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An energy conservative air-conditioning system is critical to promoting energy conservation and emission reduction. One promising alternative is liquid desiccant cooling system (LDCS), which can be driven by low-grade heat and has superior dehumidification performance. However, energy waste from traditional regeneration process restricts its application from widespread use. To overcome this disadvantage, a wood-based heat localization regenerator is presented: it localizes the thermal energy on the regeneration surface avoiding the unnecessary heating of bulk solution. The real performance of this new regenerator has been investigated theoretically and experimentally in this paper. The regeneration process of desiccant solution has been analyzed and a regeneration performance prediction model has been developed. Some performance indexes have been derived from experimental data. A regeneration performance comparison has been conducted between the heat localization method and the traditional heating method. The results show that the new method improves regeneration thermal efficiency by above 50% and the maximum value can achieve 43.6%. Besides higher performance, the reduction of energy consumption, initial cost and complexity has achieved with the heat localization regenerator. The overall improvement makes LDCS such a competitive alternative to the current air-conditioning system.

Ho3+ doped ZBLAN glass with 2.0 and 2.9 μm emission was prepared. In order to further improve the luminescence of Ho3+, halogen ions (Cl, Br, I) were introduced to reduce the maximum phonon energy and phonon state density of the sample. At the same time, Nd3+ was introduced to transfer the energy to Ho3+ pumped with a 793 nm laser (Nd3+:4F5/2,4F3/2→Ho3+:5I6). The effect of different halogen ion on the luminescent properties of the fluoride halide glass was compared. The results show that the luminescent intensity of infrared increases with the introduction of different halogen ions. By comparison, it is found that the sample with I– has the strongest luminescence of 1064 nm, 2.0 μm and 2.9 μm. This is consistent with the calculated J-O intensity parameters. In addition, the 2.0 and 2.9 μm emission of Ho3+ pumped with a 450 nm laser will not disappear. A mid-infrared sample with multi-wavelength excitation and multi-wavelength emission can be obtained. Nd3+/Ho3+ co-doped fluoride halide glasses with 1064 nm, 2.0 μm and 2.9 μm luminescence were prepared by melt quenching method. The luminescent mechanism and the energy transfer process between the two ions of Nd3+/Ho3+ co-doped fluoride halide glass were studied. The J-O parameters, luminescence lifetime and absorption emission cross-sectional area of Ho3+ and Nd3+ were calculated, respectively. It is found that the value of Ω2 in the glass matrix increases with the introduction of different halogen ions, while Ω4 and Ω6 do not change obviously in different glass compositions. This is because the environment of the crystal field around the rare earth ions changes. The crystal phase and phonon energy of the sample were analyzed by X-ray diffraction pattern and a Fourier transform infrared spectrometer, respectively. Based on the above spectra and data (phonon energy is 634.71 cm−1), it can be predicted that Nd3+/Ho3+ co-doped fluoride halide glass is a potential mid-infrared luminescent material.

Droplet motion state monitoring is important in microfluidic applications, such as biomedicine, drug delivery, and metal ion extraction. Here, a nonintrusion monitoring method of droplet motion state via liquid-solid contact electrification is proposed, and a triboelectric droplet motion state sensor (TDMSS) is fabricated. Droplet counting and droplet size monitoring can be realized by signal processing and information extracting of the voltage pulse. The experimental results show that the number of droplets increases linearly with the increase of liquid flow, and the linearity is 0.9854. Moreover, TDMSS can stably monitor the number of droplets in different motion states. In addition, the output pulse width is sensitive to droplet size, and the droplet length ranges from 3 to 13.5 mm. More importantly, TDMSS can realize the function of droplet counting and size monitoring of a conductive liquid and accurate droplet counting under different inclination angles and motion states. This work not only provides a nonintrusion method for droplet motion state monitoring but also makes a solid step for microfluidic sensing technology based on a triboelectric nanogenerator.

Perovskites have been studied because of their adjustable wavelength range, high color purity, and wide color gamut. However, they still face some problems such as poor stability and insufficient infrared luminescence. The perovskite glass can improve the stability and luminescence properties of the perovskite. In this paper, a highly stable CsPb1-xErxBr3-ZBLAN fluoride glass with mid-infrared and visible light emission was prepared. The ZBLAN fluoride glass has good inertness, which can improve the stability of the CsPb1-xErxBr3 perovskite. The CsPb1-xErxBr3-ZBLAN fluoride glass can prevent the perovskite from being destroyed by water, oxygen, and laser. The Er3+ replaces Pb2+ to bond with Br- to become the luminescent center of the CsPb1-xErxBr3-ZBLAN perovskite glass, which extends the luminescence to the mid-infrared region. In addition, its luminescent intensity is significantly higher than those of the ZBLAN-Er glass and CsPb1-xErxBr3 perovskite. After irradiation with a 365 nm UV lamp for 13 h, the luminescence intensity of the CsPb1-xErxBr3-ZBLAN perovskite glass decreases only by 10%. The EDS spectrum shows that the elements of the CsPb1-xErxBr3 perovskite are uniformly distributed in the glass matrix. The X-ray diffraction spectrum shows that the sample has both the CsPb1-xErxBr3 perovskite phase and the glass phase. This indicates that CsPb1-xErxBr3 is well crystallized in the ZBLAN glass matrix. The three parameters calculated by the Judd-Ofelt theory show that the CsPb1-xErxBr3 perovskite can increase the covalency and asymmetry around the rare earth ion Er3+. The transmission electron microscope can clearly see the morphological structure of the CsPb1-xErxBr3 perovskite in the ZBLAN glass matrix. The infrared Fourier transform spectroscopy shows that the sample has lower phonon energy. This proves that the sample has good infrared luminescence characteristics. Finally, the visible and infrared light sources were prepared. Under the irradiation of the 365 nm ultraviolet lamp and 980 nm laser, the perovskite glass produces green light and infrared emission.

