Thermocouple assembly

On the other hand, this type of cooling permits the study of increasing or decreasing temperature profiles in the jacket and their influence on the inner temperature profile, reactor performance, and stability. For this type of study a reactor tube is needed that is large enough to accommodate an inner thermowell holding a multiple thermocouple assembly. 

Metal Sheathe thermocouple assembly - Type 12-K-400 T.C. Limited, address as 10... 

The temperature of molten polymer process streams is commonly measured using a thermocouple positioned through a transfer line wall and partially immersed in the polymer stream. Process stream temperature measurements that use an exposed-tip thermocouple, however, can be misleading since the temperature of the thermocouple junction is a balance between the heat transferred from the polymer stream and from the thermocouple assembly [39]. Due to the low heat transfer rate between the polymer and the exposed tip and the high thermal conductivity of the thermocouple sheath, the temperatures measured can be different by up to 35°C depending on conditions. Extrudate temperatures, however, can be accurately measured using a preheated, handheld thermocouple probe. This method minimizes thermal conduction through the probe sheath. 

McCullough, T.W. and Spalding, M.A, Predicting Actual Temperature Distributions in a Polymer Stream Using an Adjustable-Depth, Exposed-Tip Thermocouple Assembly, /. Reinf. Plast Compos., 16, 1622 (1997)... 

Figure 6.9 shows an ordinary thermowell-and-thermocouple assembly. The thermocouple junction consists of two wires of different metals. When this junction of the wires is heated, a small electric current, proportional to the junction temperature, is produced. Different metal wires make up the three most common junctions J, H, and K. It is not uncommon for a thermocouple, regardless of the type of junction, to generate too low a temperature signal. 

For applications in adverse environments such as measurement in high-temperature furnaces, combustion chambers, and nuclear reactor cores, a protection tube is normally used with the thermocouple. Detailed descriptions on the selection of protection tubes and typical industrial high-temperature thermocouple assemblies are given in Ref. 36. 

Figure 6.21. Three-wire thermocouple assembly for high-pressure DTA apparatus 74).

Thermowells in the 1/2-inch size are used where space on the equipment will only allow a 1/2-inch connection to be made for either a thermometer or thermocouple assembly. 

The 3/4-inch thermowell is generally selected where process operating service pressures and temperatures are in the low range. It is used for mounting a thermometer or thermobulb in a thermowell and for thermocouple assemblies. This size is a few dollars cheaper than the next larger one. 

In power compensated DSC the small size of the individual sample and reference holders makes for rapid response. The temperature sensors are platinum (Pt) resistive elements. The individual furnaces are made of Pt/Rh alloy. It is important that the thermal characteristics of the sample and reference assemblies be matched precisely. The maximum operating temperature is limited to about 750 °C. High temperature DSC measurements (750-1600°C) are made by heat flux instruments using thermocouples of Pt and Pt/Rh alloys. The thermocouples often incorporate a plate to support the crucible. The use of precious metal thermocouples is at the expense of a small signal strength. Both chromel/alumel and chromel/constantan are used in heat flux DSC equipment for measurements at temperatures to about 750 °C. Multiple thermocouple assemblies offer the possibility of an increased sensitivity - recently a 20-junction Au/Au-Pd thermocouple assembly has been developed. Thermocouples of W and W/Re are used in DTA equipment for measurements above 1600°C. The operating temperature is the predominant feature which determines the design and the materials used in the con-... 

When a crucible is to be used more than once in a series of measurements it must be replaced each time in precisely the same position. One such example is in the measurement of heat capacity. Thermocouple assemblies are often designed to facilitate the repositioning of the crucible. 

The floating thermocouple assembly contains four thermocouples located 1/4, 1, 3 and 4 inches above the liquid-gas interface and which move with the interface. This arrangement permits a continuous and reliable measurement of gas temperatures in the immediate vicinity of the interface, something which was not possible with the previous system or with the fixed thermocouples because of their inherent heat capacity lag in passing from the liquid to the gas phase. 

This textile heat fluxmeter consists of a network of thermocouples (assembly of two dissimilar conductor or semiconductor), also called a thermopile, assembled into a textile auxiliary wall. Thus, heat and mass transfer properties of textile substrate used as auxiliary wall will be smdied in the first part of this work. Afterward, the principle and the production technology of the conventional heat fluxmeters and the textile heat fluxmeter will be defined. 

The principle of the gradient heat fluxmeter is to observe a heat flux due to the evaluation of the temperature gradient between the two faces of the conducting support, which has known thermal characteristics. This temperature gradient is measured by a thermocouple (assembly of two dissimilar conductors or semiconductors) or rather a number of thermocouples forming a thermopile. 

Thermocouple Size. Many factors can confound the solder-joint temperature measurement process, regardless of whether the thermocouple bead is properly deployed between lead and pad. Among these are the size of the bead and the thermal mass of the thermocouple assembly. In general, the use of finer-gauge thermocouples such as 30 to 36 American Wire Gauge (AWG) (see Table 47.1) is recommended. This will permit insertion between lead and pad even at very fine lead and pad pitches. Ideally the thermocouple bead will be completely within the solder joint to be measured. 

Thermocouples may be joined in series. The series connection, in which the output is the arithmetic sum of the emfs of the individual thermocouples, may be used to obtain greater measurement sensitivity and accuracy. A series-connected thermocouple assembly is generally referred to as a thermopile and is used primarily in measuring small temperature differences. A schematic diagram of a series-connected thermocouple is shown in Fig. M-4. 

Figure 9.9 shows an ordinary thermowell-and-thermocouple assembly. The thermocouple junction consists of two wires of different metals. When this jimction of the wires is heated, a small electric... 

For a thermocouple to read correctly, it should be fully inserted in a thermowell and the thermowell itself should extend several inches into the process liquid. If the process stream is a vapor, which has poorer heat-transfer properties than do liquids, the thermowell, especially if the external insulation is poor, should extend more than 6 in into the process flow. To check the length of the thermowell, unscrew the thermocouple assembly and pull it out, then simply measure the length of the thermocouple. This is also a good opportunity to verify the control-room reading with a portable temperature probe or a glass thermometer inserted in the thermowell. 

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