Circuit Heat Research Articles

Measurement of the controlled variable during heating of Ti6Al4V for thixoforging

Controlled heating of metal billets into the semi-solid state for thixoforming is a challenging task, mainly due to the difficulties in measuring the liquid fraction of the billet during heating. Past research primarily focused on methods measuring the liquid fraction during heating of low-melting aluminium alloys. One of these methods is time constant measurement, a contactless measurement method that uses the heating coil as a sensor. The current through the coil is used to determine the electrical time constant of the heating circuit, which itself is influenced by the specific resistance of the billet inside the coil. While previous works focused on the suitability of this method for industrial applications using aluminum alloys, this paper extends this research to the high-melting titanium alloy Ti6Al4V. This alloys shows high strength, low density and excellent corrosion resistance. It is therefore used to produce light-weight and durable components for medical and aerospace applications. Ti6Al4V is an expensive and difficult to machine alloy. Thus, it is an interesting alloy for thixoforging. However, heating of the billet into a homogeneous state of defined liquid fraction is difficult due to the poor thermal conductivity of Ti6Al4V. This paper analyses the potential of using time constant measurement for controlled heating of Ti6Al4V into the semi-solid state.

Research into energy efficiency of the underfloor heating system, assembled dry

The object of research is the thermal parameters of operation of a fragment of the floor heating system assembled dry, under conditions of actual application set in the lab premises. One of the most problematic issues in the course of our experimental study has turned out to be a small area of the investigated heating system, relative to the volume of the room. Considerable ambient air temperature fluctuations resulted in certain difficulties while the heating system entered the quasi-steady mode. We have established in our study the effect of thickness of a heat insulation layer under the heating circuit on a change in the density of heat flow from the floor surface to the air in a heated room. It is noted that the floor heating system, assembled dry, has small thermal inertia due to the absence of a relatively thick layer of the monolithic concrete slab (with high specific heat capacity), which is typically used for the installation of a heating system circuit. Specifically, it was established that the use of ceramic tiles as the finish coating, compared with laminate, significantly reduces the overall thermal resistance of heat transfer from a heat carrier to the air in a heated room. In this case, the presence of an aluminum heat-scattering plate, which is in direct contact with the outer surface of the pipe in a heating circuit, has a positive effect on the uniformity of distribution of thermal field in the plane of the floor. This in turn leads to a reduction in thermal stresses in the finish coating. Calculations show that the quantitative control over thermal load of such a system by changing the consumption of a heat carrier proves to be less effective than the qualitative control through changing its temperature. Experimental studies reveal that the density of a heat flow on the floor surface increases almost two-fold when using ceramic tiles, in comparison with laminate, at all other thermal system settings being almost identical. The research we conducted make it possible to construct a mathematical model for the operation of a floor heating system, assembled dry, whose application would enable the optimization calculations and improvement of the design of a given heater.

Cotton-like micro- and nanoscale poly(lactic acid) nonwoven fibers fabricated by centrifugal melt-spinning for tissue engineering.

Biodegradable materials in the form of nonwoven fibers have attracted increasing attention for tissue engineering applications because they offer large surface areas and interconnected networks. In this study, cotton-like nonwoven poly(lactic acid) (PLA) fibers were successfully fabricated by centrifugal melt-spinning. The effects of centrifugal speed and secondary melt-spinning processing on the morphology, mechanical properties, and cell compatibility of the fibers were investigated. Scanning electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy (FTIR), as well as cell culturing of MC3T3-E1 were used in this study. The results showed that centrifugal speeds from 350 to 1500 rpm satisfied the needs for fiber formation. The PLA fibers we prepared had three-dimensional structures with extensive diameter distribution from the nanoscale to several tens of micrometers, large pore sizes, and high porosities, significantly different from fibers produced by electrospinning. The fiber diameters and mechanical properties could be manipulated by controlling the centrifugal speed. The finest fibers were generated at 900 rpm with average diameters of 3.47 ± 3.48 μm. The fibers created by centrifugal melt-spinning exhibited lower cytotoxicity and higher cell proliferation than those obtained by electrospinning.

