Heat transfer of impinging jet and ribbed-duct flows with system reciprocation

This paper describes an experimental investigation of heat transfer for imp inging jet and ribbed duct flows under system reciprocation which focuses o n the variable reciprocating effects on these two flow systems for piston c ooling application. The experimental data reconfirmed the unsteadiness of r eciprocating flow which led to the local temporal heat transfer variations when both test sections reciprocated. For impinging jet flow, reciprocation did not modify the fundamental physics that facilitated heat transfer, but the local instantaneous heat transfer could be improved or impeded by reci procation, depending on the Reynolds number and reciprocating frequency. Fo r reciprocating ribbed duct flow, the fundamental heat transfer was conside rably modified from the nonreciprocating situation so that the distribution of heat transfer along the ribbed surface evolved toward a wavy-like patte rn from the nonreciprocating zigzag pattern when the reciprocating frequenc y or Reynolds number increased. Comparing these two reciprocating systems a t high mass flow rate and high reciprocating frequency showed a higher spat ial-time averaged heat transfer level for ribbed duct flow while the recipr ocating impinging jet flow provided better cooling performance when the Rey nolds number or reciprocating frequency was relatively low. Therefore, the ribbed duct and impinging jet flows might be suitable for piston cooling of high- and low-speed engines respectively.