Validation

The validation of the transient LCT approach in the calculation of the Nusselt number has been established from flat plate experiments for a turbulent boundary-layer. In addition, it is possible to check the energy balance by comparing wall heat flux estimated by liquid crystal thermography with the heater input on one hand and the enthalpy outflow on the other. In the experiments conducted, the energy balances obtained where within 2-5% of one another.

Law of the Wall

The local Nusselt number obtained from LCT in the main flow direction at Reynolds numbers of 13400 and 32100 are compared with those using correlations for a smooth channel in Figures 6.8 and 6.9 respectively. The agreement between experiments and the well-established correlations is quite good, the maximum deviation being approximately 8%. Overall, Figures 6.8 and 6.9 reinforce the validity of the LCT approach for the determination of the heat transfer coefficient.

Figure 6.8 Comparison of Nusselt number variation determined using LCT with that for a smooth channel at Re=13400. The Nusselt number reported is an average calculated in the direction normal to that of the main flow. The streamwise distance is presented in a suitably dimensionless form.

Figure 6.9 Comparison of the local Nusselt number variation determined using LCT with that for a smooth channel at Re=32100. The local Nusselt number reported is an average calculated in the direction normal to that of the main flow. The streamwise distance is presented in a suitably dimensionless form.