Effect of nano-sized heat transfer enhancers on PCM-based heat sink performance at various heat loads

Many passive heat controlling technologies are based on the use of phase change materials

Performance evaluation of photovoltaic thermal systems using functionalized multi-walled carbon-based nano-enhanced phase change material

Photovoltaic (PV) technology enables direct conversion of solar energy to electricity for direct consumption. Photovoltaic conversion efficiency mostly decreases with increase in temperature of the PV system; henceforth temperature management is a key issue in PV system design. A hybrid photovoltaic thermal (PVT) system is a promising development, which facilitates extraction of heat energy and electrical energy simultaneous. Meanwhile, the challenge of using conventional water-based PVT systems is that they can only be used during the daytime. Integration of phase change materials (PCM) with PVT systems to regulate the temperature as well as to facilitate thermal energy storage is a popular and viable choice. However, the PCMs suffer from lower thermal conductivity which causes lower energy storage capabilities and lower heat transfer rates. Uniform dispersion of nanoparticles into the PCM enhances the thermal conductivity. Though, there are problems pertaining to dispersion stability of the nanoparticles; after a few cycles, they get agglomerated. The main objective of the present research is to synthesize and characterize the nano-enhanced phase change materials (NePCM); develop a PVT system, analyse the energy and exergy performance of the PVT system and to evaluate the performance of NePCM-integrated PVT system. A two-step method is used to synthesize the NePCMs using salt hydrate with a phase transition temperature of 50°C as PCM and functionalize multi-walled carbon nanotubes (FMWCNT) as nanoparticle. The prepared nanocomposites were characterized using fourier transform infrared spectrum, thermo-gravimetric analysis, differential scanning calorimetry, ultraviolet visible spectrum, thermal property analyser and thermal cycler to ensure their thermo physical properties. Energy and exergy analysis is carried out to evaluate the performance of the PVT system. PVT system is investigated using a parallel pipe flow channel as proposed in the current research investigation which acts as thermal collector for extracting the heat energy. To make a comparative analysis with the conventional PV systems, three new configurations namely PVT, PVT-PCM, and PVT NePCM with flowrates (0.4, 0.6 and 0.8 liter per minute (LPM), have been studied. Results obtained ensures chemical, physical and thermal stability of the prepared NePCM. FMWCNT at a weight concentration of 0.7% depicts thermal conductivity enhancement by 100% and light transmission decrement by 93.49% when compared with pure PCM. Furthermore, the nanocomposites were chemically and thermally stable, after 300 thermal cycles. Aforementioned NePCM with enhanced characteristics were integrated with PVT system for real time investigation. Results show that the electrical power output and efficiency to improve by 29.1% and 21.9% for the PVT-NePCM system. The maximum thermal efficiency of PVT, PVT-PCM and PVT-NePCM systems were found to be 73.1%, 74.99% and 75.42% at 0.4 LPM, respectively. Overall energy efficiency of the PVT, PVT-PCM and PVT-NePCM system were calculated to be 81.9%, 84.54%, and 85 % respectively at the optimized flowrate. On the contrary, the maximum exergy efficiency was found to be 12.37% for PVT-NePCM system. The developed system generates both electrical energy and thermal energy, which can be used for the remote areas. Further, Real time experimental study on NePCM integrated PVT system is needed to investigate the real time performance of PVT system

Computational Heat Transfer and Fluid Mechanics

With the advances in high-speed computer technology, complex heat transfer and fluid flow problems can be solved computationally with high accuracy. Computational modeling techniques have found a wide range of applications in diverse fields of mechanical, aerospace, energy, environmental engineering, as well as numerous industrial systems. Computational modeling has also been used extensively for performance optimization of a variety of engineering designs. The purpose of this book is to present recent advances, as well as up-to-date progress in all areas of innovative computational heat transfer and fluid mechanics, including both fundamental and practical applications. The scope of the present book includes single and multiphase flows, laminar and turbulent flows, heat and mass transfer, energy storage, heat exchangers, respiratory flows and heat transfer, biomedical applications, porous media, and optimization. In addition, this book provides guidelines for engineers and researchers in computational modeling and simulations in fluid mechanics and heat transfer

