Characteristics Of Temperature Fluctuations Research Articles

Ground-based measurements of microwave brightness temperature and electric field fluctuations for clouds with a different level of electrical activity

Simultaneous measurements of the brightness temperature and short-period electric field fluctuations were carried out to reveal possible connections between the electrification rate and turbulence intensity in clouds. The measurements were conducted in Nizhny Novgorod, Russia (56°19′37″N 44°00′27″E) in 2013 and 2018. The 8 mm radiometer was used to measure the brightness temperature of thermal radiation, and the vertical component of the atmospheric electric field were carried out using an electrostatic fluxmeter. With the use of meteorological data and electric field measurements the state of analyzed events has been classified into 4 types: cloudless atmosphere and high-level clouds (Cs), cumulus clouds (Cu), cumulonimbus clouds without lightning that cause strong electrical field disturbances near the ground surface (Cb), cumulonimbus thunderstorm clouds with lightning discharges (Cb+). Detailed statistical characteristics of brightness temperature fluctuations and short-period electric field fluctuations are obtained for the first time for the indicated types of events.It is shown that measured spectral densities of the atmosphere brightness temperature and electric field fluctuations correspond well enough in the considered frequency range to the results of presented theoretical consideration. Precipitation particles in clouds can be considered herewith as passive scalar, and the movement of inhomogeneities in the particle density can be described by Kolmogorov theory. Since electric charges are located on the precipitation with small droplet and ice particles, an increase in the inhomogeneities of the water content means likely an increase in the inhomogeneities of the electric charge. For thunderclouds the estimates of the relative fluctuations of liquid water content give values of the order of tens of percent. There is a tendency towards a relative increase in brightness temperature fluctuations at high frequencies in the band around f ≈ 10−2 Hz (and possibly higher than fmax ≈ 0.05 Hz) for the sequence of cloud types Cu, Cb, Cb+.

Characteristics of temperature fluctuation in two-dimensional turbulent Rayleigh-Bénard convection

We study the characteristics of temperature fluctuation in two-dimensional turbulent Rayleigh–Bénard convection in a square cavity by direct numerical simulations. The Rayleigh number range is 1 × 108 ≤ Ra ≤ 1 × 1013, and the Prandtl number is selected as Pr = 0.7 and Pr = 4.3. It is found that the temperature fluctuation profiles with respect to Ra exhibit two different distribution patterns. In the thermal boundary layer, the normalized fluctuation θ rms/θ rms,max is independent of Ra and a power law relation is identified, i.e., θ rms/θ rms,max∼ (z / δ)0.99 ± 0.01, where z / δ is a dimensionless distance to the boundary (δ is the thickness of thermal boundary layer). Out of the boundary layer, when Ra ≤ 5 × 109, the profiles of θ rms/θ rms,max descend, then ascend, and finally drop dramatically as z/δ increases. While for Ra ≥ 1 × 1010, the profiles continuously decrease and finally overlap with each other. The two different characteristics of temperature fluctuations are closely related to the formation of stable large-scale circulations and corner rolls. Besides, there is a critical value of Ra indicating the transition, beyond which the fluctuation 〈 θ rms〉 V has a power law dependence on Ra, given by 〈 θ rms〉 V ∼ Ra −0.14 ± 0.01.

Spatiotemporal characteristics of interday temperature fluctuations across the Loess Plateau of China

AbstractInterday temperature fluctuations (ITFs) have a series of direct and visible impacts on human productivity, daily life, and some rapidly occurring processes in the Earth's critical zones. The Loess Plateau of China (LPC) is characterized by Chinese continental monsoon climate and fragile ecological environment, and thus, is sensitive to ITFs. To evaluate the spatiotemporal distribution of the ITF frequency and level, and the related large‐scale circulation background, we collected daily temperature data from 53 meteorological stations in the LPC for 1961–2015, and calculated the number of days per year in which the average ITF was greater than 1°C (ITFD) and the corresponding variance of the ITF (ITFL). The annual average ITFs were mostly warming; the first half of the year experienced mainly warming, while the second half underwent cooling. The level and frequency of the interday maximum temperature fluctuation contributed greatly to increases in the interday mean temperature fluctuation level and frequency. The spatial distributions of ITFD and ITFL were related to their latitude and longitude. Stations with positive ITFD indicator trends were mostly concentrated in the southwestern LPC, while stations with negative ITFL indicator trends mainly occurred in the northwestern LPC. At an 850 hPa geopotential height, the stronger ITFs in spring more strongly correlated with the Mongolian high and Aleutian low. While at a 500 hPa geopotential height, the ITF were more strongly correlated with the Mongolian high. These results suggest that ITFs are more complex than previously reported and may need to be considered in future climate change assessments.

