Heating Rod Research Articles

Experimental and numerical study on melting process of paraffin in a vertical annular cylinder

The melting process of paraffin wax in a central heating vertical annular cylinder was simulated by a numerical model based on the enthalpy-porosity method. The numerical results were validated against the experimental results. The melting experiment was performed in a thermostatic water tank which can provide good initial conditions and constant temperature boundary conditions. The electrical heating rod located in the central of the cylinder was supposed to provide heating at a constant power. Good agreements between experimental and numerical heat transfer data were achieved. Natural convection and melt front interface were well predicted by simulation. However, considerable differences appeared due to mushy zone constant in the model. A recommended value of mushy zone constant was obtained by comparison to the experiment. The influence of thermal conductivity coefficient was also analyzed numerically.

Experimental study on heat transfer of supercritical water flowing upward and downward in 2 × 2 rod bundle with wrapped wire

Heat transfer to supercritical water flowing upward and downward in a 2×2 rod bundle with wrapped wire was experimentally investigated. The rod bundle consists of four heating rods within out-diameter of 10mm. The rods are arranged in a 2×2 square array and the pitch-to-diameter ratio is 1.18. The bundle is inserted into a square assembly box with round corners. The water as coolant flows upward or downward in the channel between the rod bundle and the assembly box. The pressure ranges from 23 to 26MPa, mass flux ranges from 450 to 1200kg/(m2s), heat flux ranges from 200 to 1000kW/m2, and the fluid temperature ranges from 200 to 450°C. The effects of system parameters including mass flux, heat flux and pressure on the heat transfer are presented, respectively. The heat transfer deterioration occurs at a low G/q ratio in the upward flow, but does not appear in the downward flow. Watts-Chou correlation and Bishop correlation give the best predictions when evaluated against the experimental data both in the upward and downward flow. The experimental data are compared with the bare rod bundle. The comparison indicates that the swirl flow of wrapped wire promotes the heat transfer in the rod bundle.

Observation of nursing of warming feeding formula of the enteral nutrition associated diarrhea

Objective To evaluate the nursing effect of warming feeding formulation of the enteral nutrition associated diarrhea in the critically ill tube-fed patients. Methods A total of 60 patients with enteral feeding were enrolled and divided randomly into the warming group and the room temperature group with 30 cases in each group by random digits table method. The room temperature group received room temperature oral feeding by nutrition pump. The warming group used nutrition pump and heating rod was placed on the nutritional tube 50 cm far from patient's nose. A semi-quantitative scale based on stool volume and consistency was used for daily assessment of diarrhea. Results Patients were tube-fed for a mean duration of (11.20±2.98) and (10.93±2.69) days, respectively in the room temperature group and the warming group. There was no significant difference in these two groups (U=425.000, P > 0.05). The diarrhea score was 4.88 ±3.41 in the room temperature group and 5.51±4.44 in the warming group. There was no significant difference in these two groups (U=436.500, P > 0.05). The diarrhea per total feeding days was 10.42% (35/336) in the room temperature group and 16.24% (51/314)in the warming group. There was no significant difference in these two groups (χ2=4.862, P < 0.05). Conclusions The airtight enteral nutrition does not need warming when it is infused with the enteral nutrition pump at room temperature. Key words: Enteral nutrition; Diarrhea; Warming

Experimental investigation on natural convection heat transfer characteristics of C-shape heating rods bundle used in PRHR HX

The heat transfer performance of Passive Residual Heat Removal Heat Exchanger (PRHR HX) immerged in the In-containment Refueling Water Storage Tank (IRWST) is of great importance for the efficient and safe removal of the residual heat in the AP1000 plant. The C-shape heating rods bundle is being used in the PRHR HX, yet the heat transfer characteristics of this special C-shape heat exchanger are not completely clear. The Westinghouse Electric Corporation has performed the PRHR HX experiment using three vertical tubes to validate the design of PRHR HX. However, the horizontal sections of the C-shaped bundle were neglected, and attentions were mainly focused on the local heat transfer effect of the vertical tubes. In the present work, an overall scaled-down IRWST and PRHR HX models are built to simulate the thermal hydraulic process in the residual heat removal accident. The natural convection heat transfer characteristics of both the overall IRWST model and the local C-shaped PRHR HX bundle model are researched in the first stage. For the overall IRWST model, the natural convection flow vectors are qualitatively measured by PIV technique. The velocity and temperature distributions are influenced mutually, then thermal stratification phenomenon develops in the overall IRWST. The existence of the “thermal interface” has great influences on the thermal stratification. For the local PRHR HX heat transfer, traditional natural convection correlations for both horizontal and vertical bundles are compared to the experimental data. For the vertical bundle of the PRHR HX model, a revised Rayleigh number is proposed as a criterion for the slender vertical rod bundles, when the vertical rod bundle outside flow cannot be treated as flat plate. Then revised correlations are proposed to predict the PRHR HX average heat transfer coefficient. Moreover, the analysis shows that the forced convection also plays an important role in enhancing the heat transfer effect of the PRHR HX model upper horizontal bundle, so the modified Numix is recommended for the PRHR HX upper horizontal bundle secondary heat transfer calculation.

