Why slope the floor instead of using a flat base with an absorbent mat?

A mat holds liquid but does not steer it; on a flat base the fluid pools 2 mm to 5 mm deep and freezing lifts a random patch of liner.

Is a 12 mm port large enough for thicker coolant blends?

Yes at this slope: 200 mL clears in about 10 s. The real failure is a plug frozen into its thread, so 6 mm of thread stays exposed.

How long does 500 g of desiccant last at -30 °C?

About 27 days. Uptake at -30 °C is roughly 30% of the 25 °C figure, so cold rooms change over at 60 days, not 90.

Is a 5 mm wall enough for a fuel cell case stored at -30 °C?

Yes, if the compound is modified: a 5 mm wall absorbs 12 kJ/m² notched at -30 °C and survives a 1.2 m six-face drop, while unmodified PP fails even at 8 mm.

Can this fuel cell case ship as the outer package?

It can carry the outer packaging role; classification and declaration come from an accredited body.

Fuel Cell Case: Fuel Cell Spares Case

Quick answer: A fuel cell case keeps spares dry in cold storage with a 5 degree floor, a 12 mm drain port and 500 g of desiccant holding 40–60% RH.

Where the Residual Liquid Goes in a Fuel Cell Case
A 5 Degree Floor and a 12 mm Drain Port
500 g of Desiccant Against a 40 to 60% RH Window
What -30 °C Does to Walls, Gaskets and Latches
Monthly Recheck: Four Calls and a 32 kg Limit
FAQ

1. Where the Residual Liquid Goes in a Fuel Cell Case

Pull a 620 mm case from a -30 °C cold room into a 20 °C service bay and within a minute water beads on the walls while 30 mL to 80 mL of liquid pools in the lowest corner. None of it leaked in; it arrived with the spares as coolant left in the manifold.

The fluid expands about 4% across the 50 K swing; freezing adds 9%, enough to lift a 20 mm EPE liner by 2 mm to 3 mm.

Condensation is the second path. Open the lid in a bay at 65% RH and warm air meets walls still at -20 °C, leaving 6 mL to 10 mL of droplets that run down to join the coolant.

Water is not the problem. Still water is.

Sitting water freezes and plugs the drain; moving water finds the low point itself, so a fuel cell case assumes water is inside and gives it a route.

Where liquid settles	What is seen	Case-side measure	Set value
Centre of floor	liner lifted by ice	single-plane sloped floor	5 degrees
Channel end	beads freeze in a row	R2 fillet, end sunk 1 mm	4 mm deep
Plug thread	plug will not turn	plug stands 6 mm proud	12 mm bore

2. A 5 Degree Floor and a 12 mm Drain Port

Over 520 mm of internal length, 5 degrees gives a 46 mm drop, and gravity carries the liquid down without tipping the case.

Fuel cell case open on grey studio floor, lid lined with flat dark foam, base divided into nine square cells, two latches at front

Three channels cross the floor at 150 mm spacing, 4 mm deep and 12 mm wide, with an R2 fillet that drains the 1 mm to 2 mm film a square channel would keep, worth 30 mL of residue.

The port sits at the lowest corner at 12 mm bore, closed by an M16×1.5 plug with a 3 mm nitrile O-ring, torqued to 2.5 N·m with 6 mm of thread exposed. Twelve millimetres clears 200 mL in 10 s; anything larger cuts a hole where the floor bends most.

Below the plug sits a 260 mL sump, sized on four spare sets shedding 40 mL to 50 mL each, plus a 200 mm by 300 mm pad rated at 180 mL.

Acceptance is 50 mL: empty the case, invert it for 10 min, then measure. More means the slope or the channel profile is wrong.

Drainage stage	Construction	Size or slope	Pass value
Cavity floor	single plane, moulded in one shot	5 degrees	46 mm drop
Channels	3 runs at 150 mm spacing	4 mm deep, 12 mm wide	residue 10 mL or less
Port	lowest corner, M16×1.5 plug	12 mm bore	200 mL in 10 s
Sump	cavity under the plug	260 mL	level 20 mm below rim

3. 500 g of Desiccant Against a 40 to 60% RH Window

Humidity here has a floor and a ceiling. Below 40% RH the membrane dries and shrinks by up to 0.3%; above 60% RH any temperature drop condenses water on the surface. The case side has one narrow job: hold the cavity inside that 20 point band.

The charge is 500 g in two 250 g cartridges clipped into a lid recess. With 28 L of free volume, silica gel holds the cavity under 50% RH for about 90 days at 25 °C.

Cold weather makes the gel lazy: at -30 °C uptake falls to about 30% of its 25 °C value, so 500 g covers only 27 days.

Cards calibrated at 30%, 50% and 70% RH sit where the eye lands.

Desiccant is not a weight contest, just a question of lasting one changeover.

4. What -30 °C Does to Walls, Gaskets and Latches

Standard PP turns brittle near -20 °C; with 8% impact modifier the -30 °C notched Charpy value reaches 12 kJ/m² and a 5 mm wall holds, while an unmodified 8 mm wall cracks.

Fuel cell case display wall in the showroom, green orange and yellow shells on light grey shelves, wood floor below

The gasket goes next. An 8 mm solid EPDM cord recovers in 2 s at 20 °C; at -30 °C recovery stretches to 6 s and set climbs from 15% to 35%, leaving a 1 mm to 2 mm gap for frost.

The answer is a double seal: 8 mm solid cord outside, 5 mm hollow cord inside, 12 mm apart. Both sit in a 10 mm groove closing at 30% compression.

A PA66 latch with 30% glass fibre needs 80 N at 20 °C and 120 N at -30 °C, beyond one gloved thumb, so the pair sits 320 mm apart for two hands, on stainless pins with 0.2 mm clearance.

Drop testing follows the cold condition: 24 h at -30 °C, six faces from 1.2 m within 90 s, no cracking and no gasket displacement. The same case reaches 1.5 m at 20 °C.

Storage band	Material behaviour	Case-side response
20 °C	gasket recovers in 2 s, latch 80 N	standard build
0 °C	condensation peaks at 6 mL to 10 mL	sump plus absorbent pad
-10 °C	PP nears its brittle range	modifier, 5 mm wall
-30 °C	uptake 30%, latch 120 N	double seal, 320 mm spacing
60 °C	faster compression set	EPE raised to 45 kg/m³

5. Monthly Recheck: Four Calls and a 32 kg Limit

The monthly check is four readings: sump volume no higher than 50 mL, card not yet at the 70% RH colour, gasket set no more than 1.5 mm, latch force no more than 120 N. Any failure sends you back to slope and seal, not more desiccant.

At 32 kg loaded the handling rule is two people on a handle 40 mm in from the edge, rated at 400 N, and stacks of 2, because the lower lid carries 32 kg plus the 3 g peak of a 0.5 m drop.

You can thicken a wall all day. A hand-tight plug still beats you.

Conclusion

Three numbers carry the cold-storage performance of a fuel cell case: a 5 degree floor, a 12 mm drain and 500 g of desiccant. Slope moves liquid to one place, the port lets it out, and the gel holds 40% to 60% RH.