Performance Characterization of a Small-Scale Pillow Plate Heat Exchanger Designed with the Effectiveness-NTU Method

In recent years the design of pillow plate heat exchangers (PPHE) is attracting more and more interest both in the scientific community and in relevant industrial sectors. In this manuscript an experimental investigation has been carried out to study the thermo-hydraulic behaviour of a very compact PPHE designed in collaboration with a manufacturing company. This has allowed to design the PPHE compatible with the smallest geometric parameters currently achievable with the most advanced manufacturing technologies. This device presents a double pillow plate produced by spot-welding of two stainless steel and subsequent air-forming. The pillow plate has a length of 450 mm, width of 80 mm and thickness of 1mm while the two flowing channels present an internal inflation of 3mm. In this preliminary analysis water is used as working fluid both for hot and cold channel of the PPHE which has been installed on a purpose-built laboratory-scale setup. The design of the PPHE has been carried out by implementing the efficiency- NTU number (ε-NTU) method. The inside h1 and outside h2 heat transfer coefficients have been determined by correlations available in literature for normal types of PPHEs. The strength of the adopted approach has been verified by evaluating the errors percentage for the outlet temperatures, the efficiency and the Darcy factor referred to a wide experimental campaign. In terms of errors, the performances for predicted rating set from -15% to 15%, for thermal efficiency from -13% to 10%, and between 15% and 30% underestimation for the Darcy factor. The proposed procedure looks a promising engineering tool to be implemented for those applications involving small scale PPHE.