Inlet Temperature Conditions Research Articles

Thermal Performance of Hollow-Core Slab Ventilation System with Macro-Encapsulated Phase-Change Materials in Supply Air Duct

The aim of this research was to evaluate the effectiveness of phase-change materials (PCMs) incorporated into the supply air duct of a hollow-core slab ventilation system. Both experimental and numerical approaches were adopted in this investigation. In the experimental work, the air was passed through a PCM-incorporated aluminum air duct, and the temperature at various points of the duct was recorded. Computational fluid dynamics models of the PCM-incorporated supply air duct and the hollow-core slab were developed and validated with the respective experimental data. The validated models were used to simulate the performance of PCM-incorporated hollow-core slabs during summer in Melbourne, Australia. The results showed that the reduction in temperature fluctuation varied with the way the PCM was incorporated inside the supply air duct. The temperature difference was maximum and was maintained for a longer period when the PCM was spread to all four internal surfaces of the supply air duct. The results also showed that the effectiveness of the combined PCM–air duct–hollow-core slab system in reducing the temperature fluctuation was lower than the individual performance of the PCM–air duct and hollow-core concrete slab for a given inlet temperature condition during the simulated period. This was because the integration of PCMs in the supply air duct resulted in a precooling effect which reduced the difference between the amplitude of slab inlet temperature swing and average slab temperature. As a result, the reduction in temperature fluctuation due to the thermal mass of the hollow-core slab was 21% lower in the presence of PCMs compared to the no-PCM case.

Studying the performance of a liquid desiccant indirect evaporative cooling system

A liquid desiccant-indirect evaporative cooling (LD-IEC) system has been proposed. The design is able to dehumidify and cool the product air simultaneously in one unit. A computational model has been developed to determine the performance of the heat and mass transfer process. The validation of the model demonstrated good agreement with the experimental data to within 10%. The detailed air treatment process has been theoretically studied. The thermal performance of the LD-IEC has been evaluated. Simulation results showed that the outlet temperature and humidity ratio were influenced by the liquid desiccant film length, intake air temperature, and intake air humidity ratio. For a specific inlet temperature and humidity ratio condition, a desired outlet condition can be obtained by adjusting the length of the liquid desiccant film.

Physicochemical Properties and Oxidative Stability of Milk Fortified with Spray-Dried Whey Protein Concentrate–Iron Complex and In Vitro Bioaccessibility of the Added Iron

SUMMARYIn the present study, spray-dried whey protein concentrate–iron (WPC–Fe) complex was prepared using a laboratory-scale spray drier under the optimized conditions of inlet temperature 180 °C, flow rate 2.66 mL/min and total solids 15% with the objective to make iron compatible with food products. In order to remove the free iron from the bound iron, standardised method involving centrifugation and ultrafiltration was employed. Further, the retentate was subjected to spray drying to produce WPC–Fe complex. Milk fortified with WPC–Fe complex (γ(iron)=15 mg/L) showed non-significant difference in heat stability, rennet coagulation time, colour estimation, curd tension, viscosity and sensory attributes as compared to control milk. In vitro bioaccessibility of iron and induction period of the fat from milk fortified with WPC–Fe complex were found to be slightly higher (p<0.05) than that of milk fortified with iron alone. Therefore, milk can be fortified with up to 15 mg/L iron in the form of WPC–Fe complex without significantly affecting its physicochemical properties.

