FROST FREE HEAT EXCHANGER FOR CRYOGENIC AUTOMOTIVE PROPULSION PRESENTED BY SREEJITH V S S7 ME ROLL NO 4421

INTRODUCTION  The California Air Resources Board enacted the Low Emission Vehicle(LEV).  Zero Emission Vehicle (ZEV).  Pollution can cause aching lungs,wheezing, coughing and head aches.  Serious health problems.  Children is at particular risk.

 Currently, battery powered electric vehicle is the only commercially available technology that meet ZEV standards.  Slow recharge and high initial cost.  The energy storage medium may well be liquid nitrogen.  Frost free heat exchanger performance.

CRYOGENIC AUTOMOTIVE PROPILSION  The cryogenic automobile is a ZEV.  Operates on the thermo dynamic potential between the ambient atmosphere and a reservoir of liquid nitrogen.

 The liquid nitrogen is drawn from a tank,pumped up to system pressure.  Vaporized and superheated in a heat exchange system.  High pressure and ambient temperature gas-system’s motive work.  The spent low pressure gas is exhausted back to atmosphere.

 As nitrogen gas is the only emission,the cryogenic automobile meets California’s ZEV guide lines.  Frost free liquid nitrogen heat exchange system.

FROST FREE HEAT EXCHANGER  Operate in a variety of conditions and is structurally robust-not being hampered by the build up of frost.  Dealing with frost formation fall into two categories: 1) PASSIVE CONTROL. 2) ACTIVE CONTROL.

PASSIVE CONTROL  Either preventing frost formation, or over sizing the heat exchanger such that frost build up is unimportant.

ADVANTAGES  Mechanical simplicity.  Reliability.

DISADVANTAGES  In general,less flexible in dealing with off- design operation.

ACTIVE CONTROL  Active control of frost formation entails allowing frost to accrete and then removing it mechanically.

ADVANTAGES  More operationally robust.  Performance of an actively controlled heat exchanger is much less dependent on the ambient or operational conditions since these systems can be responsive to different loading conditions.

DISADVANTAGES  Power consumption.  Poor long term reliability.

 The operating environment can be a demanding one.  Weather conditions.  Driving conditions.  Rigorous safety.  Comfort.

PASSIVE CONTROL METHOD  To prevent frost build upon sub ambient heat exchangers, the exterior surfaces must be kept above the freezing point of water.  The principle is the same as for multi fluid heat exchange systems, where heat Is transferred from source to sink via a number of media operating in series.

 The choice of passes was based on two practical condition.  Passive heat exchangers are more tightly coupled to environmental and operating conditions.

ACTIVE CONTROL METHOD  Achieve a very compact unit.  A heat exchanger has been developed which uses rotating brushes for active frost control.

CONCLUSIONS  The cryogenic automobile is a potential contender in the ZEV market, provided certain key technologies are demonstrated.One of these technologies is the development of an all weather heat exchange system.A heat exchanger that works well in a variety of operating conditions, is structurally robust, and is not hampered by the build up of frost is a necessary technology for the cryogenic automobile.Experiments are yet to be conducted to determine the actual performance.Until road test experiments are conducted, the actual thermal performance will not be known with enough accuracy to support an overall recommendation for the final heat exchange system design.

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