Equivalent Thermal Resistance Research Articles

Experimental and numerical investigation on fire resistance of stainless steel core plate beams

The stainless steel core plate is an innovative lightweight structural material with broad application prospects. Experiments and finite element analyses were carried out to study the fire resistance of the stainless steel core plate beam in a three-sided fire. The load ratio and equivalent thermal resistance of the fireproof protective layer of stainless steel core plate beams were parametrically analyzed. A fire resistance design method for stainless steel core plate beams was presented. The results showed that the alternating sectional form of the core tube and mineral wool inside the beam resulted in an uneven temperature field distribution under a three-sided fire; with the premise that the weld was not damaged at high temperatures, the failure pattern of the core plate beam at high temperatures was the strength failure after the local instability of the web, which was the same as that at room temperature; the critical temperature of the lower flange decreased from approximately 870 °C to 485 °C, with an increase in the load ratio from 0.3 to 0.7; a prediction formula for the equivalent thermal resistance of fireproof protective layer required to reach a given fire resistance limit at different load ratios was established, which can be used for the design of stainless steel core plate beams for fire resistance.

Dynamics Model Construction and Characteristic Analysis of Heat Pipe Nuclear Reactor in Thermal State

In order to facilitate the power control method design of heat pipe nuclear reactor and avoid the high complexity of reactor core modelling, the paper adopts the lumped parameter method to build the thermal state dynamic model of heat pipe reactor. Firstly, the equivalence of the core structure and heat transfer process of the “MegaPower” heat pipe nuclear reactor is carried out to describe a single heat pipe in a hexagonal block. The complex heat transfer process in reactor core is simplified into a two-zone heat transfer model with only fuel and monolith. And the equivalent thermal resistance is used to describe the heat conduction process within gas gap and heat pipe. Then, the reactor core nuclear dynamic model is established using the neutron dynamics equation of point-reactor. Based on the principle of heat balance, the thermal dynamics models of fuel, gas gap, monolith and heat pipe are established respectively, so as to form the state equations of heat generation and heat transfer process in reactor core. Finally, the dynamic characteristics of the reactor with the reactivity disturbance without external control are simulated and analysed. The results show that the heat pipe reactor has a certain self-stability with reactivity disturbance, but the stability time is long, and the power fluctuation is large.

Inline Photothermal Surface Plasmon Detector Integrated in Titanium Dioxide Waveguides

Densely integrated photonic integrated circuits (PICs) require efficient solutions for monitoring the light intensity on chip in order to implement control and configuration operations to set and stabilize the working point of the circuit. To this end, waveguides supporting the propagation of surface plasmon polaritons (SPPs) are good candidates to realize small-footprint light detectors. In this work, we report on the realization of an in-line Surface Plasmon Detector (SPD) that exploits the photothermal effect to monitor the optical power in a titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) optical waveguide. Detailed design guidelines are provided to maximize the responsivity of the SPD, taking into account the effects of the metal geometry on the coupling between the dielectric and plasmonic modes, the power dissipated in the metal, and the equivalent thermal resistance of the structure. Experimental validation of the proposed device is provided demonstrating an ultra-compact 1.6-μm-long SPD operating at a wavelength of 1550 nm with a sensitivity of – 20 dBm and a bandwidth higher than 100 kHz. The proposed device concept can be ported to generic dielectric platforms and to other wavelength ranges where SPP propagation is supported.

