Sub-zero Ambient Temperatures Research Articles

The relationship between ambient temperature and match running performance of elite soccer players.

The influence of environmental factors on key physical parameters of soccer players during competitive match-play have been widely investigated in the literature, although little is known on the effects of sub-zero ambient temperatures on the performance of adult elite soccer players during competitive matches. The aim of this study was to assess how the teams' match running performance indicators are related to low ambient temperature during competitive matches in the Russian Premier League. A total of 1142 matches played during the 2016/2017 to 2020/2021 seasons were examined. Linear mixed models were used to assess the relationships between changes in ambient temperature at the start of the match and changes in selected team physical performance variables, including total, running (4.0 to 5.5 m/s), high-speed running (5.5 to 7.0 m/s) and sprint (> 7.0 m/s) distances covered. The total, running and high-speed running distances showed no significant differences across temperatures up to 10°C, while these showed small to large decreases at 11 to 20°C and especially in the >20°C ranges. On the contrary, sprint distance was significantly lower at temperature of -5°C or less compared to higher temperature ranges. At sub-zero temperatures, every 1°C lower reduced team sprint distance by 19.2 m (about 1.6%). The present findings show that a low ambient temperature is negatively related to physical match performance behavior of elite soccer players, notably associated with a reduced total sprint distance.

Efficient and stable subzero operation of a PEM fuel cell with a composite anode using hydrogen-methanol composition during freeze/thaw cycles

The present research deals with the adaptation of hydrogen-air fuel cells with proton exchange membrane (PEMFC) to autonomous periodic operation at subzero ambient temperatures. The main goal of the research is to limit the influence of subzero temperatures on component integrity and electrochemical performance stability of PEMFC in the cause of the freeze-thaw (F/T) cycling test. The MEAs stability in cycling from subzero (−35 °C) to operating temperature (+35 °C) was ensured without any specific preparatory operations modeling the PEMFC stop and “cold start” procedure. This is provided through the use of hydrogen-methanol compositions (no more than 4 vol % of methanol vapor) as fuel and a composite anode. Advanced membrane-electrode assembly (MEA) based on the composite anode layer (Pt 40 /C + Pt 20 /10 wt%–SnO 2 /C) for efficient and stable subzero operation during F/T cycling. High stability of electrochemical performance of the MEA with the composite anode at subzero ambient temperatures is shown. Advantages of use a two-component fuel PEMFC for autonomous periodic operation at subzero ambient temperatures are highlighted. • The hydrogen-methanol composition is applied as a fuel for cold start procedure. • Efficiency of two-component anode in methanol vapor oxidation has been proven. • Stability of fuel cell electrochemical performance at subzero temperatures is ensured.

The influence of thermal pressure on the catalytic properties of SHS converter blocks during pre-start preparation of a diesel engine

The study is aimed at solving the important environmental problem of reducing harmful exhaust gas emissions from diesel engines with pre-heaters when operating at subzero ambient temperatures. The issue of cleaning the exhaust gases of the pre-heater in the catalytic converter during the heating of the catalytic units during the pre-start preparation period of the 8Ch12/12 diesel engine is considered. It was found that an increase in the specific heat flow and volumetric thermal gas pressure on the porous SHS catalytic material leads to an improvement in catalytic properties in exhaust gas purification processes. An increase in heat flow from 1589 to 3807 mJ/(m3×h) led to a decrease in the estimated values of harmful emissions: nitrogen oxides – by 1.6 times; carbon monoxide – 1.9 times; hydrocarbons – 1.23 times; solid particles - 2.1 times. It was revealed that when the exhaust gas temperature changed from 650 to 810 K, the efficiency of cleaning from solid particles increased from 50 to 75%, from nitrogen oxides - from 20 to 83%, and carbon monoxide - from 53 to 75%. An increase in the quality of hydrocarbon purification is noted up to 790 K; the quality of purification changes from 32 to 47%.

