CONTROLLING HEAT GENERATION LOCALLY IN A HEAT-GENERATING PIPE UTILIZING SKIN-EFFECT CURRENT

摘要

1,251,095. Heat generating pipes. CHISSO CORP. 29 Oct., 1969 [29 Oct., 1968], No. 53083/69. Heading H5M. In order to satisfy the differing demands for heat along the length of a heat generating pipe of the type comprising a ferromagnetic pipe supplied with alternating heating current confined to the inside of the wall of the pipe by an inner insulated conductor supplied with A.C., one or more of the following factors is varied in accordance with the heat demand of a particular section of the heat generating pipe, during installation; the cross-sectional area of the insulated conductor; the resistivity of the insulated conductor; the magnetic permeability of the ferromagnetic pipe; the resistivity of the ferromagnetic pipe; and the inside diameter of the ferromagnetic pipe. The amplitude and frequency of the currents flowing in inner conductor and ferromagnetic pipes must be kept constant throughout their lengths. As shown, the heating pipe is installed in a fluid pipeline which has a section above ground and a section below ground which requires less heat because of the thermal insulation provided by the soil 10. It is possible to obviate temperature changes of the fluid in the two sections by using a better thermal insulator for the lagging 11 in exposed section than the buried section. However, according to the invention it is preferred to generate more heat in section 1 of the ferromagnetic pipe than section 1SP1/SP by making section 1 of a material of high resistivity and/or permeability by making the inside diameter of section 1 less than section 1SP1/SP, or by making the inner conductor 2 in section 1 of greater resistivity than the inner conductor 2SP1/SP in section 1SP1/SP. It is most convenient to use steel pipes from stock and to use different inside diameter pipes for the sections 1, 1SP1/SP. The inner conductor 2, 2SP1/SP may be electrically in series with the ferromagnetic pipe 1, 1SP1/SP or it may be connected to an A.C. supply and pass through two ferromagnetic pipes lying side by side and connected electrically at their ends so that heating current is induced in the inside skin of the walls of the pipes as in Specification 1,218,216. The ferromagnetic pipe is preferably filled with a good thermal conductor e.g. water, oil or other liquid to transfer the heat of the inner conductor to the ferromagnetic pipe. Applications specified are preventing freezing, heating roads, walls, floors, roofs, runways, railways, bridges transmission lines and tanks.