Periodic Temperature Variations Research Articles

Experimental investigation on pool boiling heat transfer enhancement using reticular bi-conductive surfaces

Pool boiling has been a research focus over the decades because of its superior heat dissipation performance. This paper provides insights into the underlying pool boiling enhancement mechanism of bi-conductive surface which is an effective modification approach. In this study, a new type of bi-conductive surface is created by embedding a reticular structure made of low-conductive epoxy into a high-conductive copper substrate. Because of the enormous difference in conductivity, the heat flux almost exclusively flows through copper. The existence of epoxy creates periodic spatial surface temperature variations and induces ordered liquid and vapor paths. The influence of the width and depth of epoxy on pool boiling is studied by conducting heat transfer experiments. According to the results, all bi-conductive surfaces exhibit critical heat flux (CHF) increases in copper zone and the improvement is more significant with the increase of epoxy width. However, the depth of the epoxy has no significant effect on pool boiling. At low superheat, the heat transfer coefficient (HTC) in copper zone is relevant to the thermal flow rate of the independent copper zone. At high superheat, bi-conductive surfaces with wider epoxy have higher HTC in copper zone. The results show that for the bi-conductive surface with 0.75 mm width of epoxy, replacing 44% of the high-conductive copper with low-conductive epoxy results in a 270% CHF increase in copper zone and a 108% increase in the maximum total effective thermal power.

Theoretical investigation of thermal and mass stratification effects on unsteady flow across a vertical oscillating plate with periodic temperature variation and variable mass diffusion

AbstractThis research paper examines the combined effects of thermal and mass stratification on unsteady flow past a vertical oscillating plate with periodic temperature variation and variable mass diffusion. The Laplace transform technique is introduced to deal with the linear coupled parabolic equations satisfying initial as well as boundary conditions and obtained solutions in closed form for concentration, temperature, and velocity. For example, to find the Laplace transform of an exponentially ordered piece wise continuous function , one can uses the formula , t being the time and s is a parameter. In this study, we explore the effects of different factors such as plate amplitude, plate frequency, thermal Grashof number, and the mass Grashof number on the concentration, velocity, and temperature profiles and shows them graphically. We see a decline in the fluid's velocity for thermal and mass stratification. Most interestingly, in presence of higher temperature gradient, as the frequency of the oscillations increases close to the plate surface, the fluid velocity declines. The reason behind this is that the flow system has a plate with very high fluctuations. We have found that the fluid's temperature goes up while the concentration goes down when there is a decrease in the thermal stratification and a rise in the mass stratification.

Aquatic photosynthetic carbon pump driven by periodic temperature variations affects dissolved inorganic carbon and hydrochemical characteristics in a groundwater-fed reservoir

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13CDIC), CO2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO2 (pCO2) and CO2 emission flux, and an increase in stable carbon isotope (δ13CDIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations.

Pyroelectricity in poled all-organic polar polynorbornene/polydimethylsiloxane-based stretchable electrets.

Pyroelectricity in a recently developed all-organic composite electret with a polar polynorbornene-based filler and polydimethylsiloxane (PDMS) matrix has been studied with the help of thermal and dielectric techniques. Measurement of the pyroelectric p coefficient using a quasi-static periodic temperature variation at RT shows a non-linear dependence with the applied poling field, which is uncharacteristic of amorphous materials. Dielectric relaxation spectroscopy (DRS) and the thermally stimulated depolarization current (TSDC) technique reveal that this behaviour can be attributed to Maxwell-Wagner interface (MWI) polarization that occurs at the filler-matrix interface. These charges released during the onset of dipolar α and β relaxations of the filler particles contribute majorly to the observed pyroelectricity at RT. The saturation of both MWI TSDC shoulders and spontaneous polarization at higher electric fields correlates with the p coefficient value reaching a plateau at these applied fields. A maximum p coefficient of 0.54 μC m-2 K-1 is calculated for a poling field of 30 V μm-1.

Investigation on permanent deformation in steel-concrete composite beam bridge deck pavement under temperature-load coupling effect

Rutting is one of the common distresses observed in asphalt pavement, influenced by temperature and load conditions. To clarify the permanent deformation behavior of steel-concrete composite beam (SCCB) bridge deck pavement under temperature-load coupling effect and provide references for the distress cause analysis, five typical SCCB bridge deck pavements were selected. The temperature distribution and the temperature stress of the pavement structures were analyzed by numerical simulation under periodic temperature variations. In addition, considering the daily variation in traffic volume, the permanent deformation of the five pavement structures were calculated under temperature-load coupling effect. Finally, the influence of heavy load on the development of rutting distress was also investigated. The results show that the temperature field and temperature stresses within the SCCB bridge deck pavement exhibit periodic variations under periodic temperature variations. Additionally, after 500,000 times of standard axle load application, “EA + SMA” exhibits the smallest permanent deformation and the best resistance to rutting distress under temperature-load coupling effect. Finally, heavy load conditions have a great influence on the permanent deformation of SCCB bridge deck pavement. In areas with severe rutting distresses, it is recommended to use “EA + SMA” pavement structure in SCCB bridge.

