Thermal Exchange Research Articles

Impact of Geometry on a Thermal-Energy Storage Finned Tube during the Discharging Process

This work focused on the modelling of latent heat thermal energy storage systems. The mathematical modelling of a melting and solidification process has time-dependent boundary conditions because the interface between solid and liquid phases is a moving boundary. The heat transfer analysis needs the interface position over time to predict the temperature inside the liquid and the solid regions. This work started by solving the classical two-phase (one-dimensional) Stefan problem through a Matlab implementation of the analytical model. The same physical problem was numerically simulated using ANSYS FLUENT, and the good match of analytical and numerical results validated the numerical model, which was used for a more interesting problem: comparing three different latent heat TES configurations during the discharging process to evaluate the most efficient in terms of maximum average discharging power. The three axial heat conduction structures changed only for the fin shape (rectangular, trapezoidal and fractal), keeping constant the volume fractions of steel, aluminium and PCM to perform a proper comparison. Results showed that the trapezoidal fin profile performs better than the rectangular one, and the fractal fin profile geometry was revealed as the best for faster thermal exchange when the solidifying frontier moves away from the steel ring. In conclusion, the average discharging power for the three configurations was evaluated for a time corresponding to a reference value (10%) of the liquid fraction: the rectangular fin profile provided 950.8 W, the trapezoidal fin profile 979.4 W and the fractal fin profile 1136.6 W, confirming its higher performance compared with the other two geometries.

Thermal-exchange HLA-E multimers reveal specificity in HLA-E and NKG2A/CD94 complex interactions.

There is growing interest in HLA-E-restricted T-cell responses as a possible novel, highly conserved, vaccination targets in the context of infectious and malignant diseases. The developing field of HLA multimers for the detection and study of peptide-specific T cells has allowed the in-depth study of TCR repertoires and molecular requirements for efficient antigen presentation and T-cell activation. In this study, we developed a method for efficient peptide thermal exchange on HLA-E monomers and multimers allowing the high-throughput production of HLA-E multimers. We optimized the thermal-mediated peptide exchange, and flow cytometry staining conditions for the detection of TCR and NKG2A/CD94 receptors, showing that this novel approach can be used for high-throughput identification and analysis of HLA-E-binding peptides which could be involved in T-cell and NK cell-mediated immune responses. Importantly, our analysis of NKG2A/CD94 interaction in the presence of modified peptides led to new molecular insights governing the interaction of HLA-E with this receptor. In particular, our results reveal that interactions of HLA-E with NKG2A/CD94 and the TCR involve different residues. Altogether, we present a novel HLA-E multimer technology based on thermal-mediated peptide exchange allowing us to investigate the molecular requirements for HLA-E/peptide interaction with its receptors.

Investigation of the thermal-flow performances of sinusoidal wavy finned-tube heat exchangers

ABSTRACT The aim of this paper is to examine the influence of wave amplitude and wave number on the thermal-flow behavior of sinusoidal wavy finned-tube heat exchangers. Thirteen geometries with various wave amplitudes (0.75–2.5 mm) and wavenumbers (2–6 waves) are analyzed for Reynolds numbers varying from 800 to 2700. The inspection revealed that the thermal exchange rate, the Colburn factor, and the friction factor increase with wave amplitude (A) and the number of waves (N w), while the fin efficiency decrease for all Re. For Re varying from 1066 to 2700, the wavy fins with A = 1.75 mm and N w = 4 provide the most outstanding values of the performance evaluation criterion (PEC). However, at Re = 800, the PEC ratios decrease with augmented A and N w. Regarding the global performance criterion, the wavy fins with the lowest amplitude values (A = 0.75 mm) and the number of waves (N w = 2) reached the highest G pc values at all Reynolds numbers.

