Central Heat Source Research Articles

Experimental Investigation on Thermal Performance of Vapor Chambers with Diffident Wick Structures

In this paper, a type of vapor chamber with a gradient pore size wick (VC-G) was developed, and its thermal performance was experimentally tested and compared with two types of VCs with uniform pore size wick (which can be defined as VC-U (200) and VC-U (50) as the powder size of the wick is 50-mesh and 200-mesh, respectively) and a VC without a wick (VC-N). In addition, a VC heat transfer ability experiment platform was built, and the thermal resistance, temperature distribution and thermal response time of the VC with different wick structures were experimentally investigated. The experiment results show that the capillary driving force provided by gradient pore size wick increases gradually from outside, which can not only promote the condensation fluid to gather in the central heat source but also facilitate the vapor to spread around. Therefore, compared with VC-U (200), VC-U (50) and VC-N, VC-G shows the best heat transfer performance, temperature uniform performance and start-up performance.

Warm Molecular Gas in the Central Parsecs of the Buried Nucleus of NGC 4418 Traced with the Fundamental CO Rovibrational Absorptions

We investigated the inner buried nucleus of a nearby luminous infrared galaxy, NGC 4418, using high-resolution spectroscopy of fundamental carbon monoxide (CO) rovibrational absorptions around 4.67 μm for the first time. This method allowed us to examine the physical and kinematical properties in the hot inner region of this nucleus. We detected a series of both very deep (partly saturated) 12CO and moderately deep (optically thin) 13CO absorption lines and inferred a large column density (N H2 = (5 ± 3) × 1023 cm−2 in front of the 5 μm photosphere) of warm (T ex ≃ 170 K) molecular gas by assuming an isothermal plane-parallel slab illuminated by a compact background mid-infrared-emitting source. We modeled that the warm CO absorber almost covers the central heating source and that it is an inner layer around the 5 μm photosphere (at r = several parsecs) of a compact shroud of gas and dust (d ∼ 100 pc). The width of the absorption lines (110 km s−1) and their small deviation from the systemic velocity (<10 km s−1) are consistent with a warm and turbulent layer with little bulk motion in the radial direction.

Design and In Situ Additive Manufacturing of Multifunctional Structures

Multifunctional structures (MFSs) integrate diverse functions to achieve superior properties. However, conventional design and manufacturing methods—which generally lack quality control and largely depend on complex equipment with multiple stations to achieve the integration of distinct materials and devices—are unable to satisfy the requirements of MFS applications in emerging industries such as aerospace engineering. Motivated by the concept of design for manufacturing, we adopt a layer regulation method with an established optimization model to design typical MFSs with load-bearing, electric, heat-conduction, and radiation-shielding functions. A high-temperature in situ additive manufacturing (AM) technology is developed to print various metallic wires or carbon fiber-reinforced high-melting-point polyetheretherketone (PEEK) composites. It is found that the MFS, despite its low mass, exceeds the stiffness of the PEEK substrate by 21.5%. The embedded electrics remain functional after the elastic deformation stage. Compared with those of the PEEK substrate, the equivalent thermal conductivity of the MFS beneath the central heat source area is enhanced by 568.0%, and the radiation shielding is improved by 27.9%. Moreover, a satellite prototype with diverse MFSs is rapidly constructed as an illustration. This work provides a systematic approach for high-performance design and advanced manufacturing, which exhibits considerable prospects for both the function expansion and performance enhancement of industrial equipment.

Magnetohydrodynamic mixed convection of TiO2–Cu/water between the double lid-driven cavity and a central heat source surrounding by a wavy tilted domain of porous medium under local thermal non-equilibrium

The magnetohydrodynamic (MHD) mixed convection of heat and mass transfer is carried out using finite difference method applied inside a tilted porous cavity saturated with a hybrid nanofluid due to the presence of the double-moving lid and the heat sources. In contrast to the earlier research, various effects which are recognized by heat generation in the local thermal non-equilibrium case at the extended Brinkman Darcy model subjected to inclined magnetic field are thoroughly examined numerically. For instance, unusual observations of the cold mass surrounding the heat source emphasize that the maximum fluid temperature highly depends on the forced convection. Additionally, solid-phase temperature acts in accordance to the heat source location while fluid temperature is agitated by the moveable sides which points up the disparity at the thermal energy transportation. However, the transfer of heat and mass at the model requires a specific conduct due to the existence of damping factors. The magnetic field, for example, suppresses the fluid flow. Moreover, the thermal non-equilibrium condition deteriorates the global heat generation.

