Effective Heat Capacity Research Articles

SIMULATION OF PREHEATING AND HEATING WHEN CONNECTING POLYETHYLENE PIPES WITH ELECTROFUSION COUPLINGS

Existing machines for electrofusion welding of polyethylene pipes provide a high-quality connection at air temperatures no lower than minus 10 °C. However, if welding is required at lower temperatures, a layer of heat-insulating material is used to reduce the cooling rate. This insulation is selected based on the air temperature and the size of the welded pipes. This paper investigates the dynamics of temperature fields at the stages of heating, temperature equalization and heating using a new technology of welding at low temperatures. The proposed technology eliminates the use of thermal insulation material and allows welding to be carried out automatically.The paper presents a mathematical model that describes the thermal process when performing all welding operations at low temperatures. The model describes the thermal process with and without phase transformation. The well-known method of end-to-end calculation with the introduction of effective heat capacity is used to consider the heat of phase transition in the temperature range. The model also considers the dependence of the thermophysical properties of polyethylene on the degree of crystallinity.The following text presents the results of preheating and temperature equalization calculations for welding polyethylene pipes of the PE 100 SDR 11 brand with a diameter of 160 mm at an air temperature of minus 40 °C. To accurately describe the thermal process of real welding, experimental temperature data was used for parametric identification. It is shown that as a result of preheating and temperature equalization in the weld and thermally affected zones and outside them at a distance of more than 10 mm, the temperature values do not exceed acceptable limits. The resulting temperature distribution allows heating according to the standard welding mode. Calculations show that when the heating is completed, the volume of the polyethylene melt corresponds to the volume of the welding melt at the allowed air temperature.These findings can be used to develop a technique for controlling the movement of the crystallization front during welding at low temperatures.

INVESTIGATION OF THE HEAT CAPACITIES OF NANOFLUIDS BASED ON NANOPARTICLES OF Al2O3, TiO2 AND CuO BY THE ADDITIVE METHOD

This study investigates the thermal properties of nanofluids, with a particular focus on their heat capacity when various nanoparticles are integrated into a base fluid. Nanofluids, which are composed of nanoparticles dispersed within a base fluid, are of significant interest due to their enhanced thermal characteristics compared to traditional fluids. The research employs the additive method, a widely used technique for estimating the effective heat capacity of nanofluids. This method posits that the total heat capacity of a nanofluid can be approximated by summing the contributions of each component according to its volume or mass fraction. This research represents the effect of nanopartilces concentration (1wt.%, 3 wt.%, 5 wt.%) on effective heat capacity of TiO2 based nanofluid. The analysis reveals that key factors influencing the heat capacity of a nanofluid, as determined by the additive method, include the heat capacities of the individual components and the concentration of the nanoparticles. Specifically, the greater the disparity in heat capacities between the base fluid and the nanoparticles, and the higher the nanoparticle concentration, the more the nanofluid's heat capacity shifts toward that of the nanoparticles. The calculations in this study indicate that the most significant decrease in heat capacity occurs in a nanofluid containing 5 wt.% Al2O3 nanoparticles with water as the base fluid. Conversely, the smallest reduction is observed in a nanofluid with 1 wt.% Al2O3 nanoparticles in a 50% aqueous ethylene glycol solution.

Numerical simulations to analyze the impact of vascular network complexity over cryosurgical treatment process of two-dimensional liver tumor tissue

Cryosurgery is a minimally invasive surgery widely used for liver cancer. The vascular network present in the tissue affects the temperature distribution across the tissue. The present study focuses upon the numerical simulations of cryosurgery for liver tumor with vascular network. The phase change which occurs in bioheat equation has been tackled using Effective heat capacity method and the vessels are constructed following Murray’s Law. Blood flow in the vascular network is assumed to be Newtonian and laminar. The continuity equation, Navier’s Stoke Equation coupled with heat energy equation is solved for the vascular network. Finite Element Method (FEM) has been implemented for the numerical simulations using COMSOL Multiphysics software. The ice balls generated in 600s around the cryoprobe are analyzed. Necrosis of the tissue with the presence of vascular network have been determined for tissue kept under freezing for 600s. The numerical results have been compared with experimental results of Ge et al.[1] and found to be in good agreement with the experimental study. Further, impact of vascular network for optimal planning of the surgery have been numerically simulated in the present study.

