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Cool storage has been considering an efficient and cost-effective means to enhance the behavior of a refrigerator. However, its drawback in temperature control of the refrigerator compartment has not received enough attention. The controllable two-phase loop thermosyphon has the prospect of solving this problem. In this study, a novel cool-storage refrigerator integrated with a controllable two-phase loop thermosyphon is built to investigate its precise temperature control capacity. The phase change material is optimized by the orthogonal experiment method. The controllable two-phase loop thermosyphon presents the optimal cooling performance for the fresh food compartment when the filling ratio is 27.0%. As the average temperature of the fresh food compartment increases, the one on–off cycle of the controllable two-phase loop thermosyphon maintains at 32.0 min, and the operation ratio varies from 86.3% to 13.6%. The temperature control accuracy can be improved from 2.1 °C to 0.6 °C and the overall time of one on-off cycle decreases from 49.8 min to 22.4 min. The operation ratio gradually increases from 7.2% to 38.6% as the ambient temperatures increase. The results demonstrate that the controllable two-phase loop thermosyphon is a feasible and effective way to improve the temperature control performance of the cool-storage refrigerator.

The heat pipe evacuated tube solar collectors, which is non-concentration, no-tracking and working at medium temperatures, suffer from low efficiency and thus rare application. The heat loss exerts serious negative influence on its performance at high operation temperatures. Thus, heat shields were introduced between the absorber plate and the glass tube to decrease the heat loss. Experimental and theoretical work were conducted to evaluate the thermal performance of the novel and traditional heat pipe evacuated tube solar collectors. According to the experimental results, the heat shields improved thermal efficiency at inlet water temperature of approximately 20 °C–150 °C, and the solar collector performed better at higher inlet water temperatures. The thermal efficiency of the novel one was enhanced by 11.8% at the inlet temperature and solar radiation of approximately 150 °C and 820 W/m2, respectively. Moreover, the novel one’s efficiency coefficients in the instantaneous efficiency curves, which can reflect the decrease rate of instantaneous thermal efficiency, resulted in decrease of 28.4% and 29.9%, respectively. Meanwhile, simulated results showed that, the thermal efficiency increments of novel collector over traditional one increased at weaker solar radiation and lower ambient temperature at each inlet water temperature.

Controllable loop thermosyphon (CLT) can be used as a significant temperature management component in solar- and electric-powered cool-storage refrigerators. However, the behaviours of CLT with non-condensable gas (NCG) under active control require further investigation. In this study, air is mixed in working fluid R134a as NCG to evaluate the steady-state and start-stop performances of CLT for selected control modes. CLT with 0–0.62% NCG is tested. The larger the amount of NCG is, the lower the heat transfer rate is. When the mass ratio of NCG reaches 0.62%, the steady-state heat transfer rate varies from 245.0 W to the minimum 118.6 W for different heat sink temperatures. This finding means that CLT loses efficacy due to the excess NCG. In addition, the start-up performances of the two modes decrease as the mass ratio of NCG increases to 0.31% and become entirely unacceptable when NCG reaches 0.47%. By contrast, the stopping time of CLT remains less than 100 s in various conditions. Results indicate that the mass ratio of NCG should be less than 0.47%, and CLT with NCG is suggested to be controlled by the valve in the vapour line.

Objective The aim of this study was to identify early warning signs for severe novel coronavirus-infected pneumonia (COVID-19).Methods We retrospectively analyzed the clinical data of 90 patients with COVID-19 at the Guanggu District of Hubei Women and Children Medical and Healthcare Center comprising 60 mild cases and 30 severe cases. The demographic data, underlying diseases, clinical manifestations and laboratory blood test results were compared between the two groups. Logistic regression analysis was performed to identify the independent risk factors that predicted severe COVID-19. The receiver-operating characteristic (ROC) curve of independent risk factors was calculated, and the area under the curve (AUC) was used to evaluate the efficiency of the prediction of severe COVID-19.Results The patients with mild and severe COVID-19 showed significant differences in terms of cancer incidence, age, pretreatment neutrophil-to-lymphocyte ratio (NLR), C-reactive protein (CRP) and the serum albumin (ALB) level (PConclusion An increased NLR can serve as an early warning sign of severe COVID-19.

