (42), with the outer surface being ribbed over at least a portion of the length of plastic piping.

Description

TITLE: Method and apparatus for cooling perishable goods

TECHNICAL FIELD:

The present invention relates to a method and apparatus for cooling perishable goods. More particularly, the invention is intended to be utilised in areas of very high humidity, for example on ships transporting fresh or frozen fistu

BACKGROUND OF THE INVENTION:

When transporting perishable goods, it is necessary to maintain the goods at a substantially constant temperature which is generally lower than ambient temperature. A typical refrigeration plant is based on the same principle of operation as a domestic refrigerator, i.e. a cooling medium such as freon is circulated in a system comprising a compressor, a condenser and a throttle valve/evaporator. The cooling medium is in a gaseous state upstream of the compressor. It passes through the compressor which increases its pressure and temperature. The cooling medium than flows to the condenser at which the gas is cooled, for example by air or water, to thereby condense. The condensed fluid is normally collected in a collector and thereafter fed to a throttle valve which separates the high pressure side of the system from the low pressure side. As the fluid passes through the throttle valve, its pressure is reduced, thereby causing the fluid to evaporate. The evaporating fluid is led through a pipe which is normally bent back on itself several times to form a compact unit, generally termed an evaporator. Normally, the evaporator is provided with a plurality of fins to thereby provide a large surface area for heat transfer. The evaporating fluid draws heat from the surroundings and is thereafter drawn through the compressor via a return conduit. After being compressed, the fluid once more passes through the condenser, whereby the heat which the fluid absorbed in the evaporator is relinquished.

It is also known to make use of so-called indirect cooling systems. Such systems offer the advantage that a smaller volume of cooling medium is needed, thereby reducing any possible negative environmental effects. An indirect cooling system comprises a primary circuit and a secondary circuit. The primary circuit co-operates with the secondary circuit via a heat exchanger. The secondary circuit is filled with a suitable heat transporting medium, such as a specially adapted salt solution. The primary circuit is generally based on the above-outlined refrigeration plant, though with the difference that the primary circuit communicates with the secondary circuit via the heat exchanger which is located downstream of the throttle valve though upstream of the compressor. The secondary circuit is at least partially located within the compartment in which the perishable goods are stored. The heat transporting medium is pumped round the secondary circuit and absorbs heat from the compartment. As the heat transporting medium passes through the heat exchanger, heat energy is transferred to the cooling medium in the primary circuit.

Cooling of areas of very high humidity, such as on ships transporting fresh or frozen fish, is subject to specific problems. For example, the cooling fins of conventional refrigeration plants quickly become iced over as a result of the very high humidity. Furthermore, the aggressive salt-laden atmosphere implies that precautions must be taken to prevent corrosion of the piping making up the secondary circuit.

The above problems can be overcome by providing a refrigeration plant in which the secondary circuit comprises straight-wall piping, i.e. no cooling fins are present, of non- corrosive material. However, since straight-wall piping is less efficient at transferring heat than piping provided with cooling fins a greater length of piping is required to achieve a comparable rate of cooling. Clearly, the greater length of piping, the more costly and bulky the arrangement becomes.

SUMMARY OF THE INVENTION:

It is therefore an object of the present invention to provide a method and apparatus for cooling perishable goods which is potentially more compact than conventional arrangements. This object is achieved by a method of cooling perishable goods in a compartment, the method comprising the steps of providing a length of plastic piping associated with a refrigeration plant, said plastic piping having an inner surface and an outer surface, said outer surface being ribbed over at least a portion of the length of plastic piping, and causing a heat transporting medium to flow through said length of plastic piping to thereby absorb heat from said compartment.

This object is further achieved by apparatus for cooling perishable goods in a compartment, the apparatus comprising a cooling arrangement and a length of plastic piping associated with the cooling arrangement. The length of plastic piping is intended to pass through at least a portion of the compartment containing the perishable goods to thereby allow a heat transporting medium flowing through the length of plastic piping to absorb heat from the compartment. The length of piping has a wall with an inner surface and an outer surface, with the outer surface being ribbed over at least a portion of the length of plastic piping.

Preferred embodiments of the apparatus according to the invention are detailed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS :

The invention will be described in the following by way of example only and with reference to the attached drawings, in which

Fig. 1 is a schematic view of apparatus according to the present invention;

Fig. 2 is a cross-sectional view along line II-II of Fig. 1, though on a larger scale, and

Figs. 3A-3C illustrate various conceivable cross-sectional shapes for a length of piping comprised in the apparatus according to the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: In the drawings, reference numeral 10 generally denotes apparatus according to the present invention, the apparatus fomiing a refrigeration plant. In the illustrated embodiment, the refrigeration plant is of the indirect type and therefore comprises both a primary circuit 12 and a secondary circuit 14. A partition wall 16 separates the two circuits, with the primary circuit being located on the warm side of the wall and the secondary circuit being almost entirely located on the cool side of the wall, i.e. in a compartment 18 in which perishable goods may be stored.

The primary circuit 12 and the secondary circuit 14 co-operate with each other via a heat exchanger 20. It will be apparent to the skilled person that any suitable type of heat exchanger may be used for this purpose. In addition to the heat exchanger, the primary circuit 12 includes a compressor 22 for compressing a cooling medium such as freon, a condenser 24, a reservoir 26 for the cooling medium, a conduit 28 connecting the reservoir 26 to the heat exchanger 20 via a tlπottle valve 30, and a return conduit 32 to transport the thus warmed cooling medium from the heat exchanger 20 to the compressor 22.

