Adsorption Refrigeration Technologies

This chapter introduces a comprehensive overview about the principles, challenges and applications of adsorption refrigeration systems (ARSs), as a promising sustainable solution for many of cooling and heating applications. In addition to the features and the basics of ARSs, the following topics have been covered such as characteristics of working pairs, trends in improving the heat and mass transfer of the adsorber; advanced adsorption cycles and performance and operational data of some adsorption refrigeration applications. In some details, the operating range and the performance of ARSs are greatly affected by the employed working adsorbent/refrigerant pairs. Therefore, the study, development and optimum selection of adsorbent/refrigerant pairs, particularly the composite adsorbents, can lead to improving the performance and reliability of ARSs. Regarding the enhancement of heat and mass transfer in the adsorbent bed, two methods are commonly used: one is the development of adsorbents through different coating technologies or new materials such as metal-organic frameworks, and the second is the optimization of the adsorber geometrical parameters and cycle modes. Finally, a brief on some adsorption chillers applications have started to find their share in markets and driven by solar or waste heats

Multi-objective optimisation of MOF-801 adsorbent packed into copper foamed bed for cooling and water desalination systems

Recently, there have been several endeavours to enhance the performance of the adsorption systems for cooling cum desalination by developing new materials and adsorbent bed designs. Therefore, this article contributes to the field by computationally studying the utilisation of state-of-the-art MOF-801 adsorbent packed into the emerging copper-foamed adsorbent bed heat exchanger and benchmarking its performance against that utilising silica gel baseline adsorbent. A multi-objective global optimisation aimed simultaneously at the best coefficient of performance, specific cooling power, and clean water productivity was undertaken. The optimisation was built on the insights from a broad parametric study for the geometric and operating conditions. Given the novelty of the adsorbent MOF-801 and bed design combination, a one-dimensional model was developed to imitate the heat transfer in the adsorbent bed and coupled with a previously validated empirical lumped analytical model for the adsorption system using the MATLAB platform. Using copper foam significantly enhanced the effective thermal performance of the adsorbent bed, improving the overall system performance under different operating conditions. Furthermore, the clean water productivity of the MOF-801-based system outperformed that of the SG-based system by 38%, as the former yielded 29.7 m3/(ton.day), while the latter 21.5 m3/(ton.day). Besides, the MOF-801-based system showed specific cooling power of 830.8 W/kg compared to 611.5 W/kg for the silica gel-based system. However, the cooling capacity per unit volume determined the systems’ form factor, and the coefficient of performance was respectively higher by 9.6% and 20.2% for the silica gel-based system than those of the MOF-801-based system, stemming from the low packing density of MOF-801

Productivity and Thermal Performance Enhancements of Hollow Fiber Water Gap Membrane Distillation Modules Using Helical Fiber Configuration: 3D Computational Fluid Dynamics Modeling

Although hollow fiber water gap membrane distillation (HF-WGMD) units offer certain advantages over other MD desalination systems, they still require enhancements in terms of distillate flux and productivity. Therefore, this work proposes a novel configuration by incorporating the helical turns of HF membranes within the water gap channel of the HF-WGMD modules. A fully coupled 3D CFD model is developed and validated to simulate the multifaceted energy conservations and diffusion mechanisms that are inherent to the transport phenomena in the proposed HF-WGMD module. Single and double helical HF membrane designs with different numbers of turns are compared to the reference modules of single and double straight HF membrane designs under various operational conditions. At a feed temperature of 70 °C, a noteworthy 11.4% enhancement in the distillate flux is observed when employing 20 helical turns, compared to the single straight HF membrane module. Furthermore, the specific productivity revealed a maximum enhancement of 46.2% when using 50 helical turns. The thermal performance of the proposed HF-WGMD module shows higher energy savings of up to 35% in specific thermal energy consumption for a one-stage module. Using three stages of single helical modules can increase the gain output ratio from 0.17 for the single stage to 0.37, which represents an increase of 117.6%. These findings indicate the high potential of the proposed approach in advancing the performance of HF-WGMD systems

Investigation of the Mechanical and Tribological Behavior of Epoxy-Based Hybrid Composite

