Heat Transfer Devices Research Articles

Numerical assessment of irreversibility in radiated Sutterby nanofluid flow with activation energy and Darcy Forchheimer

Entropy generation is a concept that is primarily associated with thermodynamics and engineering, and it plays a crucial role in understanding and optimizing various processes and systems. Applications of entropy generation can be seen in turbo machinery, reactors, chillers, desert coolers, vehicle engines, air conditioners, heat transfer devices and combustion. Due to industrial applications entropy generation has gained attention of researchers. Owing such applications, current communication aims to model and analyzed the irreversibility in Sutterby nanoliquid flow by stretched cylinder. Momentum equation is reported by considering porosity, Darcy Forchheimer and magnetic field. While in energy equation radiation and Joule heating effects are accounted. Activation energy impact is accounted in the modeling of concentration equation. Thermodynamics second law is utilized for physical description of irreversibility analysis. Through similarity transformations dimensional equations representing flow are transformed to dimensionless ones. Numerical solution for ordinary system is obtained via Runge–Kutta-Fehlberg scheme in Mathematica platform through NDsolve code. Influence of prominent variables on velocity, entropy, temperature, Bejan number and concentration are graphically analyzed. Coefficient of skin friction, gradient of temperature and Sherwood number are numerically analyzed. The obtained results show that velocity field decreases through higher porosity and Forchheimer variables. Velocity and temperature curves shows an opposite trend versus magnetic parameter. A decay in concentration distribution is noticed through larger Schmidt number. Entropy generation amplifies against magnetic parameter and Brinkman number.

Experimental study of the hydraulic resistance of plate modules of a heat and mass transfer device

Experimental study of the hydraulic resistance of plate modules of a heat and mass transfer device

A COMPREHENSIVE REVIEW STUDY ON HEAT TRANSFER IMPROVEMENT TECHNIQUES WITHIN TWISTED TUBES

Heat transfer equipment has been used in many different domestic and industrial applications. There has been a concentrated effort to create a heat exchanger design that will reduce energy requirements while saving materials and other costs. Increasing the effective heat transfer surface area or creating turbulence are two common ways to improve heat transfer and hence lower thermal resistance. The thermal Performance Factor is the ratio of the difference in heat transfer rate to the difference in friction factor and serves as a metric to assess the efficiency of heat transfer enhancement technologies. Different types of twisted tubes are used in many heat transfer improvement devices. geometrical parameters of the twisted tube encompassing the aspect ratio, twist ratio, twist direction, twist length, etc. impact the heat transfer. For Instance, oval pipes with unequal twist pitches have a thermal performance factor (1.75) and equal twist pitches have a thermal performance factor (1.98). furthermore, the thermal performance factor of the twisted tube with oval dimples is equal to 1.19 compared with the twisted tube without dimples. The thermal performance factor of the twisted tube with oval dimples is equal to 1.38 compared with the straight tube, with another improvement to the twisted tube that improves the heat transfer properties by disrupting the thermal boundary layer and destabilizing it. This paper presents a comprehensive investigation of passive heat transfer devices (twisted tubes) and their relative merits in a myriad of commercial applications.

Energy and exergy assessment of a flat plate solar thermal collector by examine silicon carbide nanofluid: An experimental study for sustainable energy