In membrane-based air dehumidification process, the membrane acts as an intermediate medium separating the humid air and the desiccant solution and be used to simultaneously transfer sensible heat and moisture. However, it produces additional mass transfer resistance reducing the performance of dehumidifier. In order to relieve the additional resistance, breakthroughs need to be found in membrane material and driving force. In this investigation, three different membranes, namely, AAc-modified PTFE with silicon oxynitride coating, neat PTFE with amorphous silica coating and neat PTFE are selected. Large temperature gradient coupled with vapor pressure difference forms the enhancement in driving force and faster desorption rate in the membrane. The composite membrane acts as a temporary solid desiccant rather than a barrier between humid air and desiccant solution. Results show that the water vapor adsorption/desorption performance of neat PTFE has been significantly improved with a thin layer of amorphous silica coating added on. Its permeation activation energy is greatly reduced from 54.8 KJ · mol−1 to 27.2 KJ · mol−1 and intrinsic resistance from 225 s · m−1 to 180 s · m−1. The thermal diffusion enhanced effect improves the latent effectiveness of AAc-modified PTFE membrane from 0.38 to 0.5 and neat PTFE membrane with amorphous silica coating from 0.3 to 0.41. These are mainly due to the decrease of sorption curve constant C and increase of water uptake at lower relative humidity. It can be regarded as the temperature gradient across the membrane applying additional driving force to the water vapor diffusion process. Then better dehumidification performance which originally require larger vapor pressure difference can be achieved, reducing energy consumption in the regeneration process.

Reducing carrier trapping in the grain boundary of semiconductor materials can improve the carrier transport. Adding Na2EDTA in the electrolyte can regulate the growth process of Cu2O thin films electrochemically deposited at low temperature, improve the crystal quality, and transform from the polycrystalline structure into a single-crystal-like structure oriented along the (111) crystal plane. As a result, the interface transfer resistance of ZnO/Cu2O heterostructure devices is reduced, the photogenerated carrier transport ability is improved, and the self-powered photoresponse properties of heterostructure devices are improved. Based on the dual-band photoresponse characteristics of ZnO/Cu2O, a device without bias voltage was applied in the “OR” gate of a UV and visible dual-band light controlling digital logic circuit. The encrypted optical signal was realized and the security of visible light communication was improved by the encoded UV and visible dual-band light.

The tunable bipolar binary photoresponse characteristics (positive and negative current value changes) of heterojunction photodetectors (PDs) are used to realize the applications of optical communications, optical information storage, and multiple logic circuit operations of light. ZnO/Cu2O heterojunction PDs with photovoltaic effects show a fast and broad-spectrum photoresponse to UV and visible light. A high light switching on/off ratio of 2.7 × 105, a responsivity of 0.55 A W−1 and a detectivity of 1.5 × 1013 Jones were obtained under 470 nm illumination without applied bias. The PDs exhibit controllable bipolar binary photoresponse characteristics by adjusting the competitive relationship between the photo-generated current and the internal junction current for the PDs under different light (intensity or wavelength) and small applied bias voltage (0 < Vbias < Voc). The PDs exhibit a binary photoresponse in a wide spectrum from UV to visible light. The binary photoresponse states used as “1” and “−1” digital codes can achieve programmable processing of digital signals. The results provide a universal example to realize the bipolar binary photoresponse by regulating the light wavelength, light intensity and applied external bias for the heterojunction PDs with the photovoltaic effect.

The fluorochloride glasses samples with good luminescent properties in the infrared region were successfully prepared by melt quenching method. The introduction of Cl− effectively improved the mid-infrared (MIR) luminescence of erbium-doped fluoride glass at 2.7 µm nearby. According to Judd-Ofelt theory, the increase in Ω2 after the introduction of Cl− indicates an increase in the asymmetry and covalence of the sample. X-ray diffraction (XRD), absorption spectrum, Raman spectroscopy, infrared Fourier (FTIR) and infrared fluorescence spectroscopy were specifically conducted. The emission cross section (1.04×10−20 cm2) and the absorption cross section (9.68×10−21 cm2) of the sample at 2.7 µm nearby were calculated by measurement. Therefore, non-oxide erbium-doped fluorochloride glass is a good luminescent material in the MIR band.

Electronic cooling has been a rising issue mainly due to the rapid development of high-throughput computing in data centres as well as battery energy storage, which release huge amount of heat through compact surfaces. The electronic cooling process is not only energy-intensive but also difficult to control. This paper proposes an effective cooling method for electronic devices by integrating phase change materials (PCMs) with three-dimensional oscillating heat pipes (3D-OHPs), where PCMs are used to store heat dissipated by the electronic device and 3D-OHPs to fast transport the stored heat from PCMs to the environment. A novel leaf-shaped structure is designed for the 3D-OHPs. Experimental study is carried out on the leaf-shaped 3D-OHPs with various working parameters including cooling air velocity, wind direction and heat input. Further, the leaf-shaped 3D-OHPs are embedded into PCMs to cool down the electronic devices. Temperature variations and thermal resistance are evaluated and compared with the conventional air cooling method. The experimental results indicate that the surface temperature of electronic devices can be well controlled below 100 °C, which is ∼35 °C lower than that with conventional air cooling. The thermal resistance is decreased up to 36.3%. The 3D-OHPs with a filling ratio of 34–44% achieve the best thermal performance. What’s more, the leaf-shaped structure of the 3D-OHPs contributes to a ∼2 °C lower temperature on the electronic device’s surface than the typical used 3D-OHPs. This research will promote the development of effective cooling for electronic devices.

