Water Mass Flow Rate Research Articles

Exergy Analysis of Supercritical CO2 System for Marine Diesel Engine Waste Heat Recovery Application

In this research is performed an exergy analysis of supercritical CO2 system which uses various waste heat flows from marine diesel engine to produce additional mechanical power. The performed exergy analysis contains whole system as well as each system component individually. The observed system produces useful mechanical power equal to 2299.47 kW which is transferred to the main propulsion propeller shaft. Additionally produced mechanical power by using waste heat only will reduce marine diesel engine fuel consumption and exhaust gas emissions. Main cooler has the highest exergy destruction of all system components and simultaneously the lowest exergy efficiency in the observed system, equal to 32.10% only. One of the possibilities how main cooler exergy efficiency can be increased is by decreasing water mass flow rate through the main cooler and simultaneously by increasing water temperature at the main cooler outlet. Observed system has five heat exchangers which are involved in the CO2 heating process, and it is interesting that the last CO2 heater (exhaust gas waste heat exchanger) increases the CO2 temperature more than all previous four heat exchangers. Whole analyzed waste heat recovery supercritical CO2 system has exergy destruction equal to 2161.68 kW and exergy efficiency of 51.54%. In comparison to a similar CO2 system which uses waste heat from marine gas turbine, system analyzed in this paper has approximately 12% lower exergy efficiency due to much lower waste heat temperature levels (from marine diesel engine) in comparison to temperature levels which occur at the marine gas turbine exhaust.

Influence of the hot water mass flow rate on heating of radiant floors of green buildings

The objective of the research is to improve space heating of green buildings by examining experimentally the influence of the heating medium mass flow rate on thermal performance. A green building was built in Cairo, Egypt, that consists of two similar rooms: one is the heated room and the other is a reference for comparison. A photovoltaic thermal (PV/T) collector is used to heat up water in a storage tank, and the hot water in the tank is circulated in the radiant floor of the examined green building. The hot water mass flow rate was varied between 0.04 and 0.08 kg/s. It was found that decreasing the water mass flow rate improves the heating of the radiant floor. The percentage improvement in floor temperature due to heating over the reference room, reaches about 17% and 6% at mass flow rates of 0.04 and 0.08 kg/s, respectively. Engineering Equation Solver (EES) was used to solve the equations for the heat transfer process between the heating water and the floor. It was found that decreasing the mass flow rate increases the residence time of the heating water in the radiant floor, consequently, increases the heat energy transfer and the floor temperature. Increasing the heating fluid mass flow rate in green buildings could have a negative effect on the heat transfer, such that the appropriate heating fluid mass flow rate should be calculated based on the green building massive material as well as the operating conditions, for example, ambient temperature and wind speed.

High performance vapor chamber enabled by leaf-vein-inspired wick structure for high-power electronics cooling

The boom of the advanced technologies, such as microprocessors, 5G, and big data, has led the thermal management to be a crucial factor in determining the operating speed, reliability, and efficiency as well as lifetime of electronic devices. As passive heat transfer devices utilizing the liquid–vapor phase change, vapor chambers are greatly attractive due to the high thermal conductivity and passive operation. Here, we present a novel vapor chamber with leaf-vein-inspired wick structure, which could effectively facilitate the condensate to flow back to the evaporation region. Besides, the capillary wick functioned as the supporting structure instead of traditional solid supporting columns to withdraw the deformation of the vapor chamber. The heat transfer performance of the proposed vapor chamber was experimentally investigated under forced water cooling condition, and the effects of the cooling water temperature and mass flow rate were analyzed systematically. The results showed that the vapor chamber could effectively tolerate a wide heat load range from 20 W to 500 W with no noticeable performance degradation, and a minimum thermal resistance of 0.029 °C/W was attained at 200 W. Additionally, increasing the cooling water temperature and decreasing the cooling water mass flow rate could lead to the increase of the total thermal resistance at all heat loads. Finally, compared to other reported works, the vapor chamber featured a lowest thickness and vapor chamber thermal resistance, demonstrating a promising solution for cooling high-power and miniaturized electronics.

