Water-filled Heat Pipe Research Articles

Water-filled heat pipes for CubeSat thermal control

Currently, the amount of electrical power that is available for CubeSat’s is very small and for this reason, simple thermal conductance through the frame of the CubeSat is sufficient for most CubeSat missions. However, deployable solar panels have been developed recently and peak powers up to 40W can now be generated. This higher generated electrical power results in more waste heat and potentially too high temperatures inside the CubeSat. For this reason, the use of water-filled heat pipes is studied, since these are cheap, widely commercially available, and can be bent in the desired shape. Both the condenser and evaporator thermal resistance and the total heat transfer capacity of these heat pipes have been measured for a wide range of temperatures with a unique automated setup that uses Peltier elements to control the temperature. Furthermore, the heat pipes have been subjected to multiple freeze/thaw cycles and start-ups from a frozen state. After these successful tests, a heat pipe was integrated in a CubeSat and tests were carried out in several orientations. The tests show that commercially available water-filled heat pipes are suitable for CubeSat thermal control.

Numerical Investigation on Heat Pipe Spanwise Spacing to Determine Optimum Configuration for Passive Cooling of Photovoltaic Panels

The uncertainty regarding the capacity of photovoltaics to generate adequate renewable power remains problematic due to very high temperatures in countries experiencing extreme climates. This study analyses the potential of heat pipes as a passive cooling mechanism for solar photovoltaic panels in the Ecohouse of the Higher Colleges of Technology, Oman, using computational fluid dynamics (CFD). A baseline model has been set-up comprised of 20 units, 20 mm diameter water-filled heat pipes, with a length of 992 mm attached to a photovoltaic panel measuring 1956 mm × 992 mm. Using the source temperature of 64.5 °C (337.65 K), the findings of this work have established that a temperature reduction in the range of up to 9 °C is achievable when integrating heat pipes into photovoltaic panels. An optimum spacing of 50 mm (2.5 times the diameter of the heat pipe) was determined through this work, which is also a proof-of-concept towards the use of heat pipe technology for passive cooling of photovoltaic panels in hot climates.

A review on using nanofluids in heat pipes

The thermophysical specifications of working fluid play a key role in thermal performance of various types of heat pipes. Fluids with high thermal conductivity, low viscosity and surface tension are more favorable to be applied in heat pipes. In order to have fluids with higher thermal conductivity, adding nanoparticles can be an acceptable idea. In the present study, the effects of using nanofluids in several types of heat pipes are reviewed. The nanofluids are categorized based on the types of particles (as carbonic, metallic, etc.). Based on the results of the literature review, applying nanostructures in the base fluid can significantly reduce the thermal resistance of heat pipes compared with utilizing pure as operating fluid. For instance, it is observed that using graphene oxide/water nanofluid in pulsating heat pipe reduces the thermal resistance up to 42% in comparison with the water-filled heat pipe. In addition, reviewed studies revealed that the type of nanoparticle, concentration and their stability are among the most important parameters affecting thermal performance. The enhancement in thermal performance of heat pipes by using nanofluid is mainly attributed to higher thermal conductivity of the nanofluids and increase in nucleation sites.

Harvesting Waste Heat Energy from Automobile Engine Exhaust Using Teg with Heat Pipes

This research investigates how the heat from car exhaust pipe line can be recovered as power using passive Thermo electric generator (TEG) using heat pipes. In this research the heat pipes are place on the cold side of TEG to remove the rising temperature and hot side of TEG is placed on the circumference of exhaust pipe line of car engine. The heat pipes with and without nano-fluids were placed on cold side of TEGs to investigate heat removal from increasing temperature and too maintain constant temperature on cold side. On the basis of results from 3D finite element simulations and experiments in the setup, the heat flow, voltage, and current were measured. The method presented in this paper gives detailed insight into how TEG modules perform in general, and also enables prediction of potential improvement in module performance by using different nano-fluids as coolants and Preliminary results were obtained. The results of Finite Element Analysis are analogous with the experimental results of TEG with water filled heat pipes with minimal possible errors. Therefore, the performance of nano-fluids in heat pipes are numerically evaluated and proposal are made for the enhancement of Module power outputs in Harnessing exhaust heat energy.