Energy-efficient solar power plants for autonomous heat supply in Russia

In the complex of measures for energy saving, partial replacement and reduction of consumption of fossil energy and electricity, water heating solar installations for heating systems have long been in practice for small energy facilities. Solar energy is one of the most dynamically developing directions of use of renewable energy sources, especially the introduction of which are associated with climatic conditions and technical requirements of their application. The territory of Russia is located mainly in the cold climatic zone and in regions with a sharply continental climate in which the operation of water heating solar plants is justified and most rational in seasonal use, in this case, their technical operation is carried out mainly during the non-heating period of the year. In such installations, in a number of cases, it is possible to avoid the need to use “non-freezing” heat carriers, and therefore the thermal schemes of the plants are simpler in design and cheaper, since heat exchangers or bivalent storage tanks can be excluded to transfer heat from the antifreeze to the water of the heating circuit or hot water system.

How much can be saved by changing the regulation of the apartment house boiler room

Boiler room for apartment building is in operation since 2009 and data are collected for cost evaluation. Question arises after a minor reconstruction. How much energy has been saved? The article selects and processes data that was available. It shows that the importance of the heating circuit pump control cannot be underestimated or overestimated. The article derives savings from gathered data.

Experimental study of natural convection heat transfer from a nonuniformly heated flat plate simulating PV panel

In view of the characteristic of Photovoltaic (PV) conversion, an experimental study has been conducted to investigate the natural convection heat transfer from a flat plate. In order to simulate the real PV cells, three electrical heating circuits were employed to achieve a linear nonuniform heat flux boundary condition. The major parameters, such as the gradient parameter of heat flux k, tilt angle θ and heat flux qw were introduced to analyze their influence on heat transfer ability. Both the local temperature distribution and the overall trend of Nusselt number have been presented. Comparing with the uniform thermal boundary condition, the results show that the local convection heat transfer coefficient is fluctuated at the positions where heat flux has changed. When gradient parameter of heat flux increases, the difference of local convection heat transfer coefficient at the top of the plate between tilt angle θ = 0° and 90° becomes smaller. Moreover, it is observed that the gradient parameter of heat flux has a promotion effect on average convection Nusselt number at larger tilt angle, but the effect becomes complex as tilt angle is smaller. Finally, a correlation combining all significant factors has been put forward to estimate the natural convection heat transfer.

АНАЛИЗ ТЯГОВО-ЭНЕРГЕТИЧЕСКОЙ ЭФФЕКТИВНОСТИ НОВЫХ ЭЛЕКТРОВОЗОВ

Objective: To study the specificities and parameters of the new, including innovative, freight and passenger electric locomotives, produced for domestic railways in the framework of the program of creating the new locomotives in 2004–2010. To analyze pull and energy efficiency parameters of direct current and alternating current electric locomotives. To estimate the maximum weight of trains and specific energy consumption of electric locomotives. To detect the advantages of new electric locomotives in comparison with those produced earlier. To develop guidelines on efficiency improvement of the new electric locomotives. Methods: Comparative analysis, methods of grade computations, linear regression analysis, power balance method. Results: The main design features and parameters of the new and earlier produced electric locomotives were studied, the former include the power of tractive motors, traction effort, as well as the speed at continuous rating of traction. The parameters of the new and earlier produced electric locomotives were compared. Key performance indicators of electric locomotives were analyzed, such as the maximum mass of a train and specific energy consumption on traction. The comparison of the above-mentioned indicators with performance indicators of earlier produced electric locomotives was given. According to calculation data and statistical data analysis the advantages of new electric locomotives were determined over those produced earlier. High performance of regenerative breaking was shown, specifically new electric locomotives. It was detected that in winter regeneration of electric energy was significantly reduced, in case of regenerative braking of passenger electric locomotives series EP1 with alternating current, as most of energy generated by tractive motors was spent on electric heating circuits of passenger cars. Guidelines on efficiency improvement of new electric locomotives were developed. Practical importance: The conditions in which new electric locomotives would implement the available advantages were determined, compared to those produced earlier. The elaborated offers make it possible to improve pull and energy efficiency of the new electric locomotives in operation.

Describing HVAC controls in IFC – Method and application

This paper describes a method to overcome current limitations in BIM software to design Building Automation and Control Systems (BACS) functions of Heating Ventilation and Air Conditioning (HVAC) systems through the extension of the IFC-files with information on control functions. The method is illustrated with the description of control functions for a use case including a boiler, a thermal storage, an air handling unit and a floor heating system modelled with a widely used BIM software tool. The focus is set on the description of three simple control functions: the definition of a heating curve, the setup of time schedules for the air handling unit and the flow temperature control for the heating circuit. The proposed method is based on available software tools linked together and enables adding complementary information on controls into the IFC-file, checking it for consistency, extracting and converting the IFC content into a linked data format. The use of semantic web technology allows for interoperability with various applications like e.g. software used for the commissioning or the supervision of HVAC systems and thus can contribute to reduce current quality and performance deficits of these systems.

