Experimental Heat Transfer Research Articles

Design, fabrication, and testing of heat conduction apparatuses at a low cost

This article presents the design, fabrication, and testing of three heat conduction apparatuses needed for engineering students. These devices are the axial heat transfer apparatus (AHTA), radial heat transfer apparatus (RHTA), and fin heat transfer apparatus (FHTA). These three devices allow students to undertake experiments in conduction heat transfer. The laboratory staff, with the help of third- and fourth-year classes, took this effective step to carry out experiments related to the heat transfer course. The use of surplus materials and locally available low-cost new instruments make them suitable for performing successful laboratory experiments at an affordable cost. The total cost of the three devices is 750 US$. Currently, the devices are in service and show excellent performance. The devices and experiments demonstrated in this work are simple and easy to create. Their design and fabrication are based on tools that are readily available in an engineering department. The experiments achieve important aspects in the study of heat transfer, which enhances students’ understanding of the conduction mechanism in solids.

Tailoring Heat Transfer and Bactericidal Response in Multifunctional Cotton Composites.

Through the execution of scientific innovations, "smart materials" are shaping the future of technology by interacting and responding to changes in our environment. To make this a successful reality, proper component selection, synthesis procedures, and functional active agents must converge in practical and resource-efficient procedures to lay the foundations for a profitable and sustainable industry. Here we show how the reaction time, temperature, and surface stabilizer concentration impact the most promising functional properties in a cotton-based fabric coated with silver nanoparticles (AgNPs@cotton), i.e., the thermal and bactericidal response. The coating quality was characterized and linked to the selected synthesis parameters and correlated by a parallel description of "proof of concept" experiments for the differential heat transfer (conversion and dissipation properties) and the bactericidal response tested against reference bacteria and natural bacterial populations (from a beach, cenote, and swamp of the Yucatan Peninsula). The quantification of functional responses allowed us to establish the relationship between (i) the size and shape of the AgNPs, (ii) the collective response of their agglomerates, and (iii) the thermal barrier role of a surface modifier as PVP. The procedures and evaluations in this work enable a spectrum of synthesis coordinates that facilitate the formulation of application-modulated fabrics, with grounded examples reflected in "smart packaging", "smart clothing", and "smart dressing".

Thermal experimental and numerical heat transfer analysis of a solid cylinder in longitudinal direction

The analysis of heat transfer in solid bodies with orthogonal geometries and knowledge thereof, is of vast importance in different fields of engineering and research. An important field of study is the thermal analysis in machine-parts that in most cases are designed and shaped with orthogonal geometries. Nevertheless, due to the high complexity and the cost that thermal experiments represent, FEM analysis and numerical solutions are used to foresee thermal fields on these components. These methodologies are certainly reliable, although may vary from real experiments. On that account, this paper presents a thermal experimental test in a solid cylinder of length and , made of ISO C45 steel that emulates a machine-part (cylindrical parts as shafts, fasteners and the like). The temperature fields along the longitudinal direction were analyzed in steady and transient state under homogeneous boundary conditions of the first kind (prescribed temperatures at the boundaries). The three solutions, experimental, numerical and FEM simulations were compared with the purpose of validating the results obtained by each method of solution respectively.

FLUID FLOW AND HEAT TRANSFER CHARACTERISTICS OF A CENTERED-WICK HEAT PIPE WITH ADDITIONAL WORKING FLUID: EXPERIMENTAL STUDY WITH VISUALIZATION

This article describes the experimental study of the centered-wick heat pipe with additional working fluid. A semi-transparent heat pipe is employed, and the heat transfer experiments are conducted in three orientation modes: horizontal, vertical, and sideways. The wick structure is a sintered copper powder, and the working fluid is water. The heat pipe has a small gap between the wick structure and the container wall. In each orientation mode, a condenser section of the heat pipe is water-cooled with a cooling jacket, and an evaporator section is heated with a heater. Fluid-flow and phase-change phenomena in the heat pipe are captured by using a video camera, and the temporal changes in the temperatures of the heat pipe are obtained by using thermocouples. Due to the additional working fluid, liquid slugs are found in vapor flow channels. The liquid slugs can be categorized into two types: a dynamic liquid slug and a static liquid slug. The experimental results demonstrate that the dynamic and static liquid slugs are distributed more effectively in the horizontal orientation mode. Thus, the thermal resistance of the heat pipe tends to be smaller and the maximum heat input to the heat pipe is larger in the horizontal orientation mode than in the other two orientation modes. The experimental results also confirm that the small gap is effective in the horizontal orientation mode. The additional working fluid is stored in the gap, which increases the thermal performance of the heat pipe.