The main target of this study is to evaluate the impact of hybrid reinforcement using Al2O3 nanoparticles and graphite on the epoxy nanocomposites’ mechanical and tribological properties. Various weight fractions of the reinforcement materials, ranging from 0 to 0.5 wt.%, were incorporated into the epoxy. The aim is to enhance the characteristics and durability of the polymers for potential utilization in different mechanical applications. The addition of hybrid additives consisting of Al2O3 nanoparticles and graphite to the epoxy resin had a noticeable effect on the performance of the epoxy nanocomposites. The incorporation of these additives resulted in increased elasticity, strength, toughness, ductility, and hardness as the concentration of reinforcement increased. The enhancement in the stiffness, mechanical strength, toughness and ductility reached 33.9%, 25.97%, 25.3% and 16.7%, respectively. Furthermore, the frictional tests demonstrated a notable decrease in both the coefficient of friction and wear with the rise of the additives’ weight fraction. This improvement in the structural integrity of the epoxy nanocomposites led to enhanced mechanical properties and wear resistance. The SEM was utilized to assess the surfaces of tested samples and provide insights into the wear mechanism

Experimental Evaluation of a Solar Low-Concentration Photovoltaic/Thermal System Combined with a Phase-Change Material Cooling Technique

The high operating temperatures of photovoltaic (PV) panels negatively affect both electrical efficiency and material degradation rate. Combining both a water-cooling-based photovoltaic/thermal (PV/T) system and a phase-change material (PCM) with/without low concentration (LC) represents a promising solution for boosting the overall energy conversion efficiency of the PV system. This approach needs to be evaluated in harsh weather where the PCM should have a high melting temperature. Therefore, this study experimentally investigates the performance of three PV cooling systems, namely PV-PCM, PV/T-PCM, and LCPV/T-PCM, compared to a reference PV without cooling, under the weather conditions of Riyadh. The results show that the PV/T-PCM attained the highest daily average electrical and overall efficiencies of 14.24% (5% increase) and 42.7%, respectively, compared to 13.56% electrical efficiency of the reference panel. The electrical efficiency of the PV-PCM was 13.64% due to inefficient natural cooling in the afternoon. The LCPV/T-PCM recorded the best performance during the two hours around noon, with an average increase in electrical power and efficiency of 11.06% and a maximum overall efficiency of 70%. Finally, the LCPV/T-PCM system can be only effectively used to support the higher demand for electricity and thermal energy around noon; otherwise, a new design configuration with low concentration is needed to establish a higher electrical efficiency in most hours of sunlight

Enhancing the Tribo-Mechanical Performance of LDPE Nanocomposites Utilizing Low Loading Fraction Al₂O₃/SiC Hybrid Nanostructured Oxide Fillers

This research work highlights the tribomechanical investigations of using a low loading fraction of two ceramics combinations, Alumina (Al2O3) and Silicon Carbide (SiC) as reinforcement for Low-density Polyethylene (LDPE) matrix. The hybrid additives with different weight percentages (0.1 + 0.1, 0.25 + 0.25 and 0.5 + 0.5 wt%) were mixed with LDPE matrix and the degree of homogeneity was controlled using double-screw extruder prior to fabricating the composite samples via the injection molding machine. The nanoparticles fillers were characterized by field emission scanning electron microscope (FESEM), EDX and particle size analyzer to check its morphology, composition and size distribution. Thermogravimetric analyzer (TGA) and melting flow index (MFI) were performed for the fabricated nanocomposites samples. The mechanical properties of the nanocomposite were evaluated by performing tensile test, bending test and Shore-D hardness test, while the tribological performance was investigated using a ball on desk apparatus under different applied loads and sliding times. Moreover, in order to confirm the load-carrying capability of the composite, contact stresses was measured via finite element model using ANSYS software. The results show that the incorporation of low fraction hybrid ceramic nanoparticles can contributed positively in the tribological and mechanical properties. Based on the experimental results, the maximum improvement in the tensile strength was 5.38%, and 8.15% for hardness LDPE with 0.5 Al2O3 and 0.5 SiC, while the lowest coefficient of friction was noticed under normal load of 10 N, which was approximately 12.5% for the same composition. The novel approach of incorporating low fraction hybrid ceramic nanoparticles as reinforcement for LDPE matrix is investigated, highlighting their positive contributions to the tribological and mechanical properties of the resulting nanocomposites