Average Heat Load Research Articles

Demonstration of a high repetition rate capillary discharge waveguide

A hydrogen-filled capillary discharge waveguide operating at kHz repetition rates is presented for parameters relevant to laser plasma acceleration (LPA). The discharge current pulse was optimized for erosion mitigation with laser guiding experiments and MHD simulation. Heat flow simulations and measurements showed modest temperature rise at the capillary wall due to the average heat load at kHz repetition rates with water-cooled capillaries, which is promising for applications of LPAs such as high average power radiation sources.

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.

Design and performance of demonstration house with active solar heating in the Qinghai–Tibet Plateau region

The project comprises 80 passive solar houses and 20 houses with combined passive and active solar heating in the Qinghai–Tibet Plateau region. The indoor thermal environment and the performance of the solar collection components are discussed through field testing during the coldest part and the transition part of the heating period. Moreover, the fractional energy savings, thermal efficiency, and fraction of the combined passive and active solar heating are analyzed. The results indicate that an auxiliary heat source should be used as a supplement. By comparing the heating of a passive solar house with a vernacular house, the energy savings of the passive solar house in the demonstration project were found to be approximately 62% during the study period. The thermal efficiency of the active solar heating system is 84.5%, and the solar energy utilization is 38.2%. The monthly average heat load index is 15.2 W m−2.

Simplified modelling the mode instability threshold of high power fiber amplifiers in the presence of photodarkening.

In this paper we present a simple model to predict the behavior of the transversal mode instability threshold when different parameters of a fiber amplifier system are changed. The simulation model includes an estimation of the photodarkening losses which shows the strong influence that this effect has on the mode instability threshold and on its behavior. Comparison of the simulation results with experimental measurements reveal that the mode instability threshold in a fiber amplifier system is reached for a constant average heat load value in good approximation. Based on this model, the expected behavior of the mode instability threshold when changing the seed wavelength, the seed power and/or the fiber length will be presented and discussed. Additionally, guidelines for increasing the average power of fiber amplifier systems will be provided.

Optimised Cockpit Heat Load Analysis using Skin Temperature Predicted by CFD and Validation by Thermal Mapping to Improve the Performance of Fighter Aircraft

Designing of optimum environmental control system (ECS) plays a major role for increasing performance of fighter aircraft depending upon requirement of engine bleed air for running of ECS. Accurate estimation of cockpit skin temperature for obtaining optimised cockpit heat load helps in estimation of engine bleed air for ECS. Present research evolved a methodology for comparing the theoretically calculated skin temperature with computational fluid dynamics (CFD) analysis to obtain optimum skin temperature. Results are validated by flight tests under critical flight conditions using thermal crayons. Based on which the optimized heat load and bleed air requirements has been computed. Uncertainty analysis of skin temperature measurement for thermal crayons have been undertaken. The results indicate that the theoretical skin temperature is -26.70 per cent as that of CFD estimated skin temperature. Optimized average cockpit heat load at critical flight profiles is 0.74 times the theoretical cockpit heat load, leading to reduction of bleed air requirement by 26 per cent as compared to theoretical. Due to this literature survey has pridicted the increase in performance parameters like increase in bleed air pressure by 78 per cent, increase in thrust by 60 per cent, and decrease in specific fuel consumption (SFC) by 40 per cent to improve the endurance of aircraft. The research has generated governing equations for variation of cockpit heat loads w.r.t aircraft skin temperatures.Defence Science Journal, Vol. 65, No. 1, January 2015, pp.12-24, DOI:http://dx.doi.org/10.14429/dsj.65.7200

Effect of summer conditions and shade on the production and metabolism of Holstein dairy cows on pasture in temperate climate

