Experimental performance analysis and modelling of liquid desiccant cooling systems for air conditioning in residential buildings

The paper presents a new desiccant cooling cycle to be integrated in residential mechanical ventilation systems. The process shifts the air treatment completely to the return air side, so that the supply air can be cooled by a heat exchanger. Purely sensible cooling is an essential requirement for residential buildings with no maintenance guarantee for supply air humidifiers. As the cooling power is generated on the exhaust air side, the dehumidification process needs to be highly efficient to provide low supply air temperatures. Solid rotating desiccant wheels have been experimentally compared with liquid sorption systems using contact matrix absorbers and cross flow heat exchangers. The best dehumidification performance at no temperature increase was obtained in an evaporatively cooled heat exchanger with sprayed lithium chloride solution. Up to 7 g kg⁻¹ dehumidification could be reached in an isothermal process, although the surface wetting of the first prototype was low. The process then provides inlet air conditions below 20 °C for the summer design conditions of 32 °C, 40% relative humidity. With air volume flow rates of 200 m³ h⁻¹ the system can provide 886 W of cooling power.A theoretical model for both the contact absorber and the cross flow system has been developed and validated against experimental data for a wide range of operating conditions. A simulation study identified the optimisation potential of the system, if for example the surface wetting of the liquid desiccant can be improved.     

Experimental investigation of solar driven desiccant air conditioning system based on silica gel coated heat exchanger

A silica gel coated heat exchanger based air conditioning system driven by the evacuated tube solar water heater has been experimentally investigated. The system has been operated for two different modes namely cooling with dehumidification mode and heating with humidification mode in summer and winter season respectively. The system performance is analyzed in terms of regeneration rate, dehumidification rate and thermal coefficient of performance (COP_th). Experimental results demonstrated that, for cooling and dehumidification mode, the process air is cooled by an average temperature of 8.5 °C. A better dehumidification rate can be achieved by using pre-cooling before dehumidification process. Post-cooling after dehumidification process is found to be advantageous for cooling capacity and COP_th. For heating with humidification mode, the process air is heated by an average temperature of 13.3 °C with an average increment in humidity ratio of 1.9 g/kg. It is found that the average COP_th of the system is 0.45 and 0.87 for cooling and heating mode respectively.     

Experimental study on a new internally cooled/heated dehumidifier/regenerator of liquid desiccant systems

For providing good performance of dehumidifier and regenerator with certain dimensions, a new type of internally cooled/heated dehumidifier/regenerator based on the plate–fin heat exchanger (PFHE) was designed. To investigate the behavior of the new equipment, an experimental setup was established in an environment chamber with regulable temperature and humidity air. By the internally cooled dehumidification testing, effects of the cooling water temperature, the air flow rate and the desiccant temperature on the dehumidification performance and the cooling efficiency were presented. The behavior of internally cooled dehumidification process was compared with that of the adiabatic dehumidification process. The results suggested that the cooling efficiency decreased with the increasing of the cooling water temperature and desiccant with low temperature could bring more mass transfer coefficients. There is an optimal air flow rate to achieve the maximum absolute humidity decrease of the air. By the internally heated regeneration testing, effects of the air flow rate and the desiccant inlet temperature on the regeneration performance and air outlet parameters were discussed and also compared with those of the adiabatic regeneration process. It was concluded that the regeneration efficiency of internally heated regeneration was more than that of the adiabatic regeneration, and the internally heated regenerator could offer better thermal performance.     

New mass transfer performance data of a cross-flow liquid desiccant dehumidification system

This paper presents new mass transfer performance data of a cross-flow liquid desiccant dehumidification system using a structured packed tower. The structured packing consists of cross-corrugated cellulose paper sheets with a surface area per unit volume ratio of 608 m² m^?3. The liquid desiccant, viz. calcium chloride, flows through the pad from top to bottom, while the air flows horizontally making it a cross-flow configuration. The experimental dehumidification effectiveness from the present study was compared with the widely used Chung's correlation (although developed for counter flow arrangement, as opposed to cross-flow in the current study) and Liu et al.'s correlation. A new empirical correlation was developed for the dehumidification effectiveness, which fitted the experimental data to within ±10%. The effect of varying air and solution inlet conditions and flow rates on the system performance was also quantified in the paper.     

