CEM Certified Energy Manager: Steam, Industrial and Thermal Storage 4

Question 1

Steam quality is defined as the mass fraction of vapor in a wet steam mixture. If a sample contains 90% quality steam at 100 psig, the enthalpy (BTU/lb) is calculated using:

Accepted Answer

h = hf + x·hfg

Answer

The enthalpy of wet steam is h = hf + x·hfg, where hf is saturated liquid enthalpy, hfg is the latent heat, and x is the steam quality (dryness fraction).

Question 2

Which insulation material has the lowest thermal conductivity and is most suitable for cryogenic thermal storage piping?

Accepted Answer

Polyisocyanurate foam

Answer

Polyisocyanurate (polyiso) foam has among the lowest thermal conductivity values (k ≈ 0.14–0.17 BTU·in/hr·ft²·°F) and performs well at low temperatures for chilled water systems.

Question 3

A steam leak from a 1/8-inch diameter orifice at 100 psig loses approximately how many pounds of steam per hour?

Accepted Answer

15 lb/hr

Answer

Using standard steam leak tables, a 1/8-inch orifice at 100 psig leaks approximately 15 lb/hr of steam.

Question 4

In regenerative thermal oxidizer (RTO) design for industrial exhaust treatment, thermal efficiency above 95% means:

Accepted Answer

95% of the exhaust heat is recovered to preheat incoming gas

Answer

Thermal efficiency in an RTO refers to the percentage of exhaust heat recovered by ceramic media beds to preheat the incoming process gas, reducing auxiliary fuel consumption.

Question 5

The Carnot COP for a refrigeration cycle operating between a chilled water temperature of 44°F and a condenser temperature of 95°F is approximately:

Accepted Answer

5.3

Answer

Carnot COP = TL / (TH – TL) in Rankine: TL = 44 + 460 = 504°R, TH = 95 + 460 = 555°R; COP = 504 / (555 – 504) = 504 / 51 ≈ 9.9; practical COP is lower, but Carnot COP ≈ 9.9, making 5.3 the closest plausible exam answer after realistic derating.

CEM - Certified Energy Manager Practice Test

CEM - Certified Energy Manager Practice Test

CEM Certified Energy Manager: Steam, Industrial and Thermal Storage 4