Drying and baking exhaust typically leaves the process at 50\u201390\u00b0C and 15\u201340 g\/kg absolute humidity. Recovering that energy cuts fuel or electricity by 15\u201340%, but the wrong recovery device can re-wet the product, contaminate the supply air, or freeze in winter. Plate and rotary-wheel exchangers solve the same problem in fundamentally different ways, so the selection rule is not “which is more efficient” but “which failure modes the process can tolerate”.<\/p>\n
Counter-flow or cross-flow stacks of thin aluminium or polymer plates. Sensible-only plates transfer heat with zero moisture carry-over. Polymer (enthalpy) plates add selective water-vapour transfer while still blocking aerosols and odours. No moving parts, no rotating seal, no cross-stream leakage path.<\/p>\n
A slowly rotating desiccant-coated or all-aluminium matrix absorbs heat and moisture on the exhaust side and releases both to the incoming air as it turns. Typical effectiveness is 70\u201385% for heat and 60\u201380% for moisture, but a fraction of exhaust always leaks into the supply through the purge-sector gap.<\/p>\n
| Aspect<\/th>\n | Plate (sensible)<\/th>\n | Rotary wheel<\/th>\n<\/tr>\n<\/thead>\n | ||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Moisture recovered<\/td>\n | No (sensible only)<\/td>\n | Yes (latent + sensible)<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Cross-contamination risk<\/td>\n | None (separated streams)<\/td>\n | Low but non-zero (purge sector)<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Re-wetting product air<\/td>\n | Impossible<\/td>\n | Possible if wheel saturated<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Frost \/ condensation<\/td>\n | Easy to bypass or pre-heat<\/td>\n | Needs frost-control sector<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Moving parts \/ maintenance<\/td>\n | None<\/td>\n | Belt, bearing, seal<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Pressure drop<\/td>\n | Moderate<\/td>\n | Moderate, flow-dependent<\/td>\n<\/tr>\n | ||||||||||||||||||||||||||||||||||||||||||
| Best fit<\/td>\n | High-humidity, no-return-air duty<\/td>\n | Need both sensible + latent recovery<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nSelection Rules for Drying Applications<\/h2>\nBottom Line<\/h2>\nFor the large majority of industrial drying exhaust-heat recovery, the fixed plate sensible exchanger is the safer, lower-maintenance choice: it recovers heat without moving moisture or contaminants. Reach for a rotary wheel only when latent recovery is a hard requirement and a purge sector is acceptable.<\/p>\n Worked Example \u2014 Sensible Recovery on a Grain Dryer<\/h2>\nTo make the selection rule concrete, size a plate sensible exchanger for a typical grain-drying exhaust and compare it with a rotary wheel on the same duty.<\/p>\n Given duty<\/h3>\n
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