Side Heat Transfer Research Articles

Influence of irregular fiber filling on the performance of hollow fiber membrane modules for cold water production

The countercurrent hollow fiber membrane-based evaporative water cooler (MEWC) offers an eco-friendly and compact solution for cold water generation. This study introduces a random sequential addition algorithm to model the real-world irregular fiber filling within the MEWC. Inspired by the honeycomb structure, the developed 3-D numerical model adopts a calculation unit featuring a hexagonal prism comprising multiple fibers. Validation against experimental data reveals an average relative error of 2.81 % concerning outlet water temperature. The effects of fiber filling patterns (regular layout and random layout) on the velocity and temperature fields of the MEWC are investigated. Comparisons of outlet water temperature, cooling efficiency, consumptive electric power ratio, and heat and mass transfer resistance composition between these layouts under various operating conditions are conducted. The results indicate that the random layout fosters severe channeling effect and large flow dead zones, impairing air side heat and moisture transfer. The random layout exhibits over 15.9 % reduction in cooling efficiency and 36.3 % decrease in consumptive electric power ratio compared to the regular layout. Irregular fiber filling leads to a notable 158.6 % increase in air side heat transfer resistance and a 35.9 % rise in mass transfer resistance. Although irregular filling compromises the cooling performance, it demonstrates potential for energy savings under certain conditions. Design schemes should be carefully tailored to meet specific application requirements by considering these trade-offs.

CFD Air Flow Evaluation of Finned Tube Evaporator for Refrigerated Display Cabinet Application

This study is aimed to develop a simulation to improve the performance of the finned tube evaporator which is applied to the refrigerated display cabinet. CFD model was developed to be able to analyse the characteristics of air flow inside the fin gap and air side heat transfer coefficient. Geometry of the model of overall finned tube evaporator is considered covering two aluminium wavy fins with an air flow in between, combination of staggered cooper tubes with refrigerant flow inside. Fin gap is designed 4 mm to anticipate frost on the fin surface that can block air flow. Turbulence models used in the study is the realizable k-ε turbulence which had the best performance turbulence model and it was validated with secondary data from previous studies and shows the lowest error only 5.9 %. The use of CFD was found to be sufficiently representative of the heat transfer characteristics of evaporators, and acted as an effective simulation tool to determine the heat transfer coefficient in order to improve efficiency in terms of improved design. The characteristics of air flow between the fin gap and around the tube was obtained various and complex. In the case study the entry velocity of 1.7 m /s at the highest turbulence condition of the first row can reach speeds of 2.75 m/s. Hight turbulence regime in flow can indicate higher the heat transfer coefficient of the evaporator.

Improved model for thermal transmission in evacuated tubes: Effect of non-uniform heat flux and circumferential conduction

Evacuated tubes are extensively utilized for converting solar energy into thermal energy owing to their exceptional thermal properties and affordability. The circumferential temperature gradient of the evacuated tube is significant to the heat and mass transfer inside, but it is often neglected. This research proposed an improved model incorporating non-uniform heat flux and circumferential conduction to obtain the temperature distribution. In the experiment, A thermal insulation material was inserted inside the inner tube to create an adiabatic boundary. Various conditions (non-uniform, rectangular, and uniform heat fluxes, circumferential conduction of the coating) were numerically compared. The enhanced combined thermal transmission model was validated, demonstrating a relative error of 6.45 % in temperature increase calculation and increasing the prediction accuracy by 42.15 % at least. The distribution of the heat flux and the thermal conduction of the coating were identified as the primary factors affecting the heat transfer properties of the evacuated tube. An imbalanced distribution of heat flux resulted in non-uniform heat transfer, whereas the circumferential conduction within the coating effectively modulated the temperature distribution to achieve uniformity. The local heat transfer coefficient exhibited non-uniformity, with calculated values ranging from 0.23 to 3.25 W/(m2∙K), and an error range of −16 to +3 %.

