Effective Specific Heat Capacity Research Articles

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.

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.

Molecular dynamics study on the impact of the development of dendritic nanostructures on the specific heat capacity of molten salt nanofluids

A dendritic nanostructure has been observed to form when one salt of the eutectic salt mixture comes into contact with a SiO2 nanoparticle, according to investigations in literature. The effective specific heat capacity of the molten salt nanofluids has been reported to be influenced by the presence of these nanostructures. Some reported studies experimentally confirmed that these nanostructures can increase the specific heat capacity of molten salt nanofluids. However, there have been no detailed theoretical or computational investigations to validate the experimental results. In this study, molecular dynamics simulations were used to investigate a eutectic mixture of Li2CO3 and K2CO3 (62:38 M ratio) doped with SiO2 nanoparticle surrounded by dendritic Li2CO3 nanostructures. The mixture's density and specific heat capacity were determined using molecular dynamics simulations. The nanofluids only containing nanoparticles did not show any significant changes in its density or specific heat capacity. The effective specific heat capacity of the mixture was improved, and density of the mixture was decreased by the presence of SiO2 nanoparticles surrounded by dendritic Li2CO3 nanostructures. The high specific surface energy associated with the large surface areas of the implanted nanoparticles as well as the dendritic nanostructures created by nanoparticle addition can explain the observed enhancements in specific heat capacity.

High-resolution dielectric anisotropy investigation of carbon nanotube-smectic-A liquid crystal dispersions: An upper limit of the latent heat and the pretransitional anomaly at the nematic-smectic-A transition.

Within the entire mesomorphic range, high-precision dielectric anisotropy data with the high-temperature resolution is presented for a highly polar smectic-A liquid crystal 8CB (octylcyanobiphenyl) as well as 8CB nanocomposites doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWCNTs). The temperature variation of the nematic order parameter across both the nematic-isotropic (N-I) and the nematic-smectic-A (N-Sm-A) phase transitions of the neat 8CB and 8CB+MWCNT nanocomposites has then been derived from the dielectric anisotropy data within the framework of the Maier-Meier theory. With the inclusion of MWCNTs, both the N-I and the N-Sm-A transition temperatures have been noted to shift to lower temperatures as compared to the 8CB host. Also, for all 8CB+MWCNT nanocomposites, regardless of the surface functionalization, it has been well documented that the N-I transition is weakly first order, whereas the N-Sm-A transition remains continuous within the experimental resolution. For all investigated samples, the temperature dependence of the nematic order parameter has been shown to be quasitricritical, within the experimental resolution. From the attentive inspection of the dielectric anisotropy data in the vicinity of the N-Sm-A transition, the upper limits for a possible latent heat ΔH_{NA} for the 8CB host and all 8CB+MWCNT composites, for the first time, have been derived. The so-derived ΔH_{NA} values for all investigated samples have also been compared with those extracted from the optical birefringence data, and an excellent consistency has then been noted. The N-Sm-A pretransitional anomaly has been investigated and the effective specific heat capacity exponent α values have been yielded from the power-law analysis of our high-resolution Δɛ(T) data across the N-Sm-A transition for all investigated samples. It has been well documented that the incorporation of MWCNTs to the 8CB host leaves the N-Sm-A transition essentially bulklike. We discussed that, to some extent, the compliance of MWCNTs does not drive the N-Sm-A transition to 3D-XY-like behavior, that is the strength of de Gennes coupling will remain the same for all nanocomposites. This issue can be ascribed to the weaker nature of MWCNT disorder. In this work, for the first time, high-resolution Δɛ(T) data has been shown to be very adequate and offer an easy way to investigate the N-Sm-A transition as compared to calorimetric methods.