The main reason behind the inefficient performance of heat transfer devices was the use of conventional fluids with poor heat transfer properties. However, remarkable improvement in efficiency was observed in thermal devices when these fluids were replaced by nanofluids with good thermal transfer properties. Various kinds of nanoparticles were used due to their increased thermal conductivity. Such nanofluids are particularly exploited in renewable energy systems like solar collectors. The most frequently used solar collectors in thermal applications are FPSCs. The current experimental research investigates how the use of nanofluids of SiC/DW impact the efficiency of a flat plate solar collector functioning in the climatic environment of Gödöllő, in Hungary. Firstly, the synthesis of nanofluid based on distilled water that contained nanoparticles of SiC (with a size 45–60 nm) at volume fractions of 0.025 %, 0.05 %, 0.075 %, and 0.1 % was performed. Various measurement instruments were used to test the thermophysical characteristics and stability. In the subsequent stage, thermal and exergy efficiencies tests were conducted on the solar collector with a range of mass flow rates including 0.025, 0.033, and 0.041 kg/s in which the collector’s efficiency was calculated according to the ASHRAE standard 93–2003. This developed collector was subjected to different flow rates, and nanoparticle concentrations to find out the effect of nanofluids on the thermal and exergy efficiencies of the solar collector. The findings indicated that an increase of up to 30.3 % was achieved in the fluid’s thermal conductivity through the addition of nanoparticles of SiC. The collector’s thermal efficiency was maximised at 77.43 % when the value of [(Ti – Ta)/GT] was zero for a volume fraction (φ) of 0.1 % and mass flow rate of 0.041 kg/s, which represented a 35.53 % increase over the base liquid. Additionally, an increase of 37.4 % was recorded for the exergy efficiency at volume fraction (φ) of 0.1 % than its value in distilled water. Ultimately, the heat transfer properties of the device showed improvement.

Investigation of thermodynamics characteristics of ternary hybrid nanofluid flow over a stretching sheet

This paper considers two-dimensional electrically conducting and incompressible ternary hybrid nanofluid flow on a stretching sheet with the convective boundary condition and heat source effect. Relevant similarity formulas are effectuated in converting the governing equations into a system of ordinary differential equations (ODEs) and are further treated numerically using the spectral quasilinearization method (SQLM), with error analysis. The prominent dimensionless parameters controlling the flow, and heat transfer characteristics are discussed. The results of this study show that Eckert number, heat source parameter, and magnetic effect boost the temperature profile. This work expected significant information for the future applications of innovative heat transfer devices, as well as a valuable reference for researchers to study flow behavior under various assumptions.

Key features and highly effective prediction of complete startup from frozen state for high-temperature heat pipe in heat pipe reactor

High-temperature heat pipe is an efficient phase change heat transfer device, widely applied in the space nuclear reactors, the China Fusion Engineering Test Reactor, solar collectors, and the thermal protection of hypersonic vehicles. In order to understand the startup characteristics of the heat pipe and to predict its transient behavior with high accuracy, this paper first experimentally investigated the startup performance of a sodium heat pipe from the frozen state under different heating powers from 534 W to 1897 W. Then, a new compressible flow model for startup from the frozen state was developed and verified, solved the independence problems of mesh number and time-step used in the numerical treatments of most traditional heat pipe codes. Finally, based on the assessed model and experimental data, the startup procedure and the influences of heating power on the working temperature, kick-in time, and temperature difference were analyzed respectively. The comparisons indicated that the new model is extremely informative and effective, and the results provided knowledge for understanding the safe and optimum working regime of a high-temperature heat pipe using in heat pipe reactor.

Numerical investigation on the start-up and heat transfer performance of dual-diameter pulsating heat pipes

The pulsating heat pipe stands out as a promising heat transfer device in various applications. Its start-up and heat transfer performance are however crucial to understand. In this study, three single-loop dual-diameter pulsating heat pipes (DPHPs) are proposed by changing both channel diameters of a uniform pulsating heat pipe (UPHP). The diameter difference is 1.0 mm, 2.0 mm, and 3.0 mm, respectively. The filling ratios range from 30 % to 70 %, and the inclination angles range from 0° to 90°. The effects of diameter differences, filling ratios, and inclination angles on the start-up and heat transfer performance are analyzed through two-dimensional transient numerical simulations. Results show that the diameter difference significantly affects the start-up and heat transfer performance of PHPs. Among the proposed diameter differences, 2.0 mm is the appropriate case for obtaining the best thermal performance. The start-up time and thermal resistance reduce by 19.1 % and 34.5 %, respectively, compared to a UPHP. In the start-up stage of DPHPs, two growth patterns of vapor bubbles are discovered, namely directed growth and swift amassing growth. They are the primary reason for the earlier start-up of DPHPs compared to UPHPs. Moreover, the start-up and heat transfer performance of DPHPs exhibit lower sensitivity to inclination angles, and the sensitivity reduces with the increasing diameter differences. However, the DPHP with a larger diameter difference (3.0 mm) causes the start-up temperature to rise. The optimum filling ratio is dependent on heating powers, 30 % and 50 % are the optimum case for the heating power of 30 W and 90 W, respectively. The present study aims to provide a reference for the design of DPHPs.