多级矩阵结构冷却除湿器的除湿性能研究

为了降低空分系统压缩机功耗,提高压缩机运行可靠性,本文提出一种用于压缩机进气除湿的多级矩阵结构的冷却除湿器,并搭建了多级冷却除湿实验台,测试了除湿器的除湿性能。实验结果表明,在进口空气含湿量和温度固定为11.7 g/(kg干空气)和24.4 ℃时,当空气质量流量由0.48 kg/s增至0.78 kg/s,空气出口含湿量由7.1 g/(kg干空气)增至7.7 g/(kg干空气);在进口空气质量流量和温度固定为0.53 kg/s和25.2 ℃时,当冷却水温度由6.9 ℃升至11.9 ℃,空气出口含湿量由7.1 g/(kg干空气)增至9.4 g/(kg干空气)。同时,建立了除湿器内部传热传质过程的稳态数值模型,将模拟结果与实验结果进行对比。结果表明,该模型对于除湿器出口空气含湿量和温度的平均误差分别为8.6%和2.1%,显示出较好的可靠性。进一步模拟研究了多级矩阵结构与单级叉流结构冷却除湿器的除湿性能,发现采用多级结构可以有效提高除湿效率,在进口空气流量和冷却水质量流量分别为0.53 kg/s和0.3 kg/s时,多级结构的除湿量可以提高4.3%,除湿效率可以提高2.5%;通过增加填料模块的长度,可以提高除湿效率。当长方体填料模块体积固定为0.054 m3,模块长度由0.14 m增至0.28 m时,传质系数可由4.3 g/(m2?s)增至6.5 g/(m2?s),除湿效率由66.4%升至79.2%。     

无霜空气源热泵系统除湿与再生工况?分析

为解决传统空气源热泵系统冬季的结霜问题,同时提升夏季机组的性能,本文提出一种"一塔三用"的无霜空气源热泵系统。通过搭建实验台研究了在除湿工况下的空气温度、含湿量、质量流量及溶液温度、质量流量、质量浓度,在再生工况下的溶液质量浓度、温度对溶液塔进出口空气?、除湿?(再生?)、系统输入输出?及?效的影响。结果表明:除湿工况下,除湿?随空气温度、空气质量流量、溶液质量流量的增加以及空气含湿量、溶液温度、溶液质量浓度的减少而增加;系统的?效随空气温度、含湿量、质量流量及溶液质量流量、质量浓度的增加以及溶液温度的减少而增加,其中空气含湿量、溶液质量浓度对?效影响较小,此模式?效最高可达0. 201。再生工况下,再生?随溶液质量浓度、温度的增加而增加;系统?效随溶液质量浓度的增加、溶液温度的减少而增加,其中溶液温度对?效影响较小,此模式?效最高可达0. 108 8。该系统?效率在实验工况下高于常规空气源热泵系统。     

Formability,mechanical and corrosive properties of Mg–Nd–Zn–Zr magnesium alloy seamless tubes

Some large Mg–3.0Nd–0.2Zn–0.4Zr (NZ30K) magnesium alloy seamless tubes were prepared by forward extrusion. The as-extruded tubes were cooled in the air or by spraying liquid N₂ after extrusion. The formability, mechanical and corrosive properties of the NZ30K magnesium alloy seamless tubes were investigated. The experimental results show that seamless NZ30K tubes with an outer diameter of 110 mm and inner diameter of 90 mm can be produced by forward extrusion and the tubes have good roundness, concentricity and straightness even without any straightening. The tensile results show that the maximum ultimate tensile strength, yield strength and elongation of the extruded tubes cooled in the air and by spraying liquid N₂ are 306.3 and 314.6 MPa, 250.4 and 270.3 MPa, 14.2% and 15.6%, respectively. The corrosion rates of the as-extruded tubes cooled in the air and by spraying liquid N₂ immersed in 5% NaCl solution for 3 days are 0.225 and 0.234 mg cm⁻² day⁻¹, respectively, which are a little inferior to the as-cast, T4 and T6 NZ30K alloys, but much lower than that of AZ91 alloy. Localized corrosion is suggested to be its corrosion pattern.     

