# Water Modification by Cold Plasma Jet with Respect to Physical and Chemical Properties
## 3 Results and Discussion
### Liquid Treatment--Basic Characteristics  
Hereafter, the specimens are treated at the optimized conditions found previously. Firstly, the liquid mass variation versus the time is given in Figure 8 for three different cases, i.e., the specimens are settled in the laboratory air, the specimens are subjected to the argon flow (plasma off) downstream of the reactor orifice, and the specimens are subjected to the argon plasma. For the prolonged time of 30 min, in the first case, the mass of both liquids remains constant, in the second case, a mass reduction of 7% in DDW and 8.5% in PBS is observed, and in the last case, the corresponding percentages are 14.5% and 15.6%. Figure 9 gives the liquid temperature variation (%) at the corresponding cases, following in-situ measurements. The representation of the temperature relative variation instead of absolute values is preferable since it offsets the different ambient temperature on different dates. The given error bars indicate the highest (worst case) deviations found between two series of experiments. Both liquids slightly cool down when they are left in the laboratory air, whereas an important cooling is noted when they are subjected to argon  
Figure 7: Distinction between the mean electric power consumed by the coaxial DBD and the plasma jet in three different cases: (i) free running plasma jet; (ii) plasma jet impinging onto water; (iii) plasma jet impinging onto buffer solution. Mean values and standard deviations are calculated from 30 (voltage \(\times\) current) waveform pairs, with each pair to be recorded over 3 voltage periods. Operating conditions: 11 kV\({}_{\text{PP}}\), 17.5 kHz, and 1.5 slm. flow downstream of the capillary tube. Interestingly, this cooling is intercepted when the plasma is activated. The effects are more intense in the case of unbuffered water. It is known that when the molecules of a liquid collide, they transfer energy to each other based on how they collide with each other. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it escapes and enters the surrounding air as  
Figure 8: Liquid mass evolution versus time in the case of (**a**) DDW and (**b**) PBS. Three different scenarios are examined: (i) liquid settled in ambient air; (ii) liquid is impinged by Ar flow only; (iii) liquid is impinged by Ar plasma jet. Mean values and standard deviations are calculated from 3 series of experiments carried out on different dates. Operating conditions: 11 kV\({}_{\text{PP}}\), 17.5 kHz, and 1.5 slm. Figure 9: Liquid temperature variation (%) with respect to the ambient temperature versus time in the case of (**a**) DDW and (**b**) PBS. Three different scenarios are examined: (i) liquid settled in ambient air; (ii) liquid is impinged by Ar flow only; (iii) liquid is impinged by Ar plasma jet. Mean values and standard deviations are calculated from two series of experiments carried out on different dates (we show here only the maximum, i.e., the worst case, standard deviation observed in each case). Operating conditions: 11 kV\({}_{\text{PP}}\), 17.5 kHz, and 1.5 slm. a gas. When evaporation occurs, the energy removed from the vaporized liquid reduces the temperature of the liquid, resulting in evaporative cooling. The evaporation continues until an equilibrium is reached when the evaporation of the liquid is equal to its condensation. Based on the present experimental data, plasma results in a higher evaporation rate than does argon gas itself. At the same time, plasma cools the liquids less than does the argon gas. Thus, a simplified evaporative cooling mechanism is not consistent with these observations. Evaporation should be attributed to momentum and energy transfer from the plasma species to the liquid molecules. More importantly, it is well established that plasma jets increase the gas velocity and its mixing with the surrounding air due to electro-hydrodynamic forces [32; 43; 44].