Effect Of Heat Source Temperature Research Articles

Study on heat transfer characteristics of cement-based honeycomb structures based on infrared imaging

The honeycomb structure may become the most potential material for constructing low-carbon and energy-saving buildings due to its excellent mechanical and thermal properties. The aim of this study was to investigate the temperature field evolution and heat transfer mechanism of cement-based honeycomb structures (CHSs) based on infrared thermal imaging technology. And the effects of heat source temperature and cavity bulk density on the temperatures of CHS were investigated. The results show that the heat transfer of CHS develops from an unsteady state to a steady state, and its thermal diffusion effect weakens layer by layer upward through the honeycomb cavities. The CHS temperatures increase linearly with increasing heat source temperature, but the temperature increase of the cavity wall is significantly higher than that of the air in the cavity. When the heat source temperatures increase from 40 to 85 °C, the temperature differences between the cavity wall and the air in the cavity increase in the range of 4.67–12.50 °C. The temperatures of the CHSs show a decreasing trend with increasing cavity volumes, and the air temperature reduction in the cavity is about 1.90–2.19 times that of the cavity wall. Moreover, it is found that the cavity wall temperature is mainly controlled by the heat source. In contrast, the air temperature in the cavity is influenced by both the heat source and the cavity volume. Ultimately, we speculate that increasing the thermal resistance of the cavity wall and the cavity volume is beneficial to improve the thermal insulation performance of the CHS.

Drying Characteristics and Odor Concentration in Tail Gas in Vacuum Drying of Municipal Sewage Sludge

As one of the most common solid wastes, municipal sewage sludge needs to be dried before its disposal and resource reuse. In this study, the effects of vacuum degree, heat source temperature and sludge thickness on drying rate and odor concentration in tail gas were studied through orthogonal experiments carried out on the lab-scale vacuum heat-conductive sludge drying device; The effects of heat source temperature on drying rate and odor concentration in tail gas were studied through comparative experiments of atmospheric state and vacuum state (-0.08MPa). The results show that the sludge thickness is the main factor affecting the sludge static drying rate, and the vacuum degree is the main factor affecting the odor concentration in the tail gas of sludge static drying. Under vacuum state (-0.08MPa), sludge can be dried efficiently while using low-grade heat source. In addition, while maintaining a high drying rate, the odor concentration in the tail gas will also be significantly reduced by reducing the generation of volatile sulphur compounds (VSCs).

Studies on long-term and buffer modes of operations of a thermal energy storage system using coupled metal hydrides

Metal hydride based thermal energy storage systems have attracted great attention due to their compactness and wide operational range. In long-term mode of operation, thermal energy is stored for long durations, whereas in buffer mode the heat storage is for immediate consumption, usually to cater for load fluctuations. This paper investigates a thermal energy storage system consisting of Mg2Ni-LaNi5 pair of metal hydrides in long-term and buffer modes of operation. Two inter-connected cylindrical reactors are simulated for multiple operating cycles using COMSOL Multiphysics®. The variations in porosity and density of hydride beds with hydrogen concentration during charging and discharging processes are considered. The effects of heat source temperature and the hydrogen storage bed temperature on the thermal performance of the system are investigated. The influence of hydrogen storage bed temperature is more significant in buffer operation than in long-term mode operation. With the heat source at 300 °C, the system achieved a storage density of 532.64 MJ m−3 with 67.8% and 430.28 MJ m−3 with 91.2% in long-term and buffer modes, respectively.

