Small Heat Transfer Coefficient Research Articles

Study on the Anti-Icing of Conical Rotating Spinners with Different Cone Angles

This paper presents an experimental study on the anti-icing performance of full-scale rotating spinners with different cone angles. The experiments were conducted in a 3 m×2 m ice wind tunnel (IWT), and the spinners were equipped with hot-air anti-icing systems. Three different cone angles (80°, 70°, and 60°) were examined. The surface temperature of the spinners was measured using an infrared (IR) camera, and ice accretion and water film flow were recorded using high-speed cameras. Numerical simulations were also performed to analyze the water collection coefficients and anti-icing heat energy. The results showed that a larger cone-angle spinner has a larger water collection coefficient but a smaller heat-transfer coefficient and total surface area, resulting in better anti-icing performance for the same conditions. Additionally, the results showed that the residual ice on the spinner exhibited small, white, discretely distributed icicles. Furthermore, the surface temperature in the icing region of the 60° spinner was found to be almost equal to the total temperature of the incoming flow, indicating rime-ice accretion even under glaze-ice conditions. This observation can be attributed to the low water collection coefficient in this region.

Numerical analysis of multipurpose shell-tube-heat exchanger withal stylized geometry at different baffle gaps and various flow rates

The effects of changing 90 mm and 110 mm plate spacings and FR factor of 0.9 kg/h, 1.3 kg/h, 1.7 kg/h, 1.9 kg/h on the total heat transfer performance and PD in the new design HX were examined. The results obtained by taking into account the change in plate spacing and FR factor of 0.9 kg/h, 1.3 kg/h, 1.7 kg/h and 1.9 kg/h, as well as variable factors, were transferred to the study and displayed in figures. In the study, firstly, the results of HCO obtained by changing FR and range were monitored. In the analysis, the interval values were 90 mm and 110 mm and the changes in the FR values of 0.9 kg/h, 1.3 kg/h, 1.7 kg/h and 1.9 kg/h increased in direct proportion. The smallest value of the heat transfer rate was obtained at 110 mm plate spacing and 0.9 kg/h FR. In addition, if the plate spacing was 90 mm, the smallest HCO was obtained at 0.9 kg/h. The largest HCO was obtained when the plate spacing was 90 mm and FR was 1.9 kg/h. In the second part of the study, the results of PD obtained by changing FR and gap were monitored. In the analysis, the interval values were 90 mm and 110 mm and the changes in FR values of 0.9 kg/h, 1.3 kg/h, 1.7 kg/h and 1.9 kg/h increased in direct proportion. The smallest value of PD level was obtained at 90 mm plate spacing and 0.9 kg/h FR. In addition, if the plate spacing was 110 mm, the smallest heat transfer coefficient was obtained at 0.9 kg/h. The largest PD value was obtained when the plate spacing was 110 mm and FR was 1.9 kg/h. In the last part of the study, the results obtained by changing FR and range of the HTPD value were monitored. In the analysis, the interval values were 90 mm and 110 mm, and the changes in FR values of 0.9 kg/h, 1.3 kg/h, 1.7 kg/h and 1.9 kg/h decreased in direct proportion. The smallest value of the HTPD level was obtained at 110 mm plate spacing and 1.9 kg/h FR. In addition, if the plate spacing was 90 mm, the smallest HTPD value was obtained at 1.9 kg/h. The highest HTPD value was obtained when the plate spacing was 90 mm and FR was 0.9 kg/h. Therefore, choosing a system with a 90 mm plate spacing and a FR of 0.9 kg/h will be more efficient in terms of thermohydraulic performance and pressure balancing. As a result, it was concluded that if the plate spacing was selected as 90 mm, a 15 % improvement could be achieved compared to the system design with a 110 mm plate spacing. As a new, it is thought that it will contribute to the literature in future studies, as the thermal performance, pressure drop and heat transfer coefficient results obtained at new flow rate values and compartment spacing values are obtained for the first time in a new STH designed in different dimensions than the literature.