A Comprehensive Literature Review on Polymer-Modified Asphalt Binder

Due to periodic variations in temperature and heavy traffic loading, hot-mix asphalt (HMA) pavements undergo considerable distress during their service life. The rheological properties of asphalt binder, when subjected to complex physical and chemical processes, make it stiff and sometimes brittle, which ultimately plays a huge part in pavement deterioration. This phenomenon is commonly known as asphalt aging. Incorporating polymer modifiers with virgin asphalt can work as an effective means to change the binder properties and alleviate the issues related to asphalt aging. Different types of polymers, including elastomers, plastomers, and reactive polymers, can mixed in different combinations with the virgin asphalt to create polymer-modified binders (PMBs). In general, polymers are typically added to the virgin asphalt binder in PMB manufacturing at weight percentages ranging from 3% to 7%. Previous research suggests that many polymer-modified binders (PMBs) show great resiliency and perform extremely well during field and laboratory testing, although the complex nature of asphalt itself makes it significantly difficult to understand the relationship and compatibility of the asphalt–polymer system. This paper aims to develop a comprehensive literature review on the chemical aspects, microscopic structure, and compatibility of polymers with virgin asphalt. It was found that swelling, storage stability, blend morphology, and the polymer mixing technique play a great role in the compatibility of asphalt–polymer systems. Thermoplastic elastomers (e.g., styrene–butadiene–styrene) and plastomers (e.g., ethylene–vinyl acetate) are the most used polymer modifiers for asphalt binders. The compatibility of the polymer–asphalt system can be improved by sulfur vulcanization, antioxidants, hydrophobic clay minerals, functionalization, and reactive polymers, among other techniques.

Air leakage detection in building façades by combining lock-in thermography with blower excitation

Air leakage in building envelopes is responsible for a large portion of the building’s heating and cooling requirements. Therefore, fast and reliable detection of leaks is crucial for improving energy efficiency. This paper presents a new approach to determining air leakages in a building’s envelope from the outside, combining lock-in thermography and thermal excitation by a blower door system. The blower creates a periodic overpressure within the building, inducing periodic temperature variations of the surfaces near the leaks on the outside surface, the façade. With the temperature variations excited at a known frequency, Fourier transforms of the time-series of the thermal images at the excitation frequency result in amplitude and phase images highlighting the areas affected by leaks. Periodic excitation and detection by an IR camera is known as lock-in thermography and is widely used to characterise semiconductor devices and in non-destructive testing. Excitation is usually achieved by optical, electrical, or mechanical energy input. For this work, measurements of outside façades have been performed with three excitation cycles of a period of 40 s at a 75 Pa pressure difference, leading to a total measurement time of only 2 min. Measurements have been performed with air temperature differences of 5 to 7 K at highly variable conditions of irradiance, wind, and cloud cover. The measurements show higher detection quality and less impact from changing ambient conditions than the state-of-the-art differential infrared thermography measurements. With the method highlighting the variations in the amplitude image only at the excitation frequency, variations caused by environmental effects are filtered out. A temperature difference as low as a few Kelvin is therefore sufficient, and large façades can be examined from the outside. This amplitude image is already clearer than an image created with differential thermography. A further reduction of unwanted artefacts in the image is demonstrated using phase-weighing of the amplitude by scalar product.

Individual Effect of Spatially Periodic Vertical Surface Temperatures and Nanoparticles on Natural Convection in Water

Abstract This paper considers the thermo-convective boundary-layer flow (BLF) of a water–copper mono-nanofluid over a flat vertical surface which is subjected to three types of periodic temperature variations described by the sinusoidal, sawtooth, and triangular waveforms. The temperature of the fluid at the flat surface is greater than the surrounding ambient temperature. The governing equations describing the BLF have been reduced to a non-similar form using an appropriate stream function formulation. The Keller-Box method is used to obtain numerical solution of the boundary-value problem. The effect of the pertinent parameters on the nature of the flow and the heat transfer has been discussed using actual thermophysical data. The results about the shear–stress and heat transfer rate at the surface are presented as well. To study the nature of BLF, the velocity and thermal boundary-layers, the streamline and isotherm plots have been considered, which reveal that the nanoparticle volume-fraction, amplitude of surface temperature variations, and the Grashof number play a pivotal role in enhancing/diminishing heat transfer. The final outcome reveals that the heat transfer is highest for the sinusoidal waveform, followed by that of the triangular and then, the sawtooth. An important inference is that a symmetric periodic temperature distribution at the surface enhances heat transfer more than that of a constant surface-temperature.

