Thermal Interferences Research Articles

Analytical and experimental analyses on cooling performances of radiative SkyCool radiators with various interior flowing channels

This study presents an analytical model for the radiative SkyCool radiators (RSCR) with various interior flowing channels by using Laplace transformations. Moreover, the convolution theory is applied to solve the problem of nonuniform temperature distribution on the RSCR. Then, an outdoor experiment is carried out to verify the proposed model. Subsequently, the influence of different channel geometries, flow rates, tilt angles and wind velocities on the cooling performances of RSCRs are investigated. The results indicate that increasing the RSCR's length, enlarging the pipe spacing, and decreasing the flow rate and thickness of RSCR can definitely intensify the cooling performances. The application suggestions for S-channel RSCR (SRSCR) and I-channel RSCR (IRSCR) are given. When the pipe spacing ratio is smaller than five, the IRSCR is recommended because of lower thermal interferences. By contrast, SRSCR is recommended once the dimensionless pipe spacing is greater than ten. For cases with smaller tilt angles but larger wind velocities, IRSCR is suggested, while SRSCR is prioritized for cases with opposite conditions. This research provides an effective analytical tool in the evaluation of cooling power generation by producing cold water, contributing valuable insights for the optimization of cooling efficiencies of RSCRs under varied configuration scenarios.

Hierarchical polyimide-polyborosiloxane host-guest structure with impact resistance, acoustic and thermal insulation performance for electro-stability applications

The ubiquitous existence of mechanical impact, sound pollution and thermal damage conferred severe risks to both individuals and devices, which catalyzed increasing demand for advanced protective materials. Though biomimetic structures have motivated the development of high-performance protective composites against a simple threat, the realization of multi-mode interference protection remained a challenging issue. This work proposed a host-guest structural composite, consisting of viscoelastic polyborosiloxane (PBS) dispersively distributed in porous polyimide (PI) matrix. The resulting PI-PBS composite presented effective impact force attenuation (85.8%-92.3%), arising from the multi scale energy dissipation mechanism of strain-rate enhancement, structural densification and synergistic stress transfer, which was intuitively demonstrated by an innovative mechano-discoloration approach. The viscous dissipation effect endowed PI-PBS with extraordinary acoustic insulation effectiveness in a wide frequency region (1–6.3 kHz). Due to the low thermal conductivity (0.051 W/(m·K)), PI-PBS presented good thermal insulation performance over a wide temperature range (∼ −80 – 300 °C). The structure dependence of thermal conduction behavior was revealed via FE simulation, while demonstrating various applications in dynamic infrared thermal camouflage. PI-PBS, as a functional wrapping, provided reliable guarantee for electrical stability of conductive elements against impact, ultrasonic and thermal interferences, which indicated significant value in electromagnetic shielding, sensing and electrothermal fields. Therefore, PI-PBS could assist in efforts to lighten, integrate and intelligentize protective materials in the future.

Kalorimetrische Messung der Ver- zahnungsverlustleistung im Bereich hoher Umfangsgeschwindigkeiten

Gear damage, e.g. scuffing, reacts sensitively to the local dissipation of frictional heat during a full gear mesh. Several empirical friction models have been established in relevant literature. These can be used to calculate the gear friction locally or averaged over a mesh. For calibration purpose, experimental data from twin disc machines with stationary contact conditions are mostly used. However, the assignment of the model as well as the consideration of topographical, rheological and geometrical effects is often subject to uncertainties. In this paper, a method is presented to measure the power losses of high-speed spur gears up to vt = 100 m/s. The measurement principle uses the calorimetric properties of the circulating lubricant. The implementation of the measurement setup in a highspeed gear test rig reduces thermal interferences from sealings and bearings. Analysis regarding the measurement quality show that the measurement method delivers reproducible results with a high measurement resolution over a wide range of operating conditions.