Fluid Flow and Heat Transfer Characteristics of a Centered-wick Heat Pipe with Additional Working Fluid: Experimental Study with Visualization

This article describes the experimental study of the centered-wick heat pipe with additional working fluid. A semi-transparent heat pipe was employed, and the heat transfer experiments were conducted in three orientation modes: horizontal, vertical, and sideways orientation modes. The wick structure was a sintered copper powder, and the working fluid was water. The heat pipe had a small gap between the wick structure and the container wall. In each orientation mode, a condenser section of the heat pipe was water-cooled with a cooling jacket, and an evaporator section was heated with a heater. Fluid-flow and phase-change phenomena in the heat pipe were captured by using a video camera, and the temporal changes in the temperatures of the heat pipe were obtained by using thermocouples. Due to the additional working fluid, liquid slugs were found in vapor flow channels. The liquid slugs can be categorized into two types: a dynamic liquid slug and a static liquid slug. The experimental results demonstrated that the dynamic and static liquid slugs were distributed more effectively in the horizontal orientation mode. Thus, the thermal resistance of the heat pipe tended to be smaller and the maximum heat input to the heat pipe was larger in the horizontal orientation mode than in the other two orientation modes. The experimental results also confirmed that the small gap was effective in the horizontal orientation mode. The additional working fluid was stored in the gap, which increased the thermal performance of the heat pipe.

Heat Transfer Experiment on the Air Side of a Radiator Using Sintered Porous Metal Fiber

Heat Transfer Experiment on the Air Side of a Radiator Using Sintered Porous Metal Fiber

EXPERIMENTAL AND NUMERICAL CONVECTIVE HEAT TRANSFER INVESTIGATION IN LAMINAR RECTANGULAR-CHANNEL FLOW ACROSS V-SHAPED GROOVES

The influence of staggered V-grooves on the hydrothermal performance of a rectangular-channel flow is systematically investigated through a combination of numerical and experimental approaches. The 3-D numerical simulation is developed adopting computational fluid dynamics (CFD) (ANSYS FLUENT) for a range of Reynolds numbers (Re) from 100 to 1000. The experiments are conducted on straight and V-grooved channels (with pitch-to-height and height-to-hydraulic diameter ratios of 2 and 0.75) for distilled water under constant wall heat flux conditions to validate the computational model. Additionally, the impact of V-shaped groove arrangements, forward V-grooved channel (FVGCH) and backward V-grooved channel (B-VGCH), on the flow and heat fields, as well as the effect of groove depths (<i>d</i> = 1.5, 2.5, and 3.5 mm), are also studied. In both experimental and numerical results, the performance evaluation criterion (PEC) grows with rising Reynolds numbers. The highest PEC values of the numerical and experimental findings for the F-VGCH are 2.18 and 2.29, respectively, at Re = 1000. Whereas the highest PEC values of the numerical and experimental results for the B-VGCH are 1.81 and 1.96, respectively, at the same Re (Re = 1000). In addition, the values of PEC for F-VGCH are greater than the PEC values of B-VGCH for all examined groove depths over the entire range of Reynolds numbers. Thus, the F-VGCH offers the best performance evaluation criterion in comparison with B-VGCH.

Experimental mass and heat transfer at a serpentine tube heat exchanger located at the wall of a square stirred tank reactor

• Rates of mass and heat transfer of a serpentine tube heat exchanger were studied. • The serpentine is located at the wall of a square stirred tank reactor. • Variables studied were impeller speed and geometry, tube diameter, and tube pitch. • Dimensionless correlations were developed to design and operate the heat exchanger. • The possibility of using the serpentine tube as a catalyst support was highlighted. Although the study of the heat transfer behavior of stirred tank heat exchangers such as helical coils, vertical tube baffles, and cooling jackets has received much attention, no study has been reported on the heat or mass transfer behavior of serpentine tube heat exchangers, so the present work aims to study rates of mass and heat transfer (by analogy) at the outer surface of a serpentine tube heat exchanger located at the wall of a square stirred tank reactor by the electrochemical technique. Variables studied were impeller rotational speed, impeller geometry, tube diameter, and tube pitch. The mass or heat transfer coefficients were found to increase with increasing impeller speed and decrease with increasing cylinder diameter and pitch. For a given set of conditions, a radial flow turbine produces higher rates of mass transfer than an axial flow turbine. The data were correlated by dimensionless mass transfer correlations which can be used to scale up and operate the heat exchanger. When the mass transfer data at the serpentine tube were compared with those at an active flat wall of equal height, it was found that the mass transfer rate at the serpentine tube is higher than that of the flat wall by an amount ranging from 10% to 210% depending on the operating conditions. The possibility of using the serpentine tube as a catalyst support for conducting diffusion-controlled exothermic immobilized cell biochemical reactions which need rapid cooling to avoid thermal degradation of the biomass was highlighted. The dual-use of the serpentine tubes as a catalyst support and a cooler would reduce the capital and operating costs of immobilized enzyme or cell stirred tank biochemical reactors compared, for instance, with the traditional stirred slurry reactor owing to the elimination of the costly and time-consuming process of separating the final product from the catalyst particles.