The controllable loop thermosyphons (CLTs) can be widely applied in temperature control applications, such as cool-storage refrigerators powered by solar energy or electricity with the TOU (time of use) price. However, the performance of the CLT requires further optimization. In this study, a new CLT is designed and reservoir structure is adopted to improve the steady-state heat transfer performance. Three control modes are available to control the start-stop of the CLT and their influence on the start-stop performances is investigated. For each control mode, the valve location and test conditions are varied; results are compared and analyzed. Control mode A performs well and is affected weakly by the valve location. The control ability of control mode B is acceptable only when the valve is located on the lower liquid line. The start-stop performance of control mode C is better than that of control mode A and B; and with its best valve location, the CLT starts up quickly in approximately 25 s and stops in about 75 s under various test conditions. The experimental investigation revealed that control mode C is the optimal one and that valves are better to be installed in lower positions for all control modes.

Given that loop thermosyphons are widely used as simple and high-efficiency heat transfer devices, their passive heat transfer performance has attracted considerable research interest. The capability of loop thermosyphons for active heat transfer adjustment can potentially improve the precision and efficiency of heat and temperature management in many fields, but has not received much attention. A variable conductance loop thermosyphon (VCLT) is developed in this study. Heat transfer is precisely adjusted by actively regulating the internal flow resistance of the working fluid. The performance of VCLT under variable flow resistances is tested. The boundary conditions are set to those of a novel cool-storage refrigerator, wherein temperature control directly affects the freshness of stored food. VCLT behaviors under static and dynamic adjustment modes are also examined with the working fluid R134a. The maximum ratio of heat transfer adjustment is approximately 85%, when decreases the mass flow rate from 1.67 g/s to 0.21 g/s with increasing the equivalent thermal resistance from 0.0074 K/W to 0.54 K/W. Finally, the performance is verified with R404a, R407a and R410a. Results demonstrate that VCLT is an efficient and low-cost temperature adjustment device for refrigerators and other applications that require precise temperature control.

Controllable loop thermosyphon in frequently start-stop operation offers an efficient heat transfer regulation. This low-cost device has a great protentional in precise temperature management of refrigerators, industrial buildings, and cutting-edge equipment. In this study, a test platform is built to investigate the thermodynamic characteristics of controllable loop thermosyphon and its effectiveness on precise temperature control of a fresh-keeping box. The comprehensive behaviours in continuous and start-stop operations are explored using R407C, R410A, R404A and R134a as working fluids. The filling ratios for above refrigerants are optimised, and the influence of thermal boundaries are studied. Given a suitable filling ratio of R407C, the average fresh-keeping temperature is reduced from 25 °C to 5 °C in 90 min and to 0 °C in 180 min during continuous operation. In start-stop operation, a minimum fresh-keeping temperature fluctuation of ± 0.3 °C is achieved at various fresh-keeping temperatures. The maximum and average heat transfer rates in the running period are 74.0–94.5 W and 48.3–80.2 W, respectively. Results indicate that the controllable loop thermosyphon with R407C provides efficient heat transfer and thermal control, and thus perform well in precise temperature management.

A controllable separate heat pipe (CSHP) combined with cool storage can be an efficient and low-cost solution to release the necessary cool power and to improve the precision in the temperature control of cool-storage refrigerators powered by solar energy or electricity with time-of-use price policy. However, the precise temperature control performance of separate heat pipes under active control depends on system design and thus should be confirmed. In this study, a CSHP was developed and an active control method was achieved by interrupting its two-phase natural circulation flow. A one-dimensional steady-state model was used to calculate the critical fill ratio, heat transfer rate, and average working temperature of CSHP. A series of experiments was conducted to analyze the start–stop and heat transfer performances of CSHP at various R134a fill ratios and heat sink temperatures. Under different test conditions, the optimum working points were obtained through fitting. The most suitable control mode was determined and the start–stop performance of CSHP was examined in detail. CSHP starts up quickly in approximately 15 seconds and the quickest stopping time of CSHP approximates to 80 seconds. Therefore, the performance of CSHP under active control can be applied to cool-storage refrigerators.

