Ambient Temperature Radiation Research Articles

The Mathematical Modeling and Performance of Sky Radiative Coolers

Sky radiative cooling is a kind of passive cooling technology that uses the “atmospheric window” to emit the object’s own heat to the low temperature of outer space; this technology has low energy consumption, no pollution, and other useful characteristics, so in recent years it has attracted widespread attention. The cooling effect of the sky radiative cooler is mainly affected by the constantly changing outdoor ambient temperature. In addition, the structure of the radiative cooler itself also means that its radiative cooling power undergoes obvious changes. Here, we utilized COMSOL simulation software to establish a numerical heat transfer model for radiative cooling, aimed at investigating the influencing factors on the sky radiative cooler and methods to enhance the structure of the radiative cooling. This study discusses outdoor ambient wind speed, the inlet flow rate of the cooler, installation angle of the cooler, and different cooler structures. Based on simulation results, it is observed that, for varying wind speeds, when the ambient radiation temperature is higher than the surface temperature of the cooler, a larger ambient wind speed leads to a poorer refrigeration effect. The maximum temperature difference in surface temperature at wind speeds of 0 m/s and 4 m/s is 0.59 °C. When the ambient temperature is lower than the surface temperature of the cooler, a smaller wind speed results in a greater net refrigeration power. The maximum temperature difference in this scenario is 0.32 °C. The net refrigeration power of the radiative cooler increases with an increase in water flow rate. As the water flow rate increases from 0 L/min to 5 L/min, the net refrigeration power increases from 25 W/m2 to 200 W/m2 and gradually stabilizes. Considering the radiative impact of the cooler on the surrounding environment, as the installation angle increases from 0° to 90°, the surface temperature of the cooler first increases and then decreases, reaching its highest temperature of 29.26 °C at 45°. The surface temperature of the cooler varies with the thickness of the air sandwich, increasing from 1 cm to 12 cm, and then decreasing. The lowest temperature of 23.4 °C is achieved at a thickness of 8 cm. The increase in the fin structure on the surface of the radiative cooler leads to a decrease in its refrigeration performance, and the difference between the inlet and outlet temperatures of the radiative cooler with a flat plate structure is always greater than that of the finned plate, and the difference in the average radiance is 23.52 W/m2. Finally, the energy-saving effect of the sky radiative cooling composite system is analyzed. Taking a typical small office building as an example, an energy consumption analysis model is set up, and the energy consumption of the composite system is simulated in four cities with different climates, using EnergyPlus software (version 8.6); the system’s power consumption is the largest in hot and humid climates. Compared with the traditional vapor-compression refrigeration system, the composite system reduces air conditioning power consumption by 25.7%, 32.5%, 37.1%, and 44.8% in Guangzhou, Shanghai, Jinan, and Shenyang, respectively. The main innovations of this paper include analyzing and studying the influence of the tilt angle change of the radiative plate on the refrigeration performance of the cooler and the relationship between the surrounding buildings, adding air sandwiches and ribs to the radiative cooler to analyze the influence of convective heat transfer on the refrigeration effect, which plays a guiding role in the design and research of the sky radiative cooler.

Calculation Of The Radiation Temperature Of The Urban Development Environment

The radiation ambient temperature is one of the microclimatic indicators of urban areas, which determines the safe stay of people in them during the warm period of the year. The ability of artificial coatings to accumulate and radiate heat energy should be taken into account in making competent urban planning decisions to eliminate or reduce the additional heat load on the urban environment. The calculation of radiation temperatures of the environment contributes to the adoption of environmentally safe urban planning decisions of specific areas. Using such "tools" as changing the orientation of the urban object to the cardinal directions, thermal properties of anthropogenic coatings, their concentration (density), and exposure, it is possible to control the radiation power of the surrounding surfaces, and, accordingly, the value of radiation temperatures. Research with the use of the globe thermometer confirms change in the radiation temperatures. In this case, the elementary area can be replaced with the reduced site, which will be the limit when calculating the irradiance coefficients of the required accuracy from the elements of urban development. The size of the reduced site is usually a uniform architectural element of the facade plane, for example, the size of a standard window or half of the average wall panel, etc., which is convenient for assigning the materials of the above sites radiation absorption coefficients and calculating or measuring the surface temperature. A method for calculating radiation temperatures, which is based on determining the irradiation coefficients from the globe thermometer to the surrounding fences of an imaginary space (parallelepiped) of the yard, with due regard for their surface temperatures, is proposed.

