An Accurate and Simple Approach to Allow for the Transient Temperature Gradient in a Vaporizing Droplet

2012 ◽  
Author(s):  
Alexander Snegirev ◽  
Victor Talalov
Keyword(s):  
Temperature Gradient ◽  
Life Time ◽  
Droplet Evaporation ◽  
Transient Temperature ◽  
Internal Temperature ◽  
Ambient Temperatures ◽  
Wide Range ◽  
Order Polynomial ◽  
Volatile Liquid ◽  
Evaporation Dynamics

The purpose of this work is to analyze the importance of considering internal temperature gradient in modeling droplet evaporation, and to demonstrate performance of simplified methods in which the temperature gradient is approximately taken into account. Based on three characteristic time scales, two dimensionless criteria have been identified which determine magnitude of the internal temperature gradient and its effect on the evaporation dynamics. Numerical values of these criteria in a wide range of ambient temperatures show that the effect of the internal temperature gradient is more pronounced in more volatile liquid at higher ambient temperatures. Although droplet life time predictions are not sensitive to the internal temperature gradient, its effect might be strong at the initial stages of droplet evaporation, and this substantiates the need in robust and computationally inexpensive methods to take it into account. Two simple and yet accurate approaches (quasi-steady higher order polynomial approximation and the integral balance method) have been favourably tested and recommended for use in CFD spray modeling.

Regulated hypothermia in the hypothyroid rat induced by administration of propylthiouracil

1997 ◽  
Vol 272 (5) ◽  
pp. R1390-R1395 ◽  
Author(s):  
Y. Yang ◽  
C. J. Gordon
Keyword(s):  
Drinking Water ◽  
Heat Stress ◽  
Temperature Gradient ◽  
Serum Levels ◽  
Male Rats ◽  
Light Phase ◽  
Grooming Behavior ◽  
Ambient Temperatures ◽  
Wide Range ◽  
The Stability

Propylthiouracil (PTU), an antithyroidal drug that reduces serum L-thyroxine (T4) and 3,5,3'-triiodothyronine (T3), is presumed to lower core temperature (T0) by impairing metabolic thermogenesis. However, it is not understood why PTU-treated animals cannot use behavioral and other thermoeffectors to maintain normal Tc. Male rats were administered PTU in drinking water (0.05 mg/ml) while the following parameters were measured: 1) Tc and motor activity (MA) recorded by radiotelemetry for 24 h at ambient temperatures (Ta) of 10-30 degrees C; 2) selected Ta, MA, and Tc in a temperature gradient; and 3) Tc, MA, and grooming behavior during exposure to heat stress (TH = 34.5 degrees C) for 2 h. PTU reduced serum levels of T4, and T3 by 95 and 60%, respectively. Tc decreased after 3 days of PTU treatment; a 0.5 degree C decrease in Tc persisted throughout the PTU treatment. PTU rats exposed to Ta of 10-30 degrees C maintained a consistent hypothermic Tc during the light phase; however, a deficit in the stability of Tc at night was noted during exposure to 10 degrees C. In the temperature gradient, PTU rats selected warmer Ta, but their Tc was maintained at the same hypothermic levels as observed at fixed Ta values of 15-30 degrees C. Heat stress caused Tc of control rats to increase to 39 degrees C, whereas Tc of the PTU rats was maintained below 38 degrees C. The regulation of Tc at hypothermic levels over a wide range of Ta values and when rats were housed in a temperature gradient indicates that chronic PTU induces a state of regulated hypothermia.

scholarly journals Subcritical and Supercritical Droplet Evaporation within a Zero Gravity Environment; On the Discrepancies between Theoretical and Experimental Results

2009 ◽  
Vol 1 (3) ◽  
pp. 317-338 ◽  
Author(s):  
Hongtao Zhang ◽  
Vasudevan Raghavan ◽  
George Gogos
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Local Maximum ◽  
Droplet Evaporation ◽  
Experimental Results ◽  
Spherically Symmetric ◽  
Transient Effects ◽  
Ambient Temperatures ◽  
Wide Range ◽  
Thermo Physical Properties

A comprehensive axisymmetric numerical model has been developed to study high pressure droplet evaporation. In this model, high pressure transient effects, variable thermo-physical properties and inert species solubility in the liquid-phase are considered. First, the axisymmetric model has been utilized to explain the discrepancy between theoretical and experimental results on microgravity droplet evaporation that has been reported in the literature [J.R. Yang and S.C. Wong, Ref. 35]. In addition, this effort led to a thorough validation of the model against the most extensive microgravity experimental data available in the literature on droplet evaporation. Second, the validated model has been utilized to investigate spherically symmetric droplet evaporation for a wide range of ambient pressures and temperatures. The predictions show that the average droplet evaporation constant decreases with ambient pressure at sub-critical ambient temperatures, becomes insensitive to pressure at ambient temperatures around the critical temperature of the fuel and presents a local maximum while increasing with the ambient pressure at super-critical ambient temperatures.

scholarly journals Three-Dimensional Electro-Thermal Analysis of a New Type Current Transformer Design for Power Distribution Networks

