Heat Release Process Research Articles

Experimental Analysis on Heat Release of Pulsating Heat Pipe Phase Change Regenerator with Different Working Fluids

In order to improve the problems of serious energy waste and low utilization rate, this paper designs and builds an experimental platform for a pulsating heat pipe type phase change heat storage device. The temperature changes with time in the heat storage and release device of the barium hydroxide octahydrate phase change material under different working conditions is studied. The results show that during the heat release process, when the pulsating heat pipe is filled with water, the cooling water temperature rises to the highest, and the heat recovery rate is as high as 64%. Otherwise, the initial temperature of the cooling water during the heat release process is studied. Result shows that the initial temperature of the cooling water increases, the longer the latent heat of phase change and the total heat release time, and the higher the temperature rise of the cooling water. The experimental design of this paper can provide a reference for researchers in related fields.

Comparative analysis and research on heat transfer enhancement of fin tube-paraffin

In order to improve the heat transfer between the air and paraffin phase change heat storage, the circular fins are arranged on the smooth circular heat storage air duct to enhance the heat transfer between the air and paraffin, and study the effects of different fin thickness, fin space and the number of heat storage air ducts on the heat storage and release process of paraffin. In this research work, the heat transfer process is studied by numerical work.The model of the heat storage device is established by using Fluent software in computational fluid dynamics (CFD)simulation software, and make simulation calculation for different fin thickness, fin space and the numbers of duct.The results of simulation calculation show that the paraffin melting degree and average temperature of paraffin regenerator with fin thickness of 15 mm is higher than that with fin thickness of 10 mm.The paraffin melting degree and average paraffin temperature of paraffin regenerator with fin space of 25 mm are highest.At the paraffin regenerator with ducts number of 16, the melting degree, average temperature and flow channel of paraffin are highest, which are 92.42%,319.64 K and 323.71 K respectively.The Nusselt number and paraffin melting degree of the best regenerator are fitted with the empirical formula by the method of curve fitting.And the curve shows that when the number of air ducts is 18, the melting degree of paraffin reaches the maximum.The heat released by the best combination regenerator can maintain the indoor heating for eight hours at night.

Kinetic features of polymerization of epoxy resin modified by silicon‐containing additives and mineral fillers

AbstractIn this article, we study the process of polymerization of a modified ED‐20 epoxy binder under conditions of highly filled systems. It is found that modifying additives affect the process of polymerization of the binder, increasing the degree of conversion of epoxy groups of ED‐20 resin, speeding up the process of polymerization, and increasing the exothermic effect of the reaction. Curing in the presence of a modifying silicon‐containing additive takes place in a mode that promotes the formation of a more ordered structure, creating opportunities for relaxation of internal stresses and favorable conditions for the formation of an ordered microstructure. The equations sufficiently fitting the measured points of the concentration of epoxy groups are calculated. We obtain the kinetic curves of curing, which illustrate the process of heat release of the ED‐20 binder and the same system modified with mineral fillers. It is found that the heat release occurs more intensively when modifiers are introduced into the epoxy binder. It is derived that the experimental data of kinetics of heat release at considered time range can be sufficiently described by a parabolic equation.

Pore-Scaled investigation on dynamic carbonation mechanism of calcium oxide particles

Carbonation of high-temperature calcium oxide is one of the main means of calcium looping thermochemical heat storage and it has unique advantages in carbon capture and energy conversion and utilization. This work is the first to construct the carbonation process of a single calcium oxide particle from pore size by using the lattice Boltzmann method. At the same time, considering the diffusion of gas in the solid, the reaction source term is optimized to a volume source term to be closer to the real situation. The results show that the establishment of the method can better reflect the micro-flow diffusion mass transfer and heat release process inside the pores. The multi-field coupling method can be extended to many areas of the porous microstructure of gas–solid reaction, which guides significance for macro-reactor design and optimization of the particle structure, and produces far-reaching value in carbon neutrality and new energy exploitation.