Heat transfer and two-phase flow of a metal foam enhanced horizontal loop thermosyphon for high power solar thermal applications

Loop thermosyphon, as an efficient heat transfer device, is considered as a potential receiver for high power solar thermal applications. A horizontal loop thermosyphon with metal foam (MF-HLTS) was proposed for further improve the thermal stability when operated in horizontal position, and experimentally investigated compared to that without metal foam (S-HLTS) in this work. The experimental results show that the filling ratio of 57.5% produced the lowest total thermal resistance of 0.056–0.093 K/W, with a maximum increase of 836% in terms of thermal performance at steady-state. Meanwhile, the start-up performance of MF-HLTS with the progressive start-up is superior to that of the S-HLTS and EF-HLTS with the overshoot start-up in terms of start-up stability and time under various filling ratios and heat fluxes. Additionally, the bidirection-oscillation flow is easy to occur inside S-HLTS, resulting in temperature and pressure fluctuations with amplitudes reaching 12.53 kPa and 2.67 °C. For MF-HLTS, the internal flow pattern exhibits stable unidirectional flow, with a maximum improvement of 78.5 times. All results demonstrated that the horizontal loop thermosyphon with the auxiliary of a metal foam in evaporator and straight section can greatly improve thermal performance and flow stability, which is promising in the energy utilization applications.

Design and experimental validation of a high capacity loop heat pipe for avionics cooling

With the rapid development of modern aviation industry, the power of avionics has been increasing continuously, bringing great challenge to thermal management. As an efficient two-phase heat transfer device, loop heat pipe (LHP) holds great application potential in avionics cooling. To address the issue of inadequate heat transfer capability, a set of kW-class LHP was specially designed and experimentally validated considering the airborne environment. A detailed introduction covering the entire design process was presented, in which some targeted design criteria were provided. Ammonia was chosen as the optimal working fluid, and stainless steel envelope with a nickel wick was adopted. Experimental validation showed that, at a heat sink temperature of 20 ℃, the designed LHP could achieve a maximum heat transfer capacity of 1021 W, confirming the efficacy of the design method. The average heat flux at the evaporator could reach 12.04 W/cm2. The LHP exhibited a maximum and minimum thermal resistance of 0.16 and 0.054 ℃/W, respectively, achieved at heat loads of approximately 50 W and 600 W. The maximum temperature fluctuation at the center of the saddle surface was no more than ±1.40 ℃. A method for estimating the heat leak between the evaporator and the compensation chamber was also developed, and the maximum heat leak rate was calculated to be approximately 5.2%. Moreover, the designed LHP also manifested excellent startup performance and operation stability.

Topology Optimization of Turbulent Flow Cooling Structures Based on the k-ε Model.

Topology optimization (TO) is an effective approach to designing novel and efficient heat transfer devices. However, the TO of conjugate heat transfer has been essentially limited to laminar flow conditions only. The present study proposes a framework for TO involving turbulent conjugate heat transfer based on the variable density method. Different from the commonly used and oversimplified Darcy model, this approach is based on the more accurate and widely accepted k-ε model to optimize turbulent flow channels. We add penalty terms to the Navier-Stokes equation, turbulent kinetic energy equation, and turbulent energy dissipation equation, and use interpolation models for the thermal properties of materials. A multi-objective optimization function, aiming to minimize the pressure drop and the average temperature, is set up to balance the thermal and hydraulic performance. A case study is conducted to compare various optimization methods in the turbulent regime, and the results show that the present method has substantially higher optimization effectiveness while remaining computationally inexpensive.

