Investigation on capacity matching in liquid desiccant and heat pump hybrid air-conditioning systems

Liquid desiccant and heat pump (LDHP) hybrid air-conditioning system provides a promising independent air dehumidification solution. Capacity matching among the four major heat and mass transfer components, i.e. dehumidifier, regenerator, evaporator and condenser, is essentially important for energy efficiency of the hybrid system. In this paper, the configuration of the hybrid system is firstly studied. Novel matching indices are proposed to evaluate the matching effect. The results show that a LDHP hybrid system with double-condenser, one solution-cooled and one air-cooled, is a feasible configuration for achieving capacity matching. To achieve dynamic capacity matching under real changing operating conditions, the effects of three critical operating variables, including solution flow rate, revolution of the compressor and air flow rate in the air-cooled condenser, on capacity matching and energy performance are studied. Simulation results show that dynamic capacity matching can only be achieved by regulating these three operating variables simultaneously.     

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.     

Performance investigation of desiccant liquid air membrane energy exchanger: Air and lithium chloride effects

The desiccant liquid air membrane energy exchanger is a promising technology used to recover both latent and sensible heat. In this paper, a numerical investigation is carried out to provide the optimal operating fluids properties as well as to enhance the exchanger performance. The physical problem involves a two dimensional model including the momentum, heat and mass transport equations in both air and desiccant liquid channels. The impact of air and desiccant liquid properties on the heat and mass transfer distributions is determined. Optimal values of inlet air and desiccant liquid properties are established. The thermal and mass fields inside desiccant liquid air membrane energy exchanger are numerically presented. This performance investigation provides a solution to improve the heat and mass transfer rates in the addressed membrane based technology.     

基于任务同步及节能的单机系统实时动态调度算法

提出了一种基于任务同步及节能的单机系统实时混合动态调度算法(HDSA), 以有效解决能耗及实时任务同步时的优先权反转所导致的缺乏实时可调度性的问题.HDSA包含静态算法及动态算法两部分.静态算法可在静态条件下, 固定临界区的运行速度, 并求出非临界区部分的静态速度. 动态调度算法在实际运行中, 在满足周期性任务实时可调度性及任务同步的条件下, 充分利用及回收任务运行时剩余的执行时间, 调节处理器的速度, 以有效降低能耗.同时也能避免高优先权任务被阻塞时, 低优先权任务的临界区继承高优先权任务的速度所造成的处理器电压开关的频繁切换, 故能有效地降低实时任务调度的成本.实验测试表明HDSA在调度性能上明显优于相关的有效算法.     

A heat pump driven and hollow fiber membrane-based liquid desiccant air dehumidification system: A transient performance study

Heat pump driven and hollow fiber membrane based liquid desiccant systems have been adopted for air dehumidification because of their capabilities to prevent liquid desiccant droplets from crossing over into the process air and to achieve high energy efficiencies. Due to the transient operating conditions like load and weather conditions, a transient model for the novel system is proposed in this study. Based on experiments and model simulations, the transient behaviors of the system are analyzed both at the start-up and in the normal operation periods. It is found that the initial concentration of the liquid desiccant and the volume of solution stored in the container play key roles at the start-up period, while the initial temperature has less influences. Adjusting the compressor speed is a feasible way to track the load and weather fluctuations. The model developed in this work is necessary for the control and optimization of the air dehumidification technology.     

Stability study of tetracyclines with respect to their use in slow release systems

In the aim of optimizing implantable slow-release systems for the local delivery of antibiotics, the stability of tetracyclines was studied in water at 37 °C or under irradiation. Four tetracyclines in their chlorhydrate form were chosen depending on their hydrophilic/hydrophobic balance. Their chemical stability was established by HPLC, and biological stability by bacteriological tests. It was shown that methacycline and doxycycline are stable in water for three days. Tetracycline and minocycline exhibit limited decomposition (less than 10%) under the same conditions. So, in vitro drug release for at most three days, appears to be possible. Besides, all four tetracyclines either in powdered form or included in a calcium phosphate matrix, kept their bacteriological activity after irradiation at 32.4 kGr. Consequently, the in vivo study of these implantable slow drug release systems, can be carried out.     