Diagnostics of coolant boiling onset based on the analysis of fluctuations of thermohydraulic parameters

When operating heat-exchange facilities, it is of interest to develop methods of diagnostic and prediction for coolant boiling onset. It is known that the surface temperature of a heating element always has stochastic oscillations around an average value, the analysis of such fluctuations will make it possible to predict the change in the heat transfer regimes.This paper presents the results of an experimental study of temperature fluctuations for an inertial heater and using of method of diagnostic are based on statistical and frequency analysis of temperature fluctuations. It is shown that there is a correlation between the frequency characteristics of heater temperature fluctuations and oscillations in the thermohydraulic parameters of the coolant (temperature, flow, pressure). The obtained results will find application in the development of an automated system for diagnostics the coolant boiling onset in power facilities.

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

The paper describes the temperature cross-correlation velocimetry method applied to flows of water or liquid metal. The technique allows us to measure temperature waveforms and averaged longitudinal velocity in a flow simultaneously. This approach is a simple and reliable method for measuring the velocity in flows of opaque coolants. At the same flow parameters, liquids of different origins provide non-similar spatial-temporal characteristics having a different impact on the applicability of the temperature correlation method. This work is devoted to the development of practical methods allowing to form a set of specific recommendations on the application of the technique of temperature correlation velocimetry and to determine the metrological characteristics of the technique in various conditions. Calibration was carried out using water and mercury as a model liquid. Used experimental facility and measuring system are described, accompanied by a detailed description of the developed temperature-correlation sensor. Measuring directly from within a flow is made possible by a unique micro thermocouple immersion probes technique. Data obtained are presented as fields of temperature and intensity of temperature fluctuations. Autocorrelation and cross-correlation functions are compared and analysed for two studied fluids under identical conditions.

Accuracy of the defining characteristics of the nursing diagnosis: Ineffective thermoregulation in newborns

ObjectiveTo identify the measures of accuracy for defining characteristics of the nursing diagnosis: Ineffective thermoregulation in newborns. MethodDiagnostic accuracy study with cross-sectional design performed in medium and high-risk maternity units, located in Fortaleza city/Brazil. A total of 216 newborns were evaluated to identify the defining characteristics of the diagnosis under study. The measures of accuracy for defining characteristics were obtained from a latent class model with random effects for the calculation of sensitivity and specificity values. ResultsThe characteristics of increased respiratory rate and warm skin to the touch had higher sensitivity values (99.9%) and lower specificity (79 and 75%) and the characteristics of body temperature fluctuations above and below the normal parameters and hypertension had the highest specificity (80.4 and 100%, respectively). ConclusionThe characteristic fluctuation of the body temperature above and below the normal parameters may be better to confirm the diagnosis, having presented a higher specificity value.

Study on trench film cooling on turbine vane by large-eddy simulation

Combined with infrared thermography experiments, large-eddy simulation was used for studying trench film cooling on C3X vane model at the mainstream Reynolds number of 2.5 × 105 based on the chord length, and nominal blowing ratios of 0.5 and 1.5. The instantaneous and time-averaged characteristics for trench film cooling were analzyed in detail. Inside the trench, a pair of recirculation vortices promotes the coolant spreading on spanwise direction, mitigates the jet penetration into mainstream, and improves cooling effectiveness. On pressure surface, hairpin vortices play the dominate role in the unsteady flow fields. Downstream of the trench, a streamwise vortex pair corresponding to anti-CRVP (Counter rotating vortex pair) is generated on both sides of hairpin structures, and causes high turbulent fluctuation. On suction surface, the mainstream boundary layer transits from laminar to turbulent flow in the upstream of the coolant exit, and large numbers of small-scale vortices dominate the flow dynamics. Spectrum analysis of pressure signals shows that, on pressure surface, trench and round-hole film cooling both exhibit strong periodicity. On suction surface, randomness is more pronounced. The statistical characteristics of velocity and temperature fluctuations were also discussed in detail. Overall, significant cooling augmentation by trench hole is seen on both the suction and pressure surfaces, especially at high blowing ratio.

