Liquid jet impingement


Liquid Jet Impingement Cooling

Liquid jets are often used to cool surfaces because the efficiency is high, and the hardware is simple. These studies aimed to develop a basis for controlled engineering application of such jets. Both experimental and analytical studies have been conducted, leading to relatively complete expressions for the radial distribution of the local Nusselt number beneath an impinging jet. Laminar, turbulent, and splattering jets have each been studied. Because the stagnation-point boundary layers are very thin, the heat transfer coefficients are enormous, sometimes exceeding 100 kW/m2K. In consequence, wall roughness and conjugate heat transfer effects can also have a nontrivial influence. Our current focus is on the cooling characteristics of high Reynolds number jet arrays. Applications of this work include temperature control in materials processing, and cooling of high-efficiency generators, microelectronics, and laser systems.

J.H. Lienhard V, “Heat Transfer by Impingement of Circular Free Surface Liquid Jets,” Invited Keynote Paper, 18th National and 7th ISHMT-ASME Heat and Mass Transfer Conference, IIT Guwahati, India, January 2006. (PDF)
J.H. Lienhard V, “Liquid Jet Impingement,” Annual Review of Heat Transfer, C.L.Tien, ed., Vol.6, Chpt.4. New York: Begell House, 1995, pp.199-270. ((PDF))
L.A. Gabour and J.H. Lienhard V, “Wall Roughness Effects on Stagnation-Point Heat Transfer Beneath an Impinging Liquid Jet,” J. Heat Transfer, Vol.116, No.1, 1994, pp.81-87. (PDF)
X. Liu and J.H. Lienhard V, “The Hydraulic Jump in Circular Liquid Jet Impingement and in Other Thin Films,” Expts. Fluids, Vol.15, 1993, pp.108-116. (PDF)
X. Liu, L.A. Gabour, and J.H. Lienhard V, “Stagnation Point Heat Transfer During Liquid Jet Impingement: Analysis with Surface Tension,” J. Heat Transfer, Vol.115, No.1, 1993, pp.99-105. (PDF)
J.H. Lienhard V, X. Liu, and L.A. Gabour, “Splattering and Heat Transfer During Impingement of a Turbulent Liquid Jet,” J. Heat Transfer, Vol.114, No.2, 1992, pp.362-372.
X. Liu, J.H. Lienhard V, and J.S. Lombara, “Convective Heat Transfer by Impingement of Circular Liquid Jets,” J. Heat Transfer, Vol.113, No.3, 1991, pp.571-582. (PDF)
X. Liu and J.H. Lienhard V, “Liquid Jet Impingement Heat Transfer on a Uniform Flux Surface,” Heat Transfer Phenomena in Radiation, Combustion, and Fires, ASME HTD, Vol.106, 1989, pp.523-530. (26th ASME/AIChE National Heat Transfer Conference, Philadelphia, Aug. 6-9, 1989). Received Best Paper Award. (PDF)

Splattering of Impinging Turbulent Liquid Jets

Liquid jets that impinge on solid surfaces often splatter violently, expelling a shower of droplets from the liquid film formed on the target surface. These airborne droplets are indicative of lowered cooling efficiency, lessened cleaning ability, or reduced coating efficiency, depending on the specific application of the impinging jet. Our work has shown that splattering is driven by disturbances on the surface of the impinging jet. Turbulent jets, in particular, develop surface roughness as a result of liquid-side pressure fluctuations driven by the turbulence, and they are thus highly susceptible to splattering. Because practical liquid manifolding and delivery systems create turbulent jets, turbulence is the usual cause of splattering in nonboiling systems. The present work is directed at quantifying the role of nozzle turbulence in producing splatter and at understanding the statistical and spectral evolution of surface roughness on the jets.

S.K. Bhunia and J.H. Lienhard V, “Splattering during Turbulent Liquid Jet Impingement on Solid Targets,” J. Fluids Engineering, Vol.116, No.2, 1994, pp.338-344. (PDF)
S.K. Bhunia and J.H. Lienhard V, “Surface Disturbance Evolution and the Splattering of Turbulent Liquid Jets,” J. Fluids Engineering, Vol.116, No.4, 1994, pp.721-727. (PDF)