Fin Temperature Research Articles

Investigation of natural-convection heat transfer coefficient on a vertical square fin of finned-tube heat exchangers

The finite difference method in conjunction with the least-squares scheme and the experimental temperature data is proposed to predict the average natural-convection heat transfer coefficient and the fin efficiency on a vertical square fin of one-circular tube plate finned-tube heat exchangers. In the present study, the radiation and convection heat transfer coefficients are simultaneously taken into consideration. The heat transfer coefficient on this square fin is very non-uniform. Thus the whole plate fin is divided into several sub-fin regions in order to predict the average heat transfer coefficient h ¯ and the fin efficiency on the fin from the knowledge of the fin temperature recordings at several selected measurement locations. The results show that the heat transfer coefficient on the bottom fin region of the tube can be markedly higher than that on the top fin region of the tube. The h ¯ value increases with the fin spacing S and approaches an asymptotical value obtained from a single square fin as S → ∞. The fin temperature distributions depart from the ideal isothermal situation and the fin temperature decreases more rapidly away from the circular center with increasing the fin spacing. In order to show the accuracy of the present inverse scheme, a comparison of the average heat transfer coefficient on the fin between the present predicated results and those obtained from the correlation recommended by current textbooks is made.

Prediction of heat transfer coefficient on the fin inside one-tube plate finned-tube heat exchangers

The finite difference method in conjunction with the least-squares scheme and the experimental temperature data is proposed to predict the average heat transfer coefficient and the fin efficiency on the fin inside one-tube plate finned-tube heat exchangers for various air speeds and the temperature difference between the ambient temperature and the tube temperature. Previous works showed that the heat transfer coefficient on this rectangular fin is very non-uniform. Thus the whole plate fin is divided into several sub-fin regions in order to predict the average heat transfer coefficient and the fin efficiency on the fin from the knowledge of the fin temperature recordings at several selected measurement locations. The results show that the surface heat flux and the heat transfer coefficient on the upstream region of the fin can be markedly higher than those on the downstream region. The fin temperature distributions depart from the ideal isothermal situation and the fin temperature decreases more rapidly away from the circular center, when the frontal air speed increases. The average heat transfer coefficient on the fin increases with the air speed and the temperature difference between the ambient temperature and the tube temperature. This implies that the effect of the temperature difference between the tube temperature and the ambient temperature is not negligent.

C154 フィン群上の着霜現象に関する実験(OS-16 先端技術に関わる熱交換過程I)

An experimental study on the frosting phenomenon in the heat exchanger was carried out. A test section consisted of the fin bundle having 40 flat plate fins which was installed to cooling block made of copper, and was installed inside a rectangular duct made of acrylic resin. The total 55 sensors to measure the temperature of 11 fins located in the third row of the fin bundle were installed into the fin surface. The local heat transfer rate in the direction of fin length and the local heat flux in the vertical direction of the fin were obtained by approximating the fin temperature measured. Also, the heat transfer rate of each fin which means the capability of the fin was obtained, respectively.

Analysis of Multiplicity Phenomena in Longitudinal Fins Under Multi-Boiling Conditions

A numerical bifurcation analysis is carried out in order to determine the solution structure of longitudinal fins subject to multi-boiling heat transfer mode. The thermal analysis can no longer be performed independently of the working fluid since the heat transfer coefficient is temperature dependent and includes the nucleate, the transition and the film boiling regimes where the boiling curve is obtained experimentally for a specific fluid. The heat transfer process is modeled using one-dimensional heat conduction with or without heat transfer from the fin tip. Furthermore, five fin profiles are considered: the constant thickness, the trapezoidal, the triangular, the convex parabolic and the parabolic. The multiplicity structure is obtained in order to determine the different types of bifurcation diagrams, which describe the dependence of a state variable of the system (for instance the fin temperature or the heat dissipation) on a design (Conduction-Convection Parameter) or operation parameter (base Temperature Difference). Specifically the effects of the base Temperature Difference, of the Conduction-Convection Parameter and of the Biot number are analyzed and presented in several diagrams since it is important to know the behavioral features of the heat rejection mechanism such as the number of the possible steady states and the influence of a change in one or more operating variables to these states.

