Heat transfer fluids are materials responsible for heat distribution, transfer and storage. Their significance is undeniable - many technological processes cannot be carried out without using heat transfer materials (for example due to overheating). These are usually mixtures of many compounds, for example glycols, silicones or water. Today's technologies constantly require more efficient, environmentally- and economically-friendly solutions for heat transfer applications. It is necessary to know the full physicochemical characteristics to design a new heat transfer fluid (mainly density, heat capacity, viscosity and thermal conductivity). Nanofluids (mixture of a basefluid and nanoparticles) were proposed as a solution for many industrial issues due to their enhanced thermophysical properties (i.e. thermal conductivity) than pure liquids. Moreover, these enhancements exhibit unusual features which make this group of materials interesting from molecular and industrial point of view. Ionic liquids, task specific materials with tuneable properties were repeatedly recommended as heat transfer fluids due to their specific properties (mainly low vapour pressure, wide liquidus range, or non-flammability) caused by the ionic structure. A very interesting material can be obtained by mixing ionic liquids and nanoparticles where specific properties of ionic liquids are preserved, and thermophysical properties are enhanced due to nanoparticles dispersion. In this work, we investigated ionic liquid - based nanofluids from the experimental and theoretical point of view, including imidazolium-, pyrrolidinium- and phosphonium-based ionic liquids with several different anions, and multiwalled carbon nanotubes, graphite, boron nitride and mesoporous carbon as nanoparticles, and also in mixtures with water. As a final result, we assessed the molecular recognition of the thermophysical properties enhancements in ionanofluids, developed the predictive models for physical properties, compared all investigated systems to commercial heat transfer fluids. The project was supported by King Faisal University (Saudi Arabia) through a research fund from the International Cooperation and Knowledge Exchange Administration department at KFU. Cytec are thanked for the generous donation of the trihexyl(tetradecyl)phosphonium chloride sample.

In a world that is constantly in need of a continuous, reliable and sustainable energy supply, concentrating photovoltaic technologies have the potential to become a cost effective solution for large scale power generation. In this light, important progresses have been made in terms of cell’s design and efficiency, but the concentrating photovoltaic industry sector still struggles to gain market share and to achieve adequate economic returns. The work presented in this thesis is focused on the development of innovative solutions for high concentrating photovoltaics receivers. The design, the fabrication and the characterization of a large cell assembly for high concentrations are described. The assembly is designed to accommodate 144 multijunction cells and is rated to supply energy up to 2.6kWe at 500 suns. The original outline of the conductive copper layer limits the Joule losses to the 0.7% of the global power output, by reducing the number of interconnections. All the challenges and the issues faced in the manufacturing stage are accounted for and the reliability of the fabrication has been proven by quality tests and experimental investigations conducted on the prototype. An indoor characterization shows the receiver’s potential to supply a short-circuit current of 5.77A and an open circuit voltage per cell of 3.08V at 500×, under standard test conditions, only 4.80% and 2.06% respectively lower than those obtained by a commercial single-cell assembly. An electrical efficiency of 29.4% is expected at 500 suns, under standard conditions. A prototype’s cost of $0.91/Wp, in line with the actual price of CPV systems, has been recorded: a cost breakdown is reported and the way to further reduce the cost have been identified and is accounted. In a second approach, the design of a natural convective micro-finned array to be integrated in a single cell receiver has been successfully attempted. Passive cooling systems are usually cheaper, simpler and considered more reliable than active ones. After a detailed review of micro-cooling solutions, an experimental investigation on the thermal behaviour of micro-fins has been conducted and has been combined with a multiphysics software model. A micro-finned heat sink shows the potential to keep the CPV temperature below 100°C under standard conditions and the ability to handle the heat flux when the cell’s efficiency drops to zero. Moreover, a micro-finned heat sink demonstrates the potential to introduce significant benefits in terms of material usage and weight reduction: compared to those commercially available, a micro-finned heat sink has a power-to-weight ratio between 6 and 8 times higher, which results in lower costs and reduced loads for the CPV tracker.

abstract: Rotary drums are commonly used for their high heat and mass transfer rates in the manufacture of cement, pharmaceuticals, food, and other particulate products. These processes are difficult to model because the particulate behavior is governed by the process conditions such as particle size, particle size distribution, shape, composition, and operating parameters, such as fill level and rotation rate. More research on heat transfer in rotary drums will increase operating efficiency, leading to significant energy savings on a global scale. This research utilizes infrared imaging to investigate the effects of fill level and rotation rate on the particle bed hydrodynamics and the average wall-particle heat transfer coefficient. 3 mm silica beads and a stainless steel rotary drum with a diameter of 6 in and a length of 3 in were used at fill levels of 10 %, 17.5 %, and 25 %, and rotation rates of 2 rpm, 6 rpm, and 10 rpm. Two full factorial designs of experiments were completed to understand the effects of these factors in the presence of conduction only (Case 1) and conduction with forced convection (Case 2). Particle-particle friction caused the particle bed to stagnate at elevated temperatures in Case 1, while the inlet air velocity in Case 2 dominated the particle friction effects to maintain the flow profile. The maximum heat transfer coefficient was achieved at a high rotation rate and low fill level in Case 1, and at a high rotation rate and high fill level in Case 2. Heat losses from the system were dominated by natural convection between the hot air in the drum and the external surroundings. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2019

