Heat Flow Rate Research Articles

Machine-Learning-Based Kinetic-Free Hybrid Gray-Box Model to Predict Sulfuric-Acid-Catalyzed Esterification Reaction.

The sulfuric-acid-catalyzed esterification reaction of 2-butanol and propionic anhydride is a vital industrial process. In this paper, several experiments are conducted via reaction calorimetry to validate that both sulfuric and propionic acids have discernible catalytic effects on the reaction. This finding complicates the accurate description of the reaction kinetics through traditional methods. So this paper turns to a kinetic-free black-box model, Gaussian process regression (GPR) model via 24 experiments, as a more adaptable approach. Besides, the best GPR model is combined with traditional heat balance model to generate a hybrid gray-box model, which can give complete knowledge of reaction process. The hybrid gray-box model finally achieves maximum root-mean-square error (RMSE) of 0.0069 for conversion, 0.6535 for temperature, and 10.6087 for heat flow rate, underscoring its pretty good predictive ability.

Utilizing waste heat from data centers with adsorptive heat transformation – Heat exchanger design and choice of adsorbent

The electricity and water consumption of data centers is growing on a global scale. A shift towards liquid cooled racks in combination with thermally driven cooling can help to reduce the electricity and water demand associated with the necessary heat rejection. To quantify the potential of adsorptive heat transformation devices in reducing the electricity and water demand, the prediction of thermal efficiency, heat flow rates and energy efficiency ratio is required. To this end, a numerical model is newly developed using basic adsorption heat exchanger theory. This model can predict the necessary performance indicators with respect to temperatures and volume flow rates, heat exchanger design and adsorbent. The full performance map of a market-available adsorption chiller (71 points) and own measurements are used for calibration and rigorous validation of the model. An average deviation (experiment vs. calculation) of 8.3 % in terms of thermal efficiency and 7.2 % in terms of heat flow rates is achieved, indicating a very good agreement for a wide range of temperatures. At a moderate liquid cooled rack outlet temperature of 50 °C, a heat rejection temperature of 26 °C and a cold aisle inlet temperature of 18 °C the cooling power of the silica gel reference chiller of 5.3 kW can be increased by 59 % to 8.5 kW at a partial energy efficiency ratio (pumps and control, no fans) of > 20 by assuming MIL-100(Fe) as adsorbent on a flat-tube lamella heat exchanger. The model can be used in subsequent annual system simulations to quantify the savings in electrical power and water consumption, which strongly depend on the ambient conditions.

Wet cooling of air on plate finned tube heat exchangers

The objective of this paper is to provide the reliable calculation procedure for determining heat and mass flow rates for plate finned tube heat exchangers in dehumidification regimes that can be used easily in engineering practice. For this purpose, the experiments are conducted on two heat exchangers, and datasets for six more heat exchangers are used from literature. Comprehensive database is established with total of 637 sets of data, and it gathers 365 new measurement sets and 272 sets from open literature. The new calculation procedure predicts heat transfer rate and condensate flow rate where new methodology approach (based on the porous velocity, the ratio of characteristic surfaces and hydraulic diameter) is used. Predicted results show 5–10 % deviation for heat duty and up to 20 % for mass flow rate from experimental results, which is of importance to industrial practice.

Multiple thermoelectric cogeneration system in an industrial thermal peeling press machine – Thermal modeling, case studies, and parametric analysis

Cogeneration systems, exploiting waste heat sources, have emerged as crucial solutions in decreasing energy consumption and mitigating CO2 emissions across diverse industrial domains. This study delves into the innovative integration of multiple waste heat recovery (MWHR) mechanisms with thermoelectric generators (TEGs) within industrial contexts, with a specific emphasis on harnessing exhaust gas heat. Through meticulous investigation, six distinct configurations of TEG placement covering three unique systems were examined to expose their influence on overall system efficacy. Findings clarify a deep correlation between TEG positioning and system performance, with TEGs strategically positioned in close to heat sources, particularly along the inner walls of exhaust pipes, demonstrating the most auspicious outcomes in terms of power generation. Furthermore, the study reveals notable metrics, including a maximum power efficiency of 0.11 W per TEG and a water heat flow rate peaking at 5114 W. However, a comprehensive analysis underscores the imperative for interpreting the primary mechanisms governing TEG placement's impact on system performance, alongside defining the practical implications of the observed power efficiency and water heat flow rate. These empirical insights underscore the transformative potential of WHR-TEG interactions in optimizing energy utilization within industrial ecosystems, highlighting the request for further research actions aimed at implementation strategies and sustainability benchmarks.

