Shielded burner

Caution Addition of 0 5 cm pieces of sodium metal to methanol or ethanol must be done in a chemical hood and behind a safety shield. Addition should be slow to minimize evaporation loss of methanol or ethanol. No flames or burner should be permitted in the area. Disposal of sodium metal must be earned out in someone s presence. 

A primary reason for use of an open field ground (matrix) flare is to reduce the visual impact of flared gas combustion in the manner of an enclosed ground flare. The open field ground (matrix) flare, however, has a significantly larger capacity than could be practically handled in a fumacelike structure, and the visual shielding is provided by tall fencing located some distance away from the burners themselves so that the fence encloses a small field. ... 

Heating the Tube.—Place the iron case with its tube in a bomb or tube furnace in such a way that the end with the capillary is raised somewhat and directed towards the wall on which a shield is fixed and close the furnace. Several tubes may be heated simultaneously. Light all the burners and heat gradually to the desired temperature, regulating the gas supply at the main tap. For aliphatic halogen compounds (and many sulphur compounds) this temperature is about 250°, for the aromatic compounds (and sul-phonic acids) it is about 300°. Most substances are completely oxidised after three to four hours, but in the case of aromatic compounds the heating is continued for some hours longer. 

Three zones arc identified in a typical heater such as that of Figure 8.19(a). In the radiant zone, heat transfer is predominantly (about 90%) by radiation. The convection zone is out of sight of the burners although some transfer occurs by radiation because the temperature still is high enough, most of the transfer here is by convection. The application of extended surfaces permits attainment of heat fluxes per unit of bare surface comparable to those in the radiant zone. Shield section is the name given to the first two rows or so leading into the convection section. On balance these tubes receive approximately the same heat flux as the radiant... 

Flame cultivation was attempted in sugarcane in the 1940s (Conrad and Lucas, 1995), but was soon abandoned. Liquid propane flamers burned broadleaf and grassy weeds as shields partially protected the crop from thermal damage. While flame cultivation was only marginally useful in sugarcane, tractor-mounted weed burners have been important in the transition from dependence on repetitive mechanical cultivation to the concept of chemical energy for weed control. 

Shield The entire burner and flask assembly should be protected from external air currents. Any efficient shield may be employed for this purpose. 

Unless otherwise directed, place a 5.0-g sample and 30 mL of water in a 125-mL Pyrex distillation flask having a side arm and trap. The flask is connected with a condenser and carries a thermometer and a capillary tube, both of which must extend into the liquid. Slowly add, with continuous stirring, 10 mL of 70% perchloric acid, and then add 2 or 3 drops of a 1 2 solution of silver nitrate and a few glass beads. Connect a small dropping funnel or a steam generator to the capillary tube. Support the flask on a flame-resistant mat or shielding board, with a hole that exposes about one-third of the flask to the low, clean flame of a Bunsen burner. 

Fig. 5. A three-slot burner modified with aluminium shields for tin determination in an entrained air—hydrogen flame.

Another method of determining the convective heat flux by direct measurement involves adding a radiant shield between the heat source and the heat flux gauge to exclude radiation from being received by the gauge. The problem is that the shield often disturbs the flow and the measured flux is not representative of the actual convective flow. Anofher problem is that the surface temperature under the shield will be lower than it would be without the shield, so the measurement would need to be done quickly before fhe wall femperature under the shield drops too much. In addition, although radiation from fhe primary source (burners) may be shielded, the rest of fhe furnace walls may still contribute radiation to the gauge. 

A series of tests were conducted in the furnace to compare CARS temperature measurements with those acquired with a suction pyrometer [84]. A suction pyrometer is an intrusive probe to measure gas temperature in a flame. The principle of the device is to insert the water cooled probe to the measurement point and draw furnace gases over a thermocouple located at the tip of the probe in an enclosure shielded from flame radiation. The gases are drawn at sufficient velocity to enhance the convective heat transfer to the thermocouple bead. Typically, the flow rate of furnace gases through the probe tip is increased until the thermocouple temperature no longer increases. At this point the thermocouple is assumed to measure the true gas temperature. The disturbance by such a measurement technique can be considerable in the near burner region where chemical reactions are occurring and there is heat release. 

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