On the influence of gas mixture composition on gas quenching uniformity and mean
(English)Manuscript (Other academic)
The use of gas mixtures is widely spread in today's industry. The fields of application go from cooling within refrigerators to the deep freezing of meat balls. One particular application is within the industry of gas heat treating of metal pieces. Such heat treatment involves the cooling of metal pieces, called quenching. The present work investigates the dependence of the performance of a given gas mixture on the geometry of the metal pieces to quench. The heat transfer coefficient and the convection Nusselt number across a short cylinder (D = 150 mm, L = 300 mm) in axial flow for mixtures of hydrogen and nitrogen were computed for six Reynolds numbers in the range 2.0 10(4) to 2.0 10(5). The Nusselt number decreased continually with increasing hydrogen content. Since the existing correlations did not adequately represent the calculated data, modified correlations were developed to describe the influence of transport properties and flow pararmeters on the convective heat transfer over the front and lateral surfaces of the cylinder These correlations are valid for the range of Reynolds numbers 2.0 104 to 2.0 105 and in the range of Prandtl numbers 0.4 to 0.73. A relation giving the heat transfer uniformity as a function of the Reynolds number and Prandtl number of the gas mixture flowing around the cylinder in axial flow has been developed. This correlation is valid within the same range of Reynolds and Prandtl numbers previously given.
thermal-conductivity, viscosity, helium
IdentifiersURN: urn:nbn:se:kth:diva-5204OAI: oai:DiVA.org:kth-5204DiVA: diva2:8020
QC 201010192005-05-312005-05-312010-10-19Bibliographically approved