Arun,

"Which cooling system is preferred for a 100V, 10KW BLDC electric car?"

As Adrian says, you might find plausible solutions using either air-cooled, fluid-cooled, or some other technology.

(if the track is only 30km long, even phase-change materials might suffice)

"What should be the Energy density & AHr rating of (Lithium ion) battery for driving a 300kg car for a 30 km circuit?"

The energy density is dictated by your chassis design and your depth of budget.

The total capacity is dictated by the type of course (stop-start driving?), the rolling resistance of your (presumably) wheels, and your aerodynamics.

You would do well to examine current solutions, and then tweak one parameter (Cd_0, for example) and see how that alters your battery requirements.

But that presumes a top-level model that relates your battery size and peak current to the rest of the vehicle's characteristics.

Summary: No one-sentence solution available. Look at an electric vehicle that already fits the desired goal, and modify that.

Arun,

"Which cooling system is preferred for a 100V, 10KW BLDC electric car?"

Define the following parameters

1. Volume of Car Chamber

2. Heat infiltration by moving components of car it self in the chamber.

3. External environment.

4.What conditions are required in the Car Chamber

Once we get these parameters solutions will be provided

Using water for cooling will involve a radiator( heat exchanger), a fan ,water jackets, water and a pump. All these will add to add to the car weight and so you need extra power to drive the car. It also depends on the ambient conditions at your place. If you are residing in a cold climate area then air cooling might suit your case provided you make some cooling fins around your engine for heat dissipation.