A novel compensating fins configuration for improving the thermal performance of latent heat thermal energy storage unit

The low thermal conductivity of phase change materials (PCMs) severely limits the performance and operational capability of latent heat thermal energy storage (LHTES) systems. In this study, the authors not only first revealed the contradiction of the optimization strategy of the fins in the melting and solidification processes but also proposed a novel compensating fins configuration based on LHTES units with double sources (heat and cold sources) for promoting the performance and flexibility of the LHTES units. A transient two-dimensional numerical model using the enthalpy-porosity method is used to study the characteristics of energy transfer during heat storage, heat release, and heat storage-release process in the LHTES unit. The five developed types of compensating fins are well compared. The results illustrated that the unequal-length compensating fins reduced the melting and solidification time by 64.2% and 82.1%, respectively. Moreover, the unequal-length compensating fins increased the heat transfer rate by 155%, and the steady-state time was shortened by 73.3% in the heat storage-release process. Compensating fins configurations effectively improved the thermal performance and flexibility of the LHTES unit.

THEORICAL STUDY ON PROPULSIVE PERFORMANCE OF OBLIQUE DETONATION ENGINE

Detonation combustion is characterized by the high thermodynamic efficiency and fast heat release. Benefitting from these potential advantages, an oblique detonation wave (ODW) is introduced into the combustion chamber and oblique detonation engine (ODE) plays an important role in hypersonic air-breathing propulsion systems. Previous studies mainly focused on the initiation structures, standing features and wave systems of oblique detonation, but the global analysis of ODE propulsive performance is still absent at the macro-level. In this paper, the flow and combustion processes of an ODE are decomposed into four basic modules, named as inlet model, mixing model, combustion mode and nozzle model, respectively. We solve these four basic flow processes using theoretical methods and propose a systematically theoretical approach that can be used to predict the ODE propulsion performance. On the basis of previous ODW initiation structures and waves systems, four different combustion modes, i.e., over-driven ODW, Chapman-Jouguet ODW, over-driven normal detonation wave and oblique shock-induced constant-volume combustion, are chosen to describe the heat release processes of combustible mixture in the ODE combustor. The effects of different combustion modes on fuel specific impulse of the ODE are also analyzed. In addition, the influence mechanisms of inflow parameters, combustor parameters and intake-exhaust parameters on the thrust performance of ODE are also obtained, and the results show that the major factor of fuel specific impulse of an ODE consists mainly of the inflow Mach number and the expansion ratio of engine nozzle. Finally, combined with precious detonation research results, such as the standing features and initiation structures of oblique detonation in a confined space, the preliminary design direction of oblique detonation engine are proposed, which mainly involve some constrained conditions, such as geometrical constraints, inflow velocity limitations and stability ranges of a detonation wave in ODE combustor.

Study on heat transfer characteristics of regenerative shell-and-tube heat exchangers

A new type of regenerative shell-and-tube heat exchanger is designed to solve the problems that the generation load of cogeneration units is limited by the amount of heat supply during the heating period, the peak shaving capacity of units decreases, and the phenomenon of wind and light abandonment in the power system is serious. Considering the advantages of nearly constant temperature and large potential heat release during the heat storage/release process ofphase change materials, paraffin is selected as the phase change material, and the phase change area of the heat exchanger is selected as the heat exchange unit. The control variates method is used to simulate the heat storage/release process of the heat exchange unit according to the key factors such as the flow rate of heat transfer fluid, the thermal conductivity of phase change materials and the thickness of phase change layer. The results show that increasing the flow rate of heat transfer fluid can enhance the heat storage capacity of the heat exchange unit and shorten the complete melting time of phase change materials. In order to control the heat at the output end of the heat exchanger during the heat release process, the flow rate of heat transfer fluid should be appropriately selected; using composite materials to improve the thermal conductivity of phase change materials can enhance the heat transfer capacity of the heat exchange unit, and the average heat transfer coefficient of the heat exchange unit is more than 2 times higher than that of pure paraffin at the same heat transfer fluid flow rate; increasing the thickness of phase change layer can prolong the time of maintaining the outlet temperature of heat transfer fluid in the process of heat release.

Effect of electrolyte conductivity and local electric field inhomogeneity on heating of an aqueous suspension of solid-state nanoparticles

This work theoretically investigates the process of heat release in an electrolyte near a solid-state nanoparticle when exposed to an external radio-frequency electromagnetic field. The effect on the heat release of the effect of a change in the electrical conductivity of the electrolyte near the nanoparticle due to the redistribution of the ion concentration and the inhomogeneity of the electric field caused by the difference in the dielectric constants of the electrolyte and the nanoparticle is taken into account. The proposed model can be useful for choosing the optimal parameters of nanoparticles and radio frequency radiation when used in biomedicine for tumor hyperthermia.