Experimental study in thermal expansion devices of phase-change material coupled to vapor chamber with gradient wettability wick

With the rapid development of electronics and communication technology, the applications of high-performance chips and large-scale integrated circuits have become more and more widespread. Most electronic devices have low heat generation in standby mode but large heat generation during operation, and the instantaneous temperature rise is fast. The problems of resistance to thermal shock and heat dissipation have become the bottleneck of the development of electronic technology. Phase-change thermal control technology uses phase change materials to control the temperature of electronic devices with short-term high output power. It has the advantages of reliable performance, economical and energy saving. The temperature uniformity of the bottom surface is conducive to heat expansion in the interior of the phase change material, which is promoting to the phase ratio with the finite volume phase change material. In this article, a kind of novel thermal expansion device coupled PCM (paraffin OP50E) heat sinks with vapor chambers was proposed, which were applied with gradient wettability capillary wick. The copper microcolumns clusters as the capillary wicks in these vapor chambers were grown by electroplating on copper substrate plates covered with photolithography masks using the progressive current method. By changing the characteristic scales of the microcolumn clusters from 100 μm to 10 μm, the gradient capillary pressure direction was concentrated from the periphery to the middle, and the surface wettabilities of the capillary wicks were changed from hydrophilic to superhydrophilic. From the analysis of the experimental results, the vapor chambers with gradient wettability wicks can shorten the thermal response time of the thermal expansion device by 81.7 %, and at the same time, reduce the temperature at the center of the heat source with a heat flux of 40 W/cm2 by 6.8 °C, which can be applied to effectively control the central heat source temperature of the pulsed short-time electronic device.

Thermo-Hydromechanical Coupling Responses Driven by a Central Heat Source in Unsaturated Soils

Based on the thermodynamic and thermoelastic theory, the coupled governing equations of deformation, heat transfer, and moisture migration in unsaturated soils were given. The coupled calculation process was realized by the finite element method. The hydrothermal coupling characteristics of two cases of unsaturated kaolin clay were studied by using a self-developed test device, and the test results were compared with the numerical results. The results showed that when the initial saturation of the soil is high, the volumetric water content of the measured point increases, and then it is in a stable state during the heating process. When the initial saturation is low, the volumetric water content near the heat source increases firstly and then decreases during the heating process. The rise and fall of temperature make the volumetric water content of the soil irreversible. The volumetric water content of each measured point is lower than the initial state. The closer it is to the internal measured heat source, the more obvious this phenomenon is; the lower the initial saturation is, the more obvious it is.

Experiment for validation of numerical models of coupled heat and mass transfer around energy cables

AbstractThe increasing decentralization of electrical energy production as well as an increasing number of fluctuating regenerative energy sources require significant investments in grid expansion. Among other assessments, an exact prediction of the thermal behavior of the cable environment is necessary to be able to design cable routes both technically and economically sufficient. To investigate the coupled thermal and hydraulic processes around a cable‐like heat source with high temporal and spatial resolution under controlled boundary conditions, a cylindrical laboratory test was designed and experiments with two soils conducted. The data collected can be used to validate models of coupled heat and mass transfer around power cables. Within this study, the experimental data was compared with a modified model approach that is based on experimentally determined input data for the thermal and hydraulic properties of the examined soils. Although overall good agreement in the temperature field around the central heat source was observed, differences in the spatial distribution of the dry‐out zone near the heat source led to some shift between the measured and simulated temperatures.

Economic comparison of 4GDH and 5GDH systems – Using a case study

For decades the focus of district heating (DH) has been on energy efficiency and minimum operating temperatures. This quest for continuous efficiency improvements led to the modern 4th generation of DH (4GDH), operating at lowest possible temperature for direct utilization by end-user. In recent years the term 5th generation DH (5GDH) has become popular for individual heat pump systems sharing thermal sources via uninsulated pipe network. While 5GDH has similarity with 4GDH it is a technically different solution, as the heat generation is moved to the end-users. When discussing 4GDH and 5GDH the focus quickly revolves about the efficiency of the distribution grid, however the discussion should be on the overall system efficiency and the levelized cost of the heat (LCOH). This paper analyzes LCOH for a mixed building area consisting of a central heat source, high or low energy buildings connected to 4GDH, 5GDH or a 4GDH variant with end-user temperature boosting for domestic hot water purposes. The analysis considers two countries: DK and UK. The analysis further explores the impact of the heat source temperature, from 10 °C to 60 °C, on the LCOH. The results indicate that 4GDH is the more competitive heat supply solution for the considered case.

