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High-temperature cascade heat pump has remarkable development potential for industrial heat generation due to its superiority in energy-saving and environment friendly. But the growing demand for higher temperature difference heating challenges the traditional cascade heat pump. One of practical solutions is the combination of cascade system and vapor injection technique. However, the introduction of vapor injection increases the complexity of the system, and the interaction between branches and the distributions of branches are to be studied to give full play to the best performance of the vapor injected cascade system. This paper focuses on temperature stage matching between the heat exchange branches of a cascade air source heat pump with vapor injection to get optimal heating performance. The optimal configurations of intermediate temperature and vapor injection branch temperature are obtained based on the optimal method. A cascade heat pump prototype with refrigerant R245fa and R410A is developed and investigated experimentally to verify the optimization method. The cascade air source heat pump could realize 140 °C heat supply and the coefficient of performance is from 1.16 to 1.58 under the ambient temperature of from −10 °C to 20 °C.

Magnetic field assisted freezing is a kind of freezing methods that can improve food quality. The objective of this study is to evaluate the effects of various magnetic field type and intensity on cherry during the freezing process. The permanent magnetic field (PMF) ranging from 0 to 20 mT and the alternating magnetic field (AMF) ranging from 0 to 2 mT were applied on the cherry. The final temperature and cooling rate of the frozen environment were −30 °C and 4 °C/min. The freezing parameters, which included the macro indexes and microstructure, were used to evaluate the freezing quality. The results show that the freezing temperature was significantly higher in the presence of AMF compared with the control group (p

This study conducted an experimental investigation on a CO2 transcritical refrigeration system with dual rotor and intermediate cooling compressor (ICC) for automobiles. Based on the typical operating conditions, the performance of the system with ICC was analyzed by comparison with the basic cycle. The results show that the performance of the system with ICC is roughly equivalent to that of the basic cycle under the condition of 35 °C ambient temperature, while it has outstanding superiority under the condition of 45 °C, with 19.8% increment in the maximum cooling capacity and 12.8% increment in the maximum COP, respectively. The effect of the system’s dynamic components on the immediate cooing is analyzed. According to the analysis of experimental data, it is figured out that the trend of the cooling capacity is consistent with the change trend of the inlet temperature of electronic expansion valve (EEV) and there exists an inflection point with adjustment of EEV.

The microchannel heat exchanger is applied as the heat exchanger of the thermosyphon for data center cooling, and the evaporative cooling experiment is carried out on the side of the microchannel condenser. The influence of evaporative cooling on the microchannel condenser is measured by using the enthalpy different laboratory in the experiment, and the temperature difference between the inlet and outlet air of the microchannel condenser and with different indoor and outdoor temperature and humidity was analyzed. The experimental results show that evaporative cooling can make the condenser inlet air temperature achieve a large temperature drop and increase the temperature drop of the inlet and outlet air, while the spraying can cool the air through the thermosyphon about 0.3-1.9 degrees and increase about 0.1-0.6kW heat transfer of the system. Moreover, the evaporative cooling can improve the heat exchange efficiency of condensers, expand the application area of the loop thermosyphon and extend the annual utilization time.

In this paper, the heating performance and flow distribution of a vapor injection air source heat pump (ASHP) designed for electric buses is experimentally investigated under different working conditions by adjusting the opening of main-branch electronic expansion valve (EEV1) and injection-branch electronic expansion valve (EEV2). Under the condition of fixed EEV1 opening, the injection mass flow rate increases nearly linearly with the increasing of EEV2 opening and the main-branch mass flow rate has slight increase about 8.5%. The heating capacity increases with the increasing of injection ratio and there exists an optimum injection ratio to get the maximum COP 1.90. Under the condition of fixed EEV2 opening, the injection ratio decreases with the increasing of EEV1 opening. The heating capacity and COP both reach the maximum at 0.193 injection ratio, corresponding to 3.8C superheat of evaporator.

Linear compressor technology employed in refrigerator shows more energy-saving potentiality, for its compact design, high efficiency and excellent variable cooling capacity. The linear compressor is designed in resonance condition to reduce the input current required, so the dynamic parameters identification for linear compressor would make a positive contribution to a better performance prediction and efficiency operating. While the valves' motion coupled with the free piston structure in linear compressor, which make the gas force is nonlinear and harmonic distortion. It caused the dynamic parameters of linear compressor time varying and nonlinear. Hence the natural frequency estimation seems an impractical task in time domain due to the nonlinear gas force. As the linear oscillating motor has an ability of restricting high harmonics, the natural frequency estimation in frequency domain is practicable. In this paper, we generalize the Fourier Series Analysis applied for linear compressor vibration analysis, including the application for the gas force linearization, the signal processing and the natural frequency estimation. We established a test bench in a refrigerator control system with Fourier Series Analysis for the signal processing and the natural frequency estimation. The effective voltage, the effective current and the power measured by discrete Fourier transform (DFT) method agree well with the results measured by an electricity parameter meter, and the linear motor efficiency achieves a value of 95% in the refrigerator by tracking the nature frequency estimated in frequency domain.

Leakage from pressurized liquid ammonia pipeline has been a serious problem in large commercial cold storages because it might release large amount of liquid ammonia and without safety supervision in daily operations. The present paper shows a detection method for a pressurized liquid ammonia pipeline with a leak. The variations of pressure, flow rate and pressure difference profile are studied. A leak indicator (σ), proposed with the one-dimensional steady-state flow model, is used to detect the leak occurrence by comparing it with a threshold value (σLe). A locating algorithm based on pressure difference profile along the pipeline is also proposed, which has considered the effect of the static pressure increase at the leak point. Experiments on different leak positions and ratios from liquid R22 and ammonia pipelines are carried out to validate this method. It is found that, with a relatively low false alarm rate (as three percent), the minimum detectable leak ratio reached 1% for the R22 pipeline and 4% for the ammonia pipeline. The locating errors are between −27% ~ 17% for R22 pipeline and −27% ~ 27% for ammonia pipeline.

