External Heat Research Articles

Simulation and analysis on heat leakage structure of cold compressor in large-scale refrigeration system

Large-scale helium cryogenic refrigeration facilities are indispensable equipment for many cutting-edge researches, and the cold compressor is the most advantageous pressurization scheme in superfluid helium systems with capacity of more than 200 watts. Due to the extremely low operating temperature zone of the cold compressor, the efficiency of the compression process decreases as the external heat leakage increases, especially when building systems with greater cooling capacity, this phenomenon becomes more significant. In order to reduce the influence of heat leakage, a conjugate heat transfer analysis is carried out on the cold compressor using commercial CFD software, and the internal structures, including thermal anchor, thermal insulation materials, are analysed and optimized base on the simulations.

Parametric analysis of the Charge-Hold-Vent method for cryogenic propellant tank chilldown

In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems.

Experimental investigation of condensation heat transfer on vertically inclined grooved aluminium surfaces

This study details the experimental investigation of surface condensation heat transfer on vertically inclined aluminium surfaces with simple modifications. A bespoke experimental apparatus was constructed to control the saturation conditions inside the condensation chamber where the test surface is located. The degree of subcooling of the test surface was precisely controlled by an external heat exchanger. The meter bar technique was used to evaluate the condensation heat flux. Using distilled water as the working fluid and a plane aluminium test surface as the baseline case, the experimental apparatus was validated by comparison of the determined heat transfer coefficient with Nusselt’s model of filmwise condensation on a vertical plane surface, where an excellent agreement was obtained. 7 different aluminium test surfaces were subsequently investigated, each one modified with grooves measuring 0.5mm by 0.5mm (height and width), with a consistent spacing of 0.5mm between them. Groove angles relative to the vertical axis of 0° (180°), 30°, 45°, 60°, 90°, 120°, and 150° were investigated, where grooves were symmetrically mirrored at the centre of each test surface. Results highlighted a significant influence of groove angle on the heat transfer coefficient, with the best-performing sample (150˚) producing a maximum enhancement of 45% and an average enhancement of 34% compared to the baseline test surface over the respective range of subcooling.

Analyzing the combustion characteristics of premixed methane-oxygen with different hydrogen addition ratios in a catalytic micro-combustor

Experimental and numerical study of premixed methane-oxygen combustion characteristics in a catalytic micro-combustor with different hydrogen addition ratios has been presented in this paper. The objective is to examine the effects of platinum catalysts and hydrogen additions on methane and oxygen combustion. The simulation of a three-dimensional micro rectangular model was carried out with a gas phase reaction mechanism combined with a surface reaction mechanism, and the model was validated with experimental results with a maximum deviation of just 1.56 percent. In the experimental phase, the effects of flammability limit, equivalence ratio, and inlet velocity were studied, while in the numerical phase, the effect of hydrogenation on combustion characteristics was investigated. Experimental results show that adding 10 % hydrogen to a premixed methane-oxygen mixture significantly increases its flammability limit. The maximum external wall temperature along the centerline was observed at an equivalent ratio of 1. Additionally, an increase in the inlet velocity leads to a corresponding increase in the external wall centerline temperature. Catalytic reaction wall temperatures show a gradual decline, with the highest temperatures located at the inlet. An observed trend revealed a decrease in the external wall centerline temperature as the hydrogen addition increased from 0 % to 40 % due to the reduced total heating value of the blended fuel. Due to its higher reactivity and ability to promote complete combustion, hydrogen also plays an important role in CH4 and O2 conversion. In addition, CO and CO2 emissions decreased with increased hydrogen percentage in fuel mixtures. Furthermore, hydrogen addition can reduce external wall heat losses as well. After adding 0–40 % hydrogen to a premixture of (CH4–O2) fuel, the total heat loss of the external wall was reduced from 19.48 W to 17.11 W.

