Dual Compensation Chamber Loop Heat Research Articles

Visualized experimental study on steady-state performance of a loop heat pipe under elevated acceleration fields

In this article, an experimental investigation was carried out to explore the steady-state operational behavior of a newly designed nickel-water dual compensation chamber loop heat pipe (DCCLHP) under elevated acceleration fields. Glass windows were fabricated and embedded on a condenser and two compensation chambers (CCs) for the purpose of visual observation of vapor and liquid distribution. The steady-state operational behaviors and any new phenomena were discussed. The heat load from 30 W to 110 W and the acceleration magnitude from 1 g to 13 g as well as four different acceleration directions were taken into account. Experimental results indicate that: (i) as the heat load increases, the steady-state operational temperature of the DCCLHP increases, while thermal resistance may increase or decrease, also depending on both the acceleration direction and magnitude. (ii) The thermal resistance at both direction A and D is significantly larger than that at both direction B and C. The minimum thermal resistance with 0.78 K/W at 11 g with 70 W and operational temperature with 72.7 °C at 3 g with 30 W are achieved at direction C. (iii) as the acceleration magnitude increases, both operational temperature and thermal resistance tend to decrease for both direction B and C, whereas an opposite tendency is observed for both direction A and D. (iv) both the vapor column and liquid column alternatively distribute in the condenser channel that could increase or decrease the loop pressure drop. Inclined vapor–liquid interface and different liquid amount in both CCs are formed at different accelerations. Stratified flow or annular flow could lead to the film condensation heat transfer in the condensation channel.

Experimental study on the thermal performance of a dual compensation chamber loop heat pipe with dual vapor and condenser lines

Experimental study on the thermal performance of a dual compensation chamber loop heat pipe with dual vapor and condenser lines

Experimental study on a dual compensation chamber loop heat pipe with a ceramic wick

The dual compensation chamber loop heat pipe (DCCLHP) has excellent application prospects in the future field of space thermal management. However, DCCLHP has some problems, such as startup difficulty with a small heat load and serious heat leakage from the back of the capillary pump. To ensure the reliable startup and efficient heat transfer of DCCLHP in the space microgravity environment, a kind of DCCLHP with an eccentric structure of silicon nitride capillary wick was manufactured and verified. The experimental results show that the DCCLHP can be started with a 2 W small heat load, with two different starting conditions. The heat transfer capacity exceeds 450 W in the 2.0 m heat transfer range. The starting temperature overshoot of DCCLHP presents an inverted “V” shape relationship with the heat load. The smaller the temperature difference between the two compensation chambers is, the heat transfer performance of DCCLHP will be promoted. This study has significant reference value for applying DCCLHP in space microgravity thermal management.

Visualization study on operating performance of a dual compensation chamber loop heat pipe under acceleration condition

In this article, a novel visual dual compensation chamber loop heat pipe (DCCLHP) under acceleration conditions was experimentally investigated. The working fluid was deionized water and the wick material was sintered nickel powder. Visual windows were installed on both compensation chambers (CCs) and condenser in order to observe the vapor and liquid distribution. The operating performance and physical mechanism of the proposed DCCLHP under both acceleration direction A and B at different heat loads and acceleration magnitudes were analysed in a systematic manner. Direction A refers the acceleration direction which was parallel to the axis of the evaporator and the CC without a bayonet placed at the outer edge of the rotating arm. While direction B is defined as the acceleration direction was perpendicular to the axis of the evaporator and the evaporator was placed at the outer edge of the rotating arm. In the current study, the heat load varies from 30 W to 130 W and the acceleration magnitude ranges from 1 g to 15 g. Experimental results revealed that: (i) The larger the heat load, the higher the operating temperature. Obviously waving of the vapor-liquid interface in the CC is observed at direction A. Bubbles generated in the CCs and the vapor-liquid interface moves back and forth in the condenser during temperature oscillation at both 70 W and 90 W for the case of 13 g and direction B. (ii) Under direction B, the DCCLHP presents lower operating temperature and higher thermal conductance. The maximum temperature is 143.2 °C at 5 g and 90 W under direction A. The maximum thermal conductance is 1.70 W/K at 13 g and 130 W under direction B. (iii) In general, the operating temperature shows a trend of decreasing first and then increasing with the increase of acceleration. Whereas the thermal conductance shows an opposite behavior. The transition acceleration, namely the acceleration magnitude at the minimum temperature, is 13 g for the case of direction A. However, under direction B, the large heat load can result in a large transition acceleration. (iv) Intermittent spattering of liquid drops is observed in the CCs at 70 W and 15 g under direction A. The flow pattern under direction A is different with that under direction B at each heat load. Multiple segments of the liquid and vapor phase alternately distribute and stratified flow forms in the condenser.