Role of micro fibres in tailoring the specific heat capacity of cementitious composites at elevated temperatures: Experimental characterisation and micromechanical modelling

The temperature dependency of specific heat capacity is crucial for thermo-mechanical analysis of fibre reinforced cementitious composites. In this study, a combined experimental and theoretical analysis was conducted to characterise the role of micro fibres in tailoring the specific heat capacity of cementitious composites at elevated temperatures. The specific heat capacity of cement mortar reinforced with four types of fibres, including polypropylene, basalt, carbon and glass fibres, was measured by means of a transient method at up to 400 °C. Based on the effective medium theory, a multiscale homogenization model was developed to predict the specific heat capacity evolution of cementitious composite with temperature from micro to macro level. The results indicate that within the measured temperature range, the addition of 2.0 vol% polypropylene and glass fibres lead to the maximum rise or drop in specific heat capacity of mortar by 8.7% and 14.1%, respectively. In addition, the thermal expansion of polymer fibre was proved to effectively enhance the specific heat capacity of mortar due to thermal expansion coupling effect. The parametric analysis suggests that stiffer inclusions with high thermal expansion govern the effective specific heat capacity coupled with thermal expansion, while the composite incorporated with softer inclusions is insensitive to the variation in thermal properties of inclusions.

From pilot knowledge via integrated reservoir characterization to utilization perspectives of deep geothermal reservoirs: the 3D model of Groß Schönebeck (North German Basin)

The Groß Schönebeck site in the North German Basin serves as research platform to study the geothermal potential of deeply buried Permian reservoir rocks and the technical feasibility of heat extraction. The structural setting of the site was investigated in more detail by a newly acquired 3D-seismic survey to improve the former conceptual model that was based on several old 2D seismic lines. The new data allow a revision of the geological interpretation, enabling the setup of a new reservoir model and providing base information for a possible further site development of Permo-Carboniferous targets. The 3D seismic allows for the first time a consistent geological interpretation and model parameterization of the well-studied geothermal site. Main reflector horizons and the corresponding stratigraphic units were mapped and the structural pattern of the subsurface presented in the 8 km × 8 km × 4 km large seismic volume. Attribute analysis revealed some fracture and fault patterns in the upper Zechstein and post-Permian units, while formerly hypothesized large offset faults are not present in the Rotliegend reservoir. However, a well-established graben-like structure at the top of the Zechstein succession is most likely related to broken anhydritic brittle intra-salt layers of some meter of thickness. Most reflectors above the salt show a rather undisturbed pattern. The main reservoir sandstone of the Dethlingen Formation (Rotliegend) was mapped and characterized. The base of the underlying Permo-Carboniferous volcanic rock sequence and hence its thickness could not be depicted reliably from the geophysical data. Based on the seismic data and the available reconnaissance drilling, logging, and laboratory data of the Groß Schönebeck research site, the thickness and distribution of the sedimentary Rotliegend (with emphasis of the sandy reservoir section) and of the volcanic rock sequence was modelled and stochastically parameterized with petrophysical properties guided by seismic facies pattern correlation, providing a more realistic reservoir description. Properties include total and effective porosity, permeability, bulk density, thermal conductivity, thermal diffusivity, and specific heat capacity. The data and interpretation constitute the basis for a better understanding of the thermo and hydromechanical processes at the site and for future measures. Further site development could include a deepening of one well to provide evidence on the volcanic rock sequence and consider deviated wells into favourable zones and the design of a fracture-dominated utilization approach.

Effect of segregation and advection governed heterogeneous distribution of nanoparticles on NEPCM discharging behavior

A numerical study is performed to investigate the role of heterogeneous distribution of nanoparticles in discharging behavior of nanoparticle-enhanced phase change materials (NEPCM). The numerical model considers solidification, multiphase convection, nanoparticles segregation, sedimentation, drags on nanoparticles and Brownian and thermophoresis diffusion phenomena. The discharging behavior of NEPCM is analyzed for the solidification of n-octadecane (PCM)-Cu-nanoparticles in a rectangular cavity. The discharging stage of NEPCM is also being investigated experimentally. The experiments were equipped with Particle Image Velocimetry (PIV), high-resolution imaging and thermocouples to measure real-time flow field, solidified layer thickness and local temperature. The numerically predicted results are compared with these experimental results to validate the model. Using the numerical model, the transient evolution of solidification interface morphology, nanoparticles concentration, fluid flow, temperature field, and thermophysical properties during solidification of NEPCM is described. Subsequently, the effect of process parameters such as initial nanoparticles concentration and Stefan number on system's thermal performance is delineated. It is noticed that adding nanoparticles up to a certain limit increases the discharging rate. The discharging time for 0 wt%, 2.5 wt%, 4.5 wt% and 6.5 wt% Cu-nanoparticles concentration are found to be 1115, 895, 980 and 1075 min, respectively. Thus, NEPCM with 2.5 wt% Cu-nanoparticles discharges 19.7 % faster than pure PCM. Furthermore, it is found that the heterogeneous distribution of the rejected nanoparticles significantly affects the solid-liquid interface morphology, solidification rate and alters the thermophysical properties locally as well as globally. The effective density and thermal conductivity increase with an increase in the local concentration of nanoparticles, whereas the effective specific heat capacity decreases with the increase in the local concentration of nanoparticles.

