TM-5855-4
(3) A simple pendant-level control at the far end of the reservoir that is moved by the ice front will
automatically stop operation of the conveyor and ice-making equipment when the reservoir becomes
completely filled.
(4) Melting of the ice front by heat transfer from the surrounding rock will allow the pendant-level
control to fall to an operating position, causing more ice to be added to the reservoir. For inspection and
maintenance of the screw conveyor, a walkway will be placed near the conveyor.
(5) Laboratory experiments have indicated that the best shape of ice for movement in a reservoir is
cubical, spherical, or cylindrical, in pieces approximately one inch in size. Ice in crushed or flake form
tends to cluster in compacted slushy masses that resist movement. Experiments have shown that the
average ice volume in a water-and-ice mixture shaped in a hollow cylinder is from 40 to 50 percent, and it
is probable that for non-hollow , small shapes, the ice volume percentage is materially greater.
5-4. Solid ice heat sinks.
a. When a concept is developed for an ice heat sink configuration, many relevant factors will be
considered. The heat sink must be available for use when the button-up signal is given. Economy of
space is a major factor in reducing the cost of deep underground excavations in rock.
(1) A block ice heat sink is available for immediate use if continuous water flow paths exist
through voids between the ice blocks. However, the voids reduce volumetric utilization, Btu's stored per
cubic foot of excavation.
(2) A solid ice cylinder heat sink provides for the maximum utilization of space; however, means
must be provided to create an annulus of water between the ice cylinder and the sink wall. The solid
cylinder must also be restrained and maintained concentric with the sink walls for proper water flow.
(3) Both types of sinks will have a spray header designed to evenly distribute incoming cooling
water over the upper ice surface for uniformity of ice melting.
b. To illustrate the space economics of water, water and ice, and solid ice underground heat sinks, a
comparison of Btu's that can be absorbed is made on a 100,000-gallon reservoir containing, respectively,
water at approximately 8.34 lb/gal and stored at rock ambient temperature of 60 "F, a 50 percent
ice/50 percent water sink, and a solid ice cylinder sink maintained at 32 F; all absorbing heat to 1600 F
final temperatures, assuming ice at 7.61 lb/gal, 144 Btu/lb latent heat of fusion, and neglecting rock heat
transfer.
(4) Although the above comparison shows that the heat storage volumetric efficiency of an ambient
water sink is approximately one-half that of a 50/50 ice and water sink and approximately two-fifths that
of a solid ice sink, other factors such as space and cost for refrigeration equipment, power cost for
maintaining the low temperature, and time to re-establish ice sink to design conditions after an
engagement will be evaluated when the heat sink configuration is selected.
54
Previous Page
