Why is the volume ratio of liquid to air for saturated vapor pressure as 1:4 according to Reid?
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Why is the volume ratio of liquid to air for saturated steam pressure as 1:4 according to Reid? Can’t it be 1:3 or 3:1? Another question is: when using this method, is the absolute pressure inside the enclosed space equal to the original air pressure (that is, atmospheric pressure) plus the saturated vapor pressure of the liquid at that temperature?
I wonder if the pressure values measured at different volume ratios of various liquids to air will vary I think as long as the liquid isn’t too little, or the space containing air isn’t particularly large, at a constant temperature, the values measured at any volume ratio will be the same. Because the total pressure in a space = air pressure + saturated vapor pressure, and it has nothing to do with ratios!!
Your understanding is correct; the specified volume ratio between the gas chamber and the liquid chamber is intended solely to reduce measurement errors. During operation, the liquid chamber and the liquid added to it need to be at a temperature of 0–1°C, while the air in the air chamber is at 37.8°C. It is difficult to ensure that the temperature remains constant in each operation, especially since the temperature of the air chamber may vary. When the temperature rises, the pressure generated by the air also varies, and if the volumes are different, this variation becomes even more uncontrollable. If the volume ratio is fixed, one influencing factor is eliminated.