No abstract

It has been established that the heat transfer of toluene in a turbulent regime of motion and at a supercritical pressure in a horizontally arranged bent pipe changes nonuniformly along the perimeter of the cross section. The basic factors are free convection and inertial forces. Computational equations for the heat-transfer coeffi cient are proposed.One radical means for increasing the power and improving the economic operation of power-generating plants is the use, in them, of a working medium or a heat-transfer agent at supercritical pressures. Therefore, substances at supercritical pressures (SCPs) have found wide application in various branches of today′s technology, in particular, in power engineering, rocketry, the gas industry, cryogenics, and other fi elds.Water is used as a working medium in power engineering, whereas hydrocarbons are utilized in cooling systems of aircraft and spacecraft and of self-contained power-generating plants. Also, there are other fi elds of technology in which different heat-transfer agents at SCPs are widely used.The operating reliability of apparatuses, among other factors, also depends on the intensity of the heat-transfer process. Maintaining the allowable value of the temperature of the apparatus wall is one basic issue of operation. This is particularly true of apparatuses operating at large thermal loads and SCPs of a substance.The distinctive features of a temperature regime for the material of the equipment at SCPs of the heat-transfer agent are attributable to the changes in the thermophysical properties of substances in a near-critical state, which are characterized by the disappearance of the difference between the liquid and the gas, by the equality of the surface-tension force to zero, and by the latent heat of vaporization. In a near-critical state, changes in the thermophysical properties of substances are of a complex character, since the heat capacity, the coeffi cient of volumetric expansion, and the Prandtl number go beyond their maximum; the density and the viscosity sharply decrease. Changes in the thermophysical properties of substances infl uence forces acting on a moving liquid. The value of one force becomes comparable to the other or dominates it, with the resulting change in the character of fl ow. For example, a strong change in the density induces free convection and fl ow acceleration. In turbulent fl ow, there can be processes of intensifi cation or attenuation of turbulent exchanges and fl ow rearrangement. The cooling capacity of the liquid improves as the heat capacity increases. A strong increase in the specifi c volume in the wall part of the fl ow and its decrease away from the wall may give rise to pressure pulsations in a cold liquid. All these effects produced by the strong change in the thermophysical properties of a substance infl uence the intensity of heat transfer and accordingly the temperature regime of the apparatus wall. It is a challenge to take account of these and other factors in calculating heat transfer theoretically; the...