Effect of the Richardson Number on Flow and Heat Transfer in a Cylinder Filled with Cu-Water Nano-fluid at Different Nanoparticle Concentrations

Fluid circulation and thermal exchange properties via integrated natural and artificial convection within a container have attracted considerable interest due to its many industrial uses. This present work concentrates on determining the effect of the Richardson number on flow and heat transfer in a cylinder filled with Cu-Water nanofluid at different nanoparticle concentrations. The governing equations: continuity and Navier Stoke fields were discretized using the finite difference approach and simulated in C++ programming language. In this work, the Richardson parameter ranged from 2.6*104 to 2.8*104, while the concentration of Cu nanoparticles ranged from 1% to 10%, and the results are presented as Nusselt number, vorticity, and stream function profiles. The results reveal that the maximum Richardson value is 2.76 x 104 at the nanoparticle volume of 0.04, resulting in a considerable increase in the convective heat transfer rate. Furthermore, as the Richardson parameters increase, the Nusselt number in the nanofluid increases exponentially while the local drag coefficient decreases. The stream function, longitudinal velocity and circulation increase as the Richardson parameters grow. The technical design for air turbulence prediction involves an understanding of the Richardson-driven connection as a mix of wind speed and convective stability variables.

Modified Lévy flight distribution algorithm for global optimization and parameters estimation of modified three-diode photovoltaic model

Many real-world problems demand optimization, minimization of costs and maximization of profits, and meta-heuristic algorithms have proficiently proved their ability to achieve optimum results. This study proposes an alternative algorithm of Lévy Flight Distribution (LFD) by integrating Opposition-based learning (OBL) operator, termed LFD-OBL, for resolving intrinsic drawbacks of the canonical LFD. The proposed approach adopts OBL operator for catering search stagnancy to ensure faster convergence rate. We validate the usefulness of our approach through IEEE CEC’20 test suite, and compare results with original LFD and several other counterparts such as Moth-flame optimization, whale optimization algorithm, grasshopper optimisation algorithm, thermal exchange optimization, sine-cosine algorithm, artificial ecosystem-based optimization, Henry gas solubility optimization, and Harris’ hawks optimization. To further validate the efficiency of LFD-OBL, we apply it on parameters optimization of Solar Cell based on the Three-Diode Photovoltaic model. The qualitative and quantitative results of all the experiments performed in this study suggest superiority of the proposed method.

Assessing the role of thermal disequilibrium in the evolution of the lithosphere–asthenosphere boundary: an idealized model of heat exchange during channelized melt transport

Abstract. This study explores how the continental lithospheric mantle (CLM) may be heated during channelized melt transport when there is thermal disequilibrium between (melt-rich) channels and surrounding (melt-poor) regions. Specifically, I explore the role of disequilibrium heat exchange in weakening and destabilizing the lithosphere from beneath as melts infiltrate into the lithosphere–asthenosphere boundary (LAB) in intraplate continental settings. During equilibration, hotter-than-ambient melts would be expected to heat the surrounding CLM, but we lack an understanding of the expected spatiotemporal scales and how these depend on channel geometries, infiltration duration, and transport rates. This study assesses the role of heat exchange between migrating material in melt-rich channels and their surroundings in the limit where advective effects are larger than diffusive heat transfer (Péclet numbers > 10). I utilize a 1D advection–diffusion model that includes thermal exchange between melt-rich channels and the surrounding melt-poor region, parameterized by the volume fraction of channels (ϕ), average relative velocity (vchannel) between material inside and outside of channels, channel spacing (d), and timescale of episodic or repeated melt infiltration (τ). The results suggest the following: (1) during episodic infiltration of hotter-than-ambient melt, a steady-state thermal reworking zone (TRZ) associated with spatiotemporally varying disequilibrium heat exchange forms at the LAB. (2) The TRZ grows by the transient migration of a disequilibrium-heating front at a material-dependent velocity, reaching a maximum steady-state width δ proportional to ϕvchannel(τ/d)n, where n≈2 for periodic thermal perturbations and n≈1 for a single finite-duration thermal pulse. For geologically reasonable model parameters, the spatiotemporal scales associated with establishment of the TRZ are comparable with those inferred for the migration of the LAB based on geologic observations within continental intra-plate settings, such as the western US. The results of this study suggest that, for channelized transport speeds of vchannel=1 m yr−1, channel spacings d≈102 m, and timescales of episodic melt infiltration τ≈101 kyr, the steady-state width of the TRZ in the lowermost CLM is ≈10 km. (3) Within the TRZ, disequilibrium heat exchange may contribute ≈10-5 W m−3 to the LAB heat budget.

