A design procedure for solar air heating systems

A natural extension of the design procedure for liquid-based solar space and water heating systems is a similar analysis for solar heating systems using air as the heat transfer fluid. In this paper, a solar air heating system incorporating a flat-plate air heater and packed bed thermal storage is described and a simulation model for the system is developed. The results of many simulations of the air heating system are used to establish the relationship between system performance and the system design and meteorological variables. The results are presented in analytic and graphical form, referred to as an f-chart for solar air heating systems. The results of simulations in several widely different climates suggest that the information presented in the f-chart is location independent. Methods of estimating the performance of air heating systems having a collector air capacitance rate and a storage capacity other than those used to generate the f-chart are included. A comparison of the performance of air and liquid based systems is afforded by a comparison of their respective f-charts. The air system is shown to perform better at high load fractions supplied by solar energy than a liquid-based system with the same collector thermal performance parameters.     

A mathematical model of thermal performance of a solar air heater with slats

A mathematical model for computing the thermal performance of a single pass flat-plate solar air collector is presented. Air channels were formed by providing metal slats running along the circulated air passage linking the absorber plate by the bottom one in an endeavor to enhance the thermal efficiency of the solar air collector. A mathematical model, therefore, is developed by which the influence of the addition of the metal slats on the efficiency of the solar collector is studied. A computer code that employs an iterative solution procedure is constructed to solve for the governing energy equations to estimate the mean temperatures of the collector. The effect of volume airflow rate, collector length, and spacing between the absorber and bottom plates on the thermal performance of the present solar air heater was investigated. Furthermore, a numerical comparison of the present design with the most common type of solar air heaters is conducted. The results of the comparison have indicated that better thermal performance was obtained by the modified system.     

大型太阳能烟囱发电站热力分析与计算

利用热力学方法建立太阳能烟囱发电系统中集热棚、烟囱及风力透平的热气流能量转换过程的理论模型及求解方法.鉴于太阳能烟囱发电站的大尺寸特征,采用一维假设建立热气流传热模型,使用龙格-库塔方法对非线性能量方程进行数值求解.对集热棚直径3 600 m,烟囱高950 m,设计功率100 MW的大型太阳能烟囱发电站进行分析与计算,给出了该电站的风力透平轴功率随质量流量和太阳辐射强度变化的规律,为风力透平机组提供热力气动设计参数,为大规模开发利用太阳能提供借鉴.     

Comparative thermal performance evaluation of an active solar distillation system

In this paper, thermal models of all types of solar collector‐integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35′N, 77°12′E, 216 m above MSL). The thermal model of flat‐plate collector integrated with active solar still was validated using the experimental test set‐up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m^?2 day^?1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd.     

A complete design data and performance parameter evaluation of a pilot scale solar updraft tower

Abstract

Renewable energy sources are the best alternative for giving solution to the energy shortage and CO₂ emission problems. Solar updraft tower is a relative novel technology for electricity production from solar energy. It consists of three main components; a solar air collector with absorber plate, central chimney, and a turbine. The objective of this work is to present complete design parameters of individual components of a small and less expensive prototype solar updraft tower. The main contents of this study are; solar radiation calculations, chimney design, solar wind turbine design calculations, heat loss and pressure loss estimations for collector. The pilot solar chimney power plant considered in this work consists of an air collector diameter of 3.5-m, the chimney diameter and height are 0.6 and 6?m, respectively. Theoretically the maximum velocity of air is achieved at chimney base is 1.9?m/s. The overall efficiency of the plant is estimated as 0.0019%.     

Combined natural convection and surface radiation in solar collector equipped with partitions

A comprehensive numerical study was carried out to study the thermal performances of a solar collector equipped with partitions attached to its glass cover. This technique is used to favorise and increase the heat transfer coefficient between the working fluid, (air) and the absorber in the solar collector. A specifically developed numerical model based on the finite-volume method and the SIMPLER algorithm is used for the solution of the mass, momentum and energy transfer governing equations. The discretized equations are solved iteratively by an algorithm based on a preconditioned conjugate gradient method. Concerning the radiation exchange, we consider that the working fluid is transparent, so only the solid surfaces contribute to the radiation exchange and assumed to be diffuse-gray. A complete parametric study is made for various partitions length Lp, aspect ratio A and Rayleigh numbers Ra for Prandtl number Pr = 0.71. Results are reported in terms of isotherms, streamlines and average Nusselt-numbers along the absorber plate.     