Implementing prosumers into heating networks

This article investigates possibilities for including prosumer structures in heating networks. Therefore, the performance of three different heating system scenarios for a new housing district is investigated. Low (60 °C) and ultra-low (20 °C) network temperatures are investigated. The case study includes about 100 different single-family and multi-family houses. Two scenarios contain networks with temperatures of 20 and 60 °C. The third scenario is extended with solar collectors and a supermarket as decentralised prosumers who supply heat to the network in times of surplus. The network can simulate bidirectional flows. Based on the principles of graph theory, a combined hydraulic and thermal model is developed and used for this study. The results show a heat loss reduction in ultra-low temperature networks due to lower network working temperatures (20 °C) of about 80% compared to a low-temperature network. The implementation of prosumers considerably reduces the demand from a central heat source. In this study, 20% of the total heating demand can be covered by excess heat of the prosumer supply.

Fountains and storms: the effects of AGN feedback and mergers on the evolution of the intracluster medium in the romulusc simulation

ABSTRACT The intracluster medium (ICM) is a multiphase environment, dynamically regulated by active galactic nuclei (AGN), the motions of cluster galaxies, and mergers with other clusters or groups. AGN provide a central heating source capable of preventing runaway cooling flows and quenching star formation, but how they achieve this is still poorly understood. We investigate the effects of AGN feedback and mergers on the ICM using the high-resolution romulusc cosmological simulation of a 1014 M⊙ galaxy cluster. We demonstrate that AGN feedback regulates and quenches star formation in the brightest cluster galaxy gently, without any explosive episodes, and co-exists with a low entropy core with sub-Gyr cooling times. In contrast, the merger disrupts the ICM structure, heating the core and cutting off the supply of low-entropy, infalling gas that until then fuelled the AGN. We find that this removal of the low-entropy phase correlates with the ratio tcool / tff increasing above 30 in the core, matching observations that cooling gas is only found in clusters where this ratio is 5–30. Importantly, we find that evolution in the inner entropy profile and the ratio of cooling to free-fall time-scale are directly connected to the quenching of star formation in the BCG. This is in line with previous results from idealized simulations and confirmed here within a fully cosmological simulation for the first time.

The Greenhouse Effect in Buried Galactic Nuclei and the Resonant HCN Vibrational Emission

Abstract Recent interferometric observations have shown bright HCN emission from the ν 2 = 1 vibrational state arising in buried nuclear regions of galaxies, indicating an efficient pumping of the ν 2 = 1 state through the absorption of 14 μm continuum photons. We modeled the continuum and HCN vibrational line emission in these regions, characterized by high column densities of dust and high luminosities, using a spherically symmetric approach, simulating both a central heating source (active galactic nucleus, AGN) and a compact nuclear starburst (SB). We find that when the H2 columns become very high, N H2 ≳ 1025 cm−2, trapping of continuum photons within the nuclear region dramatically enhances the dust temperature (T dust) in the inner regions, even though the predicted spectral energy distribution as seen from the outside becomes relatively cold. The models thus predict a bright continuum at millimeter wavelengths for a luminosity surface brightness (averaged over the model source) of ∼108 L ⊙ pc−2. This greenhouse effect significantly enhances the mean mid-infrared intensity within the dusty volume, populating the ν 2 = 1 state to the extent that the HCN vibrational lines become optically thick. AGN models yield higher T dust in the inner regions and higher peak (sub)millimeter continuum brightness than SB models, but similar HCN vibrational J = 3–2 and 4–3 emission owing to both optical depth effects and a moderate impact of high T dust on these low-J lines. The observed HCN vibrational emission in several galaxies can be accounted for with an HCN abundance of ∼10−6 (relative to H2) and luminosity surface brightness in the range (0.5–2) × 108 L ⊙ pc−2, predicting a far-infrared photosphere with T dust ∼ 80–150 K, in agreement with the values inferred from far-infrared molecular absorption.

Successive melting and solidification of paraffin–alumina nanomaterial in a cavity as a latent heat thermal energy storage