The energy consumption of HVAC&R systems is increasing rapidly, and application of hybrid source systems is an alternative solution. Utilizing three-fluid heat exchanger in hybrid source HVAC&R system can make the system more compact in construction, higher in thermal efficiency and lower in reliability risk. In this paper, a simulation model of a fin-tube three-fluid heat exchanger is built with distributed-parameter method and validated by experimental data. Based on the demand of a new type of hybrid source system, the optimal circuit arrangement type and tube diameter are achieved. The heat transfer rates of the three fluids under different working conditions are investigated. The results also show that to ensure that cold fluid 1 is superheated in the outlet for the stable running of the system, flow rate and inlet pressure of the hot fluid and air inlet temperature should be higher than certain values, while flow rate and inlet pressure of cold fluid 1 should be lower than certain values. Air flow rate can be adjusted freely without range limit. This paper will help the design of fin-tube three-fluid heat exchanger and promote its application in HVAC&R systems.

Wave energy is one of the most promising renewable energy for power generation. This research develops a novel power take-off methodology to surmount the problems associated with mooring, seawater corrosion and access for maintenance in conventional WEC (wave energy converters) with direct-driven linear generators. Its prototype consists of two bodies, the floating body acting as a buoy to extract the wave energy, while the inner body undergoes a forced oscillation, whose relative motion generates the electronic power. Its feasibility is investigated theoretically by coupling the dynamics of the wave, the floating and the inner bodies and the electromagnetic characteristics of the linear generator. As a result, the generator can induce a highly sinusoidal voltage. Furthermore, the performance of the system is investigated in detail under different conditions. The results show that, a resonance has been achieved in the case with the spring constant of 12,633 N/m, with a maximum power capture ratio of 57%. The performance of the system is shown to be sensitive to the load resistance, the wave height, and the spring constant.

The cooling energy consumption of data centers is increasing rapidly and free cooling attracts growing concern. To achieve the independent running of free cooling system all the year round, integrated system of mechanical refrigeration and thermosyphon (ISMT) is an ideal method. In this study, a distributed-parameter simulation model of an ISMT is built and validated by experimental data. The simulation results show that for thermosyphon mode, the cooling capacity increases with increasing air flow rate, temperature difference and pipe diameter, while decreases with increasing pipe length. For refrigeration mode, decreasing outdoor air temperature or increasing indoor air flow rate will improve the cooling capacity and reduce the input power of the compressor. For dual mode, applicable outdoor temperature range and indoor air flow rate range exist and the cooling capacity drops below that of refrigeration mode beyond these ranges. The critical values are 19 °C and 0.5 m 3 s −1 , respectively.

Since the performance of conventional air source heat pump (ASHP) for electric vehicles (EVs) is apt to decline sharply in low ambient temperature, it will consume more electricity of the cell, and affect driving mileage in cold regions. Aiming at developing high efficiency heating system for EVs in cold regions, an ASHP system applying refrigerant injection for EVs is designed, as well as the test bench is built to investigate its performance. According to the operation condition of EVs, heating performances are tested on different in-car inlet air temperature and various fresh air ratios under −20 °C ambient temperature. The system cycle process with refrigerant injection, as well as the influences of refrigerant injection and dryness are also analyzed and discussed. The results show that the heating capacity of the ASHP with refrigerant injection can be increased up to 31%, and in comparison with the conventional heat pump system its heating performance is better when in-car inlet temperature is above −10 °C. Therefore, ASHP with refrigerant injection has great potentiality to be applied for the EVs in cold regions.

Photolyase repairs UV-induced lesions in DNA using light energy, which is the principle of photoreactivation. Active photolyase contains the two-electron-reduced flavin cofactor. We observed that photoreactivation of Escherichia coli was impaired at growth temperatures ⩾37°C, and growth in this temperature range also resulted in decreased photolyase protein levels in the cells. However, the levels of phr transcripts (encoding photolyase) were almost unchanged at the various growth temperatures. A lacZ-reporter under transcriptional control of the phr promoter showed no temperature-dependent expression. However, a translational reporter consisting of the photolyase N-terminal α/β domain-LacZ fusion protein exhibited lower β-galactosidase activity at high growth temperatures (37-42°C). These results indicated that the change in photolyase levels at different growth temperatures is post-transcriptional in nature. Limited proteolysis identified several susceptible cleavage sites in E. coli photolyase. In vitro differential scanning calorimetry and activity assays revealed that denaturation of active photolyase occurs at temperatures ⩾37°C, while apo-photolyase unfolds at temperatures ⩾25°C. Evidence from temperature-shift experiments also implies that active photolyase is protected from thermal unfolding and proteolysis in vivo, even at 42°C. These results suggest that thermal unfolding and proteolysis of newly synthesized apo-photolyase, but not active photolyase, is responsible for the impaired photoreactivation at high growth temperatures (37-42°C).

