# Temperature Fields of the Droplets and Gases Mixture
## 3 Results and Discussion
### Hot Air Flow  
Figure 4a shows 3D surfaces illustrating the air flow temperature fields obtained by LIP. Maximum temperature fluctuations over time for the LIP technique are shown as \(\delta T\). They are approximately 11 \({}^{\circ}\)C for \(T_{\text{a}}=100\)\({}^{\circ}\)C, approximately 20 \({}^{\circ}\)C for \(T_{\text{a}}=200\)\({}^{\circ}\)C, and approximately 47 \({}^{\circ}\)C for \(T_{\text{a}}=300\)\({}^{\circ}\)C. That means, assuming the measured temperature is stationary, the LIP technique accuracy is approximately \(\pm 5.5\)\({}^{\circ}\)C at 100 \({}^{\circ}\)C, approximately \(\pm 10\)\({}^{\circ}\)C at 200 \({}^{\circ}\)C, and approximately \(\pm 23.5\)\({}^{\circ}\)C at 300 \({}^{\circ}\)C. At first glance, such high \(\delta T\) substantially limits the reliability of this measurement technique comparing to the thermocouple one, which usually has an average error of 10 \({}^{\circ}\)C for the temperature range in question. However, that would be a hasty conclusion. The temperature field data across the series of experiments similar to those presented in Figure 4, we can conclude that an average temperature across the complete measurement period for the series in the thermocouple vicinity (Figure 4) does not deviate significantly (i.e., it does not exceed the contact technique error limits) from the thermocouple measurement. However, peak (maximum) temperatures in Figure 4 in different sections of the flow do exceed the average significantly. Such nuances could not be registered in thermocouple experiments for obvious reasons: long response time and limited number of thermocouples in use. Figure 4b shows the air flow temperature variation trends obtained by two types of thermocouple. The maximum deviations of the temperature recorded by a slow and a fast thermocouple (see Section 2.4 for specifications) from the average temperature measured by LIP are as follows; approximately 2 \({}^{\circ}\)C and 0.6 \({}^{\circ}\)C for \(T_{\text{a}}\) = 100 \({}^{\circ}\)C, approximately 8 \({}^{\circ}\)C and 1.5 \({}^{\circ}\)C for \(T_{\text{a}}\) = 200 \({}^{\circ}\)C, and approximately 11 \({}^{\circ}\)C and 2.3 \({}^{\circ}\)C for \(T_{\text{a}}\) = 300 \({}^{\circ}\)C. A good correlation in general could be noted between the thermocouple and LIP measurements prior to droplet injection and when the gas temperature recovered after the droplets pass-through. Thus, the average air flow temperature deviation for all three cases does not exceed 3-5 \({}^{\circ}\)C.  
Figure 5 shows temperature variation trends of gas-vapor mixture in the trace of a droplet flow, i.e., in the area of the air flow being passed through by droplets. The crosshatched area corresponds to the period of aerosol injection. All three measurement types are compared: two thermocouples and LIP technique. The thermocouple readings differ significantly from LIP measurement results during the period when the droplets pass through the temperature measurement area. The main difference is in the temperature peak values, number of these peaks, and periods between them. It takes a slow thermocouple (Figure 5) quite a long time to recover the readings, namely, 30-40 s in our experiments. This result is apparently caused by the junction size of the slow type K thermocouple (Figure 2), which is 4 times bigger than that of the fast type S thermocouple. More liquid settles on a large junction and its complete evaporation takes more time. Figure 5 demonstrates similarity between LIP measurement and fast thermocouple measurement during the temperature recovery period (after the droplets pass through). For a thorough comparative analysis of experimental data,  
Figure 4: Temperature fields of the hot air flow (not blended with droplets) obtained by LIP (**a**), and temperature variation trends obtained by two types of thermocouples (**b**). parameters \(\tau\) and \(\Delta T_{\rm a}\) are calculated as well as the difference (\(\Delta T\)) between LIP and fast thermocouple measurements (Figure 6a).