Numerical and experimental study of a solar equipped with offset rectangular plate fin absorber plate

A mathematical model that allows the determination of the thermal performances of the single-pass solar air collector with offset rectangular plate fin absorber plate is developed. The model can predict the temperature profile of all the components of the collector and of the air stream in the channel duct. Into the latter are introduced the offset rectangular plate fins, which increase the thermal heat transfer between the absorber plate and the fluid. The offset rectangular plate fins, mounted in a staggered pattern, are oriented parallel to the fluid flow and are soldered to the underside of the absorber plate. They are characterized by high heat transfer area per unit volume and generate the low pressure losses. The experimental results of the air stream temperature will be compared with the results obtained by the theoretical model suggested.     

Analytic method for thermal performance and optimization of an absorber plate fin having variable thermal conductivity and overall loss coefficient

The absorber of a collector receives solar energy which is delivered to the transport medium to be carried away as useful energy. During this process, temperature of the absorber plate increases and therefore, thermophysical parameters engaged to determine the thermal performance of an absorber plate varies with temperature of the plate. The present study demonstrates analytically to determine the performance of an absorber plate fin with temperature dependent both thermal conductivity and overall heat loss coefficient. The decomposition method is proposed for the solution methodology. An optimum design analysis has also been carried out. A comparative study has been executed among the present results and that of existed in the published work, and a notable difference in results has been found. Finally, unlike published work, dependency parameters on the performances and optimum design have been highlighted.     

Simulation of a new concept of an indirect solar dryer equipped with offset rectangular plate fin absorber‐plate

A simulation code was developed to predict the indirect solar dryer performance of the thin beds of discs of potato, subjected to time‐varying air conditions. Two mathematical models are developed separately; the first allows the determination of the thermal performances of the solar collector with offset rectangular plate fin absorber‐plate and the second, allows to determine the kinetics of drying for the data input of the air at the exit of the collector. The latter takes into account calorific losses through the walls of the dryer and shrinkage of discs. Experimental results of the solar dryer thermal performances, using sunlight in Valenciennes (in the North of France), will be compared with the results obtained by the theoretical model suggested. Copyright © 2005 John Wiley & Sons, Ltd.     

Energy analysis of a solar air collector with rows of fins

The necessity for improving the thermal performances of the solar air collector, for some needs, encouraged us to carry out this study. Initially, to improve the efficiency factor of these solar collectors, we create an increasingly turbulent flow between the absorber and the back wooden plate. For that, we use obstacles of various forms. In this study, we chose rectangular plate fins inserted perpendicular to the flow. The fluid flows out through the interstices between fins in the same row, this allows a good distribution of the fluid and reduces the dead zones. Secondly, and for the same configuration, we undertake a study on the evaluation of the transfer coefficient. The results are compared with those obtained with a solar air collector without fins, using two types of absorbers selective (in coppersun) or not selective (black-painted aluminium).     

Heat transfer coefficient and friction factor correlations for rectangular solar air heater duct having transverse wedge shaped rib roughness on the absorber plate

As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17φ^−1.0264<p/e<12.12; and rib wedge angle (φ) of 8, 10, 12 and 15°. The effect of parameters on the heat transfer coefficient and friction factor are compared with the result of smooth duct under similar flow conditions. Statistical correlations for the Nusselt number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the flow Reynolds number.     

Performance and optimum design analysis of an absorber plate fin using recto-trapezoidal profile

This paper establishes a new profile, viz. recto-trapezoidal (RT) of an absorber plate fin on the basis of ease of fabrication as well as augmentation of heat transfer rate per unit fin volume. An analytical model has been developed for evaluating the thermal performance and optimum dimensions of an absorber plate fin using this typical profile. The present study is equally suitable for an absorber plate fin having a rectangular, trapezoidal or triangular profile also with consideration of their respective geometrical parameters. The optimization of the RT profile has been cast in a generalized form either by maximizing heat transfer rate for a given fin volume or by minimizing fin volume for a given heat transfer duty. From the optimum design analysis, significant results have been noticed when an additional constraint is imposed with the fin volume. Under this design condition, it may also be highlighted that for an optimal circumstance, the heat transfer rate through a RT profile absorber plate fin is greater than a trapezoidal or triangular profile for the same fin volume. However, this observation may be restricted to the limited values of fin volume only. The optimum design analysis for the RT profiled absorber plate fin has also been studied under the different design constants. Finally, for the variation of all the design variables, optimum design curves have been generated for a wide range of thermo-geometric parameters.     

