14.4
Tipos de fluidos
Los fluidos se pueden clasificar en newtonianos y no newtonianos según su respuesta al esfuerzo cortante. Los fluidos newtonianos tienen una relación…
Los fluidos se clasifican en dos tipos principales: newtonianos y no newtonianos. Los fluidos newtonianos tienen una viscosidad constante y su esfuerzo de cizallamiento está relacionado linealmente con la velocidad de deformación por cizallamiento.
El comportamiento de los fluidos newtonianos es predecible. Algunos ejemplos son el agua, el aire, el aceite y la gasolina.
Los fluidos no newtonianos, sin embargo, exhiben una viscosidad variable en función de la velocidad de cizallamiento. Se dividen en adelgazamiento por cizallamiento, espesamiento por cizallamiento y plásticos Bingham.
Los fluidos de adelgazamiento por cizallamiento, como la pintura de látex y las soluciones de polímeros, muestran una viscosidad aparente disminuida con una mayor velocidad de cizallamiento, lo que les permite fluir más fácilmente cuando se cortan.
Esta propiedad es útil en aplicaciones como la pintura con pincel y la impresión de inyección de tinta, donde se requiere una aplicación suave y uniforme.
Los fluidos espesantes de cizallamiento, como el almidón de maíz en agua, muestran una mayor viscosidad aparente a velocidades de cizallamiento más altas y se vuelven más resistentes al flujo cuando se agitan.
Esta propiedad única los hace útiles en equipos de protección y dispositivos de amortiguación.
Losplásticos Bingham, como la pasta de dientes y la mayonesa, se comportan como sólidos una vez que se supera el límite elástico y luego fluyen como fluidos, lo que los hace ideales para productos que necesitan extrusión o esparcimiento.
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Q1: What is the main difference between Newtonian and non-Newtonian fluids?
Newtonian fluids maintain constant viscosity with a linear relationship between shear stress and shear strain rate, making their behavior predictable. Non-Newtonian fluids exhibit viscosity that changes with varying shear rates. Examples of Newtonian fluids include water, air, oil, and gasoline, while non-Newtonian fluids include latex paint, cornstarch mixtures, and toothpaste.
Q2: How do shear-thinning fluids behave under stress?
Shear-thinning fluids, also called pseudoplastic fluids, decrease in apparent viscosity as shear rate increases, allowing them to flow more easily when subjected to force. Examples include latex paint and polymer solutions. This property makes them ideal for applications like brush painting and inkjet printing, where smooth and even application under stress is required.
Q3: What makes shear-thickening fluids useful in protective applications?
Shear-thickening fluids increase in apparent viscosity under higher shear rates, becoming more resistant to flow when agitated or stirred. Cornstarch in water is a common example. This unique property makes them valuable in protective gear and damping devices, where greater resistance under stress provides enhanced protection and energy absorption.
Q4: How do Bingham plastics differ from other non-Newtonian fluids?
Bingham plastics behave as solids until a specific yield stress is exceeded, after which they flow like fluids. Toothpaste and mayonnaise are common examples. This dual behavior makes them ideal for products requiring extrusion or spreading, as they maintain shape under low stress but flow when sufficient force is applied.
Q5: Why is understanding fluid classification important for engineering design?
Classifying fluids as Newtonian or non-Newtonian is crucial for designing and analyzing fluid systems, from pipelines to industrial processes. Newtonian fluids follow predictable viscosity patterns, simplifying calculations, while non-Newtonian fluids require specialized analysis based on their shear-dependent behavior. Proper classification ensures efficiency and functionality in fluid system applications.
Q6: What role does viscosity play in distinguishing fluid types?
Viscosity is the key property differentiating fluid types. Newtonian fluids maintain constant viscosity regardless of shear rate, following Newton's law of viscosity. Non-Newtonian fluids exhibit variable viscosity dependent on shear rate, creating three categories: shear-thinning, shear-thickening, and Bingham plastics. Understanding viscosity behavior is essential for predicting fluid performance.
Q7: How does the relationship between shear stress and shear rate define fluid behavior?
In Newtonian fluids, shear stress is linearly related to shear strain rate, creating predictable and consistent behavior. Non-Newtonian fluids deviate from this linear relationship, with viscosity changing as shear rate changes. This fundamental difference determines how fluids respond to applied forces and is essential for selecting appropriate fluids for specific engineering applications.