Effect of ambient temperature, metabolic heat and clothing insulation on the required external active heating for the survival of humans exposed to sub-zero temperatures

Active heating in extremely cold weather clothing would be useful to save the life of an injured or sick person due to low metabolic rate. A fully dressed thermal manikin is useful in evaluating the performance of the active heating ensemble. The thermal manikin tests are time-consuming and could be done only after making the complete ensemble. An experiment that is designed to evaluate the performance of an active heating fabric fixed to a set of layers of extreme cold climate clothing using a guarded hot plate instrument would save a lot of time as it skips the processes of garmenting and subsequent evaluation on the thermal manikin. In this work, a guarded hot plate placed inside a cold chamber is used to investigate the external heating required for the prolonged comfort of the wearer at various sub-zero ambient temperatures, clothing insulation and metabolic heat. A plain woven active heating fabric sandwiched between a knitted fabric and nonwoven of different insulation/thickness is used to perform experiments. The external heat required to keep the test plate (representing the human skin) at 307 ± 1 K (34 ± 1 °C) is measured at different experimental conditions. Further, a one-dimensional numerical model based on coupled conduction–radiation heat transfer with heat generation was developed and validated with experimental results. The experimental temperature profiles match well with the numerical temperature profiles at different locations, justifying the numerical methodology adopted in this work. This suggests that the developed numerical model would also be useful to estimate the required active heating as per the wearer’s requirement and an available power source. Both the experimental and numerical results suggest that the external active heating required to maintain test plate (skin) temperatures within the human skin comfortable range is a function of ambient temperature, metabolic heat and clothing (nonwoven) insulation.

Hybrid Battery Thermal Management System with NiTi SMA and Phase Change Material (PCM) for Li-ion Batteries

Poor heat dissipation and thermal runaway are most common in batteries subjected to fast charge or discharge and forced to work in hot or subzero ambient temperatures. For the safe operation of lithium-ion batteries throughout their lifecycle, a reliable battery thermal management system (BTMS) is required. A novel hybrid BTMS with a nickel-titanium (NiTi) shape memory alloy (SMA) actuated smart wire and phase change material (PCM) with expanded graphite (EG) is proposed in this study. A lumped electrochemical-thermal battery model is developed to analyze the efficiency of the proposed hybrid BTMS. The multiphysics BTMS is investigated by discharging at various electrical currents in both off-modes (inactivated SMA) and on-modes (activated SMA). Under on-mode BTMS operation, temperature elevation is reduced by 4.63 °C and 6.102 °C during 3 C and 5 C discharge, respectively. The proposed hybrid BTMS can be considered a competitive alternative for use in electrical vehicles due to its smart, compact, safe, and efficient performance in both cold and hot environments.

ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ТЕПЛОВИХ ХАРАКТЕРИСТИК ЛІТІЙ-ІОННИХ АКУМУЛЯТОРІВ

The work gives a detailed description of lithium-ion batteries and methods of their use in technical devices of various purposes. The basic technical characteristics of the main types of industrial lithium batteries are presented and it is shown that lithium-iron-phosphate, lithium-titanate and lithium-carbon-titanate batteries are currently used in autonomous electric vehicles. The work also analyzed the results of bench tests of lithium-titanate and lithium-carbon-titanate batteries in terms of their temperature state at different values of external temperature and different levels of charge-discharge currents. The results of the tests showed the limit values of the battery heating temperature, as well as a change in the charging process at sub-zero ambient temperatures, which requires the necessary measures - cooling or heating - when assembling the traction battery from the tested elements. Bibl. 8, figure, table 12.

Calculation of the temperature fields spread at subzero temperature in a monolithic beam

Monolithic construction in winter is faced with problems of concrete strength gain at subzero ambient temperatures. In order to ensure the necessary temperature conditions for hardening and hardening of concrete, various methods of heating structures are used. The relevance of this article is due to the climatic conditions of construction in most of the Russian territory and lack of a unified calculation method. The existing calculation methods are either easy to use, but give approximate answers, or exact solutions, but cumbersome and inconvenient in daily use. This paper presents group analysis method of differential equations used to predict temperature regimes for concreted structures. Solving the nonlinear differential equation of thermal conductivity by group analysis made it possible to derive, using nonlinear submodels, simple and convenient for practical application calculation formulas for modeling the temperature fields of heated structures. Experimental verification of the two proposed solutions of the nonlinear equation was carried out on the basis of the monolithic girder model, subjected to heat treatment at different powers.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Electrochemical Modeling and Simulation of Battery Systems: Approaches for Design, Control, and Multiscale Simulations

