What is Compressor: Definition and 199 Discussions

A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids.
Many compressors can be staged, that is, the fluid is compressed several times in steps or stages, to increase discharge pressure. Often, the second stage is physically smaller than the primary stage, to accommodate the already compressed gas without reducing its pressure. Each stage further compresses the gas and increases its pressure and also temperature (if intercooling between stages is not used).

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  1. P

    Air Leaking from Unloader Valve: Any Suggestions?

    I got a new pressure switch and installed it over the weekend. When I turned it on it worked well, and filled up the tanks, however once it turned off air started to leak out of the back of the unloader valve. Have you seen this happen before and do you have any suggestions? Also, can I use an...
  2. S

    Decoupling Compression and Expansion of a turbine

    Hi, I just want to double check something: My understanding is that the higher the compression pressure the higher the amount of energy per unit mass it will take to compress a given mass of gas. So my question is, would a decoupled system where the compression can take place over a longer...
  3. S

    Help to understand polytropic exponent and efficiency

    Hello all, I am new to thermodynamics applied to turbines and compressors and I am trying to get my head around what is represented when calculating the work of a compression/expansion process using the polytropic exponent as oppose to the specific heat ratio of 1.4 (I'm working with air). The...
  4. Kostis82

    Calculate the time needed to fill a compressor

    Dear all, I would like to have your help for a problem that i face. I know that it is a little bit ridiculous, but my brain is stacked right now! I have a helium compressor that i want to fill it with helium at room temperature 293K @ 1.013bar. This compressor will be connected with a pipe. As...
  5. R

    Centrifugal Compressor Performance Curve

    Hi I have uploaded centrifugal compressor performance curve. I want to know how Mass Flow vs Pressure Ratio curve plotted under different efficiency since efficiency is a constant for a compressor. Please help.
  6. M

    Calculation on a water cooled compressor

    How can i calculate the water temperatur in step 3? Do i need more information? We can assume the water temperatur in step 2 is anything between 288 and 313K. If anyone knows how to calculate step 4, ill take that as well.
  7. W

    Finding work of adiabatic compressor using ideal gas

    Homework Statement Methane at ## P_1 ## and ## T_1 ## is compressed to a pressure of ## P_2 ## adiabatically at steady-state. Calculate the work done on the compressor and the temperature ## T_2 ## of the discharge gas. Use ideal gas model. Given: ## T_1, P_1, P_2, C_p, \gamma = 1.4 ## ##...
  8. O

    Relative humidity of the air entering a compressor

    Homework Statement Air is drawn into a compressor at normal temperature and pressure (N.T.P.) and compressed to a pressure of 6 bar gauge. After compression the air is delivered at 1.2m3 min–1 and cooled to a temperature of 30°C, at which point condensate is collected at the rate of 2 litres...
  9. srinaath

    Air conditioner compressor capacity control in VRF systems

    hi guys... am working on a variable refrigerant flow (VRF) type air conditioner. my aim is to change the capacity of the compressor based on load change. i can vary compressor capacity by using inverter...now my doubt is on what basis i should change compressor speed for muti evaporator...
  10. srinaath

    Digital scroll vs inverter driven scroll compressor?

    hi guys...am not that versed in thermal engineering...am learining different VRF(variable refrigerant flow) systems...is there is fight between digital scroll vs inverter driven scroll compressor...then who will win? in terms of efficiency (EER/ and IPLV), modulating capacity...
  11. David Gin

    Internally Heated Dessicant Air Dryer Exhaust Pipe

    Hi all, Is there a correlation between an Air Dryer capacity and the exhaust pipe diameter? How would a small exhaust pipe diameter (not able to exhaust air enough) affects the capacity of an air dryer? If it does, could you expand on this? Thank you
  12. jdawg

    Isentropic Compressor Efficiency

    Homework Statement Nitrogen enters an insulated compressor operating at steady state at 1 bar, 310 K with a mass flow rate of 1000 kg/h and exits at 10 bar. Change in KE and PE is zero. Heat transfer is zero. Assume ideal gas with k=1.391. Find minimum theoretical power input required and the...
  13. S

    How Powerful Should My Compressor Be for a 3L/Day Atmospheric Water Generator?

