Showing papers on "Heat capacity rate published in 2020"

Numerical study of melting and solidification in a wavy double-pipe latent heat thermal energy storage system

Abstract: The objective of this paper is to develop the influences of channel waviness on the performance of a latent heat storage system during phase change mechanism. The heat exchanger is a vertically oriented double pipe where the heat transfers to/from the PCM in the annulus by moving the water in the inner tube. Various wavelengths, as well as wave amplitudes, are examined at various fluid Re and water temperatures (Tin) to find the effects of channel waviness on different aspects of melting/solidification time, pressure drop, pumping power and exchanged heat rate. Increasing Re, Tin and amplitude of wavy wall improves the system performance during melting and solidification mechanisms. Besides, it is found that there is an optimum dimensionless wavelength of 0.2 for achieving the minimum melting and solidification times as a result of maximum heat exchanged between the water and PCM. Furthermore, the waviness has an almost negligible effect on the pumping power which is reduced for the dimensionless wavelengths higher than 2.0. In the best scenario, the required time to melt and solidify the PCM reduces by almost 28.6% and 57.63%, respectively, using wavy channels compared with the smooth wall case.

Natural convection energy recovery loop analysis, part I: energy and exergy studies by varying inlet air flow rate

Abstract: The natural convection energy recovery loop is analyzed experimentally in different airflow rates. The system was introduced previously as a prototype of the standalone air conditioning system and its transient and steady performance was verified. As a new generation of energy recovery tool between the building return and fresh air, the system is rated from the viewpoints of energy and exergy. Different forms of effectiveness and 2nd law efficiency are studied and their values extracted for inlet airflow rates of 2–6 m3/h. The results show that the prominent factor that controls the system behavior is the concentration ratio from which the solution free- motion originated. The maximum sensible, latent, and total effectiveness of the system are 0.23, 062, and 0.54 respectively and are for the airflow rate of 2m3/h. It is confirmed that the number of a transfer unit (NTU) and capacity ratio (Cr*) are not independent and are varied oppositely to each other. By increasing the airflow rate, the mass flow rate and heat capacity rate of desiccant solution increase more than that of air streams. For flow rates less than 3.5m3/h, external heat transfer is just enough to induce natural motion of desiccant and in this way the loop performance is similar to a forced convection energy transfer loop which exchanges heat and moisture only between the air streams.

Experimental investigation of using thermoelectric cooling for computer chips

Abstract: Thermoelectric devices are currently being used in many industrial applications for cooling devices and generating electricity. This paper mainly focuses on using thermoelectric for cooling applications, specifically to cool down computer chips. In this study, experimental tests were conducted using a commercial thermoelectric module to investigate its capabilities for cooling hotspot in chip at different heat rates. Two experimental tests were conducted at steady-state condition to cool down hotspot with two different values of heat rates of 10.8 W and 12.1 W. The former heat rate represents the case of hotspot with low heat flux, whereas the latter represents the case of hotspot with high heat flux. The test results showed that at hotspot heat rate of 10.8 W, using thermoelectric current of 5.5 A has resulted in decreasing the hotspot temperature at open circuit condition (111.4 °C) by 54.0 °C. However, at hotspot heat rate of 12.1 W, using thermoelectric current of 6.0 A has resulted in decreasing the hotspot temperature at open circuit condition (138.8 °C) by 61.1 °C. The test results showed that the optimum electrical current at high heat rate was always greater than that at low heat rate. The results provided in this paper is a part of a research project that consists of a number of phases in which the ultimate goal is to develop a simple tool for designing self-cooling framework to cool down chip hotspot at different operating conditions with minimal increase in the overall power requirements. A case study for self-cooling framework is provided in this paper to demonstrate that the chip hotspot at a given operating condition can successfully be cooled at an acceptable temperature with no need for additional power requirements.

Performance analyses of coal-fired thermal power plant using parabolic solar collectors for feed water heaters

Abstract: Parabolic solar collectors have been used for feed water heating process instead of extractions from steam turbines to enhance the power output and heat rate for a coal-fired thermal power plant. I...

Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle.

Abstract: The main objective of this paper is to present and analyze an innovative configuration of integrated solar combined cycle (ISCC). As novelties, the plant includes a recuperative gas turbine and the conventional bottoming Rankine cycle is replaced by a recently developed double recuperative double expansion (DRDE) cycle. The configuration results in a fuel saving in the combustion chamber at the expense of a decreased exhaust gas temperature, which is just adequate to feed the DRDE cycle that uses propane as the working fluid. The solar contribution comes from a solar field of parabolic trough collectors, with oil as the heat transfer fluid. The optimum integration point for the solar contribution is addressed. The performance of the proposed ISCC-R-DRDE design conditions and off-design operation was assessed (daily and yearly) at two different locations. All results were compared to those obtained under the same conditions by a conventional ISCC, as well as similar configurations without solar integration. The proposed configuration obtains a lower heat rate on a yearly basis in the studied locations and lower levelized cost of energy (LCOE) than that of the ISCC, which indicates that such a configuration could become a promising technology.