Optimization in the geometry structure of the pulsating heat pipe (PHP) may provide an effective method to improve the heat dissipation capacity. In this study, tandem tapered nozzles are proposed to promote the unidirectional flow in a three-dimensional (3D) closed-loop PHP (CLPHP). For comparison, two six-turns CLPHPs comprised of 12 glass tubes with a 2 mm inner diameter (ID) and 13 silicone hoses with a 2.5 mm ID were examined to study the effect of tapered nozzles. Specifically, one (ordinary) had an equal glass tube ID, while the other one (asymmetrical) adopted glass tubes that had one tapered nozzle end formed by burning and melting the end from 2 mm into 0.95 mm ID. A series of experiments were performed to investigate the effects of filling ratios (ethanol) and heating powers on the thermal resistance, start-up time, and flow patterns. Results showed that the thermal resistance was reduced by 29.5% after the optimization, and the unidirectional flow was significantly promoted. Moreover, the dry-out phenomenon that happened in the ordinary CLPHP at the 40% filling ratio was also prevented in the asymmetrical one. Finally, we explain the variation trend of start-up time from the driving force theory. The present application of the tandem tapered nozzles in the 3D CLPHP provides an effective, reliable, and easy-to-implement method for improving the heat transfer performance, which leads to the direction for the future design of the PHP. © 2020 Elsevier Inc.

The influences of temperature on the performance of amorphous silicon (a-Si) solar cells and photovoltaic (PV) systems are extensively studied in the literature. The benefit from thermal annealing effect at a higher temperature than ambient has been demonstrated, which makes a-Si cells a promising material for photovoltaic/thermal (PV/T) system. However, the temperature-dependent performance of a-Si PV/T system in the long term operation has rarely been reported. The temperature effect will be more complicated than that on a single cell or PV system. Particularly, the exergetic efficiency and mechanical behavior of the PV/T system at different temperatures are unknown. To fill the above knowledge gap, two identical a-Si PV/T systems are developed. One operates at a water inlet temperature of 60 °C with an a-Si cell temperature of up to 70 °C. The other operates at an inlet temperature of 30 °C. Long-term outdoor tests from December 2017 to June 2019 have been conducted. Results indicate that the difference in the electrical efficiency between the two systems is 0.47% in the initial stage, and it gradually narrows to only 0.13% over time. The overall exergy efficiency at 60 °C generally exceeds that at 30 °C, which proves the superiority of the a-Si PV/T operating at medium temperature. Besides, the long-term operation at 60 °C has not led to a lower level of reliability.

Medium temperature solar thermal systems have a great prospect to be an efficient energy source for practical industrial applications. Although the evacuated flat solar collector is a potential non-concentrating collector for this application, current designs have not fully demonstrated its superiority. In this paper, a medium-scale (50.96 m2) solar thermal system based on an efficiently optimized evacuated flat plate solar collector structure is designed. A systematic four months long real-time experiment under the natural environment is conducted for medium solar thermal applications in a region with four distinct seasons. An annual performance analysis is then conducted in four different locations through a validated numerical model. Experimental results demonstrate that, when the inlet temperature is 123.0 °C, the ambient temperature is 35.7 °C and the solar irradiation is 835.2 W/m2, the thermal efficiency and exergy efficiency can reach 59.67% and 14.35%, respectively. The efficiently optimized evacuated flat plate solar collector can also achieve a stable annual average thermal efficiency at the four studied locations with values reaching up to 50%. Therefore, the superiority of this efficiently optimized evacuated flat plate solar collector design over previous ones is demonstrated.

Medium temperature photovoltaic/thermal (PV/T) systems have immense potential in the applications of absorption cooling, thermoelectric generation, and organic Rankine cycle power generation, etc. Amorphous silicon (a-Si) cells are promising in such applications regarding the low temperature coefficient, thermal annealing effect, thin film and avoidance of large thermal stress and breakdown at fluctuating temperatures. However, experimental study on the a-Si PV/T system is rarely reported. So far the feasibility of medium temperature PV/T systems using a-Si cells has not been demonstrated. In this study, the design and construction of an innovative a-Si PV/T system of stainless steel substrate are presented. Long-term outdoor performance of the system operating at medium temperature has been monitored in the past 15 months. The average electrical efficiency was 5.65%, 5.41% and 5.30% at the initial, intermediate and final phases of the long-test test, accompanied with a daily average thermal efficiency from about 21% to 31% in the non-heating season. The thermal and electrical performance of the system at 60 °C, 70 °C and 80 °C are also analyzed and compared. Moreover, a distributed parameter model with experimental validation is developed for an inside view of the heat transfer and power generation and to predict the system performance in various conditions. Technically, medium temperature operation has not resulted in interruption or observable deformation of the a-Si PV/T system during the period. The technical and thermodynamic feasibility of the a-Si PV/T system at medium operating temperature is demonstrated by the experimental and simulation results.

