utilidors will have a significant effect on the temperature distribution and will
result in lower predicted heat transfer rates.
The use of an effective conductivity for air in a numerical conduction analysis
will produce reasonably good temperature distributions on interior surfaces. How-
ever, the air temperature distribution will be in error. The procedure is relatively
insensitive to the effective conductivity, the pipe, and enclosure insulation domi-
nating the heat loss, at least for the cases investigated in this work.
A more efficient and robust numerical modeling approach is required. Two pos-
sible improvements are to (1) convert the solution procedure to a "segregated
method" where each of the governing equations are solved individually and a Pois-
son equation is substituted for the continuity equation, or to (2) incorporate an
upwinding scheme such as the Petrov-Galerkin method into the element quadra-
ture procedure.
Some temperature data from actual utilidors are available; comparisons with
these data and numerical modeling of the entire soil mass should be done. Addi-
tionally, comparisons with an effective conductivity correlation in a transient
conduction model, including the soil mass, and compared with field data, may
also produce some interesting results.
LITERATURE CITED
Arpaci, V.S., and Y. Bayazitoglu (Ed.) (1990) Fundamentals of natural convection.
American Society of Mechanical Engineers, HTD, 140.
Babus'Haq, R.F., S.D. Probert, and M.J. Shilston (1986) Improved pipeline con-
figurations for DHC distribution systems. ASHRAE Transactions, 92(2): 234245.
Boyd, R.D. (1981) A new correlation theory for steady natural convective heat-
transport data for horizontal annuli. In Proceedings of the ASME/AICHE 20th
National Heat Transfer Conference, Milwaukee, Wisconsin.
A comparison exercise. International Journal for Numerical Methods in Fluids, 3:
227248.
uids confined by two parallel plates which are inclined at various angles with
respect to the horizon. Journal of Heat Transfer, 87: 77.
Eckert, E.R.G., and W .O. Carlson (1961) Natural convection in an air layer
enclosed between two vertical plates with different temperatures. International Jour-
nal of Heat and Mass Transfer, 2: 23.
Elder, J.W . (1965) Turbulent-free convection in a vertical slot. Journal of Fluid
Mechanics, 23: 99.
Emery, A.F., O. Johansson, M. Lobo, and A. Abrous (1991) A comparative study
of methods for computing the diffuse radiation viewfactors for complex structures.
Transactions of the ASME, Journal of Heat Transfer, 113: 413422.
Ergatoudis, I., B.M. Irons, and O.C. Zienkiewicz (1968) Curved isoparametric,
"quadrilateral" elements for finite element analysis. International Journal of Solids,
Structures, 4: 3142.
Federal Guide Specification (1981) National Federal Guide Specification (NFGS)-
1570S, p. 15.
Gartling, D.K. (1977) Convective heat transfer analysis by the finite element
method. Computer Methods in Applied Mechanics and Engineering, 12: 365382.
Gartling, D.K. (1987) NACHOS II: A finite element computer program for incom-
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