PERFORMANCE IMPROVEMENT OF VAPOUR ABSORPTION SYSTEM USING LOOP HEAT PIPES

Abstract

Various industries have waste heat sources owing to the processes being followed for example Power Plants, Food Processing Plants, Solar Plants etc. This waste heat is being utilized in systems utilizing low to medium heat sources such as Vapour Absorption Refrigeration Systems (VARS) (65 – 200+ °C), Ejector Refrigeration Systems (ERS) (80 – 150 + °C), Organic Rankine Cycle (ORC) (~200 °C), etc. These systems generate a huge scope of waste heat recovery, eco-friendly operations and methods of reducing global warming and thermal pollution. The heat recovery has been done using conventional heat exchangers that are bulky and have limited effectiveness. This research work proposes the waste heat recovery & Intra – cycle heat utilization by a superconductor of heat called Loop Heat Pipe (LHP), which works on the evaporation – condensation principle. The working fluid of the LHP, i.e., Acetone, Methanol, Ethanol, Water etc., is evaporated by the heat influx in the evaporator and the vapour generated is transferred through the porous wicked structure in an insulated line to the Condenser where the vapour gets condensed and rejects the heat and the condensates are transferred back to the evaporator part through insulated lines. In this investigation of performance improvement of the VARS, intracycle heat exchange has been attempted through the LHP, preheating the mixture before entering the VARS generator and reducing the overall heat input in the generator resulting in a reduction in the irreversibility associated with the conventional heat exchangers & condensers etc. and increasing the overall COP of the system. Moreover, the Feasibility of the VARS combined with the Gas Power Cycle (GPC) through LHP has also been studied comprehensively. vi The COP for Single Effect, Half, Effect, Double Effect, Triple Effect & Quadruple Effect Systems have been observed to have increased by 65 %, 60%, 65%, 56-65 % &41 – 33 % respectively. Amongst the considered systems the refrigeration capacity of the Single Effect, Half, Effect, Double Effect, Triple Effect & Quadruple Effect Systems is 8.6 – 15.1 kW, 360.2 – 528.1 kW, 336 – 370 kW, 134.6 – 274 kW & 207.2 – 395.6 kW at 5°C Evaporator. Moreover, the mass flow rate from the absorber has been kept at 1kg/s for all the systems except single effect systems in which it is 0.05 kg/s. The Component-wise contribution to the overall Irreversibility has been presented to have decreased for the LHP. Six Eco-friendly refrigerants namely R600, R134a, R290, R152a, R125 & R124 have been used as working fluids for ORC. The combination of Water (LHP H Ex.) & R290 (ORC) is the most suited working fluid among all the 24 Combinations studied. Moreover, the First & Second Law Efficiencies of the System at 1500K Peak GPC Temperature & 65 kPa ORC Condenser Pressure have been recorded as 32% & 80 % respectively with 170 kW net-work output. The irreversibility related to each different component of the lower system has been around 80 kW. The ratio of the mass flow rate of R290 to Water has been around 1.42. In ERS new eco-friendly refrigerants such as R236ea, R1224yd (Z), R1233zd (E), R245fa, and R365mfc along with R718 have been selected for study as the working fluids. COP & refrigeration capacity of the combined system has been obtained in the range of 0.25-0.28 and 10.35kW-315kW respectively for various combinations of fluids. Based on the eco-friendliness, compactness & industrial viability the system with Water (LHP)-R1224yd (Z) (ERC) has been recommended as the mass flow required for working fluids is the least & utilization of Heat Input Available to ERC is maximum for the operations.