Eric Golliher

Loop heat pipe (LHP) development by utilizing coherent porous silicon (CPS) wicks

This paper introduces a theoretical model for a Loop Heat Pipe (LHP) utilizing a coherent porous silicon (CPS) wick. The paper investigates the effects of different parameters on the performance of the LHP such as evaporator temperature, condenser temperature, total mass charge, wick thickness, porosity, and pore size. A LHP is a two-phase device with extremely high effective thermal conductivity that uses capillary forces developed inside its wicked evaporator to pump a working fluid through a closed loop. The loop heat pipe is developed to efficiently transport heat that is generated by a highly localized concentrated heat source and then to discharge this heat to a convenient sink. This device is urgently needed to cool electronic components, especially in space applications. The LHP has been modeled utilizing the conservation equations and thermodynamic cycle. The loop heat pipe cycle is presented on a T-s diagram. A direct relation is developed between the ratio of heat going for evaporation as well as heat leaking to the compensation chamber.

MEMS loop heat pipe based on coherent porous silicon technology

This paper discusses the theory, modeling, design, fabrication and preliminary test results of the MEMS loop heat pipe being developed at the Center for Microelectronic Sensors and MEMS at the University of Cincinnati. The emphasis is placed upon the silicon micro wick and its production through a novel technique known as Coherent Porous Silicon (CPS) Technology.

Exploration of Unsteady Spray Cooling for High Power Electronics at Microgravity Using NASA Glenn’s Drop Tower

At present, there is little understanding of the application of spray cooling to electronics in the microgravity environment. Typically in closed cycle terrestrial spray cooling systems, since not all of the liquid impinging on a hot substrate is evaporated, some residual liquid is separated from its vapor component by gravity and returned to the pump. This technique of phase separation is not available to spacecraft designers. Methods to predict spray cooling performance for ground systems do exist, but they are absent for the space environment. Particularly for NASA spacecraft, there is a need to design spacecraft that use high power laser systems and other systems that use evaporative spray cooling in microgravity. Such knowledge is very important for the performance and life of the device. Reliable analytical methods of predicting thermal response of a spray cooled substrate when considering a transient heat load, such as that found during start up and shut down of a space-based laser or other high heat flux electronics, do not exist. Our goal was to use NASA Glenn’s 2.2 second drop tower to investigate unsteady heat transfer at low Bond numbers and residual fluid behavior in spray cooling. The work contrasts other experiments aboard the NASA Glenn KC-135 low gravity aircraft [1]. Our future plans are to continue the experimental work and include the use of the NASA Glenn 5 second drop tower. This paper will report on some preliminary results of an interesting experimental study performed at NASA Glenn in the summer of 2004. The high speed camera and specially-designed “S.L.O.B.” drop rig provided video and data to assess the fluid management problems that arise in a microgravity spray environment, for both heated and unheated cases. The data show unexpected residual fluid management issues, such as the development of multiple spherical liquid globs, with apparent ordered and repeatable geometry, at the point of impact. The results of these experiments provide direction for further investigation in the future.© 2005 ASME

Microscale technology electronics cooling overview

NASA requirements and subsequent technology solutions for high heat flux electronics are generally different that those for the terrestrial applications. Unlike terrestrial operations. NASA spacecraft have limited opportunities for air cooling, for example, and must rely on less efficient thermal radiation to reject heat to space. The terrestrial commercial electronics industry, as well as other Government agencies, is investing in advanced technologies for electronics cooling at the microscale. This paper gives a brief summary of metrics used in high heat flux electronics cooling, the difference between solutions developed for terrestrial requirements and those for space, and a short description of challenges as well as possible solutions for space-based high heat flux electronics cooling. The argument is made that high heat flux electronics cooling is indeed a core technology required by NASA, since the thermal and other environmental requirements are unique to NASA space missions and are not addressed ...

Evaporative Heat Transfer Mechanisms within a Heat Melt Compactor

This paper will discuss the status of microgravity analysis and testing for the development of a Heat Melt Compactor (HMC). Since fluids behave completely differently in microgravity, the evaporation process for the HMC is expected to be different than in 1-g. A thermal model is developed to support the design and operation of the HMC. Also, low-gravity aircraft flight data is described to assess the point at which water may be squeezed out of the HMC during microgravity operation. For optimum heat transfer operation of the HMC, the compaction process should stop prior to any water exiting the HMC, but nevertheless seek to compact as much as possible to cause high heat transfer and therefore shorter evaporation times.

Investigation of Loop Heat Pipe Survival and Restart After Extreme Cold Environment Exposure

NASA plans human exploration near the South Pole of the Moon, and other locations where the environment is extremely cold. This paper reports on the heat transfer performance of a loop heat pipe exposed to extreme cold under the simulated reduced gravitational environment of the Moon. A common method of spacecraft thermal control is to use a loop heat pipe with ammonia working fluid. Typically, a small amount of heat is provided either by electrical heaters or by environmental design, such that the loop heat pipe condenser temperature never drops below the freezing point of ammonia. The concern is that a liquid-filled, frozen condenser would not re-start, or that a thawing condenser would damage the tubing due to the expansion of ammonia upon thawing. This paper reports the results of an experimental investigation of a novel approach to avoid these problems. The loop heat pipe compensation chamber is conditioned such that all the ammonia liquid is removed from the condenser and the loop heat pipe is non-operating. The condenser temperature is then reduced to below that of the ammonia freezing point. The loop heat pipe is then successfully re-started.Copyright

Development of the Two Phase Flow Separator Experiment

The recent hardware development and testing of a reduced gravity aircraft flight experiment has provided valuable insights for the future design of the Two Phase Flow Separator Experiment (TPFSE). The TPFSE is scheduled to fly within the Fluids Integration Rack (FIR) aboard the International Space Station (ISS) in 2020. The TPFSE studies the operational limits of gas and liquid separation of passive cyclonic separators. A passive cyclonic separator utilizes only the inertia of the incoming flow to accomplish the liquid-gas separation. Efficient phase separation is critical for environmental control and life support systems, such as recovery of clean water from bioreactors, for long duration human spaceflight missions. The final low gravity aircraft flight took place in December 2015 aboard NASA’s C9 airplane.

Exploration of Impinging Water Spray Heat Transfer at System Pressures Near the Triple Point

The heat transfer of a water spray impinging upon a surface in a very low pressure environment is of interest to cooling of space vehicles during launch and re-entry, and to industrial processes where flash evaporation occurs. At very low pressure, the process occurs near the triple point of water, and there exists a transient multiphase transport problem of ice, water and water vapor. At the impingement location, there are three heat transfer mechanisms: evaporation, freezing and sublimation. A preliminary heat transfer model was developed to explore the interaction of these mechanisms at the surface and within the spray.