Dynamic Modeling and Comparison Study of Control Strategies of a Small-Scale Organic Rankine Cycle

The control strategy is crucial for the effective and safe operation of the ORC system. A transient model of the ORC system was developed in the present work and validated by the experimental data of a 4 kW ORC prototype. Then, the effect of heat source temperature on the dynamic response and operation characteristics of the ORC system were analyzed. Five control strategies were compared: the constant working fluid mass flow rate mode, constant vapor superheat mode, constant vapor temperature mode, constant evaporation pressure mode and constant output power load mode. Under the constraint that the working fluid at the expander inlet should be superheated, we found that the constant vapor superheat mode enabled the safe operation with the largest range of heat source temperature, while the other four modes were only available for a certain temperature range. Apart from the constant output power mode, the constant evaporation pressure mode can also provide a relatively stable performance for the ORC unit. The variation of the thermal efficiency was limited when the heat source temperature was higher than 125 °C, except for the constant vapor temperature mode. Considering the high performance and stable operation of the ORC system, it is necessary to have different operation modes combined in the control strategy according to the specific working scenarios.

How to identify trade-off of thermodynamic and economic performance of the S-CO2 cycle caused by the cycle structures?

Generally, the improvement of thermodynamic performance of supercritical CO2 Brayton cycles is realized by more complex cycle structures at the expense of expensive system cost. How to identify trade-off of the thermodynamic and economic performance of the S-CO2 cycle is a challenging issue because system structure is hard to be optimized with its nature of discrete variable. Therefore, taking the net power output and cost of electricity as the objective functions, this study tries to solve this issue by multi-objective optimization of superstructure of supercritical CO2 Brayton cycle for gas turbine waste heat recovery. Besides discussing the effect of heat source temperature and cooling temperature, the optimization results of the superstructure are compared with the traditional structures. The results show that at different heat source temperatures, the distribution regularities of the cycle structures on the Pareto-front are the same, and the structure of the trade-off solution tends to be the same. With the increase of heat source temperature, the costs of trade-off solutions are reduced by 8.86%, 11.16% and 16.51%, respectively. The change of cooling temperature has a great effect on the structure of the trade-off solution. In addition, superstructures have obvious advantages over the traditional structures in terms of trade-off solution performance and structure selection.

Analysis of H2O/EMISE absorption chiller driven by stationary solar collectors in hot-humid climate

The performance of H2O/EMISE (1-ethyl-3-methylimidazolium ethyl sulfate) absorption chiller driven by stationary solar collectors including the flat plate collector (FPC), evacuated tube collector (ETC), compound parabolic collector (CPC) in hot-humid climate is the focus of this study. As a case study, the cooling capacity of the absorption chiller is constant at 100 kW and used for air conditioning in Guangzhou, China with the inlet/outlet temperature of cooling water fixed at 32/37 °C and the inlet/outlet temperature of chilled water set at 17/12 °C. The effects of heat source temperature between 78 and 100 °C on the thermodynamic as well as economic performance of the solar absorption chiller system have been analyzed and meanwhile the application potentials of the three candidate solar collectors are compared also. The results show that there is an optimum heat source temperature makes the coefficient of performance (COP) and exergetic efficiency (ECOP) of solar absorption chiller system maximum, which is featured with a shifting to lower values compared to the optimum one that leads to the COP of absorption chiller machine maximum. Besides, while the CPC absorption chiller system has the best thermodynamic performance with the overall COP and ECOP about 0.351 and 0.027, respectively, the ETC system becomes the most economic one with the specific investment cost about 1194 USD/kW. Recommendations are given based on the findings as resources to help the design of solar driven H2O/EMISE absorption chiller systems in the hot-humid region.

Fast fabrication of Al3Ti/Al composites using combustion synthesis and melt dilution

A simple method combined combustion synthesis (CS) and melt dilution was utilized to fast fabricate Al3Ti/Al composites. This paper mainly focuses on analyzing the effect of heat source temperature (Ths) on combustion behaviors and reaction products in the 5Al-Ti system. The ultrafast heating rate induced by Ths could activate liquid-solid combustion in powder compacts. Due to the presence of Al3Ti layer acted as a diffusion barrier, it is suggested that reaction kinetics is mainly Ti-diffusion-controlled. Increasing the heating rate remarkably enhances the Ti flux across Al3Ti layer into the Al melt, which in turn releases a higher reaction exothermicity and finally promotes reaction to completion. Based on the above experimental results, a dissolution-precipitation mechanism for Al3Ti formation during CS was established.