An integrated sustainable system fueled by Co-Combustion of legume straw biomass and synthesis gas of SOFC: Optimization study using Signal-To-Noise ratio analysis

A novel tri-generation system of power, heating, and freshwater is developed in this study. The system integrates of a supercritical CO2 Brayton cycle, a solid oxide fuel cell, and a desalination system of humidification-dehumidification type. The system is fueled by a combustion of the synthesis gases of the solid oxide fuel cell helping by a legume straw biomass flow. The heat is recovered from the combusted gases and triggers the supercritical CO2 Brayton cycle and the desalination system. The key variables of the solid oxide fuel cell are evaluated and their influences on the voltages are examined in details. They are optimized using Taguchi approach and signal-to-noise ratio analysis to achieve the maximum solid oxide fuel cell power. Current density of 9375 A/m2, utilization factor of 0.7, temperature of 900 K, steam to carbon ratio of 2, anode recycling coefficient and cathode recycling coefficient of 0 are recognized to be the optimal conditions. The fuel cell power is 625.3 kW in this optimal state. The system provides 674.6 kW of net power, 157.3 g/h of mass flow rate of freshwater and 13812 kg/h of mass flow rate of hot water in its optimum condition.

Off-design condition optimization of organic Rankine cycle based on genetic algorithm

Organic Rankine cycle (ORC) has been considered as one of the most promising technologies in industrial waste heat utilization and power generation. During the actual operation of ORC system, due to the fluctuation of cooling and heat sources, the system operates under off-design conditions in most cases. In this paper, thermodynamic model, heat transfer process description and power equipment model are established to evaluate the operating parameters of ORC for the off-design conditions. Evaporation temperature and condensation temperature are taken as independent parameters for the operation of ORC system. Genetic algorithm is adopted to optimize the independent parameters under the maximum net output power. The results show that the effect of optimizing independent parameters is to make the working fluid at the outlet of the preheater as close as possible to a saturated liquid state, and the working fluid at the inlet of the screw expander should be in a saturated gas state. With the optimal power output increasing by 19.1% for every 5 °C increase in hot water inlet temperature, 9.2% for every 20 kg/s increase in hot water mass flow rate, and 3.9% for every 1 °C decrease in cooling water temperature. The optimization method of off-design operating conditions has good system performance and good engineering application prospects.

Electron Target Cooling Analyses of the KIPT ADS Using MCNP and Ansys Fluent

This study presents multiphysics analyses of the electron target cooling system of the accelerator-driven system (ADS) of the Kharkiv Institute of Physics and Technology (KIPT) using MCNP and Fluent computer programs. MCNP has been used to transport electrons, gammas, and neutrons, and to calculate the energy deposition in the target materials. The MCNP mesh-tally data have been imported into Fluent by a C subroutine that has been compiled and linked to Fluent as a user-defined function. The KIPT ADS is located in Ukraine and was in operation until February 2022. The Fluent model is based on the computer-aided design files from the manufacturing process of the target assembly. The Fluent results for the reference case match very well the literature results obtained by STAR-CCM+ during the design phase. Other cases that differ from the reference one have been analyzed; in these cases, it is assumed a malfunction of the electron accelerator or of the water cooling system. The target cooling system operates normally for all the analyzed cases except when the inlet water mass flow rate is decreased. The transient analysis showed that the target cooling system can operate for 180 s with full power when the inlet water mass flow rate is decreased down by 75%.

Semi Twisted Curve Blade Vortex Turbine Performance at Runner Rotation Speed Variation using CFD Simulation

Utilization of renewable energy potential continues to be developed at this time. One of them is a hydroelectric power plant with turbulent vortex technology. One of the vortex turbine blade designs that has been developed is the semi twisted curve. The blades shape of the blades and the position of the runners affect the performance of the vortex turbine. This research uses CFD simulation by varying the rotational speed of the runner, which is between 80 to 120 rpm. The position of the upper end of the runner is placed at a depth of 4.5 cm from the total depth of the cone basin of 33 cm, the maximum water power is set at 28.66 Watt obtained from the mass flow rate of water of 6.21 kg/s. The simulation results show that as the runner's rotational speed increases, the torque decreases, as well as the torque decreases slightly. The highest turbine power and efficiency occurred at 90 rpm runner rotation, which was 4.044 Watt and 14.11% respectively. This is because the turbine power calculation is the result of the multiplication between torque and runner rotation which produces the highest value at 90 rpm.

