Patent GB-972530-A (GB)
Title: Improvements relating to the reduction of sweat damage to a cargo in a storage compartment
IPC: F24F3/14
Filed: 1961-09-13
Abstract: 972,530. Ventilating ships' cargoes. O. D. COLVIN. Sept. 13, 1961 [Sept. 27, 1960], No. 32804/61. Heading F4V. [Also in Division B7] A ship's cargo is protected from damage by sweat by a stream of dry turbulent air. The invention is stated to be based on the discovery that, even where there is a substantial water vapour pressure differential between the air inside and the air outside a container such as a van, forced air circulation is still necessary to reduce the moisture content of the air in the container; this forced air circulation is stated to scour or sweep away moisture-bearing lamina which would otherwise build up around the surfaces of the cargo. Where the cargo comprises hygroscopic material, e.g. cardboard containers, green coffee or tobacco, the circulating dehumidified air, which may be cooled in a heat exchanger (not shown), extracts moisture therefrom, thus preventing the subsequent release of this moisture and resulting damage by condensation to other cargo. Where, on the other hand, the cargo comprises canned goods or other metallic articles which have been loaded in a cool climate and are to be discharged from the ship in a moist warm climate, the circulating air may be heated to warm up the cargo and thus prevent condensation on discharge. Graphs are provided illustrating experimental measurements of cargo temperatures during particular voyages. General arrangements.-As shown in Fig. 1, each hold on a ship has its own dehumidifier 61 and air heater 68 which are separately controlled from central control unit 69, and the cargo is contained in " vans " 52. The humidified air is blown into a system of conduits 62 having a nozzle 75, Fig. 2, opposite the inlet port 63 for each van. The nozzle includes a Venturi-type sleeve whereby the air ejected from the nozzle draws in additional air from the atmosphere in the hold. After circulating round the cargo, the air is exhausted from the van through port 63a. A " dewcell " 70 measures the dewpoint temperature either in a van, Fig. 2, or in the return air stream to the dehumidifier, Fig. 1, and a resistance thermometer 74 measures the average dry bulb temperature of the cargo. In an alternative arrangement (Figs. 7-13, not shown), each horizontal air conduits supplies air alternately to two rows of vans, one on either side, and the Venturi effect is produced by a portion of the inlet ports of the vans themselves. Air-conditioning units.-Fig. 18 shows a dehumidifier/heater unit. In operation with the damper 189 in the position shown, air is drawn by a blower 191 from the hold via exhaust duct 188 into a duct 190, only a portion of this air being by-passed through dehumidifier 186, and the air is returned to the hole supply duct 196 via heater 196a. When atmospheric conditions are suitable, the damper 189 may be moved, manually or automatically, to the broken line position in which duet 190 receives external air through duct 198 while the air from the hold is exhausted through duct 197. The dewpoint temperature of the air leaving and entering the unit may be measured by dewcells 201a and 201b. An alternative unit (Figs. 14-15, not shown) employs a silica gel or other desiccant type of dehumidifier requiring reactivation. Indicating and control unit.-The central control unit 69, Fig. 1, includes means for recording multi-colour graphs 200, 201, Fig. 23, intended to provide advance warning that sweat is likely to occur on the interior surfaces of a hold or on the cargo respectively. The data recorded on the graphs include for each hold the dewpoint temperatures measured at 201a, 201b, Fig. 18, as well as the dry bulb temperatures of the cargo and the air in the hold, and also include the dewpoint and dry-bulb temperature of the outside air, measured by devices 202, 204, and the temperature of the sea water. When the outside atmosphere or sea temperature and the dewpoint temperature of the air in a hold come close to one another, so that ship sweat is likely to occur, the dehumidifier blower for that hold may be automatically actuated (by means not described in detail). The air conditioning unit for a hold may be similarly automatically actuated when a predetermined minimum differential occurs between the dewpoint temperature in a hold and the cargo temperature. Individual control may be provided for each van in a hold e.g. by remotely controlled valves associated with the air supply nozzles.