Exploration of the Eleventh Graders Difficulties in Understanding Procedural and Declarative Knowledge in the Laboratory Experiment of Heat Transfer

Exploration of the Eleventh Graders Difficulties in Understanding Procedural and Declarative Knowledge in the Laboratory Experiment of Heat Transfer

Experimental estimation of thermal contact conductance across pressed copper–copper contacts at cryogenic-temperatures

• Present experimental work presents a valuable database of TCC in cryogenics. • Reports systematic estimates of TCC for copper contacts on which data are scarce. • Effects of broad temperature, pressure, roughness on TCC are covered in vacuum. • Anomalous TCC trend at low temperature is correlated to thermo-physical properties. • Proposes generalized empirical correlations of TCC with temperature and pressure. The accurate estimation of thermal contact conductance (TCC) is a fundamental need towards the optimal design of any cryogen-free conduction-based cooling systems, which routinely utilizes mechanically pressed components of bare copper to form the heat conduction path. There exists a dearth of databases and reliable correlation for TCC between bare copper contacts for such applications. Present work is an experimental study, which has been performed systematically to address the requirement of design engineers for such applications. A novel experimental setup has been made to carry out axial heat transfer experiments between copper contacts under a varying set of temperature and pressure parameters of 50 to 300 K and 0.5 to 8 MPa, respectively. The surface roughness at the contact between copper specimens varied between 0.8 and 10 μ m . The TCC has shown a non-linear variation with temperature in the 50 to 300 K. The temperature-dependent thermophysical properties, nature of asperities deformation, and surface topography characterization were considered in analyzing the results. This effectively helps in dealing with the coupled nature of the TCC problem and thus enhances the accuracy, reliability, and scope of the present study performed at sub-ambient ranges under a varying set of selected parameters. The TCC results have also been compared with theoretical model predictions, and the improvements needed in them are highlighted. Finally, an empirical correlation of the reduced dimensionless TCC with dimensionless temperature and dimensionless pressure has been proposed, which covers a wide deformation range of the asperities, temperature, and surface roughness than existing models in the literature. The proposed correlation consistently explains the non-linear dependence of TCC with temperature and pressure and provides a direct means to the design engineers for the TCC estimation at cryogenic temperatures.

EXPERIMENTAL INVESTIGATION ON TWO-PHASE HEAT AND FLUID FLOW IN POROUS HEAT SINKS

The current paper presents a novel experimental study on flow boiling in heat sinks with rectangular cross-section parallel microchannels fabricated by conventional powder metallurgy process. The dimensions of microchannel heat sinks are 20 mm × 20 mm. Porosities of heat sinks produced by sintering vary between 13.9% and 21.3%. A pure (nonporous) copper heat sink was also produced to compare the experimental data with each other. Channel sizes and numbers of all heat sinks used in the tests are identical. Flow boiling tests were carried out with deionized water at a flow rate of 238.2 kg/m<sup>2</sup> s and 430.32 kg/m<sup>2</sup> s. The fluid enters the heat sink at 80°C, completely liquid. The tests were carried out under constant heat flux conditions and the heat fluxes are 46.5 W/cm<sup>2</sup> and 61.5 W/cm<sup>2</sup>. Experimental studies have shown that the heat transfer coefficients in the heat sink with the highest porosity are from 28% to 33.3% higher than in the pure copper heat sink. Experimental heat transfer coefficients increase with increasing flow rate and decrease with increasing heat flux and vapor quality. On the other hand, the pressure drop values of the heat sink sample with the highest porosity were measured to be one and half times more than that of the pure copper heat sink. The imaging technique was used during the experiments. With the imaging technique, it was determined that the fluctuations in the pressure values were caused by the reverse steam flow. Additionally, the heat transfer coefficient values obtained experimentally were compared with the existing correlations in the literature. Experimental results showed that pure heat sinks are more compatible with the results given in the literature than porous heat sinks.