Energy and exergy analysis of an organic Rankine cycle under different heat source and turbine inlet temperature conditions

In this study, the effect of turbine inlet temperature change on organic fluid performance in three different Organic Rankine Cycle (ORC) models designed using R113, R123 and isopentane fluid was determined. With the MATLAB and EES program, 17 different models have been formed for the heat source temperature that changes with the turbine inlet temperature. By analyzing the determined organic fluids on the generated models, the amount of heat entering the system, the work produced by the turbine, thermal efficiency, total exergy destruction and exergy efficiency were determined. While turbine inlet temperature is 80oC and heat source temperature is 110oC, isopentane fluid can reach maximum 8.8% while R113 fluid has reached 12.4% in same design conditions. With all cases examined, it is stated that isopentane fluid needs more heat input per unit mass compared to other fluids. While the maximum value of 531.7 kJ/kg heat input is required for isopentane fluid, R113 and R123 fluids require a maximum of 220.2 kJ/kg and 246.8 kJ/kg respectively. When the work values obtained from the turbine are examined, it is stated that R113 and R123 fluids show close properties. In this study, a maximum of 21.63 kJ/kg and 26.98 kJ / kg turbines were obtained for R113 and R123, while a 45.35 kJ/kg turbine work was obtained in the model using isopentane fluid. In exergy analysis, it was found that the best exergy efficiency performance was obtained in R113 fluid with 56.3%. In addition, the effect of overheating the organic fluid on the energy and exergy efficiency of the system was determined by the constant acceptance of the turbine inlet pressure.

Experimental and numerical investigation of taper helical and spiral tube thermal performance

This paper presents the comparative experimental and numerical study of heat exchange through tapers helical and spiral tube. The efficiency of heat exchange is increase the thermal performance as well as productivity. The main study was a focus on these two shapes of pipe at various process parameters like mass flow rate and inlet temperature conditions. Co-relation equations were developed for both shapes of pipe with a linear fitting tool available in MATLAB coding software. Proper instrumentation and calibration were taken care in this work. The simple horizontal pipe was used to validate the experimental results with computational fluid dynamics (CFD) results. Experimental validation proves that CFD is an effective tool for thermal performance investigation. The main conclusion of present work was that spiral tube displays enhanced thermal enhancement than the helical tube for all process conditions. Thermal contours are also developed for more detailed study on both shapes of the tube.

Supersonic liquefaction properties of natural gas in the Laval nozzle

In view of the excellent performance of the supersonic separator for natural gas dehydration, a new type of natural gas liquefaction process using the Laval nozzle is proposed in this paper. Theoretical and numerical studies of the supersonic flow and liquefaction process of the methane-ethane binary system in this nozzle are carried out. The effects of the inlet temperature, inlet pressure, back pressure and component composition on the liquefaction process are analyzed. The results show that the critical liquefaction temperature and pressure of the methane-ethane binary system decrease under low inlet temperature or high inlet pressure conditions and the range of the liquid phase region increases, which promotes the liquefaction process. With the increase of the back pressure of the nozzle, the position of the shock wave moves forward and the liquefaction environment is more completely destroyed. For a multi-component natural gas, in which the heavy hydrocarbon content is high, natural gas is more easily liquefied using the Laval nozzle. The liquefaction efficiency range of the newly designed liquefaction process with the Laval nozzle are 0.0795–0.1321 (HYSYS results) and 0.0718–0.1505 (MATLAB results) when the inlet pressure of the process is 2–5 MPa. The nozzle more easily achieves liquefaction compared with a throttle under the same conditions.

Performance investigation of a novel closed Brayton cycle using supercritical CO2-based mixture as working fluid integrated with a LiBr absorption chiller

A novel closed Brayton cycle using supercritical CO2–Kr mixture as working fluid integrated with an absorption chiller (CBC/AC) is proposed. The waste heat of the CO2–Kr in the cold end of the top closed Brayton cycle (CBC) is utilized to drive the absorption chiller, which further chills the CO2–Kr fluid exiting the precooler before it enters the main compressor. Compared with the stand-alone supercritical CO2 (S-CO2) CBC, the CBC/AC exploits the performance improvement potentials under low ambient temperature (T0) condition and alleviates the performance penalty under high T0 condition. The energy and exergy analyses of the CBC/AC in three typical T0 conditions (10 °C, 25 °C and 40 °C) show that the thermal efficiencies are improved by 3.12%, 0.40% and 6.86%, respectively, the exergy efficiencies are improved by 3.53%, 0.54% and 7.53%, respectively. The exergy loss from the precooler is significantly reduced in the CBC/AC relative to that in the stand-alone S-CO2 CBC. The comparisons between different working conditions for the CBC/AC indicate that the improvements of the thermal and exergy efficiencies are more apparent under water-cooling and high turbine inlet temperature conditions. The effects of the component performance on the CBC/AC are also evaluated.