Visualization Study on Operating Performance of a Dual Compensation Chamber Loop Heat Pipe Under Acceleration Condition

Visualization Study on Operating Performance of a Dual Compensation Chamber Loop Heat Pipe Under Acceleration Condition

Temperature oscillation of a dual compensation chamber loop heat pipe under acceleration conditions

• Temperature oscillation of DCCLHP is studied experimentally in acceleration field. • Two loading modes on heat load and acceleration force are considered. • Impacts of different acceleration magnitudes and directions are discussed. • Physical mechanism of temperature oscillation in acceleration field is analyzed. Loop heat pipe has a wide application in the fields of airborne electronics cooling and thermal management. However, the pertinent temperature oscillation of the loop heat pipe could lead to adverse effects on the electronics. In the current study, an ammonia-stainless steel dual compensation chamber loop heat pipe was developed to experimentally investigate the temperature oscillation under different acceleration conditions. The impact of several control parameters such as different heat loads, loading modes, acceleration directions and magnitudes on the operational performance of the loop heat pipe was analyzed in a systematic manner. The heat load applied on the evaporator ranged from 25 W to 300 W. The acceleration magnitude varied from 1 g to 9 g and four different acceleration direction, i.e. configurations A, B, C and D, were taken into account. Two different loading modes were applied with different heat load and acceleration force. Experimental results show that (i) the loop temperature will change and oscillate as the acceleration force was applied under all test conditions. It can be easily found that the temperature oscillation occurred at both heat loads of 250 W and 300 W. (ii) for the case of the first loading mode, periodic temperature oscillation is observed on the liquid line, whereas for the second loading mode, periodic temperature oscillation can be easily appeared on the entire loop. (iii) the loop temperature under both configurations A and B with acceleration of 7 g does not oscillate at heat load of 150 W, 200 W and 250 W when the first loading mode is applied. Especially under configuration B, the acceleration could contribute to repress the temperature oscillation. Under the current heat loads for almost all cases, the temperature oscillation can be observed for configurations A, C and D with acceleration of 5 g. (iv) the amplitude of evaporator at heat load of 300 W under configuration C are 0.6 °C, 0.3 °C, 0.2 °C and 0.3 °C with acceleration of 3 g, 5 g, 7 g and 9 g. The corresponding period is 66 s, 36 s, 34 s and 36 s, respectively.

Performance investigation of a loop heat pipe integrated with thermoelectric cooler under acceleration field

This paper presents an experimental investigation on a novel dual compensation chamber loop heat pipe (DCCLHP) integrated with thermoelectric cooler (TEC) for improving the overall performance under various acceleration conditions. The operating characteristics of the DCCLHP with and without the assistance of TEC for configurations A and B are analyzed systematically under different acceleration magnitudes and heat loads. The heat load on the evaporator ranges from 25 W to 300 W and the power of the TEC is 10 W. The acceleration magnitude ranges from 5 g to 13 g. Experimental results show that: (i) the application of TEC is proved to improve the operating performance for the heat load not exceeding 150 W under configuration A and 100 W under configuration B; (ii) under configuration B, the increase of the acceleration normally leads to the increase of the operating temperature and the decrease of the thermal conductance. While it shows no obvious effect on the operating performance under configuration A for most cases. The maximum operating temperature and thermal conductance is 56.7 °C at 150 W under 13 g for configuration B, while 20.7 W/K at 150 W under 5 g for configuration A; (iii) temperature fluctuation occurs at 100 W under both 5 g and 7 g for configuration B, whereas there is no fluctuation under configuration A. The acceleration effect can change the vapor-liquid distribution in the loop and the external loop pressure drop, which will further change the operating performance along with the TEC effect. This research can provide valuable insight into the influence of TEC on DCCLHP under different acceleration field, which is of great significance for its practical application in mechanical and aerospace engineering.

