Range Of Temperature Differences Research Articles

Optimization of Wavy Geometries for Enhanced Condensation Heat Transfer on Vertical Plates: An Experimental Study

In this study, macro-scale wavy geometries are used to enhance condensation heat transfer on vertical plates. Three wavy plates with different amplitudes (3.33mm, 4.17mm, and 5.56mm) were compared to a flat plate over a temperature difference range of 12K to 50K. For each plate configuration, heat transfer coefficient (HTC), enhancement factor (EF), heat flux (q), and Reynolds number (Re) were measured. Several studies have demonstrated that wavy surfaces offer better performance than flat surfaces, with the highest performance showing up for the 4.17 mm amplitude plate (Wave-2). At higher temperature differences, this optimal configuration achieved enhancement factors up to 1.31. As a result of the study, Reynolds numbers for the largest amplitude plate were 2.4 times higher than for the flat plate, indicating that increasing wave amplitude does not necessarily result in better heat transfer. These findings provide valuable insights for optimizing heat exchanger design in various industrial applications, offering a practical and cost-effective approach to improving falling film condensation heat transfer efficiency.

Spatial variability of temperature inside atoll lagoons assessed with Landsat-8 satellite imagery

Sea Surface Temperature (SST) maps are necessary for managing marine resources in a climate change context, but are lacking for most of the 598 world's atolls. We assessed the feasibility of using the Landsat-8 (L8) satellite to infer SST maps for four French Polynesia atolls of aquaculture interest in Tuamotu Archipelago, namely Takaroa, Raroia, Tatakoto, and Reao. Specifically, we (1) used sensors to measure in situ the range of spatial temperature differences recorded in these four atoll lagoons; (2) calibrated and assessed the performances of SST algorithms to estimate lagoon temperature from L8 signals; (3) generated temperature maps for the lagoons and compared spatial patterns of temperature obtained from these maps with patterns highlighted by in situ sensors. Good agreements between satellite and in situ temperature data were obtained, with better results achieved when using an atoll-by-atoll optimization (average bias = −0.26 °C; RMSE = 0.55 °C). However, we also show that the range of temperature inside atoll lagoons is low, and of the same order of magnitude than RMSE achieved with SST algorithms. Because of the L8 overpass time (∼9 a.m.) and the revisit time (16 days), L8 SST could not capture the entire range of spatial differences measured in situ in the four lagoons, but could capture spatial gradients and fronts better than with few in situ sensors. Considering the achieved accuracies and the actual temperature differences at the four study sites, we discuss the usefulness of L8 derived SST maps to assist fishery and aquaculture management in atoll lagoons, as well as the possible generalization to other lagoons.

The effect of temperature difference on bending of external panel walls

One of the most common structural systems of buildings intended for various purposes is a prefabricated panel system of factory-made elements assembled on-site. Single-layer structures made of lightweight concrete are widely used as envelopes of these buildings. In buildings operated under various climatic conditions, exterior wall panels, as well as other envelopes, are exposed to thermal deformations and, accordingly, changes in the stress-strain state. As the temperature changes, corresponding stresses and deformations occur across the thickness of the exterior panels. To analyze their values, the bending moments and support reactions of single-layer lightweight concrete panels of different length and thickness in the range of temperature differences from 0 °С to 65 °С have been calculated. It was found that the bending moments and support reactions of 1,500 mm long panels decrease as the thickness of the panels increases over the entire temperature gradient. The values of bending moments and support reactions of panels with length of 3,000, 4,500 and 6,000 mm decrease only when the temperature rises from 0 to 10 °С, in the rest of the range 15–65 °С – increase as the thickness of the panel increases due to the bending stiffness.

