Baffle shielding

Deterioration of tubes near the inlet nozzle of condenser shells due to impingement of water and steam mixtures can be alleviated through the use of appropriately placed and sized baffles or impact plates or by applying clip-on impingement shields to the tubes (see Case History 11.3). 

Blende, /. blend, glance (specif., zinc blend, ZnS) blind, screen, shutter, shield, diaphragm, stop, baffle border. 

The siting, as well as the selection of type of tower, can be critical. Rotating the tower, shielding the motor, use of baffles can all help in meeting environmental noise requirements. If in doubt, consult your cooling tower designer. 

From eq. (5.2) we see that the total power emitted by 1 cm2 with e = 1 at 300 K is 45 mW corresponding to an evaporation of 70cm3/h of 4He. At 77 K, a surface of 1 cm2 emits about 0.2 mW, with a 4He consumption of 0.3 cm3/h. Hence the part of the dewar cooled at helium temperature is surrounded by radiation shields or baffles at intermediate temperatures. The latter are either gas cooled or thermally anchored to a LN2 reservoir. 

The liquid helium evaporates in the heat exchanger and thus cools dovm the cryopanel. The waste gas which is generated (He) is used in a second heat exchanger to cool the baffle of a thermal radiation shield vi/hich protects the system from thermal radiation coming from the outside. The cold helium exhaust gas ejected by the helium pump is supplied to a helium recovery unit. The temperature at the cryopanels can be controlled by controlling the helium flow. 

Fig. 2.68 shows the design of a cryopump. It is cooled by a two-stage cold head. The thermal radiation shield (5) with the baffle (6) is closely linked thermally to the first stage (9) of the cold head. For pressures below 10 2 mbar the thermal load is caused mostly by thermal radiation. For this reason the second stage (7) with the condensation and cryosorption panels (8) is surrounded by the thermal radiation shield (5) which is black on the... 

High vacuum flange Pump casing Forevacuum flange Safety valve for gas dixharge Thermal radiation shield Baffle... 

Fig. 1. A magnetic + Si(Li) combination conversion-electron spectrometer based on an "old" Siegbahn-SIStis magnet. 1) beam, 2) target,3) target-changing system, 4) collimator and current measurement, 5) Faraday-cup, 6) Pb shield, 7) anti-positron baffle, 8) detector, 10) cold fingers, 13) cylindrical plastic scintillator 14) light guide, 16) P.M. tube.

In the model pump, a LHe cryopanel (90 cm x 90 cm) made of silver-plated stainless steel is shielded at the rear by a parallel LN2-cooled wall, polished on the panel side and, facing the vacuum system, by a LN2-cooled chevron baffle (with a gas transmission of 20%). The He cryopanel is supplied from a stainless steel LHe reservoir (A = 1.75 m2), wrapped in A1 foil and protected by a LN2 radiation shield of equal area. 

A possibility to reduce the number of cold heads/compressors would be to shield the 50 K panel with a LN2-cooled baffle. This, however, would reduce Xe owing to transmission restrictions, thus requiring an equivalent increase in Ac. Further, the cost of a LN2-cooled baffle and LN2 have to be considered. An unexpected problem is that, at 80K, ps Xe is 10 2 mbar. If the sticking coefficient of Xe is significant then this may limit the minimum attainable pressure in the system. 

If, after reading these rules, you conclude that the best place for a balance is in a special room by itself, you are right. Such a room ideally should be windowless, with one separate, shielded entry and filtered, baffled vents. The room should be small, with support beam walls and very heavy benchtops, and should be maintained consistently at 20°C. 

Fig. 18. Diagram of reactive scattering apparatus for the study of non-metal reactions A, scattering chamber B, source chambers C, liquid nitrogen cooled cold shield D, detector E, source bulkheads G, liquid nitrogen trap H, oil diffusion pumps N, free radical source P, nozzle source Q, skimmer E, ion source H, liquid He trap I, ion lenses P, photomultiplier Q, quadrupole rods R, light baffle S, slide valve T, radial electric field pumps (from C. F. Carter et al. 02 by permission of the Chemical...

Cryopumping surfaces cannot generally be exposed directly to a source of gas at room temperature because the heat load due to radiation would exceed that due to the condensation of gas molecules. Therefore, the cryogenic surface is protected on the side facing the gas source. As protection against thermal radiation, an optically dense baffle comprising liquid-nitrogen-cooled blackened shields is used often. 

It has been recommended (67, 68, 255) to avoid orientation of level-measurement nozzles by angles greater than 90° from a vapor inlet or reboiler return nozzle, and to refrain from positioning these nozzles under the bottom downcomers. If the angle exceeds 90°, a shielding baffle should be provided in front of the measurement nozzle. 

Level float in a column bottom sump bounced and finals broke due to impingement of entering steam. Problem fixed by installing a shielding baffle over the level connection. 

Figure 15.5. Segmented sample head, showing filter baffles, rolls of encapsulating polyester strips, and the wraparound path between the detector and lead shield. U.S. Patent 5,614,724. (By permission of Pacific Northwest National Laboratory)...

Design of the tank (accessibility, crevices, shielded areas, baffles, and compartments). Present and future conditions of the coating and the generic type of coating employed. Whether the water is subject to freezing. 

Figure 14 Isothermal displacement calorimeter with cooling module. A, stainless-steel support tube, B, vent tube C, current and potential leads for heater D, connector for feed tube E, Teflon plug F, vent plug G, heateriwire supports H, baffles I, Teflon support ], heater wires K, stirrer magnet L, stirrer paddle A,feed tube N, thermistor P, Teflon feed cup Q, water inlet tube R, copper heat sink S, 5Q era precision-bore Dewar flask T, 0-rings U, coin-silver cooling rod V, copper cup W, coin-silver support rods X, copper heat shield Y, coin-silver bar Z, cooling module (Reproduced by permission from J. them, and Eng. Data, 1966, 11, 189)...

The major part of the air flows between the side plates of the thermal s,hield and then into the space between the bottom thermal shields. Holes in the upper plate of the bottom thermal shield distribute the air into the pebble zone and into the cooling holes of the permanent graphite. A small amount of this air goes outside the outer side plates of the thermal shield to help cool the concrete. By means of baffles in the inlet ducts some of the air is drawn between the two plates of the upper thermal shield and then through holes in the lower plate into the space above thegraphite. 

Roes and van Swaaij [35] (Pall rings) and Verver and van Swaaij [6,37] (double-channel baffle column) experimentally obtained values of the mass transfer rate constant, which were much lower than values calculated from experimental solids holdup data and the well-know Ranz-Marshall correlation [38,39]. The low experimental values are to be attributed to particle-shielding phenomena due to the formation of less diluted suspensions or trickles. 

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