Small Temperature Difference Research Articles

Optimization of a cold thermal energy storage system with micro heat pipe arrays by statistical approach: Taguchi method and response surface method

Cold thermal energy storage (CTES) technology is one of effective ways to utilize renewable energy and shift peak power load. In this paper, a novel CTES device using micro heat pipe arrays is numerically studied and optimized. Firstly, the Taguchi method is adopted to quantitatively analyze the contribution ratio (CR) of fin parameters to solidification and melting time, as well as compactness factor. Fin height has the highest CR of approximately 70 % for solidification and melting time, while fin thickness with the highest CR of 58.88 % for the compactness factor. Then, the response surface method is used to uncover the interactive effects of fin parameters and operation parameters. Next, multi-criteria optimization is performed by minimizing solidification time and heat exchange temperature difference, and maximizing the compactness factor. Compared with the original structure, the solidification time of optimized structure is reduced by 26.59 % with small heat exchange temperature difference of 4 °C and great compactness factor of 0.8219. Additionally, the phase change front of the original and the optimized CTES device are compared and analyzed to further reveal the reason for the performance improvement of the device. The research results provide inspiration and data support for the practical application of CTES.

Numerical study on the hydrothermal characteristics of a wire-wrapped rod bundle with nonuniform wire pitches

In this study, thermal hydraulic behaviors in a 19-pin bundle fuel assembly with nonuniform wire pitches is investigated by combing CFD with the Kriging method. To optimize the design, two geometric variables—the ratio of inner pitch to reference pitch (Pi/P) and the ratio of outer pitch to reference pitch (Po/P)—are selected, and the design space is sampled using Latin Hypercube Sampling (LHS). The sampled points are then subjected to CFD analysis. Convergence is considered achieved when the residuals of all variables are below 1e-5. The optimization problem aims to minimize the objective function, which is a linear combination of the cross-sectional temperature difference and friction factor. Sequential Quadratic Programming (SQP) is employed to search for the optimal point using a constructed meta-model. When compared to the reference shape, the optimal shape exhibits higher axial velocity in the inner channel, higher average temperature, smaller temperature difference at the outlet section, and reduced pressure drop in the fuel assembly. The Kriging model accurately predicts the cross-sectional temperature difference and friction coefficient for the optimal shape, consistent with the CFD calculation results. This confirms the accuracy and feasibility of the Kriging model in fuel assembly optimization.

Synthetic iterative scheme for thermal applications in hotspot systems with large temperature variance

A synthetic iterative scheme is developed for thermal applications in hotspot systems with large temperature variance. Different from previous work with linearized equilibrium state and small temperature difference assumption, the phonon equilibrium distribution shows a nonlinear relationship with temperature and mean free path changes with the spatial temperature when the temperature difference of system is large, so that the same phonon mode may suffer different transport processes in different geometric regions. In order to efficiently capture nonlinear and multiscale thermal behaviors, the Newton method is used and a macroscopic iteration is introduced for preprocessing based on the iterative solutions of the stationary phonon BTE. Macroscopic and mesoscopic physical evolution processes are connected by the heat flux, which is no longer calculated by classical Fourier’s law but obtained by taking the moment of phonon distribution function. These two processes exchange information from different scales, such that the present scheme could efficiently deal with heat conduction problems from ballistic to diffusive regime. Numerical tests show that the present scheme could efficiently capture the multiscale heat conduction in hotspot systems with large temperature variances. In addition, a comparison is made between the solutions of the present scheme and effective Fourier’s law by several heat dissipations problems under different sizes or selective phonon excitation. Numerical results show that compared to the classical Fourier’s law, the results of the effective Fourier’s law could be closer to the BTE solutions by adjusting effective coefficients. However, it is still difficult to capture some local nonlinear phenomena in complex geometries.

Heat transfer characteristics of petroleum coke particle packed bed: An experimental and CFD simulation study