Dynamic impact of climate on the performance of daytime radiative cooling materials

By strongly reflecting solar radiation and being highly emissive within the atmospheric window, daytime radiative coolers can achieve sub-ambient temperature under direct sunlight. Radiative cooling performance is strongly coupled to specific climatic conditions since cooling efficiency is strongly affected by ambient air temperature, wind speed, and solar and ambient radiation intensity. In this paper, using a well-validated thermal model, the cooling performance of three radiative cooling materials with varying optical properties was evaluated under three distinct and representative climates. This analysis permits us to better understand the sensitivity of daytime radiative cooling materials to different climatic conditions, present strategies for selecting the ideal spectral properties of materials and investigate how to enhance cooling performance under adverse climatic conditions. It is shown that radiative cooling materials have better performance in hot and arid climates. Most radiative cooling materials exhibit the greatest response to changes in ambient radiation. Higher ambient air temperatures correspond to larger sub-ambient temperature of the surfaces, but this change is lower than that of the corresponding air temperature. Furthermore, by coupling a special optical grating window onto the surface of a radiative cooler, cooling performance can be significantly enhanced by asymmetrically reflecting incoming radiation but permitting outgoing emission. While an ideal material that only emits in the atmospheric window wavelengths presents the best performance under a large range of solar radiation, ambient radiation, and air temperature, the broadband ideal emitter exhibits higher cooling potential when coupled with the optical grating window.

Thermal Simulation for Unconditioned Single Zone with Modified Roof

Roof in the Iraqi houses normally flattening by a concrete panel. This concrete panel has poor thermal properties. The usage of materials with low thermal conductivity and high specific heat gives a good improvements to the thermal properties of the concrete panel, thus, the indoor room temperature improves. A Mathcad program based on a mathematical model employing complex Fourier series built for a single room building. The model input data are the ambient temperature, solar radiation, and sol-air temperature, which have been treated as a periodic function of time. While, the room construction is constant due to their materials made of it, except the roof properties are taken as a variable generated practically from the improved mixing ratios.The result showed that using concrete panel with components (cement, sand, coarse aggregate, wood ash and Alabaster aggregates) with a ratio (1:1:2:1:1) and 3-plastic layer denoted by roof No.4, gives the best improvement of the thermal performance for the building. Where, the thermal conductivity is reduced by 42% and the specific heat increased by 41.2% compared to the traditional concrete panel mixing ratio denoted by roof No.1. Also, the mechanical properties are agreed with the Iraqi standards No. 1107 on 2002.

Acquisition of thermal field of spatial steel structure based on temperature measurements

A spatial steel structure is a kind of high-order statically indeterminate structure, and the deformation caused by repeated changes in temperature will cause fatigue damage to its members. Therefore, for the design and safe use of spatial steel structures, it is of great significance to study the thermal effect. A method of acquiring the overall thermal field based on the limited temperature measurements is proposed in the paper. Firstly, the simulated thermal field of the structure is acquired by superposing the ambient temperature and solar radiation temperature. Secondly, the optimal mode for temperature estimations is determined by inverse distance weighted interpolation. Thirdly, the thermal field of the spatial steel structure is acquired based on the temperature measurements and the optimal mode. Finally, the feasibility of the proposed method is verified in the case of the large shell of the Zhuhai Opera House.