Current imperatives of electrification and decarbonization entail significant improvements in energy density, performance, and cost metrics for battery technology.1 This has motivated active research into new materials, cell designs, and external controls to ensure safe and efficient operation. Modeling and simulation approaches have a powerful complementary function in this regard, most notably exemplified by the models for Lithium-ion batteries by Newman and co-workers.2 The overarching theme of this talk is thus the development and application of electrochemical modeling approaches at multiple scales in problems relevant to the abovementioned contexts.In the development of next-generation chemistries, continuum models can serve as a framework for the analysis and interpretation of experimental data, while providing design guidance and helping determine desirable operating regimes. Electrochemical phenomena at different length and time scales are manifested during operation through voltage and temperature signatures, cycle life, and coulombic efficiency. Optimization of cell-level metrics is thus predicated on their correlation with the internal electrochemistry.3,4 This entails the integration of electrochemical models at different levels of detail in a computationally efficient and robust manner. To this end, the first part of this talk describes our efforts to develop a unified, multiscale continuum simulation for framework Lithium-metal batteries. We first describe a robust computational framework to simulate Poisson Nernst Planck (PNP) models for Lithium symmetric cells characterized by thin double layers. This can be leveraged in applications where computational efficiency is of salience, such as cycling simulations and parameterization by coupling kinetic models of interest. This is demonstrated by a systems level method, enabling the quick evaluation of candidate mechanisms appropriately expressed as time-varying rate constants, making it useful for understanding the phenomena underpinning voltage transitions in Lithium symmetric cells.5 In a second study, we leverage these computational tools to propose an alternate mechanism for voltage signatures stemming from the interplay of transport and kinetic limitations, which is of relevance in transport-limited symmetric cells used in fundamental studies.6 We then describe the integration of electrochemical models of various levels of detail, evaluating computational approaches for numerical challenges associated with simulating moving interfaces and mechanical deformations.7 We expect this approach to advance fundamental understanding and design of Li-metal batteries, while creating accessible computational tools to complement experimental studies.At the systems level, the development of more intelligent and powerful Battery Management Systems is enabled by fast electrochemical models, which must balance competing considerations of accuracy, computational efficiency, and ease of parameterization. To this end, we report a rigorous and generalized methodology for ‘upscaling’ electrochemical models.8 This approach, based on the visualization of a battery as Tanks-in-Series, has been demonstrated for both Lithium-ion and more complex Lithium-sulfur batteries.9 With respect to full models, voltage prediction errors below 20 mV are achieved for high-energy cells in most practical cases. <30 mV errors are achieved for aggressive conditions of high-rate operation at sub-zero ambient temperatures, illustrating their practical utility. This approach results in improved computational speed since each conservation law is replaced by a relatively simple volume-averaged differential or algebraic equation. For examples of large-scale problems, this leads to >10x savings in computation time over fast implementations of conventional models, illustrating competitiveness for real-time applications.Taken together, these contributions are envisaged to advance the knowledge base for model-based design as well as Battery Management Systems, particularly in anticipation of the commercialization of emerging battery chemistries. AcknowledgmentsThe authors are thankful for financial support by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program (Battery500 Consortium). References J. Deng, C. Bae, A. Denlinger, and T. Miller, Joule, 4, 511 (2020).M. Doyle, T. F. Fuller, and J. Newman, J. Electrochem. Soc., 140, 1526 (1993).K. N. Wood, M. Noked, and N. P. Dasgupta, ACS Energy Lett., 2, 664 (2017).G. Li and C. W. Monroe, Annu. Rev. Chem. Biomol. Eng., 11, 277 (2020).A. Subramaniam, J. Chen, R. M. Kasse, M. F. Toney, T. Jang, and N. R. Geise, J. Electrochem. Soc., 166, A3806 (2019).M. Uppaluri, A. Subramaniam, L. Mishra, V. Viswanathan, and V. R. Subramanian, J. Electrochem. Soc., in press (2020).K. Shah, A. Subramaniam, L. Mishra, T. Jang, M. Z. Bazant, R. D. Braatz, and V. R. Subramanian, J. Electrochem. Soc., 167 (2020).A. Subramaniam, S. Kolluri, C. D. Parke, M. Pathak, S. Santhanagopalan, and V. R. Subramanian, J. Electrochem. Soc., 167, 013534 (2020).C. D. Parke, A. Subramaniam, S. Kolluri, D. T. Schwartz, and V. R. Subramanian, J. Electrochem. Soc., 167, 163503 (2020).

