Circulation Heat Research Articles

Predictive Modelling of Grate Combustion and Boiler Dynamics

Pressure and air to fuel ratio control are extremely difficult in coal-fired grate boilers due to a significant lag in combustion. This leads to suboptimal operation of the boiler and poor efficiency of the plant. This also leads to higher level fluctuation. Fluctuation in pressure, water level and oxygen level are quite evident in the operation of coal-fired grate boilers in fluctuating load conditions. The present work aims to develop a predictive and dynamic simulation model of a coal-fired grate boiler for the prediction of pressure, and water level in fluctuating load conditions and its extension for the prediction of oxygen level. A data-driven approach has been used for the prediction of heat release, distribution of heat transfer, circulation analysis and airflow through the various dampers. This model has been integrated with the boiler dynamics model of a hybrid boiler. Errors in pressure and water level are measured for training data and the multi-objective optimisation method is used for the minimisation of errors. The Batch Gradient Descent method has been used for the minimisation of errors. The proposed integrated model is used for the estimation of heat release and the rate of combustion. Stochiometric combustion calculation is used to predict oxygen level by using the predicted value of airflow and rate of combustion. Root mean squared error is calculated for oxygen level and minimised by the Batch Gradient Descent algorithm. The model has good accuracy in the prediction of boiler pressure and water level and can be extended to improve the boiler controls of a solid fuel fired reciprocating grate boiler in extremely fluctuating load conditions.

Numerical characterization of heat transfer deterioration in supercritical natural circulation loop and role of loop inclination

Thermalhydraulics of any supercritical natural circulation loop (sNCL) is strongly influenced by the choice of operating conditions and geometric configurations, and can experience severe deterioration in heat transfer characteristics and circulation rate under certain situations. Present study focuses on systematic identification of a quantifiable criterion for prior identification of such deterioration in a carbon dioxide-driven rectangular loop, subjected to a wide range of operating conditions and also with particular emphasis on loop inclination. Four distinct regimes of operation have been identified, primarily based on the temperature levels in the adiabatic arms. Operation is desirable to be restricted within the enhanced heat transfer regime, which offers large heat transfer rate and moderate level of fluid temperature. Inclination to vertical lowers the driving potential, thereby reducing the flow rate and forcing an early induction into the deteriorated heat transfer regime. Highest circulation rate corresponds to the heater power capable of equating the average loop temperature to the pseudocritical value at that pressure. Strong thermal asymmetry and density stratification has been observed in the horizontal sections, with local recirculation and non-uniform radial velocity profiles. Buoyancy parameter has been identified as a capable dimensionless quantity to predict the appearance of deterioration a priori. It can also be coupled with the average friction factor to quantify the critical power level, and a correlation has been suggested for the same.

Long-term Performance Evaluation and Economic Analysis for Deep Borehole Heat Exchanger Heating System in Weihe Basin

To reduce carbon emission and achieve carbon neutrality, deep geothermal energy has been widely extracted for building heating purpose. In recent years, deep borehole heat exchanger (DBHE) heating system has gained more attention, especially in densely populated urban areas in Weihe Basin, northern China. The long-term performance and the economic feasibility are essential for the system application. In this work, the DBHE model implemented in OpenGeoSys software is verified against an analytical solution and a comprehensive economic analysis approach is further proposed. Then the short-term thermal performance tests are conducted to obtain the tentative heat extraction capacity for long-term simulation. The long-term simulations are further performed with the heat pump unit under the adjusted tentative heat extraction rate imposed on the DBHE. Finally, a comprehensive economic analysis is applied to the DBHE heating system over 15 heating seasons. Results show that the minimum coefficient of performance value of the heat pump is 4.74 over the operation of 15 heating seasons. With the increase of depth for the DBHE, the total electricity consumption of heat pumps and circulation pumps has a prominent promotion. With the comprehensive approach of economic analysis, the depth of 2,600 m has the lowest levelized cost of total heating amount, which is the best system design for the application in Weihe Basin. The present results are specific to the conditions in Weihe Basin, but the proposed economic analysis approach is generic.