Anomalous Adverse Effect of Mass Velocity on Convective Flow Boiling in Small-Diameter Microfin Tubes

Abstract Recent studies report an anomalous phenomenon, particularly for small diameter microfin tubes, where the flow boiling heat transfer coefficient decreases with increasing mass velocity in the convective regime, which is contrary to that found for smooth tubes and larger diameter microfin tubes. This paper presents a critical literature review and mechanistic analysis of the anomalous phenomenon. Our analysis suggests that the anomalous phenomenon is a result of the transition of annular flow pattern from “flooded-groove” (film thickness > fin height) to “in-groove” (film thickness < fin height). The latter is associated with lower degree of turbulence, smaller wetted area, and therefore smaller heat transfer coefficient than the former. We speculated that the in-groove annular flow only occurs for small diameter tubes where the liquid film is relatively uniform, while larger tubes tend to remain flooded at the tube-bottom until dryout. This may explain the tendency of the anomalous phenomenon to occur in small diameter tubes.

Computational fluid dynamics (CFD) study of a commercial-scale methanol-to-olefins (MTO) fluidized bed reactor

Methanol-to-olefins (MTO) has been widely commercialized, yet the complex in-furnace phenomena still lack understanding. The flow characteristics and thermochemical behaviours in a commercial-scale MTO reactor are investigated by a reactive multi-phase particle-in-cell model. The spatial distribution of gas species and the impacts of key operating variables (e.g., mass flow rate, methanol to steam ratio, and wall temperature) on gas properties and reactor performance are analyzed. The results indicate the non-uniform distribution of gas variables. Methanol (i.e., CH3OH) is completely converted in a very short distance above the distributor. C2H4 and C3H6 have the largest concentrations, followed by C4H8, C3H8, CH4, and C5H10. The increased mass flow rate significantly elevates the concentration of C2H4 but highly declines the concentrations of C3H6, C3H8, CH4, and C5H10. The gas temperature rapidly rises below the gas distributor (z < 15 m) due to exothermic reactions and then shows almost no change in the axial direction (z > 15 m), demonstrating good temperature control in the reactor. Elevating the given operating parameters increases the temperature, viscosity, specific heat capacity, and thermal conductivity of gas phase but declines gas density. The vertical dispersion intensity of catalyst particles is one order of magnitude larger than the horizontal one. Heat transfer coefficient (HTC) distributions show three distinct parts, the small HTC in the lower region, the sharply increased HTC in the medium region, and the large HTC in the upper region.

집광형 태양열 발전 시스템에서의 태양열유속 분포의 변화에 따른 열전달 수치해석 연구

Concentrating solar power system (CSP) is one of the renewable energies which accumulates solar energy concentrated by condensing mirrors and reflectors in solar absorbers. Boiled water then operates steam turbines to generate electricity. So far, many studies have been conducted for optimization design of CSP which are mostly focused on comparing the materials and dimensions of the absorber to increase thermal efficiency. In this study, we tried to compare heat transfer in solar receiver from different heat flux distributions considering daily change of the azimuthal angle of the solar radiation. A Numerical study was performed using ANSYS FLUENT and appropriate temperature boundary condition was enforced at the receiver inlet using User-Defined-Function. Energy balance was modeled at the receiver inlet considering convectional and radiational loss to the surrounding. The amount of heat transfer to the receiver and heat loss to the surrounding from several characteristic heat flux distributions are compared. In addition, effects from the convective heat transfer coefficient, thermal conductivity, and porosity of the solar absorber are investigated. It has been found that eccentric distribution of the solar heat flux deteriorates thermal efficiency considerably. It is also found that heat transfer becomes larger with small convective heat transfer coefficient and large thermal conductivity. With lowering the porosity, the amount of heat transfer generally increases. But the gain is rather small at very low value with significantly high pressure drop.

Numerical analysis of wood air gasification in a bubbling fluidized gasifier with reactive charcoal as bed material

In this work, a reactive multiphase particle-in-cell model based on the Eulerian-Lagrangian framework is developed to numerically investigate the wood gasification process in a three-dimensional air-blown bubbling fluidized bed gasifier with the reactive charcoal as bed material. After the model validation, the impacts of gas velocity and initial bed height on the physical and thermophysical properties of gas-solid reacting flow are studied. The results show that lighter particles suspend at the upper part of the dense region with a larger rising velocity due to the density- and size-induced segregation. The vertical dispersion of both particle species is two orders of magnitude larger than the horizontal one. Large heat transfer coefficient (HTC) of solid phase appears in the rising path of biomass. Superficial gas velocity significantly affects the composition and the thermal properties of gas species. Heavy charcoal particles mainly distribute in the dense region with a high temperature and small HTC. Enlarging the superficial gas velocity increases the CO2 concentration whereas decreases the yields of combustible gas species. Initial bed height exerts an insignificant effect on the thermal property of gas phase, especially in the dense region.