AbstractDue to the complexity of the internal pore structure of petroleum coke loose particle‐packed beds, measuring their thermal conductivity has always been a challenging problem. This work independently developed an experimental apparatus for testing the thermal conductivity of petroleum coke particle‐packed beds and constructed a forward calculation model for the heat transfer process, which was based on one‐dimensional unsteady heat transfer. Using the Sparse Nonlinear OPTimizer (SNOPT) algorithm, a mathematical relationship between the thermal conductivity λ of the coke bed, temperature T, and equivalent particle diameter dp was established through inverse modeling. Concurrently, a digital model of the petroleum coke particle packed bed was derived utilizing three‐dimensional computed tomography (CT) scanning technology, and a pore‐scale gas–solid radiation heat transfer model was formulated based on CFD simulation technology, thereby further elucidating the heat transfer mechanism within the petroleum coke particle packed bed. The research results indicate that the temperature predicted by the established thermal conductivity model aligns well with experimental data. Further CFD simulation studies demonstrate that a smaller particle size leads to a larger temperature difference between the wall and the center of the packed bed, while a higher gas velocity results in a smaller temperature difference, with a linear correlation observed between these two factors. At high temperatures, thermal radiation between particles in the porous petroleum coke‐packed bed plays a dominant role. The research outcomes can offer significant theoretical support for a profound analysis of the heat transfer behavior of petroleum coke‐packed beds within a vertical shaft calciner.

Effect of working fluid charging amount on system performance in an ocean thermal energy conversion system

In ocean thermal energy conversion (OTEC) systems, the initial working fluid charging amount is crucial as it relates to the system’s performance and economic cost. But currently, there is no clear standard for it, and as the working fluid circulating pump is the most direct and only means to regulate the working fluid flow, it is necessary to investigate the coupled effects of it and the working fluid charging amount on the system performance. To this issue, a corresponding experimental facility was established. The coupled effects were investigated by energy and exergy analysis under varying temperature difference. The results showed that varying working fluid charging amount changed the physical state of the working fluid, and the effect on the system varied under dissimilar temperature difference conditions. Compared to the standard charge (8 kg), 75 % of the standard charging amount diminished the system thermal efficiency by 17 % and exergy efficiency by 16 % at small temperature difference (20 °C), whereas a charging amount of more than 100 % resulted in improved thermal efficiency by 14 % and exergy efficiency by 13 %. At large temperature difference (28 °C), 75 %, 125 % and 150 % of the standard working fluid charging amount all improved system performance (thermal efficiency by maximum 16 %, exergy efficiency by maximum 21 %). Besides, an increase in circulating pump frequency improved system performance regardless of the temperature difference and working fluid charging amount. This research innovatively investigates the above problems in the application scenario of OTEC, and provides theoretical and data support for the development of OTEC technology.

Sub-∘C-precision temperature imaging using phase-shift luminescence thermometry

Abstract This work explores the potential of luminescence thermometry to provide temperature imaging with high temperature resolution using the phase-shift method. Phosphor thermometry has been widely used for temperature imaging, especially with the decay-time method. However, the phase-shift method was rarely used. In this approach, excitation is modulated in time, and due to the temperature-dependent luminescence dynamics of the painted luminescent probe, the emission waveform is phase-shifted with respect to the excitation waveform. Initially, a parametric study was performed on the effect of excitation waveform frequency and shape, based on a millisecond-decay time phosphor. The study found that the best precision is achieved with a square waveform at a frequency such that the phase shift is π 4 at the target temperature. Then, this method was compared with the well-established decay-time method. Phase-shift method offered a three-fold improvement in temperature precision under identical peak excitation power. Finally, two-dimensional measurements were demonstrated on a temperature-controlled plate using a high speed CMOS camera, and an LED illumination. A temperature precision of 0.13 ∘C was obtained at a temporal resolution of 0.25 s and a spatial resolution of around 1 mm, due to a pre-processing binning of 7 by 7 pixels. This technique can be used as a robust alternative to infrared thermometry to probe the thermal processes with small temperature differences.

Boosting self-powered wearable thermoelectric generator with solar absorber and radiative cooler

The electrical output of wearable thermoelectric generators (wTEGs) has traditionally been constrained by small temperature differentials when powering microelectronics. In this study, we innovatively combine photothermal and radiative cooling mechanisms within a single wTEGs system, enabling substantial, uninterrupted power generation. Specifically, we designed a multilayer selective solar absorber (m-SSA) composed of flexible dielectric-metal stacks. This absorber demonstrates exceptional solar absorption efficiency of 93 % and significantly low thermal emissivity of 10 %. In practical outdoor conditions, it achieves a temperature increase of up to 108 °C under solar irradiation. Concurrently, we developed a flexible hierarchically porous radiative cooler (HP-RC), which reflects 96 % of solar energy and emits 97 % of thermal energy, achieving a cooling differential of up to 10 °C, even at ambient temperatures of 42 °C. Integration of the m-SSA and HP-RC with wTEGs allows for the simultaneous harvesting of heat from solar, cold space, and earth (robots or human body). This novel energy capture mechanism yielded a notable power density of 198 mW/m² for human body and 52 mW/m2 for steel robots in outdoor wearable applications. This significant advancement promotes the field toward high-performance, integrated green power technologies and holds promise for next-generation wearable self-powered devices.