A novel meshless radial basis reproducing kernel particle approach for 3D thermo-mechanical analysis of mushy zone phase-change problems

This paper presents a three-dimensional thermo-elastoplastic computational model for the analysis of phase change problems involving the mushy zone. The model utilizes a novel meshless radial basis reproducing kernel particle approach, incorporating a high-order kernel that integrates Gaussian and cosine functions. An energy balance equation for the entire domain is formulated using the effective heat capacity method, based on the enthalpy formulation. The governing equations are discretized using the Galerkin weak form to compute thermal residual stresses, with essential boundary conditions enforced through the penalty method. Plastic deformation is characterized using the von Mises criterion with isotropic hardening, and the strain term resulting from temperature-dependent material properties is incorporated into the incremental solution process. Determination of the plastic strain increment is based on the Prandtl–Reuss flow rule. The accuracy and efficiency of the proposed meshless approach were rigorously evaluated through numerical examples encompassing two- and three-dimensional problems. The computational results were compared against available analytical and validated numerical solutions. This comprehensive assessment substantiated the robustness and precision of the developed technique. The case studies presented elucidate the capacity of the novel meshless model to effectively predict temperature distributions and residual stress fields within mushy zone phase change phenomena, accommodating both regular and irregular geometries under various boundary conditions. Notably, the model demonstrated consistent stability and high accuracy across the spectrum of simulated scenarios, thus underscoring its potential as a valuable tool for investigating complex phase change processes.

Simultaneous Measurement of Thermal Conductivity and Volumetric Heat Capacity of Thermal Interface Materials Using Thermoreflectance.

Thermal interface materials are crucial to minimize the thermal resistance between a semiconductor device and a heat sink, especially for high-power electronic devices, which are susceptible to self-heating-induced failures. The effectiveness of these interface materials depends on their low thermal contact resistance coupled with high thermal conductivity. Various characterization techniques are used to determine the thermal properties of the thermal interface materials. However, their bulk or free-standing thermal properties are typically assessed rather than their thermal performance when applied as a thin layer in real application. In this study, we introduce a low-frequency range frequency domain thermoreflectance method that can measure the effective thermal conductivity and volumetric heat capacity of thermal interface materials simultaneously in situ, illustrated on silver-filled thermal interface material samples, offering a distinct advantage over traditional techniques such as ASTM D5470. Monte Carlo fitting is used to quantify the thermal conductivities and heat capacities and their uncertainties, which are compared to a more efficient least-squares method.

Phase and Amplitude Changes in Rainfall Annual Cycle Over Global Land Monsoon Regions Under Global Warming

AbstractLand monsoon rainfall has a distinct annual cycle. Under global warming, whether the phase and amplitude of this annual cycle would be changed is still unclear. Here, a global investigation is conducted using 34 CMIP6 and 34 CMIP5 models under a high emission scenario. Seasonal delays would occur in the Southern Hemisphere (SH) American (3.43 days), Northern Hemisphere (NH) African (5.98 days) and SH African (3.76 days) monsoon regions, while no robust signal is found in other monsoon regions. Except NH American monsoon, amplitude is enhanced in all the monsoon regions. Compared to amplitude, the phase changes dominate the future changes of precipitation in the SH American, NH African and SH African monsoon regions. In these phase‐dominated regions, atmospheric energetic framework is proved to be reliable at regional scale and the enhanced effective atmospheric heat capacity is found to be the dominant factor.

