Optimum Mass Flow Research Articles

Analysis of Maisotsenko humid air bottoming cycle employing mixed flow air saturator

Maisotsenko Humid Air Bottoming Cycle (MHABC) is a viable option for the waste heat recovery of gas turbine topping cycle to attain a higher efficiency point of the combined cycle power plant; thus, having a potential of lower CO2 emissions towards environment. In this work, instead of the typically proposed counter flow configuration of the air saturator, a novel mixed flow configuration is proposed. The proposed configuration uses a hybrid cross-flow and a regenerative counter-flow heat and mass exchanger (HMX). This hybrid HMX is numerically simulated to estimate optimal amount of saturated air which can lead to maximum efficiency and power output. The mathematical model of the mixed flow configuration HMX based air saturator is developed by applying mass and energy balance laws on a selected control volume. The results of the air saturator are initially validated using previously published experimental data for air cooling applications. Furthermore, simulations for high-pressure operations suitable for power generation are performed and a parametric analysis shows that optimal mass flow rate ratio between the working air in the dry channel and incoming air for cross-flow part is 0.65. Optimal mass flow ratio between the working air wet channel and working air dry channel for the counter-flow part is 0.5. The integration of hybrid air saturator in MHABC can yield a maximum of ~57 MW of output work and ~42% of thermal efficiency. The proposed system can achieve a 7% increment in total output work, and 9% increment in thermal efficiency as compared to the counter-flow configuration as an air saturator in the bottoming cycle. Furthermore, the proposed system has ~55% fewer carbon footprint as compared to counter-flow configuration alone as an air saturator.

Modeling wellbore heat exchangers: Fully numerical to fully analytical solutions

The successful modeling of wellbore heat exchangers requires tight coupling between the formation heat conduction and the wellbore thermal dynamics. In this paper, we developed three representative solutions: a fully numerical solution that treats both formation and wellbore numerically, a semi-numerical solution that treats formation analytically and wellbore numerically and a fully analytical solution that treats both formation and wellbore analytically. The outlet temperature, pressure, and heat flow rate predicted by the three solutions are compared. The results of this comparison indicate that the fully numerical solution is the only accurate solution for the early transient time. After the system reaches quasi-steady state, temperature and heat flow estimated from all three solutions are in very good agreement. The analysis of transient fluid properties and mass flow rates revealed that constant fluid property model cannot accurately estimate the pressure loss for the system. The newly proposed fully analytical solution is applied in an economic analysis problem for calculating the optimal insulation thickness and mass flow rate to minimize the cost of generated power.

Experimental investigation on a novel frost-free air source heat pump system combined with liquid desiccant dehumidification and closed-circuit regeneration

Frost build-up on the fins of the evaporator severely decreases heat transfer and subsequently reduces the performance of the heat pump system. In this paper, a novel frost-free air source heat pump system is proposed, which combines with liquid desiccant dehumidification and closed-circuit regeneration. A test setup for investigating the performance of the proposed system and the corresponding performance indexes are developed to evaluate the system performance under variable working conditions. The effects of key parameters including solution temperature, solution concentration, air flow rate and solution flow rate on the regeneration performance and heating performance of the system are analyzed experimentally. Results show that the optimal mass flow rate ratio of the solution to the air is 1.4 in the regeneration mode, while the ratio of 0.55 is recommended in the heating mode. Additionally, performance comparison between the proposed system and the conventional reverse-cycle defrosting system available in the literature is conducted. It is concluded that the proposed system is superior to the reverse-cycle defrosting system when the ambient temperature is less than 0 °C and the relative humidity is higher than 65%.

