2nd Class Power Engineering (2B3) Practice Exam

Air in a surface condenser has multiple effects that impact both pressure and heat transfer efficiency.

When air enters the condenser, it increases the overall pressure within the system. This occurs because the presence of air displaces steam, effectively reducing the volume available for steam and leading to a higher pressure condition due to the non-condensable gases. This increase in pressure can hinder the performance of the condenser, as it may prevent steam from condensing efficiently.

Additionally, air acts as an insulator and creates a barrier to heat transfer when mixed with the steam. This shrouding effect slows down the overall rate of heat exchange because air has a lower thermal conductivity compared to steam, thus retarding the heat transfer process. Efficient heat transfer is crucial for maximizing the thermal efficiency of the condenser, and the presence of air compromises this efficiency.

Furthermore, if air is present in the system due to poor evacuation or if it enters along with the steam, it can elevate the overall pressure in the system, compounding the problem of inefficient heat transfer.

Given these considerations, the correct answer encompasses all these effects, highlighting that air in a surface condenser leads to increased pressure and reduced heat transfer efficiency. This is why the option indicating all effects is correct; each aspect contributes to