Two configurations, one platform. We build the drying stage either as continuous tunnel dryers or as the panel rooms described here. Both run on the same central cashew-shell heat plant; the choice is driven by site, volume and batch-handling preference.

Process

Prepared mango (washed, peeled, sliced, pre-treated with a citric/ascorbic or sulphite dip) is loaded onto trays, trays onto wagons, and wagons rolled into a room on floor rails. The room is sealed and hot air is recirculated through the tray stacks at 55–75 °C for a 14-hour batch until the fruit reaches 12–14% moisture. Operation is single-side-door, first-in-last-out — the whole room loads and unloads as one batch.

Capacity

Rooms	6 panel rooms, internal envelope 5.90 × 2.35 × 2.39 m
Wagons per chamber	8 (2 abreast × 4 rows)
Trays per wagon	46 (23 levels × 2)
Trays per chamber	368
Tray area per chamber	165.6 m²
Capacity per chamber	828 kg fresh / batch
Line batch capacity	4,968 kg fresh mango / batch (≈497 kg dried)
Loading density (design)	5 kg fresh / m² tray

Room design & construction

Element	Specification	Reason
Walls & blind end	50 mm Rockwool sandwich panel, 100 kg/m³, TCT skins	Non-combustible A1, near a biomass plant
Ceiling	80 mm Rockwool sandwich panel	Larger loss face; suspended from PEB purlins
Floor	Insulated slab + 1.5 mm SS 304 wearing sheet, seam-welded, coved	Food-grade, washable — no timber anywhere
Doors	Insulated panel door, EPDM gasket + drop seal, single side	First-in-last-out batch loading
PEB shed	Light steel portal frame + roof sheeting over both wings + plant	Roof, weather envelope, shade
Air-seal baffles	Spring-loaded flaps, sides + top	Stop air short-circuiting the wagons

Why panel rooms. The panels ship flat-packed (efficient freight) and are erected on site, so room size is not limited by a container; the floor is a clean concrete slab with an SS 304 wearing surface — avoiding the pesticide-treated timber floor a container shell would bring. The trade-off: a building must be erected on site.

Trays & wagons

Trays and wagons are supplied in SS 304 — aluminium is rejected because mango is acidic (pH 3.4–4.5) and the dip chemistry would breach EU aluminium-release limits.

Tray — 900 × 500 × 25 mm; SS 304 angle frame with perforated deck.
Wagon — 1000 × 1050 × 1890 mm; SS 304; 23 levels at 70 mm pitch; 46 trays; flanged rail wheels.
Shipping — wagons ship knocked-down and are assembled on site.

Airflow — per-chamber recirculation

Each chamber is a closed recirculation loop: a fan at the blind end pushes hot air through a supply plenum, down through the tray stacks, turns it at the door end and returns it over a top plenum — so no return ducting is needed. A small make-up stream of hot air is mixed in, and an equal moist fraction exhausted.

Circulating air per chamber	~13,000 m³/h
Air velocity over trays	~2.0 m/s
Temperature drop across load	~9 K (65 → 56 °C)
Exhaust fraction	~13% (sets chamber humidity)
Recirculation fan	5 HP / chamber
Exhaust fan	1 HP / chamber, motorised damper
Connected load, whole line	~56 HP (vs 75.5 HP for a full-flow design)

Controls

Master PLC controls burner, hot-air generator and all six chamber zones, with a hard interlock capping tray-face air at 65 °C.
Per chamber: two PT100 sensors, an RH probe, recirculation and exhaust fan control, door switch and IP65 lighting.
Each chamber runs as an independent zone, so batches can be staggered rather than all six moving together.
MERV 8 pleated filters on the make-up air intake.

Insulated panel rooms under a steel shed.