Binary photoresponse characteristics can help realize optical signal processing and logic operations. UV photodetectors (PDs) with SnSx nanoflakes and TiO2 nanorod arrays (NRs) show a novel binary ...

It is necessary to disclose the two-phase interphase behavior in the liquid desiccant dehumidifier/regenerator applicable for air conditioning, but the present investigation is far from enough. In this paper, the surface structure of liquid desiccant solution is analyzed by molecular dynamics simulations. LiBr-H2O is chosen as the working solution with a concentration of 1 M and the system model is built with Gromacs. System temperatures vary from 300 to 350 K covering the temperature range of liquid desiccant dehumidification and regeneration. Density profiles of ions and water molecules are plotted along the vertical directions, and their distribution preferences on the solution surface are discussed. With the molecular simulation, it is found there is an ions-vapor layer with a thickness of 6–9 Å between the saturated vapor and bulk solution, which is not shown in the traditional macroscopic models. The results show that the density of water remains stable in the bulk while decreases sharply on the solution surface. However, the salt ions, i.e. Li+ and Br-, have a peak density on the surface. This ions-vapor layer behaves like a buffer to transfer water molecules from/to the bulk solution. More research will be required to investigate how to control the ions-vapor layer, so that air dehumidification and solution regeneration can be easily operated, which provides significant energy savings for the liquid desiccant air conditioning.

The morphology and geometry of semiconductors will affect the photoresponse performance of mixed-dimensional heterojunction photodetectors (PDs). Self-powered UV PDs based on mixed-dimensional heterostructure arrays are formed from two-dimensional NiO nanosheet arrays and one-dimensional TiO2 nanorod arrays. The Fermi level position and carrier concentration of the NiO nanosheets can be adjusted by the thickness of each layer and film. The enhanced built-in potential field of the NiO/TiO2 interface decreases the charge transfer resistance and the appreciated carrier transfer path improves the photogenerated carrier separation and transfer ability without external bias. The self-powered NiO/TiO2 heterojunction device demonstrates a large responsivity of 0.86 A W−1, a high detection sensitivity of 1.6 × 1013 Jones and a fast photoresponse time of 3 ms under weak UV light illumination.

Tar removal is a bottleneck in the smooth commercialization of biomass gasification technology. Based on introducing adsorption process into Quench Coupled with ABsorption Technology (QCABT) previously proposed by the author's group, Quench Coupled with ADsorption Technology (QCADT) has been developed to narrow this gap. Additionally, benzene and naphthalene, which are more similar to the real tar for containing aromatic ring structures, were adopted as light and heavy simulated tar, respectively. Also their removal behavior by QCADT was investigated. The results show that the removal mechanism of QCADT is similar to that of QCABT, except for the higher overall tar removal rate due to adsorption effect. Adsorbents with both micro- and narrow mesopores exhibit a better benzene removal performance, while narrow mesopores play dominant roles in naphthalene removal. Penetration adsorption loading of benzene and naphthalene on AC-1 can reach 0.38 g·g−1 and 0.34 g·g−1, respectively. The sawdust hardly has any tar removal effect. Combined micro- and meso-pores, will benefit both deep tar removal and large adsorption rate, providing a high tar removal efficiency.

The regenerator which is applied to recover the dilute solution plays a significant role in the liquid desiccant system. Rotating packed bed (RPB) has been demonstrated to heat and mass transfer process intensification, and successfully applied in the field of gas absorption. To validate the application of rotating packed bed in the regeneration of the dilute solution, a counter-flow RPB regenerator was studied in this work. Three groups of performance indices including moisture removal rate, heat and mass transfer coefficients, and regeneration effectiveness, were employed to evaluate the performance of the regenerator. The effects of the high gravity factor, air flux, solution flux, air inlet parameters, and solution inlet parameters on the performance indices were investigated and compared with the conventional regenerator. Correlations of heat and mass transfer coefficients were presented on the basis of the experimental data. The mass transfer coefficients of RPB regenerator locate within 12.5–35.6 kg m−3 s−1 which are higher than those in the conventional regenerators. According to the comparison, the RPB regenerator has superiority in the mass transfer performances.

The initial reactant concentration and the substrate play an important role on the nucleation and growth of MoS2 nanostructures during hydrothermal growth. In this work, MoS2 nanoflakes are grown on FTO and TiO2 nanorod arrays (NRs) substrates. The morphology, optical and photoelectric properties of MoS2 nanoflakes are affected by the initial reactant concentration. Compared with the FTO substrate, MoS2 nanoflakes tend to grow on TiO2 NRs substrates due to less mismatch between TiO2 and MoS2. The large surface roughness and the presence of surface states of the TiO2 NRs facilitate the nucleation and growth of MoS2 nanoflakes. The photoelectric characteristics of MoS2/TiO2 NRs compositions have been investigated. The MoS2/TiO2 NRs compositions prepared using the initial reactant concentration with 4 mM S atom concentration exhibit the higher photoresponse behavior, which is attributed to the better heterojunction contact interface between MoS2 nanoflakes and TiO2 NRs. MoS2 nanoflakes can not completely cover the TiO2 NRs under low initial reactant concentration, resulting in the small area of the contact interface. On the other hand, MoS2 nanoflakes tend to form the self-assembly nanoflowers under high initial reactant concentration, which induces the carriers recombination in MoS2, the poor transport properties of MoS2 and the detrimental effects on the photogenerated current.

