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Lee, Kuan-LinDevelopment of a Compact Thermal Management System Utilizing an Integral Variable Conductance Planar Heat Pipe Radiator for Space Applications
Doctor of Philosophy, Case Western Reserve University, 2017, EMC - Mechanical Engineering
In the present research an innovative space thermal management system is developed utilizing an integral planar variable conductance heat pipe (VCPHP) radiator, which can function reliably over a wide range of environmental conditions. The condenser (or radiator) of this planar shaped heat pipe is self-adjustable, and the evaporator temperature can be stabilized within a tolerable range even when the sink temperature changes significantly. This research includes the design, fabrication and test of four prototype planar heat pipe radiators, which are made with a metallic material and a thermally conductive polymer. The corresponding thermal performance of prototype VCPHPs were measured and analyzed through a benchtop heat pipe-based heat rejection system. To further support the concept, a multi-scale, steady-state heat pipe operation model (SSHPOM), which is able to capture both the thermal and hydrodynamic characteristics of the developed VCPHP radiator was developed. The mathematical model combines a theoretical thin-film evaporation model, a NCG expansion model and 2D steady-state heat transfer analysis. After validation, a feasibility of a large scale VCPHP designed for the Altair Lunar lander mission is predicted via numerical simulations with radiation cooling boundary conditions. Using the mathematical model, the influence of several design parameters can be identified and a maximum heat rejection turn-down ratio of 11.0 is achievable. Furthermore, the vapor-NCG topology within the integral planar heat pipe with a non-uniform heat load is simulated through a volume of fluid (VOF)-based approach.

Committee:

Yasuhiro Kamotani (Advisor); Jaikrishnan Kadambi (Advisor); James T'ien (Committee Member); Chung-Chiun Liu (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

heat pipes; radiator; two-phase heat transfer; space thermal control system

Barthelemy, Robert RaymondEvaporation heat transfer in heat pipes /
Doctor of Philosophy, The Ohio State University, 1975, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Heat pipes;Heat

SUH, JUNWOOTHE DYNAMIC CHARACTERISTICS OF A LIQUID-GAS INTERFACE IN MICROSCALE PORES
MS, University of Cincinnati, 2002, Engineering : Mechanical Engineering
For both Loop Heat Pipes, being developed as a thermal control device for microelectronics in space applications, and the de-watering process in a vibro-separator, the dynamic characteristics of a liquid-gas interface inside micropores greatly affects the efficiency of the entire system. In the pharmaceutical industries, product particles are discharged in the form of a dilute slurry from a reactor to a de-watering device, such as a vibro-separator. For extremely small pores, gravity is insufficient for removing the excess water through the micropore screen. For these cases, it has been suggested that the de-watering process can be initiated by utilizing a vacuum pressure beneath the screen and applying sinusoidal vibration to the screen. To understand the phenomena of de-watering from the product screen of a vibro-separator utilizing vibration and pressure, a single liquid-filled micropore is studied. In past studies [8], the Navier-Stokes and Young-Laplace equations have been used to describe the dynamic motion of the liquid column and liquid-gas interface. A major goal of this study is to experimentally verify this model. In particular, comparison is made between the amplitude and frequency of acceleration required to cause the bubble burst through predicted theoretically and measured experimentally. The Lexan wicks having several pores with a uniform diameter of 50 ìm, 100 ìm, 500ìm and 1 mm are utilized. Depending upon the size of the micropores, two different types of tests were performed. One test utilized no external pressure difference across the wick and other test utilized a pressurized upper chamber.

Committee:

Dr. Frank Gerner (Advisor)

Keywords:

Microsale Pores; Loop Heat Pipes; vibro-separator; mechanical engineering

Bowers, Charles H.Transient analysis of heat pipes with applications to selected experiments and a conceptual reactor design /
Doctor of Philosophy, The Ohio State University, 1973, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Heat pipes;Nuclear reactors

