A low-frequency ferrohydrodynamic pump for a magneto-caloric refrigerator

Ferrohydrodynamic or magnetic pumping enables the design of a magnetocaloric refrigerator with no moving parts. Existing magnetic pumps utilize travelling wave magnetic fields with frequencies in the range of 100 to 1000 Hz. Such high frequencies when utilized in the proposed refrigerator could cause heating which is detrimental to its performance. Hence, a magnetic pump that works with low magnetic field frequencies (¡ 1 Hz) is designed and its performance is experimentally characterized and compared against an one-dimensional model. The design of the magnetic pump consists of a rising and falling pipe, circumscribed by an electromagnetic coil. On application of a magnetic field, due to the inward acting force on either end of the pipes, the ferrofluid progresses in the rising pipe and reaches the falling pipe. On removal of the magnetic field, the portion of the fluid in the falling pipe falls down due to gravity, thereby achieving a net pumping action. Thus on continuously cycling the magnetic field, an intermittent motion of the ferrofluid is obtained. The maximum cross-sectional area and time-averaged mass flow rate of the proposed design is 1.8 g s^-1 cm^-2 at 0.74 Hz and 35.7 mT. This mass flow rate is comparable to pump designs that work on travelling wave magnetic fields, whose operational frequency is three orders of magnitude higher.