The Unsteady State Heat Transfer Experiment - amazonia.fiocruz.br

Remarkable, the: The Unsteady State Heat Transfer Experiment

In thermodynamics Ezperiment, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. Like thermodynamic workheat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of statefor example its internal energyor for example its enthalpy.

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This is to be distinguished from the Experimeny language conception of heat as a property of an isolated system. The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred.

For the precise Tranfser of heat, it is necessary that it occur by a path that does not include transfer of matter. Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies.

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For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy being transferredthe SI unit of heat is the joule J. The mechanisms of energy transfer that define heat include conductionthrough direct contact of immobile bodies, or through a wall or barrier that is impermeable to matter; or radiation between separated bodies; or friction due to isochoric mechanical or electrical or magnetic or gravitational work done by the surroundings on the system of interest, such as Joule heating due The Unsteady State Heat Transfer Experiment an electric current driven through the system of interest by an external system, or through a magnetic stirrer.

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When there is a suitable path between two systems with Transrer temperaturesheat transfer occurs necessarily, immediately, and spontaneously from the hotter to the colder system. Thermal conduction occurs by the stochastic random motion of microscopic particles such as atoms or molecules. In contrast, thermodynamic work is defined by mechanisms that act macroscopically and directly on the system's whole-body state variables ; for example, change of the system's volume through a piston's motion with externally measurable force; or change of the system's internal electric polarization through an externally measurable change in electric field.

The definition of heat transfer does not require that the process be in any sense smooth. For example, a bolt of lightning may transfer heat to a body. Convective circulation allows one body to heat another, through an intermediate circulating fluid that carries energy from a boundary of one to a boundary of the other; the actual heat transfer is by conduction and radiation between the fluid and the respective bodies. Although heat flows spontaneously from a hotter body to a cooler one, it is possible to construct a heat pump which expends work to transfer energy from a colder body to a hotter body.]