## 3 Results and Discussion
### Energy Analysis  
The minimum energy demand for bread baking is the sum of the energy required to cook the dough, including the amount of heat needed to gelatinize the starch within the dough, and the energy required for water evaporation [54; 55; 56]. The required energy to bake the dough is given by the following:  
\[Q_{bd}=m_{d}\;C_{pd}\;\Big{(}T_{fd}-T_{bd}\Big{)} \tag{9}\]  
where \(m_{d}\) Is the mass of dough, \(C_{pd}\) the mean value of the specific heat and \(T_{bd}\) and \(T_{fd}\) the dough's initial and final temperatures, respectively. The required energy for water evaporation is given by the following:  
\[Q_{v}=\;m_{W}\;L_{W} \tag{10}\]  
where \(m_{w}\) is the evaporated water mass during Lebanese bread baking, and \(L_{w}\) is the water latent heat. The required energy to increase the baked bread temperature is as follows:  
\[Q_{bb}=m_{b}\;C_{pb}\;(T_{fb}-T_{bb}). \tag{11}\]  
where \(m_{b}\) is the mass of baked bread, \(C_{pb}\) the mean value of the specific heat of bread and \(T_{bb}\) and \(T_{fd}\) the bread's initial and final temperatures, respectively. Determining the actual surface temperature of the bread during baking presents a unique challenge due to several factors. The measured values during baking do not precisely represent the actual surface temperature, primarily due to the influence of gas temperatures and heat fluxes in the oven. Additionally, measurements taken immediately after baking must account for rapid temperature gradients as the bread exits the oven, as cooling begins quickly. To address this, the method used to estimate surface temperatures involves averaging the recorded values, which incorporates both the experimentally measured temperatures from various points within the baking chamber and the temperature readings taken immediately post-baking. Furthermore, it is essential to acknowledge that the upper and lower surfaces of the bread do not exhibit identical temperatures during baking. This discrepancy arises because of different exposure levels to the heat sources and the variation in heat flux levels on each surface. To account for these differences, we treated the bread as two hypothetical layers representing the upper and lower surfaces and then averaged the temperatures of these layers to estimate the final overall surface temperature. Based on these considerations, the estimated average final temperature of the bread was found to be approximately 170 \({}^{\circ}\)C. This figure was used to represent the comprehensive thermal conditions experienced by the bread during the baking process. Table 4 presents the temperature, specific heat, and mass values of Lebanese bread and dough obtained from previous experimental campaigns conducted in our laboratory under conditions similar to those in this study. The total energy required to bake Lebanese bread is estimated at 667 kJ/kg. The over-rated production capacity is 150 kg/h of dough. Thus, the energy demand for cooking the dough should be only 28 kW. The efficiency of the oven is given by Equation (12):  
\[\eta=\frac{\textit{Power needed to bake the bread}}{\textit{Oven rated power}} \tag{12}\]  
Although the oven's rated power is 130 kW, our energy analysis revealed that the oven operates with a thermal efficiency of only 21% (28 kW/130 kW), consuming 3.15 MJ to bake 1 kg of Lebanese bread. The efficiency drops to 16% when 3 h of preheating are added to a 10-h daily operation. According to CFD simulations conducted on a similar industrial tunnel oven [2], approximately 37 kW of the total energy input is lost through the oven walls and exit openings. The remaining 65 kW primarily heats the circulating air, with about 50% of this heating energy subsequently lost through the chimney and 29% through the oven walls [4]. This analysis highlights the inefficiency of the Lebanese bread-baking process, where a significant portion of the energy is lost through openings and flue gases.