The effects of microfluidization on the physical, microbial, chemical, and coagulation properties of milk

This work examines the use of mild heat treatments in conjunction with 2-pass microfluidization to generate cheese milk for potential use in soft cheeses, such as Queso Fresco. Raw, thermized, and high temperature, short time pasteurized milk samples, standardized to the 3% (wt/wt) fat content used in cheesemaking, were processed at 4 inlet temperature and pressure conditions: 42°C/75 MPa, 42°C/125 MPa, 54°C/125 MPa, and 54°C/170 MPa. Processing-induced changes in the physical, chemical, and microbial properties resulting from the intense pressure, shear, and cavitation that milk experiences as it is microfluidized were compared with nonmicrofluidized controls. A pressure-dependent increase in exit temperature was observed for all microfluidized samples, with inactivation of alkaline phosphatase in raw and thermized samples at 125 and 170 MPa. Microfluidization of all samples under the 4 inlet temperature and processing pressure conditions resulted in a stable emulsion of fat droplets ranging from 0.390 to 0.501 μm, compared with 7.921 (control) and 4.127 (homogenized control) μm. Confocal imaging showed coalescence of scattered fat agglomerates 1 to 3 μm in size during the first 24 h. We found no changes in fat, lactose, ash content or pH, indicating the major components of milk remained unaffected by microfluidization. However, the apparent protein content was reduced from 3.1 to 2.2%, likely a result of near infrared spectroscopy improperly identifying the micellar fragments embedded into the fat droplets. Microbiology results indicated a decrease in mesophilic aerobic and psychrophilic milk microflora with increasing temperature and pressure, suggesting that microfluidization may eliminate bacteria. The viscosities of milk samples were similar but tended to be higher after treatment at 54°C and 125 or 170 MPa. These samples exhibited the longest coagulation times and the weakest gel firmness, indicating that formation of the casein matrix, a critical step in the production of cheese, was affected. Low temperature and pressure (42°C/75 MPa) exhibited similar coagulation properties to controls. The results suggest that microfluidization at lower pressures may be used to manufacture high-moisture cheese with altered texture whereas higher pressures may result in novel dairy ingredients.

Characteristics of Volcanic Ash in a Gas Turbine Combustor and Nozzle Guide Vanes

To understand the physics of volcanic ash impact on gas turbine hot-components and develop much-needed tools for engine design and fleet management, the behaviors of volcanic ash in a gas turbine combustor and nozzle guide vanes (NGV) have been numerically investigated. High-fidelity numerical models are generated, and volcanic ash sample, physical, and thermal properties are identified. A simple critical particle viscosity—critical wall temperature model is proposed and implemented in all simulations to account for ash particles bouncing off or sticking on metal walls. The results indicate that due to the particle inertia and combustor geometry, the volcanic ash concentration in the NGV cooling passage generally increases with ash size and density, and is less sensitive to inlet velocity. It can reach three times as high as that at the air inlet for the engine conditions and ash properties investigated. More importantly, a large number of the ash particles entering the NGV cooling chamber are trapped in the cooling flow passage for all four turbine inlet temperature conditions. This may reveal another volcanic ash damage mechanism originated from engine cooling flow passage. Finally, some suggestions are recommended for further research and development in this challenging field. To the best of our knowledge, it is the first study on detailed ash behaviors inside practical gas turbine hot-components in the open literature.

