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Helium (He) tracer method is one of the common methods used to detect tube bundle leakage in the condenser. To improve the detection accuracy, sulfur hexafluoride (SF6) is considered a tracer gas instead of He. This paper combines the N-S equation, porous medium model, flow diffusion model and steam heat transfer model to develop the numerical model of tube bundle leakage in the condenser. The simulation results show that the transport of leaked gases (He and SF6) consists of flow and diffusion patterns. The existence of the diffusion process is confirmed further through theoretical analysis. The two gases have the same transport behavior in the pure flow process. When it involves the diffusion process, the flow rate of He is 6.67 times that of SF6. In other words, the time required for He to reach the same concentration difference is 1/6.67 times that of SF6. In addition, the influence of leakage intensity and gas species on the transport is analyzed. The study results provide a theoretical basis for SF6 to replace He as a tracer gas to detect tube bundle leakage. [ABSTRACT FROM AUTHOR]

In view of the prominent and intractable problems of frequent high temperature alarms of the communication equipment and high energy consumption of air conditioners in Zhengzhou communication outdoor cabinets, a temperature control system with heat pipe as the main part and air conditioner as the auxiliary part is proposed in this paper. A prototype is developed and its applications are discussed. The annual field test shows the system works well, and it has a remarkable energy saving efficiency. [ABSTRACT FROM AUTHOR]

The refrigeration system accounts for 40-60% of the total energy consumption of the base station, so an effective energy-saving technology is much needed. This paper proposes a heat pipe air-conditioner with an additional soil heat exchange unit. When the indoor and outdoor temperature difference is small, the indoor heat can be scattered to the soil to achieve energy-saving effect. [ABSTRACT FROM AUTHOR]

In order to solve the poor heat dissipation in the outdoor mobile communication base station, especially in summer, high temperature alarm phenomenon occurs frequently, affecting the normal operation of building base band unite, this paper designs an energy-saving and efficient integrated thermal management system, which has achieved good results by applying the combined operation of heat pipe cooling and air conditioning system using the outdoor temperature switching mode. A mobile communication base station in Zhengzhou City was chosen for a pilot application. The measured results showed that the system ran stably, the temperature inside the cabinet was controlled between 12 °C and 39 °C with no high temperature alarm, the compressor running time was significantly reduced, the power consumption of the air conditioner was significantly reduced, and the annual power saving rate was as high as 58.63%. [ABSTRACT FROM AUTHOR]

By constructing the heat transfer model of the buried tube heat exchanger, using the mathematical method and numerical calculation software, the temperature of the buried tube heat exchanger is calculated numerical, so as to better understand the temperature effect of the buried tube heat exchanger on the surrounding soil. This paper establishes a mathematical model of a vertically buried heat transfer system based on the principle of thermal equilibrium and the thermal conductivity differential equation. Conduct research on the temperature field around single pipes in different soil (geological conditions), temperature field under different drilling backfill materials, and the temperature around buried pipe-lines in both short-term and long-term operation of the system. The experimental results show that the simulation results of the system's short time (10 days) and long time (90 days) performance show that the cooling and temperature cycles in different areas directly affect the heat radius of the buried pipe and the heat accumulation near the buried pipe. The thermal action radius of the short-term operation system is about 1.8 m, and the long-term operation reaches 4.5 m. [ABSTRACT FROM AUTHOR]

To address the current problem of high energy consumption in data centers, this paper proposes a data center heat pipe air-conditioning system based on the latent heat of water evaporation, which uses the latent heat of water evaporation for cooling by creating a low pressure environment to evaporate large amounts of water. In order to verify the effect of the system, a heat pipe test bench based on the latent heat of water evaporation was designed and built. Compared with the traditional heat pipe in the data center for heat dissipation, the performance and economy of the water evaporation latent heat pipe system designed in this paper are analyzed experimentally. A multi-physics coupled model of water evaporation latent heat pipe air-conditioning based on COMSOL Multiphysics was established to simulate and study the temperature field and velocity field distribution of water evaporation latent heat pipe air-conditioning system in data centers. The research shows that: -- Under the designed test conditions, compared with the traditional heat pipe system, the water evaporation latent heat pipe air conditioner can conduct 2540 kJ more heat in one day in an outdoor environment of 24 °C. -- At an ambient temperature of 3 5°C and an indoor temperature of 25.8 °C, the cooling capacity of the heat pipe in the data center water evaporation latent heat pipe air-conditioning system is twice the cooling capacity of the air conditioner, and the heat pipe can work efficiently regardless of the outdoor ambient temperature. -- The energy-saving effect of the latent heat pipe of water evaporation in the data center has a significant effect on air conditioners with an energy efficiency rating (EER) lower than 2.5-4.4. It can improve the energy efficiency of level 5 with an EER of 2.5 to level 2 with an EER of 3.22, greatly reducing the power consumption of the data center air-conditioning system. When the EER of the air conditioner exceeds 4.4, the coefficient of performance of the data center water evaporation latent heat pipe air-conditioning system will be lower than that of the air conditioner itself. [ABSTRACT FROM AUTHOR]

Commentaries are presented on Ye et al. [1]'s paper, where the authors investigated the performance of heat transfer in evaporator under the case that the parameters of the heat source and temperature of pinch point were identified. They utilized the graphical method of temperature-heat (T-Q) diagram analysis. Also, they utilized the entransy principle in their analysis. Commentaries show the reality that the graphical method of T-Q diagram analysis belongs to Professor Adrian Bejan, who first proposed it in 1977. In addition, many instances in the literature are given to indicate disputes for the entransy principle by oppositionists of "entransy" from various countries. [ABSTRACT FROM AUTHOR]

