International Journal of Refrigeration-revue Internationale Du Froid最新文献

Ice slurry is a promising functional fluid with high thermal energy density and high heat transfer rate. However, the agglomeration of the ice particles in flowing ice slurry can cause blocking of tubes. In this study, anti-freeze protein (AFP) and polyvinyl alcohol (PVA) were selected as additives to prevent the agglomeration of ice particles in ice slurry. Ice slurry was generated using the release of the supercooled state of 3 mass% NaCl solution containing the additives. The size of the ice particles in the ice slurry was observed, and the average area of the ice particles was evaluated to reveal the effects of the additives on the ice particle size. Furthermore, the flow behavior of the ice slurry in a tube was observed, and the effects of the additives on the flow behavior and prevention of the agglomeration of the ice particles were evaluated experimentally. It was found that the average area decreased with increasing concentration of the additives, and the effect of AFP on the average area was particularly significant. In the case of without the additives, the ice particles flowed in the tube while the ice particles agglomerated. On the other hand, the ice particles in the ice slurry with the additives flowed without agglomeration in the tube, especially in the case of AFP addition. It was found that AFP prevented the agglomeration of the ice particles in the ice slurry flow. Moreover, the ice slurries with AFP show the significant tendency for pseudo-plastic fluid.

The present study deals with the thermodynamic investigation of vortex tube coupled with trans-critical vapour compression refrigeration cycle (TVTC), followed by environmental analysis and multi-objective optimization. In this research, effect of various operating and design parameters is studied on the performance of TVTC. Furthermore, a comparison is made between the outcomes of TVTC and simple trans-critical vapour compression refrigeration cycle (TVCR). Results show that the optimum gascooler pressure for TVTC is observed to be lower than that of TVCR. Also, the cooling capacity and COP of TVTC are observed to be 10.1 % to 21.1 % and 2.3 % to 11.3 %, respectively, greater than those of TVCR. Moreover, the exergetic efficiency of TVTC is 2.3 % to 11.3 % higher than that of TVCR for the investigated range of evaporator and gascooler exit temperatures. The environmental penalty cost (per unit cooling capacity) of TVTC is 3.5 % to 12.2 % lower than that of TVCR. Furthermore, the coefficient of structural bond is calculated in order to choose the most sensitive parameters for system's performance. Additionally, genetic algorithm-based multi-objective optimization has been performed, with the evaporator temperature serving as the primary determining factor in establishing the optimal solution. This finding can guide the development of TVTC-based systems for a wide range of applications.

In recent years, data-driven models have enabled accurate prediction of chiller power consumption and chiller coefficient of performance (COP). This study evaluates the usage of time series Extreme Gradient Boosting (XGBoost) models to predict chiller power consumption and chiller COP of a water-cooled chiller plant. The 10-second measured data used in this study are from the Intelligent Building Agents Laboratory (IBAL), which includes two water-cooled chillers. Preprocessing, data selection, noise analysis, and data smoothing methods influence the accuracy of these data-driven predictions. The data intervals were changed to 30 s, 60 s, and 180 s using down-sampling and averaging strategies to investigate the impact of data preprocessing methods and data resolutions on the accuracy of chiller COP and power consumption models. To overcome the effect of noise on the accuracy of the models of chiller power consumption and COP, two data smoothing methods, the moving average window strategy and the Savitzky-Golay (SG) filter, are applied. The results show that both methods improve the predictions compared to the baseline, with the SG filter slightly outperforming the moving average. Particularly, the mean absolute percentage error of the chiller COP and power consumption models improved from 4.8 to 4.9 for the baseline to 1.9 and 2.3 with the SG filter, respectively. Overall, this study provides a practical guide to developing XGBoost data-driven chiller power consumption and COP prediction models.

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively.

Flexible contact gasket is a significant component affecting the sealing performance of the refrigerator. However, few studies were conducted on the permeability characteristics of moist air through refrigerator gaskets. The purpose of this study is to explore the permeability characteristics including permeation paths size, flow type, modeling and temperature-humidity-pressure-structure effect. The characteristic scale of the interface of permeation paths is observed as 10⁻⁵ m in the free-state by atomic force microscope. The equation of Knudsen number and contact stress relation is established to judgment the flow types. By comparing the critical and simulated contact stresses, it is inferred that moist air simultaneously occurs slip, transition and free-molecular flows. A multi-scale coupling model of permeation rate is constructed to obtain the apparent permeability coefficient characterizing the permeability intensity. The air pressure difference affects the permeability characteristics in the form of direct driving force and changing the contact stress of the interfaces. Free-molecular flow mainly occurs under the negative pressure condition with inhalation coefficient of 2.26 × 10⁻⁵∼2.84 × 10⁻⁵ m², while the slip flow mainly occurs under the positive pressure conditions with exhalation coefficient of 2.87 × 10⁻⁵∼4.65 × 10⁻⁵ m². The essence of enhancing the sealing performance of structural improvement is to increase the contact stress and length of permeation path. By increasing the height, increasing the inclination angle, adding the auxiliary edges and adding an auxiliary airbag, the inhalation coefficient of moist air, the exhalation coefficient of moist air and the inhalation coefficient of water vapor are decreased by 54.82 %, 51.46 % and 66.04 %.