Experimental study on a dual compensation chamber loop heat pipe with dual bayonet tubes

Dual compensation chamber loop heat pipe (DCCLHP) holds great application potential in the future aircraft thermal management. In this work, a DCCLHP with dual bayonet tubes was first proposed and fabricated, aiming to improve its startup performance especially at small heat loads in the terrestrial surroundings. Extensive experimental validation was conducted at three typical attitudes of the evaporator/CCs, i.e., the vertical attitude, 45° tilt angle and the horizontal attitude, mainly focusing on its startup characteristics and heat transport capability. According to the experimental results, the DCCLHP with dual bayonet tubes can successfully realize the startup at small heat loads in whatever attitudes of the evaporator/CCs in the ground condition, and reach a heat transport limit greater than 400 W over a distance of 2.0 m. No obvious operating instability was observed in the DCCLHP operation. In addition, a new flow mechanism was observed in the experiment, i.e., a local natural circulation of the working fluid driven by gravity occurred in the loop composed of the evaporator, the CCs, the bayonet tubes, and the branches of the liquid line. This local circulation of working fluid was identified to appear only when the evaporator/CCs were at a certain tilt angle and the heat loads were relatively small.

Experimental study on operating characteristics of a dual compensation chamber loop heat pipe in periodic acceleration fields

Systematic experiments were firstly designed and conducted to investigate the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) under periodic acceleration conditions. A new acceleration test rig was built to generate acceleration magnitude up to 11 g. The heat load ranged from 150 W to 300 W. Three different periodic acceleration patterns, two loading modes and two acceleration directions were used to study their influence on the operating characteristics of the DCCLHP. The results demonstrated that the loop temperature could periodically oscillate with the periodic change of the acceleration. A large acceleration could lead to a high operating temperature. Configuration B could cause the lower operating temperature than configuration A for a fixed case. There were stable operating temperature difference and thermal resistance variation before and after the periodic acceleration acting for the loading mode 1. Temperature overshooting after unloading the periodic acceleration was also confirmed for the loading mode 2. Such phenomena could be explained by the change of the vapour-liquid distribution in the loop and the heat leak from the evaporator to the compensation chambers (CCs). The loop temperature oscillation with different frequency and amplitude might also occur during each periodic acceleration. For the cases of 150 W and configuration A, the acceleration effect could trigger the operating temperature exceeding 60 °C. Our work proves significant phenomena existing in the DCCLHP and presents detailed analysis, which would be of great importance for the development of new generation of loop heat pipe used in aircraft thermal management system.

Experimental and analytical study of dual compensation chamber loop heat pipe under acceleration force assisted condition

In this article, a combined experimental and theoretical study has been conducted to investigate the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) with ammonia as the working fluid under acceleration force conditions. The DCCLHP with nickel wick consists of a cylindrical evaporator and dual compensation chambers at both ends of evaporator. In the current study, a new DCCLHP test rig is set up which can provide the acceleration up to 11 g. Two types of loading mode are utilized for applying heat load prior to acceleration. The heat load ranges from 25 W to 300 W. Comparisons of operating performance of the DCCLHP are carried out under both gravity and acceleration conditions. A novel acceleration force assisted concept is proposed to address the observed operating behavior. Experimental results show that: (i) the acceleration effect with the proposed orientation can improve the operating performance of the DCCLHP which may operate at the centrifugal force driven mode and capillary-centrifugal force co-driven mode. The operating temperature profile at different heat loads shows “/-shape” oblique line with the increase of the acceleration; (ii) the transition heat load from centrifugal force driven mode to capillary-centrifugal force co-driven mode changes with the variation of acceleration magnitude at both loading modes; (iii) the acceleration effect on the operating temperature is remarkably significant as the heat load is less than 100 W. The operating temperature under acceleration conditions is apparently lower than that under terrestrial gravity; (iv) the coupling change of the loop pressure, vapor-liquid distribution, two-phase flow and heat transfer caused by acceleration effect leads to the unique operating performance of the DCCLHP.

