Ceramic Flat Plate Evaporator for Loop Heat Pipe Cooling of Electronics

2005 ◽  
Author(s):  
Walter Zimbeck ◽  
Jared Chaney ◽  
Patricio Espinoza ◽  
Edward Kroliczek ◽  
David C. Bugby ◽  
...  
Keyword(s):  
Flat Plate ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Heat Sources ◽  
Two Phase ◽  
Low Thermal Expansion ◽  
Phase Loop ◽  
Cooling Of Electronics

Two-phase loops are extremely efficient devices for passively transporting heat over long distances with low temperature drop. The heat acquisition component of a two-phase loop, the evaporator, is commonly made from conventional metal materials (aluminum, copper, etc.) and has cylindrical geometry. Neither characteristic is optimally suited for close integration to common electronic or photonic heat sources, which generally have flat interfaces and are constructed from low thermal expansion coefficient (CTE) semiconductor materials. This paper describes the development of a ceramic flat plate evaporator for cooling processor chips in network computers used onboard Navy submarines. The unique requirements of submarines give added motivation for the advantages offered by two-phase loops. The ceramic flat plate evaporator is constructed of low CTE, high thermal conductivity material and thus enables a low thermal resistance interface between the heat source and the working fluid of the loop heat pipe. Alumina and aluminum nitride flat plate evaporators were integrated into a water-based two-phase loop and thermally tested to a heat flux of 30 W/cm2.

Competitive Designs of Evaporator Top Cap of the Micro Loop Heat Pipe

2004 ◽  
Author(s):  
Praveen Kumar Arragattu ◽  
Frank M. Gerner ◽  
Priyanka Ponugoti ◽  
H. T. Henderson
Keyword(s):  
Finite Element ◽  
Pressure Drop ◽  
Finite Element Modeling ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Maximum Heat ◽  
Element Modeling

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 cap 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 were 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. A trapezoidal slot top cap design was chosen for fabrication as it was relatively easy to fabricate with available MEMS fabrication technologies. The exact pressure drop calculation was performed on the fabricated top cap using commercial flow solver FLUENT 6.1 with appropriate boundary conditions. The temperature drop calculation was performed by finite element modeling in ANSYS 6.1. Obtained values of pressure drop and temperature drop for fabricated trapezoidal slot top cap was found to be within the optimal limits.

Investigation of Loop Heat Pipe Startup Using Liquid Core Visualization

2008 ◽  
Author(s):  
B. P. d’Entremont ◽  
J. M. Ochterbeck
Keyword(s):  
Heat Pipe ◽  
Liquid Core ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Buoyancy Driven Flows ◽  
Compensation Chamber ◽  
Fill Level ◽  
Heat Loads

In this investigation, a Loop Heat Pipe (LHP) evaporator has been studied using a borescope inserted through the compensation chamber into the liquid core. This minimally intrusive technique allows liquid/vapor interactions to be observed throughout the liquid core and compensation chamber. A low conductivity ceramic was used for the wick and ammonia as the working fluid. Results indicate that buoyancy driven flows, both two-phase and single-phase, play essential roles in evacuating excess heat from the core, which explains the several differences in performance between horizontal and vertical orientations of the evaporator. This study also found no discernable effect of the pre-start fill level of the compensation chamber on thermal performance during startup at moderate and high heat loads.

Design and Analysis of Ejector Powerplant System

2013 ◽  
Author(s):  
Menandro S. Berana ◽  
Edward T. Bermido
Keyword(s):  
High Pressure ◽  
Ambient Temperature ◽  
Waste Heat ◽  
Temperature Drop ◽  
Working Fluid ◽  
Low Grade ◽  
Heat Sources ◽  
Two Phase ◽  
Evaporator Temperature ◽  
Working Fluids