Latent heat thermal energy storage (LHTES) plays a main role in many industrial applications, especially in high-powered electronics cooling systems and providing the thermal energy demand when the energy supply is unavailable. In this study, the LHTES cycle process, including successive melting and solidification, investigates in a two-dimensional annular space of a square cavity filled with nanomaterial of paraffin–alumina as a nanoPCM. In the melting process, all sidewalls of the cavity are insulated. Meanwhile, a constant heat rate generates homogeneously within the central heat source. At the end of melting, the heat generation gets off, while a time-reducing temperature lower than the paraffin melting point imposes on the sidewalls, and then, solidification triggers. The numerical simulation was accomplished using control volume method and the governing equations solved using the SIMPLE algorithm. The enthalpy-porosity method was employed to model the phase-change front. The value of thermal conductivity and the viscosity of the nanofluid have been experimentally measured before the numerical modeling. In this study, the effect of volume fraction of nanoparticles (0–0.03) has been investigated on the successive melting and solidification rate for a constant Rayleigh number of 5.74 × 105. The results show that adding nanoparticles to the PCM equal to the volume fractions of 0.01 and 0.02 improves melting rate, but the nanofluid with the volume fraction of 0.03 represents a poor heat transfer rate during melting even weaker than those for nanofluid with the volume fraction of 0.01. It also observed that the nanomaterial with the volume fraction of φ = 0.03 represents the highest solidification rate. However, taking the overall performance of successive melting and solidification system into account, the nanofluid with the volume fraction of 0.02 remarked the most effective heat transfer rate in comparison with the other examined cases.

Experimental analysis of radiators’ thermal output for heat accounting

Radiators represent the most spread heating body (installed since late 1800s) and in the last decades different radiators typologies have been proposed on the market, characterized by different materials, sizes, shapes, etc. Recent EU Directive on energy efficiency has set the obligation to install individual meters for space heating in building served by a central heating source. To this aim, when direct heat meters are not technically feasible, indirect systems like heat cost allocators are applied on each radiator in a dwelling and the knowledge of single radiators’ thermal output is essential for an accurate and fair heat cost sharing. The EN 442:2014 describes a method for radiators’ thermal output measurement whose expanded uncertainty is lower than 1% in reference laboratory conditions. However, radiators’ thermal output is strongly dependent on installation and boundary conditions. Thus, to get radiators’ thermal output at operating conditions “characteristic equations” are available but, unfortunately, they do not include any possible actual operating condition among which: installation position with respect to the wall and the floor, presence of grid/shelf/niche or an obstruction (e. g. caused by curtains), thermo-fluid-dynamic condition variations (inlet flow rate and temperature), and hydraulic connections. In this paper, the experimental results of thermal output measurement of different radiators typologies (cast iron, aluminum) at different installation conditions are presented, together with an analysis of the associate technical-economic effects on space heating cost sharing. Reductions of radiators’ thermal output up to 15% due to hydraulic connections and between 10% and 20% due to flow-rate variations have been found. Furthermore, different installation conditions showed deviations between operating and standard radiators’ thermal output between 5% and 15%.

DETERMINATION OF THERMAL PROPERTIES OF COFFEE BEANS AT DIFFERENT DEGREES OF ROASTING

&lt;p&gt;The aim of this study was to determine the main thermal properties of the granular mass of coffee (specific heat, thermal conductivity, and thermal diffusivity) for different degrees of roasting, as well as to model and simulate thermal conductivity at different degrees of roasting. For determination of specific heat, the mixing method was used, and for thermal conductivity, the theoretically infinite cylinder method with a central heating source. Thermal diffusivity was simulated algebraically using the results of the properties cited above and of the apparent specific mass of the product. Thermal conductivity was also simulated and optimized through finite element analysis software. At darker roasting, there was an increase in specific heat and a reduction in thermal conductivity and thermal diffusivity. Comparing thermal conductivity determined in relation to simulated and optimized conductivity, the mean relative error was 1.02%, on average.&lt;/p&gt;

High-temperature thermal manipulator using thermal metamaterials based on transformation thermodynamics

A thermal manipulator for use in high temperature environments was designed and constructed based on the coordinate transformation method of transformation thermodynamics. The thermal manipulator has two key functions: (1) Guides the heat flux from one region (the center heat source) and (2) Concentrates the guided heat flux to multiple distributed regions outside. The thermal manipulator uses multiple fan-shaped thermal concentrators around the heat source. The fan-shaped concentrators with highly anisotropic thermal conductivities were made of two isotropic materials, copper and a synthesized silica-alumina fibrous matrix, with a working temperature upper limit of 1000°C. Simulations and experiments show that the copper-based metamaterial thermal manipulators can efficiently guide the heat flux from the central heat source and concentrate the heat flux at multiple distributed regions in a high-temperature environment. The thermal manipulator heat flux concentration efficiency was 55.4% with a region concentration ratio of 2.50 which indicates a very strong heat concentration capability which is more than twice that of traditional isotropic materials. Thus, this research provides an effective thermal manipulating method for high-temperature conditions.

