Two sunbeams back to the shop

[hamo]

The Good Guys had a special this week on EM6910s with grinder for just $549.00 so I decided to jump in.

I've been using a 6910 for 8 years now and have it pretty well mastered in terms of producing a decent shot and texturing great milk.

Well... I'm not sure what happened this week but I sent both of then back and got a refund.

Both machines had trouble texturing milk. The steam wand is powerful, but it spluttered a number of times in the texturing process rather than giving a steady flow.

That ended up with bubbles rather than smooth milk. Both machines did the same thing. If you didn't know how to texture milk you'd think it was acceptable. But it's not...

The Good Guys were very good in accepting it back. I had to demonstrate the fault to them as they didn't really 'get' the issue. (It was hot and pumping so it was all good as best they knew...)

I also didn't like the new grinders that didn't have the on/off button. They splattered a lot of coffee grounds around.

Right now I'm using the coffee machine out of my caravan until I work out where to next!

Pretty disappointing that the em6910 couldn't cut it.

[Journeyman]

Don't know if it is still going but Harvey Norman had a special on EM7000's for $400 during the week.

[hamo]

Will check it out - that would be cool

[rawill]

The steam wand is powerful, but it spluttered a number of times in the texturing process rather than giving a steady flow.


Pretty disappointing that the em6910 couldn't cut it.

Weird, I would have thought spluttering in the steam would have been water getting in and causing the "splutter", like happens when purging the wand before starting to steam.

[Yelta]

Weird, I would have thought spluttering in the steam would have been water getting in and causing the "splutter", like happens when purging the wand before starting to steam.

Steam is water that has cooled to the point that it becomes a liquid and as such begins to "sputter"

There is obviously a problem with the way the machine is set up, or the flow of steam is such that it cools and turns to water before the exit nozzle, this is where the spluttering occurs.

[Yelta]

Steam is heated water that has cooled to the point that it once again becomes a liquid and as such begins to "sputter"

There is obviously a problem with the way the machine is set up, or the flow of steam is such that it cools and turns to water before the exit nozzle, this is where the spluttering occurs.

Steam

As the temperature increases and the water approaches its boiling condition, some molecules attain enough kinetic energy to reach velocities that allow them to momentarily escape from the liquid into the space above the surface, before falling back into the liquid.

Further heating causes greater excitation and the number of molecules with enough energy to leave the liquid increases. As the water is heated to its boiling point, bubbles of steam form within it and rise to break through the surface.

Considering the molecular arrangement of liquids and vapours, it is logical that the density of steam is much less than that of water, because the steam molecules are further apart from one another. The space immediately above the water surface thus becomes filled with less dense steam molecules.

When the number of molecules leaving the liquid surface is more than those re-entering, the water freely evaporates. At this point it has reached boiling point or its saturation temperature, as it is saturated with heat energy.

If the pressure remains constant, adding more heat does not cause the temperature to rise any further but causes the water to form saturated steam. The temperature of the boiling water and saturated steam within the same system is the same, but the heat energy per unit mass is much greater in the steam.

At atmospheric pressure the saturation temperature is 100°C. However, if the pressure is increased, this will allow the addition of more heat and an increase in temperature without a change of phase.

Therefore, increasing the pressure effectively increases both the enthalpy of water, and the saturation temperature. The relationship between the saturation temperature and the pressure is known as the steam saturation curve (see Figure 2.2.1).

Fig. 2.2.1
Steam saturation curve

Water and steam can coexist at any pressure on this curve, both being at the saturation temperature. Steam at a condition above the saturation curve is known as superheated steam:

• Temperature above saturation temperature is called the degree of superheat of the steam.
• Water at a condition below the curve is called sub-saturated water.

If the steam is able to flow from the boiler at the same rate that it is produced, the addition of further heat simply increases the rate of production. If the steam is restrained from leaving the boiler, and the heat input rate is maintained, the energy flowing into the boiler will be greater than the energy flowing out. This excess energy raises the pressure, in turn allowing the saturation temperature to rise, as the temperature of saturated steam correlates to its pressure.