engleski

The analysis of single phase flow in chevron channels of plate heat exchangers

The work represents an attempt to fully understand and evaluate characteristics of single phase flow in the corrugated chevron channel as a constitutive geometry in the plate heat exchangers. For this purpose the visualization tests have been carried out at the laminar and transient flow conditions for the plates with different chevron angles as the most influencing geometrical parameter. The measurements of the heat transfer and pressure drop characteristics accompanied the visualization tests at the Re numbers varied within the range Re=2&#61624 ; ; 1400. The first part of this work gives a general overview of the plate heat exchangers related features as design, applications and calculation procedure of performances. The subsequent text concerns the physical and mathematical model of the flow in the channel being supported by the detailed information related to the fundamental analytical solutions provided for the laminar flow in the simplified models and ducts of similar but simpler geometry. A comprehensive literature survey is included in order to enable comparison with obtained results from the visualization and thermal-hydraulic measurements as well as from the mathematical model. A separate part of the work describes the measurement procedure and results, comprising mentioned comparison as well as an analysis of the influence of the sine duct geometry and working conditions on the thermal-hydraulic characteristics of the flow through the sinusoidal corrugated chevron channel. A comprehensive literature survey proved there is a lack of systematized reliable data concerning thermal-hydraulic performances of plate heat exchangers (PHEs) as well as it indicated the uncertainties related to the complex flow mechanism involved in the mass, heat and momentum transfer in the corrugated chevron channels. The results from the visualization tests indicate simultaneous occurrence of the furrow and longitudinal component in 3D flow. Their relative size and influence on performances is dependent upon the angle, aspect ratio b/l and velocities, especially for the channels with higher angles (&#61538 ; ; >45o). The thermal-hydraulic tests in the channels with the angles 28o and 65o performed using fluids with significantly different viscosity, outlined the influence of the velocities on the flow pattern. Recorded different values at same Re numbers call for redefinition of the dimensionless groups involved in presentation of thermal-hydraulic characteristics. Significant decrease of the heat transfer at Re<50 for the channel 65o without remarkable decrease of the pressure drop makes plates with lower angles being preferable at very low Re number applications. Developed physical and mathematical model and corresponding good agreement with test data pointed out an importance of the simultaneously developing viscous boundary layer in both components for heat transfer and pressure drop. As the mathematical model takes into account all flow and geometric parameters relevant to the heat transfer and pressure drop it is recommended for use at the design stage and optimization. The model also gives the guidelines for redefinition of mentioned dimensionless groups.

Plate heat exchanger; corrugated chevron channel; heat transfer coefficient; pressure drop; cell; flow pattern; angle ;; aspect ratio b/l; visualization tests; thermal-hydraulic tests; mathematical model

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