20.Which type of boiler depends on the heat input to establish differential densities between the steam-and-water mixture flowing in the riser or generating circuits and the water flowing downward in the downcomer circuits? (A)Once-through (B)Natural-circulation (C)Forced-circulation (D)Two-furnace, forced circulation superheat

9.Blowers are used with many diesel engines to supply the air necessary for combustion to the engine’s cylinders. When the pressure of this air is increased above atmospheric pressure, referred to as supercharging, the power output of engine is increased. In addition, in a two-stroke engine the air supplied by the blower helps to purge the engine’s cylinders of exhaust gas. This is referred to as scavenging. Based on these descriptions, please specify the correct statement. (A)The scavenging and supercharging processes share identical purpose of increasing the static pressure in the intake pipes. (B)The use of blow for scavenging and supercharging is due to its characteristics of high-pressure and low volumetric flow rate. (C)The blower for marine application is always the centrifugal type as it offers the high speed characteristic. (D)The scavenging in a two-stroke engine assists to purge the engine’s exhaust gas which has beneficial effect for combustion.

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