Effects of Heat Source Temperature, Nanostructure, and Wettability on Explosive Boiling of Ultra-Thin Liquid Argon Film Over Graphene Substrate: A Molecular Dynamics Study

Background: The study on explosive boiling phenomenon has received increasing attention because it involves many industries, such as advanced micro-, nano-electromechanical and nano-electronic cooling systems, laser steam cleaning, and so on. Objective: In the present work, the explosive boiling of ultra-thin liquid film over two-dimensional nanomaterial surface in confined space with particular emphasis under the three different influencing factors: various heights of nanostructures, various wetting conditions of solid-liquid interface as well as various heat source temperatures. Methods: Molecular Dynamics simulations (MDs) in present work have been adopted to simulate the whole explosive boiling process. Results: For different heat source temperature case, the higher the heat temperature is, the less time the explosive boiling spends after relaxation. For nanostructure case, nanostructure surface significantly increases heat transfer rate and then leads to the increase of phase transition rate of explosive boiling. For different wetting property case, the increase of surface wettability results in an increase of phase transition to some degree. Conclusion: The addition of nanostructures, the higher heat source temperature and good wettability between thin liquid film and substrate surface dramatically improve thermal heat transfer from solid surface to liquid film, which will give rise to explosive boiling occur. In addition, the non-vaporized argon layer still exists in these three factors despite continuous thermal transmission from the substrate surface to liquid argon film adjacent to the solid surface even other vaporized argon atoms.

Thermo-Economic Evaluation of Aqua-Ammonia Solar Absorption Air Conditioning System Integrated with Various Collector Types.

The main objective of this paper is to simulate solar absorption cooling systems that use ammonia mixture as a working fluid to produce cooling. In this study, we have considered different configurations based on the ammonia–water (NH3–H2O) cooling cycle depending on the solar thermal technology: Evacuated tube collectors (ETC) and parabolic trough (PTC) solar collectors. To compare the configurations we have performed the energy, exergy, and economic analysis. The effect of heat source temperature on the critical parameters such as coefficient of performance (COP) and exegetic efficiency has been investigated for each configuration. Furthermore, the required optimum area and associated cost for each collector type have been determined. The methodology is applied in a specific case study for a sports arena with a 700~800 kW total cooling load. Results reveal that (PTC/NH3-H2O)configuration gives lower design aspects and minimum rates of hourly costs (USD 11.3/h) while (ETC/NH3-H2O) configuration (USD 12.16/h). (ETC/NH3-H2O) gives lower thermo-economic product cost (USD 0.14/GJ). The cycle coefficient of performance (COP) (of 0.5).

Design of a hydrogen compressor for hydrogen fueling stations

Hydrogen compressors dominate the hydrogen refueling station costs. Metal hydride based thermally driven hydrogen compressor (MHHC) is a promising technology for the compression of hydrogen. Selection of metal hydride alloys and reactor design have a great impact on the performance of the thermally driven MHHC. A thermal model is developed to study the performance characteristics of the two-stage MHHC at different operating conditions. The effects of heat source temperature and hydrogen supply pressure on the compression ratio and isentropic efficiency are investigated. Finite volume method is used for discretizing the reaction kinetics, continuity, momentum and energy equations. Metal hydrides selected for this analysis are Mm0.2La0.6Ca0.2Ni5 and Ti1.1Cr1.5Mn0.4V0.1. The thermal model was validated with the results extracted from an experimental study. Validation results demonstrated that the numerical results are in good agreement with the data reported in literature.