Influence of vibration parameters and fin structure parameters on heat transfer performance under vibration conditions

The occurrence of vibration in engineering vehicles during operation is a common phenomenon, and the utilization of vibration-enhanced heat transfer serves as a viable approach to enhance the efficiency of heat transfer in radiators. This study designs a vibration test platform for heat exchangers to investigate the impact of different vibration parameters on heat transfer performance. Additionally, a fin vibration model is constructed using overlapping grid technology to simulate the behavior of flat fins under varying vibration conditions. Corrugated fins were chosen for investigation under vibration conditions, utilizing an orthogonal experimental approach to analyze the impact of fin structural parameters on heat exchanger performance. Findings indicate that vibration enhances the air side heat transfer coefficient of the heat exchanger, in experimental settings, the gas side heat transfer coefficient of the heat exchanger demonstrated a maximum increase of 12.28%. Simultaneously, vibration induces an escalation in pressure loss, with the maximum drop reaching 28.72%. The heat transfer factor j of the heat exchanger exhibits an augmentation in response to heightened vibration intensity, while they diminish with escalating speed. Furthermore, vibration alters the impact of structural factors of corrugated fins on heat transfer efficacy. During vibration, the sensitivity of fin height and wavelength intensifies, whereas the sensitivity of pitch and wave amplitude diminishes. The findings of this research offer valuable insights for further investigation into the heat transfer capabilities of fins under vibration.

Numerical Study of Thermal Performance on Fin and Tube Heat Exchanger with Flat Rectangular and Sinusoidal Winglet Vortex Generators

Generation of vortices in the fin and tube heat exchanger is one of the common methods to reduce the air-side thermal resistance. This study deals with the enhancement of heat transfer in the air side using conventional rectangular and sinusoidal sine wave vortex generators. The vortex generators are placed in the downstream location of the tube in the common flow-down configurations and the range of Reynolds number is maintained about 400 to 1100. The results of the above vortex generators are compared with baseline configuration based on thermos-hydraulic criterion parameters like variation in the flow structure, variation in the temperature distribution, variation in the pressure distribution, variation in the friction factor, and overall thermal enhancement factor. Based on the comparative numerical analysis, sinusoidal and conventional rectangular winglet shows good heat transfer enhancement in that they have a large pressure loss penalty.

Study on the effects of season, geographical location, and altitude on thermal characteristics of large airship based on meteorological data

ABSTRACT Our team built models to accurately simulate the heat transfer inside and outside the airship. In this paper, we used the models to analyze the thermal characteristics of large airship at different seasons in five different regions and at different low altitudes using Fluent software. The results show that the seasons, geographical locations, and altitudes produce great effects on the thermal characteristics of airship by affecting the solar irradiation on the envelope surface, convection heat transfer, atmospheric parameters, etc. In order to validate the accuracy of numerical calculation, we built a testing platform and conducted the experiments. The measured data are in good agreement with the numerical results.

Heat transfer performance of Al2O3-water-methanol nanofluid in a plate heat exchanger

A plate heat exchanger is one of the smallest and most efficient heat exchangers on the market. This experiment aims to assess the performance of methanol-water as a base fluid in a plate heat exchanger that affects the heat transfer performance. For this study, aluminum oxide (Al2O3) nanoparticle was used in various ratios (0.25, 0.5, and 0.75 vol. %) in a base fluid (10 vol.% methanol & 90 vol.% water) to prepare a nanofluid. At two different temperatures, such as 55?C and 60?C, with varying flow rates (2 to 8 L/min) and varying nanoparticle concentrations (0.25 to 0.75%), thermo physical characteristics and convective heat transfer studies were performed, and the results are presented. The overall inference was that there was a notable enhancement in the hot side, cold side, and overall heat transfer coefficient by the combination of Al2O3 nanoparticle and methanol-water-based fluid. It was noted that utilizing Al2O3/methanol-water nanofluid could significantly reduce the temperature gradient in the heat exchanger and improve its performance. Maximum hot fluid coefficient of 4300 W/m2?C, cold fluid coefficient of 4600 W/m2?C, and overall coefficient of 2200 W/m2?C were noted for 0.75 vol.% nanoparticle concentration and at a flow rate of 8 L/min.

CONVECTIVE HEAT TRANSFER INSIDE A ROTATING HELICAL PIPE FILLED WITH SATURATED POROUS MEDIA

In this paper, we study the hydrothermal characteristics of flow inside a rotating helical pipe filled with saturated homogeneous porous medium. The analysis is being carried out for the case of small curvature and torsion. Using the perturbation approach, velocity and temperature fields are solved for both uniform wall heat flux and uniform wall temperature boundary conditions. Perturbation expansion up to the third order is carried out to investigate the effect of rotation on the flow. The influence of rotation on velocity is noticed as early as the first order, and on temperature solution, it has an effect in the third order. The influence of rotation on the Nusselt number does not appear till third order, and it is discovered that the Nusselt number grows as dimensionless curvature increases. Moreover, the theoretical results have been verified against experimental data from existing literature for the special case of zero rotation and curvature of the pipe. The available experimental data align well with and support the theoretical results in this limiting case.