Conceptual design and analysis of a novel process for hydrogen liquefaction assisted by absorption precooling system

Hydrogen liquefaction processes have effective function in the hydrogen supply chain. However low efficiency and high liquefaction costs are still the most important concerns about the liquefaction plants. In this study a new configuration for a hydrogen liquefier process is proposed and energy-exergy analyzed. The production rate of the liquid hydrogen (LH2) is 90 tons per day that can supply the required LH2 of at least 90 k-180 k hydrogen vehicles in an urban area that results in the reduction of pollutions caused by carbon dioxide emission. The process is simulated in Aspen HYSYS simulator. In addition, it is optimized thorough a trial and error approach that is a functional and simple method of complicated systems analysis. The process includes a mixed refrigerant (MR) refrigeration cycle that precools feed gas hydrogen from 25°C temperature to −199.9°C temperature. A new MR is used in a cascade Joule-Brayton cycle that deep-cools the low-temperature gaseous hydrogen from −199.9°C temperature to −252.2°C temperature in the cryogenic section of the plant. The novel process involves also an absorption refrigeration system (ARS) that cools some hydrogen streams in the precooling and cryogenic sections of the process. The consumed energy per kilogram of produced LH2 is achieved as 6.47kWh. This quantity is 2.89kWh in the ideal conditions. The exergy efficiency of the plant is evaluated to be 45.5% that is significantly more than the exergy efficiency of the in operating hydrogen liquefiers in the world. The energy analysis reveals that the coefficient of performance (COP) of the overall system is 0.2034. The achieved COP is a higher amount in compare to the other similar processes. A sensitivity analysis is done to show the effect of the various operation conditions of the process on the features of the plant. Accordingly, the optimum mass flow of the ARS is determined as 207kg/s for the proposed configuration. As well as, the effect of the change in the temperature approach of the heat exchangers and the changes in the adiabatic efficiency of the compressors and expanders on the SEC, COP, and the exergy efficiency of the overall plant is discussed. Furthermore, financial analysis of the plant estimates the capital expenditures (CAPEX), energy expenditures (EEX), and operational and maintenance expenditures (OMEX) as 25413 €2000, 7370 €2000, and 2033 €2000 respectively. These can be specially improved be improving of the exergy efficiency of the plant. The results implicates that the proposed configuration has better performance indicators than the in-service liquefiers. Therefore, LHL plant manufacturer can be considered it in the design and development of new plants. As well as, researchers may utilize its operating conditions to improve the proposed processes.

Performance analysis of a novel thermoelectric assisted indirect evaporative cooling system

In this paper, a novel thermoelectric assisted indirect evaporative cooling system is proposed. Specifically, thermoelectric cooling (TEC) modules are sandwiched between channels of a flat plate cross flow indirect evaporative cooler. A mathematical model of the novel system is developed, and influences of main operating and geometrical parameters on the system's performance are analyzed in detail. Analytical results show that with the assistance of the thermoelectric cooling, the proposed system is able to cool primary air to a temperature much lower than inlet air wet bulb temperature, even dew-point temperature, meanwhile keep a relatively high coefficient of performance (COP), by selecting appropriate number and electric current of TEC modules. The dew point effectiveness and COP of the proposed system change monotonously with inlet mass flow rate, temperature and humidity ratio of primary air, respectively. The dew point effectiveness also varies monotonously with the mass flow rate ratio of secondary air to primary air. However, there exists an optimal mass flow rate ratio resulting in a maximum COP. Moreover, under variable number and electric current of TEC modules, there always exist optimal widths of primary air channel and secondary air channel, leading to a maximum COP.

Experimental evaluation of the separation of aromatic compounds using falling film distillation on a pilot scale

This study evaluated a new process for separation of aromatic compounds based on falling film distillation at thermosyphon-assisted atmospheric pressure (Destubcal Technology), in order to obtain enriched mass fractions of toluene in the distillate stream. Two compact experimental units were used: single-tube and multi-tubes on a pilot scale. The experimental tests were divided into two groups: isothermal and non-isothermal condition. The optimal feed mass flow rate, evaporator temperature and feed temperature conditions were found to be 25.13 kg h−1, 102.10 °C and 132.90 °C, respectively, starting from a feed concentration of 43% (m/m). The best result was found by using the single-tube unit with about 25.24% (m/m) enrichment of mass fraction of toluene in the distillate stream. There was no relevant difference in results between the isothermal and non-isothermal conditions. The results found in the single-tube and multi-tubes pilot scale units were similar, showing toluene mass flow values at the distillate stream of 2.96 kg h−1 and 44.76 kg h−1 respectively; thus, they indicate high productivity. The new alternative for distillation of aromatic compounds proposed in this article shows a satisfactory result when compared to conventional distillation, because the Destubcal Technology had a lower energetic requirement.