Analysis of the thermal state of the electromagnetic mill inductor with oil cooling in stationary operation modes

Introduction. An electromagnetic mill (EMM) for the technological processing of various substances, which is based on the stator of a three-phase induction motor, is being studied. The stator winding has an increased current density, so the mill is provided with a system of forced cooling with transformer oil. Problem. Currently, there are no works on the thermal state calculation of the EMM with the given design and oil cooling. Therefore, the study of such EMMs thermal state is relevant, as it will contribute to increasing the reliability and efficiency of their work. Goal. Formation of a mathematical model of the thermal state of the electromagnetic mill inductor and the analysis of its heating in stationary modes of operation with cooling by transformer oil. Methodology. The problem of calculating the thermal state, namely the temperature distribution in the main parts of the electromagnetic mill, is solved by the equivalent thermal resistance circuit method. The design of the EMM is provided in a sufficiently complete volume, and on this basis, a corresponding equivalent thermal replacement circuit is formed, which is supplemented by an equivalent hydraulic circuit of oil passageways. An explanation is provided for the composition and solution of the equations algebraic system that describes the distribution of temperatures by the constituent elements of the EMM. Results. The thermal calculation results of the electromagnetic mill showed that the maximum heating temperature is much lower than the allowable one for the selected insulation class. According to the hydraulic scheme, the necessary oil consumption, its average speed and the corresponding pressure at the inlet of the intake pipe are determined, which are at an acceptable level. It is noted that the rather moderate temperature state of the inductor and the hydraulic parameters of the oil path are facilitated by such innovations in the design of the EMM as the loop double layer short chorded winding and axial ventilation channels in the stator core. Originality. Now EMM thermal equivalent circuits with air cooling only have been presented. Therefore, the developed thermal circuit of the oil-cooled inductor is new and makes it possible to evaluate the operating modes of the EMM. Practical value. The proposed technical solutions can be recommended for practical implementation in other EMMs. Taking into account the identified reserves of the EMM temperature state, a forecast was made regarding the transition from its oil cooling to air cooling. But the use of air cooling requires a change in the design of the EMM.

Numerical and Experimental Analysis of the ZFC Heat Release from a YBCO Bulk and Validation of YBCO Thermal Parameters

This article presents results from a simple experimental methodology used to determine the amount of heat transferred from an yttrium barium copper oxide (YBCO) bulk to liquid nitrogen (LN2) and LN2 consumption during the process of zero-field cooling (ZFC). The thermal power can be determined from the YBCO bulk temperature variation, which is difficult to measure with accuracy. In this procedure, the thermal power from the YBCO bulk to LN2 is determined from the measured rate of LN2 evaporation, considering the LN2 latent heat. To reduce the influence of room temperature heating and make the LN2 mass variation depend as much as possible on the heat released from the YBCO bulk, a step transient from room temperature into the LN2 is performed. The precision of results is determined from the rate of LN2 evaporation due to room temperature heating with the bulk already cooled by ZFC. The temperature evolution at the bulk lateral surface where the heat transfer is higher is also measured. The results from experimental measurements are compared with 3D finite element analysis (FEA) numerical results. The obtained evolutions of the temperature and thermal power from the YBCO bulk are used to validate YBCO thermal parameters, such as thermal conductivity and specific heat capacity at constant pressure. The YBCO bulk equivalent heat capacity and thermal resistance are determined by analyzing the equivalent first-order thermal lumped parameter circuit based on the obtained evolutions in time of the YBCO temperature and heat transferred to the LN2. The characteristics of dependence of the YBCO thermal resistance and heat capacity with temperature are obtained by correlating their time evolutions with the bulk average temperature evolution in time. The YBCO-specific heat capacity at constant pressure is then calculated by dividing the obtained bulk heat capacity by the bulk mass. The YBCO thermal conductivity is calculated from the obtained thermal resistance considering an equivalent bulk section and length toward the main direction of heat flux.

