SIMULATION OF SIMULTANEOUS HEAT AND MOISTURE
TRANSFER IN SOILS HEATED BY BURIED PIPES
By
Ahmed E. Ahmed, Ph.D.
The Ohio State University, 1980
Professor Mohamed Y. Hamdy, Adviser
Heating commercial greenhouses during winter appears to be one of
the most promising agricultural uses of the reject heat from power
plants.
Subsurface soil warming and irrigation has the advantage of
raising the soil temperature in the root zone without producing excessive humidity in the greenhouse environment.
The different approaches to mathematically describe simultaneous
heat and moisture transfer in soils were reviewed. A model was selected
to describe subsoil warming and irrigation and its highly nonlinear
simultaneous differential equations were solved on a digital computer
using finite difference and the Continuous System Modeling Program (CSMP) .
The model was verified and validated with extensive experimentation in a
greenhouse at Ohio Agriculture Research and Development Center, Wooster,
Ohio. Three plots of different soils, sand, Wooster silt-loam, and a
peat-vermiculite mixture, were equipped with buried, parallel, plastic
pipes heated by warm water in the temperature range of reject heat from
the power plants.
The pipes were buried 30-cm deep and 30-cm apart. A
water table was maintained at 50-cm depth to provide subsurface
irrigation.
The model was applied to the sand and Wooster silt-loam plots
because their pertinent physical properties were available in the
literature. It was not applied to the peat vermiculite plot for lack of
information on its properties.
The mathematical model acurately predicted the transient and steady
state temperature and moisture distribution in the test plots. The
designed heating system provided a uniform root zone temperature in the
ideal range of plant growth and provided up to 30 percent of the total
heat requirements of the greenhouse. The moisture levels provided by
the subsurface irrigation were above the wilting point in the silt-loam
plot for most crops. A shallower water table, 40-cm deep, appeared
necessary in the sand plot.