Cooling and freezing time describes how fast the batch gives up its heat. The room's heat load doesn't need it, but the pull-down simulation on the Equipment page does, and this section already shows how the batch cools in air held at the set point.
- 1
Choose the Item shape and enter its size in mm. Model one item as the air reaches it: a carton if air moves between the cartons, the whole pallet if it doesn't.
- 2
Enter Surface h and Where h comes from, or take h from From Ch. 19 Table 13 below them.
- 3
Leave Density and conductivity at From composition, or choose Entered and type the Density, k unfrozen and k frozen with their Source. A figure left blank is computed from the product's composition.
- 4
Read the line at the foot of the section: the batch's mean temperature after its pull-down time, and how much of its pull-down heat is out by then.
Take h from Table 13
- 1
Choose a Table 13 row. Rows that name the room's product come first. Only rows measured in air are offered, because the product cools in the room's air.
- 2
A measured row gives its printed h. You can enter the Air speed over the product to compare it with the speeds the table prints, but h is copied as printed either way.
- 3
A correlation row needs the Air velocity over the product, which has no default, and the Characteristic length L, read off the item where the row's dimension matches it, or typed. Kelvin shows the Reynolds number and h before anything is copied.
- 4
Choose Use h to copy h and its source into the room. The button then reads Copied into this room.
A correlation is used only inside the Reynolds range it was fitted over. Outside it, Kelvin refuses, and says what air velocity would keep it inside the range at this length. The air's properties are read at the room's set point, and the hint names where they come from. A row that can't be used here is marked so, with the reason.
A copied h belongs to the room: a later edit to the library never changes it. Typing h or its source by hand makes them the page's own.
Note
Kelvin holds no default h, because it depends on the air speed over the product and its packaging. Until h and its source are in, the section lists what it still needs.
What the figure means
The temperature is the batch's mean temperature, not its centre, worked by Pham's method from the ASHRAE Handbook—Refrigeration Ch. 20. It assumes air held at the set point all the way through, as the heat load does: a plant that never falls short. The Equipment page runs the same batch against the evaporators chosen.
If the product carries no complete composition, density and conductivity can't be computed: enter them from a cited source, or pick the product again from the reference library.