Abstract
Recently interest in adsorption cooling systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption system. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption system cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and system coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
Highlights
Adsorption cooling systems are increasingly used for applications where cooling is required and low grade heat is available [1]
This paper evaluates some of the methodologies used to enhance the heat transfer performance of the adsorbent in terms of improving the bed thermal performance and the overall cooling capacity of the adsorption system
These adsorbent beds are installed in two-bed silica gel/water adsorption chiller incorporating mass and heat recovery schemes
Summary
Adsorption cooling systems are increasingly used for applications where cooling is required and low grade heat is available [1]. Many commercially available adsorption cooling systems use granular packed adsorbent bed design. Rezk et al / Applied Thermal Engineering 53 (2013) 278e284 heat and mass transfer equations was developed [5] In such model the overall heat transfer conductance was calculated using empirical correlations taking into account the operating conditions and the geometry of heat exchangers. This paper evaluates some of the methodologies used to enhance the heat transfer performance of the adsorbent in terms of improving the bed thermal performance and the overall cooling capacity of the adsorption system. All these investigations were carried out using fixed bed dimensions but at various fin spacing
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