Prototype Steam Turbine for Solar Power Production

Abstract: Fabrication of a prototype direct drive steam turbine using locally available materials provides a means to supply power and process heat for off-grid areas, which are not accessible due to rugged terrain. The use of solar power technologies to provide clean power and heat will mitigate environmental pollution and global warming that are caused by combustion of fossil fuels and other carbon-based power sources. The energy density of fossil fuels is higher than that of nonconcentrated solar power, which makes them a better option compared to nonconcentrated solar power sources. The high cost of steam thermal turbines and the limited technical skills on utilization of local materials for steam turbine construction have hampered the realization of potential of producing both small- and large-scale power in Africa. The design of the single-stage blade wheel system solar thermal turbine was done using AutoCAD 2010. The blades were made from encapsulated rice husk particle boards, and the steam casing was made from 0.0015 galvanized black iron sheet. Compensation for more stages was done by sending the fluid exiting from the turbine into the solar collector for reheating. It was coupled to a single-phase generator and gearbox. The rotor was made of galvanized iron tube. The turbine’s average efficiency was obtained as 61.6% and average isentropic efficiency was 55.3%. The combined gearbox and generator approximate efficiency was 54.7%. Locally available heat transfer fluids were used for solar thermal collection. The prototype turbine was designed to produce 500 W of power. It had a heat rate ratio of 0.08. The turbine inlet conditions were as follows: average temperature of 112.8°C, average pressure of 2.7 × 105 Nm−2, average enthalpy of 3156 kJ/kg, and average steam flow rate of 243.3 kg/hr. Outlet conditions were as follows: outlet average temperature of 97.3°C, average steam flow rate of 102.0 kg/hr, average pressure of 1.20 × 105 Nm−2, and enthalpy of 2103 kJ/kg. With use of 6 M sodium chloride solution, the turbine inlet conditions were as follows: enthalpy of 3789.1 kJ/kg at a pressure of 3.0 × 105 Nm−2 and its enthalpy at exit was 2346.3 kJ/kg at a pressure of 1.05 × 105 m−2 which can provide process heat and power for off-grid areas.

Thermohydrodynamics of a Spray Drying Installation with Convective-Radiative Energy Supply

Abstract: Results are presented of experimental investigations of the working parameters of a spray drying installation with a combined supply of heat by convection and infrared radiation, the density of the heat flux in the infrared radiation device, and the intensity of mixing the gas phase. The analysis of the obtained data shows that the supply of heat to the chamber by infrared radiation and the latter′s impact on the liquid′s spray pattern makes it possible to increase signifi cantly the moisture intensity of the chamber, to decrease the heat rate for evaporation of moisture, and to raise the installation′s efficiency.

A New Analytical Model for Calculating Transient Temperature Response of Vertical Ground Heat Exchangers with a Single U-Shaped Tube

Abstract: The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient response. In comparison to the existing models, this proposed model can account for the fluid thermal storage effect and heat rate difference between the two legs of the single U-tube. With the aid of this proposed model, we conduct a thorough sensitivity analysis to investigate the effects of different influencing factors on the thermal transient response. The calculated results show that fluid thermal storage and the rate difference can significantly influence the thermal response during the early studied period. Therefore, the effect of fluid thermal storage should not be neglected when the early-time thermal response is investigated. The thermal interference between the two legs will reduce the heat capacity of GHEs. A large distance between these two legs can be favorable for practical use.

Performance of high velocity stream heat exchangers subjected to external heat transfer

Abstract: Performance is analyzed for kinetic energy variation in high velocity stream heat exchangers that are subjected to external heat transfer. Analytical solutions are obtained using the method of inverse operators. They are verified against the reported expressions in the appropriate limits for constant kinetic energy system as well as for perfectly insulated conditions. Kinetic energy decay in hot stream enhances performance that exceeds the conventional heat exchanger effectiveness. For kinetic-to-thermal energy ratio and dimensionless characteristic length constant each equaling unity on the hot side, the terminal effectiveness under balanced operation is 136% for counter-flow arrangement and 82% for parallel-flow in the absence of external heat load. On the contrary, decay on the cold side lowers performance. For unbalanced flow, kinetic energy change in the higher heat capacity rate fluid has a lesser impact on the effectiveness. Thermal interaction with the ambient generally has a deleterious effect on the hot stream effectiveness of the cryogenic system. However, the performance improves under certain conditions such that the rise in fluid temperature caused by kinetic energy deterioration promotes heat loss to the surroundings.

