This paper presents a optimization design method on the compression ratio of the compression process and the expansion ratio of the expansion process for the compressed gas energy storage system ...using carbon dioxide as the working fluid. On this basis, from the thermal parameter perspective of the stage design, compression ratio/expansion ratio design, and compression heat temperature, the thermal characteristics are analyzed using round-trip efficiency and heat storage efficiency as measurement indicators, and a better design scheme for energy-saving and efficiency improvement is obtained. The results show that it will have a positive role in the improvement of the system performance with a three-stage compression-three-stage expansion design structure, an un-equal compression ratio-equal expansion ratio design scheme, and a compression heat temperature of 388.15K. In addition, the round-trip efficiency is up to 74.07% and the heat storage efficiency is up to 51.95%, which has good thermal performance and energy-saving effect for the energy storage system.
•A optimization design method on the compression ratio and the expansion ratio is posed.•A design scheme for energy-saving and efficiency improvement is obtained.•Sensitivity analysis is conducted on the energy storage system.•Comparative analysis of different design schemes are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
The thermal modeling and design process of highly utilized electric machines is a complex task. The main heat paths within an electric drive are influenced by a variety of different thermal ...interfaces, that can mainly be described by thermal conduction and convection. The proper selection and estimation of these design parameters is challenging especially in the early design stage. This paper provides a systematic investigation evaluating inaccuracies and design influences of single thermal resistances, such as the convective heat transfer in the rotor-stator annulus, in the cooling jacket or interfaces between different machine components. Within the study, electromagnetic finite element models and thermal lumped parameter models of two traction drives are developed and validated using test bench measurements. The thermal design parameters are varied in a range resulting from intensive literature research and own laboratory experience. The influence of the design parameters in different operational points of the drives are studied in a sensitivity analysis.
Heating and the Maillard reaction applied at the dry state of dried hen egg white (DEW) powder represent two effective approaches for improving the functionality of DEW, especially the gelling ...properties. In this study, DEW modified by dry heating (DHEW) and the Maillard reaction with maltodextrin (MDEW) was stored at 25 ± 2 °C and 65 ± 3% relative humidity for 12 months to investigate the changes in gel characteristics. The results showed that the Tgel values of DEW, DHEW and MDEW increased to 71 ± 2 °C, 68 ± 1 °C and 66 ± 2 °C, respectively, after storage for 12 months. The gel hardness of the three samples decreased linearly with increasing storage time. Coarse and porous gels of different DEWs were observed after long-term storage. The storage-induced loss of gel properties of the three DEWs was responsible for the thermal characteristics. The storage stability of MDEW was better than that of DHEW during the entire storage period, although MDEW developed a brown colour more easily than DHEW after 6 months of storage. These results provide valuable information on different egg white powders under long-term ambient storage.
•The gel hardness of all samples decreased linearly with increasing storage time.•The gel storage stability of dried egg white (DEW) was related to the thermal parameters.•DEW showed better storage stability when modified by the Maillard reaction than by dry heating.•A brown colour occurred via the Maillard reaction after 6 months of storage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
Thermal properties of building envelopes are often described using thermal conductivity or thermal resistance. And the opposite task involves the identification of thermal parameters of building ...envelopes based on the measurements of their cooling process. In this article, the authors proposed a method of identifying thermal parameters of a building envelope based on cooling measurements, using a multiple regression model for this purpose. To satisfy the research objectives, two basic experiments were carried out. The first experiment was performed in laboratory conditions. The research model was a cube of the dimensions of 1.1 m × 1.1 m × 1.1 m. The second experiment was carried out in semi-real conditions, and the used model was a small house of the dimensions of 6.0 m × 4.15 m × 5.2 m. The measurement results were also used to calibrate numerical models made in the ESP-r program. The research studies have demonstrated that the model can be used to identify thermal parameters of a building envelope. Based on the measurements and simulations, the cooling equations of the object were determined and the 95% confidence interval for the heat retention index was estimated. On that basis, using the multiple regression model, such parameters of the model as density, specific heat, and thermal conductivity were estimated. It turned out that using the Gauss–Newton approximation, we obtained the correlation of the measurement results and the analytical model with the correlation coefficient of 0.9971 (for the laboratory scale). And the multiple regression improved not only the correlation between the measurement and the analytical model, but it also allowed to obtain “almost identical” results. Similarly, promising results were obtained for the semi-real scale.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
