Heat Pipe Concept Research Articles

A Review on Experimental Validation of Heat Pipe Solar Collector for Water Heating

Now a day’s climate of growing energy needs and increasing environmental concern, alternatives to the use of non -renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy; solar water heating is the prime application of solar energy. The problem faced by the existing solar water heating system is periodic inspections, maintenance, time to time component may need repair or replacement and also sufficient quantity of hot water is not available during cloudy/rainy days. Hence to overcome these problem , the use of heat pipe concept which utilizes the low boiling temperature fluid to increase the heating efficiency, the objective of present work is to increase the heating efficiency solar water heater using low boiling temperature fluid. Key Words: Solar water heater, concept of heat pipe, low boiling temperature fluid (working fluid), thermosiphon.

Heat Pipe-Based DEMO Divertor Target Concept: High Heat Flux Performance Evaluation

The use of heat pipes (HP) for the DEMO in-vessel plasma-facing components (PFCs) has been considered because of their high capacity to transport the heat from a heat source to a heat sink by means of the vaporization and condensation of the working fluid inside and their ability to enlarge the heat transfer area of the cooling circuit substantially. Recent engineering studies conducted in the framework of the EUROfusion work package Divertor (Wen et al, 2021) indicate that it is possible to design a heat pipe with a capillary limit above 6 kW using a composite capillary structure (wherein axial grooves cover the adiabatic zone and the condenser, and sintered porous material covers the evaporator). This power level would correspond to an applied heat flux of 20 MW/m2, rendering such a design interesting with respect to a divertor target concept. To validate the results of the initial engineering analysis, several experiments have been conducted to evaluate the actual performance of the proposed heat pipe concept. The present contribution presents the experiment’s results regarding the examination of the operating limits of two different designs for an evaporator: one featuring a plain porous structure, and one featuring ribs and channels.

A wicked heat pipe fabricated using metal additive manufacturing

Additive Manufacturing (AM) has emerged as a high-potential manufacturing technology for fabricating all-in-one heat exchange devices that incorporate embedded two-phase heat transport and spreading systems. A key enabler of this technology is the capacity for AM to fabricate porous wick structures. To this end, this work experimentally investigates a simple AM-fabricated aluminum structure with an inner cavity. Within the cavity, a single-sided wick heat pipe is fabricated, again by aluminum AM. To facilitate capillary wicking within the embedded heat pipe, while being amenable to the direct metal laser sintering (DMLS) AM process, a novel cross-hatched porous wick structure is introduced. The wicks were fabricated by printing layered rows of fine wire-like features at different angles to one another in successive layers, creating a porous 3D structure. The resulting 3D wick structure was varied by controlling the hatch distance between neighboring printed wires in each layer, resulting in different wick properties. In this investigation, the capillary performance of three wicks were interrogated using the Rate of Rise technique, which also facilitated estimation of important wick properties such as permeability and effective pore radius. By varying the hatch distance between 0.6 mm and 1.0 mm, the permeability ranged between 35.6 and 39.6μm 2 with a corresponding range of 127–88 μm for the effective pore radius and 43–59% for the porosity. The efficacy of the proposed metal AM heat pipe concept was then verified by enclosing the wicks within a lid casing, creating two-part flat heat pipes, and experimentally characterizing them with acetone used as the working fluid. This study includes performance indicators such as overall thermal resistance, effective wick thermal conductivity, and effective thermal conductivity of the heat pipe cavity region.

Improved Desalination Pipeline System Utilizing the Temperature Difference under Sub-Atmospheric Pressure

Based on the principles of mass conservation, momentum, and energy, an improved version of the Desalination pipeline called Improved Desalination Pipeline System (IDPS) has been studied in the present paper. The main features of IDPS are the high transfer rate and the high raw water production rate. IDPS works with the help of thermal gradient generated due to the temperature difference between the seaside/destination. Heat injection has also been used to increase the efficiency of IDPS. In the condensation part, the heat pipe concept is adopted to facilitate the vapor-liquid process. The main portion of heat injected to the IDPS is recovered by generating electrical power using water flow due to available water head. To show the efficiency of IDPS, a case study is performed from Bandar Abbas (seaside) to Mount GNU (the destination) located30 km away with 2347 m height. The results show that IDPS does not necessarily require large diameter pipes for greater efficiencies. The energy consumption for distillation and transferring1 m3 of water is about 6.6 Kwh. In addition to the distilled transferred water, a significant amount of water is distilled on the site, which is about 25% of the transferred water.

