Enhanced Performance Of Heat Recovery Ventilators By Airflow-induced Film Vibration

Ventilation is one of the most effective means which can improve the indoor air quality, and has already accounted for about 30-40% of the building heating and cooling energy demand but as much as 70% of this energy can be reclaimed by using Heat Recovery Ventilators (HRVs). Aiming at eliminating the shortages of existing heat recovery equipment, a novel film fresh heat exchanger was put forward, which uses airflow-induced vibration.Experiments as well as numerical simulation were carried out to study the fluid-structure coupling problem inherent in the fresh heat exchanger. The experimental studies mainly include: the heat transfer performance of the vibrating film induced by airflow and mechanical method, and the prototypes design of fresh air heat exchanger with different film thickness. The experimental systems for the performance of fresh air heat exchanger were set up. During the numerical study, the dynamic and heat transfer models of the airflow-film interaction were established, the interaction between the airflow and the film and its effect on heat transfer were studied under the flow styles of two-dimensional counter-current flow and three-dimensional cross-flow.The results show that the effectiveness of the heat exchanger varies from 0.65 to 0.85 with airflow rate, the pressure drop is less than 20.0 Pa, and has remarkable energy-saving effect. The film vibration induced by airflow can improve the heat transfer, and the enhancement extent is in proportion to the film vibration intensity. The amplitude of the film deformation is the major factor in improving the heat transfer. Larger air flow rate tends to decrease the effectiveness till some point where the channel films contact each other and makes for a worse heat transfer performance. The channel deformation induced by the steady fluid flow can change the velocity field and temperature field in the channels. The geometry of channel became converging-diverging configuration or diverging-converging configuration caused by the deformation of film, and the channel deformation did not improve the overall heat transfer performance relative to rigid channels, but the pressure drop doubles at high flow speed under the conditions of counter-current flow. Under the conditions of the three-dimensional cross-flow, the amplitude of the film deformation varies in different domain, which makes the geometry of channels are not the configuration of converging-diverging or diverging-converging in a whole. As a result, the velocity field in the channels varies more intensely, and leads to the improvement of heat transfer.