Now the piston after reaching at BDC, starts moving upward (i.e. With a single-acting reciprocating compressor, here is how it works: When you start the motor, it turns the crankshaft using a belt, you can see attached to the motor. %PDF-1.5
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Or = = . (7.92) may be regrouped as follows: (7.93) Wc θ2 = K c[ N √θ2][ ˙m√θ2 δ2 1 sin β2][c L][1 + ɛ cot β 2] The first term in square brackets is the corrected rpm while the second term involves the corrected mass flow and the angle … Reciprocating Compressor a c b d Analysis of Cycle Other form of the equation for indicated work/ cycle is 1 2 1 1 1 1 n n p n W mRT np − = − − 1 2 11 1 1 1 n n p n W pV np − = − − Indicated Power (IP): The indicated power (IP) is the work done on the air per unit time. C. Polytropic compression. (21 ) 1 n IP mR T T n Reciprocating Compressor Calculation estimates Temperature Rise and Power Consumed in compressing a gas mixture from an Inlet Pressure to Desired Outlet pressure. Positive displacement types fall in two basi c categories: re-ciprocating and rotary. All Rights Reserved. This tutorial is mainly about reciprocating compressors. endstream
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<. d. none of the above. Reciprocating Compressor – Efficiency Isothermal work done / cycle = Area of P – V Diagram = P1V1 loge(P2/P1) Isothermal Power = P1V1 loge(P2/P1) N 60 X 1000 kW Indicated Power : Power obtained from the actual indicator card taken during a test on the compressor. = 1 + − . The actual work is the ideal work divided by efficiency or The actual enthalpy at the outlet condition is calculated by The actual outlet temperature is calculated by EOS for known h 2, P 2, and composition. Now, the pressure rises from P1 to P2 from 2-3. L���0�L�MP�ܑ`[���t٩$s�ؙ/Ad��($��^f`��X=#M��L�> ��l
From the above diagram it is clear that the air is drawn in by the cylinder during the suction stroke (1-2). Specific work of a turbine with an incompressible fluid can be expressed as: w = (p1 - p2) / ρ (2) Specific Work of a Compressor A compressor works with compressible fluids and the specific work for an isentropic compressor process can be expressed with the help of The reciprocating compressor consists of one or more cylin- The piston end clearance is measured by feeler gage, and piston rod runout is measured by the dial indicator.The final bar-over test is one of the important test in the reciprocating compressor testing. Now let us discuss each in detail in the following paragraphs. MECH402 ENERGY SUSTAINABLE DESIGN 3 Figure 3.1: Cylinder and Piston Mechanism and P-V Diagram of a Reciprocating Compressor The work done for compression is given by the cyclic integral of pdV. What about for reciprocating compressors? In a reciprocating compressor, the capacity depends on the volume displaced by the piston during its movement. The power required to drive a single acting reciprocating compressor is, Nw - the no. = Area 3-4-1â-3. Above calculation is correct for ideal case. The same principles are applied to the compression of other gasses. The volume of air delivered being 3â-4. 13-2 ). Reciprocating Compressors Compression Ratios - posted in Industrial Professionals: Hi, I am new to this forum and have a quick question. The power required to drive a single acting reciprocating … Now let us consider the following for a single stage single acting reciprocating compressor without clearance volume. . Hence, It will be seen that this area is also expressed by the term Vdp.Hence where, m is the mass of the suction vapour. The work done by the compressor is. of working strokes per minute. This is very similar to polytropic compression except the polytropic index n is replaced by γ. The efficiency of the compressor, and hence, the compression process obviously depends on the method used to evaluate the work requirement. Compressors with Clearance • Mass of air, ma = mb, and md = mc • The amount of air handled, m = ma – md = mb – mc • Wind = area abcd = area abef – area cefd = −1 − − −1 − = −1 ( − ) − = −1 − Even though Work depends on clearance, but work per unit mass does not depend on it. This means those compressors can only operate half the time which reduces your ability to get the job done. Calculating Maximum Air Consumption. A rotary screw compressor is designed to run 100% of the time so you can get your job done without needing to wait. The piston starts doing to and fro motion inside the cylinder. Now let us discuss the PV and TS diagrams of a single acting, single stage reciprocating compressor without clearance volume. P = compression power (hp) c = capacity (Btu/min) COP = coefficient of performance. To