Thermal Modeling and Analysis of Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Variable flux memory machine (VFMM) can be regarded as a promising candidate for electric vehicles (EVs) owing to its advantages of excellent flux adjustment capability and overall efficiency improvement over an extended operating range. However, the uncertain internal thermal behavior due to magnetization state (MS) change has an immense influence on electromagnetic performance of permanent magnet, which makes the precise MS estimation of low coercive force PM a challenging issue. To explore the benefits of MS manipulation on temperature rise reduction and provide an effective method to accurately evaluate temperature rise in VFMM, a magnetic-thermal coupling model of the newly developed hybrid-magnetic-circuit VFMM accounting for different MSs is established in this article. The lumped parameter thermal network (LPTN) model and computational fluid dynamics based finite-element (FE) method are employed to analyze the temperature characteristics, respectively. First, the losses of the investigated machine are calculated by adopting both the FE method and analytical equations. Afterward, the equivalent thermal resistances and heat transfer coefficients are determined by employing the LPTN model. Meanwhile, FE modeling is employed to analyze the three-dimensional thermal field distribution. Finally, a prototype machine is fabricated and experimentally measured, which can confirm the validity of the theoretical analyses.

Optimize the Location of Embedded Pipes by Using Low-Grade Natural Thermal Energy/Waste Heat for Thermal Activated Façade

The final effect of a thermal activated façade (TAF) wouldn’t only be influenced by the thermal character of the wall, dimensions and distance of the embedded pipes besides flow rate and temperature of the medium, but also by the location of the pipes. The location of the embedded pipes not only affects the final effect of thermoactivated, there is at the same time an obvious correspondence with the temperature of the medium. The simulations and lab investigations have concluded that the optimization the depth of embedded pipes, is necessary in order to use low-grade natural thermal energy/waste heat (LGTE) to achieve TAF. Using the bench mark of the “equivalent thermal resistance” (ER-Value), it is clear that the closer the pipes are located to the outside, the less energy grade is required. However, not all of the LGTE with higher temperature than outdoor air can be used for TAF. The limit of LGTE is the “Invalid Medium Temperature” (IVMT); although there is still a temperature difference between the medium and the outdoor environment, its thermal driving potential is not enough to form an effective heat transfer between the pipe and its surrounding per unit length, so that the medium circulation in the wall hardly contributes to changing the temperature gradient in the wall.

Thermal performance of starch/beet-pulp composite bricks for building insulation at a wall scale

This paper aims to study the thermal performance at wall scale of hollowed bricks made of starch/beet-pulp bio-composites identified as a potent solution for the development of sustainable, non-load bearing, insulation materials to be used in the construction sector. Numerical studies on thermal resistance using the COMSOL software were conducted to study the characteristics of optimal hollowed brick pattern. The numerical study results were then compared with thermal resistance calculations based on the NF EN ISO norm 6946 (2017). In a later stage, an experimental 1 m x 1 m wall made of starch/beet-pulp composite bricks and binder was built. Experimental studies on the thermal resistance and thermal imaging were carried out on the wall inserted in a bi-climatic chamber showing only a 3 °C change of the surface temperature of the wall on the one side after applying a 23 °C temperature difference on the other side for 7 h. The equivalent thermal resistances were obtained equal to 1.180 m2. K/W, 1.218 m2. K/W, 1.10 m2. K/W respectively as described previously which reflected a good agreement between the numerical and experimental results.Finally, the obtained results reflected the high thermal performance of the studied starch/beet-pulp composites.

Constructal Optimizations of Liquid-Cooled Channels with Triangle or Square Sections in a Cylindrical Heating Body

Two new integrated models with heat source–heat sink are established, in which isothermal liquid cooling channels with triangle or square sections are, respectively, embedded in a cylindrical heating body with uniform heat production. Based on constructal theory, under the conditions of a fixed cylinder cross-sectional area and the proportion of channels, taking the dimensionless maximum temperature and the dimensionless entransy equivalent thermal resistance (EETR) as the optimization goals, the influences of distribution of liquid cooling channels on the heat dissipation capacity of integrated models are studied with the number and the center distance of liquid cooling channels as design variables, and the optimal constructs with different proportions of channels are obtained. The results show that when the proportion of channels, cross-sectional area and the number of liquid cooling channels are given, there is an optimal center distance to make the overall heat dissipation performance of the integrated model reach its best, but the optimal center distances for the two indicators are different. The dimensionless maximum temperature and the dimensionless EETR decrease when the proportion of channels increases, but the optimal dimensionless center distances are almost the same for different proportions of channels. The dimensionless maximum temperature with the triangular cross-section is lower than that with the square cross-section under the conditions of constant cross-sectional area and dimensionless center distance, which is the same as the case for the dimensionless EETR. The results can furnish the theoretical guidelines for the thermal design of cylindrical devices needing efficient cooling.

