Wet Fin Research Articles

Numerical investigation of efficiency of fully wet porous convective-radiative moving radial fin in the presence of shape-dependent hybrid nanofluid

The main focus of the study is a fully wet porous fin of radial profile exposed to convective-radiative heat exchange with the hybrid nanofluid flowing past it with a constant velocity of U. In the analysis, spherical-spherical, spherical-cylindrical, and spherical-platelet shape combinations of two nanoparticles are considered. The mixture model is employed to assess all the thermophysical attributes of the hybrid nanofluid except thermal conductivity and dynamic viscosity, which are estimated by applying the nanoparticle volume fraction-based interpolation method. The fin model with the applied conditions results in an ordinary differential equation which is made dimensionless and then numerically resolved by applying the Runge Kutta Fehlberg (RKF) 4-5th ordered technique. The effect of Peclet number, wet fin parameter, thermogeometric parameter, nanoparticle volume fraction, convective parameter, radiative parameter, exponential index, empirical shape factor and ambient temperature (dimensionless) on the energy field and thermal gradient profiles of the radial fin subjected to shape-dependent hybrid nanofluid flow has been graphically analysed. Furthermore, the thermal fin efficiency has been modelled and its variation with the significant parameters has been examined. One of the major outcomes was that efficiency increases with nanoparticle volume fraction. Further, it is significantly affected by the shape factor of the nanoparticles and achieves the highest value for spherical-platelet combination. The results obtained motivate further study of nanotechnology assisted extended surface technology.

Analytical methods for the efficiency of annular fins with rectangular and hyperbolic profiles under partially wet surface conditions

In this study, we analytically investigate the performances of annular fins with rectangular and hyperbolic profiles under partially wet conditions. We propose four equations for the profiles of enthalpy difference, four equations for heat transfer rates, and four equations for fin efficiency which is a function of interface radius. We then present four equations for evaluating interface radius. Results indicate that the heat transfer rate and efficiency of an annular fin with a rectangular profile is higher than that with a hyperbolic profile. The efficiency under partially wet conditions is between those under fully dry and fully wet conditions. The efficiency of fully dry fins is independent of relative humidity; however, for fully wet and partially wet conditions, efficiencies increase with decreasing relative humidity. At the same relative humidity, heat transfer rate increases with an increasing ratio of outside radius to inside radius. In contrast, fin efficiency decreases. Highlights By analytical method, the partially wet annular fin performances are investigated. Partially wet fin efficiency of annular fin of rectangular profile is presented. Partially wet fin efficiency of annular fin of hyperbolic profile is presented.

Optimal Shape of Non-Linear Partially Wet Annular Fins for Maximum Efficiency

Heat exchangers with annular finned-tube type and partially wetted condition are utilized widely in engineering systems, such as air-conditioning systems and refrigeration systems. In addition, the physical properties of fin materials should be considered as functions of temperature in reality and thus become a non-linear problem. Based on the above two conditions, an optimal partially wet annular fin design problem, with temperature-dependent thermal properties of the fin, to yield optimal fin efficiency was investigated in the present work, which has not been examined previously and it is the novelty of this study. An iterative regularization algorithm using the conjugate gradient method (CGM) is considered as the optimization tool based on the desired fin efficiency under a fixed fin volume constraint. The partially wet annular fin condition can result if the relative humidity of surrounding air is between 80 and 90%. Finally, the optimal fin shape, with the highest computed efficiency among examined fins under identical operational conditions, can be obtained. It is found that when the Biot numbers for ambient air (Bia) and relative humidity (φ) increased, the optimum computed fin efficiency and interfacial radius between wet and dry fin domains (rwd) will be increased, and the estimated optimum fin shape also changed. However, the shape of optimal fin remained approximately unchanged when the Biot numbers for the inner tube (Bii), the thermal conductivities of the tube (kw) and fin (kf) varied. It reveals that Bii, kw and kf have an insignificant influence on the optimal shape of the annular fin in a partially wet condition.