Analysis of influencing factors of aircraft fuel tank flammability

PurposeIt is an indispensable part of airworthiness certification to evaluate the fuel tank flammability exposure time for transport aircraft. There are many factors and complex coupling relationships affecting the fuel tank flammability exposure time. The current work not only lacks a comprehensive analysis of these factors but also lacks the significance of each factor, the interaction relationship and the prediction method of flammability exposure time. The lack of research in these aspects seriously restricts the smooth development of the airworthiness forensics work of domestic large aircraft. This paper aims to clarify the internal relationship between user input parameters and predict the flammability exposure time of fuel tanks for transport aircraft.Design/methodology/approachBased on the requirements of airworthiness certification for large aircraft, an in-depth analysis of the Monte Carlo flammability evaluation source procedures specified in China Civil Aviation Regulation/FAR25 airworthiness regulations was made, the internal relationship between factors affecting the fuel tank flammability exposure time was clarified and the significant effects and interactions of input parameters in the Monte Carlo evaluation model were studied using the response surface method. And the BP artificial neural network training samples with high significance factors were used to establish the prediction model of flammability exposure time.FindingsThe input parameters in the Monte Carlo program directly or indirectly affect the fuel tank flammability exposure time by means of the influence on the flammability limit or fuel temperature. Among the factors affecting flammability exposure time, the cruising Mach number, balance temperature difference and maximum range are the most significant, and they are all positively correlated with flammability exposure time. Although there are interactions among all factors, the degree of influence on flammability exposure time is not the same. The interaction between maximum range and equilibrium temperature difference is more significant than other factors. The prediction model of flammability exposure time based on multifactor interaction and BP neural network has good accuracy and can be applied to the prediction of fuel tank flammability exposure time.Originality/valueThe flammability exposure time prediction model was established based on multifactor interaction and BP neural network. The limited test results were combined with intelligent algorithm to achieve rapid prediction, which saved the test cost and time.

Numerical investigation of heat transfer mechanism in an embedded PCM-TEG for better overall performance under the fluctuating heat source

Using phase change materials (PCM) can effectively ensure the stable operation of semiconductor thermoelectric generators (TEGs). Conventional PCM-TEG structures exhibit relatively poor output performance due to energy barriers caused by low thermal conductivity. The embedded PCM-TEGs proposed in this study can address this issue well by adopting variable structure composite forms of PCM and TEG, resulting in a more complex heat transfer mode than traditional systems. To evaluate embedded systems' characteristics and performance enhancement methods, this paper first establishes a multiphysics mathematical model for embedded PCM-TEGs. Then, employing the TOPSIS method, an optimal embedded structure that considers system output and stability is obtained. Finally, we investigate the effects of key parameters on system performance, including PCM volume, latent heat, melting point, and metal-added composite materials. The CCC PCM-TEG (embedded PCM-TEG with PCM closer to the cold side) exhibits superior performance with a 28.6 % increase compared to conventional structures. For a given PCM volume, embedded structures with equal heights show better performance due to weak influence from asymmetric configurations on internal heat flow direction. Unlike traditional PCM-TEGs, metal-added composite PCMs in embedded structures reduce the temperature difference range across TEGs and thus deteriorate system performance.

Dynamic Mechanical Properties of Heat-Treated Shale under Different Temperatures

As a typical rock, shale’s reservoir depth is about 1500–4000 m, and the temperature of the shale reservoir at this depth is 150 °C. Therefore, in order to study the dynamic strength of shale at this temperature, it is necessary to consider the effects of temperature and strain rate on the dynamic strength of shale, and then establish the damage constitutive model of shale. This paper took black shale from the Sichuan Basin as the research object, combined it with the separated Hopkinson bar experiment and temperature control system, and conducted the Hopkinson bar experiment on shale at room temperature, 60 °C, 90 °C, 120 °C, and 150 °C, and at three groups of air pressures of 0.2 MPa, 0.3 MPa, and 0.4 MPa. The stress–strain curves of shale at the same strain rate and different temperature and at the same temperature and different strain rate were obtained. In the temperature difference range of this experiment, the dynamic strength of the sample presented two opposite trends (increasing and decreasing) with the increase in temperature, which was determined via the direction of the bedding. The peak strength linearly increased with the increase in strain rate. Based on the Weibull statistical distribution and the D–P failure criterion, a statistical damage constitutive model of shale dynamic strength considering the effects of temperature and strain rate was obtained. By modifying the parameters F0 and m, the dynamic strength statistical damage constitutive model of shale was in good agreement with the experimental results.