Mathematical modeling of thermal impact on a closed hydrate-saturated reservoir

In 2014, a crater was discovered in Yamal near the Bovanenkovo oil and gas condensate field. A number of researchers indicate among the possible causes of its occurrence an avalanche-like release of gas formed during the dissociation of gas hydrates. To carry out numerical experiments for analyzing such phenomena, a mathematical model of gas-liquid flow in a saturated porous medium was constructed taking into account the phase transition “gas + water  gas hydrate”. A two-dimensional axisymmetric formulation of the problem of heating from above through impermeable rocks of a closed hydrate-saturated reservoir, initially containing gas hydrate and gas, was carried out; to take into account external heat exchange, it is assumed that the reservoir is surrounded by rocks impermeable to matter. An algorithm for numerically solving the equations of the mathematical model is presented. A series of calculations was carried out, on the basis of which an analysis was made of the processes occurring in a closed hydrate-saturated reservoir, namely, changes in temperature, phase saturations and pressure. Calculations have shown that during the dissociation of gas hydrate in a closed reservoir, for a certain set of parameters, a significant increase in pressure can occur from 2.7 to 17.4 MPa. It has been revealed that the shallower the depth of a hydrate-saturated reservoir, the smaller its size and the greater the initial hydrate saturation, the greater increase in pressure can be observed, and, accordingly, the greater risk of violating the integrity of a closed impermeable porous medium and the subsequent avalanche-like release of gas from such object.

Comparison of Microwave Versus Conventional Furnace Heat Treatments of Carbide Composite Thermal Spray Coatings

Thermal spraying has become an industrial standard in the production of wear-resistant WC-Co and Cr3C2-NiCr composite coatings. However, generating optimum wear-resistant nano-reinforced carbide microstructures within the coatings remains challenging. The alternative two-step approach in this work involves coating formation under high energy conditions to generate maximum carbide dissolution, followed by heat treatment to precipitate nanocarbides. Microwave heating of particulate materials has been reported to offer several benefits over conventional furnace heating, including faster heating rates, internal rather than external heating, and acceleration of reactions/phase transformations at lower temperatures. This novel work explored the use of microwaves for heat treatment (as distinct from melting) of WC-Co and Cr3C2-NiCr thermal spray coatings and contrasted the rate of phase development with that from conventional furnace treatment. Coatings were successfully microwave heat-treated to generate the same phase composition as furnace treatment. Both treatments generated comparable results in the Cr3C2-NiCr system. The WC-Co system achieved a much more crystalline structure in a dramatically shorter time relative to the conventional furnace-treated sample. The results are contrasted as a function of material and microstructure interaction with microwaves and the critical phase transition temperatures to account for the observed responses.

Effect of a vapor barrier in combination with active external rewarming for cold-stressed patients in a prehospital setting: a randomized, crossover field study

BackgroundUse of a vapor barrier in the prehospital care of cold-stressed or hypothermic patients aims to reduce evaporative heat loss and accelerate rewarming. The application of a vapor barrier is recommended in various guidelines, along with both insulating and wind/waterproof layers and an active external rewarming device; however, evidence of its effect is limited. This study aimed to investigate the effect of using a vapor barrier as the inner layer in the recommended “burrito” model for wrapping hypothermic patients in the field.MethodsIn this, randomized, crossover field study, 16 healthy volunteers wearing wet clothing were subjected to a 30-minute cooling period in a snow chamber before being wrapped in a model including an active heating source either with (intervention) or without (control) a vapor barrier. The mean skin temperature, core temperature, and humidity in the model were measured, and the shivering intensity and thermal comfort were assessed using a subjective questionnaire. The mean skin temperature was the primary outcome, whereas humidity and thermal comfort were the secondary outcomes. Primary outcome data were analyzed using analysis of covariance (ANCOVA).ResultsWe found a higher mean skin temperature in the intervention group than in the control group after approximately 25 min (p < 0.05), and this difference persisted for the rest of the 60-minute study period. The largest difference in mean skin temperature was 0.93 °C after 60 min. Humidity levels outside the vapor barrier were significantly higher in the control group than in the intervention group after 5 min. There were no significant differences in subjective comfort. However, there was a consistent trend toward increased comfort in the intervention group compared with the control group.ConclusionsThe use of a vapor barrier as the innermost layer in combination with an active external heat source leads to higher mean skin rewarming rates in patients wearing wet clothing who are at risk of accidental hypothermia.Trial registrationClinicalTrials.gov identifier: NCT05779722.

