Wind Chill Model for Facial Temperature Prediction
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Solution Overview
Problem
Existing methods for determining wind chill temperature are inaccurate due to assumptions such as constant skin temperature and incorrect wind velocity reduction, failing to account for altitude, insolation, and metabolic heat generation, leading to subjective and potentially dangerous assessments of cold exposure.
Innovation Solution
A comprehensive wind chill model that calculates wind chill temperature and time to freeze by accounting for altitude, accurate wind velocity at head level, metabolic heat, solar radiation, and evaporation, using equations derived from heat transfer principles to provide a more accurate prediction of facial temperature and exposure time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant skin temperature of 33°C is assumed during skin exposure, then the calculation is simplified, but the predicted wind chill temperatures are colder than actual values
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant skin temperature assumption to a dynamic model where skin temperature varies with exposure time. The skin temperature is calculated as a function of time using the equation Ts(t) = Ta + (Tb - Ta) * exp(-bt), allowing the temperature to evolve dynamically during exposure rather than remaining fixed at 33°C.
Solution Approach 2:
The patent changes the parameter of skin temperature from a fixed value (33°C) to a time-dependent variable. This parameter change allows the model to reflect real physiological responses where skin temperature decreases during cold exposure but does not reach ambient temperature, thereby improving prediction accuracy.
2Adaptability or versatility
If wind speed reduction at head level is assumed to be 50% greater, then the model accounts for boundary layer effects, but the wind chill temperatures are significantly warmer than Siple and Passel values with questionable accuracy
Solution Approach 1:
The patent applies local quality by differentiating wind velocity at different locations. Instead of using a single wind speed value, the model uses V_head = V * (1 - WRF) to represent the reduced wind velocity at head level, where WRF (wind reduction factor) accounts for the boundary layer effect locally at the head position rather than applying a uniform reduction everywhere.
Solution Approach 2:
The patent incorporates feedback by using measured or observed wind chill temperatures to calibrate and adjust the wind reduction factor. The model allows WRF to be determined from experimental data, creating a feedback loop where real-world measurements inform and refine the boundary layer correction parameter.
3Ease of operation
If wind chill temperature is combined with clothing distributions to define comfort level, then individuals can more easily relate to the temperature, but the warmer temperatures sensed by clothed body may mask dangerous frostbite risks to the face
Solution Approach 1:
The patent applies segmentation by separating the wind chill assessment into distinct body regions, specifically focusing on the exposed face rather than averaging over the entire clothed body. The model calculates wind chill temperature specifically for the facial surface, isolating this vulnerable region from the warmer clothed areas to provide targeted frostbite risk assessment.
Solution Approach 2:
The patent introduces the concept of 'exposed surface temperature' as an intermediary metric that bridges between ambient conditions and actual frostbite risk. This intermediary measurement focuses specifically on the temperature of uncovered skin surfaces, serving as a direct indicator of frostbite danger independent of clothing insulation.
4Reliability
If the Siple and Passel model is used for six decades, then it provides a long-standing reference for wind chill, but it lacks theoretical basis and yields primitive and flawed results
Solution Approach 1:
The patent replaces the empirical mechanical approach of Siple and Passel with a thermodynamic model based on heat transfer principles. Instead of using simple empirical correlations, the new model uses the heat balance equation that incorporates convection, radiation, and metabolic heat transfer, providing a theoretically grounded framework that improves upon the primitive mechanical approach.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The model provides a precise and adaptable prediction of wind chill temperature and time to freeze, accounting for various environmental conditions and individual activities, reducing subjective assessment and enhancing safety by warning of potential frostbite risks.
Implementation Method 1
The wind chill temperature model incorporates forced convection heat transfer from the facial surface due to wind, using the convective heat transfer coefficient to calculate heat loss rate
Implementation Method 2
The model includes thermal radiation heat transfer from the facial surface to the surrounding environment, using the radiation heat transfer coefficient to calculate radiative heat loss
Implementation Method 3
The wind chill model incorporates evaporation heat transfer from the facial surface, using the evaporation heat transfer coefficient to calculate heat loss due to moisture evaporation
Implementation Method 4
The model includes conduction heat transfer from the body core to the facial surface through tissue, using the conductive heat transfer coefficient to calculate internal heat flow rate
Data Source
AI summary
The present invention includes methods, systems and computer-readable media for more accurately determining wind chill temperature, Twc, equivalent temperature, Teq, time to freeze, tf, facial temperature, Tfm+Δt, as a function of time and the altitude correction factor, Δtf/1000. The wind chill model of the present invention accounts for the two major heat losses (forced convection, radiation) and a minor heat loss (evaporative cooling) from the facial surface and is also capable of accounting for the two major heat gains (metabolic, solar) at the facial surface due to the individual's physical activity and the presence of sunshine. The wind chill model of the present invention also provides a more accurate value for the wind velocity at head level.