Development of novel oval-twisted helical tube once-through steam generator: Part I: Single-phase laminar flow

The Helically coiled tube Once-Through Steam Generator (H-OTSG) offers enhanced overall thermal performance due to its high surface area per unit volume and secondary flow generation. The H-OTSG design (circular cross-sectional flow area) is considered for various Small Modular Reactor (SMR) designs due to its compactness, practical manufacturability, and higher thermal efficiency than current OTSG technologies (e.g., shell and tube). A novel conceptual H-OTSG tube design, known as the Oval-Twisted Helically coiled tube Once-Through Steam Generator (OTH-OTSG), is proposed for nuclear applications. The concept is a helically twisted coil with an oval cross-sectional flow area. The OTH-OTSG geometry simultaneously enhances the heat transfer performance through double-induced secondary flow. One through the tube twist generated swirling flow, and the second by the centrifugal force offered by the helical shape. Technology development requires two significant steps. The first is investigating the thermal performance of single-phase flow, which is the focus of this study, to develop heat transfer and friction loss models. In this step, the single-phase heat transfer performance is evaluated and compared with the H-OTSG. The OTH-OTSG and H-OTSG are evaluated for various mean coil diameters (D_c = 75–225 mm), laminar single-phase flow regime (Re = 200–2000), and isothermal wall conditions (T_wall = 320–350 K). Over the range of investigated parameters, the new proposed OTH-OTSG geometry shows an enhanced heat transfer rate (q_o/ q_C = 28.29–59.78%), heat transfer coefficient (Nu_o/Nu_c = 19.14–39.06%) and increased friction coefficient (f_o/f_c = 15.07–41.84%) over the single-phase flow in H-OTSG with a circular cross-sectional flow area. The presented heat transfer (Nu) and friction loss (f) models are within ± 9 and ± 13% with all data, respectively. The heat transfer and hydrodynamic models developed through this stage will be implemented in a two-phase flow study for the single-phase flow regime at the early stage of the innovative OHT-OTSG study, which is the next step in the development process.