STRENGTH CHARACTERISTICS OF CARBON STEEL FLAT-OVAL TUBES FOR TWO-PHASE THERMOSYPHONS OF THE LOW-TEMPERATURE RANGE

The development and improvement of heat exchangers and systems of cooling and thermal stabilisation of electronic equipment requires the use of new highly efficient heat transfer elements capable of transferring significant heat fluxes with small overall dimensions. Two-phase thermosyphons (TS) are widely used as such elements. As a rule, TS casings are made of round, solid pipes, but alternative profiles, such as flat-oval, are also used to improve the overall dimensions and heat transfer characteristics. Due to their simple manufacturing technology, convenient shape and high thermal and aerodynamic performance, flat-oval tubes have broad prospects for use as TS casings. When operating in the low-temperature range, the internal pressure in the TS can reach 4 MPa, so the key issue when using any pipes as TS casings is strength. Since there is no data on the strength characteristics of flat-oval pipes, this issue needs to be investigated. The paper presents the results of experimental studies of the strength characteristics of flat-oval tubes with a longitudinal weld made of carbon steel. To conduct the research, 3 samples of TS filled with water were made from such pipes. The internal pressure was created by supplying heat to the TS. Its value was determined by the saturation temperature, which, in turn, was determined by the readings of thermocouples installed on the outer surface of the TS casing. The obtained results showed that at temperatures up to 210°C and pressures up to 19,074·105 Pa, there was no change in the shape of the cross-section of the TS with a flat-oval tube casing. An increase in temperature and pressure led to deformation of the DTS casing with its subsequent depressurisation. In all cases, the depressurisation occurred along the sealing at the end of the filling tube. Also, the regularities of changes in the geometric dimensions of flat-oval TS depending on temperature and pressure were obtained in graphical form. The data obtained should be taken into account when designing cooling, thermal stabilisation and heat transfer systems based on flat-oval TS.