    I'm working on a project to design Atmospheric Water Generator, to generate 3 litres of water per day. and I'm using the same concept as dehumidifier. My problem is I want to figure out how powerful my compressor should be. I need to calculate that, given a heat flow rate of 352.91 kJ/hour...
  14. O

    Choosing an efficient compressor

    Hello everyone. I'm working those days on my graduation project, and I need a little assistance. I have to choose a compressor that would be driven by diesel engine. The compressor should supply about 1.7 kg air and compress it to 2 atmospheres. It seems that centrifugal compressor or axial may...
  15. Ali Durrani

    Why do we use Cp while finding the work of the compressor?

    why do we use Cp value while finding work of the compressor or the expander i.e W=CpdT=H2-H1 H= enthalpy when we know pressure inside the expander or compressor drops it basically is isentropic process why not we use isentropic work eqn
  16. M

    Gas Turbine & Psychrometric chart

    Hi Everyone, So I seem to have many problems understanding the Psychrometric chart and its physical meaning. First of all, I would be so thankful if you could introduce me a source which can be useful to physically and fundamentally understand the dew point, effect of pressure, humidity... and...
  17. Carlko26

    Turbocharger: Mass flow rate and pressure ratio

    Hello everyone, i am currently dimensioning a compression system using a vehicle turbocharger and need to find a way to relate the pressure ratio of the compressor and the mass flow rate. (flows trough compressor and turbine are of course separated) For the turbine, one can use Stodola's...
  18. David Gin

    Compressor Water Cooled Chiller Thermal Calculations

    Hi All, Is there a list of thermodynamics equations regarding the chiller process from condenser, evaporator, compressor to the regulator. Say I have chiller load at 90%, what set of equations could I use to determine the supply temperature of chill water and condenser supply temperature to...
  19. F

    What is the Outlet Temperature of a Compressed Air Flow?

    Homework Statement Air enters a compressor at 100kPa and 20 oC in steady flow rate . Air is compressed to 1 Mpa. The heat loss is 10% of the power of the compressor . Air enters with speed of 50m/s in a surface of 0,009 m2 and leaves with speed 120 m/s from a surface of 0,0005 m2. Find the...
  20. JasonHathaway

    Thermodynamics: Air compressor

    Homework Statement Air enters a compressor at 100 kPa and 290 K, where it is compressed adiabatically, where the flow rate is 0.1 kg/s. If the volume compression ratio is (V1/V2=8). Determine the following (Assuming the air is ideal with constant specific heat): 1- The temperature and the...
  21. P

    Constant RPM of gas compressor

    I would like to clear out my understanding of gas compressor. If it is moving at constant RPM, is it mean that it can only allow same volumetric flow rate all the time? So the power will remain constant too, (P=VI) then voltage and current will varies. My investigation is to find why there is...
  22. A

    How Can Input Power Improve Predictions in Scroll Compressor Modeling?

    Hi, I am currently trying to model a water-cooled scroll compressor but do not have enough data to predict output conditions. At the moment, I can collect inlet and discharge pressure, outlet temperature, water mass flow rate as well as inlet and outlet temperature. I would like to be able to...
  23. F

    Thermodynamics: Compressor Axial work

    Homework Statement [/B] Thermodynamics problem Air enters a compressor at a temperature of 290 Kelvin and pressure 100 kPa with a stable volume flow of 2.5 m^3/s. The output temperature of the compressor is is 400 Kelvin and the velocity of the flow is 30 m/s. Air is implied to be an ideal gas...
  24. C

    Increasing Compressor Efficiency Question

    I reference this forum all the time and you guys are always good at breaking down confusing questions so I decided I needed to make an account and get some help with a mental struggle I have been having for quite some time! Two commonly discussed ways of improving a compressor's efficiency in a...
  25. yangshi