A Study on the Characteristics of Summer Water Temperature Fluctuations by Spectral Analysis in Coast of Korea in 2016

A Study on the Characteristics of Summer Water Temperature Fluctuations by Spectral Analysis in Coast of Korea in 2016

Spectral Analysis of Gravity Waves from Near Space High-Resolution Balloon Data in Northwest China

Using a set of near space high-resolution balloon data released in Hami, Xinjiang, we explored the spectral characteristics of temperature fluctuations and three-dimensional wind field fluctuations. As different from previous studies, which were based on radiosondes, we have increased the height range of spectral analysis to the stratosphere (38 km), which can explore the variation of spectral features with altitude, and can analyze higher wavenumber regions. The results show that horizontal wind field disturbances are isotropic, meridional and zonal winds have relatively consistent spectral structures, while vertical wind fluctuations have completely different spectral structures, which cannot be explained by the existing “universal spectrum” theory. The observed spectrum of horizontal wind field can be explained well by the “wind-shifting” theory. The ratio of spectral kinetic energy to potential energy is approximately constant only in the high wavenumber region but it varies at different height intervals. This study is a necessary extension of the observation for the characteristics of the vertical wavenumber spectrum in northwestern China, and it is also an experimental observation of spectral characteristics using radiosonde data at higher altitudes.

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

Investigation of heat transfer in a liquid metal upflow in the MHD-channels applied to tokamak reactor blanket module

This article is devoted to experimental investigation of hydrodynamics and heat transfer in MHD flow configuration: upflow of mercury in a vertical round tube and rectangular duct with non-uniform heating in the transverse (coplanar) magnetic field. The problem is of interest for developing fusion reactor`s cooling systems. The liquid metal flow, in this case, will be complicated by influence of electromagnetic and thermogravitation forces. The experimental data were obtained by a proven probe technique for temperature measurements. The average temperature fields, wall temperature distributions, heat transfer coefficients and statistical characteristics of temperature fluctuations have been obtained and compared throughout the length of test section (pipe or duct) detecting the channel geometry influence.

Characteristics of daily water temperature fluctuations in lake kierskie (West Poland)

Abstract The paper presents the dynamics of daily water temperature fluctuations in Lake Kierskie (West Poland) and determines the effect of air temperatures and wind speed on the variability of the parameter (water temperature). The analysis was based on hourly water temperature values from the period from May 2012 to January 2018. The data analysis permitted the description of the thermal regime of waters in the lake in the hourly cycle in reference to each month, and designation of months characterised by the highest and lowest stability of water temperatures. More than half of the analysed days was characterised by a change in water temperature not exceeding 1°C. The course of water temperature showed strongly positive correlations with air temperature, and weak correlations with wind speed. Water temperatures in the lake were correlated the strongest with air temperatures with a 24 h time step.

Heat Transfer during Mixed Convection of a Molten Salt in the Presence of Magnetic Fields

Results of an experimental study of the salt melt downflow in a uniformly heated pipe under the influence of a strong transverse magnetic field are presented. The changes of heat transfer coefficients and statistical characteristics of temperature fluctuations under the influence of the magnetic field are investigated. The peculiarities of the transition of the viscous-gravitational flow in the viscous-inertial-gravitational flow at Reynolds numbers (Re = 3000–5000) under the influence of the magnetic field (Ha = 17) were studied.

A fundamental study of intelligent building envelope systems capable of passive dehumidification and solar heat collection utilizing renewable energy

Experimental studies and simulation analysis were conducted to assess the hygrothermal performance of intelligent roof systems, which perform passive dehumidification in summer and solar heat collection in winter by air circulation through the roof ventilation layer to reduce sensible and latent heat load using solar heat. A high-efficiency air conditioning system separating latent and sensible heat can be developed using fibrous insulation with excellent moisture conditioning properties. The thermodynamic-potential-based fundamental principle of the intelligent skin system, which performs passive dehumidification and solar collection, was explained based on non-equivalent thermodynamics. The performance characteristics of temperature and humidity fluctuations of the intelligent roof were experimentally and numerically demonstrated. This work enables the combined analysis of heat and moisture movement in the envelope system. The experimental and numerical simulation results indicate that significant sensible and latent heat reduction can be achieved by running the system using renewable energy.

Теплообмен при смешанной конвекции расплава соли в присутствии магнитных полей

The results of an experimental study of the salt melt downflow in a uniformly heated pipe under the influence of a strong transverse magnetic field are presented. The changes of heat transfer coefficients and statistical characteristics of temperature fluctuations under the influence of the magnetic field are investigated. The peculiarities of the transition of the viscous-gravitational flow in the viscous-inertial-gravitational flow at Reynolds numbers (Re=3000-5000) under the influence of the magnetic field (Ha=17) were studied.