Quenching of a Heated Rod: Physical Phenomena, Heat Transfer, and Effect of Nanofluids

The physical phenomena of rewetting and quenching are of prime importance in nuclear reactor safety in the event of a loss of coolant accident (LOCA). Generally, top spray or bottom flooding concepts are used in reactors. Numerical simulation of these processes entails the use of the concept of a rewetting velocity. However, heat transfer just before and after the rewetting front is often assumed in an ad hoc fashion. The present work aims to evaluate the surface heat flux during quenching as a function of surface temperature. The experiments presented herein are primarily applicable to the bottom flooding scenario with high flooding rate. In the experiments, a rod heated above Leidenfrost point is immersed in a pool of water. The surface temperature was recorded using a surface-mounted thermocouple. The surface heat flux was then determined numerically and hence can be related to a particular value of surface temperature. This type of data is useful for numerical simulations of quenching phenomena. In addition to this, high-speed photography was undertaken to visualize the phenomena taking place during the rewetting and quenching. Both subcooled and saturated water pools have been used and compared in the experiments. Surface finish was seen to influence rewetting process by a mechanism which here is termed as “transition boiling enhanced film boiling.” The effect of using nanofluids was also studied. No marked change is observed in the overall quenching time with nanofluids, however, the initial cooling is apparently faster.

Robust motion planning for a heat rod process

First, heat rod models linking temperature to heat flux density are obtained from system identification using fractional order systems. Then, motion planning of the nominal system is obtained through an open-loop control stemming from flatness principles. Usually, each model should have its own control reference in order to follow a desired output reference. Thanks to a third-generation CRONE controller, the nominal control reference is sufficient, and robust control is also guaranteed regarding model uncertainties and input/output disturbances. Robust motion planning is held on a real heat experiment and comparison between CRONE and PID controllers are proposed on this test bench.

Zinc corrosion after loss-of-coolant accidents in pressurized water reactors – Thermo- and fluid-dynamic effects

Within the framework of the German reactor safety research, generic experimental investigations were carried out aiming at thermal-hydraulic consequences of physicochemical mechanisms, caused by dissolution of zinc in boric acid during corrosion processes at hot-dip galvanized surfaces of containment internals at lower coolant temperatures and the subsequent precipitation of solid zinc borates in PWR core regions of higher temperature. This constellation can occur during sump recirculation operation of ECCS after LOCA. Hot-dip galvanized compounds, which are installed inside a PWR containment, may act as zinc sources. Getting in contact with boric acid coolant, zinc at their surfaces is released into coolant in form of ions due to corrosion processes. As a long-term behavior resp. over a time period of several days, metal layers of zinc and zinc alloys can dissolve extensively.First fundamental studies at laboratory scale were done at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Their experimental results were picked up for the definition of boundary conditions for experiments at semi-technical scale at the Hochschule Zittau/Görlitz (HSZG). Electrical heating rods with zircaloy cladding tubes have been used as fuel rod simulators.As near-plant core components, a 3×3 configuration of heating rods (HRC) and a shortened, partially heatable PWR fuel assembly dummy were applied into cooling circuits. The HRC module includes segments of spacers for a suitable representation of a heating channel geometry. Formations of different solid zinc compounds (mainly borates) were observed at the heatable zircaloy surfaces and characterized in detail during the heating-up to several coolant temperatures. As a strict consequence of their proven influence on heat removal and coolant flow behavior in the PWR core, preventive water-chemical methods were defined and tested.