Effects of heat source temperature and mixture composition on the combined superiority of dual-pressure evaporation organic Rankine cycle and zeotropic mixtures

Abstract Dual-pressure evaporation cycle is an emerging cycle type in the organic Rankine cycle (ORC) that can remarkably reduce the irreversible loss during heat absorption process and improve the adaptability to various heat sources. Introduction of zeotropic mixtures in dual-pressure evaporation ORC presents great potential to further increase the heat-power conversion efficiency due to the variable phase-change temperature. This study investigated the dual-pressure evaporation ORC using isobutane/isopentane mixtures for heat sources of 100–200 °C. Effects of heat source temperature and mixture composition on the system thermodynamic performance were analyzed. Application potential and applicable ranges of introducing isobutane/isopentane mixtures in dual-pressure evaporation ORC were evaluated. Results showed that the introduction of zeotropic mixtures in dual-pressure evaporation ORC substantially increased the power output. The maximum power output of dual-pressure evaporation ORC using isobutane/isopentane mixtures could increase by 11.9% and 15.2% at most compared with those of using isobutane and isopentane, respectively. It could increase by 25.7% at most compared with that of single-pressure evaporation ORC using isobutane/isopentane mixtures. In terms of being introduced into dual-pressure evaporation ORC, the zeotropic mixture with a high critical temperature can generally achieve larger range in applicable heat source temperature and larger increment in the power output.

High performance and thermal stress analysis of a segmented annular thermoelectric generator

Annular thermoelectric generators can eliminate the thermal contact resistance formed due to geometry mismatch when flat-plate thermoelectric generators are used with round shaped heat source or heat sink. Therefore, in this study, the numerical simulation of a segmented annular thermoelectric generator (SATEG) is investigated using three-dimensional finite element analysis. The thermoelectric and mechanical performance of the segmented annular thermoelectric generator is studied by considering temperature dependent thermoelectric material properties and elastoplastic behaviour of copper and the welding layer (solder). The influence of segmented pin geometry on the performance of the segmented annular thermoelectric generator is investigated and comparison is made with non-segmented annular thermoelectric generators. COMSOL 5.3 Multiphysics software is used to investigate the effects of heat source temperature, thermoelectric leg length and leg angle on the electrical and mechanical performance of the segmented and non-segmented annular thermoelectric generators. Results show that the segmented annular thermoelectric generator has a greater efficiency compared to the annular thermoelectric generator (ATEG) with Bismuth telluride material when the temperature difference is greater than 100 K. In addition, the efficiency of the SATEG is found to be 21.7% and 82.9% greater than that of the Bismuth telluride ATEG and Skutterudite ATEG respectively at 200 K temperature difference. Finally, the results show that increase in thermoelectric leg length can reduce the thermal stress and electrical performance of the segmented and non-segmented thermoelectric generators. Results obtained from this study would influence the design and optimization of segmented annular thermoelectric generators.

Thermal comparison and multi-objective optimization of single-stage aqua-ammonia absorption cooling system powered by different solar collectors

This paper presents the comprehensive thermodynamic modelling to compare the performance and optimization of single-stage NH3–H2O-type absorption cooling system integrated with different solar collector types for the city of Mehsana, India. A 20-kW system at 0 °C is analysed which includes four different solar collectors flat-plate collectors, parabolic-trough collectors (PTC), flat plate with compound parabolic collector reflectors and evacuated-tube collectors (ETC) attached with insulated thermal storage tank to power the NH3–H2O vapour absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. The examined performance parameters are exergetic efficiency, coefficient of performance and area of collector. Exergetic optimization of each system estimated the optimum collecting area requirement for cooling. Differentiation between optimized systems determined that the optimum cost, SCOP and ηII,system of PTC-type system are averagely 30, 11 and 0.5% higher than ETC-type system at different ambient temperatures. For effective comparison and conclusion, key performance indicator is evaluated to select optimum system configuration from both thermodynamic and economic criteria.

