Unit Operations of Chemical Engineering
Unit Operations of Chemical Engineering
7th Edition
ISBN: 9780072848236
Author: Warren McCabe, Julian C. Smith, Peter Harriott
Publisher: McGraw-Hill Companies, The
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Chapter 8, Problem 8.12P

(a)

Interpretation Introduction

Interpretation:

The work done per mole of a gas for a single stage adiabatic compressor is to be determined.

Concept Introduction:

A compressor is a device that increases the pressure of a gas by decreasing its volume. A stage in a compressor is the number of times the gas is compressed. The number of stages in a compressor is given by the compression ratio,

Compression ratio = PbPa = (PbPa)1n

  Pa = Inlet Pressure of the gas

  Pb = Outlet Pressure of the gas

For number of stages the value of (PbPa)1n should be nearly constant.

n is the number of stages.

Work done by the gas for a compressor is given as,

  W=P m ˙ ..... (1)

  P = Power of the gas in Btu/min

  m ˙ = Mass flow rate of the gas in lb mol/min

The brake horsepower is given as,

  PB=1.304×10-4Taq0ηγγ-1[(PbPa)1-1γ-1].......(2)

Ta= Inlet temperature in °R

  q0 = Volume of compressed gas in std ft3/min

PB = Brake horsepower

  γ = Heat capacity ratio

  η = Stage efficiency

Heat capacity ratio is calculated as,

  γ=CpCp-R ..... (3)

Cp = Specific heat of gas

R = Universal gas constant = 1.99 cal/mol.°C

(b)

Interpretation Introduction

Interpretation:

The work done per mole of a gas for a 2 stage adiabatic compressor is to be determined.

Concept Introduction:

A compressor is a device that increases the pressure of a gas by decreasing its volume. A stage in a compressor is the number of times the gas is compressed. The number of stages in a compressor is given by the compression ratio,

Compression ratio = PbPa = (PbPa)1n

  Pa = Inlet Pressure of the gas

  Pb = Outlet Pressure of the gas

For number of stages the value of (PbPa)1n should be nearly constant.

n is the number of stages.

Work done by the gas for a compressor is given as,

  W=P m ˙ ..... (1)

  P = Power of the gas in Btu/min

  m ˙ = Mass flow rate of the gas in lb mol/min

The brake horsepower is given as,

  PB=1.304×10-4Taq0ηγγ-1[(PbPa)1-1γ-1].......(2)

Ta= Inlet temperature in °R

  q0 = Volume of compressed gas in std ft3/min

PB = Brake horsepower

  γ = Heat capacity ratio

  η = Stage efficiency

Heat capacity ratio is calculated as,

  γ=CpCp-R ..... (3)

Cp = Specific heat of gas

R = Universal gas constant = 1.99 cal/mol.°C

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Unit Operations of Chemical Engineering
Chemical Engineering
ISBN:9780072848236
Author:Warren McCabe, Julian C. Smith, Peter Harriott
Publisher:McGraw-Hill Companies, The