Performance Analysis of Parabolic Trough Collector

Abstract—Performance evaluations of parabolic trough collector have been studied on the basis of mathematical analysis of various parameters. Mathematical expressions have been developed for the model to simulate the results of performance evaluation using   C program. On the basis of simulated results, variation of efficiency, heat removal factor, outlet fluid temperature as a function of dimensionless insolation for fixed and variable radiative loss parameter and thermal loss parameter. Outlet fluid temperature as a function of mass flow rate for a fixed value of radiative and thermal loss parameters have been studied. The effect of thermal and radiative loss parameters have been studied for variation of the difference of outlet and inlet fluid temperatures against dimensionless insolation. Keywords—Parabolic trough collector, Heat removal factor, Dimensionless insolation, Radiative and thermal loss parameters, Outlet and inlet fluid temperatures


I. INTRODUCTION
The authors describe the analytical approach to simulate the various parts of a solar thermal power plant. A simple   C program, based on that mathematical model, can be built up to obtain statistical results under the particular conditions recognized by the user. The first part of the section analyses the conversion of solar to thermal energy as shown in Fig. 1. The system consists of a solar collector and a storage device that supply thermal energy to a load, which is input to the heat engine for the solar driven power generation. The most successful solar thermal development has been the linear SEGS plants developed and installed by LUZ International Limited between 1984 and 1990 located in California. Parabolic Trough Collector technology has established its capacity to drive a commercial power plant [1]. A variety of procedures to calculate the property of the operational behaviour of solar collectors can be found in the technical literature. Milton et al. [2] studied modeling the behaviour of a solar power plant with the parabolic linear collector is most essential as a design and optimization tool that can approach a variety of situation. Yebra et al. [3] developed the design of advanced control systems to optimize the general performance of parabolic trough collectors, solar plants with direct steam generation is today a high-priority line of research. They developed the guidelines for dynamic model and control system design for such type of plants. The experimental and predicted values were compared and discussed. The cause of the change of absorber tube temperature on absorber emissivity in the LUZ systems was reported by Lippke [4]. The increase of emissivity with temperature has a main cause on collector thermal loss and collector effectiveness. A direct steam generation (DSG) collector has also been proposed as a future generation of the LUZ type trough collector by Cohen and Kearney [5]. This arrangement has the development of eliminate the expensive synthetic oil, intermediate heat transport piping loop and oil to the steam heat exchanger. Fraidenraich et al. [6] developed a closed form solution that enables to estimate the profile of the absorber temperature; fluid temperature and power deliver next to a parabolic linear focus collector. Analytical modeling of a solar power plant with parabolic linear collector was used as a basis for the development of a code implemented by Jones et al. [7] in the TRNSYS thermal simulation software. Quaschning et al. [8] also used a model based on previous works. Price [9] developed a computer model that combines an investigation of the performance of a parabolic trough solar power plant with its cost and economic parameters. The model was able to propose a Rankine cycle parabolic trough plant, with or without thermal storage and fossil fuel support. The best balance between the operational performance and cost of the plant was discussed. Forristall [10] suggested that the thermal losses of collectors are treated with a regression curve obtained from the detailed model and expressed as a utility of the fluid temperature. The different part of the solar power station is treated with great detail, even though, sometimes, it is difficult to find out the exact modeling hypothesis included in the simulation software.

II. USEFUL THERMAL ENERGY
The useful solar energy collected by a solar collector   t Q u is influenced by three major factors:  The ability of the absorbing element to absorb the available insolation that is incident on the element after being reflected from or transmitted through other collector components.  The magnitude of the thermal losses due to convection to the ambient air, and  The magnitude of thermal losses due to radiative exchange with the surroundings.
The useful solar energy can be expressed mathematically as: Thus, the first term on the right of the equation (1) is the solar energy absorbed by the absorbing element of the collector. The second term on the right of the equation (1) represents losses due to convection and conduction from collector in terms of average overall heat-transfer coefficient U times the absorbing element area c A times the difference between the average absorber surface temperature e T and the ambient temperature a T . Both e T and a T may be time-dependent. The third term on the right of the equation (1) accounts for the exchange of infrared radiation between the collector and surroundings.
A measure of the collector performance is the ratio of the useful collected energy known as collector efficiency    and expressed mathematically as: To simplify the analysis, it is desirable to put an equation (3)

As assumed, then the equation (3) becomes in dimensional form
The R F relates the average collector temperature to the more easily measured fluid inlet temperature, and the collector efficiency can now be found in terms of the fluid inlet temperature.
The net enthalpy gain   t Q u of the fluid flowing through the collector is given by and, As  approaches zero ( c m tends to zero, near stagnation conditions), equation (11) predicts [using equation (9)] that no flow or stagnation temperature of the collector is given by It can be written in terms of thermal fluid temperature at the collector entrance   fi T and at the collector exit

III. RESULTS AND DISCUSSIONS
Thermal performance of parabolic trough collector was predicted on the basis of simulated results using   C program for the system, operating and physical parameters and properties employed like K T a 300  ,

F. Effect ofThermal Loss Parameter on Fluid Outlet Temperature
Plots shown in Fig. 7 show that the effect of thermal loss parameter on outlet fluid temperature for a fixed value of relative loss parameter. It has been found that the outlet fluid temperature rises from

G. Effect of Mass Flow Rate on Outlet Fluid Temperature
The plot shown in Fig. 8 shows the outlet fluid temperature as a function of mass flow rate for various values of dimensionless insolation and a fixed value of the radiative loss parameter and thermal loss parameter.      4. The thermal loss parameter and radiative loss parameter also affect the values of the heat removal factor of the cylindrical parabolic trough collector. It has been found that the heat removal factor linearly increases with   To summarize, it can be stated that the performance of solar electric generating systems with parabolic trough collector can be considerably enhanced by modifying the configurations of parabolic trough collector and this enhancement is a strong function of the system and operating parameters. Furthermore, the parametric dependence of thermal performance as discussed above bring out clearly, the need for a judicious choice of the system and operating parameters to obtain the maximum benefit from solar thermal power generating system.