Thermal conductivity meters

Sampling valves are located at the downstream exit of the condenser ahead of the catchpot. Gas leaves in a small stream that is withdrawn continuously from file system and monitored for changes in composition by a thermal conductivity meter during predetermined intervals samples are taken from this stream for chromatographic analysis. 

Thermal conductivity meters measure the ability of a gas mixture to conduct heat away ftom a heat source (Fig. 21.8). They usually employ two thermistors, one exposed to sample gas and the other to a reference sample containing none of the gas to be measured, arranged in a conventional Wheatstone bridge. Thermal conduc-... 

Part of the results obtained withthe thermal-conductivity meter are shown in Fig, 1. The materials shown here do not include honeycombs and have sufficient... 

A sohdus indicates the quotient of two unit symbols and the word per the division of two unit names m/s for meter per second. The horizontal line or negative powers are also permissible. The sohdus or the word per is not repeated in the same expression, eg, acceleration as m/s for meter per second squared and thermal conductivity as W/(m-K) for watt per meter kelvin. 

Thermal conductivity to convert watts per meter-kelvin to British thermal unit-feet per hour-square foot-degree Fahrenheit, multiply by 0.57779 and to convert British thermal unit-feet per hour-square foot-degree Fahrenheit to watts per meter-kelvin, multiply by 1.7307. Viscosity to convert pascal-seconds to centipoises, multiply by 1000. 

Thermal conductivities tabulated in watts per meter-kelvin... 

Thermal conductivity, now denoted by the Greek letter lambda (previously known as the fc-value), defines a material s ability to transmit heat, being measured in watts per square meter of surface area for a temperature gradient of one Kelvin per unit thickness of one meter. For convenience in practice, its dimensions Wm/m K be reduced to W/mK, since thickness over area mluF cancels to 1/m. 

Thermal resistance is the reciprocal of thermal conductance. It is expressed as m KTW. Since the purpose of thermal insulation is to resist heat flow, it is convenient to measure a material s performance in terms of its thermal resistance, which is calculated by dividing the thickness expressed in meters by the thermal conductivity. Being additive, thermal resistances facilitate the computation of overall thermal transmittance values (t/-values). 

Hydrogen detection in this type of meter is achieved using an ion pump, mass spectrometry or thermal conductivity detectors. ... 

After the activation period, the reactor temperature was decreased to 453 K, synthesis gas (H2 CO = 2 1) was introduced to the reactor, and the pressure was increased to 2.03 MPa (20.7 atm). The reactor temperature was increased to 493 K at a rate of 1 K/min, and the space velocity was maintained at 5 SL/h/gcat. The reaction products were continuously removed from the vapor space of the reactor and passed through two traps, a warm trap maintained at 373 K and a cold trap held at 273 K. The uncondensed vapor stream was reduced to atmospheric pressure through a letdown valve. The gas flow was measured using a wet test meter and analyzed by an online GC. The accumulated reactor liquid products were removed every 24 h by passing through a 2 pm sintered metal filter located below the liquid level in the CSTR. The conversions of CO and H2 were obtained by gas chromatography (GC) analysis (micro-GC equipped with thermal conductivity detectors) of the reactor exit gas mixture. The reaction products were collected in three traps maintained at different temperatures a hot trap (200°C), a warm trap (100°C), and a cold trap (0°C). The products were separated into different fractions (rewax, wax, oil, and aqueous) for quantification. However, the oil and wax fractions were mixed prior to GC analysis. 

Samples are injected into the vaporizer by a metering pump or manually with septum injection the manual injection procedure is intended for method development. The sample gas mixture then passes through the chromatographic column where the sample compounds separate. Fractions pass through the thermal conductivity detector and then to a condenser collection manifold where up to five fractions can be collected. Complete control of the system is achieved via a mini-computer. 

Figure 13.3 Flow outgassing with thermal conductivity detector, (a) a, Purge gas source b, needle valve c, cold trap Dj and D2, thermal conductivity detectors e, flow selector valve f, cell with powder g, flow meter, (b) Heated filaments 1 and 3 are D2,2 and 4 are. ...

Figure 15.8 Thermal conductivity bridge electronic circuit. 12 V dc power supply, stable to 1 mV. Ripple is not significant due to thermal lag of the filaments. Pj, 100 ohms for filament current control Mj, milliamp meter, 0-250 mA P2, 2 ohms for coarse zero. Filaments 1 and 4 are detector 1 2 and 3 are detector 2. P3,1 ohm for fine zero Ri j, R12, padding resistors 64 ohms Rj-Rio, attenuator resistors 1, 2, 4. .. 512 ohms Si (DPDT) switch for polarity. Attenuator resistors are 0.25 %w/w, lowest temperature coefficient all others are 1 %.

Figure 1. Schematic of the apparatus (1) thermal conductivity cell detector, (2) column, (8) flow meter, (4) pressure regulator, (5) drying trap, (6) injection valve, (7) recording device (A) T.C. detector, (B) power supply, (C) recorder, (D) dc micro-voltmeter, (E) FM adaptor, (F) magnetic tape recorder...

Fig. 4.4-3 Thermal conductivity flow-meter for low flow-rates and a maximum pressure of 700 bar [60],...

Properties of Staple Fibers. Fiber diameters range from AAA lo G (Table 2). with the largest production volume in the range C—G. Thermal conductivity of gluss-liber products is influenced by fiber diameter, density or compactness of the liber mass, and temperature conditions. Generally, thermal eunductiv itv ranges between 0.20 and 0.80 (Blu)lin.)f(hr>Ht It F). In metric units. I his is 0.02y and 0.1 15 watl/meter-Kclvin W/ni K. 

WATT PER METER KELVIN (W/m K). The SI unit of thermal conductivity. 

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