LABORATORY WORK IN MECHANICAL ENGINEERING.
The Steam Engine Tests are made on the high-speed Ball engine, which
operates the shops. This motor has been specially equipped for the purpose.
It receives steam from the main line through a Sweet separator; humidity
determinations are thus made twice—once by a separating calorimeter
before the steam enters the separator, and again by a throttling calorimeter
as it enters the cylinder. It is fitted with proper indicators, and permanent
indicator rigging so that at any time cards may be taken and the
indicated horse-power determined. In like manner a friction brake is so
arranged that it may be at once applied for the determination of brake
horse-power. Connections are so made with a Wheeler surface condenser
that the engine may at will be operated either condensing or non-condensing.
Provisions are made for measuring the temperatures and the amounts
of the condensing water and the condensed steam produced during the
run. With these data a complete heat balance of the experimental run
is attainable.
The Steam Turbine Tests are made on a DeLaval 30 horsepower
turbine direct-connected to a 25 kva. alternating current generator. The
turbine takes steam from the main line through a Cochrane separator;
humidity tests are made with a throttling calorimeter below the separator.
Pressure gauges indicate the steam pressure before and after passing
the governor and after expansion in the nozzles. Humidity tests of
exhaust steam are made with a separating calorimeter. The turbine has
interchangeable nozzles for saturated steam exhausting to atmosphere;
for saturated steam exhausting to condenser; for superheated steam
exhausting to condenser. Steam consumption is determined by weighing
the condensate. Power output is measured at the generator, the efficiency
of the latter being known.
The Steam Pump Tests are made on a Worthington direct acting
duplex pump, receiving steam from the main line and exhausting either
to atmosphere or condenser. By weighing the condensed steam the hourly
consumption is determined. The pump draws water from a concrete tank
in the floor of the laboratory and delivers it to a copper-lined tank in the
attic under a head of forty-five feet. Water from the attic tank is
returned to a wrought-iron weir tank in the laboratory, and thence to the
concrete tank. In the weir tank quantity of water delivered is measured.
Velocity head is determined indirectly from the quantity and the known
area of the discharge nozzle. Friction head is determined independently,
and steam consumption per developed horse-power is computed.
The Air Compressor Tests are made on a Remington Ammonia compressor,
4″ × 6″ double cylinder, single acting, so arranged that it may
be connected either to the refrigerating machine or an air storage tank
of ample capacity. Temperature of the storage tank is determined at a
thermometer cup passing well across the diameter of the tank near its
central portion. From the temperature, pressure, and the known capacity
of the tank compressor-capacity is determined; a check on the capacity
from the indicator diagrams being thus obtained. Power imput is measured
by a calibrated electric motor which drives the compressor.
The Air Engine Tests are made on a 3″ × 4″ single cylinder double
acting engine receiving air from the storage tank at any desired pressure
below 100 pounds. The engine is permanently rigged for taking indicator
diagrams, the intake air temperature being determined near the cylinder.
A friction brake and a revolution counter provide means for determining
power output.
This equipment provides for the determination of (a) Mechanical
efficiency of the compressor, (b) Cylinder efficiency of the compressor,
(c) Efficiency of transmission, (d) Cylinder efficiency of the engine, (e)
Mechanical efficiency of the engine, (f) Over-all efficiency of the air plant.
For Steam Boiler Tests the boilers of the university heating and
lighting plant are available. The department is equipped with the necessary
apparatus—thermometers, gauges, steam calorimeters, fuel calorimeters,
gas analyzers, scales, tanks, and so on. Students of Mechanical
Engineering are taught by practical lessons in the boiler-room the standard
methods for boiler trials, and the class makes each session at least
one complete trial.
The Gas Engine Tests are made on an Otto machine of 15 I. H. P.
and 12 B. H. P. This is also provided with its friction brake, indicator
rigging, and indicator. The cooling water is run in from calibrated tanks
and provision is made for observing not only its amount but the initial
and final temperatures. Gasoline or alcohol is used as fuel, and is run
in from a graduated wrought-iron bottle, so that the amount consumed
is determined. The heating power is obtained by an independent test with
a Rosenhain calorimeter. Samples of the burnt gases are drawn from
the exhaust pipe and analyzed in an Orsat gas apparatus. With these
data, and the observed numbers of revolutions and explosions, the heat
balance is worked out.
The Refrigerating Tests are made on a Remington Ice Machine of
one ton capacity. This is an ammonia compression machine driven by an
electric motor. Instead of brine, plain water is used, heated by a steam
jet to 100 degrees and then cooled down to 40 degrees by the machine.
A run is first made with the pipes empty in order to determine the friction
horse-power. The ammonia is then turned on and the run is made under
load. In both cases the power consumed is measured both by wattmeter
and by ammeter and voltmeter readings. The tanks are accurately calibrated
and careful measurements of the temperature are made through
the run. Indicator cards are also taken from the ammonia cylinders and
the number of revolutions is registered by counter. With these data the
mechanical and thermodynamic performance of the machine are figured
out.
For Engine Balancing Experiments the 3″ × 4″ air engine is provided
with detachable weights which may be clamped at any desired position
relative to the crank and the axis of the main shaft. The engine is
then suspended by coil springs; the exactness of the balance from previously
computed weights being determined by the nature of vibration
of the suspended frame.
