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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
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.
01:14Mechanisms 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.
01:19Mechanism 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...
01:12Heat Flow and Specific Heat
Heat is a type of energy transfer that is caused by a temperature difference, and it can change the temperature of an object. Since heat is a form of energy, its SI unit is the joule (J). Another common unit of energy often used for heat is the calorie (cal), which is defined as the energy needed to change the temperature of 1 g of water by 1 °C, specifically between 14.5 °C and 15.5 °C, since the energy needed shows a slight temperature dependence. Another commonly used unit is the kilocalorie...
01:27Laminar Flow
Laminar flow represents a smooth, orderly fluid motion where particles move along parallel paths, resulting in minimal mixing between layers. Streamlined particle paths characterize this flow regime and occur under conditions where viscous forces dominate over inertial forces. The distinction between laminar, transitional, and turbulent flow is primarily determined by the Reynolds number, a dimensionless quantity calculated as:
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Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns
Published on: April 10, 2017
Boiling local heat transfer enhancement in minichannels using nanofluids.
Ali Ahmad Chehade1, Hasna Louahlia Gualous, Stephane Le Masson
1Université de Caen Basse Normandie, LUSAC, 120 rue de l'exode, Saint Lo, 50000, France. hasna.louahlia@unicaen.fr.
Nanoscale Research Letters
|March 20, 2013
Summary
This study investigated silver nanofluids for heat transfer in minichannels. Adding silver nanoparticles to water enhanced convective boiling heat transfer, especially near the channel entrance.
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Area of Science:
- Heat Transfer
- Nanofluids
- Convective Boiling
Background:
- Minichannel heat sinks are crucial for thermal management in electronics.
- Understanding nanofluid behavior in minichannels is vital for improving heat transfer efficiency.
Purpose of the Study:
- To experimentally investigate convective boiling heat transfer of silver-based nanofluids in parallel rectangular minichannels.
- To evaluate the effect of low silver nanoparticle concentrations on heat transfer performance.
- To assess existing heat transfer correlations for minichannel boiling.
Main Methods:
- Experimental setup with parallel rectangular minichannels (800 μm hydraulic diameter).
- Testing with pure water and silver-nanoparticle suspensions (0.000237% and 0.000475% volume fractions).
- Measurement of local heat transfer coefficient, heat flux, and wall temperature.
Main Results:
- Silver nanoparticle concentration significantly affects local heat transfer coefficient, heat flux, and wall temperature.
- The Kandlikar and Balasubramanian correlation best predicts water boiling heat transfer.
- Heat transfer enhancement by nanofluids is non-uniform, with greatest effects at the minichannel entrance.
Conclusions:
- Silver nanofluids show potential for enhancing convective boiling heat transfer in minichannels.
- Nanoparticle concentration and position along the channel influence heat transfer performance.
- Further research into nanofluid optimization for minichannel applications is warranted.