Grey-box modelling and in situ experimental identification of desiccant rotors

Abstract

This work focuses on grey-box modelling of desiccant rotors. The main objective is to enhance the accuracy of the desiccant wheel model at off-design conditions, including unbalanced flows and variable rotational speed, by introducing tuneable parameters which can be experimentally identified. In order to perform parameters’ identification on full-scale Desiccant Evaporative Cooling (DEC) units, an ad hoc measurement apparatus has been developed and tested, along with a suitable identification procedure. The core of the measurement apparatus consists of a set of eight sensors which allow measuring the process air temperature profile at the dehumidifier wheel outlet. The apparatus was installed in an experimental DEC setup. With the support of numerical modelling, a methodology to identify the physical parameters of the desiccant wheel has been developed. The method is based on a one-dimensional physical model of the generic rotor channel. The results show that the recorded temperature profiles in a few operating conditions are sufficient to identify the model’s tuneable parameters and that the model’s output is valid over a different and wide range of operating conditions. Moreover, the influence of tuneable parameters on the model predicted temperature profile and the comparison of the experimentally identified parameters with their theoretical expected values are discussed. Finally, it is concluded that the accuracy of the one-dimensional model can be improved when its physical parameters are experimentally identified rather than estimated on the basis of literature data. Therefore, grey-box models of commercial wheels would be very helpful in cases where numerical simulations are employed for the design and control optimization of real life DEC systems.