In an automotive engine cooling system, the heat rejected to the coolant by the engine and other components is transferred to the air by the radiator. The cooling system engineer must predict the coolant inlet temperature (the top water temperature) for each operating conditions of interest.
Computational fluid dynamics (CFD) computer programs have been developed to predict the cooling air flow velocities and temperatures entering the radiator.
Radiator effectiveness is measured on a calorimeter with uniform air velocity and temperature entering the radiator.
Computer programs have been developed to predict calorimeter performance for new radiators based on experimental data from existing components.
In applying the calorimeter performance model to a vehicle, some means must be used to derate the performance slightly based on the non-uniform inlet air velocity and temperature distribution entering the radiator.
In this paper we have developed a method for calculating a non-uniformity factor from the radiator effectiveness tables and from the velocity and temperature distributions provided by the CFD codes.
Instead of applying the NTU method for the whole heat exchanger, the radiator is subdivided into small cells which are effectively micro heat exchangers and the NTU/Effectiveness method is applied to each individual cell.