عنوان مقاله [English]
Usually, in a high-altitude test facility, an exhaust diffuser is applied to create and maintain a vacuum condition in the motor test chamber utilizing the energy of the exhaust gases. In this system, the temperature of the exhaust gases, which directly hit the diffuser's inner walls, is much higher than the tolerable temperature of the diffuser metal body. In the current research, a new algorithm has been developed in the design of the cooling system to remove high heat fluxes from the vacuum simulator diffuser walls. In this algorithm, the three parameters of coolant mass flow rate, channel height, and cooling channel length are calculated based on the heat flux distribution along the diffuser, in such a way that, in addition to satisfying the temperature conditions of the metal body and maintaining the ease of implementation of the design, the total pressure drop also is in the desired range. Due to the error of empirical and semi-empirical relationships used to estimate convection heat transfer coefficients in concentric annular flows with large wall surfaces and high heat flux, a numerical simulation technique has been used to find suitable correlations and evaluate the design. The present studies show that the experimental correlations of Meyer and Kaneda are suitable for estimating the Nusselt number (with a maximum error of 3.81 %) and the friction coefficient (with a maximum error of 1.06 %) in the conditions of the present problem, respectively. In the following, the high capability of the algorithm is shown by presenting design results with different heat flux distributions. So, by distributed heat flux attributed to the stable working conditions of the vacuum simulator, a single cooling channel with a height of 3.2 mm and a mass flow rate of 8.025 kg/s has been designed. While for a critical heat flux of about 2.5 MW/m2, a two-channel cooling system with different mass flow rates and channel heights has been designed.