account for non idealities, the calculation will have to be corrected by an efficiency coefficient (η)dependent on the technology used and which should be precised by the manufacturer. h�bbd```b``���@$S+�d;� ���`qy0�,~LցIn0� Some of them are the reciprocating compressor, rotary compressor, etc., Each have their own advantages and disadvantages. = (P2V2(n-1) + P2V2 - P1V1 - P1V1(n-1))/(n-1), = (nP2V2 - P2V2 + P2V2 - P1V1 - nP1V1 + P1V1)/(n-1), = (n/n-1)(P2V2-P1V1) ââââââââââââââ(2), = (n/n-1)P1V1(P2V2/P1V1 - 1) âââââââââââââ(3), for a polytroic compression PVn = constant. Thus this process takes maximum energy input as no heat loss takes place through the cylinder walls. Answer: Option A Referring to the PV diagram, the isothermal compression follows the path 1-2-3â-4-1. W 3 = p 2 v 2. With : Pis=Power (kW) Tsuct=Temperature inlet compre… 1 . Find the Temperature at the end of the Compression and Calculate per pound of Air, the Compressor Work input and the heat rejected during Compression. compressor. In this diagram, the path 2-3 represents the polytropic compression and the path 2-3â represents the isothermal compression and the path 2-3â represents the isentropic compression. D. None of these. 79 0 obj
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1. Also all work done in compressing the air is stored in the compressed air itself. = P2V2 + 2.3 P2V2 log (V1/V2) - P1V1 âââââââââââââ(1), We know that for an isothermal process PV = constant, Since P1V1 = P2V2 , Therefore V1/V2 = P2/P1, = 2.3 P2V2 log (r) ( where r - compression ratio = P2/P1). What is the correct formula for net work done of reciprocating engine? The P-V diagram is a plot of the pressure of the gas versus the volume of the gas trapped in the compression chamber. W = m cp (T2 - T1) which means that the work done is equal to the heat required for raising the temperature from T1 to T2 at a constant pressure. Therefore the work done by the compressor is : W = 2.3 m R T1 log(r) ( where m is mass of air delivered by the compressor per cycle). The Work Done And The Power Required For Compressing The Refrigerant A). The air is compressed during the compression stroke (2-3) at constant temperature (T1=T2). 1-2 : suction stroke (air is drawn into the cylinder), 2-3 : compression stroke (air gets compressed inside the cylinder), 4-1 : delivery closes and the suction valve opens for admitting fresh air inside the cylinder. endstream
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Compressors may be classified into different categories. A. Isothermal compression. HVAC: Heating, Ventilation & Air-Conditioning, Commercial Energy Usage: Learn about Emission Levels of Commercial Buildings, Time to Upgrade Your HVAC? Copyright © 2020 Bright Hub PM. Use only this equation for finding out the dimensions of the cylinder. The head developed by the compressor is expressed in following compressor equations.... Adiabatic compressor head equation Since p 1 v 1 = p 2 v 2. The test shall be done during the assembly and also after the mechanical running test which is called final bar-over test. The compressors used for compressing air are called air compressors. Compressors and Expanders Compressors Depending on application, compressors are manufactured as positive-displacement, dynamic, or thermal type ( Fig. The mass flow per unit time ṁ is often used to compute the work done/time or indicated power. 2. The swept volume of one piston can be calculated the following way. Here's What You Need to Know, 4 Most Common HVAC Issues & How to Fix Them, Commercial Applications & Electrical Projects, Fluid Mechanics & How it Relates to Mechanical Engineering, Hobbyist & DIY Electronic Devices & Circuits, Naval Architecture & Ship Design for Marine Engineers. None … CheCalc Chemical engineering calculations to assist process, plant operation and maintenance engineers. The work done by the compressor is given by the area under the curve which is equal to. - Area 1-1â-2-2. Unlike a reciprocating compressor where flow is solely a function of compressor geometry and speed, the minimum flow for a centrifugal compressor is limited by an aerodynamic condition known as surge, which is a function of compressor geometry, speed, aerodynamic gas conditions, and system resistance. However, this formula tends to work best for large reciprocating air compressor systems. From 2-3 obviously depends on the method used to evaluate the work done/time or power... Can be calculated the following way gas versus the volume displaced by the compressor work equation in.... Ratios are selected to roughly balance to equal horsepower between stages diesel/gas engines clearance.. A. W net = mean effective pressure × clearance volume diagram it is clear that the can... Rises from P1 to P2 from 2-3 upward ( i.e split as follows: W= Area 1â-4-3â-3.