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Mechanical principles of fluid and thermodynamic systems
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Barometers are used for measuring atmospheric pressure and are affected by changes in temperature and as such as used within weather forecasting. Consider Figure 3.5 which depicts a simple mercury barometer. It consists of a dish containing a reservoir of mercury and a graduated glass tube that is about 1 m in height. During manufacture, the glass tube is filled with mercury before being turned over within the reservoir to prevent air entering the tube. The level of mercury within the tube will drop until the atmospheric pressure acting upon the mercury in the reservoir is able to support the weight of the mercury within the tube. The subsequent height of the mercury column is equal to the atmospheric pressure and the void at the top of the tube becomes a vacuum. As atmospheric pressure increases it pushes down on the reservoir of mercury forcing it up the tube and hence the new height indicates an increase in pressure.
Fundamentals
Published in Mike Tooley, Lloyd Dingle, Engineering Science, 2020
The two most common types of barometer used to measure atmospheric pressure are the mercury and aneroid types. The simplest type of mercury barometer is illustrated in Figure 12.3. It consists of a mercury-filled tube, which is inverted and immersed in a reservoir of mercury.
Pressure in fluids
Published in John Bird, Science and Mathematics for Engineering, 2019
A barometer is an instrument for measuring atmospheric pressure. It is affected by seasonal changes of temperature. Barometers are therefore also used for the measurement of altitude and also as one of the aids in weather forecasting. The value of atmospheric pressure will thus vary with climatic conditions, although not usually by more than about 10% of standard atmospheric pressure.
Pool boiling heat transfer of water and nanofluid outside the surface with higher roughness and different wettability
Published in Nanoscale and Microscale Thermophysical Engineering, 2018
Wen-Tao Ji, Peng-Fei Zhao, Chuang-Yao Zhao, Jing Ding, Wen-Quan Tao
In the experiment, electric heater heats the copper block through the bottom by adjusting the voltage regulator. Then the fluid such as deionized water or nanofluid boils and converts to vapor at the atmospheric pressure. The vapor condenses in the condensing unit and the condensate flows back to the boiling pool. The condensing apparatus is cooled by air and made by finned tube. It is connected with the external atmospheric environment. In order to accurately calculate the temperature and the heat flux on the heating surface, 12 T-type copper constantan thermocouples with the precision of ± 0.2K are inserted into the very small holes along the sample copper block (Figure 2). The diameters of the holes are 3 mm and the depths are 25mm. The diameters of thermocouple wires are 0.2 mm. Using a copper rod with diameter of 2.8 mm, the thermocouple wires are pushed and firmly attached to the upper surfaces of the small holes. The thermocouple wires should be kept straight forward when entering the small holes. The position should be accurately fixed and winding is not allowed in the mounting process. The distance between the two neighboring thermocouples is finally measured with micrometer. Three platinum resistances temperature transducers (PT100), which have a precision of ± (0.15 + 0.002|t|) K in the whole test range, are installed in the boiling pool to measure the temperature of the boiling liquid. The atmospheric pressure is measured with a mercury barometer. A Keithley digital voltmeter (Keithley 2700) with resolution of ± 0.1 μV is used to measure the electric potential of thermocouples and resistances of PT100.