Stirring liquids

All calorimeters consist of the calorimeter proper and its surround. This surround, which may be a jacket or a batii, is used to control tlie temperature of the calorimeter and the rate of heat leak to the environment. For temperatures not too far removed from room temperature, the jacket or bath usually contains a stirred liquid at a controlled temperature. For measurements at extreme temperatures, the jacket usually consists of a metal block containing a heater to control the temperature. With non-isothemial calorimeters (calorimeters where the temperature either increases or decreases as the reaction proceeds), if the jacket is kept at a constant temperature there will be some heat leak to the jacket when the temperature of the calorimeter changes. 

If it is desired to carry out the combined operations of stirring, refluxing, and addition of a liquid in a stream of gas, the apparatus of Fig. 77, 7, 12, a may be used the side tube for the gas is sealed on to the separatory funnel. For the passage of a gas into a stirred liquid, the aperture carrying the modified separatory funnel may be fitted with the device shown in Fig. 77, 7, 12, 6 the glass rod inside the tube is held in position by a short length of heavy-wall rubber tubing and is employed to clear the lower end of the gas delivery tube, should it become blocked with solid reaction product. 

A 1-1. flask (Note 1) is fitted with a condenser, an efficient stirrer, two dropping funnels, a thermometer extending well into the flask, and a delivery tube which extends far enough to be below the surface of the stirred liquid. 

In the case of transdermals, the dosage form is either directly placed in a stirred liquid or it is placed in a... 

An alternative to the rotating disk method in a quiescent fluid is a stationary disk placed in a rotating fluid. This method, like the rotating disk, is based on fluid mechanics principles and has been studied using benzoic acid dissolving into water [30], Khoury et al. [31] applied the stationary disk method to the study of the mass transport of steroids into dilute polymer solutions. Since this method assumes that the rotating fluid near the disk obeys solid body rotation, the stirring device and the distance of the stirrer from the disk become important considerations when it is used. A similar device was developed by Braun and Parrott [32], who used stationary spherical tablets in a stirred liquid to study the effect of various parameters on the mass transport of benzoic acid. 

The condenser is replaced by a thermometer extending into the stirred liquid. The thermometer is inserted through a wide-bore T-tube whose side outlet is protected by a calcium chloride tube. 

Derksen, J. J., Multi-scale simulations of stirred liquid-liquid dispersions . 12th European Conference on Mixing, Bologna, Italy, pp. 447-454 (2006b). 

Schulze, K., Ritter, J., and Kraume, M., Investigations of Local Drop Size Distributions and Scale-Up in Stirred Liquid-Liquid Dispersions . Proceedings of the 10th European Conference on Mixing, Delft, Netherlands, 181-188 (2000). 

A suspension of sodium amide (0.275 mole) (Note 1) in liquid ammonia is prepared in the following manner in a 1-1. threenecked flask equipped with an air condenser (Note 2), a sealed mechanical stirrer, and a dropping funnel. Commercial anhydrous liquid ammonia (600 ml.) is introduced by pouring from an Erlenmeyer flask (Note 3). To the stirred liquid ammonia is added a small piece of sodium. After the appearance of a permanent blue color (Note 4) a few crystals of ferric nitrate hydrate (ica. 0.1 g.) are added, followed by small pieces of freshly cut sodium (Note 5) until 6.32 g. (0.275 g. atom) has been added. After all the sodium is converted to the amide (Note 6), 42.0 g. (0.250 mole) of diphenylmethane (Note 7) in 20 ml. of anhydrous ether is added (Note 8). The deep red suspension is stirred for 15 minutes. n-Butyl bromide (37.6 g., 0.274 mole) (Note 7) in... 

The calorimetry lexicon also includes other frequently used designations of calorimeters. When the calorimeter proper contains a stirred liquid, the calorimeter is called stirred-liquid. When the calorimeter proper is a solid block (usually made of metal, such as copper), the calorimeter is said to be aneroid. For example, both instruments represented in figure 6.1 are stirred-liquid isoperibol calorimeters. The term scanning calorimeter is used to designate an instrument where the temperatures of the calorimeter proper and/or the jacket vary at a programmed rate. 

This treatment, which is due to Semenov, includes two assumptions, a uniform reactant temperature and heat loss by convection. While these may be reasonable approximations for some situations, e.g. a well-stirred liquid, they may be unsatisfactory in others. In Frank-Kamenetskii s theory, heat transfer takes place by conduction through the reacting mixture whose temperature is highest at the centre of the vessel and falls towards the walls. The mathematics of the Frank-Kamenetskii theory are considerably more complicated than those of the simple Semenov treatment, but it can be shown that the pre-explosion temperature rise at the centre of the vessel is given by an expression which differs from that already obtained by a numerical factor, the value of which depends on the geometry of the system (Table 7). 

Gas-absorption rates furnish another test of the magnitude of effect (i). If the gas is pure (e.g., CO2 at a partial pressure of 1 atm.), and is absorbing into stirred liquid, then the momentum-transfer term ijiRci is always negligible thus an interfacial film can reduce 2 only through effect (i) above. The results of Davies and Kilner (1, M) show that for the absorption of CO2 into water, the limiting value of factor (i), by which the film reduces /c2, is 1.9 (i.e., 1.96/1.04). This may be compared with the figure of 2.2 quoted above for the ethylacetate-water system. 

R. Mass Transfer through the Free Surface of a Stirred Liquid... 

Preparation of tetraphenylallene. (See Eq. 24.) To 200 ml of stirred liquid ammonia containing 7.28 gm (0.0255 mole) of 1,1,1-trichloro-2,2-diphenyl-ethane is added a solution of 0.0255 mole of potassium diphenylmethide in 300 ml of liquid ammonia. The mixture turns an orange-red color and then discharges immediately. After 1 hr the mixture is worked up to give 4.46 gm (75%) of l,l-dichloro-2,2-diphenylethene. 

Although local values of the shear rate in a stirred liquid may not be uniform, the effective shear rate (S- ) was found to be a sole function of the impeller... 

Addition of solids to stirred liquids, 68 Addition tubes, 51 two-way, 51 three-way, 51 Adipic acid, 489, 494 Adipic dialdehyde, 892 Adsorbents for chromatographic adsorption, 159, 160... 

The rapid rate of stirring desirable for maximum reaction rate often causes spraying of fine droplets of mercury from the seal. This can be prevented by a layer of paraffin oil over the mercury. It is important for the gas-inlet tube to extend below the surface of the stirred liquid, for absorption of hydrogen occurs chiefly at the rapidly agitated surface. 

Stir liquid sample at a high and constant rate using a magnetic stirrer and stir bar. 

Stir-bar sorptive extraction (SBSE) is carried out using a commercially available glass stir bar (Twister, from Gerstel GmbH) coated with polydimethylsiloxane (PDMS). A special thermal desorption unit is necessary to introduce the extract into a GC. It can be applied to headspace extraction, but is intended for stirring liquid samples for extraction. The same coatings used for SPME can be used for SBSE, and thus similar selectivity should be observed. 

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