Science Buddies: "Ask an Expert"

Good afternoon,

My son and I have been trying for a week to get the wet bulb psychrometer to work, but the the wet bulb reading always starts higher than the dry bulb reading and over the last three days, the wet bulb temperature has not dropped below the dry bulb reading after blowing a fan on it for 4-5 minutes. This of course doesn't allow us to make any calculations.

We have been doing this outdoors, thinking that would give us the greatest variation of readings over the course of the week. However, we noticed the two bulbs keep the same temperature when the psychrometer is inside the house.

Why is this? And should we at least try to do this indoors over the next few days before the science fair this week?

Sincerely,

Joel Johnston

Hi,

This sounds like a frustrating problem. Knowing nothing of how you are taking measurements all I can do is guess. The fact that the psychrometer seems to work in the house suggests that the psychrometer itself is working properly. That suggests that outside the two bulbs are getting warmed differently, like maybe the wet bulb is getting direct sunlight where the dry bulb is not., or the wet bulb is resting on a warm surface and the dry bulb is not. Have you tried taking measurements where the whole instrument is shaded?

It certainly would not hurt to take a series of readings in the house, particularly if that is the only place you can get readings that you trust. It could even be more interesting to compare in house readings with outdoor readings taken at the same time of day.

Welcome to the challenges of real world research! Best wishes for a successful science fair!

Barrett Tomlinson

Thank you for your advice. We have stuck with keeping it outside and not wetting it as much. I think we were worried about it not being wet enough, but clearly we over compensated.

The problem of the two temperatures has not been resolved (they sit right next to each other on a 2 by 4), but we have been able to make it work.

Thank you again for your quick and courteous response.