Multi-step scheme and thermal effects of coal smouldering under various oxygen-limited conditions

Coal smouldering fires are global disasters and notoriously challenging to characterize. To better understand combustion and chemistry within these coal fires, TG-DSC experiments were carried out in two different coal samples in nitrogen and oxygen-limited (including ambient air) atmospheres. A mechanism with 8-step reactions simulating coal combustion was proposed, including one drying, two pyrolysis, two oxygen adsorption, and three high-temperature oxidations. The kinetic parameters were optimized via a Genetic Algorithm (GA). It was found that this 8-step mechanism created unnecessary overfitting to the TGA data. Therefore, two alternative schemes were developed with 5- and 4-step, which included and neglected oxygen adsorption, respectively. To compare the two schemes, GA and Gaussian multi-modal fitting were used to quantify the mass change rates in each step and their thermal effects as functions of oxygen concentrations. Moreover, the heat flow rates of coal samples were calculated and compared with measured DSC curves. The results indicated that oxygen adsorption could play a critical role in the transition from water evaporation to high-temperature combustion, and the 5-step scheme could reflect coal's intrinsic oxygen-limited combustion characteristics more accurately. Altogether, this study provides novel insight into coal smouldering under oxygen-limited conditions.

Continuous Synthesis of Diazo Acetonitrile: From Experiments to Physical and Grey‐Box Modeling

AbstractDiazo compounds are gathering interest for their potential in promoting greener synthesis routes. We investigate, at a lab‐scale, the continuous synthesis of diazo acetonitrile (DAN) using a micro‐structured flow reactor and a flow reaction calorimeter. Data concerning DAN formation in the former, and relative to reaction heat and gas flow rate in the latter, are collected. We present a physical and a grey‐box model, both of which are calibrated to our data. Compared to the physical model, the grey‐box approach allows to better incorporate the complex chemical reaction pathways of DAN.

Characterization and kinetics of diesel-biodiesel blends by non-isothermal thermal analysis techniques

This study investigated the combustion-pyrolysis characteristics and kinetics of blends consisting of diesel and biodiesel at varying concentrations. To assess these characteristics, thermogravimetry (TG-DTG) and a differential scanning calorimeter (DSC) were employed as innovative tools for energy source evaluation. The experimental trials were conducted in two distinct atmospheres, namely nitrogen and air, to elucidate the pyrolysis and combustion properties of the diesel-biodiesel blends. Key parameters were systematically identified and analyzed, including reaction regions, peak temperatures, heat flow rates, and mass losses within the reaction intervals. Furthermore, various kinetic methods, encompassing both differential and integral-based approaches, were utilized to determine the kinetic parameters of the reactions, specifically the activation energy and Arrhenius constant. In the air atmosphere, the activation energy values exhibited a range of 22.1–58.8 kJ/mol, while in the nitrogen atmosphere, they exhibited variability within the range of 15.6–44.5 kJ/mol.

CFD Analysis of a Latent Thermal Storage System (PCM) for Integration with an Air-Water Heat Pump

Heat pumps driven by sustainable electricity sources have been identified as a technology that can contribute to reduce carbon dioxide emissions. Furthermore, a heat pump can also provide energy savings when combined with a thermal energy storage system. Heat pumps can optimize their efficiency by accumulating thermal energy during periods of lower electricity demand, resulting in shorter operational durations and decreased overall energy consumption. In this work, the combination of a latent heat storage system with an air-water heat pump has been numerically analysed and experimentally tested. A phase change material (PCM) heat exchanger with an immersed plate was designed using a 3D CFD model (COMSOL Multiphysics®). The heat exchanger configuration with six steel plates immersed in the phase change material tank was proposed to enhance heat transfer in the storage system. The developed model is validated against experimental data from a real case study, demonstrating a maximum error of approximately 3% during the discharging phase. Additionally, the study explores the effects of different inlet heat transfer fluid temperatures and flow rates on the PCM solidification time.

