Piping heat radiation

Btu/(hr) (ft2)(°F/ft) i = inside wall pipe o = outside wall surface of pipe Heat loss from fluid inside pipe through exterior insulation to outside air. Combined convection and radiation ... 

Convection. Heat transfer by convection arises from the mixing of elements of fluid. If this mixing occurs as a result of density differences as, for example, when a pool of liquid is heated from below, the process is known as natural convection. If the mixing results from eddy movement in the fluid, for example when a fluid flows through a pipe heated on the outside, it is called forced convection. It is important to note that convection requires mixing of fluid elements, and is not governed by temperature difference alone as is the case in conduction and radiation. 

Composition 85% copper and 15% zinc. Commonly found in radiator cores, plumbing pipe, heat exchangers, and valves. 

Certainly, if the stripper tower and associated piping are radiating heat from the product, this is not contributing to stripping. To determine the temperature drop due to ambient-heat losses, proceed as follows ... 

Convection is one of the three so-called modes of heat transfer, the other two are conduction and radiation [1].[2],[3],[4]. In most real situations, the overall heat transfer is accomplished by a combination of at least two of these modes of heat transfer. However, it is possible, in many such cases, to consider the modes separately and then combine the solutions for each of the modes in order to obtain the overall heat transfer rate. For example, heat transfer from one fluid to another fluid through the walls of a pipe occurs in many practical devices. In this case, heat is transferred by convection from the hotter fluid to the one surface of the pipe. Heat is then transferred by conduction through the walls of the pipe. Finally, heat is transferred by convection from the other surface to the colder fluid. These heat transfer processes are shown in Fig. 1.3. The overall heat transfer rate can be calculated by considering the three processes separately and then combining the results. 

A 4-m-long section of a 5 cm diameter horizontal pipe in wliich a refrigerant flows passes tluough a room at 20°C. Tlie pipe is not well insulated and the outer surface temperature of the pipe is observed lo be - 10°C. The emissivity of the pipe surface is 0.85 and the surrounding surfaces arc at 15"C. The fraction of heat transferred to the pipe by radiation is... 

Natural and forced convection. The forces used to create convection currents in fluids are of two types. If the currents are the result of buoyancy forces generated by differences in density and the differences in density are in turn caused by temperature gradients in the fluid mass, the action is called natural convection. The flow of air across a heated radiator is an example of natural convection. If the currents are set in motion by the action of a mechanical device such as a pump or agitator, the flow is independent of density gradients and is called forced convection. Heat flow to a fluid pumped through a heated pipe is an example of forced convection. The two kinds of force may be active simultaneously in the same fluid, and natural and forced convection then occur together. 

Sterilization of the surfaces of vessels, pipes and valves may be achieved by heat, radiation or chemicals [81]. The use of steam has already been mentioned apart from cost it tends to be a slow procedure for sterilizing brewery vessels when steam pressures are low. Furthermore, it may carry undesirable particles and odours while the condensate is often drained unsatisfactorily. Radiation sterilization is rare although ultraviolet light irradiation is used for the treatment of water on a continuous basis. One of the simplest chemicals used for sterilization is ozone but this has proved corrosive [82]. More widely employed is hydrogen peroxide which, with peracetic acid, is added to soak baths for flexible pipes and items of fermentation equipment. 

Extraneous conductive parts are the other metal parts which do not form a part of the electrical installation the structural steelwork of the building, gas, water and central heating pipes and radiators,... 

For loss of coolant accident, it has been assumed that coolant is unavailable in the upper plenum, core and lower plenum of the reactor. Due to the absence of a heat removal medium, temperatures of the core will start increasing, leading to heating of all core components. The negative void reactivity coefficient will limit the power and thus, the temperature of the core components. The neutronically limited power would reach 200 kW(th). For this case, a system of 12 variable-conductance heat pipes, made of a carbon-carbon composite with a metallic liner, has been provided. These heat pipes penetrate the core. The condenser end of these heat pipes extends beyond the upper plenum and the interface vessels of heat-utilizing systems to the atmosphere. At the condenser end, these heat pipes have radiator fins to dissipate heat to the atmosphere. In case of a postulated accident due to loss of load or loss of coolant, core temperature will start increasing. As long as the temperature of the core is within... 

Silencers and exhaust pipes in engine rooms are usnaUy insnlated to rednce heat radiation and noise. A flexible exhaust coimection is mounted at the engine to isolate engine vibration also, the exhaust hue is sloped away from the engine with a drain to avoid the accumnlation of condensation. Additional flexible connectors are necessary to compensate for thermal growth. 

Fig. 4.4 Diagram of a helium collecting tank, (a) Cooling pipes (b) Vacuum-superinsulation (c) Outer casing (d) Heat-radiation shield ...

Cryogenic tanks (h) are built up to a volume of 100 m. Their insulation loss amounts to about 1% of the design liquid inventory per day. These low heat losses at storage temperatures of about 4 K are possible due to superinsulation, thermal radiation shields and deep vacuum in the clearances of the double-walled container. The heat radiation shields transport the heat to the pipes in which either nitrogen or helium itself evaporates. A typical layout is shown in Fig. 4.4 [4.2]. 

The heater (Figure 5.1c) is applied to a copper pipe, restricted by copper rings and closed off by an outer jacket of stainless steel. The copper pipe enables heat to be transferred uniformly from heater to nozzle and improves heating of the nozzle at the dead ends of the heater, while the jacket counters outward heat radiation. This design provides a uniform temperature distribution in the nozzle, especially at high operating temperatures, and good durability. The admissible thermal density for such heaters is up to 15 W/cm. ... 

In the early 1950s, polyethylene was the first plastic material used for radiation curing. Today, approx. 150 Mio. meters of polyethylene pipe are radiation cured for under floor heating and drinking water lines. The pipes exhibit higher heat distortion temperatures with simultaneous improvement in their characteristic creep data under compression and considerably higher resistance to stress cracking [716]. 

H. Cheung, Critical Keview of Heat Pipe Theory and Applications, DCKT-50453, Lawrence Radiation Laboratory, University of California, Livermore, Calif., 1968. 

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