Organic rankine cycle

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Analysis On Fluid Selection
for the low Temperature
Organic Rankine Cycle
(ORC)
Presented by:-
Pawan Kumar
16ME62R07

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Contents
Motivation
Background
Objective
The proposed Solar-ORC system
Analysis of low temperature Solar-ORC system
Conclusion
References

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Motivation
Fig.1[1]
:-Total Energy Consumption pattern of Major
Economies

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Motivation
Fig.2[2]
:-Total Energy Consumption by source (2013)

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Motivation
Continuous increase in Global Energy demand.
Non Renewable sources (Fossil fuels such as coal,
petroleum and natural gas) still accounting for more
than 78% of the Energy Sources being used in the
world.
Pollution and Global warming because of burning of
fossil fuels.
In this context, using renewable energies like solar
energy, wind energy, biomass and geothermal heat as
well as waste heat for energy production becomes
important.

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Background
 Between 1961 and 1962, Harry Zvi Tabor and Lucien Bronicki
built various Rankine engines using monochlorobenzene at a
maximum temperature of 140–150 °C, and with power capacity
in the 2–10 kW range.
 The first geothermal binary ORC power plant was installed in
1967 in the Kamchatka peninsula of the Soviet Union. The
working fluid was the refrigerant 12, and the power
plant featured a gross power of 680 kW. The thermal energy
source was geothermal water at low temperature (80 °C).
 Other notable ORC plants include, the 150 kW plant at Coolidge
(Arizona) in 1979; the 37 kW solar engine at Gila Bend
in 1977 ;the 19 kW solar pump at Willard (New Mexico) in 1979
realized by the Sandia National Laboratory.

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OBJECTIVE
To asses the theoretical performances as well as
thermodynamic and environmental properties of few
substances for use in low-temperature solar organic
Rankine cycle systems, using efficiencies, volume
flow rate, mass flow rate, pressure ratio, toxicity,
flammability, ODP and GWP as parameters for
comparision.

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ORC SYSTEMS
 An Organic Rankine Cycle (ORC) basically
resembles the steam cycle according to
thermodynamic principles. In an ORC, water is
replaced with a high molecular mass organic fluid
with a lower saturated boiling temperature in
comparison with water. Fluid characteristics make
ORC favourable for applications of low temperature
conditions and heat recovery applications at even
lower temperatures.

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Fig.3:- A Solar ORC system

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low-temperature solar ORC with
heat storage system
 In the present work, the selection of most suitable
fluids for a low-temperature solar organic Rankine
cycle is obtained. Hot water serving as heat source at
maximum temperature of 90 C is produced by
conversion of solar radiation into heat by solar
collectors.
Characteristics of 20 potential working fluids are
evaluated and compared for a 2 kW micro-power
system.

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Table 1:- Physical, safety and environmental data of the working fluids

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Fig.4:- Schematic of the low-temperature solar organic Rankine cycle with
heat storage system

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Fig.5:- T–s process diagram of the ORC

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low-temperature solar ORC with
heat storage system
 Input data for the analysis of the ORC
Evaporating temperature (Te)= 75 C
Condensing temperature (Tc)= 35 C
Mechanical efficiency of the turbine (eff_mt)= 0.63
Isentropic efficiency of the turbine (eff_it)= 0.70
Pump efficiency (eff_p)= 0.80

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Analysis of low-temperature solar
ORC with heat storage system
 Cycle Pressure
• Pressure values are in the range 0.1–2.5 MPa and a pressure
ratio(PR) of about 3.5 are considered as good [3][4]
• RC318 (Octafluorocyclobutane) , R600a (iso-butane), R600 (n-
butane), R114(1,2-Dichlorotetrafluoroethane), R601, R500 and
R152a are most suited based on the above criteria.

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 Turbine outlet volume flow rate
• Turbine outlet volume flow rate determines its size and the
system.
• n-Pentane, R113, cyclohexane, water, ethanol, methanol, R123
and R141b exhibit high volume flow rates.
• Fluids with low volume flow rate are preferable for economic
reasons. Among these are: R32, ammonia, R407C, R290, R500,
R134a (1,1,1,2-Tetrafluoroethane) and R152a

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Fig.6:- Turbine outlet volume flow rate versus turbine inlet temperature for
various working fluids at Tc = 35 C.

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 Cycle Efficiency
Fig.7:- System thermal efficiency versus turbine inlet pressure
for working fluids with high normal boiling points at Tc = 35
C.
Fig.8:- System second law efficiency versus turbine inlet
pressure for working fluids with high normal boiling points at
Tc = 35 C.

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Fig.9:- System thermal efficiency versus turbine inlet pressure
for working fluids with low normal boiling points at Tc = 35 C.
Fig.10:- System second law efficiency versus turbine inlet
pressure for working fluids with low normal boiling points at
Tc = 35 C.

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• For high boiling point fluids water and ethanol are more
efficient
compared to n-Pentane and R123.
• For low boiling point fluids, second law efficiency shows a
maximum) which suggests the existence of an optimal operating
condition.
• System second law efficiency for low boiling point fluids
increases in a short range 0–1.0 MPa and decreases slightly for
higher pressures.