A combined solution of thermoelectric coolers and microchannels for multi-chip heat dissipation with precise temperature uniformity control

• Conbined TEC and microchannel cooling proposed for multi-chip heat dissipation. • Based on the change of applied current, the equivalent thermal resistance of TEC is changed to realize the active temperature control of chip. • Heat dissipation with temperature uniformity control of multi-chip combined cooling is studied. Effective thermal management with precise temperature uniformity is necessary to improve the performance and stability of multi-chip devices such as active phased array antennas, semiconductor laser radar systems, and light emitting diode (LED) arrays. This study proposes a combined solution for multi-chip devices heat dissipation that integrates thermoelectric coolers (TECs) and microchannel heat sink to tune the temperature of each chip dynamically by controlling multiple TEC currents independently. The equivalent variable thermal resistance of the TEC can be dynamically adjusted under different TEC currents, thereby realizing the equivalent thermal resistance value of TECs change on the heat dissipation path of different chips and the precise temperature control and continuity at desired temperature range. A simplified thermal resistance network of multi-chip is established to illustrate the dynamic control mechanism of multi-chip temperature uniformity based on the variable thermal resistance. Not only the heat dissipation and temperature control of single chip under different operating conditions (TEC current, flow rate, and heat flux), but also the temperature uniformity control of multi-chip is studied. The combined cooling scheme is compared and analyzed with the microchannel cooling. The results show that this combined cooling scheme can achieve precise temperature control of multiple chips with maximum temperature difference less than 0.3 °C and temperature standard deviation less than 0.07 °C, which is far less than the maximum temperature difference of 7.89 °C and temperature standard deviation of 3.55 °C when the heat flux is 50 W/cm 2 . This represents a feasible solution for the realization of precise temperature uniformity and dynamic temperature control in multi-chip devices.

A novel transient thermal circuit model of buried power cables for emergency and dynamic load

In order to improve the utilization rate of cable while ensuring safety and reliability, accurate and rapid evaluation of transient temperature rise of directly buried power cables is useful to improve the management level of dynamic capacity increase and emergency load conditions. Since the existing thermal circuit model is relatively complex or not very accurate, an equivalent three-branch transient thermal circuit model is presented for the complex cable structure and heat dissipation environment based on the uniqueness of the temperature field. Considering the electric circuit similarity, the transient analysis method of the centralized parameter network in the circuit is used to establish the transient adjoint model of the thermal capacity branch, provide the node conduction matrix of the transient thermal circuit model, and write the node temperature rise equation as a function of the node heat flow. By comparing the solution of the thermal circuit model with the finite element results, and the genetic algorithm is used to optimize and obtain the equivalent thermal resistance and thermal capacity parameters of the transient thermal circuit model. The comparison of finite element calculation results proves that the proposed three-branch transient thermal circuit model is more accurate than the two-branch thermal circuit model. Compared to the traditional all-part thermal circuit model, the three-branch model can be rapidly solved and easily applied in engineering.

Hybrid thermal management strategy with PCM and insulation materials for pulsed-power source controller in extreme oil-well thermal environment

