Steady‐state heat flux measurements in radiative and mixed radiative–convective environments

Lam, Cecilia S.; Weckman, Elizabeth J.

doi:10.1002/fam.992

Cited by 30 publications

(10 citation statements)

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“…Both the manikin and THF sensors used within this work were calibrated using primarily radiant heat sources, creating a discrepancy between the calibration environment and the application environment. The difficulties associated with the calibration of heat flux sensors to measure total heat flux in mixed‐mode environments have been acknowledged in the scientific literature . In 1999 NIST reported a method for calibrating against convective heat, and yet twenty years later it remains difficult to acquire sensors calibrated for both radiation and convection.…”

Section: Discussionmentioning

confidence: 99%

“…Sensitivity to convection was not provided by the manufacturer, and thus the assumption was made that the response is linear. When used in a mixed radiative‐convective environment, the uncertainties in the measured THF are higher than those listed by the manufacturer . The performance of the THF and RHF sensors were assessed prior to and after the experimental work; no significant changes in performance were observed.…”

Section: Methodsmentioning

confidence: 99%

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Thermal sensor performance and fire characterisation during short duration engulfment tests

et al. 2020

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A small-scale reproduction of the ISO 13506-1 thermal manikin was constructed to enable the assessment of manikin sensor performance, the partitioning of energy, and the variability of the fire generated during short duration heat and flame engulfment tests. The cylindrical test apparatus simultaneously housed four total heat flux (THF) sensors, one radiant heat flux sensor, and three manikin sensors.Calibrated manikin sensors were provided by nine laboratories and were categorised as buried thermocouple, copper-based, or surface-mounted thermocouple sensors.The test apparatus was exposed to fire generated by four propane torches for three exposure durations. All sensors presented similar profiles in net heat flux over time, which could be divided into four distinct phases: transient increase, pseudo-steady state, transient decrease, and post-exposure. Over pseudo-steady state, the mean THF over all exposure durations was 88 ± 8 kW/m 2 , and the ratio of convective to radiant energy was approximately 50:50, but highly variable. For a 4-second exposure, manikin sensors from five laboratories had a bias in heat flux greater than ± 5% during pseudo-steady state when compared with the THF sensors. This bias can primarily be attributed to the sensitivity of the manikin sensors to convective heat or heat loss due to sensor design. K E Y W O R D S calibration, convection, manikin, Protective clothing against heat and flame, radiation, sensor 1 | INTRODUCTION Thermal manikins are used to evaluate the performance of complete garments exposed to short duration heat and flame engulfment. 1 Sensors embedded within the manikins' surface (manikin sensors) record the change in heat flux directly or enable the calculation of heat flux through transient changes in temperature. From heat flux, the energy transferred through the test garment over a defined time period (ISO 13506-1), and the predicted skin burn injury (ISO 13506-2) are calculated. 1,2 The manikin sensors are expected to respond to the full range of heat fluxes (approximately 0-130 kW/m 2 ) and heat transfer modes which may be encountered during tests. Heat and flame engulfment is calibrated by exposing the nude manikin (without garment) to a mean incident heat flux of 84 kW/m 2 ± 5% across all sensors over the period of pseudo-steady state* (here forth referred to as manikin exposure calibration). The heat fluxes recorded under a garment are typically much lower than those encountered during manikin exposure calibration, and are influenced by garment composition and design, and exposure duration (3-12 s). *The ISO 13506-1:2017 standard currently defines pseudo-steady state as the 'steady region' of the heat flux curve.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Thermal sensor performance and fire characterisation during short duration engulfment tests

et al. 2020

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“…Comparisons with other heat flux estimates showed the HFG design to be less than optimal (ref. [15]). …”

Section: " Diameter Housingmentioning

confidence: 99%

Description of heat flux measurement methods used in hydrocarbon and propellant fuel fires at Sandia.

Nakos¹

2010

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The purpose of this report is to describe the methods commonly used to measure heat flux in fire applications at Sandia National Laboratories in both hydrocarbon (JP-8 jet fuel, diesel fuel, etc.) and propellant fires. Because these environments are very severe, many commercially available heat flux gauges do not survive the test, so alternative methods had to be developed. Specially built sensors include "calorimeters" that use a temperature measurement to infer heat flux by use of a model (heat balance on the sensing surface) or by using an inverse heat conduction method. These specialty-built sensors are made rugged so they will survive the environment, so are not optimally designed for ease of use or accuracy. Other methods include radiometers, co-axial thermocouples, directional flame thermometers (DFTs), Sandia "heat flux gauges", transpiration radiometers, and transverse Seebeck coefficient heat flux gauges. Typical applications are described and pros and cons of each method are listed. Heat Flux Measurement Methods in Fires of 62 AcknowledgementsThe author would like to acknowledge the support of numerous colleagues who have developed these heat flux measurement methods and their use over the years. Some of these colleagues are (in alphabetical order) Bennie Blackwell, Tom Blanchat, Tom Diller, Victor Figueroa, Walt Gill, Chuck Hanks, and Ned Keltner. Thanks to Allen Ricks and Ben Blackwell for their peer review. Heat Flux Measurement Methods in Fires5 of 62 Heat Flux Measurement Methods in Fires7 of 62 List of Tables IntroductionHeat flux measurements are important because, in heat transfer applications, providing only a temperature measurement is sometimes not sufficient to fully specify the environment. Using the electrical analogy (Ohm's Law), one needs two of the three variables (current, potential difference, or resistance) to fully specify an electrical circuit. Similarly, in a heat transfer application, one needs two of the three variables (heat flux, temperature difference, and thermal resistance) to fully specify the problem of interest. The temperature difference is similar to a potential difference, heat flux is similar to current, and thermal resistance is similar to electrical resistance.Most often the metric of interest is the response of an item in a fire. This metric is more related to the heat flux than just to the temperature because the thermal resistances to radiation and convection are not captured when only the temperature is specified.The measurement of heat flux in hydrocarbon fuel fires (e.g., diesel, JP-8, etc.) is difficult due to the high temperatures (e.g., 1000qC or higher), the sooty and chemically reactive environment, and due to large temperature gradients which produce thermal stresses. Many commercially available sensors do not work well in fires because they are water-cooled. Soot builds up on the sensing surface due to thermophoresis and this layer of soot changes the gage sensitivity. Post-test soot deposit thicknesses of ¼" have been measured after fir...

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“…They used water cooled total heat flux sensors for a direct comparison of the heat flux obtained from the DFTs. Lam and Weckman [11] examined the steady state response of four heat flux gauges including DFTs under various radiative and convective conditions and compared the results. In another study, Sultan [12] investigated the performance of six different temperature sensors in fire resistance test.…”

Section: Introductionmentioning

confidence: 99%

Real-time heat flux measurement using directional flame thermometer

Najafi

Woodbury

Beck

et al. 2015

Applied Thermal Engineering

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Steady‐state heat flux measurements in radiative and mixed radiative–convective environments

Cited by 30 publications

References 10 publications

Thermal sensor performance and fire characterisation during short duration engulfment tests

Thermal sensor performance and fire characterisation during short duration engulfment tests

Description of heat flux measurement methods used in hydrocarbon and propellant fuel fires at Sandia.

Real-time heat flux measurement using directional flame thermometer

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