Experimental and artificial neural network based study on the heat transfer and flow performance of ZnO-EG/water nanofluid in a mini-channel with serrated fins

The adoptions of mini-channel and nanofluid are potential technologies to improve the heat transfer capability. The present study experimentally investigated the flow and thermal performance of EG/water based ZnO nanofluid inside a mini-channel with serrated fins with an equivalent diameter of 1.59 mm. EG/water mixture with a mass fraction of 40%/60% served as the base fluid. Nanofluids with a volumetric concentration of 0.75 vol% and 1.5 vol% were prepared. The thermophysical properties of viscosity, density and thermal conductivity were measured. It reveals that although the adding of nanoparticles is able to improve the thermal conductivity by 4.2% on average, the viscosity also enlarges remarkably by up to 18.9%. The measured density and thermal conductivity can be predicted accurately by existing formulations. As all correlations underestimate the viscosity, a new one is proposed for the fabricated nanofluid with a small Mean Absolute Relative Deviation (MARD) of 0.1%. The Nusselt number can be averagely improved by 10.6% and 13.2% for the 0.75 vol% and 1.5 vol% nanofluid with a corresponding sacrifice of friction factor augmentation of 31.2% and 47.3% respectively due to the significant augmentation of viscosity, which results in a relatively small heat transfer coefficient enhancement ratio of 0.92–1.09 under the same pumping power. In addition, the heat transfer enhancement shows a nonlinear increment with the concentration and a higher relative enhancement is found at a lower concentration. This indirectly indicates that the heat transfer does not always increase with the concentration. Even though some published correlations present acceptable predictions for the tested flow and thermal performance of EG/water based ZnO nanofluid, the newly developed Backpropagation Artificial Neural Networks (BP-ANNs) show even better prediction accuracies for Nusselt number and friction factor with the MARDs of 0.39% and 0.35% respectively. Our study is expected to give valuable data sources and inspiration for future investigation on hydrodynamic and thermal behavior of nanofluids.

High-fidelity investigation of thermochemical conversion of biomass material in a full-loop circulating fluidized bed gasifier

Olive oil production urges the energy companies to exploit the potential of the residues as biomass fuels for clean energy production. Circulating fluidized bed (CFB) gasifier gains global interest within these several years due to its promising solution for converting biomass material to renewable energy. However, the multi-physics processes and multiscale structures inside the gasifier impede the experimental measurements. As an alternative, a reactive multiphase particle-in-cell approach is developed in this work to simulate the gasification process of olive oil waste in a pilot-scale full-loop CFB gasifier. After the model validation, the heat transfer properties of solid phase and the effect of size-induced segregation on solid thermochemical properties are explored. The results show that the low-temperature biomass particles injected highly influence the spatial distribution of solid temperature and solid heat transfer coefficient (HTC). A larger particle size gives rise to a higher HTC. Moreover, the temperature and HTC of biomass are larger than that of sand. A wide and narrow residence time distribution of sand in the riser and cyclone can be observed. The scale of biomass dispersion is respectively larger and the same as that of sand in horizontal and vertical directions. Particles in the dense region have a smaller HTC, Reynolds number, and temperature. Superficial gas velocity improves the uniformity of solid distribution. Elevating the gas velocity and initial bed temperature enhances solid dispersion intensity.

Experimental studies of thermal and acoustic properties of recycled aggregate crumb rubber concrete

Recycled aggregate crumb rubber concrete (RCC) is made of recycled aggregate and rubber materials. In this paper, the particle size, composition and substitution rate of rubber material were considered; the physical performance, thermal performance and acoustic performance of normal concrete (NC), recycled aggregate concrete (RC) and RCC were compared and analyzed. The main indexes of different concretes were compared, including the bulk density, porosity, heat transfer coefficient, thermal resistance, sound absorption coefficient and noise reduction coefficient. The test results show that, compared with the NC, the RCC has the lower bulk density, smaller heat transfer coefficient, larger thermal resistance, larger sound absorption coefficient and noise reduction coefficient. Besides, the performances of thermal insulation and sound insulation and noise reduction of RCC have great functional advantages over that of NC.