The electromagnetic transduction coefficient has a strong influence on efficiency as well as the sensorless control of linear oscillation electrical machine (LOEM). This paper presents a reciprocal LOEM method for measurement of the electromagnetic transduction coefficient, to investigate the effect of the magnet length on the characteristics of the transduction coefficient. The result shows that the transduction coefficient has two regimes, a constant regime and a nonlinear regime. As the harmonic distortion begins to appear in the induced electromotive force, the electromagnetic transduction coefficient passes from the constant regime to the nonlinear regime, and the corresponding stroke is defined as critical stroke. The range of constant regime equals the observed critical stroke, and the critical stroke is 8.81 mm and 10.78 mm when the length of the permanent magnet is 11 mm and 13 mm respectively. The relationship among the geometrical dimension of yoke and permanent magnet, the critical stroke and the stroke of the LOEM are carefully investigated. Then optimal lengths for both the yoke and the permanent magnet are suggested for the LOEM design with the rated stroke, to achieve the highest efficiency and least material cost simultaneously.

The number of data centers is increasing rapidly in recent years. Huge amount of energy is consumed by the cooling equipment of data centers for its year round working. Cutting down the energy consumption of cooling equipment becomes an urgent need and free cooling is an ideal way. It is proposed an integrated system of mechanical refrigeration and thermosyphon (ISMT) by combining two independent loops, mechanical refrigeration loop and thermosyphon loop, with a three-fluid heat exchanger. The new ISMT has three modes: mechanical refrigeration, thermosyphon free cooling and dual mode. The experimental results show that it has sufficient cooling capacity of all these three working modes. The EER of the thermosyphon mode reaches 10.7 and 20.8 when the indoor and outdoor temperature difference is 10 °C and 20 °C, respectively, and the AEER of the ISMT is 12.6, which is much higher than traditional air conditioners (TAC). The annual energy consumption in four cities located in different climate zones of China is calculated and compared to TAC in a small data center. The annual energy-saving rate is 5.4%–47.3% when the indoor temperature is set on 27 °C, and it is higher in colder zones for longer working time of thermosyphon free cooling.

Cryptochromes (CRYs) and photolyases belong to the cryptochrome/photolyase family (CPF). Reduced FAD is essential for photolyases to photorepair UV-induced cyclobutane pyrimidine dimers (CPDs) or 6-4 photoproducts in DNA. In Drosophila CRY (dCRY, a type I animal CRY), FAD is converted to the anionic radical but not to the reduced state upon illumination, which might induce a conformational change in the protein to relay the light signal downstream. To explore the foundation of these differences, multiple sequence alignment of 650 CPF protein sequences was performed. We identified a site facing FAD (Ala377 in Escherichia coli CPD photolyase and Val415 in dCRY), hereafter referred to as "site 377", that was distinctly conserved across these sequences: CPD photolyases often had Ala, Ser, or Asn at this site, whereas animal CRYs had Ile, Leu, or Val. The binding affinity for reduced FAD, but not the photorepair activity of E. coli photolyase, was dramatically impaired when replacing Ala377 with any of the three CRY residues. Conversely, in V415S and V415N mutants of dCRY, FAD was photoreduced to its fully reduced state after prolonged illumination, and light-dependent conformational changes of these mutants were severely inhibited. We speculate that the residues at site 377 play a key role in the different preferences of CPF proteins for reduced FAD, which differentiate animal CRYs from CPD photolyases.

The present work aims to investigate the effect of miscible oil on the flow boiling heat transfer characteristic of ammonia in a 4 mm horizontal smooth tube. In contrast to conventional immiscible oil leading to serious deterioration in heat transfer, the results show that the miscible oil with oil concentration of 1.95% has almost no influence on the heat transfer. For the higher oil concentrations (i.e., 3.99% and 5.78%), the heat transfer coefficient of ammonia-oil mixture also appears to be remarkably similar to that of oil-free condition first, and then shows a slight deterioration trend when the vapor quality is high. Meanwhile, 13 heat transfer correlations are evaluated, and the comparison results indicate the Gungor and Winterton correlation (1987) could give a fair prediction for the experimental data even though it is developed for turbulent flow. Finally, a new correlation is developed with consideration of laminar flow and thermophysical properties change, and it can remarkably improve the prediction accuracy for the experimental data.

The rack-backdoor cooling technology used with a vertical microchannel evaporator of a loop thermosyphon system has a great application prospect in data center cooling. Thus, investigating the evaporator’s performance is necessary especially under inhomogeneous air-side conditions according to the actual operation scenarios of the rack. This study establishes a multiple heat source physical model of a 42U rack and the mathematical models of rack cooling on the basis of actual products. The entire heat transfer and temperature distribution are verified. After being heated by servers and before entering an evaporator, inhomogeneous air temperature and flow velocity data can be obtained with the physical rack model. The maximum difference is up to 6 °C and 0.6 m/s. The air temperature on top is 0.6 °C higher than that at the bottom of inside the rack due to the thermal lift in the vertical direction. The mathematical model indicates that the maximum difference of the refrigerant vapor quality among vertical tube outlets can reach 0.14, whereas the maximum air-side temperature difference of the evaporator outlet is 9.5 °C. These simulation results can provide effective guidance for the optimization design and application of vertical microchannel evaporators.

In order to enhance the heat transfer performance of spray cooling system, an integrated system is developed. The system is based on the refrigeration cycle, and uses isobutane (R600a) as the coolant. The heat transfer performance, such as the heat surface temperature, the heat transfer coefficient and the surface temperature distribution, are experimentally investigated in this paper. When the coolant mass flow rate is nearly 6.9 kg/h, the surface temperature can be kept at 57.3 °C with the heat flux of 145 W/cm2. The heat transfer coefficient can be achieved up to 35,000 W/(m2 °C) when the nozzle inlet pressure and the chamber pressure are 4.9 bar and 2.3 bar, respectively. The surface temperature uniformity is mainly influenced by the mass flow rate, the heat flux and the nozzle inlet pressure together, and the standard deviation of the surface temperature is less than 4.0 °C in this study. All the results indicate that this system is promising in the application for high heat flux removal.