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1792
Author(s):  
Bingbing Dong ◽  
Yu Gu ◽  
Changsheng Gao ◽  
Zhu Zhang ◽  
Tao Wen ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Temperature Field ◽  
Temperature Gradient ◽  
Field Distribution ◽  
Distribution Network ◽  
Current Transformer ◽  
Internal Temperature ◽  
Temperature Field Distribution ◽  
Type Design ◽  
New Type

In recent years, the new type design of current transformer with bushing structure has been widely used in the distribution network system due to its advantages of miniaturization, high mechanical strength, maintenance-free, safety and environmental protection. The internal temperature field distribution is an important characteristic parameter to characterize the thermal insulation and aging performance of the transformer, and the internal temperature field distribution is mainly derived from the joule heat generated by the primary side guide rod after flowing through the current. Since the electric environment is a transient field and the thermal environment changes slowly with time as a steady field under the actual conditions, it is more complex and necessary to study the electrothermal coupling field of current transformer (CT). In this paper, a 3D simulation model of a new type design of current transformer for distribution network based on electric-thermal coupling is established by using finite element method (FEM) software. Considering that the actual thermal conduction process of CT is mainly by conduction, convection and radiation, three different kinds of boundary conditions such as solid heat transfer boundary condition, heat convection boundary condition and surface radiation boundary condition are applied to the CT. Through the model created above, the temperature rise process and the distribution characteristics of temperature gradient of the inner conductor under different current, different ambient temperatures and different core diameters conditions are studied. Meanwhile, the hottest temperature and the maximum temperature gradient difference are calculated. According to this, the position of weak insulation of the transformer is determined. The research results can provide a reference for the factory production of new type design of current transformer.

Droplet Evaporation Dynamics on a Superhydrophobic Surface with Negligible Hysteresis

Langmuir ◽  
2013 ◽  
Vol 29 (34) ◽  
pp. 10785-10795 ◽  
Author(s):  
Susmita Dash ◽  
Suresh V. Garimella
Keyword(s):  
Superhydrophobic Surface ◽  
Droplet Evaporation ◽  
Evaporation Dynamics

Droplet evaporation dynamics on microstructured biphilic, hydrophobic, and smooth surfaces

2021 ◽  
Vol 62 (7) ◽  
Author(s):  
A. Alperen Günay ◽  
Moon-Kyung Kim ◽  
Xiao Yan ◽  
Nenad Miljkovic ◽  
Soumyadip Sett
Keyword(s):  
Droplet Evaporation ◽  
Smooth Surfaces ◽  
Evaporation Dynamics

Fuel Droplet Evaporation in a Supercritical Environment

2002 ◽  
Vol 124 (4) ◽  
pp. 762-770 ◽  
Author(s):  
G. S. Zhu ◽  
S. K. Aggarwal
Keyword(s):  
Experimental Data ◽  
Phase Equilibrium ◽  
Ambient Pressure ◽  
Droplet Surface ◽  
Fuel Vapor ◽  
Phase Solubility ◽  
Liquid Density ◽  
Ambient Temperatures ◽  
Droplet Vaporization ◽  
Wide Range

This paper reports a numerical investigation of the transcritical droplet vaporization phenomena. The simulation is based on the time-dependent conservation equations for liquid and gas phases, pressure-dependent variable thermophysical properties, and a detailed treatment of liquid-vapor phase equilibrium at the droplet surface. The numerical solution of the two-phase equations employs an arbitrary Eulerian-Lagrangian, explicit-implicit method with a dynamically adaptive mesh. Three different equations of state (EOS), namely the Redlich-Kwong (RK), the Peng-Robinson (PR), and Soave-Redlich-Kwong (SRK) EOS, are employed to represent phase equilibrium at the droplet surface. In addition, two different methods are used to determine the liquid density. Results indicate that the predictions of RK-EOS are significantly different from those obtained by using the RK-EOS and SRK-EOS. For the phase-equilibrium of n-heptane-nitrogen system, the RK-EOS predicts higher liquid-phase solubility of nitrogen, higher fuel vapor concentration, lower critical-mixing-state temperature, and lower enthalpy of vaporization. As a consequence, it significantly overpredicts droplet vaporization rates, and underpredicts droplet lifetimes compared to those predicted by PR and SRK-EOS. In contrast, predictions using the PR-EOS and SRK-EOS show excellent agreement with each other and with experimental data over a wide range of conditions. A detailed investigation of the transcritical droplet vaporization phenomena indicates that at low to moderate ambient temperatures, the droplet lifetime first increases and then decreases as the ambient pressure is increased. At high ambient temperatures, however, the droplet lifetime decreases monotonically with pressure. This behavior is in accord with the reported experimental data.