Natural convection is a phenomenon that occurs in a wide range of applications such as cooling towers, air conditioners, and power plants. Natural convection may be used in decay heat removal systems such as spent fuel casks, where the higher reliability inherent of natural convection is more desirable than forced convection. Passive systems, such as natural convection, may provide better safety, and hence have received much attention recently. Cooling of spent fuel rods is conventionally done using water as the coolant. However, it involves contaminating the water with radiation from the fuel rods. Contamination becomes dangerous and difficult for humans to handle. Further, the recent nuclear tragedy in Fukushima, Japan has taught us the dangers of contamination of water with nuclear radiation. Natural convection can perhaps significantly reduce the risk since it is self-sufficient and does not rely on other secondary system such as a blower as in cases of forced convection. The Utah State University Experimental Fluid Dynamics lab has recently designed an experiment that models natural convection using heated rod bundles enclosed in a rectangular cavity. The data available from this experiment provides and opportunity to study and validate computational fluid dynamics(CFD)models. The validated CFD models can be used to study multiple configurations, boundary conditions, and changes in physics(natural and/or forced convection). The results are to be validated using experimental data such as the velocity field from particle image velocimetry (PIV), pressure drops across various sections of the geometry, and temperature distributions along the vertically heated rods. This research work involves modeling natural convection using two-layer turbulence models such as k - ε and RST (Reynolds stress transport) using both shear driven (Wolfstein) and buoyancy driven (Xu) near-wall formulations. The interpolation scheme employed is second-order upwinding using the general purpose code STAR-CCM+. The pressure velocity coupling is done using the SIMPLE method. It is ascertained that turbulence models with two-layer formulations are well suited for modeling natural convection. Further it is established that k - ε and Reynolds stress turbulence models with the buoyancy driven (Xu)formulation are able to accurately predict the flow rate and temperature distribution.

The research work in this dissertation focuses on turbulent air jet heat transfer for commercial cooking applications. As a part of this study, convective heat transfer coefficient and its interdependency with various key parameters is analyzed for single nozzle turbulent jet impingement. Air is used as the working fluid impinging on the flat surface. A thorough investigation of velocity and temperature distributions is performed by varying nozzle velocity and height over diameter ratio (H/D). Nusselt number and Turbulent Energy are presented for the impingement surface. It was found that for H/D ratios ranging between 6 and 8, nozzle velocities over 20 m/s provide a large percentage increase in heat transfer. Single nozzle jet impingement is followed by study of turbulent multi-jet impingement. Along with parameters mentioned above, spacing over diameter ratio (S/D) is varied. Convective heat transfer coefficient, average impingement surface temperature and heat transfer rate are calculated over the impingement surface. It was found that higher S/D ratios result in higher local heat transfer coefficient values near stagnation point. However, increased spacing between the neighboring jets results in reduced coverage of the impingement surface lowering the average heat transfer. Lower H/D ratios result in higher heat transfer coefficient peaks. The peaks for all three nozzles are more uniform for H/D ratios between 6 and 8. For a fixed nozzle velocity, heat transfer coefficient values are directly proportional to nozzle diameter. For a fixed H/D and S/D ratio, heat transfer rate and average impingement surface temperature increases as the nozzle velocity increases until it reaches a limiting value. Further increase in nozzle velocity causes drop in heat transfer rate due to ingress of large amounts of cold ambient air in the control volume. The final part of this dissertation focuses on case study of conveyor oven. Lessons learned from analysis of single and multi-jet impingement are implemented in the case study. A systematic approach is used to arrive to an optimal configuration of the oven. As compared to starting configuration, for optimized configuration the improvement in average heat transfer coefficient was 22.7%, improvement in average surface heat flux was 24.7% and improvement in leakage air mass flow rate was 59.1%.

Heat exchanger fouling is the deposition of material onto the heat transfer surface causing a reduction in thermal efficiency. A study using Computational Fluid Dynamics (CFD) was conducted to increase understanding of key aspects of fouling in desalination processes. Fouling is a complex phenomenon and therefore this numerical model was developed in stages. Each stage required a critical assessment of each fouling process in order to design physical models to describe the process???s intricate kinetic and thermodynamic behaviour. The completed physical models were incorporated into the simulations through employing extra transport equations, and coding additional subroutines depicting the behaviour of the aqueous phase involved in the fouling phenomena prominent in crystalline streams. The research objectives of creating a CFD model to predict fouling behaviour and assess the influence of key operating parameters were achieved. The completed model of the key crystallisation fouling processes monitors the temporal variation of the fouling resistance. The fouling rates predicted from these results revealed that the numerical model satisfactorily reproduced the phenomenon observed experimentally. Inspection of the CFD results at a local level indicated that the interface temperature was the most influential operating parameter. The research also examined the likelihood that the crystallisation and particulate fouling mechanisms coexist. It was found that the distribution of velocity increased the likelihood of the particulate phase forming within the boundary layer, thus emphasizing the importance of differentiating between behaviour within the bulk and the boundary layer. These numerical results also implied that the probability of this composite fouling was greater in turbulent flow. Finally, supersaturation was confirmed as the key parameter when precipitation occurred within the bulk/boundary layer. This investigation demonstrated the advantages of using CFD to assess heat exchanger fouling. It produced additional physical models which when incorporated into the CFD code adequately modeled key aspects of the crystallisation and particulate fouling mechanisms. These innovative modelling ideas should encourage extensive use of CFD in future fouling investigations. It is recommended that further work include detailed experimental data to assist in defining the key kinetic and thermodynamic parameters to extend the scope of the required physical models.