Multiscale Time Series Decomposition for Structural Dynamic Properties: Long-Term Trend and Ambient Interference

In structural health monitoring (SHM), variations of structural dynamic properties are paramount to indicate the health status of structures. Structural dynamic properties are time variant due to various long-term effects (e.g., structural deterioration) and periodic effects (e.g., periodic variations of temperature, humidity, and traffic). Sometimes periodic effects will interfere with the quantification of long-term effects. Though important, there are still limited research studies aiming to distinguish these two effects. Given the amount of SHM data, it is possible to solve the issue from a data-driven perspective. This article proposes a time series decomposition methodology to divide the time series of structural dynamic properties into long-term parts, multiscale periodic parts, holiday parts, and error parts. We extract the 10-year dynamic properties of a long-span bridge using the fast Bayesian FFT identification algorithm and choose two dynamic modes of that bridge as examples to explain how our proposed methodology works. We use the long-term parts to extract the rules of structural deterioration. The multiscale periodic parts are utilized to find the relationships with the periodically varying ambient conditions (i.e., temperature and humidity) in different time scales (i.e., yearly, weekly, and daily). Then, the long-term and periodic effects can be distinguished. For the long-term effects, the modal frequencies tend to decrease but the damping ratios seem to increase. For the periodic effects, we find that the increment of temperature will lead to the decrease of both modal frequencies and damping ratios. The variations of modal frequencies induced by deterioration and temperature are of the same amplitudes. The variations of both modal frequencies and damping ratios are not significantly related with humidity. This article could provide references for damage detection and safety assessment for similar bridges.

A Practical Data-Driven Battery State-of-Health Estimation for Electric Vehicles

In this article, to estimate the battery state of health (SOH) under realistic electric vehicle (EV) conditions, a robust and efficient data-driven algorithm is developed and validated through comprehensive battery life testing. More than 50 state-of-the-art EV battery cells have been tested under a variety of cycling conditions with different charging protocols, dynamic driving cycles, voltage ranges, pulse rates, and temperatures. Some of the cells have also been tested under a combination of cycling and storage conditions, constant current and multistep charging, and a periodic temperature variation that mimics real life conditions. Only partial data (voltage, current, and temperature) within a narrow state-of-charge range under a dynamic driving condition are required to extract the health indicators. A neural network is trained to find the mapping between the health features and the battery SOH. The life test data are divided into three groups. The first dataset (≈55% of data) is used for training and initial validation and testing, whereas the second and third datasets (≈45% of data) are entirely used for the final validation and testing to minimize the network overfitting. The results show that the SOH estimation root-mean-squared error for all datasets is less than 0.9%, signifying the fidelity and reliability of the proposed method.

Dynamic Heat Transfer Characteristic of Heat Exchanger for Sensible Heat Recovery of Raw Coke Oven Gas

Abstract A simplified hybrid-dimensional unsteady heat transfer model for the ascension-pipe heat exchanger with a helically coiled tube embedded in the jacket and supported by high conductivity particles is established based on the non-thermal equilibrium theory of porous medium. This idea can also be used in the design of other heat exchange devices involving the helically coiled tube. According to calculations, the wall temperature of the ascension-pipe heat exchanger periodically varies due to the periodic variations of flow rate and temperature of raw coke oven gas. A great thermal stress will be produced due to this reason. The coal tar precipitation mainly occurs in the late stage of the coking period due to the continuous cooling of molten salt. Based on the detailed analysis, thermal conductivity of packing layer, heat capacity per unit volume of packing layer, volume of packing layer, flow rate of molten salt and inlet temperature of molten salt are important factors that should be scientifically designed in the design of this type of heat exchanger to reduce thermal stress and coal tar precipitation. Cutting off molten salt in the late stage of the coking period is an effective measure to control the wall temperature of the ascension pipe above the dew point of coal tar vapor.

Estimation of thermal hazards in surrounding rock of subway tunnel under dual periodic temperature boundaries: a case study.