Experimental analysis of a ground source heat pump in a residential installation after two years in operation

An experimental analysis was carried out in an installation with inverter operated ground source heat pump (GSHP) used for space heating with low temperature radiators, domestic hot water (DHW) production and pool heating at a single-family house during two years. The percentage contribution of each of the modes of operation are heating mode (86.5% on average) followed by pool heating (9.8% on average) and DHW production (3.7% on average). In heating mode, it was shown that the supplied temperature in the heating circuit that yields the best performance is 50 °C, since it is the lowest temperature at which the heat pump operates continuously. This work contributes to the literature with a database of actual and continuous data for 2 years. It includes the power consumption of the heat pump, the behaviour of the borehole for 2 years and the number of starts/stops and times of operation of the heat pump in each operating mode. COPs and SPFs have also been determined. During the first year the average SPF is 3.94 in heating mode, 3.24 in DHW mode and 4.11 in pool mode. In the second year 3.39 in heating mode, 3.21 in DHW mode and 4.18 in pool mode.

Thermophysical Properties of Five Industrial Steels in the Solid and Liquid Phase

The need for characterization of thermophysical properties of steel was addressed in the FFG-Bridge Project 810999 in cooperation with our partner from industry, Böhler Edelstahl GmbH & Co KG. To optimize numerical simulations of production processes such as plastic deformation or remelting, additional and more accurate thermophysical property data were necessary for the group of steels under investigation. With the fast ohmic pulse heating circuit system and a commercial high-temperature Differential Scanning Calorimeter at Graz University of Technology, we were able to measure the temperature-dependent specific electrical resistivity and specific enthalpy for a set of five high alloyed steels: E105, M314, M315, P800, and V320 from room temperature up into the liquid phase. The mechanical properties of those steels make sample preparation an additional challenge. The described experimental approach typically uses electrically conducting wire-shaped specimen with a melting point high enough for the implemented pyrometric temperature measurement. The samples investigated here are too brittle to be drawn as wires and could only be cut into rectangular specimen by Electrical Discharge Machining. Even for those samples all electrical signals and the temperature signal can be recorded with proper alignment of the pyrometer. For each material under investigation, a set of data including chemical composition, solidus and liquidus temperature, enthalpy, electrical resistivity, and thermal diffusivity as a function of temperature will be reported.

Method to investigate and plan the application of low temperature district heating to existing hydraulic radiator systems in existing buildings

This study presents a method to adapt existing hydronic systems in buildings to take advantage of low temperature district heating (LTDH). Plate radiators connected to double string heating circuits were considered in an optimization procedure, based on supply and return temperatures, to obtain the required logarithmic mean temperature difference (LMTD) for a low temperature heating system. The results of the analysis are presented as the average reduction of LMTD over the heating season compared to the base case design conditions. Two scenarios were investigated based on the assumption of a likely cost reduction in the end users' energy bills of 1% for each 1 °C reduction of return and average supply and return temperatures. The results showed possible discounts of 14% and 16% respectively, due to more efficient operation of the radiators. These were achieved without any intervention in the thermal envelope or to the heating systems, through simply adjusting the temperatures according to demand and properly controlling the plate radiators with thermostatic radiator valves (TRVs).

Development of a shape-memory-alloy micromanipulator based on integrated bimorph microactuators

This paper reports a novel structure of a shape-memory-alloy (SMA) micromanipulator with gripping mechanism. A featured integration of multiple SMA bimorph microactuators has been utilized to form a micromanipulator with three degrees of freedom. The design consists of two links (SMA sheets) and a gripper at the end of the second joint. The overall dimensions of the micromanipulator are 33mm×9mm×3mm. The displacement of each actuator is controlled by a heating circuit that generates a pulse-width modulation signal. Theoretical modeling of SMA actuators is studied and verified with simulation. The SMA micromanipulator is able to move in the x- and y-axis by 7.1mm and 5.2mm, respectively, resulting in a maximum displacement of 8.9mm. The micro-gripper has a maximum opening gap between its fingers of 1.15mm. The micromanipulator has a temporal response of 7.5s and 9s for its x- and y-axis. The maximum actuation force generated by the x- and y-axis was around 100mN and 130mN, respectively. The developed micromanipulator has been successfully used to move a small object.

