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Heat transfer by radiation is a function of both the heat-sink temperature and the temperature of the surroundings that the heat sink is optically coupled with. When both of these temperatures are on the order of 0 °C to 100 °C, the contribution of radiation compared to convection is generally small, and this factor is often neglected.
When the Biot number is greater than 0.1 or so, the heat equation must be solved to determine the time-varying and spatially-nonuniform temperature field within the body. Analytic methods for handling these problems, which may exist for simple geometric shapes and uniform material thermal conductivity , are described in the article on the heat ...
Increasing the temperature gradient between the object and the environment, increasing the convection heat transfer coefficient, or increasing the surface area of the object increases the heat transfer. Sometimes it is not feasible or economical to change the first two options. Thus, adding a fin to an object, increases the surface area and can ...
The opposite is also true: A Biot number greater than 0.1 (a "thermally thick" substance) indicates that one cannot make this assumption, and more complicated heat transfer equations for "transient heat conduction" will be required to describe the time-varying and non-spatially-uniform temperature field within the material body.
This increases to 3.57 with a heat transfer surface temperature of 100 °C (212 °F) (viscosity 2.82 × 10 −4 Pa.s), making a significant difference to the Nusselt number and the heat transfer coefficient.
The behavior of temperature when the sides of a 1D rod are at fixed temperatures (in this case, 0.8 and 0 with initial Gaussian distribution). The temperature approaches a linear function because that is the stable solution of the equation: wherever temperature has a nonzero second spatial derivative, the time derivative is nonzero as well.
In addition, a reversible heat engine operating between temperatures T 1 and T 3 must have the same efficiency as one consisting of two cycles, one between T 1 and another (intermediate) temperature T 2, and the second between T 2 and T 3, where T 1 > T 2 > T 3.
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. [1] A heat pump is a mechanical system that transmits heat from one location (the "source") at a certain temperature to another location (the "sink" or "heat sink") at a higher temperature. [2]