Computational Fluid Dynamics for Cavity Natural Heat Convection: Numerical Analysis and Optimization in Greenhouse Application

Natural convection in cavity plays a significant role in energy-related field, including the indoor heat transfer analysis in greenhouse with integrated PV roof. In this study, mathematical model is established for two-dimensional heat transfer analysis in greenhouse air cavity, with numerical simulation through computational fluid dynamics (CFD). Main natural convection impact factors, such as system configuration parameters (tilting angle and PV panel unit number) and fluid thermal–physical properties, are investigated with indoor temperature distribution and streamline comparison by finite-volume method (FVD). Preliminary results show that with rising Rayleigh number (Ra), natural convection is enhanced with growing Nusselt number (Nu). Moreover, panel slope tilting angle (θ) highly determines inside heat transfer subregions in terms of the vertical temperature gradient declines with rising θ, improving the temperature distribution uniformity inside. The solar greenhouse example illustrates that with the increasing numbers of panel group numbers (n), the air temperature gradient differences decrease, improving the temperature distribution uniformity inside, which is preferable to built environment accurate control for greenhouse in the practical engineering. This work can provide modeling method support and reference for natural heat convection applications.

Experiment study and heat resistance analysis on heat transfer characteristics in staggered tube moving bed heat exchangers

Heat transfer of high temperature granules in the moving bed heat exchanger is an important thermal process in a blast furnace slag waste heat recovery system. Gaining a comprehensive understanding of granular side heat transfer characteristics is crucial. Here, we experimentally investigated the effects of velocity, diameter, diameter distribution, inlet temperature and granule type on granular side heat transfer and the development of heat transfer in the flow direction in a staggered tube array. Furthermore, the experimental results were analysed via the thermal resistance theory. The obtained results indicate that the heat transfer coefficient increases with increasing velocity and inlet temperature and decreases with increasing diameter. Multi-sized granules and blast furnace slag have better heat transfer than mono-sized granules and phosphorus slag, respectively. The heat transfer coefficient tends to increase and then decrease in the flow direction, with the location of the peak, depending on the ratio of the contact and penetration thermal resistance. The semi-empirical formula based on experimental results can provide a theoretical basis required to design.

Heat transfer in flat tube car radiator with CuO-MgO-TiO2 ternary hybrid nanofluid

An investigation of the performance of a car radiator with CuO-MgO-TiO2 aqueous ternary hybrid nanofluid has been presented to elucidate the effect of nanoparticle concentration, flow rate, and frontal air velocity. The volume concentration of nanoparticles ranges from 0.1% to 0.5%. The effect of fluid inlet temperature, the coolant flow rate and the frontal air velocity on a flat tube radiator were investigated. The effectiveness of the radiator increases with increasing volume concentration as well as coolant flow rate. The coolant side heat transfer coefficient of 0.5% hybrid nano-coolant was 46% higher than the base fluid. The overall heat transfer coefficient was 7.65% higher than the base fluid. The friction factor and the pumping power both decrease with increasing fluid inlet temperature. The pumping power required for nano-coolant is 1.71 times the base fluid. A correlation for the overall heat transfer coefficient is also presented.

Investigation on the heat transfer characteristics of flexible vacuum glass based on cross-laminated microcavities

Vacuum glass is a key component of energy-efficient buildings. At present, the traditional vacuum glass (VG) has some problems, such as side edge heat transfer, poor thermal insulation in small sizes, high cost of indium alloy edge sealing, and poor adaptability to the rigid structure to environments, which limits its application in buildings. Vacuum interlayer heat transfer is thickness-independent. Therefore, increasing the transfer path and thermal resistance of the support structure under micrometer gaps achieves effective thermal insulation. In this study, a vacuum glass with a cross-laminated microcavity structure was proposed. The cross-laminated structure has a total thickness of several hundred micrometers and is made of polycarbonate. The heat transfer and stress-strain of the cross-laminated vacuum glass (CLVG) and VG are investigated. The results indicate that the CLVG accomplished a lower heat transfer coefficient compared with the VG at a size smaller than 30 × 30 cm2. In addition, the CLVG is edge-effect-free. As a flexible structure, the CLVG can be easily applied to existing buildings. This study contributes to the exploration of new structures for the vacuum glass.

