Principle of Electronic Cigarette Atomizers

In the world of e-cigarettes, have you ever wondered how the e-liquid precisely reaches the heating wire from the storage chamber and then turns into that satisfying puff of smoke? Many people instinctively believe that the speed of oil delivery is only related to the viscosity of the e-liquid, but the truth is far from that. Today, let's explore together the mystery of how the e-liquid is delivered to the cotton wick.
1. The driving force for oil to flow through the wick: Capillary action
The flow of the smoke oil within the cotton core mainly relies on capillary action. This is a phenomenon where a liquid spontaneously rises or diffuses in a narrow pipe or pore. The fine fiber structure of the cotton core naturally forms countless tiny pores. The smoke oil then flows through these pores, just like climbing stairs, from the oil storage chamber slowly towards the heating wire.
The greater the surface tension of the smoke oil, the greater the pressure difference generated by capillary action, and the stronger the capillary driving force accordingly. Moreover, the contact angle between the smoke oil and the cotton core also plays a crucial role. The contact angle is the angle formed when the smoke oil droplet spreads on the surface of the cotton core, and it reflects the wetting property of the smoke oil towards the cotton core:

When the contact angle θ is less than 90°, the e-liquid can effectively wet the cotton core, allowing the oil-drawing process to proceed smoothly.
When the contact angle θ is greater than 90°, the wetting property of the e-liquid on the cotton core deteriorates, making it difficult to conduct the oil.
Fortunately, the e-liquid currently used in electronic cigarettes generally has good wetting properties, and the contact angle with the surface of the cotton core is generally within the range of 0° to 90°. Within this range, the cosine function shows a monotonically decreasing characteristic. Therefore, the smaller the contact angle, the closer it is to 0°, the better the wetting property, and the greater the capillary driving force.

II. Resistance of Oil Flow Through the Smoke Oil: Viscous Resistance
Although capillary action provides the driving force for the flow of the smoke oil, the viscosity of the smoke oil itself can become a factor hindering its flow. Viscous resistance, simply put, is the friction within the liquid. The higher the viscosity of the smoke oil, the greater the viscous resistance it will encounter during the flow process.
The viscosity of the e-liquid is mainly determined by its components. Generally speaking, PG (propylene glycol) has a relatively lower viscosity, while VG (vegetable glycerin) has a higher viscosity. Therefore, e-liquids with a high VG content will have greater viscosity resistance and poorer fluidity.

III. External Driving Force: Pressure Difference Caused by User Inhalation
Apart from capillary action and viscous resistance, external pressure is also an important factor influencing the oil flow of the vaporizer. When the user inhales, the air passage inside the atomizer will generate negative pressure, which will drive the oil to flow towards the heating element. In other words, the negative pressure generated when the user inhales can significantly increase the flow speed of the oil, ensuring that the oil can reach the heating element promptly and accurately, thereby producing sufficient smoke.

IV. How to Optimize Oil Conducting Performance: Case Study Analysis
By deeply understanding the meanings of each physical quantity in the above formula, we can more effectively optimize the oil-conducting performance of electronic cigarettes. Below, through specific examples, we will analyze how to adjust the relevant parameters in different situations.

(1) Oil storage cotton equipment (mostly one-time electronic cigarettes)

The oil-absorbing cotton can be regarded as always in communication with the atmospheric environment. When the suction is stopped, the pressure relief effect is good. Under conditions permitting, the oil drainage effect can be enhanced by adjusting the negative pressure of the air passage.
The degree of contact between the oil storage cotton and the outer oil-conducting cotton will directly affect the transmission efficiency of the e-liquid from the oil storage cotton to the oil-conducting cotton. Therefore, this aspect needs to be given special attention.
3. The flow of the oil inside the oil-absorbing cotton mainly relies on enhancing capillary force by altering the pore diameters of different cotton layers. Therefore, the selection of cotton layer materials and the control of their density are of vital importance for optimizing the oil absorption performance.

(2) PureMing Oil devices (mostly rechargeable electronic cigarettes)

The oil tank of the Ming Oil device is sealed, and the e-liquid directly comes into contact with the atomization core. When the inhalation stops, the pressure relief effect is poor. The gas needs to pass through the cotton layer and enter the oil tank for ventilation to balance the pressure. Such devices are greatly affected by the negative pressure of inhalation, so it is not recommended to enhance the oil drainage by adjusting the negative pressure of the air passage.
2. The smoke oil comes into direct contact with the outer oil-conducting cotton, which results in relatively less oil leakage problem. However, when optimizing the oil-conducting performance, a balance point needs to be found between oil conduction and oil leakage.
3. Similar to the oil storage cotton equipment, the flow of the smoke oil within the conductive cotton also relies on enhancing capillary force by altering the pore diameters of different cotton layers. Therefore, the selection of cotton layer materials and the control of density are equally crucial.

V. Summary
To optimize the oil-conducting performance of electronic cigarettes, the following aspects can be considered:
Select cotton cores with appropriate porosity, pore size and wettability (contact angle) to enhance capillary force and improve oil drainage efficiency.
By adjusting the components and ratios of the smoke oil, its viscosity and surface tension can be changed, thereby improving the flow performance of the smoke oil.
Ensure the stability of external pressure, such as by reasonably designing the airway structure of the atomizer to enable users to generate appropriate negative pressure when inhaling, while avoiding excessive negative pressure that could cause the e-liquid to flow too quickly or in excessive amounts, thereby affecting the vaporization effect and taste.