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In recent years there has been significant research in the area of supercritical carbon dioxide (sCO 2 ) closed-loop Brayton cycles as a possible alternative to conventional steam Rankine cycles due to their many advantages. These advantages include, a simpler cycle configuration, higher thermal efficiency, smaller component size and strong compatibility with renewable heat sources such as concentrated solar thermal. In order to make sCO 2 power cycles commercially available, a number of design challenges remain which must be addressed.Several design challenges arise in the sCO 2 turbine component due to its reduction in relative size.This decreases the relative distance between the rotor and temperature sensitive components, such as seals and bearings. An effective thermal management zone between the rotor and these components is required to appropriately manage the temperature of the shaft. This has been done in the past by removing heat over a long shaft, managing the temperature and mitigating thermal stresses. However, as the turbine reduces in size, the shaft speed must increase in order to maintain turbine efficiency.

As technology advances, rotating machinery are operating at higher rotational speeds and increased pressures with greater heat concentration (i.e. smaller and hotter). This combination of factors increases structural stresses, while increasing the risk of exceeding temperature limits of components. To reduce stresses and protect components, it is necessary to have accurately designed thermal management systems with well-understood heat transfer characteristics. Currently, available heat transfer correlations operating within high Taylor number (above 1×10^10) flow regimes are lacking. In this work, the design of a high Taylor number flow experimental test rig is presented. A non-invasive methodology, used to capture the instantaneous heat flux of the rotating body, is also presented. Capability of the test rig, in conjunction with the use of high-density fluids, increases the maximum Taylor number beyond that of previous works. Data of two experiments are presented. The first, using air, with an operating Taylor number of 8.8± 0.8 ×10^7 and an effective Reynolds number of 4.2± 0.5 ×10^3, corresponds to a measured heat transfer coefficient of 1.67 ± 0.9 ×10^2 W/m2K and Nusselt number of 5.4± 1.5×10^1. The second, using supercritical carbon dioxide, demonstrates Taylor numbers achievable within the test rig of 1.32±0.8×10^12. A new correlation using air, with operating Taylor numbers between 7.4×10^6 and 8.9×10^8 is provided, comparing favourably with existing correlations within this operating range. A unique and systematic approach for evaluating the uncertainties is also presented, using the Monte-Carlo method.

No abstract

As technology advances, rotating machinery is becoming smaller and operating at higher rotational speeds, with increased pressure and heat concentration. This combination of factors increases structural stresses, while increasing the risk of temperature sensitive components over heating. To properly protect these components, such as bearings and seals, and reduce structural stresses, it is necessary to have accurately designed thermal management systems with well-understood heat transfer characteristics. Currently available heat transfer correlations operating within high Taylor number (above1×1010) flow regimes are lacking. In this work, the design of a high Taylor number flow experimental test rig is presented. A non-invasive methodology, used to capture the instantaneous heat flux of the rotating body, is presented. A new correlation for Taylor numbers between 0.0and 9.0×108 with airis provided using the effective Reynolds number. Capability of the test rig and methodology enables the use of high density fluids, such as supercritical carbon dioxide, providing opportunity to develop correlations up to 1×1012.A unique approach is presented, using the Monte-Carlo method for evaluating the uncertainties in the calculated values. Data of a single testis presented for a Taylor number of 8.9±1.6×107 and an effective Reynolds number of 3.3±0.2×104. This operating condition corresponded to a measured heat transfer coefficient of 3.16±0.9×102W/m2K and Nusselt number of 8.9±1.6×101. This level of detailed uncertainty analysis for heat transfer coefficient measurements is not present in existing literature. This paper represents the first comprehensive portrayal of uncertainty propagation in heat transfer coefficient measurements for Taylor-Couette-Poiseuille (T-C-P) flow heat transfer experiments.