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.     

Study and optimization of the thermal performances of the offset rectangular plate fin absorber plates, with various glazing

The low thermophysical characteristics of air used as a heat transfer fluid in the solar collectors with thermal conversion require a fully developed turbulent flow. This increases the thermal heat transfer between the absorber plate and the fluid, which clearly improves the thermal performances of the solar collector with obstacles arranged into the air channel duct. In the present work, we introduce, in solar collector, the offset rectangular plate fins, which are used in heat exchangers. An experimental investigation carried out showed the generated enhancement of thermal performance. The offset rectangular plate fins, mounted in staggered pattern, are oriented parallel to the fluid flow and are soldered to the underside of absorber plate. They are characterized by high heat transfer area per unit volume. High thermal performances are obtained with low pressure losses and in consequence a low electrical power consumption by the fan in comparison to the flat plate collector. The experimental results are all so compared by using two types of transparent cover; double and triple.     

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.     

Operating design conditions of a solar-powered vapor absorption cooling system with an absorber plate having different profiles: An analytical study

An effort has been devoted to analyze the collector performance parameters of a solar-assisted LiBr/H₂O vapor absorption cooling system with a flat-plate collector consisting of an absorber plate of different profiles. The effect of the collector fluid inlet temperature on the performance of solar collector, vapor absorption cycle, vapor absorption system and refrigerating efficiency has been studied for a wide range of design variables. A comparative study has also been made among the performance parameters of an absorber plate of different shapes with the variation of collector fluid inlet temperature. From the result, it can be highlighted that, at a particular collector fluid inlet temperature, the performances of a vapor absorption system attain a maximum value. Finally, an optimum collector fluid inlet temperature is determined by satisfying the minimization of volume of an absorber plate without affecting the cooling rate in the evaporator.     

A simulation modeling for optimization of flat plate collector design in Riyadh, Saudi Arabia

A simulation of forced convection solar heated water system is presented. A computer program is developed consisting of independent subroutines, capable of handling the variation of the collector tube diameter, tube spacing, ambient conditions, material thermal properties, collector and system design optimization.The meteorological data of Riyadh were used as the input in the program to simulate the performance of the collector system. The output of the program is analyzed to optimize the system design in the Riyadh region. The results of the simulations are compared with experimental data. There is a good agreement between the predicted and measured values.     

Performance study on plain fin filled with catalyst in a plate fin heat exchanger for hydrogen liquefaction

In order to develop the correlations of the fin performances of the catalyst filled plate fin heat exchanger (CFPFHE) for hydrogen liquefaction, a numerical model of the plain fin filled with catalyst at 30–80 K is established. The effects of temperature, the structural parameters of the fin and catalyst layer and the operating condition on the fin performances of the fin channel are analyzed and discussed. The results show that the temperature distribution patterns and fin performances at 30–40 K and above 40 K have obvious differences. The results above 40 K can be characterized by that at 70–80 K. The sensitivity analysis shows that the distributions of sensitivity at 70–80 K and 30–40 K are similar. The heat transfer and ortho-para hydrogen conversion performances are mainly affected by the structural parameters of the fin and the operating condition, while the flow performance is mainly affected by the structural parameters of the catalyst layer. The correlations of the flow and heat transfer performances at 70–80 K and 30–40 K are obtained by fitting the data points on the response surface with more than 97% of the fitting degrees and within ±15% of the deviations. Meanwhile, the correlations of the ortho-para hydrogen conversion performance show that the mass space velocities at 70–80 K and 30–40 K should be lower than 1.25 and 7.50 kg m^?3 s^?1 respectively to reach the standard of the ortho-para hydrogen conversion. The correlations of the fin performances can be used as the basis of optimization design of the CFPFHE.     

Studies on gap spacing between absorber and cover glazing in flat plate solar collectors

The air gap between absorber and cover glazing in fiat plate collectors has been optimized experimentally by designing three identical collector-cum-storage type solar water heaters with 25, 50 and 150 mm air gaps. The heater with 50 mm air gap collects 11.64% and 7.72% more energy compared with heaters having 25 mm and 150 mm air gaps, respectively. The average overall efficiencies of the heaters are 52.5%, 57.8% and 54.1% having 25, 50 and 150 mm air gaps. A 50 mm air gap has, therefore, been found to be optimum.     