Experimental Heat Transfer Analysis from Helical Coiled Tubes with the Same Surface Area

Experimental Heat Transfer Analysis from Helical Coiled Tubes with the Same Surface Area

구조용 목재의 축열성능 향상을 위한 상변화물질/바이오차 적용 복합 교차집성재 개발

In this study, phase change materials (PCM) was applied to the core-layer of cross-laminated timber (CLT) to improve the low thermal storage performance of CLT. To solve the phase leakage of PCM, PCM/biochar composites were prepared in a vacuum state by impregnating PCM (n-heptadecane) in biochars that were pyrolyzed at 400 and 500 °C, respectively. Gypsum boards with improved thermal storage performance was prepared by mixing 10 wt% of the prepared PCM/biochar composites, and these were applied to the core-layer of the CLT to develop a hybrid CLT. The physical and chemical properties of PCM/biochar composite were evaluated through FT-IR, SEM, TGA, and DSC analysis, and the thermal performance of P/B board and hybrid CLT was evaluated through heat transfer experiments. The surface temperature reduction and heat transfer delay effect of hybrid CLT to which biochar produced at a pyrolysis temperature of 400 °C was applied was excellent.

Experimental study on boiling two-phase of liquid sodium along a 7-rod bundle – Part Ⅱ: Heat transfer characteristics

Sodium boiling will occur in some hypothetical accident cases (such as additional reactivity introduction and heat discharge capacity deterioration, and Local fault propagation). Thus sodium boiling experiments are necessary for the safety analysis and the development of serious accident programs in sodium-cooled fast reactors. In the present study, the boiling two-phase heat transfer experiments of liquid sodium were carried out on the boiling liquid sodium test loop. The experimental results showed that the entire boiling process can be divided into four stages. The heat transfer coefficient of the boiling two phases in the rod bundle channel increases gradually with the increase of heat flux and grows very slowly with the increase of system pressure. Based on the 54 groups of rod channels obtained, the new correlation of transfer heat coefficient of boiling two-phase liquid sodium was developed in a 7-rod bundle. The new correlation can well predict the experimental data of boiling two-phase liquid sodium obtained by other scholars, and the prediction error is within ±50\\%. Finally, mean relative deviation (MRD), absolute mean relative deviation (MARD), and root mean square deviation (RMSRD) were introduced to evaluate the accuracy of the correlation quantitatively.

가스터빈 엔진 터빈 블레이드의 냉각성능 상사시험 평가 연구

In this study, a similarity test was designed to evaluate the cooling performance of the high-pressure turbine blades of a gas turbine engine, and a study was conducted to verify the similarity through analysis and experiments. The main similarity variables representing the cooling performance of the turbine blades were defined, and the similarity test conditions were derived from the engine conditions so that the similarity variables could satisfy the similarity. It was confirmed that the similarity was satisfied by performing a conjugated heat transfer analysis on the same test conditions, and the cooling performance of the turbine blades was experimentally evaluated by conducting a heat transfer experiment using an infrared thermal imaging camera under the same conditions. In conclusion, it was confirmed that the cooling performance of high-temperature components such as high-pressure turbine nozzles and blades operating at high temperatures in a relaxed pressure and temperature environment without simulating a high-pressure and high-temperature environment such as an engine can be evaluated through a similar test.

A Review on Heat Transfer Characteristics and Enhanced Heat Transfer Technology for Helium–Xenon Gas Mixtures

As one of the most promising working substances for space nuclear power sources, research on the heat transfer characteristics of helium–xenon gas mixtures has become the key issue in focus. In this paper, through an extensive literature research, the current research results are classified and organized. The results show that there are semi-empirical formulas for physical property parameters with high prediction accuracy, and there are also Nusselt correlations with small errors. However, both lack the support of experimental data. There is no systematic research on enhanced heat transfer technologies, and the conclusions of the existing studies are not significant, so they can only make limited reference contributions to the future study of enhanced heat transfer technologies. More flow and heat transfer experiments on helium–xenon mixtures are urgently needed, through detailed analysis of the heat transfer performance of helium–xenon flow, identifying the key factors affecting the heat transfer thermal resistance, and corresponding heat transfer enhancement measures to form an optimized design method applicable to helium–xenon heat exchangers. In this way, an enhanced heat transfer theory of helium–xenon heat exchangers can be developed.