Understanding heat and mass transfer between LiBr aqueous solution and vapor is a crucial issue in absorption refrigeration and air dehumidification for the purpose of intensifying transfer and conversion. This is difficult to be realized by macro experiments due to failing to catch detailed information of water molecules. Molecular dynamics has been resorted to for exploring mechanisms of chemical processes but the used force field dominates the simulation accuracy. In order to discover suitable force fields to describe interactions in LiBr solution, three recent models developed based on infinite dilution were evaluated in terms of static and transport properties. Results show that all models could predict the density with high accuracy. The model of Koneshan et al. achieves most properties with satisfactory accuracy and is the best one to simulate the surface tension, which indicates good interfacial performance. Further, by selecting the model of Koneshan et al., the energy and mass transport phenomenon through liquid–vapor interface was simulated and analyzed. Four behaviors of water molecules including absorption, release, replacement and reflection were observed near the interface of LiBr solution. It is found that the replacement behavior only occurs under high liquid temperature conditions and the reflection behavior is characterized by a steep energy ravine. This research provides data reference for the force field selection, setting a solid foundation for studying heat and mass transfer between LiBr solution and vapor by molecular dynamics. This research could also disclose the molecular behaviors between aqueous solution and air.

Perovskite quantum dots (PQDs) are among the most important luminescent semiconducting materials; however, they are unstable. Exposure to light, heat, and air can lead to irreversible degradation, ...

Electrodialysis (ED) is an alternative to the conventional thermal regeneration of high-salt solutions used in air conditioning systems (ACSs). In this work, a simplified mathematical model was developed to describe the solute and water transport. The solute hydration number and free water content were proposed to characterize the solute hydration properties. A laboratory-scale ED regeneration system was set up to investigate the regeneration performance of three kinds of high-salt solutions (aqueous LiCl, LiBr and CaCl2 solutions) at various initial concentrations and current densities. The results demonstrate good agreement between numerical and experimental findings. The initial concentration and applied current density have great impacts on ED performance. Firstly, higher initial concentration generally results in lower membrane permselectivity, current efficiency, solute and water transfer rate, and higher energy consumption. Secondly, higher current density has a positive effect on solute and water transport but leads to more energy consumption. The solute hydration number and free water content both decrease with increasing initial concentration. The appropriate mass concentrations of 15%, 25% and 15% are respectively suggested for aqueous LiCl, LiBr and CaCl2 solutions when applying ED in ACSs to ensure responsible performance.

In order to solve the problem of poor regeneration performance of the solar solution dehumidification air conditioning regeneration system under high temperature and high humidity weather conditions. In this paper, a novel vacuum membrane distillation (VMD) solution regeneration method was proposed for a solution desiccant air conditioning system, and a theoretical study of this novel regenerator is performed. Through the analysis of heat and mass transfer, the mathematical model of VMD regeneration is established, and the mathematical model is verified by experiments. The results indicated that VMD regenerator not only could increase the regenerate rate but also could exhibit higher energy utilization efficiency. At the same concentration, the VMD regenerator has a higher regeneration performance, and the regeneration rate is 1.6–2.4 times that of the internal heat type regenerator, and the 4.5–6 times that of the adiabatic regenerator.

Nd3+/Yb3+ co-doped fluorobromide glass samples were prepared by melt quenching. The mid-infrared (MIR) luminescence of the Nd3+/Yb3+ co-doped fluorobromide glass was investigated by Br-doping reduces the phonon state density of the matrix. The 3.9 μm MIR luminescence of the samples excited at 793 and 980 nm pump excitation was investigated in detail. There is an effective mutual energy transfer process between Nd3+ and Yb3+. It is proved under 793 nm excitation that the luminescence of Nd3+ at 3.9 μm is reduced by effective energy transfer from Nd3+:2H11/2 → Yb3+:2F5/2. At the same time, it is proved that the effective energy transfer from Yb3+:2F5/2 → Nd3+:2H11/2 under the excitation of 980 nm enhances the luminescence of Nd3+ at 3.9 μm. In addition, it is found that the samples still have good infrared (IR) luminescent properties when the temperature changes. The emission cross-sectional area and the absorption cross-sectional area are σem (3.87 × 10−20 cm2) and σabs (4.25 × 10−20 cm2). The fluorescence decay characteristics of the sample at 3.9 μm at the 2H11/2 level were investigated and the fluorescence lifetime was calculated. The gain performance of the sample was calculated and analyzed, which can reach 4.25 × 10−20 cm2. Those results prove that Nd3+/Yb3+ co-doped fluorobromide glass is the potential mid-infrared laser gain material.

Decreasing the humidity ratio of ambient air can effectively prevent the frosting on the evaporator and improve the heat capacity of heat pump in winter. This paper conducts an experimental study and theoretical analysis on the heat and mass transfer performance of the cross-flow dehumidifier in a frost-free heat pump system. A mathematical model for predicting the heat and mass transfer performance in the dehumidifier is developed, and solved by finite difference method. Experimental study is carried out to analyze the influence of key parameters, including inlet air temperature, humidity ratio and flow rate, solution temperature, concentration and flow rate, on the coupled heat and mass transfer performance under low temperature and humidity ratio conditions. Based on the mathematical models and experimental results, the correlations of heat and mass transfer coefficients are proposed, and the deviations are within ±20%. Moreover, the effects of the inlet conditions of the liquid desiccant and air on the heat and mass transfer performance are compared with the experimental results reported in literature.

Liquid desiccant regeneration is an important part of liquid desiccant air conditioning system and consumes the majority of the system’s power. Conventional methods for liquid desiccant regeneration use thermal energy to regenerate the liquid desiccant. One of the biggest problems for thermal regeneration is that the liquid desiccant should be cooled down before dehumidification. Furthermore, the efficiency for liquid desiccant regeneration drops under high temperature and humidity climates. In comparison, electrical regeneration, such as electrodialysis (ED), may solve the problems above. No phase change is involved in this process. In addition, low electrical energy is required and photovoltaic power is capable of proving the necessary energy. In this paper, the performance of liquid desiccant regeneration by photovoltaic electrodialysis (PV-ED) was experimentally investigated by considering two important factors, including the initial desiccant concentration and current intensity. The results showed that the initial desiccant concentration and current intensity had big impact on the performance of the system. Lower desiccant concentration and higher current intensity contributed to the current efficiency and solute transport, respectively. In addition, the energy consumption per unit solute migration increased with the increase of both current intensity and desiccant concentration. The results also indicated that the PV-ED regenerator performed better when the initial desiccant concentration was low and current intensity was high.

