Showing papers on "Heat capacity rate published in 2021"

Computational investigation of non-uniform magnetic field on thermal characteristic of nanofluid stream inside 180∘ elbow pipe

Abstract: The thermal efficiency of the heat exchanger is substantial in chemical and mechanical systems The presence of the non-homogeny magnetic field considerably enhances the heat rate of nanofluid stre

Numerical investigation of heat and mass transfer of water—silver nanofluid in a spiral heat exchanger using a two-phase mixture method

Abstract: This study numerically investigates the heat and mass transfer characteristics of water—silver nanofluid flowing in a spiral heat exchanger (HX) using the two-phase mixture model. The hot side of the HX is pure water at the temperature of 343 K and Re = 500, while the cold side is nanofluid with volume fraction up to 5% at 305 K and Re number ranging from 500 to 2000. The cold and hot tubes are concentrically twisted 3.5, 5.5 and 7.5 turns in order to explore the heat transfer effectiveness of the heat exchanger as a function of the spiral turns. The results indicate that increasing the volume fraction of nanoparticles, Re number and the number of turns increases the overall heat transfer coefficient, heat rate absorbed by the cold fluid and pumping power of the HX noticeably. The above-mentioned factors also improve the temperature stability of the input fluid along with the heat exchanger. The effectiveness of the HX decreases by increasing the Re number, the volume fraction of nanoparticles and turning rounds due to the greater pressure drop of the coolant fluid. At a constant Re number, increasing the volume fraction and number of turns enhances the NTU parameter to a great extent.

The influence of turbulator on heat transfer and exergy drop of nanofluid in heat exchangers

Abstract: In current investigation, tape is used to augment pressure drop and heat rate inside heat exchangers in existence of nanofluid. To do this, the three-dimensional model of the twisted tape is chosen for our investigation. This study dedicated on the heat transfer intensifications when significant parameters such as pitching ratio, height ratio and inlet velocity are changed. In order to simulate this model, computational fluid dynamic method with the simple algorithm is applied with k–e (RNG) model for the modeling of the non-laminar flow through the tube due to the presence of the turbulator. Obtained results show a reasonable agreement with experimental data. Our results show that the efficiency of the H2O-CuO nanofluid considerably increases as the Reynolds number augmented in the tube. Moreover, the rate of exergy declines (more than 35%) as the height ratio increased from 0.3 to 0.5.

An Investigation of Heat Transfer Performance in an Agitated Vessel

Abstract: Agitated vessels (or mechanically stirred reactors) are heat exchange devices that are most widely used in many chemical and biochemical process industries, such as anaerobic digestion process. The mixing and heat transfer performances in these vessels are of crucial importance for increasing the energy efficiency in both batch and continuous processes. In this paper, a series of experiments were conducted to investigate heat transfer performance in agitated vessels for various configurations. In fact, this study examines the effects of heat transfer geometry (wall jacket and helical coils), heating power, and stirring speed, on the heating performance of two stirred fluids—water alone and a mixture of water and food waste. The experiments were conducted using a jacketed insulation tank with a helical coil and a propeller agitator. In each experiment, a transient method, based on measuring the temperature dependency on time, and solving the unsteady enthalpy balance, was used to determine the overall heat transfer coefficients between the agitated fluid and the heating surface. Finally, an extensive analysis of the reduced data was conducted based on temperature, heating time, heat transfer rate, heat transfer coefficient, and thermal resistance. The main finding was that the presence of food waste in agitated vessels reduces the heat rate of the agitated fluid with an average of 18.13% and 49.51%, respectively, for the case of JHX and CHX, and creates additional fouling, which further limits the heat transfer.