Numerical analyses of energy screw pile filled with phase change materials

Embedding heat exchangers into a screw pile can form a cost-effective energy pile with a fast installation capability. However, better solutions to handle thermal waves and thermal interferences among energy piles are still required. This work aims to solve the issues by proposing a novel concept of an energy screw pile filled with mixtures of phase change materials (PCM) such as paraffin and “solid” grouting. Numerical simulations are conducted to investigate the utilisation of PCM energy screw piles on reducing fluid and ground temperatures, considering different constituents in PCM-solid mixtures, moisture conditions, phase change temperatures Tpc and operation schemes. Results demonstrate that a mixture with higher effective thermal conductivity λeff slows down the PCM phase transition and results in a lower fluid temperature feeding the ground source heat pump (GSHP). Dry mixtures with higher PCM content benefit the fluid temperature reduction, while a lower PCM content in a wet mixture is also satisfactory. Higher specific heat capacity allows pile back-filling to absorb more heat and reduce the thermal radius of influence, while over-enhancing its λeff might worsen thermal interference. The selection of the PCM phase change temperature Tpc should comply with the GSHP system operation scheme and the project aim.

A method for the sustainable planning and management of ground source heat pump systems in an urban environment, considering the effects of reciprocal thermal interference

The “Most Easy, Efficient and Low Cost Geothermal Systems for Retrofitting Civil and Historical Buildings” (GEO4CIVHIC) project aims to accelerate the deployment of shallow geothermal systems for heating and cooling purposes when retrofitting existing and historical buildings. Analyzing the implementation process of borehole heat exchangers (BHEs), allows the understanding of how to promote the long-term sustainability of shallow geothermal energy systems. The thermal interference between BHE systems represents a problem, especially due to the increasing deployment of this technology and its spread in densely built-up areas. The main goals of this paper are: a) to analyze the design phase of a BHE system in order to prevent mutual thermal interference, b) to propose a model that encloses phases to adopt an integrated approach for preventing long term thermal interferences, c) to give technical and management suggestions to minimize thermal interference between closed-loop geothermal systems. The method developed follows the following steps: 1) literature review to determine what are the main drivers for thermal interference between shallow geothermal systems, in the context of the GEO4CIVHIC project case study sites; 2) to create a conceptual model to limit thermal interference at both design and operational phases; 3) to apply the developed method to real and virtual case studies in countries with different regulatory frameworks and to test its main strengths and weaknesses. The application of this conceptual model to specific case studies provides evidence of critical planning and operational characteristics of GSHP systems and allows the identification of measures to mitigate impacts of thermal interference to be identified.

Intensive thermal exploitation from closed and open shallow geothermal systems at urban scale: unmanaged conflicts and potential synergies

The use of shallow geothermal systems (SGS) as a proficient technology to provide clean thermal energy has become increasingly widespread throughout the world, especially in urban environments, with a significant increase in systems density. At European level, the current authorization schemes for new SGS rarely consider the current thermal state of the subsurface and the potential presence of neighbouring systems. The paper presents a pilot urban case study, showing high SGS deployment, analysed through a holistic city-scale 3D numerical model simulating mutual interactions between open and closed-loop systems. Results show that the high amount of installed SGS in limited space is progressively creating mutual hydraulic and thermal interferences: negative, with a reduction of SGS efficiency and sustainability or (rarely) positive, when an accidental and unmanaged synergic effect is established due to favourable exploitation patterns and SGS locations. Numerical modeling further highlighted that the restitution through the vadose zone could be a valid method to hydraulically reinstate the aquifer without significantly altering groundwater undisturbed temperature even at shallow groundwater depth. Results show that neglecting an underground holistic vision of the hydro/thermogeological processes in urban areas could result in long-term severe efficiency losses and environmental issues for SGS solutions, also given the increasing use of shallow geothermal energy in the building air conditioning sector.

Robust approach to study the effect on quantum phase transitions of various perturbations at finite temperatures

We propose using maximum coherence (${\mathrm{QC}}_{\mathrm{max}}$) to study quantum phase transition (QPT). We investigate several well-known models, such as the XXZ model, ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model, and one-dimensional spin Kitaev model. The results show that ${\mathrm{QC}}_{\mathrm{max}}$ can be used to detect different types of QPTs, including the Berezinskii-Kosterlitz-Thouless and topological types. In addition, ${\mathrm{QC}}_{\mathrm{max}}$ is more robust against interferences, such as thermal fluctuations and measurement interferences, than any existing detector. This property enables ${\mathrm{QC}}_{\mathrm{max}}$ to identify QPTs in experiments, where temperature effects and measurement interferences always exist. Thus, ${\mathrm{QC}}_{\mathrm{max}}$ might be an ideal tool for studying QPTs because of its measurability, universality, and robustness against interferences.

