Abstract
Currently, there are no universal methods for calculating the heat transfer and pressure drop for a wide range of two-phase flow parameters in mini-channels due to changes in the void fraction and flow regime. Many experimental studies have been carried out, and narrow-range calculation methods have been developed. With increasing pressure, it becomes possible to expand the range of parameters for applying reliable calculation methods as a result of changes in the flow regime. This paper provides an overview of methods for calculating the pressure drops and heat transfer of two-phase flows in small-diameter channels and presents a comparison of calculation methods. For conditions of high reduced pressures pr = p/pcr ≈ 0.4 ÷ 0.6, the results of own experimental studies of pressure drops and flow boiling heat transfer of freons in the region of low and high mass flow rates (G = 200–2000 kg/m2 s) are presented. A description of the experimental stand is given, and a comparison of own experimental data with those obtained using the most reliable calculated relations is carried out.
Highlights
An important trend in the development of new energy conservation technologies is creating more miniature technical objects, an effort that requires extensive background knowledge of hydrodynamics and heat transfer in single-phase convection and flow boiling in mini-channels.The opportunity to accurately predict the pressure drops and heat transfer and the selection of mini-channel geometry and working conditions are important factors for the design of the optimal settings of heat exchangers
The two-phase pressure drop in micro-channels is relatively high compared to conventional channels due to their very small size and relatively high mass flow rates, the latter being necessary to achieve acceptable heat transfer coefficients
A pressure drop in a two-phase flow is a result of friction, acceleration, gravitation, and channel form change
Summary
An important trend in the development of new energy conservation technologies is creating more miniature technical objects, an effort that requires extensive background knowledge of hydrodynamics and heat transfer in single-phase convection and flow boiling in mini-channels. The opportunity to accurately predict the pressure drops and heat transfer and the selection of mini-channel geometry and working conditions are important factors for the design of the optimal settings of heat exchangers. In various fields of technology, one of the effective methods of heat transfer from heating surfaces is the boiling of liquid. It is necessary to experimentally confirm methods for calculating pressure drops and heat transfer
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