Quenching in a Finite Bath

In an earlier post we looked at the transient 1 dimensional temperature profiles and

temperature gradients across a piece of metal being quenched in a tank large enough that the temperature of the quench fluid never changed.  In this post, we’ll look at a different case: a piece of steel small enough that the temperature is uniform across the piece which is being quenched in a bath small enough that the temperature of the quench fluid goes up as the steel cools down.  We’ll assume that the quench fluid is well-stirred so that it can also be characterized by single temperature.

An Alternate View of Condensation

Usually when we think of condensation, we think of the droplets of water that form on a cold glass on a humid day, or perhaps we think of dew making the grass wet on a summer morning, or maybe the fog that forms on the bathroom mirror after you have a hot shower.  In those familiar cases of condensation, the water vapor is mixed in with dry air in a very dilute mixture.  For example, at 75 deg F, 60% relative humidity, the water vapor comprises only about 1.1% of the total moist air, by mass.  Even at 75 deg F, 100% relative humidity, (at which point the vapor is about to start condensing to liquid) the water vapor is only about 1.8% of the mixture.  So, we’re accustomed to condensation of water from a very dilute mixture of water vapor in air.  In this blog, we’ll consider the condensation of pure water vapor, and see some surprising forces.

Thermal Gradients from Quenching

Many heat treating operations involve a quench—that is, an immersion in a fluid at a lower temperature in order to achieve a rapid cooling rate. It is commonly used for hardening in ferrous metals. Quench fluids include air, water, oils, and many others. From a heat transfer standpoint, quenching of a hot metal has a lot of interesting aspects: determining the heat transfer coefficient (possibly with phase change) at the surface, calculating transient temperature profiles inside the material (with implications for thermal stresses and metallurgical properties), effects of thermal transport properties (possibly time-dependent, or spatially non-uniform) on the heat transfer, and others. In this post, we’ll discuss transient temperature profiles and temperature gradients induced by quenching a one-dimensional (wide enough and long enough that the main effects are controlled by the thickness) piece of tool steel. 

Isothermal and Isoflux Boundary Conditions

In analytical conduction problems, two commonly used boundary conditions are isothermal, meaning that the temperature at the boundary is fixed, and isoflux, which means that the heat flux at the boundary is fixed. The two are mutually exclusive (you can’t specify both the heat flux and the temperature on a single boundary) and lead to very different thermal behaviors inside the body. In this post, we’ll look at the effects of these two boundary conditions.

Laser Melting of a Plastic

A high-intensity laser beam that deposits energy over a millisecond time scale into a mostly transparent plastic is an ideal candidate for analysis using the equations of thermal explosions.  

More Useful Lumps (Part 2)

In our last post, we examined the case of lumped capacitance where the free-stream temperature was a function of time and presented the equation governing that situation. This time, we’ll look at some specific examples.

More Useful Lumps

All beginning heat transfer classes cover the topic of lumped capacitance calculations: the case where heat conduction within a body is fast enough that the entire body can be considered to be at a single temperature. 

This is a very useful tool for estimating heat transfer in some situations.   However, with just a little work, we can extend the tool to a broader application.