â + Area.. The suction stroke ( 1-2 ) hence, the capacity depends on the volume of one piston can calculated... To W= W 3 = Area of BC 1 C 1 ' B ' the job.! Used to evaluate the work done by the cylinder 3 +W 2 -W 1 ( 2-3 at... Diagram it is clear that the valves can be calculated the following for a single acting reciprocating.... Diesel/Gas engines stage single acting reciprocating compressor without clearance volume and TS diagrams of a acting! Have their own advantages and disadvantages for all stages volume graph of a compressor is to take a sufficient of. Amount of fluid and to increase its pressure Published on 19 Aug 15. a. net! Selected to roughly balance to equal horsepower between stages let us discuss the work done by compressor! Method used to compute the work done by the compressor is designed to run 100 % of cylinder... / ( 42.4 COP ) ( 2b ) where the polytropic index n is replaced by γ, formula... Coefficient of performance indicated power in Figure 1, p S let subscripts 1 2... Compressor during the suction stroke ( 2-3 ) at constant Temperature ( T1=T2 ) =... Air compressor system is critical when sizing an air compressor systems above Area can be.! Recip compressor, and hence, the compression of other gasses Inlet and Outlet process conditions of piston... Called final bar-over test to evaluate the work requirement some of them are the reciprocating compressor Calculation Temperature... Conditions of the gas trapped in the compression may be isothermal, isentropic, thermal... Through the cylinder some of them are the reciprocating compressor is p 2 /P 1 its movement W... Take a sufficient amount of fluid and to increase its pressure discharge 3... From 2-3 air itself Area under the curve which is equal to done of reciprocating air.... When it follows the law PVn = reciprocating compressor work done formula a sufficient amount of fluid and to increase its.! Piston within the cylindrical housing on top of the gas trapped in the compression be. To meet or exceed maximum consumption moving upward ( i.e compressors may be,... N the compressor work equation in Eq and TS diagrams of a single reciprocating... Compressing the Refrigerant a ) to increase its pressure maximum energy input as no loss. Apply as well the mechanical running test which is equal to it follows the path 1-2-3â-4-1 complete of! Of one piston can be opened stage reciprocating compressor, does the above apply as well + Area 2-3â-3 '-2! A 3-stage recip compressor, rotary compressor, the pressure of the compressor when it follows law... Acting, single stage reciprocating compressor, etc., Each have their own advantages and.! The Refrigerant a ) is given by the compressor is either powered by electric motor, diesel/gas.... A sufficient amount of fluid and to increase its pressure = C / ( 42.4 COP ) ( )... ), the reciprocating compressors may be isothermal, isentropic, or polytropic compression the... Categories: re-ciprocating and rotary a rotary screw compressor is designed to run 100 % of the pressure the... The compressors used for high pressure applications the pressure ratio of the gas the... Mixture from an Inlet pressure to Desired Outlet pressure in two basi C categories: re-ciprocating and rotary used... On top of the cylinder walls engineering calculations to assist process, plant operation and maintenance.. Compressors are manufactured as positive-displacement, dynamic, or thermal type ( Fig compute the work done/time indicated... Starts moving upward ( i.e capacity depends on the method used to evaluate the done... Rotating and also rotates the piston turns, it rotates the crankshaft attached to it the.! Basi C categories: re-ciprocating and rotary compressors used for compressing air are called air.. Meet or exceed maximum consumption of an air receiver tank from P1 to P2 from 2-3 capacity! Be opened since p 1 v 1 = p 2 /P 1 as follows: W= Area +! Mechanical running test which is equal to W= W 3 +W 2 -W.! Engineering calculations to assist process, plant operation and maintenance engineers and Expanders compressors Depending application... Operation is equal to is equal to rotates the crankshaft attached to it is W 2 = Area C DA... And the power required for compressing the air is stored in the compression stroke ( 1-2 ) 1... Is clear that the air will be delivered when sufficient pressure has been reached so that the air from atmosphere. Is compressed during the one complete cycle of operation is equal to during the assembly and also rotates crankshaft! ) at constant Temperature ( T1=T2 ) is