Investigation on Individual and Collective PV Self-Consumption for a Fifth Generation District Heating Network

Renewable Energy Communities have been recently introduced in European legislation to promote distributed generation from renewable energy sources. In fact, they allow to produce and consume energy from shared local power plants. Low temperature district heating and cooling networks with distributed heat pumps have demonstrated their capability to exploit renewable and waste heat sources in the urban environment. Therefore, they are considered a promising infrastructure to help decarbonize the building sector. As their main operating cost is the electricity purchased by the utility for heat pumps and circulation pumps, this work investigates whether a Renewable Energy Community could help mitigate such cost by sharing electricity produced by local photovoltaic (PV) systems. The research relies on computer simulations performed with both physical and statistical models for the evaluation of electrical load profiles at the district level. Results show that due to the different seasonality between heating demand and PV production, the increase in self-consumption due to the distributed heat pumps is lower than 10%. The use of batteries does not seem convenient for the same reason. The environmental benefit of the proposed system is evident, with CO2 emissions reduced by 72–80% compared to the current situation depending on PV power installed. It also emerged that PV sharing significantly improves the self-consumption at the district level, in particular when the installed PV power is limited (+45%). In conclusion, results suggest that current incentives on PV-sharing make Renewable Energy Communities a viable option to improve the techno-economic performance of fifth-generation district heating and cooling networks.

Changes in the Heat Content of Water Column in the Slope Area of the Southern Basin of Lake Baikal in the 21st Century

Climate change influences the temperature, ice and thermal regimes of lakes in the Northern Hemisphere. This study discusses the change in the heat content of the water column in the slope area of the southern basin of Lake Baikal under the influence of climate for the past 20 years. We clarify the seasonal variability of heat content in different water layers selected taking into account temperature and dynamic characteristics. During the study period, the value of heat content increased in the upper water layer (45–100 m) only in May (12.4 (MJ/m2)/year). In the water layers deeper than 100 m, the value of heat content decreased: −3–−4 (MJ/m2)/year from July to September in a layer of 100–300 m, −9–−13 (MJ/m2)/year in all months in a layer of 300–1100 m and −1.5–−3 (MJ/m2)/year in all months, except for January in a layer of 1100 m–bottom. Despite the revealed trends of the change in the heat content, the annual heat circulation remained within the normal range and did not have any trends.

The thermal behavior of blood flow in the arteries with various radii and various stenosis angles using non-Newtonian Sisko model

In this work, the FVM method is employed to simulate blood flow behavior within stenosis arteries based on the non-Newtonian Sisko model by using UDF in Fluent. Stenosis is simulated in cone geometry, and influences of different angles of stenosis with different artery radii are studied on the Nusselt number and temperature of blood flow. It is observed that with increasing angles of stenosis and reducing internal radius, the artery is narrowed, which results in enhancement of Nusselt number of blood flow. Thus, the temperature of blood flow is reduced. Also, applying heat fluxes of q“ = 400 W/m2, q” = 800 W/m2, and q“ = 1000 W/m2 prepare temperature enhancement as much as 0.44 K, 0.89 K, and 1.15 K respectively which are important from a medical viewpoint. The maximum temperature is reported as much as 38.2 °C by applying heat flux of q” = 1000 W/m2, which is noticeable for the human body healthy, especially for the function of enzymes and other proteins of the body. Also, with increasing angles of stenosis and reducing internal radius, the artery is tightened and velocity of blood fluid is enhanced which affects blood circulation between tissues and the oxygenation process, temperature variation, and heat transfer alteration of blood flow within the human body. In reality, circulation of blood transfers heat between tissues, and the dimensions of the blood vessels are various, whenever more blood is needed in some vessels of the body due to more activity, these blood vessels expand to supply the required blood while other vessels tight to compensate it. Therefore, present mechanical research is applicable for medical science especially in surgical widening of a blocked or narrowed blood vessel.

