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Recuperators with design temperatures at and above 800 °C can further increase the thermal efficiency of supercritical CO2 power cycles by enabling higher turbine exhaust temperatures. Mar-M247 is a well-suited nickel-based superalloy for high temperature service due to its high creep strength that prevents excessive material thickness being required for pressure containment. Additive manufacturing using a high-speed laser-directed energy deposition (L-DED) process presents a promising solution, with build trials demonstrating the ability to produce nonconventional flow channels for enhanced heat transfer. A design process is presented that includes aerothermal and mechanical evaluation to maximize performance within the constraints of the manufacturing process. A 2-D heat transfer network and pressure drop code allows prediction of flow distribution and its effect on overall thermal performance. Established literature correlations, along with CFD simulation, inform the prediction of heat transfer coefficients and friction factors for the flowpaths and enhancement features in the heat exchanger core. Mechanical evaluation using finite element analysis (FEA) modeling with the intent of the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII, Div. 2 assesses the operational safety of the design. The detailed design features annular finned passages that take advantage of helical flow paths to distribute the flow from separated headers to shared heat transfer surfaces. Performance predictions for the recuperator at a 50 kW scale provide insights into the feasibility of the additively manufactured (AM) process to produce recuperators on a commercial scale that extend existing operating envelopes. [ABSTRACT FROM AUTHOR]

In this paper, a gain-boosting transconductor with widely input linear range and tunable control voltage is presented. A novel self-biased topology is employed in the negative feedback path of the gain-boosting structure to improve the linearity of the proposed transconductor. In fact, this self-biased topology results in a linear change for the drain voltage of the input drivers under the variation of the control voltage, while the input drivers operate in the triode region. In order to confirm the improved performance of the proposed transconductor, it is employed in a third order Butterworth low pass Gm-C filter. Therefore, the self-biased topology allows having more control on the cutoff frequency of the Gm-C filter. The proposed transconductor is designed and simulated in a 0.18 µm CMOS technology under a 1.8 V power supply. The small signal transconductance of the proposed circuit can change from 2.5 to 104.3 µA/V by tuning the control voltage. In addition, simulation results of the mentioned filter also show that the cutoff frequency properly changes between 500 KHz and 20.6 MHz, while third-order intercept point (IIP3) for this filter is between 7.55 and 21.4 dBm for different applications. [ABSTRACT FROM AUTHOR]