Dechang Wang’s research while affiliated with Qingdao University and other places

To improve the adaptability of solar refrigeration systems to different heat sources, a single-double-effect LiBr–H2O absorption refrigeration system (ARS) driven by solar energy was designed and analyzed. The system was optimized using a multi-objective optimization method based on Sobol sensitivity analysis to enhance solar energy efficiency and reduce costs. The model of the solar single-double-effect LiBr–H2O ARS was developed, and the continuous operation characteristics of the system in different configurations were simulated and compared. The results show that the average cooling time of the system without auxiliary heat source is approximately 8.5 h per day, and the double-effect mode (DEM) generates about 11 kW of cooling capacity during continuous operation for one week under the designated conditions, and the system with adding auxiliary heat source meet the requirements of daily cooling time, the solar fraction (SF) of the system reaches 59.29%. The collector area has a greater effect on SF, while the flowrate of the hot water circulating pump and the volume of storage tank have little effect on SF. The optimized SF increases by 3.22% and the levelized cost decreases by 10.18%. Moreover, compared with the solar single-effect LiBr–H2O ARS, the SF of the system is increased by 15.51% and 17.42% respectively after optimization.

The rapid development of science and technology has dramatically increased the requirements for refrigeration technology in the temperature range from −190 $^\circ {\text{C}}$ to −50 $^\circ {\text{C}}$, such as biomedical science, clean energy and aerospace engineering. Mixed-refrigerant Joule-Thomson (MRJT) refrigeration technology has distinct advantages in this temperature range. The system efficiency deteriorates with the decrease of refrigeration temperature, especially at the temperature below −150 $^\circ {\text{C}}$. Precooling can effectively reduce the temperature span of the main refrigeration system and improve the system efficiency. This paper presents a low temperature refrigeration cycle coupled with a precooling system to produce the temperature below −150 $^\circ {\text{C}}$. A mathematical model based on the energy and exergy methods was established to evaluate the system performances at varied operation conditions. The results indicated that the precooling system can significantly improve the refrigeration efficiency. At the precooling temperature of −40 ℃, −50 ℃, −60 ℃, and the main cycle target temperature of −180 ℃ to −150 ℃, the composition and working pressure of the R170/R600a binary mixture in the precooling cycle and the N2/R14/Methane/Ethane quaternary mixture in the main cycle were optimized by genetic algorithm (GA). Under the optimal working conditions, the cooling capacity, power consumption, exergy are analyzed. The results obtained in this paper are of great significance to the performance analysis and optimal design of low-temperature refrigerator.

Rapid developments in clean energy, life science, and aerospace engineering have put forward more requirements for refrigeration technology with temperature below 180 K. Mixed-refrigerant Joule-Thomson (MRJT) refrigeration technology has distinct advantages in this temperature range. In this paper, the thermodynamic analysis of the Linde Hampson cycle and single-stage separation cycle at the refrigeration temperature from 100 to 180 K was carried out, and the energy and exergy models were established. Nitrogen, methane, tetrafluoromethane, ethane, propane, iso-butane, and iso-pentane were employed as the working fluids. The results showed that the performance of Linde-Hampson cycle is close to those of the single-stage separation cycle at the cooling temperature of 180 K. The COP of the single-stage separation cycle is 0.193 with 33.60% exergy efficiency at the temperature of 100 K, and in the Linde-Hampson cycle and single-stage separation cycle, the recuperator exergy loss accounts for 28.45% and 23.45% respectively, exergy losses from recuperator and condenser are the main components in the system.

Micro-nano metal-organic framework (MIL-68(Fe)) for efficient adsorption of azo anionic dye Congo red (CR) was successfully prepared by one-step hydrothermal method under acidic environment. And a MIL-68(Fe)/chitosan composite sponge (MIL-68(Fe)/CS) was prepared under the coating of chitosan (CS). After comparing the performance of MIL-68(Fe) and MIL-68(Fe)/CS, we focus on exploring MIL-68(Fe)/CS. It ensured the CR removal efficiency while reaching the adsorption equilibrium faster than MIL-68(Fe), and solved the defect that the powder was difficult to be stripped by water after adsorption. The physicochemical properties and surface morphology of the adsorbent were characterized by SEM, FTIR, XRD, TGA, BET, and Zeta potential. The effects of pH, contact time, adsorbent dosage, initial solution concentration and temperature on the adsorption performance of the adsorbent were systematically analyzed. The pseudo-second-order model and the Sips model were most consistent for the adsorption process, indicating that the adsorption process of MIL-68(Fe)/chitosan composite sponge on CR is a complex physicochemical process. The removal rates of CR by MIL-68(Fe) and MIL-68(Fe)/chitosan composite sponge reached the maximum values of 99.55 % and 99.51 % at 318 K, respectively. And the maximum adsorption capacity of CR by MIL-68(Fe)/chitosan composite sponge at 318 K was 1184.16 mg·g-1. After six cycles of adsorption and desorption, the removal rate of CR was still higher than 80 %. The synergistic effects of π-π stacking, electrostatic interactions, hydrogen bonding and pore filling have important effects on CR removal.

