ABSTRACT. The leakage in the nuclear reactor containment due to fracture/thermal stratification can cause the leakage of high-pressure fluid into the low-pressure environment. This results in the high pressure drop and phase change from liquid to vapour. This physical phenomenon is called flash evaporation; to avoid any accidental mishap, it is important to study it. This work investigates the thermodynamic phenomena of liquid film flash evaporation through an experimental inquiry. Results suggested that significant water vaporization occurs during the initial stage of the flashing, which results in a large temperature drop. The large superheat value makes the process more violent and increases the flashing intensity

ABSTRACT. Oil jet cooling and hairpin winding have become increasingly popular in electric machine design. Combining the two technologies resulted in improved motor designs with high power density and efficiency. This study examines the effect of jet configuration, nozzle diameter, and flow rate on heat extraction performance using high-fidelity numerical simulations. Results show that the axial jet, although superior in heat extraction, performs poorly at low inlet velocities. Therefore, a minimum velocity threshold is necessary.

ABSTRACT. The heat transfer benefits of static in-line enhancement devices for tubular heat exchangers in laminar flow have been investigated using experimental and theoretical approaches. A high viscosity heat transfer facility was used to characterise an existing wire matrix insert (hiTRAN) and a new plate type insert (hiVISC), with additional studies using CFD. Positron emission particle tracking (PEPT) was employed to visualise flow in an otherwise opaque system. hiTRAN and hiVISC® inserts displayed higher efficiency heat transfer in low Reynolds number laminar flows in comparison to commonly used alternative insert designs.

ABSTRACT. This experimental study analyzes heat transfer and friction factor in a rectangular duct utilizing coiled wire inserts. The experimental setup involved water as the working fluid, with Reynolds numbers spanning from 500 to 10000, covering laminar, transition, and turbulent flow regimes. A comparative study was conducted between experimental pressure drop data and existing correlations from open literature for an empty duct, demonstrating a notable agreement. Furthermore, the study delves into the impact of employing wire coil inserts on heat transfer enhancement. The results revealed that the utilization of coiled wire inserts led to significative increase in both heat transfer and friction factor within the channel.

ABSTRACT. This study reveals that the drying of acoustic levitated maltodextrin droplets is enhanced compared to suspended droplets. Heat and mass transfer dynamics are investigated during the drying of levitated droplets by combining mathematical modelling and experiments. The mathematical model previously predicted experimental data for the suspended droplets to within 4%. Results demonstrate that the heat and mass transfer coefficients of the model must be increased by a factor of 1.625 to improve the alignment between the predicted and levitated experimental data for different maltodextrin concentrations and initial droplet sizes.

ABSTRACT. There is a growing need to develop high flux cooling solutions to address thermal management challenges in a range of applications, including data centres, power electronics and microprocessors. Micro pin fin heat sinks are a state of the art liquid phase cooling solution, but high heat transfer coefficients remain dependent on high flow rates, leading to large pumping costs. This paper investigates the use of oscillating flows in micro pin fin heat sinks to enhance heat transfer at lower net flow rates. Brightfield micro particle image velocimetry was used to assess flow patterns and the turbulent kinetic energy was measured around 9 different micro pin designs. Once the flow became fully reversing the turbulent kinetic energy plateaued. The best performing pin was the 750 μm triangular pin with a normalised turbulent kinetic energy of 1.7.

ABSTRACT. The determination of various multiphase flow parameters, such as heat transfer coefficient and pressure gradient, is significantly influenced by void fraction. A comprehensive understanding of void fraction behaviour, coupled with precise prediction, is crucial for designing efficient equipment that can lead to increased production rates in the petroleum industry. Given the prevalence of higher viscous liquids in the petroleum sector, this study focuses on investigating void fraction in vertical pipes using gas-liquid mixtures with a viscosity range of 4.8-234 mPa·s. The research explores the impact of superficial gas velocity and liquid viscosity. The results showed a good agreement between the predicted and experimental data

ABSTRACT. Desalination has emerged as a technology solution to meet the global demand for clean water by treating saline water sources. One of the major drawbacks of desalination is that it generates a hypersaline by-product or brine that must be managed. In this study, a thermal brine concentrator based on air gap diffusion distillation (AGDD) is presented that uses a counterflow heat exchanger design and plastic surfaces for high-salinity desalination. A numerical model is developed to predict the performance of AGDD under a range of operating conditions, and an experimental prototype is designed to demonstrate continuous operation. The results show that a multi-pass AGDD system can achieve an overall water recovery of ~70% and gain output ratio of 7 (corresponding to latent heat recovery of 88%) with an initial feed salinity of 70 g/kg. Overall, the system outperforms its thermodynamically similar counterpart, air gap membrane distillation (AGMD), by eliminating heat and mass transport resistances associated with the membrane.