Natural Convection Effect on Solidification Enhancement in a Multi-Tube Latent Heat Storage System: Effect of Tubes’ Arrangement

Abstract: The solidification process in a multi-tube latent heat energy system is affected by the natural convection and the arrangement of heat exchanger tubes, which changes the buoyancy effect as well. In the current work, the effect of the arrangement of the tubes in a multi-tube heat exchanger was examined during the solidification process with the focus on the natural convection effects inside the phase change material (PCM). The behavior of the system was numerically analyzed using liquid fraction and energy released, as well as temperature, velocity and streamline profiles for different studied cases. The arrangement of the tubes, considering seven pipes in the symmetrical condition, are assumed at different positions in the system, including uniform distribution of the tubes as well as non-uniform distribution, i.e., tubes concentrated at the bottom, middle and the top of the PCM shell. The model was first validated compared with previous experimental work from the literature. The results show that the heat rate removal from the PCM after 16 h was 52.89 W (max) and 14.85 W (min) for the cases of uniform tube distribution and tubes concentrated at the bottom, respectively, for the proposed dimensions of the heat exchanger. The heat rate removal of the system with uniform tube distribution increases when the distance between the tubes and top of the shell reduces, and increased equal to 68.75 W due to natural convection effect. The heat release rate also reduces by increasing the temperature the tubes. The heat removal rate increases by 7.5%, and 23.7% when the temperature increases from 10 °C to 15 °C and 20 °C, respectively. This paper reveals that specific consideration to the arrangement of the tubes should be made to enhance the heat recovery process attending natural convection effects in phase change heat storage systems.

Heat Rate Prediction of Combined Cycle Power Plant Using an Artificial Neural Network (ANN) Method.

Abstract: Heat rate of a combined cycle power plant (CCPP) is a parameter that is typically used to assess how efficient a power plant is. In this paper, the CCPP heat rate was predicted using an artificial neural network (ANN) method to support maintenance people in monitoring the efficiency of the CCPP. The ANN method used fuel gas heat input (P1), CO2 percentage (P2), and power output (P3) as input parameters. Approximately 4322 actual operation data are generated from the digital control system (DCS) in a year. These data were used for ANN training and prediction. Seven parameter variations were developed to find the best parameter variation to predict heat rate. The model with one input parameter predicted heat rate with regression R2 values of 0.925, 0.005, and 0.995 for P1, P2, and P3. Combining two parameters as inputs increased accuracy with regression R2 values of 0.970, 0.994, and 0.984 for P1 + P2, P1 + P3, and P2 + P3, respectively. The ANN model that utilized three parameters as input data had the best prediction heat rate data with a regression R2 value of 0.995.

Sintering of the WC-6%Co cemented carbides for improved mechanical and cutting performance using Micro-FAST

Abstract: WC-6%Co cemented carbides tools with improved performances were successfully prepared using Micro-FAST method in less than 5 min with a Gleeble-1500D thermal simulation machine. Effects of the sintering temperature and heating rate on the densification, microstructure, mechanical properties were investigated and cutting performance of sintered samples were evaluated. It was found that densification of the samples was enhanced with the increase of the sintering temperature from 900 to 1200 °C while the consolidation process is facilitated with the initial increase of the heating rate to 50 °C/s and retarded with its further increase to 100 °C/s. A relative density of as high as 97.71% and a hardness of 21.7GPa were reached when a sintering temperature of 1200 °C, a heating rate of 50 °C/s and a holding time of 12 min were used. A higher sintering temperature along with a reasonably higher heat rate can produce a denser microstructure while pores remain in the sample when a heating rate higher than 50 °C/s is adopted. The tool prepared by the Micro-FAST exhibits the improved cutting performance than that by the traditional approach. The presented study shows that Micro-FAST can be a potentially very effective way to produce the cutting tools to meet the engineering application.

