Fin Heat Research Articles

Performance and optimum design analysis of longitudinal and pin fins with simultaneous heat and mass transfer: Unified and comparative investigations

In the present paper, the thermal analysis and optimization of longitudinal and pin fins of uniform thickness subject to fully wet, partially wet and fully dry surface conditions are carried out analytically, and also a comparative study is made between the longitudinal and pin fin for a wide range of design parameters. From the results, a significant effect on the temperature distribution in the fin and the fin efficiency with the variations in moist air psychometric conditions is noticed. For partially wet fins, the length of the wet–dry interface depends on the relative humidity RH, fin parameter Z d and geometry of the fin. From the results, it can also be highlighted that for the same thermo-geometric and psychometric parameters, a longitudinal fin gives higher efficiency than the corresponding pin fin irrespective of surface conditions. Next, a generalized scheme for optimization has been demonstrated in such a way that either heat transfer duty or fin volume can be taken as a constraint selected as per design requirement. From the optimization results, it can be pointed out that the optimum design of both the longitudinal and pin fin under the partially wet surface condition is only possible for a narrow range of relative humidity whereas for the fully wet surface, a wide range is noticed. Finally, design curves have been established for a wide range of thermo-psychometric parameters, which may be helpful to a designer for estimation of the optimum design variables of a fin with a minimum effort.

An experimental study on the quantitative interpretation of local convective heat transfer for a plate fin and tube heat exchanger using the lumped capacitance method

An experimental study has been performed to investigate the heat transfer characteristics of a plate fin and tube heat exchanger. Existing transient and steady methods are inappropriate for the measurement of heat transfer coefficients of the thin heat transfer model. In this study, the lumped capacitance method based on liquid crystal thermography was adopted. The method is validated through impinging jet and plate flow experiments. The two experiments showed very good agreements with those of the well-known transient method with the thick acryl model. And the lumped capacitance method showed similar results regardless of the thickness of the polycarbonate model if the Bi of the fin is small enough. The method was also applied for the heat transfer coefficient measurements of a fin and tube heat exchanger. Quantitative heat transfer coefficients of the plate fin were successfully obtained.

05/02710 Effect of fin pitch and number of tube rows on the air side performance of herringbone wavy fin and tube heat exchangers

05/02710 Effect of fin pitch and number of tube rows on the air side performance of herringbone wavy fin and tube heat exchangers

Study on the heat transfer characteristics of the annular fin under dry-surface, partially wet-surface, and fully wet-surface conditions

In the present study, theoretical results of the heat transfer characteristics and the fin efficiency of the annular fin are presented. Annular fin under dry-surface conditions, partially wet-surface conditions, and fully wet-surface conditions are investigated. The mathematical models based on the conservation equations of energy and mass are developed and solved by the central finite difference method to obtain temperature distribution along the fin. Effects of inlet condition of working fluids and the fin dimensions on the heat transfer characteristics and fin efficiency are considered. The results obtained from the model are validated by comparing with those obtained from the other researchers. There is a reasonable agreement between the results obtained from the present model and those obtained from the other model.

Performance of a Circular Fin in a Cylindrical Porous Enclosure

The problem of natural convection heat transfer from a vertical cylindrical fin to a saturated porous medium in a cylindrical enclosure is solved numerically. A conjugate conduction-convection analysis is accomplished by solving the equation of heat conduction in the fin together with the mass, momentum and energy balance equations in the porous medium. Numerical results are obtained by using ADI method. The effects of the conduction-convection ratio parameter, aspect ratio and Darcy number on local heat transfer coefficients and fin efficiency are discussed. Comparison of the local heat transfer coefficients and fin efficiency is shown with those for non-porous medium.

Effect of Variable Heat Transfer Coefficient, Fin Geometry, and Curvature on the Thermal Performance of Extended Surfaces

A constant heat transfer coefficient is often assumed in the computation of the temperature distribution along an extended surface. This assumption permits the use of a well-established closed form analytical solution thus simplifying the mathematical complexity of the conservation energy equation. For certain fin geometries, this assumption will lead to poor prediction of the thermal performance of the extended surface especially for tapered and triangular fins. In this study, a generalized analytical solution was developed that permits the computation of heat loss from an extended surface based on variable heat transfer coefficient, fin geometry, and surface curvature. The influence of these parameters on fin efficiency for typical fins is reported.

The effect of the number of tube rows on heat, mass and momentum transfer in flat-plate finned tube heat exchangers

The effect of the number of tube rows on heat, mass and momentum transfer in flat-plate finned tube heat exchangers

Fan supplied heat exchanger fin performance under frosting conditions

In this paper, a validated numerical model for frost growth on heat exchange fins is modified to simulate a fan-supplied finned heat exchanger under refrigeration frosting conditions. It is found that frost growth on refrigeration heat exchangers causes a dramatic drop in the fin heat rate, airflow rate, and fin efficiency while the pressure drop increases. A sensitivity study shows the effects of changing several design parameters including the type of fan.