EFFECT OF ROOF POND ON THE ENERGY AND EXERGY PERFORMANCE OF A SINGLE SPACE BUILDING

In a hot, arid zone, the load imposed on the building due to the roof is more than that for all the four walls; one of the proposed solutions to this condition is to use the roof pond. Using roof pond can reverse the performance of roof from heat source to heat sink that can withdraw the heat from building envelope. In this work a mathematical model, using the complex Fourier series was built for a single space building. Ambient temperature, solar radiation, and sol-air temperature have been treated as a periodic function of time. The effect of roof pond on the indoor temperature, heat flow to the building, temperature distribution through walls and roof were studied, as well as an exergy analysis to the roof pond was achieved. The result showed that using roof pond can reduce the mean indoor temperature by about 4 °C as compared with a building using the traditional roof. The exergy analysis showed that the maximum exergy efficiency conjunct with the maximum exergy destruction through roof pond.

Life-bearing primordial planets in the solar vicinity

The space density of life-bearing primordial planets in the solar vicinity may amount to ∼8.1×104 pc−3 giving total of ∼1014 throughout the entire galactic disk. Initially dominated by H2 these planets are stripped of their hydrogen mantles when the ambient radiation temperature exceeds 3 K as they fall from the galactic halo to the mid-plane of the galaxy. The zodiacal cloud in our solar system encounters a primordial planet once every 26 My (on our estimate) thus intercepting an average mass of 103 tonnes of interplanetary dust on each occasion. If the dust included microbial material that originated on Earth and was scattered via impacts or cometary sublimation into the zodiacal cloud, this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy.

Temperature variation of concrete box girder bridge

On the basis of theoretical analysis and measurement on site, the temperature gradients and its variation on concrete box girder bridges resulting from ambient temperature, solar radiation, and structural temperature fields were discussed. With the help of the heat transfer theory and finite element method (FEM), the heat flux of the surface of concrete box girder was carried out, and all the heat fluxes were described as the convection. The results were compared with that from field measurements, and a good correlation was found. It was revealed that the methods, the parameters, the boundary condition used in this paper were reasonable. Last, some conclusions were obtained, which could provide the basis for box girder design under solar radiation.

In situ transmission electron microscopy of ion irradiated Fe–Pt alloy thin films

We report the microstructural evolution during irradiation of FePt and FePt 25at.% thin films sputter deposited onto electron transparent silicon monoxide substrates. The films were studied in situ for 500keV Kr+ irradiation up to a fluence of 1015ions∕cm2 or 4displacements∕atom (dpa). Upon irradiation to approximately 1dpa, the initial disconnected granular morphology became continuous. In particular, for FePt, accelerated grain growth was observed once the continuous morphology was achieved during ambient temperature irradiation. No atomistic (chemical) ordering from the as-deposited A1 phase into either the L10 FePt or L12 Fe3Pt phases was observed during ambient temperature irradiation. After irradiation, the specimens were then in situ annealed. The intermetallic ordering temperature, compared to that of an unirradiated film, was lowered by ≈200°C for FePt 25at.%. No decrease in the ordering temperature was observed for irradiated FePt. The rate of FePt grain growth during annealing was very similar for both irradiated and unirradiated films over the 25–650°C temperature range investigated.

Black Hole Hawking Radiation May Never Be Observed!

Thermal Hawking emission from black holes is a remarkable consequence of the unification of quantum physics and gravitation. Black holes of a few solar masses are the only ones which can form in the present universe. However, having temperatures million times smaller than the ambient cosmic background radiation they cannot evaporate. Primordial black holes of M ∼ 1014g would evaporate over a Hubble age and considerable ongoing effort is on to detect such explosions. I point out, however, that at the early universe epochs when such black holes form, the ambient radiation temperature considerably exceeds their corresponding Hawking temperature. This results in rapid continual accretion (absorption) of ambient radiation by these holes. Consequently by the end of the radiation era their masses grow much greater so that their lifetimes (scaling as M3) would now be enormously greater than the Hubble age implying undetectably small emission.