Validation of a New Method for Continuous Flare Combustion Efficiency Monitoring

A new method is described for calculating flare combustion efficiency (CE) and destruction and removal efficiency (DRE) using a numerical parametric model. The method combines key variables that affect flare performance including the flare vent gas net heating value (NHV), flare design, flow rate, exit velocity, and inert gas composition, alongside the environmental influence of crosswind speed. Each effect is characterized using a parametric model derived from experimental testing data and computational fluid dynamics (CFD). The inclusion of CFD allows the model to be extended into the high-wind conditions that cannot be adequately controlled for in empirical testing yet represent some of the most challenging conditions in which to maintain good combustion. This new parametric model method (PMM) is coupled with ultrasonic flowmeters from which the molecular weight and net heating value of the flare gas can be derived using the vent gas speed of sound measurement. In doing so, this method provides a reliable continuous flare combustion efficiency measure that can be deployed at scale with minimum hardware updates. The system was verified using an extractive sampling method with tests conducted on three full-scale industrial flares including non-assisted, single-arm pressure-assisted, and multi-arm pressure-assisted flare designs. A total of seventy valid test points were carried out with varying flow rate and flare gas heating value, covering a CE range from 46–100%. The uncertainty of the method was assessed using both traditional error propagation and Monte Carlo methodology. The results from the new method agree with the extractive method to within 0.8% in the ≥98% DRE region where flares are expected to operate to limit the impacts of flaring as a source of methane as a greenhouse gas. Uncertainty analysis revealed that the larger DRE discrepancy for DRE ≤ 98% correlates to the measurement uncertainties for both methods.

Numerical study of flow boiling heat transfer in a mini-channel under hyper-gravity

Gravity plays a crucial role in influencing bubble behavior and heat transfer in flow boiling, and its impact can vary significantly in aerospace settings. Therefore, this study aims to numerically investigate flow boiling heat transfer in a rectangular mini-channel under hyper-gravity conditions, specifically at 12 times the normal gravity. To accomplish this, a coupled volume-of-fluid and level set method is employed, taking into account fluid-solid conjugated heat transfer as well as a nucleus site density model derived from experimental data. By reproducing the flow pattern and heat transfer characteristics under different heat flux and flow rate conditions, the study unveils the effects of hyper-gravity on flow boiling heat transfer. When the flow rate is lower under hyper-gravity conditions, a notable phenomenon occurs wherein numerous bubbles detach from the heating wall and coalesce into a vapor film at the top of the mini-channel due to increased buoyancy. In contrast, under normal gravity, bubbles merge and slide on the heating wall, leading to the formation of a dry patch below. Consequently, hyper-gravity results in a lower wall superheat, and the disparity in average wall superheat between normal and high gravities escalates as the added heat flux rises. Notably, in the hyper-gravity environment, the frequent detachment of bubbles in the middle and downstream sections of the mini-channel leads to an initial increase in wall superheating, followed by a plateau along the flow direction. As the flow rate increases, the inertial force intensifies. However, intriguingly, the discrepancy in flow boiling heat transfer between normal and high gravities does not exhibit a monotonic decrease with the increasing flow rate. This behavior can be attributed to the pressing of more bubbles onto the heating wall under normal gravity, resulting in the formation of dry patches at high velocities.

CO2/acetone mixture desorption process in a plate heat exchanger for compression/resorption heat pumps

