FLAT PLATE COLLECTOR : FLAT PLATE COLLECTOR Prepared by:
Vinay (05mg70) INTRODUCTION : INTRODUCTION It is a solar collector device for collecting solar radiation and transfer the energy to a fluid passing in contact with it.
Where temperature below 90oC are adequate, flat plate collector are convenient.
They are made in abt 1.7 to 2.9 sq. m, in area and are relatively simple to construct and erect.
They can absorb both direct and diffused radiation.
They are consequently partially effective even on cloudy days when there is no direct radiation. CLASSIFICATION OF FPC : CLASSIFICATION OF FPC Based on the type of the heat transfer fluid used it can be divided into two main classifications;
Liquid heating collector
Air or Gas heating collector CONSTRUCTION OF FPC : CONSTRUCTION OF FPC WHEN TEMPERATURE IS BELOW ABOUT 90oC IS ADEQUATE,AS THEY ARE FOR SPACE AND SERVICE WATER HEATING FLAT PLATE COLLECTORS,WHICH ARE OF THE NON-CONCENTRATING TYPE,ARE PARTICULARLY CONVENIENT.THEY ARE MADE IN RECTANGULAR PANELS,FROM ABOUT 1.7 TO 2.9 SQUARE METER IN AREA AND ARE RELATIVELY SIMPLE TO CONSTRUCT AND ERECT. FLAT PLATES CAN COLLECT AND ABSORB BOTH DIRECT &DIFFUSE SOLAR RADIATION,THEY ARE CONSEQUENTLY PARTIALLY EFFECTIVE EVEN ON CLOUDY DAYS WHEN THERE IS NO DIRECT RADIATION Slide 5: THE MAJORITY OF FLAT PLATE COLLECTOR HAVE FIVE MAIN COMPONENTS AS FOLLOWS
A TRANSPERENT COVER WHICH MAY BE ONE OR MORE SHEETS OF GLASS OR RADIATION TRANSMITTING PLASTIC FILM OR SHEETS OR SHEET.
TUBES,FINS,PASSAGES OR CHANNELS ARE INTEGRAL WITH THE COLLECTOR ABSORBER PLATE OR CONNECTED TO IT,WHICH CARRY THE WATER ,AIR OR OTHER FLUID
THE ABSORBER PLATE,NORMALLY METALLIC OR WITH A BLACK ,SURFACE ALTHOUGH A WIDE VARIETY OF OTHER MATERIALS CAN BE USED WITH AIR HEATERS Slide 6: INSULATION,WHICH SHOULD BE PROVIDED AT THE BACK AND SIDES TO MINIMISE THE HEAT LOSSES.STANDARD INSULATING MATERIALS SUCH AS FIBRE GLASS OR STYRO-FOAM ARE USED FOR THIS PURPOSE
THE CASING OR CONTAINER WHICH ENCLOSE THE OTHER COMPONENTS AND PROTECT THEM FROM THE WEATHER. Slide 8: FLAT PLATE COLLECTOR FOR WATER HEATING IS THE PLATE AND TUBE TYPE COLLECTOR.IT BASICALLY CONSISTS OF A FLAT SURFACE WITH HIGH ABSORPTIVITY FOR SOLAR RADIATION ,CALLED THE ABSORBING SURFACE. TYPICALLY A METAL PLATE USUALLY OF COPPER,STEEL OR ALUMINIUM MATERIAL WITH TUBING OF COPPER IN THERMAL CONTACT WITH THE PLATES ,ARE THE MOST COMMONLY USED MATERIALS. THE ABSORBER PLATE IS USUALLY MADE FROM A METAL SHEET 1TO 2 mm IN THICKNESS ,WHILE THE TUBES ,WHICH ARE ALSO OF METAL ,RANGE IN DIAMETER FROM 1 TO 1.5 cm Slide 9: THEY ARE SOLDERED ,BRAZED OR CLAMPED TO THE BOTTOM OF THE ABSORBER PLATE WITH THE PITCH RANGING FROM 5 TO 15 cm.IN SOME DESIGNS,THE TUBES ARE ALSO IN LINE AND INNTEGRAL WITH THE ABSORBER PLATE.FOR THE ABSORBER PLATE CORRUGATED GALVANIZED SHEET IS A MATERIAL WIDELY AVAILABLE THROUGHOUT THE WORLD. CROSS-SECTION OF FPC : CROSS-SECTION OF FPC THE USE OF CONVENTIONAL STANDARD PANEL RADIATORS SHOWN IN FIG (c) IS ONE OF THE SIMPLEST PRACTICAL APPLICATIONS . THE METHOD OF BONDING AND CLAMPING TUBES TO FLAT OR CORRUGATED SHEET ARE SHOWN IN FIG (d) &(e), WHILE FIG (f) IS THE “ TUBE IN STRIP” OR ROLL BOND DESIGN IN WHICH THE TUBES ARE FORMED IN THE SHEET,ENSURING A GOOD THERMAL BOND BETWEEN THE SHEET AND THE TUBE. Slide 12: HEAT IS TRANSFERRED FROM THE ABSORBER PLATE TO A POINT OF USE BY CIRCULATION OF FLUID ACROSS THE SOLAR HEATED SURFACE.THERMAL INSULATION OF 5 TO 10 cm THICKNESS IS USUALLY PLACED BEHIND THE ABSORBER PLATE TO PREVENT THE HEAT LOSSES FROM THE REAR SURFACE.INSULATION MATERIALS IS GENERALLY “MINERAL WOOL” OR “GLASS WOOL”” OR “FIBRE GLASS”
THE FRONT COVERS ARE GENERALLY GLASS THAT IS TRANSPERENT TO IN-COMING SOLAR RADIATION AND OPAQUE TO THE INFRARED RE-RADIATION FROM THE ABSORBER. THE GLASS COVERS ACT AS A CONVECTION SHIELD TO REDUCE THE LOSSES FROM THE ABSORBER PLATE .GLASS IS MOST FAVOURABLE MATERIAL. ITS THICKNESS IS 3 TO 4 mm. HEAT TRANSPORT SYSTEM IN FPC : HEAT TRANSPORT SYSTEM IN FPC THE HEAT GENERATED IN THE ABSORBER IS REMOVED BY CONTINOUS FLOW OF A HEAT-TRANSPORT MEDIUM ,WHICH IS WATER.
