N. Kobasko, IQ Technologies, Inc., Akron, OH
The four types of heat transfer modes are analyzed on the basis of critical heat flux densities. It is shown that prediction of the heat transfer modes can be done through comparison of initial and critical heat flux densities. To evaluate initial heat flux density hyperbolic heat transfer equation with the non-linear boundary condition should be solved. It has been shown that there exists the analytical solution of hyperbolic equation of non-stationary heat transfer with nonlinear boundary conditions. Upon immersing of steel part into the quenchant the initial heat flux density q can be at different ranges, such as: ; or . In the first case the full film boiling is observed and at the second case, when , transition boiling is observed. In the last case at film boiling is absent and nucleate boiling is establishing immediately. It means that absolutely different function of will be received depending on critical heat flux density. It follows that there is no unique dependence of a heat transfer coefficient versus surface temperature Tsf. To understand what kind of chart we should use at designing technology, it is necessary to take into account the value of and initial heat flux density.
Summary: In the paper four types of heat transfer modes are analyzed on the basis of critical heat flux densities. It is shown that prediction of the heat transfer modes can be done through comparison of initial and critical heat flux densities. To evaluate initial heat flux density hyperbolic heat transfer equation with the non-linear boundary condition should be solved. It has been shown that there exists the analytical solution of hyperbolic equation of non-stationary heat transfer with nonlinear boundary conditions. When considering cooling properties of quenchants one usually pays the basic attention to heat transfer coefficients but rarely to critical heat flux densities and saturation temperature of the quenchant. Such approach is unacceptable because at different values of critical heat flux densities different heat transfer coefficients will be observed. As is well known, upon immersing of steel part into the quenchant the initial heat flux density q can be at different ranges, such as: ; or . In the first case the full film boiling is observed and at the second case, when , transition boiling is observed. In the last case at film boiling is absent and nucleate boiling is establishing immediately. It means that absolutely different function of will be received depending on critical heat flux density. It follows that there is no unique dependence of a heat transfer coefficient versus surface temperature Tsf. To understand what kind of chart we should use at designing technology, it is necessary to take into account the value of and initial heat flux density.
