Thermal Properties of Cardioplegia Heat Exchangers

Abstract

Cardiac surgeries that involve cardiopulmonary bypass technique require a stable temperature maintenance for oxygenated blood or the cardioplegia solution. For this purpose, the heat exchangers are used. Nowadays, these exchangers consist of stainless steel tubes or bellows in a plastic shell. The blood is then warmed or cooled by water flowing in the shell around these structures. In the paper, the thermal specifications of two commercially used cardioplegia heat exchangers Capiox Cardioplegia and MYOtherm XP were evaluated and compared. For this purpose, a water was used as a substitution for blood. Both components were tested for varying flow rates in the pipes in the range 20-150 l/h and fixed flow rate 700 l/h in the shell. The thermal performances of both devices resulted similarly (up to 2.4 kW) at maximal flow rate. The performance factors for low flow rates approached values close to 0.98 and with increasing flow rate decreased down to 0.50. MYOtherm XP shows lower pressure drop than Capiox Cardioplegia due to more optimal construction. The major difference between the heat exchangers was observed in overall heat transfer coefficients at maximal flow rate and resulted in 2191.3 W/m 2 K or 1760.2 W/m 2 K for MYOtherm XP or Capiox Cardioplegia, respectively.