Nano-engineered pathways for advanced thermal energy storage systems

Nearly half of the global energy consumption goes toward the heating and cooling of buildings and processes. This quantity could be considerably reduced through the addition of advanced thermal energy storage systems. One emerging pathway for thermal energy storage is through nano-engineered phase change materials, which have very high energy densities and enable several degrees of design freedom in selecting their composition and morphology. Although the literature has indicated that these advanced materials provide a clear thermodynamic boost for thermal energy storage, they are subject to much more complex multiscale governing phenomena (e.g., non-uniform temperatures across the medium). This review highlights the most promising configurations that have been proposed for improved heat transfer along with the critical future needs in this field. We conclude that significant effort is still required to move up the technological readiness scale and to create commercially viable novel nano-engineered phase change systems

Experimental Investigation of the Heat Source Orientation on the Transient Flow and Thermal Behaviour of Phase Change Material During Phase Transition

The present study reports the characterization of transient flow and transient thermal behavior of phase change material (PCM) during solid-liquid phase change (melting) through experimental investigation. Two specific aspects of the current work, both important in the field of latent heat thermal energy storage, are to investigate the influence of the flow behavior within liquid PCM on the melting and heat transfer processes, and the impact of heat source orientation on the underlying melting and heat transfer processes. A relationship between heat source orientation and the Nusselt number was discussed. The results show that the fluid velocity is critical for both the heat transport within the liquid domain and the overall melting pattern and rate. These results further extend the understanding of phase change and the associated heat transfer processes in the PCM and provide comprehensive benchmark data for the improvement of numerical models simulating the solid-liquid phase change process

Additive Manufacturing for Phase Change Thermal Energy Storage and Management

Phase change materials can enhance the performance of energy systems by time shifting or reducing peak thermal loads. Certain electronic devices such as batteries, laser systems, or electric vehicle power electronics are highly transient and require pulse heat dissipation. Heat sinks, or thermal management devices made of a phase change material can absorb large heat spikes while maintaining a constant temperature. Additive manufacturing techniques hold tremendous potential to enable co-optimization of material properties and device geometry, while potentially reducing material waste and manufacturing time. Recently, a few efforts have emerged that employ additive manufacturing techniques to integrate a phase change material thermal energy storage into geometrically complex designs for advanced thermal management. This work contributes to the emerging field of research by reporting on the production of composite thermoplastic/phase change material filaments for fused filament fabrication 3D-printing, and their subsequent use to 3D-print advanced heat exchange topologies with intricate geometric features

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

Investigation into stability and thermal-fluid behaviour of hybrid nanofluids as heat transfer fluids