In order to solve the problem of poor refrigeration performance during operation of the refrigeration system under low temperature conditions, this paper designs a refrigeration system test bench to study the effect of different air volumes on the cooling capacity of the refrigeration system under the conditions of 32 outside the warehouse and -10 inside the warehouse. The results show that when the air volume of condenser is set to 65% of the unit air volume and the air volume of evaporator is set to 100%, the cooling capacity of the system is 8.62 kW, the compressor power is 1.88 kW, the COP is 4.55 and the energy efficiency ratio is 1.64. In comprehensive consideration, this can not only ensure the best refrigeration performance but also can save considerable energy consumption. [ABSTRACT FROM AUTHOR]

High-temperature heat pipes have broad application prospects in terms of thermal protection of hypersonic aircraft and cooling of space nuclear reactors. In this paper, a high-temperature heat pipe heat transfer performance experimental platform is built to study the heat transfer performance of high-temperature heat pipes at different inclination angles. A heat transfer network model of high-temperature heat pipes containing NCG is established to analyze the influence of NCG. The results show that as the inclination angle of the heat pipe increases, the start-up time of the heat pipe does not change. The heat transfer performance is best when the inclination angle is 30°. High-temperature heat pipes containing NCG will reduce the effective length of the high-temperature heat pipe, increase the thermal resistance, and reduce the heat transfer performance. The high-temperature heat pipe analysis model with NCG established in this paper can be used to predict the heat transfer performance of high-temperature heat pipes containing NCG. [ABSTRACT FROM AUTHOR]

A numerical simulation of energy efficiency in commercially available double pipe heat exchangers in the market was investigated based on the Second law of thermodynamics in this paper. The effects of CO2 mass-flow rate, water mass-flow rate, pressure, CO2 inlet temperature, and water inlet temperature of the double pipe heat exchanger were considered to evaluate the energy efficiency by analyzing entropy generation, exergy destruction, and entransy dissipation. The changes of the entropy generation, the changes of exergy destruction, and entransy dissipation are similar regardless of the operating conditions. Pressure has the most significant effect on the energy efficiency of the double pipe gas cooler compared to other operating conditions but negligible on the exergy destruction. The pressure, flow rate, and inlet temperature have completely different effects on energy efficiency depending on the region. The entropy generation and entransy dissipation at y = 0 m to y = 0.05 m (y-axis is the radial direction) decrease with increasing pressure and the opposite after that. The increase of CO2 inlet temperature at y < 0.5 m is accompanied by an increase of entropy generation, exergy destruction, and entransy dissipation but this situation disappears after y = 0.5 m. Entropy generation, exergy destruction, and CO2 and water mass-flow rate are first negatively and then positively correlated with the cut-off point at y = 0.1 m. [ABSTRACT FROM AUTHOR]

High speed rail vehicles need to start the emergency traction battery system in an emergency. In order to ensure that the emergency traction battery system can be quickly started in cold conditions and ensure that the high speed railway has sufficient mileage, this paper proposes a multi-stage heating method based on flat heat pipes. The thermodynamic parameters of the power battery are obtained by simulation analysis and experimental verification. According to the thermodynamic model, the heat generation model and coupled heat transfer model of the battery are established. Different heating powers are assigned to different heating points and the total heating power is kept constant. Through the analysis results, the multi-stage heating device of the emergency traction battery system can effectively reduce the heating time under cold conditions and the temperature difference between the battery system Modules. This paper can provide reference to the design of the battery pack and the matching of the heating system. [ABSTRACT FROM AUTHOR]

The inclusion of baffles in a double pipe heat exchanger is becoming increasingly important as it improves the heat exchanger's performance. The CFD analysis is used in this paper to investigate the performance of double pipe heat exchangers with and without helical baffles on both shell tube sides. The 3-D CFD model was created in Solid Works, and the FloEFD software was used to analyze the conjugate heat transfer between the heat exchanger's tube and shell sides. Heat transfer characteristic like outlet temperature of shell and tube are investigated along with pressure drop on shell and tube side. Based on CFD results of double pipe heat exchanger with helical baffle on both shell side and tube side (Type 4) gives the better results than the other type of heat exchangers with an increased pressure drop than the others, results reveals that Type 4 outlet temperature of shell side is 8% higher and on tube side it is 5.5% higher, also pressure drop on shell side is 12% higher and on tube side it is 42% higher than the other types. [ABSTRACT FROM AUTHOR]

The objective of this research is to experimentally evaluate the specific impact of a collaborative heat sink composed of gravity heat pipes (GHP) and pulsating heat pipes (PHP) on the thermal efficiency of LED light sources. The heat sink developed in this experiment is designed to improve the thermal management system, ensuring that LED operate within a safe temperature range, which is crucial as the performance of LED is directly affected by their junction temperature. An HPPHP collaborative heat sink was employed in the experiment, where PHP served as heat dissipating fins to enhance its thermal performance, while HP handles the majority of the heat transfer tasks. The results showed that under forced convection conditions, the HP-PHP collaborative heat sink can increase the maximum thermal power capacity of LED to 192 W. The HP-PHP collaborative heat sink can reduce the substrate’s temperature to below 70.5 °C in passive mode when the LED input power does not exceed 96 W. Additional experimental results show that the minimum thermal resistance of the collaborative heat sink is 0.19 K/W under natural- convection conditions, under forced convection conditions, this value drops to 0.15 K/W, which still lower than the non-collaborative heat sink. These results demonstrate that the contact thermal resistance between HP and PHP significantly enhances the thermal performance of the collaborative heat sink. Therefore, this collaborative type of heat sink is an effective method for cooling high power LED. [ABSTRACT FROM AUTHOR]