New Forward and Inverse Solutions for Wet Fins Generalized Profiles With All Nonlinear Phenomena

AbstractThis study establishes forward closed-form and inverse analyses of wet fins of various profiles involving all modes of heat transfer. Existing limitations in the literature are addressed here by choosing the appropriate nonlinear variation of thermal conductivity and radiation effects. The error between linear and nonlinear methodologies is found to be within 60%. Furthermore, the maximum error between the closed-form solution based on the differential transformation method (DTM), and the numerical solution is observed as 0.5%. After necessary validations, optimization of various fin profiles is carried out by the maximization of the net fin heat transmission rate under a defined fin volume and thermogeometrical constraints. For the optimum criterion, the suitability of the artificial bee colony (ABC)-based metaheuristic technique is established. The identification of thermogeometrical parameters is realized by analyzing combinations obtained from 100 runs of ABC and the decision-making criterion is adopted on the basis of the maximum thermal performance. Among the studied profiles, concave parabolic geometry yields the maximum heat transport rate, which is followed by triangular, convex, and rectangular geometries for the same fin volume. The present combination of DTM and ABC techniques is proposed to be useful in practical applications toward design and the selection of evaporator fins for air-conditioning and refrigeration appliances operating under wet conditions in a more accurate and optimized manner.

Analysis of thermal behavior of moving longitudinal porous fin wetted with water‐based SWCNTs and MWCNTs

AbstractIn this study, the consequences of natural convection and radiation on longitudinal porous fin are scrutinized numerically. Here, the fin is moving and is wetted with nanoliquid containing single‐walled carbon nanotubes and multiwalled carbon nanotubes. Darcy's model is employed in modeling the present physical phenomenon. The derived steady‐state energy equation has been solved numerically via the Runge‐Kutta‐Fehlberg fourth‐fifth‐order method. The impact of significant parameters on the thermal performance of the wet fin has been illustrated through graphs for both types of carbon nanotubes. The comprehensive study of carbon nanotubes explores that better heat transfer from a wet fin can be achieved in the case of multiwalled carbon nanotubes.

Numerical model of particle deposition on wet fin surfaces of heat exchanger under dehumidifying conditions

Dusty particles may easily deposit on fin surfaces of heat exchangers under dehumidifying conditions and thus seriously deteriorate the heat transfer performance. The purpose of this study is to develop a numerical model for simulating the dusty particle deposition on wet fin surfaces in practical working processes, including the shape and mass of the deposited dusty particles in the process of particle-capturing by condensate water and that of particle adhesion on wet particulate layer. The prediction method of the dusty particle deposition in the process of particle-capturing by condensate water is to simulate the motion trajectories of all particles in the air flow at first and then to choose those particles intersecting with the water surface as deposited. The prediction method of the dusty particle deposition in the process of particle adhesion on wet particulate layer is to calculate the critical sticking velocity at first and then to choose those particles with the impact velocity being smaller than the critical sticking velocity as deposited. The validation results show that, the predicted shape of wet particulate layer agrees well with the experimental images, and the predicted mass of deposited particles agrees with 91% of the experimental data within a deviation of ±20% and the mean deviation is 11.8%. Prediction results of the quantitative influence of operation conditions with this model show that the parameters of inlet air relative humidity and particle concentration are the two most important factors on dusty particle deposition on wet fin surfaces.

Forward and inverse nonlinear heat transfer analysis for optimization of a constructal T-shape fin under dry and wet conditions

This work deals with direct and inverse analysis of T-shaped dry and wet fins. Direct analysis is done to study heat transfer performance, whereas inverse analysis is performed to simultaneously estimate five optimum geometric parameters satisfying a prescribed fin volume. The modified differential evolution (MDE) search algorithm is used to explore the required geometrical parameters pertaining to the stem and the flange parts of the fin. In the present MDE, the mutant is generated using five distinct vectors instead of three as conventionally practiced. Due to the existence of multiple solutions, the selection criterion is based upon the fulfilment of different performance parameters. These involve individual maximization of heat transfer rate, fin efficiency and fin effectiveness. Since the application of the differential transformation method (DTM) is not yet demonstrated for nonlinear heat transfer analysis of T-shaped wet fins, thus, for generating the heat transfer parameters using the inversely estimated geometric parameters, a forward approach based on the DTM is used here. Parametric variations along with necessary validations of the direct method are presented. Furthermore, a comparison of the present MDE search-based inverse algorithm is done with a classical gradient-based optimization technique. It can be highlighted from the present study that only when at-least three geometrical parameters are known, then the classical method successfully yields heat transfer performance parameters comparable with the MDE algorithm. From the optimization study, it is found that a particular value of fin performance (heat transfer rate, efficiency, effectiveness) can be acquired with various values of surface area and even at a given surface area, different fin performances can be obtained. However, a single and distinct operating point is revealed where the performance index of the fin is maximized. For ensuring maximum possible performance from constructal T-shape wet fins, it is recommended that for the present type of problem, the present stochastic optimization method such as MDE must be used where the classical deterministic methods suffer from inherent limitations on multi-variables optimization.