Evaluation of Combustion Performance and Heat Release in Preheated Fuel Consumed Diesel Engines

Introduction. The expansion of the fleet of tractors and vehicles causes increased requirements for internal combustion engines. This problem can be solved by improving the work process in a diesel engine that can be achieved by heating the diesel fuel in the fuel supply system. External thermal action is carried out on the high pressure line directly in front of the injectors. Materials and Methods. To analyze and calculate the process of combustion and heat release in a diesel engine with preliminary thermal fuel preparation, bench tests were carried out using the National Instruments software and the necessary equipment. Results. Experimental data of the diesel fuel combustion process in the cylinder of the 4CHN 11.0/12.5 engine are obtained. The analysis of the combustion performance and heat release of diesel with a preliminary high-temperature effect on the fuel was carried out. Indicator diagrams, graphs of heat release, the maximum average temperature of gases in the engine cylinder, and graphs of active and total heat release were constructed. The experimental data showed a decrease in the ignition delay period, the maximum cycle temperature in the engine cylinders, and an acceleration of the start of heat release and combustion process. The values of the parameters of the diesel fuel combustion process are obtained. Discussion and Conclusion. On the basis of the conducted studies, the dependences of the parameters of the combustion process of a diesel engine with fuel heating to high temperatures are revealed. Indicator diagrams allow drawing a conclusion about the influence of the fuel heating temperature on the intensification of the combustion process. There is an acceleration of the beginning of heat release, a decrease in the rate of pressure build-up and in the rigidity of the engine.

Investigation on application temperature zone and exergy loss regulation based on MgCO3/MgO thermochemical heat storage and release process

Thermochemical heat storage (TCS) is an efficient technology for energy utilization with high heat storage density and seasonal storage. Among TCS carriers, MgCO3/MgO has a broad prospect at moderate temperatures. However, its definite application temperature range is not clear, and the issue of degradation of energy quality remains to be addressed. This research presented an intergrated test scheme to determine reaction temperature zone and optimal temperature by making connection with thermokinetics. In order to further control exergy loss, pressure regulation strategy with exergy evaluation was carried out. Results indicate that upper limit on what exothermic reaction occurs and lower limit for the endothermic deviate from thermodynamic equilibrium within 12 °C at P(CO2) = 1 bar. Exothermic reaction is motivated under the promotion of melting process for dopants, and the highest endothermic temperature depends on degradation level of TCS products. In the above temperature range, optimal temperature affected by multiple subprocedures keeps the same variation rule as the lower limit temperature either before or after adjusting pressure. Furthermore, exergy loss can be reduced to 9.97 kJ/mol with exergy efficiency 91.0% via lowering pressure of CO2 in charging process. This research provides an effective pathway to select TCS carriers and regulate its energy quality for engineering applications.

Study on the thermogravimetric and combustion of coal slime

ABSTRACT The study of the combustion characteristics of single-particle solid fuels is the basis for achieving clean combustion of solid fuels, coal slime is currently a relatively common waste solid fuel. This work uses a thermogravimetric analyzer to study the heat release and weight loss process of coal slime with different ash contents under different heating rates. Through the analysis of TG and DTG curves, the combustion characteristic parameters of slime are solved. The results show that under the same heating rate condition, as the ash content of coal slime increases, the TG and DTG curves move to the higher temperature area, the peak value of the DTG curve gradually decreases, the ignition temperature first decreases and then increases, and the ignition delay time slightly decreases, the flammability index decreases, the ignition stability characteristic first increases and then decreases, and the burnout characteristic index first decreases and then increases. The coal slime sample with 50% ash content has the best ignition stability characteristics. The 50A sample has the highest ignition stability characteristic index, which is 2.47, 2.37, and 2.26 at heating rates of 20 K/min, 30 K/min, and 50 K/min, respectively.

