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Enhanced airflow by axial fans is widely applied for efficient convective heat transfer and thermal management. The authors previously proposed the use of additional axial fans to enhance the airflow in a cold room and obtained improved cooling performance as well as increasing irreversibility through experimental thermodynamic analysis. In this study, the proposed strategy is numerically investigated via a validated computational model to evaluate distribution characteristics of airflow, temperature and entropy generation. The trade-off between cooling performance and irreversibility was analyzed under different operating conditions of additional axial fans. Numerical results indicated more homogeneous airflow and temperature distribution with increasing entropy generation caused by additional axial fans between produce bins. Additional axial fans with an operating angular velocity of 55 rad•s−1 at five positions between produce bins resulted in 18 to 37% improvement of cooling performance and 47% higher irreversibility when compared to the case without additional axial fans. An improved trade-off between improved cooling performance and increasing irreversibility could be achieved with lowering the operating angular velocity and reduced number of additional axial fans.

To observe the analgesic effect of thumbtack needling therapy and the quality of life in puerpera underwent cesarean section.One hundred and thirty-five puerpera underwent cesarean section were randomly divided into a medication group, a sham-thumbtack needling group and a thumbtack needling group, 45 cases in each group. In the medication group, the patient control analgesia (PCA) was given. In the thumbtack needling group, on the base of the regimen as the medication group, acupuncture with thumbtack needles was applied to lower abdominal point (Extra), Zusanli (ST36), Sanyinjiao (SP6), Geshu (BL17), Shenshu (BL23) and Dachangshu (BL25). The needles were retained for 48 hours. During the needle retaining, the sites with the needle embedded were pressed and kneaded for 3 times, 1 min each time, at the interval of 4 to 12 h. In the sham-thumbtack needling group, the sham-thumbtack needles were used; the acupoint selection, operation and treatment course were all the same as the thumbtack needling group. The visual analogue scale (VAS) scores of incision pain and ute-rine contraction pain, the incidence of postoperative adverse reactions, the amount of vaginal bleeding and milk amount in lactation were observed at each time point after the operation separately in each group.Compared with the medication group, the VAS score of incision pain was decreased 8, 12 and 24 h after operation (The conventional PCA combined with thumbtack needling therapy obtained better analgesic effects on incision dynamic pain and uterine contraction pain in patients after cesarean section as compared with either the simple PCA or the combined treatment with sham-thumbtack needling and medication, and both the thumbtack needling and the sham-thumbtack needling therapy can increase the milk amount of lactation from 24 to 48 h after operation.

Room cooling is traditionally used for postharvest products and is always involved with heterogeneous airflow and heat transfer. Despite the current evaluation of such heterogeneity, the irreversib...

Printed circuit heat exchanger has been recognized as a perspective mini-channel heat exchanger. Semi-circular cross-section is designed here due to the special manufacture technology. However, the...

Background Precooling is a critical step in the postharvest cold chain. Studies of the precooling of fruit and vegetables are based on the strong interactions between modelling, engineering, physiology and commercial outcomes. In recent years, new progress in precooling has been achieved. These achievements include different cooling strategies, research into precooling mechanisms, and numerical simulations. This review aims to provide the most recent information about precooling and promote its application in the fruit and vegetable industry. Scope and approach Different precooling strategies are evaluated with respect to the cooling rate, cooling uniformity, and multiscale simulation. An overview of mathematical modeling approaches used to quantitatively describe precooling processes for computer-aided designs is provided. The effect of precooling on fruit quality at the physiological and molecular levels is outlined. Key findings and conclusions Numerical simulations have become widely used to improve the precooling performance. Cooling homogeneity, in particular, has attracted increasing attention in recent studies because of the substantial effects of cooling homogeneity on the precooling efficiency and produce quality. The spatial scale of numerical simulations of the precooling process has started to become more precise and specific. Recent numerical simulations have focused on the bin and package scale. Models of transport processes at multiple spatial scales are investigated using multiscale modeling. Moreover, the effect of precooling on produce quality has recently received increasing attention. In addition, the investigation of the effect of precooling on fruit at the metabolomic and genomic levels has become an emerging trend and has provided deeper insights into the molecular mechanisms underlying the effect of precooling treatments on fruit.