Industrial processes represent one of the activities that consume the most energy, which is related to the use of fossil fuels and growing environmental problems. In this way, the recovery of residual heat energy has been presented as an efficient solution to take advantage of low-quality residual heat, where the compressor-resorption heat pump technology has proven to reach high temperature levels with a considerable Coefficient of Performance. The importance of this work lies in the validation of the ecofriendly CO2/Acetone mixture as a useful working fluid for a compressor-resorption heat pump, initiating the experimental study in the desorption process as a novel application. Even more, the cycle of the bomb has been simulated on previous research regarding a literature comparative and the present work validates it by experimental means. The process of desorption of the CO2/acetone mixture was studied in a heat exchanger of plates with operating conditions for conducts formed by 4 plates/3 channels, for compression/resorption heat pumps. Result ranges have been obtained for solution heat transfer coefficient between 0.10 and 0.50 kW × m−2 × K−1, average vapor flow rate between 0.02 and 0.16, heat flow rate between 1.50 and 5.20 kW × m−2 × K−1 and desorption mass flow rate between 2 and 5 kg × m−2 s−1 × 10−3 in the central channel of the plate heat exchanger. Finally, an empirical correlation is proposed to extend the results of the heat transfer coefficient of the CO2/acetone solution in applications outside the experimentally determined range, from the comparison between experimental data and determined by correlation of enthalpy of the solution, an average minimum, mean and maximum deviation of 0.2, 13.5 and 22.3 %, respectively, was determined. In this way, the results shows that the most influential variables are the test pressure and heating water temperature at the inlet of the desorber, where, with a concentration of CO2 (XCO2) between 22 and 25 %, the heat transfer coefficients obtained have an order of 0.50 kW × m−2 × K−1. On the other hand, viscosity favours heat transfer, thermal conductivity is a determining factor for the desorption process. This contributes to lower heat transfer coefficient and heat flow in the heat exchanger for the CO2/acetone mixture compared to the other mixtures.

Experimental and numerical analysis of variable cross-section channel liquid cooling plate for server chips thermal management

Utilizing high-performance chips results in increased heat generation, necessitating more effective heat dissipation method. To address challenges in microchannel liquid cooling plates for server chips cooling the study presents the variable cross-section channel liquid cooling plate designs. To investigate the effect of channel structure on the performance of liquid cooling plate, two types of samples, one featuring side wall ribs and bottom cavities (SC) and the other featuring side wall ribs and bottom waves (SW), are evaluated through experimental analyses under various heating power and flow rate conditions. Comparing their performance to a conventional rectangular channel (RC) liquid cooling plate, their heat transfer and flow attributes were assessed. Finally numerical analysis was conducted to investigate the flow behavior inside the channel and extreme performance prediction were made using the numerical study. Results demonstrate that the SC and SW designs outperform the RC in terms of heat transfer capabilities, despite having the weaker flow characteristics. Under 300 W heat source power, the SW variants enable the heat source surface temperature to stay below 77.8 °C with a 194 mL/min flow rate. Notably, the SW variant showcases lower average heat source surface temperature and demonstrates lower pressure drop compared to the SC variant. As the flow rate increases, the heat transfer efficiency of the SW variant is further amplified while simultaneously highlighting the relatively suboptimal flow behavior of the SC variant. Predictive numerical models underscore that the SW variants offers improved thermal performance when subjected to high heat source power scenarios. Remarkably, under the heat source power of 500 W, a mere augmentation in flow rate proves sufficient to reduce the heat source temperature below the prescribed threshold value. The combination design of side wall ribs and bottom waves should enable a low cost, simple and high efficiency electronics cooling.

How can the global temperature increase be explained to students?

The temperature increase of the system Earth-atmosphere can be described by means of a parallelism between the leaking bucket’s dynamics and the energy balance between the incoming radiant power from the Sun and the outcoming net heat flow rate to outer space. The analogy is interesting from a didactical point of view, since the stable fixed point of the temperature can be related to the height of the water inside the leaking bucket in the presence of a fixed fluid flow rate. Qualitative predictions of global temperature increase for increasing concentration of greenhouse gases in the atmosphere can be obtained by reducing the outcoming net heat flow rate, using buckets with smaller orifices.

Facile Approach for Designing Icephobic Coatings Using Polymers/Silica Nanoparticle Composites via Self‐Formation of Superhydrophobic Surfaces

AbstractIce accumulation and proliferation adversely affect the activities of various residential, commercial, and polar research stations. Although significant efforts are devoted to preventing ice adhesion to various surfaces by developing various anti‐icing coatings, it is still necessary to enhance overall performance and durability. Herein, a facile approach is proposed for fabricating an icephobic coating on an aluminum 6061 (Al) substrate, by coating a poly(dimethylsiloxane) (PDMS)/ poly(tetrafluoroethylene) (PTFE) composite through a spin‐coating method, followed by sprinkling of SiO2 nanoparticles (NPs). Crosslinker/binder‐free adhesion between PDMS and PTFE is achieved by utilizing secondary‐induced electrostatic dipole‐dipole interactions, these interactions are supported by density functional theory (DFT) calculations as well as structural studies. Moreover, the controlled addition of PTFE powder to PDMS improves the water‐repellency, mechanical strength, and surface roughness of the coating. The self‐formation of the superhydrophobic state of the PDMS/PTFE composite is achieved by sprinkling SiO2 NPs. The sprinkled SiO2 NPs are protected by the PDMS/PTFE composite, which serves as a stress concentrator to achieve low ice adhesion. Furthermore, freezing at low temperatures can be delayed by controlling the heat flow rate, interfacial contact area, and surface texture. This indicates the feasibility of the proposed method for various promising anti‐icing applications.