Developing Heat Rate and Heat Capacity Measurement Instruments of Textile Waste Solution in the Textile Dyeing Process

Abstract: Heat rate and heat capacity are widely used to determine the thermal characteristics, especially for wastewater treatment using electro coagulant. This study aimed to determine the value of heat rate and heat capacity of the waste solution in the textile industry, especially in the dyeing waste, by using a microcontroller device. The method for measuring the specific heat capacity and the textile waste solution's heat rate is based on the principle of the first law of Thermodynamics. Temperature measurements were carried out using a digital temperature sensor type DS18B20. In this research, the heat rate and specific heat of the dyeing solution and mineral water used in the textile industry have been studied. This study uses five types of dyeing waste solution as test solutions, namely green waste solution, orange waste solution, blue waste solution, brown waste solution, and mineral water. This experiment's principle is applying Joule's law by using electrical properties with a microcontroller device used to obtain the rise of temperature data each time in real-time every 2 seconds. Based on this research, it can be concluded that the instrument can be used to measure the heat rate and heat capacity of a textile waste solution. Based on this research, we also found that the specific heat of hard water (Hard water is a kind of water with high mineral content, while soft water is water with low mineral content. Apart from calcium and magnesium ions, the cause of hardness can also be other metal ions as well as bicarbonate and sulfate salts) (4.19 ± 0.77) J/ gram ℃ and the specific heat of the four types of waste solution ranged from (3.20 ± 0.72) J/gram ℃ to (6.83 ± 1.71) J/gram ℃ and also it was found that the heat rate of hard water is 0,0471 ℃/s and the heat rate of the four types of waste solution is range from 0,0289 ℃/s to 0,0617 ℃/s.

Analysis and Evaluation of Multi-Energy Cascade Utilization System for Ultra-Supercritical Units

Abstract: To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.

Method for Evaluating the Steam Turbines Operating Efficiency

Abstract: The paper considers a method for the evaluation of the power plant steam turbines operating modes efficiency. The efficiency is evaluated by comparing the specific heat rate for power generation in the reporting period with a similar indicator in the reference period reduced to the reporting period by key influencing parameters. A specific feature of the analyzed method is the reliable consideration of external influencing factors for obtaining the efficiency evaluation under compatible conditions. In particular, such external factors include the characteristics of steam, feed water, heat rate for turbine heat extraction and cleaning mode of the turbine condenser. The impact of the condenser cleaning mode on the efficiency of the turbine operating mode is considered based on the data clustering. The Affinity Propagation method has been selected for data clustering, as its special feature is working with the variable sizes and form of clusters. The efficiency evaluation with a crew-by-crew breakdown of the results allows introducing a competitive feature between the crews (operating personnel), which, in turn, will benefit from the improved efficiency of the operating modes of steam turbines. An example of evaluation based on statistical operating data for power plant turbine showing the leader among the crews according to the considered performance indicator is given. The considered method is implemented in the automated power plant energy efficiency management system, which is overviewed in the article.

Compensating for changes in heart muscle resting heat production in a microcalorimeter

Abstract: The heat production of cardiac muscle, determined by calorimetry, can be used as a measure of cardiac metabolism. However, heat produced while a muscle is actively-shortening, thereby performing force-length work, comprises both active and basal metabolic processes. In this paper, we present a method for post-experimental processing of calorimetric measurements of muscle heat production, that uncovers and compensates for the measured basal heat rate during work. In this method, the relationships between muscle length, velocity of length change and muscle heat output are coupled with a simulation of the measurement instrument, providing a model-based estimate of change of measured basal heat while the muscle is performing work. We demonstrate the use of this technique in an experiment conducted on a working cardiac muscle sample. The ability to identify the various components of heat release in these muscles provides useful insight into their mechanical and energetic capabilities.