High energy consumption is an increasingly serious problem for air conditioners in mobile communication base stations, and a composite system of the air conditioning and the heat pipe is proposed to solve the problem. The experimental data obtained in Zhengzhou City elucidated the high efficiency in energy saving. The system offers a new opportunity for wide applications in outdoor communication cabinets. [ABSTRACT FROM AUTHOR]

In response to the problems of high mass and high thermal resistance in traditional cold plate collectors, the author proposes a shaped and efficient micro-channel collector structure design for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density. The author conducted numerical and experimental studies on the laminar heat transfer in a highly efficient micro-channel shaped collector for non-normal temperature control scenarios such as high power, multiple heat sources, and highly non-uniform power density, the results show that: The relative deviation between the simulated and experimental values of the pressure drop of the micro-channel collector using perfluorotriethylamine as the working fluid is within -20%, and the relative deviation between the simulated and experimental values of the surface temperature is within +3 ° C, the predicted trend of the pressure drop and temperature field of the collector is in good agreement with the experimental values, indicating the feasibility of using numerical simulation methods for performance analysis and design optimization of 3-D printed micro-channel collectors. As the flow rate increases, the pressure drop of the collector increases approximately linearly, while the value increase of the total heat transfer coefficient gradually decreases, and increasing inlet temperature or heating power will reduce pressure drop of collector and increase total heat transfer coefficient. The influence of gravity on the pressure drop and total heat transfer coefficient of micro-channel collectors is less than 1. The straight through micro-channel collector has lower pressure drop and stronger heat transfer ability compared to the folded type collector. [ABSTRACT FROM AUTHOR]

In today's world, we are facing the problem of fossil fuel depletion along with its cost continuously increasing. Also, it is getting difficult to live in a pollution free environment. Solar energy is one of the most abundantly and freely available form of energy. Out of the various ways to harness solar energy, solar thermal energy is the most efficient as compared to photovoltaic technology. There are various cycles to convert the solar thermal energy to mechanical work, but Kalina cycle is one of the best candidates for high efficiency considerations. Therefore, the authors have proposed a novel Kalina cycle having the double separator arrangements to increase the amount of ammonia vapors at the inlet of turbine, and hence have tried to minimize the pumping power for double separator Kalina cycle by reducing the fraction of gas/vapors through it. Here, in this paper we have tried to compare ORC, Brayton cycle, and double separator Kalina cycle for low temperature heat extraction from parabolic trough collectors having arc-circular plug with slits. The effect of different operating conditions, like the number of parabolic trough collectors, mass-flow rate of fluids in different cycles, pressure difference in turbine are analyzed. The effect of these different operating conditions on different parameters like net work done, heat lost by condenser, thermal efficiency and installation cost per unit kW for double separator Kalina cycle, ORC, and Brayton cycle are studied. [ABSTRACT FROM AUTHOR]

The evaporation-capillary pumping flow of the capillary wick and the working fluid system was experimentally studied in this paper. The capillary wick used in the experiment was fiber, and the working fluid contained water, ethanol and ethanol aqueous solution with water content of 25, 50, and 75 wt.%. The results show that the capillary pumping rate with ethanol as working fluid is in range 210.0-1812.5 kg/m2s when there is no heat load added. When the heating flux is 10616, 15924, 21231, and 26539 W/m², the evaporation-capillary pumping rate is 102.5, 247.5, 390.0, and 530.0 kg/m²s, respectively. The higher the heat load power, the greater the evaporation-capillary pumping rate and the higher the final stable temperature. With the increase of heat load power, the time required to reach temperature balance becomes shorter and the temperature fluctuations after reaching temperature equilibrium become larger. The obvious temperature fluctuation has occurred when the heat flux is 26539 W/m². The evaporation capillary pumping rate corresponding to the four different concentrations of ethanol solution in the experiment gradually decreases with the increase of water content. The temperature change processes and the final equilibrium temperatures of the four working fluids are nearly the same. The differences in boiling point of the working fluids do not have much influence here. [ABSTRACT FROM AUTHOR]

A double pipe heat exchanger is significant device for many industrial applications. In this paper, an experimental study using both porous media and nanofluid to enhance heat transfer in a double pipe heat exchanger is performed. The test rig has been fabricated with inner copper pipe of 1.10 m length, 16 mm, and 14 mm outside and inside diameter, respectively. While, the outer PVC pipe is 1 m length, 31 mm, and 27 mm outside and inside diameter, respectively. The inner pipe has been filling with 3 mm diameters of steel balls porous media. The experimental tests were performed utilizing alumina nanofluid (Al2O3-water) with two volume concentrations 0.5% and 1%. The volume flow-rates are in the range of (2-5) Lpm and 10 Lpm through inner and outer pipe, respectively. It was conducted with a constant 28 °C inlet temperature of cold fluid-flow inside the inner pipe and 50 °C inlet temperature of hot fluid-flow inside the outer pipe. Results indicated that the heat transfer enhanced as nanofluid volume concentrations and volume flow-rates increase. It was observed that effectiveness increases as increase of flow-rate and nanofluid concentrations. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) is suitable to converting the normally hard to utilize low temperature thermal energies, such as geothermal energy, solar energy, and industrial waste heat, to electricity through utilizing low boiling organic working fluids. The performance of ORC system is dramatically affected by the selections of working fluid and working conditions. As a key component of waste heat recovery, the irreversible loss of evaporator also has great influence on the performance of ORC system. In this paper, we study the heat transfer performance in evaporator under the condition that the heat source parameters and pinch point temperature difference are identified. It is found that the heat transfer performance is affected by Cr, the ratio of heat capacity flow rates between the working fluid and the heat source fluid. The equivalent thermal resistance, deducing from the concept of entransy, to measure the irreversability during the heat transfer process is used. Then, the parameter κr, the ratio between latent heat and sensible heat of working fluid is defined. With the parameters Cr and κr, we investigate the relationship between the heat transfer and irreversible loss, and deduce the condition that maximum heat transfer and minimum equivalent thermal resistance occurs. Finally, a calculation method is established to choose the optimum working fluid and the evaporation condition. [ABSTRACT FROM AUTHOR]