Experimental study of a liquid desiccant regeneration system: performance analysis for high feed concentrations

Clean Technologies and Environmental Policy - Liquid desiccant air-conditioning is an energy-efficient alternative to conventional vapor compression systems due to its ability to handle sensible...     

Concerns of corrosive effects with respect to lightning protection systems

Lightning protection system elements need to be selected from materials which are resistant to corrosion and should be protected from fast degradation. However, over the time corrosion will take place in the presence of galvanically dissimilar metals in the same electrolyte (moisture). Historically, copper, aluminium and copper alloys (including bronze and brass) have been used in lightning protection applications as these materials are highly conductive and abundantly available. Corrosive effects on system components are influenced by the environmental factors such as moisture, soil type and temperature that make the corrosion process highly complex in soil. As per many standards on the installation of lightning protection systems, combinations of materials that naturally form electrolytic couples shall not be used, for example copper and steel, especially in the presence of moisture, in which corrosion will be accelerated. Similarly, the conditions within soil will have adverse effects on the ground system elements. Down conductors entering corrosive soil must be protected against corrosion by a protective covering. The paper presents the causes of corrosion and recent developments in minimising the corrosion associated with lightning protection and grounding systems.     

Possible energy saving by compensating heat inputs to liquid helium through current leads and thermal bridges

The possibility of energy saving by compensating heat inputs to liquid helium through current leads and thermal bridges is discussed. This saving is due to a suitable distribution of evaporated helium between current leads (or thermal bridges) and a regrigerator. In the analytical model considered energy savings for current leads compared to the theoretical minimum are of order 10–15%, for thermal bridges savings are possible only if the temperature of the hot end is equal to or lower than that of liquid nitrogen.     

Hybrid solar-driven interfacial evaporation systems: Beyond water production towards high solar energy utilization

Owing to its promising approach to tackling freshwater scarcity, solar-driven interfacial evaporation (SDIE) which confines the photothermal heat at evaporating surface has attracted tremendous research attention. Optimizing efforts on photothermal conversion and thermal management have greatly improved the SDIE performance. By taking advantage of the heat localization strategy, hybrid SDIE systems have been designed to enhance the solar energy utilization beyond water production. In this review, the development of SDIE and energy flow in hybrid system are discussed. The advanced conceptual designs of different hybrid applications such as electricity generation, fuel production, salt collection, photodegradation and sterilization are comprehensively summarized. Moreover, the current challenges and future perspectives of the hybrid systems are emphasized. This article aims to provide a systematic review on the recent progresses in hybrid SDIE systems to inspire both fundamental and applied research in capitalizing the undervalued auxiliary energy sources for future integrated water, energy and environmental systems.     

A study on an optimal approach temperature control strategy of condensing water temperature for energy saving

An optimal approach temperature (OAT) control strategy is proposed for resetting the condensing water temperature hourly, so to maximize the performance of the combined water chiller and cooling tower system. A system performance factor is introduced for evaluation of the system performance. A regression function is presented for the calculation of an optimal condensing water temperature at each hour of air-conditioning operation. The parameters in the regression function include the ambient wet bulb temperature, the chiller load ratio at the hour, and a dimensionless relative efficiency of chiller and cooling tower. The regression function has an R² close to 1 compared to the computed results. When applied to two cities in Taiwan, the OAT control strategy has a potential to save energy more than 4% on an annual basis. The OAT control strategy is most advantageous when applied to regions with large seasonal variation of wet bulb temperature.     

A new approach to the energy theorems for many-particle systems

Summary The energy theorems regarding a system with a large number of particles are reviewed on the basis of two distinct classes of motion and a new definition of heat is given. Consequently the first law of Thermodynamics is expressed in a more general form. Some examples are examined.With 2 Figures     

Experimental study of the copper thiosulfate system with respect to thin-film deposition

An experimental study of the copper-thiosulfate system in mild acidic (pH 5) aqueous solutions, with respect to thin-film formation, was undertaken. Thin films of Cu_xS (1 x 2) were deposited by a simple electroless technique on glass or transparent polyester films, at 50 °C. Thin films were deposited from chemical baths in which the ratios of copper to thiosulfate were varied from 1:1 to 1:10. Thin films of different compositions (Cu₂S, Cu_1.8S, Cu_1.4S and CuS) were prepared and then characterized for morphological, optical and electrical properties. The deposited films chemically close to Cu₂S were found to be amorphous, while the CuS films were a mixture of both amorphous and polycrystalline phases. The optical spectra of the Cu₂S films exhibited high transmission both in the visible region of the spectrum (beyond 600 nm) and throughout the near-infrared region (800 to 2500 nm), while CuS films were found to be highly absorptive throughout the near-infrared region, with peaked transmission in the visible region at about 560 nm. The sheet resistances of the films, determined by the standard four-probe measurements, were between 100 and 650 Ω/square.     

