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01:20Mechanisms of Heat Transfer II
In convection, thermal energy is carried by the large-scale flow of matter. Ocean currents and large-scale atmospheric circulation, which result from the buoyancy of warm air and water, transfer hot air from the tropics toward the poles and cold air from the poles toward the tropics. The Earth’s rotation interacts with those flows, causing the observed eastward flow of air in the temperate zones. Convection dominates heat transfer by air, and the amount of available space for the airflow...
01:14Mechanisms of Heat Transfer I
Just as interesting as the effects of heat transfer on a system are the methods by which the heat transfer occur. Whenever there is a temperature difference, heat transfer occurs. It may occur rapidly, such as through a cooking pan, or slowly, such as through the walls of a picnic ice box. So many processes involve heat transfer that it is hard to imagine a situation where no heat transfer occurs. Yet, every heat transfer takes place by only three methods: conduction, convection, and radiation.
01:14Mechanisms of Heat Transfer
Heat transfer between the human body and its environment occurs through four main mechanisms: conduction, convection, radiation, and evaporation.
Conduction, accounting for approximately 3% of body heat loss at rest, is the process of exchanging heat between molecules of two materials in direct contact. This can result in both heat loss and gain. For instance, when the body is submerged in water, which conducts heat 20 times more effectively than air, it can either lose or gain significant heat.
Conduction, accounting for approximately 3% of body heat loss at rest, is the process of exchanging heat between molecules of two materials in direct contact. This can result in both heat loss and gain. For instance, when the body is submerged in water, which conducts heat 20 times more effectively than air, it can either lose or gain significant heat.
01:22Couette Flow
Couette flow represents the flow of fluid between two parallel plates, with one plate fixed and the other moving with a constant velocity. This configuration allows for a simplified analysis using the Navier-Stokes equations, which govern fluid motion under conditions of viscosity and incompressibility. For Couette flow, the assumptions include a steady, laminar, incompressible flow with a zero-pressure gradient in the flow direction. This flow type is beneficial for understanding shear-driven...
01:17Steady, Laminar Flow Between Parallel Plates
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
01:19Mechanism of heat transfer
Understanding heat transfer mechanisms is essential for understanding how our bodies maintain balance in different environmental conditions. When the environment is thermoneutral, the body is in a state of balance, neither using nor releasing energy to maintain its core temperature. However, when the environment is not thermoneutral, the body employs four heat transfer mechanisms to maintain homeostasis: conduction, convection, evaporation, and radiation. These mechanisms facilitate heat...
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07:32
Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns
Published on: April 10, 2017
Enhanced heat flow in the hydrodynamic collisionless regime.
R Meppelink1, R van Rooij, J M Vogels
1Atom Optics and Ultrafast Dynamics, Utrecht University, P.O. Box 80,000, 3508 TA Utrecht, The Netherlands.
Physical Review Letters
|October 2, 2009
Summary
We observed enhanced heat conduction in a cold thermal cloud due to atoms with high angular momentum. These nearly collisionless atoms significantly contribute to heat transfer in the asymmetric trap.
Area of Science:
- Atomic, Molecular, and Optical Physics
- Quantum Gases
- Thermodynamics
Background:
- Understanding heat conduction in confined quantum systems is crucial for various applications.
- Previous studies often focused on homogeneous systems, leaving the behavior in asymmetric traps less explored.
- Cold thermal clouds exhibit unique properties due to quantum effects and reduced dimensionality.
Purpose of the Study:
- To investigate the heat conduction properties of a cold thermal cloud in a highly asymmetric trap.
- To analyze the influence of trap geometry on thermal transport mechanisms.
- To identify and characterize emergent hydrodynamic and sound modes.
Main Methods:
- Utilized a cold thermal cloud confined in a highly asymmetric trap.
- Locally heated the cloud to excite a thermal dipole mode.
- Measured the oscillation frequency and damping rate of the excited mode.
Main Results:
- Observed significantly enhanced heat conduction compared to homogeneous systems.
- Identified that atoms with high angular momentum, spiraling in nearly collisionless trajectories, contribute to this enhanced heat transfer.
- Detected a second oscillating hydrodynamic mode, identified as a standing wave sound mode.
Conclusions:
- The asymmetric trap geometry fundamentally alters heat conduction in cold thermal clouds.
- Collisionless, high angular momentum atomic trajectories are key to the enhanced heat transport.
- The study reveals complex hydrodynamic behaviors, including standing wave sound modes, in such systems.