Suh, JunwooProof of Operation in a Planar Loop Heat Pipe (LHP) Based on CPS Wick
PhD, University of Cincinnati, 2005, Engineering : Mechanical Engineering
As electronic design allows higher throughput in small packages, dissipating the heat load becomes a critical design factor. Available cooling approaches, such as extruded heat sinks, are insufficient to meet these ever-increasing cooling needs. The industry has found an ideal solution in heat pipes. Due to the emergence of high power equipment, development of more effective thermal control devices is warranted. During the past decades, many microscale heat pipes were invented, developed, and are still being researched. The micro Loop Heat Pipe (ìLHP) under development is a next generation micro heat transfer device that utilizes the latent heat of a working fluid and has excellent heat transport capability as compared with that of standard metallic cooling devices. A family of planar LHPs based upon the use of a radically different type of wick structure made of planar coherent porous silicon (CPS) was researched, modified, and developed for several years at the University of Cincinnati. In this work, histories, configurations, principles, and mathematical modeling of the microscale heat pipes are surveyed. The description of the visualization LHP and the fourth generation LHP, their operation principles, operating ranges, and energy transport capability are discussed. The former one was constructed to improve our understanding of the complex phenomena in the loop and demonstrate operation, by observing through the transparent materials. The latter one was a series of planar LHP consisted of evaporator, condenser, and stainless steel tube and tested under vacuum conditions. Both systems showed the excellent heat dissipation capability.

Committee:

Dr. Frank Gerner (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Electronic Cooling; Microscale Heat Pipes; Loop Heat Pipe; Thermosyphon; Coherent Porous Silicon Wick

ARRAGATTU, PRAVEEN KUMAROPTIMAL SOLUTIONS FOR PRESSURE LOSS AND TEMPERATURE DROP THROUGH THE TOP CAP OF THE EVAPORATOR OF THE MICRO LOOP HEAT PIPE
MS, University of Cincinnati, 2006, Engineering : Mechanical Engineering
The Micro Loop Heat Pipe (LHP) is a two-phase device that may be used to cool electronics, solar collectors and other devices in space applications. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference developed between the evaporator and condenser and capillary forces developed inside its wicked evaporator to circulate a working fluid through a closed loop. While previous experiments have shown reduction in chip temperature, maximum heat flux was less than theoretically predicted. This paper addresses the main problem with the past designs of top caps which has been the conduction of heat from the heat source to the primary wick. The new top cap design provides conduction pathways which enables the uniform distribution of heat to the wick. The provision of conduction pathways in the top cap increases the pressure losses and decreases the temperature drop. The feasible competitive designs of the top cap with conduction pathways from the fabrication point of view are discussed in detail. Calculation of pressure drop and temperature drop is essential for the determination of optimal solutions of the top cap. Approximate pressure drop was calculated for the top cap designs using simple 2-D microchannel principles. Finite element modeling was performed to determine the temperature drop in the conduction pathways. The conditions used for arriving at the optimal design solutions are discussed and presented. A trapezoidal slot top cap design and trapezoidal mesas top cap were chosen for fabrication as they were relatively easy to fabricate with available MEMS fabrication technologies. Geometry of the external vapor reservoir for the trapezoidal slot top cap was designed for optimum pressure drop. Variation of pressure drop in the top cap with respect to the porosity in the coherent porous silicon wick was discussed and analyzed in detail. The exact pressure drop calculations were performed numerically using a finite volume commercial flow solver FLUENT 6.1 with appropriate boundary conditions. The temperature drop calculations were performed using finite element modeling in ANSYS 6.1. It was assumed that all the pores have uniform mass flow rate and were at saturation conditions during the phase change. Obtained values of pressure drop and temperature drop for chosen geometries of trapezoidal slot and trapezoidal mesa top cap were found to be within the optimal limits and are ready to be fabricated.