Characterization of Local Nano-Heat Transfer Fluids for Solar Thermal Collection

Abstract: Performance of organic oils in solar thermal collection is limited due to their low thermal conductivity when they are compared to molten salt solutions. Extraction of organic oils from plants can be locally achieved. The purpose of this study was to investigate the effect of use of copper nanoparticles in some base local heat transfer fluids (HTFs). Addition of volume fraction of 1.2% of the copper nanoparticles to oil-based heat transfer fluids improved their thermal conductivity as deduced from the thermal heat they conducted from solar radiation. The oil-based copper nanofluids were obtained by preparation of a colloidal solution of the nanoparticles. Impurities were added to increase the boiling point of the nano-heat transfer fluids. Stabilizers were used to keep the particles suspended in the oil-based fluids. The power output of the oil-based copper nano-heat transfer fluids was in the range of 475.4 W to 1130 W. The heat capacity of the steam in the heat exchanger was 93.7% dry and had a thermal capacity of 5.71 × 103 kJ. The heat rate of flow of the oil-based copper nano-heat transfer fluids was an average of 72.7 Js−1·kg−1 to 89.1 Js−1·kg−1. The thermal efficiency for the oil-based copper nano-heat transfer fluids ranged from 0.85 to 0.91. The average solar thermal solar intensity was in the range 700 Wm−2 to 1180 Wm−2. The heat exchanger used in this study was operating at 4.15 × 103 kJ and a temperature of 500.0°C. The heat transfer fluids entered the exchanger at an average temperature of 381°C and exited at 96.3°C and their heat coefficient ranged between 290.1 Wm−2°C and 254.1 Wm−2°C. The average temperatures of operation ranged between 394.1°C and 219.7°C with respective temperature efficiencies ranging between 93.4% and 64.4%. It was established that utilization of copper nanoparticles to enhance heat transfer in oil-based local heat transfer fluids can mitigate energy demand for meeting the world’s increasing energy uses, especially for areas inaccessible due to poor land terrain.

Experimental Study on Thermal Performance of Aluminous Vapor Chamber

Abstract: In this paper, a large size aluminous vapor chamber (650 mm × 350 mm × 5 mm) with high effective thermal conductance and light weight was developed for heat dissipation of high heat flux point heat source in aircrafts near space. The heat performance of aluminous vapor chamber (VC) was tested in a power range of 50 W to 159 W. The heat resistance is about 0.2 ℃/W under a heat flux of 25 W/cm2, and the chamber works normally without dryout under a power condition as high as 159 W (~43 W/cm2), which indicates its capability under high heat flux. To enhance thermal performance of aluminous vapor chamber, an integration heat spreader which integrated of advanced carbon materials (annealed pyrolytic graphite, multilayer graphene) and aluminous vapor chamber was fabricated. The test result shows integration heat spreader can significantly reduce the heat spreader resistance of aluminous vapor chamber: the temperature difference between the evaporator section and condenser section decreases from 39.6 ℃ to 9 ℃ under a heat rate of 130 W (heat flux 36.5 W/cm2), while the heat resistance reduces from 0.3 ℃/W to 0.07 ℃/W. Also, the effect of gravity has been studied under horizontal placement and vertical placement. The result shows the thermal resistance under vertical placement is about 3–4 times of that under horizontal placement.

Power plant systems for enhancement of efficiency and reduction of heat rate

Abstract: Provided is a power generation system for enhancing efficiency and reducing a heat consumption rate. According to one embodiment of the present invention, a power generation system for enhancing efficiency and reducing the heat consumption rate comprises: a turbine unit which includes a high-pressure turbine, a middle-pressure turbine, and two low-pressure turbines, and is connected to a power generator; a condensate pump unit which condenses the steam discharged from the low-pressure turbines in a condenser, and supplies the condensed condensate; a plurality of supplied water heaters which heat the water supplied from the condensate pump unit by the steam added from the turbine unit; a boiler which heats the water supplied from the supplied water heaters, generates high-temperature overheated steam, and supplies the overheated steam to the high-pressure turbine; a reheater which reheats the steam discharged from the high-pressure turbine, and supplies the steam to the middle-pressure turbine; and a heat consumption rate reduction unit which increases at least one of the pressure and the temperature of the main steam supplied from the boiler to the turbine unit and the temperature of the reheated steam supplied from the reheater to the turbine unit.

Heat Treatment Strategy to Improve the Structural Characteristic and Electrochemical Performance of LiNi0.6Mn0.2Co0.2O2 Cathode Material

Abstract: LiNi0.6Mn0.2Co0.2O2 (NMC622) is one of the cathode materials of lithium-ion battery which has a high specific energy, high specific power, long life cycle, and low cost. Various attempts have been performed to obtain high capacity NMC622. In this research, high capacity NMC622 was obtained by tuning the sintering heat rate during NMC cathode material formation. The NMC622 precursor was obtained via facile oxalate precipitation. The heating rate during the sintering process was 5, 7.5, and 10°C/min. NMC cathode material is characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-obtained NMC622 cathode material was applied directly in a 18650 cylindrical cell where artificial graphite was utilized as the anode. Based on the results, the optimum heat-rate was established at 7.5°C/min with a specific discharge capacity of~130.19 mAh/g using 20 mAh/g charge-discharge current.