scholarly journals Sesquiterpene emissions from vegetation: a review

2008 ◽  
Vol 5 (3) ◽  
pp. 761-777 ◽  
Author(s):  
T. R. Duhl ◽  
D. Helmig ◽  
A. Guenther
Keyword(s):  
Plant Species ◽  
Emission Rates ◽  
Sample Collection ◽  
Ambient Temperatures ◽  
Relative Contribution ◽  
Environmental Controls ◽  
Weather Events ◽  
Wide Range ◽  
Experimental Protocols ◽  
Selection Of Species

Abstract. This literature review summarizes the environmental controls governing biogenic sesquiterpene (SQT) emissions and presents a compendium of numerous SQT-emitting plant species as well as the quantities and ratios of SQT species they have been observed to emit. The results of many enclosure-based studies indicate that temporal SQT emission variations appear to be dominated mainly by ambient temperatures although other factors contribute (e.g., seasonal variations). This implies that SQT emissions have increased significance at certain times of the year, especially in late spring to mid-summer. The strong temperature dependency of SQT emissions also creates the distinct possibility of increasing SQT emissions in a warmer climate. Disturbances to vegetation (from herbivores and possibly violent weather events) are clearly also important in controlling short-term SQT emissions bursts, though the relative contribution of disturbance-induced emissions is not known. Based on the biogenic SQT emissions studies reviewed here, SQT emission rates among numerous species have been observed to cover a wide range of values, and exhibit substantial variability between individuals and across species, as well as at different environmental and phenological states. These emission rates span several orders of magnitude (10s–1000s of ng gDW-1 h−1). Many of the higher rates were reported by early SQT studies, which may have included artificially-elevated SQT emission rates due to higher-than-ambient enclosure temperatures and disturbances to enclosed vegetation prior to and during sample collection. When predicting landscape-level SQT fluxes, modelers must consider the numerous sources of variability driving observed SQT emissions. Characterizations of landscape and global SQT fluxes are highly uncertain given differences and uncertainties in experimental protocols and measurements, the high variability in observed emission rates from different species, the selection of species that have been studied so far, and ambiguities regarding controls over emissions. This underscores the need for standardized experimental protocols, better characterization of disturbance-induced emissions, screening of dominant plant species, and the collection of multiple replicates from several individuals within a given species or genus as well as a better understanding of seasonal dependencies of SQT emissions in order to improve the representation of SQT emission rates.

Energy intake and fur in summer- and winter-acclimated Siberian hamsters (Phodopus sungorus)

2001 ◽  
Vol 281 (2) ◽  
pp. R519-R527 ◽  
Author(s):  
Alexander S. Kauffman ◽  
Alessandra Cabrera ◽  
Irving Zucker
Keyword(s):  
Food Intake ◽  
Energy Intake ◽  
Ventral Surface ◽  
Phodopus Sungorus ◽  
Ambient Temperatures ◽  
Siberian Hamsters ◽  
Daily Food ◽  
Brown Adipose ◽  
Wide Range ◽  
The Impact

Few studies have directly addressed the impact of fur on seasonal changes in energy intake. The daily food intake of Siberian hamsters ( Phodopus sungorus) was measured under simulated summer and winter conditions in intact animals and those with varying amounts of pelage removed. Energy intake increased up to 44% above baseline control values for approximately 2–3 wk after complete shaving. Increases in food intake varied with condition and were greater in hamsters housed in short than long day lengths and at low (5°C) than moderate (23°C) ambient temperatures. Removal of 8 cm2 of dorsal fur, equivalent to 30% of the total dorsal fur surface, increased food intake, but removal of 4 cm2 had no effect. An 8-cm2 fur extirpation from the ventral surface did not increase food consumption. Food intake was not influenced differentially by fur removal from above brown adipose tissue hot spots. Fur plays a greater role in energy balance in winter- than summer-acclimated hamsters and conserves energy under a wide range of environmental conditions.

Transient Temperature Involving Oscillatory Heat Source With Application in Fretting Contact

2007 ◽  
Vol 129 (3) ◽  
pp. 517-527 ◽  
Author(s):  
Jun Wen ◽  
M. M. Khonsari
Keyword(s):  
Heat Source ◽  
Oscillation Amplitude ◽  
The Body ◽  
Transient Temperature ◽  
Dimensionless Frequency ◽  
Heat Sources ◽  
Infinite Body ◽  
Fitting Method ◽  
Wide Range ◽  
Analytical Expressions

An analytical approach for treating problems involving oscillatory heat source is presented. The transient temperature profile involving circular, rectangular, and parabolic heat sources undergoing oscillatory motion on a semi-infinite body is determined by integrating the instantaneous solution for a point heat source throughout the area where the heat source acts with an assumption that the body takes all the heat. An efficient algorithm for solving the governing equations is developed. The results of a series simulations are presented, covering a wide range of operating parameters including a new dimensionless frequency ω¯=ωl2∕4α and the dimensionless oscillation amplitude A¯=A∕l, whose product can be interpreted as the Peclet number involving oscillatory heat source, Pe=ω¯A¯. Application of the present method to fretting contact is presented. The predicted temperature is in good agreement with published literature. Furthermore, analytical expressions for predicting the maximum surface temperature for different heat sources are provided by a surface-fitting method based on an extensive number of simulations.

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