Spray cooling with high-speed airflow down the bore of an electromagnetic (EM) railgun has the potential for effective cooling, while the airflow limits the amount of water present in the bore at the end of the cooling period. An experimental study was conducted to measure the convective heat transfer coefficient under the proposed conditions at a representative scale. A transient experiment was conducted using a copper bar with a cross section of 135 mm $times$60 mm. The temperature response of thermocouples embedded in the copper bar was used to determine the heat transfer coefficient. Results are presented showing the influence of nozzle pressure and air velocity on the heat transfer coefficient. The electrical resistance was also measured across the bore in order to demonstrate the effectiveness of the air velocity in removing the water spray. Finally, a numerical study was conducted to show that the heat transfer coefficients obtained could effectively cool a large-scale EM railgun.
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