The secondary circuit 14 of the apparatus according to the present invention comprises a length of plastic piping 34 through which a heat transporting medium is made to flow via a pump 36 in the secondary circuit. The heat transporting medium may be any suitable solution, such as brine. In order to efficiently extract as much heat as possible from the compartment 18 while still utilising a compact arrangement, the length of plastic piping 34 is advantageously laid out in looped pattern in which the piping is bent back on itself a plurality of times. The actual length of piping will depend on the chosen application, but for use in the cargo bay of ships, a total pipe length of between 500 m and 1 000 m is typical. The length of piping is preferably made from a them oplastic polymer material. Suitable such materials are of polyethylene, polypropylene and polyvinylidenflouride.

As is most clearly derivable from Fig. 2, the piping 34 has an annular wall 38 having an inner surface 40 and an outer surface 42. Preferably, the inner surface 40 defines a substantially circular cross section to thereby facilitate flow of the heat transporting medium. The outer surface 42 is provided with one or more ribs 44 to thereby present a ribbed outer surface. In this context, the expression "ribbed" means that the outer surface is shaped so as to provide a surface of greater area than if the outer surface were uniformly smooth. Thus, and merely to exemplify what is covered by this definition, if the length of piping were to have a rectangular cross-section, the piping would be ribbed if there were projections or recesses on the outer major surface of at least one side of the rectangular cross-section, i.e. the projections or ribs would increase the surface area exposed to atmosphere compared to a smooth sided length of piping. In this respect, reference can be made to Fig. 3B.

In order to obtain an adequate increase in surface area, the number of ribs is preferably at least 4, preferably at least 5 and most preferably at least 6. In the embodiment illustrated in Fig. 2, the length of plastic piping is provided with 6 ribs 44 having a rounded profile. As is apparent from Figs. 3 A, 3B and 3C, however, the actual profile of the ribs may be varied. The embodiment illustrated in Fig. 3C presents a wall 38 of substantially uniform thickness. For other embodiments, it may be advantageous from a manufacturing point of view to vary the thickness of the wall between a minimum thickness Tj and a maximum thickness T₂. Thus, and with particular reference to Fig. 2, the minimum thickness Tj is between 20%o and 90%>, preferably between 50% and 80% of the maximum thickness T₂.

The actual thicknesses Ti and T₂ of the wall are selected depending on the intended application of the cooling apparatus. Typically, the length of plastic piping may have an internal diameter of 20 mm and a minimum external diameter of 25 mm. Thus, the minimum wall thickness in this case is 2.5 mm.

The apparatus according to the present invention may also be provided with a heater arrangement 46 in the secondary circuit 14 to assist in de-icing of the length of piping. The actual type and capacity of the heater will depend on the intended application, but may for example be resistive electrical heater of some 5 to 10 kW capacity. The heater may be positioned downstream of the heat exchanger 20, though upstream of the looped piping.

It is not necessary that the entire length of piping 34 of the secondary circuit be constituted by ribbed piping. Rather, to facilitate manufacture and assembly, the piping may be ribbed in that portion which leads from the heater 46 to the pump 36. Indeed, the invention is intended to cover applications in which only a portion of the length of plastic piping which is present in the compartment 18 is ribbed.

The invention has been described above by way of example only and it is to be understood that the invention may be varied within the scope of the appended claims.

Claims

CLAIMS:

1. A method of cooling perishable goods in a compartment (18), said method comprising the steps of: providing a length of plastic piping (34) associated with a refrigeration plant, said plastic piping having an inner surface (40) and an outer surface (42), said outer surface being ribbed over at least a portion of the length of plastic piping, and causing a heat transporting medium to flow through said length of plastic piping to thereby absorb heat from said compartment.

2. Apparatus (10) for cooling perishable goods in a compartment (18), said apparatus comprising a cooling arrangement and a length of plastic piping (34) associated with said cooling arrangement, said length of plastic piping being intended to pass through at least a portion of said compartment (18) to thereby allow a heat transporting medium flowing through said length of plastic piping to absorb heat from said compartment, said length of piping further having a wall (38) with an inner surface (40) and an outer surface (42), with said outer surface being ribbed over at least a portion of the length of plastic piping.

3. The apparatus as claimed in claim 2, wherein said length of plastic piping (34) is made of a thermoplastic polymer material.

4. The apparatus as claimed in claim 3, wherein said thermoplastic polymer material is selected from the group consisting of polyethylene, polypropylene and polyvinylidenflouride.

5. The apparatus as claimed in any one of claims 2 to 4, wherein said wall (38) of said length of piping has a minimum thickness (Ti) and a maximum thickness (T₂ ), said minimum thickness being between 20% and 90% of said maximum thickness, preferably between 50% and 80% of said maximum thickness.

6. The apparatus as claimed in any one of claims 2 to 5, wherein said portion of the length of plastic piping (34) is ribbed by a plurality of ribs (44).

7. The apparatus as claimed in claim 6, wherein said plurality of ribs (44) is at least 4, preferably at least 5, most preferably at least 6, in number.

8. The apparatus as claimed in any one of claims 2 to 7, wherein said inner wall (40) of said length of plastic piping defines a substantially circular cross section.

9. The apparatus as claimed in any one of claims 2 to 8, wherein said cooling arrangement comprises an indirect cooling system having a primary circuit (12) and a secondary circuit (14), said primary circuit co-operating with said secondary circuit via a heat exchanger (20), wherein said length of plastic piping (34) is included in said secondary circuit.