查看更多>>摘要：In recent years, the refrigerant drop-in replacement of R134a has been mainly motivated due to environmental issues. This study aims to experimentally compare the operating characteristics in light commercial refrigeration using a display refrigerator when R134a is substituted with pure R1234ze(E) and R1234ze(E)-R134a blends. The refrigerants R450A (R1234ze(E)-R134a 58-42wt% blend), and R1234ze(E)-R134a 90-10wt% blend with GWP of 547 and 150 respectively are evaluated. The adequate refrigerant charge is determined, and the performance evaluation is carried on under controlled ambient temperatures of 24, 32, and 40°C. The results show a slightly reduced refrigerant charge for higher operating temperatures. Pure R1234ze(E) and its mixtures with R134a are a suitable short-term solution in light commercial refrigeration, satisfying ambient regulations with the maximum electric energy input increase by 6% under ambient temperature of 40°C. Its reduced operating pressure of 36% at the condenser might result of interest for some applications.
查看更多>>摘要：The improper defrosting operation would not only cause severe performance deterioration and energy waste but also reduce comfort. The dynamic control strategy of electric vehicle heat pumps is more complicated than that of other heat pumps. To find an efficient defrosting control logic, a transcritical CO2 heat pump test bench for electric vehicles was built. First, the thermodynamic dynamic characteristics in the defrosting process were analyzed, based on which a method for accurately determining the end of defrosting was proposed. Then, a comparative experiment on the core parameters that affected the defrosting speed was carried out, and suggestions for optimizing defrosting control strategy were given. In addition, the dynamic thermodynamic characteristics in the continuous frost-defrosting process under different humidity were further studied. It was found that the humidity decided whether additional dehumidification strategies should be adopted after defrosting. Finally, detailed dynamic control logic of the operation process from heating and frosting to defrosting was proposed. The research will promote the development of the electric vehicle industry by improving defrosting efficiency and meeting the requirements of socially sustainable development through saving energy.
查看更多>>摘要：To prevent hydrophobic phase change materials (PCMs) from phase separation in water, a novel technique based on a super-hydrophobic gel, known as marshmallow-like gel, has been suggested as an effective solution. In this study, marshmallow-like gel particles, which only adsorb hydrophobic substances, were used as a carrier of a hydrophobic PCM (paraffin) to evaluate their heat transportation performance. The tetradecane-adsorbed marshmallow-like gel particles showed a latent heat of 123 kJ·kg–1, which is 56% of that of pure tetradecane (219 kJ·kg–1). Sodium carboxymethyl cellulose (CMC) was used as a dispersant for the superhydrophobic gel in water. An aqueous soliton of CMC (0.6 wt%) was used to prepare the slurry containing 10 wt% of tetradecane-adsorbed marshmallow-like gel particles. The heat transfer of the slurry under laminar flow was characterized, and experiments were performed in a homemade heat transfer apparatus based on a double-tube heat exchanger with an inner tube diameter of 8 mm. The heat transfer coefficient was compared with the results of the CMC solution without the particles. Due to the latent heat of tetradecane, the particles with hydrophobic PCM showed a positive effect on heat transfer characteristics. Additionally, an adequate model to describe the heat transfer under laminar flow was proposed using a modified Prandtl number to consider the effect of latent heat.
查看更多>>摘要：In this study, the reclamation of Halon 1301 from an industrial waste gas mixture using an existing heat-pump-assisted batch distillation system was investigated. A cold water circuit and a hot water circuit are added to the conventional vapor compression heat pump for easy operation. To design and optimize the separation, where several design variables and constraints must be verified and satisfied, a modification of the design methodology proposed by Long et al. (2020) was used. Following design using Aspen Hysys software in the simulation of the shortcut column and heat pump system and Aspen Batch Modeler in the simulation of batch distillation, experimental operation of the existing heat-pump-assisted batch distillation system was performed to purify Halon 1301. The experimental performance matched well with that in the simulation. The purification of Halon 1301 with purity of 99.9% was accomplished after 22 h under the designed and optimized operating conditions. The results show that the reboiler duty and operating costs of the existing industrial system can be saved by as much as 100.0% and 36.5%, respectively, compared with a conventional batch distillation column. In addition, the total CO2 emission was reduced by as much as 43.7% compared with that of the conventional process. Moreover, the proposed design is convenient and gives reliable performance. This study demonstrated that the use of an advanced distillation configuration in industrial applications is practically viable and economical.
查看更多>>摘要：A heat pump cycle with refrigerant injection is one of the effective means to enhance the heating performance of electric vehicles in low temperature climate. The control strategy is very critical for the application of refrigerant injection technology in electric vehicles. In this paper, the variation of cabin load demand with ambient temperature is first presented for electric vehicles. Secondly, a test bench of heat pump system with refrigerant injection is built to compare the system heating performance under different control strategies. Considering the compressor discharge temperature and the load demand, the applicable temperature range under different control strategies is determined. The experimental results show that the control strategy of the main branch with slightly wet can effectively reduce the compressor discharge temperature and improve the heating performance of the system. The compressor discharge temperature can be reduced by up to 23°C with above control strategy. The system heating capacity and COP can be increased by up to 5.7% and 4.7%. Vapor injection cycle can meet the demand at the ambient temperature above -15°C. The two-phase injection cycle further extends the temperature range of the system operation at low temperature, and the lowest temperature can reach -22°C.
