The temperature in this process is considered to be uniform at a given time. Such an analysis is called Lumped parameter analysis because the whole solid, whose energy at any time is a function of its temperature and total heat capacity is treated as one lump.
What is the criteria for the applicability of lump system analysis?
What is the criterion for the applicability of lump system analysis? Explanation: The first set in establishing criteria for the applicability of lump system analysis is to define a characteristics length. 7.
Is lumped system analysis applicable?
Heat transfer analysis which utilizes this idealization is known as the lumped system analysis. It is applicable when the Biot number (the ratio of conduction resistance within the body to convection resistance at the surface of the body) is less than or equal to 0.1.
What is meant by lumped system analysis?
temperature remains essentially uniform at all times during a heat transfer process. ∎ The temperature of such bodies can be taken. to be a function of time only, T(t). ∎ Heat transfer analysis that utilizes this. idealization is known as lumped system.
When we can use lumped heat capacity method?
The lumped-heat-capacity method of analysis is used in which no temperature gradient exists. This means that the internal resistance of the body (conduction) is negligible in comparison with the external resistance (convection).
Which substance has highest value of thermal conductivity?
|Common metals ranked by thermal conductivity|
|Rank||Metal||Thermal Conductivity [BTU/(hr·ft⋅°F)]|
In what medium is the lumped system analysis more likely to be applicable?
11-9C The lumped system analysis is more likely to be applicable in air than in water since the convection heat transfer coefficient and thus the Biot number is much smaller in air.
Which material is suitable for lumped analysis?
Therefore, small bodies with high thermal conductivity are good candidates for lumped system analysis. Note that assuming h to be constant and uniform is an approximation. A thermocouple junction, which may be approximated by a sphere, is to be used for temperature measurement in a gas stream.
What is effectiveness of fin?
2 Fin Efficiency and Surface Effectiveness. Fin efficiency is defined as the ratio of actual heat flow of the fin to that which would be obtained with a fin of constant temperature uniformly equal to the base surface temperature, that is, one with infinite thermal conductivity.
What is the criterion of the lumped system analysis?
Lumped system analysis assumes a uniform temperature distribution throughout the body, which implies that the conduction heat resistance is zero. Thus, the lumped system analysis is exact when Bi = 0. Therefore, small bodies with high thermal conductivity are good candidates for lumped system analysis.
What is LC in heat transfer?
Lc [m] is the characteristic length of a material, h [W/(m² * K)] is the heat transfer coefficient at the material’s surface, k [W/(m * K)] is the thermal conductivity of the material. Bi is the resulting Biot number.
What is K in Nusselt number?
In the case of the Biot number, k is the thermal conductivity of the solid. In the case of the Nusselt number, k is the thermal conductivity of the fluid flowing around the body.
How do you increase fin effectiveness?
- P.Kh.Ac should be greater than unity if the rate of heat transfer from the primary surface is to be improved.
- If the ratio of P and Ac is increased , the effectiveness of fin is improved.
- Use of fin will be more effective with materials of large thermal conductivities.
What is lumped capacity method?
Definition. The lumped thermal capacity model is the simplest transient heat conduction approach. In this model, the temperature of the solid body is a function of the time only, which means that the temperature is assumed to be spatially independent (uniform).
What is the correct formula for the rate of heat transfer?
q = k A l ΔT.
What is the purpose of using fins in heat transfer?
In the study of heat transfer, fins are surfaces that extend from an object to increase the rate of heat transfer to or from the environment by increasing convection. The amount of conduction, convection, or radiation of an object determines the amount of heat it transfers.