Simulation and Evaluation of Solar Thermal Combi Systems with Direct Integration of Solar Heat into the Space Heating Loop

Usually, solar heat in combi systems is used via a buffer storage. In contrast to that, the solar collectors may be connected directly to the space heating circuit in order to store the heat in the building itself. Such a direct solar integration is investigated within system simulations for different layouts and heating elements. The simulations show significant reductions in the final energy demand as well as an increasing solar yield due to less thermal losses of the storage tank compared to the usual solution with one buffer storage. A prototype of one of the investigated heating concepts within a single family house proofs the functionality of the system concept and the high solar yield, particularly at low radiation levels. Since only a few manufacturers provide such system solutions with a direct solar integration, the results may have an important impact on the future development of combi systems.

Analysis of system improvements in solar thermal and air source heat pump combisystems

A solar thermal and heat pump combisystem is one of many system alternatives on the market for supplying domestic hot water (DHW) and space heating (SH) in dwellings. In this study a reference solar thermal and air source heat pump combisystem was defined and modelled based on products available on the market. Based on the results of an extensive literature survey, several system variations were investigated to show the influence of heat pump cycle, thermal storage and system integration on the use of electricity for two houses in the climates of Zurich and Carcassonne. A singular economic cash flow analysis was carried out and the “additional investment limit” of each system variation was determined for a range of economic boundary conditions. This is the maximum extra investment cost for the system variant compared to the reference system that will give a break even result for a 10year period. The results show that variations in electricity price affects the additional investment limit far more than the other economic parameters. Several of the variants show potential for achieving a cost benefit, but the potential varies a lot depending on load and climate boundary conditions. For all variants, the biggest difference in electricity savings was found for Zurich rather than in Carcassonne, which is explained by the larger heating load. However, in three cases the largest savings were for the SFH45 house despite the fact that the annual electricity use of the system is much lower than that for the SFH100 house, 3581kWh/year compared to 8340kWh/year. This was attributed to the fact that, in these cases, the operating level of the space heating circuit played a significant role, the SFH45 house being supplied with a 35/30°C heating system while the SFH100 was supplied with a 55/45°C heating system.

Direct integration of solar heat into the space heating circuit

Solar heat in solar thermal combisystems is usually used via a buffer storage. Alternatively, the solar collectors may be connected directly to the space heating circuit in order to store the heat in the building itself. Such a direct solar integration is investigated within system simulations for different layouts and heating elements. The operation of these systems requires a control strategy, which distributes the solar heat optimally between the potential heat sinks leading to the lowest overall energy consumption. This way a solar fraction may be achieved which is comparable to usual combisystems equipped with a three times larger buffer storage. A prototype of one of the investigated heating concepts within a single family house proofs the functionality of the system concept and the high solar yield, particularly at low radiation levels. The direct solar heating increases the solar fraction of combisystems significantly or alternatively decreases the necessary storage volume considerably if a certain system performance is desired.

"Walczak's Pipes" in the Greenhouse Heating System

Diversified heating circuits inertia is particularly important by high variability of external conditions were the greenhouse is often overheated or large heat losses are noted. To meet these needs a new generation of heating pipes were used. They are hexagram-shaped pipes called “Walczak’s pipe”. Tubes of such shape have several times smaller volume in comparison with traditional heating pipes of the same outer diameter and higher stiffness. The preliminary assessment of the “Walczak’s pipe” installed in the greenhouse is highly positive. Compared with the traditional system it enables better heat management. In the first research stage, the thermal efficiency was defined in different ambient conditions at selected flow parameters and various water temperatures. With regard to the accepted flow values, it is notable that “Walczak’s pipe” has greater thermal efficiency per unit of power comparing with traditional tube. During the study, there was also a thermographic analysis of pipes’ surface performed and the heat flow distribution was determined. Analyzing the temperature distribution on the “Walczak’s pipe” remarkable are the areas with higher values ​​comparing with standard tube. It can be concluded that in the heating system with “Walczak’s pipe” energy transferred by radiation increases. This is particularly advantageous solution to use in greenhouses. It allows to obtain a higher leafs temperature with respect to the ambient temperature (vegetation heating). This parameter has a beneficial effect on the vegetative growth of cultivated plants.