ABSTRACT. Passive safety systems in nuclear reactors rely on gravity as driving force for transferring heat from the core or a hot region into a large reservoir thanks to natural circulation. They are designed to function without the intervention of the operators for several hours or days. Given the large scale of the current SMR designs, the Rayleigh number is expected to be in the order of 10^15. Currently, there are very few experiments that have reached such a high number, so new experiments are necessary to validate thermal hydraulics codes used to predict such behaviour in an accident scenario. The paper shows preliminary calculations using Computational Fluid Dynamics (CFD) to help sizing a new experimental set up at the PANDA facility (PSI, Switzerland) within the OECD/NEA PANDA project.

ABSTRACT. This paper presents a distributed optical fibre sensor for real-time detection of solid-liquid phase changes in thermal energy storage material (n-octadecane). The sensor probes, made by splicing a no-core fibre (NCF) between two single-mode fibres (SMFs), form a sensor array. Due to differing refractive indices (RI) of solid and liquid n-octadecane, the array exhibits a step-like output power change during phase transitions. Optical fibre sensors are crucial in phase change energy storage materials as they offer precise, real-time monitoring and can be integrated into various systems with minimal intrusion. Experimental results confirm the sensor's ability to monitor phase changes, highlighting its potential to enhance thermal energy storage systems and advance distributed optical fibre sensing technology.

ABSTRACT. External process fluid injection into the screw pump with a progressive spindle pitch counteracts the decrease in delivery rate at high gas volume fractions (GVF) and increases both the volumetric and isothermal efficiency. In experiments with a progressive spindle, the injection position, injection volume flow, rotational speed, differential pressure and gas content are varied to determine the impact of process fluid injection on the conveying behaviour. Pressure-side injection shows the highest improvement potential in the experimental investigations. This result is confirmed by measured local state variables (p, T).

ABSTRACT. This study employs discrete element modelling to investigate the heat transfer phenomena within granular flow across various porous shape scenarios. The result showed that spline with staggered shape exhibited highest maximum and average temperature with longer duration compared to other porous shape scenarios. In addition, the agglomeration of solid particles in the interstitial region of porous structure was predicted in all scenarios. This study underscores the potential for optimising porous structures to enhance the heat transfer in granular flow systems.

ABSTRACT. Heat pipes have grown to become a pivotal technology in the development of high-level thermal management systems. Their functionality relies on the two-phase circulation of an active fluid within a hermetically sealed metal envelope. An internal porous structure is used to pump the liquid condensate back to the evaporator via capillary action. To predict their maximum thermal load capacity at a given temperature, many numerical models have been postulated and experimentally tested over the past five decades. Until now, however, there is no freely available tool utilizing these developed models to aid in wider design, application and research of heat pipes beyond very basic sales tools. In this paper, a fully parametric analysis tool to predict the performance of both sintered and mesh heat pipes is presented. Its target use is aimed at aiding both the commercial design and manufacture of heat pipes as well as more fundamental research and development, creating a versatile modelling tool for rapid parametric analysis. Additionally, its user interface is aimed to be simple enough to be accessible to engineers who have not previously worked with heat pipes but may be considering them for new commercial applications. The program has the ability to estimate the optimal wall thickness, wick thickness and fill volume for a given heat pipe outer diameter to aid in their design and manufacture.

ABSTRACT. Additive Manufacturing opens novel frontiers in thermal science but it also comes with several challenges, This work presents a few applications of the metal additive manufacturing to different heat transfer problems: single phase forced convection, pool boiling, and solid-liquid phase change.

