Screening of novel water/ionic liquid working fluids for absorption thermal energy storage in cooling systems

Abstract

Absorption thermal energy storage (ATES) is significant for renewable/waste energy utilization in buildings. The ATES systems using ionic liquids (ILs) are explored to avoid crystallization and enhance the performance. Property model and cycle model have been established with verified accuracies. Based on the preliminary screening, seven ILs are found feasible to be ATES working fluids, while four ILs ([DMIM][DMP], [EMIM][Ac], [EMIM][DEP], and [EMIM][EtSO 4 ]) have been selected for detailed comparisons. The coefficient of performance (COP) and energy storage density (ESD) of the ATES using different H 2 O/ILs are compared with H 2 O/LiBr. Results show that the operating temperatures of LiBr are constrained by crystallization, limiting the COPs and ESDs under higher generation temperatures and lower condensation temperatures. With varying T g , [DMIM][DMP] yields higher COPs with T g above 100°C and [EMIM][Ac] yields comparable ESDs (67.7 vs 67.1 kWh/m 3) with T g around 120°C, as compared with LiBr. The maximum COP is 0.745 for [DMIM][DMP]. With varying T c , [DMIM][DMP] yields higher COPs with T c below 38°C and [EMIM][Ac] yields higher ESDs with T c below 33°C, as compared with LiBr. The maximum ESD is 87.5 kWh/m 3 for [EMIM][Ac]. Nomenclature: B i , second virial coefficient of species i, cm 3 /mol; C p,IL , molar heat capacity of ionic liquid, J/(mol•K); f , cycle circulation ratio; H, molar enthalpy, J/mol; h in , inlet specific enthalpy, kJ/kg; h out , outlet specific enthalpy, kJ/kg; m in , inlet mass flow rate, kg/s; m out , outlet mass flow rate, kg/s; m r , refrigerant mass flow rate, kg/s; M s , solution mass, kg; M r , refrigerant mass, kg; p, system pressure, kPa; p S i , saturated vapor pressure of species i, kPa; Q, heat duty, kW; Q e , evaporator heat duty, kW; Q g , generator heat duty, kW; R, universal gas constant, J/(mol•K); T, temperature,°C or K; T a , absorption temperature,°C; T c , condensation temperature,°C; T e , evaporation temperature,°C; T g , generation temperature,°C; V L i , saturated molar liquid volume of species i, cm 3 /mol; V s , solution tank volume, m 3 ; V r , refrigerant tank volume, m 3 ; W, power, kW; W p , power of pump, kW; X i , liquid molar fraction of species i, mol/mol; x, refrigerant mass fraction, kg/kg; x in , inlet refrigerant mass fraction, kg/kg; x out , outlet refrigerant mass fraction, kg/kg; x s , refrigerant mass fraction in the strong solution, kg/kg; x w , refrigerant mass fraction in the weak solution, kg/kg; Y i , vapor molar fraction of species i, mol/mol; α, τ, adjustable parameters of the activity model; η e , electricity generation efficiency; ρ, density, kg/m 3 ; γ i , activity coefficient of species i; Φ i , correction factor of species i; ΔH mix , mixing enthalpy of the solution,

Vapor-Pressure Measurement of Ternary System CaCl2 + [Emim]Br + H2O, CaCl2 + [Emim]Cl + H2O, CaCl2 + [Emim]Ac + H2O, and CaCl2 + [Emim]NO3 + H2O

“…The [Dmim][DMP] aqueous solution had the highest COP and ESP values in the system. 6,7 Therefore, IL aqueous solutions have been proven in the laboratory to be substitutes for traditional 20,21 Standard uncertainties are u(T) = 0.07 K, u(w) = 5 × 10 −5 , and u(p) = 0.067 kPa. reduce the vapor pressure of traditional absorption solutions and improve the performance of systems.…”

Desiccant solutions, membrane technologies, and regeneration techniques in liquid desiccant air conditioning system

“…{P 4441 } {DMPO 4 } is non‐corrosive and highly stable in comparison with other considered ILs given in Table 2. Wu et al 63 investigation of ILs for thermal energy storage in cooling systems was also reported in the table. 1‐Ethyl‐3‐methylimidazolium acetate {EMIM OAc} was found to have about 90 mPa.s viscosity which is not as high as most ILs reported in the literature.…”

“…{P 4441 } {DMPO 4 } is noncorrosive and highly stable in comparison with other considered ILs given in Table 2. Wu et al 63 The main limitations to existing IL usage as potential liquid desiccant in LDACs are due to high viscosity, nonbiodegradability, and toxicity nature. 31 These limitations were substantively reported in the literature.…”

Thermodynamic properties and performance evaluation of [EMIM] [DMP]‐H 2 O working pair for absorption cooling cycle

“…NRTL is a local composition‐based thermodynamics model that considers interaction of ion and molecules. Many IL‐H 2 O 14,50,53,54 systems have considered the NRTL model to fit the VLE data because of its verified accuracy.…”

“…NRTL is a local composition-based thermodynamics model that considers interaction of ion and molecules. Many IL-H 2 O14,50,53,54 systems have Vapor absorption cycle (VAC) modeling and performance assessment methodology. SHE, solution heat exchanger [Colour figure can be viewed at wileyonlinelibrary.com]…”