In recent years, it has been possible to observe a significant expansion of the refrigeration and air conditioning industry. Considering that food refrigeration systems (blast chilling or freezing, cold storage, retail display, etc.) and air conditioners are large energy consumers, this work presents a methodology for evaluating the performance and behaviour of these systems using the thermoeconomic diagnosis concept. The thermoeconomic model used allowed the definition of the condenser and expansion device products, which is not trivial for these components. With that, the thermoeconomic diagnosis was used to evaluate the degradation of refrigeration system components, together with the influence of individual component degradations on efficiency, cooling capacity, operating parameters, and power consumption of the whole system. Through this analysis, a prognosis of system behaviour was obtained, which can be used for maintenance scheduling, as well as for the comprehensive energetic and exergetic analysis of a refrigeration system and each of its components.

Previous studies on cascade air source heat pumps (CASHPs) mainly focused on overall performances, while impacts of the low temperature stage (LTS) and high temperature stage (HTS) on overall performances were paid less attention to. Therefore, operating performances of a CASHP in LTS and HTS were investigated in this paper, to provide a solution for the optimization of the CASHP. A CASHP unit with a variable speed compressor in LTS and a constant speed compressor in HTS was adopted, and its operating performances were investigated under 26 cases. Results showed that the pressure ratio and COP in LTS and HTS were affected differently by the compressor speed. Specifically, as the speed of the compressor in LTS increased from 30 rps to 90 rps, P_rL increased by 151 % ∼ 178 %, and P_rH reduced by 38 % ∼ 54 %. Meanwhile, COP in LTS reduced by 21 % ∼ 52 %, but the COP in HTS rose by 54 % ∼ 96 %. Besides, it was found that adjustments of the compressor speed in LTS could improve heating performances of the CASHP. However, when the ambient air temperature and the supply water temperature were consistent, COP changes of the CASHP were limited, only by 0.3 % ∼ 9 %. Furthermore, empirical models of the COP in LTS and HTS were established to predict the COP of the CASHP on different operating conditions. Results of this study were helpful in promoting the configurations and operation control optimization of CASHPs.

Absorption cooling systems present an appealing alternative to conventional compression systems as they can leverage low-grade heat sources to generate a cooling effect. The choice of the working fluid in the absorption system plays a crucial role in its performance and applications, making it a critical factor in the system's design and operation. While specific hypotheses in the literature propose advantages of using ternary mixtures over typical binary working fluids, existing experimental studies lack conclusive evidence. Therefore, further research on this topic is imperative. This study experimentally assesses the performance of a single-effect absorption cooling system using the ternary NH₃-H₂O-LiBr mixture. The results are then compared to those of the binary NH₃-H₂O mixture. The assessment and comparison cover a wide range of operating conditions and similar concentration values. The results indicate that, from an operational standpoint, the ternary mixture offers significant advantages regarding system pressures and operational stability. However, from a performance perspective, at least within the tested mixture concentrations, the ternary mixture generally appears less attractive than the binary mixture. Nevertheless, it is worth noting that when driven by heat sources at higher temperatures, the ternary mixture could exhibit relevant performance characteristics.

In the background of energy shortage and climate change, transcritical CO₂ heat pump(HTP) technology has attracted lots of attention because of its energy-saving and environmentally friendly advantages. In this research, an experimentally verified simulation model of transcritical CO₂ HTP is established to investigate multi-factor coupling optimization of heat recovery effectiveness(η_IHX). First, the coupling optimization mechanism of η_IHX and discharge pressure(p_dis) is analyzed. Moreover, this research explores the influence of η_IHX on heating capacity, power consumption, discharge temperature(t_dis), and internal heat exchanger(IHX) cost, and further proposes a comprehensive heat recovery index to optimize the above factors. Based on this index the optimal heat recovery effectiveness(η_IHX,opt) for each operating condition is obtained. Also, a failure boundary for the coupling optimization of the η_IHX is also indicated. In addition, the optimal discharge pressure(p_dis,opt) prediction correlation for different η_IHXs is proposed, which can be used for heat recovery effectiveness collaborative optimization control. Finally, a general method for evaluating IHX is provided. Taking Xi'an as an example, the optimal heat recovery area(A_IHX,opt) of this HTP system is 0.42m², with which the optimized HTP system operates safely at extreme operating conditions, resulting in an annual lucre of 1,211 CNY.

Knowledge of the density of n-nonane + cyclopentane plays an important role in the design calculation, process simulation, and quality control of fuel industry. The liquid densities of n-nonane + cyclopentane binary mixtures (x₁ = 0, 0.2010, 0.3962, 0.6049, 0.8023, and 1) were measured using a high pressure vibrating-tube densimeter at 293–363 K and pressures up to 100 MPa. The density data obtained in this work were correlated using the modified Tait equation over the entire temperature and pressure range, and the absolute average deviations of the experimental and calculated values were 0.010 %, 0.016 %, 0.009 %, 0.011 %, 0.010 %, and 0.014 %, respectively. Comparisons have also been made with the available literature and satisfactory agreement was found. Finally, the isothermal compressibility, isobaric thermal expansivity, and excess molar volume were derived from the density data.