DH Jeggels and RT Dobson

Theoretical and Experimental Simulation of a Li-Br Water Dual Function Absorption system • DH Jeggels and RT Dobson • Department of Mechanical Engineering,University of Stellenbosch,Stellenbosch, Western Cape Province, South AfricaDawood Jeggels and RT Dobson presentation for EPC2013 as at 8 August 2013

Preamble  The world, in general, has become very aware of the fact that we are polluting the planet irreversibly; “you don’t get nothing for free” so if “If it isn’t green, paint it green”.  Environmental impact studies, global warming, ozone depletion, pollution, renewable energy such as solar, “CSP”, wind, tidal, hydroelectric and waste minimization have all become important words in both business and academic circles.  Power utilities and big-business must be seen to be saving energy, generating power more efficiently, reducing their carbon footprint, and reducing their production of polluting and global warming effluent/waste/toxic materials.

Pre-amble (cont.) Power stations using a Rankine cycle or a Brayton cycle reject some 33% of the energy supplied, “irreversibly”, back into the environment. The higher the source temperature the higher the thermal efficiency The lower the waste temperature the higher the thermal efficiency BUT the rate of improvement decreases and the power generating equipment becomes exponentially more expensive The idea is then to combine a Rankine cycle which is more efficient at higher temperature with another cycle which is more efficient at a lower temperature and thereby increase the overall efficiency

Pre-amble (cont.) 14% of 100°C waste heat can be recovered using a DFAC Stirling cycle engine (SC) Rankine cycle (RC) Dual function absorption cycle (DFAC) Thermal efficiency as a function of heat source temperature

Contents Preamble Why a dual function absorption cycle Objectives: To build and test an absorption system that can be used to get a better understanding of its functioning and control strategies and to assist in validating the theoretical simulation model of the cycle Experimental Apparatus Transient theoretical modelling Discussion, Conclusions and Recommendations

Dual function (power and refrigeration) ammonia-water (or Li-Br water) absorption system Waste heat supply Power How does it work Cooling water Refrigeration

Experimental apparatus Heat exchangers Evaporator and absorber Stand, generator and condenser

Theoretical Simulation Process Conservation of mass Conservation of energy (Ignoring KE and PE ) and noting that h = u + PdV Conservation of energy where Conservation of mass

Results For example, for the Generator-Condenser, and similarly for the rest

Discussion, Conclusions and Recommendations We have shown what an absorption cycle works and how it can generate both power and cooling using a low-grade (low temperature) source of (waste) heat We have shown how we mathematically simulate such a system We have so far completed the generator-condenser/turbine part, the absorber-evaporator, the pump. We have manufactured the parts but still need to complete the assembly of the system parts

Acknowledgements South African Heat Pipe Association University of Stellenbosch Thanks

Stand Generator Condenser Back

Heat exchangers Back

Evaporator and absorber Back Evaporator Absorber

DH Jeggels and RT Dobson