Precooling is of significant importance for postharvest fruits and vegetables to control the quality degradation and prolong the shelf-life. Current precooling methods include room cooling, forced-air cooling, hydrocooling, vacuum cooling, contact or package icing, and cryogenic cooling, all of which have their advantages and disadvantages. The first two methods with the cooling medium of air are extensively used because of the wide applicable range of fruits and vegetables. Numerous studies have been devoted to cope with the drawbacks of these two air-based precooling methods with various evaluation criteria and optimization methods. A systematic literature review on these studies is firstly conducted with respect to experimental and numerical investigations respectively for the two methods. The main contributions from the previous studies are also summarized respectively with the research objectives and performance metrics. The literature review indicates that the current performance evaluation is limited to apparent parameters and the optimal design is only proposed based on the performance evaluation and comparison. Furthermore, with inspiration from the research in other domains, a scheme of advanced evaluation and optimization for air-based precooling methods is proposed with thermodynamic evaluation metrics and constructal optimization methods from the interdisciplinary perspective.

Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf life in food cold chain. Many efforts had been devoted to the study about the impact of ventilation design on airflow and temperature distribution inside ventilated packages. This paper reviews relevant research methods, commonly used quantities for the measurement of precooling effectiveness, attractive design parameters, and their impact on precooling effectiveness. These allow us to know exactly the characteristic and deficiency of each research method, identify dominant design parameters, and seek a promising way for the future improvement of the ventilated packaging system.

Supercritical fluid based natural circulation loop (NCL) systems have been proposed and used in many energy conversion systems in recent years. Supercritical fluid systems can contribute to new generation system design as well as thermo-hydraulic theories of functional fluids. In this study, the flow transition characteristics of supercritical CO2 based NCL system are discussed both numerically and experimentally. Numerical models with variable heat input conditions are simulated, which are focused on the flow transitions during the input changes. It is found that the supercritical NCL flow is very sensitive to heat influx changes. The numerical results are also discussed together with experimental results on the general trends in this study. Experimental results show that besides several kinds of transition flows, the heating control and cooling control can be both effective during the continuous operations of a supercritical loop system. The heater/cooler effect and parameter analysis are also conducted, which contributes to the design of active control of supercritical NCL system.

In this paper, we study the thermalization process of an enclosed fluid mixture near its liquid-vapor critical point subjected to cross-boundary mass diffusion. We reveal that the mass piston effect, a fast and efficient thermalization phenomenon can take place, as a result of three cooperative or competing mechanisms: the boundary velocity, the Dufour effect, and the concentration variation. We propose a theory to formulate the mass piston effect on the acoustic timescale, including the amplitudes of the acoustic wave, the wave’s propagation, and the energy and temperature efficiencies measuring the performance of the mass piston effect in terms of energy transfer and thermalization. We apply our theory to the representative C 2 H 6 - CO 2 mixture, and present the behavior of various thermodynamic indicators in the critical region over the whole concentration range. We identify that the boundary velocity is the main factor that restricts the efficiency of the thermalization. By comparing with numerical simulations of different initial states and boundary conditions, the theoretical predictions are quite satisfactory. The current work adds a new member to the family of piston effect and gives new insights into the thermalization process in the critical region.

In this study, the flow and heat transfer of non-Newtonian Al2O3-water nanofluid in Rayleigh-Benard cavity are numerically studied. Power-law model is used to describe the non-Newtonian effect of nanofluids in which the flow behavior index depends on the nanoparticle volume fraction. We present a systematic study of the Al2O3-water nanofluid for Rayleigh number of 1000 ≤ Ra ≤ 500000, cavity aspect ratio of 0.25 ≤ AR ≤ 4.0 and nanoparticle volume fraction of 0% ≤ ϕ ≤ 3%. The flow pattern inside the cavity changes complicatedly as Ra increases and the heat transfer performance of the system is strongly affected by the flow pattern. The convectional structure is influenced by both of the shear-thinning effect and the variation of effective viscosity. The average Nusselt number changes non-monotonically because of the flow pattern change under the variation of Ra and n. The consideration of Brownian motion and thermophoresis could bring about 3% increase of average Nusselt number, and the value varies slightly with different AR and ϕ . The comparison between non-Newtonian and Newtonian models shows that noticeable underestimation of heat transfer performance could be resulted by Newtonian model. The average Nusselt number of non-Newtonian model is approximately 1.5 times to that of Newtonian model, and the deviation is more pronounced with the increase of particle volume fraction.