Chemical dehumidification by liquid desiccants: theory and experimentDeshumidification chimique par des substances absorbantes liquides: theorie et expérimentation

Chemical dehumidification of air by a liquid desiccant in a packed tower has been investigated both theoretically and experimentally for air conditioning and industrial applications. A computer model of a packed tower, able to determine heat and mass transfer between air and desiccant, has been developed and a parametrical study was carried out considering the solutions H₂O/LiBr and H₂O/CaCl₂ to determine the optimum operative conditions. An experimental apparatus including a packed tower and a desiccant regenerator has been described together with experimental results: a set of 70 experimental runs with H₂O/LiBr. Data have been reported and compared against the results of the computer code simulations.     

Oxidation behaviour of the sintered Si3N4-Y2O3-Al2O3 system

The oxidation behaviour of silicon nitride composed of Si₃N₄, Y₂O₃, Al₂O₃, AlN and TiO₂ was investigated in dry and wet air at 1100–1400 °C. The oxidation rates were confirmed to obey the parabolic law. An activation energy of 255 kJ mol^–1 was calculated from the Arrhenius plots of the results of oxidation in an air flow. In still air the oxidation rate was larger than that in an air flow, but the oxidation rate in flowing air was not affected by the air flow rate. -cristobalite and Y₂O₃·2SiO₂ were formed in oxidized surface layers. These crystal phases increased with increasing oxidation temperature. In particular, a higher content of -cristobalite was obtained in still air oxidation. The existence of water vapour in flowing air greatly promoted the oxidation.Concurrent with Kanagawa Academy of Science and Technology.     

Preparation of Exfoliated Graphite Modified with Magnesium Ferrite

A magnetic sorbent based on exfoliated graphite modified with magnesium ferrite has been prepared by impregnating oxidized graphite in a mixed solution of FeCl₃ and Mg(NO₃)₂, followed by heat treatment of the impregnated oxidized graphite in air. X-ray diffraction and Mössbauer spectroscopy results demonstrate that the structure of the magnesium ferrite is an inverse spinel with a degree of inversion of 0.59. The saturation magnetization of the magnesium ferrite-containing exfoliated graphite is 16.1 emu/g, whereas its oil sorption capacity is as high as 54 g/g. Compaction of the exfoliated graphite to a density of 0.03 g/cm³ reduced its sorption capacity to 26 g/g. Further increasing the density of the material led to a considerable decrease in its sorption capacity.     

An experimental study on the dehumidification performance of a counter flow liquid desiccant dehumidifier

This paper presents an experimental study on the dehumidification performance of a counter flow liquid desiccant dehumidifier using structured packing with a high specific surface area (650 m² m⁻³). New empirical equations correlating the moisture effectiveness and the enthalpy effectiveness with critical inlet parameters are developed, which can be used to conveniently predict the performance of a similar dehumidifier. The empirical correlations are validated using the experimental data of this study, and compared with the experimental data reported by another researcher. The deviations are within ±10% for the former and within ±15% for the latter. The performance of the present type of packing is also compared with other two types of structured packing available in literature. The influences of the inlet conditions of the air and the desiccant as well as the packing height on the dehumidification performance are also investigated and compared with the results reported in previous studies.     

Textile Inspired Lithium–Oxygen Battery Cathode with Decoupled Oxygen and Electrolyte Pathways

The lithium–air (Li–O₂) battery has been deemed one of the most promising next‐generation energy‐storage devices due to its ultrahigh energy density. However, in conventional porous carbon–air cathodes, the oxygen gas and electrolyte often compete for transport pathways, which limit battery performance. Here, a novel textile‐based air cathode is developed with a triple‐phase structure to improve overall battery performance. The hierarchical structure of the conductive textile network leads to decoupled pathways for oxygen gas and electrolyte: oxygen flows through the woven mesh while the electrolyte diffuses along the textile fibers. Due to noncompetitive transport, the textile‐based Li–O₂ cathode exhibits a high discharge capacity of 8.6 mAh cm^?2, a low overpotential of 1.15 V, and stable operation exceeding 50 cycles. The textile‐based structure can be applied to a range of applications (fuel cells, water splitting, and redox flow batteries) that involve multiple phase reactions. The reported decoupled transport pathway design also spurs potential toward flexible/wearable Li–O₂ batteries.     

