The relevance of this study is explained by the growing interest in increasing heat transfer by the development of high-performance thermal systems. Increasing the thermal characteristics of heat-exchanger systems is necessary for the efficient use of an energy source. The purpose of this study is to review the existing methods of heat-transfer intensification and examine the mathematical model of such an increase in efficiency when using petal turbulators. This study is based on a high-quality, reliable combination of proven theoretical methods (analysis, synthesis, concretization, generalization, modelling), and empirical methods. It is the introduction of turbulators into the flow channel that is one of the best methods of increasing passive heat exchange through such advantages as ease of manufacture and operation in combination with low operating and production costs. This study contains both passive and active methods of heat-exchange intensification that have been extensively investigated over the past decade. For this purpose, the newest studies of mainly authors from other countries were used, their detailed analysis was conducted and the results were summed up. In addition, a mathematical model of increasing the thermal efficiency of convective heating surfaces in a bundle of smooth pipes using petal turbulators was investigated, the results of which were tested on an experimental installation. The paper may interest a circle of readers interested in the problem of improving the thermal characteristics of heat exchangers, including researchers, teachers and students of higher educational institutions in the field of heat-power engineering.

An axial flow tubular heat exchanger has been experimentally investigated to augment the heat transfer rate with a novel swirl flow of air past the heated tubes. The novel design has been based on circular baffle plates provided with trapezoidal air deflectors of various inclination angles. The arrangement of tubes is kept the same throughout the experiment, in accordance with the longitudinal airflow direction. The tubes maintained a constant heat flux condition over the surface. Four deflectors with equal inclination angles were developed on each baffle plate, generating air swirl inside a circular duct carrying the heated tubes that increase air-side turbulence and, consequently, the surface heat transfer rate. The baffle plates were placed equidistant from each other at variable pitch ratios. The Reynolds number was kept in the range of 16000– 28000. The effect of pitch ratios and inclination angles on the thermo-fluid performance of the heat exchanger was studied. The investigations revealed an average improvement of 3.75 times in thermo-fluid performance for an exchanger with a deflector baffle plate with a baffle inclination angle of 50_ and a pitch ratio of 1.4 when compared to other inclination angles and pitch ratios.

An experiment was conducted to analyze a tubular heat exchanger's turbulent heat transfer characteristics. The heat ex-changer was equipped with a newly designed perforated (rectangular) conical baffle plate consisting of two rectangular opposite-oriented flow deflectors with adjustable tilt angles. The baffle plate was installed at the entrance of the heat ex-changer, resulting in a counter-swirling flow pattern downstream. Three baffle plates were installed along the flow direction with different pitch ratios (spacing between baffle plates divided by the diameter of the heat exchanger). The experiment examined the effects of pitch ratio (ranging from 0.6 to 1.2), deflector tilt angle (ranging from 30° to 50°) and Reynolds numbers (ranging from 16 500 to 30 000) on the heat transfer performance. The results showed that the pitch ratio and tilt angle significantly affected the performance of the heat exchanger. In particular, a configuration with a tilt angle of 30° and a pitch ratio of 1 resulted in an average improvement of 26.9% in the heat exchanger's performance compared to a heat exchanger without a conical baffle plate under similar operating conditions.