Precision heater

Electrical heating is accomplished with resistance bauds or ribbons which must be electrically insulated from the machine body but in good thermal contact with it. The heaters must be carefully spaced to avoid a succession of hot and cold areas. Sometimes they are mounted in aluminum blocks shaped to conform to the container walls. Their effective temperature range is 150 to 500°C (about 300 to 930°F). Temperature control is precise, maintenance and supervision costs are low, and conversion of electrical energy to useful heat is almost 100 percent. The cost of electrical energy is usually large, however, and may be prohibitive. 

In differential scanning calorimetry (DSC), higher precision can be obtained and heat capacities can be measured. The apparatus is similar to that for a DTA analysis, with the primary difference being that the sample and reference are in separate heat sinks that are heated by individual heaters (see the following illustration). The temperatures of the two samples are kept the same by differential heating. Even slight... 

Chiron provides a microwell plate heater, a luminometer, and data management software. The plate heater is specially designed to provide precise control of the hybridization temperature (0 0.5°C) and to distribute heat evenly throughout the microwell plate. The luminometer maintains a temperature of 37°C and accommodates the 96-well plates. The data management software runs on an IBM PC or compatible computer with a minimum of 80386,16-Mhz microprocessor, 2 Mb of RAM, monitor, mouse, compatible printer, MS DOS (version 5.0 or greater), and Windows (version 3.1 or greater). 

We use differential scanning calorimetry - which we invariably shorten to DSC - to analyze the thermal properties of polymer samples as a function of temperature. We encapsulate a small sample of polymer, typically weighing a few milligrams, in an aluminum pan that we place on top of a small heater within an insulated cell. We place an empty sample pan atop the heater of an identical reference cell. The temperature of the two cells is ramped at a precise rate and the difference in heat required to maintain the two cells at the same temperature is recorded. A computer provides the results as a thermogram, in which heat flow is plotted as a function of temperature, a schematic example of which is shown in Fig. 7.13. 

Both the Departments of the Army and the Navy have used mineral-insulated band heaters for various superheating applications. For example, the Department of the Navy uses similar equipment to test chemical stability of components within artillery shells (AEA, 2001a). In addition to high watt densities, these heaters provide even temperature profiles and fairly precise temperature control. 

We will note how the shadow is in a state of continual movement. The patterns are caused by eddy currents around the heater as the air warms and then rises. After just a quick glance, it s clear that the movement of the warmed air is essentially random. By extension, we see that, as an electroanalytical tool, electrode heating is not a good form of convection, because of this randomness. Conversely, a hydrodynamic electrode gives a more precisely controlled flow of solution. In consequence, the rate of mass transport is both reproducible and predictable. 

Fuel oils are petroleum products that are used in many types of engines, lamps, heaters, furnaces, stoves, and as solvents. Fuel oils come from crude petroleum and are refined to meet specifications for each use. Fuel oils are mixtures of aliphatic (open chain and cyclic compounds that are similar to open chain compounds) and aromatic (benzene and compounds similar to benzene) petroleum hydrocarbons. In addition, they may contain small amounts of nitrogen, sulfur, and other elements as additives. The exact chemical composition (i.e., precise percentage of each constituent) of each of the fuel oils discussed in this profile may vary... 

Pump flow rate accuracy and gradient accuracy Detector linearity of response, noise, drift, and wavelength accuracy Injector precision, linearity, and carryover Column heater temperature accuracy... 

This paper describes an ebulliometric system for routine and special determinations of molecular weights. The system uses a simple ebulliometer, an immersion heater, and a Cottrell-type pump. Temperature sensing is by differential thermopile. Precision varies from about 1 to 6%, and values compare well with those from other laboratories and those from other methods. Values as high as 170,000 have been successfully measured. Some problems encountered in using the ebulliometric method are selection and effect of reference temperature, limitations of the vapor lift pump and a possible substitute for it, measurement of equilibrium concentrations within the operating ebulliometer, and the experimentally determined ebulliometric constant and some factors which influence its value. 

Established via Precision Scientific circulating heater, Model 200, cat. no. 66613, serial no. 20 AK-5 sensed at Hj. 

Lagally et al. [74] developed an integrated device for PCR and NCE with electric field control and fluorescence detection. Furthermore, the device had integrated heaters and temperature sensors, as well as PDMS membrane valving to control analyte transport. The PDMS unit was fabricated as membrane valves between a glass PCR chamber and the glass NCE channel, allowing precise control of both process unit operation and analyte transport. 

Fig. 18. Details of electron heater used for precision evaporations in gravimetric studies. [After Rhodin, Disc. Faraday Soc. 5, 215 (1949).]...

A quartz crystal thermometer sustains a capacitance if the frequency of the RLC circuit is precisely tuned to 14 or 20 MHz (depending on the exposed crystal faces). The quartz crystal will then transmit a very precise frequency, which has a temperature coefficient (typically 1 kHz per degree centigrade). If the temperature fluctuations are precisely compensated by a feedback heater circuit, then a quartz crystal oscillator is precise to about 1 part in 1.4 x 108. 

In contrast, DSC, designed in 1960 by Watson184 and O Neill,185 is a newer, more quantitative technique that does measure Ts and TR, but also measures very precisely the electrical energy used by separate heaters under either pan to make Ts = TR (this is power-compensated DSC, useable below 650° C). The power input into S minus the power input into R is plotted against Tr. High-temperature DSC (useful for TR > 1000°C) measures the heat fluxes by Tian-Calvet thermopiles rather than the electrical power, as a function of Tr. In a heat-flux DSC, both pans sit on a small slab of material with a calibrated heat resistance. The temperature of the calorimeter is raised linearly with time. A schematic DSC curve is shown in Fig. 11.80. 

Experimental. A Parr model 1221 oxygen bomb calorimeter was modified for isothermal operation and to ensure solution of nitrogen oxides (2). The space between the water jacket and the case was filled with vermiculite (exploded mica) to improve insulation. A flexible 1000-watt heater (Cenco No. 16565-3) was bent in the form of a circle to fit just within the jacket about 1 cm. above the bottom. Heater ends were soldered through the orifices left by removing the hot and cold water valves. A copper-constantan thermocouple and a precision platinum resistance thermometer (Minco model S37-2) were calibrated by comparison with a National Bureau of Standards-calibrated Leeds and Northrup model 8164 platinum resistance thermometer. The thermometer was used to sense the temperature within the calorimeter bucket the thermocouple sensed the jacket temperature. A mercury-in-glass thermoregulator (Philadelphia Scientific Glass model CE-712) was used to control the jacket temperature. 

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