Over the past millennium, there have been several precipitation–temperature cycles characterized by instabilities in the eastern monsoon region in China, but the processes, factors, and anthropogenic activities potentially responsible remain poorly understood. In this study, we present an analysis of phytoliths from borehole core drilled through an ombrotrophic peat mire in Jiangxi Province, China. Our results record three climatic episodes over the past 1300 year: a warmer interval, c. 800–1305 CE, similar to the Medieval Warm Period (MWP); a cooler interval, c. 1305–1860 CE, similar to the Little Ice Age (LIA); and another warmer interval, as the climate entered the Present Warm Period (PWP) after c. 1860 CE. Quantitative analysis of phytolith assemblages demonstrates that the MWP comprised two intervals: the early MWP, c. 800–1140 CE, was progressively wetter in a warm–dry setting and late MWP, c. 1140–1305 CE, was warm and humid. The LIA also comprised two intervals: the early LIA, c. 1305–1610 CE, was cool and dry, and the late LIA, c. 1610–1860 CE was cool and humid. Some abrupt climate events occurred at: (1) c. 1050, 1110–1130, and 1780–1845 CE (wet events); (2) c. 1980–1990 CE (dry events); (3) c. 920 and 1770 CE (warm events); (4) c. 980 and 1050 CE (cold events). The transition from the MWP to the LIA, as indicated by phytoliths, was a gradual process that took c. 100 years, and exhibited frequent temperature fluctuations. Correlations between the phytolith assemblages and the solar activity, East Asia Summer Monsoon, El Nino, and La Nina are evident. Solar maxima and La Nina-like conditions are related to warmer and humid conditions that led to clay–sand accumulation during the MWP. Solar minima and El Nino-like conditions were associated with a cold and wet climate that led to peat accumulation during the LIA. These observations provide important insights into paleoclimatic change in the eastern monsoonal region of China, and provide a basis on which to understand the response of the Xishan Mountains in SE China to the MWP and LIA, and explore centennial-scale climate fluctuations and their driving mechanisms.

The transcritical carbon dioxide vapor compression cycle is commonly used for heating and cooling applications because of the high discharge temperature and large evaporation heat. Whereas, high return water temperature is usually required by the heating demands, which significantly degrades the system performances. Nowadays, various kinds of subcooling methods have been proposed for the transcritical carbon dioxide vapor compression cycle, but a systematic comparative study based on the trade-off between the thermodynamic efficiency and economic cost is needed to analyze the applicability of these methods for large-scale district heating and cooling applications. In this work, the hot water temperature increases from 323.15 K to 343.15 K for district heating, and chilled water temperature reduces from 285.15 K to 280.15 K for district cooling. The simple single-stage transcritical carbon dioxide vapor compression cycles using subcooling methods with and without expansion work recovery, including internal heat exchanger, dedicated mechanical subcooling, cooling tower and dry cooler, are respectively modeled from the energetic, exergetic and economic perspectives. Based on the dual-objective Jaya algorithm and Technique for Order of Preference by Similarity to Ideal Solution decision-making method, the parametric study is conducted with optimized system performances to analyze the effects of different ambient conditions, namely the winter mode with ambient temperature from 248.15 K to 278.15 K and the summer mode with ambient temperature from 288.15 K to 318.15 K, and the relative humidity from 30% to 90%. Afterwards, the optimal subcooling methods under different ambient temperatures are selected based on the overall optimization and comparative study. The effects of different ambient temperatures on the system performances vary with different subcooling methods without expansion work recovery, and the dry cooler is the optimal subcooling method at the ambient temperatures from 248.15 K to 268.15 K, while the cooling tower is suggested under ambient temperatures higher than 278.15 K in spite of the performance degradation with high relative humidity. Insignificant differences of system performances using different subcooling methods can be observed with expansion work recovery, and the internal heat exchanger is selected as the optimal subcooling method for winter-mode operations, while the cooling tower is also suggested as the suitable subcooling method in the summer mode.

A 3D microporous metal-organic framework Al(OH)(bpydc) (MOF-253, bpydc = 2,2′-bipyridyl-5,5′-dicarboxylic acid) containing uncoordinated bipyridyl groups was synthesized and structurally characterized. Then the uncoordinated bipyridyl groups were used as postsynthetic modification sites to encapsulate Eu3+ cations into the pores of MOF-253. The intense luminescence of Eu3+ incorporated MOF-253 products Eu3+@MOF-253 indicates that the framework is rigid, permanently porous and non-coordinated bipyridyl groups are efficient scaffolds for hosting and sensitizing Eu3+ cations. Photoluminescence measurement demonstrates that Eu3+@MOF-253 displays excellent selectivity, and high sensitivity (detection limit, 0.66 μM) for Cu2+ ions in aqueous solution due to a great depression of the Eu3+-luminescence, which represents a rare Cu2+ fluorescent probe based on lanthanide-loaded MOFs constructed by postsynthetic method (PSM).