Startup characteristics of a dual compensation chamber loop heat pipe with an extended bayonet tube

Dual compensation chamber loop heat pipe (DCCLHP) is an advanced two-phase heat transfer device, which features an orientation-free operation in the terrestrial surroundings and promises great application potential in the aircraft thermal management. In this work, a DCCLHP with an extended bayonet tube was designed and fabricated, aiming to improve its startup performance especially at a small heat load. The startup characteristics of the DCCLHP in five different orientations was experimentally investigated and theoretically analyzed. According to the experimental results, some important conclusions have been drawn: 1) The DCCLHP with an extended bayonet tube could achieve successful startup under the heat load ranging from 10 to 100 W in the horizontal orientation, and no startup failure occurred. 2) The DCCLHP could start up successfully even at a small heat load of 10 W from -90° to +90° tilt angle in the terrestrial surroundings. 3) Different startup phenomena such as the unique change of the temperature overshoot were observed in the experiments. 4) Operating instability such as the temperature oscillation occurred during the startup process in the favorable directions.

Experimental investigation on operating behaviors of loop heat pipe with thermoelectric cooler under acceleration conditions

An experimental study was carried out in this article to investigate the transient operating performance of a Dual Compensation Chamber Loop Heat Pipe (DCCLHP) with Thermoelectric Cooler (TEC) under acceleration conditions and ammonia was selected as the working fluid. For the purpose of comparison, experimental work was conducted under terrestrial gravity. Sensitivity analysis was performed to explore the effect of several control parameters such as the heat load, acceleration magnitude and TEC assist on the startup and operating performance of the DCCLHP. Experimental results indicate that the DCCLHP can get to a steady-state operation when the heat load changes from 25 W to 300 W under terrestrial gravity. While under acceleration conditions, the DCCLHP can work at a high operating temperature or even fail to operate, which shows the acceleration effect plays a significant impact on the loop operation. The TEC assist with power of 10 W can improve the operating performance and reduce the operating temperature for the case of small heat load and acceleration magnitude. When the acceleration exceeds 3g at large heat load, the effect of TEC assist on the operation at large heat load can be ignored.

Experimental investigation on transient characteristics of a dual compensation chamber loop heat pipe subjected to acceleration forces

In this article, an experimental study has been conducted to provide better understanding of the transient characteristics of a dual compensation chamber loop heat pipe (DCCLHP) subjected to the acceleration force. A new acceleration test rig was set up to provide the acceleration up to 11g with three different directions. The heat load on the evaporator ranging from 25 W to 300 W was applied with the acceleration force simultaneously. Experimental results indicated that the DCCLHP could start up at a small heat load of 25 W and the startup behavior was different under acceleration direction conditions because of the vapor-liquid distribution change in the evaporator and compensation chambers (CCs). Under the current operating conditions, the effect of acceleration force was significant to the operating performance at small heat loads whereas was weak at large heat loads. Experimental results also clearly showed that both acceleration magnitude and direction can alter the operating mode. What’s more, it was found that temperature oscillation, reverse flow and evaporation in the evaporator core phenomena occurred under acceleration conditions.

Experimental investigation on the operating characteristics of a dual compensation chamber loop heat pipe subjected to acceleration field

High power and high local heat flux electronic devices employed in aircraft and spacecraft sustain the high acceleration condition in maneuvers and take-off stage. Loop heat pipe (LHP) are promising in dissipating high heat load to meet the increasing cooling needs. This article presents an experimental investigation on the operating characteristics of a dual compensation chamber loop heat pipe (DCCLHP) under elevated acceleration conditions. A centrifuge with a 2 m-long arm is used to provide the acceleration up to 7 g with four different acceleration directions. The heat load applied on the evaporator ranges from 80 W to 300 W. The typical performances in terrestrial were obtained and the influence of the different acceleration direction and magnitude on the operating characteristics was analyzed. Experimental results show that the change of the vapor–liquid distributions induced by the acceleration force results in some specific operating characteristics of the DCCLHP. The operating temperature becomes lower as the effect of the acceleration force improves the liquid returning. The operation of the DCCLHP demonstrates the sensitive behavior to the acceleration direction at small heat load and insensitive behavior at large heat load. It was also found that the acceleration magnitude can alter the operating mode. A number of unstable phenomena are observed under both terrestrial gravity and elevated acceleration conditions.

Research on the Applications of Heat Pipes in Cooling Aircraft Electrical Equipment

In order to ensure proper temperatures for electronic equipment and to meet the increasing heat dissipation capacity needs of airborne electronic equipment, a suitable heat-pipe for use in aircraft equipment needs to be found. Considering both the acceleration and the changes in tilt angle of the aircraft, performance analysis of five main types of heat-pipes showed that dual compensation chamber loop heat pipe and micro-channel plate heat pipe were the most suitable for use in airborne electrical equipment.

