Heat transfer of confined impinging jet onto spherically concave surface with piston cooling application

This paper describes a detailed experimental investigation of heat transfer for confined impinging jet onto spherically concave surface with piston co oling application. The experimental conditions involved several nominal Rey nolds numbers ranging from 17 500 to 43 200 with five different reciprocati ng frequencies, namely 0, 0.833, 1.25, 1.67 and 2.08 Hz. It resulted in the pulsating number, which represented the ratio of reciprocating force to in ertial force effect, varying from 0 to 1.85E-4. Along the spherically conca ve heating surface the evolution of flow structure from separation point in to laminar and then turbulent annular flows was demonstrated by examining t he variations of power index suffixed to Reynolds number in the non-recipro cating Nusselt number correlations. The typical effects of flow reciprocati on on heat transfer were then illustrated by examining the distributions of temporal Nusselt number variation along the heating surface. When test sec tion reciprocated, the Nusselt numbers at measurement locations periodicall y oscillated and the amplitude of such temporal Nusselt number variation wa s mostly pronounced at the stagnation point and became location and Reynold s number dependent. At the stagnation paint, there were coupling effects of Reynolds and pulsating numbers on heat transfer and, in general, the heat transfer level increased with the increase of Reynolds or pulsating numbers while kept one of these two flow parameters unchanged. At Reynolds and pul sating numbers of 40 000 and 8.41E-5, the reciprocating Nusselt number valu e at the stagnation point could be increased up to a level about 3.2 times of the non-reciprocating level. Less reciprocating effects were found in th e spherically concave heating area; and reciprocation reduced the time-aver aged heat transfer to the levels abut 80% - 95% of non-reciprocating heat t ransfer values after flow passed the concave surface. As the reciprocating force significantly modified the heat transfer from Iron-reciprocating situ ation, it needed to account for the effect of reciprocating motion on the h eat transfer within the coolant channels of piston in order to achieve the optimum design of cooling system.