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Engine cooling by nucleate boiling requires a profound knowledge of cooling systems components: heat exchangers, water pumps, eventually liquid-vapor separators, on the part of equipment manufacturers. Experimental and theoretical studies of the principal heat exchanger, I.E., the vapor-condensor, were effected. The experimental phase required the development, after careful study, of a test set-ups specifically designed for vapor-condensors. Tests are conducted under controlled intake pressures and temperatures, and sub-cooled outlet conditions. Under varying air-flows, outlet-liquid measurements yield instructive information relative to exchanger thermic performance. The influence on performance of tube shape, direction of liquid circulation (horizontal or vertical) and number of passes was also studied. Concurrently, thermic visualization by infra-red camera permits qualitative evaluation of vapor distribution within the condenser.

The cooling conditions of electric vehicles are completely different when compared to the cooling conditions of internal combustion engines for passenger cars, particularly the liquid flow rate and the coolant temperature. The electric vehicle has a flow rate of approximately 500 L/h at low coolant temperatures and the internal combustion engine may have a flow rate as high as 5 000 L/h at high coolant temperature. Without optimization the same size radiator for the heat dissipation for an internal combustion engine of 30 kW can only satisfy 3 kW of heat dissipation for the electric vehicle. We have developed two solutions to cool the electric vehicle: A conventional cooling solution by using the same cooling liquid mixture, Ethylene Glycol-water 50-50%, that is to say, we adapted and optimized the cooling radiator for low flow rate and low coolant temperature. An evaporative cooling solution by using a new fluid, called, Fluorinert FC72.

The previous study presented during the last VTMS 4 showed the following results, for all engine cooling system and depending on the vehicles: Cost reduction by - 10 to -15%, Weight reduction by -15 to - 21%, Coolant volume reduction by -25% Fuel consumption by -3%, Thermal comfort improvement. Despite of these good results, most of car manufacturers hesitated to use this new concept due to this technological breakthrough of engine cooling system because of expensive durability studies. In this paper the electric fan has been simply suppressed and replaced by the heating blower allowing to cool the engine at idle and at low vehicle speed. By suppressing the electric cooling fan, the advantages of this new economical engine cooling system become: cost reduction up to - 30%, weight reduction up to - 30%.

A fundamental vehicle study for a new engine cooling system, the so called NUCLEATE BOILING ENGINE COOLING SYSTEM, has been tested under real and critical conditions in a climate controlled wind-tunnel. Using this cooling system requires a profound knowledge of the cooling circuit and all cooling components such as: condenser, waterpump, liquid/vapor-separator, expansion tank, fan control unit. After preliminary experimental and theoretical studies, two types of cooling circuits were realized and tested in a car: Completely filled nucleate boiling cooling system Partially filled nucleate boiling cooling system Both types of circuits were sealed systems. This meant there was no evaporation or loss of liquid into the environment. By using the nucleate boiling cooling system, the heat of the cylinder head was dissipated while the boiling process change of liquid phase to vapor at constant boiling temperature.

In order to reduce the cost of engine cooling systems in particular the turbo Diesel engines with charge air coolers, we want to understand the relationship between oil sump temperatures and engine coolant temperatures and their impact on one another. Several cars have been tested in the climatic wind tunnel. The following are the cooling specifications: hill climbing with 12% grade with or without a trailer at a 20°C ambient max. speed at 35°C ambient. The main results of these studies were: a great variation of oil sump temperature versus coolant temperature a small variation of coolant temperature versus oil sump temperature a very small variation of heat flux in the oil, in the coolant and the output of engine versus oil sump and coolant temperature.

This paper deals with engine evaporative cooling on the VW TDI diesel engine at high heat rejection running points. Engine tests and thermohydraulic 3D computations inside the engine head are used. First, the basic engine is studied. Then, the flow rate corresponding to evaporation is determined. Around this flow rate, the influence of inlet coolant temperature and circuit pressure are studied. The engine tests and 3D calculations give hydraulic ways of improvements consisting in balancing the flows around the different cylinders. Geometrical modifications of the inside engine circuit (gasket....) are then tested to achieve these improvements.

The targets of this study are: cost reduction of all engine cooling components, gasoline consumption reduction, weight reduction of the engine cooling system, improvement of the thermal comfort in passenger compartment. To reach these targets, Valeo Engine Cooling is developing a new concept in engine cooling. This basic concept consists of adding a small electric water pump, 30 to 60W, instead of the conventional engine driven water pump of up to 1 to 2 KW. This small electric water pump provides a flow rate of approximately 1000L/h. With a liquid flow rate of 1000L/h, this conceptual system can ensure engine cooling at speeds up to 120 Km/h under convective cooling in normal conditions. That is to say, it can supply 95% of the flow requirements (see appendix ) of a vehicle at the same performance level as a conventional cooling system.