Experimental investigation on product and temperature distribution in a continuous flow packed-bed reactor for dodecahydro-N-ethylcarbazole dehydrogenation

The dehydrogenation of dodecahydro-N-ethylcarbazole (H12-NEC) generates enormous gas accompanied by intense heat absorption, affecting heat and mass transfer in porous catalysts. A packed-bed reactor equipped with a temperature measurement device was designed to investigate the continuous flow dehydrogenation of H12-NEC. The effects of weight hourly space velocity (WHSV), reaction temperature, catalyst particle size, and pressure were evaluated. The results reveal that the volume flow rate of hydrogen will increase with the increase of WHSV. And the reduction of gas–liquid ratio and catalyst particle size facilitates heat transfer causing a more uniform axial temperature distribution within the reactor. As the temperature rises, the hydrogen yield increases along with more by-products. 456 K and 2 mm of catalyst particle size are determined to be the optimal reaction conditions in the study, achieving the hydrogen production rate of 9.61 molH2·gPd-1·h-1. With pressure increasing, the hydrogen yield gradually decreases, but the decreased evaporation of H12-NEC results in a smaller temperature difference between the reactor and heating wall. A comparison with the thermodynamic equilibrium model reveals that the effect of pressure on chemical equilibrium may be more significant than the temperature.

Early detection of thermal image based T1 breast cancer using enhanced multiwavelet denoised convolution neural network with region based analysis

Medical Thermography image is used for the detection of breast cancer at an earlier stage. Thermography image shows the temperature change in the body due to cells. The metabolic rate of cancer cells is high compared to normal cells. A high metabolic rate increases the blood flow in cancer cells. High blood leads to changes in body temperature. The change in body temperature is used for cancer cell detection at an earlier stage. However, T1-stage cancer cells are smaller and have small temperature differences undetected with thermography. In this paper, a T1-stage cancer cell is heated by an external source; then, thermal images are acquired for earlier detection of small-size cancer cells. External heat source amplifies T1 stage cancer cell temperature. Amplified cancer cell images are analyzed using the proposed Multiwavelet-Deep Denoised Convolutional Neural Network (MWTDnCNN) algorithm for T1 cancer cell detection. Amplified T1 stage cancer cell has higher thermal conductivity (k) and heat capacity (Cp), which helps to detect T1 cancer cell tissue due to the enhanced pixel feature. The proposed MWTDnCNN algorithm has a T1-stage cancer cell detection accuracy of about 98% compared with traditional algorithms. The proposed MWTDnCNN algorithm detects T1-stage cancer of size 1.29 mm.

Lab study on the physiological thermoregulatory abilities of older people with different frailty levels

The advent of an aging society has increased the need for a better understanding of thermal comfort requirements, especially for older people's health. Differences in thermal comfort needs among older individuals with varying frailty levels are noted, but the impact of health on physiological thermoregulation is underexplored. This study, based on the frailty classification method characterized by Fried, selected 12 non-frail (age:71.00 ± 5.41) and 12 pre-frail (age:72.68 ± 5.7) older individuals for laboratory experiments. This experiment set sudden temperature change experiments to illustrate differences in subjective perceptions and physiological changes between non-frail and pre-frail older people. Results show that non-frail individuals are more likely to complain in warmer environments. Significant differences in perception only emerged when the temperature differential between neutral and warm conditions exceeded 5 °C. Pre-frail individuals exhibited slower skin temperature changes and required more time to stabilize with the environment, particularly in the foot. Pre-frail individuals tend to sweat less in changing environments and require more time to reach stable sweating. There is positive evidence indicating that heart rate of pre-frail individuals is higher than non-frail individuals, with different changing trends observed between the two groups. When the temperature difference exceeds 5 °C, the pulse intensity trend in pre-frail individuals diverges from that of non-frail individuals. In controlling indoor environments for older people, it is essential to consider both subjective comfort and physiological thermoregulation capabilities. For older adults with frailty characteristics, applying localized warming, using small temperature differences, gradually adjusting the environment may better meet their comfort needs.