• Thermal management strategy for PPS controller are experimentally investigated. • Metal PCM can lower thermal resistance from 1.7 to 1.1 K/W compared to paraffin. • Silica aerogels can alleviate heat transfer from external environment by 59.9%. • Chip operating time can be prolonged when using present thermal management strategy. The application of pulsed-power source (PPS) can effectively improve the efficiency of shale oil exploitation. However, the severe underground environment with high temperature, pressure and viscosity will bring great challenges to electronic components. This study presents a hybrid thermal management strategy (HTMS) for the PPS controller. The heat storage unit filled with phase change materials (PCMs) is applied for internal thermal management, and the performance of PPS is evaluated when paraffin and low melting temperature alloy (LMTA) are respectively used as PCMs. On the other hand, glass wool, phenolic foam and silica aerogels are implemented to construct a sandwich structure for external thermal protection. Results show that the LMTA can extend the safe operating time of equipment from 50 min to over 250 min in comparison to paraffin while lowering the average equivalent thermal resistance from 1.7 K/W to about 1.1 K/W. Besides, the application of glass wool and phenolic foam is eligible to extend the operating time by 63 % and 57 %, respectively, with external ambient temperature at 100 °C. After replacing by the silica aerogels, the thermal insulation effect can be further improved. As the result, with the application of HTMS, the PPS controller is tested under more severe thermal environment with ambient temperature of 150 °C. It is noticed that the operating time prolongs to 50 min within the maximum junction temperature of 80 °C.

Heat transfer performance and prediction of open pulsating heat pipe for self-cooling cutting tool

The pulsating heat pipe (PHP) can be used to transfer massive heat to reduce the thermal damage to the cutting tool when machining difficult-to-cut materials. To select a better open PHP, the heat transfer performance was experimentally investigated in this study. The operating characteristics of different types of working fluids under different heat flux were analyzed compared with the closed PHP. Visual experiments were established to verify the experimental characteristics. The effects of heat flux, length, ratio of inner/outer diameter, and inclination angle on equivalent thermal resistance were analyzed. Based on the experimental data and four boosting integrating learning methods, a model for heat transfer performance prediction was proposed. The prediction model based on the CatBoost method had better goodness-of-fit and the best prediction effect. The R2, MAPE, and RMSE of the validation set were the best, which are 0.9258, 7.2564, and 0.1057 respectively. In addition, the contribution of input parameters to the output results was evaluated, while L, Di/Do, and Pr were the top three variables. Sub-tree structures used to explain the prediction model were also presented. This proposed prediction model can be used to select the most suitable open PHP before designing PHP self-cooling tools.

Contribution to the Research and Development of Innovative Building Components with Embedded Energy-Active Elements

The research described in this study focuses on the innovation and optimization of building envelope panels with integrated energy-active elements in the thermal barrier function. It is closely related to developing and implementing the prototype prefabricated house IDA I with combined building-energy systems using renewable energy sources. We were inspired by the patented ®ISOMAX panel and system, which we have been researching and innovating for a long time. The thermal barrier has the function of eliminating heat loss/gain through the building envelope. By controlling the heat/cold transfer in the thermal barrier, it is possible to eliminate the thickness of the thermal insulation of the building envelope and thus achieve an equivalent thermal resistance of the building structure that is equal to the standard required value. The technical solution of the ISOMAX panel also brings, besides the use of the thermal barrier function, the function of heat/cold accumulation in the load-bearing part of the building envelope. Our research aimed to design and develop a panel for which the construction would be optimal in terms of thermal barrier operation and heat/cold accumulation. As the production panels in the lost formwork of expanded polystyrene (according to the patented system) proved to be too complicated and time consuming, and often showed shortcomings from a structural point of view, the next goal was to design a new, statically reliable panel construction with integrated energy-active elements and a time-saving, cost-effective, unified production directly in the panel factory. In order to develop and design an innovative panel with integrated energy-active elements, we analyzed the composition of the original panel and designed the composition of the innovative panel. We created mathematical–physical models of both panels and analyzed their energy potential. By induction and an analog form of formation, we designed the innovative panel. Based on the synthesis of the knowledge obtained from the scientific analysis and the transformation of this data, most of the building components and all the panels with integrated energy-active elements were manufactured directly in the prefabrication plant. Subsequently, the prototype of the prefabricated house IDA I was realized. The novelty of our innovative building envelope panel solution lies in the panel’s design, which has a heat loss/gain that is 2.6 times lower compared to the ISOMAX panel.

