Manufacture of heat pipes

C What are the important considerations in the design and manufacture of heat pipes ... 

A number of recent references have focused on the problems associated with the design and manufacture of heat pipes. Most notable are early works by Feldman [16] and Brennan and Kroliczek [17], and more recent ones by Peterson [7] and Faghri [8]. In addition to such factors as cost, size, weight, reliability, fluid inventory, and construction and sealing techniques,... 

As pointed out by Thermacore Inc. (McGlen et al., 2003), the major manufacturer of heat pipes for electronics thermal control, the microelectronics, telecommunications, power electronics and, to some extent, the electrical power industries, are constantly striving towards miniaturisation of devices that inevitably result in greater power densities. Therefore, there is a challenge to develop efficient management of heat removal from these high flux devices. 

The copolymers have been used in the manufacture of extruded pipe, moulded fittings and for other items of chemical plant. They are, however, rarely used in Europe for this purpose because of cost and the low maximum service temperature. Processing conditions are adjusted to give a high amount of crystallinity, for example by the use of moulds at about 90°C. Heated parts of injection cylinders and extruder barrels which come into contact with the molten polymer should be made of special materials which do not cause decomposition of the polymer. Iron, steel and copper must be avoided. The danger of thermal decomposition may be reduced by streamlining the interior of the cylinder or barrel to avoid dead-spots and by careful temperature control. Steam heating is frequently employed. 

Four complete extrusion lines for the manufacture of PE pipes are described which are to be supplied by Battenfeld for Moscow s district heating system. The heating system utilises freely layable steel pipes the conveying the superheated steam, the steel pipes being protected and insulated by means of the PE pipes. The cavity is filled with an insulating layer of PU foam. 

Plastics are divided into two basic groups, thermosetting and thermoplastic, both of which are used in the manufacture of plastic pipe. Thermoplastics, as the name implies, soften upon the application of heat and reharden upon cooling they can be formed and reformed repeatedly. This characteristic permits them to be easily extruded or molded into a wide variety of useful shapes, including pipe and fittings. Because thermoplastics are shaped, by a die or mold, while in a molten state their properties are essentially isotropic (i.e., independent of direction). In some processes and under some conditions, some anisotropy (i.e., direction dependence) may result. 

By virtue of its chemical and thermal resistances, borosilicate glass has superior resistance to thermal stresses and shocks, and is used in the manufacture of a variety of items for process plants. Examples are pipe up to 60 cm in diameter and 300 cm long with wall tliicknesses of 2-10 mm, pipe fittings, valves, distillation column sections, spherical and cylindrical vessels up 400-liter capacity, centrifugal pumps with capacities up to 20,000 liters/hr, tubular heat exchangers with heat transfer areas up to 8 m, maximum working pressure up to 275 kN/m, and heat transfer coefficients of 270 kcal/hz/m C [48,49]. 

Here I /G. is the heat exchanger contact resistance. The reason for rhe contact resistance is that there exists a resistance to heat flow between the outer surface of the pipe and the collar of the plate tins. Normally, the fins are attached to the pipes by mechanical expansion of the tubes out into rhe plate-fin collars. Because of this manufacturing method, the contact will not be ideal. Small gaps between the pipe surface and rhe collar of the tins will occur. 

Fleat transfer cements are quite useful for transferring the heat from an external tracing when attached outside of the process pipe, Figures 10-167 and 10-168. To determine the number of heat transfer steam tracers, it is important to contact the manufacturer of the heat transfer cement. The illustrations here should be considered preliminary for approximating purposes. The information/data that follows is used with permission from Thermon Manufacturing Co./Cellex Div. Except for specific conditions, most applications represent the requirements to maintain a pipe (or vessel) system temperature, not to raise or lower the temperature. 

Figure 10-168. Installation of heat transfer cement with tracing on valves, pumps, and pipe. (Used by permission Bul.T-109-M, 1994. Ther-mon Manufacturing Co./ Cellex Div.)...

American Society of Heating, Refrigeration and Air Conditioning Engineers — H. R. Kornblum Chemical Manufacturers Association — D. R. Frikken Copper Development Association — A. Cohen Ductile Iron Pipe Research Association — T. F. Stroud Edison Electric Institute — R. L. Williams International District Heating Association — G. M. Von Bargen... 

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