A two-node mechanistic thermophysiological model for pigs reared in hot climates – Part 1: Physiological responses and model development

Due to the climate change and the increasing heat production of modern pigs (e.g. larger size sows having a larger number of piglets nowadays), pigs are more frequently suffering heat stress. In order to prevent the occurrence of heat stress, there is a need to develop a model which can effectively and efficiently predict the effect of ambient thermal environments on pigs. This study developed a two-node mechanistic model to simulate processes of pig thermoregulation and heat release to an ambient hot environment based on biophysical laws. The two-node model consists of a passive system, which can simulate the heat transfer processes occurring in the body core and at the skin surface, and an active system, which controls the thermoregulatory system based on a positive deviation of core temperature from its reference value under thermal neutral conditions. Vasodilatation and panting in relation to the ambient environment were specifically investigated and mathematically described based on the experimental data from previously published studies. The functions to predict vasodilatation and panting provided a relatively more detailed modelling of the thermo-physiological processes of the pigs compared to the available mechanistic models. The proposed two-node model was expected to effectively predict the thermal status of pigs under various combinations of environmental conditions without further tuning. • A mathematical model simulating pig thermoregulatory processes in hot climates. • Correlation between skin blood flow rate and ambient air temperature. • Correlation between pulmonary ventilation rate and ambient air temperature. • A novel active system developed with emphases on vasodilatation and panting.

Temperature regulating fibers of high latent heat and strength: Mass production, characterization and applications

A kind of temperature regulating fibers (TRFs) with excellent mechanical and thermal properties were prepared by bi-component melt spinning technology on an industrial mass production equipment, in which the core material chips are composed of paraffin wax (PW), polyethylene (PE) and olefin block copolymers (OBC), having the preferable latent heat and thermostability at an onset volatilization temperature of 224.91 °C, and the sheath layer is polypropylene (PP). The prepared TRFs have significant heat absorption and release processes in the range of 20-35 °C with a latent heat up to 26.96 J/g. At the sheath/core ratio of 6:4, the TRFs are 2.09 cN/dtex in the breaking strength and 30.4 % in the elongation after further drawing at a winding speed of 1400 m/min, which fully meet the requirements of the fabric manufacture. After woven with cotton yarn, the TRF/cotton fabrics can effectively reduce the temperature fluctuation by 3 °C in the cooling process, displaying good thermal storage and regulating ability.

Numerical simulation of flow and cooling heat transfer of supercritical pressure refrigerants in chevron-type plate heat exchanger

In industrial fields, heat sources exceeding 130°C are necessitated; hence, the development of industrial high-temperature heat pump systems is anticipated. For the heat release process in such heat pump systems, the use of a plate heat exchanger (PHE), in which high-pressure working refrigerant flows, is examined. In this study, to predict the cooling heat transfer coefficient and pressure drop of supercritical pressure refrigerants flowing in a chevron-type PHE, a computational fluid dynamics model is developed. HFC134a and HFO1234ze(E) are selected as the working refrigerants. Calculations are performed by changing the inlet fluid enthalpy under three reduced pressure conditions from 1.01 to 1.21 and two mass flow rate conditions. The heat transfer coefficient and pressure drop obtained from the simulation reproduced the experimental results well, including the effects of pressure and mass velocity. Therefore, the present model can be applied to existing and new refrigerants if their physical properties are available. Furthermore, it can be used to optimize the plate shape of chevron-type PHEs. Finally, based on the simulation results, the characteristics of the flow behavior and heat transfer of refrigerants in the PHE are discussed.

A comparative study of gasoline skeletal mechanisms under partial fuel stratification conditions using large eddy simulations

Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at −300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of −160, −50, −35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion.

Experimental study on the application of bioethanol in dual-fuel intelligent charge compression ignition (ICCI) engine

Recently, the intelligent charge compression ignition (ICCI) combustion mode was proved to be very efficient for the internal combustion engine. Bioethanol is one of the most available renewable fuels at present. In order to improve the utilization efficiency of ethanol in internal combustion engine, this study tested the combustion and emission characteristics of bioethanol-diesel in ICCI mode at various bioethanol substitute ratios and injection strategies. The results demonstrated that with bioethanol substitute ratio of 64% ~ 68%, the indicated thermal efficiency of the engine reached high level (50.1%), and the engine emissions decreased to a low level with ultralow NOX (below 1 g/kwh) and particulate matter (particle number close to 1 × 106/cm3). The bioethanol double-injection strategy at 3:1 split ratio intensified the stability of the local heat release process, increasing thermal efficiency by 1.4%. Increasing bioethanol injection pressure diminished the possibility of local misfire increasing combustion efficiency. The dilemma of nucleation particle, HC, and CO emissions due to the low average temperature at the end of combustion could be solved by increasing bioethanol injection pressure.

