Steady-State Operating Characteristics Analysis of Loop Heat Pipes with Flat-Plate Evaporator

2021 ◽  
pp. 101070
Author(s):  
Changzheng Li ◽  
Zheng Liu ◽  
Xiantao Zhang
Keyword(s):  
Steady State ◽  
Flat Plate ◽  
Heat Pipes ◽  
Operating Characteristics ◽  
Loop Heat Pipes ◽  
Characteristics Analysis

scholarly journals Literature review: Steady-state modelling of loop heat pipes

2015 ◽  
Vol 75 ◽  
pp. 709-723 ◽  
Author(s):  
Benjamin Siedel ◽  
Valérie Sartre ◽  
Frédéric Lefèvre
Keyword(s):  
Steady State ◽  
Literature Review ◽  
Heat Pipes ◽  
Loop Heat Pipes

Modeling, Fabrication, and Testing of Micro Heat Pipes: An Update

1996 ◽  
Vol 49 (10S) ◽  
pp. S175-S183 ◽  
Author(s):  
G. P. Peterson
Keyword(s):  
Flat Plate ◽  
Recent Work ◽  
Analytical Techniques ◽  
Heat Pipes ◽  
Test Results ◽  
Operating Characteristics ◽  
Current Test ◽  
The Status ◽  
Micro Heat Pipes ◽  
Made In

In 1992, an overview was presented which summarized the status and progress made in the development of very small, “micro” heat pipes, manufactured as stand alone devices or fabricated as an integral part of silicon wafers. Since that initial review, significant advances have been made in the analysis, fabrication and testing of these devices, for use in a wide variety of applications. Following, is a review of the more recent work in this rapidly emerging field. Included is a summary of the analytical techniques developed, the various proposed methods of fabrication, and a summary of the most current test results achieved to date. Because the fundamental operating characteristics of micro heat pipes larger than 1 mm in diameter are similar to that of conventional heat pipes, this review focuses on the analysis, fabrication, and testing of micro heat pipes with characteristic dimensions of less than 500 μm. Particular emphasis is placed on research, related to the development of arrays of micro heat pipes and flat plate micro heat pipes fabricated as an integral part of semiconductor devices.

Steady State Parametric Modeling of Non-Conventional Loop Heat Pipes

2013 ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Heat Pipes ◽  
Parametric Model ◽  
Parametric Modeling ◽  
Working Fluid ◽  
Loop Heat Pipes

Loop Heat Pipes (LHPs) are used in many thermal management applications, especially for micro-electronics cooling, because of their ability to passively transport thermal energy from a source to a sink. This paper describes the development of a parametric model for a non-conventional LHP operating in steady state, employed to cool Light Emitting Diodes (LEDs). This device is comprised of a flat evaporator, and a finned circular loop wherein condensation and sub-cooling of the working fluid takes place. Unlike a conventional LHP, this device has no compensation chamber. In the mesh screen of the evaporator, the vapor flow entrains liquid and hence the quality of the two-phase mixture leaving the evaporator (xevap) is less than unity (unlike in a conventional LHP where saturated vapor leaves the evaporator). Since this lower quality (approximately 0.2) results in a smaller ratio of latent energy to sensible energy being removed by the condenser and sub-cooler respectively; the ratio of the length of the sub-cooler to condenser length is significantly larger. This results in more stable and controlled operation of the device. Mathematical models of the evaporator, the condenser and the sub-cooler sections are developed, and two closure conditions are employed in this model. For consistency and accuracy, some parameters in the model, such as the natural convection heat transfer coefficient (h o) and a few thermal resistances in the evaporator, are estimated empirically from test data on the device. The empirically obtained value of the heat transfer coefficient is in very good agreement with correlations from the literature. The parametric model accurately predicts the LED board temperature and other temperatures for a specific amount of thermal energy dissipated by the LEDs.

Steady State Numerical Modeling of Non-Conventional Loop Heat Pipes (LHPs)

2012 ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja ◽  
Praveen Medis
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Single Phase ◽  
Heat Pipes ◽  
Working Fluid ◽  
Vapor Interface ◽  
Loop Heat Pipes ◽  
Led Array ◽  
Fill Volume ◽  
Liquid Vapor

