Flow and heat transfer in the separation region behind a backward-facing step with convergently mounted plates of longitudinal vortex generator

The paper presents the results of an experimental study of the dynamics of separated flow and heat transfer behind a backward-facing step when using longitudinal vortex generators (LVGs) at an angle of -30º at Re = 4000. Longitudinal vortex generators represent a pair of plates with a height of 6 mm, located symmetrically relative to the flow. Along with the average values, the pulsation characteristics of the flow are considered. The thermohydraulic efficiency was estimated by the found dynamic and thermal characteristics.

INCREASED EFFICIENCY OF RING HEAT EXCHANGERS FOR TRANSPORT POWER PLANTS

Для повышения теплогидравлической эффективности кольцевых теплообменников транспортных силовых установок предложено использовать в них гладкие трубки с турбулизатором пограничного слоя. To increase the thermohydraulic efficiency of the ring heat exchangers of transport power plants, it is proposed to use smooth tubes with a boundary layer turbulizer in them.

Thermohydraulic Performance and Entropy Generation of a Triple-Pass Solar Air Heater with Three Inlets

In this paper, a triple-pass solar air heater with three inlets is analytically investigated. The effects of airflow ratios of the second and third passes (ranging from 0 to 0.4), and the Reynolds number of the third pass (ranging from 8000 to 18,000) on the thermohydraulic efficiency and entropy generation are assessed. An absorber plate equipped with rectangular fins on both sides is used to enhance heat transfer. The air temperature change in the passes is represented by ordinary differential equations and solved by numerical integration. The results demonstrate that the effect of the third pass airflow ratio on the thermohydraulic efficiency and entropy generation is more significant than that of the second pass airflow ratio. The difference in air temperature through the collector shows an insignificant reduction, but the air pressure loss is only 50% compared with that of a traditional triple-pass solar air heater. Increasing the air flow ratios dramatically reduces entropy generation. Multi-objective optimization found a Reynolds number of 11,156 for both the airflow ratio of the second pass of 0.258 and airflow ratio of the third pass of 0.036 to be the an optimal value to achieve maximum thermohydraulic efficiency and minimum entropy generation.

Features of air flow and heat transfer control behind a backward-facing step using a vortex generator pair

The paper presents experimental results on the study of flow dynamics and heat transfer in the separation region behind the backward-facing step with longitudinal vortex generators (VG) installed at an angle to the flow of 30° at Re = 4000. The VG installation reduces the recirculation region and the induced longitudinal vortices and rearranges the flow structure in the separation region. The influence of a VG on the local and average thermal characteristics behind the backward-facing step is investigated and their thermohydraulic efficiency is estimated.

Evaluating the Performance of a Modified Solar Air Heater With Pierced Cover and Packed Mesh Layers

An experimental study was conducted to evaluate the thermal efficiency of a modified solar air heater. In the current design, air enters the collector through holes in front glass, passes through mesh layers, and exits at the backside of the air heater. A centrifugal fan was used to circulate air through the system. The design offers low construction costs and less solar radiation reflected from the collector. The modified collector was examined with various bed heights (30, 50, and 70 mm) and different mass flowrates of air varying from 0.011 kg/(s m2) to 0.043 kg/(s m2). The results showed that a counter flow collector with pierced cover had 5.6–9.7% higher efficiency than the single-pass one. The average efficiencies of the current design collector were found to be 55.2%, 44.6%, and 39.7% for the single-pass and 60.8%, 50.9% and 45.4% for the double-pass collector at 30, 50, and 70 mm bed heights and airflow rate of 0.043 kg/(s m2), respectively. The thermohydraulic efficiency, temperature difference, and perforated cover surface temperature were analyzed at each test and their effects on the system performance were evaluated. The highest amount of pressure drop through the collector was measured in the collector with a 70-mm bed height and a maximum air flowrate.