Ultralong mean free path phonons in HKUST-1 and their scattering by water adsorbates

Metal-organic frameworks (MOFs) have shown big potential in energy storage and thermal management, which are closely related to their thermal properties. It has been believed for some time that the vibrational mean free path in MOFs is relatively small and the resulting thermal conductivity has weak size dependence. By studying one of the typical MOFs, i.e., ${\mathrm{Cu}}_{3}{(\mathrm{BTC})}_{2}$ where BTC is benzene-1,3,5-tricarboxylate, also referred to as HKUST-1, we computationally prove that the mean free path of these small wave vectors or equivalently low-frequency vibrations in HKUST-1 can be as large as \ensuremath{\sim}120 nm and the corresponding thermal conductivity is strongly size dependent, which is attributed to its good crystallinity. We further find that these long mean free path phonons are strongly scattered by the adsorbed water molecules and the thermal conductivity is decreased by \ensuremath{\sim}51.3% when the water molecules are adsorbed. Consequently, the thermal conductivity of HKUST-1 with water molecules is weakly size dependent. Two pathways for the thermal energy exchange, e.g., the phonons and the water molecules, exist in HKUST-1 with water molecules. The thermal conductivity of the adsorbed HKUST-1 is found to decrease and then increase with the quantity of the adsorbates owing to the competition between the two thermal pathways. Our study here provides a fundamental understanding on the thermal transport mechanisms in the metal-organic framework with consideration of adsorbates, which offers useful guidance for thermal management design in these thermal-related applications such as adsorption-driven heat pumps.

Thermal and Mechanical Improvement of Filling Mixture for Shallow Geothermal Systems by Recycling of Carbon Fiber Waste

The reuse of waste materials such as carbon fiber (CF) as filling additive for closed-loop vertical geothermal probes in shallow geothermal systems has been evaluated as a new grout mixture for the improvement of geothermal energy systems efficiency and a sustainable supply of raw materials from special waste. The study evaluates the improvement in both thermal exchange characteristics and mechanical properties of the filling grout for geothermal purposes through the addition of 5% of CF to standard (ST) materials currently on the market. Uniaxial and flexural tests investigating the material response after 14 and 28 days from sample preparation on samples of both standard and mixed grout material as well as non-stationary hot wire method were used to define the thermal conductivity for both the standard and innovative mixtures. The experimental analysis provides evidence for increasing the thermal conductivity by about 3.5% with respect to standard materials. Even the mechanical properties are better in the innovative mixture, being the compressive strength 187% higher and flexural strength 81% higher than standard materials. The obtained results become useful for the optimization of low enthalpy geothermal systems and mostly for the design of the vertical heat exchange system in terms of depth/number of installed probes. Principally, thermal conductivity improvements result in a reduction of about 24% of the geothermal exchanger’s length, affecting the economic advantages in the implementation of the entire system. A simple analysis of the reuse of CF waste shows the reduction of industrial waste and the simultaneous elimination of disposal costs, defining new perspectives for industrial waste management. This research provides essential elements for the development of a circular economy and is well integrated with the European challenges about the End of Waste process and reduction of environmental impact, suggesting new perspectives for economic development and sectorial work.

Narratives and Benefits of Agricultural Technology in Urban Buildings: A Review

The literature on agricultural technology (ag-tech) for urban agriculture (UA) offers many narratives about its benefits in addressing the challenges of sustainability and food security for urban environments. In this paper, we present a literature review for the period 2015–2022 of research carried out on currently active UA installations. We aim to systematise the most common narratives regarding the benefits of controlled environment agriculture (CEA) and soil-less growing systems in urban buildings and assess the existence of peer-reviewed data supporting these claims. The review was based on 28 articles that provided detailed information about 68 active UA installations depicting multiple types of ag-tech and regions. The results show that most research conducted for commercial UA-CEA installations was carried out in North America. Standalone CEA greenhouses or plant factories as commercial producers for urban areas were mostly found in Asia and Europe. The most often cited benefits are that the integration of multiple CEA technologies with energy systems or building climate systems enables the transfer of heat through thermal airflow exchange and CO2 fertilisation to improve commercial production. However, this review shows that the data quantifying the benefits are limited and, therefore, the exact environmental effects of CEA are undetermined.

