Temperature and Pressure Measurement

Huid Saturation temperature Isat [°C] Liquid density Pl [kg/m ] Liquid specific heat rp,L [J/kg K] Vapor density Pg [kg/m ] Latent heat of vaporization h-LG [kJ/kg] Surface tension (TX id [N/m] 

Phase-change cooling systems make do with smaller sizes without necessarily imposing a larger pumping power requirement compared with single-phase systems. 

The saturation thermophysical properties of some liquid coolants are presented in Table 2.5 (Mudawar 2001). 

Poor flow distributions may result in localized dry hotspots which, absent control of the temperature fluctuations, may cause rapid overheating. Temperature and pressure fluctuations, and poor flow distribution, are the main problems that accompany the use of two-phase micro-channels. 

The lower chip contains the micro-channel test section with inlet and exit plenums, eight static pressure tap lines intersecting the micro-channel at equally spaced intervals, and one tap line per plenum. The tap line to the micro-channel 

It is assumed here that the pressure and temperature measuring devices are properly calibrated. They should be traceable to the National Institute of Standards and Testing (for USA). The problem is to measure what one thinks is being measured. Here is a hst of potential problems and their consequences. 

Sample temperature problems can arise from inhomogeneous temperature of Ae sample. 

With respect to this problem, a highly exothermic adsorption can have a significant effect on sample temperature. (Significant in this case means 0.01°C or more.) The solution to this is to be patient in allowing the adsorption to settle down. Advice about this has already been given in both experimental sections. 

Insufficient low-pressure pump-out and degassing can lead to false conclusions. 

For high-energy materials, such as ceramics, a monolayer can already exist on the surface of the sample at 10 atm (10 Torr) which is low vacuum. Although the surface area can be measured for most samples from this point, false conclusions can be drawn if one takes the data too seriously. A pump-out and degas should be performed to at least 10 atm and preferably lower. Most gravimetric systems are capable of this and 10 atm is not unusual. 

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Turbomaehinery operating pressures, temperatures, and speeds are very important parameters. Obtaining aeeurate pressures and temperatures will depend not only on the type and quality of the transdueers seleeted, but also on their loeation in the gas path of the maehine. These faetors should be earefully evaluated. The aeeuraey of pressure and temperature measurements required will depend on the analysis and diagnosties that need to be performed. Table 19-2 presents some eriteria for seleetion of aerothermai instrumentation of pressure and temperature sensors for measurement of eompressor effieieney. Note that the pereentage aeeuraey requirements are more eritieal for temperature sensors than pressure sensors. The requirements are also dependent on the eompressor pressure ratio. 

We attempt here to describe the fundamental equations of fluid mechanics and heat transfer. The main emphasis, however, is on understanding the physical principles and on application of the theory to realistic problems. The state of the art in high-heat flux management schemes, pressure and temperature measurement, pressure drop and heat transfer in single-phase and two-phase micro-channels, design and fabrication of micro-channel heat sinks are discussed. 

Fig. 9.9 Experimental set-up 1 test module, 2 heater, 3 electrical contact, 4 micro-channel, 5 Pyrex, 6 peristaltic pump, 7 and 8 pressure and temperature measurements, 9 cooler, 10 reservoir, 77 IR camera, 72 microscope, 13 high-speed video camera, 14 PC, 75 synchronizer, 16 video recorder. Reprinted from Peles et al. (2001) with permission...

Since we did not measure the conversion during the experiment, we computed the equilibrium vapor pressure at the average solution temperature. We believe that, for safety design, the equilibrium vapor pressure is an adequate estimate of the styrene vapor pressure. For example, even at a 50% conversion, the difference is only 10 at the experimental temperatures. Figures 6, 7 and 8 compared the observed pressures with the computed total pressures. The latter were based on the equilibrium vapor pressure. As expected, there were increasing variations in Tests 1, 2 and 3 respectively because of their higher initial conversions. From these figures we can verify that our pressure and temperature measurements were in phase with respect to time. 

Principal component regression (PCR) is an extension of PCA with the purpose of creating a predictive model of the Y-data using the X or measurement data. For example, if X is composed of temperatures and pressures, Y may be the set of compositions that results from thermodynamic considerations. Piovoso and Kosanovich (1994) used PCR and a priori process knowledge to correlate routine pressure and temperature measurements with laboratory composition measurements to develop a predictive model of the volatile bottoms composition on a vacuum tower. 