Effect of ambient gas flow on the instability of Marangoni convection in liquid bridges of various volume ratios

Instability of Marangoni convection in liquid bridges (LBs) of high Prandtl number (Pr) fluids has been studied by focusing on the effect of ambient gas flow on the LBs of various volume ratios. The working fluids are 2 cSt (Pr=28) and 5 cSt (Pr=67) silicone oils. The LB is suspended in a gap between the upper heating rod and the lower cooling rod and it is surrounded by a coaxial cylindrical wall to form an annular passage between the LB and the inner wall surface. The ambient gas motion is given to this annular passage in the range from −35mm/s (vertically downward) to +35mm/s (vertically upward). The ratio of the LB volume to the gap volume is varied from 0.80 (slender LB) to 1.10 (slightly fat LB). The critical temperature differences for the onset of instability are measured and corresponding critical Marangoni numbers are determined. Numerical computations are carried out to understand the flow and temperature fields both in the LB and in the ambient gas at each measured critical temperature difference. The computation results are used to evaluate the convective and the radiative heat transfers from the LB. The effect of the ambient gas motion on the relationship between the critical Marangoni number and the volume ratio is revealed. The effect is discussed in terms of the Biot number defined using the heat transfer and the critical temperature difference. It is shown that the Biot number increases with the ambient gas velocity for slender LBs while it is nearly constant for slightly fat LBs. It is found that the critical Marangoni numbers plotted as a function of the Biot number for various volume ratios and ambient gas velocities fall on a single profile corresponding to each Pr. Such a behavior is shown to be in accord with the previous data taken under various ambient gas temperatures and cooling rod temperatures.

COPRA: A large scale experiment on natural convection heat transfer in corium pools with internal heating

During a severe accident in light water reactors, the core may melt and relocate into the lower plenum of the reactor pressure vessel. The decay heat will threaten the structural and thermal integrity of the reactor vessel if there is no effective cooling mechanism. Natural convection plays an important role in determining the thermal-hydraulic behaviors inside the debris pool, which is directly relevant to the problem of retention of molten corium inside the lower plenum. The COPRA (COrium Pool Research Apparatus) experiments were performed to study the natural convection heat transfer behavior in an internally heated melt pool with high Rayleigh numbers. The COPRA test facility is a two-dimensional 1/4 circular slice vessel with an inner radius of 2.2 m to simulate the lower plenum of reactor vessel for the Chinese advanced PWR in a full scale. The inner width of the slice is 20 cm and the curved vessel wall has a thickness of 30 mm. 20 electrical heating rods, each with a diameter of 16 mm but different lengths according to their locations, are uniformly distributed in the vessel to simulate homogenous internal decay heat. They can provide a maximum of 30 kW power to the melt pool. The outside of the curved wall is enclosed with a regulated external cooling path to keep the boundary temperature nearly isothermal. The top surface of the pool can be maintained insulated with an adiabatic lid. 79 thermocouples are installed in the melt pool to measure the melt pool temperature field and 48 in the curved wall to obtain local heat flux distribution along the curved wall. In the first series of experiments, water was employed as the simulant material. Due to the full scale geometry, the Rayleigh number within the pool could reach up to 1016, matching that in the prototypical situation for PWR. The heat transfer characteristic with volumetrically internal heat was investigated by using the full scale facility COPRA. Relations of pool temperature and heat flux distribution, as well as Nudn-Ra′ were developed. The results have been compared with the results and correlations from other experiments.

Assessing the Thermal Performance of District Heating Twin Pipes with Vacuum Insulation Panels

In Sweden, around 10% of the energy supplied to the district heating networks are lost through heat losses from the distribution pipes. In cylindrical geometries it is preferable to improve the insulation as close to the center as possible. This has resulted in a hybrid insulation district heating pipe concept with a combination of vacuum insulation panels at the center, held in place by polyurethane foam. In the twin pipe concept, the vacuum insulation panel cover the supply pipe. This creates a complex temperature profile over the section and measured results on single pipes might not be applicable. Therefore, there is a need for a method to evaluate the improvement of hybrid insulation twin pipes in the laboratory. This paper presents a method where two guarded hot pipe apparatuses is used, one heating rod for each pipe, to measure the heat losses from hybrid pipes and compare to a conventional polyurethane pipe. The measurements indicate an improvement in thermal performance by 12%-18% for the total losses and by 29% -39% for the supply pipe losses.