An improved thermal and electrical model for a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to investigate the thermal and electrical performance of a solar photovoltaic thermal (PV/T) air collector. A detailed thermal and electrical model is developed to calculate the thermal and electrical parameters of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections are done on heat loss coefficients in order to improve the thermal model of a PV/T air collector. A better electrical model is used to increase the calculations precision of PV/T air collector electrical parameters. Unlike the conventional electrical models used in the previous literature, the electrical model presented in this paper can estimate the electrical parameters of a PV/T air collector such as open-circuit voltage, short-circuit current, maximum power point voltage, and maximum power point current. Further, an analytical expression for the overall energy efficiency of a PV/T air collector is derived in terms of thermal, electrical, design and climatic parameters. A computer simulation program is developed in order to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. Since some corrections have been down on thermal and electrical models, it is observed that the thermal and electrical simulation results obtained in this paper is more precise than the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency and overall energy efficiency of PV/T air collector is about 17.18%, 10.01% and 45%, respectively, for a sample climatic, operating and design parameters.     

Design concept and mathematical model of a bi-fluid photovoltaic/thermal (PV/T) solar collector

This paper presents an improved design of a photovoltaic/thermal (PV/T) solar collector integrating a PV panel with a serpentine-shaped copper tube as the water heating component and a single pass air channel as the air heating component. In addition to the electricity generated, this type of collector enables the production of both hot air and water, increasing the total efficiency per unit area compared to the conventional PV/T solar collector. The use of both fluids (bi-fluid) also creates a greater range of thermal applications and offers options in which hot and/or cold air and/or water can be utilized depending on the energy needs and applications. In this paper, the design concept of the bi-fluid PV/T solar collector is emphasized with 2D steady state energy balance equations for the bi-fluid configuration are developed, validated and used to predict the performance of the bi-fluid solar collector for a range of mass flow rates of air and water. The performance of the collector is then compared when the fluids are operated independently and simultaneously. The simulations indicate that when both fluids are operated independently the overall thermal and electrical performance of the solar collector is considered as satisfactory and when operated simultaneously the overall performance is higher. The bi-fluid PV/T solar collector discussed in this paper will add insights to the new knowledge of optimizing the utilization of solar energy by a PV/T solar collector and has potential applications in various fields.     

Theoretical and experimental study of a two channel air heater with perforated first absorber

The performance of a two channel solar air collector with perforated first absorber plate is discussed. The transient equations, written by considering the energy balance for every individual component of the air collector, are solved explicitly. The effect of some of the design parameters are discussed. The mentioned design is investigated experimentally. It was found that there is a strong relationship between collector efficiency and first absorber plate thickness, holes density and dimensions.     

Thermal performance of an n-pass solar air heater

A mathematical model is developed for the prediction of the thermal performance for an n-pass solar air collector. The thermal efficiency and the temperature rise in teh collector are increased by preheating the air within the collector before it comes into contact with the absorber plate. The thermal losses to the ambient, through the bottom plate, are minimized due to the lower bottom plate temperature. The analysis describes how the governing equations are manipulated with the aid of the boundary conditions to obtain a set of equations which is solved numerically. In order to demonstrate the capability of the model, the analysis is applied to investigate the effect of increasing the number of air passes within the collector on the thermal efficiency and the temperature rise for a range of air mass flow rates. The results indicate that the thermal efficiency of the collector increases rapidly and approaches the optical efficiency of the collector as the mass flow rate is increased. In general, the model can be used to analyze the effect of various design parameters on the thermal performance.     

Modeling of the CSU heating/cooling system

This paper resents a thermal simulation of the Colorado State University solar house. A computer model of the solar energy system was developed and computer runs were made using one year of meteorological data to determine the important design features. The system consists of a flat plate solar collector, main storage tank, service hot water storage tank, auxiliary heater, absorption air conditioner with cooling tower and heat exchangers between the collector and storage, storage and service hot water tank and storage and residence. This system very closely models the CSU house in operating mode one.The results are in the form of monthly integrated values for the pertinent energy quantities. In addition, results are presented which show the effect on the system performance of the collector tilt, collector area and number of covers.     

Modeling and numerical simulation of solar chimney power plants

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to conduct a more detailed numerical analysis of a solar chimney power plant. A mathematical model based on the Navier-Stokes, continuity and energy equations was developed to describe the solar chimney power plant mechanism in detail. Two different numerical simulations were performed for the geometry of the prototype in Manzanares, Spain. First, the governing equations were solved numerically using an iterative technique. Then, the numerical simulation was performed using the CFD software FLUENT that can simulate a two-dimensional axisymmetric model of a solar chimney power plant with the standard k-epsilon turbulence model. Both the predictions were compared with the available experimental data to assess the validity of the model. The temperature, velocity and pressure distributions in the solar collector are illustrated for three different solar radiations. Reasonably good quantitative agreement was obtained between the experimental data of the Manzanares prototype and both the numerical results.     

