Travel appliances

the frequency is pretty much tied to the voltage on commercial products, if you have the correct voltage it ought to follow.

but have you written your question correctly?? 120-140 is not dual voltage, that's just a fluctuation range which is needed because mains voltage can never be guaranteed to be exactly the same at all times and locations on a network. If that is really what it says it won't be suitable for Europe at all. For europe you need mention of something between 220 and 240 volts, almost double north american ranges.

the adapter depends on which countries you visit, most of mainland europe uses type C/F plugs but UK and Ireland have the more secure type G

https://en.wikipedia.org/wiki/Mains_electricity_by_country

In case you are not aware: European lodgings nearly always provide hair dryers--if not in the room, upon request at the desk. Irons are often available as well, but that's something I'd want to ask each lodging about.

Those three appliances will add a great deal of weight and bulk to your luggage. I'd do just about anything to leave at least two of them at home.

That's not dual voltage. Europe is on 220-240. In fact, some places are 330. You'll burn them out in a quick second. Just buy what you find you need in Europe and bring them home for another trip, or give them away if you are never returning.

"the frequency is pretty much tied to the voltage on commercial products, if you have the correct voltage it ought to follow."

Some further clarification on that point. Dual voltage appliances will be designed to operate on either 50 or 60 Hz, but optimally on one or the other. There are no practical solutions for changing the frequency, so the appliance may not operate at peak efficiency when it's operating on the secondary frequency and voltage.

"How do you tell if an appliance is 50/60 HZ?"

Look on the nameplate, which will be affixed to every appliance. Look for the words input Voltage and the frequency will be specified there. The nameplate may be hot-stamped into the plastic, or may be on a metallized foil label.

Are you sure the appliances list the dual voltage as "120-140V"? That's not really "dual voltage" and appliances with that rating should NOT be used in Europe.

Note , I have been in European hotels that forbid ironing ( clothes ) in your room

The device nameplate should identify input voltage and utility frequency. As a generality, line frequency for 110-120 VAC is 60 Hz and frequency for 220-240 VAC is 50 Hz. Frequency is less of a problem than voltage. If your device is synchronized to line frequency like the old electric motor driven clocks, a 60 Hz device will just run slower on 50 Hz alternating current.

Hopefully your device is dual or variable voltage rated for 120 to 240 VAC, not 140.

Much smarter to bring clothes that don't need ironing. Of course if you are staying in a full-service hotel they can handle that for you.

I have yet to get a hotel room in Europe that did not have a hair dryer and provide an iron if needed. As to a flat iron for your hair, you may want to buy when you get to where you going as there have been stories of them over-heating, frying hair and blowing circuits. I used to bring a dual-voltage curling brush but have since found a way to style my hair that doesn't require it.

Some good advice here - packing light

Go casual, simple, and very light. Remember, in your travels you’ll meet two kinds of tourists — those who pack light and those who wish they had. Say it out loud: “PACK LIGHT PACK LIGHT PACK LIGHT.”