Radiation baffles

The nature of electromagnetic radiation baffled scientists for many years. At times light appears to behave like a wave at other times it behaves as though it were composed of small particles. While we now understand the wave-particle duality of all matter, including electromagnetic radiation, in terms of quantum mechanics, it is still convenient to consider electromagnetic radiation as having the properties of waves in many cases. 

Vapour cooled radiation baffles or a suspended deck in the cold vapour space. 

Vapour-Cooled Radiation Baffles and Suspended Decks... 

In practice, such a device introduced into the neck or ullage space of a containing vessel or tank has never been observed to reduce the liquid boil-off and is not recommended. Indeed, removal of the flow isolator, and replacement with a set of horizontal radiation baffles has led to significant (i.e. 50 % or more) reduction in BOR for several applications. 

Ambient temperature radiation can funnel down neck tubes and pipelines by internal specular reflection, without significant diminution, directly into liquid baths. Even if the tubes are vapour cooled, the radiation is not absorbed at the walls of the tubes, during internal reflection. To reduce radiation funnelling, the inner surfaces must therefore be rough so as to promote diffuse reflection at the relevant infra-red wavelengths. It is also advisable to use radiation baffles and traps, in all neck tubes and lines entering a cryogenic system. 

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 baffle mounted on the rod is primarily designed to catch any substance which may jump out of the crucible during measurement. In addition, it provides the balance with protection against heat radiation. When the crucible support is inserted, the baffle rest in a socket and thus separates the reaction chamber or furnace chamber from the balance housing. 

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... 

A study carried out at the Lawrence Radiation Laboratory of the University of California by Vanderveen (Vl) strongly suggests another type of interaction model see also Vermeulen (V5). Vanderveen measured the drop size at different distances from the impeller of a baffled, stirred tank reactor in which two immiscible liquid phases were contacted, and found that a very substantial increase in drop size occurs at remote distances. The increase, which was attributed to coalescence, appeared to be dependent on the physical properties of the phase system. 

Baffles. The use of baffles (louvres/chevrons) is of significant practical interest. Baffles are used to reduce backstreaming with diffusion pumps and also to reduce thermal radiation in cryopump applications. They are also used to minimise the effects of X-radiation generated in, for example, electron beam welders. 

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. 

Fig. 4.2. Waste heat boiler for a copper smelting flash furnace (Peippo et al, 1999). Note, left to right (i) flash furnace gas offtake (ii) boiler radiation section with water tubes in walls (iii) suspended water tube baffles in radiation section to evenly distribute gas flow (iv) convection section with hanging water tubes. Steam from the boiler is used to generate electricity, to power the acid plant s main blower and for general heating and drying.

Baffling complexity of solution of nuclear, radiation and environmental safety challenges at the TSF in question is further aggravated by poor condition of its infrastructure giving presently no way of performing radiation-hazardous operations on TSF rehabilitation. 

This report summarizes conventional methods for UV irradiation of air sensitive organometallic compounds at ambient or subambient temperatures. Of the irradiation sources available (l ) the medium pressure Hanovia 450 W arc lamp systems (2) are of moderate price, reliable, and versatile in our experience. Caution Powerful arc lamps can cause eye damage or blindness within seconds and UV protective goggles (available from most scientific supply houses) must be worn. Never look directly at the radiation source. For safety of other workers lamps should be enclosed in a vented box with baffles. If Pyrex transmits enough UV radiation for an efficient reaction, as for photochemical reactions of metal-metal bonded complexes (3), then conventional Schlenkware can be used for photolysis and no special glassware is needed. Since a 2 mm thick wall of Pyrex transmits only 10% of the UV light at 300 nm, UV transparent quartz reaction vessels are often needed for photoreactions of mononuclear organometallic complexes. 

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. 

Materials of construction are copper and stainless steel. All surfaces of the cold plate are plated to provide low emissivity in order to minimize radiant heat absorption. The chevron panels provide optically tight baffles. Chevron surfaces are coated black with a high-emissivity coating in order to minimize transmission of radiation to the cold plate by reflection through chevrons. 

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