Lithium heat pipe has broad applications in heat pipe cooled reactors and hypersonic vehicles due to its ultra-high working temperature which is around 1700 K. In this paper, a lithium heat pipe based experimental facility has been designed to test the heat transfer performance of the lithium heat pipe. A simplified mathematical model of heat pipe has been implemented into a CFD approach, which is used to verify the design of lithium heat pipe and its experimental facility. Results showed that the CFD approach is in good agreements with some well-known existing models and experimental data, and deviation between the results is within 5% range. The adjustment range of mixed gas thermal resistance and cooling water flow rate was obtained by analyzing the effects of different cooling conditions on the performance of the experimental facility. It is necessary to ensure the cooling water flow rate is above 0.11 Lph to prevent water boiling when the heating power is 10 kW around, and the optimal proportion of helium is 70-90%. The operation characteristics of the lithium heat pipe under unsteady-state with varying heating power were simulated numerically. The results show that the proportion of helium must be less than 60% for normal operation of the lithium heat pipe. This work provides a reference and numerical verification for the design of lithium heat pipe based experimental facility, which can be used to reveal the heat transfer mechanisms of the lithium heat pipe during the experiment. [ABSTRACT FROM AUTHOR]

To increase the efficiency, elliptical tubes are often used in cross-flow heat exchangers. For these kinds of heat exchangers the flow field in the tubes exhibits irregularities. Therefore, various flow regimes can be observed: the turbulent, the transitional, and even the laminar one. Therefore, applying typical turbulence models for numerical calculations may cause significant errors, when flow in the heat exchanger tubes is in the transitional or laminar regime. Hence, the average values of flow velocities and temperature in heat exchanger tubes can be calculated incorrectly. The paper presents empirical verification of applying the basic two-equation turbulence models for a transitional flow of water in an elliptical pipe of a heat exchanger. [ABSTRACT FROM AUTHOR]

Heat pipe is a two-phase heat transfer device with high effective thermal conductivity and transfer huge amount of heat with minimum temperature gradient in between evaporator and condenser section. This paper objective is to predict the thermal performance in terms of thermal resistance, R, and heat transfer coefficient, h, of screen mesh wick heat pipe with deionized water-TiO2 as working fluid. The input process parameters of heat pipe such as heat load, Q, tilt angle, θ, and concentration of nanofluid, ϕ, were modeled and optimized by utilizing response surface methodology with MINITAB-17 software to attain minimum thermal resistance and maximum heat transfer coefficient. The minimum thermal resistance of 0.1764 °C per W and maximum heat transfer coefficient of 1411.52 W/m² °C was obtained under the optimized conditions of 200 W heat load, 57.2° tilt angle, and 0.159 vol.% concentration of nanofluid. [ABSTRACT FROM AUTHOR]

A comparison of heat transfer efficiency between the heat pipe and tube bundles heat exchanger is made based on heat transfer principle and the analysis of thermal characteristics. This paper argues that although heat pipe has the feature of high axial thermal conductivity, to those cases where this special function of heat transfer is unnecessary, heat pipe exchanger is not a high efficient heat exchanger when it is just used as a conventional heat exchanger in the industrial fields. In turn, there are some deficiencies for heat pipe exchanger, such as complicated manufacturing process, critical requirements for manufacturing materials, etc. which leads to a higher cost in comparison to a tubular heat exchanger. Nonetheless, due to its diverse structural features and extraordinary properties, heat pipe exchanger still has wide applications on special occasions. [ABSTRACT FROM AUTHOR]

A single-bed finned tube adsorption refrigeration system model was established to compare the adsorption characteristics of three metal organic framework materials, MIL-101(Cr), MIL-101(Cr)/CaCl2-10%, MIL-101(Cr)/CaCl2-20%. The change of material properties under different thickness/length/number of fins was characterized, and the most suitable adsorption bed structure for different materials was obtained. The results show that the number of fins has little effect on the COP and specific cooling power of the material in the system. Choosing thinner fins can improve the COP of the system. With the increase of fin height, the COP showed a trend of increasing first and then decreasing. The three materials, MIL-101(Cr), MIL-101(Cr)/CaCl2-10%, MIL-101(Cr)/CaCl2-20%, obtained the highest COP when the fin heights were 50 mm, 60 mm, and 70 mm, respectively. The maximum specific cooling power was obtained when the fin heights were 20 mm, 60 mm, and 70 mm, which were 21.7 W/kg, 90.1 W/kg, and 174.5 W/kg, respectively. The height of the fin has a great influence on the performance of the system. When designing the adsorption bed, the appropriate fin height should be selected for the specific adsorbent. [ABSTRACT FROM AUTHOR]