Entropy generation analysis for magnetohydrodynamic flow of chemically reactive fluid due to an accelerated plate

BackgroundThe mixed convection flow of viscous fluid due to an oscillating plate is inspected. The external heating effects and chemical reaction assessment are predicted. Moreover, the flow applications of the entropy generation phenomenon are claimed.ResultsThe dimensionless system is expressed in partial differential forms, which are analytically treated with the Laplace scheme. The physical aspects of the flow model are graphically observed. The optimized phenomenon is focused on flow parameters. The results for the Bejan number are also presented. The dynamic of heat transfer and entropy generation phenomenon is observed with applications of Bejan number.ConclusionsIt is claimed that an enhancement of entropy generation phenomenon is noticed due to heat and mass Grashof coefficients. The Bejan number declined due to mass Grashof number. Furthermore, the velocity profile boosted due to Grashof constant.

An experimental investigation of constrained melting of a phase change material (PCM) in circular geometries, part I: Velocity characterization

This study is focused on the detailed characterization of the transient velocity fields of a phase change material (PCM) enclosed in a geometry with a circular cross-section subjected to uniform external heating. Particle image velocimetry (PIV) was used to study the velocity behavior related to the buoyancy-driven convection. The PCM was initially subcooled, and the walls suddenly heated to exceed the melting temperature. Experiments were conducted using Rubitherm RT26 in a quasi-2D circular enclosure at three applied heating conditions. Detailed velocity fields show strong symmetric convective vortices at the sides of the PCM chamber, and a three-dimensional recirculation was detected near the bottom. These structures strongly influence the melting behavior. The results suggest self-similarity in flow behavior between heating conditions. Detailed transient temperature fields and an extended discussion of the associated heat transfer behavior are presented in the companion paper (Part II).

Numerical modelling of thermal jet assisted rock cutting with double PDC cutters

AbstractPreconditioning of rock for drilling operations is a potential method to facilitate the mechanical breakage and mitigate the tool wear. This paper numerically investigates one such preconditioning technique, namely, the thermal jet assisted rock cutting. For this end, a numerical method for solving the governing thermo‐mechanical problem is developed and validated. The continuum approach is chosen to describe the rock failure, being based on a damage‐viscoplasticity model with the Drucker–Prager yield surface and the modified Rankine surface as the tensile cut‐off. In the damage part, separate scalar damage variables are employed for tension and compression. The cutters are modelled as rigid bodies and their interaction with the rock is modelled by imposing contact constraints by the forward increment Lagrange multiplier method, which is compatible with the chosen explicit time integration scheme. A damage‐based erosion criterion is applied to remove the contact nodes surrounded by heavily damaged elements. The thermal jets are modelled with a moving external heat flux boundary condition. The global thermo‐mechanical problem is solved with a staggered approach explicitly in time while applying mass scaling to increase the critical time step. The novel 3D numerical simulations involving two cutters demonstrate the capabilities of the method with a special emphasis on cutter‐thermal jet configurations. Therefore, the present method provides a potential tool for the bit design in thermal jet assisted drilling.

New and effective combination of an absorption desalination systems with adsorption and humidification-dehumidification desalination systems utilizing internal heat recovery methods

