Cryogenic Oscillating Heat Pipe Research Articles

Experimental studies on the heat transfer characteristics of helium-based cryogenic oscillating heat pipes

Experimental studies on the heat transfer characteristics of helium-based cryogenic oscillating heat pipes

Simulation study on thermal performance of two turns helium cryogenic oscillating heat pipe for superconducting accelerator

Simulation study on thermal performance of two turns helium cryogenic oscillating heat pipe for superconducting accelerator

Experimental Investigation of Flat Plate Cryogenic Oscillating Heat Pipe

Recent developments in applications such as high-temperature superconducting magnets, infrared detectors, and electronics components have led to an alarming increase in heat dissipation rate, which now far exceeds the capability of conventional heat pipe cooling systems. This trend is responsible for a recent transition to flat plate oscillating heat pipes. A new flat plate cryogenic oscillating heat pipe (FPC-OHP) has been developed and validated through experimentations. The performance evaluation of FPC-OHP was investigated with temperature measurements. FPC-OHP consisted of evaporator, condenser, and adiabatic section with the dimensions of 93 × 70 × 8 mm3. The FPC-OHP was made of copper alloy and fabricated by a vertical milling machine, having square channels with a hydraulic radius of 0.66 mm. Liquid nitrogen was used as a working fluid with a charge ratio of 60%. Experimental results revealed the maximum heat transport capability up to 300 W. Moreover, the thermal resistance decreased from 0.25 to 0.11 K/W corresponding to an increase in the heat load from 25 to 300 W. The average temperature difference between evaporator section and condenser section reached up to 34 K for 300 W. The measured effective thermal conductivities were found to be 7353 W/m K.

Cryogenic Oscillating Heat Pipe for Conduction-Cooled Superconducting Magnets

The cryogenic oscillating heat pipe (OHP) is considered as a convenient thermal link between the crycooler head and the superconducting magnet due to the employment of flexible capillary tube. In this paper, a cryogenic OHP using nitrogen as the working fluid is fabricated. The copper blocks connecting with the evaporator of the cryogenic OHP are used as a mock-up superconducting magnet, and a heating sheet is attached on the copper blocks to simulate the heat generation of the superconducting magnet system during the operation process. The cooling down processes and the operation characteristics of the cryogenic OHP at the different condenser temperature are investigated. The results show that the cryogenic OHP has not only large cooling capacity during the cooling down process, but also excellent heat transfer performance during the operation process.

NUMERICAL INVESTIGATION OF THERMAL PERFORMANCE OF A CRYOGENIC OSCILLATING HEAT PIPE

The oscillating heat pipe (OHP) with simple structure and high heat transfer effi ciency has been proposed recently for cryogenic use. In this paper, a model of fluid flow and heat transfer on multiple liquid slugs and vapor plugs in an OHP has been developed. The cryogenic OHP with working fluid of nitrogen is studied using the model. Oscillatory flow and circulatory flow are observed. The mass flow rate of liquid slugs and the mean wall temperature of the evaporator section are calculated. Furthermore, the effective thermal conductivity of the cryogenic OHP is determined, which shows much higher thermal performance than that of high purity metal. The effects of the heat input and the filling ratio on the effective thermal conductivity are discussed. Finally, the calculated effective thermal conductivity is compared with experimental results, and it is seen that this model correctly predicts the thermal performance of a cryogenic OHP in the case of a medium and low heat input.

Study on a neon cryogenic oscillating heat pipe with long heat transport distance

An experimental study is carried out to study the heat transfer characteristics of a cryogenic oscillating heat pipe (OHP) with long heat transport distance. The OHP is made up of a capillary tube with an inner diameter of 1.0 mm and an outer diameter of 2.0 mm. The working fluid is neon, and the length of the adiabatic section is 480 mm. Tests are performed with the different heat inputs, liquid filling ratios and condenser temperature. For the cryogenic OHP with a liquid filling ratio of 30.7% at the condenser temperature of 28 K, the effective thermal conductivity is 3466–30,854 W/m K, and the maximum transfer power is 35.60 W. With the increment of the heat input, the effective thermal conductivity of the cryogenic OHP increases at the liquid filling ratios of 30.7% and 38.5%, while it first increases and then decreases at the liquid filling ratios of 15.2% and 23.3%. Moreover, the effective thermal conductivity increases with decreasing liquid filling ratio at the small heat input, and the maximum transfer power first increases and then decreases with increasing liquid filling ratio. Finally, it is found that the thermal performance of the cryogenic OHP can be improved by increasing the condenser temperature.

Effects of filling ratio and condenser temperature on the thermal performance of a neon cryogenic oscillating heat pipe

A cryogenic oscillating heat pipe (OHP) made of a bended copper capillary tube is manufactured. The lengths of the condenser section, adiabatic section and evaporator section are 100, 280 and 100 mm, respectively. Neon is used as the working fluid. Effects of liquid filling ratio and condenser temperature on the thermal performance of the OHP are studied. A correlation based on the available experimental data sets is proposed to predict the thermal performance of the neon cryogenic OHP with different filling ratios and condenser temperature. Compared with the experimental data, the average standard deviation of the correlation is about 15.0%, and approximately 92.4% of deviations are within ±30%.