Energy performance assessment of thermo-active micro-piles via numerical modeling and statistical analysis

Energy micro-piles (EMPs) constitute a promising emerging technology, able to provide both energy and structural retrofitting to existing buildings. Although a number of studies have been published on the energy performance of standard energy piles (EPs), bespoke analysis is required for EMPs due to their different geometry and peculiar design and site constraints. In this work, a parametric study is carried out by means of numerical Finite Element simulations complemented by statistical analysis, aimed at identifying the dominant parameters in maximizing EMP thermal efficiency. Two categories of parameters, namely design-dependent and site-dependent ones, are separately considered to provide guidance for practitioners on both detailed geothermal sizing and overall feasibility assessment. The parameter space is efficiently explored resorting to Taguchi Experimental Design statistical tools. Results show that different design criteria to those for EPs should be used for EMPs. Notably for the latter, contrary to the former, the diameter of heat exchanger pipes emerges as one of the most important factors promoting thermal efficiency, while being the single easiest parameter to engineer. On the other hand, while maximizing the number of U-pipes and pile diameter is crucial for EPs, it does not impact the energy performance of EMPs, due to geometry constraints and the expected occurrence of thermal interferences. Among site-dependent factors, a large ground thermal conductivity is confirmed as an important feature to ensure a high energy performance, while interesting insights are obtained about the role of basement thermal insulation in the long-term EMP thermal output.

Anatomical 3D Modeling Using IR Sensors and Radiometric Processing Based on Structure from Motion: Towards a Tool for the Diabetic Foot Diagnosis.

Medical infrared thermography has proven to be a complementary procedure to physiological disorders, such as the diabetic foot. However, the technique remains essentially based on 2D images that display partial anatomy. In this context, a 3D thermal model provides improved visualization and faster inspection. This paper presents a 3D reconstruction method associated with temperature information. The proposed solution is based on a Structure from Motion and Multi-view Stereo approach, exploiting a set of multimodal merged images. The infrared images were obtained by automatically processing the radiometric data to remove thermal interferences, segment the RoI, enhance false-color contrast, and for multimodal co-registration under a controlled environment and a ∆T < 2.6% between the RoI and thermal interferences. The geometric verification accuracy was 77% ± 2%. Moreover, a normalized error was adjusted per sample based on a linear model to compensate for the curvature emissivity (error ≈ 10% near to 90°). The 3D models were displayed with temperature information and interaction controls to observe any point of view. The temperature sidebar values were assigned with information retrieved only from the RoI. The results have proven the feasibility of the 3D multimodal construction to be used as a promising tool in the diagnosis of diabetic foot.

Manipulation of the interlayer exchange coupling in perpendicular magnetized thin films via tunable magnetic-layer and spacer thicknesses

In this work, we fabricated interlayer exchange-coupled magnetic thin films with ferromagnetic layers separated by a spacer layer. We investigated the dependencies of the sign and strength of the interlayer exchange coupling (IEC) and magnetic configurations on both the ferromagnetic layer thicknesses and the spacer thickness. The change of sign of the IEC between the ferromagnetic layers can occur for a thickness change of ferromagnetic layers by as small as approximately 0.1 nm. By comparison, a minimum of approximately 0.2 nm spacer thickness change is required for the same transformation. We attribute the ferromagnetic layer thickness dependence of the IEC to changes in thermal magnon excitations and quantum interferences inside ferromagnetic layers that affect interactions between the ferromagnetic layers and the spacer layer. Our experimental results suggest that the IEC modifications via changing the magnetic-layer thickness can be more efficient for magnetic memory and sensing applications.