Spatial influence of exposure to green spaces on the climate comfort of urban habitats in China

This study aimed to improve the number of days with comfortable climate by increasing urban green space exposure. Geographic information technology and a spatial econometrics model were used to analyze the spatial influence and heterogeneity of urban green spaces on the climate comfort of urban habitats in China. The model was built using urban green space data extracted from remote sensing images, and days with comfortable climatic conditions, measured through the temperature and humidity index. The results showed that exposure to green space was generally high in Northeast and Southwest China, and low in Northwest and Southeast China. The exposure to green space of high urbanization level cities is generally lower than cities with low urbanization level. The climate comfort of urban habitats in the northeast and northwest is relatively cold, whereas that of those in the south, central and east is relatively hot. Southwest China has a complex and diverse range of climates. The climate of North China experiences greatly extremes of cold and heat in a year. The significance and mechanism of the influence of exposure to urban green space on climate comfort are differences in different regions. High exposure to green space can adjust thermal comfort by means of water storage, transpiration and heat absorption, reducing the range of temperature difference between day and night, and blocking cold and warm air flow. In addition, moderate human activities and sustainable land use can improve exposure to green space to help vegetation fully contact the air, affecting climate comfort by promoting evaporation and reducing thermal radiation.

Building Energy Saving for Indoor Cooling and Heating: Mechanism and Comparison on Temperature Difference

Reducing the heat transfer temperature difference via reasonable indoor temperature determination and air conditioning system design is a confirmed building energy-saving approach for space cooling and heating. However, the energy-saving mechanism cannot be explained scientifically and comprehensively while maintaining the cognitive level of the heat transfer law. In this paper, based on the same climatic conditions and decreasing range of indoor and outdoor temperature difference, the yearly and monthly absolute energy-saving amount (ESA) and relative energy-saving ratio (ESR) are investigated and compared for cooling and heating, respectively, to reveal the energy-saving mechanism for cooling and heating from the microscopic perspective. Two new concepts, including ESA by temperature difference and behavioral ESA by measure itself, are defined. The yearly ESA for cooling or heating caused by the decreasing of temperature difference is composed of those two factors. For cooling, the contribution rate of the behavioral ESA at those moments within the decreasing range of the temperature difference can be up to 78%, while for heating is only 7%. This work can provide theoretical support for building energy system design optimization and method reference for energy-saving analysis of building air conditioning systems with temperature difference considerations for cooling and heating, respectively.

Numerical Predictions of Laminar Free and Mixed Convection Heat Transfer to Supercritical Water from a Non-Isothermal Vertical Plate

Numerical predictions of heat transfer have been made for laminar free and mixed convective heat transfer from non-isothermal vertical plane surface to supercritical water. Variation of all the thermo-physical properties of the supercritical fluid under investigation have been considered. The numerical scheme employed in the present investigation is first validated with respect to experimental data for isothermal wall conditions and good agreement is achieved with maximum deviation not exceeding 15 %. Linear and parabolic variation of wall temperatures are considered for the present investigation. Computations are made for two pressures of 225 Bar and 235 Bar, for wide range of temperature difference from 4K to 20K. The values of temperature difference are chosen. Based on the results obtained, correlations have been proposed to evaluate the Nusselt numbers for both free and mixed convection with pressure ratios of P/Pc = 1.02 (p = 225 bar) and P/Pc = 1.065 (p = 235 bar). The correlations cover a range of Rayleigh numbers, Rax from 106 to 109 for Free Convection and grashoff Number/Reynolds Number2 ranging from 0.4 to 8 for Mixed convection. The proposed correlations for local Nusselt numbers do not exceed maximum deviation of 15% from the predicted values. It has been found that the maximum deviation occurs for those cases for which the pseudo-critical temperature, T* is within the boundary layer. It is further observed that for these cases both the velocity and temperature profiles are distorted at locations where the temperature is close to the pseudo-critical temperature thereby affecting the gradients at the wall, which in turn influences the heat transfer coefficient.

Freestanding graphene heat engine analyzed using stochastic thermodynamics

We present an Ito-Langevin model for freestanding graphene connected to an electrical circuit. The graphene is treated as a Brownian particle in a double-well potential and is adjacent to a fixed electrode to form a variable capacitor. The capacitor is connected in series with a battery and a load resistor. The capacitor and resistor are given separate thermal reservoirs. We have solved the coupled Ito-Langevin equations for a broad range of temperature differences between the two reservoirs. Using ensemble averages, we report the rate of change in energy, heat, and work using stochastic thermodynamics. When the resistor is held at higher temperatures, the efficiency of the heat engine rises linearly with temperature. However, when the graphene is held at higher temperatures, the efficiency instantly rises and then plateaus. Also, twice as much entropy is produced when the resistor is hotter compared to when the graphene is hotter. Unexpectedly, the temperature of the capacitor is found to alter the dissipated power of the resistor.