Why Do CO2 Quadrupling Simulations Warm More Than Twice as Much as CO2 Doubling Simulations in CMIP6?

AbstractWe compare abrupt CO2‐quadrupling (abrupt‐4xCO2) and ‐doubling (abrupt‐2xCO2) simulations across 10 CMIP6 models. Two models (CESM2 and MRI‐ESM2‐0) warm substantially more than twice as much under abrupt‐4xCO2 than abrupt‐2xCO2, which cannot be explained by the non‐logarithmic scaling of CO2 forcing. Using an energy balance model, we show that increased warming rates within these two models are driven by both less‐negative radiative feedbacks and smaller global effective heat capacity under abrupt‐4xCO2. These differences are caused by a decrease in low cloud cover and shallower ocean heat storage, respectively; both are linked to smaller fractional declines in the Atlantic Meridional Overturning Circulation (AMOC) under abrupt‐4xCO2 (relative to abrupt‐2xCO2). On a global scale, higher climate sensitivity under larger forcing can be explained by a feedback‐temperature dependence; however, we find that forcing‐dependent spatial warming patterns due to AMOC decline are an important physical mechanism which reduces warming in a way that is not captured by a global‐mean framework.

An approach for topology optimization of heat sinks for two-phase flow boiling: Part 1 – Model formulation and numerical implementation

Two-phase flow boiling in heat sinks and cold plates is attractive for various thermal management applications due to high effective heat capacity rates and high heat transfer coefficients compared to single-phase operation. In addition, multi-physics topology optimization is sought for generation of high performance thermal management components. Yet, the design of heat sinks using topology optimization has been restricted to single-phase flow physics, due to incompatibility between available two-phase flow models and traditional single-phase topology optimization approaches. Interface-capturing two-phase flow models are too computationally expensive for optimization; mixture and two-fluid models that treat the liquid and vapor phases as an interpenetrating continuum with interfacial transport phenomena captured through empirical correlations are computationally tractable for heat-sink-scale optimization. However, the penalization approaches commonly used to define the structures formed during topology optimization results in arbitrary fin and channel geometries for which a universal two-phase flow correlation is not available. To enable coupling with two-phase mixture models, this work leverages a homogenization approach to topology optimization wherein heat sink designs are represented using spatially varying microstructures with optimized dimensions. A predefined microstructure geometry is chosen for which two-phase flow correlations exist and therefore topology optimization can be performed. This work is the first to develop a topology optimization algorithm using a mixture model for simulating two-phase flow boiling to design heat sinks and cold plates. Part 1 of this study develops and implements the algorithm to investigate topology optimized heat sinks at various heat inputs, topology optimization grid sizes, and maximum vapor quality constraints. Topology optimized heat sinks designed for single-phase versus two-phase flow are compared. There are significant differences in hydraulic and thermal responses of the single-phase and two-phase designs due to high effective heat capacity rates and high heat transfer coefficients of flow boiling. A companion paper (Part 2) focuses on manufacturing, model calibration, and experimental validation of the topology optimized heat sinks under two-phase flow boiling. The algorithm demonstrated in this work extends the capabilities of topology optimization to two-phase flow physics, and thereby enables the design of various two-phase flow components such as evaporators, condensers, heat sinks, and cold plates.

An approach for topology optimization of heat sinks for two-phase flow boiling: Part 2 – Model calibration and experimental validation

