Correction For Bob B's AH page

[PhantomWolf]

I note on your page you say:

Water sprayed into a vacuum experiences a very rapid drop in pressure and, consequently, temperature. Hence, when a small amount of water was sprayed onto a cooling element on the rear of the spacesuit, its temperature dropped so much that it would immediately freeze onto the element.

This is wrong from what I understand. The Sublimator didn't have water sprayed onto it, but it "leaked" through the semi-permiable nickel plates. NASA's PLSS page states:

The feedwater flows into the sublimator, where it is added to a layer of ice and, ultimately evaporates and carries away excess heat.

Which admittedly isn't entirely helpful. However Jay states this on Clavius.

A device used in a space suit or a space craft that provides a method of cooling in space. Water is allowed to seep through the pores in a porous nickel plate into the surrounding vacuum where it freezes into an ice cake covering nearby coils of tube. Coolant pumped through the coils is cooled by the ice, which then sublimates into the vacuum carrying away the heat with it. The sublimated ice is replaced by more water through the plate.

Anyway, thought you might was to fix it. (After all why should I be the only one re-writing my PLSS section 20 odd times.

[Bob B.]

I'm aware that description is incorrect and it is on my list of things to fix. I've got some other changes I want to make as well but I've been working on other things lately. I was planning to put it off until I can set aside enough time to get everything done, but I might go ahead and fix the PLSS section. Thanks for pointing out the error. If you see any other mistakes don't hesitate bringing them to my attention.

[Bob B.]

How does the following sound? Is my description of the system's operation correct? In keeping with the format of my page, I've tried to explain the concept in as few words as possible.

The cooling system consisted of a cooling garment worn by the astronaut, a heat exchanger, and a porous plate sublimator. Water was circulated through tubes in the cooling garment where it absorbed heat from the astronaut’s body and then carried it to the heat exchanger in the backpack. As water passed through the heat exchanger, heat was transferred to a layer of ice on the surface of the porous plate sublimator causing the ice to sublimate and the resulting gas carried away the unwanted heat. The ice was replaced by continually seeping a small amount of water through holes in the metal plate of the sublimator. When the water was exposed to the vacuum of space, the sudden drop in pressure caused it to immediately freeze onto the plate’s surface.

[PhantomWolf]

Sounds good, and like I understood it, however, after reading this page I'm not sure that the heat from the Cooling Loop water was passed to the ice via the heat exchanger, but rather to it seems to have been transfered to the feedwater for the subliminator.

The water then flowed out of the LCG, through a connecting hose, and into the backpack where it was cooled before flowing back to the LCG. This supply of LCG cooling water flowed in a closed-loop system and there was never any appreciable loss during the course of the mission. Inside the backpack, there was another supply of water called the feedwater; this was fed at a controllable rate through a heat exchange coil where it extracted heat from the LCG water. After being heated in the coil, the feedwater was then allowed to sublimate into the lunar vacuum and, thereby, carried away the excess heat.

[Bob B.]

I’ve never heard the operation described that way. I question how accurate that is because it seems to me that a water-to-water exchange would be very inefficient. I thought the whole idea behind a sublimator was that the heat required to sublimate the ice was extracted directly from the water in the cooling loop.

In a water-to-water exchange, it takes one calorie of heat to raise the water temperature one degree Celsius. How much heat can reasonably be transferred, perhaps a few calories per gram of water? On the other hand, the heat of sublimation of water is 680 calories per gram. One gram of ice can extract many times as much heat as can be transferred between water circuits.

We’ve done the math on this before and it seems to me the only way the amount of water carried can provide the amount of cooling necessary is with a water-to-ice exchange.

[Moon Man]

bob said:

If you see any other mistakes don't hesitate bringing them to my attention.

Um, I tried this and you still haven't made the correction.

[PhantomWolf]

He said mistakes, not things you don't undeerstand because of ignorance and refusal to learn.