1. A gas detector is used to determine concentration of a flammablé gas ll Normally the gas concentration is 1% by volume which is below the alarm limit of 4% and the lower flammability limit of 5%. If the gas concentration is above the lower flammability limit it is flammable. The dynamic behavior of a particular gas detector can be expressed as a first-order transfer function (in deviation variables) that relates the measured concentration Ym to the actual concentration Y' Ym (s) Y'(s) 1 5s +1 where Ym and Y' are in volume percent and the time constant is in units of seconds. At a particular time the gas stream is flowing at a rate of q = 1.0 m³/s through a duct with a cross- sectional area of 1 m². a) If the flammable gas concentration suddenly increases from 1% to 7% by volume, how many cubic meters of the gas stream with the flammable gas component pass through the detector before the alarm is sounded? b) Is it possible for a plug of flammable gas to pass the detector without the alarm ever being sounded? Explain.

Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
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1. **Gas Detector Dynamics**

A gas detector is used to determine the concentration of a flammable gas in a gas stream. Normally, the gas concentration is 1% by volume, which is below the alarm limit of 4% and the lower flammability limit of 5%. If the gas concentration is above the lower flammability limit, it is flammable. The dynamic behavior of a particular gas detector can be expressed as a first-order transfer function (in deviation variables) that relates the measured concentration \( Y'_m \) to the actual concentration \( Y' \).

\[
\frac{Y'_m(s)}{Y'(s)} = \frac{1}{5s + 1}
\]

where \( Y'_m \) and \( Y' \) are in volume percent, and the time constant is in units of seconds. At a particular time, the gas stream is flowing at a rate of \( q = 1.0 \, \text{m}^3/\text{s} \) through a duct with a cross-sectional area of \( 1 \, \text{m}^2 \).

a) If the flammable gas concentration suddenly increases from 1% to 7% by volume, how many cubic meters of the gas stream with the flammable gas component pass through the detector before the alarm is sounded?

b) Is it possible for a plug of flammable gas to pass the detector without the alarm ever being sounded? Explain.

**Explanation of Transfer Function:**

The transfer function provided relates the change in measured concentration to the change in actual concentration over time. It is a first-order system with a time constant of 5 seconds, indicating how quickly the detector responds to changes in gas concentration. This behavior impacts how quickly the alarm system can respond when the concentration exceeds safety thresholds.
Transcribed Image Text:1. **Gas Detector Dynamics** A gas detector is used to determine the concentration of a flammable gas in a gas stream. Normally, the gas concentration is 1% by volume, which is below the alarm limit of 4% and the lower flammability limit of 5%. If the gas concentration is above the lower flammability limit, it is flammable. The dynamic behavior of a particular gas detector can be expressed as a first-order transfer function (in deviation variables) that relates the measured concentration \( Y'_m \) to the actual concentration \( Y' \). \[ \frac{Y'_m(s)}{Y'(s)} = \frac{1}{5s + 1} \] where \( Y'_m \) and \( Y' \) are in volume percent, and the time constant is in units of seconds. At a particular time, the gas stream is flowing at a rate of \( q = 1.0 \, \text{m}^3/\text{s} \) through a duct with a cross-sectional area of \( 1 \, \text{m}^2 \). a) If the flammable gas concentration suddenly increases from 1% to 7% by volume, how many cubic meters of the gas stream with the flammable gas component pass through the detector before the alarm is sounded? b) Is it possible for a plug of flammable gas to pass the detector without the alarm ever being sounded? Explain. **Explanation of Transfer Function:** The transfer function provided relates the change in measured concentration to the change in actual concentration over time. It is a first-order system with a time constant of 5 seconds, indicating how quickly the detector responds to changes in gas concentration. This behavior impacts how quickly the alarm system can respond when the concentration exceeds safety thresholds.
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