Flow boiling offers increased heat transfer coefficients and effective heat capacity rates that can be leveraged by topology optimization (TO) to generate high-performance microchannel heat sinks. Topology optimization of heat sinks having two-phase flows can be accomplished using the homogenization approach wherein designs are represented as spatially varying distributions of microstructures, as demonstrated in Part 1 of this two-part study. Flow and heat transfer within the microstructures are captured using a two-phase mixture model featuring an effective porous medium formulation. However, closure of these governing equations requires empirical correlations for pressure drop and heat transfer that are specific to the operating conditions, geometry, and surface finish. Therefore, it must be demonstrated these available correlations can be successfully calibrated over a range of microstructural variations present within the homogenization framework, so as to attain the required prediction generality and accuracy needed to ensure the resulting designs achieve Pareto-optimality. This Part 2 of our study successfully demonstrates a comprehensive end-to-end process for two-phase flow model calibration, topology optimized design generation, and experimental validation of optimized performance for flow boiling heat sinks. To this end, a TO algorithm with the homogenization approach and a two-phase mixture model is implemented using available flow boiling correlations for microchannels. A set of uniform pin fin calibration samples are additively manufactured and experimentally tested under flow boiling at various flow rates and heat inputs for model calibration. All of the unknown/free coefficients in the adopted correlations are determined by minimizing the error between the model predictions and the experimental measurements using gradient-based optimization. The calibrated topology optimization algorithm is then used to generate a Pareto-optimal set of heat sinks optimized for minimum pressure drop and thermal resistance during flow boiling. Experimental characterization of these additively manufactured heat sinks, unseen during the model coefficient calibration process, reveals that the measured Pareto optimality curve matches that predicted by the topology optimization algorithm. Lastly, a heat sink design is generated for a design space involving multiple hot spots and background heating to showcase the capability of the experimentally calibrated two-phase topology optimization algorithm at handling complex boundary conditions. The optimized heat sink intelligently distributes an adequate amount of coolant flow to each of the heated regions to avoid local dry-out. This work demonstrates a complete framework for two-phase topology optimization of heat sinks through experimental calibration of flow boiling correlations to the porous medium used by the homogenization approach.

Fire Protection of Steel Structures of Oil and Gas Facilities: Multilayer, Removable, Non-Combustible Covers

Fire protection is required to protect metal structures of oil and gas facilities from fires. Such fire protection should provide high fire resistance limits: 60, 90, 120 and more minutes. Specialists of LLC “RPC PROMIZOL ” developed a multilayer, removable type of fire protection made of superfine basalt fibre and ceramic materials for operation in Arctic conditions. Five experimental studies were carried out in standard and hydrocarbon fire regimes. The fire protection effectiveness of the products for I20 beams without load was obtained: a 50 mm thick coating provided 130 min of a standard fire regime; a 15 mm thick coating provided 60 min. The 15 mm thick coating provided 30 min of a hydrocarbon fire regime and the 50 mm thick coating provided 93 min of a hydrocarbon fire regime. The I40 beam under a load of 19.9 tf showed an R243 for the standard fire regime. The coefficients of effective thermal conductivity and specific heat capacity of fire-retardant compositions were determined by solving the inverse heat conduction problem. The problem was solved by modelling using the QuickField 7.0 software package, which implements FEM. Modelling showed that for obtaining the fire resistance limit R120 under the standard fire regime for the sample steel structure from an I40 beam, it is enough to apply fire protection with a thickness of 25 mm instead of 50 mm, which agrees with the experimental data. For the hydrocarbon regime, it is predicted that R120 can be obtained at a thickness of 45 mm instead of 50 mm.

Retaining Short‐Term Variability Reduces Mean State Biases in Wind Stress Overriding Simulations

AbstractPositive feedbacks in climate processes can make it difficult to identify the primary drivers of climate phenomena. Some recent global climate model (GCM) studies address this issue by controlling the wind stress felt by the surface ocean such that the atmosphere and ocean become mechanically decoupled. Most mechanical decoupling studies have chosen to override wind stress with an annual climatology. In this study we introduce an alternative method of interannually varying overriding which maintains higher frequency momentum forcing of the surface ocean. Using a GCM (NCAR CESM1), we then assess the size of the biases associated with these two methods of overriding by comparing with a freely evolving control integration. We find that overriding with a climatology creates sea surface temperature (SST) biases throughout the global oceans on the order of ±1°C. This is substantially larger than the biases introduced by interannually varying overriding, especially in the tropical Pacific. We attribute the climatological overriding SST biases to a lack of synoptic and subseasonal variability, which causes the mixed layer to be too shallow throughout the global surface ocean. This shoaling of the mixed layer reduces the effective heat capacity of the surface ocean such that SST biases excite atmospheric feedbacks. These results have implications for the reinterpretation of past climatological wind stress overriding studies: past climate signals attributed to momentum coupling may in fact be spurious responses to SST biases.

