Apparent Temperature Difference Research Articles

Thermal performance of thermochromic smart windows in different indoor environments

Thermochromic (TC) smart windows can passively respond to the exterior and interior temperature, which further adjust their indoor thermal environments due to the varied photo-thermal parameters. This study investigated the thermal performances of practical TC windows in a room with/without air-conditioning or with stratified temperature distribution through a validated 3D CFD model. The application of TC windows could decrease the window, indoor ambient and floor temperatures, and also improve their temperature uniformity. The upper interior window could be 3.13 °C higher than the bottom in a room without air-conditioning, which could be reduced to 2.48 °C if the TC window was utilized. The uniformity improvement could be more significant for indoor environments with apparent air temperature differences, especially for the air-conditioning case. It is suggested that the indoor air temperature and its uniformity may affect the temperature and uniformity of the TC window surface in turn, specifically its phase transition time.

Examining differences in associations between apparent temperature difference and preterm birth by census-tract level utility-bill burden, North Carolina, 2011-2015

Examining differences in associations between apparent temperature difference and preterm birth by census-tract level utility-bill burden, North Carolina, 2011-2015

Longitudinal temperature acquisition system of ground freezing and its application in solving temperature field

We developed a longitudinal temperature acquisition system to address the inaccuracies in the determination of temperature fields in a large-scale artificial ground freezing project. The system can determine the temperature field distribution inside a freezing pipe. The results indicate the apparent temperature differences among different freezing pipes, and the brine temperature in the freezing pipes has an evident nonlinear distribution along the length of the freezing pipes. Therefore, using a single temperature boundary condition to obtain the freezing temperature field may not be sufficient to accurately reflect the freezing temperature of the different layers. The proposed system offers a new method to determine the heat flux function. Moreover, the dynamic heat flux boundary was built for numerical simulation to solve the temperature field. Through comparison, it is found that the dynamic heat flux boundary can be used to obtain the frozen curtain morphology and temperature field distribution more accurately. After adopting the new solution method in a large-scale freezing project in Guangzhou, China, the accuracy of determination of frozen wall thickness increased by approximately 53%. This study can provide a new way of thinking about temperature field calculation in practical engineering problems.

On the Leidenfrost effect of water droplet impacting on superalloy plate surface

The boiling of liquid water on the superalloy surface is important in applications such as steam and gas turbines, for which it is necessary to explore the mechanisms of the Leidenfrost phenomenon. The molecular dynamics simulation method provides an effective way to study this phenomenon at the nanoscale. Previous studies, however, have not revealed the Leidenfrost effect of liquid molecules on a superalloy surface. This work investigated the effects of surface temperature and impact velocity on the nanoscale Leidenfrost phenomenon of water droplet over the Fe-Cr superalloy plate. When the surface temperature is higher than 798 K, the Leidenfrost phenomenon occurs on the superalloy surface with apparent temperature, stress, and pressure differences. The results indicate that the Leidenfrost phenomenon is related to the high surface temperature, rather than its impacting velocity. Furthermore, it is found that the Leidenfrost phenomenon is the combined results from the temperature and pressure differences exist in the vapor film, as enough kinetic energy can be generated by the thermal motion to cause the bounce phenomenon of droplet. The revealed mechanisms are critical for the design of a gas turbine, in which vapor film could be dominant in determining the film cooling effectiveness of gas/vapor on the blade surface.

Direct Measurement of the Selective Microwave-Induced Heating of Agglomerates of Dipolar Molecules: The Origin of and Parameters Controlling a Microwave Specific Superheating Effect.

Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiation. The magnitude of the selective heating was directly measured by using the temperature dependence of the intensities of the Stokes and anti-Stokes bands in the Raman spectra of p-nitroanisole (pNA) and mesitylene. Under dynamic heating conditions, a large apparent temperature difference (ΔT) of over 100 °C was observed between the polar pNA solute and the nonpolar mesitylene solvent. This represents the first direct measurement of the selective microwave heating process. The magnitude of the selective microwave heating was affected by the properties of the agglomerated pNA. As the concentration of the pNA increases, the magnitude of the selective heating of the pNA was observed to decrease. This is explained by the tendency of the pNA dipoles to orient in an antiparallel fashion in the aggregates as measured by the Kirkwood g value, which decreased with increasing concentration. This effect reduces the net dipole moment of the agglomerates, which decreases the microwave absorption. After the radiation was terminated, the effective temperature of the dipolar molecules returned slowly to that of the medium. The slow heat transfer was modeled successfully by treating the solutions as a biphasic solvent/solute system. Based on modeling and the fact that the agglomerate can be heated above the boiling temperature of the solvent, an insulating layer of solvent vapor is suggested to form around the heated agglomerate, slowing convective heat transfer out of the agglomerate. This is an effect unique to microwave heating.

