China
Africa
Explore chapters and articles related to this topic
Applications of Nanofluids in Direct Absorption Solar Collectors
Published in K.R.V. Subramanian, Tubati Nageswara Rao, Avinash Balakrishnan, Nanofluids and Their Engineering Applications, 2019
M.E. Zayed, S.W. Sharshir, J. Shaibo, F.A. Hammad, Mohamed Kamal Ahmed Ali, Sajjad Sargana, K.K. Salman, Elbager M.A. Edreis, Jun Zhao, Chun Du, Ammar H. Elsheikh
Specific heat is an important property used to characterise any thermal fluid as it plays a vital role in the heat transfer and heat storage processes. It is also very important in any theoretical analysis performed on thermal systems such as heat flow, energy, and exergy analyses [63–65]. Some researchers claimed that specific heat of nanofluids decreases with the increase of volume fraction [66–68]. However, other researchers claimed that specific heat increases with the increase of volume fraction [69–71]. The high surface area of nanoparticles results in the increase of the interfacial thermal resistance, which acts as additional thermal storage due to the interaction of vibration energies between nanoparticles and their surrounding fluid molecules [72]. Consequently, the specific heat of nanofluids increases. Most researchers claimed that the specific heat of nanofluids increases when the temperature rises. However, others researchers claimed that the specific heat of nanofluids dropped at high temperature. Therefore, more investigations are required to determine the optimal operating temperature range as well as particles concentration of specified types of nanoparticles and base fluids.
Absorption Thermodynamic Cycles
Published in Eduardo Rincón-Mejía, Alejandro de las Heras, Sustainable Energy Technologies, 2017
Antonio Lecuona-Neumann, Pedro A. Rodríguez-Aumente, Mathieu Legrand, Antonio Famiglietti
In thermally activated layouts there is one or several loops of thermal fluids that bring the driving heat to the generator heat exchanger (e.g., Figure 8.5). If these loops can be eliminated, drawing the working fluid of the cycle directly through the heat recovering exchanger, a more compact and efficient system will be constructed if the loop extension can be minimized. Moreover, these thermal fluids can be expensive and polluting as a residue, as specialty oils are often required, which also pose fire risks. When using steam, a nonnegligible installation cost will have to be amortized with the durable cost.
Low-energy approaches for the thermal control of buildings
Published in Paul Tymkow, Savvas Tassou, Maria Kolokotroni, Hussam Jouhara, Building Services Design for Energy-Efficient Buildings, 2020
Paul Tymkow, Savvas Tassou, Maria Kolokotroni, Hussam Jouhara
An indirect way of collecting and utilising solar energy is through solar collectors which collect solar energy on absorber plates, as shown in Figure 9.6. Selective coatings are often applied to the absorber plates to improve the overall collection efficiency. A thermal fluid absorbs and transfers the energy from the collector plates to a storage tank from where it can be used for domestic hot water heating, space or process heating.
Enhanced Thermochemical Heat Capacity of Liquids: Molecular to Macroscale Modeling
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Peiyuan Yu, Anubhav Jain, Ravi S. Prasher
Thermal energy storage plays a broad and important role in transforming our energy economy [1, 2]. With over 90% of the world’s primary energy generation consumed or wasted thermally, technologies for the efficient storage and transfer of heat have numerous applications and huge impact on reducing energy-related emissions and improving energy efficiency [3]. As the typical thermal energy storage medium and carrier, thermal fluids (or heat transfer fluids) are critical in heating, ventilation, and air conditioning (HVAC), power generation, and various industrial applications, including oil, gas, chemical, pharmaceutical, and food processing [4]. They are also crucial in enabling renewable energy technologies such as concentrating solar power (CSP) [5]. The specific energy (stored energy/mass) or energy transport density (transported energy rate/mass flow rate) of thermal fluids is given by CΔT, where C is the specific heat capacity of the fluid and ΔT is the temperature rise. The specific heat (C) of current thermal fluid technologies has remained significantly below that of water (4.2 J/g·K), which itself suffers from a relatively low boiling temperature (100°C). Thermal fluid technologies capable of operating in extended temperature ranges require large quantities of fluid to compensate for low C, increasing pressure drop, cost and space requirements and requiring transport systems/pumps capable of large mass flow rate.
