Mechanical seal coolers often are
considered a basic accessory, with littleeffort placed on selecting the optimalone. A seal cooler directly affectsperformance of a mechanical seal andextends its mean time between failures(MTBF). The heat removal andthermosiphoning capabilities of thecooler, its hydraulic characteristicstics,as well as its ability to remove trapped air(ventability) influence mechanical sealperformance. Industry has longconsidered the single coiled tube heatexchanger, known as “coil in a can”, thestandard for mechanical seal cooling.Recent comparative testing concludedthat helically coiled heat exchangers aresuperior in terms of heat rejection,pressure drop, thermosiphoningcapability and venting of trapped air.This article introduces helically coiledmechanical seal coolers and acquaintsthe reader with the construction featuresand material options for this type ofdevice. An analysis of the comparativetesting is also presented.
Helically Coiled Seal Cooler
Helically coiled heat exchangers offercertain advantages: compact size, higherfilm coefficient (the rate at which heat istransferred through a wall from one fluidto another) and more effective use ofavailable pressure drop. These combinedfeatures result in more efficient and lessexpensive designs.
True counter-current flow fully uses theavailable LMTD (Logarithmic Mean
Temperature Difference). Helicalgeometry enables the handling of hightemperatures and extreme temperaturedifferences without high-inducedstresses, High operating pressurecapability and an ability to fully clean theservice fluid flow area add to theexchanger’s advantages. Gas bubbles area frequent cause of seal coolerperformance problems. As the seal fluidwithin a pump is heated, soluble gascomes out of solution and forms bubblesin the liquid flow. A single-tubed sealcooler in this situation will encounterperformance problems, especially with anAPI Plan 23 arrangement. A multi-tubedseal cooler can handle such two-phaseflow without problem. A single-tubedunit must have sufficient upstreampressure to force the bubble from the sealcooler. This often is difficult with Plan 23configurations. A multi-tubed unit, whichhas several parallel flow paths, performsproblem-free. Furthermore, a multi-tubedunit may be oriented so that venting ofthe gas is possible. Although variousconfigurations are available, the basicand most common design consists of aseries of stacked, helically coiled tubes.The tube ends are connected tomanifolds that act as fluid entry and exitlocations. The tube bundle isconstructed of a number of tubes stackedon top of each other, and the entirebundle is placed inside a casing
