Specifics of gravity flow of hot air in an air flue over a finned beam


Аuthors

Sukhotskij A. B., Sidorik G. S.

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Abstract

The article analyzes the results of the study on air heating system implementation in buildings and facilities, allowing ensure both heating and ventilation with a single unit, as well as high hygienic and sanitary conditions of the premises air ambient. It also ensures less metal consumption and system inertia as well as more uniform temperature distribution in large premises. The studies on mixed convection application in recirculating air-heating calorifiers were analyzed.

A two-row chess bunch of the air heater, composed of bimetallic finned pipes with an equilateral pipes configuration with longitudinal step of 50 mm, cross step of 58 mm, length of 300 mm, and finned surface factor of 20 was studied. To organize a hot air mixed convection two types of air flues, namely with rectangular and circular cross sections, were being set over the experimental beam. For the gravity flow inside the shaft of rectangular cross section air-movement indicators were installed. The article presents the results of experimental research of the gravity flow of heated air in an air flue over the heat exchange beam in the mixed convection mode in the form of dependences of Nusselt numbers from Grasgof numbers. The heat emission increase in mixed convection mode of 2–3 times compared to the heat emission in conditions of free air convection was established. The article describes the dynamics of geyser flow of the heated air in the air flue under the impact of gravitational forces.

The heat transfer of the chess double-row bundle is reduced by 20–50% due to the presence of geyser air flows with the most negative effect being on the second row of the double-row beam (30–40% reduction in heat transfer). The way of reducing the negative impact of the air geyser flows on a heat interchange is offered.

The results of experimental studies can be used while developing the energy efficient air heating systems as well as for modernization of installations with air-cooled heat exchangers by installing air flues.

Keywords:

air heating, gravitational movement of air, bimetallic finned pipe, discharge shaft, mixed convection, heat-transfer coefficient, Nusselt number, Grashof number, air geyser flow

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