Thermal-hydraulic CFD study in louvered fin-and-flat-tube heat exchangers

Heat transfer performance prediction by CFD codes is of major interest. Usually air-side heat transfer characteristics of fin-and-tube heat exchangers are determined from limited experimental data. The ability of CFD code to predict flow patterns and thermal fields allows determining the heat transfer characteristics by performing ‘numerical experiments’. CFD calculations of a 1-row automotive condenser are compared to experimental results and correlations of the literature matching the fin design and the flow conditions. Calculations are performed for different air frontal velocities. 2D models, with uniformly constant fin temperature overestimate significantly the heat transfer coefficient. 3D models, taking into account tube effects, conjugate heat transfer and conduction through the fin are in better agreement with the experimental results. However, even if an offset in noticed between CFD calculations and the experimental results, the trends are comparable and CFD study permits to reach local information, leading to better understanding of the physical phenomena involved in compact heat exchangers. An attempt for 2D unsteady flow has also been performed. Results are discussed in terms of flow pattern and heat transfer coefficient behaviour.

二輪車エンジンにおけるフィンの空冷効果 : 第5報,フィンとフィンとの間の導風板効果(エンジンの新しい計測技術とモデリング(4),エンジンの新しい計測技術とモデリング)

An air coded engine with a firmed cylinder may have reeidiial heat between the fins. In oader to rediioe the residiid heat, the baffle plates were installed between the fins. The teinperature in the cylinder and on the surface of the fins was measured at various air speeds in the wind tunnel The eflects of positions of the baffle plate to the cylinder on fin temperature were examined. Results indicated that when the position of the baffle plate was set so that it was easy for the air to flow between the fins, the heat transfer from the fin was higher and the fin temperature was more uniform in circumference.

Computer programs for temperature in fins and slab bodies with the method of Green's functions

AbstractHeat conduction in fins and slab bodies, a traditional undergraduate topic, is treated with the Green's function (GF) method. A variety of boundary conditions and heating conditions are included. Computer programs are described which are designed to improve student learning of the GF method. The programs are available from the author. © 2004 Wiley Periodicals, Inc. Comput Appl Eng Educ 12: 189–197, 2004; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20010

Analysis of a Finned Heat Exchanger Working in an Adsorption Refrigeration System Using Zeolite and Methanol

A new refrigeration system that uses a specially designed finned plate heat exchanger and works with zeolite and methanol is proposed. The integration of heat transfer and adsorption via a finned surface coated with zeolite CBV 901 and the use of a connected, twin active bed system to enable heat recuperation are novel features. The thermophysical properties of zeolite and methanol were first studied with the intention of designing a high performance heat exchanger (generator) for the adsorption refrigeration system. Here, the major problem is related to poor conductivity at the interface between the heat exchanger and the zeolite. The adsorbent must be heated (desorption phase) and then cooled (adsorption phase) back to ambient temperature in order to complete a thermodynamic cycle.To manufacture a sufficiently small system, there must be high rates of heat transfer in and out of the adsorbent. Therefore, the surface of the heat exchanger is finned in order to increase the heat transfer area (the fins are coated with 2 mm layer of specially prepared zeolite paste). The following characteristics were estimated from initial calculation: heating temperature, 120°C; outside tube temperature, 119.6°C; middle fin temperature, 117°C; and coated layer of zeolite paste temperature, 115.3°C.The mathematical code developed to calculate the effects of operating conditions and the Coefficient of Performance (COP) was presented at HPC 2001 in Paris. It is based on the Dubinin-Astakhov equation and thermodynamic analyses. The results obtained shows that 0.535 is the COP for a single bed and 0.925 for a double bed.

Operating characteristics of an air-source heat pump under frosting/defrosting conditions

This paper presents an experimental investigation on the behavior of an air-source heat pump operating under frosting/defrosting conditions. Dynamic data of parameters, such as the frost layer thickness, compressor suction/discharge pressures, fin temperature, heating capacity, power consumption, and fan electric current, were acquired during the test. Based on these experimental data, the operating characteristics of the heat pump under frosting/defrosting conditions were analysed, and the influence of frosting/defrosting on the performance and reliability of the heat pump was investigated. It was shown that a critical frost layer thickness existed, below which the heat pump presented no noticeable parameter changes. When the frost layer grew above the critical value, the compressor discharge pressure increased rapidly with a slight decrease in the suction pressure, but the shaft power remained almost unchanged. However, due to the increase in airflow resistance, the airflow rate dropped and the fan electric current increased abruptly, leading to fan performance deterioration and a reduction in the system heating capacity. At 50 per cent nominal airflow rate, the frost layer formed later and grew slower than at the nominal airflow rate. Under defrosting conditions, the suction pressure experienced a large drop, which led to frequent on-off switching of the compressor due to pressures falling beneath the low-level limit. This could be avoided by recirculating a portion of the high pressure gas in the compressor receiver back to the compressor inlet through a pipe fitted with a solenoid valve controller.