In this paper, the possibility on electro-osmosis regeneration of macro-porous silica gel (MSG) desiccant has been investigated by testing the adsorption and electro-osmosis characteristic. The measured saturated moisture content of MSG is 113% in 300 K temperature and 95% relative humidity. Its zeta potential is −10.92 mV, which shows it has both good moisture absorption and electro-osmosis characteristic. The experiment bench is built to test the electro-osmosis regeneration performance on MSG by means of changing initial moisture content (105% and 110%) and applied voltage (40 V, 50 V and 60 V) respectively. The D -value of moisture content between the bottom and upper half with voltage is much higher than that without voltage. For the 110% initial moisture content, there are many visible condensing water droplets on the inside surface of plastic film under the cathode. Based on experimental results, it can find electro-osmosis flow exists when the moisture content is lower than the saturated moisture content. Besides, the electro-osmosis regeneration is one potential method of MSG desiccant when it is applied in dehumidification.

The experimental studies of fin-tube type internally-cooled dehumidifiers are still limited until now. In the present paper, the performance of a cross-flow internally-cooled dehumidifier is studied by both of experiment and simulation. The dehumidifier is made up of fin-tube heat exchangers with high corrosion resistance. Compared with the dehumidifier of the literature, it is found that the dehumidifier of this work performs well in terms of the dehumidification efficiency. Meanwhile, the heat transfer coefficient is correlated on the basis of the experimental data. By applying the correlated coefficient, the theoretical model can predicate the performance of the dehumidifier with an acceptable accuracy. Then the validated model is employed to give suggestions for optimizing the geometry design and operating conditions of the dehumidifier. Through calculation, it is discovered that the best length of the air flow direction for the present dehumidifier is about 0.3 m. In addition, the ratio of solution to air flow rate can be decided by the simulation as well.

The stroke and natural frequency are key controlling quantities for linear compressor controller. This paper proposes a phasor algorithm for the linear compress stroke and natural frequency calculation. The phasor algorithm employs vectors to express the voltage, current and velocity respectively for the calculation in frequency domain. A test bench has been installed, and the feasibility of phasor algorithm is verified with the linear compressor load changing. The relative deviation of the calculated stroke can be achieved within ± 3% compared to the experimental results at 0.4 MPa, 0.5 MPa and 0.6 MPa discharge pressure respectively. The calculated results shows that the computation time of phasor algorithm is one-third shorter than that of time domain algorithm, which means it is possible to employ relatively low energy consumption and low cost hard ware. The calculation natural frequency decreases with the stroke increases at 0.4 MPa, 0.5 MPa and 0.6 MPa discharge pressure respectively, and the tested motor efficiency reaches a maximum when the calculated natural frequency equals to the operating frequency.

A whole-process simulation platform is established for linear compressor to analyze the performance characteristics on different piston displacement conditions from small oscillation without pumping till to rushing out of the top dead center (TDC). The measuring methods of the related parameters in the model are presented and the values of these parameters are obtained from an actual test. The simulated results agreed well with the experimental results under the same working conditions. The errors of the effective voltage, the effective current, the compression efficiency and the phase angle between the current and the displacement were within ±6.9%, ±8.5%, ±6.2% and ±13.4%, respectively. Based on this simulation platform, the performance characteristic around the TDC of the linear compressor on different working conditions is analyzed. The performance comparison on 60 Hz shows that the compression efficiency near to the TDC on 0.7 MPa is higher than that on 0.5 MPa because the phase angle α under that condition is around 90°, but the operation reliability on 0.7 MPa is worse than that on 0.5 MPa because the jump phenomenon happens when the piston displacement goes near to the TDC. The jump phenomenon results in unstable operation as the piston displacement jumps from the position before the TDC to the position after the TDC. According to the simulation on different power frequency, two important performance characteristics are inferred. One is that there is an inflection point in the curve of the phase angle α versus the displacement at the TDC. This characteristic is a good choice for the TDC detection. The other is that the jump phenomenon is prone to happening when there exist different displacement responses on the same voltage value, becoming inconspicuous when the power frequency is decreased and disappearing when the power frequency is increased. Based on this characteristic, the jump phenomenon can be avoided through suitable system configuration and frequency adjustment.

The growing demand for electricity and the increasing size of the carbon footprint of data centers worldwide bring a severe challenge to sustainable development of human civilization. The cooling energy consumption takes up around 30–50% of the total consumption of data centers due to the inefficient cooling system. Free cooling is an effective solution for reducing the power consumption of cooling systems. This paper reviews the advancements of data center free cooling mainly focusing on configuration features and performances. Three kinds of free cooling methods, airside free cooling, waterside free cooling and heat pipe free cooling are discussed and performance characteristics of each are analyzed. Further, the criteria of performance evaluation for free cooling of data centers are summarized, and an overview of free cooling systems based on these criteria is demonstrated in order to help researchers acquire the latest developments in this area.

The huge energy consumption of data centers has reached 416.2 billion kWh of electricity, which is responsible for 2% of the world’s total electricity consumption in 2017. Data center heat recovery for district heating is one of the most promising methods to reuse data center low grade waste heat. This paper proposes a heat recovery system with a heat pump/heat pipe integrated unit based on three-fluid heat exchanger. The system operates in three modes: heat recovery mode, heat pipe mode and mechanical cooling mode. Experimental results show that the comprehensive energy efficiency ratio of heat recovery mode reaches 4.47 when the heating supply water temperature is 50 °C. Annual performance of the heat recovery system in a 5 kW data center is analyzed in Tianjin. Results show that the comprehensive energy efficiency ratio of the whole system throughout the year is 4.75, which indicates great potential in heat recovery for district heating at cold regions.

