‘To heat a planetary surface’ for dummies; Part 3

We’re still discussing Willis Eschenbach’s ‘Steel Greenhouse’.

How come the warming EFFECT of putting the shell around the sphere is real but Eschenbach’s “back radiation” EXPLANATION of how it comes about is wrong?

Simply put, it’s because the effect doesn’t violate the 2nd Law of Thermodynamics, but the explanation does.

In Part 1 and Part 2 we established some fairly basic principles of thermodynamics that we can now put to use in analysing Eschenbach’s explanation of why and how the radiating central sphere needs to warm with the steel shell surrounding it:

“In order to maintain its thermal equilibrium, the whole system must still [after the steel shell is placed around the sphere] radiate 235 W/m2 out to space. To do this, the steel shell must warm until it is radiating at 235 watts per square metre. Of course, since a shell has an inside and an outside, it will also radiate 235 watts inward to the planet. The planet is now being heated by 235 W/m2 of energy from the interior, and 235 W/m2 from the shell. This will warm the planetary surface until it reaches a temperature of 470 watts per square metre. In vacuum conditions as described, this would be a perfect greenhouse, with no losses of any kind.”

The first part of this paragraph simply describes the necessary conditions for reaching a new dynamic equilibrium upon putting the steel shell up around the radiating sphere. Nothing mysterious about it at all.

But then (in the bolded part) Eschenbach starts ‘explaining’ how he sees this new state of dynamic equilibrium to be accomplished.

And this is where any connection to basic, ordinary physics – and hence, to the real world – appears to be lost.

Let’s parse what he’s saying: Continue reading

‘To heat a planetary surface’ for dummies; Part 2

For something – anything – to acquire a temperature above absolute zero (0 K), it somehow needs to be able to warm. The only real requirement for something to be able to warm is for it to possess a ‘thermal mass’, or simply ‘mass’. A thermal mass provides the thing in question with what is (a bit awkwardly) called a ‘heat capacity’, meaning a capacity to absorb and store energy from some energy source (external or internal).

We already know, from basic thermodynamic principles, how energy can be transferred to (or from) an object. It can be transferred in the form of ‘heat’ [Q] or in the form of ‘work’ [W]. Whenever energy is transferred to an object, the ‘internal energy’ [U] of that object increases as a result, which simply means that the object in question has absorbed (energy isn’t ‘transferred’ to a system until it’s actually become ‘absorbed’ by it) the energy to store it inside its mass, as microscopic kinetic and potential energy of its atoms and molecules.

We already know, from the first post in this series, how system ‘internal energy’ [U] relates to system ‘temperature’ [T]. We know that a system with a high ‘heat capacity’ will warm more slowly than a system with a low ‘heat capacity’, both systems absorbing equal energy inputs, the high-heat-capacity system simply storing a larger portion of the absorbed energy as internal/molecular PE rather than as internal/molecular KE (determining the temperature). Both systems, however, will warm, only at different rates. U and T invariably move in the same direction. Unless there is an ongoing phase transition. Then U will increase and T will not. There is no process, though, where U increases and T decreases. The two correspond.

OK. We know that to make an object warm, we must make it accumulate ‘internal energy’. If it doesn’t, it cannot warm. Continue reading