Natural gas must be preheated prior to pressure reduction in city gate stations. Indirect water bath heaters are employed in city gate stations for preheating, consume a considerable amount of natural gas for the process. This type of heater has a low efficiency therefore a significant amount of energy is wasted. Due to the high capacity of thermosyphon heat pipe, its utilization in city gate stations heater were investigated experimentally in this paper. For this purpose, a heater set-up was manufactured and its thermal efficiency was calculated. The thermosyphon heat pipe were then designed, manufactured, and utilized between the fire tube and the gas tube. Further the type of working fluid and the range of filling ratio were discussed and the most effective state was suggested. Moreover, the thermal efficiency of the heater in the presence of thermosyphon heat pipe was investigated. The obtained results showed that the thermal efficiency of the heater improved up to 13% with the addition of thermosyphon heat pipe. The most effective state of thermosyphon heat pipe was associated with the water as working fluid with 20% filling ratio in the front route and methanol as working fluid with 30% filling ratio in the back route of the fire tube. [ABSTRACT FROM AUTHOR]

The evaporation of a drop deposited on a heated substrate is a complex process, which combines several phenomena such as the Marangoni effect, mass and thermal transfers, etc. We developed, in this paper, a mathematical model and a numerical simulation code used to carry out an in-depth study about the evaporation of a drop deposited on a heated substrate surrounded by air. This numerical study was supported by experimental work. The numerical findings obtained showed the existence of a condensation phenomenon for certain configurations. At the beginning of the experiment, the evaporation started at the triple point. However, a local region of the interface remained relatively cold. In this region, the concentration gradient (Cv, Csat) directed from the liquid-gas interface to the air resulted in condensation of water steam. Although this phenomenon is temporary and visible only at the start of evaporation process, its study makes it possible to better understand and optimize the evaporation kinetics. [ABSTRACT FROM AUTHOR]

In this paper, the experimental performance of a SS304 heat pipe under natural and forced convection modes using two different wick mesh sizes is reported. Deionised water was used as a working fluid with different heat inputs. The wick material is made up of SS303 with two mesh sizes (such as, 100 and 200 mesh). The heat pipe was positioned at three orientations (such as, horizontal, inclined, and vertical). During experiments, the ambient temperature was maintained at 30 ± 2 °C. The results showed that the heat pipe at an inclined position of 45° has about 71% higher heat transfer coefficient with minimum thermal resistance when compared to the horizontal and vertical positions. Moreover, the results confirmed that, the heat pipe using wick with 200 mesh specification at inclined position is an optimal configuration when compared to other configurations. [ABSTRACT FROM AUTHOR]

Air-cooled condensers in thermal power plants have recently become increasingly popular. Besides all the advantages they have, like no demands for water supply on the plant site and no need for taking care of environmental regulations, they also have some serious disadvantages. One of the biggest disadvantages air-cooled condensers do have is precisely the nature of the Earth's atmosphere being their low temperature reservoir. Low density and low heat capacity of the air as the cooling medium combined with extremely stochastic behavior of the atmosphere itself put some serious challenges in front of the air-cooled condenser's proper and steady functioning. In this paper, the operating parameters of the air-cooled condenser in the chosen thermal power plant were investigated to gain a clearer insight into the influence of the atmospheric changes on its entropy generation and consequently on its efficiency. Also, the acquired results were further proposed as a starting point for potential optimization of the process inside the device. [ABSTRACT FROM AUTHOR]

In this paper, a heat pipe evacuated tube solar collector has been investigated both theoretically and experimentally. A detailed theoretical method for energy and exergy analysis of the collector is provided. The method is also evaluated by experiments. The results showed a good agreement between the experiment and theory. Using the theoretical model, the effect of different parameters on the collector's energy and exergy efficiency has been investigated. It is concluded that inlet water temperature, inlet water mass flow rate, the transmittance of tubes, and absorptance of the absorber surface have a direct effect on the energy and exergy efficiency of the heat pipe evacuated tube solar collector. Increasing water inlet temperature in heat pipe evacuated solar collectors leads to a decrease in heat transfer rate between the heat pipe's condenser and water. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer analysis for an air-air heat exchanger was experimentally carried out to find its thermal performance and effectiveness. Air-air heat exchanger equipped with finned heat pipes was considered for the experimentation. Mass flow rate of air was considered in between 0.24 to 0.53 kg/s. The temperature at the condenser side of the heat pipe heat exchanger was kept constant at around 23 °C and at the evaporator part it was varied from 88 to 147 °C. The performance of heat pipe heat exchanger was evaluated at different mass flow rate of air, in terms of effectiveness and compared with its corresponding value found by theoretical analysis. [ABSTRACT FROM AUTHOR]

This study used aluminum powder as a raw material to fabricate a wick for loop heat pipes by the powder metallurgy method and took advantage of the excellent corrosion resistance, low density and low cost of aluminum. The average pore diameter, porosity and permeability of the aluminum wicks were 9 µm, 47.65%, and 2.1 × 10-13 m-2, respectively. Then, to verify the feasibility of the aluminum wick, it was installed into a loop heat pipe to test the heat transfer performance. The experimental results showed that the loop heat pipe could transport a heating load of 130 W with a thermal resistance of 0.04 K/W under horizontal condition. A steady-state loop heat pipe mathematical model was developed, and the numerical results were compared with the experimental data. The results show that the model data are consistent with the experimental data, which means that Al wicks are suitable for use in the case of a high heating load and light weight. [ABSTRACT FROM AUTHOR]