Electrochemical-thermal modeling of lithium plating/stripping of Li(Ni0.6Mn0.2Co0.2)O2/Carbon lithium-ion batteries at subzero ambient temperatures

Electrochemical performance of lithium-ion batteries drops significantly at low temperatures, especially under charging, because the lithium ions are prone to deposit as lithium metal on instead of intercalating into the solid matrix of anode. At discharging, the existence of lithium stripping leads to the capacity reversed partially, whose amount is proportional to the width of extra voltage plateau displayed at the beginning. A physics-based electrochemical-thermal model considering effects of lithium plating/stripping is developed and validated to explore the degradation mechanism and behaviors of NMC/Carbon cells undergoing prolonged cycling. The temporal and spatial analyses of overpotential of lithium plating and surface concentration in solid phase at various operating conditions demonstrate that lithium plating starts to take place at the interface between composite anode and separator, and the degradation can be accelerated by the decreasing ambient temperatures and increasing charging current rates. The degradation effects including loss of recyclable lithium ions, loss of anode active material, growth of plated lithium and secondary solid electrolyte interphase (SEI) and consumption of electrolyte solvents are considered. The model is capable of estimating capacity as a function of cycle number with an overall accuracy of 3% if the capacity fade is less than 30%.

Atypical biological features of a new cold seep site on the Lofoten-Vester\xe5len continental margin (northern Norway)

A newly discovered cold seep from the Lofoten-Vesterålen margin (Norwegian Sea) is dominated by the chemosymbiotrophic siboglinid Oligobrachia haakonmosbiensis like other high latitude seeps, but additionally displays uncharacteristic features. Sulphidic bottom water likely prevents colonization by cnidarians and sponges, resulting in fewer taxa than deeper seeps in the region, representing a deviation from depth-related trends seen among seeps elsewhere. O. haakonmosbiensis was present among carbonate and barite crusts, constituting the first record of frenulates among hard substrates. The presence of both adults and egg cases indicate that Ambylraja hyperborea skates use the site as an egg case nursery ground. Due to sub-zero ambient temperatures (−0.7 °C), we hypothesize that small, seepage related heat anomalies aid egg incubation and prevent embryo mortality. We place our results within the context of high–latitude seeps and suggest they exert evolutionary pressure on benthic species, thereby selecting for elevated exploitation and occupancy of high-productivity habitats.

Low-Temperature Deposition Modeling of β-TCP Scaffolds with Controlled Bimodal Porosity.

Low-temperature deposition modeling (LDM), otherwise termed freeze-form extrusion fabrication or rapid freeze prototyping, involves dispensing an aqueous-based ceramic paste or polymeric hydrogel along predefined paths in subzero ambient temperatures, followed by freeze-drying. The solidification of the material after the deposition of each layer enables large parts to be built without the need for organic binders, which can often have cytotoxic effects. Freeze-dried parts obtained from LDM typically exhibit pores with openings that range in average between 1 and 40μm. The technique offers the ability to control their size distribution and orientation through varying a number of processing and material parameters. Herein, we describe the construction of an LDM system from readily available electromechanical components, as well as the preparation of a β-ΤCP paste formulation with the appropriate flow characteristics for fabricating hierarchical scaffolds with tailorable bimodal porosity for applications in bone tissue engineering.

Avian torpor or alternative thermoregulatory strategies for overwintering?

It is unclear whether torpor really is uncommon amongst passerine birds. We therefore examined body temperature and thermoregulatory strategies of an Austral passerine, the white-browed babbler (Pomatostomus superciliosus), which has characteristics related to a high probability of torpor use; it is a sedentary, insectivorous, cooperative breeding species, which we studied during winter in a temperate habitat. Wild, free-living babblers maintained normothermy overnight, even at sub-zero ambient temperatures, with a mean minimum body temperature of 38.5±0.04°C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a low basal metabolic rate and evaporative water loss, but their body temperature and thermal conductance were typical of those of other birds and they had a typical endothermic response to low ambient temperature. Huddling yielded significant energy savings at low temperatures and a roost nest created a microclimate that buffered against low temperatures. Low basal energy requirements, communal roosting and the insulation of a roost nest confer sufficient energetic benefits, allowing babblers to meet energy requirements without resorting to heterothermia, even in their depauperate, low-productivity landscape, suggesting that passerine birds use alternatives to torpor to balance their energy budgets when possible.