The potential of decentralized power-to-heat as a flexibility option for the german electricity system: A microeconomic perspective

One fundamental challenge of the German energy transition for the electricity market is the growing imbalance between inflexible generation and generally inelastic load. Against this background, we investigate the future potential of decentralized Power-to-Heat (P2H) as an additional demand-side flexibility option for the German electricity system. Precisely, we analyze the case of hybrid systems, where conventional gas and oil condensing boiler systems are equipped with an electric heating rod. In contrast to previous approaches, we set our focus on the economic incentives at household level: only if the switch to a P2H-hybrid system can reduce individual heating expenses significantly, a considerable number of these systems will be installed. For this purpose, we implemented an integrated approach combining three distinct simulation modules. First, a stochastic simulation of the electricity spot market prices in 2020 was conducted. Second, average heat load profiles were generated based on a standard bottom-up analysis. Both results were then fed into an optimization model calculating the cost-minimizing paths of heat generation at household level during the year 2020. The simulated annual savings prove modest as long as household electricity prices are not heavily reduced through political influence.

COPRA experiments on natural convection heat transfer in a volumetrically heated slice pool with high Rayleigh numbers

Large scale COPRA experiments were performed to study the natural convection heat transfer in corium pools inside the reactor pressure vessel lower plenum during severe accidents. The test facility is designed to simulate the lower plenum of reactor vessel at 1:1 scale for the Chinese advanced PWR, which is a two-dimensional 1/4 circular slice structure with an inner radius of 2.2m. A non-eutectic binary mixture of 20mol%NaNO3–80mol%KNO3 compositions was selected as the simulant material. Twenty custom-designed heating rods were located in the facility to provide homogenous internal heating. Due to the full scale geometry, The Rayleigh numbers within the corium pools could reach to 1.188×1015–1.784×1016, matching those in the prototypical situation during severe accident. The pool temperature field and heat flux distribution, as well as the crust thickness distribution from tests with different pool heights and heating powers were obtained and compared in the experiments. Influences of the relocation position and upper cooling on the heat transfer characteristics were also studied in the experiments. Relations of pool temperature and heat flux distribution, as well as Nudn–Ra′ relation were developed. Comparison with previous experiments showed that the downward heat transfer Nudn prediction from COPRA experiments were in good agreement with SIMECO and LIVE salt experimental results.

The performance of the novel vapor chamber based on the leaf vein system

With the upgrade of the miniaturization of the electronic equipment, heat in per area increases dramatically, which leads to the strong need for a high efficient device of heat dissipation. As the result of the nature evolution, leaf vein system is an excellent structure for heat and mass transfer but has not been widely studied. Based on the leaf vein system, a conceptual structure is designed to form the wick of a vapor chamber, in which the leaf-vein-like fractal network and the micro fin-pins are used to simulate the leaf vein network and mesophyll tissue respectively. In the experiment, the leaf-vein-like structure is manufactured by chemical etching, and two different vapor chambers (diameter is 90mm, the evaporator and condenser have the same wick structures) with and without strength boiling are compared concerning their cooling performances. The experiment result shows that when the diameter of the heating rod is 35mm, the vapor chamber can perform good temperature uniformity and small thermal resistance with the input power Q⩽90W. When the deionized water is used as the working fluid, the thermal resistance of the vapor chamber is smaller than 0.3°C/W.

The Effect of Position of Heated Rod in Tube Banks on the Heat Transfer Coefficient

Heat transfer in flow across a bank of tubes is of a particular importance in the design of heat exchangers. Heat exchangers are used in numerous services and industrial applications. Experimental studies were performed, carried out in cross-flow tube banks. They contain copper heated rod and 17 Aluminum rods arranged in the form of staggered and at arrange of Reynolds number 2700 to 21530. The experimental results indicated that the location of the heated rod in the work section affects the value of heat transfer coefficient thus this value is increased when the heated rod location changes both the y and x-directions. The experimental data revealed good agreement with Zukauskas correlation in four columns.

Marine Gear Reducer Design Device of Lubricating Oil Temperature Control System

Signal of PLC controller by PID operation after the output of numerical simulation between 0~1, and solid state relay can receive only signal, digital or switched on or off. Only connected the two, temperature control system can be realized. The experimental approach is to learn from PWM pulse width modulation technology, the numerical analog PID controller output into the heating time in a cycle, namely, solid state relay on time. By this method, the indirect control heating rod of equivalent power, the power output of the heating rod according to the control signal of controller output, so as to realize marine gear oil temperature PID regulation. This paper designs the control system used in the experiment. The temperature control experiment system; design of the electrical schematic diagram of the temperature control system, including two parts electrical schematic diagram of control circuit and main circuit of temperature control system design process. At the same time, the experimental scheme is designed. Analysis of the mechanism of temperature balance control object, and focus on the temperature within the experimental results are analyzed.

