Kaijun Dong

Heating control strategy for variable refrigerant flow air conditioning system with multi-module outdoor units

The heating control strategy is key technology for stable and reliable heating operation of variable refrigerant flow air conditioning system with multi-module outdoor units. The synoptic control strategy is that the host module coordinates the system operation and adjusts the operation frequency of every module based on equal frequency allocation principle for suction pressure balance among modules. The heating control model including heating frequency adjustment, module switching condition and frequency allocation model has been built. Considering the discharge pressure disturbance, a certain discharge pressure region is taken as the control objective to adjust the frequency. And considering the lag between pressure and frequency, the restriction condition of discharge pressure and a certain judgment time are introduced into the model to avoid frequent module switching. Furthermore, different frequency allocation models have been built for increase and decrease of module number. In the model, when the module number increases and evenly allotted frequency to every module is less 70 Hz, one or two certain frequencies 70 Hz are distributed to the pre-existing thermo-on module(s) and the remaining frequency is distributed to ensuing thermo-on module so as to avoid sharp frequency fluctuation and inferior heating effect. Experiments demonstrate the feasibility of the control strategy.

CFD simulation on ice slurry concentrating hydrocyclone

A CFD simulation on the flow filed inside the ice slurry concentrating hydrocyclone (ISCH) was performed. The single-phase flow field inside the ISCH was simulated using the Renormalization k-ε Model (RNG k-ε), Reynolds Stress Model (RSM) and Large eddy Simulation (LES) Model, separately. The simulation results showed that LES achieved the best accuracy among the three models. Further, the ice particles were introduced using Discrete Phase Model (DPM), and the simulation results showed that the Rietema hydrocyclone was not applicable for concentrating ice slurry. Thus the proportion of the hydrocyclone needs to be further improved.

The Thermal Performance of a Novel Phase Change Emulsion

Abstract Phase change emulsion, mentioned in this article, is a category of novel phase change fluid used as heat storage and transfer media. It is made of micro-particles of a phase change wax as a phase change material with the melting temperature ranging from 80 to 90°C, which can be used as the working fluid in a heating system. Phase change emulsion of 10, 20, and 25 wt% were prepared. The melting point and the heat of fusion of phase change emulsion were measured by a differential scanning calorimeter. The phase change emulsion of 20 wt% was chosen to analyze the applicable feasibility. Its thermal physical properties were measured, and the pump consumption of a conventional (water) system and a phase change emulsion system were compared. Results show that this phase change emulsion can reduce pump consumption 87% compared to water as the heat transfer media when the working temperature zone is 82–90°C. Furthermore, by addition of nanoparticles, the thermal conductivity of the phase change emulsion was increased greatly with a little mass concentration.