Numerical model for determining the effective heat capacity of macroencapsulated PCM for building applications

This paper presents a finite difference model of macroencapsulated PCM panels coupled with the genetic algorithm for the determination of effective heat capacity of whole panels via inverse method. This provides an accurate characterization of the thermal properties of macroencapsulated PCMs for building envelope applications. A novel definition of the effective heat capacity is proposed based on the superimposition of two Gaussian curves, applicable to any PCM whose phase transition is characterized by a single peak. Three PCMs were tested, subjected to temperature variation rates typically experienced in building envelopes: 0.5 °C/h and 1 °C/h. Surface temperature and heat flux were measured and used in the inverse method procedure. The developed model is accurate, as numerical results greatly agree with the experiments: the root mean square difference between the experimental and numerical heat fluxes ranged between 0.543 and 1.246 W/m2. Significant differences in the effective heat capacity were found between the whole macrocapsule and small quantities of PCM (specified in the datasheets). The effective heat capacity specified in the datasheets is sensibly greater than that of the whole macrocapsules determined through the inverse method: the specific heat in the solid phase was up to 107.39 % higher in the datasheet values, the specific heat in the liquid phase up to 184.04 %, and the peak effective heat capacity, between 18.28 % and 164.11 %. The same happened to the enthalpy: datasheet values were 61.24 % – 175.55 % greater than inverse method results. This proves that latent heat is overestimated if small quantities of PCM are analyzed, and not the whole panels. The scale effect was assessed by comparing two capsules with the same material, but with different quantities of PCM: 0.5 kg and 1 kg. A greater mass of PCM over the total mass of the capsule implies a different relationship between the effective heat capacity and temperature, with higher peak heat capacity. The capsule with 1 kg of PCM showed a peak effective heat capacity up to 30.65 % greater than that of the panel with 0.5 kg of PCM. Thus, adequate modeling in building applications requires characterization of whole macroencapsulated PCMs. The determination of the relationship between temperature and effective heat capacity of macroencapsulated PCMs presented in this work could easily be incorporated into other simulation software, facilitating the assessment of adaptive envelopes with PCM macrocapsules.

Numerical investigation on rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel

Rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel are investigated with different mass fractions, Reynolds numbers and particle size distributions. The deviations of the two-phase model and the single-phase model from experiments are also examined and compared. The solid-liquid phase change process of MPCMS is described by the effective heat capacity method. The results show that as the mass fraction Cm increases up to 30%, the MPCMS flow starts to transform from the Newtonian fluid to pseudoplastic behavior (shear rate 0–110 s−1), and the resultant performance evaluation factor (PEF) increases from 1 to 1.27. As the Reynolds number is raised from 96 to 960 (Cm = 15%), the viscosity remains nearly constant (shear rate 100–1000 s−1) flowing as a Newtonian fluid, and the PEF decreases from 1.24 to 1.14. With the particle size increasing (dp = 0.1–10 μm), non-Newtonian characteristics of the suspension become more obvious (shear rate 9300–15,000 s−1), and the PEFs are all 1.15. The average deviation of the single-phase model is 12.3% compared with the experimental data, while it is only 3.65% for the two-phase model. The results provide a reference for the optimization of MPCMS application in microchannel from a rheological perspective.