Heat Reduction in CVTs using Peltier Air Conditioner

CVT(Continuously Variable Transmission), is the mechanism used in few automobiles(like cars), which is one of the biggest deciding factor on the performance of the automobile, because of the large amount of heat it dissipates due to extreme friction on rotation, thereby increasing the mechanical losses. This heat dissipated can be reduced using the peltier cooling system. The heat from the peltier module is removed by employing the concept of heat pipes.

Hybrid heat pipe based passive in-core cooling system for advanced nuclear power plant

After the Fukushima accident in 2011, passive safety of nuclear reactors available under station blackout accidents like Fukushima has become the most pressing issue in the nuclear energy industry. For passive in-core cooling system (PINCs), the concept of a hybrid heat pipe, which is the combination of the heat pipe and neutron absorber was proposed to enhance the safety of advanced nuclear power plants. With the unique features of heat pipe and control rod, the hybrid heat pipe can remove decay heat directly from the core as it is inserted into the reactor pressure vessel with the same drive mechanism of a control rod. In this study, a two-step numerical analysis was performed for evaluating the concept of the hybrid heat pipe and its applications. The thermal performance of a single hybrid heat pipe was numerically analyzed using a commercial CFD code for designated designed features under reactor operation conditions. As a result, the hybrid heat pipe concept was found to remove 18.20 kW per rod with total thermal resistance of 0.015 °C/W. Using MALTAB, the one-dimensional thermal hydraulic analysis of reactor was conducted for the proposed PINCs to calculate the coolant temperature for evaluating the cooling performance of hybrid heat pipe. It revealed that the hybrid heat pipe was able to delay core heat-up at the station blackout accidents and extensions. If the hybrid heat pipe had enhanced heat removal capacity, it could continue cooling the core during accidents while preventing the core uncovery.

A Compact Remote Heat Transfer Device for Space Cryocoolers

In this paper a compact remote heat transfer device (CRHD) for cryocoolers is proposed. This device is especially attractive in cases where cryocoolers are not easy to set near the heat source, generally the infrared sensor. The CRHD is designed on basis of the concept of loop heat pipes, while the primary evaporator is located near the cryocooler cold head and a simple tube-in-tube secondary evaporator is remotely located and thermally connected with the heat source for cooling. With such a device a cooling power of 1W is achieved across a heat transfer distance of about 2 m. The major problem of this device is the low heat transfer efficiency (1W of net cooling power at the cost of about 7W of cooling power from the cryocooler), and in the future a secondary wicked evaporator will be used instead of the tube-in-tube evaporator in order to improve the efficiency.

A novel design of pulsating heat pipe with fewer turns applicable to all orientations

This study presents a novel pulsating heat pipe (PHP) concept that is functional even when PHP is with fewer turns and is operated horizontally. Two heat pipes were made of copper capillary tubes with an overall size of 122mm×57mm×5.5mm is investigated, one had 16 parallel square channels having a uniform cross-section of 2mm×2mm (uniform CLPHP), and the other had 16 alternative size of parallel square channels (non-uniform CLPHP; a cross-section 2mm×2mm and a cross-section of 1mm×2mm in alternating sequence). Test results showed that the performance of PHP rises with the inclination but the uniform channel CLPHP is not functional at horizontal configuration whereas the proposed non-uniform design is still functional even at horizontal arrangement. The thermal resistance for uniform PHP is relative insensitive to change of inclination when the inclination angle exceeds certain threshold value.

Economic evaluation of latent heat thermal energy storage using embedded thermosyphons for concentrating solar power applications

An economic evaluation of a latent heat thermal energy storage (LHTES) system for large scale concentrating solar power (CSP) applications is conducted. The concept of embedding gravity-assisted wickless heat pipes (thermosyphons) within a commercial-scale LHTES system is explored through use of a thermal network model. A new design is proposed for charging and discharging a large-scale LHTES system. The size and cost of the LHTES system is estimated and compared with a two-tank sensible heat energy storage (SHTES) system. The results suggest that LHTES with embedded thermosyphons is economically competitive with current SHTES technology, with the potential to reduce capital costs by at least 15%. Further investigation of different phase change materials (PCMs), thermosyphon working fluids, and system configurations has the potential to lead to designs that can further reduce capital costs beyond those reported in this study.

