Experimental study of heat transfer performance in a novel stacked granule flow heat exchanger: Strengthening mechanism based on multi-parameter coupling

This paper investigates the impacts of granule initial temperature, velocity, diameter, and cooling water flow rate on thermal performance via a novel experimental packed-bed system. Results indicate that higher initial temperatures and flow velocity enhance heat transfer, increasing outlet water temperature, heat flow rate, temperature drop rate, and heat transfer coefficients. Granule size is a dominant factor affecting heat transfer. Larger granules have a smaller specific surface area and a poorer heat transfer effect. Granule diameter increasing from 1 × 10⁻³ m to 9 × 10⁻³ m reduces outlet temperature by 50.22 % (353 - 313 K), heat flow rate by 79.89 % (5494 - 1105 W), and heat transfer coefficient by 83.61 % (114.54–18.77 W/(m²·K)). Regarding the cooling water flow rate, as it ascends from 1.5 × 10⁻⁵ m³/s to 3.5 × 10⁻⁵ m³/s, the heat flow rate and the heat transfer coefficient first rise and then decrease. Their peak values are achieved at 2.5 × 10⁻⁵ m³/s, with the heat flow rate being 4497.84 W and the heat transfer coefficient being 83.68 W/(m²·K), respectively. The correction coefficients of temperature and water flow rate were introduced to obtain a prediction correlation for the comprehensive heat transfer coefficient. Its average relative error with experimental values is 6.81 %, showing it can accurately predict the coefficient.