Twin-cell

In the vei tical-tube single-row double-fired heater, a single row of vertical tubes is arrayed along the center plane of the radiant section that is fired from both sides. Usually this type of heater has an overhead horizontal convec tion bank. Although it is the most expensive of the fired heater designs, it provides the most uniform heat transfer to the tubes. Duties are 21 to 132 GJ/h (20 to 125 10 Btu/h) per cell (twin-cell designs are not unusual). 

Another fresh-water method which holds some promise for seawater analysis is twin cell potential sweep voltammetry, as proposed Afghan et al. [138]. In this method, semicarbazones are formed by reaction with semicarbazide... 

For the more vigorous reactions, a twin-cell calorimeter was devised (188). It consisted of two nickel cylinders connected by a stainless steel needle valve and tubing and held rigidly to a metal top-plate. The cylinders and connections were immersed in a wide-necked Dewar vessel containing carbon tetrachloride which would react mildly with any BrF3 that escaped. Bromine trifluoride contained in one cylinder was transferred to the solid contained in the other cylinder by opening the valve and applying controlled suction. All measurements were made externally on probes in the carbon tetrachloride. 

All modern heat flow calorimeters have twin cells thus, they operate in the differential mode. As mentioned earlier, this means that the thermopiles from the sample and the reference cell are connected in opposition, so that the measured output is the difference between the respective thermoelectric forces. Because the differential voltage is the only quantity to be measured, the auxiliary electronics of a heat flux instrument are fairly simple, as shown in the block diagram of figure 9.3. The main device is a nanovoltmeter interfaced to a computer for instrument control and data acquisition and handling. The remaining electronics of a microcalorimeter (not shown in figure 9.3) are related to the very accurate temperature control of the thermostat and, in some cases, with the... 

In the CSM laboratory, Rueff et al. (1988) used a Perkin-Elmer differential scanning calorimeter (DSC-2), with sample containers modified for high pressure, to obtain methane hydrate heat capacity (245-259 K) and heat of dissociation (285 K), which were accurate to within 20%. Rueff (1985) was able to analyze his data to account for the portion of the sample that was ice, in an extension of work done earlier (Rueff and Sloan, 1985) to measure the thermal properties of hydrates in sediments. At Rice University, Lievois (1987) developed a twin-cell heat flux calorimeter and made AH measurements at 278.15 and 283.15 K to within 2.6%. More recently, at CSM a method was developed using the Setaram high pressure (heat-flux) micro-DSC VII (Gupta, 2007) to determine the heat capacity and heats of dissociation of methane hydrate at 277-283 K and at pressures of 5-20 MPa to within 2%. See Section 6.3.2 for gas hydrate heat capacity and heats of dissociation data. Figure 6.6 shows a schematic of the heat flux DSC system. In heat flux DSC, the heat flow necessary to achieve a zero temperature difference between the reference and sample cells is measured through the thermocouples linked to each of the cells. For more details on the principles of calorimetry the reader is referred to Hohne et al. (2003) and Brown (1998). 

Diret compression using a twin-cell mixer, theophylline and HPMC are mixed for lOmin then Mg stearate is added and mixed for 2min. 

This work is a continuation of our earlier study [1] of the hydrogen interaction with intermetallic compound (IMC) AB2-type Tio.9Zro.1Mn . 3V0.5. The measurements were carried out in twin-cell differential heat-conducting Tian-Calvet type calorimeter connected with the apparatus for gas dose feeding, that permitted us to measure the dependencies of differential molar enthalpy of desorption (AHdes.) and equilibrium hydrogen pressure (P) on hydrogen concentration x (x=[H]/[AB2]) at different temperatures simultaneously. The measurements were carried out at 150°C, 170°C and 190°C and hydrogen pressure up to 60 atm. 

Figure 3.37. Coupled torsion-Knudsen effusion apparatus of Ferro el a). 16). A, electro-balance B. tungsten torsion wire C. reflecting, mirror D. braking disc E. torsion cell F. twin cell G. thermostatic sand bath.

Calorimetric methods may be classified either by the principle of measurement e.g. heat compensating or heat accumulating), or by the method of operation (static, flow or scanning) or by the construction principle (single or twin cell). These will be discussed further in Chapter 5. 

The construction may have a single measuring system, or a twin or differential measuring system. Simple solution calorimeters have a single cell, while a DSC has twin cells and operates in the scanning mode. The use of twin cells reduces the effects of internal and external noise and transient fluctuations. 

Full potential process was demonstrated in a small laboratory batch unit (0.3 ft 2 area, but no basic design data was obtained. This chapter concerns work done with a one square foot, twin cell commercial unit to develop the basic data needed for a firm economic evaluation. 

Guidelines for the construction of viable electrodialysis cells for silica sols process were prepared. This was needed because the commercial one square foot electrodialysis twin cell used in this project develops eternal and internal leaks under the temperature and flow rate conditions specified by our colloidal silica process. 

In order to explore if the shear in the mini-Couette cell was in fact affecting phase transitions we made a twin cell compatible with SXRD and designed to fit the motor assembly used for prototype I. We modified the shaft, replacing its bottom part with Lexan of same dimensions as the Teflon shaft. The temperature control was the same used for the NMR modified probe. The cell was successfully tested at the ExxonMobil beamline XIOA of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (Upton, NY). The x-ray beam was sent perpendicular to the cell and the diffraction pattern was captured with a single point detector moving in the 20 angle. 

Figure 2.4 Block diagram of the p-jump apparatus with conductivity detection and the twin cell arrangement from Dialog (Germany). A, autoclave Ci and C2, conductivity cells E, electrodes M, elastic membrane D, metal diaphragm P, pressure pump m, manometer G, 40 kHz generator driving the conductivity bridge Cg and C4, tunable capacitors and Rj, helipot resistances Rg, potentiometer Os, oscilloscope (now replaced by a computer).

Some of the cells are shown in Figure 1. Two com partment Knudsen cells (Figure ID) are used if the vapour species formed from two different com pounds with very different vapour pressures have to be investigated. They can also be used to get unsatu rated vapours. The second compartment is replaced by a gas inlet system if gases are involved in the che mical reactions to be studied. Russian doll type and a twin cell with a connecting channel (Figures IB and 1C) allow generation of saturated and unsatu rated vapours of the sample. 

Figure 1 (A) Knudsen cell (B) Russian doll (C) twin cell with connecting channel (D) two compartment cells (E) twin cell (F) four Knudsen cell units (multiple cells).

Figure 4 Ion current intensity as a function of the deflecting plates potential. Twin cell with NaF-AIFj in one section and KF-UF4 in the other. The distance between effusion holes Is 8 mm. Distance resolution is 5.2 V mm ...

---