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Expressing Power Cycle Performance
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
Pressure (p) is the force per unit area exerted on or by a fluid. Pressure, expressed in pounds per square inch (psi), Pascal, or bar, is typically expressed as either absolute pressure, e.g., psi absolute (lbf/in2 abs, or psia), or gauge pressure, e.g., psi gauge (lbf/in2 g or psig). Absolute pressure (psia), which is generally used in steam tables and most fluid and thermodynamic equations, is the true force per unit of area expressed as pounds per square inch exerted by a fluid on the wall of the vessel containing it. Standard atmospheric pressure is 14.696 lbf/in2 abs, or 29.92 in. of mercury atmospheric (in. Hg atm) at sea level, or 406.8 inches of water (in. wg). In SI units, standard atmospheric pressure is 1.013 Bar, 101,325 Pascal (P), or 76.0 centimeters of mercury (cm HgA).Gauge pressure (psig) is the difference between absolute pressure of a fluid and ambient atmospheric pressure. Since atmospheric pressure at sea level is about 14.7 psia (101,325 P), absolute or true pressure is determined, using approximate values, simply by adding 14.7 (101,325) to gauge pressure.Vacuum, or negative gauge pressure, is pressure below atmospheric pressure.
Instruments and Instrument Terminology
Published in Samuel C. Sugarman, Testing and Balancing HVAC Air and Water Systems, 2020
The pressure exerted upon the earth’s surface by the air because of the gravitational attraction of the earth. Standard atmosphere pressure at sea level is 14.7 pounds per square inch (psi). Measured with a barometer.
Water/Wastewater Conveyance
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
As mentioned, many pressure-measuring instruments are called gauges. Generally, pressure gauges are located at key points in piping systems. Usually expressed in pounds per square inch (psi), there is a difference between gauge pressure (psig) and absolute pressure (psia). Simply, “gauge pressure” refers to the pressure level indicated by the gauge. However, even when the gauge reads zero, it is subject to ambient atmospheric pressure (i.e., 14.7 psi at sea level). When a gauge reads 50 psi that is 50 pounds gauge pressure (psig), the true pressure is the 50 pounds shown plus the 14.7 pounds of atmospheric pressure acting on the gauge. The total “actual” pressure is called the absolute pressure: gauge pressure plus atmospheric pressure (50 psi + 14.7 psi = 64.7). It is written 64.7 psia.
Effect of magnetic field on a loosely packed, tightly packed and an over-tightly packed metal powder bed
Published in Particulate Science and Technology, 2021
Kavin Sundarnath J. Ayyanathan, Sarada Kuravi
The pressure drop measurements inside a metal powder bed were made for decelerating compressed airflow, with and without the external magnetic field for the three packed bed samples of iron (III) oxide powder. The setup that was constructed to measure the pressure drop across the packed bed is shown in Figure 1 and the corresponding schematic is shown in Figure 2. A compressed air supply with a peak pressure value of 150 psig is used in the experiment to supply the working fluid. The inlet valve is open to higher flow rate of 29.5 SCFM and measurements are taken from 29 SCFM to 27 SCFM at 0.5 SCFM intervals, as the flow rate goes down. The deceleration was estimated to be 0.001 m/s2 by measuring the time it takes for the flow rate to go down by 1 SCFM. A tape heater was wrapped around a 0.5-inch (12.7 mm) aluminum tube for a length of 18 inches (457.2 mm) to heat the air if the temperature drops much below the room temperature, which is possible as the compressor is located outside the building and supplied through metal piping and valves. All measurements in the experiment were made at the inlet temperature of 21 °C, which is same as the room temperature. After the exit from the heater, the compressed air is then expanded through a PVC elbow into 2-inch PVC piping along which the bed is placed. Here, the temperature drops to 20.5 °C due to expansion. A flow straightener is placed before the packed bed to attain parallel flow in the air stream. The flowrate and velocity are measured separately using RCM industries’ flowmeter (3% accuracy) and Omega’s FMA 1000 series (velocity indicator) respectively. The pressure drop measurements were carried out using two pressure gauges, Omega’s DPG4000 series gauge (0.05% accuracy, P1) at the inlet of the bed and Omega’s DPG7000-300 (0.05% accuracy, P2) at the outlet of the bed. The air is then vented to the atmosphere through a 9.37 mm hole, which creates a back pressure in the system. The pressure gauges used in the experiment are calibrated in pound per square inch (psi), and the flow meter was calibrated in standard cubic feet per minute (SCFM). Hence, the same units were adopted throughout this study, unless a change in unit was required.