Hydrophilicity degradation and steam-induced rewetting during capillary-fed boiling

Capillary-fed evaporation/boiling is a crucial process that occurs within two-phase heat transfer devices. Herein, we delve into the capillary-fed boiling performance of a grooved wick with an upper width of 200 μm and a depth of 150 μm fabricated by ultrafast laser micromachining and observe a substantially 51.8% reduction in critical heat flux (CHF), from 145.0 ± 3.3 W/cm2 to 70.1 ± 2.9 W/cm2, following five boiling cycles. Comprehensive experimental investigations are conducted to gain insights into the underlying mechanisms. Our analyses confirm that the diminished CHF arises from the hydrophilicity degradation of the evaporator, attributed to the surface adsorption of airborne organics after the dry-out. The superhydrophilic evaporator becomes highly hydrophobic with static contact angles (CAs) greater than 140° after five boiling cycles. Liquid wicking in subsequent boiling tests initiates through a steam-induced rewetting process. Moreover, we present compelling evidence that the undesired hydrophilicity degradation is effectively mitigated on nanoporous surfaces. Consequently, a microgroove-nanoparticle composite wick successfully retains its original boiling performance during repeated boiling tests. These findings enhance the understanding of capillary-fed boiling performance and offer promising avenues for the design of high-performance wicks tailored for ultrathin two-phase heat transfer devices.

Experimental study on the pressure drop characteristics of a supercritical CO2/R134a mixture in a rectangular microchannel

The proper addition of additives to pure CO2 can improve the performance of CO2 as a working fluid. By working fluid, we mean a fluid used for the CO2-based transcritical power cycle characterized by the addition of R134a to CO2. Hence, an experimental investigation of the pressure drop characteristics of a supercritical CO2/R134a mixture in a rectangular microchannel was conducted. For this purpose, an accurate and stable CO2/R134a mixture thermal-hydraulic experimental system was designed and built. The experimental results show that the pressure drop of the CO2/R134a mixture is lower than that of pure CO2 under the same conditions. The proportion of friction resistance to the total pressure drop decreases with an increase in R134a composition. Finally, a frictional resistance correlation that fully considers the effects of CO2/R134a mixture components and thermophysical property variations is proposed, which can guide the design of mixture heat transfer devices.

Heat transfer and pressure drop characteristics of the silicone-based plate heat exchanger

The paper presents an experimental investigation of a silicone based heat exchanger, with passive heat transfer intensification by means of surface enhancement. The main objective of this paper was to experimentally investigate the performance of a heat exchanger module with the enhanced surface. Heat transfer in the test section has been examined and described with precise measurements of thermal and flow conditions. Reported tests were conducted under steady-state conditions for single-phase liquid cooling. Proposed surface modification increases heat flux by over 60%. Gathered data presented, along with analytical solutions and numerical simulation allow the rational design of heat transfer devices.

Accelerating flow for engine oil base fluid with graphene oxide and molybdenum disulfide nanoparticles: modified fractional simulations

Thermal assessment of hybrid nanofluid presents novel applications in enhancing heat transfer devices, solar energy production, extrusion systems, chemical processes, nuclear reactors, cooling processes, etc. Owing to such conveying applications of hybrid nanomaterials, the aim of current research is to justify the impressive thermal mechanism engine oil with the utilization of hybrid nanoparticles. The molybdenum disulfide and graphene oxide nanoparticles are used to reflect the improvement in engine oil thermal performances. The motivations for considering such hybrid nanofluid model are to improve the thermal aspect of engine oil which play a key contribution in the vehicle systems and automobile industry. The problem is further improved with mixed convection and Newtonian heating applications. The oscillating surface is used to endorse the flow. The fractional simulations with the implementation of Caputo–Fabrizio (CF) technique are performed. In contrast to traditional attempts, the modern -Laplace transform is used to compute the integration task.

