OVERVIEW

In this Chapter, we will discuss the main components of the heat pipe and the materials used. Since the 4th Edition of Heat Pipes was written, the materials and components of heat pipes have remained essentially the same. Nevertheless, life tests have had an opportunity to extend over a further 10-year period, and some working fluids have lost their attractiveness. This may be dictated by health and safety considerations (see also Chapter 5) or by environmental pressures - for example the use of chlorofluorocarbons is now banned, and in some countries in Europe the application of hydrofluorocarbons (HFCs) is being phased out in favour of fluids that contribute less to global warming.

The temperature range affected by these trends is principally between 50 C and +100 C. This affects products in the electronics thermal control, domestic and heat recovery areas, as well as (although less important in the context of global warming) spacecraft - see Chapter 7 and Chapter 8 on applications.

The issue of compatibility and the results of life tests on heat pipes and ther-mosyphons remain critical aspects of heat pipe design and manufacture. In particu-lar, the generation of noncondensable gases that adversely affects the performance of heat pipes in either short-term or long-term must be taken particularly seriously in the emerging technology of micro-heat pipes and arrays of such units (see also Chapter 6, where micro-heat pipes are discussed).

An aspect of heat pipes that has always been of interest to researchers is the compatibility...