## 2 Numerical Simulation Methodology
### Definition of Materials and Boundary Conditions
#### 2.2.2 Boundary Conditions  
In order to study the actual operating performance of the CCKEF system, the boundary conditions were defined reasonably according to the literature and actual situations and included three parts: (1) kitchen: envelope including ceiling, walls and floor, lamps, personnel, cooktop and stoves; (2) exhaust fume system: exhaust hood, exhaust air duct, electrostatic purifier and outlet; and (3) make-up air: door 1, door 2, mechanical fresh air inlet and supply air duct. As for the kitchen part, exterior walls can be defined as the wall boundary with constant temperature [29], while the ceiling, interior walls and floor were often set as adiabatic walls [30; 31]. The lamps were set as wall boundaries with a heat flux of 130.6 W/m\({}^{2}\). The body surface of cooks in a residential kitchen was previously defined as a wall boundary with a heat flux of 27.7 W/m\({}^{2}\)[11], 50 W/m\({}^{2}\)[13], or 58.15 W/m\({}^{2}\)[14] or with a constant temperature of 32 \({}^{\circ}\)C [16], 31 \({}^{\circ}\)C [32], or 30 \({}^{\circ}\)C [29]. In this paper, the metabolic rate of cooking personnel in the commercial kitchen was set as 115 W/m\({}^{2}\)[7]. The cooktop was set as an adiabatic wall boundary [15]. The particulate boundary of the above was \"reflect\". The boundary condition of stoves was a difficult point in the simulation of the CCKEF system, as the cooking process is very complex and difficult to simulate accurately. The boundary conditions of stoves given in the literature were not uniform (Table 1). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Position** & **Type** & **Pollutant** & **Detail Parameters** & **Reference** \\ \hline \multirow{2}{*}{Emit} & Mass-flow inlet & Aerosol particle & Release rate = 3.3 \(\times\) 10\({}^{-7}\) kg/s; & [33] \\ \cline{2-5}  & Mass-flow inlet & CO\({}_{2}\) & \
\begin{tabular}{c} Release rate = 4.7 \(\times\) 10\({}^{-3}\) kg/s; \\ T = 127 \({}^{\circ}\)C; \\ Mass fraction = 100\% \\ \end{tabular} & [30] \\ \hline Boiler & Velocity inlet & Water vapor & V = 2 m/s; T = 70 \({}^{\circ}\)C & [14] \\ \hline Pot (exterior) & Wall & - & T = 120 \({}^{\circ}\)C & [15] \\ \hline Pot (top) & Wall & - & T = 310 \({}^{\circ}\)C & \\ \hline \multirow{2}{*}{Emit} & \multirow{2}{*}{Velocity-inlet} & Ultrafine particles & V = 0.1 m/s; T = 210 \({}^{\circ}\)C & [11] \\ \cline{2-5}  & & Mass-flow inlet & CO\({}_{2}\) &
\begin{tabular}{c} T = 1400 K; \\ Release rate = 1.28 \(\times\) 10\({}^{-3}\) kg/s \\ \end{tabular} & [13] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Boundary conditions of stoves given in the literature. In this paper, the boundary condition of stoves was determined based on the type of stove according to the heat and mass transfer process. In CCKs, cauldron stoves, frying stoves and stockpots are commonly used, the heat and mass transfer processes of which are shown in Figure 4. As displayed, the burner of a cauldron stove is located inside the cooktop. The heat of combustion is directly transferred to the pot to heat the oil and ingredients. Cooking fumes are generated from the top surface, and exhaust gas is discharged from a special smoke outlet. For a frying stove or stockpot, the burner is located above the cooktop. The heat of combustion is partly transferred to the pot and partly exchanged with the air near the burner through convection. The heat transferred to the pot is used to heat the food. The exhaust gas from the burner is discharged into the air. As indicated in Table 1 and Figure 4, the top surface of cauldron stoves is regarded as the source of cooking fume. Spherical particles with a diameter of 2.5 um are released from the top surface with an estimated emission rate and temperature of 0.12 mg/s and 70 \({}^{\circ}\)C, respectively [32]. The particle boundary of the top surface of cauldron stoves was \"escape\". The exterior surface of cauldron stoves was set as a wall boundary condition, and the temperature was set with the measured value.