ABSTRACT. Enhanced Geothermal Systems (EGS) hold high potential as a generating technology, but cost reduction uncertainties persist. To assess EGS’s potential role in the context of this uncertainty, we here address the following question: How much cost reduction is required for EGS to be competitive in a highly decarbonised European energy system and how crucial is heat (co-)generation? To do so, we employ the sector-coupled energy system model PyPSA-Eur and optimise investment and dispatch over a full year, while incorporating EGS at different cost levels and as a generator of electricity only, low-grade heat and power or low-grade heat only. Our findings indicate that with heat generation, EGS deployment accelerates by approximately 15 years. Assuming cost reductions projected by a recent paper, this yields an installed capacity of ~100 GW borehole capacity by 2030 (equalling approximately 30% cost reduction). However, electricity generation only becomes competitive with cost assumptions for 2035 (50% cost reduction), unlocking a market exceeding 1 TW borehole capacity across Europe.

ABSTRACT. Globally, most electricity is still generated using fossil fuels, however, the share of electricity generated from renewables continues to grow rapidly. As electricity grids across the world decarbonize, electrifying end-uses that are currently fossil fuel fired presents a promising path towards decarbonization. Next generation heat pumps are a viable solution for decarbonizing fossil fuel fired steam boilers. In collaboration with the Colorado State University, AtmosZero has built a prototype ambient-temperature-source, steam-generating heat pump system operating from 15°C heat source and providing steam at temperatures as high as 150°C. Here, we present on the experimental performance of the as-built prototype system.

ABSTRACT. This paper delves into the intricate dynamics of bubble microlayers by conducting fully-resolved simulations of single-bubble growth phenomena in pool boiling conditions using OpenFOAM. A comprehensive parametric analysis is presented, exploring the influences of fluid superheat, solid surface wettability (quantified by the contact angle of a specific fluid-surface combination), and the impact of superheat of the solid surface during bubble growth.

ABSTRACT. High cycle thermal fatigue (HCTF) induced cracking in the turbulent thermal mixing areas of T-junction piping systems is a vital safety concern in the nuclear power plants. We present a URANS study (with conjugate heat transfer) of hot thermal transients (linear ramp over a short period, for different Froude numbers 0.4 to 0.9, at the branch pipe inlet) through a T-junction configuration (working fluid is water), having constant ratio of mass flow rate (main / branch, 5:1). The analysis indicates that small Froude number transients lead to potential risk of thermal fatigue. Additionally, complex physical phenomena in these flows are also explored.

ABSTRACT. This paper presents comparisons of Computational Fluid Dynamics (CFD) techniques for modelling the flow, heat and mass transfer of pressuriser sprays. Experimental data obtained in a pressuriser test-rig facility at the University of Manchester has been used to validate a range of Eulerian, multiphase modelling techniques with a focus on establishing methods for modelling sprays in an industrial context. The two fluid method was found to recreate the unique shape of sprays driven through a plain orifice with cross wires when applied to a RANS or LES approach, showing promise in the modelling of sprays in the nuclear industry.

ABSTRACT. Unsteady Reynolds-Averaged Navier-Stokes (URANS) computations have been validated against analogous Large Eddy Simulation (LES) benchmark cases concerning a Natural Circulation (NC) loop. Simulations were run to achieve a statistically steady state before transient events were introduced to the loop flow. Both cold flow injection with varying mass flow rates, and zero heater power transients were considered. For the first injection case, presented within this abstract, both models observed a decrease in mass flow and temperature within the loop, with recovery occurring shortly after the injection was stopped. The URANS data exhibits a temperature offset at both the heater and cooler outlets, approximately 2.5% below the LES throughout the transient. The mass flow comparison also demonstrates how the URANS results follow the general flow behaviour of the LES, indicating URANS is capable of predicting whether the perturbation will stall the loop.

ABSTRACT. Numerical simulations of a test facility for sodium-cooled fast nuclear reactors are performed using RANS and LES to better understand these reactors' thermal stratification and mixing-jet phenomena. A thermal transient is simulated in which the temperature of the inlets, located at the bottom of the domain, decreases rapidly. Thermal stratification occurs above the outlet due to limited thermal mixing. The flow from the inlets is in the form of three jets, which are a significant source of temperature fluctuations due to the instability of the jets themselves and the interactions between them. The magnitude of the fluctuations remain elevated due to the delayed decrease in temperature near the bottom of the domain.

