Compact and Highly Efficient Heat Exchanger Based on Packed Beds of Nanoparticle-Doped Spheres

Abstract

Abstract In this work, we demonstrate at a laboratory scale the possibility of using a radio frequency (RF) heating system as a heat exchanger, with future applications for heavy oil processing. This laboratory work is the base for further improvements in heavy oil operations. The system consists of a pipe packed with nanoparticle-doped, superparamagnetic spheres as the bed material. The experimental results are compared to the data obtained with a volume average numerical method. In the RF heating system, the spheres are excited when subjected to oscillating electric fields ensuing thermal energy dissipation; this mechanism is called the Neel relaxation, a type of electrical induction heating. We have tested this system’s performance using water and heavy crude oil flowing in non-electrically conductive ceramic pipes packed with different sizes and spheres materials. Pressure, temperature and electric consumption data corresponding to varying flow rates have been collected and the numerically solved heat transfer equations are used to extend the system characterization; this will allow for industrial apparatus design considerations. Steady state data indicate that fluid heating is achieved at smaller residence times than in conventional heaters; temperature can be controlled with a great accuracy by varying the parameters of the RF generator. When heat leakage could be contained (through insulating the pipe outer wall and relatively low temperature gradients), heating efficiencies were significantly higher than 80 %. The volume average numerical method shows that the liquid flowing through the packed bed gets uniformly heated. Thermal and flow characterization are achieved for Reynolds and Nusselt numbers in the range of 10−2−102 respectively. This set up is able to heat in an efficient and temperature accurate manner for a wide range of flow conditions, and can be potentially used as a highly efficient heat exchanger for production operations (e.g., steam generation) in areas where the construction of surface facilities (fuel storage tanks, boilers) is not possible, either for environmental reasons or for lack of land space. A RF heat exchanger would only require a reliable source of electricity.