1D simulation analysis and optimization design of engine cooling system

The engine cooling system takes away the heat absorbed by high-temperature parts during the operation of the car engine in a timely manner, keeping it working within the normal temperature range. This article applies Flowmaster software to establish a one-dimensional cooling system model for a certain model of National Five diesel engine. Relevant boundary conditions are inputted to complete steady-state simulation calculations of the system under different operating conditions, obtaining the flow rate, pressure distribution, and temperature rise of each component. At the same time, three optimization schemes are designed based on the original cooling system to predict and evaluate the working capacity of the cooling system, Based on the calculation and analysis results, improvement suggestions are proposed to guide the structural design and testing of the cooling system, greatly reducing research and development time and reducing research and development costs. The calculation results show that the flow rate of each component in the rated point, heating test condition, and idle condition of the original plan has decreased compared to the flow rate of a certain four machine on the same platform under the same working condition (the air compressor flow rate is higher than the limit value), and the temperature difference of the radiator and heating flow rate do not meet the specification requirements. Suggest using Plan 3 to increase the water pump speed ratio to 1.25, with a warm air flow rate of 5.33L/min under idle conditions, which is 72% higher than the original plan and meets the vehicle limit requirements. In addition, to ensure the accuracy and reliability of the model and calculations, this project conducted cooling system tests on an engine bench. The comparison between the simulation calculation data and the experimental data showed that the simulation calculation results were consistent with the experimental results.

General numerical method for hydraulic and thermal modelling of the steam superheaters

Two methods for modelling high-temperature tubular cross-current heat exchangers are presented. Superheated steam flows inside the tubes, and flue gas flows outside perpendicular to the axis of the tubes. The methods proposed are based on the conservation equations of momentum and energy. In both methods, the heat exchanger is divided into finite volumes. The fluid temperatures at the outlet of the finite volume are calculated using closed-form explicit formulas. This makes the computer calculation time for the entire superheater very short. The pressure distribution in the superheater is determined from the numerical solution of the momentum conservation equation. A power correlation was determined to calculate the limiting Reynolds number above which the friction factordepends only on the relative roughness of the tube surface. Convective and radiative heat transfer were taken into account in the calculation of the heat flow rate on the gas side. The results of the calculation of a two-pass co-current heat exchanger were compared to assess the accuracy of the two methods, finding that the two methods give very similar results. The strength of method I is that the steam and flue gas temperatures inside a given finite volume can be determined. A model of a two-pass live steam superheater in a supercritical pressure boiler is presented. The calculated average steam and flue gas temperatures downstream of the superheater show good agreement with the corresponding temperatures determined using the heat exchanger's effectiveness and the measured results.

Influence of hydrogen blending on the operation of natural gas pipeline network considering the compressor power optimization

Blending hydrogen into the existing natural gas pipeline network is regarded as the most potential transportation mode on the utility-scale. However, the impact of hydrogen on the operation performance of the pipeline remained unclear. This paper analyzes the economic and environmental performance of natural gas pipeline under different hydrogen blending ratios and different hydraulic boundary conditions. In order to reduce the operation costs and carbon emissions in each condition, this paper establish a non-linear optimization model to get the new operation plan of the pipeline system. Further, in order to characterize different boundary conditions of the system, four scenarios, namely, the baseline scenario (BS), the setpoint of flow rate scenario (SF), the setpoint of pressure (SP), and the setpoint of heat flow rate (SH) are proposed in this paper. Two studied cases demonstrated that: (1) the original compressor for natural gas can adapt to a hydrogen blending without change the type of compressor. (2) The optimization model has significant potential in reducing the economic cost and carbon emissions of the system with an average decrease of 11.48%. (3) For every 1% of hydrogen added, the annual operating cost of the system is reduced by $0.73 million (3.29%) in SF, 0.017 million (0.08%) in SP, or increased by $1.67 million (7.50%) in SH. Moreover, the annual carbon emission is reduced by 0.38 kt (3.53%) in SF, 0.047 kt (0.44%) in SP, or increased by 0.76 kt (7.14%) in SH. However, when the hydrogen mixing ratio is more than 8%, the contrary trend may occur. (4) The maximum blending ratio at different points of the multi-source pipeline network are physically interdependent. The paper proposed an optimization model for the 2-E analysis of the pipeline and can provide theoretical guidance for the further application of this transportation mode.