Performance of flat-plate, flexible polymeric pulsating heat pipes at different bending angles

The heat transfer performance of a flat-plate, flexible polypropylene pulsating heat pipe (PHP) is evaluated experimentally when the device is bent at different angles, and for different layouts of the evaporator and the condenser. Flexible pulsating heat pipes are a passive thermal management technology with important prospective applications in foldable portable electronics, deployable systems (such as cube satellites), soft robotics, and many others. While a number flexible PHPs have been developed in the recent past, to date, there is insufficient information about the influence of the bending angle (conformation) and of the reciprocal positions of the heat sink and source (configuration) on their thermal performance. Several polypropylene PHP prototypes (250 mm ×100 mm ×1.5 mm) with a channel width of 5 mm and different loop geometries were fabricated using selective transmission laser welding technology. Ethanol and FC-72 were used as heat transfer fluids at a filling ratio of 50%. The PHP performance was evaluated through the equivalent thermal resistance of the device, calculated from the surface temperatures of both the evaporator and the condenser during an ascending/descending stepped heat input ramp applied to the evaporator. The experimental results show that conformation arrangements have no significant effect on the thermal performance, however it may affect the PHP start-up.

No-vacuum Mono-Tube Compound Parabolic Collector Receiver for Linear Fresnel Concentrator: Numerical and Experimental Approach for Dynamic Behavior Assessment

The present paper aims to develop a novel simplified transient model to investigate the dynamic behavior of a no-vacuum mono-tube receiver equipped with a compound parabolic collector. Considering the intermittency of solar radiation, predicting receiver thermal behavior is critical for linear Fresnel concentrator design and operation. From this standpoint, this research focuses on determining whether or not the steady-state assumption influences the receiver’s performance. Unlike the current models accounting for all the receiver components, the proposed model considers the absorber tube as the primary node and focuses on the heat transfer fluid temperature distribution. The remaining components form an equivalent thermal resistance through which heat loss occurs. The global heat losses are then characterized using an experimental receiver prototype with tube diameter of 70 mm, an aperture of 500 mm, and a secondary reflector. The overall receiver heat loss coefficient was determined at different absorber temperatures ranging between 60 and around 265 °C. The heat loss coefficients measured varied from 4.7 to 8.5 W/m2 K. The model computes receiver performance using the measured overall heat loss coefficient based on real solar data. The receiver response at steady and transient states has been conducted and discussed according to several design parameters, including the heat transfer fluid nature and mass flow rate, the receiver length, and the absorber tube thickness. For the same working conditions, synthetic oils fluid allows achieving higher efficiencies whereas molten salts enable reaching higher outlet temperatures. For the metal wall thicknesses ranging between 2 and 3 mm and the fluid outlet temperature varying between 250 and 300 °C, the receiver thermal efficiency during the day remains relatively close to 75 %. The impact of the absorber tube thermal inertia has been investigated by analyzing the dynamic behavior under various close-to-real-world scenarios. Results have shown that the steady-state assumption does not influence if the metal wall tube thickness is lower than 3 mm.

Led source of light with high light circuit

THE PURPOSE. Consider the problems of the heat transfer process in the structural elements of the LED light source. Describe the cooling system of an LED light source using an equivalent circuit and thermal resistances. Conduct a comparative analysis of cooling systems for LED lighting devices. Perform thermodynamic calculations of the light device radiator using computer programs of automatic design systems. Suggest a way to improve the heat transfer properties of the radiator of the LED light source.METHODS. When solving the tasks set, the method of retrospective-prospective meta-analysis was used, computer programs of automatic design systems and direct determination of technical parameters using measuring instruments were used.RESULTS. The article describes the relevance of the topic, discusses the features of the heat transfer process in the structural elements of the LED light source. Thermodynamic calculations of the radiator of the lighting device were made using computer programs of automatic design systems KOMPAS and SolidWorks. The article proposes a method for improving the heat transfer properties of the radiator of an LED light source.CONCLUSION. There are many different cooling systems with their own advantages and disadvantages. The most efficient cooling systems are forced cooling systems, however, their use entails an increase in the final cost of the lighting device and a decrease in its light output due to an increase in energy consumption. Passive cooling systems are relatively cheap, but to provide effective cooling of LEDs, they must have a sufficient area of contact with the heat source, have good thermal conductivity and heat dissipation. In this case, the best way to improve the heat transfer properties of the radiator is to apply a special coating with a high heat transfer. This will increase the cooling efficiency with minimal cost without resorting to a significant change in the design features of an existing system.

