What Is Working Orinciple Of Steam Type Electronic Cigarette Vape

Exploring the working principle of steam type vapings

The new tobacco products are divided into heated no burnt electronic cigarettes and steam style vapes. Heating not burn electronic cigarettes are aerosols containing nicotine produced by heating tobacco flakes to 200-300 ℃. Steam type vapes are made by extracting nicotine from tobacco leaves into e-liquid, and then using electrical energy to drive metal wires to generate heat to atomize e-liquid, producing aerosols containing nicotine. This study mainly focuses on the atomization process of steam type vapes, exploring the main factors affecting the atomization process from the aspects of heating wire, e-liquid, oil conducting cotton, and heat transfer path during atomization.

The heating wire material and heating characteristics of vapes

The equation for the steady-state heat transfer process of a heating wire can be obtained from Fourier’s law of thermal conductivity as follows:
Φ=-λ · A · gradt

• Φ is the heat transferred during the thermal conduction process, measured in (W).
• λ is the thermal conductivity of the material, measured in (W/m ·° C).
• A is the cross-sectional area, measured in m㎡.

The non steady state heat conduction equation is:
∂t/∂τ = a * (∂²t/∂x² + ∂²t/∂y² + ∂²t/∂z²) + Φν / (ρc)
a = λ / (ρc)

• a is the thermal diffusivity of the material.
• ρ is the density of the material, measured in kg/m³.
• is the specific heat capacity of the material, measured in J/kg · °C.
• Φν is the internal heat source, measured in (W).

Thermal diffusivity, also known as thermal conductivity, reflects the speed of material temperature changes. The larger the value of a, the faster the heating rate of the heating wire, and the stronger the explosive force.

For heating wires made of the same material, the higher the input power (Φ ν), the faster the heating rate of the wire. Taking the mesh heating wire as an example, the temperature of the heating zone was measured using an infrared thermal imager at constant powers of 5w, 7w, 9w, and 12w. The average temperature of the heating zone is shown in Picture 1. From the picture, it can be seen that when the power reaches a certain value, continuing to increase the power does not increase the steady-state temperature, and the heating rate does not increase significantly. At this time, the latent heat of phase change absorbed by the liquid to gas state of the e-liquid dominates, and the atomization process enters the steady state. The consumption of e-liquid will increase. If the oil is not guided in time, it is highly likely to cause local high temperatures, resulting in changes in fragrance or even sticking of the core. Therefore, determining the critical power is very important. When the input power is less than the critical power of the atomizer, the power and heating wire play a major role in the atomization process; On the contrary, when the input power is greater than the critical power, the main factor affecting the atomization process is the oil transmission rate of the cotton.

What Is Working Orinciple Of Steam Type Electronic Cigarette Vape (2)

Temperature distribution characteristics of vape heating wire

The overall temperature distribution of the heating wire is mainly determined by the heating zone and the heat dissipation conditions. Taking the mesh wire heating element (Figure 2a) as an example, in the case of no airflow, the temperature measured by the infrared thermometer (Figure 2b) and the numerical simulation results (Figure 2c) show that the temperature distribution decreases from the center to the surrounding areas. The temperature in the heating zone is higher, which is due to the poor heat dissipation conditions at the center, causing heat accumulation.

What Is Working Orinciple Of Steam Type Electronic Cigarette Vape (3)

In the presence of airflow, taking the spiral transverse heating wire as an example, through infrared thermography temperature measurement (Figure 3b) and numerical simulation calculation (Figure 3c), it was found that the high-temperature area is concentrated at the center of the heating wire located above. As air flows in from the bottom, it exchanges heat with the heating wire located below first, and then the airflow continues to flow along both sides, cooling the heating wire on the side. For the heating wire located above, the airflow is difficult to exchange heat with it, so the high-temperature area is concentrated here.

What Is Working Orinciple Of Steam Type Electronic Cigarette Vape (4)

Changing the distribution of heating temperature can be achieved by altering the overall heat exchange conditions of the heating wire. Currently, there are two main ways to make changes: one is to change the heat exchange conditions of the heating wire itself, and the other is to change the external heat exchange conditions..
Changing the self heat exchange conditions of the heating wire can be achieved by adjusting parameters such as the spacing, wire diameter, and angle of the heating wire. Taking the mesh heating wire as an example, as shown in Figures 4a and 4b, changing the spacing of the heating wire can show a change in the temperature distribution of the heating wire. The heat of the heating wire with small spacing accumulates more in the center, so the center temperature is higher than that of the heating wire with large spacing.