Damage evolution in Xe-ion irradiated rutile (TiO2) single crystals

Rutile (TiO2) single crystals with (110) and (100) orientations were irradiated with 360 keV Xe2+ ions at 300 K to fluences ranging from 1×1017 to 5×1020 Xe/m2. Irradiated samples were analyzed using Rutherford backscattering spectroscopy combined with ion channeling analysis (RBS/C) and transmission electron microscopy (TEM). RBS/C results showed that much of the instantaneous displacement damage produced under ion irradiation is recovered under ambient temperature irradiation conditions. Upon irradiation to a fluence of 2×1019 Xe/m2, the radiation damage-induced microstructure was observed by TEM to consist of three distinct layers: (1) a layer near surface (thickness about 12 nm) exhibiting relatively homogeneous TEM contrast; (2) a second layer with a low density of relatively large-sized defects; and (3) a third layer consisting of a high concentration of small defects. After the fluence was increased to 5×1019 Xe/m2, a buried amorphous layer was observed by TEM. The thickness of the amorphous layer was found to increase with increasing Xe ion fluence. The uppermost damage layer, which accounts for the surface subpeak in RBS/C spectra, was found to be polygonized by ion irradiation.

Improvement of imaging of skin thermal properties by successive thermographic measurements at a stepwise change in ambient radiation temperature

Imaging of skin thermal properties was attempted by successive thermographic measurements of the skin surface with a stepwise change in ambient radiation temperature. In order to produce the stepwise change in ambient radiation temperature, two hoods maintained at different temperatures, 20 degrees C and 60 degrees C, were mechanically switched. A total of 65 thermograms were taken from 2 s before to 32 s seconds after the hood switching. Images of skin emissivity, emissivity-corrected skin temperature and thermal inertia were obtained by least-squares fitting at each pixel of 64 thermograms. Measurements were performed on the forehead, cheek, forearm, palm and back of the hand of 10 healthy male subjects. Differences in emissivity between sites and subjects were insignificant. Significant differences were observed in thermal inertia values between sites. Great improvements in the imaging of thermal inertia have been achieved by applying least-squares fitting to 64 thermograms instead of by computations from only two thermograms as in the previous study. Non-contact measurement and visualization of skin thermal properties are significant advantages of this method.

Measurement of the thermal inertia of the skin using successive thermograms taken at a stepwise change in ambient radiation temperature

Skin thermal properties are difficult to measure in vivo in the steady state because there is a constant temperature gradient across the skin surface. However, measurement of skin thermal properties is postulated in quantitative evaluation for thermographic observation. Here, imaging of the thermal inertia of the skin was attempted by thermographic measurements at a stepwise change in ambient radiation temperature achieved by quickly switching 2 hoods maintained at different temperatures. Using this technique, a total of 65 thermograms were sequentially recorded at intervals of 0.5 s beginning 2 s before the stepwise change. The image of skin thermal inertia was estimated by applying statistical curve fitting at each pixel of the thermograms. In addition, the emissivity and true temperature of the skin were also determined, together with thermal inertia, in a single measurement. Measurements were made at different sites on 10 subjects. The average values of thermal inertia of normal skin were scattered throughout a range from 1.4*103 to 2.1*103 W s1/2 m-2 K-1. Investigations of the relationship between skin blood flow and thermal inertia were also made by imaging thermal inertia when skin blood flow was changed by applying a vasodilator or vasoconstrictor on the skin surface. In a comparison with the data measured by laser Doppler flowmetry, the average slope of skin blood flow versus thermal inertia was 2.88*10-4 V per W s1/2 m-2 K-1, and the thermal inertia of the skin with no blood flow was 1.03*103 W s1/2 m-1 K-1. The results also show an almost linear correlation between skin blood flow and thermal inertia in each individual, but interindividual differences were also observed. The results suggest that skin blood flow distribution can be estimated by noncontact imaging of thermal inertia.