Porous Si/C has been fabricated by dehydrating Si/sucrose mixed powder with concentrated H2SO4. The obtained Si/C presents excellent cycling stability with a capacity retention of 85.6% in the 920th cycle at 100 mA g-1, compared with only 13.2% for pure Si in the 100th cycle.

The performance of self-powered UV photodetectors (PDs) without an external power source is far from satisfactory for practical applications. The nanostructure heterojunction-based self-powered UV PDs can enhance light absorption and provide more interface areas for photogenerated carrier separation. However, they suffer from a large dark current and low signal-to-noise ratio for carrier recombination due to thermal excitation. The p-NiO nanoflakes/n-ZnO nanorod array (NR) heterojunctions prepared by chemical bath deposition (CBD) demonstrated good rectifying characteristics and a distinct photovoltaic effect. The UV PDs based on p-NiO/n-ZnO nanostructure heterojunctions exhibited good spectral selectivity, high responsivity and a fast response speed without an external electric field under weak light radiation. The introduction of an MgO interfacial layer between NiO and ZnO NRs could modify the surface defect states of ZnO NRs and decrease the carrier recombination at the heterojunction interface, enhancing the performance of the self-powered UV PDs. The investigation of the energy band structure of the heterojunctions revealed that the self-powered photocurrent of the devices is correlated to the built-in potential of the heterojunctions. The results demonstrate that the p-NiO/n-ZnO nanostructure heterojunctions with interfacial layers are promising for the development of self-powered visible-blind UV PDs with a high performance.

Drying performance of a novel compressed air drying method using different liquid desiccants, including LiCl solution, LiBr solution and mixed solutions (LiCl/CaCl2), is compared by experiments. It is found that drying performance of LiCl solution is better than that of LiBr solution. Besides, drying performance of three mixed solutions (44%, 46% and 49%) selected is similar to that of 40% LiCl solution, verifying the feasibility of substituting single solution with much cheaper mixed solution. The water vapor pressure of mixed solutions and LiCl solution is same in experiments, therefore it can be selected as an indicative factor to evaluate substitute of LiCl solution. Moreover, the cost of the three mixed solutions is 18% cheaper than that of 40% LiCl solution at least, which shows significant economization in application. Finally, system performance of the compressed air drying system is analyzed. The dew point of outlet compressed air could reach −7.7 °C at operating pressure of 0.8 MPa, indicating the dryness can satisfy requirement of various industrial applications which used typical electricity-driven cooling-drying method. The solution temperature of regeneration could reach 70 °C, validating that it is feasible to use waste heat recycled from the air compressor to drive solution regeneration.

Frost build-up on the fins of the evaporator severely decreases heat transfer and subsequently reduces the performance of the heat pump system. In this paper, a novel frost-free air source heat pump system is proposed, which combines with liquid desiccant dehumidification and closed-circuit regeneration. A test setup for investigating the performance of the proposed system and the corresponding performance indexes are developed to evaluate the system performance under variable working conditions. The effects of key parameters including solution temperature, solution concentration, air flow rate and solution flow rate on the regeneration performance and heating performance of the system are analyzed experimentally. Results show that the optimal mass flow rate ratio of the solution to the air is 1.4 in the regeneration mode, while the ratio of 0.55 is recommended in the heating mode. Additionally, performance comparison between the proposed system and the conventional reverse-cycle defrosting system available in the literature is conducted. It is concluded that the proposed system is superior to the reverse-cycle defrosting system when the ambient temperature is less than 0 °C and the relative humidity is higher than 65%.

Based on the steady-state efficiency of the engine and the motor and characteristic curve of Lithium iron phosphate (LiFePO4) battery, an energy management strategy is proposed for a coaxial parallel hybrid-power gas engine heat pump (HPGHP) with V-belt continuously variable transmission (CVT) by using logic threshold approach to control the dynamical transitions between the various operation modes. The torque distribution between engine and motor, and CVT ratio are regulated through predetermined optimal operation lines of hybrid powertrain system in different operations. The results demonstrate that the energy management strategy can satisfy heat pump demand performance and reduce gas consumption effectively, as well as keep battery state of charge (SOC) in reasonable range. The average thermal efficiency of driving system in three main operating modes is 3.8%, 1.9% and 2.5% higher than that of multi-stage transmission system respectively, indicating that the system has better energy saving performance.

Liquid desiccant air conditioning system has unique advantages and prospects in both humidity control and low-grade heat driven cooling. The liquid film wettability is one of the significant factors governing the efficiency of dehumidification/regeneration processes in the system. In this paper, the effect of the LiCl solution properties on falling-film plate wettability characteristic is studied using a VOF method. This paper analyzes the dehumidification and regeneration processes respectively and gets the recommended amount of spray, which was 0.619 m3/(m·h) for dehumidification and 0.662 m3/(m·h) for regeneration. The recommended amount of spray can not only ensure the full-film flow, but also avoid the excessive solution flow rate which may increase the possibility of droplets entrainment. Since the wettability is determined by the coupled effects of the solution density, viscosity and surface tension, the effects of dynamic properties of liquid desiccant on the wettability are studied to explain the influence of the solution temperature and concentration on the wettability. Finally, least squares method is used to fit a formula to describe the effect of solution properties on falling-film plate wettability, which can guide the control of the amount of spray in actual operation.