Performance of an inverted flat plate solar collector

In this note an analysis of an inverted flat plate solar collector has been presented. Effect of various parameters, namely thickness of the insulation, air conductance between flowing water and top of the bottom insulation, length of the collector and flow velocity of water on the performance of the collector have been studied. Numerical calculations have been made for typical cold day in Delhi, namely 26 January 1980.     

Design and analysis of solar thermoelectric power generation system

This article reports on the design and performance analysis of a solar thermoelectric power generation plant (STEPG). The system considers both truncated compound parabolic collectors (CPCs) with a flat receiver and conventional flat-plate collectors, thermoelectric (TE) cooling and power generator modules and appropriate connecting pipes and control devices. The design tool uses TRNSYS IIsibat-15 program with a new component we developed for the TE modules. The main input data of the system are the specifications of TE module, the maximum hot side temperature of TE modules, and the desired power output. Examples of the design using truncated CPC and flat-plate collectors are reported and discussed for various slope angle and half-acceptance angle of CPC. To minimize system cost, seasonal adjustment of the slope angle between 0° and 30° was considered, which could give relatively high power output under Bangkok ambient condition. Two small-scale STEPGs were built. One of them uses electrical heater, whereas the other used a CPC with locally made aluminum foil reflector. Measured data showed reasonable agreement with the model outputs. TE cooling modules were found to be more appropriate. Therefore, the TRNSYS software and the developed TE component offer an extremely powerful tool for the design and performance analysis of STEPG plant.     

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.     

Two-dimensional fin efficiency of plate fin-tube heat exchangers under partially and fully wet conditions

This paper presents the two-dimensional analysis for the efficiency of continuous plate fin-tube heat exchangers in staggered and in-lined arrangements under the dry, partially wet, and fully wet conditions for different heat transfer coefficient (h = 20 W/m2K to h = 80 W/m2K) and air relative humidity over the full range from φ= 0 % to φ= 100%. It is shown that the fin efficiencies of the staggered arrangement are higher than those for the in-lined arrangement, and the fully wet fin efficiency is 10~20% lower than that for a dry fin. The conventional 1-D sector method underestimates the fin efficiency up to 4 % as compared to the 2-D analysis.     

Parametric optimum design of an irreversible heat-transformer based on the thermo-economic approach

The thermo-economic objective function of a heat transformer may include other objective functions such as the coefficient of performance and specific heat pumping load. It is defined as the heat-pumping load divided by the total cost per unit time and its expression is derived from the general cycle model of an irreversible heat-transformer. The general objective function is used to analyze the thermoeconomic and thermodynamic optimum performance of a heat transformer affected by multi-irreversibilities. The bounds of some important parameters are determined. The problem of how to choose optimally these parameters are discussed. The results obtained here can provide some new theoretical guidance for the optimal design and operation of heat transformers and heat engines.     

Transient performance of normal/reverse flat plate collector with selective absorber surface

This paper presents the performance of an optimized collector system [1], employing light heat transfer oil as working fluid, operated in normal and reverse configurations under simulated solar conditions. Expressions for transient and stagnation temperatures of the working fluid have been derived. Experimental and theoretical values of efficiencies for different incident intensities show good agreement. The results indicate that shallow (10 mm) liquid stream results in more efficient solar thermal performance for the normal and the reverse configurations.     

Performance analysis and parametric optimum criteria of an irreversible Atkinson heat-engine

Multi-irreversibilities, mainly resulting from the adiabatic processes, finite-time processes and heat loss through the cylinder wall, are considered in the cycle model of an Atkinson heat engine. The power output and efficiency of the cycle are derived by introducing the pressure ratio and the compression and expansion efficiencies. The performance characteristic curves of the cycle are presented. The bounds of the power output and efficiency are determined. The optimum criteria of some important parameters, such as the power output, efficiency and pressure ratio are given. The influences of the various design parameters on the performance of the cycle are analyzed in detail. The results obtained may provide a theoretical basis for both the optimal design and operation of real Atkinson heat engines.     