Al2O3–H2O nanofluids for cooling PEM fuel cells: A critical assessment

Polymer electrolyte membrane (PEM) fuel cells are promising eco-friendly and sustainable power generation technology. Thermal management of these cells is one of the main challenges facing their commercialization. Alumina nanofluids, in addition to others, have been proposed to overcome excess heat generated within the PEM fuel cell stacks. However, most the previous studies investigated the hydrothermal performance of the nanofluids as a function of Reynolds number (Re). It is evident that all parameters must be kept constants except one to examine its effect on the performance. To this end, choosing Re as a parameter (independent variable) is problematic as it is a function not only of nanofluid's velocity, but also its density and viscosity. In this study, a well-validated CFD model has been built to simulate the hydrothermal performance of alumina nanofluids of different volumetric concentrations (0%, 0.05%, 0.1% and 0.2%) as functions of Re (170 < Re < 530), flow rate (20 ml/min ≤ Vf ≤ 50 ml/min), and pumping power (0.025 mW < Pp < 0.3 mW). This study shows a maximum reduction of 7.9% in the thermal effectiveness and a maximum increase of 6% in the pumping power when using the nanofluids instead of water. This deterioration in the hydrothermal performance is due to the reduction in the effective specific heat capacity and increase in viscosity of the nanofluids. Also, it is concluded that it is incorrect to use Re as an independent variable in analysing the hydrothermal performance of nanofluids because of the dependency of Re on some of the thermophysical properties of the nanofluids, which are functions of the concentration. Adopting such analysing procedure leads to false conclusions.

Modelling thermal diffusivity of meat during freezing

Abstract When modelling a thermal process such as freezing, it is convenient to make use of thermal property models based on the food’s composition; however, there does not appear to be any suitable models specifically for thermal diffusivity. In the absence of such models, thermal diffusivity may be determined from models for effective thermal conductivity, specific heat capacity and density as functions of composition, as well as an appropriate ice fraction model. However, the accuracy of the predictions is strongly dependent on the choice of effective thermal property models. In particular, the effective specific heat capacity model must incorporate the effect of latent heat release as a function of temperature. For meat during freezing, it is recommended that the Dul’Nev Novikov effective thermal conductivity model, Pham’s ice fraction model and Chen’s effective heat capacity model are used.

Tunable melting temperature of Sn encased by Cu nanoparticles for high temperature energy storage

With respect to high temperature thermal storage systems, there is a critical need to develop advanced metallic phase change materials (PCM) for improving storage efficiencies. However, the melted metal is generally in a high temperature state, and exhibits a high chemical corrosion to iron and other shell materials. In this work, a new kind of nanocomposite with leakage prevention is probed, which is prepared by using excellent-adsorption-capacity nanoparticles to encircle the metallic PCM densely. By using Cu nanoparticle as additive and Sn material as the PCM, Sn/Cu nanocomposite is prepared by cold pressing methods and then sintering treatment. Cu nanoparticles can not only serve as thermal-conductivity enhancer, but also could greatly encircle Sn to prevent the leakage of molten Sn in the thermal storage process. Most importantly, the phase change temperature of Sn matrix can be effectively adjusted and the effective specific heat capacity of the whole system can be obviously enhanced, by regulating the weight fraction of Cu nanoparticles in the composite, because of the appearance of many Sn nanowires after sintering treatment. For the addition of 50 nm Cu nanoparticles, the melting temperature of Sn PCM can be reduced by 5 °C, and melting temperature can be further reduced by decreasing the size of Cu nanoparticles. When the weight fraction of Cu nanoparticles in the composite is 5 %, the specific heat capacity can be enlarged nearly 10 % than the normal composites without Sn nanowires forming. This work provides a new idea for the preparation of nanocomposite PCM, which can significantly reduce or even overcome the phenomenon of liquid leakage during the phase change process, obviously improve the specific heat capacity of the PCM, effectively adjust the melting temperature, and make PCM possess high strength but maintain lightweight.

