Convection Heat Transfer: Principles and Applications

A: Start with area: about 1 m². To dump 1 kW with a plausible ΔT of a few tens of kelvin, h has to live in single digits. Free convection in air on a vertical plate usually lands there when Rayleigh numbers sit near the laminar–transition boundary. Option B feels tempting if you've spent time around air-cooled electronics, but that smuggles in forced flow. Option C ignores the buoyancy limit; you don't get that turbulence without velocity. Option D underestimates buoyancy-driven mixing; air isn't that lazy once it warms.

A: Air-side convection rarely carries fouling allowances that large; that's a liquid-service habit bleeding over. Option B sounds reasonable until you remember air-side resistance often dominates U. Option C mixes up bookkeeping with physics; fouling lives where the dirt is. Option D would be nice, but real datasheets stack resistances explicitly, even when one dwarfs the rest.

A: Convection on the air side lives and dies by mass flow. Option A attacks that directly. Option B tightens instrumentation, but a perfect sensor won't fix low h. Option C matters for energy balance, yet the symptom already shows temperature compliance. Option D tells you the valve is open, not that air is actually moving across the coil.

A: Sealed means sealed. External fins boost area without breaking the boundary. Option B only homogenizes internal air; the external film still throttles heat. Option C violates the seal and drags in dust. Option D works thermally but explodes scope, interfaces, and failure modes for 800 W.