Heat effects modelling on the efficiency loss of the lubricating interface between piston and cylinder in axial piston pumps

This work presents a systematic analysis of the tribological properties of the lubricant and the thermal exchange effect on the deformation of the solid-fluid structure between the piston and cylinder block in an axial piston pump. A thermo-elastohydrodynamic model is established and used to study the pump. Fluid film properties, friction forces and leakage of the solid-fluid structure are calculated and analysed under normal operating conditions of the axial piston pump s. The friction and leakage losses representing the direct total power loss are analysed for different conditions. Furthermore, the thermal effects on the oil film properties and lubrication mechanisms are calculated and discussed. This work provides sufficient methods and processes to evaluate the causes of the lubrication failure. It proves that the effects of heat exchange in the energy loss and efficiency loss between piston and cylinder are critical. Finally, some suggestions are given for a better design of the axial piston pump.

Exhuming and Preserving Epizonal Orogenic Au‐Sb Deposits in Rapidly Uplifting Orogenic Settings

AbstractEpizonal orogenic Au‐Sb deposits are generally Phanerozoic in age, possibly as a consequence of erosion that can entirely remove older mineral deposits in rapidly uplifting orogenic setting. Quantifying post‐mineralization thermotectonic processes is essential for documenting the exhumation and preservation of epizonal deposits, which in turn is critical for constraining regional deformation. This study focuses on the giant Zaozigou deposit, and documents cooling rates using amphibole and biotite Ar‐Ar, zircon U‐Th/He, and apatite fission track dating. Six cooling phases are identified, including Early to Middle Triassic very rapid cooling, Late Triassic rapid cooling, Early Jurassic slow cooling, Middle to Late Jurassic rapid cooling, Cretaceous to Oligocene slow cooling, and Miocene to present rapid cooling. Initial cooling corresponds to thermal exchange between magmatic rocks and wall rocks. Phases two through five are related to a sequence of post‐mineralization compressional, strike‐slip, compressional, and extensional events, pointing to multi‐phase tectonic evolution of the Qinling Orogen since the Late Triassic. Late exhumation is probably related to lateral growth of the Tibetan Plateau and/or to rapid erosion induced by intensification of the Asian monsoon. In total, ∼6.3 km of rock was removed post‐mineralization. We conclude that Cretaceous to Oligocene extension retarded the continuous erosion and thus played an important role in the preservation of Zaozigou. Combined with known orogenic processes, our results demonstrate that a long‐lived extension is a favorable tectonic environment for the preservation of epizonal orogenic Au‐Sb deposits in rapidly uplifting orogenic setting.

Temperature regulation in the Balkan spadefoot (Pelobates balcanicus Karaman, 1928) at the beginning of nocturnal activity.

On land, the amphibians interact with the environment in a complex way-even small changes in the physiological conditions may significantly impact the behaviour and vice versa. In ectothermic tetrapods, the transition from inactive to active phase may be related to important changes in their thermal status. We studied the thermal ecology of adult Balkan spadefoots (Pelobates balcanicus Karaman, 1928) in northeastern Bulgaria. These toads spend the daytime buried between 10 and 15 cm in sandy substrates, and emerge after sunset. On the substrate, their thermal energy exchange is defined by the absence of heat flow from the sun. Secondary heat sources, like stored heat and infrared radiation from the soil play an important role for the thermal balance of the active spadefoot toads. At the beginning of their daily activity, we measured substrate temperature (at a depth of 11–12 cm), toad’s surface body temperature, and also provided thermal profiles of the animals and the substrate surface in their microhabitats. In animals which recently emerged from the substrate, the temperature was comparatively higher and was closer to that of the subsoil on the spot. After that, body temperature decreased rapidly and continued to change slowly, in correlation with air temperature. We detected a temperature gradient on the dorsal surface of the toads. On the basis of our measurements and additional data, we discuss the eventual role of air humidity and the effects of surface and skin water evaporation on the water balance and activity of the investigated toads.