A Metal‐Free,Free‐Standing,Macroporous Graphene@g‐C3N4 Composite Air Electrode for High‐Energy Lithium Oxygen Batteries

The nonaqueous lithium oxygen battery is a promising candidate as a next‐generation energy storage system because of its potentially high energy density (up to 2–3 kW kg^?1), exceeding that of any other existing energy storage system for storing sustainable and clean energy to reduce greenhouse gas emissions and the consumption of nonrenewable fossil fuels. To achieve high energy density, long cycling stability, and low cost, the air electrode structure and the electrocatalysts play important roles. Here, a metal‐free, free‐standing macroporous graphene@graphitic carbon nitride (g‐C₃N₄) composite air cathode is first reported, in which the g‐C₃N₄ nanosheets can act as efficient electrocatalysts, and the macroporous graphene nanosheets can provide space for Li₂O₂ to deposit and also promote the electron transfer. The electrochemical results on the graphene@g‐C₃N₄ composite air electrode show a 0.48 V lower charging plateau and a 0.13 V higher discharging plateau than those of pure graphene air electrode, with a discharge capacity of nearly 17300 mA h g^?1 _(composite). Excellent cycling performance, with terminal voltage higher than 2.4 V after 105 cycles at 1000 mA h g^?1 _(composite) capacity, can also be achieved. Therefore, this hybrid material is a promising candidate for use as a high energy, long‐cycle‐life, and low‐cost cathode material for lithium oxygen batteries.     

气调冷库加湿分析与软件算法

气调冷库内的果蔬在被冷却的同时,由于自身呼吸热和干冷空气的吸湿作用会不断失去自身水分,这不但会加速自身营养成分的流失和破坏,而且会减少自身的质量,造成较大的经济损失。因此,对气调冷库内的果蔬及时、准确地加湿是一项非常重要的技术工作。本文分析阐述减湿和加湿的原理及过程,并提出修正的湿空气物性参数模型方程,依据牛顿迭代算法,开发冷库果蔬加湿计算机辅助计算软件,其计算结果与现有冷库工作过程的实测数据相吻合。     

A modified model of solar collector/regenerator considering effect of the glazing temperature

Solar liquid collector/regenerator (C/R), combining the functions of solar collector and regenerator of absorbent solution together, can be effectively utilized in solar energy-driven liquid desiccant cooling systems. Based on thermal balance of the glazing of solar C/R, a group of modified heat and mass transfer models, validated by experimental results to reflect solution regeneration process more truly, were put forward in this paper. Numerical simulation showed only preheating air stream, keeping an equal humidity ratio, did raise the performance of solar C/R, but preheating solution increased the regeneration efficiencies to reach twice that of preheating air stream. There occurred optimum mass flow rates for both air stream and solution film reaching 36–48 kg m⁻¹ h⁻¹ and 4∼6 kg m⁻¹ h⁻¹ respectively for solar C/Rs of 3∼6 m long. As for effect of the length of solar C/Rs, the regeneration efficiency η_r reached a maximum value at about 4 m and shorter or longer solar C/Rs failed to increase solution regeneration efficiencies.     

Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors

Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180°C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H₂SO₄ solution. A remarkable specific capacitance of 602.36 Fg^?1 (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs^?1 in 1 M H₂SO₄ solution and 155.78 Fg^?1 for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.     