Ultrahigh Thermal Rectification at Small Temperature Difference Achieved by Near‐Field Thermal Photon Manipulation

AbstractThermal diodes, which allow heat to flow in a preferential direction, are an essential component of thermal circuitry and will find applications in many fields ranging from thermal photon controls to quantum information. The quality of a thermal diode is defined by the thermal rectification ratio (TRR). Here, an ultrahigh TRR exceeding 105 at a small temperature difference (1–5 K) is presented based on near‐field thermal photon (NFTP) manipulation, by utilizing asymmetric gap‐variated dual terminals based on graphene/Si heterostructures and materials with contrasting thermal expansion coefficients. Analyses of the photon tunneling probability show that the colossal TRR comes from coupled and decoupled graphene surface plasmon polaritons under opposite temperature biases, remaining robust across a wide operating temperature range. Further enhancement can be achieved by tuning the Fermi level of graphene. This work demonstrates the significance of asymmetry in NFTP manipulation for thermal diode performance, achieving an ultrahigh TRR, which is at least three orders higher than the state‐of‐the‐art structures at the same small temperature difference (1–5 K), and is comparable to state‐of‐the‐art electronic diodes.

Sub-millikelvin-resolved superconducting nanowire single-photon detector operates with sub-pW infrared radiation power

Abstract The noise equivalent temperature difference (NETD) indicates the minimum temperature difference resolvable by an infrared detector. The lower the NETD is, the better the sensor can register small temperature differences. In this work, we proposed a strategy to achieve a high temperature resolution using a superconducting nanowire single-photon detector (SNSPD) with ultrahigh sensitivity. We deduced the model for calculating the NETD of a photon-counting type detector and applied it to our SNSPD-based setup. Experimentally, we obtained a NETD as low as 0.65 mK, which is limited by the background radiation of the environment, and the required infrared radiation power is calculated to be less than 1 pW. Furthermore, the intrinsic NETD of this SNSPD is estimated to be less than 0.1 mK. This work demonstrated a sub-mK temperature resolution with the SNSPD, paving the way for future remote infrared thermal imaging with high temperature resolution.

Enhancement of the subcritical boiling heat transfer in microchannels by a flow-induced vibrating cylinder

The flow boiling heat transfer in microchannels has been extensively used in engineering due to its high heat dissipation with a small temperature difference. This study employs a hybrid method to numerically investigate the effects of a flow-induced vibrating cylinder on enhancing the subcritical boiling heat transfer in microchannels. The hybrid approach integrates the pseudopotential multiphase lattice Boltzmann method for modeling unsteady flows, the finite difference method for solving the heat transfer equation, and the immersed boundary method for handling the boundary condition at the fluid–cylinder interface. Flow boiling simulations in the microchannel are performed for three setups: a smooth vertical channel, a vertical channel with a stationary cylinder, and a vertical channel with a flexibly supported cylinder. Simulations have been conducted by varying the Reynolds number based on the diameter of the cylinder (Red) from 35 to 333.3, the dimensionless boiling number (Bo) from 0.001 84 to 0.045 97, and blockage ratio (BR) of 3.0, 4.0, and 5.0. It is found that the vortical wake of the cylinder is important in enhancing the heat transfer in microchannels, which is quantified by the (Red). Specifically, when Red<48.0, both stationary and flexibly supported cylinders have almost the same effect on heat transfer during the flow boiling process, as there is no vortex shedding from both cylinders; when 48.0≤Red<68.2, the flexibly supported cylinder achieved higher enhancement than the stationary cylinder, which is due to the vortical wake generated by the flow-induced vibration in a subcritical Reynolds number regime; when 68.2≤Red, both stationary and flexibly supported cylinders have comparable effect on the rates of heat transfer, because both cylinders generate similar vortical wakes. Flow field analysis indicates that the disturbance due to the vortex wakes on the thermal boundary and/or the vapor insulation layer is the mechanism of the heat transfer enhancement in channels.

