How Does Room Temperature and Humidity Affect Water Evaporation Rates?

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SUMMARY

The discussion focuses on the impact of room temperature and humidity on water evaporation rates, specifically in a controlled environment. An HVAC professional conducted an experiment in a small, unheated basement room maintained at 50°F and 40% relative humidity (RH) using a 12-cup cylindrical coffee carafe. Over 18 days, the water level decreased by only 3/8 inch, indicating a very slow evaporation rate. The participant seeks a formula to compare these empirical results against established evaporation predictions.

PREREQUISITES
  • Understanding of relative humidity and its measurement
  • Knowledge of basic thermodynamics related to evaporation
  • Familiarity with empirical experimentation methods
  • Experience with mathematical modeling of physical processes
NEXT STEPS
  • Research the Penman equation for estimating evaporation rates
  • Explore the concept of saturation vapor pressure
  • Learn about the effects of temperature on evaporation rates
  • Investigate the role of air currents in evaporation processes
USEFUL FOR

This discussion is beneficial for HVAC professionals, environmental scientists, and anyone interested in understanding the dynamics of evaporation in controlled environments.

tinkeringone
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HVAC man here, still tinkering with humidification. Trying to get a baseline on the rate of evaporation of undisturbed water in a full container in a room with a fixed RH & temperature and no air currents. It's a cool (unheated) very small, room in my basement with a door on it. The room has been at a constant 50F & 40% RH. Used a 12 cup (untapered, i.e. perfectly cylindrical) coffee carafe and filled it with water (with no lid on it). It's 5 1/2" in diameter and 4 1/2" deep. In 18 days, the water level has dropped a measly 3/8". So it's kinda like watching grass grow.

I tried to make this as empirically simple as possible to create a "worst-case" scenario for a rate of evaporation, and to see if I could compare it to a simple formula for predicting the rate of evaporation.

Can anyone recommend a formula to compare the results of my current experiment with?
 
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It is not clear whether the bulk humidity in the room is being maintained at 40%, or whether the air is being allowed to become more saturated.
 

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