Stabilization and blowout characteristics of lean premixed turbulent flames behind a backward-facing step in a rectangular combustor with heated propane-air mixtures

The flame stabilization and blowout velocity of lean premixed turbulent flames in a backward-facing step combustor were investigated experimentally with well-defined stable flames. The dynamic pressure in the combustor was monitored to select a stable regime among overall flame behaviors. The responses in the flame behaviors to changes in the initial conditions of equivalence ratio, inlet temperature, and Reynolds number were simultaneously captured using high-speed CH∗ chemiluminescence. The results showed that the flame modes were categorized into four representative regimes according to their dynamic behavior, overall sound pressure level, and frequency spectrum: (1) stable regime, (2) unstable regime, (3) quasi-unstable regime, and (4) transition regime. For lean premixed turbulent flames in the stable regime, the flame distance, defined as distance x from the step to flame appearance, increased with the decrease in the initial equivalence ratio, and blowout occurred near the lower flammability limits. The blowout velocities linearly correlated with both the inverse of chemical reaction time (α0/SL,02)−1 and extinction strain rate εext,0 under different initial conditions. The two chemical time scales were obtained using different flame models based on either the premixed laminar flame-speed or premixed opposed-flow flame model. In addition, the flame distances showed a linear correlation of df ∝ U0/SL,02 for all the data in the stable regime. This result implies that the lean premixed turbulent flames could be stabilized at flame distances where the local mean flow velocity is balanced with the turbulent flame speed, which is proportional to the square of laminar burning velocity.

Heat rejection efficiency research of new energy automobile radiators

The driving system of new energy vehicle has larger heat load than conventional engine. How to ensure the heat dissipation performance of the cooling system is the focus of the design of new energy vehicle thermal management system. In this paper, the heat dissipation efficiency of the radiator of the hybrid electric vehicle is taken as the research object, the heat dissipation efficiency of the radiator of the new energy vehicle is studied through the multi-working-condition enthalpy difference test. In this paper, the test method in the current standard QC/T 468-2010 “automobile radiator” is taken, but not limited to the test conditions specified in the standard, 5 types of automobile radiator are chosen, each of them is tested 20 times in simulated condition of different wind speed and engine inlet temperature. Finally, regression analysis is carried out for the test results, and regression equation describing the relationship of radiator heat dissipation heat dissipation efficiency air side flow rate cooling medium velocity and inlet air temperature is obtained, and the influence rule is systematically discussed.

The effects of nonuniform inlet fluid conditions on crossflow heat exchanger

The influences of uneven inlet flow and temperature conditions on performance of crossflow heat exchanger using supercritical pressure CO2 (S-CO2) as working fluid were investigated from the viewpoint of distributed coordination. The inlet flow maldistribution and inlet temperature nonuniformity in either side of both fluids could deteriorate or enhance heat transfer, and the deterioration or enhancement effect of both fluids could be superimposed. The inlet conditions with enhancement effect eases the uneven distributions of heat transfer coefficient and temperature difference, and improves the distributed coordination between them, and eventually enhances the heat transfer. The total heat transfer rate depends not only on the values of heat transfer coefficient and temperature difference, but also on their coordination. The distributed coordination analysis indicates that the uneven inlet flow and temperature conditions could be used to enhance heat transfer using the special characteristics of S-CO2 without a significant increase of pressure drop. The present work may provide a new way to the optimization design of heat exchanger for the fluids with sharply variable properties.

