Heat Transfer Fluid Circulation Research Articles

Performance Evaluation of Novel Heat Pipe‐Assisted Thermal Storage System with Parabolic Trough Solar Collector Using Nanofluid

The experimentation has been performed in Central Indian climatic conditions to investigate the performance of the novel heat‐pipe‐assisted thermal storage system with parabolic trough solar collector and nanofluid. The present thermal energy storage system is nanofluid (Al2O3/soybean oil) based and the eutectic mixture of KNO3 and NaNO3 (nitrate salt) in the molar ratio of 40:60 has been used as phase change material to store the heat energy. The system is based on the natural circulation of heat transfer fluid (thermo‐syphon) and the receiver to arrest the solar radiation is parabolic trough solar collector using an evacuated tube. The major and novel incorporation in this system is the heat pipe insertion in the storage unit of the system, which provides better heat transfer, and hence the improved storage capacity is achieved. The final remark of this study has been done with the comparison of the present system with the existing and similar kinds of thermal energy storage systems. For the same charging cycle time and same climatic conditions, the compared value of specific heat storage capacity is 67% higher as compared to the average value of other considered systems.

Experimental investigations on a sensible heat thermal energy storage system towards the design of cascaded latent heat storage system

ABSTRACT In the present work, a system comprising cylindrical vertical type sensible-based thermal energy storage (TES) tanks integrated with external type compound parabolic concentrating (XCPC) solar collectors and heat loading device was designed, fabricated, constructed, experimented, and analyzed. The XCPC solar collector system transfers the solar energy to charge the insulated TES tanks through heat transfer fluid circulation and discharge the energy to the selected application. The primary objective of the present research is to study the performance and stratification effects during the charging and discharging cycles through various parameters to select the suitable phase change materials (PCMs) for the proposed cascaded latent heat storage (CLHS) system. Further, experiments were conducted under simultaneous and sequential modes of charging and discharging processes. The performance analysis of the overall system on a time-average basis (0.125 hr) was carried out. The results revealed that simultaneous mode would help to collect more energy from the solar collector, and it increases the cumulative energy stored in the tank and the average charging efficiency of the tank. The same was also ensured from the stratification performance parameters, such as stratification number, Richardson number, and mix number. The higher stratification achieved in both modes revealed that the CLHS system with three different PCMs of phase change temperatures of 70°C, 63°C, and 53°C, located at three different zones, will enhance the performance of the storage system. The results are highly beneficial for practicing engineers toward designing the CLHS system integrated with solar collector for any application.

ПОРІВНЯЛЬНИЙ АНАЛІЗ ГЕОТЕРМАЛЬНОГО ПОТЕНЦІАЛУ ЗАКРИТИХ ШАХТ ДОНЕЦЬКОГО ТА РУРСЬКОГО ВУГІЛЬНИХ БАСЕЙНІВ

Purpose. This study aims to perform a comparative analysis of the geothermal potential for closed mines in the Donbas and Ruhr regions in terms of the operation efficiency of geothermal systems of various types. Methods. The proposed approach includes ranking closed mines in the Ruhr (Germany) and Donetsk (Ukraine) coalmining areas according to the major parameters of geothermal system efficiency that includes the maximum and net thermal capacity, heat pump coefficient of performance COP, energy efficiency of heat recovery. The last parameter, introduced by the authors earlier, is defined as the ratio of the produced thermal energy to the thermal equivalent of the electricity required for running the heat pumps and the heat transfer fluid circulation. Results. The average expected thermal capacity of open loop geothermal systems at mine drainages in Germany was found higher than the similar indicator for the selected mine drainages in Ukraine, with slightly lower indicators of mine water heat recovery compared to the drainages in the Donbas. The average expected thermal capacity of closed loop geothermal systems based on coaxial probes at the current water level in the mines of two areas is estimated to be within the range of 30-34 kW, and the average indicators of geothermal heat recovery in the mines of two areas differ by no more than 5%, while the mines in the Donbas demonstrate a higher dispersion of calculated indicators. Similarity of operating conditions and energy efficiency indicators of geothermal systems evaluated for two areas indicates the feasibility and the potential of operating such systems in Ukraine. Scientific novelty. The approach to ranking of closed mines according to their geothermal potential based on parameters of mine water heat recovery efficiency has been substantiated and implemented. The developed approach enables identifying the promising sites to install geothermal systems of various types at inactive mines. Practical significance. The proposed approach allows to preliminarily evaluate the ranges of indicators for the effective operation of geothermal systems of various types with identification of the most promising areas for further detailed technical and economic justifications.

Characteristics analysis of an exhaust thermoelectric generator system with heat transfer fluid circulation

Low heat transfer performance in the exhaust channel limits the thermoelectric conversion efficiency of the internal combustion engine exhaust thermoelectric generator. Enhanced heat transfer of exhaust channel improves the thermoelectric performance of the generator, though with an increase in exhaust back pressure. A new type of thermoelectric generator with heat transfer fluid circulation is proposed. A heat transfer fluid replaces the exhaust after heat exchange with the exhaust into the generator. It is possible to improve the thermoelectric performance of the system, counting on the high heat transfer coefficient of the heat transfer fluid in the generator without changing the exhaust channel. A mathematical model of the novel system is constructed, considering the system structure, resistance power consumption, temperature dependence of the physical properties of the module. The influence of structural parameters and heat transfer fluid parameters on thermoelectric performance are analyzed using this model. It is found that the peak net output power of the new generator can be increased by 77.5 % compared with the traditional generator, while the number of modules can be reduced by 83.2%. Therefore, an optimal exhaust heat exchanger configuration is obtained to maximize the net output of the system. In addition, as the heat transfer fluid flow rate increases, the net output power goes up and then down, an optimal heat transfer fluid flow rate can be obtained. The results also give technical guidance on the design and operation criteria of the thermoelectric generator.