Thermal-economic multi-objective optimization of plate fin heat exchanger using genetic algorithm

Thermal modeling and optimal design of compact heat exchangers are presented in this paper. ε–NTU$\epsilon ''–''\mathit{NTU}$ method was applied to estimate the heat exchanger pressure drop and effectiveness. Fin pitch, fin height, fin offset length, cold stream flow length, no-flow length and hot stream flow length were considered as six design parameters. Fast and elitist non-dominated sorting genetic-algorithm (NSGA-II) was applied to obtain the maximum effectiveness and the minimum total annual cost (sum of investment and operation costs) as two objective functions. The results of optimal designs were a set of multiple optimum solutions, called ‘Pareto optimal solutions’. The sensitivity analysis of change in optimum effectiveness and total annual cost with change in design parameters of the plate fin heat exchanger was also performed and the results are reported. As a short cut for choosing the system optimal design parameters the correlations between two objectives and six decision variables with acceptable precision were presented using artificial neural network analysis.     

B-spline curve based optimum profile of annular fins using multiobjective genetic algorithm

Thermal stress in annular fins, which influences the life of a fin, still needs its detail analysis. Heat transfer in annular fins is studied here as a multiobjective optimization problem. Representing fin profiles by B-spline curves, fin geometries are obtained primarily by maximizing heat transfer rate and minimizing thermal stress. Fin performance is further assessed by minimizing fin volume and maximizing fin efficiency and effectiveness. Evaluating temperature and thermal stress by hybrid spline difference method, non-dominated sorting genetic algorithm II is applied to approximate the Pareto-optimal front. The proposed procedure would be helpful for designers to adopt suitable fin configurations from the Pareto front.     

Performance investigation of single- and double-pass solar air heaters through the use of various fin geometries

This paper presents an experimental comparative study on the thermal performance of the following three single-pass types of solar air heaters (SAHs): (i) without obstacles, (ii) with rectangular obstacles and (iii) with a new form of obstacles in the air flow duct. Thus, we carried out studies to compare the best system with (iiii) a double-pass flat plate collector having the same type of obstacles in order to determine the best-performing model. All collectors were designed, constructed and tested in the University of Biskra (Algeria) in a stand facing South at an inclination angle equal to the local latitude. In comparison with the recent literature, at different air mass flows, the highest efficiencies were obtained from the double-pass SAH with trapezoidal obstacles. In addition, this study has allowed us to show that the use of obstacles, in the air flow duct of the SAHs, is an efficient method to improve their performances.     

Experimental Study on Heat Transfer and Pressure Drop Characteristics of Four Types of Plate Fin－and－TUbe Heat Exchanger Surfaces

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Performance evaluation and optimum design strategies of an acid water electrolyzer system for hydrogen production

The performance of a new acid water electrolyzer system for hydrogen production is investigated, based on semi-empirical equations of a phosphoric acid water electrolyzer. The circulating electrolyte concentrations under differently operating temperatures are optimized so that the minimum input voltages of the electrolyzer are determined for other given conditions. The optimum electrochemical characteristics of the electrolyzer are revealed. Moreover, it is expounded that the Joule heat resulting from the irreversibilities inside the electrolyzer is larger than the thermal energy needed in the water splitting process. The general performance characteristics of the phosphoric acid water electrolyzer system are discussed, from which the lower bound of the operating current density is determined. The upper bound of the operating current density is further determined by introducing a multi-objective function including the system efficiency and hydrogen production rate. Consequently, some optimum design strategies of a phosphoric acid water electrolyzer system are obtained and may be chosen according to different practical requirements.     

Analysis of an open type flat plate collector for tannery effluent treatment

In this paper, analysis of an open type flat plate collector for tannery effluent treatment is presented. The effects of parameters like orientation of collector, film thickness, insolation, ambient temperature and relative humidity on the effluent evaporation rate are studied. It is found that the collector facing south at an inclination of 12.68° and having a solution film thickness of 5 mm gives maximum year round performance. The performance of this open type flat plate collector is compared with that of the conventional pond.