Development of bubble absorption refrigeration technology: A review
TL;DR: In this paper, the development of bubble absorption refrigeration technologies is discussed from the aspects of driving energies, performance enhancement and application extension, and methods of enhancing bubble absorption performance were researched, and also the influence mechanisms of these physical and chemical methods were explained.
Abstract: This study reviews the developments of bubble absorption refrigeration technologies. Firstly, the principles of the bubble absorption refrigeration systems as well as bubble absorbers were introduced; And then bubble behavior characteristics during the absorption process were observed and expressed graphically; Thirdly, available bubble absorbers were investigated, modeled and compared; In addition, current and potential refrigerant-absorbent pairs in the bubble absorption refrigeration systems were analyzed, and about fifty fluids were involved totally. What’s more, methods of enhancing bubble absorption performance were researched, and also the influence mechanisms of these physical and chemical methods were explained; Finally, the development of bubble absorption refrigeration technologies were discussed from the aspects of driving energies, performance enhancement and application extension. The tendency of bubble absorption refrigeration technologies is expected to be high efficiency, miniaturization, and intellectualization. The expressed contents in this paper are expected to be useful for readers in the fields of absorption refrigeration technologies and the medium-low grade heat utilization technologies, especially for the equipment operating in the unsteady conditions (e.g. swing, bump, jolt, scram, etc.).
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TL;DR: In this paper, the influence of different amounts of TiO2 nanoparticles on the coefficient of performance (COP) of the ammonia-water absorption refrigeration system (AARS) was investigated.
Abstract: This paper experimentally investigated the influence of the different amounts of TiO2 nanoparticles on the coefficient of performance (COP) of the ammonia–water absorption refrigeration system (AARS). Based on our previous experimental results and other researchers’ literature, TiO2 nanofluids in mass fractions of 0.1%, 0.3%, and 0.5% were prepared and added to the newly built miniaturized AARS, also, the mixture of 0.5 wt% TiO2 and the 0.02 wt% SDBS was also applied. In the test conditions, evaporation temperatures ranged from −18 °C to 0 °C, generation temperatures ranged from 105 °C to 150 °C, and inlet cooling water temperatures ranged from 22 °C to 33 °C. Experimental results show that: the TiO2 nanoparticles have great effects on AARS, and the COP can be increased by up to 27%; the mixture of 0.5 wt% TiO2 and the 0.02 wt% SDBS has the most significant effect on the improvement of the COP compared to other nanofluid; the improvement of COP is strongly corresponded to the numbers of nanoparticles stably dispersed in the base fluid, not just the nanoparticles added; this paper provides evidences for the application of nanoparticles on AARS.
63 citations
TL;DR: In this paper, four kinds of DESs were prepared from choline chloride (HBA) and glycerol, ethylene glycol, N-methylurea, and trifluoroacetamide.
58 citations
TL;DR: In this article, the flammability characteristics of forty-eight HFOs and blends have been relatively comprehensively and systematically summarized, for a variety of experimental conditions on the basis of the results reported in academic journal papers, professional books, conference proceedings, technical reports, patent applications, material safety data sheets, and presentations.
Abstract: Hydrofluoroolefins (HFOs) have been attracting increasing attention over the recent decade, and some of them are regarded as candidates for next-generation refrigerants. In this paper, the flammability characteristics of forty-eight HFOs and blends have been relatively comprehensively and systematically summarized, for a variety of experimental conditions on the basis of the results reported in academic journal papers, professional books, conference proceedings, technical reports, patent applications, material safety data sheets, and presentations. The following flammability characteristics of HFOs are reviewed, including the lower flammability limit, upper flammability limit, burning velocity, minimum ignition energy, hot surface ignition temperature, autoignition temperature, thermal decomposition temperature, heat of combustion, product of combustion, etc. Besides, a new correlation equation has been suggested to roughly indicate the burning velocity and heat of combustion rankings of the fluorinated hydrocarbons once their basic molecular characteristics are known. In addition, the experimental methods, influencing factors, inerting mechanism, and developing tendency of the flammability of the HFO refrigerants are discussed. The details presented are expected to be useful for researchers working in the field of heating, ventilation, and air conditioning and refrigeration.
53 citations
TL;DR: In this article, the authors identify, summarize, and review the experimental studies dealing with the enhancement of vapour absorption processes in absorbers by means of passive techniques i.e. advanced surface designs and the use of additives and nanofluids.
32 citations
TL;DR: In this article, a hybrid SA-PVA-SiO2 capsule was fabricated via the one-step titration-gel method that directly dripped the spherical droplet of the SA, PVA and tetraethyl orthosilicate (TEOS) mixed solutions into the bath with calcium chloride (CaCl2), NaCl and oversaturated boric acid (H3BO3) cross-linking agents.
30 citations
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TL;DR: In this paper, the authors have produced nanotube-in-oil suspensions and measured their effective thermal conductivity, which is anomalously greater than theoretical predictions and is nonlinear with nanotubes loadings.
Abstract: We have produced nanotube-in-oil suspensions and measured their effective thermal conductivity. The measured thermal conductivity is anomalously greater than theoretical predictions and is nonlinear with nanotube loadings. The anomalous phenomena show the fundamental limits of conventional heat conduction models for solid/liquid suspensions. We have suggested physical concepts for understanding the anomalous thermal behavior of nanotube suspensions. In comparison with other nanostructured materials dispersed in fluids, the nanotubes provide the highest thermal conductivity enhancement, opening the door to a wide range of nanotube applications.
2,546 citations
TL;DR: In this paper, the authors explore four possible explanations for the anomalous thermal conductivity of nanofluids: Brownian motion of the particles, molecular-level layering of the liquid at the liquid/particle interface, the nature of heat transport in the nanoparticles, and the effects of nanoparticle clustering.
2,008 citations
TL;DR: It has been found nan ofluids have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional fluids, which can be considered as one of the key parameters for enhanced performances for many of the applications of nanofluids.
Abstract: Nanofluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer performance can be applied in many devices for better performances (i.e. energy, heat transfer and other performances). In this paper, a comprehensive literature on the applications and challenges of nanofluids have been compiled and reviewed. Latest up to date literatures on the applications and challenges in terms of PhD and Master thesis, journal articles, conference proceedings, reports and web materials have been reviewed and reported. Recent researches have indicated that substitution of conventional coolants by nanofluids appears promising. Specific application of nanofluids in engine cooling, solar water heating, cooling of electronics, cooling of transformer oil, improving diesel generator efficiency, cooling of heat exchanging devices, improving heat transfer efficiency of chillers, domestic refrigerator-freezers, cooling in machining, in nuclear reactor and defense and space have been reviewed and presented. Authors also critically analyzed some of the applications and identified research gaps for further research. Moreover, challenges and future directions of applications of nanofluids have been reviewed and presented in this paper. Based on results available in the literatures, it has been found nanofluids have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional fluids. This can be considered as one of the key parameters for enhanced performances for many of the applications of nanofluids. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. However, few barriers and challenges that have been identified in this review must be addressed carefully before it can be fully implemented in the industrial applications.
1,558 citations
TL;DR: A literature review on absorption refrigeration technology is provided in this paper, where a number of research options such as various types of absorption refrigerator systems, research on working fluids, and improvement of absorption processes are discussed.
Abstract: This paper provides a literature review on absorption refrigeration technology. A number of research options such as various types of absorption refrigeration systems, research on working fluids, and improvement of absorption processes are discussed.
752 citations