A low-grade waste heat driven solid/vapour adsorption chiller has been successfully designed and tested. A simple model was developed to aid the design and predict the performances. The system comprised two identical sorption reactors operating out of phase in order to ensure continuous cold production. One sorption reactor consisted of six commercially available automotive plate/fin heat exchangers in which silica gel grains were accommodated between the fins. The system was tested as to the power delivered at 12 °C and the power density. The average cooling power was 3.6 kW. This is only 72% of the design value and can be largely attributed to the lower heat transfer fluid flow rate through the sorbent reactor. The thermal efficiency, COP, was 0.62 and the power density was 17 kW/m 3 for the system as a whole. Higher power densities are possible. At present, the adsorption chiller is integrated in a prototype trigeneration system, which is tested at CRF's Eco-building in Turin.
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A high temperature high lift solid sorption based heat transformer has been successfully designed and tested. The sorption reactor concept is based on a tube-fin heat exchanger where the heat exchanging fluids can flow through the hollow fins. The plates were brazed together with porous metal foam that was impregnated with either of the sorbents, LiCl and MgCl 2. The adsorbate is ammonia. The batch system was tested as to the power delivered at high temperatures, 150-200°C. Peak power at 200°C was about 0.8 kW, the average power about 0.4 kW. The thermal efficiency, COP, was calculated from the experimental results to be 0.11. This is only 40% of the expected theoretical value and can largely be attributed to the thermal mass of the reactor.
A sandwich plate heat exchanger has been designed for application in a high temperature solid sorption heat pump. The heat exchanger consists of two metal sheets that are brazed together with a metal wire mesh in between. This results in a lightweight construction with favourable heat transfer properties and sufficient mechanical strength to resist cyclic pressure variations. The flow distribution in a circular sandwich plate heat exchanger was determined experimentally as well as the average internal heat transfer rate. The results of these experiments were in good agreement with results of simulations that determined the local and average flow, temperature and heat transfer. Finite element calculations were done to select plate thickness and wire mesh dimensions of a sandwich plate heat exchanger to be applied in solid sorption heat pump where it should resist up to hundred thousand load cycles.
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