Evaluation of in-situ coated foam structures for adsorption heat storage and heat pumping

Adsorption technology has long been established as a promising and sustainable alternative, especially when waste heat or heat from renewables is available. Several applications have been investigated, namely, refrigeration, air conditioning, heat pumping, heat/cold storage [1] and commercial system have been released on the market. However, the next generation of products, aiming at a wider diffusion of sorption systems, need improved heat and mass transfer. Different options were explored to enhance these features, such as coated adsorbers [2], in-situ direct synthesis of zeolite on the heat exchanger [3] and composites of zeolites inside silicone foams [4]. In order to evaluate the performance of this kind of enhanced materials, in terms of adsorption dynamics, a well-established method is the Large Temperature Jump method. It was first suggested in a volumetric version, and then extended to gravimetric, calorimetric, and thermal versions. An exhaustive discussion about methods and techniques for sorption kinetics measurements is presented in [5]. In particular, a modified version of the LTJ method, named as G-LTJ (gravimetric large temperature jump) has been applied to the study of representative pieces of adsorbers [6] under isobaric conditions typical of an adsorption chiller/heat pump operation. The LTJ method has been proven useful for the assessment of different materials or materials configurations, such as FAM Z02, silica gel, coated heat exchangers with FAM Z02 and, more recently, to evaluate the dynamic behaviour of MOFs and composite sorbents. In the present work, the testing of in-situ SAPO-34 coated aluminum foam structures, to improve heat transfer inside adsorbers, is presented. In particular, dynamic evaluation of the adsorption process through a Gravimetric Large Temperature Jump (LTJ) apparatus was carried out on representative heat exchangers, under the typical conditions of adsorption storage and heat pumping. The results were employed for the sizing of a sorption module that can enhance the performance of a compression chiller.