Thesis (PhD (Mechanics))--University of Pretoria, 2021.The need to improve the poor thermal conductivity of conventional fluids to produce adequate heat transfer fluid cannot be over-emphasized, knowing fully well that heat transfer is key in any engineering process line. Hence, the birth of nanofluids, which is the formulation of a composite of suspended nanoparticles in a basefluid. Nanofluids have found wide applications ranging from heat exchangers, electronic cooling, automotive industry, medical, military, solar energy, manufacturing industry, to mention but a few. But the limitations of nanofluids led to the entrance of a new working fluid named binary nanofluid and ternary nanofluid. This study experimented with the trio influence of temperature (T), percent weight ratios (PWRs), nanoparticles size (NS) on the thermophysical behaviour of MgO–ZnO/Deionised water binary nanofluids (BNFs). 20 nm nano-size of ZnO nanoparticles were hybridised with MgO nanoparticles of nano-sizes 20 nm and 100 nm, and dispersed in deionised water to prepare 0.1 vol% binary nanofluids for percent weight ratios of MgO:ZnO (20:80, 40:60, 60:40 and 80:20). The viscosity (μ), electrical conductivity (σ), pH, and thermal conductivity (κ) of the binary nanofluids were experimentally evaluated for temperature 20 to 50 °C. Morphology was checked, and stability was monitored. The impact of temperature, PWRs, and nano-size on the pH, μ, σ, and κ of the binary nanofluid were ordered as PWR >NS >T, NS> PWR>T, T>NS >PWR, and T >NS >PWR, respectively. Using the obtained experimental dataset, correlations were proposed for the thermal property of each binary nanofluid as a function of temperature. Also, investigating the trio impact of PWR, temperature and � on the thermophysical characteristics of MgO-ZnO/DIW BNFs, to help close up the scarce literature gap. 20 nm nanoparticle sizes of MgO and ZnO were hybridized together and dissolved in deionized water to formulate 0.1 vol% and 0.05 vol.% binary nanofluids (NFs) for PWR of 20:80, 40:60, 60:40, 80:20 (MgO:ZnO). The κ for all BNFs was enhanced under the impact of rising temperature, with maximum κ enhancement of 5.60% and 22.07% relative to the deionised water (DIW) achieved for 0.05 vol% and 0.10 vol%, separately. The σ was enhanced slightly under the influence of increasing temperature, with maximum enhancement of 21.82% and 30.91% achieved for 0.050 vol% and 0.10 vol%, respectively. In addition, viscosity under temperature increase exhibited a decreasing pattern for all nanohybrids and basefluid. Furthermore, to better harness the benefit of the BNFs for thermal application, thermoelectrical conductivity (TEC) was evaluated with BNFs of 0.05 vol% observed to have higher TEC values than 0.10 vol% BNFs. The BNFs were found suitable as thermal fluids. A novel manner of furthering thermo-convection behaviour of thermal applications is the use of BNFs as heat transfer fluids. This study experimented the natural convection behaviour of MgO-ZnO NPs suspended in basefluid for � = 0.050 vol.% and 0.10 vol% at percent weight ratios of 20:80, 40:60, 60:40, 80:20 (MgO:ZnO) inside a square enclosure. Factors like Rayleigh number, Nusselt number (Nuav), coefficient of convective heat transfer (hav), and heat transfer rate (Qav) for various temperatures (20°C to 50°C) were examined. PWRs and temperature gradient of BNPs inside the binary nanofluids was observed to augment Nuav, hav, and Qav. Also, highest improvement of 72.60% (Nuav), 76.01% (hav), and 72.20% (Qav) was achieved. Employing BNFs in square enclosure yielded fine improvement for natural convection behaviour. Artificial intelligence (AI) methods, like artificial neural network (ANN) and surface fitting method were deployed to model the thermal conductivity of BNFs. For the ANN model, a learning algorithm was developed to determine the optimum neuron number. The ANN having 19 neurons in the inner layer got the optimized performance. A surface fitting method was also used on the experimental data, and the generated surface shows the behaviour of the BNFs. The outcome affirmed that the designed ANN model is best for predicting the thermal conductivity of MgO-ZnO/DIW binary nanofluids for different temperatures, nanoparticle sizes, PWRs and volume concentration over the surface fitting method.University of Pretoria Postgraduate Bursary for Doctoral Students.Olabisi Onabanjo University, Ago-Iwoye, Nigeria.Tertiary Education Trust Fund (TETFund), Abuja, Nigeria.Mechanical and Aeronautical EngineeringPhD (Mechanics)Unrestricte

Nanofluids based on molten nitrates for thermal energy storage and heat transfer in concentrated solar power.

385 p.El suministro de energía es un tema de vital importancia que afecta especialmente a la sociedad debido a la emisión de Gases de Efecto Invernadero (GEI) y la necesidad de reducir el uso de combustibles fósiles. Es bien conocido que estas emisiones contribuyen al cambio climático y el calentamiento global, al mismo tiempo que conducen a una seria degradación del entorno y provocan enfermedades. Además, existen otras cuestiones serias relacionadas con el uso de fuentes de energía no renovable, como la seguridad en la cadena de suministro y su disponibilidad limitada.En este contexto, la energía solar de concentración (CSP, por sus siglas en inglés) destaca como una opción muy valiosa dentro del marco de las energías renovables. Su disponibilidad es su característica principal comparada con otras energías alternativas. La energía solar no está disponible bajo demanda cuando y donde es necesaria. Como consecuencia, la mayoría de las plantas CSP cuentan con un sistema de almacenamiento térmico. Este sistema almacena la energía térmica como calor sensible, a través de dos tanques a diferentes temperaturas llenos con una sal fundida (Sal Solar, NaNO3:KNO3 60:40 %masa). El mismo material se utiliza como fluido de transferencia térmica para transportar el calor del campo solar al bloque de potencia. La madurez de esta tecnología está más que probada después de varias décadas desde que la primera planta CSP se puso en funcionamiento. Sin embargo, existen aún muchas oportunidades para desarrollar nuevos métodos de almacenamiento térmico o mejorar los que existen actualmente.Las modestas propiedades termofísicas (calor específico y conductividad térmica) están entre las principales desventajas de la Sal Solar utilizada actualmente, lo que obliga al uso de una gran cantidad de sal para poder almacenar calor durante el tiempo necesario. Varias soluciones se han propuesto, como el uso de otras sales inorgánicas dentro de complicados sistemas de almacenamiento térmico para alcanzar una tasa de transferencia de calor adecuada. Recientemente, ha emergido una opción que considera el uso de la nanotecnología. Esta solución consiste en añadir pequeñas cantidades de nanopartículas a las sales para mejorar su comportamiento térmico. Estos innovadores materiales se han denominado como nanofluidos basados en sales fundidas o materiales de cambio de fase nanomejorados, dependiendo del método empleado para almacenar la energía térmica: calor sensible o latente, respectivamente.Esta tesis analiza detalladamente el diseño, síntesis y caracterización de estos materiales. Su reciente descubrimiento, unido a las dificultades técnicas de trabajar con sales fundidas, han ocasionado que ciertas propiedades apenas se hayan estudiado. Se ha puesto especial atención en el desarrollo de un método preciso para medir el calor específico y un proceso de síntesis adecuado y escalable. La caracterización de los materiales incluye propiedades térmicas como el calor específico, la conductividad térmica, el calor latente y la temperatura de cambio de fase. También se han estudiado otras propiedades interesantes como la estabilidad de las nanopartículas en la sal fundida durante largos periodos y su comportamiento reológico.Zabalduz Tecnali