Non-contact imaging of thermal properties of the skin

Non-contact measurement of thermal properties of the skin was performed by using a thermovision camera and a mechanical system that provides a step change in ambient radiation temperature. A hood maintained at 20 degrees C was initially placed so as to cover the object surface towards which a thermovision camera was directed. Then the hood was quickly replaced by another hood maintained at 40 degrees C. Thermograms before, immediately after and 20 s after switching the hoods were taken. Then the image of emissivity was computed from thermograms taken before and immediately after hood switching, and the emissivity-corrected thermograms were computed by using the emissivity value obtained at each pixel. The images of the square root of the product of thermal conductivity, density and specific heat were computed from thermograms taken immediately after and 20 s after hood switching. While images of the emissivity obtained and the thermal parameter defined above contained significant noise, differences in these quantities between sites could be clearly demonstrated.

Changes in sun-related attitudes and behaviours, and reduced sunburn prevalence in a population at high risk of melanoma

This study aimed to determine trends in exposure to sunlight in the context of a melanoma prevention programme by monitoring the prevalence of sunburn and sun-related attitudes and behaviours. Telephone interviews were conducted in a baseline summer (December 1987 to February 1988) and two subsequent summers after the introduction of the SunSmart health promotion campaign. Interviewing a sample of 4,428 adult residents of the Australian city of Melbourne took place throughout summer on Monday evenings. Behavioural and sunburn data were reported for the previous weekend and relevant attitudinal data were collected. After adjusting for ambient ultraviolet radiation levels and temperature, survey month, age, sex and skin type, a significant reduction in sunburn was found. The crude proportion of sunburnt dropped from 11% to 10% to 7% over 3 years and the adjusted odds ratios (and 95% confidence intervals) were as follows: Year 1/Year 2; 0.75 (CI 0.57-0.99) and Year 1/Year 3; 0.59 (CI 0.43-0.81). Substantial attitudinal shifts occurred over the 3 years. Hat wearing increased significantly each year (19%, 26%, 29%), as did sunscreen use (12%, 18%, 21%). However, the trends in mean proportion of body surface area covered by clothing were less clear cut (0.67, 0.64, 0.71). It is concluded that melanoma risk factor exposure of populations can change fairly rapidly and that well-conducted health promotion campaigns can play a part in producing such change.

THERMOLUMINESCENCE GEOTHERMOMETRY — A CASE STUDY OF THE OTWAY BASIN

The thermoluminescence (TL) of quartz of detrital origin in a sedimentary basin is affected by time and temperature in two different ways:TL due to natural radiation (NTL) shows a first glow peak (which is commonly also the dominant peak) the glow temperature of which is a function of ambient radiation temperature and time. Progressive burial and increase of temperature results in a thermally 'cleaned' TL peak. Uplift, erosion or a decrease of temperature produces a new TL peak of lower temperature, with or without retention of the earlier formed TL peak. The glow temperature of those peaks can be evaluated in terms of time and ambient temperature of the basin. A comparison with palaeotemperatures estimated from vitrinite reflectance (VR) and apatite fission track analysis (AFTA) has shown very good agreement between NTL, VR and AFTA for those wells in the Otway Basin where present temperatures are at their maximum. In the case of uplift and a cooling trend the NTL temperatures reflect the most recent thermal regime, plus some effects from earlier thermal stages.Artificial TL (ATL) shows at basin temperatures exceeding 50°C a gradual change of intrinsic TL parameters. The changes are probably due to a decrease in the number of certain defects. The ATL effects are cumulative and reflect the whole thermal flux. In this sense ATL is comparable with VR. Although absolute calibration of ATL is not yet possible, relative changes due to differential uplift, erosion and cooling can be interpreted once the prevailing thermal gradient is known from NTL data. In this way, ATL indicated an uplift differential of 500 m between certain wells in the Otway Basin. The same results are confirmed by VR and AFTA data.

