•The steady-state operation of high-temperature water flow boiling was investigated within 100–250 °C for space heat dissipation.•Four parameters of heat exchanger efficiency (HEE), heat transfer ...power (HTP), liquid-side outlet quality (LSOQ), and two-phase heat transfer coefficient (HTC) were analyzed under different operating pressures and mass flow rates.•The parameter values were calculated and variation rules were summarized.
With the development of space nuclear reactors, the transmission and emission of a large amount of waste heat in space are inevitable. Because of its large heat transfer, clean nature, and safe working medium, flow boiling of high-temperature water is ideal for space applications. This study focuses on high-temperature heat dissipation and experiments on the flow boiling heat transfer of high-temperature water. The steady-state operation characteristics of high-temperature water flow boiling heat transfer in the operating temperature range of 100–250 °C are studied with an emphasis on the variations in heat exchanger efficiency (HEE), heat transfer power (HTP), liquid-side outlet quality (LSOQ) of the high-temperature heat exchanger, and two-phase heat transfer coefficient (HTC). The HTP can be improved to a peak of 16 kW under a moderate air mass flow rate, and the LSOQ can be increased to approximately 0.95. The maximum HTC in this system could reach approximately 2100 W/(m2*K), which offers significant design guidance for the high-temperature water flow boiling system.
In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized ...to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers.
Heating, Ventilation, and Air Conditioning (HVAC) systems can maintain the space air temperature of residential buildings, either directly by heating/cooling the air, or indirectly via heat transfer ...to and from the building structure that acts as a thermal mass. Hence, HVAC systems can help achieve load shifting, peak load reduction, and/or energy cost saving, thus enabling grid-interactive HVAC operation. A home thermal model that can accurately reflect the dynamics of the space air and interior wall surface temperatures, is therefore valuable. This paper develops such a model using the standard RC (resistance-capacitance) approach. The model contains a virtual envelope node and an internal space node and is thus second-order. A hybrid parameter identification scheme, made up of the least-squares and optimal search methods, is also developed. The proposed model and scheme were validated using data collected from a test home. It was found that a modest amount of training data was sufficient to yield reliable parameter estimates and accurate prediction. It was also found that when making 24-hour-ahead prediction of the space air temperature, both methods had comparable performances when the training data began in a transition season. However, when they began in an HVAC season, the optimal search method performed better. Furthermore, the least-squares method is recommended during a transition season due to its lower computational burden, while the optimal search method is recommended during an HVAC season due to its better estimation performance.
Beam blank reheating is a key process in the production of high-quality H-beam. To gain better insight into the heat transfer process of the beam blank in reheating furnace, a heat transfer model ...considering radiative heat transfer of furnace gas and conductive heat transfer in beam blank simultaneously is established. The main variable-correction method and zonal method are adopted to solve heat transfer problems in reheating furnace. The best productivity point (BPP) and optimal productivity range (OPR) of the reheating furnace based on the relationship between the specific heat consumption and furnace efficiency are firstly proposed to guide the production process. Then, the effects of the length of soaking zone and preheating temperature of air and fuel on thermal characteristics of walking reheating furnace for beam blank are analyzed. The results show that the reasonable length of soaking zone can obtain high reheating quality of the beam blank, reasonable temperature of furnace gas and exhaust gas. The preheating air has a more influence than preheating fuel on the reheating process of reheating furnace for beam blank. This work can provide valuable reference for the determination to make thermal schedule of beam blank and on-line supervisory control of the production process.
•The 2-Dimensional heat transfer model of walking reheating furnace for beam blank is established•The best productivity point and the optimal productivity range of the reheating furnace are proposed•The effect of the length of soaking zone on the heating quality of the beam blank is analyzed•The effect of fuel and air preheating on the thermal characteristics of the reheating furnace is studied
•Electrochemical and thermal inconsistencies of energy storage battery are unveiled using three-dimensional coupling model.•Full-size coupled model performs better than lumped model in describing ...thermal inconsistency.•An electro-thermal-fluidic model is developed to assess three cooling strategies at battery module-level.
