# What heating?

I have a metal box( sizes 40 cm x 12cm x12cm) and inside there is overpressure ( from 6 to 8 atmospheres).
Can anyone advise a way how to achieve inside temperature between 40 °C to 60 °C?
What heating element and thermostat to use? Any idea?
Thanks for help

Hi, 8 atmospheres? That's quite a scary box! What is it for and how is this project Arduino related?

How about a heat exchanger. Pass hot water slowly through a coil inside the box. If the water is 50o at the input and 50o at the output, then the inside of your box will be at 50o. The inside of your box will never be hotter than the water temperature.

Put it inside an oven set to your target temperature?

A resistor can act as a heater. You can calculate power (in Watts) as (Voltage Squared)/Resistance (or as Voltage x Current). Of course, make sure your power supply can supply the necessary current.

I'm not sure how to calculate how many watts you need... It's probably best just to experiment... The electrical power required will depend on the outside air temperature and on how fast you need to hit the target temperature. I'd start with 10-20 Watts and see how it goes. The heat rise should be proportional to the power dissipation (wattage). So, if 10W gives you 10 degrees above the outside ambient temperature, 20W should give you 20 degrees of heat rise, etc.

[u]This style[/u] of resistor makes a good heating element. It's good practice to "derate" your resistor to half it's power rating. i.e. If you have a 50W resistor, try not to dissipate more than about 25W.

You can use an [u]LM35[/u] as a temperature sensor.

If the temperature needs to be uniform inside the box, you'll probably need a fan inside to circulate the air around.

Thanks for the replies
@DVDdoug: It is an interesting idea but would not be a better to use resistance wire only and not resistors? Or what is advantage of using the resistors?

Jane1:
Thanks for the replies
@DVDdoug: It is an interesting idea but would not be a better to use resistance wire only and not resistors? Or what is advantage of using the resistors?

Take a look at the specs of resistance (I assume we're talking nichrome) wire. As an example, for 10W of heat and a 12V source you need about 2' of 30ga wire (7 ohms/foot) and that wire will be around 170C. That's a pretty long, thin, HOT wire and figuring a way to mount it inside the box is nontrivial. You'd have to make some kind of glass or ceramic pillar to do it (can't use metal y'know).

If you want to spread the heat around the box a bit more you can use multiple, smaller resistors in series. For example you could use ten of these 5W, .5 ohm resistors to equal the 5 ohm, 50W resistor Doug linked. And those ten resistors would be cheaper as well.