Design considerations for an Ericsson engine equipped with high-performance gas-to-gas compact heat exchanger: A numerical study

A new simulation model is presented for the simulation of the open cycle Ericsson engine operation on a crank-angle basis. The model simulates the compressor and expander operation as well as their interactions with a compact gas-to-gas heat exchanger selected from the literature based on its high heat-transfer-area-to-volume ratio. Hot gases passing through the hot side of the exchanger are the heat source that heats the compressed air, which is considered the working gas. The analysis considers both sides of the heat exchanger. Factors such as pressure drops in the air and gas streams, free-flow areas, heat transfer coefficients, heat exchanger effectiveness and heat transfer rate are considered to determine the engine performance. These factors guide the threefold numerical investigation presented herein. The effects of heater geometry and configuration (single- or multi-passing) are first analyzed and elucidate the importance of gas-side pressure drop. Next, the effect of the heat exchanger size is considered that highlights the importance of heat transfer areas and heater pressure fluctuations that affect the work produced. Finally the effect of heat source temperature on the engine performance is determined. All trends observed are analyzed and explained on a crank-angle basis, to elucidate the essential variables that link the overall engine performance to the physical phenomena evolving in the devices.

Vapor absorption system powered by different solar collectors types: Cooling performance, optimization, and economic comparison

The current article presents the comprehensive thermodynamic modeling to compare the performance and optimization of single-stage LiCl-H2O and LiBr-H2O type absorption cooling system integrated with different solar collector types for the Gujarat, India. A 10 kW system at 7°C is analyzed which includes four different solar collectors (flat-plate collectors, parabolic-trough collectors, flat plate with compound parabolic collector reflectors, and evacuated-tube collectors) attached with insulated thermal storage tank to power the LiCl-H2O and LiBr-H2O vapor absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl-H2O pair is found to be lower in comparison to LiBr-H2O pair for all collectors type system. The examined performance parameters are exergetic efficiency, coefficient of performance, and area of collector. Exergetic optimization of each system estimated the required optimum collecting area for cooling. At optimum collector areas, capital cost is evaluated. Differentiation between optimized systems determined that evacuated-tube collectors-based technology is most economic and from exergetic point-of-view, parabolic-trough collectors is recommended. For effective comparison and conclusion, key performance indicator is evaluated to select optimum collector and working fluid pair from both thermodynamic and economic criteria.

Thermodynamic and economic analysis of zeotropic mixtures as working fluids in low temperature organic Rankine cycles

Organic Rankine cycle (ORC) is one of the most technically feasible methods to convert low-grade thermal energy into shaft power. An efficient approach to improve the thermodynamic performance is using zeotropic mixtures that enables better temperature match with the heat source and sink. In this article, a thorough assessment of thermodynamic and economic performance is conducted for the low grade ORCs using pure fluid and zeotropic mixtures. This work also examines the effects of heat source temperature and mixture mass fraction on the net power output, heat exchanger size, and cost-effective performance, and discusses the according basis for the selecting pure fluid or zeotropic mixtures. The results show that zeotropic ORC is capable of producing more net power than pure ORC, particularly for heat source with larger temperature difference. However, it needs much more heat exchanger area and therefore causes an unfavorable economic performance. Under the same heat exchanger area, pure cycle has lower pinch point temperature and higher net power output than zeotropic cycle. Therefore, the selection between pure fluid and zeotropic mixtures is also dependent on whether the power demand can be satisfied in pure ORC under the given pinch point condition.