For dairy cattle on pasture in temperate regions, it is largely unknown to what degree hot summer conditions impact energy metabolism, milk yield and milk composition and how effective shade is in reducing these negative effects. During the summer of 2012, a herd of Holstein cows was kept on pasture without access to shade (treatment NS). During the summers of 2011 and 2013, the herd was divided into a group with (treatment S) and a group without (treatment NS) access to shade. Shade was provided by young trees combined with shade cloths (80% reduction in solar radiation). A weather station registered the local climatic conditions on open pasture, from which we calculated daily average Heat Load Index (HLI) values. The effects of HLI and shade on rectal temperature (RT), blood plasma indicators of hyperventilation and metabolic changes due to heat stress, milk yield and milk composition were investigated. RT increased with increasing HLI, but was less for S cows than for NS cows (by 0.02°C and 0.03°C increase per unit increase of HLI, respectively). Hyperchloraemia (an increased blood plasma concentration of Cl−), a sign of hyperventilation, increased for NS cows but not for S cows. The plasma concentration of alkaline phosphatase, a regulator of energy metabolism in the liver, decreased with increasing HLI for NS cows only. Access to shade, thus, reduced the effect of HLI on RT, hyperchloraemia and the regulation of metabolism by the liver. As HLI increased, the plasma concentration of cholesterol decreased (indicating increased lipolysis) and the plasma concentration of creatinine increased (indicating increased protein catabolism). These effects did not differ between S and NS cows. For NS cows, after a lag-time of 2 days, the milk yield decreased with increasing HLI. For S cows, the milk yield was unaffected by HLI and its quadratic factor. The milk concentrations of lactose, protein and fat decreased as HLI increased, but only the effect on milk protein content was remediated by shade. In conclusion, access to shade tempered the negative effects of high HLI on RT, hyperchloraemia and a blood plasma indicator of changing energy metabolism (generally) as well as prevented the decrease in milk yield observed in cows without access to shade.

Effect of transient heating loads on beryllium

Beryllium will be used as a plasma facing material for ITER first wall. It is expected that erosion of beryllium under transient plasma loads such as the edge-localized modes (ELMs) and disruptions will mainly determine a lifetime of ITER first wall. The results of recent experiments with the Russian beryllium of TGP-56FW ITER grade on QSPA-Be plasma gun facility are presented. The Be/CuCrZr mock-ups were exposed to upto 100 shots by deuterium plasma streams with pulse duration of 0.5ms at ∼250°C and average heat loads of 0.5 and 1MJ/m2. Experiments were performed at 250°C. The evolution of surface microstructure and cracks morphology as well as beryllium mass loss are investigated under erosion process.

Temperature distribution in a field of long Borehole Heat Exchangers (BHEs) subjected to a monthly averaged heat flux

A method to evaluate the long-term temperature distribution in a field of long Borehole Heat Exchangers (BHEs) subjected to a monthly averaged heat flux is presented, under the assumption that the effects of the groundwater flow are negligible. Each BHE is considered as a cylindrical heat source with diameter D and length L. For each ratio L/D and dimensionless radial distance r/D, the g-function (time-dependent dimensionless temperature, averaged along the BHE length, due to a uniform and constant heat load) is determined by finite-element simulations and written in polynomial form through accurate interpolations, in a very broad range of values of the dimensionless time. Tables of the coefficients of the polynomial functions are provided. The g-functions are then used to determine the time evolution of the mean dimensionless temperature at the interface BHE-ground, averaged among BHEs, for some BHE fields subjected to a monthly averaged heat load.

Impact of the Combustor-Turbine Interface Slot Orientation on the Durability of a Nozzle Guide Vane Endwall

The combustor-turbine interface is an essential component in a gas turbine engine as it allows for thermal expansion between the first stage turbine vanes and combustor section. Although not considered as part of the external cooling scheme, leakage flow from the combustor-turbine interface can be utilized as coolant. This paper reports on the effects of orientation of a two-dimensional leakage slot, simulating the combustor-turbine interface, on the net heat flux reduction to a nozzle guide vane endwall. In addition to adiabatic effectiveness and heat transfer measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed in the vane stagnation plane. Four interface slot orientations of 90 deg, 65 deg, 45 deg, and 30 deg located at 17% axial chord upstream of a first vane in a linear cascade were studied. Results indicate that reducing the slot angle to 45 deg can provide as much as a 137% reduction to the average heat load experienced by the endwall. Velocity measurements indicate the formation of a large leading edge vortex for coolant injected at 90 deg and 65 deg while coolant injected at 45 deg and 30 deg flows along the endwall and washes up the vane surface at the endwall junction.