Drying Kinetics, Quality Assessment, and Economic Analysis of Bitter Gourd Flakes Drying Inside Forced Convection Greenhouse Dryer

A greenhouse dryer under forced convection mode is designed and fabricated with the integration of solar collector and variable speed exhaust fan. The developed system is used for bitter gourd flakes drying under three different air mass flow rates (0.0275, 0.0551, and 0826 kg/s). Moisture content of bitter gourd flakes was decreased effectively from 96.8% to 12.2% in 17 h with optimum air mass flow rate 0.0551 kg/s, whereas open sun drying has taken 26 h to reach 20.7% moisture content. The average greenhouse dryer efficiency was found to be 19.7% at 0.0551 kg/s air mass flow rate. Shrinkage (in terms of percentage) of dried bitter gourd flakes was found to be higher as 74% at 0.0275 kg/s air mass flow rate because of higher greenhouse room air temperature. Hardness of dried bitter gourd flakes was found to be highest as 365 g at 0.0275 kg/s air mass flow rate due to less air exchange rate and high inside room temperature. On the basis of statistical analysis, Prakash and Kumar model and Logarithmic model were selected as best drying models for greenhouse and open sun drying, respectively. The dehydration of higher moisture content crops inside developed greenhouse dryer was found to be more consistent. The designed greenhouse system is recommended for small farmers.

Theoretical Analysis of Continuous Heat Extraction from Absorber of Solar Still for Improving the Productivity

This paper communicates the theoretical analysis of continuous waste heat extraction from the other side of absorber plate. For theoretical analysis two conditions are determined one is the mass of water in the absorber and another one is mass flow rate of water around the absorber plate. Results indicated that the water temperature is reached maximum at 10 kg of mass and 5 kg/hr mass flow of water and the heat extracted from the absorber is higher at optimum mass flow of 5 kg/hr. Also, the higher temperature difference between the water and the collector cover is found during the off-shine period. The maximum achievable hourly productivity of 0.9 and 0.5 kg is found for the solar still with and without circulation respectively. The yield from present model with continuous heat extraction is increased from 3 to 5.5 kg/m2. As the approached method is more new to the society it may be determined by Agouz- Nagarajan- Sathyamurthy (ANS) model.

Evaluation of metal foam based thermoelectric generators for automobile waste heat recovery

This paper focuses on harvesting heat emitted by exhaust systems efficiently using thermoelectric generators (TEGs) and converting it to electricity. In a TEG that employs gaseous working fluid, up to 80% of the thermal resistance is due to the gas side. Maximizing the energy transferred from the hot exhaust gas to the hot side of the thermoelectric modules by suitable enhancement techniques can result in an efficiency gain for the TEG. To this end, we have investigated the performance of metal foam-based heat exchangers for reducing thermal resistance of the hot side in TEGs. A computational model of the metal foam-enhanced TEG, solving for the coupled thermal and electrical energy transfer processes, was developed to investigate the enhancement in system performance for a range of metal foam porosities and pore densities, and mass flow rates of the exhaust gas. Skutterudites with multiple cofillers were selected as thermoelectric materials. The primary performance metrics that were analyzed include the electrical power output and the associated pressure drop for various inlet conditions of the exhaust gas. Based on the trade-off between the increased pumping power required to offset the increase in pressure drop, and the gain in heat transfer coefficient with increase in mass flow rate of the exhaust gas, an optimal mass flow rate that maximizes the net electric power produced by the metal foam-enhanced TEG was obtained. The results show a critical exhaust flow rate for different pore densities of metal foam beyond which the net electric power produced by the TEG is less than of the TEG with no metal foam. At this critical flow rate, the maximum net electric power produced from exhaust waste heat by metal foam enhanced TEG is 5.7 (20 PPI) to 7.8 (5 PPI) times higher than that generated by the configuration without metal foam.