Temperature uniformity optimization with power-frequency coordinated variation in multi-source microwave based on sequential quadratic programming

Abstract The focus of this study is to regulate the variation in the input parameters of multiple microwave sources in a high-frequency multimode resonant heating system to achieve uniform heating. First, this study deeply expands the theoretical process of frequency change and proposes a frequency-shifting strategy with hot spot alternation to ensure that the temperature difference range of each hot spot does not continuously expand during the heating process. Then, a sequential quadratic programming algorithm is introduced to reconstruct the input power values to improve the heating efficiency according to the different microwave absorption efficiencies of the heated material at different frequencies. Finally, a numerical calculation model for multi-source microwave power-frequency cooperative heating is established based on the finite-element method, and the temperature uniformity index is effectively calculated. Numerical calculations show that the proposed method can improve the uniformity in single-material heating and multi-material heating cases by 56.8–94.3% and 44.4–76.6%, respectively, over that of fixed-frequency heating while achieving improved heating efficiency on the basis of frequency conversion.

Comparative Study of a Fixed-Focus Fresnel Lens Solar Concentrator/Conical Cavity Receiver System with and without Glass Cover Installed in a Solar Cooker

The glass cover is often situated at the aperture of a cavity receiver in concentrating collectors to reduce heat dissipation. However, the decrease in optical efficiency due to the reflection loss on the surface of the glass cover will directly reduce the thermal efficiency of a collector, especially for a fixed-focus solar concentrator, whose optical axis is generally not coincident with the central axis of the receiver. To fundamentally evaluate the effect of a glass cover on the efficiency of a fixed-focus Fresnel lens solar concentrator/conical cavity receiver system, its performances with and without a glass cover considered under different incidence angles were comparatively investigated. To obtain the optical performance, optical models of the system were first built with TracePro® 7.0 software. An experimental setup was then constructed to test the thermal performance of the system. The results show that the optical efficiency of a system without a glass cover is much higher than that with a glass cover. The difference between them remains unchanged for incidence angle at a range of 0–20°. The time constant of the system with a glass cover is much less than that without a glass cover, in the ranges of 29–33 s and 48–59 s, respectively. The system with a glass cover for a wide range of higher temperature differences also has better thermal efficiency.

Sensitivity analysis of temperature effects on guided wave-based damage detection

This paper presents a sensitivity analysis of guided wave-based damage detection to temperature uncertainty in the signal measurements. The effects of temperature variations on the damage index (DI) and consequently damage detection under varying operational temperature is investigated. Measurements from both the pristine and damage states are collected using an environmental chamber at a 5°C temperature interval. The correlation coefficient DI is utilized for the damage detection and a stochastic metamodel is developed to study the influence of temperature by implementing Gaussian Process Regression (GPR) and Monte Carlo (MC) sampling. The separation range between the pristine and damage states is used to quantify the system’s detection performance in the temperature difference range of ±20°C, imposing constrains on the acceptable false negative and false positive rates. Then, the sensitivity of the separation range is used to identify how variations on the baseline and current temperature affect the system’s reliability. The results obtained indicate that the system’s performance is improved when the baseline temperature is selected to be lower than that of the current temperature. The proposed method is validated on a second panel with a similar damage located at the corner and it is also applicable to other structures with varied requirements of temperature conditions and damage detection reliability.

Dependency of transition in thermocapillary convection on volume ratio in annular pools of large-Pr fluid in microgravity

Thermocapillary convection driven by the horizontal temperature gradient is a typical nonlinear dynamical system. As the applied temperature difference increases, the flow undergoes a series of transitions into turbulence. Volume ratio of the liquid layer Vr (liquid volume/volume of the container) is a critical parameter that affects transition behaviors of the convection. Direct numerical simulations on thermocapillary convection in annular liquid pools with various volume ratios are carried out. Characteristics of the oscillatory convection are detected by time series and frequency spectrum analyses. The dynamic mode decomposition (DMD) method is also adopted to investigate inherent structures of the flow field. Effect of Vr on oscillation characteristics under a wide range of temperature differences from 10K to 90K is discussed. Results show that in annular pools with lager volume ratios, the thermocapillary convection is chaotic under very large ΔT and its transition behaviors are more complicated.

