Compressor displacement

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

The compressor displacement rate is volume swept through by the pistons (product of the cylinder number n, and volume of cyhnder V = stroke d K/4) per second. In reahty, the actual compressor delivers less refrigerant. 

No. Refrigerant Chemical Name or Composition (% by mass) Evaporator Condenser Pressure, Pressure, i MPa MPa Refrigerant Compression Net Refrigerating Circulated, Ratio Effect, kJ/kg g/s Specific Volume of Liquid Circulated, Suction Gas, L/s m /kg Compressor Displacement, L/s Power Consumption, kW Coefficient of Performance Comp. Discharge Temp., K... 

COMPRESSOR DISPLACEMENT - Volume, in cubic inches, represented by the area of the compressor piston head or heads multiplied by the length of the stroke. 

This reduction in permeabiUty due to cake consoHdation or coUapse may be so large that it may nullify or even overtake the advantage of using high pressures in the first place and there is then no reason for using the generally more expensive pressure filtration hardware. While a simple Hquid pump may be cheaper than the vacuum pump needed with vacuum filters, if air displacement dewatering is to foUow filtration in pressure filters, an air compressor has to be used and is expensive. 

Compressors used in a typical refrigerator/freezer are of the positive displacement type, utilizing either reciprocating or rotary motion (Eig. 5) and... 

The Gifford-McMahon cryocooler consists of displacer, regenerator, compressor and intake/exhaust valves that can be staged to reach cryogenic temperatures. 

To be able to decide which type of compressor would best fit the job, we should first divide the compressors into three main categories positive displacement, centrifugaf and axial flow In general terms, positive displacement compressors are used for high pressure and low flow characteristics centrifugal compressors are used for medium to high pressure dehvery and medium flow and axial flow compressors are low pressure and high flow... 

Continuous-Flow Compressors Continuous-flow compressors are machines where the flow is continuous, unlike positive displacement machines where the flow is fluctuating. Continuous-flow compressors are also classified as turbomachines. These types of machines are widely used in the chemical and petroleum industiy for many services. They are also used extensively in many other industries such as the iron and steel industry, pipeKne boosters, and on offshore platforms for reinjection compressors. Continuous-flow machines are usually much smaller in size and produce much less vibration than their counterpart, positive displacement units. 

Positive Displacement Compressors Positive displacement compressors are machines that are essentially constant volume machines with variable discharge pressures. These machines can be divided into two types ... 

Many users consider rotaiy compressors, such as the Rootes -type blower, as turbomachines because their behavior in terms of the rotor dynamics is very close to centrifugal and axial flow machineiy. Unhke the reciprocating machines, the rotary machines do not have a veiy high vibration problem but, like the reciprocating machines, they are positive displacement machines. 

FIG. 10-78 Approximate performance curves for a rotary positive-displacement compressor. The safety valve in discharge line or bypass must he set to operate at a safe value determined hy construction. 

Compressors These could be classified by one criteria (the way the increase in pressure is obtained) as positive-displacement and... 

Positive-Displacement Compressors Reciprocating compressors are built in different sizes (up to about one megawatt refrigeration capacity per unit). Modern compressors are high-speed, mostly direct-coupled, single-ac ting, from one to mostly eight, and occasion-aUy up to sixteen c inders. 

Ratio of the ac tual flow rate (entering compressor) to the displacement rate is the volumetric efficiency T va- The volumetric efficiency is... 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

API Std 619, Rotary-Type Positive Displacement Compressors for Petroleum, Chemical, and Gas Industry Services, 3rd Edition, June 1997... 

Compressors using the intermittent compression mode are referred to as positive displacement compressors, of which there are two distinct types reciprocating and rotary. Continuous-mode compressors are also characterized by two fundamental types dynamic and ejector. 

The rotary compressor portion of the positive displacement family is made up of several compressor configurations. The features these compressors have in common are ... 

The reciprocating compressor is a positive displacement, intermittent flow machine and operates at a fixed volume in its basic configuration. 

The second reason for modification of the displaced volume is that in real world application, the cylinder will not achieve the volumetric performance predicted by Equation 3.4. It is modified, therefore, to include empirical data. The equation used here is the one recommended by the Compressed Air and Gas Institute [1], but it is somewhat arbitrary as there is no universal equation. Practically speaking, however, there is enough flexibility in guidelines for the equation to produce reasonable results. The 1.00 in the theoretical equation is replaced with. 97 to reflect that even with zero clearance the cylinder will not fill perfectly. Term L is added at the end to allow for gas slippage past the piston rings in the various types of construction. If, in the course of making an estimate, a specific value is desired, use, 03 for lubricated compressors and. 07 for nonlubricated machines. These are approximations, and the exact value may vary by as much as an additional. 02 to. 03... 

Step 2. Find the total volume displaced per revolution using Equation 3.1 for a single-acting compressor. 

The displacement of the screw compressor is a function of the interlobe volume and speed. The interlobe volume is a function of rotor profile, diameter, and length. Table 4-1 provides some typical rotor diameters and corresponding L/d ratios. The interlobe volume can be expressed by the following equation. 

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