Feeder components and instrumentation for the JT-60SA magnet system

The modifying of the JT-60U magnet system to the superconducting coils is progressing as a satellite facility for ITER by both parties of Japanese government and European commission in the Broader Approach agreement. The magnet system requires current supplies of 25.7kA for 18 TF coils and of 20kA for 4 CS modules and 6 EF coils. The magnet system generates an average heat load of 3.2kW at 4K to the cryogenic system. The feeder components connected to the power supply provide current supply. The cooling pipes connected to the cryogenic system provide coolant supply. The instrumentation of the JT-60SA magnet system is used for its operation.

On the importance of the location of PCMs in building walls for enhanced thermal performance

Phase change materials (PCMs) are used to enhance the thermal storage capacity of building walls. PCM incorporation into building walls poses several design challenges; a critical one being the integration method (e.g., micro- vs. macro-encapsulation) as well as the location of PCMs within the volume of the walls. Such location is critical for wall performance in terms of controlling heat transfer rates for purposes of energy conservation and peak load shifting. This paper highlights the dependence of wall thermal performance on PCM location leading to the most optimal PCM location for the system under study. In this study, PCMs were incorporated in walls via “thermal shields” where the PCM material was encapsulated in polyethylene flat bubbles “sandwiched” between two layers of protective aluminum foil. This system is herein referred to as “PCM thermal shield (PCMTS)”. The thermal performance of the walls with and without PCMTS was evaluated experimentally using a dynamic wall simulator. PCM thermal shields (PCMTSs) were placed within the wall insulation at varying distances from the internal surface of the bounding wallboard, which happened to be the bounding layer furthest from the heating sources of the simulator. For the system under study, the results showed that the optimal location for a PCMTS was at a distance of 1/5L from the internal surface of the bounding wallboard, where L was the thickness of the insulation cavity. At this location, the average peak heat flux reduction and load shifting time were approximately 41% and 2h, respectively, when compared to the peak heat fluxes across walls without PCMTS.

Daily heat load variations in Swedish district heating systems

Heat load variations in district heating systems are both seasonal and daily. Seasonal variations have mainly its origin from variations in outdoor temperature over the year. The origin of daily variations is mainly induced by social patterns due to customer social behaviours. Heat load variations cause increased costs because of increased peak heat load capacity and expensive peak fuels. Seasonal heat load variations are well-documented and analysed, but analyses of daily heat load variations are scarce. Published analyses are either case studies or models that try to predict daily heat load variations. There is a dearth of suitable assessment methods for more general analyses of existing daily load variations.In this paper, a novel assessment method for describing daily variations is presented. It is applied on district heating systems, but the method is generic and can be applied on every kind of activity where daily variations occur. The method was developed from two basic conditions: independent of system size and no use of external parameters other than of the time series analysed. The method consists of three parameters: the annual relative daily variation that is a benchmarking parameter between systems, the relative daily variation that describes the expected heat storage size to eliminate daily variations, and the relative hourly variation that describes the loading and unloading capacity to and from the heat storage. The assessment method could be used either for design purposes or for evaluation of existing storage.The method has been applied on 20 Swedish district heating systems ranging from small to large systems. The three parameters have been estimated for time series of hourly average heat loads for calendar years. The results show that the hourly heat load additions beyond the daily averages, vary between 3% and 6% of the annual volume of heat supplied to the network. Hereby, the daily variations are smaller than the seasonal variations, since the daily heat load additions, beyond the annual average heat load, are between 17% and 28% of the annual volume of heat supplied to the network. The size of short term heat storage to eliminate the daily heat load variations has been estimated to a heat volume corresponding to about 17% of the average daily heat supplied into the network. This conclusion can also be expressed as an average demand of 2.5m3 of heat storage volume per TJ of heat supplied by assuming a water temperature difference of 40°C. The capacity for loading and unloading the storage should be equal to about half of the annual average heat load for heat supplied into the network.

Convective boiling of R-134a and R-123 on an enhanced tube bundle with standard pitch, RP-1316

The current article presents the experimental investigation of the heat transfer performance of highly enhanced surfaced tube bundles. The two bundles studied are high pressure and low pressure TBII tubes for R-134a and R-123, respectively. The tube bundle is a staggered triangular arrangement with a tube pitch of (P/D 1.167). Twenty enhanced tubes were used in the bundle; the tube outer diameter and length are 19.05 mm (3/4 in.) and 1 m (39.36 in.), respectively. Three input variables were studied: heat flux 5–60 kW/m2 1585-19020 BTU/hr.ft2), mass flux 15–55 kg/m2.s (3–11 lb/s.ft2), and quality (10–70%). The test saturation temperature was 4.44°C (40 °F) for R-134a and 14.44°C (58 °F) for R-123. The local heat transfer performance of the bundle is reported. A local method employing the enthalpy based heat transfer technique was implemented in the data reduction. Both tube bundles showed a strong dependency on heat flux as expected. The R-134a bundle showed a performance lower than that of pool boiling. The R-123 bundle showed a secondary dependency on quality. The quality effect becomes pronounced at high qualities and high average bundle heat load. In the latter case, enhanced tubes performance drops quickly and reaches that of a smooth tube.