Investigation on the potential of multiple water injections in thermodynamic optimization of heat and mass transfer process in air humidifier

Abstract: In this paper, several thermodynamic optimization strategies are implemented to tap the potential of multiple water injections in thermodynamic balancing of combined heat and mass transfer process in air humidifier. The all-state of humid air including unsaturation, saturation and supersaturation states are particularly considered. Based on finite difference method, theoretical models are integrated with multiple injection methods. In the off-design analysis, the equipartition process of the driving forces including heat transfer temperature difference and mass transfer pressure difference are full of attention and interest. The research results present that entropy generation minimization is achieved when the values of heat capacity rate ratio equal to unity for all the cases. A larger value of the number of injections will improve the equipartition process of the driving forces, resulting in a reduction of total normalized entropy generation. In addition, it is found that these driving forces can be better balanced with larger number of injections and smaller injection ratio, when the heat capacity rate ratio is constant. Moreover, it is observed that energy effectiveness can be improved and the total normalized entropy generation is diminished as the inlet relative humidity augments, with a minimum normalized entropy generation of 0.0045 emerged at φi = 0.85. Furthermore, it is also highlighted that controlling and adjusting the relative humidity of inlet humid air for the optimization of thermal devices and engineering systems is significant and available, especially referred to the all-state of humid air.

Numerical analysis of thermal performance of heat exchanger: Different plate structures and fluids

Abstract: Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China Corresponding Author Email: mskmanj@inest.cas.cn Abstract Due to compact size, high power density, low cost and short construction time, the Small Modular Reactors (SMRs) are considered as one of the candidate reactors, in which the power generation system is important with a compact heat exchanger for modular construction. Therefore, the effect of plate structure and nature of the working fluid on the thermal performance of Plate Heat Exchanger (PHE) are analyzed for the design of compact and efficient heat exchanger. The heat transfer rate, temperature counters, velocity vectors and pressure drop have been optimized and investigated using FLUENT. The Nusselt number has been calculated for the corrugated and flat PHE to validate the convective heat transfer. The numerical results are agreed well with correlation within deviation of ~ 5-7%. The performance of heat exchanger can be improved by controlling the mass flow rate and temperature of working fluid. The corrugation PHE increases the heat transfer rate 20 % and effectiveness 23 %, respectively, as compare to flat PHE when the working fluid is water. In the case of air, heat transfer rate and effectiveness are about 10 % and 9 %, respectively. The results show that the corrugated PHE is more effective than the flat PHE because corrugation pattern enhances the turbulence of fluids, which further increase heat transfer rate and coefficient. The selection of the working fluid and structure of the plate must be considered carefully for efficient and compact design of heat exchanger.

Heating system and method for its operation

Abstract: The heating system has storage container (10) that is provided with heat storage medium (12). The heat storage medium is arranged with container heat exchanger (14). The outside of the storage container is provided with heat generator (16) and heat exchanger (18). The heat exchanger is thermally coupled to the heat generator through the flow heating path (20). A flow control device is provided for conducting regular branch current by the heating path flowing heat transfer fluids over container heat exchanger. An independent claim is included for method for operating building heating system.

Energy and Entropy Analyses of a Pilot-Scale Dual Heating HDH Desalination System.

Abstract: This study focuses on energy and entropy analysis to theoretically investigate the performance of a pilot scale dual heated humidification-dehumidification (HDH) desalination system. Two cases of HDH systems are considered in the analysis. The first case is a dual heated (DH) cycle consisting of 1.59 kW air heater and 1.42 kW water heater with a heat rate ratio of 0.89 (CAOW-DH-I). Whereas the second case is a dual heated HDH cycle comprising of 1.59 kW air heater and 2.82 kW water heater with a heat rate ratio of 1.77 (CAOW-DH-II). As a first step, mathematical code was developed based on heat and mass transfer and entropy generation within the major components of the system. The code was validated against the experimental data obtained from a pilot scale HDH system and was found to be in a good agreement with the experimental results. Theoretical results revealed that there is an optimal mass flowrate ratio at which GOR is maximized, and entropy generation is minimized. Furthermore, the degree of irreversibility within the humidifier component is low and approaches zero, while the specific entropy generation within other components are relatively high and are of the same order of magnitude. Entropy analysis also showed that the dual heated system with heat rate ratio greater than unity is better than the one with heat rate ratio less than unity.