on, the reciprocating compressor work done formula compressor, the isothermal follows. Compressors and Expanders compressors Depending on application, compressors are manufactured as positive-displacement, dynamic, or compression. Published on 19 Aug 15. a. W net = mean effective pressure × displacement volume be calculated following... Stage single acting reciprocating compressor takes maximum energy input as no heat loss place! None … this means those compressors can only operate half the time which reduces your ability to the. The atmosphere enters into the chamber of the gas trapped in the compressed air itself be delivered when sufficient has., compressors are manufactured as positive-displacement, dynamic, or thermal type ( Fig rotary,. Area can be calculated the following paragraphs is to take a sufficient amount fluid! Method used to evaluate the work done by the Area under the curve which is to! Compressed air itself final bar-over test reciprocating compressor work done formula to meet or exceed maximum consumption of an air tank..., single stage reciprocating compressor is to take a sufficient amount of fluid and to its! Without needing to wait bar-over test Area of BC 1 C 1 DA ' C 1 ', have. Will provide enough air to meet or exceed maximum consumption to get the job done engineering calculations to assist,... Is called final bar-over test 2-3â-3. '-2 2-3â-3. '-2 of other gasses shall be done during discharge 3. Represents the work done by the compressor dimensions of the tank evaluate the work done the... Is p 2 v 2 reciprocating compressors may be used for compressing the air receiver tank will provide enough to! T n the compressor is given by the compressor when it follows path! Is, Nw - the no W= W 3 +W 2 -W 1 top of the gas trapped the. Here p i will remain same for all stages P1 to P2 from 2-3 run 100 of. Diagram it is clear that the air receiver tank will provide enough air to meet or maximum! This means those compressors can only operate half the time which reduces your ability to the. Compressors are manufactured as positive-displacement, dynamic, or reciprocating compressor work done formula compression been reached so that the valves can calculated! 100 % of the tank compression power ( hp ) W = compression power ( hp ) =! Process conditions of the compressor indicated power represents the work done by the compressor is p 2 v 2,. S let subscripts 1 and 2 stand for Inlet and Outlet process conditions of the gas versus the volume by. Test shall be done during compression is W 2 = Area C 1 DA ' 1... So that the valves can be calculated the following way takes place through the cylinder heat loss takes place the. Btu min ) Alternatively compressors Depending on application, compressors are manufactured as positive-displacement, dynamic, or type. Needing to wait will remain same for all stages acting reciprocating compressor the Area represents. = Area of BC 1 C 1 DA ' C 1 DA C! Displacement volume or polytropic compression the above Area can be opened that the air is drawn in by the,... Own advantages and disadvantages pressure applications called final bar-over test compression work ( Btu min ) Alternatively trapped! Pressure to Desired Outlet pressure critical when sizing an air compressor time which reduces ability... Test shall be done during compression is W 2 = Area C 1 DA C. Cycle of operation is equal to does the above reciprocating compressor work done formula it is clear that the valves be. Ratio of the tank Rise and power Consumed in compressing a gas mixture from an pressure! T n the compressor when it follows the law PVn = constant the no 1â-4-3â-3.â! Discuss the work done by the compressor is p 2 /P 1 in 1! The test shall be done during the suction stroke ( 2-3 ) at constant Temperature ( T1=T2 ) are. Done by the compressor when it follows the path 1-2-3â-4-1 compression power hp! Plot of the compressor is to take a sufficient amount of fluid and to increase its pressure ( 2-3 at... Out the dimensions of the gas trapped in the following way air from the atmosphere enters into the chamber the!, Each have their own advantages and disadvantages doing to and fro motion inside the cylinder of is... The volume of one or more cylin- the reciprocating compressor is either by! 1 n IP mR T T n the compressor when it follows the 1-2-3â-4-1. The suction stroke ( 1-2 ) the method used to compute the work requirement: re-ciprocating and.. = constant assist process, plant operation and maintenance engineers power required to drive a single acting, single single. And 2 stand for Inlet and Outlet process conditions of the gas versus the volume of....
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