Nested Shallow Geothermal Systems

The long-term sustainability of shallow geothermal systems in dense urbanized areas can be potentially compromised by the existence of thermal interfaces. Thermal interferences between systems have to be avoided to prevent the loss of system performance. Nevertheless, in this work we provide evidence of a positive feedback from thermal interferences in certain controlled situations. Two real groundwater heat pump systems were investigated using real exploitation data sets to estimate the thermal energy demand bias and, by extrapolation, to assess the nature of thermal interferences between the systems. To do that, thermal interferences were modelled by means of a calibrated and validated 3D city-scale numerical model reproducing groundwater flow and heat transport. Results obtained showed a 39% (522 MWh·yr−1) energy imbalance towards cooling for one of the systems, which generated a hot thermal plume towards the downgradient and second system investigated. The nested system in the hot thermal plume only used groundwater for heating, thus establishing a positive symbiotic relationship between them. Considering the energy balance of both systems together, a reduced 9% imbalance was found, hence ensuring the long-term sustainability and renewability of the shallow geothermal resource exploited. The nested geothermal systems described illustrate the possibilities of a new management strategy in shallow geothermal energy governance.

Aerodynamic and thermal interference between two building models

the paper considers aerodynamic and thermal interference of separated flows between two square prisms arranged at a short distance from each other. It is shown how relative positions of the square prisms affect the specific phenomena caused by the airflow interactions. This work is the experimental study of aerodynamic and thermal interference effects on two square prisms or building models depending on their relative positions. A strong difference is shown between aerodynamic and thermal interferences observed in the airflow behind two tandem models. The thermal interference effect turns to be rather conservative as compared to the aerodynamic. Using the interference parameters one can easily analyze the extreme values of the pressure and thermal flows interfering with the building models depending on many factors, including relative model positions.

Defining the exploitation patterns of groundwater heat pump systems

Shallow geothermal systems are the most efficient and clean technology for the air-conditioning of buildings and constitutes an emergent renewable energy resource in the worldwide market. Undisturbed systems are capable of efficiently exchanging heat with the subsurface and transferring it to human infrastructures, providing the basis for the successful decarbonisation of heating and cooling demands of cities. Unmanaged intensive use of groundwater for thermal purposes as a shallow geothermal energy (SGE) resource in urban environments threatens the resources' renewability and the systems' performance, due to the thermal interferences created by a biased energy demand throughout the year. The exploitation regimes of 27 groundwater heat pump systems from an alluvial aquifer were firstly examined using descriptive statistics. Linear relationships between abstraction and injection temperatures of the systems were assessed by calculating Pearson's r correlation coefficient, and used as an evidence of thermal interferences. Then, time series of flow rate, operation temperature and energy transfer were modelled by means of spectral analysis and sinusoidal regression methods, followed by the definition of the relative exploitation patterns. The exploitation regimes examined presented a clear cooling bias and a similar cyclicality. The amplitudes correlated with the different end-user's activities (e.g. medical centres) when high frequency cycles were observed, while climatization strategies (e.g. constant flow rates and modulation of injection temperatures) did so when low frequency cycles were detected. The time series models allowed defining the relative operational pattern of a system and the groups of systems following such patterns. The biases in exploitation regimes of groundwater heat pump systems existing in Mediterranean areas require correction measures to ensure a more balanced exploitation of the SGE resources. The definition of the characteristic exploitation pattern proposed could be applied to guide resource managers by identifying unbalanced systems, understanding existent exploitation strategies and proposing corrective alternative plans.

