Effect of Water Flow over the Glass on the Performance of a Solar Still Coupled with a Flat Plate Solar Collector†

In this communication a transient analysis of a solar distillation system with water flow over the glass cover is presented. The system comprises of a single basin solar still coupled with a flat plate solar collector. Due to the increased difference between water and glass temperatures the yield of this system is significantly increased. The performance of this system has been compared with that of a simple single basin solar still (SBSS), SBSS with water flow over it and SBSS coupled with a flat plate collector; and it is concluded that a SBSS with water flow over it shows the best performance.     

Single basin solar still coupled with flat plate collector

This paper presents the transient performance of a single basin solar still coupled with a flat plate collector. The average daily production of distilled water has been found to be 24% higher than for a simple single basin solar still     

PERFORMANCE ANALYSIS OF A COLLECTOR COUPLED SOLAR STILL

Performance analysis is presented of a basin-type solar still coupled to a tubular solar energy collector. Explicit expressions are derived for the water temperature, the yield and overall efficiency of the system as a function of time, collector's and the still's parameters. Effects of length of the collector and flow velocity have been studied on the yield and overall efficiency the solar still.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

Effect of dye on the performance of a double basin solar still

The use of single basin solar stills for water distillation has been well demonstrated. However, the amount of distilled water produced per unit area is fairly low which makes the single basin solar still unacceptable in situations where space is a limitation. Malik has suggested a new conceptual design of a double basin solar still to overcome the above problem partially. The relative results obtained on a double basin as opposed to a single basin solar still are reported here with reference to (a) its performance, (b) the effect of dye in the lower basin, and (c) the effect of maintaining the raw water level in the basins.     

A new type of solar water heater

This investigation reports a new type of solar water heating system without water pipes on the collector surface or a separate storage tank. The water to be heated continuously flows perpendicularly from an upper transparent cover to a porous absorber and is stored in a small volume beneath this assembly. Three different systems were designed, manufactured and tested but only one proved to be successful; this design indicated higher thermal efficiency compared to conventional collectors at high flow rates whereas at low flow rates the opposite is true.     

A solar test collector for evaluation of both selective and non-selective absorbers

A solar test collector has been designed for the testing of thermally absorbing coatings under controlled conditions. The design consists of a collector fed by a controlled temperature fluid within the range of 25–90°C (77–194°F). This temperature is maintained by a custom electronic controller. A small variable flow pump circulates water through three collector pipes at selected flow rates. Strip heaters coupled with a differential temperature controller compensate for edge losses associated with small collectors. Detailed design and operation data are presented and three black chrome and one non-selective absorber are analysed in detail by test collector measurements. Results show that efficiencies as high as 77 and 75 per cent (ΔT = 0) are obtained for 1.0 μm black chrome on copper and nickel plated steel, respectively. The lowest loss coefficients are about 3.8 W/m^2°C for all black chrome/metal surfaces, with the highest being 8.4 W/m^2°C for the black paint/metal sample. Also, a collector model is presented for comparison.     

Refrigerant-charged integrated solar water heater

The performance of two R-11-charged integrated solar water heater collectors was investigated experimentally for forced and natural circulation water flows. The heat transfer from the refrigerant loop to the hot water storage tank took place through a condenser of novel design integrated within the collector frame. The effect of the condenser inclination on the system efficiency was remarkable for natural circulation water flow but had no significant effect for forced circulation flow. The difference in thermal response between the refrigerant and water loops caused buildup of stored energy in the condenser. This energy affected the buoyancy forces and generated flow pulsation that caused a harmonic-like variation of the system efficiency. This effect vanished with forced water circulation flow. The system efficiency varied between 20 and 50% depending on the solar insolation.     

Determination of rational design parameters of a multi-stage solar water desalination still using transient mathematical modelling

The paper describes the experimental investigations of the performance of a multi-stage water desalination still connected to a heat pipe evacuated tube solar collector with aperture area of 1.7 m². The multi-stage solar still water desalination system was designed to recover latent heat from evaporation and condensation processes in four stages. The variation in the solar radiation during a typical mid-summer day in the Middle East region was simulated on the test rig using an array of 110 halogen floodlights covering the area of the collector. The results of tests demonstrate that the system produces about 9 kg of fresh water per day and has a solar collector efficiency of about 68%. However, the overall efficiency of the laboratory test rig at this stage of the investigations was found to be at the level of 33% due to excessive heat losses in the system. The analysis of the distilled water showed that its quality was within the World Health Organization guidelines. The still's operation was numerically simulated by employing a mathematical model based on a system of ordinary energy and mass conservation differential equations written for each stage of the still. A computer program was developed for transient simulations of the evaporation and condensation processes inside the multi-stage still. Experimental results obtained and theoretical predictions were found to be in good agreement. The results on the determination of rational design dimensions and number of stages of the still for a given aperture of the solar collector are also presented in this work.     

A step basin type solar water heater-cum-solar still

This communication reports the design details, performance and testing of a step basin type solar water heater-cum-solar still. The combined efficiency of the system is 64.5 per cent.     

Experimental and theoretical investigation of dual purpose solar collector

Experimental data indicate that high temperature and high performance can be obtained using dual purpose solar collector (DPSC) compared to single water or air collector. A mathematical model based on effectiveness method has been developed for the investigation of thermal performance of DPSC. In the collector two fluids (water and air) flow simultaneously. Three different kinds of channels are used to enhance the performance of collector, such as: rectangular fin, triangular fin and without fin. Simulation results show that channels with rectangular fin have better performance compared with others. The effect of water inlet temperature and air flow rate on heat delivery by air and water has been investigated.     

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.     