Investigating Taconis oscillations in a U-shaped tube with hydrogen and helium

Taconis oscillations are thermally induced spontaneous excitations of acoustic modes in tubes subjected to large temperature gradients. Cryogenic systems that experience these excitations suffer from increased heat leak and vibrations. This heat leak may also increase boil-off in long-term storage vessels for liquid hydrogen. In this study, U-shaped closed-end tubes with a cold mid-section are experimentally investigated to quantify the oscillation characteristics for hydrogen- and helium-filled systems at various mean pressures, including supercritical hydrogen states. Experimental measurements of the temperature distribution along the tube and acoustic pressure amplitudes and frequencies are taken in constant- and variable-diameter configurations near the onset of oscillations. Thirty different conditions are recorded with mean pressures ranging from 126 kPa to 1127 kPa for helium and 161 kPa to 1816 kPa for hydrogen. A low-amplitude thermoacoustic model is applied to predict the cold temperature and frequency corresponding to the onset of Taconis oscillations. The findings of this study indicate that Taconis oscillations in systems with hydrogen occur at smaller temperature differences than in more traditional helium systems by approximately 10 K. Hydrogen in the constant-diameter configuration excited when cryogenic temperatures reached 35–40 K, whereas helium excited when cryogenic temperatures reached 20–30 K. Special tubing networks, such as wider segments in the warm portion, can drastically elevate the excitation cold temperature resulting in onset temperatures between 50–60 K for both fluids. Taconis oscillations are also found to exist in conditions when liquid hydrogen starts forming in the cold zone of the system, as well as in supercritical states. The presented measurements are useful for designing cryogenic hydrogen storage systems to control these oscillations.

Accuracy of 3D real-time MRI temperature mapping in gel phantoms during microwave heating

BackgroundInterventional magnetic resonance imaging (MRI) can provide a comprehensive setting for microwave ablation of tumors with real-time monitoring of the energy delivery using MRI-based temperature mapping. The purpose of this study was to quantify the accuracy of three-dimensional (3D) real-time MRI temperature mapping during microwave heating in vitro by comparing MRI thermometry data to reference data measured by fiber-optical thermometry.MethodsNine phantom experiments were evaluated in agar-based gel phantoms using an in-room MR-conditional microwave system and MRI thermometry. MRI measurements were performed for 700 s (25 slices; temporal resolution 2 s). The temperature was monitored with two fiber-optical temperature sensors approximately 5 mm and 10 mm distant from the microwave antenna. Temperature curves of the sensors were compared to MRI temperature data of single-voxel regions of interest (ROIs) at the sensor tips; the accuracy of MRI thermometry was assessed as the root-mean-squared (RMS)-averaged temperature difference. Eighteen neighboring voxels around the original ROI were also evaluated and the voxel with the smallest temperature difference was additionally selected for further evaluation.ResultsThe maximum temperature changes measured by the fiber-optical sensors ranged from 7.3 K to 50.7 K. The median RMS-averaged temperature differences in the originally selected voxels ranged from 1.4 K to 3.4 K. When evaluating the minimum-difference voxel from the neighborhood, the temperature differences ranged from 0.5 K to 0.9 K. The microwave antenna and the MRI-conditional in-room microwave generator did not induce relevant radiofrequency artifacts.ConclusionAccurate 3D real-time MRI temperature mapping during microwave heating with very low RMS-averaged temperature errors below 1 K is feasible in gel phantoms.Relevance statementAccurate MRI-based volumetric real-time monitoring of temperature distribution and thermal dose is highly relevant in clinical MRI-based interventions and can be expected to improve local tumor control, as well as procedural safety by extending the limits of thermal (e.g., microwave) ablation of tumors in the liver and in other organs.Key PointsInterventional MRI can provide a comprehensive setting for the microwave ablation of tumors.MRI can monitor the microwave ablation using real-time MRI-based temperature mapping.3D real-time MRI temperature mapping during microwave heating is feasible.Measured temperature errors were below 1 °C in gel phantoms.The active in-room microwave generator did not induce any relevant radiofrequency artifacts.Graphical

A longitudinal study of volatile organic compounds from cooking under ventilation and purification intervention: Health risk assessment and odor nuisance control

Cooking oil fumes (COFs) expose occupants to hazardous air pollutants and nuisance odors, hence the real controlling effects of different intervention methods deserve to be explored. This longitudinal study conducted year-round field measurements in 10 apartments to explore the synergistic effects of dual ventilation and purification interventions on the exposure level, odor intensity, and health risk control of gaseous organic compounds during cooking. Gas chromatography-mass spectrometry (GC‒MS) and high performance liquid chromatography (HPLC) were used for quantification of volatile organic compounds (VOCs) and carbonyls. A total of 59 VOCs were detected during cooking, and the average ΣVOC concentrations in summer, the transition seasons, and winter were 483.16 μg/m3, 233.97 μg/m3, and 282.82 μg/m3, respectively, and the proportion of aldehydes was approximately 50 %. The small temperature differences between the indoors and outdoors led to a 24 % reduction in the effective air changes per hour (ACH) in the summer compared with that in other seasons. The average estimated carcinogenic risks of formaldehyde, acetaldehyde and benzene were 9.20 × 10−5, 1.11 × 10−5, and 6.05 × 10−6, respectively, for daily cooking conditions. It is difficult to guarantee a healthy cooking environment by mechanical ventilation alone. The inhalation carcinogenic risk of these 3 hazardous VOCs was reduced by approximately 130.9 % under air purification intervention but was still greater than 1E-6. The noncarcinogenic risk of acrolein under the different intervention modes ranged from 69.8 to 84.9. Moreover, acetaldehyde and hexanal were found to be the key odorants in kitchen. When the effective exhaust air rate was greater than 12 m3/min with air purifier in operation, the average inhalation health risk was 1.05–1.78 times that before cooking, and more than half of the users would not smell obvious odors during the cooking process. This study quantifies the effectiveness of the synergetic control strategy of independent purification modules combine with kitchen mechanical ventilation, with a view to implementing a healthy & comfortable living environment.