Experimental investigation on the performance of a neon cryogenic oscillating heat pipe

An experimental investigation is conducted to study the performance of a cryogenic oscillating heat pipe (OHP) using neon as the working fluid. The stainless steel OHP with an inner diameter of 0.9mmhas 4 turns, and the lengths of the evaporator, condenser section and adiabatic section are 35mm, 35mm and 95mm, respectively. The temperature of the evaporator and condenser and the pressure of the OHP are measured. The results show that the cooling down process of the OHP from room temperature to the working temperature can be significantly accelerated by charging with neon. During the pseudo steady-state operation process, the temperature of evaporator and the pressure of the OHP increase with increasing heat input. When the dry out appears, the temperature of evaporator rises quickly, and the pressure of the OHP drops sharply. In addition, the effective thermal conductivity of the OHP at the different heat inputs and the different filling ratios is calculated. It increases with increasing heat input, and there exists an optimum filling ratio which makes the maximum effective thermal conductivity. For this OHP, the optimum filling ratio is 24.5%, at which the effective thermal conductivity is 6100–22,180W/mK.

Experimental investigation of the characteristics of cryogenic oscillating heat pipe

Abstract The oscillating heat pipe (OHP) with high thermal performance and easy manufacturing has been increasingly studied in the recent years. In this paper, the OHP for cryogenic application is investigated. An OHP system is manufactured with 3 sections of evaporator, condenser and adiabatic section. The temperature of evaporator and condenser and the gas pressure of the OHP are measured. The experiments with working fluid of nitrogen are carried out. When the heat input increases, the temperature and pressure increases were observed experimentally. When the dry-out takes place, the evaporator temperature rises quickly, the gas pressure drops sharply and the amplitude of the pressure oscillation reduces largely. The effective thermal conductivity is obtained and compared to other literatures. The relation between the effective thermal conductivity and the gravity, and the relation between the gas pressure and the gravity are attempted to interpret. The cryogenic OHP system shows much higher thermal performance than high purity metal, and it requires more study on the geometric optimization, the selection of working fluid and the operating limitations.

Enhancement of Thermal Properties of HTS Magnets Using Built-in Cryogenic Oscillating Heat Pipes

Enhancement of the thermal properties of high- $T_{\rm c}$ superconducting (HTS) magnets has been investigated using built-in cryogenic oscillating heat pipes (OHPs). A cryogenic OHP is built into windings of an HTS magnet to improve the thermal properties of windings and to protect them from damage caused by a large temperature gradient. It is rather difficult for an HTS magnet to quickly remove the heat generated in windings, especially, in a protection operation when a magnet quenches, because the thermal diffusivities of component materials of windings decrease with an increase of temperature. Therefore, a local hot spot can be formed in a magnet, and there are possibilities of having degradation of superconducting properties and/or mechanical damages by thermal stresses. A flat-plate cryogenic OHP has been developed that is suitable for imbedding in magnet windings as a high-performance heat transportation device in order to increase the thermal conductivity and the thermal diffusivity at the same time. By using hydrogen, neon, and nitrogen as working fluid, its excellent thermal transport properties have been proved in the operating temperature range of 18–84 K.

Development of a Flat-plate Cryogenic Oscillating Heat Pipe for Improving HTS Magnet Cooling

Abstract A new method of including cryogenic oscillating heat pipes (OHPs) in the HTS coil windings as a thermal transport device has been studied. In this work, two type of OHPs are tested in low temperature. Employed working fluids are H2, Ne, N2. We have attained high performance thermal property using a bent-pipe cryogenic OHP as a prototype. Obtained effective conductivities have reached to 46000 W/m K. Then a flat-plate cryogenic OHP has been developed, that is suitable for imbedding in magnet windings. Preliminary experiments have been conducted and the result has been promising.

Development of Cryogenic Oscillating Heat Pipe as a New Device for Indirect/Conduction Cooled Superconducting Magnets

Cryogenic oscillating heat pipes (OHPs) have been proposed as a new heat transfer device for conduction/indirect cooling of high-temperature superconducting (HTS) magnets. OHP is a highly effective two-phase heat transfer device which can transport several orders of magnitude greater heat flux than the heat conduction of solids. The performance of cryogenic OHPs has been intensively examined and the results indicate the ability of dramatically improving the performance of HTS magnets. Semi-empirical correlations stating thermo-physical properties of cryogenic OHPs are introduced based on those of room temperature OHPs. The modeling with non-dimensional quantities is useful for the design of cryogenic OHPs.