RETRACTED: Thermal behavior of wet porous and solid fin–Experimental and analytical approach

RETRACTED: Thermal behavior of wet porous and solid fin–Experimental and analytical approach

Heat transfer improvement of a wet fin under transient response with a unique design arrangement aspect

A unique design arrangement for longitudinal and pin fins involving surface dehumidification is proposed for improving the fin’s heat transfer enhancement under transient operating condition. The new design arrangement involves dual primary fin surfaces. For the present analysis, the assessment of Fourier and non-Fourier effects is made, and a closed form solution methodology involving separation of variables is adopted to evaluate the fin performance. The proposed closed form methodology for the non-Fourier heat transfer effect in the wet fin is well-validated with the corresponding numerical solution obtained under finite differencing framework. Furthermore, for a dry surface condition, the validation of the present non-Fourier model is done with the pertinent results available in the literature. The Fourier and the non-Fourier heat transfer effects are investigated with various design variables of the wet fin and surface conditions. It is highlighted that the effect of air dehumidification in fins promotes waviness in the temperature distribution. The efficiency is determined to be higher in the case of the longitudinal fin than that of the pin fin, whereas, an opposite behavior is revealed in terms of the fin effectiveness. Higher fin efficiency is observed at lower values of the Fourier number and higher values of the Vernote number. It is apparent from the present study that the proposed new fin design considerably enhances the rate of heat transfer as compared to the conventionally used design. Additionally, the proposed design results in a compact geometry that in turn provides additional mechanical strength resulting in the savings of space utilization and costs related to fin manufacturing.

Establishment of non-Fourier heat conduction model for an accurate transient thermal response in wet fins

In this work, transient heat transfer response of wet fins is carried out using both Fourier and non-Fourier heat conduction models. The separation of variables is used to establish a classical analytical model defining the actual transient thermal response. The present analysis has been focused and generalized for both longitudinal and pin fins under isothermal and convective base conditions. During the analysis, the instantaneous efficiency has been introduced with both Fourier and non-Fourier heat conduction models in fins operating under dehumidifying conditions. The analysis shows for a significant deviation in temperature response with the non-Fourier heat conduction as compared with that of the Fourier model. The effect of different design variables and fin surface conditions is reported. From the present analysis it becomes apparent that the instantaneous fin efficiency for wet fin surface is always less than the dry one and the condensation of vapor on the fin surface amplifies the non-Fourier heat conduction. Hence, the present analysis of non-Fourier heat transfer for determining the performance parameters of wet fins would help to have actual design information under transient behavior conditions.

Direct and inverse approaches for analysis and optimization of fins under sensible and latent heat load

An inverse methodology is introduced by differential evolution (DE) search algorithm to determine optimal dimensions of a wet fin for a given volume for to maximize heat transfer rate. The DE optimization method is first employed to explore multiple combinations of geometrical fin parameters satisfying a constraint volume. The pertinent rates of heat transfer are computed using a forward analysis based on the differential transform method. In this study for a fixed fin volume, a same value of heat transfer rate in wet fins can be acquired for multiple values of surface areas, and also, even a given surface area can yield multiple values of heat transfer rates. Hence, the local temperature distribution acts as an important factor in selecting a unique set of fin dimensions towards maximizing the rate of heat transfer. The evaluation of sensitivity coefficients reveals that among various geometric parameters, the fin thickness plays an influential role significantly to govern the heat transfer rate.

Experimental Research and Simulation of Fin and Tube Heat Exchanger

The paper provides the results of experimental and theoretical test of a wavy fin and tube heat exchanger used to cool air in a ventilation system when the wavy fin of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number applying LMTD-LMED methodology, determined the dependency of the heat transfer coefficient on the supplied air flow rate with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating and 6 heat exchangers in cooling mode. After processing the results of the experimental tests, empirical equation defining the characteristics of the heat transfer coefficient of all heat exchangers were derived. The maximum heat transfer coefficient deviation is 11.6 percent. The correction factor of the wet fin (Lewis number) depending on the number of Reynolds, which ranges from 0.75 to 1.1 also is determined. Maximum capacity deviation equals 3.7 percent. The obtained equations can only be applied to a certain group of heat exchangers (with the same shape of fins or the distance between the tubes). The results of the experimental test and simulation with ANSYS program are compared and the heat transfer coefficients vary from 6.5 to 11.4 percent.