In this study, a novel integrated thermal management (ITM) system combining vapor injection (VI) with battery heat dissipation was proposed. The model of this novel system was developed and validated. On this basis, the effects of injection pressure, battery heat dissipation, and ambient temperature on the heating performance of the novel system were analyzed. Results showed that a maximum COP based on injection pressure existed for the novel ITM system. Compared with the basic vapor injection system, heating capacity and COP of the ITM system with 1 kW waste heat corresponding to the optimum injection pressure were increased by 13.57% and 7.88% at the ambient temperature of −20 °C, respectively. With the increase in battery heat dissipation from 1 kW to 3 kW, heating capacity and COP were improved by 25.81% and 10.80% at the ambient temperature of −20 °C, respectively. The heating performance improvement of the novel ITM system over the basic VI system gradually diminished with increasing ambient temperature.

Linear compressors have received more and more attention for their compact structure and high efficiency. They are highly sensitive to the working condition, thus the control system is essential to ensure linear compressors are able to operate reliably and efficiently. Operating in a resonant state would improve linear compressor efficiency, while the natural frequency is also sensitive to the operating condition. This paper proposes the analysis of energy transfer process during linear compressor operation. Compared with force analysis, energy analysis uses the electromechanical analogy to show the energy conversion from electrical energy into mechanical energy during linear compressor operation. The principle for the control to achieve high efficiency is proposed and verified in a refrigeration system. The result shows it is practical and reliable to applied energy analysis in the control of linear compressor to achieve highly efficient driving.

Based on the trade data and three international competitiveness evaluation indexes, namely, international market share, trade competitive index and revealed comparative advantage index, this paper analyzes the international competitiveness of Chinese publishing industry from horizontal and vertical dimensions. The results show that, the international competitiveness of Chinese publishing industry is enhanced year by year. However, compared with the USA, the UK, Germany and other developed countries, it is still significantly weaker, and the gap between each other has the potential to expand.

A multi-unit heat pump is presented for simultaneous humidity and temperature control to improve the energy efficiency and the thermal comfort. Two parallel connected condensers are employed in the system, locating at the back of the indoor evaporator and the outdoor unit, respectively. The heat pump can operate in four modes, including heating, cooling and dehumidification without and/or with partial or total condensing heat recovery. The experimental investigation shows that the temperature control capacity is from 3.5 kW for cooling to 3.8 kW for heating with the cooling and heating efficiency higher than 3.5 kW kW−1, and the dehumidification rate is about 2.0 kg h−1 with the efficiency about 2.0 kg h−1 kW−1. The supply air temperature and humidity can be simultaneously regulated with high accuracy and high efficiency by adjusting the indoor and/or outdoor air volumes. It provides an integrated and effective solution for simultaneous indoor air temperature and humidity control for all-year-round operation in residential buildings.

Nanofluids show clearly a very interesting alternative for working fluids of microchannels. This paper presents an experimental study on heat transfer and flow features of Al 2 O 3 –water nanofluids through a circular microchannel with the 0.5 mm inner diameter. Al 2 O 3 –water nanofluids with particle volume concentrations of 0.25%, 0.51% and 0.77% are prepared. The effect of particle concentration and Reynolds number on the heat transfer and flow features of nanofluids-cooled microchannel are examined and then compared with the data for water-cooled microchannel. The results show that Nusselt number of Al 2 O 3 -water nanofluids is higher than that of deionized water, and increases with increasing Reynolds number and particle concentration. The maximum heat transfer enhancement achieves 10.6% in the test conditions. Meanwhile, the enhancement effect is more apparent at higher Reynolds number in the range of laminar flow. A Nusselt number correlation for nanofluids flowing in microchannels is proposed, and the predicted Nusselt numbers agree with the experimental data with deviations of −4% and +5%. The friction factor of the nanofluids has an increase within 7.9% compared with that of deionized water. A friction factor correlation is proposed, and the predictions agree with the experimental values with deviations of −3% and +5%.

In this paper, the electro-osmotic flow (EOF) in micro-porous media is investigated regarding to the flow rate caused by the combined effect of electro-osmosis force and the gravitational force. It is noticeable that the actual electro-osmosis pumping force can be achieved at flow rate of 10 μL/min in our designed system. With a constant external DC electric field supplied, in which the external electric field exerts the same effect of voltage density on the whole particle interface, the flow resistance inside the pores deceases when water entering into the electro-osmosis pumping section. Moreover, the mass flow rate by the effect of electro-osmosis pumping can be achieved at 1.49 × 10−4 g/s under 5 V DC supply. To simplify the practical flow pattern in the micro-porous media, a specific micro-channel is assumed with a compact spherical stacking-up model. To simulate this geometrical model, a modified lattice Boltzmann method is set up in order to form the electro-osmotic flow of a practical problem from our experiment. The numerical results are obtained and analysed for fitting the present model with the micro-porous media. Both the experimental and numerical results have provided some useful instructions of electro-osmosis performance for designing micro-porous channels in such as filtering the compounds of drug delivery, particle purification and liquid separation applications etc.

Moving-magnet linear compressors with sensorless top dead center (TDC) control method are an efficient solution for domestic refrigerators to save energy. TDC can be determined by the inflection point of phase difference between the sinusoidal current and piston displacement (I-Xphase difference). A digital correlation method is used to calculate theI-Xphase difference to obtain the TDC position for control. The TDC determining system using digital correlation method is manufactured and the error is 2.29% under various discharge pressures.

