A comparative study to critically assess the designing criteria for selecting an optimal adsorption heat exchanger in cooling applications

Abstract

• Adsorption heat exchanger (AdHEx) type, fin dimension and body material are studied. • Different design criteria for comparing AdHExs are employed. • Rectangular finned-flat tube and annular finned-tube AdHExs are compared. • The AdHEx superiority in terms of chiller performance and compactness is examined. • A powerful numerical tool for designing the most efficient AdHExs is provided. In an adsorption cooling system (ACS), it is essential to design the most efficient AdHEx in terms of compactness, heaviness, and ACS performance parameters. For this purpose, the coupled effects of structural type, body material, and fin geometrical specifications of its adsorber heat exchanger (AdHEx) need to be investigated. Therefore, a three-dimensional distributed-parameter model is developed and validated to conduct a comprehensive parametric study on finned flat-tube and annular finned-tube AdHExs. In this regard, two different design criteria of AdHEx heat transfer area to adsorbent mass ratio (S/m ads ) and inter-particle mass transfer resistance are adopted as common bases of the comparisons. The results indicate that for any given bed geometrical configurations, there exists a certain threshold value for the thermal conductivity of AdHEx body material. For values greater than it, the specific cooling power (SCP) and volumetric cooling power (VCP) are approximately invariant. In contrast, the coefficient of performance (COP) is mainly influenced by the volumetric heat capacity (VHC) of the AdHEx body material such that it steadily decreases by increasing VHC. Independent of body material, utilizing the smallest fin dimensions for an AdHEx leads to the highest SCPs at the cost of lowering COP, dramatically. However, maximizing VCP is more complicated because the variations of VCP with fin height show entirely distinct behaviors for different body materials and AdHEx type. It is found that estimating the superiority of an AdHEx over another is beyond the ability of common rules of thumb because of complicated transport phenomena within the adsorber beds. In light of this, the approach and results of this study properly bridge the gap between the scientific and practical aspects of designing an AdHEx based on application constraints.