Integration of Computational Fluid Dynamics and Artificial Neural Network for Optimization Design of Battery Thermal Management System

The increasing popularity of lithium-ion battery systems, particularly in electric vehicles and energy storage systems, has gained broad research interest regarding performance optimization, thermal stability, and fire safety. To enhance the battery thermal management system, a comprehensive investigation of the thermal behaviour and heat exchange process of battery systems is paramount. In this paper, a three-dimensional electro-thermal model coupled with fluid dynamics module was developed to comprehensively analyze the temperature distribution of battery packs and the heat carried away. The computational fluid dynamics (CFD) simulation results of the lumped battery model were validated and verified by considering natural ventilation speed and ambient temperature. In the artificial neural networks (ANN) model, the multilayer perceptron was applied to train the numerical outputs and optimal design of the battery setup, achieving a 1.9% decrease in maximum temperature and a 4.5% drop in temperature difference. The simulation results provide a practical compromise in optimizing the battery configuration and cooling efficiency, balancing the layout of the battery system, and safety performance. The present modelling framework demonstrates an innovative approach to utilizing high-fidelity electro-thermal/CFD numerical inputs for ANN optimization, potentially enhancing the state-of-art thermal management and reducing the risks of thermal runaway and fire outbreaks.

Effect of aspect ratio and nonuniform temperature on mixed convection in a double lid-driven cavity

The impact of aspect ratio and nonuniform temperature on mixed convection in an enclosure is examined numerically. The chosen shape is an enclosure with a sinusoidal temperature TH in its lower wall, while the upper wall is considered adiabatic. The sidewalls of the cavity move at a descending speed with a uniform temperature TC. The inspection is performed for different Richardson numbers and aspect ratios (AR) varying from 0.25 to 5, while the numbers of Prandtl (Pr = 0.71) and Grashof (Gr = 104) remain constant. The isothermal, streamline, and Nusselt numbers flow distributions inside the cavity are highlighted and discussed. Compared to uniform heating, significant changes in the flow rate are observed when receiving nonuniform heating on the lowest cavity surface. Two cells of flow rotating in opposing directions are formed inside the cavity when the cavity aspect ratio AR = 0.25. When the cavity aspect ratio becomes higher than the unity, these cells change with the development of Ri; they take an oval form and move to the heated side. The non-uniform heating yielded a sinusoidal localized thermal exchange rate with the lowest amounts at the edges and considerable amounts at the bottom center (Ri = 1 and 100).

Hydrothermal challenges in low-temperature networks with distributed heat pumps

Low-temperature networks (≤60 °C) combined with heat pumps allow for efficient heating and cooling of buildings and thermal energy exchange between buildings. Thus, such networks are a key technology to reduce the carbon footprint of urban areas. However, they are far more complex in operation than traditional district heating networks at high temperatures (>60 °C). To simplify future network planning, we present various challenges of low-temperature networks and offer solutions. We study the dependency of heat pump efficiencies on flow rates across the evaporator and present methods to cope with flow variations through heat pumps during operation. We introduce the concept “agent authority” and show that for an agent authority >≈0.7, flow variations during dynamic operation are within ≈20%. In a first case study, the total electricity consumption of a thermal network is minimised by reducing the flow rates through the heat pumps by ≈ 14%, however having only minor impact (0.3%) on the total electricity consumption. In a second case study, a decision matrix for selected network types is developed. We show that apart from quantifiable parameters such as energy efficiency or costs, qualitative criteria such as control and resilience are relevant in decision making.

Life Cycle Saving Analysis of an Earth-Coupled Building without and with Roof Evaporative Cooling for Energy Efficient Potato Storage Application

Preservation of potatoes in a controlled cool environment (i.e., in cold storage) consumes a substantial amount of energy. The specific energy consumption in Indian cold storage has been estimated to be between 9 and 26 kWh/ton/year. In this article, the potential for minimizing the energy consumption in the refrigeration process of cold storage through passive cooling concepts (i.e., roof evaporative cooling and the earth integration of the storage building) was explored. These passive concepts of cooling have shown significant potential for lowering the cooling loads and the energy consumption in different types of buildings. Therefore, a feasibility analysis for a potato storage building, considering the effect of the passive cooling concepts, was conducted for three different climatic conditions (i.e., hot–dry, warm–humid, and composite) in India. The energy saving potentials in the cold storage were assessed by quantifying the thermal energy exchange between the indoor and outdoor environments using the modified admittance method. The effect of heat transfer through the building envelope on total energy consumption was estimated for the building having various sunken volumes (buried depths) without and with roof evaporative cooling. Further, the economic feasibility of adopting passive concepts was assessed in terms of life cycle saving compared to the base case. Results indicate that earth coupling without and with evaporative cooling has substantial potential to reduce the cooling load and can produce significant savings.