Approximate analytical model for two-phase solidification problem in a finned phase-change material storage

During the phase change in a phase-change material (PCM) storage system, the solid–liquid interface moves away from the heat transfer surface and the surface heat flux decreases due to the increasing thermal resistance of the molten or solidified medium. Heat-transfer enhancement techniques such as fins and honeycombs have to be used to increase the heat-transfer fraction in the store. The purpose of this paper is to develop a simplified analytical model which predicts the solid–liquid interface location and temperature distribution of the fin in the solidification process with a constant end-wall temperature in the finned two-dimensional PCM store. The storage is initially in a liquid state and its temperature is greater than the solidification temperature of the PCM. The analytical results are compared to the numerical results calculated using the heat-capacity method. The results show that the analytical model gives a satisfactory estimation for the fin temperature and the solid–liquid interface when the length-to-height ratio ( λ) of the storage cell is smaller than 6.0 and the fin length is smaller than 0.06 m. The error made in the fraction of solidified PCM is ±10% when the analytical model is used rather than the two-dimensional numerical model.

Comparison of Standard and Heat-Pipe Fins with Specified Tip Temperature Condition

Analytical expressions for heat-pipe fin temperature distribution and efficiency were obtained for a fin with uniform cross-sectional area, convection, thermal conductivity, and where the fin-tip temperature is specified. The results were compared to a standard (solid conductor) fin. It was observed that under most conditions, the heat-pipe fin would have a higher efficiency than a geometrically similar standard fin. The important parameters needed to compare the two types of fins are presented.

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.

Analysis and testing of a silicon intrinsic-point heater in a micropropulsion application

Efficient heating of a fluid is demonstrated using a novel heat exchanger in which bulk silicon forms both the heater structure and the resistive heating elements. Current passed through the heater raises the temperature of the heater fins and this energy is transferred to a fluid flowing between adjacent fins. By exploiting the change in sign of the temperature coefficient of resistivity of the heavily doped silicon, the temperature of the system is stably maintained at the intrinsic point. A heat exchanger of this nature is integrated with a nozzle, resulting in a microthruster with elevated chamber temperature, which greatly improves the specific impulse, or thrust per unit weight flow of propellant. A numerical model is presented to optimize the heater design. Benchtop tests demonstrate the inherent stability of the intrinsic point heater design, while thrust tests demonstrate the improved fuel economy of the micropropulsion system.

Non-adiabatic catalytic combustion at a fin surface involving heat extraction from the fin edge

The steady state catalytic combustion of fuel borne air, flowing parallel to a catalytic fin surface, has been studied. Experimental studies determined the temperature profiles of a catalytic fin when heat is extracted from the fin by a heat sink at the fin edge. A mathematical model of the catalytic fin was developed from the basic equations of change and the model predictions of fin temperature are compared with experimental results with combustion of propane or carbon monoxide fuel/air mixtures over a platinum/alumina catalyst. The heat fluxes from the fin to the heat sink were calculated and the effect of process variables on this are reported.

Performance of Rectangular Fin in Wet Conditions: Visualization and Wet Fin Efficiency

An experimental study concerning the performance of a rectangular fin in both dry and wet condition was carried out. The visual observation of the dehumidifying phenomenon identified four regions, including the fully dry, very fine droplet, larger droplet, and film-like region. Experimental results showed that the effect of dry bulb temperature on the wet fin efficiency is very small. The dry fin efficiency is about 15–25 percent higher than that of the corresponding wet fin efficiency. For fully wet condition, the effect of relative humidity on the fully wet fin efficiency is also small. For partially wet surface, a considerable influence of the relative humidity on the fin efficiency is encountered. Test results for the fully wet fin efficiency agree well with some of the previous studies but disagree with some of the previous investigations. The main cause to this controversy may be attributed to the formulation of the relation between the humidity ratio and the fin temperature. The fully wet fin efficiency decrease slightly with increase of fin base temperature. However, the effect of fin base temperature on the dry fin efficiency is relatively small.