These instruments, designed by CSIRO and Milestone, include, in addition to pressure and temperature measurement and control, a number of other features allowing for greater safety and reproducibility of reaction conditions, such as stirring to minimize temperature gradients, rapid cool-down at the end of the heating period and energy shut-down if temperatures or pressures exceed safe levels. 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

The clean, dry, calibrated bulb is attached to a vacuum system, such as site A on the line illustrated in Fig. 5.2, and evacuated to 10-3 torr or lower. Gas may be admitted to the calibrated bulb by isolating the working manifold from vacuum and opening the stopcocks and valves leading to one of the upper gas storage bulbs, C, while the pressure is monitored by manometer D. When the desired pressure is reached, the valve on the storage bulb is turned off, pressure and temperature measurements are made, and then the stopcock on the calibrated bulb is turned off. At this stage we know the pressure, temperature, and volume of the gas in the calibrated bulb, which permits the calculation of the number of moles via the ideal gas equation. 

For industrial applications, determining the stable hydrate structure at a given temperature, pressure, and composition is not a simple task, even for such a simple systems as the ones discussed here. The fact that such basic mixtures of methane, ethane, propane, and water exhibit such complex phase behavior leads us to believe that industrial mixtures of ternary and multicomponent gases with water will exhibit even more complex behavior. Spectroscopic methods are candidates to observe such complex systems because, as discussed earlier, pressure and temperature measurements of the incipient hydrate structure are not enough. 

The accuracy of the pressure and temperature measurements was verified by measuring the vapor pressure curves and critical points for pentane and for toluene. Vapor pressures were measured by observing the formation of a liquid phase as pentane or toluene was injected into the constant-volume view cell under isothermal conditions. The observation of critical opalescence was used to determine the critical point. The measured vapor pressures and critical points are given in Table I. Vapor pressures deviate from... 

Aranovich L. Y. and Newton R. C. (1996) H2O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium. Contrib. Mineral. Petrol. 125, 200-212. 

The DPET s electrodes are in the form of concentric cylindrical plates suspended from the top of the vessel and are connected to a high-voltage transformer such that adjacent plates are given opposite charges. As the oil passes through the electrodes, water droplets are influenced by the field to create a sinusoidal migration between plates of opposite charge. This motion serves two purposes to restrict the upward flow of the water in relation to the oil and to enhance the rate of collision of water droplets, which are distorted to form dipoles under the electric field, and thereby increase the rate of coalescence. Clean oil leaves from the top of the vessel, while water is drained out from the bottom. Instrumentation available on this unit permits pressure and temperature measurement of both the feed and vessel conditions and the treated oil and outlet water flow rates. 

The instrumentation on this unit includes pressure and temperature control of the preheated emulsion pressure and temperature measurement... 

In a similar manner the diluent gas was delivered to a T-connection upstream of the ozonator. The gas flow rate was measured by an orifice manometer, with suitable connections for pressure and temperature measurement. All flowmeters had been previously calibrated according to accepted standard procedures. 

Take pressure and temperature measurements to verify that the steam is 100% saturated during the dwell period. 

Figure 10.3-4 Schematic diagram of a high-pressure vapor-liqud equilibrium cell in which both the vapor and liquid are constantly circulated to ensure that the vapor and liquid phases are in equilibrium. The detachable bombs are used to collect samples for chemical analysis. Items P and T are ports for pressure and temperature measurement, respectively.

Having estimated the optimum primary drying parameters, a pilot study should be performed. It is not good practice to carry out such a study either in an incompletely filled drier or by filling up shelves partly with empty vials. The reliability of pressure and temperature measurements should be checked at this stage. It has sometimes been found that the (apparent) product temperature exceeds the shelf temperature. Since this is an obvious physical impossibility, such an anomaly is due to faulty calibration of the thermocouple probe. 

I Which of the above graphs best represents the relationship between the pressure and temperature (measured in kelvins) of one mole of an ideal gas ... 

Steam injection continued for a period of two years using wells 257 and 258. At first, injection well 256 was also used, but later it had to be excluded for technical reasons. The continuous steam flooding was carried out under the following regime volume of steam injected ranged from 120 to 170 t/day injection pressure and temperature, measured at the wellhead, were 28-30 kg/cm2 and 22J0-225°C. 

In addition to pressure and temperature measurements, duplicates of some pumps and control valves are installed in parallel. This allows the equipment to be bypassed and serviced during operation of the plant, which avoids the costly necessity to shut down the process. The choice of installing spares depends on many factors but it is generally recommended for major feed and product streams and for lines that are considered critical for safe operation of the plant. 

Reproducible processes in continuously operated reactors depend on, in addition to pressure and temperature measurements, precise control of the mass throughput of chemicals. To meet these demands, metering devices in modern microreaction... 

Connections should be available for pressure and temperature measurement. 

BAUMANN,H. Pressure and temperature measurements by vapour deposited thin layer transducers in an EHD line contact (in German), Ph.D. Thesis, Karlsruhe University, Germany, 1985... 

The combustion chamber should be provided with sight glasses, connections for pressure and temperature measurements, and other instruments as appropriate. 

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