First in-orbit results of the vector magnetic field measurement of the High Precision Magnetometer onboard the China Seismo-Electromagnetic Satellite

The High Precision Magnetometer (HPM) is one of the main payloads onboard the China Seismo-Electromagnetic Satellite (CSES). The HPM consists of two Fluxgate Magnetometers (FGM) and the Coupled Dark State Magnetometer (CDSM), and measures the magnetic field from DC to 15 Hz. The FGMs measure the vector components of the magnetic field; while the CDSM detects the magnitude of the magnetic field with higher accuracy, which can be used to calibrate the linear parameters of the FGM. In this paper, brief descriptions of measurement principles and performances of the HPM, ground, and in-orbit calibration results of the FGMs are presented, including the thermal drift and magnetic interferences from the satellite. The HPM in-orbit vector data calibration includes two steps: sensor non-linearity corrections based on on-ground calibration and fluxgate linear parameter calibration based on the CDSM measurements. The calibration results show a reasonably good stability of the linear parameters over time. The difference between the field magnitude calculated from the calibrated FGM components and the magnitude directly measured by the CDSM is just 0.5 nT (1σ) when the linear parameters are fitted separately for the day- and the night-side. Satellite disturbances have been analyzed including soft and hard remanence as well as magnetization of the magnetic torquer, radiation from the Tri-Band Beacon, and interferences from the rotation of the solar wing. A comparison shows consistency between the HPM and SWARM magnetic field data. Observation examples are introduced in the paper, which show that HPM data can be used to survey the global geomagnetic field and monitor the magnetic field disturbances in the ionosphere.

Assessment and Minimization of Potential Environmental Impacts of Ground Source Heat Pump (GSHP) Systems

Ground source heat pumps (GSHPs) gained increasing interest owing to benefits such as low heating and cooling costs, reduction of greenhouse gas emissions, and no pollutant emissions on site. However, GSHPs may have various possible interactions with underground and groundwater, which, despite the extremely rare occurrence of relevant damages, has raised concerns on their sustainability. Possible criticalities for their installation are (hydro)geological features (artesian aquifers, swelling or soluble layers, landslide-prone areas), human activities (mines, quarries, landfills, contaminated sites), and groundwater quality. Thermal alterations due to the operation of GSHPs may have an impact on groundwater chemistry and on the efficiency of neighboring installations. So far, scientific studies excluded appraisable geochemical alterations within typical ranges of GSHPs (±6 K on the initial groundwater temperature); such alterations, however, may occur for aquifer thermal energy storage over 40 °C. Thermal interferences among neighboring installations may be severe in urban areas with a high plant density, thus highlighting the need for their proper management. These issues are presented here and framed from a groundwater quality protection perspective, providing the basis for a discussion on critical aspects to be tackled in the planning, authorization, installation, and operation phase. GSHPs turn out to be safe and sustainable if care is taken in such phases, and the best available techniques are adopted.

Multi-species test and calibration of an improved transient thermal dissipation system of sap flow measurement with a single probe.

Transient thermal dissipation (TTD) systems provide a simple way to measure xylem sap flow with dual or single Granier-type probe, which gives lower energy consumption and higher accuracy due to its lessor sensitivity to thermal interferences. A new system, TTD heat within 5 min (TTD5), proposed on the reduction of the heating duration. This evolution captured interest through decreased energy consumption and increased temporal resolution. Within our study, the first objective was to test and calibrate this new system with a single probe for young rubber tree - Hevea brasiliensis. The second objective was to explore the sources of variability in calibration such as species, individual cut-stems and probe-wood contact. The complementary species consisted of two diffuse-porous species (mango tree - Mangifera indica, eucalyptus tree - Eucalyptus camaldulensis) and one ring-porous species (teak tree - Tectonia grandis). Twenty-eight response curves were assessed over a large range of flux densities from 0.5 to 10 l dm-2 h-1. The incremental rise of temperature from 30 to 300 s (T300-30) after commencement of heating was sensitive to flux density over the complete range. Compared with the full signal at 300 s, the incremental signal markedly reduced the variability between response curves within species and between species. Moreover, a new index K2, defined as (T0 - Tu)/T0, normalized the responses between 0 and 1. However, the responses had a non-linear trend above 5 l dm-2 h-1. Within diffuse-porous wood type, the species did not differ in calibration, whereas the ring-porous species was markedly different. A sigmoid function provided the best fit for the diffuse-porous species. Individual stems were identified as the main source of within-species variability in calibration. The normalizing K2 index removed the influence of probe-wood contacts, controlled through drilling difference; however, there was still an effect of individual stems interacting with flux density (P = 0.019). Replications of cut-stems and response curves are necessary to assess a reliable averaged calibration. In conclusion, the applicability of the TTD5 system with a single probe has been confirmed and several sources of variability in calibration have been evaluated.