The corrosion problem of traditional liquid desiccants hinders the development of solar liquid desiccant air conditioning system. Ionic liquids (ILs) could be a possible substitute because of their low corrosion to metals. According to the characteristic of cation and anion, two ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and 1,3-dimethylimidazolium acetate ([Dmim]OAc) were selected for possibility investigation. The experimental results demonstrated that the surface vapor pressure of [Bmim]BF4 aqueous solution was so high that it was not suitable for dehumidification. With comparing the structure of [Bmim]BF4 and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), it was found that for imidazole salts with the same anion, as the alkyl chain of the cation becomes shorter, the surface vapor pressure of its aqueous solution would be lower. In addition, simulation model was used to compare the dehumidification performance of [Dmim]OAc and [Emim]BF4 with that of the traditional desiccants lithium Chloride (LiCl) and lithium bromide (LiBr). The results showed that in the same condition, [Dmim]OAc with an inlet mass concentration of 81.7% and [Emim]BF4 of 85.5% could reach the same dehumidification rate as LiCl of 40.9% and LiBr of 45.0% mass concentration. Better dehumidification performance of [Dmim]OAc than that of [Emim]BF4 was achieved, thus, like [Emim]BF4, [Dmim]OAc can also be a promising substitute for traditional desiccant.

Multi-unit air conditioners (MUACs) are widely used in light commercial buildings and residential buildings due to their higher thermal comfort and energy efficiency. To investigate the transient characteristics of MUACs, a dynamic simulation model with the framework of two-phase fluid network is developed. The state-space forms are used to model the system and components, and the component submodels are embedded in the fluid network model, which makes it possible to update the system model and components submodels independently. In the model of state-space form, the differentials are obtained by taking the inverse of coefficient matrix, and then the state parameters are calculated by integrating the differentials with time. The simulation outputs are compared with the experimental data in the step changes of the compressor speed and electronic expansion valve openings. The comparison shows that the proposed model can catch the dynamic characteristics of MUACs with high accuracy. Therefore, it can be used as an effective tool to analyze the transient performance and optimize the control algorithm of MUACs.

Some ionic liquids have dehumidification capacity and are non-corrosive to metals. Based on the Finite Difference Method, the heat and moisture transfer model of the counter-flow dehumidifier was established. Using this model, the dehumidification capacity of one kind of ionic liquids 1-Ethyl-3-methylimidazolium Tetrafluoroborate ([EMIM]BF4) and traditional desiccant lithium bromide (LiBr) was compared in equivalent conditions. The results show that the dehumidification performances of the two solutions both improve with the increase of air flow rate, solution flow rate and air humidity. Even though the dehumidification rate of [EMIM]BF4 is a little lower than that of LiBr, such difference could be reduced by increasing the mass concentration of [EMIM]BF4. Meanwhile, compared with traditional desiccants, [EMIM]BF4 solution has significantly lower corrosion to metals and does not crystallize at high mass concentration, which render it a possible substitute of existed desiccants in liquid desiccant air conditioning systems.

The dual-cylinder opposed linear compressor (DOLC) contains a couple of symmetrical gas loads on the two sides of the movement components. Because the gas loads are symmetrical, the balanced position of movement components will not be offset by gas force during the operating process, and piston displacement can be detected and controlled more easily. Based on the kinetics and thermodynamics theory, the non-linear gas load of the DOLC was linearized by the Fourier method. The relationship between the supply voltage and displacement is presented. Through air compression experiments, the operation features of the DOLC with different syntonic spring groups were analyzed. The performance of the DOLC was considerably affected by work conditions and the stiffness of syntonic spring groups; the closer the work condition was to the sympathetic vibration, the higher the observed efficiency of the DOLC. A jump, hysteresis, and an unstable phenomenon in the process of voltage regulation occurred around sympathetic vibration conditions. In the process of increasing voltage on a certain discharge pressure condition, the displacement jump phenomenon occurred when the intrinsic frequency approacheds power frequency, causing the discharge pressure to drop synchronously. In the process of decreasing voltage on the lower discharge pressure condition, the displacement shrink phenomenon occurred when the intrinsic frequency approached power frequency. Because sympathetic vibration conditions changed with discharge pressures, a hysteresis district existed between the displacement jump point and shrink point. The DOLC worked unstably on the hysteresis district because the discharge pressure fluctuated between the two values. To make the DOLC work stably on higher efficiency, the intrinsic frequency should be configured to a slightly larger value than the power frequency by setting the syntonic spring groups and the mass of movement components to the ratings on the work conditions. Controlling the power frequency after is needed to adhere to the intrinsic frequency of the variable work conditions.

Electro-osmotic regeneration for the solid desiccant has been proved to have many merits such as regeneration without the heat source; energy-saving and simple structure. However; the previous work has revealed that its performance is seriously limited by the severe Joule heating effect and electrode corrosion; which demands further improvement to meet the practical requirement. In this paper; four possible improvement methods are investigated experimentally; including changing the material of anode; changing layout of cathode; applying the interrupted power and optimizing the electrical field strength. Through detailed experiments and analysis; we found that applying the platinum-plated titanium mesh as anode could improve the working lifetime from 6 h to over 120 h and effectively reduce Joule heating effect simultaneously; laying a piece of filter cloth under the cathode could enhance the EO regeneration rate up to 0.0021 g s−1; the application of interrupted power could increase the regeneration rate up to 1.5 times; the optimal on–off-time was found at 30 s:1.3 s with 17 V cm−1 electric field strength and 30 s:0.8 s with 11 V cm−1; and the most suitable value of electric field strength was observed as ranging from 8.5 to 13 V cm−1 in our EO regeneration system.