An Improved Comprehensive Model of Pyrolysis of Large Coal Particles to Predict Temperature Variation and Volatile Component Yields

In this work, an improved comprehensive model was developed for large coal particles to predict temperature variation and volatile component yields. The kinetics model of volatile component yields, where the volatile matters were assumed to comprise nine species, was combined with heat transfer model. The interaction between volatile yield and heat transfer during pyrolysis of large Maltby coal particles was investigated. An apparent temperature difference has been observed between the surface and core of particles at the initial heating stage. The non-uniform temperature distribution inside coal particles causes non-simultaneous volatile yields release from the surface and core area. The volatile release occurs after the coal temperature rises higher than 350 °C, and its yield steeply increases within the temperature range of 450–520 °C. The peak of volatile release rate corresponds to about 485 °C due to the rapid release of tar and H2O. The tar is almost completely released at around 550 °C. With the increasing particle size, the difference in temperature and volatile yield between the surface and core increases at the end of heating. The results are expected to provide insights into the interaction between heat transfer and volatile yields during pyrolysis of large coal particles.

Analysis of heat transfer critical point in LT-MEE desalination plant

Based on the internal relationship of thermodynamic and structure parameters of the low-temperature multi-effect evaporation (LT-MEE) desalination plant, calculation of the temperature difference distribution in a typical horizontal-tube falling film evaporator was carried out. Results show that the reduction of effective temperature difference caused by various thermodynamic losses occupies a large proportion of the apparent temperature difference in horizontal-tube falling film evaporator. The distribution of effective heat transfer temperature difference is extremely un-uniform in tube bundle. Under some conditions, the local effective temperature difference in the evaporator could be zero, and reverse heat transfer might even appear. Through the analysis of the thermodynamic losses in a desalination plant, the heat transfer critical point and the effective heat transfer critical point are proposed for better guiding the thermal design of multi-effect evaporation desalination plant.

海面环境中红外偏振成像系统作用距离模型

The fact that infrared radiation of sea surface is polarized has been proved by many experiments. Searching and detecting ability of infrared polarization imaging systems in sea-surface environment was a major concern for polarization imaging research. Sea surface was realized by using a statistical model of oceanographic literature which originated from the spectrum for long and short wind-driven waves proposed by Eifouhaily. A Monte Carlo reverse ray-tracing method was used to investigate the behavior of mid/long-wave infrared Stokes radiance which included the information of radiance intensity, degree of polarization and angle of polarization, at the realized wind roughed sea surface. The minimum resolvable temperature difference(MRTD) parameters for Stokes-vector components were proposed based on standard error propagation method. Finally, detectable range of infrared polarization imaging used in sea surface environment was analyzed by comparing apparent-temperature differences(ATD) between target and sea background with the MRTD of Stokes-vector components.

Heat and mass transfer at a free surface with diabatic boundaries in a single-species system under microgravity conditions

In this paper, we analyzed the heat and mass transfer at a free surface under microgravity conditions. The SOURCE-II (Sounding Rocket COMPERE Experiment) experiment was performed on a suborbital flight in February 2012 from Esrange in North Sweden. It provided representative data with respect to solid, liquid, and vapor temperatures as well as the visible surface position. The objectives were to quantify the deformation of the free liquid surface and to correlate the apparent contact angle to a characteristic temperature difference between subcooled liquid and superheated wall. Furthermore, the influence of evaporation and condensation at the liquid/vapor interface and at the superheated wall must be taken into account to analyze heat and mass fluxes due to a characteristic temperature difference. In the following, we show evidently that the magnitude of the apparent contact angle depends on the exerted specific pressurizations of the vapor phase during the experiment and hence on the change in the saturation temperature at the free surface. The characteristic temperature difference is defined with respect to the wall temperature in the vicinity of the contact line and the saturation temperature. Therefore, apparent contact angle and temperature difference can be correlated and indicate a specific characteristic. Concerning the heat and mass transfer at the free liquid surface and the contact line, two different methods are presented to evaluate the net mass due to phase change within a certain time interval. In the first approach, the mass flow rate is calculated by means of the ideal gas law and its derivatives with respect to temperature and pressure. The second approach calculates the heat flux as well as the mass flux at the wall and in the region of the free liquid surface. In these cases, a specific heat transfer coefficient and a thermal boundary layer thickness are used.