Non-contact skin emissivity: measurement from reflectance using step change in ambient radiation temperature

A method of estimating skin emissivity based on reflectance measurement upon transient stepwise change in the ambient radiation temperature was proposed. To effect this change, two shades at different temperatures were switched mechanically, and the change in radiation from the skin surface was recorded through an aperture for each shade by a high-resolution, fast-response radiometer having a sensitivity within the 8-14 microns range. Measurements were made on the forehead, forearm, palm and back of the hand in 10 male and 10 female subjects. No significant differences in emissivity were observed among sites and between sexes. The overall average of the skin emissivity obtained was 0.971 +/- 0.005 (SD). This result is inconsistent with most reported skin emissivity values. However, as the former studies had many inherent inadequacies, both theoretical and experimental, it is considered that most of these reported skin emissivities are unacceptable. The method proposed in this study has the following advantages: (1) relative calibration between instruments is unnecessary, (2) non-contact measurement can be achieved, and (3) each measurement can be made within one minute.

Effects of ion irradiation on the normal state and superconducting properties of NbN thin films.

The effects of ion-beam-induced damage on the normal state and superconducting properties of NbN were investigated in both single crystal and polycrystalline thin films. Three sets of films were damaged by 200-keV ${\mathrm{Ar}}^{+}$ ions with dosages up to 5\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$. The superconducting critical temperature (${T}_{c}$) of the single crystal films decreased by 20% at the highest ion dosage. Changes in the resistivity, ${T}_{c}$, and critical field (and its slope at ${T}_{c}$) suggest that ${T}_{c}$ is suppressed by a reduction of the electron density of states at the Fermi energy due to the vacancies created by ion irradiation. The effects of ion damage are much less pronounced for the polycrystalline films. In situ grain growth was observed during the ambient temperature irradiation processes, which confirms the role of grain boundaries as a sink for ion-induced defects, hence minimizing the effects of irradiation in polycrystalline films.

Quantitative measurements of ambient radiation, emissivity, and truth temperature of a greybody: methods and experimental results

By regarding the total ambient radiation falling on a greybody as an equivalent radiation of a blackbody at temperature TB and by using two standard reference plates, we are able to measure accurately the ambient radiation. In addition to the ambient radiation, there are two factors still affecting the self-radiation of a greybody, i.e., the emissivity ɛ and the truth temperature T. We point out theoretically that the emissivity could be determined by changing the ambient radiation. In this paper two simple methods are proposed for measuring the emissivity and good results are obtained for a variety of greybodies. These methods are not only practical in the laboratory but also in the field. The experimental results agree well with the data published by other investigators. After TB and ɛ are measured, the truth temperature T of the greybody can be obtained. Based on the theory presented here, we designed and produced a new infrared thermometer which can directly read out the truth temperature.

Optical absorption in fused silica during irradiation: Radiation annealing of the C-BAND

The results of extensive measurements of the optical transmission of Corning 7940 u.v. grade fused silica made during ambient and elevated temperature irradiations are described. The irradiations include high dose rate pulsed reactor irradiation, moderate dose rate steady state reactor irradiation and a selectable dose rate steady state 1·5 MeV electron irradiation. The growth of the C-band absorption at 2150 Å during ambient temperature irradiation indicates that this absorption is due to the trapping of free electrons at defects; the free electrons and defects both being generated by ionization process. During prolonged elevated temperature irradiation, the C-band absorption reaches a steady-state value due to the combined effects of the generation and annealing of color centers. At a given dose rate, these steady state values decrease with increasing temperature due to the corresponding increase in the annealing rate. Above a dose rate of 0·4 Mrad/sec the steady-state absorption coefficient decreases with increasing dose rate due to radiation annealing. A mathematical model describing the temporal behavior of the C-band absorption during irradiation is also presented.