Internal combustion engine diagnostics using statistically processed Wiebe function

The aim of the article is to present the concept of an indirect diagnostic method using the assessment of the variability of the amount of released heat (mass fraction burn) and the heat release rate. The Wiebe function for the assessment of variability has been used. The Wiebe function parameters from the course of the high-pressure indication in the cylinder of internal combustion engine using linear regression have been calculated. From a sufficiently large number of measured samples, the upper and lower limits of the Wiebe function parameters have been statistically determined. Lower and upper limits characterize variability of the heat release process not only in terms of quantity but also in terms of heat release rate. The assessment of variability is thus more complicated than using one integral indicator, typically the mean value of amount of the released heat. The procedure enabling a more accurate estimation of heat generation beginning has been shown. For the combustion process variability assessment of the engine, statistical test of relative frequencies has been used.

PENINGKATAN KAPASITAS TERMAL PENAMPUNG AIR PANAS SOLAR HEATER MENGGUNAKAN CAPSULATED PARAFFIN

Solar power is considered as the most essential renewable energy in human life, particularly for daily activities. The application of solar water heater is significantly able to reduce the electric load of water heating so that this method is indirectly able to save energy needs. The biggest challenge is increasing the energy density of warm water storage. The best storage medium is paraffin, but it is constrained by the low thermal conductivity of the paraffin and also the wrapping media. This study focuses on efforts to improve thermal conductivity of paraffin as a heat storage medium by using nickel mixture at a ratio (volume) of 10 - 50%. Samples of paraffin and nickel paraffin mixture are inserted into the wrapper of aluminum 6063 material and then tested for heat absorption and release process. The best heat absorption is shown by the sample with the most nickel content, while in the heat release process the best performing sample is shown with a nickel mixture between 20–40%. These results are directly related to the power rate of each sample. The results of this study can be used as a reference for increasing the thermal capacity of warm water storage from solar water heaters.

Effects of fuel trapping in piston crevice on unburned hydrocarbon emissions in early-injection compression ignition engines

Early injection strategy is employed in many advanced combustion concepts of modern compression-ignition engines to promote the fuel-air premixing, but it could result in fuel spray impingement on the cylinder wall and potential fuel trapping in the crevice regions. The impact of the fuel trapping on the formation and distribution of unburned hydrocarbon (UHC) in the advanced compression-ignition concepts is not well understood. In this study, the planar laser-induced fluorescence (PLIF) technique was applied in a single-cylinder optical engine to visualize the fuel distribution before combustion and the formaldehyde formation during combustion. A three-dimensional computational model was established to explore the detailed mechanism of UHC formation in the piston crevice. Three cases with injection timings of 20°, 40° (SOI-40), and 100° (SOI-100) were compared. The PLIF and simulation results indicate that, under early injection conditions, the squish region and piston crevice trap a considerable amount of fuel, resulting in increased UHC emission and reduced engine work, and the main combustion zone resides in the squish region. The simulation shows that the amount of UHC formation from the trapped fuel is highly dependent on the local equivalence ratio distribution formed by different injection timings. The local equivalence ratio within the piston crevice region for the SOI-40 case exceeds 2 before combustion; the charge sequentially undergoes both low- and high-temperature heat release (LTHR and HTHR) processes and produces less UHC in the crevice region. However, the SOI-100 case produces an overall leaner mixture with a local equivalence ratio lower than 1 before combustion; the charge undergoes LTHR without noticeable HTHR and becomes UHC near the cylinder wall. The injector dribbling results in more UHC formation in the central part of the cylinder under very early injection timing, and thus an accurate injector dribbling model is required to better reproduce the UHC emissions.

Distributed Thermal Energy Storage Configuration of an Urban Electric and Heat Integrated Energy System Considering Medium Temperature Characteristics

Distributed thermal energy storage (DTES) provides specific opportunities to realize the sustainable and economic operation of urban electric heat integrated energy systems (UEHIES). However, the construction of the theory of the model and the configuration method of thermal storage for distributed application are still challenging. This paper analyzes the heat absorption and release process between the DTES internal heat storage medium and the heat network transfer medium, refines the relationship between heat transfer power and temperature characteristics, and establishes a water thermal energy storage and electric heater phase change thermal energy storage model, considering medium temperature characteristics. Combined with the temperature transmission delay characteristics of a heat network, a two-stage optimal configuration model of DTES for UEHIES is proposed. The results show that considering the temperature characteristics in the configuration method can accurately reflect the performance of DTES, enhance wind power utilization, improve the operation efficiency of energy equipment, and reduce the cost of the system.