Preparation and Characterization of Bi2Te3/Sb2Te3 Thermoelectric Thin-Film Devices for Power Generation

A device based on a new double-layer-leg thin-film concept has been successfully fabricated by flip-chip bonding of 242 pairs of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs electrodeposited on top substrates to those processed on bottom substrates. Based on the output voltage–current curve, the internal resistance of the double-layer-leg thin-film device was measured to be 3.47 kΩ at an apparent temperature difference of 25.9 K across the device. The actual temperature difference across the thin-film legs was estimated to be 3.51 K, which is ∼13% of the apparent temperature difference ΔT of 25.9 K applied across the thin-film device. The double-layer-leg thin-film device exhibited an open-circuit voltage of 0.43 V and maximum output power of 13.1 μW at an apparent temperature difference ΔT of 25.9 K.

Thermoelectric Power Generation Characteristics of a Thin-Film Device Consisting of Electrodeposited n-Bi2Te3 and p-Sb2Te3 Thin-Film Legs

A thermoelectric thin-film device of the cross-plane configuration was fabricated by flip-chip bonding of the top electrodes to 242 pairs of electrodeposited n-type Bi2Te3 and p-type Sb2Te3 thin-film legs on the bottom substrate. The electrodeposited Bi2Te3 and Sb2Te3 films of 20-μm thickness exhibited Seebeck coefficients of −59 μV/K and 485 μV/K, respectively. The internal resistance of the thin-film device was measured as 3.7 kΩ, most of which was attributed to the interfacial resistance of the flip-chip joints. The actual temperature difference ΔTG working across the thin-film legs was estimated to be 10.4 times smaller than the apparent temperature difference ΔT applied across the thin-film device. The thin-film device exhibited an open-circuit voltage of 0.294 V and a maximum output power of 5.9 μW at an apparent temperature difference ΔT of 22.3 K applied across the thin-film device.

Three-dimensional FE model for calculation of temperature of a thermosensitive disc

An effect of variations of the temperature-dependent thermophysical properties of materials of a pad and a disc on the temperature generated due to friction was studied. A three-dimensional boundary-value problem of heat conduction of the disc heated locally within the contact area by the moving with the constant deceleration heat flux and the intensity proportional to the specific capacity of friction was formulated. An issue was solved numerically using the finite element method (FEM). The experimental dependences curves of the thermal conductivity and the thermal diffusivity on the temperature ranging from 20 to 500 °C indispensable for the calculations were approximated using Chichinadze's methodology. The comparative analysis of temperature values on the contact surface of the disc obtained with and without influence of temperature dependence of the four different pad and the same quantity of the disc materials was carried out. It was demonstrated that apparent temperature differences arose for each friction couple combining temperature-dependent and constant properties of materials, however, the largest observed discrepancy (13.7%) occurred for the disc made of aluminium alloy series Al MMC. Other disc materials i.e. iron alloy series FCD50, cast iron ChNMKh and steel EI-696 revealed relatively equal temperature differences of order of 6.4%. Furthermore incorporated in the formula for the heat partition temperature variability of the thermophysical properties of materials affected the resulting contact temperature of the disc for friction couple combined exclusively with the titanium pad VT-14 (3.1%).

A spatio-temporal index for heat vulnerability assessment

The public health consequences of extreme heat events are felt most intensely in metropolitan areas where population density is high and the presence of the urban heat island phenomenon exacerbates the potential for prolonged exposure. This research develops an approach to map potential heat stress on humans by combining temperature and relative humidity into an index of apparent temperature. We use ordinary kriging to generate hourly prediction maps describing apparent temperature across the Greater Toronto Area, Canada. Meteorological data were obtained from 65 locations for 6 days in 2008 when extreme heat alerts were issued for the City of Toronto. Apparent temperature and exposure duration were integrated in a single metric, humidex degree hours (HDH), and mapped. The results show a significant difference in apparent temperature between built and natural locations from 3 PM to 7 AM; this discrepancy was greatest at 12 AM where built locations had a mean of 2.8 index values larger, t(71) = 5.379, p < 0.001. Spatial trends in exposure to heat stress (apparent temperature, ≥ 30°C) show the downtown core of the City of Toronto and much of Mississauga (west of Toronto) as likely to experience hazardous levels of prolonged heat and humidity (HDH ≥ 72) during a heat alert. We recommend that public health officials use apparent temperature and exposure duration to develop spatially explicit heat vulnerability assessment tools; HDH is one approach that unites these risk factors into a single metric.

