scholarly journals Thermal Switch Based on an Adsorption Material in a Heat Pipe

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5130
Author(s):  
Markus Winkler ◽  
Christian Teicht ◽  
Patrick Corhan ◽  
Angelos Polyzoidis ◽  
Kilian Bartholomé ◽  
...  
Keyword(s):  
Heat Flow ◽  
Heat Pipe ◽  
Working Fluid ◽  
Evaporator Temperature ◽  
Water Release ◽  
Thermal Switch ◽  
Novel Approach ◽  
Thermal Switching ◽  
Adsorbent Characterization ◽  
Good Agreement

For many applications, the possibility of controlling heat flow by “thermal switching” could be very beneficial. Several concepts for heat switches were already proposed and tested, however, many drawbacks of these concepts are evident. In this work, we present a novel approach for thermal switching using a water-loaded adsorbent as part of the evaporator of a heat pipe. The basic idea is that the adsorbent releases water upon exceeding a certain evaporator temperature, and thus “activates” the heat pipe by providing the working fluid for thermal transport. The first part of this work concentrates on the adsorbent characterization by analyzing the adsorption isobars and isotherms and thus understanding the behavior of the system. Furthermore, a model to predict the release of water from the adsorbent in dependence of temperature was developed. Subsequently, the adsorbent was integrated into an actual heat pipe demonstrator to verify these predictions and demonstrate the thermal switching ability. Overall results revealed a very good agreement between the predictions concerning water release and the heat pipe’s thermal behavior. The obtained thermal switching ratio depends on the heating power and temperature range that is considered. Depending on whether evaporator/condenser or the adiabatic zone are considered, average switching ratios of circa 3 and 18 were found, respectively.

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

2009 ◽  
Author(s):  
Eric Golliher ◽  
Jentung Ku ◽  
Anthony Licari ◽  
James Sanzi
Keyword(s):  
Heat Pipe ◽  
Freezing Point ◽  
Thermal Control ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
The Moon ◽  
Novel Approach ◽  
Condenser Temperature ◽  
Extreme Cold ◽  
Compensation Chamber

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.

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.

Experimental Study on Heat Transfer Capability of a Miniature Loop Heat Pipe

2016 ◽  
Author(s):  
Guohui Zhou ◽  
Ji Li ◽  
Lucang Lv
Keyword(s):  
Heat Pipe ◽  
Heat Load ◽  
Electronics Cooling ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Evaporator Temperature ◽  
Liquid Line ◽  
Horizontal Orientation ◽  
Flat Evaporator

In this paper, a miniature loop heat pipe (mLHP) with a flat evaporator is illustrated and investigated experimentally, with water as the working fluid. The mLHP can be applied for the mobile electronics cooling, such as tablet computers and laptop computers, with a 1.2 mm thick ultra-thin flat evaporator and a thickness of 1.0 mm for the vapor line, liquid line and condenser. A narrow sintered copper mesh in the liquid line and a part of the condenser as the secondary wick can promote the flow of the condensed working fluid back to the evaporator. The experimental results showed that the mLHP could start up successfully and operate stably at low heat load of 3 W in the horizontal orientation, and transport a high heat load of 12 W (the heat flux of 4 W/cm2) with the evaporator temperature below 100 °C in different test orientations by natural convection, showing good operational performance against gravity field. The minimum mLHP thermal resistance of 0.32 K/W was achieved at the input heat load of 12 W in the horizontal orientation.

scholarly journals Experimental Investigation on the Thermal Performance of Pulsating Heat Pipe Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 269 ◽  
Author(s):  
Kai-Shing Yang ◽  
Ming-Yean Jiang ◽  
Chih-Yung Tseng ◽  
Shih-Kuo Wu ◽  
Jin-Cherng Shyu
Keyword(s):  
Heat Exchanger ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Filling Ratio ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Evaporator Temperature ◽  
Inner Diameter ◽  
Air Streams

In this study, the vertically-oriented pulsating heat pipe (PHP) heat exchangers charged with either water or HFE-7000 in a filling ratio of 35% or 50% were fabricated to exchange the thermal energy between two air streams in a parallel-flow arrangement. Both the effectiveness of the heat exchangers and the thermal resistance of PHP with a size of 132 × 44 × 200 mm, at a specific evaporator temperature ranging from 55 to 100 °C and a specific airflow velocity ranging from 0.5 to 2.0 m/s were estimated. The results show that the heat pipe charged with HFE-7000 in either filling ratio is likely to function as an interconnected array of thermosiphon under all tested conditions because of the unfavorable tube inner diameter, whereas the water-charged PHP possibly creates the pulsating movement of the liquid and vapor slugs once the evaporator temperature is high enough, especially in a filling ratio of 50%. The degradation in the thermal performance of the HFE-7000-charged PHP heat exchanger resulted from the non-condensable gas in the tube became diminished as the evaporator temperature was increased. By examining the effectiveness of the present heat exchangers, it is suggested that water is a suitable working fluid while employing the PHP heat exchanger at an evaporator temperature higher than 70 °C. On the other hand, HFE-7000 is applicable to the PHP used at an evaporator temperature lower than 70 °C.