In this study, a solar single/double-effect switching LiBr-H2O absorption refrigeration system was investigated to make full use of solar energy and give full play to the advantages of solar refrigeration systems. A corresponding thermodynamic dynamic mathematical model was developed. The operation characteristics of the system operating continuously for one week were analyzed. In order to highlight the advantages of the solar single/double-effect switching absorption refrigeration system, it was compared with other forms of solar refrigeration systems and compression refrigeration systems. The practical application potential of the single/double-effect switching LiBr-H2O absorption refrigeration system was evaluated from the perspective of economy and environmental effect. The results showed that the system could achieve the switching operation between single-effect mode and double-effect mode under weather conditions of high solar radiation intensity, and the daily cooling efficiency on such days was relatively high. After an auxiliary heater was added, the primary energy savings of the solar single/double-effect switching LiBr-H2O absorption refrigeration system were 25–52%, depending on the area of the collector and the volume of the storage tank. The solar fraction of the system was about 71.99% for continuous operation during the whole refrigeration season. However, the initial investment cost of the system equipment accounted for 89.66% of the total cost. Compared with the traditional compression refrigeration system, the initial investment cost of the solar single/double-effect switching LiBr-H2O absorption refrigeration system was higher, but it had a better environmental protection effect.

Air source heat pump is recognized as an effective environmental protection and energy-saving technology. The heating temperature lift is one of the key factors affecting the performance of heat pump systems. In this paper, an in-depth quantitative thermodynamic comparison of cascade heat pump, recuperative heat pump and CO2 heat pump for direct-heating and space heating was conducted. Aspen HYSYS was used to invoke advanced genetic algorithm in MATLAB to optimize the system parameters. The temperature matching in heat exchangers was employed to reveal the essence of the performances of different heat pump systems. The recuperative heat pump is more suitable for direct-heating with the temperature lift 60 °C, and its COP is up to 4.81 at the ambient temperature of 20 °C. The cascade heat pump performs best in space heating with the maximum COP of 2.47. The exergoeconomic factor of the compressor is less than 7%, which illustrated that the investment in compressor should be increased to further improve the system efficiency. The annual CO2 and SO2 lowest emissions is 4431 kg and 130 kg of recuperative heat pump for direct-heating, and the cascade heat pump has the lowest annual 4234 kg CO2 and 127 kg SO2 emissions for space heating.

Low efficiency is one of the major concerns associated with absorption refrigeration cycle (ARC). The performance of ARC is affected by internal parameters such as the solution distribution ratio and the generator outlet solution concentration, especially to the absorption-generation heat exchange (AGX) LiBr–water variable-effect ARC. Therefore, the performance of the AGX variable-effect ARC was optimized and analyzed. AGX variable-effect ARC thermodynamic model has been implemented in Engineering Equation Solver (EES). Operation parameters including temperatures of all the units of ARC, solution distribution ratio, and generator outlet solution concentration had been optimized. The effects of the solution distribution ratio and generator outlet solution concentration on constraint conditions, coefficient of performance (COP), exergy efficiency (ηex), and operating range had also been analyzed. Multi-island genetic algorithm (MIGA) was used to optimize the solution distribution ratio and generator outlet solution concentration. The results showed that the optimal COP for the AGX cycle was from 0.885 to 1.249 for THG from 95 °C to 140 °C. The optimized COP was increased by 10.65% on average and 45.49% on maximum, compared with the COP obtained at the same temperature. The MIGA optimization method had proven to be an effective and robust tool that could be utilized to the optimization of AGX variable-effect ARC.