Numerical Prediction of 45° Angled Ribs Effects on U-shaped Channels Heat Transfer and Flow under Multi Conditions

AbstractRibs effects on the heat transfer performance and cooling air flow characteristics in various aspect ratios (AR) U-shaped channels under different working conditions are numerically investigated. The ribs angle and channel orientation are 45° and 90°, respectively, and the aspect ratios are 1:2, 1:1, 2:1. The inlet Reynolds number changes from 1e4 to 4e4 and rotational speeds include 0, 550 rpm, 1,100 rpm. Local heat transfer coefficient, endwall surface heat transfer coefficient ratio and augmentation factor are the three primary criteria to measure channel heat transfer. Ribs increase the heat transfer area and improve heat transfer coefficient of ribbed surfaces significantly, especially in the 1st pass, while the endwall surface contributes more to channel heat transfer because of the larger area and relatively smaller heat transfer coefficient. The wide channel (AR =2:1) owns the better augmentation factor than the narrow channel (AR =1:2) and ribs heat transfer weight increases with an increase of the inlet Reynolds number. Rotating slightly reduces the ribs heat transfer weight in channel and the trailing surface in 1st pass is the main influence object of rotating.

Experimental study of falling film evaporation in tube bundles of doubly-enhanced, horizontal tubes

Falling film evaporation (FFE) involves complicated physical phenomena and mechanisms such as wavy liquid film, bubbly flow, capillary-driven evaporation and nucleate boiling. FFE heat transfer characteristics in four doubly-enhanced tube bundles were investigated experimentally with R134a. For single tube, heat transfer coefficient (HTC) first increases then decreases with increase in heat flux, the turning points occurs around 20 kW/m2. Tubes with different positions in tube bundle own similar HTCs when tested individually. In tube bundle, with decreasing film Reynolds number (ReΓ), HTC firstly keeps a quasi-plateau stage (increasing or keeping constant for upper tubes, decreasing for lower tubes), then after a certain threshold film Reynolds number, HTC decreases sharply with ReΓ. At lower heat fluxes (10 kW/m2 and 20 kW/m2), tubes with different positions exhibit similar HTCs and threshold ReΓ. At higher heat fluxes (30 kW/m2 and 40 kW/m2), bottom tubes own much smaller HTCs and larger threshold ReΓ than upper ones due to partial dryout occurrence. The tube bundle with top plate exhibits higher HTCs and lower threshold ReΓ than those of the open-ended tube bundle indicating that counter-current vapor flow can deteriorate the heat transfer of FFE. Effect of heat flux on the bundle-averaged HTC increases with tube pitch.

Effects of Nanoparticle Enhanced Lubricant Films in Thermal Design of Plain Journal Bearings at High Reynolds Numbers

Performance investigation of oil journal bearings is of particular importance given the growing use of them as a support for rotary components in a wide range of industrial machines. Frictional forces and shear stresses, which are proportionate to the velocity of lubricating layers at different points in the bearing space, provide the basis for changing temperature conditions. Various factors such as rotational velocity increase, slip width reduction, and small heat transfer coefficient of lubricant cause intensification of lubricant temperature changes. In the present study, with using computational fluid dynamic (CFD) thermohydrodynamic (THD) numerical simulations, the effect of nanoparticles on the performance features of plain journal bearings is evaluated. Particularly, 3D simulation of a journal bearing is implemented using CFD which considerably improves the accuracy of results, coupled with conjugate heat transfer model for metal parts of bearings. Reynolds equation model is used to calculate the oil-film pressure developed in hydrodynamic journal bearings by applying the nano-based lubricants. The configuration of thrust bearing consists of six pads in this study. In order to reduce the modeling complexity and computational cost and because of the symmetrical geometry of the pads, simulation of a single pad is considered instead of the entire domain. In this study, TiO2 nanoparticle with different volume fraction percentages are used. The parameters that are changed to evaluate the performance of the bearing include volume fraction percentage of the nanoparticle, type of lubricant, and rotational speed. Based on the results, for all different lubricant types, the dissipation power, average shear stress, and temperature rise are increased with augmenting the rotational speed. By increasing the rotational speed from 500 to 1500 rpm, the average shear stress increases by more than 100%, 120%, and 130% for DTE 26, DTE 25, and DTE 24 lubricant types, respectively. Moreover, by increasing the rotational speed from 500 to 1500 rpm, the dissipation power, and temperature rise are increased around 600% and 800%, respectively. Furthermore, increasing nanoparticles volume fraction from 0% to 10%, increases all parameters by approximately 10% for all lubricant types and in all rotational speeds.