Dual-Input/Single-Output Extremum-Seeking System for Jet Control

A dual-input/single-output extremum-seeking control system has been developed to manipulate a turbulent round jet based on a radially injected unsteady minijet. The Reynolds number , based on the nozzle diameter of the main jet, is from 5700 to 13,300. It has been demonstrated that this system may obtain rapidly and simultaneously the optimum excitation frequency and mass flow rate of the minijet, thus achieving the maximum decay rate of the jet centerline mean velocity, as confirmed by the open-loop control results. This technique is robust to the parametric uncertainty with respect to within the tested range and adaptable when the initial control parameters are varied. It has been further found that the maximum remains the same, be it a decrease or increase in , that is, the control performance is essentially independent of .

A hybrid system using direct contact membrane distillation for water production to harvest waste heat from the proton exchange membrane fuel cell

In this paper, a hybrid system consisting of PEMFC (proton exchange membrane fuel cell) and DCMD (direct contact membrane distillation) was proposed to recover the waste heat from PEMFC for brine water desalination. Parameters determining the performance of this hybrid system were systematically investigated. Results indicate that there exist optimal PEMFC current density and DCMD fresh water inlet mass flow rate, respectively, leading to the maximum energy gain from the fuel chemical energy. In order to analyze the optimal performance of the proposed hybrid system, with the maximum energy gain as the objective function, genetic algorithm method was employed to obtain the optimal PEMFC current density and DCMD fresh solution inlet mass flow rate, thereby, the performance specifications of the hybrid system under different operating temperatures of the PEMFC subsystem. Compared with the single PEMFC system, as operating temperature varies from 328.15 K to 348.15 K, the energy utilization degree can be increased by 201%–266%.

Performance Analysis of Solar Air Dryer for Multi Crop Drying Effect of Varying Air Mass Flow Rate

In India open sun crop drying is very popular technique for drying, however solar air dryers are used for crop drying in many places. The solar air dryers are designed and fabricated for a particular crop and have limited usage. The solar air dryers are available in different sizes and configurations. The solar dryer performance depends on various input parameters such as inlet temperature of the air, type of absorber material, type of configuration of solar air dryer, mass flow rate of air, overall heat transfer coefficient, solar radiation, etc. The present article discusses the effects of various parameters on the useful heat gain, instantaneous thermal efficiency of solar air dryer, temperature rise with change in mass flow rate of air, input air temperature, overall heat transfer coefficient and solar air collector area. It is observed that the optimum mass flow rate of air for maximum useful heat gain is 0.05 kg/s. Further, increase in the area will not yield any advantage for overall heat gain. The instantaneous thermal efficiency for various mass flow rates is around 88%. The overall heat transfer effect increases the instantaneous thermal efficiency up to 0.1 kg/s air mass flow rate and thereafter no significant change in the efficiency. The input air temperatures do not yield much effect on the useful heat gain and rise in temperature.

Experimental and theoretical investigation on the effects of lower concentration CeO2/water nanofluid in flat-plate solar collector

Heat transfer characteristics of solar flat-plate collectors are improved by applying various nanofluids as the heat transfer media nowadays. In the present work, the theoretical and experimental analysis was performed for a flat-plate solar collector operating with water and CeO2/water nanofluid as the working fluids. The flat-plate solar water heater with 100 L per day capacity along with ladder-type heat exchanger having collector area of 2 m2 is fabricated for the experimental study. The average particle size and volume fraction of nanofluids were considered as 25 nm and 0.01%, respectively. The flow rate of water and nanofluid was varied from 1 to 3 lpm, and the efficiency was calculated as per ASHRAE standards. Due to the enhanced thermophysical properties of the nanofluid, it gives better performance and results showing that the maximum efficiency of solar water heater with CeO2/water nanofluid is 78.2%, which is 21.5% higher when compared with the water as base fluid. Also a correlation was developed for predicting the outlet temperature of a flat-plate collector. The maximum collector efficiency of nanofluid was obtained at the optimum mass flow rate of 2 lpm in experimental study. The developed mathematical model was reasonably matching the experimental results with the error of ± 7.5%.