    Choked flow out of air compressor and wind tunnels

    I posted this on Eng-tips and no replies yet:( I'm trying to design an as-simple-and-cheap-as-possible supersonic wind tunnel using an air compressor (this even possible? given the energy losses from shock waves...). I have access to a Porter-Cable 150psi, .8hp air compressor. Questions: 1...
  26. Vlad137

    Physics behind turbochargers and compressors

    Hi everyone, I need to do a presentation to a high school class about the physics behind a turbocharger and was looking for some help getting which principals/laws explain what happens when a turbocharger is used within a car i.e.; Thermodynamics, gas laws. I just need a direction in which...
  27. K

    Resultant force acting on axial compressor

    Hello, I've got one problem with fluid flow reaction force which acts on compressor. I hope you can help me with that. Here is a sketch to my question: I wonder in which direction resultant force will be directed. I understand that air is flowing from left to right with inlet velocity V1...
  28. S

    What is compressor blade loading and its effects on a compressor blade?

    I want to know what is compressor blade loading. When it is said that a compressor blade will be overloaded near the hub, what does it means?
  29. R

    Design of Vapour Compression Refrigeration Cycle

    Hi! For our class project, we have to design a system that freezes an amount of water as quick as possible. The refrigerant is R134a. The compressor is known. I don't really know how to get started here. How do I choose the evaporator pressure and the superheating, and equally the condensor...
  30. A

    The second law efficiency of compressor in gas turbine cycle

    hi friends, I've used the following equation in Thermodynamics: an engineering approach(Cengel) for calculating exergy efficiency of compressor. In fact, for an adiabatic compressor with negligible kinetic and potential energies, the second-law(exergy) efficiency becomes...
  31. C

    Intermediate pressure in a two-stage compressor

    Homework Statement The prompt says that there's a 2-stage adiabatic compression cycle where the first compressor pressurizes atmospheric air (0psig or 14.7psia) to P2, and the compressed air is cooled by a cooler to the initial temperature, and passes through another compressor to 350psig or...
  32. F

    Help calculating swept volume of scroll compressor

    I think I am having brain fade! I am trying to estimate the swept volume of a scroll compressor. I will use simple values for calculation. Assuming the diameter of each scroll is 4" and the scroll fin height or depth is 2". If I remember correctly, the scroll will intake 360* of rotation...
  33. J

    Compressor - Regulator - Plenum - Exit. Regulator problem

    Hi, I have a workbench test set up which consists of a compressor, followed by a 6bar supply line, followed by a regulator (for bringing the pressure down to 2bar) followed by a plenum chamber that leads to a slot that vents to atmospheric. The slot is approximately the same area as the supply...
  34. F

    Calculating Compressor and Turbine Work in an Air Standard Gas-Turbine Cycle

    Homework Statement The pressure ratio of an air standard gas-turbine cycle is 8/1 and the inlet conditions to the compressor are 200 KPa and 30C. The turbine is limited to a temperature of 1500K and the compressor and turbine adiabatic efficiencies are 60 and 90 respectively. Calculate...
  35. N

    Mechanical efficiency of a compressor #polytropic compression

    Hy please help me .i am strugling to calculate the mechanical efficiency of a compressor as i am not given power output and power output
  36. R

    Compressor aftercooler power load

    Hi, I want to use a compressor aftercooler and to size it I tried to calculate the heat load needed for lowering the outlet Tª to about 50ºC. I was checking the heat load of compressed air at 7bar 100L/min, the compressor manufacturer says outlet Tª should be about 150ºC. Input electrical...
  37. Chacabucogod

    Refrigerator Cycle Compressor Function

    I understand that you need certain work for the refrigerator to work, and that it comes from the compressor. Why isn't a pump used instead? Why do you have to compress and heat the air so much? Thank you
  38. C

