# Homework Help: Rate of heat transfer for a steel object in light oil

1. Apr 29, 2012

### Ezza_Eng

1. The problem statement, all variables and given/known data
I am required to conduct a thermal shock test where by a stainless steel object (complicated geometry) is to go from one tank of light oil at -55°C to another tank of the same light oil at +140°C, then back the -55°C tank. This is to be repeated 5000 times.

In order to roughly determine how long the test shall take (primarily for costing reasons), I need to know once the test object is at -55°C and it is transferred to the hot tank at +140°C, how long it takes to reach +140°C.
I assume to go from +140 to -55°c will take the same time?
The transfer time between the two tanks is known and will be quoted as a maximum time. This will be added to the heat transfer time that I am looking for.

Both tanks are to be constantly held at their respective temperatures.

2. Relevant equations
Q=mCΔT

3. The attempt at a solution
I can find values for specific heat capacity and coefficient s of heat transfer, but I am not sure how to use them in this situation. Do I use the difference of the heat capacities of the steel and the light oil? It seems correct to consider the properties of both the test object and the fluid it is submerged in.

Is it as simple as using the equation above and then applying the work that can be done by the heating/cooling equipment of the relevant tanks? But as I stated earlier, the tanks are to be held at temperature.

I am sure this is a fairly simple solution and I am missing something key to it! any help will be greatly appreciated.

2. Apr 29, 2012

### Staff: Mentor

Hello Ezza_Eng, Welcome to Physics Forums.

"Consider a spherical cow".... Your problem has enough vague patches that I think you're entitled to make some crude assumptions. For example, if you assume that that the oil baths are agitated you won't have to worry about temperature gradients therein.

A lumped-mass model of the object along with an estimate of its surface area in order to find a figure for thermal resistance at its boundary will probably suffice for ballpark calculations of cooling/heating times. Assume that its internal thermal conduction rate is sufficiently larger than the heat transfer rate at the surface so the object has an essentially uniform temperature.

Of course, if the object is pathologically shaped -- like a large ball of metal with giant heat sink fins attached by a thick rod to one point, you're going to be in deep weeds