knudsen number

简明释义

克努曾数

英英释义

例句

1.In microfluidics, engineers often calculate the knudsen number to optimize device performance.

在微流体学中，工程师们经常计算knudsen number以优化设备性能。

2.A low knudsen number suggests that continuum mechanics can be applied.

低knudsen number 表示可以应用连续介质力学。

3.When the knudsen number exceeds 1, it indicates that the mean free path of molecules is larger than the characteristic length scale.

当knudsen number 超过1时，表明分子的平均自由程大于特征长度尺度。

4.In gas dynamics, the knudsen number is crucial for determining flow regimes.

在气体动力学中，knudsen number 对于确定流动状态至关重要。

5.The knudsen number plays a significant role in predicting heat transfer in rarefied gases.

在稀薄气体中，knudsen number 在预测热传递方面起着重要作用。

作文

The concept of the Knudsen number is essential in the field of fluid dynamics and gas kinetics. It provides a dimensionless quantity that helps to characterize the flow regime of gases, particularly when the mean free path of gas molecules is comparable to the characteristic length scale of the system. The Knudsen number is defined as the ratio of the mean free path of gas molecules to a representative physical length scale, such as the diameter of a pipe or the distance between two surfaces. This parameter is crucial for understanding how gases behave under different conditions, especially in micro and nano-scale systems where traditional fluid dynamics may not apply. When the Knudsen number is much less than one (Kn < 1), it indicates that the flow can be described by continuum mechanics, meaning that the gas behaves like a continuous fluid. This is the regime where classical fluid dynamics equations, such as the Navier-Stokes equations, are valid. In contrast, when the Knudsen number is greater than one (Kn > 1), the mean free path becomes significant compared to the size of the system, leading to non-continuum effects. In this case, the behavior of the gas can no longer be accurately described by classical fluid dynamics, and kinetic theory must be applied to understand the flow. The transition between these regimes is critical in various applications, including microfluidics, aerospace engineering, and vacuum technology. For instance, in microfluidic devices, the dimensions of channels are often on the order of micrometers, making the Knudsen number an important factor in designing efficient systems. Engineers need to consider whether the flow can be treated as continuum or if they need to account for molecular effects, which can significantly impact the performance of the device. In aerospace applications, the Knudsen number plays a vital role at high altitudes where the air density is low, and the mean free path of air molecules increases. Understanding the behavior of gases in these conditions is crucial for the design of aircraft and spacecraft, as aerodynamic forces can differ dramatically from those predicted by classical theories. Moreover, the Knudsen number is also relevant in the study of gas adsorption in porous materials, where the pores can be on the same scale as the mean free path of gas molecules. In such cases, the interaction between gas molecules and the solid surface becomes significant, influencing the overall transport properties of the material. In conclusion, the Knudsen number serves as a fundamental parameter that bridges the gap between molecular and continuum descriptions of gas flow. By understanding this concept, scientists and engineers can better predict and manipulate gas behavior in various applications, leading to advancements in technology and improved designs across multiple fields. As our ability to work with smaller scales continues to grow, the importance of the Knudsen number will only increase, making it a critical topic of study in modern physics and engineering.

“Knudsen数”这一概念在流体动力学和气体动力学领域中至关重要。它提供了一个无量纲的量，帮助表征气体的流动状态，特别是在气体分子的平均自由程与系统的特征长度尺度相当时。Knudsen数被定义为气体分子的平均自由程与代表性物理长度尺度（如管道直径或两个表面之间的距离）之比。这个参数对于理解气体在不同条件下的行为至关重要，尤其是在微观和纳米尺度的系统中，传统的流体动力学可能不适用。当Knudsen数远小于1（Kn < 1）时，表明流动可以通过连续介质力学来描述，这意味着气体表现得像是一个连续流体。这是经典流体动力学方程（如Navier-Stokes方程）有效的状态。相反，当Knudsen数大于1（Kn > 1）时，平均自由程相对于系统的大小变得显著，导致非连续效应。在这种情况下，气体的行为无法通过经典流体动力学准确描述，必须应用动理论来理解流动。这些状态之间的过渡在各种应用中至关重要，包括微流体技术、航空航天工程和真空技术。例如，在微流体装置中，通道的尺寸通常在微米级别，使得Knudsen数成为设计高效系统的重要因素。工程师需要考虑流动是否可以视为连续的，或者他们是否需要考虑分子效应，这可能会显著影响设备的性能。在航空航天应用中，Knudsen数在高空中扮演着重要角色，因为空气密度低，空气分子的平均自由程增加。理解这些条件下气体的行为对于飞机和航天器的设计至关重要，因为气动力学力可能与经典理论预测的差异很大。此外，Knudsen数在多孔材料中的气体吸附研究中也相关，其中孔的大小可能与气体分子的平均自由程相当。在这种情况下，气体分子与固体表面之间的相互作用变得显著，影响材料的整体传输特性。总之，Knudsen数作为一个基本参数，架起了分子和连续气体流动描述之间的桥梁。通过理解这一概念，科学家和工程师可以更好地预测和操控气体在各种应用中的行为，从而推动技术进步并改善多个领域的设计。随着我们处理更小尺度的能力不断提高，Knudsen数的重要性只会增加，这使其成为现代物理和工程中一个关键的研究主题。