Fluid flow and infrared image analyses on endwall fitted with short rectangular plate fin

An experimental investigation is carried out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays ( 7×7 ) of short rectangular plate fins of different pattern (co-angular and zigzag) for different pitch ratio. Experiments were conducted in a rectangular duct of 50 mm height for an air flow of Reynolds number ranged from 18750 to 62500 based on the equivalent diameter and air velocity of the duct. Infrared image analysis technique was employed to make clear the characteristics of local heat transfer coefficients on fin base, endwall and overall surface. Flow pattern around the short rectangular plates were visualized by inducing fluorescent dye in a water channel and longitudinal vortices were observed. Increasing the distance between plates in flow direction causes heat transfer enhancement for co-angular pattern, while decreasing the distance causes heat transfer enhancement for zigzag pattern. Zigzag pattern with pitch ratio 2 is found to be more effective in heat transfer enhancement than any other cases investigated.     

Effective efficiency of solar air heaters having different types of roughness elements on the absorber plate

The use of an artificial roughness on a surface is an effective technique to enhance the rate of heat transfer to fluid flow in the duct of a solar air heater. This paper presents a comparison of effective efficiency of solar air heaters having different types of geometry of roughness elements on the absorber plate. The effective efficiency has been computed by using the correlations for heat transfer and friction factor developed by various investigators within the investigated range of operating and system parameters.     

Battery module thermal management based on liquid cold plate with heat transfer enhanced fin

Battery, as the main energy storage element, directly affects the performance of electric vehicle. Battery thermal management research is required as the battery performance influenced by temperature obviously. This article selects liquid cold plate with different heat transfer enhanced fins as the research object. The angle and length of fins are chosen as the variables. Computational fluid dynamics (CFD) methods and experiments are used in this research. The fin angle of 15°, 30°, and 45° and fin length of 8, 10, 12 mm are selected to compose enhanced fins. The results indicate that heat transfer fins inside liquid cold plate can significantly decrease the highest temperature of battery module and temperature difference among cells. Otherwise, different fin angle and fin length can achieve different heat dissipation performance, which is not positive correlation. Then the design reference of heat transfer enhanced fin in liquid cold plate is offered.     

Heat transfer and friction in solar air heater duct with W-shaped rib roughness on absorber plate

Artificial roughness in form of ribs is convenient method for enhancement of heat transfer coefficient in solar air heater. This paper presents experimental investigation of heat transfer and friction factor characteristics of rectangular duct roughened with W-shaped ribs on its underside on one broad wall arranged at an inclination with respect to flow direction. Range of parameters for this study has been decided on basis of practical considerations of system and operating conditions. Duct has width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/D_h) 0.018-0.03375 and angle of attack of flow (α) 30-75°. Air flow rate corresponds to Reynolds number between 2300-14,000. Heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition to determine thermo-hydraulic performance. Correlations have been developed for heat transfer coefficient and friction factor for roughened duct.     

The air solar collectors: Comparative study, introduction of baffles to favor the heat transfer

Concerning the solar air collectors, various techniques favorise and increase the heat transfer coefficient between the caloporting fluid (air) and the absorber; such as the fixation of small wings to the absorber, the manner in which the air flows vis à vis the absorber, the shape of the collector itself and those of its inlets and outlets. Studies achieved at the University of Valenciennes–France, Laboratory of Aerodynamic, Energetic and Environmental (current naming), were especially interested in another factor: the creation of turbulence in the air channels by using obstacles or baffles. The efficiency reached 80% for an air flow rate of 50 m³/h/m², allowing a temperature increase of 70 °C to be achieved. All the configurations of baffles are subjected to visualizations of air flow, measurement of pressure drop and instantaneous energetic efficiency. The best configuration is the one that permits extending the trajectory of the air flow and increases the speed of the air within the collector and therefore the heat transfer.     

