单束圆形射流冲击在小尺寸加热面上的局部换热特性

实验研究了液体射流垂直冲击在加热竖直小壁面上的局部换热特性,在Re_d=4.04×10~3～1.37×10~4范围内,驻点换热可以用方程 Nu_d=1.29P_r~m·Re_d~(0.5)表示,对于湍流,势流核心长度L/d与速度无关,L/d=5,建议势流核心外驻点Nu与Z/d的关系用 Nu_d/Nu_(max)=(L/d)/(Z/d)]~(0.5)表示,势流核心区内换热系数的径向分布用以下方程表示: 驻点区:Nu_d/Nu_(max)=(r/d)~(-0.5)tanh~(0.5)(0.88r/d) 壁面射流区:Nu_d/Nu_(max)=0.348Re_(d,u_0)~(n-0.5)·(r/d)~(-1.25)实验比较了自由射流与浸没射流的换热效果,发现驻点及径向分布结果相同,喷距的影响有差别。

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.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;within the potential core the radial distribution of heat transfer coeffi- cients can be well expressed asStagnation Zone Wall Jet ZoneThe 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.