This study aims to explore the dryout characteristics of two-phase closed thermosiphon. It involves the design and experimentation on low-liquid filled heat pipes. We investigated the effects of different fill ratios, heating water temperatures, and cooling water flow rates on the start-up characteristics of two-phase closed thermosiphon. Based on the network model, we proposed an analytical expression for the thermal resistance, R, of two-phase closed thermosiphon, and provided an explanation of the various thermal resistance components. This research expands our understanding of dryout and provides insights for optimizing heat pipe design and addressing heat conduction issues with low fill ratios. [ABSTRACT FROM AUTHOR]

This paper deals with development and studies of a trapezoidal axial grooved nitrogen heat pipe. A special liquid nitrogen cryostat has been designed and developed for evaluating the performance of heat pipe where the condenser portion is connected to the cold sink externally. Experiments have been performed on the heat pipe as well as on an equivalent diameter copper rod at different heat loads. The steady-state performance of the heat pipe is compared with that of copper rod. [ABSTRACT FROM AUTHOR]

This paper discuses the use of self rewetting fluids in the heat pipe. In conventional heat pipes, the working fluid used has a negative surface-tension gradient with temperature. It is an unfavourable one and it decreases the heat transport between the evaporator section and the condenser section. Self rewetting fluids are dilute aqueous alcoholic solutions which have the number of carbon atoms more than four. Unlike other common liquids, self rewetting fluids have the property that the surface tension increases with temperature up to a certain limit. The experiments are conducted to improve the heat transport capability and thermal efficiency of capillary assisted heat pipes with the self rewetting fluids like aqueous solutions of n-butanol and n-pentanol and its performance is compared with that of pure water. The n-butanol and n-pentanol are added to the pure water at a concentration of 0.001 moles per liter to prepare the self rewetting fluids. The heat pipes are made up of copper container with a two layered stainless steel wick consisting of mesh wrapped screen. The experimental results show that the maximum heat transport of the heat pipe is enhanced and the thermal resistances are considerably decreased than the traditional heat pipes filled with water. The fluids used exhibit an anomalous increase in the surface tension with increasing temperature. [ABSTRACT FROM AUTHOR]

Objectives of this paper are to investigate the effects of dimensionless numbers on the thermal performance, and to establish correlations to predict the thermal performance of the vertical and a horizontal closed-loop pulsating heat pipe. The heat pipes were made of long copper capillary tubes with 26 meandering turns and both the ends were connected together to form a loop. R123, R141b, acetone, ethanol, and water were chosen as variable working fluids with a constant filling ratio of 50% by total volume. The inlet temperature of the heating medium and the adiabatic section temperature were constantly controlled and maintained at 80 °C and 50 °C, respectively. The thermal performance was represented in terms of the Kutateladze number. It can be concluded that when the Prandtl number of the liquid working fluid, as well as the Karman number, increases, the thermal performance increases. On the other hand, when the Bond number, the Jacob number, and the aspect ratio increase, the thermal performance decreases. These effects of the dimensionless numbers on the thermal performance are valid for both the heat pipes, except in the case of Bond number which has no effect on the thermal performance as far as the horizontal heat pipe is concerned. Moreover, correlations to predict thermal performance have been successfully established. [ABSTRACT FROM AUTHOR]

The icing events for the wind turbine blade is the key problem in the low temperature conditions. Heating is considered to be the most efficient approach to prevent from the ice formation on the turbine blade surface. However, this kind of method consumes a certain amount of energy. In this present study, an anti-icing method, using the heat pipe technology, is proposed to prevent from icing on the blade surface, and the anti-icing energy is from the waste heat generated during the operation of a wind turbine, which can reduce the assumption of the energy. The researches on the anti-icing temperature characteristics of the test model, based on the heat pipe anti-icing method, are carried out in an icing wind tunnel combining with the low natural temperature. The effects of the wind speed and heat source temperature on the heat transfer of heat pipes are investigated. The icing distribution and the temperature change of the anti-icing process of an airfoil with NACA0018 are explored, and the variation of the icing thickness of the airfoil with icing time, under the different heat source temperature conditions, is analyzed. The results indicate that the blade surface temperature, which is lower than 0 °C, is more beneficial to the heat transfer of the heat pipe, and the ice prevention, based on the heat transfer of the heat pipe, can achieve a better anti-icing effect. [ABSTRACT FROM AUTHOR]

For the sake of comprehend the influence of locally enhanced heat dissipation of the polar on Li-Ion power batteries, coupling the thermal effect of anode and cathode, the heat generation model of Li-Ion battery with different discharge magnification is obtained. Based on this model, the discharge process simulation analysis of the single battery is carried out and compared with the experimental results. The experiment results show that battery polarity heat effect has great influence on the temperature field distribution of the battery. Then, a locally enhanced heat dissipation structure is set up near the polar region and a comparative experiment is carried out by changing the discharge rate. Although the heat pipe can only slightly improve the discharge capacity of Li-Ion battery by enhancing the heat dissipation capability of polarity, the heat generated under low discharge rate can be reduced by using the heat pipe with low emission rate, the heat generated by the polar region can be effectively and timely exported to reduce the temperature of the polar region and it can greatly reduce the overall temperature of the battery. Then, according to the thermal characteristics and the results of locally enhanced heat dissipation analysis, a new battery module is designed and simulated. The prototype is completed and tested. The results show that this method can effectively reduce the temperature rise and temperature difference of the battery module by using locally enhanced heat dissipation structure. Finally, combined with the simulation and the experimental results, some useful suggestions are put forward for the design and manufacture of battery modules and battery boxes. [ABSTRACT FROM AUTHOR]

