Cooling By air

The second important component is the cooling agent or reactor coolant which extracts the heat of fission for some usefiil purpose and prevents melting of the reactor materials. The most common coolant is ordinary water at high temperature and high pressure to limit the extent of boiling. Other coolants that have been used are Hquid sodium, sodium—potassium alloy, helium, air, and carbon dioxide (qv). Surface cooling by air is limited to unreflected test reactors or experimental reactors operated at very low power. 

Drawdown from the die to nip is typically ca 10%. Sheet extmsion requires that the resin be of high melt viscosity to prevent excessive sag of the melt between the die and the nip. The melt should reach the nip before touching any other part of the middle roU to prevent uncontrolled cooling of the resin. The appearance of the lower surface of the sheet is deterrnined by the middle roU, ie, its poHsh, surface temperature, and freedom from condensed materials. The upper surface is cooled by air and has a more glossy appearance. Neither the top roU nor the bottom roU greatly affect the appearance of the top surface of the sheet. Edges of the sheet are trimmed. 

Checking Against Optimum Design. This attempts to answer the question whether a balance needs to be as it is. The first thing to compare against is the best current practice. Information is available ia the Hterature (13) for large-volume chemicals such as NH, CH OH, urea, and ethylene. The second step is to look for obvious violations of good practice on iadividual pieces of equipment. Examples of violations are stack temperatures > 150° C process streams > 120° C, cooled by air or water process streams > 65° C, heated by steam t/ urbine 65% reflux ratio > 1.15 times minimum and excess air > 10% on clean fuels. 

In the Prilling Process, such as practiced by the Lion Oil Co (Division of Monsanto Chemical Co, El Dorado, Arkansas), the production centers around a prilling tower, where a coned soln of AN forms into small droplets which flow downward against a stream of air. The resulting slightly moist prills are screened, dried and cooled by air Slid sgmn screened... 

Windscale reactors, and some US reactors of the 1950 period, the fuel was cooled by air blown straight to atmosphere, and no use was made of the heat to produce power. In all power reactors now operating, the coolant is contained in a closed-circuit pressure vessel. Outer containment buildings, which can also withstand some pressure in the event of failure or leakage from the pressure circuit, enclose the US pattern pressurised water and boiling water reactors, but no such provision was made for the Russian boiling water reactor at Chernobyl. All defences (cans, pressure vessel, containment building if provided) must be breached before fission products can be released to atmosphere. 

When Bi is very small, the thin body approximation can be used, e.g. a small metal sphere cooled by air (kso large, 8 and / nUld small). When Bi is very large, the external resistance is negligible, e.g. large body with low thermal conductivity immersed in a flowing liquid (fcsoiid small, 8 and hauid large). 

Most vapors condense inside tubes cooled by a falling curtain of water. The water is cooled by air circulated through the tube bundle. The bundles can be mounted directly in a cooling tower or submerged in water. 

After final cooling by air or cooling water, the synthesis gas is compressed (6) and sent to the synthesis loop (7). The synthesis loop is comprised of a straight-tubed boiling water reactor, which is more efficient than adiabatic reactors. Reaction heat is removed from the reactor by generating MP steam. This steam is used for stripping of process condensate and thereafter as process steam. Preheating the... 

Fig. 8.8 The contact-free batch reactor (CFBR) and its main components the MP Hg lamp and the reflector are installed within a safety cabinet and efficiently cooled by air ventilation. The batch tank optionally consists...

The partial condenser (D) is cooled by air, water, alcohol, etc., depending on the desired efficiency. For example, the condenser can be... 

Fire or explosion hazards require special motor enclosures. Hazards include combustible gases and vapors such as gasoline dust such as coal, flour, or metals that can e3q)lode when suspended in air and fibers such as textile lint. The kind of motor enclosure used depends on the type of hazard, the type and size of motor, and the probability of a hazardous condition occurring. Some available enclosures are explosionproof motors, which can withstand an internal ejq)losion force-ventilated motors cooled with air from a safe location and totally enclosed motors cooled by air-to-water heat exchangers and pressurized with safe air, instrument air, or inert gas. 

A transistor with a height of 0,4 cm and a diameter of 0.6 cm is mounted on a circuit board. The transistor is cooled by air flowing over it with an average heat transfer coefficient of 30 W/m °C. If the air temperature is 55°C and the transistor case temperature is not to exceed 70°C, determine the amount of power this transistor can dissipate safely. Disregard any heal transfer from the itansiscor base. 

A 15-cm X 15-cm circuit board dissipating 20 W of power uniformly is cooled by air, which approaches the circuit board at 20 C with a velocity of 6 m/s. Disregarding any heat transfer from the back surface of the board, determine the surface temperature of the electronic components (o) at the leading edge and (b) at the end of the board. Assume the flow to be turbulent since the electronic components are expected to act as turbulators. 

The components of an electronic system are located in a t.5-m-long horizoniat duct whose cross section is 20 cm X 20 cm. T he coinponenls in the duct are not allowed to come into direct contact with cooling air, and thus are cooled by air at 30°C flowing over the duct with a velocity of 200 m/min. If the surface temperature of the duct is not to exceed 65°C. determine the total power rating of the electronic devices that can be mounted into the duct. /In.siver 6A0 W... 

A 0.4-W cylindrical electronic componeal with diameter 0.3 cm and length 1,8 cm and mounted on a circuit board is cooled by air flowing across it at a velocity of 240 m/min. If the air temperature is SS C, determine the surface temperature of the component. 

The principle of condensation is analogous to that of evaporation. One may cool by air or by water, or by freezing mixtures,... 

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