Comparison of Continuous and Pulsating Water Jet during Piercing of Ductile Material.

More efficient ways to process materials are constantly being sought, even in the case of continuous water flow technology, which acts on materials mainly by stagnant pressure. An alternative method is an ultrasound-stimulated pulsating water jet, the basis of which is the repeated use of impact pressure, which reduces the time interval for mechanical relaxation. This article focuses on a comparative study from the point of view of water mass flow rate on material penetration and its integrity. Relatively low pressures (p = 20, 30, and 40 MPa) with varying nozzle diameters (d = 0.4 and 0.6 mm) were used to identify the effectiveness of the pulsating water jet. The time exposure of the jet at a fixed place was varied from t = 0.5 to 5 s for each experimental condition. The results showed that with an increase in the pressure and diameter values, the disintegration depth increased. In addition, the surface topography and morphology images showed signs of ductile erosion in the form of erosion pits, upheaved surfaces, and crater formation. The microhardness study showed an increase of 10% subsurface microhardness after the action of the pulsating water jet as compared to the original material.

Analysis of Variance of the Heat and Mass Transfer Coefficients in an Evaporative Condenser

Modelling of evaporative condensers relies heavily on the correct choice of the correlations for transport coefficients to give an accurate estimate of the dissipated thermal load and evaporated water mass flowrate, yet the literature does not cover all flow arrangements, nor operating conditions. In order to avoid expensive, and often impractical, experimental campaigns devoted to the determination of these quantities for a specific piece of equipment, a statistical approach based on the analysis of variance can be adopted: by analysing the sensitivity of the dependent variables on the choice of the transport coefficients, the best set of correlations can be determined, depending on whether a more accurate estimate is desired for the heat flux or evaporated mass flowrate, or if both are equally important.

Performance analysis of nuclear powered desalination unit based on MED-TVC: a case study for Saudi Arabia

Abstract Nuclear desalination has been identified as an alternative option with much lower carbon dioxide emissions to provide fresh water by driving high capacity desalination plants. This work considers a theoretical analysis of using nuclear desalination to provide fresh water in three selected Saudi Arabian cities. It presents a theoretical model that integrates the characteristics of nuclear reactor, power cycle and desalination blocks. The power block includes three steam turbines and five feed water heaters. It is coupled via low pressure turbine to a multiple effect desalination unit integrated with a thermal vapor compressor encompassing eight effects, seven feed preheaters and a down condenser. The output includes work generated as function of fuel mass and reactor type, enrichment percentage, power and water production with different nuclear reactor type. Desalination performance indicators such as the fresh water production rate, gain output ratio (GOR), specific energy consumption (SEC) and specific cooling water mass flow rate have been evaluated and analyzed as function of sea water temperature for three specific Saudi cities. It was found that these indicators reflect better performance along a year for Jizan city than for Jubail and Tabuk. The case of Jizan city gives over the whole year more uniform values of water production rates, gain output ratio, specific energy consumption and cooling water mass flow rates.

Thermodynamic assessment of a new PTC operated polygeneration system for fresh water, cooling, electricity and hydrogen production for a residential community

The current study aims to design a new parabolic trough collector (PTC) operated polygeneration system to produce freshwater, hydrogen, cooling, and electricity in a residential society. Dowtherm A (a heat transfer fluid) is used to transfer the heat from PTC to the Organic Rankine Cycle, which is used to produce electrical power. The produced electrical power is utilized in three different ways, namely, to run the home appliances, to produce hydrogen (via water electrolysis), and to produce cooling (through a vapor compression cycle). The cooling produced by the vapor compression system is utilized to preserve the food, milk, and to operate the freezing desalination process. Effects of several factors, such as direct normal irradiance, evaporator temperature, and seawater inlet temperature, have been analyzed on the overall system behavior. Thermodynamic study results show that for a PTC area of 2000 m2, an electrical output obtained is 72 kW, the cooling rate is 112 kW, and the mass flow rate of fresh water produced is 18.4 l/day and 10.8 kg/day of hydrogen for mean solar irradiation of 700 W/m2. The energy efficiency of the system is found to be 17.5%, and the exergy efficiency of the system is around 10.9%.