Sub-zero temperature thermo-electrochemical energy harvesting system using a self-heating negative temperature coefficient CNT-vanadium oxide cathode

In this study, we report for the first time a simple method that directly converts heat into electrical energy at sub-zero ambient temperatures. The thermo-electrochemical cell was constructed with negative temperature coefficient (NTC) carbon nanotube-vanadium oxide (CNT-VO x ) self-heating cathode, which provided thermal energy through an induced Joule effect. The electrical energy was obtained by creating in situ temperature difference between the electrodes (ΔT) and with subsequent redox reactions. A decrease in the cell resistance with an increase in the ΔT, and enhanced electrical energy conversion through a charge-transfer mechanism (i.e., Faradaic redox reaction) was observed. In addition, the advantage of using NTC CNT-VO x cathode as a self-heating source at various ΔT (i.e., without the support of any external source) in a thermo-electrochemical system for sub-zero temperature energy conversion is presented.

Risk-based winterization to prevent hydrate formation in northern harsh environment

With the increasing demand for energy around the globe, hydrocarbon explorations move towards the Arctic region that holds a majority of unexploited oil reserves. The harsh environmental conditions with sub-zero ambient temperatures and high winds demand winterization techniques for pipes, instruments and equipment to carry out uninterrupted plant operations. The natural phenomenon: hydrate formation, is considered to be a major flow assurance problem starting from the wellhead through the final point in the delivery system which could be addressed through winterization. Developing winterization strategies for arctic conditions is a challenging task demanding rigorous and robust approaches. Risk-based winterization is a novel approach, adapted for vessels operating in arctic environments. In this paper a new model is proposed to calculate the probability of hydrate formation and its associated risk for a given loading scenario. The winterization requirement is determined based on the estimated risk. Two case studies presented here demonstrate the applicability of the proposed model and compare several winterization methods to find an optimal solution.

Modeling the hydrodynamics of heap leaching in sub-zero temperatures

Heap leaching involves the application of a leach solution onto stacked low grade ores. Solution percolates through the ore, dissolving metals from various minerals, and is recovered at the base. This process is conceptually a simple one, but quickly becomes complex when considering the sub-processes, such as dissolution chemical reactions, oxidation, precipitation, ore with different leaching characteristics, and multi-lift heaps with dynamically changing irrigation schemes.In addition, changing meteorological conditions, such as heavy rain, evaporation and extreme ambient temperatures have a significant effect on the hydrodynamics. Various factors, such as large variations in ore hydraulic properties, saturated–unsaturated flow, preferential flow pathways, perched water tables, infiltration into dry ore or possible freezing of solution within the heap, can lead to reduced leaching efficiency.This contribution describes the methods employed within a computational fluid dynamics heap leach model to account for freezing climate conditions. Validation of one-dimensional thermal phase change is performed and a theoretical column of coarse and fine ore is partially frozen to illustrate how the preferred flow path can be counter-intuitive. Finally, a three-dimensional heterogeneous gold oxide ‘test’ heap is simulated assuming non-thermal reactions and sub-zero ambient temperatures. The results demonstrate how recovery can be affected by cold weather changing the hydrodynamics of the heap.

Numerical investigation of thermal behaviors in lithium-ion battery stack discharge

Thermal management is critically important to maintain the performance and prolong the lifetime of a lithium-ion (Li-ion) battery. In this paper, a two-dimensional and transient model has been developed for the thermal management of a 20-flat-plate-battery stack, followed by comprehensive numerical simulations to study the influences of ambient temperature, Reynolds number, and discharge rate on the temperature distribution in the stack with different cooling materials. The simulation results indicate that liquid cooling is generally more effective in reducing temperature compared to phase-change material, while the latter can lead to more homogeneous temperature distribution. Fast and deep discharge should be avoided, which generally yields high temperature beyond the acceptable range regardless of cooling materials. At low or even subzero ambient temperatures, air cooling is preferred over liquid cooling because heat needs to be retained rather than removed. Such difference becomes small when the ambient temperature increases to a mild level. The effects of Reynolds number are apparent in liquid cooling but negligible in air cooling. Choosing appropriate cooling material and strategy is particularly important in low ambient temperature and fast discharge cases. These findings improve the understanding of battery stack thermal behaviors and provide the general guidelines for thermal management system. The present model can also be used in developing control system to optimize battery stack thermal behaviors.