Experimental and Theoretical Study on Operation Characteristics of an Oscillating Heat Pipe

An oscillating heat pipe (OHP) is an effective heat transfer device for the thermal management of electronic devices. However, the heat transfer mechanism of the OHP was not fully understood due to its complicated operation characteristics. In this paper, the thermal performance of an OHP was experimentally studied. The condensation and evaporation temperature variations were monitored under different heat inputs and were then used to evaluate the OHP system operating characteristics. Thermal resistance was used as a key parameter to evaluate the thermal performance of the OHP system. The results indicated that as the heat input increased from 25 to 100 W, the average thermal resistance decreased while the stable evaporating and condensing temperatures increased. The equivalent heat transfer coefficient was derived theoretically. It showed that the reciprocal of the radial heat transfer coefficient increased with increasing liquid film thickness. Based on this result, an empirical correlation was proposed to evaluate the thermal resistance of an OHP system. This correlation was validated using both the experimental data provided in this study and the data collected from the open literature. The comparison results indicated that the proposed empirical correlation could reasonably predict the thermal resistance under different filling ratios and heat inputs.

Effect of Flow Resistance of Floating-Type Check Valves on Heat Transfer Characteristics of an Oscillating Heat Pipe

Abstract An oscillating heat pipe with check valves (CVOHP) is an attractive heat transfer device for future spacecraft with considerable heat dissipation and ground applications. This study aims to clarify the effect of the flow resistance of floating-type check valves on the heat transfer characteristics of the CVOHP using a one-dimensional slug flow model, which simulates the five-turn CVOHP used in the on-orbit experiment by the authors. The numerical simulations were conducted for different flow resistances, positions, and numbers of check valves. The results showed that the thermal resistance of the CVOHP increases with the flow resistance of the check valves, while there is no significant effect on the startup characteristics. The thermal resistance increased by more than 100% in the worst case, and the recommended flow resistance coefficient of the check valve was below 100 in this study for high thermal performance. The thermal resistance increases with an increasing number of high-resistance check valves but is less affected by the position of the valve. Additionally, the higher the heat input, the greater the effect of the flow resistance of the check valves. According to the findings in this study, it is necessary to control the flow resistance of the floating-type check valves at a low level for the high thermal performance of a CVOHP.

Biomimetic Copper Forest Structural Modification Enhances the Capillary Flow Characteristics of the Copper Mesh Wick

In a two-phase heat transfer device, achieving a high capillarity of the wick while reducing flow resistance within a limited space becomes the key to improving the heat dissipation performance. As a commonly used wick structure, mesh is widely employed because of its high permeability. However, achieving the desired capillary performance often requires multiple layers to be superimposed to ensure an adequate capillary, resulting in an increased thickness of the wick. In this study, an ultra-thin biomimetic copper forest structural modification of copper mesh was performed using an electrochemical deposition to solve the contradiction between the permeability and the capillary. The experiments were conducted on a copper mesh to investigate the effects of various conditions on their morphology and capillary performance. The results indicate that the capillary performance of the modified copper mesh improves with a longer deposition time. The capillary pressure drops can reach up to 1400 Pa when using ethanol as the working fluid. Furthermore, the modified copper mesh demonstrates a capillary performance value (ΔPc·K) of 8.44 × 10−8 N, which is 1.7 times higher than that of the unmodified samples. Notably, this enhanced performance is achieved with a thickness of only 142 μm. The capillary limit can reach up to 45 W when the modified copper mesh is only 180 μm. Microscopic flow analysis reveals that the copper forest modified structure maintains the original high permeability of the copper mesh while providing a greater capillary force, thereby enhancing the overall flow characteristics.