Machine learning-assisted tri-objective optimization inspired by grey wolf behavior of an enhanced SOFC-based system for power and freshwater production

In recent years paying attention to the generation of clean and sustainable power and fresh water along with having lower cost and emission has increased. In the present research, a novel scheme for generating efficient power using the flame-assisted fuel cell is introduced, which has higher efficiency than ordinary fuel cells due to increased hydrogen concentration in the flame-rich combustion chamber. The waste heat is then introduced to a multi-effect desalination unit through a heat recovery steam generation unit to generate fresh, drinkable water. In order to make the system have higher efficiency, lower cost, and lower emission, the machine learning techniques are applied to optimize the operational conditions of the system, and find out the best solution point based on the cutting-edge algorithm of the grey wolf. Also, a complete techno-economic analysis and a parametric study are necessary to figure out the best solution point based on the TOPSIS method. The results indicate that the maximum value of exergy efficiency and drinkable water generation is 67.5% and 3.4 kg/s, respectively, while the minimum energy cost is 90.1 $/MWh. Moreover, results show that for the second optimization scenario considering the drinkable water production, energy cost, and pollution index as the objectives, the net produced power, energy efficiency, exergy efficiency, and water mass flowrate improve by around 1059 kW, 5.1%, 1.3%, and 1.6 kg/s than the design condition. Besides, energy cost and emission index are reduced by about 22 $/MWh and 51.9 kg/MWh, respectively.

Experimental Study of Double Pipe Helical Coil Heat Exchangers in the Laminar to Transitional Flow Regime

This study experimentally investigates various heat transfer characteristics, pressure drop, friction factor, Nusselt number, and Dean Number in a double-pipe helical coil heat exchanger. The study examines the hot water mass flow rates ranging from 0.02 to 0.12 kg/s and the cold-water mass flow rates ranging from 0.055 to 0.15 kg/s. The cold-water inlet temperature was maintained at 29°C, while the hot water inlet temperature varied between 65-75°C. Based on the hydraulic diameter of the annular space between the two tubes, the Reynolds number ranged from 1000-6000. All required parameters, such as the inlet and outlet temperatures of the inner coil and annulus fluids and the flow rate of fluids, were measured using appropriate instruments. Seventy-two test runs were conducted, from which the heat transfer coefficients of the inner coil side and annulus side were calculated. The calculated heat transfer coefficients of the inner coil were compared with available correlations from the literature, and a reasonable agreement was found.

Performance investigation and numerical evaluation of a single-effect double-lift absorption chiller

This study deals with innovative integrated absorption refrigeration systems. This cycle could be useful for converting low-temperature energy sources into useful outputs like cooling. The Single Effect Double Lift Absorption Chiller (SE-DL AC) was introduced and energetically evaluated. A detailed modeling based on the first law of thermodynamics is built to investigate the performance of this novel system. This model was initially validated considering a reference SE-DL AC from the Hitachi company with a nominal cooling capacity of 106.1 kW. This system is compared to a conventional single-effect absorption chiller while maintaining the same operating parameters and boundary conditions in both configurations to ensure a fair comparison in terms of the internal and external baseline operating conditions. A parametric study of the driving hot water inlet temperature, the solution mass flow rate, the effectiveness of the solution heat exchanger, and internal and external temperatures on the Coefficient of Performance (COP), Cooling capacity (CC), and Glide Temperature (ΔT) are conducted. The final results demonstrate that the cooling production capability of the SE-DL is increased by an average of about tenfold when compared to the conventional SE AC at a thermal source temperature of 88.7 °C and an inlet hot water mass flow rate of 1 kg/s. The COP results produced under the same operating conditions are quite similar. The cooling generation capability of the SEDL is, on average, 10 times greater than that of the traditional SE AC. This explains that the SEDL-AC is well suited for a wide range of low-temperature heat sources (e.g., solar energy). Furthermore, the SE-DL AC enables efficient use of low-grade heat with a high glide temperature in the driving heat stream of about 10 times (36 °C instead of 3.5 °C). This large temperature difference exemplifies that the SE-DL AC absorption chiller is an alternative for extracting as much heat as possible, thereby improving cold production.

