The cross flow heat exchanger design includes the configuration of the hot fluid flowing one direction and the cold fluid flowing perpendicularly. Heat transfer is calculated using rate of flows, temperatures of the hot and cold fluids and total surface area of the exchanger. Industrial applications include boiler superheaters and economizers. These units utilize waste heat gases from boilers and furnaces and preheat water or other process fluids. The gases are blown across tubes to transfer heat from the gas to the fluid in the tubes. Often fins are used on the tubes to enhance heat transfer.
One type of cross flow heat exchanger uses air as the cooling medium. Typically, a hot liquid or gas flows through tubes while air is forced past the tubes transferring heat from the liquid or gas, through the tube material and into the air. The air is forced over the tubes by fans that either push or pull the air mechanically. Examples of air-cooled cross flow heat exchangers are air conditioner evaporator coils and car radiators. An air conditioner transfers heat through evaporator coils from a refrigerant. The refrigerant is used to pull heat from a space or provide heat, depending on the design. A car radiator uses a fan to push air across tubes with heat transfer fins. The coolant in the tubes transfers heat picked up from the automobile engine.
One of the most common types of heat exchanger is the shell and tube design. Various designs are possible including parallel flow (hot and cold fluids flowing in the same direction), countercurrent flow (hot and cold fluids flowing in opposite directions) and cross flow (hot and cold fluids flowing in perpendicular directions). The use of cross flow heat transfer is found in hybrid flow shell and tube heat exchangers. The internal baffles, which change the direction of flow, are configured to allow one fluid to flow parallel or countercurrently in one part of the exchanger and change directions to cross flow in another part of the unit. This allows for a more efficient heat transfer design.