Automotive HVAC and Engine Cooling News Item No. 112306 How does the durometer of engine mounts affect Engine Cooling and HVAC? How is the required radiator air flow determined and measured? Why is knowing the refrigerant quality one of the most important variables in sizing the AC system? Is the AC compressor load greater than wheel HP? How does the AC load affect fuel economy and emissions? When and how does coolant pump cavitation occur? Send me your questions- alkareng@aol.com The topic for this session is Automotive De-aeration Systems. Refer to pages 37, 56, 58-59, 69, 73.1-75, 85.17 in the text "Design and Development of Automotive Engine Cooling Systems". The de-aeration of engine coolant of condensible and non-condensible gases has been known by engine designers as far back as the development of the first IC engine.  It is not a so called "trade secret" and an experienced mechanic, technician or engineer can design and develop a fully functional de-aeration system using the basic principles of fluid dynamics and heat transfer. The cylinder and engine block coolant flow direction and rate are designed to ensure that hot spots do not occur outside the combustion chamber, the engine oil does not exceed a specified temperature range and the coolant delta temperature (temperature out minus temperature in) is within a specified thermal shock/fatigue  range, during all vehicle operating modes. The coolant flow rate and direction vectors through the cylinder head and block are mapped in detail relative to:  cooling passage geometry and cross sectional area, coolant mass flow and velocity, combustion chamber geometry, combustion and surface temperatures, block and head configuration, coolant flow scheme, and convection, nucleate boiling and departure from nucleate boiling heat and mass transfer mechanisms.  There are several methods of de-aerating the coolant, including recovery bottle, surge tank, pressurized hot bottle, pressurized flow-through hot bottle, etc. The pressurized flow-through hot bottle is the preferred method of de-aerating the coolant.  This system requires vents located at high spots, particularly at the cylinder heads.  A non-vented cap (not open to the atmosphere) or full pressure (not open to vacuum)  is used.  A measured amount of coolant immediately flows from the vents through an adequately sized orifice and into the bottle. The coolant is de-aerated as soon as the engine is activated.  The de-aerated coolant is drawn from the bottom of the bottle and is returned to the engine. The pressurized flow-through  hot botlle system is well known and has been in production for many years.  It was introduced in the Jeep Cherokee in 1984 and in other production vehicles, including off-highway, military and agriclutural vehicles.   The selection of de-aeration system design depends on coolant pump pressure and flow characteristics, pump RPM, type of pressure cap used (vented , non-vented, full pressure), coolant temperature functional objectives, type of coolant, de-gassing (i.e. diesel engines) specifications, etc. The de-aeration system, being a sub-system of the engine, is designed within the confines of any engine coolant flow schema. The next topic to be discussed will be the methodology of the development and testing of a cooling system.         A copy of this News Item and all others to date are available free on request. Send your request to alkareng@aol.com.