Steady-state Heat Transfer Characteristics Research Articles

Preparation and steady-state heat transfer characteristics analysis of building insulation phase change composite material

The compatibility of Ba(OH)2?8H2O with aluminum alloy and copper after 50 heating cycles was studied using SEM and high power X-ray diffraction technique. Analyze the effect of temperature on thermal stability. The results show that Ba(OH)2?8H2O has some corrosion resistance to aluminum alloys and is similar with copper. The Ba(OH)2?8H2O/foam copper phase transition composites were prepared by a simple vacuum adsorption filling method. The experimental process of phase change energy storage device with and without copper foam was established, and the continuous heat transfer and transformation of Ba(OH)2?8H2O/foam copper phase change composites were carried out at room temperature. The results show that compared with pure Ba(OH)2?8H2O, Ba(OH)2?8H2O/foam copper phase converter has faster heat transfer and better thermal conductivity, effectively reducing the supercooling effect of Ba(OH)2?8H2O. Heat transfer experiment at high temperature shows that the heat capacity of Ba(OH)2?8H2O/foam copper phase changes with the increase of temperature. When the temperature of the zone is higher than the material phase changes in temperature, some insulation measures should be taken for phase shifting components.

Enhancement of pool boiling performance through an asymmetric dual V-groove microchannel structured surface

In pool boiling, microchannels on the heated surface change the bubble dynamics and consequently improve the heat transfer. In this study, two new microchannel configurations, i.e., asymmetric dual V-groove microchannels (VM) and orthogonally intersecting asymmetric dual V-groove microchannels (OIVM) have been introduced to study enhancement in pool boiling. The heat transfer enhancement due to the modified surfaces was established by comparing the heat transfer rates from the reference flat surface. Experiments have been performed using deionized water under saturation temperature at one atmosphere to evaluate the steady state heat transfer characteristics. The bubble dynamics and interface morphology at various heat flux levels have been captured using high-speed camera. The experimental observations have revealed that both the microchannel configurations exhibit a substantial improvement in heat transfer compared to that of flat surfaces. The OIVM surface demonstrates the highest rates of heat transfer and increase of 5.3 times in the maximum heat transfer coefficient (HTC) and 2.4 times in the critical heat flux (CHF) were observed compared to that of flat surfaces. Similarly, the VM surface demonstrates an improvement of 2.2 fold in HTC and 1.7 fold in CHF compared to the flat surface. Moreover, the OIVM surface demonstrates better heat transfer rates than that of modified surfaces investigated in the past studies. The increased heat transfer rate with the OIVM surface can be ascribed to large area for heat exchange, increased bubble initiation sites, bubble motion promoted macroconvection and efficient rewetting mechanism.

Numerical analysis of steady-state heat conduction behavior in high-temperature superconductor Roebel cable

In this work, the steady-state heat transfer characteristics of REBCO tape and impregnated Roebel cable are studied numerically. By establishing three-dimensional finite element models of tape and impregnated cable, the temperature-dependent equivalent thermal conductivities of REBCO tapes and impregnated Roebel cables are estimated based on numerical homogenization technique. Effects of different geometric and material parameters are discussed. The steady-state heat transfer characteristics of a transposed tape in Roebel cable are further investigated. The equivalent thermal conductivities of REBCO tape or impregnated cable show strong anisotropy. Various sensitivities to geometric and material parameters are observed in equivalent thermal conductivities. The total heat flux distribution of the transposed tape is closely related to the Roebel angle and the curvature radius at outer corner or inner corner of this region. The corresponding structure and components should be optimized in actual application.