Modelling Thermal Diffusivity of Heterogeneous Materials Based on Thermal Diffusivities of Components with Implications for Thermal Diffusivity and Thermal Conductivity Measurement

Effective thermal diffusivity models are useful for predicting thermal diffusivities of heterogeneous materials. The literature contains models that may be broadly categorised into four different types: (1) effective thermal diffusivity for highly specific applications (e.g. empirical curve fitting of measured data); (2) effective thermal diffusivity as a weighted averages of the components’ thermal diffusivities and volume fractions; (3) effective thermal diffusivity calculated from effective thermal conductivity, effective density and effective specific heat capacity known as the ‘lumped parameter’ approach (which is the most commonly employed method); (4) comparison of times for a fixed quantity of heat to be transferred to a composite material with the heat transfer time for a material with an effective thermal diffusivity. The latter three modelling methods were tested on theoretical composite materials, and none performed consistently better than the others, suggesting there is scope for further work in this area. Of the three methods, the least accurate on average was the lumped parameter method. Given that this relationship is often used to derive thermal conductivity data from thermal diffusivity data (or vice versa), it is possible that significant error is introduced to the derived property in addition to any measurement error, which is often not acknowledged.

Experimental investigation of thermal architected metamaterials for regulating transient heat transfer

Metamaterials have innovative functionalities as a result of artificial design. By arbitrarily designing thermal conductivity, thermal metamaterials have achieved thermal invisible cloaks, camouflages, and deceptions in steady-state. However, density and specific heat capacity have sometimes been overlooked, despite the fact that they are critical for managing transient heat flow and that density are an indicator of creating lightweight materials. The traditional materials are incapable of synchronously controlling thermal conductivity, density, and specific heat capacity. In this research, we experimentally investigate a novel thermal architected metamaterial that can modulate (accelerate or decelerate) transient heat transfer velocity without disrupting the steady-state. The novel type of thermal architected metamaterial achieves efficiency using a topology based on neutral inclusion theory. The transient heat transfer velocity is regulated by altering the effective density and specific heat capacity on the one hand, while the steady-state heat transfer is maintained by keeping the effective thermal conductivity on the other. The density of the architected metamaterial could be adjusted by selecting an appropriate specific heat capacity. The method we provide can be utilized to create lightweight energy-efficient materials (by accelerating transient heat transfer) as well as lightweight engineered thermal protection materials (by decelerating transient heat transfer). Moreover, the proposed thermal architected metamaterial could control heat flow velocity continuously, and this characteristic covers the gaps left by natural materials.

Thermophysical properties of balsa wood used as core of sandwich composite bridge decks exposed to external fire

The load-bearing performance of sandwich bridge decks comprising a balsa core and fiber-reinforced polymer composite face sheets exposed to fire is a main concern regarding the application of these deck systems. In order to obtain the thermal responses of the balsa core exposed to fire, the temperature-dependent values of thermal conductivity and specific heat capacity are required. Furthermore, information about the char depth and charring rate and the temperature-dependent coefficient of thermal expansion is also needed for the subsequent thermomechanical modeling. In the current study, the effective thermal conductivity and specific heat capacity of balsa up to 850 °C were obtained from one-dimensional transient heat transfer models and experimental data using an inverse heat transfer analysis. The results showed that both properties depend significantly on the stages of combustion, direction of heat flow (in the tracheid or transverse direction) and density. Moreover, charring temperatures and rates were obtained, again as a function of direction and density. Finally, the coefficient of thermal expansion was measured in the transverse direction during evaporation and pyrolysis.

A Layer-Dependent Analytical Model for Printability Assessment of Additive Manufacturing Copper/Steel Multi-Material Components by Directed Energy Deposition.