查看更多>>摘要：The loop thermosyphon, which has an excellent heat transfer performance, can effectively solve the problem of high heat flux heat transfer in outdoor high-power electronic equipment. In order to solve the problem of high heat flux heat transfer, the researchers focused on the new evaporator, but the impact of the condenser on the entire system cannot be ignored. This paper designed an air-cooling type loop thermosyphon with a condenser composed of a serpentine copper tube and corrugated aluminum fins. The experiment confirmed the serpentine tube condenser is a condenser with excellent performance. It can be used in conjunction with the loop thermosyphon to realize the 266.7 W?cm?2 heat flux transfer. Intriguingly, using a serpentine tube evaporator will bring about two kinds of flow instability, and the filling ratio is the key to restraining the flow instability. A high filling ratio is a suitable choice, which avoids flow instability and has a fast transient response. Moreover, the air temperature has little effect on the thermal resistance and the maximum temperature difference of the loop thermosyphon; therefore, this loop thermosyphon can be used in various weather conditions. However, extreme weather conditions (extremely high/ low temperature) may affect the performance of the loop thermosyphon. Consequently, the loop thermosyphon with serpentine finned tube condenser at an optimized high filling ratio is worthy of being employed in outdoor high-power electronic equipment.
查看更多>>摘要：Gas wave refrigerator (GWR) is a new type of refrigeration machinery that uses pressure waves to transfer energy between gases. In this paper, the flow characteristics and refrigeration mechanism in the wave rotor are numerically simulated. The nozzle angle is introduced to improve the overall refrigeration performance and expand the efficient operating range of the equipment. After verifying the model and method, the potential mechanism of refrigeration loss in the oscillating tube and the effect of loss on refrigeration efficiency are discussed in detail. Then the influence of incident angle on flow loss, refrigeration temperature drop, and power consumption are discussed. The association model of velocity development pattern and the maintenance of pressure performance at the inlet position of the oscillating tube is established during the high-pressure gas incident. The obtained numerical results show that flow loss and shock intensity loss are the main energy loss factors in the wave rotor. The incident angle determines the loss of the refrigeration process. The optimal incident angle of the device at the working point is obtained. The "balance" of velocity distribution in the oscillating tube can effectively reduce vortex loss. Arranging nozzles in the same rotation direction as the wave rotor can reduce work consumption, and the variation law is approximately negative linear correlation. Furthermore, based on the current simulation results, a set of nozzle design methods are obtained. It laid the foundation for the subsequent experimental research and optimization of GWR equipped with adaptive nozzles.
查看更多>>摘要：Both temperature control and humidity control are important in buildings. However, usually only temperature is controlled in small and medium-sized buildings using direct expansion (DX) air-conditioning (A/C) systems, while dehumidification is a by-product of cooling, and indoor humidity is in an uncontrolled state. Weights-based fuzzy logic control algorithm (WBFLCA) is a novel fuzzy control algorithm that can be applied to DX A/C systems with good simultaneous temperature and humidity control performance. However, the setting of weight values for WBFLCA is still highly dependent on expert experience and lacks a systematic optimization theory, which hinders the application of WBFLCA. In order to establish a weights setting rule for WBFLCA used in DX A/C systems, a coupled control simulation model is built in this paper to simulate the effect of simultaneous control of temperature and humidity with all 16 basic weights distribution mode combinations. All the 16 combinations are also experimentally tested on an experimental DX A/C system to reveal the control performance of different combinations in a real system. Four of them with good control performance are found. The reasons why these four combinations are good are also analyzed in this paper. Based on the simulation and experimental results, the weights setting rule of WBFLCA applicable to the simultaneous temperature and humidity control of DX A/C systems are summarized. The approach proposed in this paper of finding appropriate pattern combinations from the basic weights distribution patterns has the potential to be applied to solve other decoupling control problems as well.
查看更多>>摘要：Since the onset of the 21st century, the number of data centers has been increasing continuously, and the energy consumption of these data centers has aroused people's attention. Many experiments have been conducted to reduce the energy consumption in data center cooling, and free cooling utilization based on the mechanically driven two-phase cooling loop (MTCL) system has been proven to be an effective solution for energy saving. This paper reviews the research on and developments in the practical application of the MTCL system for data center cooling in recent decades. It presents a detailed summary of the progress of research on the MTCL system in data centers. The aim is to provide an improved understanding of the system and promote the application of this system in data center energy saving.
查看更多>>摘要：The back-pressure mechanism plays an important role in the performance and efficiency of the scroll compressor. In this work, the level of back pressure of an asymmetrical algebraic scroll compressor is experimentally measured and it is shown that the back pressure decreases with the increase of compressor frequency under all tested operating conditions. The mathematical model of the scroll compressor is also developed in order to further investigate other influence factors of back pressure. The predicted back pressure is compared with experiment result, showing a similar trend to them. The pressures in each working chamber and back-pressure chamber are studied to identify the effect of leakage through flank and radial leakage gaps. The influences of compressor frequency, leakage gap size, back-pressure volume on back pressure are discussed in detail based on developed model. The axial forces and stability of the orbiting scroll are also evaluated under these operating conditions by using interpolation method to calculate the pressure distribution on tips.
NSTL
Elsevier