Flat Miniature Heat Pipes for Electronics Cooling: State of the Art, Experimental and Theoretical Analysis

An experimental study is realized in order to verify the Mini Heat Pipe (MHP) concept for cooling high power dissipation electronic components and determines the potential advantages of constructing mini channels as an integrated part of a flat heat pipe. A Flat Mini Heat Pipe (FMHP) prototype including a capillary structure composed of parallel rectangular microchannels is manufactured and a filling apparatus is developed in order to charge the FMHP. The heat transfer improvement obtained by comparing the heat pipe thermal resistance to the heat conduction thermal resistance of a copper plate having the same dimensions as the tested FMHP is demonstrated for different heat input flux rates. Moreover, the heat transfer in the evaporator and condenser sections are analyzed, and heat transfer laws are proposed. In the theoretical part of this work, a detailed mathematical model of a FMHP with axial microchannels is developed in which the fluid flow is considered along with the heat and mass transfer processes during evaporation and condensation. The model is based on the equations for the mass, momentum and energy conservation, which are written for the evaporator, adiabatic, and condenser zones. The model, which permits to simulate several shapes of microchannels, can predict the maximum heat transfer capacity of FMHP, the optimal fluid mass, and the flow and thermal parameters along the FMHP. The comparison between experimental and model results shows the good ability of the numerical model to predict the axial temperature distribution along the FMHP.

High Flux Value Micro-Heat Pipe Arrays

The concept of heat pipes was introduced by R.S.Gaugler in 1940s and Cotter first introduced the idea of “micro” heat pipes in 1984. Cotter in his paper, defined the micro heat pipe as being one in which the mean curvature of the vapor-liquid interface is comparable in magnitude to the reciprocal of the hydraulic radius of the total flow channel. The Micro Heat Pipes (MHPs) work efficiently through the use of two-phase heat transfer. Various working fluids have been tried in combination with various substrate materials. In this experimental work the main focus was to study the behavior of liquid metal filled MHPs made from silicon as the substrate material. Specially designed MHPs were assembled and charged with mercury as the working fluid. A special test setup was designed and built for the experimental work and the response of the MHPs to the controlled increment in the input power is presented. A number of experiments were carried out on the specimen MHPs to determine their effective thermal conductivity, the variation of the temperature along the axial length and the performance enhancement factor. Effective thermal conductivities as high as 900 W/m-K with a silicon equivalence of 6 were achieved with the liquid metal MHP. Based on the results from the various performance testing parameters, it was observed that the liquid metal charged MHPs performed substantially better than conventional MHPs filled with organic working fluids. The limitations and the possible methods of improving the performance of the MHPs are discussed.

Integration of Heat Pipe into Fuel Cell Technology

This paper describes recent applications of heat pipe technology in fuel cell systems, which include new stack designs with heat pipes to improve heat transfer as well as work on fuel cell system level design and engineering with adopting the heat pipe concept. In one design, micro-heat pipes are inserted and bonded in bipolar plates for thermal control in the fuel cell stack. In another design, flat heat pipes are integrated with a carbon bipolar plate for improving thermal control in the fuel cell stack. Finally, based on the heat pipe concept, we specifically developed a series of direct methanol fuel cell (DMFC) systems characterized as passive technology for methanol fuel delivery, water recirculation, and air and thermal management. Long-term durability and stability of the passive DMFC systems have been proved experimentally.

Experimental and Theoretical Analysis on Enhanced Flat Miniature Heat Pipes

A combined experimental and analytical study is realized to verify the miniature heat pipe (MHP) concept for cooling high-power dissipation electronic components and determine the potential advantages of constructing arrays of miniature channels as an integrated part of a heat pipe. A theoretical model is developed to predict the capillary limit and the thermal resistance of the flat MHP (FMHP). The model includes flow analysis and thermal study of the heat transfer modes in the capillary structures. To verify the mixed capillary structure concept and validate the proposed analytical model, an FMHP including a mixed capillary structure, rectangular grooves and screen wick, is manufactured, and a filling apparatus is developed charge such FMHPs. The heat transfer improvement obtained by comparing the heat pipe thermal resistance to the heat conduction thermal resistance of a copper plate having the same dimensions as the tested heat pipe is demonstrated for different heat input flux rates.