太阳能空气集热建筑模块的运行控制策略

该研究利用可调控的风机和风门,对两种类型集热模块的热输送过程进行了优化实验研究,系统探讨了在供热模式下空气循环方式、模块类型以及质量流率等因素对模块内部空气升温速度、供热量及集热效率等的影响,并提出集热模块运行控制的基本策略。同时通过对模块的简化计算模型进行理论分析,提出了集热模块的运行控制参数方程,为实现模块运行的优化控制提供理论依据。     

新型管板式太阳能PV/T集热器光热特性研究与优化

为提高太阳能光伏/光热（PV/T）集热器全年运行效率,提出一种新型管板式太阳能PV/T集热器结构,并针对该集热器光热传递与光电转换过程进行分析,建立水和空气同时运行时的二维非稳态传热数学模型;在验证模型可靠性的基础上,模拟研究空气流道高度和空气流量等设计参数对PV/T集热器光热、光电特性的影响。结果表明,空气流道高度为15 mm时,PV/T集热器光电光热综合性能效率最佳;在所研究的工况下,该集热器的光电光热综合性能效率为0.84~0.87。     

Performance analysis of direct solar dryer driven by photovoltaic thermal energy recovery and solar air collector for drying materials and electricity generation

The direct-type solar dryer is characterized by very simple construction, less maintenance, cost-effectiveness, and is easy to handle. The present study aims to enhance the performance of a direct-type solar dryer. To achieve this, the photovoltaic (PV) panels with thermal energy recovery and solar air collector were integrated with the direct-type solar dryer. In this study, the PV panels with thermal energy recovery and solar air collector were utilized as preheating units to raise the air temperature before entering the direct solar dryer. Moreover, the PV panels were utilized to drive the air blower. In this study, three incorporated models are suggested to study the performance of the solar dryer integrated with PV panels with thermal energy recovery and solar air collector. The model of each component was validated by the previously recorded empirical data. The results confirmed that the dual utilization of the PV panels with thermal energy recovery and solar air collector as a preheating unit raised the air temperature entering the direct solar dryer by the rate varying between 29°C and 42°C within the period 9:00 a.m.–4:00 p.m. Also, the moisture content of banana samples inside the direct solar dryer reduced from the initial value of 72% (wb) to the value of 33.4% (wb) within 7 h (9:00 a.m.–4:00 p.m.). During this operating period, moisture removal from the banana samples varied between 110 and 400 g/h.     

Experimental performance of a solar air heater with a “V” corrugated absorber

The performance of a “V” corrugated-plate solar air heater was investigated experimentally. The collector was tilted at 20° in summer and 40° in winter for maximum heat collection during the period of maximum solar irradiance. The collector performance parameters were evaluated during clear days in winter and summer. The mass flow rate of air was varied from 0.016 to 0.0385 kg/s·m², and an air outlet temperature of 70°C was obtained in summer at midday with an average collector efficiency of 42%. The contribution of solar energy from the collector for winter space heating was estimated.     

Radiative Property of Absorbing Materials and its Collection Efficiency

Based on the previous research of the plate-type solar collector by the author, the analysis of the relationship between the spectral radiative property of the absorbing and transparent plates and their collector efficiency is firstly discussed on a simplified solar collector model. This analytical technique is then applied to evaluate the performance of water solar collector in practical use and the performance of five sorts of the commercial solar collectors are compared each other on both the collection efficiency and equilibrium temperature. Consequently, it is made clear that those solar collectors in Japan are of excellent quality of high collection efficiency.

Secondly, the performance of a unit-type air solar collector with carbon fiber sheet (CF-sheet) as the absorbing material, which was developed by the author in cooperation with a company, is analyzed and examined in the same way as above. Lastly, a large scale house-type air solar collector is tested, and this type of solar collector using carbon fiber' might be one of the most feasible methods to use solar energy in the industrial field including cost-performance.     

Improved multiple linear regression based models for solar collectors

Mathematical modelling is the theoretically established tool to investigate and develop solar thermal collectors as environmentally friendly technological heat producers. In the present paper, the recent and accurate multiple linear regression (MLR) based collector model in Ref. [1] is empirically improved to minimize the modelling error. Two new, improved models called IMLR model and MPR model (where MPR is the abbreviation of multiple polynomial regression) are validated and compared with the former model (MLR model) based on measured data of a real collector field. The IMLR and the MPR models are significantly more precise while retaining simple usability and low computational demand. Many attempts to decrease the modelling error further show that the gained precision of the IMLR model cannot be significantly improved any more if the regression functions are linear in terms of the input variables. In the MPR model, some of the regression functions are nonlinear (polynomial) in terms of the input variables.     

Thermal performance study of two-pass solar air heaters

The operation of a conventional solar air heater with two covers in a two-pass mode offers an inexpensive method of improving the collector efficiency by about 10–15 per cent. Heat transfer models are developed for two such two-pass flow arrangements and are compared with the performance of the single pass design. The computer models are validated by comparing with the experimental data from a series of collector testing experiments. The collector performance is examined over a wide range of design and operating conditions and the two-pass designs are found to perform better than the single pass system. For closed-loop systems with air recirculation the two-pass designs have some limitations in performance. Design curves for two-pass systems over a range of variables are presented.