Thermomechanical Analysis of Plasma-Facing Components for SST-1 Tokamak

Plasma-facing components (PFCs) are an important part of the Indian Steady State Superconducting Tokamak (SST-1) design. The main consideration in the design of PFCs is steady-state heat removal of up to 1 MW/m2, which is nearly the limit for incident heat flux of mechanically attached graphite tiles for tokamak PFCs. SST-1 PFCs consist of divertors, passive stabilizers, baffles, and limiters and are designed for long-pulse operation, which requires active cooling of these components. During steady-state operation, the average heat loads on the divertor and passive stabilizers are expected to be 0.6 and 0.25 MW/m2, respectively. Design considerations include two-dimensional steady-state and transient tile temperature distribution and the resulting thermal loads in PFCs during plasma operation. Thermal analysis is carried out to evaluate the thermomechanical behavior of the SST-1 PFCs. In this technical note, temperature distribution and thermally induced stresses and strains in PFCs are analyzed using a finite element method, and the effect of stress and strain on different materials used in PFCs is discussed.

Radio frequency emission from high-pressure xenon arcs: A systematic experimental analysis of the underlying near-anode plasma instability

High-pressure Xe discharge lamps at DC operation can show unwanted strong RF (radio-frequency) emission to beyond 1 GHz, correlated to a sharp periodic lamp-voltage instability in the near-anode plasma with a pulse repetition rate ε of 1–10 MHz. The physical origin of the instability is unclear. Here, its existence and pulse rate have been measured as a function of arc current I = 0.2–1.2 A and anode temperature Ta = 1700–3400 K independently, in experimental lamps with pure-tungsten electrodes and a Xe operating pressure around p = 10 MPa. Surprisingly, the instability is not affected by I or current density j but exists if Ta is lower than a threshold value around 2800–2900 K. The pulse rate ε is simply a rising linear function of the inverse anode temperature 1/Ta, with only a small I-dependent correction. The average anode heat load is slightly lower in the unstable regime and possibly depends on ε. The results allow a consistent re-interpretation of earlier and present experimental observations and should be both a valuable help in practical lamp engineering and a tight constraint for future theories of this effect.

The procurement and testing of the stainless steel in-vessel panels of the Wendelstein 7-X Stellarator

320 In-vessel water cooled stainless steel panels, poloidal closure plates and pumping gap panels, covering an area of approximately 100 m 2, are used in Wendelstein7-X to protect the plasma vessel. The panels are manufactured at Deggendorf, Germany by MAN Diesel & Turbo SE. The panels consist of a laser welded sandwich of stainless steel plates together with a labyrinth of cooling channels and have a complicated geometry to fit the plasma vessel of Wendelstein 7-X. The hydraulic and mechanical stability requirements whilst maintaining the tight tolerances for the shape of the components are very demanding. The panels are designed to operate at up to an average heat load of 100 kW/m 2 and a maximum heat load of 200 kW/m 2 with a water velocity of approximately 2 m s −1. High heat flux testing of an un-cooled panel at a time averaged load of 200 kW/m 2 for 10 s were successfully performed to support the start up phase of Wendelstein 7-X operation. Extensive testing both during manufacture and after delivery to IPP-Garching demonstrates the suitability of the delivered panels for their purpose.

