CONSTRUCTING AND EQUIPPING A REFRIGERATED LABORATORY 260009
Because of the great increase in the winter use of automobiles resulting from general highway improvement and a doubling of the percentage of closed cars produced in the last 5 years, the problem of satisfactory operation of automobiles at low temperatures has assumed far greater importance than prior to 1920. It has therefore become necessary to make a more intensive investigation of the difficulties encountered in winter driving and of means for their avoidance. Study of low-temperature operation on the road is unsatisfactory because of the many variables in the conditions and the sudden and extreme changes that occur; consequently a refrigerated laboratory in which cars and engines can be tested under constant conditions that simulate as nearly as possible those met in road driving in winter is highly desirable.
By preliminary investigations it was found that driving in present closed cars is almost as comfortable at speeds up to 35 or 40 m.p.h. as driving at lesser speeds and that in many parts of the Country a car is expected to operate satisfactorily in air temperatures as low as - 20 deg. fahr. Therefore the Dodge Bros. laboratory for studying the characteristics of automobile performance at low temperatures was designed to meet these two conditions. The laboratory was built in one of the assembly buildings of the plant and consists of a cold room and equipment for reducing the temperature to - 20 deg. or lower and maintaining it at that point, apparatus for testing cars and engines and provisions for assuring the safety and health of the observers.
The walls of the cold room are built of cork-board blocks cemented together with asphalt. Refrigerator-type entrance doors, protected by a vestibule, are provided and an observation window that is made of five sheets of window glass with ½-in. air spaces between is provided for the dynamometer observer. The glass is kept free from frost and ice by calcium chloride placed at the bottom of the air spaces. Collection of frost at the doors is avoided by finishing the room inside and outside with cement plaster, which does not have the hygroscopic characteristic of lime plaster, and the room is remarkably dry at all times. This construction of the cold room results in an almost negligible transmission of heat through the walls. Communication between the inside and outside is by telephone, with numerous convenient connections within the room, and a warning signal, operated by push-buttons or automatically by accidental disconnection of the telephone, gives audible notice if the observer in the room needs help.
An ammonia refrigerating system reduces the inside temperature and absorbs a calculated total of 210,000 B.t.u. per hr. It includes an automatically controlled compressor, having a rated capacity of 49 tons when operating at 20-lb. back-pressure, and a 25-ton condenser. A blower circulates 24,000 cu. ft. of air per min. and passes the entire volume of air in the room over the cooling coils 11 times per min. The normal velocity of the air in the room is from 2½ to 3 m.p.h., but the direction of air-flow in any part of the room is controlled by louvers in a partition that separates the blower compartment from the main body of the room. The blower directs a current of cold air from the cooling coils against the radiator of a test car at a velocity of 35 m.p.h.
The room is provided with an engine test-stand and a floor-type chassis test-stand, both arranged to transmit the engine power to an electric dynamometer located outside the room. The chassis stand has four inter-connected pulleys housed in a pit for transmitting rear-wheel torque. A drain-pipe removes any collection of water from the pit and another at the lowest part of the floor proper keeps the floor dry. Exhaust gas is conducted from the engine in the chassis or on the engine-stand down through the floor and to the outer atmosphere. The crankcase breather is similarly vented to prevent dispersion of noxious gas into the room.
Air used for operation of the test-engines is admitted to the room by balanced valves in ports in the blower tunnel and is chilled to the room temperature. Provision is made, however, for warming the intake air for experimental purposes by an external heater. Fuel kept outside the room is fed to the engines as required and is measured accurately. Positive determinations of the consumption reveal transmission power-losses due to heavy lubricant, which losses heretofore have been attributed solely to faulty carburetion.
Some characteristics of the cold room are as yet unknown, but it is believed that the temperature of the room and of a 3000-lb. automobile in it can be reduced from 70 to - 20 deg. fahr. in 4 hr. and also that it will be possible to reduce the temperature to - 50 deg. fahr. with the equipment provided. As such a low temperature cannot be measured by a mercury or spirit thermometer, owing to the freezing of mercury at - 39 deg. and the separating of the indicating column in a spirit instrument, experiments are being made in the recording of temperatures at various locations in the room with a Leeds & Northrup recorder and thermocouples.
This refrigerated laboratory is thought to be complete in every detail for all necessary investigations of low-temperature automobile operation, such as starting and warming-up characteristics of the engine, discharge capabilities of storage-batteries, channeling of gear lubricants, crankcase-oil dilution and the collection of water in the crankcase, effects of sudden temperature-changes on body finishes, and carburetion and fuel-mixture distribution.