The concept of hybrid utilization of daytime photovoltaic (PV) conversion and nighttime radiative cooling (RC), namely, PV–RC, was proposed and experimentally demonstrated. A PV–RC hybrid module with a size of 1380 mm × 720 mm was manufactured and characterized, and a corresponding PV–RC hybrid system was established. The PV–RC hybrid system can generate electricity at daytime by PV conversion and simultaneously obtain cooling energy by nighttime RC. PV performance of the hybrid system was tested on a mostly sunny day, and measured results showed that the daily average electricity output and electrical efficiency were 94.0 W·m −2 and 14.9%, respectively. Besides, nighttime RC performance of the hybrid system was measured on a mostly clear night sky and net cooling power of the PV–RC system was evaluated as 72.94 W·m −2 when temperature of the PV-RC panel was equal to ambient air temperature. Furthermore, a validated thermal analysis model was used for parametric study and results show that nighttime RC performance will be enhanced by dry atmosphere and low parasitic cooling loss. In summary, this work presented an experimental and simulation study for PV–RC hybrid system, which acts as a demonstration project of a real system. This study is a new attempt towards a real-world application of comprehensive utilization of solar energy and RC, which provides a good choice for cooling demand dominated buildings.

The Mengxi-Tianjingnan 1000kV UHV project will put into operation in 2016; the power grid of Beijing will be injected and consumed the UHV. But the three-phase short-circuit current of 500kV Shun Yi station may exceed its breaking capacity, and also the operating characteristics of the peripheral placement of UHV grid will change significantly. In order to better respond to the effect of UHV power grid bring access to Beijing, the two-port power equivalent theoretical analysis is used in this paper, and next the BPA power system analysis software is used to simulate and verify the Beijing power grid. And then the reasons of excessive short-circuited and interaction effects of all voltage levels of short circuit current are analyzed. The different current limited measurements are analyzed and compared. At last, the current limitation measures of Beijing power grid are put forward, which provide the technical support for the grid operation.

Battery state of charge is related with available capacity. Battery available capacity varies with discharge current. Peukert's equation is a good way to estimate available capacity. But the practicability of Peukert's equation for Li-ion battery has to be verified. Especially, available capacity of Li-ion battery is influenced by temperature obviously. In this paper, discharge experiments under different current are undertaken at room temperature 25℃, and the Peukert coefficients n and k are calculated by available capacities and discharge times at the maximum discharge current and the minimum current. The result indicates battery available capacity estimated by Peukert's equation is practical in 25℃. In order to verify the practicability of Peukert's equation for Li-ion battery at low temperatures, these discharge experiments are done at low temperature. The result indicates, at low temperatures, Peukert's equation is practical for Li-ion battery at low current and unpractical in high current. An improved Peukert's equation with Temperature Correction Factor for the Li-ion battery is proposed. The calculated data catch well with experimental data.

Based on a randomly mixed model, in which the constituent parts of the multi-phase medium are all cubic in shape, uniform in size and randomly dispersed, the effective thermal conductivity of the medium is obtained from the thermal properties and volume fractions of the components. Compared with the experimental data, the present model can give fine predictions of the effective thermal conductivity of soils. Factors related to the thermal conductivity and heat storage coefficient of the soil are investigated, and the results show that the effective thermal properties of the soil dependent on the type of soil, the porosity, the degree of saturation and the state of the water. In addition, the difference of the thermal characteristics between the frozen and unfrozen soils is discussed.

For the efficiency problem of contactless charging in type of electromagnetic induction, this paper establishes a mathematical model of contactless charging in type of electromagnetic induction and the theoretical derivation. This contactless charging simulation model is founded by Matlab/Simulink, which uses the frequency of PWM generator, the mutual inductance value of the coil and load resistance of RL to simulate some conditions, such as the working frequency in practical work, the distance of coil, whether the coils are directed at the central, and changing of loads. Then through the influence of the changing frequency, load and mutual inductance, contactless charging in type of electromagnetic induction is analyzed. By the whole simulation experiment on contactless charging, the theory deduced from the mathematical model is verified, and the method to improve inductive contactless charging is proved.