外文文献及翻译：压缩机泵制冷工程

外文文献及翻译：压缩机泵制冷工程内容摘要：

ce show that disengagement of the rod chambers is more advisable. Thus, in NPTs32 type of pump having cylinders of 90, 100, 115, and 127 mm diameter and rods of 45 mm diameter the delivery can be reduced – times by removing the valves from the rod chambers. At low loads (pressure drop not more than 15 MPa and minimal delivery), the engine of the motor vehicle KrAZ250 can run steadily at a rotation speed of 550 rpm. In the second gear with minimum engine rotation speed, the delivery of a pump with a cylinder of 90 mm 外文翻译 第 8 页 共 20 页 diameter can be reduced down to m3/h. Unlike the SIN32 pump, the delivery of the NPTs32 pump can be controlled during the technological operation and reducing or raising the delivery can change the pump output. Removal and installation of two valves do not take too long. Let us see how the uniformity of pump delivery will change upon removal of the valves. It is well known that the instantaneous output of a singlecylinder singleacting pump is q = Frsin = where r is the radius of the crank and is the crankshaftturning angle. The ratio of the maximum instantaneous delivery to the average delivery of the pump is called coefficient of delivery nonuniformity: = Qmax/Qav. The average delivery of a fourchamber pump in one turn of the crank Qav = 2(2F – ƒ)S/2. The maximum instantaneous delivery of a pump having four chambers and cranks turning at a 90176。 angle (Fig. 3 a)Qmax = FSsin45176。 = FS. For the NPTs32 type of duplex pump (Dc = 90– 127 mm and dr = 45 mm), = – . After this, as the delivery (pressure) valves are removed from the rod chambers, the average delivery of a twochamber differential (differentiallyacting) pump (Fig. 3b) Qav = 2FS/2 = FS/ . For such pumps, the maximum instantaneous delivery Qmax = (F – ƒ)Ssin45176。 = ( F – ƒ)S。 = – . For all other types of delivery variation on account of removal of valves (in succession, all front pressure valves or crosswise, one of the front chambers and another of the rod chambers in another cylinder), the coefficient will be much higher. In general, in differential pumps, to reduce the nonuniformity 外文翻译 第 9 页 共 20 页 in the pump delivery, the rod diameter is so chosen that its crosssectional area is half that of the cylinder, ., ƒ = . In that case, the delivery nonuniformity coefficient will be the lowest for twocylinder differential pumps: = FS 4 /FS = . For each cylinder, in order to get the coefficient = , it will be necessary to make a rod of a fixed diameter (63,70, 80, and 90 mm, respectively). But then, if the pump operates with all the valves, there will be a substantial increase in delivery nonuniformity and decrease in pump delivery. If the NPTs32 pump is required to operate in two modes, it is perhaps advisable to make a rod of 55 mm diameter (for cylinders of 90 and 100 mm diameter) and of 70 mm diameter (for cylinders of 115 and 127 mm diameter). In that case, the delivery nonuniformity coefficient will be identical for both modes of pump operation: = – . The theoretical pump delivery on account of increase in the diameter of the rod in a duplextype pump will decrease roughly by 10%. Let us see how the delivery nonuniformity will change if the pressure (delivery) valves are removed from the front chambers (Fig. 3c). The delivery, as was noticed earlier, will decrease more than twofold. The average delivery of a seriesproduced NPTs32 pump operating with two rodchambers is Qav = 2(F – ƒ)S/2 = ( – )FS/ . The maximum instantaneous pump delivery (forward stroke) is Qmax = FSsin45176。 = FS. The minimum instantaneous delivery (back stroke) is Qmin = FSsin45176。 = FS = (– )FS. The delivery nonuniformity coefficient is = (Qmax + Qmin)/Qav = – . If the rod diameter of such a differential pump is increased, the delivery 外文翻译 第 10 页 共 20 页 nonuniformity will increase further and,therefore, it will be necessary to remove valves only from the rod chambers. In seriesproduced NPTs32 type of pumps having four working chambers, the nonuniformity of the fluid flow in the delivery (pressure) and suction (intake) lines will be identical and will depend on the rod diameter. The smaller the crosssectional area of the rod, the greater will the fluid flow uniformity be. In the suction (intake) line of a differential pump, the flow nonuniformity increases considerably because only two chambers operate and the cranks of the crankshaft are turned by not 180176。 , as is usual for single acting two。