Reversible CO2 capture by ZnO slurry leading to formation of fine ZnO particles

ZnO powders were synthesized by heating precursors, prepared by the addition of ethylene diamine tetraacetate to an aqueous solution of zinc acetate, at 500?°C in air. A ZnO slurry was prepared by adding distilled water to the synthesized ZnO powder. X-ray diffraction studies confirmed that the ZnO slurry adsorbed CO₂ at 25?°C under a CO₂ gas flow to produce Zn₅(CO₃)₂(OH)₆. The CO₂ adsorption ratio of the ZnO slurry was influenced by the amount of added water. When the weight ratio of water/ZnO was 1, the ZnO slurry had the largest CO₂ adsorption ratio. Scanning electron microscopy and thermal gravimetry showed that the plate-like Zn₅(CO₃)₂(OH)₆ particles thermally decomposed at 300?°C in air leading to a single-phase ZnO powder consisting of nanoparticles with approximately 20?nm in diameter. The specific surface area of the reformed ZnO powder increased to approximately 82?m²/g through the thermal decomposition of Zn₅(CO₃)₂(OH)₆. The ZnO slurry was capable of adsorbing CO₂ under a CO₂ flow at 25?°C and desorbing CO₂ under an air flow at 300?°C. The CO₂ adsorption ratio of the ZnO slurry reached 80%–90% at 25?°C even after the fifth CO₂ adsorption and desorption cycle.     

Augmented desalination with cooling integration

Humidification–dehumidification (HDH) desalination works based on a water cycle principle and involves air humidification and condensation (dehumidification). The cooling of humid air with chilled water increases the desalination and results in cold air suitable for air conditioning process. The merits of the proposed HDH desalination and cooling are not analyzed and compared in the literature. Therefore, the performance results of HDH with normal water (current technology) and HDH with chilled water (proposed idea) are compared to highlight the merit of this cycle. The combined cycle for desalination and cooling has been solved thermodynamically with psychrometric properties. The results are validated with a laboratory experimental setup. The examined operational process conditions are hot water inlet temperature, efficiency of humidifier, and vapor absorption refrigerator's (VAR's) evaporator exit temperature. The focused results are desalination, cooling and energy utilization factor (EUF). The comparative study recommends the use of chilled water in the final stage. The two stage desalination with dehumidification by normal water in the first stage and chilled water in combined two stages improves the cycle EUF from 0.18 to 0.33. Out of 300 W of cooling generation, 100 W is used for dehumidification and the remaining 200 W is available for air conditioning process at 15 N⋅m³ h⁻¹ of air.     

Heat transfer in the flow of low-density air in narrow channels

Results are given from measurements on air flow in narrow channels; relationships in dimensionless terms are derived for the heat transfer over a wide range in speed (1–120 m/sec) and in pressure (1 · 10⁵ > P > 1.33 · 10³) N/m².Notation V volume flow rate of air - N total number of buret divisions - P₀ pressure in measuring tank - l length of measuring section of buret - t time of oil column rise to the height h_i - n number of buret division corresponding to_i - _o, _m specific weights of oil and mercury - c scale division of buret - h₂ height of oil drop in measuring cylinder - v₀ total volume of system from needle throttle to heat exchanger inlet - P_p pressure at heat exchanger inlet - T_p, T₀ temperature at heat exchanger inlet and of surrounding air - G flow rate in mass terms - c_p mean specific heat of air - t temperature variation over measuring section - Nu, Re Nusselt and Reynolds numbers - l, d length and diameter of channel Translated from Inzhenerno-Fizicheskii Zhurnal, vol. 20, No. 5, pp. 879–883, May, 1971.     

Improvement of production efficiency of spray-synthesized HKUST-1

Spray synthesis of metal–organic frameworks (MOFs) is desirable for scaled production. In this study, we designed a new apparatus for spray-synthesizing MOFs, wherein an upward spraying and swirling air flow was applied to prevent loss of the precursor solution. We evaluated the effects of the flow rate and temperature of swirling air, temperature of the reactor tube, initial feed rate of the precursor solution, and precursor concentration on the yield, purity, space–time yield (STY), BET surface area, and average particle size. The swirling air flow along with re-spraying of the solution accumulated on the upward spray nozzle improved yield significantly. The highest STY was 45.7 kg/m³/day obtained at a precursor feed rate of 5 mL/min; the highest surface area was 1,872 m²/g obtained at a precursor concentration of 1.38 mol/L. The sample with the highest surface area exhibited 2.60 wt% of hydrogen adsorption capacity at 77 K and 1 bar, with 7.6–6.1 kJ/mol of heat of hydrogen adsorption.