Second Law Analysis for the Experimental Performances of a Cold Heat Exchanger of a Stirling Refrigeration Machine The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate      N S     , the irreversibility distribution ratio xcfx95 and the Bejan number         B e       N S        based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a doublepipe type heat exchanger crossed by a coolant liquid (5545 by mass ethylene glycolwater mixture) in the temperature range 240 K u003c TC u003c 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and         B e       N S    xe2x86x92 1     and xcfx95 xe2x86x92 0 for mass flow rates      m xcbx99  xe2x86x92 0.1     kg.sxe2x88x921.

Energy and Exergy Evaluation of a TwoStage Axial Vapour Compressor on the LNG Carrier Data from a twostage axial vapor cryogenic compressor on the dualfuel dieselxe2x80x93electric (DFDE) liquefied natural gas (LNG) carrier were measured and analyzed to investigate compressor energy and exergy efficiency in real exploitation conditions. The running parameters of the twostage compressor were collected while changing the main propeller shafts rpm. As the compressor supply of vaporized gas to the main engines increases, so does the load and rpm in propulsion electric motors, and vice versa. The results show that when the main engine load varied from 46 to 56 rpm at main propulsion shafts increased mass flow rate of vaporized LNG at a twostage compressor has an influence on compressor performance. Compressor average energy efficiency is around 50%, while the exergy efficiency of the compressor is significantly lower in all measured ranges and on average is around 34%. The change in the ambient temperature from 0 to 50 xc2xb0C also influences the compressorxe2x80x99s exergy efficiency. Higher exergy efficiency is achieved at lower ambient temperatures. As temperature increases, overall compressor exergy efficiency decreases by about 7% on average over the whole analyzed range. The proposed new concept of energysaving and increasing the compressor efficiency based on precooling of the compressor second stage is also analyzed. The temperature at the second stage was varied in the range from 0 to xe2x88x9250 xc2xb0C, which results in power savings up to 26 kW for optimal running regimes.