Plate Heat Exchangers are unquestionably the fastest way to chill your wort to yeast pitching temperature. It can chill 10 gallons of boiling wort to pitching temperature within 5 minutes when using 15°C cooling water at 5 gpm.
Heat transfer occurs when there is a difference in temperature between two mediums. Heat will travel from the hot source to the cold source. The rate at which the heat transfer occurs at is determined by many factors such as the heat conductivity of the two materials andthe difference in temperatures of the two mediums. Convective heat transfer occurs when the materials are moving against each other.
Fluid A passes from the port on the left of the heat exchanger through every other channel created by the plates to the opposite end port on the left of the heat exchanger (looking at it the long way). Fluid B passes from the port on the right through the other channels created by the plates and comes out the other port on the right side. The fluids are essentially touching each other through the plates and heat is transferred from the hot fluid to the cold fluid. (but the fluids do not mix)
Plate heat exchangers have significantly good heat transfer rates because they use metal plates which have high heat conductivity rates and the plates are extremely thin. The plate heat exchangers also achieve high amounts of heat transfer through convective forces with both working fluids. With large temperature differentials, great amounts of heat transfer can be achieved using a plate heat exchanger.
This is especially great for brewers in Tropical climates!