The fast growth in population and the need for human comfort leads to a significant rise in freshwater shortage and energy usage. This article provides new and effective combinations between absorption (ABDC), adsorption (ADDC), and humidification-dehumidification (HDH) desalination plants. Four new configurations employing different external and internal heat recovery methods between the plants and their components are proposed to enhance the overall system performance, water production, and utilization of the used energy. In all configurations, the solar water heating system is used to power the ABDC. While the ADDC and HDH were powered by the heat recovery from condensation, absorption, or generation processes. Internal heat recovery methods are also applied between the evaporator and condenser in ABDC and ADDC plants to increase energy utilization. The results are evaluated and compared with standalone ABDC results and with previous related studies at different conditions. The production share percentage (%) from each plant for the suggested configurations with regeneration temperatures is also investigated. The maximum water production is achieved by the fourth configuration (3 m3.day−1 with a gain output ratio (GOR) of 1.316 at 120 °C) when the ADDC is worked by the outlet hot water from the ABDC, and internal heat recovery utilized between the condensation and evaporation components of both ABDC and ADDC. The highest GOR is obtained from the second configuration (1.714 at 90 °C). The finding expressed that the proposed configurations have a better performance than traditional ABDC systems. Also, the proposed configurations express another advantage over traditional ABDC, that the configurations have the potential at low-temperature heat sources (55–65 °C) to improve the water productivity to about 455 % and GOR to about 120 %.

Comprehensive investigation of the electro-thermal performance and heat transfer mechanism of battery system under forced flow immersion cooling

Efficient cooling during rapid battery charging/discharging necessitates forced circulating flow in immersion cooling systems. However, under forced flow immersion cooling (FFIC), the comprehensive impact on the electrical and thermal performance of battery modules remains inadequately explored. This study constructs an immersion-cooled battery module test platform for experimental research on the evolution of electrical and thermal characteristics. The results show that under FFIC, when the depth of discharge (DOD) during 2C and 3C discharges is below 85 %, the voltage deviation of module (δU,t) remains stable within 1 % and 2 %, respectively. At DOD of 100 %, the maximum δU,t for 2C and 3C are 10 % and 24.5 %, respectively. Furthermore, the analysis of Pearson correlation coefficient under FFIC reveals that the δU,t exhibits a very strong positive correlation with temperature difference of battery module and cell, with correlation coefficients of +0.94 and + 0.87, respectively. Higher flow rates accelerate the recovery of module temperature and facilitate voltage distribution equalization after discharge. Additionally, to elucidate the influence of flow rate on FFIC, module-scale heat transfer characteristics during battery discharge are theoretically analyzed, establishing a fitting relationship between C-rates, flow rates, and the Nusselt number (Nu). This study provides a comprehensive understanding of integrated electro-thermal performance and external heat transfer capability for flow regulation in immersion cooling.

Analysis of Fluid-Solid coupling heat transfer characteristics of hydrogen circulating pump

The hydrogen circulating pump (HCP) is in a high-temperature state during operation due to the heat generated by the pressure change of the transported gas. The current research on the flow characteristics of the HCP has not taken into account the influence of internal heat transfer factors, resulting in significant errors between the research results and actual test results. In this article, we define the contact modes of the fluid–solid interfaces based on heat transfer theory, propose a step-by-step calculation method based on different time scales, and complete the simulation of the fluid–solid coupling model. Compared with the test flow rate of 15.44 g/s, the fluid–solid coupling model considering heat transfer factors calculated a flow rate of 15.15 g/s with an error of only 1.85 %, while the single fluid model without considering heat transfer effects calculated a value of 14.67 g/s with an error of 5.0 %. Analyzing the internal mechanism of heat transfer leading to an increase in simulated flow rate, the external surface heat dissipation and internal heat conduction on one hand lead to a decrease in gap leakage flow rate, thereby reducing leakage volume, and on the other hand, increase the density of gas transported in the rotor cavity area, thereby improving the conveying capacity. The calculation method proposed in this article solves the problem of the large time difference between instantaneous fluid flow and slow heat transfer, shortens the calculation time, has higher calculation accuracy, and plays an important role in the precise design process of HCPs.