A new moving boundary model for evaluating the performance of wet fins: Application to minichannel evaporators

In this paper, firstly, an innovative numerical model (Fin1D-MB) for wet fins of a minichannel evaporator was developed and verified. The proposed model is based on fin theory in conjunction with the moving boundary (MB) technique between wet and dry portions along the fin height. Secondly, a comparative study between the Fin1D-MB model and a comprehensive two-dimensional model (Fin2D-W) was implemented under different dehumidifying conditions. The results showed a good agreement between the two models in predicting the fin temperature profile and dehumidifying condition. However, the Fin1D-MB model saved computational cost by up to 95%, compared to the Fin2D-W model. Nevertheless, the relative deviations in the air-side heat transfer rates should be taken into consideration, especially in the partially wet fin region. The main source of these deviations is the assumption of uniform air temperature and humidity ratio along the fin height used by the Fin1D-MB model.

Thermal analysis of natural convection and radiation in a fully wet porous fin

Purpose The purpose of this paper is to take the thermal analysis of natural convection and radiation heat transfer in fully wet porous fins. The wet porous fins taken for the analysis are straight fins in nature and wet. Their profile being straight helps heat transfer process of fins faster. The analysis is performed using the Darcy’s model to generate the heat equation to analyze the variation of convection and radiation parameters. The porous nature of the fins allows the flow to penetrate through the porous material of the fins leading to solid-fluid interface. The obtained non-dimensional ordinary differential equation involving three highly nonlinear terms are solved numerically by using spectral collocation method after which they are reduced into algebraic equations using Chebyshev polynomials. The study is analyzed using the mathematical analysis on heat equation and generating graphs for finding the parameters important to the heat transfer in the straight fins. Design/methodology/approach This study is performed using Darcy’s model to formulate heat transfer equation. To study the thermal performance, the authors considered a finite length fin with insulated tip. The effects of the wet fin parameter m2, porosity parameter Sh, radiation parameter G and temperature ratio CT on the dimensionless temperature distribution and heat transfer rate are discussed. Findings The results show that the base heat flow increases when the permeability of the medium is high and/or when the buoyancy effect induced in the fluid is strong. Research limitations/implications The analysis is made for the Darcy’s model. Non-Darcy effects will be investigated in a future work. Practical implications The approach is useful in enhancing heat transfer rates. Originality/value The results of the study will be interest to the researchers of the field of heat exchanger designers.

Establishment of Modified-One-Dimensional and Two-Dimensional Models for Two-Directional Heat Conduction in a Wet Fin Assembly

This paper deals with an analysis of two-dimensional temperature distribution within a rectangular fin assembly under wet conditions and subject to convective condition at the primary inner wall. An analytical method based upon the separation of variables was suggested to determine the two-dimensional temperature field. A modified one-dimensional model was used to more closely approximate the results of the two-dimensional model; a one-dimensional classical model was also elaborated to provide a basis for comparison, allowing the two-dimensional effect to be established in the case of wet fins. Next, wet fin efficiency was determined. To establish the merit of the present work in considering the two-dimensional effect in wet fins, the results of the two-dimensional model were compared with those obtained from the one-dimensional classical models, demonstrating a considerable difference in their results for various design and psychrometric conditions. The wet-fin analysis presented herein is equally suitable for dry-surface fins by accounting for the absence of latent heat transfer.

A Study on Nonlinear Wet Fin Problem Using Homotopy Analysis Method

Homotopy analysis method (HAM) is used to study a rectangular wet fin with variable thermal conductivity. Unlike most theoretical investigations which have been carried out by considering a constant thermal conductivity and a linear relationship between the specific humidity of air and temperature, in this work, thermo-geometric and psychrometric variations are assumed to be nonlinear. The above considerations make the fin problem highly nonlinear due to nonlinearities in the governing equation as well as in the boundary conditions. HAM is used to determine the closed-form solution (i.e., temperature field) and the efficiency of the fin. It is noticed that the fin efficiency is obtained as a function of thermo-geometric fin parameter. The effects of the wet surface and variable conductivity on the temperature field as well as on the fin efficiency are analyzed. The present results of HAM are found to be in very good agreement with the available results of relevant literature. It is shown that the thermo-geometric fin parameter has a significant role on the fin efficiency. The present study reveals that the simultaneous heat and mass transfer across the fin surface is thermally less efficient compared to the fin surface involving heat transfer only.