An ejector is a device with no moving components and is made up of four main parts: converging-diverging nozzle, suction chamber, mixing section and diffuser. It has become popular in refrigeration system as it gives the advantage of recovering expansion energy from high pressure difference into compression energy. In this study, the potential use of ejector in powerplants that use low-grade or low temperature heat sources was conceptualized and analytically investigated. A novel combination of the ejector and the organic Rankine cycle (ORC) was proposed. The driving fluid in the ejector of the proposed powerplant cycle is the high-pressure liquid in the separator that is just circulated back to the evaporator in the ORC. Further increase in turbine temperature drop (TTD), which can increase the power output and efficiency of the plant, can be achieved through expansion, mixing and recompression processes in the ejector. Ocean thermal energy conversion (OTEC), solar-boosted OTEC (SOTEC), solar-thermal, waste-heat driven, biomass and geothermal powerplants were considered in the analysis. Mathematical models in our previous studies were developed and used to calculate for nozzle and ejector parameters. The geometric profile of the ejector for optimization with categorized heat sources was determined. Isentropic, internally reversible, and irreversible two-phase nozzle expansions were analyzed. Two-phase flow calculations were continued in the mixing section. It was assumed that the constant-pressure mixing of the primary and secondary fluids occur at the hypothetical throat inside the constant-area section. Calculation for shock wave in the mixing section was also done. The diffuser was analyzed in a similar manner with the nozzle. Calculation for other components and plant efficiencies was finally conducted. Ammonia and propane which are both natural working fluids were used in the analysis. Evaporator temperature range from 293.15 K to 393.15 K and condenser and ambient temperatures range from 283.15 K to 308.15 K were used in the analysis. The lowest ambient temperature of 283.15 K was used for the OTEC and SOTEC powerplants. It was shown that ammonia and propane can operate up to 11 K and 12 K below the ambient temperature, respectively. Ejector efficiency ranged from 90 to 95% for both working fluids. The maximum efficiencies of the ejector powerplant were 19.2% for ammonia and 14.9% for propane, compared to 11.7% and 9.8% of the conventional ORC. It was analytically determined that the efficiency of the ejector powerplant is higher than that of the ORC powerplant for the same working fluid and conditions of the evaporator, condenser and the ambient.

Minimizing the Wick Thickness in a Planar Microscale Loop Heat Pipe Using Efficient Thermodynamic Design

2011 ◽  
Author(s):  
Navdeep S. Dhillon ◽  
Jim C. Cheng ◽  
Albert P. Pisano
Keyword(s):  
Heat Flow ◽  
Heat Pipe ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Loop Heat Pipes ◽  
Evaporator Section ◽  
Compensation Chamber

Theoretical and numerical thermodynamic analysis of the evaporator section of a planar microscale loop heat pipe is presented, to minimize the permissible wick thickness in such a device. In conventional cylindrical loop heat pipes, a minimum wick thickness is required in order to reduce parasitic heat flow, and prevent vapor leakage, into the compensation chamber. By taking advantage of the possibilities allowed by microfabrication techniques, a planar evaporator/compensation chamber design topology is proposed to overcome this limitation, which will enable wafer-based loop heat pipes with device thicknesses on the order of a millimeter or less. Thermodynamic principles governing two-phase flow of the working fluid in a loop heat pipe are analyzed to elucidate the fundamental requirements that would characterize the startup and steady state operation of a planar phase-change device. A three dimensional finite element thermal-fluid solver is implemented to study the thermal characteristics of the evaporator section and compensation chamber regions of a planar vertically wicking micro-columnated loop heat pipe. The use of in-plane thermal conduction barriers to reduce parasitic heat flow into the compensation chamber is demonstrated.