An experimental feasibility study of vanadium oxide films on metallic bipolar plates for the cold start enhancement of fuel cell vehicles

An experimental study of vanadium oxide polycrystalline films deposited onto 316L stainless steel bipolar plates as an efficient Joule heating source for fuel cell vehicles was conducted by carefully modulating the negative temperature coefficients of the electrical resistance of the films at subzero temperatures. To fabricate the thin films, a well-mixed precursor solution of vanadium alkoxide and organic cosolvent was prepared by the hydrolytic sol-gel route and then coated on the pre-cleaned flat surface of 316L stainless steel plates with natural passive oxide layers by a dip-coating method. Subsequently, the variation of the nonlinear electrical resistance of the thin film was measured simultaneously over a wide temperature range of −20 to 80 °C, allowing direct detection of the surface temperature of the thin films. In addition, the adhesion, microstructures, compositions, and morphologies of the vanadium oxide thin films were investigated using the ASTM D3359 method, XRD, FE-SEM, and XPS analyses. A remarkable result from this study was that a temperature increase of 41.65 °C was induced by significant Joule heating of the vanadium sesquioxide films on metallic bipolar plates, i.e. approximately 1.8-folded more than the minimum requirement of Joule heating, at a current density of 0.1 A·cm −2 at −20 °C. Thus, it was concluded that thermal dissipation from the resistive vanadium oxide films with a negative temperature coefficient can be effectively used as a self-heating source to melt frozen water at subzero ambient temperatures, particularly for fuel cell vehicles.

Thermal Calculation of the Operation of an Insulated Water Pipe at Subzero Ambient Temperatures

Thermal Calculation of the Operation of an Insulated Water Pipe at Subzero Ambient Temperatures

Foraging strategies of Great Cormorants Phalacrocorax carbo carbo wintering north of the Arctic Circle

This study describes how 30 Great Cormorants Phalacrocorax carbo carbo managed to catch sufficient food for their daily energetic needs under conditions of reduced daylight and cold while wintering north of the Arctic Circle. Activity observations showed that the Great Cormorants' daily foraging pattern was generally bimodal, with morning and evening feeding peaks. They compensated for shorter daylengths in midwinter by starting to forage later and ending progressively earlier at lower light intensities. Fishing constituted only a minor part of their time–activity budget, and was one of the most efficient reported in marine birds. The Great Cormorants spent less than 60 minutes a day fishing in midwinter. Although subzero ambient temperatures and blizzards contributed to increased heat loss in midwinter, this potential energy loss did not seem to be compensated for by an increase in fish intake. Instead the Great Cormorants seemed to economize energy expenditure by halving the time spent at sea, and halving the number but doubling the mass of each fish taken.

Some aspects of thermoregulation in newborn reindeer calves (Rangifer tarandus tarandus).

At birth reindeer calves often are exposed to sub-zero ambient temperatures (Ta) sometimes even combined with wind and precipitation. The resting metabolism was measured in three different age groups (1, 7 and 14 days old) at Ta's of -20, -5, 10 and 20 degrees C. Resting metabolism in the thermoneutral zone decreased from 5.1 W X kg-1 at day 1 and 7 to 4.8 W X kg-1 at day 14. At day 1 apparent lower critical temperature (Tlc) was 11 degrees C, while at day 7 it was 7.7 degrees C and at day 14 7.3 degrees C, but total body conductance continued to decrease below apparent Tlc. At Ta's of -5 and -20 degrees C total body conductance was: 0.77 and 0.72 W X degrees C-1 at day 1, 0.98 and 0.92 W X degrees C-1 at day 7, 1.08 and 0.91 W X degrees C-1 at day 14, respectively. Thermal conductance of pelt samples from the trunk was determined in vitro at different combinations of windspeed, Ta and wetness. The conductance of dry fur increased from 5.9 to 11.8 W X m-2 X degrees C-1 at a windspeed of 0 and 10 m X s-1, respectively, as compared to 28.7 W X m-2 X degrees C-1 when wetted without wind. Newborn reindeer calves seem to be heavily dependent on non-shivering thermogenesis in brown adipose tissue for their cold defence since deep body temperature in a calf subjected to propranolol infusion when exposed to a Ta of -25 degrees C in combination with a 10 m X s-1 windspeed increased its cooling rate five times.