Achievement of High Heat Removal Characteristics of Superconducting Magnets With Imbedded Oscillating Heat Pipes

Oscillating heat pipes (OHP) for cryogenic use are being developed to improve the heat removal characteristics of high-temperature superconducting (HTS) magnets. It is generally difficult to remove the heat generated in HTS windings, because the thermal diffusivities of component materials decrease with an increase of the operating temperature. Therefore, a local hot-spot can be rather easily generated in HTS magnets, and there are possibilities of observing degradation of superconducting properties and/or mechanical damages by thermal stresses. As a new cooling technology to enhance the heat removal characteristics in HTS magnets, the cryogenic OHP is proposed to be imbedded in magnet windings. The feasibility of cryogenic OHP has been confirmed by fabricating proto-types and by observing stable operations using hydrogen, neon and nitrogen as the working fluid. A high thermal conductivity was achieved that surpasses those of high-purity metals. We also propose a modified-type OHP to mitigate the orientation dependence.

Heat transfer performance of cryogenic oscillating heat pipes for effective cooling of superconducting magnets

The cryogenic oscillating heat pipe (OHP) for conduction cooling of superconducting magnets was developed and the function was demonstrated successfully. OHP is a highly-efficient heat transfer device using oscillating flow of two-phase mixture. The working fluids that are employed in the present research are Nitrogen, Neon and Hydrogen, and the operating temperatures are 67–91 K, 26–34 K and 17–27 K, respectively. The estimated effective thermal conductivities from the measurement data of the OHP were higher than one of the solids such as copper at low temperature. These results revealed that the cryogenic OHP can enhance the performance of cooling system for magnets.

Development of Highly Effective Cooling Technology for a Superconducting Magnet Using Cryogenic OHP

A highly effective cooling technique for a superconducting magnet is proposed by incorporating the cryogenic oscillating heat pipes (OHP) as cooling panels in the coil windings. The OHP is a high performance two-phase heat transfer device, which can transport several orders of magnitude larger heat loads than heat conduction of solids. The cryogenic OHP using , Ne, and as working fluids have been developed and tested at the operating temperature ranges of 17-25 K (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), 26-32 K (Ne), and 67-80 K (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The measured effective thermal conductivities were reached to 500-3,000 W/m · K (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), 1,000-8,000 W/m · (Ne) and 10,000-18,000 W/m · K (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The high thermal transport properties of the cryogenic OHP and its application as the cooling components of superconducting magnets are also discussed.

Experimental investigation of cryogenic oscillating heat pipes

A novel cryogenic heat pipe, oscillating heat pipe (OHP), which consists of an 4 × 18.5 cm evaporator, a 6 × 18.5 cm condenser, and 10 cm length of adiabatic section, has been developed and experimental characterization conducted. Experimental results show that the maximum heat transport capability of the OHP reached 380 W with average temperature difference of 49 °C between the evaporator and condenser when the cryogenic OHP was charged with liquid nitrogen at 48% (v/v) and operated in a horizontal direction. The thermal resistance decreased from 0.256 to 0.112 while the heat load increased from 22.5 to 321.8 W. When the OHP was operated at a steady state and an incremental heat load was added to it, the OHP operation changed from a steady state to an unsteady state until a new steady state was reached. This process can be divided into three regions: (I) unsteady state; (II) transient state; and (III) new steady state. In the steady state, the amplitude of temperature change in the evaporator is smaller than that of the condenser while the temperature response keeps the same frequency both in the evaporator and the condenser. The experimental results also showed that the amplitude of temperature difference between the evaporator and the condenser decreased when the heat load increased.

Investigations on the heat transport capability of a cryogenic oscillating heat pipe and its application in achieving ultra-fast cooling rates for cell vitrification cryopreservation

Theoretically, direct vitrification of cell suspensions with relatively low concentrations (∼1 M) of permeating cryoprotective agents (CPA) is suitable for cryopreservation of almost all cell types and can be accomplished by ultra-fast cooling rates that are on the order of 10 6–7 K/min. However, the methods and devices currently available for cell cryopreservation cannot achieve such high cooling rates. In this study, we constructed a novel cryogenic oscillating heat pipe (COHP) using liquid nitrogen as its working fluid and investigated its heat transport capability to assess its application for achieving ultra-fast cooling rates for cell cryopreservation. The experimental results showed that the apparent heat transfer coefficient of the COHP can reach 2 × 10 5 W/m 2·K, which is two orders of the magnitude higher than traditional heat pipes. Theoretical analyzes showed that the average local heat transfer coefficient in the thin film evaporation region of the COHP can reach 1.2 × 10 6 W/m 2·K, which is approximately 10 3 times higher than that achievable with standard pool-boiling approaches. Based on these results, a novel device design applying the COHP and microfabrication techniques is proposed and its efficiency for cell vitrification is demonstrated through numerical simulation. The estimated average cooling rates achieved through this approach is 10 6–7 K/min, which is much faster than the currently available methods and sufficient for achieving vitrification with relatively low concentrations of CPA.