What Is Working Orinciple Of Steam Type Electronic Cigarette Vape (5)

There are many methods to change the external heat exchange conditions, such as changing the intake method, atomizing core tube wall material, e-liquid storage, oil guide cotton area, and so on.

Vaping e-liquid and porous substance

The e-liquid is mainly composed of propylene glycol, glycerol, nicotine and essence. During the atomization process, with the increase of temperature, the components in the e-liquid undergo the process of transforming from liquid to gas, and the gas condensation and air form aerosols. The amount and order of atomization of each component directly affect the reduction of aroma and taste.
During the atomization process, e-liquid serves as the source of aroma and smoke, but also exists as a fluid and cold source in the heat and mass transfer process of e-liquid. The higher specific heat capacity and latent heat of vaporization allow e-liquid to absorb more heat, and its viscosity changes with temperature, which in turn affects its fluidity and heat exchange capacity.

Cotton and ceramics are both porous substance that play a role in transporting and storing e-liquids in atomizers. According to Darcy’s law, the flow rate of porous media can be expressed as:

Q=(K/μ)*A*(Δp/L)

• Q is the flow rate through porous media, measured in m³/s.
• K is the permeability of porous media, measured in m². Permeability is an inherent property of porous substance, which characterizes the ability of liquids to pass through porous structures.
• It is only related to the material, pore size, and porosity of the porous substance, and is independent of the properties of the liquid itself.
• A is the cross-sectional area of seepage, measured in m³.
• Δp is the pressure difference between the cross-sections at both ends of the porous structure, measured in Pa.
• μ is the viscosity of the fluid, measured in Pa · s.
• L is the distance between the cross-sections at both ends of the porous structure, measured in m.

When standing still, the seepage flow rate Q changes very little; When the atomizer is working, the temperature of the e-liquid inside the cotton or ceramic will increase, and the μ viscosity of the e-liquid will decrease with the increase of temperature, resulting in an increase in the permeation flow rate Q within the same time period.
At the same time, the airflow velocity in the airway increases, causing a decrease in pressure on the atomization surface, resulting in an increase in Δp and a corresponding increase in the permeate flow rate Q. Therefore, the temperature and air flow velocity of e-liquid have a significant impact on the transport of e-liquid during the atomization process. In the case where the diameter of the atomization core is fixed, the flow velocity of air is mainly determined by the air flow rate entering the atomization core, so the size and position of the inlet hole are quite important for the atomization process.

Heat transfer pathway during vape vaporization process

The heating atomization method uses electric energy to drive the heating wire, which generates heat under the Joule effect, causing the atomization of e-liquid to produce aerosols. During the atomization process, the input heat is:
Q(input)=I²Rt

• I is the input current, measured in Α
• R is the resistance, measured in Ω
• t is time, measured in S.

The amount of heat that needs to be absorbed when the temperature of e-liquid rises from room temperature to the critical temperature before vaporization is:
Q=Cm*(T-T)

• Cm is Atomized e-liquid.
• T-T is Boiling temperature subtracts starting temperature
• C is the specific heat capacity of e-liquid, measured in (J/kg·°C).
• m is the mass, measured in kg.
• T is the temperature, measured in °C.

The heat absorbed by the vaporization of e-liquid is:
Q=r x m

• r is the latent heat of vaporization of e-liquid, measured in kJ/kg.
• m is Atomized e-liquid, measured in kg.

The effective heat during the entire atomization process is the heat absorbed by the heating and vaporization of the e-liquid, which is: Heating and heat absorption of e-liquid+vaporization and heat absorption of e-liquid.

The ineffective heat lost during the atomization process is: Heating heat of heating wire+heating heat of non atomized e-liquid and cotton+heating heat of pipe wall+heat of air replacement.

Therefore, the methods to improve atomization efficiency can start from two aspects: increasing effective heat and reducing ineffective heat.

Other articles or references of vape working orinciple:

How Electronic Cigarettes Work | HowStuffWorks

We welcome professionals from all walks of life to supplement our article and explore together. Welcome contact us – a professional vape manufacturer in China.