Experimental chiller with silica gel: Adsorption kinetics analysis and performance evaluation

• Published in: Energy conversion and management 2017-01, Vol.132, p.172-179
• Main Authors: Vodianitskaia, Paulo J., Soares, José J., Melo, Herbert, Gurgel, José Maurício
• Format: Article
• Language: English
• Subjects: Adsorbates; Adsorbents; Adsorption; Adsorption chiller; Adsorption kinetics; Air conditioners; Air conditioning; Coefficient of performance; Heat and mass transfer; Heat exchangers; Kinetics; Mathematical models; Performance assessment; Performance evaluation; Porosity; Reaction kinetics; Refrigeration; Silica; Silica gel; Silicon dioxide; Solar collectors; Specific cooling power; Studies; Technology assessment; Thermal conductivity; Tubes
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2016.11.028

•A silica gel-water adsorption chiller achieved 0.53 COP, 68W/kg SCP at 80/30/15°C.•Highest COP stands in 70–80°C range, compatible with flat-type solar collectors.•If adsorbate uptake was uniform, maximal COP would be 9.4% higher.•Main performance improvements: shorter fluid pathways in adsorber, and 0.5mm dia. beads. Adsorption technology is a promising, low carbon intensity option for air conditioning and refrigeration. Adsorption kinetics is a key performance factor for such systems. This paper presents an adsorption kinetics and performance assessment of an experimental adsorption chiller with silica gel and water as working pair. The adsorbent bed heat exchanger is equipped with silica gel in loose grains fitted between finned tubes. Pressure, temperature and adsorbate flow measurements along the thermodynamic cycle are performed for two different options of adsorbent particle fraction sizes to compare the resulting dynamics and performance. COP is 0.53 and SCP is 68W⋅kg−1 for 2.0mm dia. silica gel and a 80/30/15 °C triplet. COP is 4 % worse when 0.26mm silica gel is used, due to the lower porosity and lower thermal conductivity presented by the crushed adsorbent. A mass diffusion algorithm is considered in the numerical model. Good agreement between experimental and calculated data has been reached. The maximum temperature level needed for desorption in the 70–80°C range is compatible with the use of water heated by flat-type solar collectors, and low-grade waste heat from industrial processes.