ECOSS

This project aims to focus on compact evaporator in sorption system using water as refrigerant in order to give guidelines to design them properly. Indeed, the interest in these systems has grown again those last years as they can use solar energy or waste heat as main energy source. However, their development suffers from two main drawbacks: low compactness and high investment cost. These drawbacks are partly due to the use of falling film shell and tube heat exchangers as evaporator which are more expensive than plate heat exchanger used in mechanical compression refrigeration systems. However, these exchangers are the only proven solution so far to prevent any evaporation onset failure. Indeed, the low operating pressure (typically a few mbar) has major effects on the evaporator behaviour: • the vapour density is low which could result in high velocity vapour stream and consequently high pressure losses, • the liquid height inside the evaporator has a strong impact on the saturation temperature (3 to 4 K increase for each 5 cm of liquid column height) • the water physical properties at these low pressures could potentially result in large bubble diameter with consequently a risk of wall drying out and heat-transfer decrease if the confinement is too strong. In a compact heat exchanger, all these three aspects will be problematic. Furthermore, there is a lack of scientific knowledge at these pressures, so that the prediction of the fluid behaviour remains empirical. For this purpose, three research laboratories (CNAM, CETHIL and LOCIE) and one industrial implied in sorption system conception and commercialisation (CARRIER) will work together. To succeed in designing such compact evaporator, the project will rely on fundamental approach in order to characterize the physical phenomena occurring during boiling or evaporation at low pressure. It will rely also on a practical approach by designing heat exchanger prototypes, thanks to the results gathered from the fundamental approach. Moreover, these evaporators will be tested on real sorption systems: an adsorption based one having a cooling power of 5 kW and an absorption machine with a cooling power of 10 kW.