Page 1 :
1. Study of Solar Water Heater, , Water heating is one of the simplest applications of solar energy. Hot, water is required for domestic activities as well as industrial activities. For, house hold requirement hot water is used for taking bath, cleaning, utensils,, washing cloths and floors etc. It has been observed that 100 litres solar water, heater can save about 2000 units of electricity annually., , Advantages of Solar Water Heater:, , (1) Simple in construction and installation., (2) Almost no maintenance and operating cost., (3) It saves time and energy for heating water., (4) _ Easily retro-fittable to existing houses as per requirement., (5) Economically viable as compared to electric water heater., (6) Moderate temperature required, domestic affairs could easily, , achieved., , Types of Solar Water Heater:, (A) Collector coupled to storage tank, (B) Collector cum storage system., (A) Collector coupled to storage tank:, , This type of solar water heater can extract heat from solar collectors in, two ways as (i) Natural convection (thermosiphon effect) and (ii) forced flow, of water using an electrically operated pump. Collector coupled to storage tank, type of water heater is used as domestic water heater where the maximum, temperature required is not more than 70 I A typical system consists of, , solar collector (front glazing), metallic absorber, back insulation and collector, box, insulated storage tank, piping, controls and pump., Heating is accomplished by collection of solar radiation with flat plate, , Edit with WPS Office
Page 2 :
collector on south facing roof or walls. The collector is usually placed below, the storage tank. Cold water from the storage tank flows down to the inlet of, the collector, gets heated on the collector and rises to the tank by, thermosyphonic effect. A density difference created by the temperature, gradient causes the fluid to flow up in the collector., , The collectors are usually oriented towards south with an inclination, , angle equal to latitude of the place. However, for winter use, it is preferable to, , keep angle of inclination at latitude + 15°. The required collector area for 100, , liter hot water demand at 50 % is about 2 m2.In the cold climates, it is, essential to mix anti freeze materials in the heat extracting fluid. In this case a, heat exchanger may also be used and which prevent antifreeze fluid to flow, directly through the collector. It is known as indirect natural circulation type, solar water heater., , (B) Collector cum storage system type of Solar Water Heater:, , In case of collector cum storage type solar water heater, all three, functions i.e. solar energy collection, storage and control are combined into a, single unit. A typical collector cum storage water heating system consists of, three main components, front glazing (solar flat type collector), absorber sheet, and insulated storage tank. Solar radiation passes through the front glazing, and gets absorbed by the absorber which further heats the water. The storage, tank acts as a collector cum storage for hot water., , To find out optimum size of the solar water heater, the load, requirements on daily and on seasonal basis need to be known. This will help, in deciding the collector area and also the storage capacity. The effectiveness, of solar water heater depends on proper matching of solar collection with hot, water demand., , Normally the solar water heaters are either installed on the roof top or, on the ground. For system to be installed on the roof top roof construction and, load bearing capacity, orientation of building, avoiding shadow due to nearby, structures and trees and availability of cold water at a required height must be, , Edit with WPS Office
Page 3 :
ensured. Similar care is taken for the systems to be installed on the ground., The solar collectors could be either be made a part of the south facing, , wall of the building or could be installed on the window / door overhangs., Normally four types of collectors are being used in solar water heaters, , for different temperature requirements:, , (1) Unglazed polymer collector for heating of swimming pool water., , (2) Metallic collector with black painted absorbers (copper tube / copper, , she — and copper tube aluminum sheet etc.) for temperature, application up to 60 Qc., (3) Collector with selectively coated metallic absorber for temperature up, , to 80-85 °C and, , (4) Evacuated tubular collector for temperature above 80 °c., , In thermosiphon type of solar water heater, the flow of water from, bottom of the tank through the collector to the top of the tank takes place, because of the temperature gradient created in the collector under the sunlight., Since there is no moving part in such a system, the chances of failure are very, rare. In the forced flow type of solar water heater pumps with controls are, added at appropriate place in the system to ensure the flow of water through, all the collectors. This type of system can either be a single pass system, where the water enters the collector array at one end and leaves at the other, end or a recirculation type system. Where water is taken from the storage tank, circulated through collector array and returns back to the tank repeatedly., Since in a single pass system the collector operates at comparatively lower, temperature than in recirculation type. The system efficiency is better in single, pass system., , Assignment: Draw a Diagrams of Thermosiphon type Solar Water Heater,, , Indirect Natural Circulation Solar Water Heater and Collector- Cum storage, type Solar Water Heater & label them properly., , Edit with WPS Office
Page 4 :
2. Study of Solar Cookers, , Solar cooking: | Solar cooker works on solar energy and need no fuel, no, , smoke, no soot's spoil cooking utensils and keeps the environment clean., , The principle methods of cooking food are boiling, frying, roasting and, baking. For preparation of pulse, vegetables and rice, the process temperature, of food being cooked is about 100 9G. For frying and boiling heat is supplied, from all the sides of the material being cooked. In most of food water is, already present in raw material. Further some water is also added to get, homogenous mixture of food for cooking. In such cases once the boiling, temperature close to 100 OC is reached, not much heat is required except the, , thermal loss from the vessel. The thermal losses are evaporation loss from the, , food, radiation and convection losses from vessel., , In the design of solar cooker attention is given to following points:, (1) _ It should provide sufficient heat for quick boiling of water., (2) Heat loss is minimized by incorporating insulation on the sides of, , vessel and keeping vessel covered with a lid., , (3) The temperature for cooking food by boiling is about 100 °c, but to, , Edit with WPS Office
Page 5 :
have high heat transfer rates, the temperature of the heat source should be, high. Therefore a solar collection of sufficient size be adopted., , Classification of solar cooker:, (A) Direct or focusing type:, i) Point focusing type, ii) Conical reflector type, iii) | Paraboloidal reflector type, iv) Step reflector, Vv) Spherical reflection (umbrella) type., , vi) | Multi faced spherical reflector type, , (, , (, , (, , (, , (, , (, , (vii) Cylindro-parabolic reflector type, (viii) Spherical parabolic type, , (B) Indirect or box type solar cooker:, (i) Single reflector type (Box type), (ii) Multi reflection type (Solar oven), , (iii) Flat plate collector with plane side reflector, (, , iv) Flat plate collector with compound side reflector., , (C) Advanced type or Separate collector and cooking chamber type solar, cooker:, , (i) Heat transfer system type solar cooker., , (ii) | Energy storage type solar cooker, , (iii) | Combination of heat transfer and energy storage., , Indirect or Box type solar cooker:, It is a good reflector, absorber and transmitter. In this type of solar, cooker there is direct interception of solar radiation through glazing. There is, indirect interception through reflection from plane mirror is made on the black, , W Edit with WPS Office