Energy management of ultra-short-term optimal scheduling of integrated energy system considering the characteristics of heating network

In view of the differences in transmission delay and transmission loss between heating network and power-grid in the integrated energy system, an ultra-short-term optimal scheduling energy management considering the characteristics of heating network is proposed in this pape. Based on graph theory, a heating network model suitable for system optimal scheduling is established. Considering the transient characteristics of the thermal medium temperature, the theoretical basis for judging the transient and steady-state heat transfer characteristics of the pipeline according to the scheduling period and the length of the pipeline is derived. The optimal operating state and daily operating cost of the equipment under three scenarios (considering the transient heat transfer characteristics of the heating network, considering the steady-state heat transfer characteristics of the heating network, and not considering the heat transfer characteristics of the heating network) are respectively compared. The calculation example analysis and verification show that the heat storage characteristics caused by the complex topology and transmission delay of the heat network change the matching of the supply and demand of the thermal power of the system, and the thermal power of the supply and demand side is no longer matched in real time. The ultra-short-term optimal scheduling energy management considering the transient heat transfer characteristics of the heating network has the regulation potential of the IES electric-thermal economic optimal operation under the excitation of time-of-use electricity price, and effectively makes use of the complementary characteristics of the electric and thermal systems to reduce the operation cost of the integrated energy system.

Correlations for heat transfer characteristics of the onset of nucleate boiling in submerged jet impingement

The submerged jet impingement boiling is one of the most effective heat transfer methods in dissipating both transient and steady concentrated heat loads. However, studies on the submerged jet impingement boiling still lack experimental data, especially for the heat transfer characteristics of the onset of nucleate boiling (ONB). Therefore, an experimental study of a submerged circular jet impinging on a polished copper surface is conducted in the subcooled water. The experiments investigate the steady-state heat transfer characteristics at the stagnation point from single phase convection to partial nucleate boiling. The effects of jet Reynolds number, liquid subcooling, and nozzle diameter on the onset of nucleate boiling are systematically studied. The experimental results show that the single phase convective heat transfer can be enhanced by increasing jet velocity at a fixed nozzle diameter or decreasing nozzle diameter under the same jet Reynolds number. The liquid subcooling seems to have negligible effect on the single phase heat transfer coefficient. For the ONB point, it is found that the ONB wall superheat is not influenced by liquid subcooling or jet parameters. The ONB heat flux, on the other hand, is found to depend on the experimental parameters. Increasing the jet Reynolds number and liquid subcooling, or decreasing the nozzle diameter could broaden the single phase convective regime and delay the onset of nucleate boiling, in terms of heat flux. Empirical correlations are proposed for predicting the stagnation point heat transfer coefficient, heat flux, and wall superheat at the ONB point. The comparison between the predicted values and the experimental data indicates that the empirical correlations are able to predict the heat transfer characteristics of the onset of nucleate boiling within an acceptable accuracy under the applicable range.

A Numerical Approach to Study the Steady State Heat Transfer Characteristics of an Annular Porous Heat Exchanger

Heat exchangers are one of the most heavily studied devices and extensive work has been performed over the years to increase their effectiveness. The present work investigates the heat transfer characteristics of an APHE (annular porous heat exchanger) in terms of different parameters. A modified design for the APHE is proposed, which resembles a conventional double pipe heat exchanger, with the annular portion of the outer pipe filled with a specific type of porous medium in order to intensify the heat transfer process. Commercial CFD package ANSYS Fluent has been utilized to investigate the performance of the proposed design numerically. Introduction of porous medium induces an increase in pressure loss which is undesirable; hence, a trade-off is present between hydrodynamic and thermodynamic performance. In the present work different inlet parameters have been modified such as different values of porosity (70% to 90%), different inlet velocities of hot fluid (1 m/s to 9 m/s), different inlet velocities of cold fluid (5 mm/s to 25 mm/s), and different inlet temperature of hot fluid (400 K to 480K), and their effects on the outlet parameters have been studied. The change in heat transfer has been presented quantitatively along with other significant parameters such as mass flow rate, pressure drop and hot gas outlet temperature. These results have been compared with the values for conventional heat exchangers in order to establish the effectiveness of APHE.