Cooling options for ASTROMAG

A comparison of the various cooling options for the ASTROMAG particle physics experiment is presented. The baseline design for the cryogenic system involves using a natural circulation fountain-effect driven flow loop (Hofmann type). The present paper considers two alternative options for cooling. The first design involves a thermal strap made of a high-conductivity metal, e.g., high-purity aluminium or copper, which connects the coil to the helium reservoir. Venting helium vapour can also be used to minimize the temperature of the magnet and recover from a quench. The second design is based on a He II heat pipe concept where steady state heat transport is by counterflow. Cavitation is prevented by use of a porous plug. Forced flow He II is also available but only during extraordinary operating conditions.

Steady-State Modeling and Testing of a Micro Heat Pipe

A combined experimental and analytical investigation was conducted to identify and understand better the phenomena that govern the performance limitations and operating characteristics of micro heat pipes—heat pipes so small that the mean curvature of the vapor—liquid interface is comparable in magnitude to the reciprocal of the hydraulic radius of the flow channel. The analytical portion of the investigation began with the development of a steady-state model in which the effects of the extremely small characteristic dimensions on the conventional steady-state heat pipe modeling techniques were examined. In the experimental portion of the investigation, two micro heat pipes, one copper and one silver, 1 mm2 in cross-sectional area and 57 mm in length, were evaluated experimentally to determine the accuracy of the steady-state model and to provide verification of the micro heat pipe concept. Tests were conducted in a vacuum environment to eliminate conduction and convection losses. The steady-state experimental results obtained were compared with the analytical model and were found to predict accurately the experimentally determined maximum heat transport capacity for an operating temperature range of 40° C to 60° C. A detailed description of the methodology used in the development of the steady-state model along with a comparison of the predicted and experimental results are presented.

Thermal Management for Large Space Platforms

This paper provides an evaluation of heat rejection techniques applicable to multihundred-kilowatt space platforms. A number of promising heat rejection concepts were parametrically weight-optimized over a wide range of conditions to provide a 99% reliability of achieving a 10-yr life for the multihundred-kilowatt space platform. Three panel designs were considered: (1) an advanced meteoroid-bumpered hybrid heat pipe concept, (2) a bumpered liquid concept, and (3) a space constructable heat pipe radiator. The following are some of the significant findings from the study: (1) A single subsystem approach can be used with the heat pipe system, whereas several smaller subsystems are required for the pumped fluid systems. (2) The space constructable radiator approach offers a 10% weight reduction and operational advantages over the conventionally deployed panels.

Foodservice Equipment: Technological Trends

A major incentive for development of improved foodservice equipment is the need for energy conservation. Despite contrary popular belief, preservation of foods in the frozen form provides sufficient comparative advantages and economies to keep frozen foods in the market-place for the foreseeable future. Equipment is being developed for rapid chilling and freezing of bulk foods and for defrosting and heating those foods. Liquid nitrogen is often used. Convection, directed hot air, infrared and microwave heating are being used singly and in combination to temper, thaw and heat frozen foods rapidly and efficiently. The heat pipe concept, a space technology product, has been adapted for use in grills.

Electrohydrodynamic heat pipe experiments

Experiments with two electrohydrodynamic heat pipes are reported. Both devices employ an electromechanical flow structure for axial liquid flow and a capillary wicking structure for (i) collection of condensed liquid at the cooled end and (ii) distribution of this liquid at the heated end. One device has circumferential grooving for the capillary structure and the other has feltmetal wicking. The experiments successfully demonstrate the electrohydrodynamic heat pipe concept. Compatibility of the two circumferential wick structures with an axial electromechanical flow structure is also demonstrated. A significant mismatch of the capillary groove and electrohydrodynamic pumping capabilities results in severe hydrodynamic burn-out limiting in the first heat pipe. Both devices have very poor over-all thermal conductances of the order of 1–2 W/°C, reflecting the generally poor heat-transfer properties of the dielectric working fluids required in electrohydrodynamic heat pipes.