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

Modeling of thermal processes in vertical heat exchangers of ground-source heat pump

The basic directions for perfection heat supply systems are the tendency of transition to the low-temperature heating systems based at application heat pump installations. We consider heat supply systems with ground-source heat pump. The paper considers modeling the efficiency of ground-source heat pumps with the account of Ukrainian climate conditions. The paper presents the energy performance criteria which show the way to rational implementation of ground-source heat pumps for heating. A computational model based at non-stationary heat exchange processes in elements of ground-source heat pumps is developed. Generalization and analysis of theoretical and experimental dates allow establishing nature of dependence thermophysical properties on temperature insoil around ground heat exchangers during long term operation of the system. Numerical simulation of thermal processes in vertical ground pipes for ground-source heat pump working with low-temperature heating systems has been worked out. The results of numerical modeling demonstrated perfection and technical adaption of ground-source heat pump for low-temperature heating systems with rational using ground energy potential. The novelty of our method is complex usage theoretical and experimental results which enable to prevent freezing in the ground during long term exploitation This provides insights at effects of different resource mixes and may serve as a new approach to analysis of future heat pump systems using ground source energy development.The proposed method contributes to the field of creation and implementation the sustainable heating technologies using renewable energy sources. The ground heat exchange pipes quantities that are necessary for effective operation heat pump installation, capacity and coefficient of performance with the account of climate conditions are calculated.

Asymmetric Arctic and Antarctic Warming and Its Intermodel Spread in CMIP6

Abstract Under the background of global warming, the Arctic region has warmed faster than the Antarctic, which is referred to as asymmetric Arctic and Antarctic warming. The new generation of model simulations from the CMIP6 offers an opportunity to identify the major factors contributing to the asymmetric warming and its intermodel spread. In this study, the preindustrial and abrupt-4 × CO2 experiments from 18 CMIP6 models are examined to extract the asymmetric warming and its intermodel spread. A climate feedback-response analysis method is applied to reveal the contributions of external and internal feedback processes to the asymmetric warming and its intermodel spread, by decomposing total warming into the partial temperature changes caused by individual factors. It is found that a seasonal energy transfer mechanism (SETM) dominates in both polar warmings. The direct consequence of the sea ice declining in response to the anthropogenic forcing is an increase in the effective heat capacity of the ocean surface layer. Such an increase in the effective heat capacity temporally withholds most of the extra solar energy absorbed during summer and then releases it during winter, contributing to stronger warming in winter. However, the background oceanic circulation in the Southern Ocean, namely, the Antarctic Circumpolar Current, continually transports energy equatorward, resulting in a suppressed SETM and surface warming in the Antarctic. The key factor that accounts for intermodel spread in the asymmetric warming is the difference in their strengths of SETM. The poleward atmospheric transport and water vapor feedback also contribute to the intermodel spread. Significance Statement The asymmetric Arctic and Antarctic warming, as a response to the increase in CO2, can regulate global atmospheric and oceanic circulations via meridional temperature gradient. Previous studies have all ascribed the key role of the ocean in the asymmetric warming over the two poles with a lack of comprehensive understanding of the roles of other feedback processes. This study emphasizes that oceanic circulation is the root of the asymmetric warming via suppressing sea ice retreat and the associated SETM in the Antarctic, instead of increasing ocean heat uptake and equatorward transport only. For the intermodel spread in the asymmetric warming over two poles, the differences in the strength of all processes involving the SETM among models are the prominent issue.

Osmolality based effective heat capacity model for cryoablation scenarios

Osmolality based effective heat capacity model for cryoablation scenarios

Energy and exergy analysis of photovoltaic thermal collectors: Comprehensive investigation of operating parameters in different dynamic models