Thermal performance of an air solar collector with an absorber plate made of recyclable aluminum cans

The present paper describes the development and testing of an efficient single-glass air solar collector with an absorber plate made of recyclable aluminum cans (RAC). This collector was designed as a proposal to use recycle recyclable materials to build absorber plates of air solar collectors at an acceptable cost. The absorber plate of the collector consisted of eight circular cross section air flow channels of 128 recyclable aluminium cans. Each channel was built with 16 recyclable cans blackened with common opaque black paint of 0.903 absorptance and 0.097 reflectance. The design parameters to determine the size of the collector were obtained by implementing a simulation model for double flow air solar collectors. Also, to determine the appropriate configuration for a uniform air flow distribution inside the eight RAC air channels, a hydrodynamic numerical study was carried out. The RAC air solar collector designed and built was tested outdoors following the ASHRAE 93-86 standard to determine the time constant, the thermal efficiency and the incidence angle modifier. Comparison between the predicted theoretical temperatures and the measured ones were in good agreement. Comparison between the thermal efficiency of the RAC air solar collector with the ones reported in the literature is presented.     

Numerical investigation of thermal enhancement of plate fin type heat exchanger with creases and holes in construction machinery

The present study aims to develop a new shape of plate fin heat exchanger by applying ceases and holes on the plate fin which is used in the construction machinery under the poor environment where the dust content is high and much extraneous materials are generated. In the present study, the louver fin heat exchanger, the plate fin heat exchanger and the heat exchanger of the shape newly proposed in this study were analyzed comparatively using three-dimensional numerical simulation. The fully developed airflow in the unit cell of heat exchangers considered was modeled with k–ω turbulence model using steady incompressible Reynolds-Averaged Navier–Stokes (RANS) equations. The calculated pressure drop and heat transfer capacity for the louver fin heat exchanger, the plate fin heat exchanger and the heat exchanger of the shape newly proposed in this study were assessed in terms of the Fanning friction factor (f factor) and Colburn j-factor (j factor) while the overall performance was estimated using the volume and area goodness factors.     

Analysis of heat transfer augmentation and flow characteristics due to rib roughness over absorber plate of a solar air heater

A computational analysis of heat transfer augmentation and flow characteristics due to artificial roughness in the form of ribs on a broad, heated wall of a rectangular duct for turbulent flow (Reynolds number range 3000–20,000, which is relevant in solar air heater) has been carried out. Shear stress transport k−ω turbulence model is selected by comparing the predictions of different turbulence models with experimental results available in the literature. A detailed analysis of heat transfer variation within inter rib region is done by using the selected turbulence model. The analysis shows that peak in local heat transfer coefficient occurs at the point of reattachment of the separated flow as observed experimentally. The results predict a significant enhancement of heat transfer in comparison to that for a smooth surface. There is a good matching between the predictions by SST k−ω and experimental results. In this work, nine different shapes of rib are examined using SST k−ω model and compared on the basis of heat transfer enhancement, friction characteristics and performance index considering heat transfer enhancement with the same pumping power.     

Optimization of parameters in solar thermal collector provided with impinging air jets based upon preference selection index method

The present study examines the effect of flow and geometric parameters on the performance of solar thermal collector provided with impinging air jets. The investigation has been carried out in terms of performance defining criterions which are pertinent to determine the optimal design of impinging jet solar thermal collector. The experimental investigation indicated that the impinging air jets enhances the thermal performance but at the same time the friction power penalty also increases which depress the overall performance of the system. In view of this the preference selection index (PSI) approach based methodology has been applied using various performance criterions in order to determine the optimal design of the parameters which deliver maximum thermal performance with minimal increase in friction factor inside the collector duct. The optimum configuration of the parameters obtained as a result of proposed method is: streamwise pitch ratio of 0.435; spanwise pitch ratio of 0.869; jet diameter ratio of 0.065 and flow Reynolds number of 16,000.     

Influence of geometrical factors and pressing mould wear on thermal-hydraulic characteristics for steel offset strip fins at low Reynolds number

Aiming at achieving a more comprehensive understanding of influence factors on thermal-hydraulic characteristics for high-pressure-direction type steel offset strip fins, this paper constructed a single fin core assembly test rig with lubricant oil as work media at low Reynolds number. Six fin schemes were experimentally investigated only varying in fin height and fin wavelength due to mould restrictions. Twenty fin schemes changing in fin width, fin angle, fin thickness and staggered fin wavelength were simulated for supplement, and the geometrical influences in fin performance were put forward. Both Taguchi method and uniform design were introduced to study the contribution of each geometrical factor to fin global thermal-hydraulic performance, verifying that fin wavelength and fin height have the most significant contributions. Based on signal to noise ratio distributions, fin geometries were optimized for 16% elevation of global performance at Reynolds number of 430, then the ‘cost-based fin performance’ was put forward and compared quantitatively, proving that above optimum fin scheme is also economical. Finally, mould wear influence in fin performance was tested in different wear periods of a vacuum heat-treated Cr12MoV mould pair, then three stages of initial wear, stable wear, and overdrive wear were defined based on pressing times. The influences were analyzed and regulations were deduced relating to mould pressing times and oil Reynolds number. The suggested lifetime for this type of mould pair is 1050 thousand pressing times. The paper intends for fin performance evaluation, optimization, and pressing mould improvement.     

