Patent GB-750719-A (GB)
Title: Improvements in or relating to evaporators
IPC: F25B39/02
Filed: 1954-03-09
Abstract: 750,719. Refrigerating. CARRIER ENGINEERING CO., Ltd. March 9, 1954 [July 16, 1953], No. 6910/54. Class 29. [Also in Group XXIX]  In an absorption refrigerating system using water as the refrigerant and a saline solution as the absorbent, the evaporator comprises a plurality of tubes from which vapour is withdrawn in part through the point of introduction of the water so that variation in the flow of vapour varies the amount of water supplied. As shown in Figs. 2 and 3, upper and lower headers 23, 24 are connected by tubes 21 each of which has an angular portion 22 extending into the upper header. A trough 25 in this header supplies the tubes in parallel and receives water from the condenser through pipe 12. Vapour flows from the top and bottom of the tubes, passes from the upper to the lower header through a pipe 28 and is withdrawn by a pipe 14. As the vapour leaves the upper end of the tubes it drags on the water flowing down the angular portion 22 and, hence, the greater the flow of vapour, the less is the supply of water. This ensures an adequate supply to each tube and equalizes the supply to the tubes. The tubes are internally, helically grooved at 26. In modifications, the upper part of the angular portion 22 has a fixed or adjustable internal projection to give an increased rate of vapour flow over the water surface ; and the water may be fed to the angular portion through an orifice on the underside of the angular portion near its junction with the vertical part of the tube. In a further modification, Fig. 6, water flows from trough 25 down angular portion 22 and enters the vertical tube 21 through an aperture 35 and evaporates inside the tube. Unevaporated water collects in a cup 33 and overflows into the lower part 37 of the tube 21 from which vapour passes through a vertical pipe 32 forming a continuation of the angular portion 22. Thus the water supply will not be restricted until evaporation occurs within the lower part 37 of the tube. The tubes are connected between the upper and lower headers 23, 24 (not shown). In a further modification, Fig. 10, vertical tubes 58 extend between upper and lower headers (not shown), and are surrounded at the top by a cylindrical member 61, the bottom wall of which has orifices 60 through which water flows from a feed trough 73 to overflow into the tubes. When the tube is fully supplied with water, vapour leaving its top sweeps up into a passage 70 and then through an aperture (not shown) into the upper header. Because passage 70 has a smaller cross-section than the upper end of the tube, the vapour velocity is higher there and water is sucked from the bottom of the member 61 through passages 63 formed between the wall of member 61 and an inner cylinder 62. This reduces the water supply to the tube. The invention can also be applied to varying the water supply in accordance with the cooling load on the system, Figs. 8 and 9. As shown in Fig. 8, water flows from a feed trough 43 through an angular portion 45 and orifice 46 in to the upper end of the topmost of a bank of inclined evaporator tubes 40. These are supplied with water in series and vapour is withdrawn from both ends of each tube through headers 41, 42. When the load is being met, i.e. when water is being supplied to the lowest tube, vapour flows from the lower end of that tube up a pipe 44 and so through angular portion 45 to reduce the water supply. As shown in Fig. 9, water which has not been evaporated in the lowest tube 40 flows through a heater 51 and the resulting vapour passes up pipe 54 to a jet 55 facing an orifice 53 through which water flows from the feed trough 52 to the topmost tube 40. The issuing vapour impinging on the orifice 53 prevents or reduces the water supply to the tubes. The heater 51 is preferably heated by condensate coming from the condenser through pipe 56 and passing to the feed trough 52 through pipe 57. In the embodiments of Figs. 8 and 9, a plurality of banks of tubes are provided in parallel.