Experimental investigation of a dual compensation chamber loop heat pipe

This work performs a fundamental study of a Dual Compensation Chamber Loop Heat Pipe (DCCLHP) through partial visualization of the flow phenomenon inside its compensation chambers and the condenser. Both startup and steady-state performance of the DCCLHP and the influence of initial vapor–liquid distribution, startup heat load, heat sink temperature and relative orientations on the performance of the DCCLHP are studied. The result shows a typical ‘V’ curve operation temperature at heat loads over 50 W at the steady-state, and reveals some unique phenomena during the startup of the DCCLHP such as bubble generation in the liquid core, reverse flow, fluctuated flow and liquid re-distribution between the compensation chambers and the external loop, which are caused mainly by the radial heat leak from the evaporator. Some unstable phenomena during the startup, steady-state operation and unloading period of the DCCLHP are also revealed in this study including temperature fluctuations, temperature hysteresis and transient penetration of vapor.

Experimental investigation on operating instability of a dual compensation chamber loop heat pipe

The operating instability of a dual compensation chamber loop heat pipe (DCC-LHP) including temperature hysteresis, reverse flow and temperature oscillation is described and explained in this paper. Test results indicate that the steady state operating temperature under the variable conductance mode is not the same during the power cycle tests with the same heat load, and it is lower during the power reduction cycle than that during the power increase cycle. Orientation has an effect on the heat load range when temperature hysteresis occurs, and the effect of power variation amplitude can be ignored. Reverse flow tends to occur in some of the startups at low heat loads, even if vapor existed in the vapor grooves initially, which is caused by a higher pressure inside the wick due to evaporation in the evaporator core or vapor penetration into it. Temperature oscillation tends to occur in some of the startups at low head loads or some steady-state operations at high heat loads. Especially when the compensation chamber with the bayonet through is above the evaporator, the incidence rate of temperature oscillation is high.

Experimental investigation of startup behaviors of a dual compensation chamber loop heat pipe with insufficient fluid inventory

To address the problem of the relative orientation limit between the evaporator and the compensation chambers (CCs), a dual-compensation chamber loop heat pipe (DCCLHP) was developed, and its startup characteristics with small heat loads and insufficient fluid inventory were experimentally investigated in this work. Based on the experimental results, the conclusions below can be drawn: (1) The DCCLHP can start up reliably at small heat loads, but sometimes the temperature overshoot is rather high. (2) The startup performance of the DCCLHP is different when its evaporator and CCs are at different attitudes due to different liquid/vapor composition in the evaporator and heat leak from the evaporator to the CCs. (3) In general, evaporation in the evaporator core is inevitable, which results in a large heat leak from the evaporator to the CCs and generates large temperature overshoot during the startup process. (4) Because the superheat of liquid to initiate nucleate boiling reduces as its temperature rises, nucleate boiling can also occur in the vapor grooves although the temperature of the evaporator rises at the same rate as that of the CCs. (5) The startup performance of LHPs mainly depends on the heat load and thermal resistance between the evaporator and CCs. When the startup heat load is big enough, the DCCLHP has no start-up difficulty.

Development and Test Results of a Dual Compensation Chamber Loop Heat Pipe

A dual compensation chamber loop heat pipe is developed to solve the problem of the relative orientation limit between the evaporator and the compensation chambers. The construction of the evaporator and the compensation chambers is presented. The concurrent design method of the working fluid charge mass and the compensation chamber volumes, that can realize the objectives where, within a certain temperature range, the dual compensation chamber loop heat pipe cannot only start up and operate normally at any orientation, but can also avoid the most difficult startup situation, is introduced. The operation and the thermal control characteristics of the dual compensation chamber loop heat pipe are investigated. Test results indicate that in some heat load regions, the operating temperatures vary with the relative orientation between the evaporator and the compensation chambers. This is explained by the thermal equilibrium of the compensation chamber and the usage efficiency of the return liquid subcooling. The test results and discussion of the dual compensation chamber loop heat pipe suggest that part of the return liquid subcooling that cools the liquid to be locally subcooled must be considered in the mathematical modeling of the loop heat pipe.