THE MULTIFACTORIALITY OF THE PROCEDURE FOR OPTIMIZING THE DESIGN OF A TWISTED HEAT EXCHANGER LOCATED IN AN ANNULAR CHANNEL DURING LAMINAR MOTION

Abstract

Cryogenic units that operate on the J-T (Joule-Thomson) cycle have found wide application due to the relatively simple design of the main elements, low operating costs, reliability and long service life. To a large extent, the efficiency of the installation depends on the choice of the coolant, the schematic solution, as well as on the design of the recuperative heat exchanger. The ability to compensate for temperature and mechanical stresses due to the twisted structure ensures long-term and trouble-free operation of the heat exchange equipment. The main goal of many studies was to determine the influence of thermophysical properties of the coolant, its mode parameters and geometric characteristics of the surface on heat exchange and hydrodynamics. On the basis of the results of the research, the optimization of the structure was carried out and empirical dependencies were given for calculating its parameters. The analysis of the presented empirical dependencies does not give a final answer regarding the development of a generalized method of calculating microheat exchangers of the Hampson type used in cryogenic installations. It is proposed to calculate the geometric characteristics of this type of heat exchangers, taking into account the influence on the intensity of heat exchange not only of the mode parameters of the heat carrier and the working fluid, but also of the design characteristics of the equipment, namely: the diameter and length of the pipe, the diameter of the coil, the gap between the heat exchange surface and the outer and inner casings, step characteristics of the coil. The work implements the methodology of calculation and optimization of the design of a twisted heat exchanger located in an annular channel with forced convection and laminar flow regime. The main emphasis is made on taking into account the change in the intensity of heat exchange along the length of the heat exchange surface, the length of the initial heat section is determined. An experimental study of heat exchange processes during forced convection of gas in a coiled heat exchanger in the laminar mode of movement of the heat carrier made it possible to establish the dependence of the heat transfer coefficient aк on the main geometric characteristics of the heat exchanger: the relative pitch of the coil, the gap between the heat exchange pipe and the outer and inner surfaces of the housing. On the basis of research results, dimensionless corrections were determined, with the help of which variational calculations of twisted heat exchanger structures located in annular channels are performed in order to optimize their geometric characteristics. Bibl. 31, Fig. 1.