An experimental and numerical study of a de-fouling evaporator used in a wastewater source heat pump

摘要

One challenge of recovering heat from waste bathwater using a heat pump is the build-up of bio-fouling on the heat exchanger surfaces. To solve this problem, a novel Dry-Expansion Shell-and-Tube Evaporator (DESTE) with a de-fouling function was developed. The evaporator performance was experimentally and numerically evaluated. Experimental results show that its heat transfer capacity increased with waste-water flowrate and temperature; the coefficient of performance (COP) of heat pump increased with wastewater flowrate; and drop of wastewater temperature through DESTE enlarged with wastewater temperature. A steady-state model was also developed. The evaporator was numerically divided into 45 sections, and the wastewater and refrigerant temperatures in each section were simulated. Statistical comparisons show that the simulated results were not significantly (p > 0.05 for all cases) different from the measured results, thus, making this model useful for predicting evaporator performance at conditions when experimental measurements were difficult. Predicting results show that the heat transfer capacity of DESTE would experience three different stages and can achieve 15.5 kW; fouling would reduce evaporator heat transfer capacity, especially when its thermal resistance was higher than 2.5E-4 m~2 K W~(-1); and cleaning of the fouling could increase heat recovery, although heat transfer coefficients of the refrigerant was slightly decreased in the overheat regions.