Efficiency of Surface Heat Transfer Intensifiers for Laminar and Turbulent Flows in Heat Exchanger Channels

Abstract

The present work presents the comparison of efficiency of surface-type intensifiers in a wide range of geometric parameters and in the range of Reynolds numbers corresponding to rated laminar and turbulent flow regimes in a channel on the basis of a single general criterion. It is also aimed to clarify objective thermal and hydraulic properties of intensifiers, to present a table of intensifier optimal parameters for the further theory and practice development, to formulate practical recommendations for selecting intensifier types and parameters in the design of promising energy-saving heat transfer equipment. The comparison of intensifiers efficiency was carried out under identical conditions for constricted and unobstructed channels containing intensifiers of various shapes. It is shown that intensifiers in the form of transverse annular ridges and systems of spherical holes show high thermal and hydraulic efficiency at specific flow operating parameters and design parameters of both, a channel and intensifier. The acquired results and recommendations on optimal parameters of surface-type intensifiers make it possible to calculate and design heat exchangers with intensifier optimal configurations and sizes. To confirm the obtained fundamental knowledge in the field of surface heat transfer augmentation based on a system of spherical holes/ridges several heat exchanger prototypes were developed.

Calculation and Experimental Study of Heat Exchange in a System of Plane-Parallel Channels with Surface Intensifiers

“…Structured surface elements -vortex generators of different forms which are applied on heat-exchange surfaces -are promising means for heat transfer intensification in cooling systems of radioelectronic and power equipment and in channels of various power-generating equipment and transportation facilities [11][12][13]. This type of heat transfer intensifiers destroys the laminar boundary layer or the viscous sublayer of the turbulent boundary layer without affecting the main flow and ensures a high thermal and thermohydraulic efficiency [14,15]. The flow past dimples of variable depth under different flow conditions has special features due to the fact that tornado-like vortex structures have two orientations of their axes at the exit from the surface dimple: to the left or to the right, or they are in the stage of change of orientation.…”

Energy-efficient intensifiers of laminar heat transfer

“…As applied to the channel B (Fig. 1a), use was made of the model from [13]. In the flow, there is formed, a recirculation zone (RZ1) downstream of the low protrusion ( )…”

“…It is well known that the basic features of the flow pattern in the discretely rough channels (DRC) insignificantly depend on the main flow conditions in the channel [13]. The scheme of the flow (and calculation) in the channel E (Fig.…”

“…Calculations of thermohydraulic parameters of the channels were conducted at the conditions that are similar to those in [5,13,14]. The region of calculations corresponds to the rated laminar regime in the smooth channel ( Re 50.…”

“…So, for instance, the sizes of the groove and protrusion were varied within the range of 2 0.1-3.5; l D = 1 1 100 l h = − for the channel C. As a criterion of the channel efficiency and of the optimal variant of the HEI size, we used the relative coefficient of energy (borrowed from [2,5,13,14,15,16] The results of comparing the calculation on the model with experimental data [8] for the channel B at 0.1; h = 25 t h = are presented in Figs. 2 and 3.…”