The current research work numerically discusses the influence of rectangular winglets (RW) on the thermohydraulic performance of a fin-tube heat exchanger using an aqueous solution of carboxymethyl cellulose as a working fluid. Three-dimensional numerical simulations were performed on a rectangular channel with three rows of the inbuilt cylinder in an inline pattern equipped with rectangular winglet pair (RWP). These RWPs, half of the channel's height, are arranged in a common flow up (CFU) configuration and are mounted at an angle of attack (160°) at regular intervals nearby tubes inside the channel. The Reynolds number (Re) range of 50-200 with a concentration of 2000 ppm of carboxymethyl cellulose (CMC) has been considered. The simulation results in the form of Nusselt number (Nu), apparent friction factor (f_app), and vorticity of the channel with RWPs and without RWPs have been shown. The inclusion of RWPs in the channel comparatively enhances heat transfer and similarly enhances the frictional losses. Additionally, the channel's overall performance, including heat transfer and friction loss characteristics, has been compared for different Re. Results show that the overall performance increases with an increase in Re. The channel's overall performance also increases while using an aqueous solution of CMC (2000 ppm) instead of water.