Experimental and theoretical investigation of thermal conductivity of some water-based nanofluids
Published in Chemical Engineering Communications, 2018
Ali Vakilinejad, Mohammad Ali Aroon, Mohammed Al-Abri, Hossein Bahmanyar, Myo Tay Zar Myint, G. Reza Vakili-Nezhaad
Nanofluids and their contributions to higher efficiencies in transfer processes have become an important research field in the past two decades. Nanofluids are referred to the fluids that consist of a base-fluid in which nanoparticles are dispersed. Nanoparticles are particles with nanometer scale dimensions. The dimensions of a nanoparticle should not exceed 100 nm to be considered as a nanoparticle (Jahanshahi et al., 2010; Kazemi-Beydokhti et al., 2014; Aybar et al., 2015). Base fluids of nanofluids can be water or ethylene glycol or any alike fluids. In heat transfer involved systems, heat transfer fluid which is called thermal fluid, has the main contribution. Vast researches have shown that dispersion of nanoparticles in the base fluid leads to the enhanced heat transfer rate of the fluid by virtue of the higher thermal conductivity of the solid particles compared to that of the base fluid. Several techniques exist for measuring the thermal conductivity of fluids including thermoreflectance, 3-omega, transient hot wire, and modified transient plane source (MTPS) (Teng et al., 2010). Results obtained from all of these methods coincide with the fact that the presence of nanoparticles in the base fluid increases the thermal conductivity of the fluid. Because of the importance of this characteristics of the nanofluids, various theoretical and semi-empirical models are presented by researchers for the prediction of thermal conductivity of nanofluids (Aybar et al., 2015). There have been some discrepancies between the behavior of the obtained results with the presented models. Results have demonstrated different expanse of increment ranging from values highly above what classical theories such as Maxwell–Garnett predict, to or less than the values which are predicted by effective medium theory (Timofeeva et al., 2007). Furthermore, other thermophysical properties of nanofluids such as viscosity have been studied by various researchers and all of these properties were observed to be different from those of the base-fluids of the studied nanofluids (Vakili-Nezhaad and Dorany 2009, 2012). These results show potential application of nanofluids in diverse fields.
Heat transport analysis in buoyancy-driven flow of Maxwell fluid induced by a vertically stretching sheet inspired by Cattaneo Christov theory
Published in Waves in Random and Complex Media, 2022
Zahoor Iqbal, Masood Khan, Muhammad Shoaib, N. Ameer Ahammad, Maawiya Ould Sidi
Nanofluids are liquid-solid mixture two-phase fluids that can be called new-generation heat-transfer fluids. Nanofluids have demonstrated a bright future as thermal fluids in a variety of heat transfer applications. Solid nanoparticles with typical length scales of 1–100 nm and strong thermal conductivity have been shown to improve effective thermal conductivity and convective heat transfer for the base fluid when suspended in it, see Das [19]. Nanofluids have advanced concepts and practical applications in comparison to conventional heat transfer fluids, such as solar collectors [20], the application of electrical transformers [21], and the cooling of electronics [22]. Choi and Eastman [23] were the first to create the term ‘nanofluid’. Originally, the phrase referred to the dispersion of nanometer-sized copper particles in water to improve its heat conductivity. A nanofluid is now more precisely described as a colloidal suspension of nanoparticles in a base fluid that has been manufactured. Nanoparticle concentrations typically range from 0.01 to 5% by weight, with a mean particle size of 10–100 nm. Metals, metal oxides, carbides, and carbon compounds can all be used as nanoparticles. Water and mineral oils are commonly used as base fluids. Nanofluids have a lot of potential in a variety of industries, including solar applications, where they can improve the heat-transfer coefficient of solar water heaters or the capacity of thermal energy storage systems, and refrigeration, where they can improve the performance of refrigeration systems. Despite the fact that nanofluids have a lot of potential [24] their use as a heat-transfer fluid (HTF) or refrigerant is currently uncommon. The use of nanofluids in solar-heat collectors, on the other hand, has been a major study issue in the recent decade. Parveen et al. [25] explored the hybrid nanofluid by incorporating particles (AlO-Cu/Water). Shoaib et al. [26] numerically explored the characteristics of MHD nanofluid flow caused by a rotating surface. Awais et al. [27–29] explored the different nanofluid flows over in their studies by utilizing several effects on nanofluid flows. More progressive studies on nanofluids can be found in [30–38].