Thermal hazards of the surrounding rock of subway tunnels are becoming apparent, in which the heat transfer in the surrounding rock plays a crucial role. Due to the shallow buried depth, the subway tunnel encounters a more complicated heat exchange under the duplicate effects of periodic temperature fluctuation of ground atmosphere and periodic temperature variation of tunnel wind, but this issue has not been fully addressed. In this work, a transient heat transfer model of tunnel surrounding rock based on dual periodic temperature boundaries was established. A solver was developed to estimate the temperature rise and heat transfer of surrounding rock. The correctness of this model was then verified by comparing with previous empirical values and semi-empirical equations. The results show that the temperatures of the surrounding rock at different depths still fluctuate following the simple harmonic waves, and there are some regions that are heavily affected by the duplicate effects, such as the overlying strata of the tunnel. The surrounding rock generally exhibits heat storage in annual cycle, but the total heat storage decreases year by year until it tends to stabilize. Furthermore, the shallower the tunnel is buried, the greater the influence of ground temperature and the higher the temperature rise in the tunnel surrounding rock. This research provides an alternative approach to determine the heat storage of tunnel surrounding rock and evaluates the process of thermal disaster manifestation of subway.

Towards Accurate, Cost-Effective, Ultra-Low-Power and Non-Invasive Respiration Monitoring: A Reusable Wireless Wearable Sensor for an Off-the-Shelf KN95 Mask.

Respiratory rate is a critical vital sign that indicates health condition, sleep quality, and exercise intensity. This paper presents a non-invasive, ultra-low-power, and cost-effective wireless wearable sensor, which is installed on an off-the-shelf KN95 mask to facilitate respiration monitoring. The sensing principle is based on the periodic airflow temperature variations caused by exhaled hot air and inhaled cool air in respiratory cycles. By measuring the periodic temperature variations at the exhalation valve of mask, the respiratory parameters can be accurately and reliably detected, regardless of body movements and breathing pathways through nose or mouth. Specifically, we propose a voltage divider with controllable resistors and corresponding selection criteria to improve the sensitivity of temperature measurement, a peak detection algorithm with spline interpolation to increase sampling period without reducing the detection accuracy, and effective low-power optimization measures to prolong the battery life. The experimental results have demonstrated the effectiveness of the proposed sensor, showing a small mean absolute error (MAE) of 0.449 bpm and a very low power consumption of 131.4 W. As a high accuracy, low cost, low power, and reusable miniature wearing device for convenient respiration monitoring in daily life, the proposed sensor holds promise in real-world feasibility.

Analysis of Te Inclusion Striations in (Cd,Zn)Te Crystals Grown by Traveling Heater Method

The growth of (Cd,Zn)Te (CZT) crystals and the improvement of the crystal quality are part of a research project towards experiments under microgravity using the Traveling Heater Method (THM). In order to determine the experimental parameters, we performed a detailed ground-based program. Three CZT crystals with a nominal Zn content of 10% were grown using THM from a Te-rich solution. The size and distribution of the Te inclusions were evaluated by transmission infrared microscopy (IR). From the three-dimensional mapping of the inclusions, we observed striation-like patterns in all of the crystals. The correlation between the growth parameters and the formation of these striations was explored and discussed. We found that the inclusion striations are related to periodic temperature variations.

Quantile regression averaging‐based probabilistic forecasting of daily ambient temperature

AbstractThe inclusion of conductor temperature variations for numerous power system planning and operational studies has long been recognized in the literature. The conductor temperature is majorly affected by environmental factors such as the ambient temperature. An efficient forecasting technique for forecasting ambient temperature is the need of the hour to prevent unexpected hazards in power systems and other areas caused due to temperature variations. Numerous researches have proposed different point forecasting and probabilistic forecasting models for the forecasting of ambient temperature. The probabilistic forecasting of ambient temperature provides complete information about future uncertainties, therefore quantifying the effects of daily temperature variations. A forecast combination approach, such as the quantile regression averaging, has never been utilized in this context. The selection of suitable point forecasters that complement each other's effects by characterizing different aspects of the ambient temperature data for averaging and the use of frequency components that explain the daily and periodic seasonal variations of ambient temperature to construct a forecasting model are the significant features of this paper. The proposed model is used with four varieties, and each is compared with the others. It is found that the variant using all the complementary individual point forecasters performs better in making probabilistic forecasts than the other options as well as better than the popular quantile k‐nearest neighbors, quantile egression forests, and basic quantile regression as inferred from the quantile score, Winkler score, and reliability plots.