One cavitation structure in which the channel cross section expanded suddenly was introduced in single straight microchannel. The experiment was carried out with R-134a as the fluid medium, which was driven by a gear pump. The flow pattern was observed by a charged coupled device (CCD) camera and microscope. The average boiling heat transfer coefficient was estimated with the calculation method proposed in this paper. The experimental results show that the boiling began at the cavitation structure, and stable flow boiling was maintained. When heat power rose, the boiling became strong; then the pressure drop in the micro-channel increased and heat transfer was enhanced. The liquid percentage in two-phase flow increased and the length of boiling area became small when the liquid subcooling degree rose with the fixed heat power.

Hunan University Campus is an architecturally and historically relevant academic facility complex set in the city of Changsha, in People's Republic of China Hunan Province. Its modern era masterplan construction started in the 1920s, Teaching and Research Building Two" was the first building finished in 1926. In 2015 has been enlisted in "China Sites of Cultural Relics Protected at National Level" lists. As an international and multidisciplinary team the authors were, with different roles, called to study the building history, define its problems and decay episodes, and design solutions for its preservation and social and functional reactivation. In this scenario the present work will outline the results of the researches done on the building giving a brief overall view but mainly focusing on those aspects that had major impact on many choices in the subsequent phases. Then the general field diagnostic on the building will be presented, focusing again briefly on the general methodologies and results, then getting more specific into those aspects that had major influence in the project part. The design phase will be constituted by two aspects: The Preservation and the Reuse Design. As it might be evident, the first will concentrate on removing the most prominent decay episodes and their causes from the structure, the second will focus on the insertion of new functions and the subsequent user needs to ensure a contemporary life to the building. Apart from these basics it will be though evident that the reuse design strategies that are intended to enhance the user experience are directly connected to the conservation guidelines, trying to trace a common "minimum intervention driven" and "immediate awareness of the contemporary additions in the palimpsest" design strategy that will not hinder the problem solving aims nor the contemporary standards and expectations. In fact these two design aspects, even if presented as separate chapters for better comprehension, will appear as solidly interwoven: the common conservation aim and the firm interdependence of the strategies between the preservation and the reuse project as well as how these strategies are intermixed in the historical palimpsest layers of the building will possibly result as one of the most interesting aspect of this paper, and potentially an interesting case-study in modern building preservation design methodologies panorama.

This paper presents a method of piston stroke design optimization for linear compressor to get high efficiency.Two linear compressor prototypes were designed and developed with the same discharge volumes and different piston strokes to compare the performance. The prototypes were operated without air load to measure the friction damping coefficient firstly. Then the prototypes were operated with air load of 0.7MPa discharge pressure. The experimental result shows that the input power of the prototype with longer stroke is lower than that of the prototype with shorter stroke although the discharge volume, the friction damping coefficient and the frequency ratio of these two prototyps are almost the same. The iron and coil loss of the prototype with longer stroke is lower than that with shorter stroke, while the mechanical loss of the prototype with longer stroke is larger than that with shorter stroke. According to the results of the performance analysis, a design optimization model for piston stroke is developed to make the energy loss be the least. Through this design optimization model, acquire the optimal piston stoke of the linear compressor on the same conditions with the experiment. The optimization results agree well with the experimental results.

Compared to conventional compressors, the linear compressor with a free piston can improve efficiency and save energy, but the displacement varies due to different load conditions, which seriously influences its performance. In this paper, based on the theoretical analysis, a self-sensing control system with a SPWM inverter and a PC software interface for a moving-magnet linear compressor is developed, and the displacement of the linear compressor which is under control is tested. The result shows the error of the control system is under 0.2mm, and the accuracy fulfils the requirements.

It is essential to ensure the stability of a refrigeration system if the oscillation in evaporation process is the primary cause for the whole system instability. This paper is concerned with an experimental investigation of two-phase flow instabilities in a horizontal straight tube evaporator of a refrigeration system. The relationship between pressure drop and mass flow with constant heat flux and evaporation pressure is measured and determined. It is found that there is a negative slope section in the middle of positive slope pressure drop versus mass flow velocity thus making the velocity a multi-valued function of pressure drop. Three types of dynamic instabilities including the density-wave instability, pressure drop instability and thermal instability are found under the conditions of heat flux from 5 to 17 kW/m 2 , mass velocity from 150 to 1500 kg/(m 2 s), and evaporating pressure from 0.5 to 0.8 MPa. The density-wave oscillation occurs at almost all mass velocities; its period is about 1–3 s and its amplitude is the lowest. The pressure drop oscillation takes place in a negative slope section; its period is about 10 s. The thermal oscillation can be induced at a high mass flow velocity, and its period is of 60 s and the amplitude is the highest among the three oscillations. The boundary as the onset of pressure drop oscillation and that of thermal oscillation are obtained experimentally. Finally, the empirical equations for the boundaries between three types of oscillations are obtained according to the mathematical model and test data.

It is essential to ensure the stability for the normal operation of refrigeration systems. This paper reviews the researches on the theory and solutions of the instability of refrigeration systems. The instability of refrigeration systems includes two aspects: the two-phase flow instability in refrigeration system, the instability on refrigeration system control characteristics. As an inherent characteristic of two-phase evaporating flow, several separate explanations for the formation of oscillation of mixture–vapor transition point in the evaporation process by different scholars had been given but there is no general explanation till now. The investigation of instability on refrigeration system control characteristics focused on both static and dynamic researches. The minimum stable signal line theory, as a very important finding for the static instability of the evaporator and thermal expansion valve control loop, presented the different result to other researches. Dynamic researches on simulation and frequency-domain analysis provided various means for forecast and validation with considerable precision while their application range was still confined. With the development of variable capacity compressor and electronic expansion valve, further researches should be carried out to analyze the instability of the variable capacity refrigeration system with considering the influence of parameter coupling and control algorithm.