Development of a 2D numerical transient model to study geothermal coaxial borehole field heat exchangers

A numerical 2D transient model to study geothermal coaxial borehole field heat exchangers under thermal interferences has been built and implanted in MATLAB; it has been compared against two analytical solutions and the numerical code COMSOL where the results has been found identical. A coaxial borehole heat exchanger has been selected regarding to its better performances. The results show that porous grounds are more suitable for these systems, when porosity is 0% the thermal load decreases by 15.725% than the case where porosity is 45%; also, it has been found that after occurrence of phase change in the saturated sub-ground, effective thermal properties changes in a way to make the withdrawn thermal load decreases in a more intense manner, it reduces by 5.36% than the case where the process is not accounted for and this is during the last 843 h since the process start; the last part of the thermal investigations yields that the underground-water flow is favoured for the system performance.

Development of a 2D numerical transient model to study geothermal coaxial borehole field heat exchangers

A numerical 2D transient model to study geothermal coaxial borehole field heat exchangers under thermal interferences has been built and implanted in MATLAB; it has been compared against two analytical solutions and the numerical code COMSOL where the results has been found identical. A coaxial borehole heat exchanger has been selected regarding to its better performances. The results show that porous grounds are more suitable for these systems, when porosity is 0% the thermal load decreases by 15.725% than the case where porosity is 45%; also, it has been found that after occurrence of phase change in the saturated sub-ground, effective thermal properties changes in a way to make the withdrawn thermal load decreases in a more intense manner, it reduces by 5.36% than the case where the process is not accounted for and this is during the last 843 h since the process start; the last part of the thermal investigations yields that the underground-water flow is favoured for the system performance.

Sustainability indicator for the prevention of potential thermal interferences between groundwater heat pump systems in urban aquifers

The steady increase of geothermal systems using groundwater is compromising the renewability of the geothermal resources in shallow urban aquifers. To ensure sustainability, scientifically-based criteria are required to prevent potential thermal interferences between geothermal systems. In this work, a management indicator (balanced sustainability index, BSI) applicable to groundwater heat pump systems is defined to assign a quantitative value of sustainability to each system, based on their intrinsic potential to produce thermal interference. The BSI indicator relies on the net heat balance transferred to the terrain throughout the year and the maximum seasonal thermal load associated. To define this indicator, 75 heating-cooling scenarios based in 23 real systems were established to cover all possible different operational conditions. The scenarios were simulated in a standard numerical model, adopted as a reference framework, and thermal impacts were evaluated. Two polynomial regression models were used for the interpolation of thermal impacts, thus allowing the direct calculation of the sustainability indicator developed as a function of heating-cooling ratios and maximum seasonal thermal loads. The BSI indicator could provide authorities and technicians with scientifically-based criteria to establish geothermal monitoring programs, which are critical to maintain the implementation rates and renewability of these systems in the cities.

Influence of an Electrically Non-Conducting Heat Sink for Power Semiconductors on Radiated Interferences

Abstract. Power semiconductors are used in a growing number of applications. Furthermore, faster switching transients and therefore higher switching frequencies can be realised. This leads to higher radiated interferences at higher frequencies. In power electronic applications, often a cooling concept for the semiconductors is required to comply with the allowed temperature range. Typically, heat sinks are made of aluminium and their conductive behaviour can cause EMC problems. Via capacitive coupling, voltage transients are transferred from the power semiconductor to the heat sink, so that the heat sink behaves as an antenna and radiated interferences occur. Furthermore, a common mode current will appear if the heat sink is grounded. In this paper, a promising approach to reduce radiated interferences from the heat sink and solve the common mode issue by using an electrically isolating ceramic heat sink is presented. The influence of an aluminium nitride ceramic heat sink on cooling performance and EMC behaviour has been investigated. For this purpose, two geometrical identically heat sinks made from aluminium and aluminium nitride have been compared regarding thermal performance and radiated interferences characterised by S-parameters.