Analysis on the influences of atomization characteristics on heat transfer characteristics of spray cooling

The development of big data leads to the increasing heat dissipation of data center chips. As an efficient pattern to remove high heat flux, spray cooling has huge potential for data center cooling. Spray cooling system was established combined with PIV (Particle Image Velocimetry) system. The PIV was used to measure the flow pattern distribution of different nozzle sprays, while the surface heat flux and heat transfer coefficient were obtained by the thermocouples. The results show that as the spray diameter decreases, the outlet pressure and outlet velocity of the droplet increase, and the spray cone angle increases, causing only a small amount of droplets actually participate in the heat exchange, resulting in a higher velocity and a smaller heat transfer coefficient. It is also inferred that better uniformity of droplets velocity is beneficial for the heat transfer performance. Moreover, to further enhance the heat transfer performance, nano-alumina solution with five different fractions was applied to the experimental system. It is found that the heat transfer coefficient of the surface reaches an optimum value with a maximum velocity obtained by the PIV when the mass fraction of the solution is 0.08%.

Optimization of Helium Inflating on Heat Dissipation and Luminescence Properties of the A60 LED Filament Lamps

LED filament lamp has the characteristics of nearly 360° lighting angle, high brightness, and low energy consumption, turning it gradually into the best substitute for traditional incandescent lamps. At present, due to the limitations of heat dissipation, the development of high-power LED filament lamp is restricted. Helium is a rare gas with small density and high heat transfer coefficient. It can be used as a cooling and protective gas for LED filament lamp. In this paper, we investigated the effects of helium on the heat dissipation and luminescence performance of the A60 LED filament lamps by detecting the changes of junction temperature, color temperature, and luminous flux of different ratios helium inflating in the different power A60 LED filament lamps. Through the experiment, we found the most cost-effective ratio of helium gas in the A60 LED filament lamps without improving the lamp size and the filament diameter.

The effect of different types of window for residential building based on intermittent heating supply

Aiming to lessen energy consumption and heating cost, this paper analyzes the effect of different types of window for residential building based on intermittent heating supply. The research results show that the type of window with a smaller heat transfer coefficient has higher energy consumption. Otherwise, the rate of temperature rising is slightly affected by the change of window with different heat transfer coefficient and window-to-wall ratio. Based on the economic and technical analysis, through changing the better window, energy-saving ratio can be arrived to 10.4%-16.8% and economic recovery period is 4.4-10.4 years. The research findings can be used for reference to thermal design in new residential buildings and provide improvement of building performance for existing residential buildings.

Effect of Convection on Equiaxed Solidification of Ni-based alloy

It has been found that the crystal morphology during equiaxed solidification can be strongly changed by the applied physical fields, such as the electromagnetic field, ultrasonic treatment or mechanical stirring. Theoretically, the applied external fields cause melt flow to impact the crystal growth and thus change the solidification structure. However, the previous relevant works mainly focused on obtaining grain refinement rather than studying the crystal morphology evolution. To study the equiaxed solidification under forced convection, the crystal growth in multidirectional flow was numerically simulated in the present work. The simulation results indicate the flow direction of forced convection strongly impacts the crystal growth and the morphology evolution. The multidirectional flow would cause much different conditions during the equiaxed solidification, which eventually changes the crystal morphology. In the present study, the different cooling conditions were used to study the impact of solidification process parameters. For the case of simulation with small heat transfer coefficient, corresponding to the low cooling rate for practical solidification processes, the effects of the forced convection on crystal growth is more significant than that with larger cooling coefficient.

Investigation on flow condensation of refrigerant in annulus of smooth and enhanced tube-in-tube heat exchanger

An experimental investigation of R22 and R410A condensation outside a horizontal smooth tube, a herringbone tube and a newly developed 3D enhanced heat transfer (1EHT) dimple tube has been conducted. The herringbone tube has a fin root diameter of 11.43 mm, a helical angle of 21.3 °, 48 fins with a fin height of 0.262 mm and an apex angle of 36 °; the 1EHT tube has an inner diameter of 11.5 mm with a dimple enhancement; while the smooth tube has an inner diameter of 11.43 mm; and all the tubes have an outer diameter of 12.7 mm. Experiments were performed for a constant saturation temperature of 45°C; with a constant inlet vapor quality of 0.8 and a constant outlet vapor quality of 0.1; for a mass flux ranging from 5 kg/(m2 s) to 250 kg/(m2 s). In addition, annular side condensation experiments were performed using an outer shell tube with outer diameters of 17 mm and 25.4 mm. Heat transfer performance varied with mass flux. At a low mass flux the enhanced dimple tube had the smallest heat transfer coefficient; while at higher values of mass flux, the smooth tube had the smallest heat transfer coefficient. Finally, the effect of average vapor quality on the heat transfer coefficient was also investigated. Characteristic analysis was performed in order to account for the various phenomena found in this series of experiments. Annular side heat transfer performance combined with pressure drop measurements reveal that the herringbone tube generally had a better heat transfer performance than the other tubes, and can be a good choice for use in annular side condensation applications.

