How to convert 2 liters per hour to milliliters per second .

Divide by a factor of 3.6.
To see why, consider the conversion factors between liters and milliliters as well as hours and seconds.
1 Liter = 1000 Milliliters
1 Hour = 3600 Seconds
For example, if you encounter the misfortune of springing a leak in your father's antique water bed one night when playing darts with your best friend, and it is losing water at 2 Liters / Hour, you can deduce that it is losing 2 * 1000 milliliters every hour (2 000 Liters / hour), and because there are 3 600 seconds in an hour then you're only losing 1 / 3 600 * 2 000 milliliters of water every second, so 5/9 milliliters per second.