Experimental temperature fronts for adsorptive heat pump applications

Adsorptive heat pumps are promising for providing a safe alternative to CFC-based refrigeration devices. The temperature fronts process (also called thermal regeneration) has been claimed by several authors in recent years as a way for improving performance of adsorptive refrigerating devices. Cooling COPs of at least one are possible. However, up to now, almost no experimental results have been published. Efficient heat transfer is a key point for efficient thermal regeneration. Consolidated composite adsorbents (expanded natural graphite + zeolite) have much better heat transfer characteristics than granular packed beds: from 50 to 100 times larger, according to Guilleminot ct al. [Proc. Int. Absorption Heat Pump Conf., ASME, AES 31, 401-406 (1993)]. Therefore, temperature fronts have been studied in an adsorber containing such composite adsorbents. The adsorber is 1 m long, 10 cm in diameter and it is built on the principle of a double pipe (adsorbent inside, heat transfer fluid outside). The heat transfer fluid flows in one direction during the hot front (heating period), and in the ther direction during the cold front (cooling period). This experimental set-up permits simulating real refrigeration cycles. Performance analysis deduced from the experimental data (axial and radial temperature gradients in the adsorber, inlet and outlet temperatures and flow-rate of the heat transfer fluid) demonstrates the respective influences of heat transfer fluid mass flow-rate and cycle time. Experimental COPs of 0.9 were obtained.