Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: Randall Osczevski x
  • Refine by Access: All Content x
Clear All Modify Search
Randall Osczevski

With an average temperature of −63°C and winter lows of −120°C, Mars sounds far too cold for humans. However, thermometer readings from Mars are highly misleading to terrestrials who base their expectations of thermal comfort on their experience in Earth's much thicker atmosphere. The two-planet model of windchill described here suggests that Martian weather is much less dangerous than it sounds because in the meager atmosphere of Mars, convection is a comparatively feeble heat transfer mechanism. The windchill on Mars is expressed as the air temperature on Earth that produces the same cooling rate in still air, in Earth's much denser atmosphere. Because Earth equivalent temperature (EET) is identical to the familiar wind chill equivalent temperature (WCET) that is broadcast across much of North America in winter, it provides a familiar context for gauging the rigors of weather on another planet. On Earth, WCET is always lower than the air temperature, but on Mars the equivalent temperature can be 100°C higher than the thermometer reading. Mars is much colder for thermometers than for people. Some frontier areas of Earth are at least as cold as midlatitude Mars is, year round. Summer afternoons in the tropics of Mars might even feel as comfortable as an average winter day in the south of England. Sunshine on Mars should be about as warm as it is on Earth. Heat balance and clothing emissivity are also briefly discussed.

Full access
Randall J. Osczevski

Wind chill equivalent temperatures calculated from a recent vertical cylinder model of wind chill are several degrees colder than those calculated from a facial cooling model. The latter was based on experiments with a heated model of a face in a wind tunnel. Wind chill has sometimes been modeled as the overall heat transfer from the surface of a cylinder in cross flow, but such models average the cooling over the whole surface and thus minimize the effect of local cooling on the upwind side, particularly at low wind speeds. In this paper, a vertical cylinder model of wind chill has been modified so that just the cooling of its windward side is considered. Wind chill equivalent temperatures calculated with this new model compare favorably with those calculated by the facial cooling model.

Full access
Randall Osczevski and Maurice Bluestein
Full access
Randall Osczevski and Maurice Bluestein

The formula used in the U.S. and Canada to express the combined effect of wind and low temperature on how cold it feels was changed in November 2001. Many had felt that the old formula for equivalent temperature, derived in the 1960s from Siple and Passel's flawed but quite useful Wind Chill Index, unnecessarily exaggerated the severity of the weather. The new formula is based on a mathematical model of heat flow from the upwind side of a head-sized cylinder moving at walking speed into the wind. The paper details the assumptions that were made in generating the new wind chill charts. It also points out weaknesses in the concept of wind chill equivalent temperature, including its steady-state character and a seemingly paradoxical effect of the internal thermal resistance of the cylinder on comfort and equivalent temperature. Some improvements and alternatives are suggested.

Full access
Peter Tikuisis and Randall J. Osczevski

A dynamic model of facial cooling was developed in conjunction with the release of the new wind chill temperature (WCT) index, whereby the WCT provides wind chill estimates based on steady-state considerations and the dynamic model can be used to predict the rate of facial cooling and particularly the onset of freezing. In the present study, the dynamic model is applied to various combinations of air temperature and wind speed, and predictions of the resultant steady-state cheek skin temperatures are tabulated. Superimposed on these tables are times to a cheek skin temperature of 10°C, which has been reported as painful, and times to freezing. For combinations of air temperature and wind speed that result in the same final steady-state cheek temperature or the same WCT, the initial rate of change of skin temperature is higher for those combinations having higher wind speeds. This suggests that during short exposures, high winds combined with low temperatures might be perceived as more stressful than light winds with lower temperatures that result in the same “wind chill.” This paper also discloses the paradox that individuals having a low cheek thermal resistance are predicted to experience a more severe WCT, but be at less risk of cooling injury than individuals with higher thermal resistances. The advantages of cooling- time predictions using the dynamic model are discussed with the recommendation/conclusion that safe exposure limits are more meaningful and less ambiguous than the reporting of the WCT.

Full access
Peter Tikuisis and Randall J. Osczevski

Abstract

Recent modifications to windchill forecasting have motivated the development of a rate-of-tissue-cooling model for the purpose of predicting facial cooling times. The model assumes a hollow cylindrical geometry with a fixed internal boundary temperature and adherence to the dimensions and tissue thermal properties of the cheek. Convective and radiative heat exchanges at the skin surface are also taken into account. The explicit finite-difference solution of the thermal conduction problem was applied to predict the transient temperature profile in the cheek model, composed of 25 concentric annular compartments with equally spaced nodes. Model predictions compare favorably to reported incidents of facial frostbite and to several laboratory studies on facial cooling. A sensitivity analysis demonstrates the effect of varying the values of tissue thermal resistance and cheek dimensions on the predicted facial cooling rate.

Full access