ABSTRACT. Flow boiling in microchannels plays an important role in the future of cooling systems. However, to design efficient devices that exploit the benefits of latent heat cooling, it is necessary to develop a detailed understanding of the several complex phenomena that interact with each other and are extremely challenging to capture mathematically with physics-based models. This study explores the application of machine learning (ML) algorithms to demonstrate their predictive abilities in the absence of detailed deterministic knowledge. The work leverages the extensive Brunel Two-phase Flow Database to extract the explanatory variables needed for predictions and uses various regression models to predict the heat transfer coefficient in single small to micro tubes with diameters ranging from 0.52 to 4.26 mm. The preliminary results demonstrate that the ML algorithm can predict accurately, albeit caution is needed when extrapolating beyond the ranges of the data used for training.

ABSTRACT. We investigate the role of rationally selected surfactant and nanoparticle surface treatment on the stability of a Al2O3/Eicosane nanosuspension as a phase change material. The resulting better dispersion of Al2O3 led to superior stability of the nanosuspension under multiple heating/freezing cycles, and suggesting excellent thermophysical properties. The nanosuspension with functionalized nanoparticles and sodium dodecylbenzene sulfonate (SDBS), as a surfactant showed better stability compared with pristine Al2O3. The present work provides a route to enhance the performance of nanosuspensions as phase change materials (PCMs) for thermal management.

ABSTRACT. To effectively analyse the interaction of thermal energy storage units within complex energy systems, accurate yet simplified models are essential. Although three-dimensional models offer accurate simulation results, these demand significant computational resources. Following this line, a low-order, one-dimensional dynamic model for latent heat thermal store is presented. The store unit is based on plate-type heat exchangers to facilitate heat exchange between the heat transfer fluid and the phase change material.

ABSTRACT. The desorption process in hydrogen storage, particularly in metal hydrides, poses challenges regarding efficiency and desorption speed. This study explores the utilization of microwave energy to accelerate the desorption process, thereby yielding hydrogen as a feasible option for energy storage. Numerical simulations were conducted using COMSOL Multiphysics software and the finite element method (FEM) in this research. The analysis compares two heat application methods for metal hydrides: conventional heat exchangers and concentrated microwave heating systems. The objective is to assess and contrast the effectiveness of various hydrogen release techniques in minimizing desorption time. Results indicate that employing microwave energy at 100 W and 2.45 GHz significantly reduces desorption time from 105 to 39 minutes, compared to applying 100 W/m2 of heat via a heat exchanger. This reduction addresses the challenge of hydrogen release, marking a substantial advancement in energy storage technology.

ABSTRACT. The present experimental investigation analysed the non-dimensional heat transfer study for the phase-changing phenomena during the phase change material (PCM) solidification. Thermal performance is characterized by measuring the degree of subcooling through solid Stefan number and measuring the superheating of the PCM at the onset of freezing through liquid Stefan Number. Meanwhile, a parameter termed as the dimensionless temperature is included to represent the instantaneous bulk-to-fusion temperature difference concerning Fourier number. It is found to be an inverse function of the initial Stefan Number.

ABSTRACT. The reversible reaction of CaO/Ca(OH)2 for thermochemical thermal energy storage system has shown a great potential for applications in concentrated solar power (CSP) plants. However, the reversibility of the reaction is still lacking due to many factors, one of them is the formation of agglomeration. The goal of this paper is to investigate the effectiveness of mechanically crushing of agglomeration after each cycle on the efficiency and stability of the reaction. It has been found that crushing of agglomeration had led to more stable powder bed, more loose powder with larger surface area, which resulted in an increase in the generated heat, and the captured CO2.

ABSTRACT. This study investigates numerical performance of the latent heat thermal energy storage (LHTES) system based on plate-type heat exchanger with roll-bond (RB) pattern. A detailed 3D CFD model was developed to evaluate the PCM melting performance in the charging process of the LHTES unit. These investigations are beneficial for the optimum design of the RB pattern for thermal energy storage (TES) applications.