Modeling of convective heat transfer processes between inhomogeneous gas mixtures and surfaces of a small-caliber artillery barrel

Modern models of aviation artillery weapons are pulsed heat engines that convert the energy of a powder charge into the energy of highly compressed and heated powder gases (hereinafter referred to as gases), which, when expanding, perform work on communicating kinetic energy to the projectile. In the context of artillery science, aviation artillery weapons and ammunition are structured as a system that interacts with heat sources and the environment, sequentially completing thermodynamic cycles. The main element that is most intensively subjected to thermophysical loads and has a significant impact on the combat qualities and cost of aviation artillery weapons is a small-caliber artillery barrel (hereinafter referred to as the barrel). As a result, the problem of determining the temperature field of the barrel is one of the central problems of designing aviation artillery weapons and optimizing firing modes. The successful solution of this problem largely depends on the accuracy of modeling the processes of heat transfer to the channel and from the outer wall of the barrel during firing. At the same time, an adequate synthesis and calculation of the relations describing the phenomenon of convection accompanying the shot is difficult, which is due to the presence of phase transformations in the state of gases; the simultaneous presence of supersonic and subsonic zones in the solution regions; the existence of laminar, turbulent flows and other non-linear formations. The aim of the work is to develop a relatively simple and acceptable for engineering practice mathematical model of heat transfer inside and around the wellbore with near-wall coolant flows (hereinafter referred to as the model). Achieving the goal of the work is carried out by a concentrated choice of criterial equations of the apparatus of thermodynamic similarity, corresponding to the geometric and physical conditions for the uniqueness of the processes of loading the shaft. The introduction of functions that take into account the dependence of the thermophysical properties of gases on temperature made it possible to increase the accuracy of determining the parameters of heat transfer during a shot by 19% in comparison with the known results. The developed model can be used in applied calculations related to determining the thermal state of the wellbore. The specialization of the object of study does not exclude the possibility of refining the model for the purpose of mathematical representation of thermal effects in thermally stressed structures of complex shape.

Coupled natural convection heat transfer inside and outside a closed cylindrical cavity with a uniform temperature heat source

In order to understand the influences of Rayleigh number, geometric dimensions of closed cylindrical cavity and cylindrical heat source, the coupled natural convection inside and outside a closed cylindrical cavity with a uniform temperature heat source in the center of the cavity is simulated. The results indicate that the secondary vortex will appear in the closed cavity with the increasing dimensionless height of the internal heat source and the aspect ratio of the closed cavity. The heat transfer ability of the coupled natural convection reduces with the increasing dimensionless height and the radius of the heat source, and the decreasing the aspect ratio of the closed cavity. Compared with the results in an isothermal closed cavity, the heat transfer ability exhibits a different variation. Eventually, a heat transfer correlation on the heat exchange between the internal heat source and the external environment is obtained, which can be used as a reference for the heat dissipation calculation of electronic devices.

Linear and Nonlinear Stability Analysis of Molten Salt Natural Circulation Loop

Abstract A molten salt natural circulation loop (MSNCL) has been setup to study the steady-state, transient, and stability characteristics of molten nitrate salt, mixture of sodium nitrate, and potassium nitrate in 60:40 ratios by weight. Natural circulation experiments in a temperature range of 290 °C–600 °C have been performed. A semi-analytical linear model was derived for stability analysis of rectangular natural circulation loops with conventional localized surface heating and cooling. The developed model includes the effect of wall thermal inertia, variable internal heat transfer coefficient, finite secondary side heat transfer coefficient at cooler, and heat losses for predicting the stability map. These effects are incorporated considering their significant role in modeling high-temperature molten salt-based natural circulation systems. The developed model has been first validated with the experimental data of water loop available in literature. The developed model is then validated with the experimental data generated in MSNCL. Validation of in-house developed nonlinear model has also been performed against the same experimental data. The comparison of both linear and nonlinear stability analysis with the experimental data shows good agreement and articulates the importance of various parameters which have been included in the developed model.

Experimental investigation on heat transfer performance of the grooved spiral wound heat exchanger

To enhance the heat transfer efficiency of the spiral wound heat exchanger, a grooved spiral wound heat exchanger (GSWHE) was proposed. A test platform was accomplished to experimentally investigate the heat transfer performance with the comparison of a spiral wound heat exchanger (SWHE). The uncertainty analysis of the experiment was conducted, with the maximum relative error being not more than ±5%. The comprehensive heat transfer coefficient of the GSWHE is higher than that of the SWHE when the cooling water flow rate is low. To determine the heat transfer coefficient of both sides, the Wilson plot method was applied. The tube side heat transfer coefficient in the SWHE is found to have an error of about ±30% compared to the empirical correlations. The results also clearly suggest that grooves enhance the heat transfer of the shell side in the GSWHE. By employing effectiveness as a criterion, the comprehensive performance of the GSWHE was found to be 1.23 times higher than that of the SWHE.