Testing of loop heat pipes showed that the heat-load dependence of the operating temperature was not always unambiguous. It may have hysteresis phenomena. The temperature hysteresis had a certain relationship with previous history of the power variation, and also related to the initial parameters of the loop heat pipes. It has been found that the temperature hysteresis of the loop heat pipes was related to the gas-liquid distribution in the compensation chamber which depended on the interaction between heat leak of evaporator and the reflux liquid from condenser. The temperature of the loop heat pipes evaporator rose with the gas phase in the compensation chamber increased. [ABSTRACT FROM AUTHOR]

Prospects for low-cost utilization and storage of solar energy are promising. In this study, the change of shallow geo-temperature was monitored, and the influence of solar radiation on shallow geo-temperature was discussed. Three series of field experiments on heat transfer of aboveground pipes were designed, and the variations of water temperature in the aboveground pipes were also monitored. According to the experimental data, the relevant factors affecting the water temperature inside the pipe (such as solar radiant intensity, pipe's material, pipe's spatial location, heat-accumulating wall and so on) were analyzed. Based on the field test, a 3-D model of aboveground pipe heat transfer was established to verify and temperature prediction was carried out. The results show that the water temperature in the pipe is most significantly affected by solar radiation, and is also related to the color of the pipe and its spatial position. The water temperature of galvanized steel pipe wrapped with black plastic film is the highest under solar radiation, and the optimum distance between the pipe and the heat-accumulating wall and the Earth's surface is, respectively, 0.90~1.25 times of the outer diameter of the pipe. The way the pipe is covered has a great influence on the water temperature inside the pipe. When the black and polyethylene pipe covered with the white plastic film is in the best spatial position, the highest heat of the three series of tests is obtained, and the difference between the water temperature inside the pipe and the atmospheric temperature reaches 36.3 °C. [ABSTRACT FROM AUTHOR]

In the present study thermal performance of heat pipe were validated experimentally. Circular, auxiliary grooved heat pipe were charged with graphene nanofluid with different concentrations (0.6%, 0.75%), orientation, and flow rate are fixed as 90° and 100 mL per minute. All the experimental results are validated and compared to base fluid (deionized water). From the experimental results, increasing nanofluid concentrations increases thermal performance and decreases thermal resistance. Although the wall temperature of heat pipe higher with graphene/water nanofluid than base fluid. Thus, graphene nanoparticles are suitable for heat pipe to increase their performance and capillary action. [ABSTRACT FROM AUTHOR]

A correction for the article "Performance and Impact of Cryogenic Pulsating Heat Pipe Using a Different Number of Turns and Helium Gas" is presented, which is published in the previous 2022 issue of the periodical.

At temperatures below 60 °C, the best way to use geothermal sources for heating is to use heat pumps. A heat pump can provide air conditioning for a residential, commercial, etc., all year round by heating in winter and cooling in summer using a low temperature source. Also, a heat pump can be used for water distillation through evaporation. The ground source heat pump with a high COP and low temperature thermal energy sources is one of the best technologies for using RES. In the present study, the effects of changing ambient temperature and soil temperature on a heat pump's overall COP and energy efficiency are investigated using a simulated geothermal heat pump with an economizer. The system's thermodynamic simulation is first performed in the engineering equation solver software for R134a and R513a working fluids. The exergy destruction of different components for both working fluids was calculated and displayed as a figure. The COP of the heat pump for R134a working fluid is equal to 3.916, equal to 3.729 for R513a working fluid, which indicates that R134a fluid has about 5% better performance. The COP of the system for R134a working fluid is equal to 3.662, which is equal to 3.504 for R513a working fluid, which indicates that R134a fluid has about 4.5% better performance. [ABSTRACT FROM AUTHOR]

The need for energy and material savings, as well as environmental concerns, have helped to increase the demand for high efficiency heat exchangers in the modern era. In practice, a heat exchanger or the direct ejection of the hot working fluid is used to recover the waste heat from a heat engine or thermal power plant into the environment. Waste heat of a heat engine or power plant is recovered to the environment via a heat exchanger or by direct ejection from the hot working fluid. In many situations, waste heat recovery removes or greatly reduces the necessity for additional fuel energy input to achieve this goal. The double pipe heat exchanger equipment is taken in this research, heat from engine exhaust recovers due to its superior qualities. The design characteristics of the heat pipe will be changed in order to increase overall efficiency by studying the concepts of various authors. Different design parameters for a double pipe heat exchange system as well as different working fluid-flow rates are tested with the suggested device. Additionally, ANSYS performs CFD for the proposed heat exchanger system in order for the results to support the experimental findings. [ABSTRACT FROM AUTHOR]

A heat pipe solar collector system for winter heating is investigated both experimentally and theoretically. The hourly heat collecting capacity, water temperature and contribution rate of solar collector system based on Zhengzhou city typical sunshine are calculated. The study reveals that the heat collecting capacity and water temperature increases initially and then decreases, and the solar collector system can provide from 40% to 78% heating load for a 200 m² villa with in Zhengzhou city from November to March. [ABSTRACT FROM AUTHOR]