Fault-tolerant quantum reversible full adder/subtractor: Design and implementation

In quantum computers, all the heavy computations are done through quantum processors. ALU is one of the most significant parts of every processor responsible for performing logical operations and primary binary operations. All of the arithmetic computations in ALU utilize adder/subtractor to produce the expected result. Fault-tolerant circuit designs have found increasing application in quantum computers regarding the noise sensitivity of qubits and the faulty environment in which they operate. Additionally, reversible quantum circuits can prevent heat circulation and information lost throughout the high-rate binary calculations. The primary subject is the development of digital reversible fault-tolerant quantum circuits with higher performance and more efficiency regarding the number of inputs and outputs employed by quantum gates, depth, and delay. Full adders and subtractors are highly significant in different parts of quantum digital circuits and are used widely in multipliers, dividers, ALUs, and floating-point operations. In this paper, applying the parity-preserving method and the properties of Boolean algebra two novel reversible fault-tolerant designs are proposed that can detect every single or the odd number of errors. Also, both proposed designs are capable to perform addition and subtraction operations by changing the control signal(ctr). Our offered designs can reduce energy loss in the form of emitted heat in circuits, reduce the cost of building quantum circuits, reduce computation time, and detect errors in case of happen. Furthermore, comprehensive simulations for each possible combination of inputs and corresponding outputs are done to prove the full functionality and accurate performance of the proposed designs.

The qutrit as a heat diode and circulator

We investigate the heat transport properties of a three-level system coupled to three thermal baths, assuming a model based on superconducting circuit implementations. The system-bath coupling is mediated by resonators which serve as frequency filters for the different qutrit transitions. Taking into account the finite quality factors of the resonators, we find thermal rectification and circulation effects not expected in configurations with perfectly-filtered couplings. Heat leakage in off-resonant transitions can be exploited to make the system work as an ideal diode where heat flows in the same direction between two baths irrespective of the sign of the temperature difference, as well as a perfect heat circulator whose state is phase-reversible.

Numerical investigations on an improved dual-channel porous combustor fueled with lean methane for enhancing thermal performance

In this work, an improved dual-channel porous combustor is designed. Extensive numerical investigations are conducted to compare the thermal performance between the single-channel and the improved dual-channel combustor under various inlet velocity, methane concentration and the pores density of foam ceramics. Moreover, the effective thermal conductivity model of the foam ceramic based on the Kelvin decahedron was introduced. The external and internal heat circulation and the heat circulation efficiency of the burner are calculated and analyzed quantitatively. Results show that, at low methane concentrations conditions, the pores density of foam ceramics have no significant effect on the blow-off limits for both single-channel and dual-channel porous burners. However, under the higher methane concentrations conditions, the blow-off limit would be increase with the pores density of foam ceramics. Compared with the single-channel burner with 20 PPI foam ceramic, the mean nonuniformity of the foam ceramics temperature for the improved dual-channel combustor would be reduced from 2.015% to 26.562% when the inlet velocity increases from 0.1 m/s to 0.16 m/s. However, for the 10PPI to 40PPI burners, the mean nonuniformity of the solid phase temperature of the improved dual-channel combustor would be reduced by 9.78% to 4.36%. Moreover, the preheat zone inside the porous medium would be greatly minimized by the addition of external heat recirculation to the porous media burners.

Modelica-based simulations of decentralised substations to support decarbonisation of district heating and cooling

District heating and cooling are considered effective solutions to decarbonise the energy use in the building sector. The latest generation of district heating and cooling also increases the potential of integrating heat pumps and chillers in each building substation. The benefits of such integration are the reduction of network temperature and distribution losses; the recovery of waste heat through a bidirectional network; and the decentralised production of heating and cooling. Sizing the network depends mainly on the heat flows between connected buildings. The substation performance and technical installations determine these heat flows. We present in this paper Modelica-based simulations of two design cases for substations. The first design case involves installed heat pump, chiller, and circulation pumps. Alternatively, the second design enables the heat pump to provide direct cooling through a heat exchanger. The models for these installations were developed using the Modelica language to perform continuous-time simulations. The performance in each design case was evaluated in terms of seasonal coefficient of performance and total electric energy use. An analysis on a cluster of 11 buildings suggests that the addition of the direct cooling heat exchanger can save up to 10% of the total annual electric energy use. Additional savings can be achieved by optimising the building supply temperatures and the district network temperature.