Johnson准则在红外成像系统外场识别性能评估中的应用

The apparent average temperature difference and critical dimension of actual target and background were acquired through retrieving infrared target image.The retrieved apparent temperature difference and the measured MRTD curve were combined to determine the corresponding spacial frequency.And,a quantitative relationship between the target infrared image and the probability of detection and recognition was established with Johnson criteria and target transfer probability function(TTPF).The method avoids operater′s subjective judging,so the result is more impersonal.This method was experimentally validated in evaluating the detection and recognition probability of IR system.

Field Performance Prediction Method Based On Contrast Metric Of Target Sub Regions

The field performance prediction of infrared imaging system is an important subject in infrared imaging field. In this paper, a novel method for predicting TA (target acquisition) performance is proposed, which combines the TOD (triangle orientation discrimination) threshold curve with an improved contrast metric based on the temperature in target sub regions. Specifically, the target is first subdivided into some sub regions with different target/background differential temperatures according to its thermal structure distribution. The number of equivalent triangle patterns across each sub region is calculated utilizing its effective size, the apparent temperature difference line, and the TOD curve. Further, the total number of equivalent triangle patterns over the integral target is achieved. Combining the TOD criteria, the target acquisition ranges for different discrimination (detection, recognition, and identification) levels are obtained by solving a set of equations. Comparisons with the preliminary experimental results show that this new TA approach can provide reasonable prediction of field performance.

Water status response of corn and cotton to altered irrigation

Water is a primary limiting factor to crop production and thus crop water status is essential information for management decisions. Corn and cotton were grown in the field under two constant water regimes. The low water level (WL) was 0.66×PET (potential evapotranspiration) in corn and rainfall for cotton. The high water level (WH) was 1.0×PET for both crops. Two transient water treatments in each crop began as the two constant water level treatments but then the water inputs were reversed and the change in water status was monitored. When the transient water treatments were initiated, corn was at the V14 and V16 growth stages in the WL and WH treatments, respectively, and cotton was 2 weeks past first bloom for both water levels. The purpose of the experiment was to compare the sensitivity of leaf water potential (LWP) and crop canopy temperature to changes in irrigation rate. The transient water treatment of each crop that relieved water stress (TLH) changed from WL to WH and the treatment which induced water stress changed from WH to WL (THL). The LWP values of the transient water treatments reversed 5 and 8 days after reversing water input rates to corn in 1998 and 1999, respectively, and after 3 days in both years for cotton. A reversal in canopy temperatures, expressed as the amount of daily time that the temperature was above 28°C (DST), was not detected between the TLH and THL treatments of corn after 25 days in 1998 or after 13 days in 1999. The DST values of the cotton transient water treatments reversed after 4 days in 1998 and 5 days in 1999, when the values of THL became greater than for TLH. Corn tassels, which apparently transpire less than leaves, were forming at the beginning of the transient water treatments and their presence in the view of the infrared thermocouples may have reduced the apparent radiometric temperature difference between the transient water treatments. During the water status adjustment period following the initiation of the transient water treatments, there were significant linear relationships between LWP and DST in cotton in both years but only in 1998 in corn. Cotton canopy temperature could be used to rapidly monitor an entire field in contrast to LWP which accurately measures plant water status but cannot provide automated measurements across a large area.