Screen-printed radial structure micro radioisotope thermoelectric generator

The micro radioisotope thermoelectric generator can be invoked as a long-life power supply in low-power device applications. Improving the current, voltage and power of power sensors by enhancing the properties of thermoelectric material composites matters in low-power device applications. The micro radioisotope thermoelectric generator driven by the temperature difference between radial thermoelectric legs printed on polyimide substrate and the loaded central heat source is reported in this study. The electrical conductivity of n-type Bi2Te2.7Se0.3, p-type Bi0.5Sb1.5Te3, and p-type Sb2Te3 radial thermoelectric legs are 24.57–165.8 S·cm−1, with Seebeck coefficients of −176.6, 223.3 and 139.7 µV·K−1 respectively. Thermoelectric legs are prepared by screen printing with a paste consisting of epoxy resin and BiTe-based powders. The generator has five couples of radial thermoelectric legs, and their material properties are optimized through selecting the preliminary curing temperature. The electrical conductivity of n-type Bi2Te2.7Se0.3, p-type Bi0.5Sb1.5Te3, and p-type Sb2Te3 thermoelectric legs are 24.57–165.8 S·cm−1, with Seebeck coefficients of −176.6, 223.3 and 139.7 µV·K−1 respectively. When loaded with 1.5 W isotope heat sources, the prototype generator would generate an open-circuit voltage of 68.41 mV, a short-circuit current of 329.0 µA, and an output power of 5.81 µW at 39.20 mV. Stacking and series-parallel can harvest considerable energy.

A new heat cost allocation method for social housing

To promote energy saving in the residential sector Directive 2012/27/EU has set the obligation for buildings supplied by central heating sources to install individual heat metering and accounting systems. However, in social housing, bills based exclusively on individual consumption should be unfair due to some unfavourable situations, such as first and top floors, presence of unheated common spaces, north oriented dwellings. Nevertheless, fair heat accounting rules should be introduced especially in social housing buildings, which are often thermally underperforming with inefficient heating plants and tenants are commonly low-income people and elderly. On the other hand, common regulations for heat accounting providing compensation to avoid inequalities among tenants have not been set and different approaches on this topic are present among EU Member States. In this paper the authors present a new heat accounting method for social housing based on the estimation of extra-consumptions due to building inefficiencies. According to this method, extra-consumptions are charged to all tenants in order to encourage energy efficient retrofit interventions. Finally, the new method has been experimented in a typical social housing building in Italy and compared to other methods applicable in EU, evidencing some advantages and weaknesses.

Estimating the impact of heat accounting on Italian residential energy consumption in different scenarios

Directive 2012/27/EU has set the obligation for buildings supplied by central heating sources, or by district heating/cooling networks, to install individual heat metering and accounting systems. In Italy, almost 5 million dwellings are potentially subject to this obligation. To estimate the related potential benefit the knowledge of the energy saving achievable from the installation of such systems is needed. Unfortunately, in literature a wide range of variability of this benefit has been found and studies regarding Italian buildings are still lacking. The present study is aimed to estimate the impact of this EU policy in terms of potential energy saving in Italy. To this end, the authors first performed an experimental campaign on about 3000 dwellings located in major Italian cities, to assess the potential benefit obtainable. A model to estimate the energy consumption for space heating in the residential building stock has then been developed considering the building typologies and their main technical characteristics. An average benefit of about 11% has been found, leading to an estimated energy saving at national level ranging from 0.3% to 1.9% of whole energy consumption for space heating, depending on the effectiveness of applicable economic incentives and legal obligation scenarios.

Analysis of the energy efficiency of the implementation power electric generated modules in the CHS

Application on the Central heat source (CHS) local generation of electricity is primarily aimed at solving problems of own needs of electric energy that not only guarantees the independence of the work of the CHS from external electrical networks, but will prevent the stop of heat supply of consumers and defrosting heating networks in case of accidents in electrical networks caused by natural or anthropogenic factors. Open the prospects of electric power supply stand-alone objects, such commercial or industrial objects on the territory of a particular neighborhood.

Investigating the effect of Brownian motion models on heat transfer and entropy generation in nanofluid forced convection

In this study the influence of Brownian motion models on fluid-flow, heat transfer, and entropy generation in nanofluid forced convection with variable properties has been numerically inspected in a enclosure with central heat source. The governing equations were solved by finite volume method and SIMPLER algorithm. The numerical study was carried out for Reynolds numbers between 10 and 1000 and nanoparticles volume fraction between 0 and 0.04. The numerical results show that for all investigated models the average Nusselt number increases by nanoparticle volume fraction increment in all Reynolds number. The overall entropy generation behavior is similar to average Nusselt number variation for all inspected models. Among all analyzed models the estimation of Maxwell-Brinkman and Das-Vajjha are mainly closed to each other.