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Module 2: Characteristics of Gases - Dry Basis Conversions - Answers
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#1
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When a gas concentration is corrected to a dry basis, does its concentration increase or decrease?
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Answer: Increase
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As you can see from the equation below, any positive value for moisture concentration makes the denominator a fraction, which results in the dry concentration being greater than the wet one.
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Figure 1 also illustrates this fact with an example.
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#2
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When a gas flow rate is corrected to a dry basis, does its value increase or decrease?
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Answer: Decrease
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It is important to remember that when a gas flow rate value is converted to a dry basis it decreases. This is the opposite of the change that occurs when a concentration value is converted to a dry basis. The reason for this difference is simple. In the case of the gas flow rate, the conversion of the value to a dry basis simply involves the subtraction of the moisture content (moisture volume %) from the total as the equation below shows.
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Therefore, the dry basis value is smaller. In the case of the concentration data, it is important to remember that it is a ratio as indicated below.
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When the total volume is reduced by subtracting the water volume %, the denominator becomes smaller. Therefore, the concentration increases when it is converted to a dry basis.
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