Search results for "Temperature difference"

Mapping Actual Evapotranspiration by Combining Landsat TM and NOAA-AVHRR Images: Application to the Barrax Area, Albacete, Spain

1998

Abstract A method that permits determination of actual evapotranspiration, ET, in heterogeneous areas has been proposed. It is based on the relation ET = ET m − B ( T s − T sm ), which combines meteorological, National Oceanic and Atmospheric Administration advanced very high resolution radiometer (NOAA-AVHRR), and Landsat thematic mapper (TM) data. Thus, the maximum evapotranspiration for each crop, ETm, is obtained from in situ measurements carried out in a meteorological station; the temperature difference between each pixel and the pixel that has the maximum evapotranspiration, Ts−Tsm, is calculated for each crop from NOAA-AVHRR data; and the crop distribution in the area is known throu…

2015

Abstract. Long term meteorological records (> 100 years) from stations associated with villages are generally classified as rural and assumed to have no urban influence. Using networks installed in two European villages, the local and microclimatic variations around two of these rural-village sites are examined. An annual average temperature difference ($\\Delta{T}$) of 0.6 and 0.4 K was observed between the built-up village area and the current meteorological station in Geisenheim (Germany) and Haparanda (Sweden), respectively. Considerably larger values were recorded for the minimum temperatures and during summer. The spatial variations in temperature within the villages are of the sam…

PERFORMANCE EVALUATION OF CASCADE REFRIGERATION SYSTEMS USING DIFFERENT REFRIGERANTS

2012

Due to the negative effects of synthetic refrigerants on the environment, natural refrigerants have obtained again interest as alternative refrigerants for different applications because of their zero ODP and negligible GWP. This paper presents a thermodynamic analysis of different two-stage cascade refrigeration systems using as refrigerant carbon dioxide (R744) in low-temperature circuit, and, respectively, ammonia (R717), propane (R290), butane (R600), R404A, R410A and R134a in high-temperature circuit. The operating parameters considered in this study include condensing and evaporating temperatures in high-temperature circuit, temperature difference in the cascade heat exchanger, and e…

Estimating Maize (Zea mays) cvapotranspiration from NOAA-AVHRR thermal data in the Albacete area, Spain

1994

Abstract We have estimated evapotranspiration from maize (Zca mays) using NOAA thermal images infrared and meteorological data, by means of the relation where Ed is the daily evapotranspiration, is the daily net radiation expressed in mm of water per day, (Ta−Ts)i is the temperature difference between air and corn surface obtained near midday, and Bi is a semi-empirical constant which has been calculated as 0·53±0·10mm day−1K−1. We have tested the method obtaining actual daily evapotranspiration of maize with an acceptable precision (±0·9 mm day−1 taken Penman's method as the standard). Finally, a practical example is included, in which the different steps followed for applying the develope…

On the solution growth of single crystals of solid solutions

1986

Abstract Homogeneous solid solution crystals are needed for studying the behaviour of systems with a glass state or incommensurate phases. A simple solution growth procedure is described. It is based on a temperature difference growth method with thermally enforced convection and the use of equilibrated solid and liquid solutions. First results of its application to the [(CH3)4N]2ZnCl 4−xBrx and the Rb1−x(NH4)xH2PO4 systems are presented.

Wall assemblies U-value calculation in test buildings using constant power heating

2018

Abstract Building envelopes under various climates behave differently, in this paper the actual thermal transmittance or U-value of five different wall assemblies are evaluated and compared with values, calculated using standard EN ISO 6946. The experiment is carried out in five test buildings with equal spatial orientation, the same ceiling and floor assemblies as well as the same windows and doors mounted in each building. The thermal transmittances for these partitions are assumed to be well known and therefore, by knowing temperature difference and heat sources inside the building, the thermal transmittance of wall assembly can be calculated. It is shown that for small buildings the cor…

Weakening of annual temperature cycle over the Tibetan Plateau since the 1870s

2017

The annual cycle of extra-tropical surface air temperature is an important component of the Earth's climate system. Over the past decades, a reduced amplitude of this mode has been observed in some regions. Although attributed to anthropogenic forcing, it remains unclear when dampening of the annual cycle started. Here we use a residual series of tree-ring width and maximum latewood density from the Tibetan Plateau >4,000 m asl to reconstruct changes in temperature seasonality over the past three centuries. The new proxy evidence suggests that the onset of a decrease in summer-to-winter temperature difference over the Tibetan Plateau occurred in the 1870s. Our results imply that the influen…

A methodology for obtaining the crop temperature from NOAA-9 AVHRR data

1991

Abstract In this paper a methodology for obtaining the crop temperature from NOAA-9 AVHRR data has been developed, which is based on a theoretical model that permits interpreting the remote sensing temperature measurement in heterogeneous and rough surfaces. This procedure determines the crop temperature by evaluating prsviously: (1) the temperature difference between crop and ground, (2) the atmospheric and emissivity corrections, (3) the ground and vegetation emissi-vities in the AVHRR bands 4 (10-3-11-3 μm) and 5 (11 -5-12-5 μm), and (4) the proportion of ground in each pixel. We have applied this method to obtain a map of orange-tree temperatures for the Valencian region and satisfactor…

Measurement of the Convective Heat-Transfer Coefficient

2014

We propose an experiment for investigating how objects cool down toward the thermal equilibrium with its surrounding through convection. We describe the time dependence of the temperature difference of the cooling object and the environment with an exponential decay function. By measuring the thermal constant tau, we determine the convective heat-transfer coefficient, which is a characteristic constant of the convection system.

On lead-scandium tantalate solid solutions with high electrocaloric effect

1992

Abstract The PbSc0,5Ta0,5O3 solutions are found to be a useful material for active elements of microcryogenic devices based on electrocaloric effect. A temperature difference of ΔT = 1. 0-1.8 K at field intensities 20–30 kV/cm in the interval of 210–310 K can be achieved by simultaneous or separate introducing of Sb and Co ions in B-sites of the lattice. The most important contribution to the electrocaloric effect is due to field-induced Fn3m → R3m phase transition in the case of high ordering of B-ions in the perovskite structure ABO3.