Assessing the performance of a gas-water heat exchanger based on micro-heat pipe technology

ABSTRACT The paper presents a gas-water heat exchanger based on the technology of a microheat pipe. The heat exchanger parameters, such as inlet and outlet temperature of flue gas, wind speed and inlet and outlet temperature of the water, were measured in practice. The analysis data showed that the temperature difference between the flue gas and the flue gas before and after heat exchange increased with the inlet temperature. At the same time, the water temperature difference remained unchanged. This paper analyzed the influence of different inlet temperatures and wind speed on heat transfer using the control variable method. It was found that the inlet temperature of flue gas was 190°C and the heat transfer efficiency was stable above 0.7 when the heat transfer was maximum, which was higher than the national standard. The irreversibility of the heat transfer process was analyzed by introducing the dimensionless equivalent thermal resistance R* and the thermal conductivity N*, which were derived from the dissipation number of the entransy. It was found that the heat exchanger operated stably when the flue gas temperature and the wind speed were constant. However, when the flue gas temperature or wind speed was increased, it was appropriate to use a lower wind speed to maintain the heat transfer performance before the temperature reached the critical temperature. After getting the critical temperature, the heat transfer performance was compared with the effective degree-NTU method and the effective degree-thermal conductivity method.

Analysis of heat transfer characteristics and entransy evaluation of high viscosity fluid in a novel twisted tube

• A novel twisted tube is to improve the secondary flow distribution inside the tube. • Heat transfer performance and entransy evaluation are investigated numerically. • The novel twisted tube reduces the entransy dissipation compared with the plain tube. • Effects of geometry parameters and Reynolds number are analyzed comprehensively. The non-uniformity of the secondary flow distribution in the twisted oval tube has impeded its further improvement of the heat transfer performance. A novel twisted tube (NTT) improves the distribution of the secondary flow and enlarges the effect of the secondary flow on the main flow, intensifying the radial mixing and equalizing the temperature distribution of the fluid, which strengthens the convective heat delivery in the near wall region and the core zone comprehensively. Heat transfer characteristics and entransy evaluation of water and engine oil in the NTT are investigated in the low Reynolds number ( Re ) region. The heat delivery performance of the NTT improves with the reduction of the distance ratio ( DR ) and the twist pitch ratio ( PR ), and also raises with the increase of Re . The friction factor of the NTT increases with the reduction of DR and PR , and decreases with the rise of Re . Compared with the twisted oval tube, the NTT could elevate the Nusselt number and enlarge the friction factor by 1.49–1.56 times and 1.32–1.41 times, respectively. Compared with the plain tube, the NTT could improve the Nusselt number and increase the friction factor by 2.42–2.76 times and 1.48–1.56 times, respectively. The equivalent thermal resistance of the NTT decreases with the reduction of DR and PR and reduces with the increase of Re . The Case 4 with the minimum DR and the smallest PR shows the supreme heat transfer performance and the lowest equivalent thermal resistance. The NTT could reduce the entransy dissipation remarkably, compared with the plain tube, the NTT could decrease the equivalent thermal resistance by up to 58% for water under the condition of constant wall temperature and could reduce the equivalent thermal resistance by as much as 53% for engine oil under the condition of given heat flux on the tube wall.

Contribution to research on ground heat storages as part of building energy systems using RES

Contribution to research on ground heat storages as part of building energy systems using RES