Transient heat transfer characteristics of swirling and non-swirling turbulent impinging jets

A multitude of research has already been undertaken to examine the effects of imparting swirl (S), Reynolds number (Re), and nozzle-to-plate distance (H/D) on the steady-state heat transfer characteristics of turbulent impinging jets. However, no studies to date have compared the transient development of such jets in both swirling and non-swirling conditions. The current paper addresses this gap by using highly resolved (time series) imaged (infrared) data in conditions spanning Re = 11,600, 24,600, and 35,000. The experiments are based on an electrically heated foil (0.025 mm) with jets over S = 0–1.05 and nozzle-to-plate-distances of H/D = 2, 4, and 6.For non-swirling impinging jets, at greater Reynolds numbers, the location of the highest Nusselt number remains fixed for all the time steps in contrast to jets with low Reynolds number. The transient characteristics for H/D = 4 are distinct compared to H/D = 2 and 6, with impingement heat transfer taking more time to reach steady-state for H/D = 4. It is also seen that heat transfer distribution over the impingement plate changes significantly over the small interval of time. For swirling jets, the impingement plate heat transfer characteristics develop simultaneously for the stagnation and wall jet region. The peak Nusselt number shifts to the wall jet region as the intensity of swirl increases. Two correlations (first for non-swirl and low-swirl, later for moderate to high swirl) are proposed to predict the time needed to reach steady-state for Re = 35,000.

Experimental study on steady-state heat transfer characteristics of the Nozzle-atomized dispersed flow

The fast neutron reactor, one of the promising generation-IV nuclear reactors, particularly requires its coolant to have a strong capacity of transferring heat allied with a weak ability of moderating neutrons, and thus a new scheme of applying the dispersed flow as the coolant is presented in this study. Such a flow was generated by injecting subcooled droplets into the overheated steam with the help of a nozzle, simply referred to as the nozzle-atomized dispersed flow. The obtained heat transfer coefficients maintain high values, vary from 40 to 90 kW/m2/K and are greatly improved as high as 50 times compared to those of the traditional annular-mist flow. The result implies that the nozzle-atomized dispersed flow, especially in the saturated boiling region, meets the heat transfer requirements of the coolant for a fast neutron reactor. Through meticulous analyses, appropriately higher inlet pressure, increased wall heat flux, larger inlet quality, boosted mass flow rate and shorter mix chamber length were found to either reinforce the heat transfer process or shorten the boiling regions along the tube. The standard database on hydrodynamic and heat transfer characteristics of the nozzle-atomized dispersed flow under violent conditions at the pressure of ∼7 MPa and the mass flow rate of ∼250 kg/m2/s was established and laid foundations for further engineering design.

Experimental Investigation of Methane Convection and Boiling in Rocket Engine Cooling Channels

The steady-state heat transfer characteristics under internal forced convection of liquid methane were experimentally investigated using a rectangular channel with a cross section of and square channels with a cross section of ; three square channels had surface finishes typical of milled channels and another three square channels had internal longitudinal fins. A high heat flux test facility capable of handling cryogenic temperatures, which was developed at the Center for Space Exploration Technology Research for the purpose of simulating the high heat load conditions, representative of regeneratively cooled rocket engines, was used in this study. Subcooled film-boiling phenomena were discovered for all the channels presented in this study. Film-boiling onset at critical heat flux was correlated to the boiling number . The convective Nusselt number follows predicted trends for Reynolds number with a wall temperature correction for both the boiling and nonboiling regimes.

Investigation on Heat Transfer Behaviour of Molten Salt Natural Circulation Loop using Numerical Simulations

Molten salts are used as a coolant/heat transfer fluid in various high temperature engineering systems owing to their high boiling point at low pressure. Natural circulation of molten salt is being preferred in some systems like solar thermal power plant or in some nuclear reactors. Such systems can be studied with the help of a natural circulation loop. In this work, heat transfer characteristics of Molten Salt Natural Circulation Loop (MSNCL) are studied using 3D CFD simulations. Molten Nitrate salt, NaNO3+KNO3 (60:40 ratio by weight), is used as a fluid in MSNCL. In the MSNCL, in heater section, flow is developing and also mixed convection flow regime exists. The local Nusselt number variation in heater is calculated from computed data and is compared with that from Boelter correlation. Steady state heat transfer characteristics are obtained over a wide range of Reynolds number using CFD simulations. Unsteady heat transfer characteristics in the oscillatory flow formed in MSNCL with horizontal heater configuration are also studied and are found to be different as compared to vertical heater placed in vertical heater horizontal cooler configuration.

