Readers’ Forum
OPINION
Readers’ Forum submissions should be emailed to George Lee, PEG Editor, at glee@apega.ca. Please limit them to 300 words or less. Longer letters are printed at the discretion of the editor. Letters may be edited for brevity, taste, clarity and legality. Please note: Readers’ Forum items are treated as opinions and therefore are NOT peer reviewed. They do not necessarily reflect the views of APEGA Council, Executive Committee or staff.
GEOTHERMAL
Strictly speaking, this is correct. But as a railroad enthusiast, I’d like to expand on the topic. Railroad engineers came up with a smarter and more cost- effective solution than a differential. The riding surface of a train wheel is not a parallel-sided cylinder, but rather a truncated cone. The diameter of the rim adjacent to the flange is greater than the diameter at the outside edge of the wheel. Thus, on a bend the outside wheel tends to ride against the flange, while the inside wheel rides closer to the edge. Both wheels travel at the same rotational speed, but the outside wheel covers a slightly greater distance owing to its slightly greater effective circumference. In practice the effect may be diminished by the dynamic condition of the train. JIM BLUM, P.ENG. Calgary
ARTICLE SHOULD HAVE DUG DEEPER
Re: The Other Energy Sector, Part IV, The PEG , Winter 2014.
This is a timely article on an alternate energy source, but unfortunately it is redolent of the style of Popular Science magazine — lots of happy examples of positive things and almost no mention of real-world problems. Where is the discussion of the corrosivity of many deep and hot water systems? Does one pump the super-hot ground water to the surface and deal with the corrosion and other problems there? Or does one circulate pure water down to the hot region and deal with the corrosion below? Where is the discussion of the electrical energy consumption of heat pump compressors necessary to pump the latent heat of the barely warm shallow water systems up to a minimal usable temperature level for even hot water heating? Where is the discussion of the cost of a natural gas-derived BTU versus an electrically derived BTU, most especially in today’s environment? Where is the discussion of the appallingly low efficiency of steam turbines driven by low heat/low pressure (perhaps 150 pounds per square inch) steam? The geothermal power station at Lake Taupo in New Zealand runs at this input level and is a massive installation, generating very modest electrical output for massive capital input. Geothermal can be viable — but let’s press on with our eyes wide open! RICHARD WILSON, P.GEOPH. Life Member Calgary
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Mr. Spencer raises some interesting challenges on rail tank car design. Yes, a safer rail car can be designed, but more work is necessary for ensuring the safe shipment of crude oil out of this province. And some of Mr. Spencer’s points of view need clarification. The centre of gravity is dramatically different when a rail car is loaded than when it is empty. When empty, a tank car weighs about 65,000 lb. (the North American rail system usually uses non-metric numbers) and when loaded can weigh up to 286,000 lb. A round cross-section of tank is definitely more economical to build, because flat plate is rolled into cylinders during manufacturing. An egg cross-section may encourage sloshing in a partly loaded car, which is not safe. Regarding wheels, there is some interesting geometry that comes into play with the wheel rims to minimize skidding in corners. The wheel camber is designed so the wheel on the inside has a smaller diameter of wheel in contact with the rail, while the opposite wheel makes contact at a slightly larger diameter. Train speed is not limited by wheels. Take a page from the high-speed passenger trains in Europe and Japan. Rather, the track bed, ties and ballast have to be able to withstand the dynamic rolling forces of a fully loaded freight train. And yes, there are bad examples of wavy, lumpy track. But you will find the tracks for Class 1 railroads, such as CPR and CN Rail, to be in good condition.
TRAIN LETTER GETS MANY WHEELS TURNING
Re: Tank Cars Present a Design Challenge, by Henry A. Spencer, P.Eng., Readers’ Forum, The PEG , Winter 2014.
The writer states that rail car axles have no differential, thus causing a problem when trains traverse a curve in the track.
46 | PEG SPRING 2015
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