Some confusing issues encountered in the calculation of safety valves
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I have been working on marine air cylinders recently, with a design pressure of 1.1 MPa and a design temperature of 100°C. During the calculation of the safety valve discharge capacity, according to GB150, the safe discharge volume Ws for pressure vessels is given by the formula 2.83×10-3×ρvd2. I learned from forum posts that the value of ρ needs to be obtained from the \"Handbook of Chemical Property Tables\", but the examples in this handbook refer to absolute pressure; hence I am unsure whether the design pressure refers to absolute pressure or relative pressure. GB150 defines pressure as gauge pressure, unless otherwise specified. ①So gauge pressure = relative pressure? ②The ratio method originally used by the company specified an atmospheric pressure of 0.1 MPa and an air density of 1.293 Kg/m3; using the formula ρ=273*1.293*Pd/(0.1*273), the gas density under the release pressure was calculated to be 11.92 Kg/m3 (where Pd represents the release pressure). However, this calculated value differs significantly from what I found in the \"Handbook of Chemical Property Tables\" – could it be that my information is incorrect, or that the calculation method used is wrong? I’ve attached the images I used; I would be grateful if the experienced seniors could share their insights.
1. Relative pressure is gauge pressure, which equals absolute pressure minus atmospheric pressure. 2. Another parameter of the gas state is temperature. Is the air density of 0.1 MPa that you found corresponding to normal temperature (20°C), or 0°C? In the formula p/ρ=RgT, both p and T must be in absolute values; that is, p represents the absolute pressure, and if the discharge pressure is gauge pressure, the atmospheric pressure of 0.1 MPa must be added to it ； The unit of temperature is K; if it’s not 0°C, add 20. Give it a try and check. 3. The temperatures shown in the figures are in degrees Celsius; pay attention to this when consulting the table.