A flow meter with temperature and pressure compensation – does the flow rate decrease as temperature rises?
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A flow meter with temperature and pressure compensation – does the flow rate decrease as temperature rises? What exactly is the relationship between these two? Please give me some guidance, senior. Keep it simple – no need for too much jargon.
Answer: Gas pressure is proportional to gas density. Gas temperature is inversely proportional to gas density. Gas density is proportional to gas flow rate. Therefore, an increase in temperature means that the gas density decreases, which in turn means that the flow rate decreases.
"An increase in temperature alone means that the gas density decreases, which in turn means that the flow rate decreases. " Is there something wrong with this sentence? The volumetric flow rate must have increased.
The so-called temperature and pressure compensation is used to calculate density when converting volumetric flow rate to mass flow rate. So as the temperature rises, the flow rate remains the same. Of course, if you mean that the temperature measurement is too high, that will result in the measured mass flow rate being lower than the actual value.
The premise of the original poster’s question is thermal and pressure compensation. The essence of temperature and pressure compensation is to adjust the fluid density, that is, to convert the real-time density into the density under standard operating conditions – only in this way can there be a unified standard for measuring flow rates. When the gas temperature rises while the pressure remains constant, the number of molecules per unit volume decreases, and the mass decreases as well. In this way, when the flow conditions remain unchanged, since the volume flow rate per unit time stays constant, the mass flow rate per standard condition volume flow rate decreases
The poster needs to confirm two issues first: 1. When the temperature rises and the flow rate decreases, is it the volume or the mass that is being measured? Are the measurement values still accurate? 2. What type of flow meter is being used?
Just an increase in temperature will cause the gas density to decrease; with other pressures and flow rates remaining constant, the flow rate under actual operating conditions will not change, but the flow rate under standard conditions will be lower. Flow meters with temperature and pressure compensation display the value corresponding to the flow rate under standard conditions.
Flow rate can be expressed in three forms based on flow formulas or measurement units: Volumetric flow rate: It is expressed as volume/time or capacity/time. For example: m3/h, l/h. Volumetric flow rate (Q) = average flow velocity (v) × cross-sectional area of the pipe. Mass flow rate: expressed in mass per unit time. For example: kg/h. Mass flow rate (M) = density of the medium (ρ) × volume flow rate (Q) = density of the medium (ρ) × average flow velocity (v) × cross-sectional area of the pipe. Weight flow rate: expressed in force per unit time. Such as kgf/h. Weight flow rate (G) = specific weight of the medium (γ) × volume flow rate (Q) = density of the medium (ρ) × acceleration due to gravity (g) × volume flow rate (Q) = acceleration due to gravity (g) × mass flow rate (M). There are two ways to express the flow rate depending on the state of the medium: Actual flow rate: refers to the flow rate under the current conditions of the medium ； Standard flow rate: refers to the flow rate of a medium under specified conditions. For example, for a certain gas with the same mass flow rate, its volumetric flow rate is 1 m3/h when it is under compressed conditions; whereas at standard conditions (1 atmosphere and 20°C), its volumetric flow rate may be 10 m3/h. Temperature and pressure compensation for flow rate: As can be seen from the flow rate formula, to determine the mass flow rate or weight flow rate, it is necessary to know the density (ρ) of the medium ； For volumetric flow rate, it is necessary to convert between the actual flow rate and the standard flow rate; likewise, it is important to know the density (ρ) of the medium under different conditions. In terms of practical application, most flowmeters are calibrated using standard flow rates. Most flow meters, except for specialized mass flow meters, operate on the principle of measuring flow velocity. In the expression of flow rate, the medium density (ρ) is artificially specified based on the actual operating conditions of the medium. When the actual operating conditions change and deviate from those designed, the measurement results of the flow meter will be inaccurate. In most cases, the density of the medium decreases as the temperature rises; this means that, at the same flow rate or actual volumetric flow rate, an increase in temperature results in a decrease in volume, mass, and weight
Density increases, volumetric flow rate decreases, and mass flow rate increases. As the temperature rises, the volumetric flow rate increases while the mass flow rate decreases. The purpose of compensation is to convert the actual flow rate into a standard flow rate. Of course, this is related to the requirements of the consulting calculation document for flowmeters.
That’s correct; when the operating conditions remain unchanged and the temperature rises, the flow rate decreases, and this has nothing to do with whether temperature and pressure compensation is applied or not.