A variable-capacity power system driven by geothermal energy: research methodology and preliminary experimental study

To match for the different temperature of the geothermal resource and strengthen the flexibility of organic Rankine cycle (ORC), this paper proposes a variable capacity power generation superstructure based on Flash and ORC for geothermal energy. A combined Flash-ORC experimental prototype is newly established to investigate its performance on both steady and dynamic conditions in this paper. Pressured hot water is adopted as the extensive worldwide existed hydrothermal geothermal resource, eliminating the influence of the used heat transfer oil on evaporating process. Important variables are investigated including the working fluid mass flow rate, loads quantity and outdoor environment of ORC subsystem in the preliminary experimental study. Firstly, steady experiment indicates that the maximum net power generation of ORC subsystem is 0.74 kW, revealing the existing optimal working fluid mass flow rate of the specific system. Secondly, dynamic on-off investigation of working fluid pump illustrates that ORC system has a certain extent self-adaption capacity and reliability. In addition, power generation increases with the decrease of the loads, and the condensing temperature makes a big influence on system performance when ORC using the cooling tower.

A numerical model for optimal receiver array and mass flow rate in residential solar water heating systems

ABSTRACTIn this paper, the performance of a pressurised evacuated tube solar collector system using internal heat pipes is presented. The system was optimised for the seasonal supply of hot service water for residential use in Pretoria, South Africa. The prediction of seasonal hourly performance trends along with the maximum thermal performance at the optimal receiver array and manifold mass flow rate was of major concern in this investigation. A mathematical model representing the thermal performance of the system was developed and numerically implemented in Engineering Equation Solver. The dynamic performance of collectors with 15, 20 and 25 tubes was determined throughout all the seasons. Moreover, the performance of the residential solar water heating system with a 20-tube collector was investigated in detail for mass flow rates of 0.03, 0.05 and 0.07 kg/s.

Performance analysis of a multi-pass solar thermal collector system under transient state assisted by porous media

An enhanced forced convective multi-pass solar air heating collector (MPSAHC) system aided with granite pebble bed has been investigated in this present article. The air heating collector system was tested in the outdoor solar research site of Universiti Teknologi PETRONAS, Malaysia (4.385693° N and 100.979203° E). Transport pipe for movement of heated air around the system was eliminated in the design of the MPSAHC facility to minimise the thermal losses, pressure drop and the pumping cost of the hot air in the control volume. The daily ambient temperature and relative humidity range recorded during the repeated tests are 21.09–36.64 °C and 48.04–87.9%, respectively. The collector unit achieved a peak temperature of 80.29 °C while the optimum system air mass flow rate of 0.016 kgs−1 was applied. Despite high relative humidity of the environment, the stream of ambient air was heated to 48.53 °C, 57.75 °C and 71.19 °C at different positions in the MPSAHC which correspond to single pass, double pass and multi-pass effects, respectively. The porous matrix exhibited slow energy discharge at night time with air temperature difference of 14.27 °C at 18:00 h to 4.54 °C at 24:00 h over environmental air temperature. MPSAHC system delivered specific energy demand (SED) of 11.51 kWh kg−1 while the maximum thermal collector and daily average transient collector efficiencies of 72.59% and 36.38% were achieved, respectively. A good agreement has been established between reported studies and the present investigation. Although continuity of system operation at night was achieved using porous matrix but improvement is still needed to optimise the system performance.

Scenario-Based Multi-Objective Optimization of an Air-Based Building-Integrated Photovoltaic/Thermal System