Parameter Tuning of a Vapor Cycle System for a Surveillance Aircraft

Surveillance aircraft perform long-duration missions (>eight hours) that include detection and identification of objects on the ground, the water, or in the air. They have surveillance systems that require large amounts of cooling power (typically 10 s of kW) for long durations. For aircraft application, vapor cycle systems (VCS) are emerging as a more efficient alternative to conventional cooling systems. In this study, a two-part method was applied to a cooling system with a VCS that can be installed on a surveillance aircraft. The first part focused on a parameter tuning study set-up and demonstrated how after identifying the operating conditions, constraints, and requirements, the only cooling system parameter available for tuning was the VCS compressor speed. The second part focused on a modelling and solving strategy for the cooling system and showed how the capacity of an aircraft cooling system was impacted by tuning the VCS compressor speed (Hz) for a surveillance system heat flow rate from 10 kW to 70 kW. The results from this study can be used to design a control strategy for the compressor. In a broader perspective, the two-part method and the results analysis presented can serve as a preliminary method for aircraft VCS control optimization studies.

Conceptual Design of Experimental Test Rig for Research on Thermo-Flow Processes During Direct Contact Condensation in the Two-Phase Spray-Ejector Condenser

Abstract The paper presents the conceptual design of a prototype experimental facility for mixing jet-type flow condensers investigations when the steam in exhaust gases is condensed on the water jet in the presence of CO2. The proposed experimental test rig was designed to give abilities to investigate the effectiveness of jet condensers experimentally as part of the CO2 capture phase and especially to investigate Spray-Ejector Condensers (SEC) developed as the combination of ejector and condenser devices. The paper presents the design and key features of the prototype installation components. The basic design was developed based on the simulation results, and for this purpose, model of installation, including characteristics of individual components, was built. The developed model helps to evaluate the main performances of the conceptual test rig and supports the test-rig design process. The main components and the features of the steam generation unit, CO2 supply and mixing with steam, process water preparation, and H2O and CO2 separation subsystem are discussed. The measuring system was designed to test the efficiency of compression and condensation processes of the SEC fed by the CO2/H2O gas mixture. The performances of the two-phase jet condensers can be analyzed by experimental investigation and calculation of heat transferred to the cooling water during direct contact condensation with the presence of CO2. The paper presents the results of heat flowrates and their uncertainties for the selected period of the experimental test, confirming the application of the novel developed test rig.

Investigation of Single-Phase Immersion Cooling for Modern Data Centers

Compact servers with a high energy density are the result of the telecommunications industry's rapid advancement. Innovative cooling solutions are required due to the expanding scale of data centers and related cooling needs. Servers in the data center might be cooled via immersion cooling by immersing them in a thermally conductive die electric fluid. In this study, three distinct dielectric liquids were used with variable circulation rates to examine the effectiveness of single-phase immersion cooling with varying heat inputs of 300, 400 and 500 Watts. Deionized water, white mineral oil and propylene glycol were the three dielectric fluids being considered, at circulating rates of 1, 2 and 3 litres per minute. Among the three fluids tested, deionized water consistently outperformed the others by maintaining the lowest outlet temperature across various heat inputs and flow rates. The average heat transfer coefficient for deionized water was calculated as the highest, with a value of 349.29 W/m²·K. Propylene glycol had an intermediate heat transfer coefficient, which was 194.69 W/m²·K, and mineral oil exhibited the lowest heat transfer coefficient at 74.44 W/m²·K.