Flow Characteristics and Heat Transfer Performances of Quadrant Helical Baffle Heat Exchanger with Grooved Joint

Helical baffle heat exchanger has a wide application in many industrial fields because of its high efficiency and low resistance. A new structure of the grooved helical baffle is proposed to strengthen the stability between the overlapped baffles during the spiral flow of fluid. Based on this structure, the liquid water was selected as the working medium in the tube side and shell side, the flow field characteristics and heat transfer performances of the quadrant helical baffle heat exchanger are numerically analyzed using software FLUENT 2017. The results show that when the helical angle is large (50°) and the overlapped amount is small (0.5), the comprehensive performance of the heat exchanger is the best. Therefore, the heat exchanger performance can be improved by choosing the appropriate combination of helical angle and overlapped amount. The correlation formula of the shell side heat transfer coefficient with helical angle, overlapped amount and mass flow rate is obtained by means of regression analysis, which can provide a reference for engineering application and optimal design of grooved helical baffle heat exchanger.

Heat transfer evaluation of liquid lead-bismuth eutectic cross flow tube bundle: Experimental part

Helical coil once-through tube steam generator (HCOTSG) is an excellent form of heat exchanger. HCOTSG is adopted in various industries, such as Lead-bismuth Fast Reactor (LFR). The flow and heat transfer in the shell side of HCOTSG are important for its design and optimization. It is of great significance to carry out relevant experiments to obtain empirical correlations. In this paper, experimental study on the lead-bismuth eutectic (LBE) cross flow around the tube bundle is carried out to investigate the thermal-hydraulic characteristics based on geometric approximation of local region. Three test sections with different inclination angles of 0°, 4°, 8° are adopted in the experiments with Peclect number (Pe) up to 350. The experimental sections are uniformly heated with heat flux ranging from 20 to 100 kW/m2. The heat transfer characteristic of LBE cross flow around inclined tube bundle is obtained, considering the effects of inclination angle of the test section. The heat transfer correlation of LBE cross flow around inclined tube bundle is proposed for the first time. By comparing the data of the experiments, the results are all within the error range of 10%. The correlation is appropriate for the program development of LBE HCOTSG. This study can provide essential experimental data for the design and code development of LBE HCOTSG.

Numerical and experimental study on temperature and heat transfer characteristics in centrifugal compressor diffuser

Lubrication oil aerosol deposit and coking in the compressor diffuser is a typical issue for the high power density internal combustion engine (ICE) using the closed crankcase ventilation (CCV) system. The aerosol coking significantly negatively influences the compressor's performance, leading to a penalty on ICE performance. The severity of the coking effect is highly dependent on temperature. In order to predict occurrence of coking and to clarify how to avoid aerosol coking in the compressor, the temperature distribution and heat transfer characteristics are investigated in this study. An experimental investigation on the diffuser temperature distribution at shroud side was carried out first. Numerical simulations that consider the heat transfer between the solid domain and the fluid domain are conducted, aiming at analyzing the temperature distribution of inner surface. The detailed simulation model of small high-pressure-ratio compressor for predicting coking risk is established. Furthermore, the simulation model is validated by the experimental results. The results indicate that the shroud side of the diffuser sees the highest temperature level in the diffuser. Under typical operation conditions, the temperature at the diffuser wall exceeds the threshold coking temperature of lubrication oil aerosol, this location most likely to have severe coking issues. Thus, the location of the shroud plate is the primary region that needs to be cooled down to mitigate the coking issue. Meanwhile, the intensity of heat transfer between the fluid and solid domain in the diffuser region degrades significantly along the flow direction and sees an 80% drop from diffuser inlet to outlet, indicating the requirements for further enhancement of heat transfer in diffuser shroud side along streamwise.

Numerical Analysis of Heat Transfer within a Rotary Multi-Vane Expander

In this paper, the results of numerical investigations on heat transfer in a multi-vane expander (MVE) are reported. MVEs are very interesting for various technological applications because of their advantages (such as, for example, low gas flow capacity and a low expansion ratio). According to a literature study, the heat exchange mechanisms occurring in these machines have not yet undergone in-depth analysis. As a result, there have been very few experimental or modeling results connected to these unquestionably significant processes from both a scientific and practical perspective. Despite the fact that several analytical models have been developed for these phenomena, there is no numerical model dedicated to an MVE. This model was developed by the authors and presented in this paper together with modeling results. Numerical simulations were executed in the ANSYS CFX and focused on defining the expander heat transfer coefficients under various flow circumstances. The results showed inside heat transfer processes in MVEs and, moreover, it was discovered that, in the gap between the vane and the cylinder, there are changes in the fluid’s velocity profile.