Dewar vessel apparatus

This is followed by a specification for a new apparatus which includes the description of the pseudo-Dewar , reaction vessel [5]. This is a Dewar vessel, the Dewar-space of which can be filled with air or evacuated through a side-arm. Thus the contents can be cooled... 

The historical development of titration calorimetry has been addressed by Grime [197]. The technique is credited to have been born in 1913, when Bell and Cowell used an apparatus consisting of a 200 cm3 Dewar vessel, a platinum stirrer, a thermometer graduated to tenths of degrees, and a volumetric burette to determine the end point of the titration of citric acid with ammonia lfom a plot of the observed temperature change against the volume of ammonia added [208]. The capabilities of titration calorimetry have enormously evolved since then, and the accuracy limits of modern titration calorimeters are comparable to those obtained in conventional isoperibol (chapter 8) or heat-flow instruments (chapter 9) [195,198],... 

Figure 11.1 (a) Scheme of an isoperibol titration calorimetry apparatus A Dewar vessel B lid C stirrer D electrical resistance E thermistor F titrant delivery tube G O-ring seal, (b) Vessel for isothermal operation A stainless-steel, platinum, or tantalum cup B water-tight stainless steel container C heater D Peltier thermoelectric cooler E O-ring seal F heater and cooler leads. Adapted from [211],... 

Fig. 9.4.6 Apparatus for the matrix isolation method. Organic liquids are sublimed into a Dewar vessel through a solvent feeder to form a cryogenic matrix on the Pyrex glass wall cooled with liquid nitrogen. Inert gas is introduced via gas inlet. A target material in a crucible is heated in a gas to form ultrafine particles, which are deposited on a cryogenic matrix. The processes are repeated several times until enough particles are accumulated on a cryogenic matrix. (From Ref. 10.)...

Latent heats of evaporation of liquefied gases at low temperatures have been determined by various methods. Dewar, and Behn, dropped pieces of metal of known specific heat into the liquid and measured the gas evolved. Estreicher heated the liquid in a double Dewar vessel electrically and measured the volume of gas evolved. In Donath s apparatus (Fig. 4.VIII L) the gas passed through a copper spiral in a block of lead A, so assuming a constant temperature about 2° above the temperature in the metal calorimeter B. The gas then passed to a vessel inside B connected by a thin German-silver tube. The calorimeter was in two parts, between which was a platinum heating spiral for determining the thermal capacity. Outside was an adiabatic mantle C. The whole was in a vacuous copper jacket D. The temperature differences between A and B, and B and C, were determined by thermocouples. The rise in temperature... 

Low-temperature distillations of very small amounts of liquefied gases (about 5 ml) may be carried out with the apparatus of Simons [106], which fits into a Dewar vessel (Fig. 180). 

Whereas in combustions the measured heat change is usually about 5,000 cal, in the type of solution calorimetry just considered the heat changes are rarely more than one-tenth of this, some 500 eal. Consequently for the same percentage accuracy, 0 05 per cent, cruder apparatus is permissible, and Dewar-vessel calorimeters have been used with success. 

The apparatus is shown diagrammatically in Fig. 6. The reaction chamber is immersed in water, as the calorimetric fluid, which is contained in a Dewar vessel. A stream of nitrogen gas, saturated with water vapour, bubbles through the lithium butyl in the reaction chamber and then through a heat exchanger before passing out of the calorimeter. 

Since many of the Group III addition compounds are volatile, easily dissociated compounds, the high-temperature bulb vapour pressure apparatus of Burg and Schlesinger has proved well suited to studies of dissociation equilibria. Direct calorimetric measurements have generally been made in simple Dewar-vessel calorimeters. ... 

It is interesting to consider an insulation of this type as a support for the inner shell of a dewar vessel, heat transport due to support members thus being reduced to zero. With this problem in mind we measured the stress—strain curve of a stack of 160 fiber glass papers and 160 aluminum foil reflectors. The result is shown in Fig. 5. This result does not mean very much unless we know how the conductivity varies with the applied stress, because there is probably an optimum density for a minimum conductivity. At the present time we cannot measure this effect in our apparatus. However, the curve does show that at loads below about 5 psi the sample is still fairly loosely packed. 

The temperature variation in the liquid and vapor phases of helium contained in a dewar vessel has been measured along the axis and side of the dewar. Such information is helpful in the evaluation of data in cryogenic experiments in which a significant portion of the apparatus lies in a temperature gradient. The work described below was prompted by this consideration. However, the unexpected nature of the temperature variation led to a more detailed investigation. 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

Figure 6.15. The apparatus of Schnepf and Schnockel (2002) for the preparation and co-condensation of A1 (or Ga) mono-halide. 1 stainless steel vessel, 30/ 2 solvent input LM/D 3 drainage channel 4 A1 in the graphite cell with resistance heating 5 cooling shield 6 Dewar with dry ice (—78°C) 7 cooling water. HX hydrogen halide gas HV high vacuum.

Similar data can also be obtained for vapour pressure systems from the DIERS bench-scale apparatus operated in the open mode (see Figure A2.5). A high back pressure is superimposed on the containment vessel to suppress, boiling of the sample. An adiabatic Dewar calorimeter can also be operated in this mode if it has the facility to vent to an external containment vessel. 

Moderate-Temperature Reaction. Gas-kinetics apparatus as shown in Fig. 2, including vacuum line with greaseless stopcocks, sample reservoir bulb, reaction vessel, heated mercury manometer regulated oil bath thermometer 500-mL beaker 1-qt Dewar stopwatch or other timer. 

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