Comparison of clinical efficacy between percutaneous endoscopic transforaminal discectomy and coblation nucleoplasty in the treatment of inclusive lumbar disc herniation

To observe clinical efficacy of percutaneous endoscopic transforaminal discectomy (PETD) and target radioffrequency thermal coblation nucleoplasty(CN) on inclusive lumbar disc herniation(LDH) in different age groups, and provide a basis for clinical formulation of precise and individualized treatments. A retrospective analysis of 219 patients with lumbar disc herniation treated with PETD and CN between January 2018 and June 2021 was performed, in which 107 patients were treated with PETD and 112 with CN. Patients were stratified by age into young group(≤45 years old), middle-aged group(>45 years old and <60 years old) and older group(≥60 years old). Before treatment, 3 days, 1 month and 6 months after treatment, visual analogue scale (VAS), Japanese Orthopaedic Association (JOA) score, infrared thermal imaging temperature difference (△T) and lumbar range of motion (ROM) were evaluated and clinical efficacy were compared in the different age groups between two treatment methods. ①VAS and JOA score outcomes, in the same age group and the same treatment method, the VAS and JOA scores at different time points postoperatively were obviously improved (P<0.05). For the same age group and the different treatment methods, the older group had lower VAS and higher JOA scores after PETD than after CN (P<0.05), and there was no significant difference between the young group and middle-aged group (P>0.05). There was no significant difference in VAS and JOA scores at the same time between age groups by PETD treatment (P>0.05). The VAS was higher and the JOA score was lower in older group than in young group and middle-aged group at 1, 6 months after CN treatment(P<0.05). ②△T and ROM outcomes, in the same age group and same treatment method, postoperative △T and ROM at different time points were obviously improved(P<0.05). There was no significant difference in △T between two methods of PETD and CN at the same age(P>0.05), there was no significant difference in ROM between young group and middle-aged group(P>0.05), ROM was higher after PETD treatment than after CN treatment(P<0.05). There was no significant difference in △T and ROM at the same time between age groups by PETD treatment(P>0.05). There was no significant difference in △T between age groups by CN treatment, but the ROM was smaller in older group than in young group and middle-aged group after CN treatment(P<0.05). Both PETD and CN for inclusive LDH have good efficacy, the curative benefit for older patients receiving PETD within 6 months after surgery more than CN, and CN is more appropriate for young and middle-aged patients.

Quantum synchronization and entanglement of indirectly coupled mechanical oscillators in cavity optomechanics: A numerical study

It is often conjectured that quantum synchronisation and entanglement are two independent properties which two coupled quantum systems may not exhibit at the same time. However, as both these properties can be understood in terms of the second order moments of a set of conjugate quadratures, there may exist specific conditions for simultaneous existence of entanglement and quantum synchronization. Here we present a theoretical scheme to achieve the same between two mechanical oscillators, which are indirectly coupled with each other via a coupling between two cavities. We show that in the presence of the cavity-oscillator coupling, quadratically varying with their displacements, these oscillators can be synchronized in the quantum sense and entangled as well, at times much longer than the decay time-scale of the cavity modes. Precisely speaking, we show that in the presence of quadratic coupling, entanglement criterion and quantum synchronization measure are simultaneously satisfied in steady state. This behaviour can be observed for a range of quadratic coupling, temperature, and frequency difference of the two oscillators.

Variation of the Urban Heat Island Intensity over One Year in Putrajaya, Malaysia

This research was conducted to evaluate the variation of the urban heat island (UHI) effects in the planned city of Putrajaya over one year. Putrajaya, the administrative capital of Malaysia, is known for its meticulous town planning. The main observations are temperature variation, the changes in wind speed, percentage of relative humidity, and subsequently, the intensity of UHI in the research area. Putrajaya Corporation Complex Precinct 3 (P3) and Precinct 9 (P9) are located in the central business district (CBD) and residential areas respectively. These two places are representatives of UHI's effects on CBD and residential areas. Ultrasonic anemometers which measure 3 components of wind velocities and temperature were employed to analyse temperature and wind patterns. The result indicates the city experienced high temperatures during the day causing human heat stress and discomfort. The UHI intensities of the city are within the range of temperature differences 2 to 3 °C. Land surface cover and numbers of the population are the vital effects of the UHI. Thus, strategies to reduce the existing high air and surface temperature are required in the future.

