In this study

a simulation model of a water-cooled direct contact cold thermal energy storage system using compressed CO2 hydrate was established

and the charging characteristics and total cold thermal energy storage capacity of the cold thermal energy storage system under charging pressures of 3.5 MPa

3.6 MPa

3.7 MPa

and 3.8 MPa were simulated. The results show that the relative errors between the simulation and experimental results of the cooling curve are 4.02%

4.43%

3.38%

and 1.89%

and those of the total cold thermal energy storage capacity are 0.82%

3.41%

1.45%

and 1.81% for the four charging pressures

respectively. All the relative errors are less than 5%; thus

the model has a good prediction ability. The model is used to optimize the system to improve its cold storage performance: when the cooling water flow rate increased from 65 mL/s to 100 mL/s

the pre-cooling time of the system decreased from 22.5 min to 20.8 min

and the COP of the system first increased and subsequently decreased. When the cooling water flow was 95 mL/s

the system COP reached maximum. When the cooling water temperature increased from 22 °C to 30 °C

the pre-cooling time of the system increased from 16.1 min to 21.9 min

and the COP of the system decreased from 1.77 to 1.53. When the charging pressure increased from 3.5 MPa to 5.0 MPa

the discharge pressure increased from 5.4 MPa to 12.1 MPa. When the charging pressure was 5.0 MPa

the discharge pressure was 12.1 MPa

which exceeded the maximum operating pressure of the compressor. Therefore

the charging pressure should be lower than 5.0 MPa for the sake of safety.