Heat Flow Estimation in Polymer Films during Orientational Drawing at the Local Heater.

The optimization of the process of polymer film orientational drawing using the local heater was investigated. One of the problems with this technology is that the strength of the resulting fibers differs significantly from the theoretical estimates. It is assumed that one of the reasons is related to the peculiarity of this technology, when at the point of drawing the film is heated only on one side, which creates a temperature difference between the sides of the film in contact with the heater and the non-contact sides of the film in the air. Estimates show that even a small temperature difference of just 1 °C between these surfaces leads to a significant difference in the rate of plastic deformation of the corresponding near-surface layers. As a consequence, during hardening, in the stretching region, tensile stress is concentrated on the "cold" side of the film, and this effect can presumably lead to the generation of more defects overthere. It has been suggested that defects arising during first stage of hardening, namely, neck formation, can serve as a trigger for the formation of defects such as kink bands on the "cold" side with further orientational strengthening due to plastic deformation of the resulting fibrillar structure, at the boundaries of which microcracks are formed, leading to rupture of the oriented sample. The numerical calculation of heat propagation due to heat conduction in the film from the local surface of the heater is carried out and the temperature distribution along the thickness and width of the film during drawing is found. The temperature difference in the heated layer of the film between the contact and non-contact sides with the heater was calculated depending on the thickness of the film and the speed of its movement along the heater. It was found that the most homogeneous temperature distribution over the film thickness, which is required, by default, for the synchronous transformation of the unoriented initial folded lamellar structure into a fibrillar structure, is observed only for films with a thickness of less than 50 μm. The calculation allows us to scientifically justify the choice of orientation drawing speed and optimal thickness of the oriented polymer film, which is extremely important, for example, for obtaining super-strong and high-modulus UHMWPE filaments used in products for various purposes: from body armor to sports equipment and bioimplants.

Thermoelectric generator for energy production from renewable sources

Thermoelectric generators (TEG) produce electrical energy from a temperature difference between the cold and hot side of TEG modules (Seebeck effect); in principle, they can be used at temperature differences greater than 3 K [1]. Thermoelectric energy generation is primarily known for supplying self-sufficient sensors or in exhaust systems of motor vehicle internal combustion engines [2], where high temperature differences of up to 700 K are used. In this paper, basic investigations are carried out in order to expand the power range of thermoelectric energy generation and their potential for the energy transition. To this end, the area of application should be expanded to include medium and small temperature differences. The output characteristic of a TEG module has a power maximum, which increases quadratically with the temperature difference and linearly with the module area. At a temperature difference of 40 K, an output of 250 W/m2 can be generated. A solar module can generate 150 W/m2 in full sunlight; this output is only available for 12 % of the year given the 1000 full-load hours of sunshine that are usual in our latitudes. A continuous thermoelectric energy source could provide energy all year. Under optimal conditions, an annual usage time of 5000 hours and a service life of 10 years, electricity production costs of around 10 Cents/kWh can be expected [3]. This price is quite comparable to other renewable energy sources (photovoltaics, wind).

Thermodynamic and Exergoeconomic Analysis of a Novel Compressed Carbon Dioxide Phase-Change Energy Storage System

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system.

Temperature variability, natural disasters and bank systemic risk: Evidence from Chinese city commercial banks

This paper examines the impact of temperature variability on bank systemic risk and the mediating effect of natural disasters. By employing data of 105 Chinese city commercial banks and 30 provinces from 2008 to 2020, we find a positive relationship between temperature variability and bank systemic risk, as well as the mediating effect of natural disasters. Moreover, heterogeneity analysis demonstrates that the relationship between temperature variability and bank systemic risk is only significant for banks in regions with small seasonal temperature differences and southern provinces of China.