The comparative analysis of a transient two-dimensional model and a lumped parameter model for photovoltaic thermal (PV/T) devices were presented, focusing on the energy and exergy performance under different operating conditions. The lumped parameter model involves the effective heat capacity for solar collectors and a zero-dimensional dynamic model for the calculation of the heat transfer coefficient. The study established both models and examines their differences in temperature distribution and computational results. Results indicate that the lumped parameter model, considering computational efficiency and simplified processes, serves as an effective tool for evaluating PV/T device performance, with a maximum relative error of 3.51 % in calculated results. Additionally, the impact of irradiance and flow rate on energy efficiency and exergy efficiency was investigated. After mass flow reaching 0.02 kg/m2/s, the thermal efficiency is 50.15 %, reaching a stable state. The research highlights the significant influence of operating conditions on the overall performance of PV/T collectors. The exergetic flow distribution of PV/T collector was obtained, with an overall exergy efficiency of 13.13%–14.96 % in different operation, and the research further analyzed the causes of exergy loss of PV/T collectors and possible improvement directions. The findings contribute to advancing the understanding and optimization of PV/T systems for enhanced energy conversion and exergy utilization.

Dynamic heat-transfer mechanism and performance analysis of an integrated Trombe wall with radiant cooling for natural cooling energy harvesting and air-conditioning

Natural cooling energy and high-efficient radiant cooling techniques are essential to mitigate energy resources shortage crisis, breakthrough on traditional convective air-conditioning systems in isolation between indoor and outdoor environment with high indoor air quality. In this paper, a polyethylene aerogel (PEA) and phase change material (PCM) integrated novel Trombe wall was proposed, involving natural cooling energy harvesting, cooling energy storage, indoor ventilation and radiant cooling. A two-dimensional unsteady numerical model based on surface-to surface (S2S) radiation model and effective specific heat capacity method was developed in the commercial software Ansys Fluent to evaluate the cooling performance and dynamic heat-transfer mechanism of the novel Trombe wall. Subsequently, climate-responsive operation strategies on ventilation modes were proposed to maximize natural cooling energy utilization and fresh air supply. Parametrical and comparative studies were conducted on optimal structural design and robust operation. Our results showed that, with the novel design and advanced operation strategies, passive cooling capacity of 0.64 kWh/m2·day can be provided, together with fresh air supply of 2705.2 kg/day (1.4 m2 Trombe wall), corresponding to air change rate per hour (ACH) of 1.15. In terms of active cooling system, the integration of PEA and PCM can effectively prevent moisture condensation and shift peak cooling load. Hence, radiant cooling capacity of 0.99 kWh/m2·day and radiant cooling ratio of 47 % can be achieved by the novel Trombe wall, with electricity consumption only at valley period. Moreover, economic saving of 55.0 CNY/day and decarbonization potential of 23.8 kg CO2,e/day can be achieved when the novel Trombe wall is integrated into a typical office building in subtropical climate Guangzhou. This study provides a novel structural design and optimal operation strategies on a Trombe wall, together with guidelines on techno-economic-environmental performance improvement, promoting effective natural cooling energy utilization and energy-flexible/efficient radiant cooling for decarbonization of buildings in cooling-dominant regions.

Assessment of the performance of metaheuristic methods used for the inverse identification of effective heat capacity of phase change materials

Phase change materials (PCMs) are one of the promising technologies for the carbon neutral future, since they can be effectively used for thermal energy storage (TES), and therefore can mitigate the energy supply/demand mismatch characteristic for renewable energy resources. Mathematical models describing thermal behaviour of PCMs require various material properties, such as specific heat capacity, thermal conductivity or density, which are in many cases difficult to obtain experimentally. This paper introduces an inverse identification procedure which utilises heuristic optimisation methods to solve the inverse problem. The air-PCM heat exchanger was considered as a studied device. In order to avoid any uncertainties tied to the experimental measurement, the exact solution was generated by the numerical model directly (referred to as “pre-simulated” scenario). The cost function was constructed as a root mean square difference between the given calculated and pre-simulated outlet air temperatures. In total seven different case studies (five with a base model and two with an extended model) were investigated for the inverse identification of the effective heat capacity of a PCM and seven different heuristic optimisation methods were utilised for each case study. The results have shown that the LSHADE and DE methods were the best performing ones and that one method outperformed the other depending on the problem settings.