Nanofluids based on molten nitrates for thermal energy storage and heat transfer in concentrated solar power.

385 p.El suministro de energía es un tema de vital importancia que afecta especialmente a la sociedad debido a la emisión de Gases de Efecto Invernadero (GEI) y la necesidad de reducir el uso de combustibles fósiles. Es bien conocido que estas emisiones contribuyen al cambio climático y el calentamiento global, al mismo tiempo que conducen a una seria degradación del entorno y provocan enfermedades. Además, existen otras cuestiones serias relacionadas con el uso de fuentes de energía no renovable, como la seguridad en la cadena de suministro y su disponibilidad limitada.En este contexto, la energía solar de concentración (CSP, por sus siglas en inglés) destaca como una opción muy valiosa dentro del marco de las energías renovables. Su disponibilidad es su característica principal comparada con otras energías alternativas. La energía solar no está disponible bajo demanda cuando y donde es necesaria. Como consecuencia, la mayoría de las plantas CSP cuentan con un sistema de almacenamiento térmico. Este sistema almacena la energía térmica como calor sensible, a través de dos tanques a diferentes temperaturas llenos con una sal fundida (Sal Solar, NaNO3:KNO3 60:40 %masa). El mismo material se utiliza como fluido de transferencia térmica para transportar el calor del campo solar al bloque de potencia. La madurez de esta tecnología está más que probada después de varias décadas desde que la primera planta CSP se puso en funcionamiento. Sin embargo, existen aún muchas oportunidades para desarrollar nuevos métodos de almacenamiento térmico o mejorar los que existen actualmente.Las modestas propiedades termofísicas (calor específico y conductividad térmica) están entre las principales desventajas de la Sal Solar utilizada actualmente, lo que obliga al uso de una gran cantidad de sal para poder almacenar calor durante el tiempo necesario. Varias soluciones se han propuesto, como el uso de otras sales inorgánicas dentro de complicados sistemas de almacenamiento térmico para alcanzar una tasa de transferencia de calor adecuada. Recientemente, ha emergido una opción que considera el uso de la nanotecnología. Esta solución consiste en añadir pequeñas cantidades de nanopartículas a las sales para mejorar su comportamiento térmico. Estos innovadores materiales se han denominado como nanofluidos basados en sales fundidas o materiales de cambio de fase nanomejorados, dependiendo del método empleado para almacenar la energía térmica: calor sensible o latente, respectivamente.Esta tesis analiza detalladamente el diseño, síntesis y caracterización de estos materiales. Su reciente descubrimiento, unido a las dificultades técnicas de trabajar con sales fundidas, han ocasionado que ciertas propiedades apenas se hayan estudiado. Se ha puesto especial atención en el desarrollo de un método preciso para medir el calor específico y un proceso de síntesis adecuado y escalable. La caracterización de los materiales incluye propiedades térmicas como el calor específico, la conductividad térmica, el calor latente y la temperatura de cambio de fase. También se han estudiado otras propiedades interesantes como la estabilidad de las nanopartículas en la sal fundida durante largos periodos y su comportamiento reológico.Zabalduz Tecnali