Theoretical And Experimental Study Of Organic Rankine Cycle For Low And Medium Grade Heat Source Utilization

Organic Rankine Cycle (ORC) is an effective technique to generate power from low and medium temperature heat source, including industrial waste heat, solar heat, geothermal and biomass etc. Advantages of ORC are high efficiency, simple system, environment friendly, and so on. This work presents the theoretical analysis of Organic Rankine Cycle, as well as experiment study. The experiment system is the first 1kW experiment ORC project in China, and the maximum power of this system achieves 1.1kW. Detail of this work is as follows:1 Performance of simple Organic Rankine Cycle was presented in this work. Properties of working fluid, including isentropic properties, were firstly presented and analyzed. The difference between organic fluids and water was showed by a sample calculation, the result shows that the advantages of organic fluids is dry expansion process, proper system pressure, low enthalpy drop. Then, performance of ORC under different working parameters was showed, one of the most important result is that first law efficiency is a weak function of superheat temperature. This work also studied the effect of reheat ORC, regenerative ORC, and the result proves that ORC with reheat can improve the output power of waste heat recovery ORC system.2 Evaporator, which generates the highest irreversibility in ORC system, is analyzed by both static and dynamic model. The process of an evaporator includes preheating, boiling and superheating. A single stage counter flow evaporator was studied by its temperature distribution, entropy generation and exergy efficiency. The result shows that irreversibility of evaporator includes both internal and external irreversibility. The increasing of evaporating pressure decreases the internal entropy generation, but increases the external entropy generation. So a minimum entropy generation exists, which is also the maximum exergy efficiency for evaporator. Partial differential equations were established to describe the dynamic model of evaporator. The equations were dispersed in the space direction manually, and solved by S function of Matlab simulink. Theoretical analysis of scroll expander was presented according to geometrical study. The expansion ratio was firstly calculated. And then the change of status parameters during the expanding process was studied. At last their irreversible loss of expander is presented.3 Heat recovery efficiency describes the performance of waste heat recovery ORC system better than cycle efficiency. The reason is that waste heat flow can not transfer its all exergy to working fluid, so it still has some exergy when leaving evaporator. This process result in external loss, and heat recover efficiency can describe both external loss and internal loss exactly. Ideal heat recovery efficiency for a waste heat recovery system was presented, and it was also proved the equilibrium between maximum heat recovery efficiency and minimum entropy generation rate. The effect of working conditions on heat recovery efficiency was presented, and one of the results shows that heat recovery has a maximum value when changing evaporating pressure. At last, a triple stage hybrid system using MCFC-GT-ORC was treated as an example of waste heat recovery system, and the result shows that an increment of 3.8% can be received by combing ORC system.4 Firstly established a 1kW waste heat recovery ORC system in China. Isobutane was selected as the working fluid of the experimental system, hot water as heat source, and scroll expander as expander. The experimental system was successfully operated, a maximum power of 1.1kW and 2.9% first law efficiency has been received.5 The experiment results were analyzed by studying the performance of evaporator, expander. The testing results of evaporator show that evaporating pressure effects exergy efficiency greatly. The testing results of expander prove that expander's inlet volume flowrate effects rotating speed of expander greatly. Maximum rotating speed during the experiment is 4828 rpm, and maximum efficiency is 0.501.6 The testing results of whole system show that expander output power has a maximum value when changing evaporating of working fluid flowrate. The reason is the two phase flow entering expander when evaporating pressure and flowrate is high. Detail test proved that the optimum evaporating pressure or fluid flowrate increases with waste heat flow temperature. The maximum cycle efficiency of the testing system is 2.9%. Cycle efficiency also has maximum value, the reason is similar. Maximum heat recovery efficiency is 0.9%, and it also has a maximum value when changing evaporating pressure or working fluid flow rate.