Energy storage batteries have emergeda promising option to satisfy the ever-growing demand of intermittent sources. However, their wider adoption is still impeded by thermal-related issues. To understand the intrinsic characteristics of a prismatic 280 Ah energy storage battery, a three-dimensional electrochemical-thermal coupled model is developed and experimentally verified. The purpose of this study is to explore the physiochemical and thermal behaviors of battery under different operational scenarios. Since electrochemical reactions show inhomogeneous distribution, the maximum heat generation and temperature position move from tab-near region towards central region during the discharge process. When the ambient temperature declines from 25 to 5 °C, total heat generation shows an increment ratio of 36.9 % because of the increase in ionic transport resistance and polarization effect. Additionally, five electrochemical-thermal coupled models that incorporate different levels of simplification are comprehensively discussed. In contrast to lumped model, full-size coupled model demonstrates superior prediction accuracy in describing temperature inconsistency. Furthermore, an electro-thermal-fluidic model is established to evaluate the efficacy of three cooling strategies at battery module level. Results reveal that the indirect liquid cooling provides a higher heat transfer efficiency than air cooling and immersion cooling, but adds 16.3 % to the weight of battery module.
•Geopolymer binder based on local materials from Burkina Faso improves the usability properties of CEBs.•Adding 10–20% geopolymer significantly improves the mechanical properties of CEBs, which ...become comparable to those of cement-stabilized CEBs.•Thermal conductivities of geopolymerized CEBs are lower than those of cement-stabilized CEBs and are close to those of CEBs without stabilizer.
The main objective of this study is to evaluate the feasibility of stabilizing compressed earth blocks with a geopolymer binder that is less polluting than Portland cement. Thus, a performance evaluation of these materials compared to non-stabilized or Portland cement-stabilized earth blocks was the main aim this study.
The geopolymer was synthesized from a mixture of metakaolin and sodium hydroxide solution. Laterite formed the principal matrix of the bricks. Compressed Earth Bricks (CEBs) stabilized with 5, 10, 15 and 20% of geopolymer were produced and compared to both CEBs containing 8% of Portland cement and CEBs without stabilizer. After a cure of 14 days for the specimens without stabilizer and geopolymerized CEBs and 21 days for Portland cement-stabilized CEBs, the blocks were subjected to several characterization tests in order to evaluate their properties (physical mechanical and thermal properties).
The results showed that geopolymerization of CEBs significantly improved their mechanical performance and gave them thermal properties that were very similar to those of non-stabilized blocks. For a 15% geopolymer content, these materials displayed properties comparable to those of Portland cement-stabilized CEBs, in particular with regard to their stability in water.
•An electrochemical-thermal cycling model is presented for lithium ion battery cell.•Thermal behavior between charge and discharge processes are compared.•More capacity is charged during constant ...voltage charge at higher rate.•Heat generation and contribution are obtained at each part of the cell.
The comparison of thermal characteristics between charge and discharge processes for lithium ion battery is usually neglected but has a strongly effect on its performance and safety. In this paper, an electrochemical-thermal cycling model is presented for a 5 Ah LiNi1/3Co1/3Mn1/3 26650 type lithium ion battery to evaluate and compare the thermal characteristics, includes the temperature distribution, heat generation and contribution during charge and discharge processes. The model is validated during cycling by experiment firstly. The results show that the constant current charge process displays a shorter duration, a higher peak temperature, and a quicker temperature rise rate compared with the corresponding discharge process. The heat generated at charge process is larger than that at discharge of lower rate (0.5 C and 1 C), while that of discharge accounts for 52.97%, exceeding the charge process at 1.5 C. The constant current charge ends at state of charge of 91.31%, 84.62% and 78.06% for 0.5 C, 1 C and 1.5 C, respectively, which means that more capacity is charged and more heat is generated during constant voltage charge at higher rate. Moreover, the dominant heat generation in charge process is the polarization heat of negative electrode, while the dominant heat generation in discharge process is the polarization heat of positive electrode.