Non-autoclaved foam concrete for layers of highways surface dressing

The article is devoted to the problems associated freeze with the calculated estimation of the parameters of the structural and heat-insulating antifreeze layer in the subgrade of non-rigid roads on various soil bases. The main physical, technical and deformation characteristics of monolithic dispersed non-autoclaved foam concrete reinforced with polypropylene fiber of grades of density from 600 to 1000 kg/m3 are investigated. Freezing of subsoil waters directly under the roadway pavement and, as a result, its increase in volume, leads to significant deformations of the road surface. Under such conditions, the period of defectfree operation of the roadway pavement is significantly reduced, which in turn leads to the need to repair it in a more intensive mode. One of the ways to reduce the operating cost and maintenance costs of the road transport infrastructure is to introduce into the design and construction practice new structural concepts for road surface dressing that ensure high quality pavement during the normative operational period. This can be achieved by introducing an effective heat-insulating material into the pavement structure as an anti-frost layer in order to elimi-nate the effect of frost lift of the roadway pavement of non-rigid roads. Since domestic and foreign experience freeze in the road construction has proven the effectiveness of the use of heatinsulating materials in the road surface dressing construction, in recent years in Ukraine there has been increased interest in the use of non-autoclaved foam concrete as a modern and highly effective heat-insulating material in road construction. The installation of a heat-insulating layer made of non-autoclaved foam concrete allows us to completely or partially prevent freezing or overheating of the surface dressing base, reduce the influence of periodic variations in environmental temperature, which in turn will increase the durability of the pavement structure. The publication presents nomograms for determining the optimal thickness of the heat-insulating anti-frost heavy course (layer) of road surface dressing (based on sand, loamy sand, clay and loam) done at the street and road network for all climatic and geographical regions of Ukraine.

Ice giant seismology: prospecting for normal modes.

The properties of ice giant normal mode oscillations, including their periods, spatial structure, stratospheric amplitudes and relative influence on the external gravity field, are surveyed for the purpose of formulating the best strategy for their eventual detection. Measurement requirements for detecting a normal mode's periodic pressure and temperature variations, including a possible stratospheric signal, and its effect on the external gravity field, are discussed in terms of its radial velocity amplitude at the 1 bar pressure level. It is found that for reasonable amplitudes, detection of the pressure and temperature variations of ice giant normal modes presents an extraordinary technical challenge. The prospects for detecting their gravitational influence on an orbiting spacecraft are more promising, with requirements that lie within the range of current technology. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.

Thermodynamics of cyclic quantum amplifiers

We develop a generic model for a cyclic quantum heat engine that makes it possible to coherently amplify a periodically modulated input signal without the need to couple the working medium to multiple reservoirs at the same time. Instead, we suggest an operation principle that is based on the spontaneous creation of population inversion in incomplete relaxation processes induced by periodic temperature variations. Focusing on Lindblad dynamics and systems with equally spaced energy levels, e.g. qubits or quantum harmonic oscillators, we derive a general working criterion for such cyclic quantum amplifiers. This criterion defines a class of candidates for suitable working media and applies to arbitrary control protocols. For the minimal case of a cyclic three-level amplifier, we show that our criterion is tight and explore the conditions for optimal performance.

Heave performance of a ballastless track subgrade of double line high-speed railway filled with micro-expansive andesite under water immersion

Due to the swelling–shrinkage behaviors of expansive fillings, railway subgrade defects in expansive soil regions are prominent, which are difficult to repair, easy to relapse and exist for a long time. Field investigation reveals that some micro-expansive fillings have the potential to construct the railway subgrade and then solve the shortage of railway fillings. However, the swelling characteristics of the railway subgrades filled with the micro-expansive fillings remain unclear. To solve the problem, this paper describes an indoor physical model experiment of a ballastless track-subgrade filled with micro-expansive andesite at 1:2 scale. By simulating the immersion of the foundation (area below the subgrade) in rising groundwater, the effects of the foundation swelling on the mechanical and deformation characteristics of the entire subgrade are analyzed. The results show that the railway subgrade undergoes heave deformation under water immersion, where a significant reduction is observed in the heave deformation from the foundation to the surface of the subgrade. For a double-line railway subgrade, the heave deformation of the foundation increases with horizontal distance from the subgrade centerline. It is also found that the heaves at the track slab and subgrade surface show cyclic fluctuations with a 24-hour cycle due to the periodic variations in the ambient temperature.

Thermodynamic Geometry of Microscopic Heat Engines.

We develop a general framework to describe the thermodynamics of microscopic heat engines driven by arbitrary periodic temperature variations and modulations of a mechanical control parameter. Within the slow-driving regime, our approach leads to a universal trade-off relation between efficiency and power, which follows solely from geometric arguments and holds for any thermodynamically consistent microdynamics. Focusing on Lindblad dynamics, we derive a second bound showing that coherence as a genuine quantum effect inevitably reduces the performance of slow engine cycles regardless of the driving amplitudes. To show how our theory can be applied in practice, we work out a specific example, which lies within the range of current solid-state technologies.