It can be expected that the waste heat energy from the lower temperature heat sources like refrigeration water, intercooler and aftercooler will be difficult to use in Rankine cycles。 These waste heat sources represent half of the analyzed total  waste  energy。 See Table 2。 This will be discussed later  on。

The following procedure has been used for analyzing engine energies and calculating theoretical Rankine cycles: First, the engine   steady   point  has   been  modelled  with  OpenWAM™   to

estimate possible waste heat sources。 Second, the calculated available heat energies have been used in theoretical Rankine cycles, calculated with different fluids, where efficiencies, temper- atures and powers have been estimated。

4。Configuration with all waste heat sources。 A single cycle

The performance of a bottoming Rankine cycle can be evaluated under perse working conditions for the pre-selected working fluids (R245fa, FC72, FC87, HFE7000, HFE7100, R236fa, RC318    and

water)。 This pre-selection was performed by means a study similar to studies that can be found in the literature on selection of working fluid for Rankine cycles [28]。 The analysis assumes the following: steady state conditions, no pressure drop in the vaporizer and condenser, and isentropic efficiencies for the expansion machine and pump of 100%。 Regarding the implementation of these configurations in the industry applications, an appropriated expander machine must be selected to obtain an acceptable effi- ciency and to consider the most important internal irreversibilities of these cycles。 For this objective, the Japiske Turbine Chart [29] or Barber-Nichols Turbine Chart [30] can be utilized to approximate the most effective expander machine。

A parametric-iterative method has been employed for choosing the optimum working fluid and to obtain the maximum working fluid mass flow for each investigated vaporizer and superheater temperatures。 Aiming  to recover all  of  the  available waste    heat

Steam Cycle Output Power (kW)

Working Fluid mass flow (kg/s)

480 Optimum 480

Optimum

460 36 460 0。06

0。058

440 35 440 0。054

420 34 420 0。05

400 32 400 0。046

380 30 380 0。042

260 18 260

220 240 260 280 300 320 220 240 260 280 300 320

Evaporation  Temperature [ºC] Evaporation Temperature (ºC)

Cycle Efficiency ( )

0。3

260

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