A new garnet-orthopyroxene thermometer based on reversed Al2O3solubility in FeO-Al2O3-SiO2orthopyroxene

Reversed phase-equilibrium data, collected over the P-T range 12-20 kbar at 850-1100 degrees C, define the solubility of Al 2 O 3 in ferrosilite (Fs) in equilibrium with almandine garnet (Alm). The new data indicate significantly lower Al 2 O 3 solubility in Opx in the Fe-bearing system compared with the Mg-system and extrapolate well to merge with the higher pressure bracket of Kawasaki and Matsui (1983). Orthopyroxene-garnet thermometry in crustal rocks, based on the equilibrium studied here (Alm = 3 Fs+Al 2 O 3 ), is considerably more robust than previous calibrations based on the equivalent equilibrium in the Mg system. Results for several granulite terrains show that Al-Opx temperatures based on the new experimental data are generally higher than results based on Fe-Mg exchange thermometry, consistent with suggestions of previous workers. For many samples, the difference in apparent closure temperature between these equilibria (generally 50-130 degrees C) is within the combined uncertainty of their calibration ( approximately 75 degrees C) and is not as extreme as differences calculated on the basis of Harley9s (1984) unreversed experimental data (Begin and Pattison 1994). The lack of sensitivity of this new thermometer to late Fe-Mg exchange makes it a powerful tool for deciphering near-peak P-T conditions for high-grade rocks.

Monitoring the Solar Temperature: Empirical Calibration of the Temperature Sensitivity of Ciλ5380

We observed a set of six dwarf stars spanning a range in temperatures around the solar value, and from them we have determined empirically the temperature sensitivity of C I λ5380.32, a line that has been monitored in the solar flux spectrum for nearly two decades at Kitt Peak. When the C I line is compared to the adjacent Fe I λ5379.58 line, it should be possible to detect apparent temperature differences of a fraction of 1 K.

Electrochemical concentration cell ozone soundings at two sites during the Stratospheric Ozone Intercomparison Campaign

The Stratospheric Ozone Intercomparison Campaign (STOIC) was designed to compare proposed instruments for the Network for the Detection of Stratospheric Change (NDSC) with established measurement techniques. Ground‐based measurements were conducted at Table Mountain, California (34.4°N, 117.7°W), and rocket profiles were made at San Nicolas Island, California (33.3°N, 119.5°W). In an effort to estimate site‐to‐site differences during the intercomparison, daily soundings were made with balloon‐borne electrochemical concentration cell (ECC) ozonesondes at the two sites. Comparisons have been made of the mean values for the soundings at each site. The soundings showed small temperature differences between the two sites with the nighttime Table Mountain measurements up to 2°K cooler than the daytime San Nicolas Island temperatures. Day/night temperature corrections based on the emissivity and absorptivity of the thermistors in the balloon instruments can account for these apparent temperature differences. Ozone partial pressure profiles from the ECCs have been used to estimate atmospheric ozone variability during STOIC. Above 20 km, the lowest altitude for the STOIC comparisons, the average data sets from both sites showed standard deviations that were at or below the estimated 5–6% profile‐to‐profile repeatability for the ozonesondes. This indicates that atmospheric ozone variability was only of the order of a few percent above 20 km during the 2 weeks of the STOIC campaign. Above 20 km the ozone partial pressures over the Table Mountain site averaged 2.0% lower than over San Nicolas Island.

Thermoelectric effects in miniature permanent magnet probes used for velocity measurement in flowing sodium

Velocities in liquid sodium at temperatures of 300°C and above have been measured using miniature magnet probes for two types of turbulent shear flow. Heated and unheated jets were studied using a high-sensitivity probe with an output of 48 μV·s/m. Buoyancy-influenced pipe flows were investigated with less sensitive, but more robust, probes generating about 15 μV·s/m. All velocity profiles measured with the probes were asymmetric, whether for heated flow or isothermal flow. Skew in the profiles was caused by the zero offsets of the probes changing with position, and an analysis of probe behavior suggests that the changes were thermoelectric effects due to inhomogeneities in the thermocouple materials forming the probe electrodes. Furthermore, the analysis shows that calibration offsets may be related to the apparent temperature difference across the probe indicated by the thermocouples when the probe is operating in isothermal conditions. The variation of zero offset with position seemed to be most severe when the probes were close to walls at the limits of their travel. The accurate determination of zero offsets for miniature magnet probes requires careful probe calibration in isothermal flow. Any small temperature difference across a probe during this process will produce errors in the signal. Similarly, temperature differences produced by turbulence during normal operation influence the results, particularly for probes of low sensitivity. This effect was seen during the present investigation in scatter in the velocity profiles for pipe flows, particularly at high test section powers and in downward flow. High heat fluxes produce correspondingly large temperature fluctuations; in downward flow, turbulence levels are increased by the buoyancy forces opposing the motion.