Copper/steel bimetal, one of the most popular and typical multi-material components (MMC), processes excellent comprehensive properties with the high strength of steel and the high thermal conductivity of copper alloy. Additive manufacturing (AM) technology is characterized by layer-wise fabrication, and thus is especially suitable for fabricating MMC. However, considering both the great difference in thermophysical properties between copper and steel and the layer-based fabrication character of the AM process, the optimal processing parameters will vary throughout the deposition process. In this paper, we propose an analytical calculation model to predict the layer-dependent processing parameters when fabricating the 07Cr15Ni5 steel on the CuCr substrate at the fixed layer thickness (0.3 mm) and hatching space (0.3 mm). Specifically, the changes in effective thermal conductivity and specific heat capacity with the layer number, as well as the absorption rate and catchment efficiency with the processing parameters are considered. The parameter maps predicted by the model have good agreement with the experimental results. The proposed analytical model provides new guidance to determine the processing windows for novel multi-material components, especially for the multi-materials whose physical properties are significantly different.

RESEARCH INTO THE THERMOPHYSICAL CHARACTERISTICS OF MUSCLE AND ADIPOSE TISSUES IN THE FREEZING–THAWING PROCESS

The paper presents a study of the thermophysical characteristics of meat systems based on minced beef and pork with different morphological composition in the freezing–thawing process, and those of model systems based on minced beef with addition of adipose tissue (raw fat). The method used to detect and compare the thermodynamic changes consisted in determining the effective specific heat capacity by freeze-thaw thermograms and was based on a set of informational parameters related to it (cryoscopic temperature, cryoscopic interval of temperatures, specific heat of phase transition in the cryoscopic temperature interval, change of enthalpy in the interval of temperatures of the sample tested, proportion of moisture that changes its physical state in the cryoscopic temperature interval). It has been shown that the morphological structure of meat (the ratio of muscle, connective, and adipose tissues) significantly affects the thermophysical parameters of meat systems during freezing and defrosting. It has been found that under the conditions of a freeze–thaw cycle, an increase in the content of connective tissue leads to a higher proportion of moisture that changes its physical state in the cryoscopic temperature interval, while an increase in the adipose tissue content in a meat system reduces the moisture that changes its physical state in the cryoscopic temperature interval. When adipose tissue was introduced into meat systems, the freezing process resulted in a higher rate of formation of ice crystals and a lower rate of moisture migration from cells to the intercellular space, and crystal formation became a controlled process. When manufacturing semi-finished frozen meat products, regulating the ratio of muscle and adipose tissues makes it possible to influence the stability of the properties of meat systems in the technological cycle “freezing – storage – thawing” and to create products with the required functional, technological, and thermophysical parameters. This research can be a basis for developing the recipe compositions and technological parameters of manufacturing semi-finished frozen meat products and finished products based on them

A novel model for predicting the effective specific heat capacity of molten salt doped with nanomaterial for solar energy application

In order to establish instructions for high-performance molten salt preparation, this paper focuses on accurate prediction method on the effective heat capacity of nanomaterial-enhanced molten salt (NMS). With carbon nanotube (CNT) enhanced carbonate eutectic (Li2CO3-K2CO3) taken as the study subject, the microscopic mechanism of nanomaterial on the effective specific heat capacity enhancement of molten salt is revealed. The nanolayer content is calculated, and the specific heat capacity of CNT and nanolayer is quantified. Accordingly, the effective heat capacity prediction model is completed. In addition, the CNT-enhanced carbonate eutectic is experimentally prepared with a high-energy ball milling method. Its effective specific heat capacity is measured and used to validate the prediction model. The results show that, firstly, the thickness of nanolayer is 0.65 nm and 0.98 nm in the single-walled CNT case and multi-walled CNT case, respectively. Secondly, the specific heat capacity of CNT is 1.613 J·g−1·K−1 at 800 K, and the specific heat capacity of nanolayer increases with increasing the surface atom ratio. Finally, the effective specific heat capacity of CNT-enhanced carbonate salt is predicted and validated with experimental results. It is revealed that, in the cases of well-dispersed nanomaterial-enhanced molten salt, the prediction method presented in this research has considerable accuracy (error < 2.90%). Furthermore, the effective specific heat capacity of NMS doped with CNT of various diameter is given.