Investigating thermal performance of a partly sintered wick heat pipe filled with different working fluids

Heat pipes are important cooling devices which are widely used to transfer heat loads. In this paper thermal performance of a novel type of sintered wick heat pipe, namely, partly sintered wick heat pipe has been investigated. The heat pipe was filled with degassed water and acetone, as working fluids, and effects of filling ratio, orientation and heat inputs were tested. Moreover, conditions at which dry-out occurs were presented. Results showed that the best filling ratio for both working fluids is 20%. The heat pipe filled with water has better thermal performance compared with acetone, so that thermal resistances of the 20% water-filled heat pipe are approximately 7%, 27%, and 75% lower than those of the 20% acetone-filled one in the vertical, horizontal, and vertical reverse modes, respectively. This novel type of sintered wick heat pipe has good thermal performance in the horizontal mode and can be used in no-gravity conditions, i.e. space applications.

Heat transfer and Marangoni flow in a circular heat pipe using self-rewetting fluids

In this study, Marangoni flow and heat transfer enhancement in a heat pipe have been investigated. The experiments were carried out at different heat inputs. A constant temperature water bath was used at the condenser section at three temperature levels. Heat transfer coefficients and thermal resistances of the heat pipe were measured for pure water and water/butanol solutions. The experimental results confirmed that the heat pipe filled with butanol solutions showed better thermal performance than the water-filled heat pipe. At maximum heat flux, 25% heat transfer improvement was obtained when 7 wt% butanol solution was used instead of pure water.

Effects of graphene oxide nanofluids on heat pipe performance and capillary limits

In the present study, thermal performances of water-filled and 0.01 and 0.03 vol% graphene oxide (GO)/water nanofluids-filled heat pipes with a screen mesh wick were studied in order to investigate the effects of nanofluids on the heat pipe operation. The wall temperatures of the GO/water nanofluids-filled heat pipes were found to be lower than those of the water heat pipe. Also, the heat pipes charged with GO/water nanofluids showed lower evaporator thermal resistances by about 25% compared with the water-filled heat pipe, although the condenser thermal resistances were similar in both cases. The 0.01 vol% GO/water nanofluid-filled heat pipe showed better boiling heat transfer than 0.03 vol% GO/water nanofluid because of the different structures of the deposited nanoparticle layers on the wicks. The capillary limit of the heat pipes containing GO/water nanofluids was higher than for the water heat pipe, because the nanoparticles-coated layer modified the effective capillary radius and meniscus, resulting in an increase of the maximum liquid flow rate through the wick structure. The SEM images and wetting properties for wicks of the heat pipes with nanoparticles-coated layers support the thermal performance characteristics of the heat pipes obtained in the study.

Performance of annular flow path heat pipe with a polymer insert controlling compactness for energy applications

This study experimentally investigates the effect of the cross-sectional area of vapor path on the heat transfer performance of a water-filled heat pipe with a polymer insert for optimizing its design. The thermal resistance and the heat transfer coefficient of the heat pipe with a screen mesh wick were measured at a saturation pressure ranging from 6.0kPa to 12.5kPa. It is observed that the changes of the capillary limit and the overall heat transfer coefficient come from the reduction of the vapor space. When the cross-sectional area of the vapor path is reduced to 48.3%, the capillary limit of the heat pipe is decreased by 22.9%. But the overall heat transfer coefficient of the heat pipe is slightly decreased by 3–7%. When the cross-sectional area of the vapor path is reduced to 76.8%, the capillary limit and the heat transfer coefficient of the heat pipe are decreased by 40.7% and 21.0%, respectively. Therefore, the reduction of the overall heat transfer coefficient of the heat pipe has no great effects according to the cross-sectional area of the vapor path. The experimental results suggest the direction of the optimization of the heat pipe in terms of space management for compact devices. Or, if there is enough margin in capillary limit, the optimized compact vapor path without losing heat transfer performance too much can be acquired or excess space can be used for special applications such as neutron absorber in nuclear control rods and structural supports in the electronic cooling for compactness.

