Open AccessThe paper presents a conducted experimental study of the heat exchange intensification on the surfaces covered with a regular vortex-generating relief that is an in-line array of the shallow hemispherical dimples. Using 12 configuration options with the Reynolds numbers in the range of (0.2-7.0) 106 as an example, it analyses how a longitudinal and cross step of the in-line dimple array (density dimples) effects on the processes of heat exchange intensification and resistance.
The monocomponent strain-gauge balance allows us to define a value of the resistance coefficient by direct weighing of models (located in parallel in a flow of "relief" and smooth "reference" ones being under study). Distribution fields of heat – transfer factor are determined by recording a cooling process of the surface of studied models having high spatial and temporary resolution. All researches were conducted with one-shot data record of these thermal and hydraulic measurements for the smooth (reference) surfaces and the studied surfaces covered with a regular vortex-generating relief (dimples). The error of determined parameters was no more than ±5%.
The oil-sooty method allows us to visualize flow around a regular relief and obtain a flow pattern for 12 options of dimples configuration. The analysis has been carried out and a compliance of the flow patterns with the field of heat-transfer factors has been obtained.
It has been found that for the in-line configuration a Reynolds analogy factor for most models is nonlinearly dependent on the Reynolds number. The friction intensification, at first, falls (to some Reynolds number) and, further, starts increasing, tending to the friction intensification value with self-similarity flow around. Thus with increasing Reynolds number, the heattransfer factor intensification falls (more slowly than resistance intensification).