Numerical Study of Heat Transfer Characteristics of mPCM Slurry During Freezing

Microchannels with microencapsulated phase change slurry (mPCM) have gained attention due to their compactness and large surface area to volume of fluid ratio. The phase change process also helps in sustaining high heat exchange over small temperature changes. This paper is focused on numerical investigation of heat transfer characteristics of mPCM slurry flow during its freezing phase in microchannels under convective boundary conditions. The phase change process was incorporated in numerical modeling by considering the rectangular profile of an effective specific heat capacity model. Numerical simulations were peformed for mPCM slurry with 5 to 15% mass concentration, and the results were compared with those obtained with pure water. The effects of mass concentration of mPCM slurry on pressure drop, local Nusselt number, and local temperatures along the length of the channel were investigated. It was noticed that the increase in mass concentration enhanced the local Nusselt number than pure water. At the outlet of microchannel for flow velocity of 0.55 m/s, the bulk and surface temperatures were found to be 3.12 K and 1.2 K higher than those recorded with pure water. With a mass concentration in 5–15% range the pressure drop for mPCM slurry was found to be 5.1–36% higher than the pure water case.

Improved prediction of thermal properties of refrigerated foods

Thermal properties are essential parameters for performing heat transfer calculations. The thermal properties of foods can have a strong dependence on temperature during thermal processing, particularly during freezing, which has posed a challenge to those attempting to develop generic models that can be applied to a wide range of foods. Ideally, thermal property models should not incorporate any parameters whose value would need to be determined by a physical measurement (since this may defeat the purpose of the model). Instead it is preferable to perform a prediction based only on composition data, in terms of the major food components. This study presents an evaluation of thermal property models requiring only composition data as inputs. It is recommended that the Additive model incorporating a new correlation equation of the specific heat capacity of water should be used for effective specific heat capacity predictions. The thermal conductivity predictions from a little-known model developed by Dul'nev and Novikov provided more accurate predictions on average than more widely known models that have been recommended in previous studies. • A comparison of different composition-based thermal property models is presented. • The Additive model is recommended for effective specific heat capacity predictions. • The Dul'nev and Novikov model shows the best thermal conductivity predictions.

Mathematical modelling of vacuum ohmic evaporation process

Ohmic evaporation is a complex process in which heat and mass transfers take in place simultaneously. In this study, finite difference-FD and finite volume-FV models simulating the changes of temperature and water removed from tomato juice during the vacuum ohmic evaporation process (VOEP) were developed. Models considering the heat and mass transfer equations were combined. Experimental effective electrical conductivity and specific heat capacity relations were taken into account. For heating period, final temperature was predicted with errors of 3.4 ± 1.3 °C and 0.7 ± 1.3 °C, while the evaporation time prediction errors were 1.3 ± 1.6 min and − 2.1 ± 1.6 min for FV and FD models, respectively. It was concluded the effect of mixing was not important on temperature distribution for such a high consistency tomato paste compared to the heat generation effect during the ohmic evaporation process. The developed models could be used to predict process time, temperature history, and volume fraction at any time during the ohmic evaporation process.

Numerical investigation on integrated thermal management via liquid convection and phase change in packed bed of spherical low melting point metal macrocapsules

This paper is dedicated to investigate the integrated cooling modality that the spherical low melting point metal (LMPM) macrocapsules were introduced and filled as phase change material (PCM) into a convective cooling heat sink. The fluid-solid heat transfer process coupled with phase change in the packed bed was numerically calculated based on the local thermal non-equilibrium theory and the effective specific heat capacity model which were validated in advance by conceptual experiments. The thermal management ability of composite heat sink packed with spherical LMPM-PCM macrocapsules under typical operating conditions has been revealed. In addition, the influences of different stacking patterns of LMPM particles, particle diameter and inlet velocity on the heat transfer enhancement in the packed bed were comprehensively investigated, respectively. It is found that compared with convective cooling heat sink alone, the composite heat sink filled with LMPM-PCM macrocapsules presents excellent thermal management performance. The temperature increment of heat source in the pulse heat load is reduced by 73.4%, which fully demonstrates the advantages of filling spherical particles. Besides, the Orthoclinal Stacking method achieves the largest volumetric heat transfer coefficient among different stacking patterns of equal-diameter spherical LMPM-PCM macrocapsules. What is more, the plateau duration of the solidification is gradually shortened with the decreasing diameter of the spherical LMPM-PCM macrocapsules and the increasing inlet velocity, which is advantageous for the system to quickly rehabilitate to normal operating temperatures during the de-pulse stage. Overall, this novel integrated cooling modality is proven to be a powerful and practical way to sustain extreme thermal management challenge.