Thermometer calorimetric

The calorimetric thermometer measures temperature changes within the calorimeter bucket. It must be able to provide excellent resolution and repeatability. High single-point accuracy is not required since it is the change in temperature that is important in fuel calorimetry. Mercurial thermometers, platinum resistance thermometers, quartz oscillators, and thermistor systems have all been successfully used as calorimelric thermometers. 

Figure 1. Schematic diagrams of sections through adiabatic-type calorimeters. A Adiabatic shield calorimeter. B Semiadiabatic calorimeter, a, calorimetric vessel b, air or vacuum c, thermostatted bath d, thermometer e, stirrer f, calibration heater g, adiabatic shield.

Special thermometers are made for calorimetric and cryoscopic work, where it is desired to measure very accurately (to 0.01 or even 0.001 K) a temperatiue difference of the order of a few kelvin. For these thermometers the fineness of scale graduation has little to do with the accuracy with which the thermometer measures a single temperature. The scale may be in error by several tenths of a kelvin, but this error cancels out in taking differences. A typical thermometer for bomb caloiimetiy has a range of 19 to 35°C, with graduations of 0.02°C. For measuring freezing-point depressions with water or cyclohexane... 

The results are in very good agreement. For r/ohexane all four sets of investigators obtained a result within 0 2 kcal mole i of the mean, or within 0 02 per cent, which amply confirms the claimed accuracy of 0 02 per cent. It is noteworthy, too, that while investigators a, c, and d used approximately the same calorimetric technic ue, b used one which differed in important respects. The Amsterdam workers, b, used a Beckmann thermometer to measure the temperature rise and m.easured the amount of combustion by... 

The calorimetric method used for gases ( 2.VII E) was adapted by Regnault for liquids by replacing the heating spiral by a metal cylinder provided with a thermometer above and a delivery tube and tap below, the tube passing to the calorimetric reservoir. 

Differential scanning calorimetry (DSC) is a calorimetric method that finds widespread use in many fields, including protein dynamics, polymers, pharmaceuticals, and inorganic materials. DSC measures energy (heat) flow into a sample and a reference substance as a function of controlled increase or decrease of temperature. In a typical power-compensated DSC (Fig. 3.2), the sample and reference are placed on metal pans in identical furnaces each containing a platinum resistance thermometer (thermocouple) and heater. During a thermal transition (e.g., when a physical change in the sample occurs),... 

Figure 4.1. Main parts of the calorimeter. A — calorimetric vessel, B — calorimetric cover, C — thermometer,...

Presently, resistance thermometers are the most suitable temperature meters because of their high precision and stability. Mainly, they are used when resistance elements are wound directly on the surface of the calorimetric vessel and cover. Change of resistance with temperature can be in the current range of the temperature change of the calorimeter (less than 3 K) regarded as linear. 

For the drop technique, the isoperibolic calorimeters are most frequently used. The calorimetric device consists of two main parts a furnace and a heated block. Between the calorimetric block and the furnace, there is a system of shields controlled by a mechanic, hydraulic or electromagnetic device, which prevents the heat transfer from the furnace to the calorimetric block. The calorimeter is made of copper with a cavity closed by a shield. A resistance thermometer wound on the block measures its temperature. Such a calorimeter can work up to 1700°C, especially when the furnace... 

The measurement of very small absorption coefficients (down to lO-5 cm-1) of optical materials has been carried out by laser calorimetry. In this method, the temperature difference between a sample illuminated with a laser beam and a reference sample is measured and converted into an absorption coefficient at the laser energy by calibration [13]. Photoacoustic spectroscopy, where the thermal elastic waves generated in a gas-filled cell by the radiation absorbed by the sample are detected by a microphone, has also been performed at LHeT [34]. Photoacoustic detection using a laser source allows the detection of very small absorption coefficients [14]. Photoacoustic spectroscopy is also used at smaller absorption sensitivity with commercial FTSs for the study of powdered or opaque samples. Calorimetric absorption spectroscopy (CAS) has also been used at LHeT and at mK temperatures in measurement using a tunable monochromatic source. In this method, the temperature rise of the sample due to the non-radiative relaxation of the excited state after photon absorption by a specific transition is measured by a thermometer in good thermal contact with the sample [34,36]. 