A Novel Thermal Solution for Electronics: Alumina Flat-Plate Oscillating Heat Pipe

2019 ◽  
Author(s):  
Bohan Tian ◽  
Hongbin Ma ◽  
Yang Deming ◽  
Jiujun Xu ◽  
Zhiyong Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Pipe ◽  
Printed Circuit Boards ◽  
Ct Scanning ◽  
Working Fluid ◽  
Micro Computed Tomography ◽  
Two Phase ◽  
Oscillating Heat Pipe ◽  
Two Phase Cooling

Abstract The heat flux in electronics requires the thermal management of printed circuit boards (PCBs) using two-phase cooling methods. In this study, an integrated ceramic heat transfer device, the alumina flat-plate oscillating heat pipe, is developed. The device was fabricated by pressing and sintering procedures, and the inner serpentine channels were simultaneously formed during sintering without brazing or separated caps. This novel manufacturing process simplifies the fabrication of the macrochannels inside ceramic devices and provides a new method for fabricating ceramic two-phase cooling devices. This paper presents an analysis of the internal channel’s formation mechanism and illustrates the major factors of densification. Micro-computed tomography (Micro-CT) scanning was adopted to assess the macrostructure, and SEM was used to characterize the microstructure of the alumina OHP. Water was charged inside the device as the working fluid. The effects of the power input, orientation, operating temperature and filling ratio on the heat transfer performance were investigated. The experimental results show that the alumina OHP has a high heat transport capability. When the OHP structure is embedded inside the alumina and charged with water, the thermal resistance can be reduced by 97%.

Gravitational effects on electroosmotic flow in micro heat pipes

2019 ◽  
Vol 30 (2) ◽  
pp. 535-556
Author(s):  
Fun Liang Chang ◽  
Yew Mun Hung
Keyword(s):  
Heat Pipe ◽  
Electroosmotic Flow ◽  
Temperature Drop ◽  
Working Fluid ◽  
Vapor Flow ◽  
Two Phase ◽  
Condenser Section ◽  
Content Type ◽  
Micro Heat Pipe ◽  
Gravity Forces

Purpose This paper aims to investigate the coupled effects of electrohydrodynamic and gravity forces on the circulation effectiveness of working fluid in an inclined micro heat pipe driven by electroosmotic flow. The effects of the three competing forces, namely, the capillary, the gravitational and the electrohydrodyanamic forces, on the circulation effectiveness of a micro heat pipe are compared and delineated. Design/methodology/approach The numerical model is developed based on the conservations of mass, momentum and energy with the incorporation of the Young–Laplace equation for electroosmotic flow in an inclined micro heat pipe incorporating the gravity effects. Findings By inducing electroosmotic flow in a micro heat pipe, a significant increase in heat transport capacity can be attained at a reasonably low applied voltage, leading to a small temperature drop and a high thermal conductance. However, the favorably applied gravity forces pull the liquid toward the evaporator section where the onset of flooding occurs within the condenser section, generating a throat that shrinks the vapor flow passage and may lead to a complete failure on the operation of micro heat pipe. Therefore, the balance between the electrohydrodyanamic and the gravitational forces is of vital importance. Originality/value This study provides a detailed insight into the gravitational and electroosmotic effects on the thermal performance of an inclined micro heat pipe driven by electroosmotic flow and paves the way for the feasible practical application of electrohydrodynamic forces in a micro-scale two-phase cooling device.

A Hybrid CFD-Mathematical Model for Simulation of a MEMS Loop Heat Pipe

2004 ◽  
Author(s):  
M. Ghajar ◽  
J. Darabi ◽  
N. Crews
Keyword(s):  
Pressure Drop ◽  
Heat Pipe ◽  
Heat Transport ◽  
Capillary Tube ◽  
Heat Rate ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Transport Distance ◽  
Compensation Chamber

A Hybrid CFD-Mathematical (HyCoM) model was developed to predict the performance of a Micro Loop Heat Pipe (MLHP) as a function of input heat rate. A micro loop heat pipe is a passive two-phase heat transport device, consisting of microevaporator, microcondenser, micro-compensation chamber (CC), and liquid and vapor lines. A CFD model was incorporated into a loop solver code to identify heat leak to the CC. Two-phase pressure drop in the condenser was calculated by several two phase correlations and results were compared [2]. Capillary tube correlations [3] were used for pressure drop calculations in fluid lines. Effects of working fluid and change in geometry were studied. For a heat transport distance of 10 mm, the base model MLHP was 50mm long, 16mm wide and 1mm thick. In the base model, widths of the grooves, liquid and vapor lines, evaporator, and condenser were 55μm, 200μm, 750μm, 2mm, and 4mm respectively.

