Thermocouples pressure measurement

AU the modern scientific microwave units have the capabiUty to measure temperature during the course of a reaction. This can be done remotely using an infrared sensor located in the waU or the bottom of the microwave cavity. In many cases it is also possible to record the temperature inside a reaction vessel using a fiber-optic probe or thermocouple. Pressure measurement is also possible in many cases. The contents of a reaction mixture can be stirred by means of a magnetic stir plate located beneath the microwave cavity and a Teflon stir bar in the vessel. 

Fig. 4.61 illustrates that the mould temperature is quite different from the set oven temperature (330°C) or indeed the actual oven temperature, throughout the moulding cycle. An even more important observation is that in order to control the rotational moulding process it is desirable to monitor the temperature of the air inside the mould. This is possible because there is normally a vent tube through the mould wall in order to ensure equal pressures inside and outside the mould. This vent tube provides an easy access for a thermocouple to measure the internal air temperature. 

In addition to absolute pressure measurements, pressure sensors can be used to determine flow rates when combined with a well-defined pressure drop over a microfluidic channel. Integration of optical waveguide structures provides opportunities for monitoring of segmented gas-liquid or liquid-liquid flows in multichannel microreactors for multiphase reactions, including channels inside the device not accessible by conventional microscopy imaging (Fig. 2c) (de Mas et al. 2005). Temperature sensors are readily incorporated in the form of thin film resistors or simply by attaching thin thermocouples (Losey et al. 2001). 

The Jerguson gage is immersed in a constant temperature bath with silicon fluid as the heat-transfer medium, that also thermostats the density meter. The bath temperature is controlled to . 01 K with a Thermomix 1460 temperature regulator and temperature is measured with a calibrated mercury-in-glass thermometer to within. 01 K. The lines external to the bath are maintained at the bath temperature with the help of heating tapes and temperature at several points is monitored with thermocouples. Pressure is measured with two calibrated Heise pressure indicators to within .16 bar for pressures up to 160 bar and to within .4 bar for pressures up to 350 bar. 

The typical rate curve shown in Figure 3 was observed for nitrogen adsorbed on the diamond dust at 90.1° K. The points in circles are based on McLeod gage readings and the balance of the curve was recorded from the thermocouple gage data. A steady-state surface coverage (0) of 0.055 (10.1-micron pressure) was realized after only about 200 minutes. All pressure measurements have been corrected for thermomolecular diffusion. 

For our system we chose the simplest approach — a fast sample conduit with quick quench into an evacuated sample container. For temperature measurements we used a similar probe outfitted with platinum/6% rhodium-platinum/30% rhodium thermocouple. For pressure measurements the same general type probe mentioned was employed but without extracting samples. This probe had one hole opening perpendicular to the longitudinal axis of the probe such that when inserted into the reactor it could be rotated 360°. In this manner the pressures were read from a precision pressure gauge with the opening facing 0°, 90°, 180°, and 270° relative to the direction of flow in the reactor. 

The thermocouple pressure gauge is a bimetallic pressure gauge (range 10 mbar to 10 3 mbar), invented by Voege in 1906115 it measures the temperature between the "hot" junction and a reference cold junction, as affected by collisions of gas molecules and concomitant heat loss from the wire. 

The high-pressure inlet is attached to a f in. cross to provide ports for gas introduction, pressure measurement, and thermocouple placement just in front of the frit. The Bourdon gauge (0-10 bar) should be connected via a tee to a purge valve to facilitate gas changes. Before use the assembly should be tested at 10 bar for leaks. Thermal insulation such as glass wool should be wrapped around the frit assembly to keep the expansion as adiabatic as possible. 

For wall temperature measurements 10 thermocouples are fixed on the heated part of the tube. Entrance and exit manifolds have pressure taps and thermocouples to measure the fluid pressure and temperature. A differential pressure sensor is also placed between the test section inlet and outlet. Heating the test section is performed by means of a low voltage U (0 - 2 V), high intensity 7(100-1800 A) power supply. 

Figure 4(a) shows details of the test chamber. The teflon jacket-copper block assembly was mounted on a stainless steel plate. The sprayed liquid was drained back to the reservoir installed below the test section. Thermocouples to measure the liquid temperature were installed both upstream of the flow meters and downslream of Ihe orifiee plate. Another thermocouple was used to measure the ambient temperature. The HAGO nozzle and the orifiee plate (for microjets) were attached to the end of a pipe whieh eould be moved up and down. Thus the distance between the sprays or jets and the heated surfaee eould be varied. The liquid pressure was measured using a pressure transducer (0 - 2.07 MPa, 0.25% aeeuraey) just before the sprays or jets were formed. All the data were recorded using two lOTech 16-bit data aequisition boards. 

Incidentally, the thermal sensitivity of the thermocouple to measure the r /, or the temperature of the chemical, increases naturally with decreasing the wall thickness of the glass capillary tube of the glass capillary flange in the meantime, the pressure resistance of the tube decreases naturally with decreasing the wall thickness. Therefore, it is required to achieve a proper balance between the thermal sensitivity of the thermocouple and the pressure resistance of the tube. The glass capillary tube, which has a very small radius of curvature, is, however, able to bear far higher external pressures than may be expected. 

Process dead time refers to the delay in time before the process starts responding to a disturbance in an input variable. It is sometimes referred to as transportation lag or time delay . Dead time or delays can also be encountered in measurement sensors such as thermocouples, pressure transducers, and in transmission of information from one point to another. In these cases, it is referred to as measurement lag. 

The decomposition temperatures of hydrates were measured by means of differential thermal analysis (DTA) under the conditions of excess gas in a stainless steel flask that was developed specially for the investigation of hydrate formation with a gaseous guest at high hydrostatic pressure. The hydrate decomposition temperature was measured with a chromel-alumel thermocouple to the accuracy of 0.3 K. The thermocouple was calibrated with the use of temperature standards. Pressure was measured with a Bourdon-tube pressure gauge. The error of the pressure measurements did not exceed 0.5 %. This procedure was described in more detail previously.The gases used in the investigation... 

The power supply to the electrolyser was a Model 710 from The Electrosynthesis Company, Inc. of Lancaster NY. It was operated in constant current mode rather than in constant voltage mode. The maximum current and maximum voltage available was 50 amperes and 20 volts, respectively. In addition to current measurement provided by the power supply, a calibrated shunt was connected to the output to allow for independent measurement of current. Voltage taps independently connected to the cell electrodes were connected to the data acquisition system (DAS). The instrument signals from thermocouples, pressure gages, and flowmeters were connected to the DAS, which was comprised of a Dell computer with special acquisition boards and Labview software. Observations and some data were manually recorded in a laboratory notebook. 

Catalytic combustion of SO2, toluene and 1,2-dichloroethane were conducted at atmospheric pressure in a tubular flow reactor with an inner diameter of 18 mm. Catalyst extrudates or monoliths were packed into the reactor with glass wool plugs at each end. The reactor was placed in a furnace equipped with a temperature control to maintain a constant reactor temperature, and two thermocouples to measure the inlet and outlet reactor temperatures. Gas compositions and flow rates were set by mass flow controllers. The following reaction conditions were used to test the cataljTic activity of the 0.2 wt. % Pt supported samples ... 

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