THERMOHYDRAULIC DISTRIBUTION IN TWISTED MICRO HEAT EXCHANGERS MOUNTED IN ANNULAR CHANNELS

Abstract

The design of twisted heat exchangers provides a possibility to compensate for temperature and mechanical stresses thus ensuring continuous and failsafe operation of the equipment. The authors use fins and multiturn pipe bundles to reduce the mass and size characteristics of the heat exchangers. Such design significantly complicates the calculating method. The main aspect of swirling flows is the presence of radial and axial pressure gradients. When vapor or gas flows swirl, the flow velocity near the walls is much higher than the average values, while at the axis the flow is significantly slower and in some cases its values can become negative. The liquid flowing near the axis has a notably lower pressure, which can cause it to boil. Considerable radial gradients of axial and rotational speed, as well as static pressure contribute to turbulent pulsations. Given that the working fluid flows along a helical line, the flow in the near-wall area is similar to the flow around curved surfaces. The study analyses how the pipe bundle geometry impacts hydraulic distribution and scrutinizes the main components of pressure loss in the twisted heat exchanger. The analysis allowed simplifying the method of hydraulic calculation of the multiturn twisted heat exchanger. Solving the outer heat transfer and hydrodynamics problem for the twisted heat exchanger allowed determining the effect of the main factors and the relationship between the parameters of the coolant and the working mass on the distribution values. The paper presents the equations for determining geometry of the pipes with different coiling diameters, as well as the equation for finding hydraulic distribution in individual pipes in the layers of the pipe bundle. The obtained results can help increase the accuracy of thermal calculation. The authors propose to use sectioning of twisted heat exchangers as a way to reduce hydraulic distribution. Bibl. 12, Fig. 1.