Numerical and experimental analysis on shell side thermo-hydraulic performance of shell and tube heat exchanger with continuous helical FRP baffles

The present work deals with the numerical and experimental investigation of heat and fluid flow in shell and tube heat exchanger with continuous helical baffles on shell side. Seven helix angles, namely 10°, 19°, 21°, 25°, 30°, 38°, and 50° are investigated numerically by modeling a full length continuous helical baffled shell-and-tube heat exchanger for different mass flow rates and inlet temperature conditions. Results revealed that the larger helix angles (30°, 38° and 50°) adds to lower heat transfer and lower pressure drop, and smaller helix angles (10°, 19°and 21°) resulted in higher heat transfer as well as higher pressure drop. The experiments were carried out on shell and tube heat exchanger for helical baffles with 25° helix angle and results were compared with segmental baffles. New baffle material, FRP (Fiber Reinforced Plastic) is introduced on the shell side of the proposed heat exchanger. For material comparison between FRP and stainless steel, the deviation of heat transfer coefficient is 8–10%, which can serve as a potential replacement for conventional baffle material, thereby reducing the capital and operating cost of the tubular heat exchanger.

Thermoeconomic and environmental analysis of solar flat plate and evacuated tube collectors in cold climatic conditions

In the current study, a thermoeconomic analysis of two different solar hot water systems based on two types of flat plate collector (FPC) and evacuated tube collector (ETC) are studied under the cold climate conditions of Iran. The annual solar collector energy output and the collectors' output temperature are calculated using the TRNSYS16 software. As a result, it is found that the inlet temperature and weather conditions are the two major variables which affect the collector performance. Finally, according to the thermal and economic analysis, the performance of ETC system is 41% better than FPC system, and the yearly useful energy gain of ETC is 30% more than that of FPC in cold climate. So, applying ETC in cold climate is recommended. Additionally, this simulation will be extendable and applicable for every zone with any climatic condition.

Onset of Nucleate Boiling in narrow, rectangular channel for downward flow under low pressure

Bubble nucleation itself is less important safety issue for nuclear reactor, but it can easily lead to critical thermal-hydraulic events such as OFI (Onset of Fluid Instability) or CHF (Critical Heat Flux) when a research reactor operates under atmospheric conditions. Thus, the ONB (Onset of Nucleate Boiling) margin for normal operation in research reactor is recommended. In the IAEA-TECDOC-233 report (IAEA, 1980), the ONB margin for a research reactor is recommended as well. Although the ONB margin in a research reactor is emphasized for such reasons, only a few experiments have been performed for downward flow direction in a narrow, rectangular channel. In addition, several existing ONB prediction correlations are arguably applicable to the flow boiling condition in the narrow rectangular channel because most of them are developed based on Hsu’s model, which was developed in the pool boiling cases. In the study, ONB experiments for various inlet temperature conditions and mass flux conditions were performed with increasing heat flux step by step. Based on experimental data, the effect of inlet temperature and mass flux on the wall superheat and heat flux at ONB was investigated. In addition, existing ONB prediction correlations were evaluated for predicting wall superheat and heat flux at ONB based on the experimental data. A new ONB prediction correlation was then developed for better-evaluation and was compared with other correlations.

Exergoeconomic investigation of power utility based on air film blade cooled gas turbine cycle

Worldwide increase in population growth and improvement in general standard of leaving especially in the developing nation has seen sharp increase in demand for electricity and that to at a lower cost. This higher energy demand challenges the energy manufacturer for efficient energy production. In this regard it becomes essential to analyse the power utilities on exergoeconomic basis so that the utility developers can come up with power islands meeting these demands. The present work deals with such a power utility, based on gas turbine cycle with air film blade cooling. The exergoeconomics of power utility has been carried out for base case (rpc=18, TIT=1500K, ηAC=88% and ηGT=90%) and aforesaid system is also subjected to exergoeconomic investigation under varying operating conditions of compressor pressure ratio and turbine inlet temperature. The results so obtained for base case exhibits energy efficiency of around 40.26%, electricity cost of 2.97cents/kWh, total cost rate of 19.64$/h with plant specific work of 433.89kJ/kg.