    Understanding and Incorporating Air Compressor and Air Filter Characte

    Very new to these matters, so please bear with me if my basic HVAC understanding is imprecise: To start, I had a system in which airflow through a pipe was A) filtered for contaminants before flowing on to B) a compressor which outputted the flow at an increased discharge pressure. The A)...
  39. G

    Air Compressor Free Air Delivery question

    Hi all, Currently I am undertaking a project and I am a little bit confused about the free air delivery (F.A.D.) of an air compressor because I need to purchase an air flow meter and don't want to buy something completely out of the ball park. From the information sheet, the compressor has...
  40. R

    Thermodynamics Polytropic Process Compressor

    I was revising for my course exam and encountered a question in my book (Applied Thermodynamics for Engineering Technologists, p 66 example 3.3) which stated that a compressor follows a polytropic process to compress air; I understood the calculation process which resulted in heat being...
  41. K

    How does a compressor stall affect the operation of a gas turbine?

    Hi, I went through many resources but I am not able to understand as to what stall/surge means for an axial compressor means. I am not able to imagine or correlate it. I want to physically understand what happens in a compressor when it is stalled. For eg: Can a ceiling fan stall when the angle...
  42. E

    Compressor wanted - produce up to 100 bar/1450 psi @ 40Vdc

    Compressor wanted -- produce up to 100 bar/1450 psi @ 40Vdc I'm searching for a compressor that is compact but is able to produce up to 100 bar/1450 psi. It also should work on max 40V DC. Please say if you know similar compressors! Thanx already :)
  43. marellasunny

    How much should the compressor generate?

    Suppose the 2 passengers in my car generate 1000W of heat and the sunlight falling inside the car generates 1000W of heat, how much heat should my compressor add on the refrigerant to suck away all the 2000W of heat in the car? I realize that a compressor is rated in pressure but I would like...
  44. J

    Relativistic Compressor Paradox

    Relativistic compressor "paradox" Let's say we have a metro tunnel that is a circular loop with 1 m x 1 m rectangular cross section. The tunnel is 100 m long. There's a 50 m long train in the tunnel, the train fits snuggly in the tunnel. And there's air in the tunnel, at 1 atm pressure, and...
  45. gfd43tg

    Multistage Compressor: Power Distribution

    Hello, When using a multistage compressor that is assumed to be isentropic with no interstage temperature increases, is it assumed each stage does the same amount of power?
  46. S

    Thermodynamics Compressor problem

    Homework Statement A chlorinator operates at twice the pressure of the Cl2 recovery stream. To recycle the Cl2, it has to be compressed. Whats the minimium energy consumption of the compressor (per mol of Cl2) if it leaves the recovery stream at 100 Degrees. Assume isentropic and Q = 0 Cp =...
  47. gfd43tg

    Adiabatic Air Compressor: Calculating Shaft Work for Isentropic Process

    Homework Statement A small adiabatic air compressor is used to pump air into a 20-m3 insulated tank. The tank initially contains air at 25°C and 101.33 kPa, exactly the conditions at which air enters the compressor. The pumping process continues until the pressure in the tank reaches 1,000...
  48. F

    Work performed by a compressor

    Homework Statement Nitrogen was compressed from initial pressure of 101 kPa to a higher pressure. The respective enthalpies are: 54 kJ/kg and 350 kJ/kg. The compression process is adiabatic and ideal. The volume flow rate is 0.05 m^3/s. Density of Nitrogen before entering the compressor is...
  49. G

    How can I efficiently compress and utilize flue gas in an off-grid house?

    I've been lurking on these forums for years now; so much of my idea-seeking brings me here, it's remarkable, even to me, that I've never created an account. Here I am now though, so let's jump in shall we? Background: I'm designing an off-grid house for myself. I have most of the details...
  50. P

    How Can I Calculate and Choose the Right Compressor for a Replacement?

    Hello to everyone that reads this, I have to replace an old compressor with a new one. The trick is that i need to calculate the everything about the new one before i put it in. So i can convince everyone that it's a smart choice. The vapor compression cycle will remain the same, will still...
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