ABSTRACT. In this study, a partial immersion cooling system is used for cooling a battery pack equipped with cylindrical Li-ion batteries considering various flow rates of the coolant. The partial immersion method is used to reduce the total weight of the battery pack and thus increase the power density. A tiny gap of 2 mm is considered between the cells to have a high cell density. Both pressure drop and temperature distribution are evaluated to find the optimum conditions of the cells. Different flow rates of the coolant as well as heat generation rates of the cells are evaluated to achieve the temperature target with the lowest pressure drop. The results show that during fast charging (15 kW), considering the coolant flow rate of 21.5 lpm, the average temperature of 33°C can be achieved in the battery pack while the hot spot temperature is 51°C. While for the heat generation rate of 3kW, the average temperature of 33.8°C can be achieved using the flow rate of 2.15 lpm.

ABSTRACT. In this study, a cold plate with U-shaped channels is investigated to cool the adjacent pouch cell Li-ion batteries. The U-shaped cold plate consists of two parallel sets of channels with seventeen mini channels to cover the whole surface area of the batteries. The thermal management system is evaluated based on the maximum and uniformity of the surface temperature of the batteries. The uniformity of the fluid flow distribution inside the mini channels is also investigated to reach a uniform temperature distribution on the surface of the batteries. The important geometrical features of the U-shaped channels are studied toward a higher performance of the system. The cold plates are designed based on the electrical requirements for placing the bus bar as well as the safety of the battery pack operation. The material of the cold plate is peek which can tolerate the expansion of the pouch cell batteries during charging. Due to the low thermal conductivity of peek material, the thickness of the cold plate is considered as small as possible. The results show that for the flow rate of 1 LPM and flow inlet temperature of 25 °C and the heat input of 16 W (8 W for each side) for the batteries, the average and maximum surface temperature of the batteries are achieved at 28°C and 30°C, respectively, showing the acceptance of the employed U-shaped cold plate. A uniform temperature distribution is achieved across the surface of the battery except the centreline. By increasing the heat generation to 32 W, the average and maximum temperatures raise to 31 °C and 35 °C, respectively, which are still in the acceptable range.

ABSTRACT. Two-phase immersion cooling has the potential to maintain electric vehicle batteries at uniform temperatures thus offering effective battery thermal management. In this study, the effects of changing the refrigerant used, and varying the space between each battery cell were investigated using Computational Fluid Dynamics (CFD) simulations. Results showed that all used refrigerants achieved similar temperature distribution, but R245fa achieved the highest power from cooling 27,000 battery cells, the maximum number used in Volvo lorries, by enabling the production of electricity using organic Rankine cycle.

ABSTRACT. This study endeavours to address the thermal concerns related to rechargeable batteries of electric vehicles by isolating them from external climatic conditions and controlling temperature spikes caused by battery operation. Using a three-dimensional model the thermal regulation of cylindrical lithium polymer-based battery modules is numerically analysed for various cases of hybrid cooling mechanisms with two different C-rates of 0.5C and 1C respectively.

ABSTRACT. The study explores thermal management strategies for Li-ion batteries crucial for Electric Vehicles and Hybrid Electric Vehicles, highlighting the challenges posed by thermal runaway and uneven temperature distribution. Active and passive cooling mechanisms are evaluated, with existing systems facing issues of weight and complexity. Addressing these limitations, a novel composite casing with variable thermal conductivity is proposed, featuring strategically placed copper pins for enhanced heat dissipation. Experimental and simulation results demonstrate the effectiveness of this approach, emphasizing its potential for improving efficiency and safety in Li-ion battery systems. Overall, the study advocates for innovative thermal management solutions to meet the demands of evolving vehicle technologies.

ABSTRACT. This study proposes a battery thermal management system (BTMS) for the 4680 battery module using a double-layer cold plate design, with aerogel utilized as a heat insulation material between the cells. A 2-dimensional finite element model is established to simulate both the thermal behaviour of battery cells and the heat transfer and hydrodynamic characteristics within the system. The design parameters of this proposed cooling strategy were globally optimized using the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, coupled with a surrogate back propagation (BP) neural network model to reduce computational cost.