# Lumped Capacitance Analysis

Question asked by Andrew DeMedeiros on Nov 3, 2010
Latest reply on Nov 6, 2010 by Andrew DeMedeiros

I am trying to run a transient analysis of a lumped capacitance problem, it is a school assignment. Unfortunately I am having a very difficult time getting my simulation to work out correctly. The piece in question is a steel bar, 6cm in diameter and 20cm long. Calculating out the respective biot number proves that it is in fact a lumped capacitance system. The problem provides us with various material properties (Density, Cp,k) and with the convection coefficient of the fluid. Intial temperature and fluid temperature are given also.

It is required that I find the temperature at time=50s, doing this out by hand I come to about 270C or so. The problem arises when I try to simulate it, I set the study to transient, with a time of 50s and a step of 1s. I set the initial temperature of the piece, and I set the respective convection parameters, after meshing and running I get ridiculous results. It tells me that the temperature of the piece is 93K, so -180C. This is impossible as my fluid temperature is 20C.

Can anyone help me out with this?

Problem parameters are:

Diameter=6cm

Length=20cm

K= 43 W/mK

C = 473 J/kgK

Density = 7800 kg/m3

h = 110 W/m2K

To = 300 °C

Tfluid = 20 °C

Thanks!!!