Experimental Study on the Performance of CO 2 -Based Photovoltaic-thermal Hybrid System

Abstract The electric energy generation from photovoltaic solar panel is much influenced by the temperature of photovoltaic solar panel. It is the fact that the efficiency decreases when the temperature of photovoltaic solar panel becomes higher. To prevent the efficiency drop and to combine the thermal energy usage, CO 2 -based photovoltaic-thermal hybrid system (abbreviated as CO 2 hybrid collector) has been investigated. In the present study, a newly designed CO 2 hybrid collector is introduced and evaluated as a sub-system integrated into the supercritical CO 2 solar Rankine cycle system for increasing the overall system performance and to strengthen the sustainability in electric and heat generation of the system. The basic performance of the CO 2 hybrid collector is experimentally verified and reported by the manner for examining a reference CO 2 inlet temperature condition to the hybrid collector. The results show that the effectiveness gives advantage for 2% higher efficiency in electric power generation compared with ordinary photovoltaic solar panel in a reference winter condition.

Numerical analysis on the flow instability of parallel channels in water wall of an ultra-supercritical CFB boiler

Abstract A general calculation model based on the time-domain method is established for analyzing flow instability in parallel channels. In this model, the governing equations of mass, momentum, and energy are discretized and solved using the first-order upwind scheme. A numerical computational program called Dynsys is developed in Fortran language to analyze the flow instability occurring in the water wall of an ultra-supercritical CFB boiler with annular furnace. Comparing the calculation results of Dynsys with the experimental results shows that the model is reasonable and accurate for practical engineering application. On the basis of the validated model, the typical parallel channels in water wall of ultra-supercritical CFB boiler are simulated. Results show that, under the condition of invariable inlet pressure, temperature, and total mass flow rate, as well as 1.2 times heat flux disturbance applied on the parallel channels of ultra-supercritical CFB boiler, the fluctuation of inlet flow rate versus time in two channels is out of phase. In addition, the amplitude of flow pulsation decreases with time first and then returns to the steady state. Therefore, the flow in the parallel channels of ultra-supercritical CFB boiler with annular furnace is stable. Compared with the flow instability in single channel, the calculating results show that the flow in parallel channels was more stable within the range of parameters in the present paper.

Experimental assessment and model validation of a vertical cooling panel

The energy used for cooling has increased in recent decades and the predicted future rise in consumption is driving a pressing need for more efficient technologies. Some technologies use environmental sinks as heat dissipation alternatives. This paper presents a model validation with experimental data from a passive vertical cooling panel. The novelty of the solution lies in two main characteristics. The first is that the panel is in a vertical position, and thus the heat sink is the ambient temperature and surrounding instead of the sky temperature. The second is that the panel is north-oriented. Avoiding the sun lengthens the operating time to the entire day, while most studies explore options that are limited to night radiation. The aim is to include this element as a heat exchanger before water moves into the cooling tower from the condenser stage in cooling systems. The results have shown that the model approaches significantly the experimental data with an average error of 1.5% in the dissipated heat. Besides, the cooling capacity of the panel varies from 107 to 230W/m2 depending on the inlet temperature and fluid flow conditions, confirming the viability of the integration in buildings.

Effect of spray drying on physical properties of sugarcane juice powder (Saccharum officinarum L.).

The aim of the present study was to investigate the spray drying behavior of sugarcane juice with (PSJ) and without (CSJ) citric acid the effects of different levels (10-50%) of carrier agents (maltodextrin (MD), Gum Arabic, liquid glucose and carrot fiber) at varying operating conditions of inlet and outlet temperature and feed concentration during spray drying was also studied. Spray dried powders from PSJ and CSJ were analyzed for physical properties such as wettability, cohesiveness, dispersibility, flowability, hygroscopicity, particle morphology etc. Different correlations between product recovery and operating conditions were obtained. Amongst the different carrier agents used maltodextrin (30%) proved to be the best in terms of sensory properties and product yield. Spray dried powder without citric acid (PSJ) proved to be superior in terms of porosity, flowability and other reconstitution properties with low hygroscopicity. Moreover PSJ powder revealed regular spherical shape with smooth surface and less agglomeration between particles.