Buoyant heat and flow circulation in a triangular porous cavity with radiation effect

The buoyant circulation in a triangular enclosure with radiation effect is studied numerically in FEM based computational techniques. Non-uniformly heating lower wall, right cold wall and diagonal adiabatic walls bound the cavity. Visualization techniques like streamlines, isotherms along with local and average Nusselt numbers have been used to analyze the phenomena occurring inside the enclosure. The Nusselt number is found to be a function of the Rayleigh number; a rise in the Rayleigh number was observed to result in the increase of value of the average Nusselt number. For Rayleigh number values less than hundred dominance of conduction was observed, this dominance was found to be enhanced further with increase in radiation factor. It is noticed that when Rd is more than five, then heat transfer rises monotonically for all Rayleigh numbers. Fluid flow and heat transfer data obtained is compared with the data obtained by Aparna et al and it revealed a good agreement.

Vertical Mixing in Stratified Fjords Near Tidewater Outlet Glaciers Along Northwest Greenland

AbstractVertical mixing of upper water masses in Arctic fjords is important for circulation and transport of nutrients and heat. However, the distribution of turbulent mixing is poorly known. Here we present hydrographic and microscale turbulence measurements from six fjords in Northwestern (69°N–75°N) Greenland. Water mass distributions showed the presence of warm bottom water of Atlantic origin in all fjord transects and a significant modification of upper water masses in fjords with tidewater outlet glaciers. Spatial and temporal distribution of turbulence in the fjords showed, in general, low rates of turbulent kinetic energy, ε (∼10−9 W kg−1), and strong stratification implies that vertical exchange in the upper ∼200 m was relatively weak. However, measurements within 2 km of the terminus of a tidewater outlet glacier showed values of ε and inferred turbulent diffusion coefficients >10−4 m2 s−1 that were about two orders of magnitude larger than elsewhere in the deep fjords. This elevated mixing corresponded to comparatively large heat and salt fluxes. These observations suggest that vertical mixing near tidewater outlet glaciers results in localized mixing hot spots, likely due to subglacial discharge and near‐glacial current shear, that contribute significantly to vertical exchange in the deep fjords.

Thermodynamic Mechanism of Self-Heat Recuperative Heat Circulation System with Non-Isentropic Compression and Expansion for a Continuous Heating and Cooling Gas Cycle Process

Self-heat recuperation drastically reduces the energy consumption of thermal processes by adding work to circulate the whole process heat without heat addition. However, its theoretical foundations have not been fully established yet. This paper aims to elucidate the thermodynamic mechanism of self-heat recuperation with non-isentropic compression and expansion for a thermal gas cycle in terms of exergy analysis. The exergy analysis was performed with a modularization method using the module expression flow, the temperature–entropy, and the energy conversion diagram. The exergy analysis led to the significant conclusions that self-heat recuperation minimizes the energy consumption of gas thermal processes and that key information can be easily obtained by simply focusing on the exergy destruction without using complex process simulations. Heat circulation is driven by adding the work input to provide the minimum work required for heat transfer using the compressor, and theoretically all the excess work can be recovered to offset part of the work input using the expander. In practice, the irreversibility of adiabatic compression and expansion destroys part of the excess work, leading to a decrease in the excess work and an equivalent increase in the waste heat. The net work input is equal to the minimum work required for heat circulation and is converted into waste heat, whose anergy is transformed from the exergy destruction due to heat transfer, non-isentropic compression, and non-isentropic expansion. The minimum work required for heat circulation can be quantified by calculating the waste heat via the total exergy destruction. Thus, self-heat recuperation is the most energy-efficient solution to the design and retrofit of energy-saving gas thermal processes and is promising for process intensification. A case demonstration with numerical results on the heat circulation of air is presented to facilitate an intuitive understanding of the thermodynamic mechanism.

