ANS:A - the heat transfer rate is low in view of the large temperature drop.

Film boiling is typically not desired in commercial equipment for several reasons:

1. Low Heat Transfer Rate: Film boiling tends to have a low heat transfer rate due to the insulating layer of vapor that forms between the heated surface and the liquid. This is indeed related to the large temperature drop across this vapor layer.
2. Difficulty in Maintenance: Film boiling can be difficult to maintain because it often occurs under conditions where there's a high temperature gradient, leading to potential challenges in controlling the process and preventing unwanted side effects like equipment damage.
3. Economic Concerns: Film boiling might not be economically viable due to its inefficiency in heat transfer and the potential costs associated with mitigating its negative effects or replacing damaged equipment.