In this paper, a genetic algorithm-based multi-objective optimization of a building-integrated photovoltaic/thermal (BIPV/T) system is carried out to find the best system configurations which lead to maximum energetic and exergetic performances for Kermanshah, Iran climatic condition. In the proposed BIPV/T system, the cooling potential of ventilation and exhaust airs are used in buildings for cooling the PV panels and also heating the ventilation air by heat rejection of PV panels. Four scenarios with various criteria in the form of system efficiencies and useful outputs are considered to reflect all possible useful outputs in the optimization procedure. This study models a glazed BIPV/T system with various collector areas (Apv=10,15,25,and30m2) and different length to width ratio (L/W=0.5,1,1.5,and2) to determine the optimum air mass flow rate, bottom heat loss coefficient, depth of the channel as well as the optimum depth of the air gap between PV panel and glass cover that maximize two defined objective functions in different scenarios. Results showed that using fourth scenario (with the annual total useful thermal and electrical outputs as objective functions) and first scenario (with the annual average first- and second-law efficiencies as objective functions) for optimizing the proposed BIPV/T system leads to the highest amount of useful thermal and overall outputs, respectively. Moreover, it was concluded that, if the electrical output of the system is more important than the thermal output, the first scenario gives better results.

Aerodynamic Design and Performance Assessment of a Centripetal-Flow Fan

In this paper, the aerodynamic and mechanical design of a centripetal-flow fan has been undertaken at a particular thermal environment in which the working fluid behaves as an ideal gas. A preliminary design (one-dimensional analysis) study was conducted at first, based on which three-dimensional modeling and optimization were subsequently applied to the design of the centripetal-flow fan. The aerodynamic performance of the designed fan and its operating characteristics in different working conditions were assessed by means of numerical simulations. Our results suggest that isentropic efficiency and pressure ratio of the centripetal-flow fan at design operating conditions can reach 81.14% and 1.0833, respectively, which satisfy the requirements for fans in commercial and industrial applications. From the fan performance curves, it is found that as the mass flow rate increases, the efficiency of the fan operating at the designed rotational speed first increases and then decreases. There exists an optimal mass flow rate which leads to the maximum efficiency of the fan. Similarly, the fan pressure ratio first increases as the mass flow rate increases, attains a maximum value and then decreases as the mass flow rate further increases. At off-design rotational speeds, although the fan characteristic curves show the same tendency as those observed at the design condition. Moreover, the fan characteristic curve becomes steeper with an increased rotational speed, which means that the variations of isentropic efficiency and pressure ratio with change in mass flow rate become much greater. The results of our present study confirm the feasibility of using the centripetal-flow fan for various industrial applications.

Pseudo-online optimization of condenser pressure for the cold-end system with variable speed pumps

The operation conditions of the cold-end system have significant impact on the unit thermal economy. However, due to the difficulty of online determination of some key parameters, the condenser pressure optimization has been a challenging task for a long time. This paper proposes an online applicable approach to optimize the condenser pressure with variable speed pumps, taking the mass flow rate of the circulating water as the manipulating variable, to achieve better thermal economy. After the exhaust steam wetness fraction is online identified, the condenser thermodynamic characteristics under varying working conditions are investigated based on the effectiveness and steady-state energy balance of the condenser. By maximizing the net power benefit, defined as the difference between the unit power increment and the pump power consumption increment, the optimal mass flow rate of the circulating water is derived. To validate the approach, pseudo-online simulations are conducted with the history data from an ultra-supercritical unit. The retention time during which the set value of the mass flow rate of the circulating water remains constant is studied in context with the implementation of the manipulation strategy under on-site scenario. Simulation results reveal the energy-saving potential of condenser pressure optimization with the proposed approach.

Thermal investigation and performance analysis of a novel evaporation system based on a humidification-dehumidification process

A novel humidification-dehumidification (HDH) system is designed to enhance the evaporation capacity. A more rigorous mathematical model of humidifier is proposed. A simulation programme of the whole system is built. Theoretical investigation is performed to investigate the effect of various parameters on the evaporation capacity and gained input ratio. The results demonstrate that the reflux ratio and inlet solution temperature of the humidifier are proportional to the evaporation capacity. An optimum mass flow rate of air exists for which the evaporation capacity is maximized. The gained input ratio (GIR), defined as the ratio between the total latent heat of evaporated water and the external heat input, decreases with the increase in air mass flow rate and increases with the increase in the reflux ratio. The optimum value of the gas-liquid ratio for maximum evaporation capacity is near 1.17, regardless of conditions. A multi-index comprehensive evaluation is introduced to assess the overall performance of the system. And a practical case is carried out to illustrate how to select the optimum operational parameters under different circumstances.