In favor of renewable energy and using green refrigerant, the absorption air-conditioning system is a good measure for overcoming energy shortage and environmental deterioration. With the thermal method, its performance is not good enough because of much heat loss in the regeneration process. For optimal performance, capacitive deionization (CDI) regeneration method was proposed by regenerating absorbent with electrodes in electric field. Previous research shows the theoretical COP of the CDI based system could attain 3. However, these results lack experimental support. Therefore, this paper presents the experimental research on the actual performance. The influence of concentration and other parameters has been analyzed in the experiments. Based on the experimental results, the energy recovery characteristic also gets confirmed and it provides a new way to improve the performance of the CDI based system. Electricity and energy models have been developed; some important parameters have been investigated. The experimental results present the actual regeneration capacity and corresponding COP. The theoretical results expose the improvement of COP with energy recovery and the influences of equivalent series resistance, flow rate and capacitance. It found the COP has potential to further increase by 2 or even 3 times, could reach 6 with appropriate energy recovery.

Carbon is an economy and effective material for improving the electron conductivity of Li4Ti5O12, coating carbon on Li4Ti5O12 is commonly through the means of calcinating the mixture of titanium, lithium and organic compounds in an inert atmosphere, which needs a careful control to avoid the reduction of Ti4+ in Li4Ti5O12 by the in-situ formed carbon. In this work, a facile way is applied to fabricate carbon on Li4Ti5O12 by using filter paper to absorb the solution containing Ti(OC4H9)4 and LiAC with a calcination at 700 °C in air. The formation of carbon on Li4Ti5O12 mainly related with the swelling property of the crystalliferous region in cellulose fiber. TEM image shows Li4Ti5O12 particles have the average diameter about 100 nm, which are coated by a thin layer of carbon with the thickness around 5 nm, and Li4Ti5O12 particles connect with each other by carbon, forming porous fiber, which facilitates the transfer of electron and Li+. In comparison with Li4Ti5O12 synthesized by sol-gel method, Li4Ti5O12/C present superior rate capability with the discharge capacity of about 165 mAh g−1 at 0.2 C and 141 mAh g−1 at 20 C.

Total heat recovery in an air-conditioning system can recycle both heat and mass from return air to preprocess fresh air. This study analyzes liquid desiccant total heat recovery (LDTHR) devices with a counter-flow path or a cross-flow path. The inlet states of fresh air and return air are divided into two types for analysis, namely Type I: on the same iso-relative humidity line (φin); and Type II: on different iso-relative humidity lines (φin). With respect to Type I, the single-stage LDTHR with a counter-flow path is investigated by using an analogy with a sensible heat recovery device in which the performance is optimized under matched heat and mass transfer ability ((NTUm)F = (NTUm)R) and matched flow rates (mRcp.e = mFcp.e = mscp.s). With respect to type II, the liquid desiccant solution of a single-stage device works at a fixed iso-relative humidity line, and this limits the mass transfer between air and solution. Increases in the stage number alleviates the problem and improves humidity efficiency (ηω). For certain heat and mass transfer abilities (NTUm), the single-stage counter-flow LDTHR device exhibits the highest enthalpy efficiency (ηh). The application of the counter-flow device is restricted by the height and complex arrangement of air and solution flow. The enthalpy and humidity efficiency of a double-stage cross-flow device is close to that of the counter-flow device, and this is a practical method that is an alternative to the counter-flow device.

The window energy consumption plays an important role in the building energy consumption. Recent researches on the double-glazed window filled with PCM (DW + PCM) show that in summer, the released unwanted heat into the room in the discharge period of PCM in summer night is considerable as well as the overheating phenomenon from the completely melted PCM is non-ignorable, both of which have an adverse effect on the building insulation performance. In order to solve the problems, a configuration of triple-glazed window filled with PCM (TW + PCM) is proposed and the mathematical model is established in this paper. Through the simulation, the dynamic thermal performances of the TW + PCM are obtained. The results show that in typical sunny summer day, the temperature decrement factors are 0.75 and 0.63 respectively, and the energy consumption of TW + PCM is reduced by 21.30% and 32.80% respectively, compared with DW + PCM and triple-glazed hollow window (TW). In addition, the TW + PCM shows a good performance under the typical winter conditions. In conclusion, TW + PCM can avoid overheating phenomenon effectively and has advantageous performance on heat preservation and insulation.

In this paper, a novel heat pump system is proposed, which operates as a heat-source-tower heat pump with no frosting in winter, and as a hybrid refrigerant system consisting of a conventional chiller combined with a liquid desiccant dehumidification and evaporative cooling subsystem in summer. A validated mathematical model of the proposed system operating in summer is established to investigate the effects of key parameters, including solution to refrigerant flow ratio (FR), condensation heat recovery ratio (Rcond) and ambient parameters, on the cooling performance. Besides, this paper analyzes key factors that should be considered in designing the heat exchange area of the solution-cooled condenser (SCC). The results show that the maximum COP and ECOP of the heat pump system are 13.4% and 10.3% higher than those of conventional vapor compression refrigerant systems under the typical summer condition of Nanjing, respectively. The recommended range of FR is from 1.2 to 6 and that for Rcond is from 16% to 40%. Moreover, the proposed system is more superior to conventional ones when applied in hot and humid regions.

