Recent content by amrmohammed

Homework Statement [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts)...

What are the available liquid polymers that would keep its physical state at continuous expose to high temperatures (like 100 C), without curing or evaporating? I guess some grads of PDMS (Polydimethylsiloxane) works, I don't know what would happen to Polyester or Epoxy and whether or not there...

You are right, but is still better than conventional MI cables as it is immune against hot spots. Circulating steam is a thing for pipelines. However, it is difficult to do downhole due to the geometry and hole limitation and the fact that steam will condense in the way, in addition to...

I mentioned oil and gas as an example where high density power output is on demand to heat the reservoir. You are right, they use steam extensively to heat oil reservoirs, but it can not be used at deep formations because of the effect of high pressure and because it will loose a lot of its...

The reseitivity of this type of cables increases with increasing temperature. This means that at hot spots the resistance is high thus low current pass though it, and prevents it from burning.

Ceramic bar will most likely not work as it needs a cable to carry electricity from the end of the bar and back to surface, where the power supply is. There will be issues on the installation, as small damage in the ceramic bar will cause a hot spot and a failure in the whole system. Also, they...

There is a huge need for heaters that is able to go as high as 300 W/ft in the oil and gas industry. What about the heat transfer constrain that I talked about in the comment above, how higher heat capacity can be transferred in such small surface area (the width of the cable * the length)...

I am not fixing the voltage input. These cables are made for oil and gas applications, so getting more than 120 V is not an issue. The 240 V cable also have ~ 20 W/ft limit. So, it is not the voltage supplied that put the limitation on power output, because the resistance change with changing...

I don't think cable's insulating sleeve is what limiting the power output. If melting the insulating material was the problem, the cable could still provide higher power rising the temperature from -10 to 20 C, for example. If this was the case, the limit would have be on the working temperature...

the company stated "can provide up to 20 W/ft". So if I can supply more current, what puts a constrain on the power output? in other words, why can't I put 50 Amp through 180 ft with 120 V and have much more heat density than the 20W/ft that the manufacturer set as a limit...

Hello, Why do self regulating heating cables have such low power output per foot? Power output in these cables does not exceed 20 W/ft at 10 degree C, and decreases as the temperature goes up. Many of the cables I saw can withstand high temperatures (250 degree C power off and 150 degree C...

So to sum up, current commercial heating cables handle a maximum of 2 kV, because the currently available insulation (MgO) can not insulate higher voltages in field conditions?

Power is transmitted through coaxial conducting cables that is insulated by a dielectric material, could capacitance play any rule?

That will limit the operating temperature (different from temperature gradient across the insulator that @Bystander mentioned), how is that related to the limit on maximum operating voltage? I guess the voltage limit should be somehow related to the dielectric strength of the insulator or the...

Please refer to this pdf file. The resistivity of MgO do decrease with temperature but it is still very high. and in...