Thermal Energy Storage Using Horizontal Shell-Tube Heat Exchanger: Numerical Investigation on Temperature Variation of HTF

Abstract- Latent Heat Thermal Energy Storage (LHTES) is a method to store thermal energy in a Phase Change Material (PCM). Due to the higher energy density, the efficiency of the size of the container might happen. However, the thermal energy storing (charging) time on LHTES is considerably inefficient. The increasing velocity of HTF was conducted using a modified fin and encapsulation to improve the charging time. Similarly, with this motivation, numerical analysis with modified density modelling was conducted to investigate the effect of temperature of heat transfer fluid (HTF) on PCM. This investigation was validated with shell-tube geometry experiment. The experiment set-up was divided into two parts where shell part used as circulation of Heat Transfer Fluid (HTF) and tube part containing PCM (RT-52). This simulation carried out using ANSYS FLUENT 17 to observe evolution on radial-axial temperature, melting time, melting contour and natural convection as the effect of HTF temperature variation. The natural convection got higher and induced the circulation in tube as well. Thus, the melting area was much more at the top cylinder. Melting time decreased significantly as the rising of HTF temperature.

MODELING OF AN ADVANCED HEAT EXCHANGE UNIT WITH MICROCHANNELS FOR A COMBINED PHOTOENERGY SYSTEM

Purpose. Mathematical modeling of the heat exchange unit main parameters for photoenergy system based on general models with forced circulation of heat transfer fluid. Methodology. To determine the coefficient of heat transfer at a given coolant temperature and surfaces temperature necessary to determine the temperature gradient in the wall of the heat exchanger. Temperature gradients can be determined by solving the equation of energy, which depends on the distribution of the flow rate in the flow. In general, a solution of convective heat transfer fluid to flow along the plane comes to solution of the system of differential equations. Results. In the paper features of the selection of theoretical basis and mathematical modeling of thermal processes in the heat exchange unit for combination photoenergy system are presented. As a result of the simulation conducted we improve and develop high-efficiency heat exchange unit with microchannels. Testing of the proposed unit proved its high efficiency through the implementation of turbulent flow of coolant with heat transfer coefficient at 18 kW/(m 2 ×K). Analytical testing of the heat exchanger allowed showing that heat exchanger unit provides a stable operating temperature at less than 50 °C with the coolant flow rate is less than 0.3 m/s. Originality. Novelty of the proposed heat exchanger is in the optimal design of microchannels to improve the heat transfer coefficient. Practical value. The use of this heat exchanger will improve the quality and uniformity of cooling solar panels and reduce energy costs for circulation of fluid.

Studying Issues of Compressed Gas Energy Recovery

Background/Objectives: One of promising researches to increase efficiency of oil and gas production is connected with compressed gas energy recovery. Potential gas energy may be converted to thermal energy or electric power using special gas turbines. Methods: The known methods for converting compressed gas energy into thermal or electric energy involve the use of impulse and reaction turbines. But high price for turbines hinders works on the use of compressed gas energy. Development of technologies for compressed gas energy recovery should be aimed at creating simpler and cheaper equipment. When developing new turbines for thermal generator, options using looped blades have been analyzed. Findings: At this stage of research and development work we have developed a new thermal generator, equipped with a gas turbine and a heat transfer fluid circulation loop. Looped blades were used in the turbine creation. A distinctive feature of the created turbine is that the working gas flow is directed along a plane that is perpendicular to the turbine rotation axis. In the known turbines, equipped with looped blades, the working gas flow is directed along the turbine rotation axis. Application of these results brings about the opportunity for creating simpler and less expensive power plants operating by means of compressed gas energy for a wider power range - from a few kilowatts to several hundred kilowatts. Application/Improvements: The basic field of application for the created plant is associated with the production facilities of oil and gas industry. However, individual results can be used in other industries, for example, when creating machinery for sea and air transport, where weight reduction and improving the reliability of the equipment is particularly relevant.

METHOD FOR DETERMINING OF CAPACITY OF FLAT-PLATE SOLAR COLLECTOR WITH NATURAL CIRCULATION OF HEAT-TRANSFER FLUID IN THE URAL REGION

The article describes a model for calculating capacity of a flat-plate solar collector with natural circulation of heat-transfer fluid, depending on the basic constructive, thermal and climatological parameters. This article estimates energy and exergy efficiency of the system for the conditions of the Ural region as well. The proposed method can be used for quantitative and qualitative assessment of power and exergy generation by the flat-plate solar collector with natural circulation of heat-transfer fluid on the basis of publicly available data for any region.

An Open Source Low-Cost Wireless Control System for a Forced Circulation Solar Plant

The article describes the design phase, development and practical application of a low-cost control system for a forced circulation solar plant in an outdoor test cell located near Milan. Such a system provides for the use of an electric pump for the circulation of heat transfer fluid connecting the solar thermal panel to the storage tank. The running plant temperatures are the fundamental parameter to evaluate the system performance such as proper operation, and the control and management system has to consider these parameters. A solar energy-powered wireless-based smart object was developed, able to monitor the running temperatures of a solar thermal system and aimed at moving beyond standard monitoring approaches to achieve a low-cost and customizable device, even in terms of installation in different environmental conditions. To this end, two types of communications were used: the first is a low-cost communication based on the ZigBee protocol used for control purposes, so that it can be customized according to specific needs, while the second is based on a Bluetooth protocol used for data display.