An experimental study of closed loop intermittent spray cooling of ICs

Spray cooling is one of the most prominent high heat flux removal schemes, for various applications including electronics cooling. In the past there has been extensive study conducted on the various factors (nozzle type, location, fluid, heat flux, surface conditions, pressure and mass flow rate) affecting the cooling performance. However, all study has been limited to steady state conditions, and the steady state heat transfer coefficient alone has been investigated. In most of the systems, the heat flux varies temporally and the object to be cooled needs to be maintained at the same temperature. One way of achieving it is by intermittent spray cooling (ISC), in which the spray mechanism is activated only when the temperature starts rising above a set limit. Transient temperature fluctuations, transient heat transfer coefficients and frequency of the process were recorded for pressures of 2, 4 and 6 bar for heat fluxes of 11, 22, and 33 Watt/cm 2 at 5, 10 and 15 °C above the steady state temperature (under continuous spray). This paper attempts to understand the various physical mechanisms involved in such a system and discusses a demonstration of ISC to a simulated, variable heat flux-cooling problem. It is also shown that the ISC is energetically more efficient than steady continuous spray. ► Intermittent spray cooling is studied using a thermal test die. ► Temperature transients reflect sinusoidal variation at periodic steady state. ► High heat flux and low set point temperature give low frequency, high duty cycle. ► Closed loop feedback control for a temporally varying heat flux is demonstrated. ► Energy efficiency of intermittent spray cooling is shown to be high.