Operating parameters of a membrane-based parallel-plate liquid desiccant dehumidification system are investigated in this paper. The liquid desiccant and air are in a cross-flow arrangement, and separated by semi-permeable membranes to avoid carry-over problem. A numerical model is developed to simulate the system performance, and validated by experimental and analytical results. Impacts of main operating parameters on the system performance (i.e. sensible, latent and total effectiveness) are evaluated, which include dimensionless parameters (i.e. solution to air mass flow rate ratio * and number of heat transfer units ), solution properties (i.e. concentration and temperature ) and inlet air conditions (i.e. temperature , and relative humidity , ). It is found that * and are two of the most important parameters influencing the system effectiveness. Even though the system performance can be improved by * and , its increasing gradient is limited when * and exceed 1 and 4 respectively. Decreasing solution temperature does not make a great improvement to the system performance, however, increasing solution concentration is a good approach to enhance the latent effectiveness without influencing the sensible effectiveness. The system shows the broad adaptability in various weather conditions, and has the ability to provide relative stable state supply air.

Air dehumidification is of vital importance in building air conditioning and production safety. Semi-permeable membrane module is a novel heat and mass exchanger, which separates the air and liquid desiccant to overcome desiccant droplet carry-over problem in traditional direct-contact systems. Recently, some research works have been carried out in mathematical modelling and experimental testing of membrane-based liquid desiccant dehumidification technology. Compared with the experimental testing, the mathematical modelling has advantages of significant time and cost reductions, practically unlimited level of detail, more profound understanding of physical mechanism and better investigation of critical situation without any risks. This paper presents a comprehensive review of various modelling methods for two types of membrane-based liquid desiccant modules: flat plate and hollow fiber.

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Compact linear Fresnel reflector (CLFR) system employing multiple receivers is promising with better optical performance and cost effectiveness compared to linear Fresnel reflector (LFR) system, especially for applications with limited ground availabilities. Nevertheless, only few researches have been conducted to evaluate optical design and performance of the CLFR system. In this study, geometrical models for the CLFR system with flat mirrors and receivers are developed on the basis of polar orientation. A comparative study of concentration characteristics among the LFR, CLFR-complete and CLFR-hybrid systems is conducted based on numerical, ray tracing simulation and experimental results. In addition, optical design analyses of the CLFR-hybrid system are carried out from various design aspects. It is noteworthy that the mirror arrangement and focal length should be optimized for the CLFR-hybrid system with considerations of the associated geometrical characteristic and optical performance. For a small-scale CLFR-hybrid system with a solar field width of 2100mm and a focal length of 1500mm, the geometrical concentration ratio of 15.14 and ground utilization ratio of 0.95 are achieved respectively. The findings demonstrate the feasibility of the CLFR-hybrid system with flat mirrors and polar orientation, which provide progress to the concentrated solar power technology.

A membrane-based liquid desiccant dehumidification cooling system is studied in this paper for energy efficient air conditioning with independent temperature and humidity controls. The system mainly consists of a dehumidifier, a regenerator, an evaporative cooler and an air-to-air heat exchanger. Its feasibility in the hot and humid region is assessed with calcium chloride solution, and the influences of operating variables on the dehumidifier, regenerator, evaporative cooler and overall system performances are investigated through experimental work. The experimental results indicate that the inlet air condition greatly affects the dehumidification and regeneration performances. The system regeneration temperature should be controlled appropriately for a high energy efficiency based on the operative solution concentration ratio. It is worth noting that the solution concentration ratio plays a considerable role in the system performance. The higher the solution concentration ratio, the better the dehumidification performance. However simultaneously more thermal input power is required for the solution regeneration, and a crystallization risk in the normal operating temperature range should be noted as well. The system mass balance between the dehumidifier and regenerator is crucial for the system steady operation. Under the investigated steady operating condition, the supply air temperature of 20.4°C and system COP of 0.70 are achieved at a solution concentration ratio of 36%.

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Introduction Phase change materials (PCMs) absorb, store, and passively release available thermal energy via latent heat transfer during phase change, thereby reducing peak demand and improving thermal comfort (Salunkhe and Shembekar, 2012; Kalnaes and Jelle, 2015; Wang et al., 2020). The thermal performance of PCMs is based on their melting point, thermal conductivity, and energy storage density. For this reason, when applied as energy storage, they require an instant melting and solidification point (Ji et al., 2014; Ma, Lin and Sohel, 2016). Paraffins, salt hydrates, and fatty acids are the most commonly used PCMs, having a melting temperature within human thermal comfort, making them suitable for building applications. However, such materials have major drawbacks, including low thermal conductivity, especially for organic PCMs. As a result, performance enhancements of PCMs are eagerly researched, to develop improved techniques (Fan and Khodadadi, 2011). Such methods require the addition of highly conductive materials, which can be done by modification of the encapsulation material, the shape of the container, using heat pipes, heat exchangers, micro-and macro-encapsulation, or the addition of highly conductive nanoparticles in the base fluid, creating nano-enhanced PCM (Babaei, Keblinski and Khodadadi, 2013; Ma, Lin and Sohel, 2016). Further techniques proposed the integration of metallic fins, foam wools, and graphite (Ji et al., 2014; Fan et al., 2013). The literature views of PCM enhancement materials have identified graphite, aluminium, and carbon as the most frequently applied materials for organic PCM enhancement. There are two methods to integrate PCM in building elements. The first method, "shape-stabilized", considers the direct addition of the PCM into a building element, such as a gypsum wall (Silva, Vicente and Rodrigues, 2016). The second method requires the PCMs to be encapsulated for technical use, as otherwise the material would disperse from the location (Cabeza et al., 2011). For this reason, the encapsulation method is the most commonly used form of integration and has become a topic of analysis in recent years. The geometry of the encapsulation can take any shape, but the most popular forms are tubes, pouches, spheres, and panels. Encapsulation geometry could potentially be harnessed as a heat enhancement method, improving the thermal conductivity of the PCMs (Amin, Bruno and Belusko, 2014). Additional benefits of encapsulation include the capacity to counteract phase segregation, which is a regular phenomenon particularly prevalent with salt hydrates, in which the high storage density of the material disperse in layers, leading to the decline in the storage efficiency.

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