WHEN WATER IS USED,IT IS MOST COMMONLY PSSED THROUGH METAL TUBES WITH EITHER CIRCULAR OR RECTANGULAR CROSS-SECTION
THE TUBES ARE CONNECTED TO COMMON HEADERS AT EACH END OF THE COLLECTOR.IN ORDER TO MAXIMIZE THE EXPOSURE TO SOLAR RADIATION,COLLECTOR ARE ALMOST INVARIABLY SLOPED.COOLER WATER THEN ENTERS AT THE BOTTOM HEADER,FLOWS UPWARD THROUGH THE TUBES WHERE IT IS WARMED BY THE ABSORBER AND LEAVES BY THE WAY OF THE TOP HEADER SOME DRAWBACKS OF WATER AS A HEAT-TRANSPORT MEDIUM. : SOME DRAWBACKS OF WATER AS A HEAT-TRANSPORT MEDIUM. THE POSSIBILITY OF FREEZING IN COLLECTOR TUBES IN COLD CLIMATES DURING COLD NIGHTS
CORROSION OF METAL TUBES BY THE WATER &THIS IS AGGRAVATED IF THE WATER IS DRAINED AT NIGHT SO IT ALLOWING AIR TO ENTER SOLAR AIR HEATER : SOLAR AIR HEATER Fig. shows a schematic flat plate collector where an air stream is heated by the back side of the collector plate.
Fins attached to the plate increase the contact surface.
The back side is heavily insulated with mineral wool or some other material. CLASSIFICATION : CLASSIFICATION Air heater are classified in the following two categories.
Non-porous absorber- in which the air stream does not flow through absorber plate. Air may flow above or behind the absorber plate.
Porous absorber- that includes slit and expanded metal, transpired honey comb and over lapped glass plate absorber. NON-POROUS ABSORBER PLATE TYPE COLLECTORS : NON-POROUS ABSORBER PLATE TYPE COLLECTORS It may be cooled by the air stream flowing over both side of the plate.
In most common design air flows behind the absorbing surface.
Air flowing above the upper surface increases the convention losses from the cover plate and therefore not recommended if the air inlet temperature rise at the collector are large. Slide 19: Performance of air heater is improved by :
Roughening the rear of the plate
Adding Fins to plate DRAWBACKS OF NON-POROUS ABSORBER PLATE TYPE COLLECTOR : DRAWBACKS OF NON-POROUS ABSORBER PLATE TYPE COLLECTOR Main drawback is the necessity of absorbing all incoming radiation over the projected area from a thin layer the surface, which is in order of a few microns.
Unless selective coatings are used, radiative losses from the absorber plate are excessive, therefore collection efficiency can not be improved.
Too many surfaces and too much restriction to air flow will require a large fan and a larger amt of energy to push the air through. The energy required for this cancels out savings from using solar energy, particularly if fan is electrical. POROUS-ABSORBER TYPE COLLECTOR : POROUS-ABSORBER TYPE COLLECTOR The defects in the non-porous absorber type collector is eliminated in this type of collector by following way:
The solar radiation penetrates to greater depths and is absorbed gradually depending on the matrix density.
The cool air stream introduced from the upper surface of the matrix is first heated by the upper layer which are cooler than the bottom layers. The air stream warms up, while traversing the matrix layers. Slide 22: The lower matrix layers are hotter than the upper ones, therefore, the air stream can be effectively transfer heat from the matrix.
Improper selection of the matrix porosity and the thickness may result in reduced efficiencies since the additional matrix layers beyond on optimum may no longer absorb the solar radiation and heat the air stream further. APPn OF SOLAR AIR HEATER : APPn OF SOLAR AIR HEATER The solar air heater which supply hot air that could be mainly used for the following purposes:
Drying agricultural products.
Heating green house.
Seasoning of timber.
Curing of industrial products. ADVANTAGES OF SOLAR AIR HEATERS : ADVANTAGES OF SOLAR AIR HEATERS The use of air as heat transport fluid eliminates both freezing and corrosion problems
Small air leakage are of less concern than the water leaks.
The heated air can directly used for space heating while in water heating it can not be used directly for the same purpose. DISADVANTAGES OF SOLAR AIR HEATERS : DISADVANTAGES OF SOLAR AIR HEATERS Need of handling larger volume of air due to low density of air.
Thermal capacity of air is low.
Due to lower heat transfer rate efficiencies are lower than liquid solar heater.
They have relatively high fluid circulation costs.
Relatively larger volume of storage.
They have higher noise level.
Space is required for ducting.
Difficulty of adding conventional absorption air conditioners to air systems. ADVANTAGES OF FPC : ADVANTAGES OF FPC can be use both direct and diffuse solar radiation.
do not required orientation towards the sun.
require little maintenance.
mechanically simpler than concentrating reflectors absorbing surfaces and orientation devices of focusing collectors. THANK YOU : THANK YOU REFRENCE:
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