Abstract: The invention is a passenger compartment heating system for a bus heating system having a closed circuit through which there flows a heat transfer medium. A heat exchanger which is fed on the primary side by a heat-generating unit is used as heat-absorbing part. The inlet temperature and the heat transfer medium are matched to one another in such a way that there is a two-phase liquid/vapor mixture in the passenger heaters, which are arranged in series. The heat exchanger is designed as a capillary block or as a capillary-active porous wall into which the heat is fed on the primary side. The porous wall furthermore divides the vapor-only side from the liquid-only side of the closed circuit of the passenger compartment heating system and, in this region, has virtually only capillary-active channels.

Abstract: A heat pipe of aluminum is provided on the inside on all sides thereof with a completely closed fluid-tight coating of a water-resistant nickel in order to make the same resistant against water as heat carrier medium or to make the same vacuum-tight for long periods of time. Also, a coating of hard solder material is possible. The coating thickness is no less than 10 .mu.m and no more than 15 .mu.m. Individual parts of the heat pipe, prior to the soldering, are coated with the nickel material, each by itself, completely up to the joint areas. A process of making the heat pipe is also provided.

Abstract: A road heating installation which is supplied by heat stored in the ground and which includes heat pipes placed heat-conductingly with the road surface, is provided with sensors for detecting the climate factors relevant for the road condition and is equipped with a control apparatus that controls the heating installation as a function of the climate. In order to remove the heat energy stored in the ground only in case of need and to avoid the unnecessary exhaustion thereof, the invention provides that the heat transfer capacity of the heat pipe is controllable by a reversible blocking of the condensation zones of the heat pipes and the blocking is brought about in case of a dry-cold by the supply of an inert gas into the condensation zones of the heat pipes which is quantity-regulatable directly from the outside.