Silicon (Si) has attracted researchers’ attention because of the high theoretical capacity of 4200 mAh g−1. However, the electrochemical performance of Si is often worsened by the structure deterioration originated from the huge volume variation during charge/discharge process. To improve the electrochemical performance, the porous structure is initially fabricated in Si by removing aluminum from Si-Al alloy powder with HCl solution, and then a carbon layer coats on the surface of porous Si by pyrolyzing toluene at 700 °C under nitrogen atmosphere, forming porous Si/C composite. In this composite, carbon helps greatly to transfer electrons and stabilize the structure of Si, resulting in an enhanced charge/discharge performance in comparison with porous Si. Porous Si/C presents an enhanced Li-storage performance; at 200 mA g−1, porous Si/C can deliver 1402 mAh g−1 after 100 charge/discharge cycles, but only 585.3 mAh g−1 for porous Si; and at 3200 mA g−1, the reversible specific capacity of Si/C is 505.1 mA h g−1, while that for porous Si is 41.7 mAh g−1.

For improving the accuracy of the effective heat capacity model and increasing the computing speed of the enthalpy model, an improved numerical model for phase change material wallboard was proposed in the research. This improved model was expected to combine the advantages of the enthalpy model and the effective heat capacity model. This improved model was firstly validated by the literature results, and then it was compared with the enthalpy model and the effective heat capacity model. Based on the simulation results from the improved model, it was concluded that the accuracy of this improved model was the same as the enthalpy model and higher than that of the effective heat capacity model. In addition, the computing speed of this improved model was much higher than that of the enthalpy model because of its much lower number of iterations.

In order to improve the anti-frosting performance of superhydrophobic fin-tube heat exchanger (SFHE) in ASHP, a frost suppression method was put forward, by using air flow action on the SFHE surface intermittently to remove the condensate droplets at early stage of frosting. The anti-frosting performance of the improved method was analyzed, and its energy consumption was evaluated. Experimental results showed that the frost suppression method could significantly improve the anti-frosting performance of the SFHE, and the degree of the improvement increased with the increase in velocity and temperature of the air flow. When the additional energy consumption for achieving the air flow was considered, the total heating capacity of the ASHP increased by 14.8–32.0% and the mean COP 11.8–29.4% in a comparison period. Therefore, the frost suppression method combining SFHE and air flow, not only improved the anti-frosting performance of the SFHE but also increased the heating performance of the ASHP.

Defrosting performance is closely related to surface wettability and defrosting conditions. In this paper, the effects of surface wettability, initial frost mass and defrosting temperatures on defrosting performance of fin-tube heat exchanger were studied experimentally. The contact angles of hydrophilic, bare and superhydrophobic heat exchangers were 13.7°, 95.3° and 156.8°, respectively. Five parameters were defined to provide quantitative analysis of the defrosting performance. Defrosting performance is greatly affected by surface wettability. The superhydrophobic heat exchanger has the best defrosting performance followed by the hydrophilic one. Initial frost mass and defrosting temperature have different levels of influences on different heat exchangers. For example, the retained water mass on the bare heat exchanger increases by 62.2% when the frosting time increases from 30 min to 90 min, while it has little change on the superhydrophobic one. And the defrosting temperature has no influence on retained water mass of each heat exchanger.

Heating towers which can take advantage of energy from air for heating supply is drawing more and more attention. However, the solution dilution problem exists in both open-type and closed-type heating towers, resulting an increasing risk of system freeze. This paper presents an alternative way for heating tower solution regeneration based on packed beds. A cross-flow regenerator equipped with PVC structured packing was established and glycol aqueous solution was selected as the circulating fluid. The effects of the inlet parameters on moisture removal rate, humidity effectiveness and thermal efficiency are experimentally investigated. Correlation expressions of heat and mass transfer coefficients are also proposed, which can be primary parameters for simulation and optimization. Besides, performance comparation between heating tower solution regeneration and liquid desiccant regeneration available in the literature is figured out. The results indicate that the impacts of inlet parameters show similar tendency with those in liquid desiccant regeneration. While the regeneration temperature required in heating tower is much lower than that in liquid desiccant regeneration, due to the lower required solution equivalent humidity ratio and regenerated air humidity ratio. That makes it possible to utilize low-grade energy.

Thermal contact resistance plays an important role for the appropriate application of nanoparticles, and the thermal performance of nanoparticles can be further improved by tune thermal contact resistance. In this work, cold-pressing, acetic treatment and sintering treatment are introduced to study the methods to tailor thermal contact resistance of copper nanoparticles. With the effect of preparation pressure, acetic acid treatment and sintering treatment on the thermal contact resistance studied, results show that pressing pressure can effectively tune the thermal contact resistance of nanoparticle beds by increasing heat-transfer routes and contact areas. Sintering treatment can tailor thermal contact resistance significantly by change grain size and lattice defect on the contact area. Acetic acid treatment can reduce thermal contact resistance obviously by destroying oxide layer coating on the copper surface. This work is expected to supply some information for improving the thermal conductivity of nanoparticles.

The phase change cooling (PCC) technology combined with porous media is a promising way to enhance the performance of photovoltaic thermal (PV/T) system. Nevertheless, the application of this method is rarely mentioned in PV/T system. This paper aims to build a new phase change self-circulation (PCSC) PV/T system based on PCC technology and porous media. The system is constructed under outdoor conditions using commercial solar panel with the size of 550 mm × 460 mm × 25 mm. The performance of the system is accessed from energetic and exergetic concept under varying operating conditions (such as solar irradiance, mass flow rates, operating temperature). The obtained data shows that the proposed system is feasible with an average cooling efficiency of 34.6%, and the maximum panel temperature difference is 4.2 °C. The average daily electrical energies of the PCSC PV/T system under mass flow rates of 0.004 kg/s, 0.007 kg/s, 0.009 kg/s are 95.36 W/m2, 94.68 W/m2, and 95.79 W/m2, respectively. The results are competitive compared with other works. In addition, the results also prove that the attached glass cover is beneficial to harvest thermal energy but not to electrical energy. Moreover, LCOE results indicate that the proposed system is economical compared with reference PV system.

