Plunger-cylinder flow

First we want to gain some insight into the nature and mechanism of positive displacement flow. In the next two examples we examine the plunger-cylinder... 

The flow required to lubricate the packing and cylinders is quite small, and the pressure necessary to inject the lubricant at these locations is quite high. Therefore, small plunger pump (force-feed lubricators) sys-... 

Back extrusion is an important method for determining the yield force required for food materials that are homogeneous and that flow. The yield force is the point where flow is initiated. Using a plunger and a cylinder open at one end (Figure H2.2.5), it is possible to extrude food material back through the annular gap. Extrusion occurs beyond the rupture point of the food. This method is commonly performed with cooked materials such as peas and rice. 

Syringe Pump—A pulseless pump made up of a motor-driven piston or plunger in a solvent-filled cylinder. Useful only when small solvent volumes are to be pumped often used in micro-flow or nano-flow HPLC systems. 

Fig. 6.37 Schematic representation of four geometrical configurations utilizing external mechanical pressurization giving rise to positive displacement flow, (a) Axially moving plunger in a cylinder, (b) Squeezing disks, (c) Intermeshing gear pump, (d) Counterrotating intermeshing twin screws.

Melting (plasticating) the plastic is accomplished in a plasticator (screw in barrel as described in Chapter 3). This melt is forced into a clamped mold cavity. The liquid, molten plastic from the injection cylinder of the injection machine is transferred through various flow channels into the cavities of a mold where it is finally shaped into the desired object by the confines of the mold cavity. What makes this apparently simple operation complex is the limitations of the hydraulic or electrical circuitry used in the actuation of the injection plunger and the complicated flow paths involved in the filling of the mold (Chapter 17). Finally opening the mold to eject the plastic after keeping the material confined under pressure as the heat in the melt is removed to solidify the plastic into the shape desired. 

In the first measurement the device is well insulated so there is no flow of heat to or from the gas, and the piston is slowly moved inward, compressing the gas, and its temperature is found to increase In the second measurement the piston is Plunger (piston) free to move and the external pressure is constant. Air in pump cylinder amount of heat is added to the gas in the... 

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