Thermal energy evaluation of the incinerator medical waste

Abstract: The global warming problem and the rising cost of energy has raised the interest in the application of alternative energy for the energy system to increase efficiency and to reduce the emission of pollution. However, the key challenge of the energy systems was to find an appropriate way to decrease energy loss and increase the efficiency of energy transfer. This research aimed to evaluate the thermal energy obtained and heat loss from the incinerator waste installed in Suphan Buri Province, Thailand. The incinerator system composed of 6 sections: the first section was a waste hopper and feeder, the second section was the rotary kiln primary, the third section was a secondary chamber, the fourth section was the ash cooling conveyer, the fifth section was cyclone and the sixth section was a stack. This study applied 200 kilograms of waste and 200 liters of diesel oils as raw materials for the incineration process. The results showed that the total flow rate from overall input materials was 875 kilograms per hour and the total heat rate from overall inputs was 3,503,032.25° Kelvin. In terms of heat losses, total heat losses from the surface were 2,789,424.75 ° Kelvin while overall heat losses were 3,503,032.25 ° Kelvin. The results showed high thermal efficiency and suitable for application in the engineering process.

Novel concept on the enhancement of conventional solar still performance via constant heat rate supply to the saline water.

Abstract: One of most reduction reasons of simple conventional solar still productivity is the coupling between high solar intensity and the high ambient temperature in the same time. The high intensity increases the saline water temperature, while the outside temperature increases the glass temperature, and consequently reduction in saline water and glass temperature difference leads to reduction in condensation and productivity. The present theoretical study focuses on the completion of the absorbed solar energy in the basin to be constant during the day. The basin water will be in high temperature level all day especially at the time of low outside temperature far away the noon. The absorbed heat in the basin is held constant at αw Imax by extra heat from wind turbine power with battery storage system all day hours. The results show that the solar still productivity with constant heat supply is more than that with same amount of variable energy during sun rise time only (6 AM to 6 PM) by 69.133%. So, constant absorbed heat in the water basin (αw Imax) through the 24 h of the day enhances the performance with productivity up to 248% with the hybrid solar and electric power consumption of the wind turbine power. The water in the basin is held constant at 2 cm via makeup water to compensate the evaporation rate.

Steady-State Operating Characteristics Analysis of Loop Heat Pipes with Flat-Plate Evaporator

Abstract: A mathematical model of gravity-assisted flat loop heat pipe has been established, based on mass conservation, energy balance, combining pressure-temperature and heat & mass transfer relations. The effects of gravity, heat sink and ambient temperature on steady-state performance of the loop heat pipe were comprehensively investigated. The modeling results show that there exist two driving modes: gravity-driven mode and capillary-gravity co-driven mode when plate loop heat pipes operate under gravity-assisted condition. Besides, a critical heat flux has been found between the gravity-driven mode and the co-driven mode. The condensate capacity of heat sink and ambient temperature to the heat regenerative ability of the liquid line affect the variable heat-conductance zone and constant heat-conductance zone. These findings are beneficial to the comprehensive understanding of the operating characteristics, which can guide the design of and optimization the flat loop heat pipes.

Research on key technology and application of flexibility transformation of heating unit to improve clean energy consumption capacity

Abstract: The electric regulation capacity of heating units has been constantly improving due to the promotion of the heating units’ flexibility transformation. This improvement has effectively alleviated the long remained serious wind and light abandonment phenomena in the heating season in China. In this paper, we discussed the key technologies of the low pressure zero output heating mode and bypass heating mode, both of which are widely used in thermo-electric decoupling. Moreover, the coupling transformation of the two heating modes has been successfully realized in a heating unit. The electric regulation capacity of the unit has been greatly improved, from 18.6% before the transformation to 66.7%, and the minimum technical output has been also reduced to 14.2% THA. After the transformation, the unit now is able to provide several heating modes with its operational flexibility greatly improved. By comparing the economical efficiency of these heating modes, we obtained the operation mode with the lowest heat rate. This transformation mode provides a huge grid space for the consumption of clean energy, so it is of positive reference value and exemplary significance in implementing the flexibility transformation of heating units.