Results of KEPCO HTS cable system tests and design of hybrid cryogenic system

In order to investigate the compatibility as a power utility facility, Korea Electric Power Corporation (KEPCO) had installed a 22.9kV, 1250A, 100m long high temperature superconducting (HTS) power cable system. Using the HTS cable, various tests have been performed to investigate electrical and thermo-mechanical properties. Since 2005, a series of thermal cycle tests between liquid nitrogen (LN2) and ambient temperatures have been conducted using a vacuum-pump driven open-loop cryogenic system with a capacity of 3kW. In the tests, although the open-loop cryogenic system was reliable to operate the HTS cable system, it was not effective in economic view point because LN2 consumption was larger than expected. In order to secure against unexpected emergencies and solve the problem of LN2 consumption, a hybrid cryogenic system was designed and installed. A stirling cryocooler was employed and combined with the open-loop cryogenic system. Considering the average heat load at rated condition, the cooling capacity of the cryocooler was determined to 4kW at 77K. In this paper, results of performance tests and the design of the hybrid cooling system are presented.

Overview on spallation target design concepts and related materials issues

From a modest beginning of a few kW of beam power spallation sources have now evolved into systems that must be able to handle several MW, mostly delivered in short pulses of less than microsecond duration. The high radiation field and high instantaneous heat deposition which spallation targets, in particular for the new high power sources, are subject to have led to several different design concepts which aim at circumventing or reducing the deleterious effects on the materials in the targets. Efficient cooling and high neutron source density are competing requirements which can be best reconciled by moving the target material out of the reaction zone and removing the heat elsewhere before returning the material back into the proton beam. One option is the use of a flowing liquid metal, which has been the method of choice in most of the recent spallation source designs, but requires solutions to a variety of new problems, such as liquid metal corrosion, cavitation erosion and e.g. in the case of PbBi, or Pb, high temperature gradients. Using a rotating solid target is an option in certain cases but still has to cope with the instantaneous load levels. While it may help to keep the average heat load and radiation damage in the target material low and thus extend the target life time by more than an order of magnitude, it still has its own design and materials issues. Opportunities to carry out research in this field are rather limited because the effects can hardly be simulated off line and, apart from spallation targets in operation, almost no facilities are available.

Numerical Investigation on Unsteady Effects of Hot Streak on Flow and Heat Transfer in a Turbine Stage

This paper presents a detailed flow and heat transfer characteristic analysis on gas turbine first-stage turbine under hot streak inlet conditions. Two kinds of inlet total temperature conditions are specified at the turbine stage inlet. The first is uniform inlet total temperature, and the second is hot streak 2D total temperature contour. The two kinds of inlet conditions have the same mass-averaged total temperature and the same uniform inlet total pressure. The hot streak total temperature contours are obtained according to the exit shape of an annular-can combustor. The ratio of the highest total temperature in the hot streak to the mass-averaged total temperature is about 1.23, and one hot streak corresponds to two vane passages and four blade passages. Six hot streak circumferential positions relative to the Vane 1 leading edge varied from −2% to 81% pitch are computed and analyzed. The results show that hot streak obviously increases the nonuniform degree of vane heat load in comparison with the uniform total temperature inlet condition. The change in hot streak circumferential position leads to the circumferential parameter variation at stator exit and also leads to different transient periodic fluctuating characteristics of heat load and pressure on the rotor blade surface. The hot streak of relative pitch at 65% obtains a similar heat load for the two vanes corresponding to one hot streak and small fluctuation in the averaged heat load on the rotor blade.

Design and manufacturing of the ITER ECRH upper launcher mirrors

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control magnetohydrodynamic (MHD) instabilities [1,2]. In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized and peaked current density profile over a broad poloidal steering range is required. In the present optical configuration eight 2 MW mm-wave beams enter each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam line comprises consecutive corrugated waveguide sections with two mitre bends, orientating the poloidal and toroidal directions and three sections of quasi-optical transmission [3]. The beam waist locations and beam shaping properties in free space propagation are defined by two additional mirrors, the first being a static focusing mirror and the second a plane poloidally steerable mirror. Each mirror reflects a group of 4 mm-wave beams. The three types of UL mirrors (mitre bend, focusing and steering) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces and the nuclear and thermal radiation coming from the plasma. While the average heat load is within reasonable engineering limits, three elements condition the actual mirror design, the peak ohmic heat load (Gaussian or Bessel type heat deposition profiles), the electromagnetic forces generated in vertical disruption events (VDE), and the ITER cooling water requirements. This paper provides an overview of the different upper port-plug mirror designs and cooling schemes and an outlook on the prototype manufacturing activities and the future test program. The optimized mm-wave layout within the ECH port plugs is also presented.