Rate of Heat Transport. When heat is supplied or withdrawn from a calorimeter, temperature differences will occur throughout all parts of the calorimetric system, including the wall, the sample, and even the thermometer. These differences constitute a source of errors, the magnitude of which depend on the rate of heating, the sizes of the system components, and the heat conductivities of the construction materials. The magnitude of these errors has been calculated by Smit (31). 

Temperature is undeniably the most important property for all calorimetric measurements, because it is the common denominator. Two different techniques for temperature measurements are used for pulse calorimetry contact thermometry (e.g. thermocouples) and radiation thermometry or pyrometry. Because pulse calorimetry is often used to handle and measure liquid materials, non-contact radiation thermometry is far more common in pulse-heating than contact thermometry. Other reasons for non-contact temperature measurement methods include the fast heating rates and temperature gradients (inertia of the thermocouples), difficulties mounting the contact thermometers (good thermal contact needed), and stray pick-up in the thermocouple signal because the sample is electrically self-heated. 

With aU these corrections discussed, it may be useful to practice an actual loss calculation, using the data in Table 4.2 (answer AT = 1.3710 K). If the temperature is measured with a calorimetric mercury-in-glass thermometer, an emergent stem correction becomes necessary if the thermometer extended out of the bath liquid. This emergent stem correction can be made as the last correction for the calculated AT, using the equation derived in Fig. 4.4. 

The adiabatic calorimeter assembly shown in Figure 3.11 consists of a calorimetric bomb (Figure 3.12), a calorimetric vessel filled with water, a stirrer, and a thermometer. 

During testing, the calorimetric bomb is immersed into the inner calorimetric vessel equipped with a stirrer and a thermometer. The vessel is filled with water to the precisely defined level, and it is placed in the water-jacketed cylindrical outer calorimetric vessel, which ensures the maintenance of a constant temperature inside the inner vessel. 

The sample may be freely poured into the sample vessel or pressed in the form of a pastille using a special hand-operated press. The wire for the electric ignition is inserted through the middle of the sample. To ensure successful ignition, the middle part of the wire is coiled. Finally, the bomb is closed with the screw cap, and the air is evacuated by the vacuum pump until a vacuum of only a few millibars is attained. The calorimetric bomb is now placed into the inner calorimetric vessel. The electric conductors for the sample ignition are connected with the connectors on the cap of the bomb. A previously measured volume of water at operating temperature is poured into the inner calorimetric vessel. The cover of the calorimetric vessel is then closed, followed by the ignition via the electric switch. The temperature increase in the inner calorimetric vessel is followed by the Beckman thermometer. 

Salicylic acid, C7H6O3, has been suggested as a calorimetric standard. Its heat of combustion is -3.023 X 10 kJ/molC7H603. From the following data determine the heat capacity of a bomb calorimeter assembly (that is, the bomb, water, stirrer, thermometer, wires, and so forth). 

Calorimeters - Even if it is not a neutron detector, calorimetric methods are useful for reactor density power monitoring A typical sensor is a gamma thermometer, in which gamma rays are absorbed increasing the temperature difference between a point close to a region surrounded by vacuum and a point in contact with the reactor coolant Since within the reactor the gamma flux is proportional to the fission rate, therefore, proportional to the power density, the temperature difference can be easily measured by a differential thermocouple, and related to the reactor power density... 

Figure 13 Calorimetric sensor for quasi-adiabatic ultrafast scanning developed in Alien s group. The upper scheme shows the cross section of the sensor consisting of a siiicone frame and a free-standing SisN membrane of 30 nm thickness. The thin-film polymer sample is spin coated on top of the sensor. The bottom scheme shows the shape of the metal film simultaneously used as a resistive heater and a thermometer. Reproduced with permission from Efremov, M. Y. Warren, J. T. Olson, E. A. etal. Macromolecules 2m2, 35,1481-1483. ...

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