The adoption of pressure independent control valves (PICVs) for the simultaneous optimization of energy consumption and comfort in buildings

The optimization of energy consumption in buildings’ HVAC systems plays a crucial role in reducing greenhouse gas emissions worldwide. In new and deeply-renovated buildings, characterized by modulating terminal units and aiming at the maximum exploitation of renewables, an accurate hydraulic balance of the distribution network may become critical, resulting in a significant increase of pumping energy consumptions and a deterioration of indoor thermal comfort conditions. In the present paper, we compare the performance of traditional manual balancing valves and new pressure independent control valves (PICVs), used to balance the hydronic loop of HVAC systems. To perform this analysis, a new MATLAB-Simulink model has been specifically developed to simulate the behavior of PICVs and has been used in an application case study. The efficiency of manual and pressure independent control valves is evaluated numerically by simulating a multi-zone distribution network under variable operating conditions and considering different control strategies of the circulating pump. Results show that in off-design conditions, when some of the branches of the hydraulic network are closed, traditional manual balancing valves are not able to guarantee the nominal mass flow rate in the remaining loops. On the contrary, no significant variations of water mass flow rate are observed when PICVs are adopted, even in partial load conditions. Despite their additional cost, PICVs allow to ensure better indoor thermal comfort sensations for individuals, avoiding under/over-heating of rooms and, moreover, yield a decrease of the pump electric consumption with respect to traditional manual balancing valves. In addition, based on the obtained results, general rules concerning the adoption of PICVs are provided, depending on the extension of the hydraulic loop and the adopted pump control logic. The reported results highlight the role that PICVs can play to ensure energy savings in HVAC systems without penalizing users’ indoor comfort conditions.

Innovative solar natural vacuum desalination system

The main target of the work is a design of an innovative solar natural vacuum desalination (SNVD) system and improve performance of such systems. The natural vacuum is developed by raising up an evaporation chamber to 9.8 m above the ground. The waste heat is efficiently utilized in that system to minimize the system heat loss. The fresh water is first preheated by condensing vapor from the evaporation chamber before it is heated by a flat-plate collector as a heat source of the evaporation chamber. On the other side, the sea water is preheated by the produced warm water, and it is reheated by the exit brine water before it is supplied into the evaporation chamber. A mathematical model and a transient simulation were established to investigate the annual performance of system. A heat balance of each system component was provided to estimate the inlet and outlet temperature and flow rate of it. Moreover, the collector area was estimated based on assumed mass flow rates of both feed sea water and coolant water. It was found that the system can produce a daily production of 6.2 L of pure water per a quadratic meter of collector on annual average basis. That Productivity can be estimated as 1.12 L of water per kWh solar radiation. Accordingly, the evaporation rate was estimated as 2.82% while the gain output ratio (GOR) was obtained as 0.63. The system performance can be accepted compared with the corresponding published systems.