CFD analysis of different working gases in Ranque-Hilsch vortex tube

The Ranque-Hilsch vortex tube is a tubular device that divides a pressurised gas stream into two lower-pressure gas streams of differing temperatures. The temperature separation behaviour is the key characteristic of the RHVT. The energy separation method of vortex tube is influenced by several geometrical and operating characteristics. Apart from these parameters, fluid properties also affect the range of temperature differences. Selecting an appropriate working fluid in a geometrically optimised RHVT at its standard operating parameters makes its operation most efficient. A 3D CFD study is performed in RHVT over the five different working gases using the BSL k-ω turbulence model to predict the nature of turbulence. This paper compares the fluid flow behaviours of different working fluids, namely nitrogen, helium, argon, CO2 , and air. As a result, nitrogen is the best suitable working fluid for cold temperature separation. At the hot outlet, argon is found, showing maximum hot temperature separation. The computational investigation on different working fluids also revealed that maximum temperature separation is independent of the heat transfer rate.

Natural convection of Boussinesq and non-Boussinesq airflows simulated in a tall annular cavity

Natural convection of air in a tall annular cavity is explored by numerical solutions of the fully compressible Navier­Stokes equations in transient, axisymmetric (two-dimensional) form. A temperature difference is imposed on the two vertical walls, each isothermal, with the two horizontal boundaries adiabatic; the outer cylindrical surface is heated and the inner cylindrical surface cooled. Thermophysical properties of air, including density, viscosity, thermal conductivity, and specific heat are all variable with temperature. Laminar flow inside a tall annular cavity is prone to an instability which takes the form of a multicellular cat’s eye pattern drifting downward in the cavity. In this study, non-Boussinesq effects on the cat’s eye instability are explored by simulating flows in an annular cavity of aspect ratio A = 40 and diameter ratio η = 0.8, for Rayleigh numbers less than 14,000. A range of dimensionless wall temperature differences are investigated, 0 < ε ≤ 0.2, where ε is the temperature difference between the two vertical walls, Th – Tc , divided by the sum of the absolute temperatures, Th + Tc . The dimensionless wall temperature difference is shown to have pronounced effects on: the onset of the cat’s eye instability, subsequent flow bifurcations, wave speeds, oscillation time-periods as well as local heat transfer rates. The critical Rayleigh number, Rac , signifies a transition from steady unicellular flow to transient multicellular flow; Rac is found to increase with ε. At higher values of dimensionless wall temperature difference ε, mono-periodic oscillatory flows are predicted to occur over a smaller range of Rayleigh numbers, prior to the onset of quasiperiodic flow.

Investigation of convective heat transfer from a high temperature prolate spheroid to moving fluid

Most of the currently used fluid-solid heat transfer models assume that solid particles are perfect spheres. Heat transfer between non-spherical particles and flowing fluids acquires great importance in many engineering appliances. A numerical study is performed on airflow past a stationary confined prolate spheroid under the forced convective heat transfer regime, and the influence of non-sphericity of the particle on their heating rate is examined. The prolate spheroid is assumed to be maintained at a constant wall temperature. The effect of Reynolds number (Re) and Aspect Ratio (AR) on convective heat transfer rate and Nusselt number was investigated by solving steady-state Navier-Stokes and energy equations. The influence of the flow in terms of Reynolds number and the prolate spheroid aspect ratio was investigated. The spheroid’s surface temperature (Ts) was varied between 294 K and 1500 K. The simulations show that the mean Nusselt number has a positive dependence on Ts, AR, and Re. A new correlation was developed to predict the mean Nusselt number for a wide range of temperature differences. The new correlation consolidates the influence of aspect ratio, surface temperature, and Reynolds number, in contrast to the existing correlations that assume merely isothermal conditions to calculate the mean Nusselt number for spheroid particles.