Polymeric Materials Selection for Flexible Pulsating Heat Pipe Manufacturing Using a Comparative Hybrid MCDM Approach.

The right choice of polymeric materials plays a vital role in the successful design and manufacture of flexible fluidic systems, as well as heat transfer devices such as pulsating heat pipes. The decision to choose an acceptable polymeric material entails a variety of evaluation criteria because there are numerous competing materials available today, each with its own properties, applications, benefits, and drawbacks. In this study, a comparative hybrid multi-criteria decision-making (MCDM) model is proposed for evaluating suitable polymeric materials for the fabrication of flexible pulsating heat pipes. The decision model consists of fourteen evaluation criteria and twelve alternative materials. For this purpose, three different hybrid MCDM methods were applied to solve the material selection problems (i.e., AHP-GRA, AHP-CoCoSo, and AHP-VIKOR). According to the results obtained, PTFE, PE, and PP showed promising properties. In addition, Spearman's rank correlation analysis was performed, and the hybrid methods used produced consistent rankings with each other. By applying MCDM methods, it was concluded that PTFE is the most suitable material to be preferred for manufacturing flexible pulsating heat pipes. In addition to this result, PE and PP are among the best alternatives that can be recommended after PTFE. The study supports the use of MCDM techniques to rank material choices and enhance the selection procedure. The research will greatly assist industrial managers and academics involved in the selection process of polymeric materials.

Thermal and phase change process analysis in a porous vented circular cavity under the impacts of inner rotating surface and inclined magnetic field during nanoliquid convection

In this study, thermal and phase change process in a circular porous vented cavity (P-VC) are numerically analyzed with finite element method considering magnetic field and inner surface rotation during nanofluid convection. The control of convective heat transfer and thermal management in porous cavities are crucial in applications for electronic cooling, heat exchangers, convective drying, and many other heat transfer devices. The numerical analysis is carried out for various values of the relevant parameters (Reynolds number—Re, rotational Reynolds number—Rew, Hartmann number—Ha, opening ratio—Ri) as follows: 500≤Re≤2000, −5000≤Rew≤5000, 0≤Ha≤80, 1≤Ri≤3. The phase change process often accelerates with higher Re when rotations are active. The rotations cause the full phase transition time (TR) to decrease by roughly 15% at the highest Re. The phase change process speeds up when both CW and CCW rotations are used at their highest values. The impacts of Ha on the TR variation is found as 33%. The thermal performances are slightly influenced by the variation of inner surface rotations and magnetic field strength. However, highest impact on thermal process and phase change is obtained when varying the inlet port size. The TR variation becomes 57% while heat transfer enhancement factor is obtained as 3.5. The optimal parameter combination to provide the highest thermal performance is (Ha, Rew, Ri) = (30.85, −4145, 2.98).

Entropy optimized flow of Sutterby nanomaterial subject to porous medium: Buongiorno nanofluid model

Owing to enhanced thermal impact of nanomaterials, different applications are suggested in engineering and industrial systems like heat transfer devices, energy generation, extrusion processes, engine cooling, thermal systems, heat exchanger, chemical processes, manufacturing systems, hybrid-powered plants etc. The current communication concerns the optimized flow of Sutterby nanofluid due to stretched surface in view of different thermal sources. The investigation is supported with the applications of external heat source, magnetic force and radiative phenomenon. The irreversibility investigation is deliberated with implementation of thermodynamics second law. The thermophoresis and random movement characteristics are also studied. Additionally, first order binary reaction is also examined. The nonlinear system of the governing problem is obtained which are numerically computed by s method. The physical aspects of prominent flow parameters are attributed graphically. Further, the analysis for entropy generation and Bejan number is focused. It is observed that the velocity profile increases due to Reynolds number and Deborah number. Larger Schmidt number reduces the concentration distribution. Further, the entropy generation is improved against Reynolds number and Brinkman parameter.