Local Characteristics of Heat Transfer from A Small Heater to an Surrounding Liquid of Impingement

Local heat transfer characteristics of an impinging circular liquid jet on a small vertical heater were experimentally investigated. For stagnation point heat transfer of working fluid the Pr number of which ranges from 0.7 to 20, the equation for the local Nussclt Number has been well accepted:
Nu_d-1.29Pr^mRe_d^0.5 ???19890304-1???0.7 < Pr < 7 m=0.4
???19890304-2???Pr≈20 m=0.312
Because of the effect of properties of working fluids, the exponent on Pr number decrease with the increase of Pr number itself. For turbulent jet, the non-dimensional potential core length L/d is a constant 5 regardless of the jet velocities. Beyond the potential core the stagnation point heat transfer coefficients may be well expressed by the formula;
Nu_d/Nu_max=(L/d)/(Z/d)^0.5
within the potential core the radial distribution of heat transfer coeffi-cients can be well expressed as
Stagnation Zone Nu_d/Nu_max=(L/d)^-0.5tanh^0.5(0.88r/d)
Wall Jet Zone Nu_d/Nu_max=0.348Re_d^n-0.5(r/d)^-1.25
The free jet impingement heat transfer rate was compared with that of submerged jet, resulting in that the free jet impingement heat transfer rates at stagnation point and the radial distribution are very similar to those of submerged jet, however, the variation of heat transfer coefficients with nozzle-to-plate spacing is quite different.