Comparison of thermal performances of water-filled, SiC nanofluid-filled and SiC nanoparticles-coated heat pipes

In the present study, thermal performances of water-filled and 0.01 and 0.1vol% SiC/water nanofluids-filled heat pipes with a screen mesh wick and water-filled heat pipe with a SiC nanoparticles-coated screen mesh wick were compared in order to investigate the effects of nanoparticles depositions on inner surface structures of heat pipes. The wall temperatures of the SiC nanoparticles-coated heat pipe were found to be higher than those of an uncoated heat pipe while the thermal performance for the heat pipe using a SiC/water nanofluid was not enhanced compared to the heat pipe using water as a working fluid. Also, the heat pipes containing SiC/water nanofluids and SiC-coated wick showed slight increases in evaporator thermal resistances, but minute changes in condenser thermal resistances compared to the water-filled heat pipe. Moreover, the overall thermal resistances of the heat pipes with the SiC/water nanofluids and SiC-coated wick were similar with those of the heat pipe charged with water. In terms of heat transfer performance, the boiling heat transfer of the evaporator zone is explained by changes of the number of activated nucleation sites due to nanoparticle deposition on the wick structure, whereas heat transfer characteristics of the adiabatic and condenser zones are attributed to the liquid film layer which is formed on the wick structure by capillary wicking and is considerable as additional thermal resistance. The SEM images for wicks of heat pipes with nanoparticles-coated layers support the thermal performance characteristics of three types of heat pipes investigated in the study.

The inclination effect on the performance of water-filled heat pipes

Heat pipes have been used in wide ranges of applications today including solar engineering. During this research study, the inclination dependent performance of water filled heat pipes was investigated both theoretically and experimentally for solar energy applications. The results showed that the performance of water-filled heat pipes are strongly dependent on the inclination and the heat source temperatures. As a general result, the heat transfer capability of water filled heat pipes is reduced dramatically below a 45° tilt angle.

Neutron radiography study of pulsed boiling in a water-filled heat pipe

The boiling and condensation processes in a water-filled industrial heat pipe have been investigated by dynamic neutron radiography. Pulsed boiling was visualized and analysed up to a characteristic temperature depending on the filling quantity. Three typical regions were distinguished in the heat pipe: that constantly filled by the liquid; a periodically wetted zone; and a region constantly filled by the vapour. Pulsation was found to be not strictly periodic and its mean amplitude and frequency were determined. It is concluded that any models based on the equilibrium state are incorrect.

4548258 Method and means for inhibiting corrosion in a heat pipe: John A Nelson, Joan D Banks assigned to Whirlpool Corporation

In the present study, thermal performances of water-filled and 0.01 and 0.1 vol% SiC/water nanofluids-filled heat pipes with a screen mesh wick and water-filled heat pipe with a SiC nanoparticles-coated screen mesh wick were compared in order to investigate the effects of nanoparticles depositions on inner surface structures of heat pipes. The wall temperatures of the SiC nanoparticles-coated heat pipe were found to be higher than those of an uncoated heat pipe while the thermal performance for the heat pipe using a SiC/water nanofluid was not enhanced compared to the heat pipe using water as a working fluid. Also, the heat pipes containing SiC/water nanofluids and SiC-coated wick showed slight increases in evaporator thermal resistances, but minute changes in condenser thermal resistances compared to the water-filled heat pipe. Moreover, the overall thermal resistances of the heat pipes with the SiC/water nanofluids and SiC-coated wick were similar with those of the heat pipe charged with water. In terms of heat transfer performance, the boiling heat transfer of the evaporator zone is explained by changes of the number of activated nucleation sites due to nanoparticle deposition on the wick structure, whereas heat transfer characteristics of the adiabatic and condenser zones are attributed to the liquid film layer which is formed on the wick structure by capillary wicking and is considerable as additional thermal resistance. The SEM images for wicks of heat pipes with nanoparticles-coated layers support the thermal performance characteristics of three types of heat pipes investigated in the study.