Development of FEM Calculation Methods to Analyse Subcooled Boiling Heat Transfer in Minichannels Based on Experimental Results

Even though two-phase heat transfer of refrigerants in minichannel heat sinks has been studied extensively, there is still a demand for improvements in overall thermal performance of miniature heat transfer exchangers. Experimental investigation and sophisticated heat transfer calculations with respect to heat transfer devices are still needed. In this work, a time-dependent experimental study of subcooled boiling was carried out for FC-72 flow in a heat sink, comprising of five asymmetrically heated minichannels. The heater surface temperature was continuously monitored by an infrared camera. The boiling heat transfer characteristics were investigated and the effect of the mass flow rate on the heat transfer coefficient was studied. In order to solve the heat transfer problem related to time-dependent flow boiling, two numerical methods, based on the FEM were applied, and based on the Trefftz functions (FEMT) and using the ADINA program. The results achieved with these two calculation methods were explored with an emphasis on the impact of the mass flow rate (range from 5 to 55 kg/h) on the resulting heat transfer coefficient. It was found that, with increasing mass flow, the heat transfer coefficient increased. Good agreement was found between the heat transfer coefficients, determined according to two numerical methods and the simple 1D calculation method.

Investigation of condensation with non-condensable gas in natural circulation loop for passive safety system

The system-integrated modular advanced reactor 100 (SMART100), an integral-type pressurized water small modular reactor, is based on a novel design concept for containment cooling and radioactive material reduction; it is known as the containment pressure and radioactivity suppression system (CPRSS).There is a passive cooling system using a condensation with non-condensable gas in the SMART CPRSS. When a design basis accident such as a small break loss of coolant accident (SBLOCA) occurs, the pressurized low containment area (LCA) of the SMART CPRSS leads to steam condensation in an in-containment refuelling water storage tank (IRWST). Additionally, the steam and non-condensable gas mixture passes through the CPRSS heat exchanger (CHX) submerged in the emergency cooldown tank (ECT) that can partially remove the residual heat. When the steam and non-condensable gas mixture passes through the CHX, the non-condensable gas can interrupt the condensation heat transfer in the CHX and it degrades CHX performance.In this study, condensation heat transfer experiments of steam and non-condensable gas mixture in the natural circulation loop were conducted. The pressure, temperature, and effects of the non-condensable gas were investigated according to the constant inlet steam flow rate with non-condensable gas injections in the loop.

Using Numerical Analysis to Develop a Retort Process to Enhance Antioxidant Activity and Physicochemical Properties of White Radish (Raphanus sativus L.) in Different-Sized Packages

Thermal processing of white radish using retort sterilization at different temperatures was investigated according to the dimension of the package. Four different samples with the same weight and volume were placed in packages with different dimensions. The degree of sterilization (i.e., F0-value) at the cold point targeted at 6 min was determined based on experimental data and heat transfer simulation. The sterilization time was considerably increased with a decrease in surface area to unit volume ratio (φ) at each temperature. The sterilization time for the sample with the highest φ (155.56) was approximately five times faster than the sample with the lowest φ (72.22) at all heating temperatures. Numerical simulation conducted with a proper heat transfer coefficient (h) showed mostly good agreement with the experimental data (RMSE < 2 °C). Changes in color and total phenolic content were higher for samples heated at higher temperatures. Hardness values of white radish samples measured for center and edge parts separately were more uniform for samples with a high φ. Results in this study suggest that optimizing heating conditions of root vegetables must consider their package dimensions to satisfy quality attributes after sterilization. Numerical simulation can be utilized as a useful tool to design the sterilization process.

A novel strategy to improve steam heat utilization and reduce carbon emissions during heavy oil development

In recent years, the green transformation of the traditional energy industry and the reduction of carbon emissions have attracted widespread societal attention. In the thermal recovery process of heavy oil, the low heat utilization rate has always been the bottleneck restricting its production. In addition, the associated flue gas emissions also pose a considerable challenge to environmental protection. In this paper, flue gas and SiO2 aerogel were jointly applied to reduce steam heat loss while achieving exhaust gas sequestration. Condensation heat transfer experiments were carried out to explore the mechanism of the two affecting the heat dissipation process of steam liquefaction. A series of displacement experiments with different injection methods in a one-dimensional sandpack were performed to select combinations of developing heavy oil with high efficiency and low carbon. By detecting the temperature changes of the model and calculating the final storage volume, the effects of promoting steam chamber expansion and flue gas sequestration were evaluated. The results showed that the aerogel adsorption layer could change the wettability of the condensing surface, thereby showing the characteristics of film condensation. Flue gas molecules could be captured by aerogel nanofluids, further exerting a synergistic thermal insulation effect, and the temperature of the deep reservoir increased by 7.7 °C. Simultaneously, the crude oil recovery increased by 8.8% compared with pure steam flooding. Moreover, the numerous nanoparticle-stabilized foams generated via this method were noted as an essential way to sequester carbon in a high water-cut formation, and the final sequestration rate reached 77.4%.