Core heat transfer studies in a circulating fluidized bed

In some large capacity Circulating Fluidized Bed (CFB) boilers with water walls, additional heat transfer surfaces are necessary to control the furnace temperature while restricting the boiler height to about 40 m due to commercial considerations. These surfaces could be in the form of (1) External Heat Exchanger (EHE) in the solids recycle loop, (2) wing wall and omega panels at the very top of the furnace, or (3) a division or a curtain wall running through the core region of the upper dilute zone of the boiler. It is necessary to know the heat transfer characteristics for these core surfaces from design and operating considerations. In this context, experimental heat transfer studies have been conducted on a 0.6-m high single vertical tube, 0.5- and 1.0-m high U-tubes, and a 0.5-m high finned U tube, located in the top 10% height of a 100 mm×100 mm cross-section and 5.5-m tall CFB riser using silica sand of three mean sizes in the range of 143 to 363 μm as the bed material. The fluidizing air velocity and solid circulation flux were varied in the range of 4–8 m/s and 13–80 kg/m 2/s, respectively. The resulting cross-sectional average suspension density and measured total (gas convective plus particle convective) surface-average convective heat transfer coefficients for U-tubes were in the range of 9 to 25 kg/m 3 and 30 to 105 W/m 2/K, respectively. For single vertical tube at axis, they were in the range of 10 to 20 kg/m 3 and 60 to 128 W/m 2/K, and at off-axis positions, they were in the range of 10 to 20 kg/m 3 and 70 to 140 W/m 2/K, respectively. The results confirmed the increasing trend of the heat transfer coefficient from the axis towards the riser wall, thus reflecting the core-annulus flow structure of the CFB riser. It was observed that the length of the tube influences the heat transfer coefficient and fins augmented the heat transfer rate. Gas convective contribution was found to be substantial especially at high gas velocities and for large particles. Experimental data were compared with published heat transfer results under somewhat similar conditions. Using the experimental data points for the U-tubes, two empirical heat transfer correlations were developed in terms of the important design and operating parameters.

One-Dimensional Fin-Tip Boundary Condition Correction II

Exact expressions are presented for the corrective terms for a one-dimensional fin temperature and heat lost when the insulated tip assumption is used for the case where the tip is maintained at a constant temperature. Both straight rectangular and uniformly thick annular fin geometries are discussed. Numerical examples are shown to highlight the considerable error in assuming an insulated tip condition.

An Experimental Study on Quantitative Interpretation of Local Convective Heat Transfer for the Fin and Tube Heat Exchanger Using Lumped Capacitance Method

An experimental study has been performed to investigate the heat transfer characteristics of fin and tube heat exchanger. The existing transient and steady methods are very difficult to apply for the measurements of heat transfer coefficients of a thin heat transfer model. In this study the lumped capacitance method was adopted. The heat transfer coefficients were measured by using the lumped capacitance method based on the liquid crystal thermography. The method is validated through impinging jet and flat plate flow experiments. The two experiments showed that the results of the lumped capacitance method with polycarbonate model showed very good agreements with those of the transient method with acryl model. The lumped capacitance method showed similar results regardless of the thickness of polycarbonate model. The method was also applied for the heat transfer coefficient measurements of a fin and tube heat exchanger. The quantitative heat transfer coefficients of the plate fin were successfully obtained. As the frontal velocity increased, the heat transfer coefficients were increased, but the color-band shape showed similar patterns regardless of frontal velocity.

Steady and transient numerical analysis of the performance of annular fins

This article presents a simple, straightforward and accurate numerical technique that can be used to predict the steady and transient temperature distributions in an annular fin with uniform cross-section. Both convection and/or thermal radiation ambient conditions are considered in this study. The heat transfer rate and fin efficiency are also calculated. Results are compared with the exact solution for the steady case where excellent agreement was observed for an insulated tip fin and with approximate solutions for the transient case for a non-insulated tip condition. Copyright © 2001 John Wiley & Sons, Ltd.

Comparison between one-dimensional uncoupled and convection-conduction conjugated approaches in finned surface heat transfer

This work studies the forced convection problem in internal flow between concentric annular ducts, with radial fins at the internal tube surface. The finned surface heat transfer is analyzed by two different approaches. In the first one, it is assumed one-dimensional heat conduction along the internal tube wall and fins, with the convection heat transfer coefficient being a known parameter, determined by an uncoupled solution. In the other way, named conjugated approach, the mathematical model (continuity, momentum, energy and K-e equations) applied to tube annuli problem was numerically solved using finite element technique in a coupled formulation. At first time, a comparison was made between results obtained for the conjugated problem and experimental data, showing good agreement. Then, the temperature profiles under these two approaches were compared to each other to analyze the validity of the one-dimensional classical formulation that has been utilized in the heat exchanger design.

