Document Detail


On the Problems Related to Natural Wet Bulb Temperature Indirect Evaluation for the Assessment of Hot Thermal Environments by Means of WBGT.
MedLine Citation:
PMID:  22805751     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
This paper deals with the indirect evaluation of the natural wet bulb temperature, t (nw), one of the two quantities forming the basis of the well-known wet bulb globe temperature (WBGT) index, considered worldwide to be a suitable and user-friendly tool for the preliminary assessment of hot thermal environments. This quantity can be measured by a wet bulb thermometer (a temperature sensor covered with a wetted wick naturally ventilated) or, if this is not available, calculated from other microclimatic parameters (i.e. the air temperature, the globe temperature, the air velocity, and the humidity) using a quite trivial energy balance equation. Because of the strong non-linear structure of such an equation, the risk of a multiplicity of steady state solutions could result in the failure to obtain a reliable index evaluation. To dispel all doubts, this work carries out an in-depth analysis of the heat balance equation to be solved for the indirect evaluation of the natural wet bulb temperature. A preliminary investigation of each heat flow term involved in the heat balance on the sensor has been carried out; in a second phase a special continuation method has been implemented, highlighting the effect of microclimatic parameters on the multiplicity of solutions. Results show that under free convection the evaluation produces a single solution only under uniform conditions, whereas in the presence of even slight differences between the air temperature and the mean radiant temperature, there can be as many as three solutions. This phenomenon, if confirmed by a further experimental investigation, could become a difficult matter since a sensor, in principle, has to read a unique value of the quantity measured. In any case, from a numerical point of view, the presence of many values of t (nw) greatly reduces the possibility of an indirect WBGT calculation from the other involved physical quantities; as a consequence, the indirect evaluation of WBGT should be clearly avoided based on ISO 7243 Standard.
Authors:
Francesca Romana D'ambrosio Alfano; Boris Igor Palella; Giuseppe Riccio
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-7-17
Journal Detail:
Title:  The Annals of occupational hygiene     Volume:  -     ISSN:  1475-3162     ISO Abbreviation:  -     Publication Date:  2012 Jul 
Date Detail:
Created Date:  2012-7-18     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0203526     Medline TA:  Ann Occup Hyg     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
DIIN-Dipartimento di Ingegneria Industriale, Università di Salerno, Via Ponte Don Melillo, 84084 Fisciano (Salerno), Italy;
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