In this research, a one-way fluid-thermal-solid numerical coupling model of a scroll expander for a waste heat recovery system was developed and used to investigate the deformation of the scroll pair. The pressure and thermal loads were firstly calculated by a CFD model, and the surface pressure and body temperature distributions of the scroll members were used as boundary conditions in the FEM model to obtain the deformation distributions of the scroll parts. Three time instants that may have significant adverse impacts on the maximum forces were selected to determine the most critical time for the occurrence of the maximum deformation of the scroll wraps. The results showed that the deformations induced by inertial force only occurred at the orbiting scroll tail, whereas the deformations in other regions negligible. At the time instants of t/T equaled to 13/15 and 1, the deformations induced by pressure loads had the opposite direction compared to that of the thermal loads and thus the two deformations canceled each other out and the coupling deformations decreased. The deformations induced by pressure loads were less significant than the thermal loads, therefore the coupling deformation was dominated by the thermal loads. The results also confirmed that the critical time at t/T equaled to 7/20 for the occurrence of the largest deformation resulted from the maximum axial forces that were exerted on the fixed scroll.
Scroll expanders are currently attracting interest for integration in small scale organic Rankine cycle (ORC) waste
heat recovery applications and have been subject to significant research over the last two decades. The most common
geometrical design uses a scroll profile generated by the involute of a circle with a constant wall thickness. A major
disadvantage of this approach is that the increase of the geometric expansion ratio is constrained, since it is accompanied
with a large increase in the scroll profile length and is associated with a decreased efficiency. In this paper, the
published literature related to scroll expander geometry is reviewed. Investigations regarding the influence of varying
scroll geometrical parameters on the performance of scroll expanders with a constant wall thickness are first examined.
The use of variable wall thicknesses and their effects on the performance are then considered. Finally, the impact of
scroll expander geometries using unconventional scroll profiles and scroll tip shape variations on the performance is
discussed and summarised. The major conclusion to be drawn from this review is that scroll expanders with variable
wall thickness scrolls should be further designed and developed. It is possible to increase the geometric expansion ratio
without increasing the length of the scroll profiles. CFD simulations are a promising tool to illustrate and understand
the non-uniform and asymmetric inner flow and temperature fields. The related benefits could lead to scroll devices
with variable wall thickness not only improving the performance of organic Rankine cycle (ORC) systems but also
opening a broad new field of applications such as refrigeration cycles and other power cycles where a high pressure
ratio is preferred.
With the increasing pressure of fossil fuel consumption and pollutions from vehicles powered by internal combustion engines, much attention has been attracted for hybrid and electric vehicles. With this background, an increasing demand for compact and high power density engines is being developed for the purpose of hybrid vehicles. In this paper, the design of a novel opposed rotary piston engine was investigated. In comparison with conventional reciprocating engines, this design has no crank connecting rods and intake/exhaust valves, and the operation cycle takes 360° crank angle to complete but similar to a four stroke cycle. 3D and 1D simulations were conducted to analyse the in-cylinder flow and evaluate the engine performance. The simulation results indicated the air velocity was very high at the end of intake stroke due to the lack of intake valves. The opposed rotary piston engine had a higher fraction of constant volumetric combustion that yielded to less heat loss, which contributed to a higher power output per combustion cycle than a reciprocating engine at low engine speed. The estimated minimum brake specific fuel consumption and maximum power density were 240 g/(kW·h) and approximately 80 kW/L, respectively.
The built-in volume ratio of variable wall thickness scroll expanders can be increased without increasing the number of scroll turns and the expander size in contrast to constant wall thickness expanders. CFD models for these novel scroll-type designs are presented in this research paper. The validation, verification and the findings have proven consistency with the theory of small scale ORC scroll expanders. The performance analysis indicates that the optimum performance point was reached at a pressure ratio of 3.5. The decrease of radial clearance from 200¼m to 75¼m had a significant effect on the isentropic efficiency and the specific power output, with the isentropic efficiency significantly increasing from 31.9% up to 53.9%. Based on the second-law analysis, it is found that exergy of 336.5W (75¼m) and 864.2W (200¼m) were destroyed during the expansion processes. Furthermore, characteristic pressure imbalances were observed in the expansion chambers. The studies also reveal that the large-scale vortices, generated during the suction process, were completely dissipated in the expansion chambers at a crank angle of 600°. Analysis of the pressure-volume diagram shows that variable wall thickness scroll expanders with built-in volume ratios above 4.5 could fully expand the working fluid to the defined outlet pressure.