When quantitative meets qualitative: enhancing OPM conceptual systems modeling with MATLAB computational capabilities

Conceptual modeling is an important initial stage in the life cycle of engineered systems. It is also highly instrumental in studying existing unfamiliar systems—the focus of scientific inquiry. Conceptual modeling methodologies convey key qualitative system aspects, often at the expense of suppressing quantitative ones. We present and assess two approaches for solving this computational simplification problem by combining Object-Process Methodology (OPM), the new ISO/PAS 19450 standard, with MATLAB or Simulink without compromising the holism and simplicity of the OPM conceptual model. The first approach, AUTOMATLAB, expands the OPM model to a full-fledged MATLAB-based simulation. In the second approach, OPM computational subcontractor, computation-enhanced functions replace low-level processes of the OPM model with MATLAB or Simulink models. We demonstrate the OPM computational subcontractor on a radar system computation. Experimenting with students on a model of an online shopping system with and without AUTOMATLAB has indicated important benefits of employing this computation layer on top of the native conceptual OPM model.     

A semi-Markovian model allowing for inhomogenities with respect to process time

A non-homogeneous semi-Markov process is considered as an approach to model reliability characteristics of components or small systems with complex test resp. maintenance strategies. This approach generalizes previous results achieved for ordinary inhomogeneous Markov processes. This paper focuses on the following topics to make the application of semi-Markovian models feasible: rather than transition probabilities Q_ij(t), which are used in normal mathematical text books to define semi-Markov processes, transition rates λ_ij( ) are used, as is usual for ordinary Markov processes. These transition rates may depend on two types of time in general: on process time and on sojourn time in state i. Such transition rates can be followed from failure and repair rates of the underlying technical components, in much the same way, as this is known for ordinary Markov processes. Rather than immediately starting to solve the Kolmogorov equations, which would result in N² integral equations, a system of N integral equations for frequency densities of reaching states is considered. Once this system is solved, the initial value problem for state probabilities can be solved by straightforward integration. An example involving 14 states has been solved as an illustration using the approach.     

A methodology for augmenting sparse pairwise comparison matrices in AHP: applications to energy systems

Multiple-attribute decision making (MADM) techniques can be used to provide a systematic approach to selection problems in energy engineering and management. They may be used for selecting the best technologies or policies based on environmental, technical, and socio-economic criteria. Among the many available MADM techniques, the analytic hierarchy process (AHP) has become one of the most widely used due to its effective hierarchical decomposition of complex problems. However, AHP may be tedious due to the large number of pairwise comparisons needed in large problems. Furthermore, in many cases, relevant information may also be available for determining criteria weights based on past decisions that have proven satisfactory in retrospect. Thus, we propose a simple methodology for augmenting sparse pairwise comparisons in AHP through a non-linear programming model that extracts a set of consistent weights from a priori ranking of a subset of alternatives. Two case studies on the ranking of bioethanol feedstocks and of CO₂ storage sites are then shown to illustrate this technique.     

Review: Density measurements in liquid metals and liquid binary alloy systems — A survey

A survey is given of the principal methods which have been used by various workers for the determination of the density (or specific volume) of pure metals and binary alloy systems in the liquid state. A selection of results obtained with the various methods for certain pure metals (Ag, Cu, Zn, Sn) and alloy systems (Cu-Sn, Ag-Sn, Bi-Sn, Pb-Sn, Cu-Pb, Ag-Bi, Ag-Pb and Hg-Tl) is displayed and discussed. The need for further systematic study of the density of alloy systems e.g. in the case of the Group Ib-IVb systems is stressed. A comprehensive survey of references to existing density measurements made on binary alloy systems up to the present time is given in an appendix.