•An ammonia-304L stainless steel flat loop heat pipe with a secondary wick was designed, fabricated and tested.•A new type structure for liquid-returning line was designed.•The loop could start ...successfully and operated stably under heat load range from 20W to 110W.•The system could rapidly respond to the heat load cycle.
In the present paper, the combination of a primary wick and a secondary wick was put forward and applied to the loop heat pipe. The evaporator was constructed from 304L stainless steel, and anhydrous ammonia with a purity of 99.995% was selected as the working fluid. A secondary wick made of 400-mesh stainless steel wire mesh was inserted into the evaporator, and a blind hole was made in its radial direction. Some partial grooves at the end of liquid line served as the returning liquid exit, and it was wrapped by the blind hole for fear that it be directly exposed to the compensation chamber, potentially causing it to be blocked by the vapor. The experimental results demonstrated that the loop could start up successfully and operated without temperature oscillations under the given heat load range from 20W to 110W in the horizontal orientation. In addition, the system rapidly responded to heat load cycle. The thermal resistance of the loop and the evaporator heat-transfer capacity were analyzed, and two operation modes existed because of the different distributions of the operating temperature with the evaporator wall temperature above or below 60°C.
•A novel flat ELR evaporator LHP has been proposed and tested.•The novel LHP can overcome the shortcoming of traditional flat ELR evaporator LHP.•The LHP was investigated at different orientations ...and heat sink conditions.•The LHP can effectively dissipate a maximum heat load of 750 W (83.33 W/cm2).
A novel flat evaporator loop heat pipe (LHP) has been designed and proposed to overcome the shortcoming of the traditional flat evaporator LHP that cannot operate normally in some positive gravity direction (especially +90º), and to solve the heat dissipation challenges of high heat flux electronic chips. The vapor channels of the capillary wick for the novel LHP were arranged in double rows. And a 1 mm thick smaller particle size copper powder embedded with two 0.5 mm thick stainless steel rings was sintered on the internal surface of the compensation chamber. The thermal characteristics of the novel LHP were investigated at nine different LHP orientations at heat sink temperature from 10 to 40 °C and flow rate of the cooling water of 1 to 4 L/min. The experimental study indicated that the novel flat evaporator LHP can operate normally in some positive gravity directions (especially +90º). And the LHP orientations have a significant influence on the junction temperature and the thermal performance of LHP. Compared with other LHP orientations, the junction temperature at the most favorable LHP orientation was only of 83.60 °C under the highest heat load of 750 W (83.33 W/cm2). The junction temperature increased from 86.67 to 88.64 °C at the maximum heat load of 750 W when the heat sink temperature was increased from 10 to 40 °C. The effect of flow rate of cooling water on the thermal characteristics of the novel LHP was less considerable in the range from 1 to 4 L/min
Thermal characteristics of lithium-ion battery cells are crucial in the thermal design of power battery packs for electric vehicles. In this paper, a calibration calorimetry method of considering the ...heat loss is proposed to investigate the thermal characteristics of a commercial cylindrical 21700 cell. In the meantime, an existing heat-flux meter method is employed to analyze the present method effectiveness. Furthermore, a cell thermal model by considering the physical specifications and thermal parameters is established to predict the cell's temperature rise during its operation. It is shown that the proposed calibration calorimetry method matches well with the existing heat-flux meter method in determining the cell heat generation rate. The cell heat generation rate increases as the decreasing temperature and the increasing discharge rate, and there exists a quadratic-relationship in them between each other. The established thermal model to predict the cell temperature rise is effective with accuracy of within 3.0 °C. This work is fast and cost-effective in characterizing the thermal characteristics of the commercial cylindrical cells, without resorting to the specialized instruments.
•A calibration calorimetry method to analyze cell thermal characteristics is proposed.•The present method is compared with the heat flux meter method.•Cell heat generation is increased at ascending discharge rate and lower temperature.•The established thermal model predicts cell temperature profile is highly feasible.
