The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a.

The use of a Kalina cycle (KC) with a superheater to recover waste heat from an internal combustion engine (ICE) is described in this paper. The thermodynamic and economic analyses are performed for KC. The results indicate that using KC with a superheater is a feasible method to recover waste heat from ICE. The maximum thermal efficiency of KC is 46.94% at 100% ICE percentage load. The improvement of thermal efficiency is greater than 10% at all ICE loads, and the maximum improvement of thermal efficiency is 21.6% at 100% ICE load. Both the net power output and thermal efficiency of the KC subsystem increase with ICE percentage load and ammonia mass fraction. A lower turbine inlet pressure leads to a higher net power output of KC and a greater improvement of thermal efficiency when the ammonia mass fraction of the mixture is greater than 0.34. In the paper, if the same KC, which uses the largest capital investment, is used at different ICE loads, the payback period decreases with ICE load and ammonia mass fraction. In addition, both longer annual operation times and lower interest rates lead to shorter payback periods. However, it is worth noting that the payback period will be longer than the ICE’s lifetime if the ICE load is low and the annual operation time is too short.

The nucleate subcooled boiling is an efficient heat transfer form and plays an important role in many cooling applications. The size and distribution of bubbles in subcooled boiling have considerable influence on boiling heat transfer. In this paper, subcooled flow boiling experiment is carried out to investigate the nucleation point density and detachment frequency of bubbles under different system pressure, and the test section is full transparent. Since the whole body of the test section is composed of transparent materials, it can be observed from different directions to obtain high quality images. A bubble tracking algorithm has been developed, which can effectively determine the diameter and position of detached bubbles, thereby inferring the nucleation point density and detachment frequency of bubbles. Besides, the distinctive properties of bubble nucleation within narrow rectangular channel are verified by comparing bubble detachment diameters with existed models. Finally, models for bubble nucleation point and detachment frequency under different operating conditions were proposed and verified through experimental results.