Name: heat transfer calculations with conduction, convection
Uploaded: 2023-09-18T17:11:17.000Z
Duration: 1 min 20 s
Channel: JoVE

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NC K-12 Science Standard Course of Study

9-12

Physical Science

Energy

PS.PSc.7.1

conduction-convection-and-radiation-problem-solving

Conduction, Convection and Radiation: Problem Solving

Una parete spessa 13 cm con un'area di 100m2 e una conducibilità termica di 1,5 W/mK separa una stanza dall'atmosfera esterna, che si trova a 3 gradi Celsius.
La superficie esterna del muro è a 10 gradi Celsius e la sua emissività è 0,8. Se il coefficiente di scambio termico convettivo è 15 W/m2K , trovare il tasso di perdita di calore totale nell'ambiente circostante. Inoltre, calcola la temperatura della superficie interna del muro.
In questo caso, sono coinvolti tutti e tre i meccanismi di trasferimento del calore. Il calore viene trasferito dalla superficie interna a quella esterna della parete attraverso la conduzione, mentre la perdita di calore nell'ambiente circostante avviene a causa della convezione e dell'irraggiamento.
Il tasso di perdita di calore per convezione dipende dal gradiente di temperatura, dalla superficie e dal coefficiente di scambio termico.
Quindi, la perdita totale di calore nell'ambiente circostante a causa della convezione e dell'irraggiamento può essere calcolata come 13,27 x 103 W.
Utilizzando la conservazione dell'energia e sostituendo i termini nell'equazione del calore, è possibile calcolare la temperatura della superficie interna della parete.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/1-6-mechanisms-of-heat-transfer">https://openstax.org/books/university-physics-volume-2/pages/1-6-mechanisms-of-heat-transfer</a></li>
</ol>

conduzione, convezione e radiazione: risolvere i problemi

Ci sono tre metodi attraverso i quali il trasferimento di calore può avvenire: conduzione, convezione e radiazione. Ogni metodo ha caratteristiche uniche ed interessanti, ma tutti e tre hanno due cose in comune: trasferiscono calore solamente a causa di una differenza di temperatura; e maggiore è la differenza di temperatura, più veloce è il trasferimento di calore.

Per risolvere un problema relativo al trasferimento di calore, innanzitutto, la situazione deve essere esaminata per determinare il tipo di trasferimento di calore coinvolto. Questo potrebbe essere conduzione, convezione, radiazione, o tutti e tre. Il secondo passo è identificare e scrivere le grandezze sconosciute nel problema. Si può preparare un elenco di ciò che è dato o ciò che può essere dedotto dal problema come enunciato, cioè le grandezze conosciute, seguite dalla risoluzione dell'equazione appropriata per la grandezza da determinare.

Per il trasferimento di calore attraverso la conduzione, dovrebbe essere utilizzata la seguente equazione.

<img alt="Equation1" src="/files/ftp_upload/14166/14166_Equation_1.svg" style="text-align: center; height: 46px;" />

Per la convezione, il tasso di perdita di calore dipende dal gradiente di temperatura, dall'area superficiale e dal coefficiente di trasferimento del calore.

<img alt="Equation2" src="/files/ftp_upload/14166/14166_Equation_2.svg" style="text-align: center; height: 18px;" />

La seguente equazione fornisce il tasso netto di trasferimento di calore per radiazione.

<img alt="Equation3" src="/files/ftp_upload/14166/14166_Equation_3.svg" style="text-align: center; height: 25px;" />

Sostituendo le grandezze conosciute insieme alle loro unità nell'equazione appropriata e risolvendola numericamente si ottiene la soluzione corretta.

Conduzione, convezione e radiazione: risolvere i problemi

Esistono tre metodi con cui può avvenire il trasferimento di calore: conduzione, convezione e irraggiamento. Ogni metodo ha caratteristiche uniche e interessanti ...

Education

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Physics

Fisica

Unit 1

Unità 1

Temperature and Heat

Temperatura e Calore

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

heat transfer calculations with conduction, convection

Heat transfer calculations with conduction and convection use the temperature difference to find the rate of heat flow. Radiation can also be part of the process. The main idea is that heat moves only because one area is hotter than another, and a larger temperature difference leads to faster transfer.

To solve a heat transfer problem, first identify the type of transfer involved. It may be conduction, convection, radiation, or a combination of all three. Next, write down the unknown quantities and sort the given information from the problem statement.

After the known values are listed, choose the correct equation for the type of heat transfer. Use the conduction equation for heat flow through materials. For convection, the rate of heat loss depends on the temperature gradient, the surface area, and the heat transfer coefficient. For radiation, use the equation for net heat transfer rate.