Parametric analysis of organic Rankine cycle based on a radial turbine for low-grade waste heat recovery

Organic Rankine cycle (ORC) is one of the promising technologies to convert low-grade waste heat into electricity. This study comprehensively investigates the thermodynamic performance of ORC system and the aerodynamic characteristics of radial turbine. An optimized coupling model for the ORC with a radial turbine is developed, and the particle swarm optimization algorithm is applied to maximize the turbine efficiency dynamically. The model is used to evaluate the effect of heat source temperature on the cycle performance and parameter selection for turbine design optimization. The results show that optimal turbine efficiency can be achieved within the considered heat source outlet temperature range, as high pressure ratio and high mass flow rate can both degrade the turbine efficiency. Among the four studied organic fluids, the ORCs using R123 and R245fa can achieve desirable cycle performances. For the turbine design, lower degree of reaction is beneficial for turbine efficiency gains. The optimized rotational speed and ratio of wheel diameter are dependent on heat source temperature, while which has almost no effects on velocity ratio, loading coefficient, and flow coefficient. The reasonable ranges of partial turbine design parameters are also proposed in this work.

Modeling the Effect of Heat Source Temperature on the Performance of Two-stage Air Cooled Silica Gel + Water Adsorption System

Adsorption systems can utilize low grade waste heat (temperature <100 degrees C) or energy from renewable sources like solar for cogeneration i.e. cooling and desalination. The throughput and performance of such systems are sensitive to the available temperature difference between heat source and sink. This paper presents a modelling study of two-stage 2-bed air cooled silica gel + water adsorption system wherein the effect of heat source temperature variation in the range of 65-85 degrees C on system performance parameters viz. SCC, SDWP and COP are investigated for the first time. It is shown that the optimum half cycle time for SCC and SDWP increases from 1800 s to 2700 s as the source temperature decreases from 85 degrees C to 65 degrees C; thereby necessitating the use of adaptive cycle time control for maximum throughput. However, it is observed that the COP is relatively insensitive to such alterations.

Optimization of powered Stirling heat engine with finite speed thermodynamics

Popular thermodynamic analyses including finite time thermodynamic analysis was lately developed based upon external irreversibilities while internal irreversibilities such as friction, pressure drop and entropy generation were not considered. The aforementioned disadvantage reduces the reliability of the finite time thermodynamic analysis in the design of an accurate Stirling engine model. Consequently, the finite time thermodynamic analysis could not sufficiently satisfy researchers for implementing in design and optimization issues. In this study, finite speed thermodynamic analysis was employed instead of finite time thermodynamic analysis for studying Stirling heat engine. The finite speed thermodynamic analysis approach is based on the first law of thermodynamics for a closed system with finite speed and the direct method. The effects of heat source temperature, regenerating effectiveness, volumetric ratio, piston stroke as well as rotational speed are included in the analysis. Moreover, maximum output power in optimal rotational speed was calculated while pressure losses in the Stirling engine were systematically considered. The result reveals the accuracy and the reliability of the finite speed thermodynamic method in thermodynamic analysis of Stirling heat engine. The outcomes can help researchers in the design of an appropriate and efficient Stirling engine.

Performance investigation of a solar hot water driven adsorption ice-making system

A solar hot water driven solid adsorption ice-making system with heat storage was designed and constructed. The finned-tube absorbent bed in the water tank, which also acted as heat storage unit, was heated by the hot water from the solar vacuum tube collector in desorption process. The water in the tank was also auxiliary heated by electric heater to keep at the set desorption temperature. Activated carbon–methanol was utilized as the working pairs in the system. Effects of heat source temperature on system performance were experimentally investigated under four conditions: maintaining the water temperature in the tank at 94°C (boiling point), 85°C, 75°C, respectively, and heating the water to reach 94°C then naturally cooling the hot water without maintaining heating in desorption process. The experimental results showed that the temperatures around the finned-tube of the adsorbent bed was homogeneous, which was beneficial for desorption of the adsorbate. The maximum daily ice-making capacity of 8.4kg and the lowest temperature of −8.6°C were achieved when the hot water temperature was maintained at 94°C. The maximum refrigeration cycle coefficient of performance (COP) of 0.139 was obtained under the condition of heating the water to reach 94°C then cooling naturally the hot water without maintaining heating. The system heat utilization efficiency decreased with the increase of heat source temperature due to the greater heat loss in desorption process.