Research Of Implementing Liquid-separation To Heat Pump Water Heater With Wrap-around Microchannel Condenser Coil

Air source heat pump water heater（ASHPWH）is known as secure,environmental-friendly and efficient.The objective of carbon neutrality and emission peak proposed in 2020 pointed out the significance of more environmental protection and higher quality in future work.Although heat pump water heat（HPWH）had reached an important level of maturity,the potential of performance improvements have been an ongoing concern.Conducting experiments are able to evaluate system performance,while building theoretical model can be effective method of revealing system characteristic and optimizing performance.Being part of HPWH,condenser is essential to system performance.Liquid separation technic is a way to elevate heat transfer coefficient and lower pressure drop,which means performance improvement of HPWH feasible when applying it.In this thesis,a model of HPWH of warp-around microchannel condense with liquid separation is proposed,which adopts“quasi-steady-state”and“segment-tube-pass”for calculation as well as flowing pressure drop and utilizes separation efficiency and conservation of power and energy for liquid separation process.Compared with experimental parameters,the predictions are in good agreements for both condenser with separation（LMC）and without separation（CMC）.For integrated water tank and condenser,the average error of pressure are 0.66%and 0.59%for LMC and CMC respectively,and temperature are 6.28%and 3.30%for LMC and CMC respectively.For HPWH with liquid separation,average simulation errors of pressure,time-average power,heating time are5.29%,4.49%and 2.78%respectively.Experiments for system performance comparisons were conducted under different temperature of dry and wet bulb that set as 27^OC/19^OC,20^OC/15^OC and 7^OC/6^OC.Among these experiments,the temperature of 27^OC/19^OC had higher time-average power consumption,however its heat capacity was higher than others and heating time was shortened most,leading to highest value of coefficient of performance（COP）.Another comparisons ware carried out by mean of changing heating method,called static heating and mixing heating.The results revealed that under the same structure,system performance with static heating process was better than mixing heating method in term of higher COP of 10.33%for system with CMC and 6.92%for LMC.A mathematical model of integrated water tank and condenser was established and validated.Local performance of condenser coil with（LMC-1）and without liquid separation（CMC）were deeply explored.During heating-up transient,LMC-1 has higher heat transfer capacity of 2.50%,126.81%and 107.95%averagely over CMC for the second,fifth and sixth passes respectively.Enhancement of heat transfer coefficient was observed at inlet of the second and third passes.However,its pressure drop is significantly reduced by 34.48%averagely relatively to CMC.Optimized condenser with pass arrangement of 444433332（LMC-2）has superior heat transfer capacity of 78.2 W,shorter heating time of 162s and larger proportion two-phase heat transfer area of 7.62%by average than CMC.At system level,pass arrangement of 9873,76644,765333,5544333 were found to have highest COP for pass number from four to seven respectively when optimizations of pass arrangement were done.Further optimizations on separation efficiency among these four types condenser were studied,and COPs continue to raise with separation efficiency set as 0.4,0.7/0.2,0.7/0.2,0.8/0.2/0.2,respectively.Finally,these four kinds of system contain COP enhancement of 1.68%,3.84%,3.84%,2.64%.The best system,pass arrangement of765333 and separation efficiency of 0.7/0.2,was selected to detailedly compare with prototype system with LMC.It was found that the optimized one had superior performance mainly at the beginning.During entire heating process,the optimized system had higher pressure and temperature of averagely 7.83%and 4.89%at condenser inlet than the prototype.Furthermore,it saved power consumption of 7.16×10~3J and shortened heating time of 8.55%,which contributes to higher COP of 0.27 and subsequently reaches the first energy efficiency grade.It is found experimentally that ASHPWH with wrap-around microchannel condenser coil is dramatically affected by environmental conditions and heating measure.By building mathematical model and sequentially carrying out reasonable optimization of condenser,performances of both heat exchanger and heat pump system are improved greatly,which prove the effective and efficient performance of HPWH with liquid separation technic and tremendous potential of its performance enhancement.