Flow Boiling Heat Transfer Enhancement by Using ZnO-Water Nanofluids

Nanofluids are liquid suspensions containing nanoparticles that are smaller than 100 nm. There is an increased interest in nanofluids as thermal conductivity of nanofluids is significantly higher than that of the base liquids. ZnO-water nanofluids with volume concentration of ZnO particles varying from 0.0001 to 0.1% were prepared using ultrasonic vibration mixer. Thermal conductivity of the ZnO-water fluids was investigated for different sonication time using thermal property analyzer (KD2 Pro). Thermal conductivity of nanofluids for a given concentration of nanoparticle varies with sonication time. Heat transfer coefficient and pressure drop in an annular test section with variable pressure (1–2.5 bar) and heat flux (0–400 kW/m2) at constant mass flux of 400 kg/m2s were studied for samples having maximum thermal conductivity. Surface roughness of the heating rod was also measured before and after the experimentation. The study shows that heat transfer coefficient increases beyond the base fluid with pressure and concentration of ZnO.

Development of Measurement Method of Void Fraction Distribution for Boiling Water Flow in Heated Rod Bundle

SubChannel Void Sensor (SCVS) consisting of electrodes with 6-wire by 6-wire and 5-rod by 5-rod electrodes has been developed to acquire boiling two-phase flow dynamics in 5×5 rod bundle geometry. The SCVS can acquire a local void fraction in 32 points (=6×6-4) of central subchannel regions and 100 points (=4×25) of near rod surface regions. The temporal resolution is up to 5000 frames (cross sections) per second. The devised sensors are installed every 500mm in the heated rod bundle and exhibits the quasi three-dimensional boiling two-phase flow structures, i.e. void fraction distribution.

Fouling of a Heated Rod in a Stirred Tank System

A batch stirred tank device has been developed for measuring fouling from oil samples. The unit consists of a baffled tank equipped with a centrally mounted long blade stirrer, and an electrically heated rod located at 40% of the radius of the tank. Heat transfer from the rod was first characterized. The velocity field was measured, from which the approach velocity to the probe was determined, which allowed the wall shear on the heating probe to be calculated from a literature equation. Fouling of a heavy oil fraction was studied in 1- to 2-day experiments with bulk oil temperatures typically at 320°C, initial probe surface temperatures to 536°C, and stirrer speeds of 100–900 rpm. Micrometer-sized iron oxide particles were added to the oil, such that fouling was due to a combination of particle deposition and coke formation. Deposition rates were measured thermally from the change in heat transfer coefficient when fouling was relatively heavy, and by thickness and mass accumulation when fouling was light. Effects of oil type, film temperature, stirrer rotation speed (or probe wall shear stress), and concentration of suspended particles on deposition rate and deposit composition are presented.

Evaluation And Comparison Of Kalman-Filter-Based Distributed State Estimators For Large-Scale Systems

This paper presents a performance comparison of Kaiman-filter-based distributed state estimations techniques for large-scale systems. Three distributed Kaiman filter schemes are selected to be implemented in simulation, namely, distributed and decentralized Kaiman filter (DDKF), distributed Kaiman filter with state consensus (DKF-SC) and distributed Kaiman filter with diffusion strategy (DKF-DS), using the heat rod dynamical system as benchmark. The heat conduction and convection in a solid rod dynamic is used as test bed. The comparison is performed by evaluating prediction error and convergence of each scheme, considering the partition of the system into two, three and four subsystems.

Experimental Investigation of Water Flow Heat Transfer in Metal Foams

This paper aims at finding the best pore density and porosity of metal foams for heat transfer, as well as the most proper operating conditions. A circulating water cooling system were designed which include micro-channel heat sink, heat exchanger, micro-pump, rot meter, electric heating rods, and conversion fans for the experiment. The comparison was made between different metal foam samples in terms of flow rate and equilibrium temperature of heating boundary. The results presented that a relatively low temperature can be achieved when flow rate is large, but at the same time the pressure drop increased. The excellent heat dissipation performance of metal foams has a close relationship with its specific surface area.