Turbulent heat transfer, pressure drop and fin efficiency in annular regions with continuous longitudinal rectangular fins

Abstract Experiments were performed to determine average heat transfer coefficients and friction factors for turbulent flow through annular ducts with continuous longitudinal rectangular fins. In addition, the fin efficiency was also determined by means of a numerical two-dimensional heat transfer analysis. The total number of fins attached to the inner wall of the annular region was 20. The measurements were made by using a double-pipe heat exchanger. The fluids were, air flowing in the annular section, and water through the inner tube. The average heat transfer coefficients were obtained from the experimental determination of the overall heat transfer coefficients of the heat exchanger. To attain fully developed conditions at the entrance and exit, the heat exchanger was built with additional lengths before and after the test section (30 hydraulic diameters). The double-pipe heat exchanger and fins were made of brass. Due to the high thermal conductivity of the brass and the small water temperature variation, the surface of the inner tube was practically isothermal. The external tube was well insulated and can be considered adiabatic. The results are presented in dimensionless forms, in terms of the average Nusselt number, friction factor and fin efficiency, as functions of the flow Reynolds number. A comparison of the present results with those for smooth sections (without fins) is also presented. The purpose of such comparison is to study the influence of the presence of the fins on the pressure drop and heat transfer rate.

Numerical prediction of high efficiency boiler heat exchanger performance

A three-dimensional (3-D) code which can predict the complete performance of high efficiency boilers is described in this paper. The model is in two parts. The combustion chamber is modelled in the first part and the heat exchanger in the second. The thermal efficiency is calculated from the predicted results. The computational model was based on the two-dimensional (2-D) TEAM code which has been extended into 3-D and extensively modified by the present authors. In the code, the gaseous combustion was modelled by Simple Chemical Reaction System concept; the Radiation process was handled by the ‘Discrete Transfer’ method. The modelling results of the combustion chamber were used as input for the calculation of the consequent finned tube heat exchanger. The heat exchanger calculation included conduction, convection and radiation. Predictions were performed for a low Reynolds number boiler and compared with existing data. Good agreement was obtained.

CONJUGATE HEAT TRANSFER OF A FINNED OVAL TUBE PART B: HEAT TRANSFER BEHAVIORS

Conjugate heat transfer in a high-performance finned oval lube heat exchanger element has been calculated for a thermally and hydrodynamically developing three-dimensional laminar flow. The influence of Reynolds number in the range 100–500 and of a Jin parameter Fi, the product of the dimensionless fin thickness and its thermal conductivity, on the heat transfer behavior have been studied. In part I, the computed velocity field was presented. Here we present the heal transfer behavior, including heat flux on the tube, fin temperatures, fin Nusselt numbers and heat flux distributions, fin efficiencies, Colburn j factor, and apparent friction factor fapp For the investigated configuration, the ratio of heat transfer on the tube to that on the fin remains under 10%. The fin temperature and fin efficiency depend weakly on Fi.

Air-side flow and heat transfer for a two-row lanced finned tube heat exchanger

A numerical study has been performed to obtain the air-side flow and heat transfer characteristics for a two-row lanced finned tube heat exchanger with 7 mm tube outer diameter. The increases of dimensionless local heat flux at the leading edge of slit and bottom surface of the fin were noticed. The temperature of air at downstream of the 2nd row of the lanced fin becomes more uniform than that of the plain fin because the mixing of energy increases by the slit and the side-slit. As the inlet velocity increases, the contribution of the 1st row to heat transfer decreases and that of 2nd row increases.

Heat Transfer Performance of a Plate-Finned Tube Heat Exchanger. A Three-Dimensional Steady Numerical Analysis for a Single Row Tube in Low Reynolds Number Range.

A three dimensional steady numerical analysis has been made for a one unit of single row plate-finned tube heat exchanger located in a uniform flow. The structures of the flow and thermal fields have been examined for conduction-convection conjugate heat transfer problem of the studied fin-and-tube model. The results of the numerical analysis revealed some important effects of geometric parameters on heat transfer from the fin-and-tube surface. The effects of fin thickness, fin pitch, fin length, tube pitch and Reynolds number on Nusselt number, heat transfer rate, fin efficiency and pressure coefficient were examined parametrically. Upstream half of the fin surface yielded a much higher heat transfer coefficient than the downstream half of the fin surface. Especially, the values of fin local heat transfer coefficient is nearly zero in the near region of the tube. As Reynolds number increases, the fin efficiency and the pressure coefficient decrease.

5540276 Finned tube heat exchanger and method of manufacturer

5540276 Finned tube heat exchanger and method of manufacturer

1-D Fin Tip Boundary Condition Corrections

Exact expressions are presented for the correction terms for the one-dimensional fin tip temperature and heat lost when the insulated tip assumption is used for the convective tip case. Both straight rectangular and uniformly thick annular fin geometries are discussed. Numerical examples are shown. For some conditions in these examples, sizable corrections are needed, which increase as the Biot number decreases.