Thermal Resistance of a 3-D Flux Channel With Nonuniform Heat Convection in the Sink Plane

Heat sinks are designed in different types and shapes depending on temperature distribution along the sink plane, where sometimes intense cooling is only required in the high-temperature regions. Thus, a nonuniform heat transfer coefficient might be present along the sink plane. In this paper, the temperature distribution and thermal resistance of a 3-D flux channel with a nonuniform heat transfer coefficient along the sink plane is modeled and analyzed by solving the problem analytically. A single concentric heat source is considered in the source plane, while the conductance along the sink plane is modeled by a symmetric conductance function. This function is used to define different conductance distributions along the sink plane from the most intense conductance in the central area to a uniform conductance along the sink plane. Furthermore, a convective cooling condition with uniform conductance is assumed along the lateral edges of the channel, which can be turned into adiabatic edges by assuming a very small heat transfer coefficient along the edges. The problem is solved analytically using the method of separation of variables combined with the method of least squares. A dimensionless total thermal resistance is then introduced to study the effect of different aspect ratios between the heat-source dimensions, cross-sectional dimensions, and channel thickness for different Biot numbers and different conductance distributions along the sink plane. For validation of the presented solution, the analytical results were compared with numerical solution results obtained by solving the problem with the finite-element method using the ANSYS commercial software package.

Size dependences of hydraulic resistance and heat transfer of fluid flow in elliptical microchannel heat sinks with boundary slip

As a well-accepted interfacial property, boundary slip condition is believed to affect hydraulic and thermal performances of various micro/nanofluidic applications. By considering the boundary slip for water flow through a microchannel heat sink, size dependences of hydraulic resistance and heat transfer of the water flow in a group of elliptical microchannel heat sinks with the same channel cross-sectional area but different length ratios of semi-major and minor axes are re-examined. The present work finds that hydraulic resistance and heat transfer of water flow in a microchannel are strongly dependent on the geometric parameters of the channel and the boundary slip condition. Both the hydraulic resistance and the convective heat transfer coefficient of the water flow in the elliptical shaped microchannel decrease with the increasing hydraulic diameter of the channel. An elliptical shaped microchannel having the largest hydraulic diameter, namely a microtube with the minimum length ratio of semi-major and minor axes being equal to one, has the smallest hydraulic resistance and the smallest heat transfer coefficient. Boundary slip at the solid-liquid interface can attenuate the hydraulic resistance and enhance the heat transfer capacity of the water flow in a microchannel, and these effects of slip on the mass and heat transfer are size-dependent. For the microchannel with a smaller hydraulic diameter, slip has a more significant attenuation effect on the hydraulic resistance and a more significant enhancement effect on the heat transfer. Geometric size optimization combined with the effective regulation of boundary slip can be a potential method to improve the mass and heat transfer of fluid flow over the micro/nanoscale.

광폭 루버 핀이 장착된 핀-관 열교환기의 습표면 성능에 대한 실험적 연구

One method of increasing the heat-transfer rate is to increase the heat-transfer area. In this study, we test a wide louver fin-and-tube heat exchanger with Pt/Pl = 1.03, and we compare the results with those of a louver fin-and- tube heat exchanger with Pt/Pl = 0.6. The results obtained show that the heat-transfer capacities of the wide louver samples are larger (16% in one row, 29% in two rows, and 38% in three row samples) than those of the louver samples. Considering the area ratio of 2.17, the increase in the heat-transfer capacity is somewhat small. The reason for this may be due to the smaller heat-transfer coefficient and fin efficiency of the wide louver sample. The effect of the fin pitch on the j and f factors are not profounded . The j and f factors decreased as the number of tube rows increased. We compare the data obtained with existing correlations.