The heat-driven pulse pump has been invented in an effort to satisfy a need for pumps that can circulate heat-transfer fluids at low flow rates with high reliability over long operational lifetimes. The heat-driven pulse pump (HDPP) is so named because it generates pumping action by exploiting periodic (pulsed) heating and vaporization alternating with cooling and condensation of the fluid to be pumped. To be amenable to pumping by an HDPP, a fluid must, therefore, be one that can be vaporized and condensed within a convenient range of pressure and temperature. Anhydrous ammonia is one example of such a fluid that could be useful in many applications.
A basic HDPP includes a grooved cylinder, a wick, inlet and outlet check valves, strip heaters, and a cooling block (see figure). The cylinder and other parts are sized to suit the specific application. The two check valves are the only moving parts.
Initially, the cylinder is filled with the liquid phase of the fluid to be pumped. At the beginning of the pumping cycle, power is supplied to the strip heaters for a specified interval of time (pulse). During this interval, some of the liquid in the cylinder vaporizes. The resulting expansion causes the pressure in the cylinder to rise and the outlet check valve to open. Once the pressure rises to the point where it overcomes the pressure drop in the fluid circuit, the pressure forces some of the liquid through the wick and the outlet check valve; meanwhile, the liquid in the grooves is wicked toward the heater strips and sustains vaporization until the heating power is turned off.
When the heating power is turned off, the vaporization stops. The cooling block is used, if needed, to ensure that during this part of the pumping cycle, the temperature in the cylinder falls to somewhat below the saturation temperature of the fluid-circulation loop. This decrease in temperature causes some or all of the vapor in the cylinder tocondense, and the concomitant contraction and decrease in pressure cause the outlet check valve to close and the inlet check valve to open. The vapor is further condensed by the cold liquid that enters through the inlet check valve, so that the wick, grooves, and interior space of the cylinder become refilled with liquid. The system is then ready for the heat pulse that marks the beginning of the next pumping cycle.
A fluid-circulation system can be made to include a pumping subsystem that comprises three HDPPs connected in parallel. To obtain continuous flow in the portion of the fluid-circulation loop external to the pumping subsystem, the three HDPPs are operated in sequence, with two pumps in the recovery (condensation) part of the pumping cycle while the remaining pump is in the pulse (vaporization) part of the cycle.
A prototype system of three HDPPs with anhydrous ammonia as the pumped fluid was tested in experiments. The pressure drop in the fluid-circulation loop was 0.5 psi (3 kPa). A variety of power settings, fluid pressures, timing sequences, and cooling-block temperatures were investigated. The best combination of settings determined in these experiments was a cooling-block temperature of 15 °C, saturation pressure of 28 psia (193 kPa absolute), and heater power of 50 W applied to each pump during 30-second pulses. With these settings, the temperature in each pump varied sinusoidally between 29 and 35 °C, and the flow rate was 14 grams per minute, which would provide 300 W of continuous heat dissipation. This combination of settings did not allow any pump to become fully flooded before heating power was resupplied, so that liquid was pushed out quickly when the heat was turned on. This concept would also be applicable to a microgravity environment.
This work was done by Steve Matthew Benner of Goddard Space Flight Center and Mario Santos Martins of Jackson & Tull.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Goddard Space Flight Center; (301) 286-7351
Refer to GSC-13739