Abstract
The paper presents an investigation into the energy performance of a novel irregular heat and mass exchanger for dew point cooling which, compared to the existing flat-plate heat exchangers, removed the use of the channel supporting guides and implemented the corrugated heat transfer surface, thus expecting to achieve the reduced air flow resistance, increased heat transfer area, and improved energy efficiency (i.e. Coefficient of Performance (COP)) of the air cooling process. CFD simulation was carried out to determine the flow resistance (K) factors of various elements within the dry and wet channels of the exchanger, while the ‘finite-element’ based ‘Newton-iteration’ numerical simulation was undertaken to investigate its cooling capacity, cooling effectiveness and COP at various geometrical and operational conditions. Compared to the existing flat-plate heat and mass exchangers with the same geometrical dimensions and operational conditions, the new irregular exchanger could achieve 32.9%–37% higher cooling capacity, dew-point and wet-bulb effectiveness, 29.7%–33.3% higher COP, and 55.8%–56.2% lower pressure drop. While undertaking dew point air cooling, the irregular heat and mass exchanger had the optimum air velocity of 1 m/s within the flow channels and working-to-intake air ratio of 0.3, which allowed the highest cooling capacity and COP to be achieved. In terms of the exchanger dimensions, the optimum height of the channel was 5 mm while its length was in the range 1–2 m. Overall, the proposed irregular heat and mass exchanger could lead to significant enhanced energy performance compared to the existing flat-plate dew point cooling heat exchanger of the same geometrical dimensions. To achieve the same amount cooling output, the irregular heat and mass exchanger had the reduced size and cost against the flat-plate ones.
Highlights
Conventional mechanical vapour compression air conditioning systems consume high power, create high carbon emission and cause severe environmental impact
The results indicated the Indirect Evaporative Cooling (IEC) heat exchanger could obtain higher cooling capacity and increased cooling effectiveness when spraying water against the cooling air
Zhao et al [16] conducted a numerical study into a novel counter-flow flat-plate heat and mass exchanger for dew point cooling, indicating that cooling effectiveness and energy efficiency of the exchanger were largely dependent on the dimensions of the air flow passages, air velocity and working-tointake air ratio, and less dependent on the temperature of the feed water
Summary
Conventional mechanical vapour compression air conditioning systems consume high power, create high carbon emission and cause severe environmental impact. Zhao et al [16] conducted a numerical study into a novel counter-flow flat-plate heat and mass exchanger for dew point cooling, indicating that cooling effectiveness and energy efficiency of the exchanger were largely dependent on the dimensions of the air flow passages, air velocity and working-tointake air ratio, and less dependent on the temperature of the feed water. The geometry-related pressure drops at the both channels will be simulated using CFD in order to determine the relevant air flow resistance factors, pressure drop and energy consumption of the fans Operational procedures of both the irregular and flat-plate heat and mass exchangers for dew point cooling are same. The typical geometrical set-up of the computational element and the whole modular exchanger are listed in Table 1, where the surface roughness of the wet channel material, i.e., fabric, is quoted from Ref. [20]
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