Finally, substitute the known quantities and their units into the selected equation. Solve the equation numerically to find the answer. This method helps students work through heat transfer problems in a clear, step-by-step way.

Heat Transfer Calculations with Conduction, Convection

heat-transfer-calculations-with-conduction-convection

temperature and thermal equilibrium

Heat, Temperature, and Everyday Energy

Heat and temperature are key ideas in thermodynamics and in everyday life. People often connect temperature with hot and cold, but science gives it a more precise meaning. Temperature is the quantity measured with a thermometer. It is also linked to the average translational kinetic energy of particles. Heat is different from temperature. Heat is energy that moves from one place or material to another because there is a difference in temperature. That difference in temperature keeps heat...

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The zeroth law of thermodynamics explains thermal equilibrium between objects. If object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is also in equilibrium with object C. This transitive relationship is the key idea behind the law. A simple example uses metal blocks and a metal plate at room temperature. A cold metal block and a hot metal block are both placed on the plate. Over time, the cold block and the plate reach thermal equilibrium, and...

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gas thermometers and the kelvin scale

Kelvin Temperature and Gas Thermometer Standards

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Thermal Expansion in Air, Water, and Solids

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Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile. This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up. When gaps...

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mechanisms of heat transfer i

Three Ways Heat Moves Between Objects

Heat transfer happens when there is a temperature difference. It can move fast, like through a cooking pan, or slowly, like through the walls of a picnic ice box. Heat transfer appears in many everyday situations, so it is hard to find a place where it does not occur. There are only three ways heat is transferred: conduction, convection, and radiation. A fireplace shows all three at once. Radiation carries most of the heat into the room. Conduction also moves heat into the room, but much more...

mechanisms of heat transfer ii

Convection and Radiation in Heat Transfer

Convection and radiation are two major ways heat moves. In convection, thermal energy is carried by the large-scale flow of matter. Warm air and water rise because they are less dense, so ocean currents and large-scale atmospheric circulation move heat from the tropics toward the poles and move cold air from the poles toward the tropics. Earth’s rotation changes these moving air currents. It interacts with the flow and helps produce the eastward movement of air in the temperate zones.

conduction, convection and radiation: problem solving

Heat transfer calculations with conduction and convection use the temperature difference to find the rate of heat flow. Radiation can also be part of the process. The main idea is that heat moves only because one area is hotter than another, and a larger temperature difference leads to faster transfer. To solve a heat transfer problem, first identify the type of transfer involved. It may be conduction, convection, radiation, or a combination of all three. Next, write down the unknown...

radiation: applications

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Earth’s energy balance and the greenhouse effect help explain its average temperature. Earth is in radiative contact with both the Sun and dark space. It receives almost all of its energy from solar radiation, and it reflects some of that energy back into outer space. Dark space is very cold, about 3 K, so Earth also radiates energy into it. Heat can move quickly from soil and grasses, and frost can form on clear summer evenings, even in warm latitudes. In a first approximation, Earth’s...

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Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins. The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation...

key terms and concepts

Learn how to solve heat transfer problems by identifying conduction, convection, or radiation, choosing the right equation, and calculating the unknowns.

Heat Transfer Calculations with Conduction, Convection | JoVE K12

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Energy Basics

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Mechanisms 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 ...

Mechanisms 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 ...

There are three methods by which heat transfer can take place: conduction, convection, and radiation. Each method has unique and interesting ...

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Conservation of Mechanical Energy

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Non-conservative Forces

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Conservation of Energy

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Conservation of Energy: Application

When solving problems using the energy conservation law, the object (system) to be studied should first be identified. Often, in applications of energy ...

Use mathematics and computational thinking to explain the Law of Conservation of Energy in a mechanical system in terms of kinetic and potential energy.

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Work

Work is done when energy is transferred from one object to another. In other words, work is when a force acts on something that undergoes a displacement ...

Positive, Negative, and Zero Work

Work is done on an object when energy is transferred to the object. In other words, work is done when a force acts on a body that undergoes a displacement ...

Work-energy Theorem

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Work Done Over an Inclined Plane

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Work Done by Many Forces

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Work Done by Gravity

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Use mathematics and computational thinking to explain work in terms of the relationship among the applied force to an object, the resulting displacement of the object, and the energy transferred to an object.

PS.PSc.7.3

Power

The concept of work involves force and displacement; meanwhile, the work-energy theorem relates the net work done on a body to the difference in its ...

Power Expended by a Constant Force

The relationship between work done and the time taken to do it can be explained using the concept of power. For example, several sprinters in a race may ...

Construct an explanation to infer the relationship between work and power, both quantitatively and qualitatively.

PS.PSc.7.4

Analyze energy transfers and transformations within a mechanical system.

Heat Transfer Calculations with Conduction, Convection

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