In the present paper, a novel separated structure shell-and-tube waste heat boiler is investigated through both experimental and numerical methods. The whole numerical model based on a scaled experimental facility is developed to analyze the shell-side thermal-hydraulic performances. Instead of using isothermal boundary condition on the tube wall, a linear heat flux is alternative according to the temperature difference measured in the experiment. The Drift-Flux model is used to solve the vapor-liquid two-phase flow across tube bundle. The commercial software ANYSY Fluent is adopted to conduct numerical computation, and a considerably good accuracy is obtained by comparing with experiment. The pressure drop, void fraction, flow field and heat transfer characteristic of two-phase mixture flow boiling across tube bundle are presented and analyzed in detail, respectively. The results show that the maximum pressure loss occurs at the inlet of risers, which can severely weaken the overall natural circulation. The HTC of heating tubes on the shell-side is mainly determined by void fraction rather than velocity inside the tube bundle, as the latter changes little along flow direction. This work can be as a reference for designers and operators. (C) 2017 Elsevier Ltd. All rights reserved.