Thermodynamic Limit for the Ising Model on the Cayley Tree

While the Ising model on the Cayley tree has no spontaneous magnetization at nonzero temperatures in the thermodynamic limit, we show that finite systems of astronomical sizes remain magnetically ordered in a wide temperature range, if the symmetry is broken by fixing an arbitrary single (bulk or surface) spin. We compare the behavior of the finite size magnetization of this model with that of the Ising model on both the Sierpinski Gasket, and the one-dimensional linear chain. This comparison reveals the analogy of the behavior of the present model with the Sierpinski Gasket case.Comment: 5 pages, 4 figure

Experimental investigation on water injected twin screw compressor for fuel cell humidification

A water injection in Twin Screw compressors was examined in order to develop effective humidification and cooling schemes for fuel cell stacks as well as cooling for compressors. The temperature and the relative humidity of the air at suction and exhaust of the compressor were monitored under constant pressure and water injection rate and at variable compressor’s operating speeds. The experimental results showed that the relative humidity of the outlet air was increased by the water injection. The injection tends to have more effect on humidity at low operating speeds/ mass flow rates. Further humidification can be achieved at higher speeds as higher evaporation rate becomes available. It was also found that the rate of power produced by the fuel cell stack was higher than the rate used to run the compressor for the same amount of air supplied. The efficiency of the Balance-Of-Plant (BOP) was therefore higher when more air is delivered to the stack. However, this increase in the air supply needs additional subsystems for further humidification/ cooling of the BOP system

Operation and performance of screw machines with high built-in volume ratio

A performance calculation of a screw compressor with increased built-in volume ratio was performed in this paper to establish how increased built-in volume ratio influences its efficiency. It is known that screw compressors have limited built-in ratio which is determined by their standard discharge port size and position. However, if the discharge port is reduced beyond its cusp position, the screw machine built-in volume is increased. In such a case, influence of the oil volume in the air-oil mixture of oil-flooded compressors increases the machine built-in volume further. The performance improvement achieved if the built-in volume ratio is doubled in comparison with the standard port during the machine operation at high pressure ratio of more than 20, is up to 26% for the specific power and adiabatic efficiency. This confirms superiority of the reduced size high pressure port for compressors which operate at high pressure ratio