Cheeseburgers per hour?

In the last two posts, we considered the units of food energy, and some of the issues associated with calculating human energy use. Today we’ll look at different views of calculating energy use from exercise.

Cheeseburgers per day?

Last post we talked about the units used for describing the energy content of food.  For the purposes of an energy balance on the body, we also have to consider the efficiency of converting food energy into activity.

How many Calories in a cheeseburger?

Sometimes it seems like most of the people you meet are on a diet of some kind—either to lose weight, gain weight, or stay the same. In any case, it seems reasonable to assume that diets ultimately have to be about the amount of energy that you take in as food or drink, and the amount of energy that your body burns through exercise or just existing. Today we’ll talk about the units used to measure energy in food.

Applied Contact Temperature

We’ve talked before about the contact temperature and the effect that different materials have on the temperature that you feel when you first touch them.  Today we’ll look at that effect in a more applied way.

Snow Sublimation

If you live in an area with snow, you’ve probably experienced a snowfall followed by several cold clear days. If it lasted long enough, you may have noticed that the snow gradually starts to disappear (sublimate) even when the air temperature never gets above the melting point. In this post, we’ll look at the speed of that effect.

More Lumped Capacitance

Last post we looked at another extension of lumped capacitance beyond our original exploration here and here.  In the last post, we looked at a case where the heat transfer coefficient increased linearly with time, which might be a good approximation for the initial moments of the heat transfer for an object in a duct with the fan just starting up.  Today we’ll look at a case where the heat transfer coefficient is decreasing.

Lumped Capacitance Revisited

Lumped capacitance is a very useful heat transfer approximation that we mentioned originally here,  and explored in more depth with extensions here and here.  Today, we’ll look at another extension of the basic lumped capacitance approach.

Refrigerant 718

News flash! A major spill of refrigerant R718 occurred on the Interstate last night!  The refrigerant soaked the highway and surrounding ground.  Luckily, in a few hours it dried up with no effect other than helping nearby plants and small animals.  Because, of course, refrigerant R718 is the designation for pure water.  Today we’ll consider advantages and disadvantages of using water as a refrigerant.

The Ideal Gas Law and the Superheated Region

Last post we talked about using the ideal gas law on the right side of the steam dome and found that it could be used as a decent approximation for very low pressures, even when the vapor is about to start condensing into liquid.  Today we’ll look at the accuracy of the ideal gas approximation out in the superheated region.

The Ideal Gas Law and the Steam Dome

The ideal gas law describes the approximate behavior of gases at temperatures that are high relative to the critical temperature and at pressures that are low relative to the critical pressure.  This figure shows the approximate region where the ideal gas law applies best. 

Normally, one would use steam tables to determine properties close to the saturation region, and only use the ideal gas approximation far away, as shown in the figure. Today we’ll look at the error introduced by the ideal gas approximation as we get close to the saturation region.