Is there a relationship between viscosity and density?
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This post was last edited by Xiaotong Luzhu on 2010-7-21 08:26. There has always been a question that has puzzled me: what is the relationship, or rather, is there any inherent connection, between the viscosity and density of liquids and gases? According to the principles of chemical engineering, the viscosity of gases increases as temperature rises, while the viscosity of liquids decreases as temperature rises. From what perspective is it reasonable to explain this?
Viscosity is independent of density. Liquids with similar densities can have vastly different viscosities. When the temperature of a liquid changes, its density remains essentially constant, but its viscosity usually changes significantly with temperature.
This post was last edited and replied to by Xiaotong Luzhu on 2010-7-9 at 18:01. Reply 2# koma: Could you explain why this is the case? I mean an explanation from a scientific perspective. Thank you
Viscosity is a property of a substance, and it is only related to temperature!
Viscosity has nothing to do with density; I’ve heard that for the first time； For example, when a gas is heated, it expands, its volume increases, its density decreases, and mass is conserved ； Let’s start with the definition of viscosity
Viscosity is independent of density; both are properties of the substance itself. Under normal circumstances, viscosity depends only on temperature
This post was last edited by Lantian Fuyun on 2010-7-29 at 14:13. In terms of characteristics, there is indeed a certain relationship. Like salt solutions, the higher the concentration, the greater the viscosity and the density as well ； For hydrocarbon substances, as the molecular weight increases, their density increases gradually, while their viscosity also increases to some extent ； For polymeric materials, the higher their molecular weight, the greater the viscosity of their melt.
As the gas temperature rises, the distance between molecules increases, and their kinetic energy grows, resulting in them being more likely to \"hit the walls\". When the liquid is heated, it becomes more active; the forces acting between its molecules decrease, and the force of contact with the \"walls\" also diminishes
The last edit to this post was made by qugd on 2010-7-15 at 22:10. From a scientific perspective, density is an effect resulting from the force of gravity acting on a substance, and it is expressed as the weight per unit volume； Viscosity is the effect of the forces acting between molecules; it is divided into dynamic viscosity and kinematic viscosity, and represents the macroscopic manifestation of the microscopic interactions among a substance’s molecules. Kinematic viscosity is dynamic viscosity divided by density. However, there is no essential correlation between the density of a fluid and its viscosity. A representative of substances with high density and low viscosity is mercury. However, for the same substance, a stronger gravitational field results in an increase in both its static density and apparent viscosity. Is this explanation scientific enough?
Viscosity is a property of a substance, and it is only related to temperature!
For the same substance, temperature is related to viscosity, but there is no associated relationship