Box with reflectors contd:-
Box with double reflector/Box with three reflectors/Box with four reflectors/
Box with four plus four reflectors
The Gosh type cooker would work well during summer in most part of India but Reflector during winter, at least in north India, additional boosters would be essential and this has resulted in the development of the box-type cookers with double reflectors. In Type BDM 1 (Figure 45) Agarwal adds (1981) another reflector at right angles to the first, his drawings do not suggest any mechanisms for tilting, which would be essential. But een without such tilting mechanisms Agarwal reports faster cooking during October. In Type BDM 1a, (Concept VIII, the author suggests two reflectors, both with tilting facility. This design worked well reducing the cooking time (Figure 46).
Concept IX, Type BDM 2, (Figure 47) presented by the author in this review envisages incorporating the cooker with two reflectors inside the house as illustrated (Kundapur 1995). Advantages are many and it is very easy to incorporate the cooker in the house. In our country lowery easy to incorporate the cooker in the house. In our country low-roofed huts are common and in all such cases this design could be used.
The author feels that even in multi-storied buildings, such extensions could be provided in every floor at proper height to place this type or other designs of cookers, such that, cooking could be done from inside the house.
The above concept was conceived during 1980's but I do not wish to have any claims on the same. But I note with interest that such a design is now being used, and finds a mention in SCI site. The Wall Oven found at SCI site is of this type, but only difference is that it does not have a reflector where as my design has two reflectors.
Wall Oven ( Source SCI site )
Source:- TIDE., March 1998, 8-1, pp 1-37, For Comments, suggestions,contributions contact < ashok_kundapur@yahoo.com>
In this type of cooker, one of the reflectors has to be adjusted seasonally while the other requires daily adjustments. In Cheema's ( 1984 ) design the lid opens to form double reflector one above the other.
Prof. Cheema had presented an interesting variation ( BDM 3 ) as early as 1983. This is a double reflector design one on top of the glazing and another reflecting the light thropugh a side window. The arrangement appears to be interesting and Cheema reports a stagnent temperature of 206º C compaared to 164 º C of ordinary coker.
To improve the performance further three reflector designs were proposed and the Reflectors Concept X (Type BTM 1, Figure 48) proposed by the author does just that. Two configurations were tried, they did not, however, reduce the cooking time by one thirds, besides, adjustment was also cumbersome. Of the two proposals, the one with configuration 2 was better. The reflectors could be adjusted and tilted individually after setting. The box has to be turned to face the sun. the space between the mirrors could be fitted with triangular mirrors to increase the efficiency further. It is further proposed that these additional mirrors would come as ‘add-ons’ (to reduce cooking time) rather than as part of the cooker.
Better and ideal confugaration could be to have a two triangular reflector along the main reflector as shown in the diagram. As Prof. Bowman had observed a triangular reflector ccasts abetter image on the cooker. ( Fig 47b )
Box type cooker with three reflectors available in the market
Details and principles of the design. ( source SCI )
Source:- TIDE., March 1998, 8-1, pp 1-37, For Comments, suggestions,contributions contact < ashok_kundapur@yahoo.com>
Halacy (1974) had gone a step further by suggesting a cooker with four reflectors (Figure 49). Bowman, Blatt (1979), who tried to build such a cooker, found that adjustment of the reflectors took a long time and required several supports. The cooking time was not reduced by one-fourth as compared to the single mirror cooker. However, it is essential that a designer know about the existence of such a design, as it would avoid any further attempts in designing such a cooker.
Recently this design, namely Halacy type 4 reflector seems to have surfaced and we find it being referred to in Solar Cooker International (SCI) site.
Halacy type Cooker ( source SCI site )
Box with four plus four reflectors
Maria Telkes (1959) was probably the first lady to design a solar cooker,Reflectors popularly known as the Telkes design which was one of the best in the series and could develop a temperature of 2250 C. The box was a rectangular double-walled insulated box with a door on each side. The box had double glazing fixed at the top, and the there were four main reflectors set at an angle of 60o to the horizontal. The corner spaces between these main reflectors were fitted with four triangular mirrors. The insulated box had a cradle frame to hold the cooking vessel and to assist in tilting. The whole cooker was mounted on to an ‘A’ type frame. Hoda (Type BFF 1a) suggests some improvement in the stand to reduce the cost. Type BFF 1b, designed in Senegal, has a funnel – like reflector. Telkes also suggested a modification such as a box with an aperture set at 450. Bowman, Blatt (1978) tried to maximize the dimensions of the Telkes cooker. The outer ‘A’ type of stand was eliminated, but the inner cradle was retained. Alzek reflectors were used instead of glass mirrors. A new type of insulation material foam glass was used to make the box. A temperature of 2250C was reported (Figure 50). The author tried this variation, that is concept XI, here at Udupi, but as foam glass was not available, a box of GI sheets was used and insulated with mineral wool. Regular glass mirrors a transparent PVC sheet was used on top. To effect the tilting, a steel frame support was incorporated. The assembly worked well but compared to the single or double mirrored Gosh type design the cooking time was not reduced to one-fourth as expected. (Type BFF le, Figure 51).
As the Telkes design was costly but more efficient, Rose (1981) of VITA designed a cooker based on similar design but with cardboard (Type BFF 1f). Muzumdar (1980) made a similar design also with cardboard, but the box had only a single polyester sheet as glazing, the reflectors were also made of cardboard and coated with aluminized polyester. The cost of the unit was claimed to be just Rs. 95/- (Type BFF 1g). Type BFF 1h is a patented design from the US (Patent no. 4 292 957). Weyer (1980) uses GI sheets as reflectors (Type BFF li).
Source:- TIDE., March 1998, 8-1, pp 1-37, For Comments, suggestions,contributions contact < ashok_kundapur@yahoo.com>
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