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.

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

Experimental and Numerical Simulation for Thermal Investigation of Oscillating Heat Pipe Using VOF Model

2020 ◽  
Vol 38 (1A) ◽  
pp. 88-104
Author(s):  
Anwar S. Barrak ◽  
Ahmed A. M. Saleh ◽  
Zainab H. Naji
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Input ◽  
Cfd Simulation ◽  
Working Fluid ◽  
Maximum Deviation ◽  
Inlet Temperature ◽  
Maximum Heat ◽  
Oscillating Heat Pipe ◽  
Vof Model

This study is investigated the thermal performance of seven turns of the oscillating heat pipe (OHP) by an experimental investigation and CFD simulation. The OHP is designed and made from a copper tube with an inner diameter 3.5 mm and thickness 0.6 mm and the condenser, evaporator, and adiabatic lengths are 300, 300, and 210 mm respectively.  Water is used as a working fluid with a filling ratio of 50% of the total volume. The evaporator part is heated by hot air (35, 40, 45, and 50) oC with various face velocity (0.5, 1, and 1.5) m/s. The condenser section is cold by air at temperature 15 oC. The CFD simulation is done by using the volume of fluid (VOF) method to model two-phase flow by conjugating a user-defined function code (UDF) to the FLUENT code. Results showed that the maximum heat input is 107.75 W while the minimum heat is 13.75 W at air inlet temperature 35 oC with air velocity 0.5m/s. The thermal resistance decreased with increasing of heat input. The results were recorded minimum thermal resistance 0.2312 oC/W at 107.75 W and maximum thermal resistance 1.036 oC/W at 13.75W. In addition, the effective thermal conductivity increased due to increasing heat input.  The numerical results showed a good agreement with experimental results with a maximum deviation of 15%.

Thermodynamic analysis of triple effect ammonia–water absorption compression (hybrid) cycle

2021 ◽  
pp. 095440892199568
Author(s):  
CP Jawahar
Keyword(s):  
Water Absorption ◽  
Energy Analysis ◽  
Cooling Capacity ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Performance Parameters ◽  
Evaporator Temperature ◽  
Ammonia Water ◽  
Absorption Cycle ◽  
Hybrid Cycle

This paper presents the energy analysis of a triple effect absorption compression (hybrid) cycle employing ammonia water as working fluid. The performance parameters such as cooling capacity and coefficient of performance of the hybrid cycle is analyzed by varying the temperature of evaporator from −10 °C to 10 °C, absorber and condenser temperatures in first stage from 25 °C to 45 °C, degassing width in both the stages from 0.02 to 0.12 and is compared with the conventional triple effect absorption cycle. The results of the analysis show that the maximum cooling capacity attained in the hybrid cycle is 472.3 kW, at 10 °C evaporator temperature and first stage degassing width of 0.12. The coefficient of performance of the hybrid cycle is about 30 to 65% more than the coefficient of performance of conventional triple effect cycle.

scholarly journals Numerical simulation of flattened heat pipe with double heat sources for CPU and GPU cooling application in laptop computers

2020 ◽  
Author(s):  
Wisoot Sanhan ◽  
Kambiz Vafai ◽  
Niti Kammuang-Lue ◽  
Pradit Terdtoon ◽  
Phrut Sakulchangsatjatai
Keyword(s):  
Experimental Data ◽  
Heat Pipe ◽  
Graphics Processing Unit ◽  
Processing Unit ◽  
Heat Sources ◽  
Final Thickness ◽  
Laptop Computers ◽  
Central Processing ◽  
Graphics Processing ◽  
Good Agreement

Abstract An investigation of the effect of the thermal performance of the flattened heat pipe on its double heat sources acting as central processing unit and graphics processing unit in laptop computers is presented in this work. A finite element method is used for predicting the flattening effect of the heat pipe. The cylindrical heat pipe with a diameter of 6 mm and the total length of 200 mm is flattened into three final thicknesses of 2, 3, and 4 mm. The heat pipe is placed under a horizontal configuration and heated with heater 1 and heater 2, 40 W in combination. The numerical model shows good agreement compared with the experimental data with the standard deviation of 1.85%. The results also show that flattening the cylindrical heat pipe to 66.7 and 41.7% of its original diameter could reduce its normalized thermal resistance by 5.2%. The optimized final thickness or the best design final thickness for the heat pipe is found to be 2.5 mm.

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