A Planar Evaporator Design to Counter Parasitic Heat Flow During Device Startup of a Microscale Loop Heat Pipe

2019 ◽  
Author(s):  
Navdeep S. Dhillon
Keyword(s):  
Heat Flow ◽  
Heat Pipe ◽  
Latent Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Flow Loop ◽  
Negative Effects ◽  
Two Phase ◽  
Loop Heat Pipes

Abstract Due to increasing power densities and decreasing device footprints, thermal management has become an important design requirement in modern electronic devices. Loop heat pipes are phase change-based devices that can absorb and transport large heat fluxes via the latent heat of evaporation of a working fluid. However, these devices are bulky and difficult to miniaturize due to the constraining effect of undesired parasitic heat flow and other thermodynamic considerations of the two-phase flow loop. Here, we present experimental results demonstrating the operation of an ultra-thin microscale loop heat pipe that employs a planar evaporator wick designed to counter the negative effects of parasitic heat flow. Despite the extremely low wick thickness (< 0.5 mm), the device is able to successfully startup, with no apparent observation of a wick dry-out due to parasitic heat flow-induced disruptions of liquid supply to the evaporator. A latent heat flux of approximately 6.7 W/cm2 is absorbed per unit area of the evaporator during the device startup phase.

Operating Ranges of the Planar Loop Heat Pipe Under Non-Vacuum Conditions

2005 ◽  
Author(s):  
Junwoo Suh ◽  
Ahmed Shuja ◽  
Praveen Medis ◽  
Srinivas Parimi ◽  
Frank M. Gerner ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Heat Dissipation ◽  
Energy Transport ◽  
Technical Conference ◽  
Open Loop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Vapor Line ◽  
Compensation Chamber

As the trend of high throughput in small packages continues, the heat dissipation becomes a very critical design issue in electronic devices and spacecrafts. The two phase loop heat pipe utilizes the latent heat of working fluid. It consists of an evaporator, compensation chamber, condenser, and liquid and vapor line. The primary wick used as a core part to circulate the working fluid is located in the evaporator. The planar loop heat pipe uses coherent porous silicon (CPS) wick as opposed to the conventional cylindrical configuration, which uses a sintered amorphous metal wick. The clear evaporator machined from Pyrex glass and transparent silicone tubes were utilized to monitor the complex phenomena which occur in the evaporator. Tests were conducted under the non-vacuum condition without a secondary wick. DI-water was used as a working fluid. Like an open loop test previously conducted, there was an operating range in which the liquid could be properly pumped from the compensation chamber to the vapor line under the pumping motion. In this device, more than 6 Watts could be convected from the evaporator to the ambient. Therefore circulation was not observed until powers greater than 6 Watts. There was a circulation of working fluid occurring due to energy transport within the loop when the input power was from 7.94 Watts to 17.6 Watts. The quantity of heat transportation to the loop was calculated by acquiring the empirical heat transfer coefficient. From this calculation it was found that, roughly, 12.1 Watts was transported to the loop and 5.51 Watts was convected to the ambient from the evaporator itself when the applied power was 15.27 Watts.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

USAGE OF A DIATOMITE-CONTAINING NANOFLUID AS THE WORKING FLUID IN A WICKLESS LOOP HEAT PIPE: EXPERIMENTAL AND NUMERICAL STUDY

2018 ◽  
Vol 49 (17) ◽  
pp. 1721-1744 ◽  
Author(s):  
Adnan Sözen ◽  
Erdem Çiftçi ◽  
Selçuk Keçel ◽  
Metin Gürü ◽  
Halil Ibrahim Variyenli ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Numerical Study ◽  
Working Fluid ◽  
Loop Heat Pipe
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