Channel inclination influence on MHD-heat transfer of liquid metal downflow in a pipe

Experimental studies have been conducted regarding heat transfer of liquid metal downflow in a pipe with different inclination angles in a transverse magnetic field with uniform heating. The probe measuring method has been used to obtain averaged and fluctuation temperature fields. Using these data distributions of local and average heat transfer coefficients, Nusselt numbers and statistical characteristics of temperature fluctuations were calculated.

Investigation of Hydrodynamics and Heat Transfer of an Upward Liquid Metal Flow in a Rectangular Channel under a Coplanar Magnetic Field

Hydrodynamics and heat transfer were investigated of an upward liquid metal flow through a rectangular channel having an aspect ratio of approximately 3 : 1 and one-sided heating under a coplanar magnetic field (MF). The flow in the cooling system’s cooling channel for a liquid metal blanket module of a Tokamak type thermonuclear reactor is simulated. Experiments were carried out in the mercury magnetohydrodynamic (MHD) test facility. Local heat transfer characteristics were measured using a probe technique. Two types of thermocouple probes were used: a lever-type pivoted probe for detailed measurements of velocity and temperature fields in a channel cross-section and a longitudinal probe for taking measurements along the heated zone in the channel. A correlation method was used for measuring local velocity. The distributions of averaged velocity and temperature, the distributions of dimensionless wall temperature along the cannel perimeter, and characteristics of flow temperature fluctuations are presented. The distributions of averaged and instantaneous wall temperatures along the channel were obtained. The effects caused by an increase in the intensity of temperature fluctuations in a coplanar magnetic field were revealed. It is the authors' opinion that natural convection is responsible for formation and separation of large-scale vortex structures, the axis of which is parallel to the magnetic field induction vector, at the heated wall. These vortices bring about temperature fluctuations that often exceed the level of turbulent fluctuations. The data on heat transfer should be considered in designing MHD cooling channels of a fusion reactor.

The characteristics of temperature fluctuations in thermal insulation covered with layer of PCM

Energy performance of opaque elements of building envelope can be improved by the decrease of heat losses by conduction or by effective utilization of solar heat gains. Enhancement of thermal insulation by application a thin layer of phase change material as an external finishing coating contributes to the attenuation and delay of heat flux transferred through partition. Based on the real scale experiment of one-year measurements, dynamics of temperature fluctuations in thermal insulation covered with external layer of PCM was characterized and analysed. It was concluded that outer application of PCM contributes to the attenuation of temperature fluctuations of the whole wall component.

Numerical investigation of the core outlet temperature fluctuation for the lead-based reactor

The temperature fluctuations induced by incomplete mixing of coolants with different temperature may cause thermal fatigue at the components of the lead-based reactor core outlet. Thus the accurate analysis of the phenomenon is very crucial for reactor safety operation. In this paper, the temperature fluctuations of the lead-based reactor core outlet were simulated by using large eddy simulation (LES) method in the simplified core outlet models. In order to analyze the temperature fluctuation sensitivity for the fuel assembly design parameters, such as the fuel assembly size and the gap between two adjacent fuel assemblies, five geometry models were constructed with different fuel assembly design parameters. The time histories of temperature fluctuations at different monitoring points on the center of three fuel assemblies were obtained. Then the amplitudes and the power spectrum density (PSD) of temperature fluctuations were analyzed, in order to compare temperature fluctuations of different geometry models at the same locations of core outlet. Finally the distribution characteristics of core outlet temperature fluctuations were obtained in axial directions, and the temperature fluctuation sensitivity with fuel assembly parameters was also analyzed based on the amplitudes, PSD and the normalized root-mean square temperature analysis. It is found that the temperature fluctuation intensity is enhanced with the increase of the gap size between adjacent fuel assemblies and the opposite edge width of each fuel assembly. The analysis results could provide important references for optimized design and engineering guidance of lead-based reactor.

Late summer temperature reconstruction based on tree-ring density for Sygera Mountain, southeastern Tibetan Plateau

Abstract Although several tree-ring density-based summer/late summer temperature reconstructions have been developed on the Tibetan Plateau (TP), the understanding of the local/regional characteristics of summer temperature fluctuations on a long-term scale in some regions is still limited. To improve our understanding in these aspects, more local or regional summer temperature reconstructions extending back over several centuries are required. In this study, a new mean latewood density (LWD) chronology from Abies georgei var. smithii from the upper tree line of Sygera Mountain on the southeastern TP was developed to reconstruct the late summer temperature variability since 1820 CE. The bootstrapped correlation analysis showed that the LWD chronology index was significantly and positively correlated with the late summer (August-September) mean temperatures (r1950–2008 = 0.63, p