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 Mass Flow Rate
• Water, ethanol and methanol yield lowest maximum pressures
and highest enthalpy heat of evaporation. Hence require lower
mass flow rates.
• Ammonia, has a higher evaporating pressure, but yields a low
mass flow rate and high heat of vaporization.
• For economical reasons, fluids with low mass flow rates like
ammonia, ethanol and methanol are interesting especially for
large capacity systems

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Fig.11:- Mass flow rate versus turbine inlet temperature for various working
fluids at Tc = 35 C.

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 Analysis of the heat input
System heat input is of great importance in a solar ORC. It
determines the size of the collector array and constitutes major
part of system cost.
• The heat required for a 2 kW power output falls in the range 40–
47 kW. Fluids such as water, ethanol, methanol and ammonia
require lower heat rates.
• The heat transfer rate required decreases as the temperature of
saturated vapor entering the Turbine increases. So depending on
the application, one could choose between system with large
collector area-low temperature and a system with small collector
area-high operating temperature.

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 Environmental considerations
• Some substances, mainly refrigerants, deplete the ozone layer
or/and contribute to the global warming. Because of their
negative effects, there is a necessity to choose those with less
harmful effects on the environment
• R12, R113, R114 and R500 cannot be selected owing to their
high ODP and high GWP. RC318 has a GWP of about 10250
and is excluded from the selection.
• There are few substances with low ODP or/and low GWP, like
R141b, R123, R407, R134a, R407C and R32.
• Water, ammonia, and alkanes families are environmentally
friendly substances.

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 Safety considerations
• Based on ASHRAE 34 safety classification for refrigerants.
• Alkanes non-toxic but flammable are classA3. They require
safety devices.
• R152a is classified A2 (lower flammability and non-toxic). R12
is B1 (non-flammable but toxic). Ammonia classified B2 (toxic
and has lower flammability limit) could be used in an open space
with lesser precaution compared with alkanes. R134a is of class
A1(non-flammable and non-toxic), i.e. safer compared to other
refrigerants and therefore is the preferred fluid.

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 Overall analysis
• From the analyses carried out in the previous Sections, none of
the fluids yields all the desirable.
• It is difficult to find an ideal working fluid which exhibits high
efficiencies, low turbine outlet volume flow rate, reasonable
pressures, low ODP, low GWP and is non-flammable, non-toxic
and non-corrosive.

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 Overall analysis
• Based on different considerations, the following fluids are not
selected
• RC318 (high GWP),
• Cyclohexane (high volume flow rate, high pressure ratio),
• R407C (high evaporator pressure, low efficiency),
• R32 (high evaporator pressure, low efficiency, high moisture
after expansion),
• Ethanol, water, methanol (non-convenient pressure values, high
turbine outlet volume flow rates),
• R12, R113, R114 and R500 (high GWP, high ODP),
• R141b (high turbine outlet volume flow rate, high ODP).

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• Table 2:- Comparison of the performances of different working fluids for a 2 kW
power output.

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Conclusion
 Thermodynamic characteristics and performances of different
fluids were analyzed for selection as working fluids in a low-
temperature solar organic Rankine cycle.
 Several criteria were used for comparison: pressures, mass and
volume flow rates, efficiencies, cycle heat input, safety and
environmental data.
• Fluids favored by the pressure values are: isentropic fluids,
butanes, n-Pentane and refrigerants R152a, RC318 and R500.
• Low volume flow rates are observed for R32, R134a, R290,
R500 and ammonia.
• High latent heat of vaporization presented by water, methanol,
ethanol and ammonia has as consequences low mass flow rate
and small heat input, which are advantages over the rest of fluids.

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Conclusion
• From an efficiency point of view, fluids with high boiling point
like ammonia, methanol, ethanol and water are very efficient but
the presence of droplets during the expansion process is a
drawback.
• Following the International regulations (Kyoto and Montreal
Protocols), R12, R500, RC318, R114 and R113 are harmful for
the environment.
 Concluding, R134a followed by R152a, R600, R600a and
R290 are most suitable fluids for low-temperature
applications driven by heat source temperature below 90 C.

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References
 Bertrand Fankam Tchanche , George Papadakis, Gregory
Lambrinos, Antonios Frangoudakis, Fluid selection for a low-
temperature solar organic Rankine cycle, Applied Thermal
Engineering 29 (2009) 2468–2476.
 [1] Enerdata Consulting, https://yearbook.enerdata.net/
 [2] Wikipedia, Renewable energy
https://en.wikipedia.org/wiki/Renewable_energy#/media/File:Total_
 [3] O. Badr, S.D. Probert, P.W. O’Callaghan, Selecting a
working fluid for a Rankine cycle engine, Applied Energy 21
(1985) 1–42.
 [4] B. Saleh, G. Koglbauer, M. Wendland, J. Fischer, Working
fluids for low temperature organic Rankine cycles, Energy 32
(2007) 1210–1221.

Organic rankine cycle

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