J0230102 プラスチック平板に形成した熱サイフォンの熱輸送特性に関する研究 : 水とエタノールを用いた基礎実験([J023-01]多相界面問題とバイオ、エネルギー、環境との関係セッション(1))

Fundamental experiments have been conducted on the heat transfer characteristics of the thermosyphon fabricated on the plastic plate by using water and ethanol as the working fluid. The thermosyphon is the gravity-assisted thermal device to transport heat by utilizing the latent heat of evaporation and condensation of the working fluid; it works without any external power. In experiments, the temperature distributions of the thermosyphon with water and ethanol are measured respectively by changing the heat input and the liquid volume inside the thermosyphon. The experimental results are shown on the transient and the steady-state heat transfer characteristics of the thermosyphon. The discussion is also made on the difference between the cases of water and ethanol. Furthermore, based on the thermal resistance network model, the effective thermal conductivity of the thermosyphon is evaluated. It is confirmed that the heat transfer performance of the thermosyphon with water is better than that with ethanol in the present experimental range.

Study on heat transfer performance of an aluminum flat plate heat pipe with fins in vapor chamber

The heat transfer performance of a novel flat plate heat pipe (FPHP) for electronic cooling was investigated experimentally. A variety of performance tests of FPHP were carried out with different air flow velocities (1.5m/s<u<6m/s), working fluid filling ratios (10%<FR<50%), and the vacuum degrees (0.002Pa<VD<0.25Pa). Using distilled water and acetone as working fluids, the influence of the above parameters on steady-state heat transfer characteristics of the FPHP was also examined. The experimental results indicated that the filling ratio and vacuum degree had a significant influence on thermal performance of FPHP. Compared with cooling performance using distilled water and acetone, the FPHP cooling component using acetone had a stronger heat dissipation capacity for the same filling ratio.

Experimental investigation on flow and heat transfer performance of a novel heat fin-plate radiator for electronic cooling

Within the electronics industry, high degree of integration and enhanced performance has led to high heat dissipation electronic devices. This has identified the future development of very high heat flux components. In this paper, a novel and high efficient diffusion welded heat fin-plate radiator (HFPR) was proposed and designed. Various parameters affect the thermal performance of HFPR. The effect of three parameters: the working fluid filling ratios (8% < FR < 70%), the vacuum degrees (0.001 Pa < VD < 0.1 Pa), and the air flow velocities (0.5 m/s < u < 6 m/s) were investigated experimentally. Using distilled water and ethanol as working fluids, a series of tests were carried out to find the influence of the above parameters on steady-state heat transfer characteristics of HFPR. The experimental results indicated that the filling ratio and vacuum degree had a significant influence on thermal performance of HFPR. Also compared with cooling performance using distilled water and ethanol, the HFPR cooling component using distilled water had a stronger heat dissipation capacity for the same filling ratio. The results also can provide a basis for optimal design of HFPR structure.

Theoretical and experimental characterization of heat dissipation in a board-level microelectronic component

In this study, the steady-state heat transfer characteristics of a board-level microelectronic component in natural convection are investigated through numerical modeling and experimental validation. A typical plastic ball grid array (PBGA) package assembled to a piece of printed circuit board (PCB) is considered as the test vehicle. To achieve the goal, a three-dimensional (3D) finite element (FE) modeling technique that utilizes an effective heat conduction FE model together with empirical heat transfer (HT) coefficient correlation models for describing surface heat transfer of the electronic assemblies is applied for theoretical characterization while an infrared thermography-based technique (IRT) that incorporates FE modeling and IR thermography measurement, and a thermal test die measurement (TTDM) technique are applied for experimental validation. To facilitate the IR thermography measurement, the black paint coating technique is applied. The emissivity and optimal thickness of the specific black paint are explored through simple experiments. Besides, the uncertainty in the TTDM for the chip junction temperature measurement is also assessed. By the validated theoretical analysis model, numerical investigation of heat transfer enhancements, such as thermal balls and thermal vias, in the board-level microelectronic component is also accomplished, and eventually, an extensive thermal design guideline is accordingly provided.

