| 31. |
|
|
| 32. |
|
|
| 33. |
- Geng, Q., et al.
(författare)
-
Temperature limit values for touching cold surfaces with the fingertip
- 2006
-
Ingår i: Annals of Occupational Hygiene. - : Oxford University Press (OUP). - 1475-3162 .- 0003-4878. ; 50:8, s. 851-862
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives: At the request of the European Commission and in the framework of the European Machinery Directive, research was performed in five different laboratories to develop specifications for surface temperature limit values for the short-term accidental touching of the fingertip with cold surfaces. Methods: Data were collected in four laboratories with a total of 20 males and 20 females performing a grand total of 1655 exposures. Each touched polished blocks of aluminium, stainless steel, nylon-6 and wood using the distal phalanx of the index finger with a contact force of 1.0, 2.9 and 9.8 N, at surface temperatures from +2 to -40 degrees C for a maximum duration of 120 s. Conditions were selected in order to elicit varying rates of skin cooling upon contact. Contact temperature (T-C) of the fingertip was measured over time using a T-type thermocouple. Results: A database obtained from the experiments was collated and analysed to characterize fingertip contact cooling across a range of materials and surface temperatures. The database was subsequently used to develop a predictive model to describe the contact duration required for skin contact temperature to reach the physiological criteria of onset of pain (15 degrees C), onset of numbness (7 degrees C) and onset of frostbite risk (0 degrees C). Conclusions: The data reflect the strong link between the risk of skin damage and the thermal properties of the material touched. For aluminium and steel, skin temperatures of 0 degrees C occurs within 2-6 s at surface temperatures of -15 degrees C. For non-metallic surfaces, onset of numbness occurs within 15-65 s of contact at -35 degrees C and onset of cold pain occurs within 5 s of contact at -20 degrees C. The predictive model subsequently developed was a non-linear exponential expression also reflecting the effects of material thermal properties and initial temperature. This model provides information for the protection of workers against the risk of cold injury by establishing the temperature limits of cold touchable surfaces for a broad range of materials, and it is now proposed as guidance values in a new international standard.
|
|
| 34. |
|
|
| 35. |
- Ghaddar, Nesreen, et al.
(författare)
-
Experimental and Theoretical Study of Ventilation and Heat Loss From Isothermally Heated Clothed Vertical Cylinder in Uniform Flow Field
- 2010
-
Ingår i: Journal of Applied Mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:3
-
Tidskriftsartikel (refereegranskat)abstract
- The flow characteristics and heat transfer are studied in a vertical annulus of a heated cylinder surrounded by a permeable cylinder, subject to cross uniform wind with open end to the environment and in the presence of natural convection. The objective here is to develop a computationally efficient model capable of capturing the physics of the flow and heat transport to predict air renewal rates in the vertical annulus. The small quantities of air infiltrating/exfiltrating through the porous cylinder over its upstream/downstream regions do not substantially affect the external flow pattern around the clothed cylinder. The air annulus flow and heat transport model predicted the radial and vertical mass fluxes and the mass flow rate at the opening as a function of environment conditions, porous cylinder thermal properties, wind speed, and annulus geometry. Experiments were performed in a low speed wind tunnel (0.5-5 m/s), in which an isothermally heated vertical cylinder surrounded by a clothed outer cylinder was placed in uniform cross wind. The tracer gas method is used to predict total ventilation flow rates through the fabric and the opening. Good agreement was found between the model and experimental measurements of air renewal rate and predicted heat loss from the inner cylinder at steady conditions. A parametric study is performed to study the effect of wind speed and temperature difference between the wind and skin temperature on induced ventilation through the clothing and the opening. It is found that natural convection enhances ventilation of the annulus air at wind speed, less than 3 m/s, while at higher speeds, natural convection effect is negligible. As the temperature difference between external wind and inner cylinder surface increases, the vertical air temperature gradient and total upward airflow through the opening increase.
|
|
| 36. |
- Gudmundsson, Anders, et al.
(författare)
-
Dust in Buildings - A Method for Identifying Particle Sources
- 2005
-
Ingår i: Environmental ergonomics XI : proceedings of the 11th International Conference, 22-26 May, 2005, Ystad, Sweden - proceedings of the 11th International Conference, 22-26 May, 2005, Ystad, Sweden. - 9163170620 ; , s. 507-510
-
Konferensbidrag (refereegranskat)
|
|
| 37. |
|
|
| 38. |
- Havenith, Bensahbat, et al.
(författare)
-
The UTCI-Clothing Model
- 2012
-
Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 1432-1254 .- 0020-7128. ; 56:3, s. 461-470
-
Tidskriftsartikel (refereegranskat)abstract
- The Universal Thermal Climate Index (UTCI) was conceived as a thermal index covering the whole climate range from heat to cold. This would be impossible without considering clothing as the interface between the person (here, the physiological model of thermoregulation) and the environment. It was decided to develop a clothing model for this application in which the following three factors were considered: (1) typical dressing behaviour in different temperatures, as observed in the field, resulting in a model of the distribution of clothing over the different body segments in relation to the ambient temperature, (2) the changes in clothing insulation and vapour resistance caused by wind and body movement, and (3) the change in wind speed in relation to the height above ground. The outcome was a clothing model that defines in detail the effective clothing insulation and vapour resistance for each of the thermo-physiological model's body segments over a wide range of climatic conditions. This paper details this model's conception and documents its definitions.
|
|
| 39. |
- Havenith, George, et al.
(författare)
-
Apparent latent heat of evaporation from clothing: attenuation and “heat pipe” effects
- 2008
-
Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 104:1, s. 142-149
-
Tidskriftsartikel (refereegranskat)abstract
- Investigating claims that a clothed person’s mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34°C in ambient temperatures of 10, 20, and 34°C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (Emass) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (Eapp) were compared. A clear discrepancy was observed. Emass overestimated Eapp in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34°C, apparent latent heat ((lambda)app) of pure evaporative cooling was lower than the physical value ((lambda); 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, (lambda)app increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, (lambda)app even exceeds (lambda) by four times that value at 10°C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.
|
|
| 40. |
|
|