Expression of Cconcern: A numerical study of CsSnIxBr3-x perovskite material as an electron transport layer (ETL), in the perovskite solar cell of a photovoltaic system by molecular dynamics method with LAMMPS software: The effects of external convective heat transfer

Expression of Cconcern: A numerical study of CsSnIxBr3-x perovskite material as an electron transport layer (ETL), in the perovskite solar cell of a photovoltaic system by molecular dynamics method with LAMMPS software: The effects of external convective heat transfer

Energy efficiency analysis of novel combined open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer

Energy intensive thermal desalination and compressed air-drying processes coupled with low grade heat recovery units can significantly contribute to carbon and energy footprint reduction. In this paper, a novel combined system based on an open absorption multifunctional heat pump and FlashME desalination system with a compressed air dryer is proposed to recover the latent heat from flue gas and efficiently utilize it to drive the desalination process for seawater treatment and supply the compressed dry air. The energy performance of the combined system is analyzed under the effect of various key operational parameters by simulating the validated process model. The results of energy analysis indicate that the novel system can recover the latent waste heat from flue gas with an efficiency of 83.02 % and supply the compressed dry air at low humidity of 1.41 g/kg by operating at a thermal COP of 1.95. Furthermore, the system can efficiently utilize the recovered low-grade heat to produce freshwater at a recovery rate of 23.14 %. The findings of the critical performance analysis show that the drying, and latent heat recovery performance of the coupled system is dependent mainly on the inlet parameters of the spray solution and the flue gas humidity. However, the water recovery of FlashME is totally dependent on heat capacity and the regeneration pressure such that the performance ratio increases from 1.51 to 4.03 by operating with hot seawater of 60–80 °C, when the regeneration pressure is raised up to 53.48 kPa. Moreover, the coupled system configured in parallel double stage can lower 11.43–37.78 % regeneration load along with 54.24 % improvement in distillate productivity when the operating pressure is raised up to 800 kPa and the rise in airflow rate in dryer can decrease the 10.41–52.45 % regeneration load on external heat source.

One-click startup operation of a micro-tubular solid oxide fuel cells using propane/air/steam

The design and performance of a tubular solid oxide fuel cell (SOFC) integrated with a one-click startup thermal self-sustaining reformer is presented, allowing the tubular SOFC to operate without any external heat source by using propane/air/steam. Double conductive Ni-pads (DCNPs) are utilized as anode current collector in μT-SOFC. The reformer consists of a combustion chamber for initial heating and a reforming chamber for syngas production for the SOFC. The thermal energy generated by complete propane combustion is adequate to achieve thermally self-sustaining operation and efficiently raise the cell temperature above 700 °C. Operating at 700 °C with pure H2, a cell with a length of 12 cm achieves a maximum power density of 138 mW cm−2, which decreases by 13 %–120 mW cm−2 when using syngas produced by steam-propane reforming. The syngas composition from steam-propane reforming reaches 7.6 % CO and 61.7 % H2. COMSOL Multiphysics software is used to simulate the multi-physical field of a single cell exposed to various syngas compositions, showing that syngas produced by steam-propane reforming exhibits excellent electrochemical performance in tubular SOFCs compared to catalyst partial oxidation (CPOX).

The pool boiling heat transfer of ammonia/Fe3O4 nano-refrigerant in the presence of external magnetic field and heat flux: A molecular dynamics approach

Pool boiling is distinguished by its capacity to eliminate excessive heat fluxes (HFs) at low temperatures. In recent decades, the optimal design of flooded evaporators elevated the significance of pool boiling HT with refrigerant to conserve natural resources and energy. The industry highly regards this process on account of its superior heat transfer (HT) coefficient in comparison to other HT mechanisms. Among the types of boiling, pool boiling has a special place due to its ability to remove HFs at low temperatures. This study was the first to investigate the boiling characteristics of the ammonia/Fe3O4 nano-refrigerant in a copper (Cu) nanochannel (NC) through molecular dynamics (MD) simulations. The primary goal was to investigate the effect of external HF (EHF) and external magnetic field amplitude (EMFA) on nanostructures' atomic behavior (AB) and thermal behavior (TB). The research findings indicate that increasing the applied EHF led to increased particle movement and the HT rate. By changing the EHF, boiling behavior in the nano-refrigerant may also be seen. Maximum (Max) velocity (Vel.) increased to 8.970 Å/ps when the EHF increases to 0.5 W/m2. Atomic collisions and particle mobility both increase when the EHF increases. Therefore, the maximum temperature value increases to 359.46 K. When the EMFA applied to the nano-refrigerant reaches to 0.5 T, the maximum values of the parameters, such as the Temp. and the velocity, reach to 410.07 K, and 11.802 Å/ps, respectively.

