Suggested Response - Q4

*/** A Bourdon pressure gauge indicates a gauge pressure of 150 kN/m2. What would be the absolute pressure, if the atmospheric pressure is 740 mm Hg? You may assume the density of mercury is 13,600 kg/m3.

Response:

Let us remind ourselves of the relationship between gauge, atmospheric and absolute pressures:

P subscript A b s o l u t e end subscript space equals space P subscript G a u g e space end subscript space plus space P space subscript A t m o s p h e r i c end subscript

So, in order to sum the gauge pressure, given by the Bourdon gauge and atmospheric pressure, we first need to convert the atmospheric pressure from mm Hg to kN/m2. We do this by considering the 740 mm Hg as a head and converting it as follows:

P subscript A t m end subscript space equals space rho g Z space equals space 13 comma 600 space cross times space 9.81 space cross times space 0.740

P subscript A t m space end subscript equals space 98.73 space k N divided by m squared

Therefore, we can calculate the absolute pressure equivalent to a gauge pressure of 150 kN/m2:

P subscript A b s o l u t e space end subscript equals space 150 space plus space 98.73 space equals space 248.73 space k N divided by m squared

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