Collector efficiency of upward-type double-pass solar air heaters with fins attached

The collector efficiency of upward-type double-pass flat plate solar air heaters with fins attached and external recycle is investigated theoretically. The double-pass device was constructed by inserting the absorbing plate into the air conduit to divide it into two channels (the upper and lower channels). The double-pass device introduced here was designed for creating a solar collector with heat transfer area double as well as the extended area of fins between the absorbing plate and heated air. Moreover, the advantage of external recycle application to solar air heaters is the enhancement of forced heat convection strength, resulting in considerable device heat transfer performance improvement. This advantage may compensate for the remixing at the inlet which decreases the heat transfer transfer-driving force decrement (temperature difference).     

Investigating the effect of various fin geometries on the thermal performance of a heat sink under natural convection

Experimentally investigates heat dissipation by different longitudinal fins fitted to a cylindrical heat sink under natural convection conditions. Five aluminum fin configurations at base temperatures (70°C, 85°C, 100°C, and 115°C) were studied. The first fin was plain (fin1), while second fin had a triangular edge (fin2). The rest fins have the same triangular edge but with six 1cm circular perforations near the edge (fin3). While the perforations in fin4 were in the middle longitudinal fin length. The last fin (fin5) had twelve 0.5 cm circular perforations distributed into two columns. The measurements were validated with theoretical correlation with an acceptable deviation. The results showed that fin2, fin3, fin4, and fin5 dissipate more heat by 2.4%, 8.7%, 11.4%, and 5% than the flat fin with 9.8%, 11.85%, 11.85%, and 10.82% weight reduction, respectively. The heat transfer coefficient enhanced by 7.98%, 16.81%, 12.35%, and 5.44% for fin5, fin4, fin3, and fin2, respectively. Large circular perforation was more effective to dissipate heat especially when located near the heat source as in fin4 which gives the best heat dissipation with more weight reduction. The proposed fins efficiency were greater than 92%.     

Design and thermal performance evaluation of a novel solar air heater

In the present scenario, numerous applications perform on solar energy for cooking, heating and cooling, and power generation, globally. Solar air heaters are one of these applications purposely used for, drying, timber seasoning and space heating. In the present work, a solar air heater (SAH) has been designed to produce a good exhaust temperature for long hours especially in the case of poor ambient conditions or during off sunshine hours. A mixture of desert and granular carbon in the ratio of 4:6 has been used as thermal heat storage inside the SAH. Two halogen lights of 300 W are used to increase the exhaust temperature of the SAH by placing them in the inlet and outlet ducts. All the experiments have conducted on natural and forced convection for performance evaluation on two similar design solar air heaters (with and without heat storage). The comparisons are made with two similar design solar air heaters carrying desert and granular carbon, as an individual heat storing media, to find out an optimum design of a SAH with long term heating. The thermal efficiencies of the novel SAH range from 18.04% to 20.78% of natural convection and 52.21%–80.05% with forced convection.     

Combustion characteristics and thermal enhancement of premixed hydrogen/air in micro combustor with pin fin arrays

Targeted at improving the combustion stability and enhancing heat transfer in micro combustor, the combustion characteristics and thermal performance of micro combustor with pin fin arrays are numerically investigated by employing detail H₂/O₂ reaction mechanism. It is shown that the micro combustor with staggered pin fin arrays exhibits the highest average temperature and heat flux of external wall, while the micro combustor with in-line pin fin arrays displays the most uniform temperature distribution of external wall. When the equivalence ratio is 1.1, all micro combustors exhibit the highest mean temperature and heat flux of external wall. The micro combustor materials with high thermal conductivity can not only improve the average temperature and heat flux of external wall, but also enhance heat transfer to the upstream which can preheat the mixed gas. Therefore, the materials with high thermal conductivity, such as red copper and aluminum, can make up for the nonuniform temperature distribution of micro combustor with staggered pin fin arrays, so as to realize uniform high heat flux output of external wall.