Loop heat pipes (LHPs) transport energy from an evaporator to a condenser in the form of latent heat. In conventional LHPs, the vapor pressure is significantly higher than the liquid pressure across the liquid-vapor interface due to the small pores and the corresponding capillary forces in the wick. This large pressure difference transports the single phase vapor after evaporation from the evaporator to the condenser and once the vapor is condensed, a single phase liquid from the condenser back to the evaporator. This current work involves the development of a steady state design model of the LHP system consisting of a planar evaporator package and a finned copper tube loop, which serves as an air-cooled condenser. Although evaporation due to the heat transfer creates the pressure in the vapor which drives the flow, contrasting to the conventional loop heat pipes, the pressure drop across the liquid-vapor interface is much smaller. A positive hydrostatic head is applied to the liquid above the wick and there is entrainment of liquid from the wick in the evaporator. Therefore, the fluid flow leaving the evaporator package is a two-phase flow, assumed to be saturated liquid and saturated vapor in equilibrium. The primary objective of this non-conventional LHP device is to remove the thermal energy dissipated from a Light Emitting Diode (LED) array. A major portion of this energy causes evaporation of the working fluid within the wick. The remaining energy reheats the liquid in both the liquid return line and within the evaporator package. The evaporator package is modeled as a one-dimensional thermal resistance network and these resistances are empirically determined from experiments. It is found that the convective heat transfer co-efficient of air plays a pivotal role in the heat dissipation and hence, is empirically determined in this work. This value is fairly agreeable with the Nusselt number correlation on the air side developed by Hahne et al. [1]. A mass balance relates the fill volume with the length of the condenser. The temperatures within the LHP are predicted by applying the principle of conservation of energy over the evaporator, the condenser and the sub-cooler sections of the heat exchanger loop. Finally, this LHP model predicts an approximate fill volume necessary for the LHP to operate properly.

The Study of PTFE Wicks Application to Loop Heat Pipes with Flat Evaporator

2015 ◽  
Vol 775 ◽  
pp. 54-58
Author(s):  
Shen Chun Wu ◽  
Shih Syuan Yan ◽  
Chen Yu Chung ◽  
Shen Jwu Su
Keyword(s):  
Heat Flux ◽  
Flat Plate ◽  
Pore Radius ◽  
Operating Temperature ◽  
Heat Pipes ◽  
Loop Heat Pipes ◽  
Heat Leakage ◽  
Flat Evaporator ◽  
Temperature And Pressure ◽  
Effective Pore Radius

This study investigates the application of PTFE wicks to flat-plate loop heat pipes (FLHPs). PTFE’s low heat transfer coefficient effectively prevents heat-leakage, which is a problem with using metal wicks, lowering the operating temperature and pressure. This paper uses PTFE particles to form wicks, and the effect of PTFE on flat-plate LHP performance is investigated. Experimental results shows that the highest heat load reached was 100W, with lowest thermal resistance of 0.61°C/W, and heat flux of about 10W/cm2, For the wick properties, the wick had an effective pore radius of the wick was around 9.2μm, porosity of 47%, and permeability of 1.0 x 10-12m2. Compared to the highest heat flux reported in literature thus far for PTFE flat-plate LHPs, the heat flux in this study was enhanced by around 50%.

Development of Flat-Plate Loop Heat Pipes for Spacecraft Thermal Control

2019 ◽  
Vol 31 (4) ◽  
pp. 435-443 ◽  
Author(s):  
Hongxing Zhang ◽  
Guoguang Li ◽  
Ling Chen ◽  
Guanglong Man ◽  
Jianyin Miao ◽  
...  
Keyword(s):  
Flat Plate ◽  
Heat Pipes ◽  
Thermal Control ◽  
Loop Heat Pipes ◽  
Spacecraft Thermal Control

Derivation and Validation of a Figure of Merit for Loop Heat Pipes With Medium Temperature Working Fluids

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Wukchul Joung ◽  
Jinho Lee ◽  
Sanghyun Lee ◽  
Joohyun Lee
Keyword(s):  
Steady State ◽  
Thermal Performance ◽  
Figure Of Merit ◽  
Saturation Pressure ◽  
Heat Pipes ◽  
Working Fluid ◽  
Medium Temperature ◽  
Working Fluids ◽  
Loop Heat Pipes ◽  
Compensation Chamber

The working fluids of loop heat pipes (LHPs) play an important role in the operation of the LHPs by influencing the operating temperatures and the heat transfer limits. Therefore, the proper selection of a working fluid is a key practice in LHP fabrication, and there has been a high demand for an appropriate index that enables the quantitative comparison of the steady-state thermal performance of the working fluids. In this work, a figure of merit for LHPs was theoretically derived and experimentally verified. In particular, the pressure losses in the LHP operation were balanced with the saturation pressure difference between the evaporator and the compensation chamber to derive the figure of merit. This derived figure of merit for LHPs successfully predicted the steady-state thermal performance of the tested working fluids within the variable conductance regime. In the constant conductance regime, the differences in the condenser cooling capacity and in the liquid subcooling for different working fluids determined the thermal performance of each working fluid. The limitations and prospects of the proposed figure of merit were discussed in detail.

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