Having high and most effective thermal conductance value heat pipe is widely used for heat transformation. The heat pipe is having unique properties like compact size, light weight and indirect conductance. The heat pipe is used in the cooling of electronic components of computer applications, controlling of temperature in aerospace parts, excess heat recovery in exhaust gases of internal combustion engines. Heat pipes with rectangular cross section can be used for handling large heat transfer sections when weight and space are considered. The working medium that is entrapped in the heat pipe is under phase change from liquid to vapor and vice versa. The vapor condenses in the condenser region by removing heat to the sink and back to the evaporator passing through the porous wick using capillary pumping pressure for re-evaporation. There will be pressure drop in the wick and vapor channel volume. The simple theory of the heat pipe enumerates the capillary pressure in the wick should be more than the sum of the pressure drops in the vapor core and pressure drop in the wick.