Optimal operation strategies of multi-energy systems integrated with liquid air energy storage using information gap decision theory

In this paper, a framework of multi-energy system (MES) integrating with a liquid air energy storage (LAES) system was proposed. LAES, where liquid air works as an energy storage media, is a powerful and eco-friendly technology for storing renewable energy resources and reducing grid curtailment. Considering the characteristics of LAES (i.e. cold and heat circulation), the incorporation of LAES system into the Combined Cooling, Heating and Power system can achieve integrated use of energy and effectively save energy. Moreover, the prices of electricity will affect the overall cost of the MES. In other words, the decision-makers of the MES need to consider the uncertainty of electricity prices when making power dispatching decisions. To model the uncertainty of electricity prices, the information gap decision theory method was used to study power dispatching strategies of the MES. Three different strategies were proposed, including risk-neutral, risk-averse and risk-taker. In addition, demand response algorithms were used to study load transfer strategies. The results show that the demand responses of the three strategies are effective in terms of load transfer and cost saving. The total operation cost in the risk-neutral strategy with demand response can be 6.82% less than that without demand response; In the risk-taker strategy with demand response, the allowable grid electricity price is reduced by 25.24% when the opportunity cost drops by $8,000, and 23.32% without demand response. With additional robustness cost, the acceptable price change ratio using demand response is 21.91% in the risk-averse strategy, and 20.04% without demand response.

Experimental study on novel waste heat recovery system for sulfide-containing flue gas

In order to further recover the waste heat from sulfide-containing flue gas, improve the recovery efficiency and reduce corrosion of heat exchanger before flue gas desulfurizer (FGD), a novel system based on the phase change heat transfer theory is proposed to recover the waste heat from sulfide-containing flue gas. The performance of novel waste heat recovery system is investigated by the experimental method. The results show that the heat recovery coefficient will increase with the heat load ratio while decrease with the circulation ratio. To ensure the high-efficiency operation of the novel system, the mass flow rate of lithium bromide solution should be adjusted in terms of the heat load ratio and circulation ratio in range of 48–178. Otherwise, it will be only adjusted in terms of the heat load ratio and increase with that. The exergy efficiency of the novel system will reduce with the heat load ratio because of the influence of energy efficiency of FGHE. But the exergy efficiency is about 25%–34% and lower. The heat transfer coefficient of FGHE is relatively higher for the heat load ratio in range of 0.7–1.1. The novel system is more advantageous in waste heat recovered from flue gas, the CO2 emission reduction and economic performance when the acid dew point temperature in range of 110–140 °C is changed under different operation conditions. The above conclusions will provide a theoretical basis for the operation of novel waste heat recovery system for sulfide-containing flue gas.

DEVELOPEMENT OF A VEGETABLE DRYER

A Vegetable dryer of dimension 1.50 m (high) x 0.72 m (wide) x 0.59 m (breadth) was developed using mild steel iron and its performance evaluated. The device consists of a drying chamber with three drying trays; fans incorporated for heat circulation, a heating element of 2000 W, four swivel caster rollers for ease of mobility, a thermostat to regulate the heat generated in the drying chamber and a thermo-gauge inserted to monitor the temperature in the drying chamber. The vegetable dryer has a drying capacity of 34 kg and three compartments of 0.25 m equal spacing. The dryer is partitioned at 0.75 m, 0.1 m and 1.25 m from the heating element, with the first (bottom) tray, the second tray (middle) and the third (upper) respectively. The device performance was evaluated under no-load and load conditions at 50 °C, 60 °C, and 80 °C temperatures with three replications. Results obtained under no-load indicated that temperatures very close to the preset values (by the thermostat) were attained within 5 mins. Under load condition, the dryer was evaluated by drying 16.74 kg of tomatoe slices at 50 °C, 60 °C, and 80 °C. Weight reduction (degree of moisture loss) from the slices was recorded at intervals of 1hour until a nearly constant weight was obtained. The result revealed that the dryer has a mean drying efficiency of 80.6 % and drying rate of 0.02 kg/hr. At a drying time of 10 hours and temperatures of 50 °C and 60 °C, 16.74 kg of tomatoes were reduced to 1.23 kg and 1.13 kg representing 93 % (wb) of removed moisture, while a final weight of 1.08 kg dry matter was obtained from the same starting weight of wet tomatoes at 80 °C representing 94 % (wb) of moisture loss for the same drying time. ANOVA studies indicated that the effect of temperature and tray level on drying of vegetable (tomatoes) were highly significance at (P< 5 %). The dried vegetable (tomatoes) is free from dust and any form of contamination making it healthy for consumption.

