THE HEAT FACTOR...
THE HEAT FACTOR...
(OP)
I have a design that would solve a hindering problem if I could simply charge one end of an actuator with about 200 psi of oil and not tie it into a circulating system. My question is would it heat up too much in doing this? The other end of the actuator is going to fluctuate from about 200 psi to 1200 psi...so it would spike the trapped end to these pressures as well...in some cases it will see this fluctuation 120 times per second. How much heat would this generate...and what affect would it have on the piston that separates the two chambers? Can it be done?





RE: THE HEAT FACTOR...
Unless there is some type of thermal path besides the oil I would have to say heat will be a problem. Most hydraulic seals are only good to ~225 deg F. It's also hard on the oil.
I can think of two heat sources.
1. fluid compression - I haven't had a fluid dynamics class but I would think that it will heat when compressed but cool equally when allowed to expand - so it should be a net gain of 0.
2. Friction - This will add heat, which must be dealt with.
ISZ
RE: THE HEAT FACTOR...
RE: THE HEAT FACTOR...
Also, the seals in almost all hydraulic cylinders leak - its just to what degree. Even if you could pressurize one side of the cylinder it would eventually loose pressure and have to be recharged somehow. The leakage would get worse at higher temps.
Some ideas
1) If the one end is dry - You might be able to apply pressurized air. (Like shop air at 90psi) Might be an explosion hazard though if it gets mixed with an oil mist.
2) Install an orifice on the back side to restrict the flow, which will generate the pressure. You could use a "tee" and check valve to limit the restriction to one direction only if needed. This would not be very effective at low speeds or displacements.
ISZ
RE: THE HEAT FACTOR...
Trapped oil in itself won't do anything for you, other than take up space. If it's shock absorbtion, then a traditional accumulator will work, these typically being charged with nitrogen.
Your needs sound specialized however in that a 120hz pressure wave requires attenuation. Flexible hosing or coiled steel tubing should buffer this.
RE: THE HEAT FACTOR...
RE: THE HEAT FACTOR...
RE: THE HEAT FACTOR...
A volume of oil trapped will absorb little or no shock. The bulk modulus of oil is far less than that of air, it will compress slightly, however, at such low pressures the compression will be almost zero.
Energy that is stored in oil will be transfered to heat if it is not used. When compressing the oil, if it is done isothermally, i,e slowly, there will be almost no heat increase. When pressurised 120 time per second, the oil may tend to warm up. However, the amount of energy required to compress the oil could be very low. By the way, what is the volume of the actuator? The size of the actuator makes a big difference to the oil temperature. Specific heat capacity of oil...the more oil the more energy required to raise the temperature. The bigger the surface area of the actuator, the more heat it will disipate.
If the "other" end of the actuator is to be charged by a pump you may find that there is an inherent ripple that is transmitted from the pump. Almost all hydraulic pumps have a ripple of some sort. In most hydraulic systems the ripple is absorbed by the components. In this application there would be no way to absorb the ripple. Depending on the rotational speed and the type of pump, the frequncy of the ripple could be as high a 500Hz. If the pump is working upto 1200 PSI, that is the pressure that will be seen in the actuator.
As I amagine the system to work, there will no oil flowing at the actuator and the volume of oil is such the low power required to raise the pressure will limit the heat input.
There are many other hidden factors that can effect that heat input, can you provide more details about the pump and the pressure controls etc...?
Regards
Adrian
RE: THE HEAT FACTOR...
RE: THE HEAT FACTOR...
Your heat problem if it occurs, will likely be developed with the sealing elements, or within the flexation of metalic components.
RE: THE HEAT FACTOR...