Effect of Temperature Dependent Internal Heat Transfers on the Performance of a Solar Still

In this paper, an effect of the temperature dependence of internal heat transfer coefficients on the performance of a single basin solar still has been studied by incorporating the change of water mass in the basin with time, initial basin water temperature etc. On the basis of numerical calculations based on simple transient analysis, the following conclusions have been drawn:

i) the evaporative heat transfer coefficient is a strong function of brine temperature, and

ii) the change of brine mass with time has insignificant effect on the performance of the still in nocturnal production which is in accordance with the assumption made by Malik and Tran (1973). This is true for other cases also.

These have also been validated by experimental results.     

Flow distribution in a solar collector panel with horizontally inclined absorber strips

The objective of this work is to theoretically and experimentally investigate the flow and temperature distribution in a solar collector panel with an absorber consisting of horizontally inclined strips. Fluid flow and heat transfer in the collector panel are studied by means of computational fluid dynamics (CFD) calculations. Further, experimental investigations of a 12.5 m² solar collector panel with 16 parallel connected horizontal fins are carried out. The flow distribution through the absorber is evaluated by means of temperature measurements on the backside of the absorber tubes. The measured temperatures are compared to the temperatures determined by the CFD model and there is a good similarity between the measured and calculated results.

Calculations with the CFD model elucidate the flow and temperature distribution in the collector. The influences of different operating conditions such as flow rate, properties of solar collector fluid, solar collector fluid inlet temperature and collector tilt angle are shown. The flow distribution through the absorber fins is uniform if high flow rates are used. By decreased flow rate and decreased content of glycol in the glycol/water mixture used as solar collector fluid, and by increased collector tilt and inlet temperature, the flow distribution gets worse resulting in an increased risk of boiling in the upper part of the collector panel.     

Collector efficiency improvement of recyclic double-pass sheet-and-tube solar water heaters with internal fins attached

The sheet-and-tube solar water heater is a convenient and common heater to be used as domestic hot water heating. This paper investigates the effects on collector efficiency of a double-pass sheet-and-tube solar water heater with fins attached under various arrayed density. In addition, the number of pair ducts and total mass flow rate are taken into account during the calculation procedure. The theoretical prediction shows that the higher collector efficiency is obtained under the suitable designing and operating parameters. Considerable improvement in collector performance is obtained by employing a recyclic operation with fins attached and under various arrayed density, instead of employing a single-pass flat-plate device. The effect of the recycle ratio, arrayed density and number of fins attached on the collector efficiency enhancement as well as the power consumption increment has also delineated.     

Solar absorption cooling plant in Seville

A solar/gas cooling plant at the Engineering School of Seville (Spain) was tested during the period 2008-2009. The system is composed of a double-effect LiBr + water absorption chiller of 174 kW nominal cooling capacity, powered by: (1) a pressurized hot water flow delivered by mean of a 352 m² solar field of a linear concentrating Fresnel collector and (2) a direct-fired natural gas burner. The objective of the project is to indentify design improvements for future plants and to serve as a guideline. We focused our attention on the solar collector size and dirtiness, climatology, piping heat losses, operation control and coupling between solar collector and chiller. The daily average Fresnel collector efficiency was 0.35 with a maximum of 0.4. The absorption chiller operated with a daily average coefficient of performance of 1.1-1.25, where the solar energy represented the 75% of generator’s total heat input, and the solar cooling ratio (quotient between useful cooling and insolation incident on the solar field) was 0.44.     

Experimental study on a horizontal tube falling film evaporation and closed circulation solar desalination system

A specifically designed solar desalinization system with a solar collector (about 2.01 m² in area) has been developed and tested under practical weather conditions. In this system, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a condensation cavity and heat exchangers. The thermal performance of the system is greatly improved because of the falling film evaporation technology used. As a result, the yield is about two to three times more than that of a conventional single basin type solar still under the same conditions. The transient-state performance of the system, the relationships with the solar radiation, the operating temperature, the feedstock flow rate and the productivity are presented. Other factors influencing the freshwater are also discussed.     

Performance study of forced circulation solar water heaters using packed-bed collectors

A performance study of forced circulation solar water heaters using packed-bed solar collectors is presented. Iron chips, gravel and stones have been used as packing materials. Thermal energy stored in the tank, system overall efficiency and pay-back capital for these solar water heaters are compared with those for solar water heaters using a plane collector. It is observed that the performance of the solar water heater is improved appreciably by packing its collector with packing material. A solar water heater using an iron chip, packed-bed collector shows the best performance.     

Study of a solar water heater using stationary V-trough collector

There are various types of solar water heater system available in the commercial market to fulfill different customers’ demand, such as flat plate collector, concentrating collector, evacuated tube collector and integrated collector storage. A cost effective cum easy fabricated V-trough solar water heater system using forced circulation system is proposed. Integrating the solar absorber with the easily fabricated V-trough reflector can improve the performance of solar water heater system. In this paper, optical analysis, experimental study and cost analysis of the stationary V-trough solar water heater system are presented in details. The experimental result has shown very promising results in both optical efficiency of V-trough reflector and the overall thermal performance of the solar water heater.     

An experimental investigation into the performance of a domestic forced circulation solar water heater under varying operating conditions

An experimental investigation is carried out on a forced circulation solar water heater to assess its performance under various operating conditions. The system consisted of two identical collectors of total absorber area of 3.45 m² and a storage tank of 200 litre capacity. Experiments were carried out during clear days with and without system loading for two water mass flow rates through the collector; namely 0.1305 kg/s and 0.06525 kg/s. The system was operated without thermostat control and with thermostat control at maximum and minimum settings. The collector efficiency improved with system loading. The improvement was better with increased hot water withdrawal from the system.