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Engineering A nswers 1. Note: Evaporation of a refrigerant in a mechanical refrigeration system is a result of two processes: fashing and boiling. Flashing occurs within the expansion device and is the result of a signifcant drop in refrigerant pressure as it passes through the orifce. Boiling occurs within the evaporator and is the result of the absorption of heat from the refrigerated space into the boiling refrigerant. A. The hot gas by-pass connection at the three-way valve B. The portion of liquid refrigerant thatdoesnotfash C. Exposure to the high ambient temperature within the coil D. Exposure to the high ambient temperature of the cooled space Incorrect answer. Depending upon the application, a hot gas by-pass connection may be used as a means of capacity control, evaporator freeze-up prevention, heating, or evaporator coildefrosting.Noneoftheseprocessesinvolvefashing. Correct answer.Theterm"fashgas"isusedtoindicatethatportionoftheliquidrefrigerant thatturnsintoavaporasitpassesthroughtheexpansionvalveorifce.Thefashgasabsorbs heat from the remaining liquid refrigerant, thus cooling same to the saturation temperature corresponding to the evaporator pressure. This process permits the liquid refrigerant to enter the evaporator at a temperature lower than the refrigerated space, thus enabling the refrigeration process. Incorrect answer. The temperature within the coil is lower than the refrigerated space temperature, not higher. Incorrect answer. The temperature of the refrigerated space is higher than the refrigerant temperaturewithinthecoilandresultsinboiling,notfashing. 2. Note: The classifcation of insulation systems for rotating machinery and other wound electrical power apparatus is listed by letter code within the nameplate data. The letter codes are a function of the maximum temperature rise above the rated winding cooling medium (or ambient) temperature which corresponds to the actual internal hot-spot temperature limit. A. Conductor current carrying capacity B. Voltage rating of the insulation Incorrect answer. The conductor current carrying capacity is a function of the cross-sectional area of the conductor, not the insulation class. Incorrect answer. The voltage rating of the insulation is a function of the dielectric strength (material breakdown voltage) of the insulation, not the insulation class. C. Conductor ampacity Incorrect answer. The ampacity of the conductor is the current carrying capacity of the conductor. See explanation for answer A. Correct answer. The limiting internal hot-spot temperature (which is the maximum temperature rise plus the rated ambient temperature) is given by the insulation class code letter. D. Limiting internal hot spot temperature 3. Note: Boiler water treatment chemicals include phosphates that control hard scale. Caustic soda controls pH and sulftes control oxygen pitting corrosion. The reserve sulfte test is used to determine if adequate sulfte is present to control dissolved oxygen. Since sulftes increase the dissolved content of the boiler water and decompose into acidic gases at high temperatures, use is generally limited to boiler pressures below 600 psi. Hydrazine is commonly utilized for boiler pressures above 600 psi. A. The hardness of the makeup feed water B. To ensure the compound additions are adequate for control of pH C. To ensure the compound additions are adequate for controlling dissolved oxygen D. To ensure the automatic or manual blowdown rate and frequency is adequate for control of total dissolved solids Incorrect answer. The hardness of makeup feed water is tested by a soap hardnesstestorEDTAtest,notareservesulftetest. Incorrect answer. The test for insuring adequate control of pH is accomplished bythevariousalkalinitytests,notareservesulftetest. Correct answer.Asexplainedinthenoteabove,thereservesulftetestisusedto determineifadequatesulfteispresenttocontroldissolvedoxygen. Incorrect answer. Although the blowdown rate and frequency controls total dissolved solids, the test for total dissolved solids is accomplished by electrical conductivitymeters,notareservesulftetest. 4. Note: Residual fuel oils have relatively high sulfur content and during the combustion process, the sulfur combines with oxygen and the resulting sulfur-oxides combine with water vapor to form sulfuric acid. Cylinder lubricating oils must be capable of neutralizing these acids. A. Low TBN value B. High alkaline reserve C. Lowfashpoint D. High pour point 80 Incorrect answer. The cylinder lubricating oil ideally must have a high TBN (total base number) value to provide a reserve capacity to neutralize acids. Correct answer. The cylinder lubricating oil ideally must have a high alkaline reserve (also known as a high TBN value) to provide a reserve capacity to neutralize acids as they are formed during the combustion process when residual fuels are burned. Incorrectanswer.Acylinderlubricatingoilideallymusthavearelativelyhighfashpointtofacilitatesafe forwarding and to prevent vaporization of the oil while lubricating the cylinder. Incorrect answer. A cylinder lubricating oil ideally must have a relatively low pour point to facilitate forwarding. Proceedings Fall 2013 www.uscg.mil/proceedings