Conjugate heat transfer in lattice frame materials based on novel unit cell topologies

This article presents conjugate heat transfer characteristics of strut-based sandwich-type configurations obtained through reticulation of unit cell topologies of Tetrakaidecahedron, Octet and Rhombic dodecahedron shapes (porosity ∼0.90) with water as working fluid. Tetrakaidecahedron lattice exhibited the highest overall heat transfer coefficient, followed by Octet and Rhombic dodecahedron, respectively. Pressure drop was the highest for Octet, followed by Rhombic dodecahedron, and Tetrakaidecahedron, respectively. Thickness of struts in contact with endwall played a dominant role in conjugate thermal exchange of sandwich configurations. For the investigated conditions, Tetrakaidecahedron-shape based lattice provided the least thermal resistance value at any given pumping power condition.

Correction to: Effect of light intensity and air velocity on the thermal exchange of indoor-cultured lettuce

Correction to: Effect of light intensity and air velocity on the thermal exchange of indoor-cultured lettuce

Fluid flow and heat transfer of porous TPMS architected heat sinks in free convection environment

Heat dissipation in electronic devices is challenging due its limited size and cooling space constraint. Implementing Triply Periodic Minimal Surfaces (TPMS)-based cellular structures could enhance the thermal exchange mechanism due to their novel architected, interconnected, and inter wind porous topologies and high surface area to volume ratio. In this study, three novel mathematically-driven TPMS heatsink structures were investigated using computational fluid dynamics (CFD) based models. TPMS heat sinks consisting of seven triply periodic unit cells were examined to investigate their thermal performance and fluid flow behavior in free convection air environment. The thermal performance indicators as convection heat transfer coefficient and surface temperature under parametric variation of applied heat load, fluid enclosure boundary condition, and TPMS structure orientation were determined. Enclosure boundary conditions found to have a significant effect on the thermal behavior of each heat sink structure; including radiation contribution was found to account for approximately 23% of the overall heat transfer in due to the complex TPMS internal structure. Three empirical Nusslet number correlations were then derived for the investigated TPMS structures. The results showed that TPMS-based heat sinks outperform conventional heat sinks by 48–61% owing to the random perturbations of flow and high packing density. This work shows the potential of TPMS porous architectures as very promising heat sinks.

Clinical Evaluation of Micro-Embolic Activity with Unexpected Predisposing Factors and Performance of Horizon AF PLUS during Cardiopulmonary Bypass.

Background: During Cardiopulmonary Bypass (CPB) gaseous micro-emboli (GMEs) decrease the quality of the blood flow and the capillary oxygen delivery, increasing the incidence of postoperative neurocognitive disorders (POCD) following cardiac surgery. In these circumstances, the use of an efficient device, could be crucial for the removal and reduction of micro-embolic activity. Methods: From February 2022 to March 2022, we prospectively collected data from 40 consecutive patients undergoing conventional and minimally invasive cardiac surgery that used the Horizon AF PLUS (Eurosets, Medolla, Italy). We collected, during the CPB’s time, the incidence of unexpected predisposing factors for micro-embolic activity reported in the literature with the GMEs count and their diameter through the GAMPT BCC 300 (Germany). Results: The group of patients without unexpected predisposing factors for micro-embolic activity (55%) reported a GME volume of 0.59 ± 0.1 (μL) in the arterial line (p-value 0.67). In both groups were no reported performance deficit during the procedures for oxygenation and CO2 removal. Conclusions: Our clinical analysis showed that Horizon AF PLUS is an effective and safe device without iatrogenic perioperative complications, for the reduction of micro embolic activity during CPBs procedures, with high efficiency in terms of oxygenating performance and thermal exchange.