What is a lumped system?
A lumped system is one in which the dependent variables of interest are a function of time alone. In general, this will mean solving a set of ordinary differential equations (ODEs) A distributed system is one in which all dependent variables are functions of time and one or more spatial variables.
What is meant by lumped heat analysis?
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).
What does the transient conduction mean?
During any period in which temperatures changes in time at any place within an object, the mode of thermal energy flow is termed transient conduction. Another term is “non-steady-state” conduction, referring to time-dependence of temperature fields in an object.
What is the use of lumped 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 distributed resistance?
In some analyses, the actual flow geometry may contain a large number of holes or obstructions. This resistance simulates the effect of the obstructions without using an inordinate number of elements. Other examples of porous media include radiators, vents, screens, filters and packed beds.
What is the difference between a lumped and distributed system?
“Lumped System” – the dependant variables (V & I) are only a function of time. “Distributed System” – the dependant variables (V & I) are a function of time AND space. – We say that any conductor that has Length, needs to be treated as a distributed system.
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.
What is meant by transient heat transfer?
Transient Heat Transfer In transient heat transfers, the heat energy transferred through the medium is not constant. The heat flow rate keeps changing, and the cause of the varying rates of heat transfer can be either fluctuating temperature differences over the medium or changes in properties of the medium.
What does transient heat transfer mean?
Transient Heat Transfer This type of heat transfer only exists for a short duration of time. In transient heat transfers, the heat energy transferred through the medium is not constant. In the physical world, heat transfer starts as transient and then reaches a steady-state until thermal equilibrium is reached.
What is semi infinite solid?
A semi-infinite solid is an idealized body that has a single plane surface and extends to infinity in all directions except one. If a sudden change is imposed to this surface, transient one-dimensional conduction will occur within the solid.
What is meant by natural or free convection?
Natural convection, known also as free convection is a mechanism, or type of mass and heat transport, in which the fluid motion is generated only by density differences in the fluid occurring due to temperature gradients, not by any external source (like a pump, fan, suction device, etc.).