Direct-contact total heat exchange with liquid desiccant produces enormous gains in both sensible and latent heat recovery of low-grade flue gas. Previous studies related to that has tended to focus on the system performance rather than the heat and mass transfer characteristics, which is equally essential to their design, simulation and operation. This paper establishes an experimental system to investigate the heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas total heat recovery. Ceramic structured packing is adopted considering its corrosion and high-temperature resistances; calcium chloride aqueous solution is employed as the coolant and absorbent for its low cost and high latent heat recovery capability. Based on those, the effects of flue gas and solution inlet parameters on the performance indices, including sensible and latent heat recovery capacities, latent heat rate and total heat recovery rate, are tested and analyzed. Coupled heat and mass transfer models between flue gas and solution in this process are developed, which feature the enthalpy of dilution. By combining the models and experimental data, heat and mass transfer coefficients are calculated and fitted. In addition, the effect of packing height on total heat recovery capacity and ratio is investigated through simulations. The results show that the total heat recovery rate of 74.7% can be achieved at packing height to 1.5 m when liquid–gas ratio is 5.172.

The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO2 nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiOx thin film can improve the morphological and carrier transport properties of TiO2 NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO2 nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 104 and 1.45 × 105 for NiO/TiO2 NRs and NiO/TiO2 NRs/TiOx, respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast respons...

The melting process and the solidifying process of phase change material (PCM) are usually considered symmetrical in the traditional PCM heat transfer models, but there are inevitable calculation errors using these models. In this paper, a new heat transfer model of PCM based on the energy asymmetry was built, and it was validated by experimental data. It was found that the two main reasons for the energy asymmetry of the PCM were the melting temperature range and the solidifying temperature range were not the same and the supercooling problem during the cooling process. No matter for only one thermal cycle or for the multiple thermal cycles, the results from the asymmetrical model and the symmetrical model were different. Apparently, compared with the symmetrical model, the asymmetrical model had higher accuracy, and the heating/cooling process in the asymmetrical model was more consistent with the real heating/cooling process of the PCM.

The surface-bound ligands of a semiconductor nanocrystal can affect its electron transition behavior. We investigate the photoluminescence (PL) properties of Cu-doped Zn-In-Se quantum dots (QDs) through the exchange of oleylamine with 6-mercaptohexanol (MCH). Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, and mass spectrometry reveal that the short-chain MCH molecules are bound to the QD surface. The emission peaks remain unchanged after ligand exchange, and the PL quantum yield is reduced from 49% to 38%. The effects of particle size and defect type on the change in PL behavior upon ligand substitution are excluded through high-resolution transmission electron microscopy, UV–Vis absorption, and PL spectroscopies. The origin of the decreased PL intensity is associated with increased ligand density and the stronger ligand electron-donating abilities of MCH-capped QDs that induce an increase in the nonradiative transition probability. A lower PL quenching transition temperature is observed for MCH-capped QDs and is associated with increasing electron-acoustic phonon coupling due to the lower melting temperature of MCH.

To discover the falling film absorption performance over a vertical tube using LiCl solution in a high-pressure absorber involved in a two-stage absorption refrigeration system, an experimental study on heat and mass transfer performance of the absorption process was conducted. Effects of operating parameters such as solution mass flow rate, absorber pressure, concentration and cooling water temperature on absorber performance are analyzed. Besides, a coupled heat and mass transfer model is applied and solved with a finite difference method in order to determine the heat and mass transfer coefficients. Mass absorption rates of absorption processes respectively using LiBr solution and LiCl solution are compared under the conditions of the same temperature and saturated vapor pressure of the solution. Results show that the mass absorption rate using LiCl solution is up to 19.7% higher than LiBr solution. In addition, dimensionless formulations of heat and mass transfer coefficients are correlated with the average absolute error below 15%. The study is also helpful to design and optimize such kind of absorbers using LiCl solution as working fluid.

A two-dimensional steady-state heat and mass transfer mathematical model is established to study the performances of air-to-liquid dehumidifier with PVDF ultrafiltration membrane in liquid desiccant dehumidification in this paper. Terms in this mathematical model are amended with experimental data and improved with the method of calculating enthalpy of lithium chloride solution. The mean Nusselt number in air channel and mean Sherwood number are calculated and the correlations are fitted with the relevant quantities for predicting the heat and mass transfer coefficients. Furthermore, the corresponding heat and mass transfer coefficients are obtained and substituted as initial conditions into the mathematical model. Meanwhile, according to the relationship between the moisture content difference and water vapor partial pressure difference between inlet and outlet on air side, the diffusion coefficient is modified to meet the actual situation of the experiment. Joint surface renewal rate is proposed and regarded as a comprehensive index describing the relative motion of the fluids on both sides in the membrane dehumidification process. After analyzing the influences of controlled variables on mass transfer coefficient divided by density, the conclusion is obtained that the variable solution temperature group is inferior to the variable solution concentration group. The importance of maintaining low solution temperature during the dehumidification process is emphasized.

The effective heat capacity method and the enthalpy method are the two most common methods to build the numerical heat transfer models for phase change material (PCM) board. The objective of this research was to compare the PCM heat transfer models which were built by the effective heat capacity method and the enthalpy method respectively. Based on the numerical results of these two models, it was found that when the model was built with the effective heat capacity method, the calculation error was inevitable when the state (solid, molten or liquid) of PCM was changed during the calculation of one time step, while there was no such error when the model was built with the enthalpy method. The phase change temperature range could affect the magnitude of the calculation error when the model was built with the effective heat capacity method. When the phase change temperature range was very small, the calculation error of the model with the effective heat capacity method could be significant. However, the model with the effective heat capacity method needed less computing time than the model with the enthalpy method.