Avaliação numérico-experimental do resfriamento de ambientes por um sistema ciclônico-psicrométrico

Abstract

Thermal comfort is a necessity present in many environments such as houses, stores, and public spaces, especially in a tropical country like Brazil that has well defined dry periods, which are mainly characterized by high temperature the low relative humidity. Hot, dry air causes a thermal cooling effect when it interacts with some structure dampened with water – psychrometric effect – due to the evaporation of the fluid that absorbs latent heat in the process. In ideal conditions, thermal decays of up to 18ºC can be obtained in the structure, depending on the observed temperature and relative humidity values. Thus, this dissertation proposes and experimentally investigates a sustainable and low energy consumption air conditioning system by combining the potentiality of dry air with the characteristics of the flow within a cyclone covered with a wet fabric structure. For this purpose, a new cyclone geometry was proposed to enhance the heat transfer between fluid and walls. The new cyclone family with 0.2627 m² of surface area was satisfactory for application in thermal exchange phenomena, since it presented convective coefficients of heat transfer ranging between 37.6 and 56.9 W/(m²°C) and Euler numbers between 1525 and 2821. The proposed cyclonic-psychrometric system provided thermal decays in the fluid between 3.9 and 13.1°C, whereas the system achieved an average thermal efficiency of 60.5%. The results also indicated that the water consumption to maintain tissue humidification is relatively low, in which about 16.02 g of liquid is needed to cool 1 m³ of air flowing through the cyclone. The numerical simulations indicated that, in 15 minutes, a cyclonic-psychrometric system consisting of 10 cyclones can provide a reduction of up to 7.0ºC in a room of 20.0 m² during a hot day (32.0ºC) at a relative humidity of 20.0%. Energy balances and economic analysis showed that the electric power consumed by the proposed system would represent only 19.8% of the power required by a conventional 18,000 Btu air conditioner to promote the same reduction of temperature. This energy-saving would certainly have a direct and positive impact on the user’s budget, especially those with low income and who live in dry and remote regions.