Efficient Surrogate-Assisted Parameter Analysis for Coal-Supercritical Water Fluidized Bed Reactor with Adaptive Sampling

Supercritical water fluidized beds (SCWFBs) are promising and efficient reactors for the gasification of coal in supercritical water. The understanding and investigation of multi-phase flows as well as the gasification process usually rely on time-consuming experiments or numerical simulations, which prohibit fast and full exploration of the single and coupled effects of the operation and geometric parameters. To this end, this paper builds an efficient surrogate-assisted parameter analysis framework for the SCWFB reactor. Particularly, (1) it establishes a steady numerical simulation model of the SCWFB reactor for the subsequent analysis; and (2) it employs a Gaussian process surrogate modeling via efficient adaptive sampling to serve as an approximation for predicting the carbon conversion efficiency (CE) of the reactor. Based on this parameter analysis framework, this paper investigates the effects of five independent parameters (the mass flow rate of supercritical water, mass flow rate of the coal slurry, temperature of supercritical water, temperature of the outer wall and reactor length) and their interactions on the reaction performance in terms of the carbon conversion efficiency (CE). We found that the CE increases as a function of the temperature of supercritical water, the temperature of the outer wall and the reactor length; while it decreases as a function of the mass flow rate of supercritical water and the mass flow rate of the coal slurry. Additionally, the global sensitivity analysis demonstratesthat the influence of the temperature of the outer wall exerts a stronger effect than all the other factors on the CE, and the coupled interaction among parameters has a slight effect on the CE. This research provides useful guidance for scaled-up designs and optimization of the SCWFB reactor.

Numerical study and experimental validation of a solar powered humidification-dehumidification desalination system with integrated air and water collectors in the humidifier

This paper presents a numerical study and experimental validation of humidification-dehumidification solar desalination unit. This unit consists of a solar evaporator and a tubular condenser. The design particularity of the evaporator is the integration of the humidifier in the solar air and water collectors. A mathematical model based on the heat and mass balances has been developed in the desalination unit. The finite difference method is adopted for discretization of the equations and the resolution is done by MATLAB software. Numerical results are compared with literature and experimental results. An acceptable agreement is observed. A parametric study was conducted to test the influence of the different operating parameters on the unit production and the Gained output ratio GOR. The production of the desalination system increases with air and water temperatures of the water in the evaporator and the inlet humid air temperature at the dehumidifier. It should be noted that the production reaches its maximum value for a feed water mass flow rate in the humidifier of 5.5 kg/h and a cooling water mass flow rate in the dehumidifier of 0.2 kg/s.

Modeling an Evaporative Cooling System to Improve Gas Turbines Performance

Abstract Evaporative cooling systems are commonly used in thermoelectric plants to cool the air at gas turbines inlet, improving the performance of these engines. Normally, the evaporative cooling is modeled as adiabatic saturation and, in this case, the water-air equilibrium temperature depends only on the atmospheric air properties. However, other factors such as the water temperature that supplies the equipment and the ratio between the mass flow rates of water and air, also affect the equilibrium conditions of these systems. This work presents three methodologies to calculate the air temperature in equilibrium state, considering all the factors mentioned. The methodologies were implemented in a computer program written in fortran. In all cases tested, the results obtained by the three models showed high convergence. As an example, for 70 different sets of inputs, the absolute and relative differences of the results were below 0.3236 °C and 1.2480%, respectively. A statistical study, also on this sample of results, revealed that, for a confidence level of 99%, the hypothesis of the equivalence between the methods cannot be rejected.

Hybrid thermosolar-LPG dehydrating plant installed in Xochitepec, México. Case study: Pineapple

A hybrid thermosolar plant for the dehydration of food products was designed and installed in Xochitepec, Morelos, Mexico. The plant is integrated by a semi-continuous drying chamber with a drying area of 56.3 m2. The required energy is provided by two solar thermal systems: an air heating system and solar water heating system, both with 16 solar collectors (40 m2), a thermotank (2500 l), and an air/water heat exchanger. The plant has a fossil energy backup system of Liquefied Petroleum Gas (LPG) to heat air with hot water and the air/water heat exchanger. The monitoring system measures and records different process variables (temperature, relative humidity, solar irradiance, air velocity, and water mass flow rate). The average thermal efficiency of the field of solar water heaters and air heaters was 38.80 % and 50.40 %, respectively. Both thermosolar systems are able to deliver air temperature above 40 °C required during the process. The return of investment analysis is developed according to life cycle analysis and payback period methods. According to the results, different kinds of food products can be dried on the thermosolar plant, resulting in attractive payback periods and environmental benefits.