Determination of the sensible heat effectiveness and pressure loss of a rotary regenerative heat exchanger using CFD

Abstract

The paper presents a new method to determine the sensible effectiveness and pressure loss of rotary regenerative heat exchangers using computational fluid dynamics (CFD). It is based on CFD simulations of a single thermal wheel microchannel with a small cross-sectional area and thin walls, with cyclic inlet and outlet boundary conditions. Two unique measurement set-ups were designed and built for the experimental measurement of the heat exchanger characteristics. Five different types of thermal wheels were manufactured, measured, and simulated in ANSYS Fluent. All wheels achieve an effectiveness greater than 73% under certain (air flow) conditions, which is the minimum effectiveness required by Ecodesign (in the EU). For the examined exchangers, the effectiveness ranges from 66.5% to 83.3%, depending on the boundary conditions and geometric parameters of the rotors. The highest sensible effectiveness is achieved by heat exchangers with the largest heat exchange surface Ac; on the other hand, these wheels have the largest pressure loss. The paper discusses the use of a simplified ε-NTU correlation model for the HVAC systems (typically C* = 1). The correlation model and CFD results were compared and found to be different from each other. The results of the CFD simulation were compared with measurements to prove that the proposed simulation method can predict the behaviour of the real heat exchanger as a whole. It was demonstrated that the sensible effectiveness and pressure loss of the rotary heat exchanger predicted by the CFD simulations correspond well to the measured values within the measurement uncertainty ±1.3%. The proposed method can be used for the comparison of different rotary regenerative heat exchangers before their manufacturing and for verification that they meet the EU Ecodesign requirements set by the current legislation. It reduces the cost of the initial optimisation and testing of new designs.