The viscosity of ethylene glycol is a critical property that significantly affects its performance in various applications, such as mold cooling, heat transfer fluids, and automotive coolants. Understanding the behavior of ethylene glycol’s viscosity under different conditions is essential for designing and optimizing its use in these applications.
Understanding the Factors Affecting Ethylene Glycol Viscosity
The viscosity of ethylene glycol is influenced by several factors, including temperature and concentration. Let’s explore these factors in detail:
Temperature Dependence of Ethylene Glycol Viscosity
The viscosity of ethylene glycol is highly dependent on temperature. As the temperature increases, the viscosity of ethylene glycol decreases significantly. This relationship can be described by the Arrhenius equation:
η = A * exp(E_a / (R * T))
Where:
– η is the dynamic viscosity of ethylene glycol (in Pa·s)
– A is the pre-exponential factor (in Pa·s)
– E_a is the activation energy for viscous flow (in J/mol)
– R is the universal gas constant (8.314 J/mol·K)
– T is the absolute temperature (in K)
Figure 1 from [1] shows the experimental data on the viscosity of ethylene glycol as a function of temperature. The figure demonstrates the dramatic decrease in viscosity as the temperature increases.
Example 1: Calculate the viscosity of ethylene glycol at 20°C and 80°C, given the following parameters:
– A = 0.0002 Pa·s
– E_a = 24.4 kJ/mol
Solution:
At 20°C (293.15 K):
η = 0.0002 * exp(24400 / (8.314 * 293.15)) = 0.0183 Pa·s
At 80°C (353.15 K):
η = 0.0002 * exp(24400 / (8.314 * 353.15)) = 0.0041 Pa·s
The viscosity of ethylene glycol decreases from 0.0183 Pa·s at 20°C to 0.0041 Pa·s at 80°C, a significant reduction.
Concentration Dependence of Ethylene Glycol Viscosity
In addition to temperature, the concentration of ethylene glycol in water mixtures also affects its viscosity. As the concentration of ethylene glycol increases, the viscosity of the solution increases as well. This relationship can be described by the following equation:
η_mix = η_water * (1 + 2.5 * φ + 10.05 * φ^2 + 0.00273 * exp(16.6 * φ))
Where:
– η_mix is the dynamic viscosity of the ethylene glycol-water mixture (in Pa·s)
– η_water is the dynamic viscosity of water (in Pa·s)
– φ is the volume fraction of ethylene glycol in the mixture
Example 2: Calculate the viscosity of a 50% (by volume) ethylene glycol-water mixture at 20°C.
– η_water at 20°C = 0.001002 Pa·s
– φ = 0.5
Substituting the values:
η_mix = 0.001002 * (1 + 2.5 * 0.5 + 10.05 * 0.5^2 + 0.00273 * exp(16.6 * 0.5))
η_mix = 0.0045 Pa·s
The viscosity of the 50% ethylene glycol-water mixture at 20°C is 0.0045 Pa·s, which is significantly higher than the viscosity of pure water at the same temperature.
Comparison of Ethylene Glycol Viscosity to Other Liquids
The viscosity of ethylene glycol can be compared to that of other liquids, such as ethanol and glycerol, to understand its relative behavior.
Ethylene glycol has a higher viscosity than ethanol due to its molecular structure, which includes two hydroxyl (OH) groups attached to an ethylene group. This leads to intramolecular hydrogen bonding, increasing the viscosity of ethylene glycol.
On the other hand, glycerol has a more complex molecular structure with three hydroxyl groups, resulting in extensive hydrogen bonding and a higher viscosity compared to ethylene glycol.
Example 3: Predict the relative viscosity of ethylene glycol, ethanol, and glycerol at the same temperature.
– Ethylene glycol: Higher viscosity than ethanol due to intramolecular hydrogen bonding
– Glycerol: Higher viscosity than ethylene glycol due to more extensive hydrogen bonding
The order of viscosity from lowest to highest would be:
Ethanol < Ethylene glycol < Glycerol
Ethylene Glycol-Water Mixture Properties
The viscosity of ethylene glycol-water mixtures is an important consideration in various applications, such as automotive coolants and heat transfer fluids. The viscosity of these mixtures depends on both the temperature and the concentration of ethylene glycol.
According to [5], an ethylene glycol-water mixture will be slightly viscous, with the viscosity increasing as the temperature decreases. The lower the temperature, the thicker and more viscous the solution will become, making it harder to pump and handle, and potentially requiring larger pumps.
However, it is important to note that solutions of ethylene glycol are less viscous at lower temperatures than solutions containing propylene glycol, another common antifreeze agent.
Example 4: Determine the viscosity of a 30% (by volume) ethylene glycol-water mixture at 0°C and 20°C.
– At 0°C (273.15 K):
– η_water = 0.001792 Pa·s
– φ = 0.3
– η_mix = 0.001792 * (1 + 2.5 * 0.3 + 10.05 * 0.3^2 + 0.00273 * exp(16.6 * 0.3)) = 0.0038 Pa·s
– At 20°C (293.15 K):
– η_water = 0.001002 Pa·s
– φ = 0.3
– η_mix = 0.001002 * (1 + 2.5 * 0.3 + 10.05 * 0.3^2 + 0.00273 * exp(16.6 * 0.3)) = 0.0024 Pa·s
The viscosity of the 30% ethylene glycol-water mixture increases from 0.0024 Pa·s at 20°C to 0.0038 Pa·s at 0°C, demonstrating the significant impact of temperature on the viscosity of these mixtures.
Conclusion
The viscosity of ethylene glycol is a critical property that varies with temperature and concentration, making it essential to understand its behavior under different conditions. Experimental data, theoretical models, and empirical correlations can provide measurable and quantifiable data on the viscosity of ethylene glycol, which are crucial for designing and optimizing its performance in various applications, such as mold cooling, heat transfer fluids, and automotive coolants.
By understanding the factors affecting ethylene glycol viscosity, as well as its comparison to other liquids and the properties of ethylene glycol-water mixtures, physics students can gain a comprehensive understanding of this important property and its practical implications.
Reference:
- Viscosity Matters – Smartflow USA: https://www.smartflow-usa.com/viscosity-matters.htm
- Viscosity and Density Measurements of Poly(ethyleneglycol) 200: https://pubs.acs.org/doi/abs/10.1021/acs.jced.2c00578
- Viscosity of ethylene glycol as a function of temperature: https://www.researchgate.net/figure/Viscosity-of-ethylene-glycol-as-a-function-of-temperature_fig4_280096034
- Predict the viscosity of ethylene glycol, relative to that of ethanol and glycerol: https://homework.study.com/explanation/predict-the-viscosity-of-ethylene-glycol-relative-to-that-of-ethanol-and-glycerol-explain-your-reasoning.html
- Ethylene Glycol / Water Mixture Properties – CORECHEM Inc.: https://corecheminc.com/ethylene-glycol-water-mixture-properties/
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