Heat transfer characteristics of a two-phase closed thermosyphon

The applications of closed two-phase thermosyphons are increasing in heat recovery systems in many industrial practices because of their high effectiveness. Various parameters affect the heat transfer performance of thermosyphons. In this paper, the effect of three parameters: input heat transfer rates ( 100 < Q ˙ < 900 W ), the working fluid filling ratios (30% ⩽ FR ⩽ 90%), and the evaporator lengths (aspect ratios) were investigated experimentally. The aspect ratios for these experiments were 7.45, 9.8, and 11.8. A series of experiments were carried out to find the influence of the above parameters on steady-state heat transfer characteristics of a vertical two-phase closed thermosyphon. A smooth copper tube of total length of 980 mm with inside and outside diameters of 25 and 32 mm was employed with distilled water as working fluid. The temperature distribution along the thermosyphon was monitored; input heat to evaporator section and output heat from condenser were measured, as well. The experimental boiling heat transfer coefficients were compared with existing correlations. Conclusions have been drawn for the optimum-filling ratio at which the thermosyphon operates at its best for a certain aspect ratio.

Conjugate free convection along a thin vertical plate with internal nonuniform heat generation in a porous medium

The steady state heat transfer characteristics of a thin vertical strip with internal heat generation placed in a porous medium is studied in this work. The non-dimensional temperature distribution in the strip is obtained as a function of the intensity and distribution of the internal heat sources. Both the thermally thin as the thick wall approximations are considered in this paper. The mass flow rate of fluid induced by heating the strip decreases as the longitudinal heat conduction effects along the strip decreases.

The conjugate conduction–natural convection heat transfer along a thin vertical plate with non-uniform internal heat generation

The steady state heat transfer characteristics of a thin vertical strip with internal heat generation is studied in this work. The nondimensional temperature distribution in the strip is obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the strip and (d) the Prandtl number of the fluid. Both the thermally thin and the thick wall approximations are considered in this paper. The total thermal energy or averaged temperature of the strip is found to decrease as the influence of the longitudinal heat conduction effects in the strip decreases in the thermally thin wall regime. After reaching a minimum, it increases again in the thermally thick wall regime.

Heat transfer in a thin facing up horizontal strip with internal heat generation

The steady state heat transfer characteristics of a thin facing-up strip with internal heat generation is studied in this work. The nondimensional temperature distribution in the strip is obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the strip and (d) the Prandtl number of the fluid. Both the thermally thin and the thick wall approximations are considered in this paper. The total thermal energy or averaged temperature of the strip is found to decrease, as the influence of the longitudinal heat conduction effects in the strip decreases, in the thermally thin wall regime. After reaching a minimum, it increases again in the thermally thick wall regime.

Heat transfer characteristics of the supercritical helium in a cable-in-conduit conductor

To study the thermal stability of a forced-cooled superconducting coil with a cable-in-conduit conductor (CICC), it is important to measure the steady-state heat transfer characteristics of the supercritical helium in the narrow channel like a CICC at various conditions. The measured heat transfer coefficient is compared with one calculated by the Giarratano correlation and other studies. The results obtained show that measured values for turbulent flow scatter widely and the values for laminar flow are 1.5-1.8 times larger than those calculated from Nu=4.36. The stability of a CICC is discussed with the relation between the Stekly's stability limit and the measured heat transfer coefficient. >

Heat transfer to liquid and supercritical helium in superconducting rotors

Cooling designs of superconducting generator rotors are important for maintaining a stable superconducting state of field windings, and it is essential to comprehend the heat transfer characteristics of helium in rotating fields. Experiments were carried out using a large-scale rotating cryostat with a cold rotor diameter of approximately 800 mm. Clear differences among the steady-state heat transfer characteristics of helium were confirmed between low centrifugal acceleration fields and high centrifugal acceleration fields, resulting in the collection of heat transfer data under the supercritical state necessary for cooling designs. The heat transfer characteristics of liquid and supercritical helium under conditions of gravitational and centrifugal acceleration fields are discussed. >