Water boils at 100 degrees Celsius, so you could increase the heat all you want, but it would not cause the food to cook any faster. The water would transfer the 100 degrees of temperature to the food until the water all evaporated away as steam. When the food makes contact with the cooking container, heat will be transferred due to conduction, which is heat transfer by direct contact. For conduction, more heat would cause the food to cook faster. Another method that would cause the food to cook faster would be the use of a pressure cooker, which seals the water and air inside the cooking container. You could apply higher heat to the pressure cooker, it would raise the pressure inside the cooker, which would cause the water to boil at a higher temperature due to the higher pressure. So, with the use of a pressure cooker, one could cause food to cook faster by applying more heat.