Linear oscillation motor (LOM) is the key assembly for a linear compressor, and its efficiency has great impact on the integral compressor performance. This paper presents a novel gas load method to measure the efficiency of LOM, analyses the effects of some main factors on the LOM efficiency in theory, and shows the efficiency test results. Different load conditions can be simulated by adjusting the discharge pressure of the gas and the load force presents nonlinear periodical curve. In the experiment, we changed the syntonic springs of the tested LOM to measure the LOM efficiency on different work conditions. The results of both theoretical analysis and experiment show that the LOM efficiency is the highest when the phase angle between current and displacement is 90◦. While the springs stiffness coefficient is 54.44N/mm, the highest efficiency of the tested LOM is 85.97% on the condition that the discharge pressure is 0.25MPa. While the springs stiffness coefficient is 44.64N/mm the highest efficiency of the tested LOM is 84.67% on the condition that the discharge pressure is 0.4MPa. While the springs stiffness coefficient is 38.4N/mm the highest efficiency of the tested LOM is 78.35% on the condition that the discharge pressure is 0.5MPa.

This paper aims to investigate the possibility and performance of a novel electro-osmotic regeneration method for the solid desiccant system, which could adsorb water from the moist air and be regenerated by the electro-osmotic force at the same time, by detailed experimental validation. The zeolite powder with both electro-osmotic and adsorptive characteristics was selected to make the solid desiccant. The quantity of the removed water was measured in the condition with and without an applied electric field to validate the possibility of the electro-osmotic regeneration. The test data show that there was an obvious electro-osmotic regeneration effect in the experiments. The whole electro-osmosis process was divided into three phases because of the Joule heating effect and electrode corrosion, which limited the performance of the experimental system. In particular, a filter cloth under the cathode made a superior electro-osmotic regeneration effect than without the cloth. The experimental results illustrate that the system has the potential of energy-saving and low regeneration temperature. So the electro-osmotic regeneration method is a potential regeneration method for the solid desiccant system.

There are often abnormal working conditions at evaporator outlet of a refrigeration system, such as two-phase state in transient process, and it is essential to investigate such transient behaviours for system design and control strategy. In this paper, a dynamic lumped parameter model is developed to simulate the transient behaviours of refrigeration system with variable capacity in both normal and abnormal working conditions. The appropriate discriminant method is adopted to switch the normal and abnormal conditions smoothly and to eliminate the simulated data oscillation. In order to verify the dynamic model, we built a test system with variable frequency compressor, water-cooling condenser, evaporator and electronic expansion valve. Calculated values from the mathematical model show reasonable agreement with the experimental data. The simulation results show that the transient behaviours of the variable capacity refrigeration system in the abnormal working conditions can be calculated reliably with the dynamic model when the compressor rotary speed or the opening of electronic expansion valve changes abruptly.

This paper is on a new device developed to measure the piston stroke length (PSL) of the variable displacement swash plate compressor (VDSC), with which the test bench for the VDSC and test system for automotive air conditioner with VDSC is constructed. The volumetric efficiency, PSL and displacement control, and transient behavior along with air conditioning load or compressor rotary speed are investigated experimentally. The experiment results show that the volumetric efficiency of the VDSC is directly proportional to the PSL due to the constant absolute clearance at different piston stroke lengths. When the air conditioning load keep constant, the PSL and displacement of the VDSC are regulated to meet the air conditioning load at different compressor rotary speeds or vehicle speeds. When the air conditioning load changes gradually, the PSL has a number of small step changes so that the refrigerating capacity of the VDSC can well fit the air conditioning load. When the compressor rotary speed changes abruptly, the piston stroke length, refrigerant mass flow rate, and other parameters change with a very short time delay to ensure a nearly constant refrigerating capacity of compressor.

A mathematical model of control mechanism used in the variable displacement swash plate compressor (VDSC) is developed firstly based on the force balance equation, mass and energy conservation equation. The model of moving components dynamics is developed then by analyzing the forces and force moments acting on the pistons and the swash plate. The compression process model is obtained by fitting the data from our experiments. And finally, the steady-state mathematical model of VDSC is developed by combining the three sub-models above. In order to verify the mathematical model, a test bench for control mechanism and the test system for VDSC have been established, and the simulated results agree well with the experimental data. The simulation results show that, like the variable displacement wobble plate compressor, there are four operation modes for the VDSC, i.e. constant rotary speed and constant piston stroke length (PSL), variable rotary speed and constant PSL, constant rotary speed and variable PSL, variable rotary speed and variable PSL, which have included almost all operation modes of the refrigeration compressor in common use. And there is a hysteresis zone and multiple-valued relationship between the compressor parameters when PSL changes.

A test system with the variable displacement compressor (VDC) for automotive air conditioning system is built to study the changing rule of piston stroke length (PSL). It is found from our experiments that the critical suction pressure where the PSL starts to decrease is less than that where the PSL starts to increase for the same PSL; between the two critical lines, a hysteresis zone is formed, within which all the steady-state points fall and there is a multiple-valued relationship between VDC parameters; and the PSL is kept invariable when the VDC parameters change within the hysteresis zone. In order to find out the reason causing the hysteresis zone and to analyze the influence of the compressor parameters on the hysteresis zone, a steady-state mathematical model of VDC is developed and verified by our experimental data. The theoretical analysis indicates that the hysteresis zone is caused by the frictional forces among the moving components of VDC, and the greater the frictional forces, the broader the hysteresis zone and the larger the changing range of suction pressure. The influence of the discharge pressure and rotary speed on the hysteresis zone is that the hysteresis zone moves in the direction of the suction pressure decreasing along with the increase of the discharge pressure or rotary speed.