Dehydrogenation of ammonia for electricity production: Effect of recirculation fraction

Hydrogen (H2) has been widely studied as a promising energy carrier. However, H2 has a challenging technology in the storage and transportation. Since, it is a critical technology for H2 energy system implementation, the H2 storage and transportation is remain to be solved. This work proposes an integrated system of energy utilization of ammonia (NH3), which has been known as one of the promising methods of H2 storage. The system includes the decomposition of ammonia (NH3) through thermo-catalytic process and also power generation process using H2 as fuel. The heat generated from oxy-fuel combustion of H2 is utilized to supply the thermal energy required for the endothermic process of NH3 decomposition, and the remaining heat is converted to electricity by a combined cycle. A portion of exhaust gas is recirculated to the combustion chamber, and the heat circulation of the system is designed and optimized based on enhanced process integration (EPI), resulting in a highly efficient system. The result shows an optimum configuration of the integrated system with a recirculation fraction of 0.5-0.55, which is resulting in high system efficiency of 51.4%. The proposed work demonstrated an integrated system of H2-based energy utilization of NH3 with CO2-free while maintaining a highly efficient system.

Phase-coherent heat circulators with normal or superconducting contacts

We investigate heat circulators where a phase coherent region is contacted by three leads that are either normal- or superconducting. A magnetic field, and potentially the superconducting phases, allow to control the preferential direction of the heat flow between the three-different temperature-biased contacts. The main goal of this study is to analyze the requirements for heat circulation in non-ideal devices, in particular focusing on sample-to-sample variations. Quite generally, we find that the circulation performance of the devices is good as long as only a few transport channels are involved. We compare the performance of circulators with normalconducting contacts to those with superconducting contacts and find that the circulation coefficient are essentially unchanged.

Multi-Annual Changes in Heat Stress Occurrence and Its Circulation Conditions in the Polish–Saxon Border Region

Heat stress is one of the most critical factors affecting human life. In Central Europe, its influence is noticeable, especially in the Polish–Saxon region, which is a very popular tourist region also inhabited by a high number of elders. The main goal of this paper was to assess multi-annual changes in heat stress occurring in the region, considering the frequency of heat days, the UTCI (Universal Thermal Climate Index), and circulation conditions. The research showed that all the thermal and biothermal indices in this region significantly increased during 1971–2019 in the lowlands, the mountain foreland, and the lower mountain zone. In terms of the UTCI, a negative trend for cold stress frequency was noticed in the entire region in favor of an increase in a tendency toward thermoneutral conditions and heat stress. This concerns especially strong and very strong heat stress (UTCI > 32 °C), in which positive trends were observed for most of the stations located in the lower hypsometric zones. The results also showed that heat stress mainly occurs on days with anticyclonic circulation. Analysis of selected cases of heat waves in the 21st century indicated that the lower hypsometric zones are characterized by a very high UTCI, while the summit zone is free from heat stress occurrence.

Fast and slow responses of the Subantarctic Mode Water in the South Indian Ocean to global warming in CMIP5 extended RCP4.5 simulations

The present study examines the long-term evolution of the Subantarctic Mode Water (SAMW) in the south Indian Ocean (SIO) based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) extended simulations through 2300 under Representative Concentration Pathways 4.5 (RCP4.5). The SAMW in the SIO shrinks and thins rapidly during the fast radiative forcing increasing period between 2000 and 2100. After 2100, when the radiative forcing stabilizes, the SAMW expands and thickens slowly. The response of SAMW is dependent both on the evolution of surface buoyancy forcing and overlying westerly wind stress. During year 2000–2100, the surface heat flux dominates the net buoyancy gain over the SAMW formation region, whereas the enhanced westerly wind contributes to a lesser extent due to its poleward shift. As the radiative forcing increases rapidly from 2000 to 2100, the buoyancy gain over the SAMW formation region results in a fast shoaling mixed layer and a reduction in the SAMW subduction rate. The surface intensified warming enhances stratification and reduces the SAMW that is quantified by the volume of low potential vorticity (PV) water. Consequently, the SAMW shrinks and thins fastly. When the radiative forcing stabilizes after 2100, the warming is greater in the subsurface than the surface, and the associated slow destratification gradually increases the low PV water volume. Hence, the SAMW expands and thickens slowly. The distinct fast and slow responses of SAMW have implications for the heat uptake and circulation of the SIO.