Thermal-Rectified Gradient Porous Polymeric Film for Solar-Thermal Regulatory Cooling.

Solar-thermal regulation concerning thermal insulation and solar modulation is pivotal for cooling textiles and smart buildings.Nevertheless, a contradiction arises in balancing the demand to prevent external heat infiltration with the efficient dissipation of excess heat from enclosed spaces. Here, a concentration-gradient polymerization strategy is presented for fabricating a gradient porous polymeric film comprising interconnected polymeric microspheres. This method involves establishing an electric field-driven gradient distribution of charged crosslinkers in the precursor solution, followed by subsequent polymerization and freeze-drying processes. The resulting porous film exhibits a significant porosity gradient along its thickness, leading to exceptional unidirectional thermal insulation capabilities with a thermal rectification factor of 21%. The gradient porous film, with its thermal rectification properties, effectively reconciles the conflicting demands of diverse thermal conductivity for cooling unheated and spontaneously heated enclosed spaces. Consequently, the gradient porous film demonstrates remarkable enhancements in solar-thermal management, achieving temperature reductions of 3.0 and 4.1°C for unheated and spontaneously heated enclosed spaces, respectively, compared to uniform porous films. The developed gradient-structured porous film thus holds promise for the development of thermal-rectified materials tailored to regulate solar-thermal conditions within enclosed environments.

An empirical study on thermal efficiency and dusty moisture removal efficiency using enthalpy wheel in industrial waste incineration plant

In this work, an empirical study is conducted on the waste heat recovery and moisture removal performance of an enthalpy wheel installed in an industrial waste incineration plant. The enthalpy wheel made of a metal mesh is placed in parallel with the wet scrubber of the incineration plant to exchange heat with high-temperature exhaust at 200 °C. In the enthalpy wheel, exhaust gas and external air exchange heat in the form of a counter flow, and the condensation effect is maximized by installing a water-spray nozzle at the inlet of the enthalpy wheel. Empirical data were collected over 100 days spanning July to October. To evaluate the performance of the enthalpy wheel, thermal efficiency, moisture removal efficiency, and dust removal efficiency were tested under high-temperature humid conditions. In some results, the overall thermal efficiency reached peaked at 61.2 %. Regarding moisture removal performance, the average moisture removal rate was 493 kg/h, affording an efficiency of 49.2 %. In terms of dust removal performance, the average dust removal efficiency was 79.6 %.

Sex-specific effects of environmental temperature during gestation on fluctuating asymmetry in deciduous teeth.

External environmental heat exposure during gestation impacts the physiology of human development in utero, but evidence for these impacts has not yet been explored in dentition. We examined deciduous teeth for fluctuating asymmetry (FA), a measure of developmental instability, together with gestational environmental temperature data drawn from historical weather statistics. We measured dental casts from the longitudinal Burlington Growth Study, representing 172 participants (ages 3-6 years) with health records. FA was calculated from crown dimensions and intercuspal distances that develop during gestation. Multiple regression separated by sex (nfemale = 81) examined the effects of mean temperatures in each trimester, controlling for birth year. In females, increased temperatures during the first trimester are significantly associated with an increase in FA (p = 0.03), specifically during the second and third prenatal months (p = 0.03). There is no relationship between temperature and FA for either sex in the second or third trimesters, when enamel is formed. Dental instability may be sensitive to temperature in the first trimester in females during the scaffolding of crown shape and size in the earliest stages of tooth formation. Sexual dimorphism in growth investment strategies may explain the differences in results between males and females. Using enduring dental characteristics, these results advance our understanding of the effects of temperature on fetal physiology within a discrete period.