Two-dimensional numerical modeling for the air-side of minichannel evaporators accounting for partial dehumidification scenarios and tube-to-tube heat conduction

This paper presents a comparative study between the air-side heat transfer results of a two-dimensional numerical model for minichannel evaporators (Fin2D-W), and the results of the classical ε–NTU approach. This study is carried out for different dehumidifying conditions, and for scenarios with different degree of temperature difference between tubes due to the refrigerant superheat. The Fin2D-W model solves the two-dimensional heat conduction in the fin wall considering also a 2D discretization for the air flow in contact with it. Thus, the presented model is able to capture the partial dehumidification scenarios and the effect of the heat conduction between tubes. The results analyze the differences, due to these phenomena, between the proposed model and the classical approach. Significant deviations between the two models are reported, especially in the cases of partially wet fin and high values of superheat, resulting in being up to ≈ 52% in total heat transfer.

Thermal performance and optimization of hyperbolic annular fins under dehumidifying operating conditions – analytical and numerical solutions

The thermal performance of hyperbolic profile annular fins subjected to dehumidifying operating conditions is studied. An analytical solution for completely wet fin is derived using an approximate linear temperature–humidity relationship. A numerical solution using actual psychrometric relationship for completely and partially wet operating conditions is then obtained to account for the actual temperature–humidity ratio psychrometric relationship under both partially and fully wet operating conditions. An excellent agreement is observed between analytical and numerical solutions for completely wet fin. The fin optimization is presented based on the analytical solution of completely wet fin. Finally, a finite element formulation is used for studying the two-dimensional effects of orthotropic thermal conductivity on the thermal performance of fin under partially and fully wet operating conditions.

Effects of psychrometric properties on fin performances of minimum envelope shape of wet fins

A method based on the variational principle is used to determine a minimum shape of wet fins for effective transfer of heat in fins. In many air-cooling applications, fin surface becomes wet as the surface is lower than the dewpoint temperature of the surrounding air. On the wet surface, both the sensible and latent heat transfer take place due to an existence of respective driving forces. The fin temperature is also dependent upon the latent heat released on its surface from the condensed moisture. The humidity ratio of air adjacent to the fin surface for the latent heat transfer is a psychrometric function with temperature. Due to this, the analysis of wet fins is always difficult as the governing fin equation is complex in nature. A simple model based on a linearity function between humidity ratio and temperature has been an alternative approximate model. The present analysis is attempted to estimate an envelope shape of wet fins by minimising fin volume for a constraint heat transfer rate for an actual variation of humidity ratio with temperature. The effect of psychrometric properties of air on the minimum shape of wet fins has been studied in the present work. The fin performance for the least envelope shape of wet fins is proposed with the variation of thermo-psychrometric parameters. A comparison of results for the variation of linear and nonlinear humidity ratio with temperature on the analysis of the minimum envelope shape has been systematically investigated. This study is also highlighted errors in connection with the linear model to determine the least fin shape for efficient heat transfer. This analysis may be extremely important in those augmentation heat transfer apparatuses where a gain in weight creates always an excessive overburden. Due to this, the selection of the function of humidity ratio as a fin surface temperature may be extremely important for calculating minimum weight of a fin for the same heat transfer duty.

Determination of Temperature Distributions of Fully Wet Rectangular, Triangular, and Parabolic Straight Fins

A numerical simulation is performed to determine the temperature distribution along fully wet fins of different geometric profiles under different relative humidity and surrounding temperature conditions. Four straight fin profiles are considered in this study: rectangular, triangular, concave parabolic, and convex parabolic. The same base thickness and length are used for consistency. The current work extends equations formulated in previous studies and applies them to the different fins to characterize their temperature distributions. The impact of the variation in the operating conditions on the fin tips and temperature distributions along the fin profiles is investigated. The simulation results confirm that increasing the surrounding temperature and relative humidity levels increases the temperature along the fins for all profiles. In addition, parametric studies indicate that the assumption of fully wet fins may be violated depending on the operating conditions. This is an important deviation from previous works that may have not considered the fully wet fin assumption.