Committee:

Dr. Frank Gerner (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

LHP; Loop Heat Pipe; CPL; Heat Pipes; Electronics Cooling; Pressure drop; Temperature Drop; Fluent; Ansys; CPS Wick; Microchannel; porosity modeling

Ababneh, MohammedNovel Charging Station and Computational Modeling for High Thermal Conductivity Heat Pipe Thermal Ground Planes
PhD, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering
Thermal ground planes (TGPs) are planar, thin (thickness of 3 mm or less) heat pipes which use two-phase heat transfer. TGPs are innovative high-performance, integrated systems able to operate at a high power density with a reduced weight and temperature gradient. Moreover, being able to dissipate large amounts of heat, they have very high effective axial thermal conductivities and can operate in high adverse gravitational fields due to nano-porous wicks. A key factor in the design of the TGP is evacuation prior to filling and introduction of the proper amount of working fluid into the device. The major challenge of this work is to fill heat pipes with a total liquid volume of less than 1 ml, without being able to see into the device. The new filling station is an improvement over the current state of the art as it allows for accurate filling of micro liter sized volumes. Charging station validation demonstrated the capability of charging TGPs with accuracy of ±1.64 µ A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). This work shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that this model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. A three-dimensional ANSYS model is used to predict the temperature field in the TGP, the effective axial thermal conductivity, and the evaporation and the condensation rates. A key feature of this model is that it relies on empirical interfacial heat transfer coefficient data to very accurately model the interfacial energy balance at the vapor-liquid saturated wick interface. Wick samples for a TGP are tested in an experimental setup to measure the interfacial heat transfer coefficient. Then the experimental heat transfer coefficient data are used for the interfacial energy balance. To verify the results of the ANSYS model several of the experimental work was done for different TGP samples. The results show the comparison of temperature distributions between the ANSYS model and the experimental results for the TGP with LTGP= 9, 15 cm, different input power levels (Qin= 10W, 15W and 20W) and condenser temperature Tcondenser = 60, 75, and 90 °C. The ANSYS model showed excellent agreement with the experimental results. CFD model is introduced to determine the capillary limit in TGPs. In addition, the effect of wall shear stress and the interfacial shear stress in the liquid pressure of the TGP is studied. This model shows that the vapor pressure to the liquid pressure is not significant and the FLUENT results verify this conclusion. Finally, this dissertation offers a design for heat pipe charts that avoids the effects of vapor pressure, wall shear stress and the wick-vapor interface to the liquid pressure for most well-known working fluids.

Committee:

Frank Gerner, PhD (Committee Chair); Tao Deng, PhD (Committee Member); Rupak Banerjee, PhD PE (Committee Member); Michael Kazmierczak, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

heat pipes;Thermal ground planes;Charging;

PONUGOTI, PRIYANKASTUDY OF TRANSIENT BEHAVIOR OF THE EVAPORATOR OF THE MICRO LOOP HEAT PIPE AND MODIFICATIONS TO THE EXISTING GLOBAL MODEL
MS, University of Cincinnati, 2006, Engineering : Mechanical Engineering
The Micro Loop Heat Pipe (ìLHP) is a self-circulating cooling device with extremely high thermal conductivity where heat is removed by phase change and the working fluid circulates by means of the thermodynamic pressure difference developed between evaporator and condenser. Theoretical steady state models have been developed to explain the effect of different parameters on the performance of the ìLHP that utilizes a Coherent Porous Silicon (CPS) wick. The evaporator package being huge thermal mass, the time required to reach steady-state is large. In this study, the planar evaporator component was analyzed to study the behavior of LHP’s during the transient state. Two-dimensional transient state analysis was performed on the evaporator component of the LHP with necessary boundary conditions using Ansys 9.0. Analysis was performed in two steps with change in the boundary conditions on the surface of the silicon wick. In the first step, the surface of the wick was assumed to be adiabatic until it reached 700C where it was assumed to be evaporating. Evaporating boundary condition was then applied on the surface of the wick, which constituted the second step. It is analyzed for different values of ‘h’ ranging from 0.45 W/m2K to 4500 W/m2K to study the effect of convection cooling. The existing steady-state model developed at University of Cincinnati uses saturation temperature and pressure in the condenser as the independent parameters which is an ideal assumption. To modify the model, as a first step, the present generation condenser, shell and tube heat exchanger was designed and over-all heat transfer coefficient was determined. The new global model was then developed by rewriting the closure equations to be dependent on the new real independent parameters mass and temperature of the inlet cooling water in the condenser.

Committee:

Dr. Frank Gerner (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Loop Heat Pipe; LHP; CPL; Heat pipes; Ansys; Temperature drop; pressure drop; condenser design; global model