To study energy recovery from low temperature wastewater during industrial production, a water-boiling heat transfer experimental device was built. A casing evaporator with a length of 1450 mm, an inner tube diameter of 30 mm, and an annular space gap of 14.2 mm is taken as the main research object. The boiling heat transfer characteristics of water in the annular tube area of the casing evaporator were experimentally studied by adjusting the inlet temperature (60-85 °C) of hot water and the pressure in the annular tube (12.1-57.6 kPa). The results show that, as the pressure of the system decreases, the boiling phenomenon in the annular tube becomes more intense and the convective heat transfer coefficient increases. The boiling flow and average surface convective heat transfer enhancement rates, β, were 2.2 and 1.5 when an initial pressure of 1 kPa was used. When the flow rate of the working medium in the annular tube was 1.69 kg·m²/s, the convective heat transfer coefficient gradually increased with the temperature and then stabilized when the inlet temperature reached between 80 °C and 85 °C. These results reveal the characteristics of boiling-water heat transfer in an annular tube and aid in the design of heat pipe systems for waste-heat recovery. [ABSTRACT FROM AUTHOR]

The use of new generation low GWP refrigerants in cooling systems is becoming increasingly common due to thermal performance and less environmental impact. In this study, the thermal performance of the new generation R290 refrigerant and the old generation R404A refrigerant in the same cooling system were investigated experimentally and numerically. The thermal performance values of both gases were compared, provided that the temperature of the cold room cooled by the vapor compression cooling system drops to 0 °C. -5 °C, 0 °C, 5 °C evaporator temperatures and 25 °C, 30 °C, 35 °C condenser temperatures were used as operating parameters. The experimental results revealed that the highest COP values in the system for R290 and R404A were 4.68 and 3.94, respectively. An average of 9.38% increase in cooling capacity was detected with R290 compared to R404A refrigerant. In the numerical analysis part of the study, the evaporator surface temperature and air velocity distributions of both refrigerants in the cold room were shown numerically by using ANSYS FLUENT 19.1. As a result of the study, it was stated that R290 had higher thermal performance than R404A, according to both experimental and numerical analysis results. [ABSTRACT FROM AUTHOR]

The influence of void ratio on phase change of thermal storage unit for heat pipe receiver under microgravity is numerically simulated. Accordingly, mathematical model is set up. A solidification-melting model upon the enthalpy-porosity method is specially provided to deal with phase changes. The liquid fraction distribution of thermal storage unit of heat pipe receiver is shown. The fluctuation of melting ratio in phase change material canister is indicated. Numerical results are compared with experimental ones in Japan. The results show that void cavity prevents the process of phase change greatly. Phase change material melts slowly during sunlight periods and freezes slowly during eclipse periods as void ratio increases. The utility ratio of phase change material during both sunlight periods and eclipse periods decreases obviously with the improvement of void ratio. The thermal resistance of void cavity is much higher than that of phase change material canister wall. Void cavity prevents the heat transfer between phase change material zone and canister wall. [ABSTRACT FROM AUTHOR]

The wettability patterned micro structure (WPMS) arrays by laser etching are proposed to enhance the thermal performance of wickless thin vapor chamber (TVC). The effects of filling ratio and inclination angle on the thermal performance of wickless TVC with WPMS are investigated, and the untreated bare wickless TVC is also studied as comparison. The results show that the wickless TVC with WPMS can work stably at filling ratio ranging from 19.0% to 42.8%, and the optimum filling ratio is 42.8%. The maximum heat transfer capacity is 190 W with the lowest thermal resistance of 0.146 K/W. Since WPMS is superhydrophilic, it can provide nucleate sites to promote early onset nucleate boiling and capillary pressure to enhance the liquid supply. Thus, the wickless TVC with WPMS shows 10.98% lower thermal resistance and 18.75% higher maximum heat transfer capacity than that of the untreated bare wickless TVC. In addition, the thermal performance of wickless TVC with WPMS is insensitive to the orientation of the TVC. [ABSTRACT FROM AUTHOR]

To promote energy-saving potentials of the energy recovery unit under all-year conditions, a composite system combining pump-driven loop heat pipe with heat pump was firstly proposed, and the mathematical models were established. The operating characteristics of the composite system were studied in the whole year and compared with the traditional heat pump heat recovery system. The results show that the heating capacity of the composite system is in line with the heating load in winter. Compared with the traditional heat pump system, the composite system has higher energy efficiency ratio and lower deviation degree of temperature effectiveness in the whole year. The heat pump composite pump-driven loop heat pipe heat recovery system is generally superior to similar system reported in literatures, which indicates that it can replace heat pump system in buildings ventilation. [ABSTRACT FROM AUTHOR]

This study's primary purpose is to optimize the multistage refrigeration system with statistical methods. Taguchi optimization and ANOVA methods were applied to statistically determine the effects of components on system performance. The best operational conditions were defined for the maximum COP and exergy efficiency. Critical parameters have been determined to maximize the system's performance. The evaporator temperature was defined as the most vital parameter (46.32%), and it is followed by condenser temperature (32.65%) for the maximum COP. The most important two parameters are determined as evaporator temperature with 29.14% and condenser temperature with 20.34% for maximum exergetic performance. As a result of 27 tests, the highest COP of the system was calculated as 2.67 and exergy efficiency as 55.22%. By using the optimum levels determined by Taguchi, it was ensured that the system's COP was increased to 3.326 and its exergy efficiency to 71.23%. The ANOVA analyses indicate that the results' confidence level is relatively high, to be 99.9%. Another parameter examined in this study is the inter-stage level determination method and its effect on system performance. The method of determining the optimum inter-stage level may vary according to the objective function and system conditions. [ABSTRACT FROM AUTHOR]