Thermal resistance of high power LED influenced by ZnO thickness and surface roughness parameter

Purpose – The purpose of this research is to study the effect of thickness and surface properties of ZnO solid thin film for heat dissipation application in LED. Heat dissipation in electronic packaging can be improved by applying a thermally conductive interface material (TIM) and hence the junction temperature will be maintained. ZnO is one of the oxide materials and used as a filler to increase the thermal conductivity of thermal paste. The thickness of these paste-type material cannot be controlled which restricts the heat flow from the LED junction to ambient. The controlled thickness is only possible by using a solid thin-film interface material. Design/methodology/approach – Radio Frequency (RF)-sputtered ZnO thin film on Cu substrates were used as a heat sink for high-power LED and the thermal performance of various ZnO thin film thickness on changing total thermal resistance (R th-tot) and rise in junction temperature were tested. Thermal transient analysis was used to study the performance of the given LED. The influence of surface roughness profile was also tested on the LED performance. Findings – The junction temperature was high (6.35°C) for 200 nm thickness of ZnO thin film boundary condition when compared with bare Cu substrates. Consecutively, low R th-tot values were noticed with the same boundary condition. The 600 nm thickness of ZnO thin film exhibited high R th-tot and interface resistance than the other thicknesses. Bond Line Thickness of the interface material was influenced on the interface thermal resistance which was decreased with increased BLT. Surface roughness parameter showed an immense effect on thermal transport, and hence, low R th (47.6 K/W) value was noticed with low film roughness (7 nm) as compared with bare Cu substrate (50.8 K/W) where the surface roughness was 20.5 nm. Originality/value – Instead of using thermal paste, solid thin film ZnO is used as TIM and coated Cu substrates were used as a heat sink. The thickness can be controlled, and it is a new approach for reducing the BLT between the metal core printed circuit board and heat sink.

Investigation of Thermal Losses in a Soft Magnetic Composite Using Multiphysics Modelling and Coupled Material Properties in an Induction Heating Cell

The complex interaction between material properties in an induction heating circuit was studied by multi physics simulation and by experimental verification in a full-scale laboratory heater. The work aims to illustrate the complexity of the system of interacting materials, but also to propose a method to verify properties of soft magnetic composite materials in an integrated system and to identify which properties are the most critical under different circumstances and load cases. Heat losses at different loads were primarily studied, from DC currents to AC currents at 15, 20 and 25 kHz, respectively. A FE model for magnetic simulation was correlated with a corresponding model for heat simulation. The numerical model, as well as the established input material data, could be verified through the experimental measurements. In this particular study, the current loss in the litz wire was the dominant heat source, thus making the thermal conductivity of the SMC the most important property in this material.

Temperature monitoring using fibre optic sensors in a lead-bismuth eutectic cooled nuclear fuel assembly

In-core temperature measurements are crucial to assess the condition of nuclear reactor components. The sensors that measure temperature must respond adequately in order, for example, to actuate safety systems that will mitigate the consequences of an undesired temperature excursion and to prevent component failure. This issue is exacerbated in new reactor designs that use liquid metals, such as for example a molten lead-bismuth eutectic, as coolant. Unlike water cooled reactors that need to operate at high pressure to raise the boiling point of water, liquid metal cooled reactors can operate at high temperatures whilst keeping the pressure at lower levels. In this paper we demonstrate the use of optical fibre sensors to measure the temperature distribution in a lead-bismuth eutectic cooled installation and we derive functional input e.g. the temperature control system or other systems that rely on accurate temperature actuation. This first-of-a-kind experiment demonstrates the potential of optical fibre based instrumentation in these environments. We focus on measuring the surface temperature of the individual fuel rods in the fuel assembly, but the technique can also be applied to other components or sections of the installation. We show that these surface temperatures can be experimentally measured with limited intervention on the fuel pin owing to the small geometry and fundamental properties of the optical fibres. The unique properties of the fibre sensors allowed acquiring the surface temperatures with a resolution of 30mK. With these sensors, we assess the condition of the test section containing the fuel assembly during different steps of the operation of the facility, including the heating and verification of the vacuum of the loop as well as the filling and draining of the LBE loop. We also identify a simulated electrical shut-down and heating circuit failure in the primed installation.

Examination and Optimization of a Heating Circuit for Energy‐Efficient Buildings

AbstractThe conference center darmstadtium in Darmstadt is a prominent example of energy efficient buildings. Its heating system consists of different source and consumer circuits connected by a Zortström reservoir. Our goal was to reduce the energy costs of the system as much as possible. Therefore, we analyzed its supply circuits. The first step towards optimization is a complete examination of the system: 1) Compilation of an object list for the system, 2) collection of the characteristic curves of the components, and 3) measurement of the load profiles of the heat and volume‐flow demand. Instead of modifying the system manually and testing the solution by simulation, the second step was the creation of a global optimization program. The objective was to minimize the total energy costs for one year. We compare two different topologies and show opportunities for significant savings.