Strategic integration of single flash geothermal steam cycle (SFGSC) and ejector assisted dual-evaporator organic flash refrigeration cycle (EADEOFRC) for power and multi-temperature cooling: 2nd law performance study

ABSTRACT

In the present study, an ejector-assisted dual-evaporator organic flash refrigeration cycle (EADEOFRC) is integrated with a single flash geothermal steam cycle (SFGSC). The EADEOFRC also consists of a two-phase expander extracting power from the high pressure fluid before the flashing. Isopentane and n-pentane are used as the working fluid of the EADEOFRC. It is observed that EADEOFRC can be operated at an organic fluid flash pressure corresponding to which refrigeration effects of both evaporators are equal. Corresponding to this operating condition of EADEOFRC, the integrated cycle yields higher second law efficiency compared to that of the SFSC. However, this yielded second law efficiency is lower than that of the dual flash steam cycle (DFSC). In the absence of the flash chamber, the ejectors and the evaporators, the EADEOFRC becomes merely a trilateral cycle (TLC), yielding only power output. Integration of SFSC and TLC yield substantially higher second law efficiency compared to that of the DFSC. Performance of the combined cycle slightly improves if n-pentane is used as the working fluid instead of isopentane.

KEYWORDS:

• Geothermal steam cycle
• Organic flash refrigeration cycle
• 2nd law efficiency
• cooling effects
• Isopentane

Nomenclature

Symbols

$\mathrm{h}$Enthalpy (kJ/kg)

${\dot{E}}_{\mathrm{F}\mathrm{u}\mathrm{e}\mathrm{l}}$Fuel exergy (kW)

${\dot{E}}_{\mathrm{D}}$Exergy destruction (kW)

${\dot{E}}_{\mathrm{G}\mathrm{W}\mathrm{i}}$Exergy input with the geothermal water (kW)

${\dot{E}}_{\mathrm{G}\mathrm{W}\mathrm{o}\mathrm{u}\mathrm{t}}$Exergy of outgoing geo-fluid

${\dot{E}}_{\mathrm{L}}$Exergy los (kW)

${\dot{E}}_{\mathrm{P}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}}$Product exergy (kW)

$\dot{m}$Mass flow rate (kg/s)

P_OFFOrganic fluid flash pressure (MPa)

P_SFSteam flash pressure (^oC)

${\dot{Q}}_{\mathrm{R}\mathrm{E}}$Refrigeration effect (kW)

sEntropy (kJ/ kg ^oC)

tTemperature (^oC)

$\dot{W}$Power (kW)

$\mathrm{x}$Quality (Dimensionless)

Greek symbols

${\eta }_{\mathrm{I}\mathrm{I}}$Second law efficiency (Dimensionless)

$\mu$Ejector entrainment ratio (Dimensionless)

Subscript

CCCombined Cycle

ConCondenser

EjEjector

SFGSCSingle flash geothermal steam cycle

GWGeothermal water

iInlet

HTEVHigh temperature evaporator

HRUHeat recovery unit/Organic fluid heater

LTEVLow temperature evaporator

OFOrganic fluid

OFConOrganic fluid condenser

OFTVOrganic fluid throttle valve

OFPuOrganic fluid pump

$\mathrm{P}\mathrm{F}$Primary fluid

sIsentropic

SConSteam condenser

$\mathrm{S}\mathrm{F}$Secondary fluid

SPSingle-phase

SPuSteam pump

STSteam turbine

STVSteam throttle valve

TPTwo-phase

TPTTwo-phase turbine

0Ambient state

1-19, A, M, N, a, m, nState points

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.