Experimental study on the performance of a compact heat sink for LSI packages

The cooling performance of compact heat sinks composed of small fins, investigated in conditions of both natural and forced air convection, should also be explored in designing the heat sink on an LSI package. An experimental study was performed with respect to natural air convection and forced air convection. Several kinds of compact heat sink which have different base areas, fin intervals and fin heights were heated by an attached electrical heater, which could supply a specific heat flux. The increase in fin temperature was measured by small thermocouples. In natural air convection experiments, the effect of the supplied wattage on the temperature rise of the heat sink was examined for different fin intervals and fin heights. In forced air convection experiments, a wind tunnel was used. The heat sink was set downstream in the wind tunnel and a specific heat flux was applied to it. The correlation between supplied air velocity and temperature rise in the heat sinks was explored. Furthermore, from these results, non-dimensional expressions to evaluate the cooling performance of compact heat sinks were examined.

Investigation of catalytic combustion within a fin boundary layer

A mathematical model of a catalytic fin, a flat plate coated with a catalyst, operating under steady-state conditions where air carrying a fuel flows parallel to the surface, is developed. The model equations are derived from the basic equations of change, and model predictions of fin and boundary layer temperature are compared with experimental data for the combustion of propane and carbon monoxide (CO) over the flat plate coated with platinum(Pt)/alumina catalyst. Good qualitative agreement is found between the results of the experiments and the model predictions, although the model generally predicts higher fin temperatures and ignition of reaction to occur at lower temperatures.

Boiling on a straight pin fin with variable thermal conductivity

This work theoretically investigated the thermal performance and stability characteristics of a straight pin fin subject to boiling considering a temperature-dependent thermal conductivity of fin, k=ksat(1+b(T−Tsat)). Steady-state temperature distribution and the associated fin base heat flow were for the first time analytically found, whose stability characteristics were evaluated by linear stability analysis. A positive temperature coefficient b will raise both the fin's temperature and base heat flow. The corresponding stability for stable fin boiling was enhanced. A negative b results in an opposite trend. The use of a mean thermal conductivity in fin boiling calculations is discussed.

Reaction and Heat Transfer Characteristics of Catalyst-Coated Fins. Theoretical Analysis of Fins with an Endothermic Reaction.

The reaction and heat transfer characteristics of catalyst coated fins, which are used to circumvent low catalyst loadings in wall-supported catalytic reactors, are investigated theoretically in an attempt to examine the effects of important non dimensional parameters on fin performance for endothermic reaction cases. The fin efficiency of the reaction rate is found to decrease markedly, more than that of convection heat transfer, with an increase of heat absorption rate by the reaction and/or the convection heat transfer rate, for the case in which the conversion rate is governed by the intrinsic kinetics of the catalyst. The increase of bulk fluid temperature to the fin base temperature increases the fin efficiency of the reaction rate, under chemical kinetics limitation, due to convection heating of the fin while the fin temperature decreases along the structure due to heat absorption. An increase of the effect of convective mass transport on the reaction rate increases the fin efficiency of the reaction rate.

Effect on noncondensable gas on laminar film condensation along a vertical plate fin

Abstract Laminar film condensation along a vertical plate fin in the presence of a noncondensable gas is numerically investigated. In the present analysis, the gas mass fraction and temperature at the liquid–vapor interface is regarded as the spatial variation along the fin surface. Governing boundary layer equations together with their corresponding boundary conditions for the condensation system and the one-dimensional fin heat conduction equation with its negligible tip leakage are cast into dimensionless forms. The resulting system of equations is solved by using the central finite-difference approximation for the fin and local nonsimilarity method for boundary layer equations. Results show that the fin efficiency decreases with increasing the thermal resistance ratio of fin-to-liquid Nc, and relatively small amounts of the noncondensable gas in the bulk of the vapor have a significant effect on the fin efficiency for small values of Nc. In addition, the interface temperature is not equal to the fin temperature along the vertical fin, and the local heat transfer coefficient is not uniform, either.