Star would you please calculate pi to infinity. Get back to us when your done.
Of course, A computer code based on the thermodynamic model
described above was generated for performance evaluation of
R718 refrigeration cycles enhanced with 3-port condensing
wave rotors. The evaporator temperature (T1) and heat rejecter
temperature (T3) are commonly fixed by the application. The
objective is to get the highest increase in coefficient of
performance (COPgain) compared to the baseline cycle.
Independent design parameters are the mass flow ratio
(K=m6/m2) that relates the mass flow of the cooling cycle to the
mass flow of the refrigerant cycle, and the pressure ratio of the
wave rotor (PRW=p3/p2).
Additional assumptions considered in the thermodynamic
model are the following:
• For comparison of baseline and enhanced cycles, the
evaporator and condenser inlet temperatures are considered
to be the same (T1 =T1b and T3=T3b).
• Temperature difference across the heat rejecter is kept
constant (T5 -T3=3 K).
• Pressure drop in heat rejecter, evaporator, and pipes is
neglected.
• The condenser and evaporator outlet states are fully
saturated.
• Same polytrophic compressor efficiency is used for baseline
and enhanced cycles. Its value of 0.72 is obtained by
assuming an isentropic efficiency of 0.7 for a compressor
with a pressure ratio of 2.
• The superheated vapor is considered as an ideal gas
(Îł=1.33).
• One-dimensional gasdynamic shock wave equations are
used to calculate the flow properties across the moving
normal shock wave. Reflected shock waves are not
considered.
• The hydraulic efficiency of the pump is 0.9.
Figure 8 shows the relative COPgain versus the evaporator
temperature (T1) for different mass flow ratios. By increasing
evaporator temperature T1, the COP of the wave-rotorenhanced
cycle is increased relative to the COP of the baseline
cycle. This trend is seen until the compressor pressure ratio in
the enhanced cycle (Î c=p2/p1) is reduced to a value that is
equal to the wave rotor pressure ratio (Î c=PRW). After that the
relative COPgain drops dramatically.
Figure 9 represents the relative COPgain versus mass flow
ratio for different evaporator temperatures, like a side view of
Fig. 8. It shows only the increasing branches of Fig. 8 up to an
evaporation temperature where the pressure ratio of the turbo
compressor is reduced to the value of the wave rotor pressure
ratio. Increasing the mass flow ratio above 200 appears as
ineffective according to Fig. 9.
Figure 10 shows the effect of the wave rotor pressure ratio
(PRW) on the relative COPgain for different mass flow ratios.
Each curve has a maximum point that indicates the best choice
of wave rotor pressure ratio for the given system specifications.
The location of this point depends on several parameters
including the hydraulic efficiency of the pump, compressor
polytropic efficiency, evaporator temperature, and temperature
lift (T3-T1), but not the mass flow ratio. One common
characteristic shown in Fig. 8, 9 and 10 is that a continued
increase of the independent value does not always increase the
COPgain. While Fig. 10 shows this effect for the wave rotor
pressure ratio, Fig. 8 reveals a growing gradient of COPgain up
to the point where further increase of evaporator temperature
