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Energy and exergy analysis of a novel dual-ejector booster transcritical CO2 refrigeration system for applications in warm climates

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Abstract

This paper presents a thermodynamic analysis of a novel dual-ejector transcritical CO2 refrigeration system for applications in warm climate. Dual-ejector flow-pressurization and flow-splitting for higher ambient temperature operation are implemented to improve the performance. The proposed system is compared with various previously published CO2 systems including B1 (Standard CO2 booster system), B2 (CO2 booster system with parallel compression), B3 (CO2 booster system with flooded LT evaporator), B4 (CO2 booster system with work recovery expander), B5 (CO2 booster system with parallel compression integrated with flooded LT evaporator and work recovery expander) and also with a multi-stage ejector system. The investigation is carried out at ambient temperatures ranging from 34 to 43 °C. Ambient temperature and gas-cooler pressure were found to have a significant effect on the effective flow area of the ejectors. The COP of the proposed system is found to be 32% higher than B5 and 26% higher than the multi-ejector system. Exergy analysis is also carried out to comprehend system response to various parameters including extent of flow-splitting and change in inter-cooler pressure. The ejector Ej-2 was found to have the highest contribution to irreversibility accounting for an increment of 30% with the increase in ambient temperature from 34 to 43 °C. A detailed analysis of the ejector performance is also presented. Mixing chamber diameter is found to be an important parameter affecting the energetic and exergetic performance of the ejector. An enhancement of 29.63% in pressure lift and reduction of 61.11% in the irreversibility contribution of the ejector is possible by increasing the mixing chamber diameter from 0.012 to 0.015 m.

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Abbreviations

a :

Speed of sound (m s−1)

\(\alpha \) :

Void fraction

A :

Area (m2)

d :

Diameter (m)

h :

Enthalpy (J kg−1)

V :

Velocity (m s−1)

v :

Specific volume (m3 kg−1)

\(\eta \) :

Efficiency

m :

Mass flow rate (kg s−1)

Q :

Cooling load (kW)

c pj :

Specific heat capacity at constant pressure (J kg−1 K−1)

C :

Capital cost ($)

C pv :

Volumetric heat capacity of vapour (J m−3 K−1)

C pl :

Volumetric heat capacity of liquid (J m−3 K−1)

CO2 :

Carbon dioxide

COP:

Coefficient of performance

C1, C2, C3:

Compressor 1, 2 and 3

ω :

Entrainment ratio

β :

Thermal expansion coefficient (K−1)

PL:

Pressure lift generated by the ejector

ρ :

Density (kg m−3)

W :

Work (kW)

P :

Pressure (kPa)

p r :

Pressure ratio

r :

Quality

s :

Entropy (J kg−1 K−1)

AC:

Air-conditioning

Ex:

Exergy destruction

SEER:

Seasonal energy efficiency ratio

TEWI:

Total environmental warming impact

HFC:

Hydrofluorocarbon

HCFC:

Hydrochlorofluorocarbon

Ej-1, 2:

Ejector 1 and 2

R-1, 2:

Receiver 1 and 2

BPV:

By-pass valve

Exp-1, 2, 3:

Expansion valve 1, 2 and 3

Wrec:

Work recovered by ejectors (kW)

Wrec_max:

Maximum work recovered by ejectors (kW)

T :

Temperature (°C)

LF:

Load factor

min:

Minimum fraction of design load

p :

Motive

suc:

Suction

int:

Inter-cooler

e :

Evaporators

GC:

Gas cooler

gco:

Gas cooler outlet

amb:

Ambient

mn:

Motive nozzle

sn:

Suction nozzle

mni:

Motive nozzle inlet

sni:

Suction nozzle inlet

d :

Diffuser

eff:

Effective

m :

Mixing chamber

mo:

Mixing chamber outlet

do:

Diffuser outlet

s :

Suction

sv:

Saturated vapour

sl:

Saturated liquid

LT:

Low temperature

MT:

Medium temperature

ds:

Isentropic diffuser

fan:

Fan

w :

After shock wave

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Authors and Affiliations

  1. Department of Mechanical Engineering, BITS Pilani, Pilani, Rajasthan, 333031, India

    Ayan Sengupta & Mani Sankar Dasgupta

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  1. Ayan Sengupta
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  2. Mani Sankar Dasgupta
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Correspondence to Ayan Sengupta.

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Sengupta, A., Dasgupta, M.S. Energy and exergy analysis of a novel dual-ejector booster transcritical CO2 refrigeration system for applications in warm climates. J Therm Anal Calorim 148, 2749–2764 (2023). https://doi.org/10.1007/s10973-022-11623-x

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