Math Problem Statement

  1. From a test of an air compressor driven directly by a steam engine, the following data and results were obtained: capacity, 800 cfm; suction at 14.7 psia; discharge at 110 psia; indicated work of the compressor, 155 hp; indicated work of the steam engine, 172 hp. Calculate (a) the compression efficiency and (b) the overall efficiency. Answers: (a) 90.06%; (b) 81.16%

Solution

To calculate the compression efficiency and the overall efficiency, let’s break down the problem step by step:


Given Data:

  1. Compressor capacity: 800cfm800 \, \text{cfm}
  2. Suction pressure: 14.7psia14.7 \, \text{psia}
  3. Discharge pressure: 110psia110 \, \text{psia}
  4. Indicated work of compressor: 155hp155 \, \text{hp}
  5. Indicated work of steam engine: 172hp172 \, \text{hp}

(a) Compression Efficiency

The compression efficiency (ηc\eta_c) is defined as:

ηc=Indicated Work of CompressorIndicated Work of Steam Engine×100%\eta_c = \frac{\text{Indicated Work of Compressor}}{\text{Indicated Work of Steam Engine}} \times 100\%

Substitute the given values:

ηc=155hp172hp×100\eta_c = \frac{155 \, \text{hp}}{172 \, \text{hp}} \times 100

ηc=90.06%\eta_c = 90.06\%


(b) Overall Efficiency

The overall efficiency (ηo\eta_o) is defined as:

ηo=Indicated Work of CompressorIndicated Work of Steam Engine×Compression Efficiency×100%\eta_o = \frac{\text{Indicated Work of Compressor}}{\text{Indicated Work of Steam Engine}} \times \text{Compression Efficiency} \times 100\%

Substitute the values:

ηo=155172×0.9006×100\eta_o = \frac{155}{172} \times 0.9006 \times 100

Perform the calculation:

ηo=81.16%\eta_o = 81.16\%


Final Answers:

  1. Compression Efficiency (ηc\eta_c): 90.06%90.06\%
  2. Overall Efficiency (ηo\eta_o): 81.16%81.16\%

Would you like to discuss further details or need assistance with related concepts?

Here are 5 follow-up questions to deepen your understanding:

  1. How is indicated power measured in steam engines and compressors?
  2. What factors can affect the compression efficiency of a compressor?
  3. What is the difference between indicated power and brake power?
  4. How does the suction and discharge pressure impact compressor efficiency?
  5. How can the overall efficiency of a system like this be improved?

Tip: To ensure accurate calculations, always double-check unit conversions and verify the consistency of data provided.

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Math Problem Analysis

Mathematical Concepts

Efficiency Calculations
Ratios and Percentages

Formulas

Compression Efficiency (η_c) = (Indicated Work of Compressor / Indicated Work of Steam Engine) × 100%
Overall Efficiency (η_o) = (Compression Efficiency × 100%)

Theorems

Basic Efficiency Definition

Suitable Grade Level

Grades 10-12