The effect of SiC nano-phases (nano-particles and nano-fibers) addition into SAC0307 solder paste was investigated on the thermal and microstructural properties of the composite solder joints. The ...nano-phases were used between 0.125 and 1 wt%, and they were mixed into the solder paste by ball milling process. For the study power MOSFET (metal oxide semiconductor field effect transistor) components were soldered onto metal core printed circuit boards (MCPCBs). The thermal impedance Zth(t) and thermal resistance Rth of MOSFETs were measured by an indirect electrical method. Furthermore, the void formation and the microstructure of solder joints were also studied. The solderability and voiding properties of the composite solder alloys were acceptable. It was found that in 0.5 wt% amount, SiC nano-particles have positive effects on the thermal parameters of the solder joints, which could be explained by the IMC (intermetallic compound) layer growth suppression effect of the nano-phases. The microstructural analysis revealed that the microstructural refinement of the composite solder joints differs in the case of nano-particles and nano-fibers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
The unique electro-thermal property of temperature self-controlled concrete (TSC) offers significant potential for actively controlling the surface temperature of concrete structures and eliminating ...cracks induced by large temperature differences. However, devising an active temperature control strategy for TSC is challenging due to the non-uniformity and time-dependent nature of the heat generation process. To address this issue, this paper investigates the electro-thermal performance and active temperature control strategy of TSC. Firstly, a three-factors orthogonal experiment is conducted to optimize the mix proportions based on mechanical properties and electrical resistivity. Subsequently, electro-thermal experiments are performed on the optimized TSC using different power supply strategies under fixed and fluctuating temperature conditions. Furthermore, theoretical formulations for temperature rise and an energy consumption evaluation method are developed to quantify the heating process of TSC. The results demonstrate that the optimized TSC mixture achieves a stable electrical resistivity of 8.2 Ω⋅m at 28 days, with only a 20% increase after 360 days. Moreover, employing a low heating power facilitates a more uniform temperature distribution and reduces the impact of changes in electro-thermal parameters on system safety. Considering safety and stability, strategies to enhance energy utilization and optimize the design and operation of the TSC heating system are proposed. These findings provide valuable guidance for determining appropriate power, current, and voltage for heating systems, as well as recommendations for the safe operation of TSC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
This study investigates the stratification of soil thermal properties induced by soil organic carbon (SOC) and its impacts on the parameterization of the thermal properties. Soil parameters were ...measured for alpine grassland stations and North China flux stations, with a total of 34 stations and 77 soil profiles. Measured data indicate that the topsoils of alpine grasslands contain high SOC contents than underlying soil layers, which leads to higher soil porosity values and lower thermal conductivity and bulk density values in the topsoils. However, this stratification is not evident at the lowland stations due to low SOC contents. Evaluations against measured data show that three thermal conductivity schemes used in land surface models severely overestimate the values for soils with high SOC content (i.e. topsoils of alpine grassland), but they are better for soils with low SOC content. A new parameterization is then developed to take the impacts of SOC into account. The new one can well estimate the soil thermal conductivity values in both low and high SOC content cases, and therefore, it is a potential candidate of thermal conductivity scheme to be used in land surface models.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In the paper, selected problems that are related to the measurements of thermal parameters of power MOSFETs that are placed on a common heat sink are analysed. The application of the indirect ...electrical method, the contact method, and the optical method in measuring self and mutual transient thermal impedances of these transistors is presented. The circuits that are required to perform measurements are presented and described. The errors of measurements are assessed for each of the considered methods. In the case of the indirect electrical method, an additional influence of the selection of a thermo-sensitive parameter and the function approximating thermometric characteristics on the measurement error are taken into consideration. The measurement results of the thermal parameters of the investigated transistors that were obtained using the considered measurement methods in various supply conditions are presented and discussed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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