Experimental and Numerical Study on a Dry-expansion Shell-and-Tube Evaporator Used in Wastewater Source Heat Pump (WWSHP)

Aiming at the issue of bio-fouling build-up on heat exchanger’s surface in wastewater source heat pump (WWSHP) systems, a novel dry-expansion shell-and-tube wastewater evaporator (DESTE) with defouling function was developed. Based on reasonable assumptions, a steady-state model of the DESTE was built to carry out the investigation, which was validated by comparing the simulation results with experimental data. The DESTE at different velocities of refrigerant and wastewater before and after cleaning was simulated. The simulation results, which included the distributions of refrigerant’s pressure, enthalpy, void fraction, heat transfer coefficient and the temperature of wastewater and refrigerant along the flow-line before and after cleaning, suggested that the cleaning can improve the performance of the DESTE effectively. The effect of wastewater flow rate and the growth of fouling were studied as well. The results indicated that, for the DESTE designed in this paper, the minimum wastewater flow rate was 51×10·m·s and the optimal wastewater flow rate was 63×10·m·s; the optimal fouling thermal resistance to defouling was Rf=25×10 -5. m 2. K . W -1 . All these results can be used as a key reference for designing and operating waste bath water source heat pump systems in future.