Both primary and secondary liver cancers are common and the majority of patients are not eligible for surgical resection or a liver transplant, which are considered the only hope of cure. Mortality rates are high and there is a need for alternative treatment options. New forms of local treatment work best on small tumours; large ones, however, remain difficult to treat. Hyperthermia involves heating tumours to 40??-44?? C. The aim is to heat the entire tumour without damaging the surrounding normal tissue. Treating deep seated tumours is technically challenging. Ferromagnetic embolisation hyperthermia (FEH) is a novel method of treating liver tumours. Magnetic microspheres are infused into the hepatic artery and lodge primarily in the tumour periphery. An applied alternating-current magnetic field causes the microspheres to heat. Animal experiments have shown that this is a promising technique. There is a need for modelling of FEH prior to commencement of clinical trials. Analytical and numerical models of tumour heating during FEH treatment are presented here. The models help predict the temperature distributions that are likely to arise during treatment and give insight into the factors affecting tumour and liver heating. The models incorporate temperature-dependent thermal properties and blood perfusion rates of the tissues and a heterogeneous clustering of microspheres in the tumour periphery. Simulations show that the poorly perfused tumours heat preferentially while the liver is effectively cooled by blood flow from the portal vein. A peripheral distribution of heat sources produces a more even temperature field throughout the tumour, compared to a heat source that is centred within the tumour core. Large tumours reach higher temperatures and have higher heating rates, supporting experimental findings. Using temperature-dependent, rather than constant, values for thermal conductivities and blood perfusion rates results in higher temperatures within the tumour. The uneven clustering of microspheres in the tumour periphery leads to a more heterogeneous temperature distribution in the core, but it has less of an effect on the wellperfused liver. The results show that FEH has the potential to effectively treat liver tumours and the technique merits further investigation.

This work deals with the study of heat transfer between a porous medium and a free medium, using multi scale approaches. First, we derive the boundary conditions that must be applied at a free-porous interface for laminar heat transfer at local thermal equilibrium and, then, at local thermal non-equilibrium. For turbulent heat transfer, a direct numerical simulation is performed supplying a better understanding of the physic at the free-porous interface. Then, we determine a turbulent model with associated jump conditions. These studies answer fundamental questions regarding the physical meaning of the jump conditions, the values of the jump parameters and the location of the interface for heat transfer.

<p>A literature survey on modelling of the resistance spot welding process has been carried out and some of the more interesting models on this subject have been reviewed in this work. The underlying physics has been studied and a brief explanation of Heat transfer, electrokinetics and metallurgy in a resistance spot welding context have been presented.\nl\hsLastly a state of the art model and a simplified model, with implementation in the FEM software LS-DYNA in mind, have been presented.</p>

The Purpose of this thesis is to experimentally demonstrate an inversion analysis technique, developed by Dr. Jay Frankel (UTK), that utilizes transient temperature data from probes embedded at known locations in a material. This allows one to determine thermal properties (thermal diffusivity and thermal conductivity) of the material, surface temperature, and the surface heat flux as they change with time. Dr. Frankel’s inversion method can be used to determine surface temperature and heat flux of a one-dimensional semi-infinite slab based on the transient data from one or two embedded probes, if the thermal conductivity and thermal diffusivity of the material are known. Frankel’s theory suggests that the thermal properties of the material can be determined if transient data from two thermocouple (TC) probes at known locations and the heat flux at the surface are known. This thesis investigates finding the thermal properties and surface temperature of materials using a two embedded thermocouple approach. As an initial check to the inversion analysis, the theoretical temperature solution for a one-dimensional semi-infinite slab was used. This validated that the analysis could converge to the constant thermal properties for the theoretical material. An experiment was run again to provide data for the materials copper and aluminum. Using a real material is fundamentally different from using theoretical determined (analytical) data, because the thermal properties for a real material vary with temperature. Since the inversion analysis converged to a constant solution for the theoretical temperatures, it was believed that the real material will converge to a solution. However, it was seen that the thermal diffusivity for the real materials never converged to the expected value. Although, when a constant handbook value for the thermal diffusivity is used to calculate the thermal conductivities from the experimental temperature data collected from the internal probes, the inversion analysis resulted in good agreement with experiment.