Construction and testing of a parabolic solar concentrator

Introduction. Solar cooking devices provide environmentally friendly energy and benefit one-third of the world's population who currently breathe toxic gases from cooking using traditional fuel resources [1]. An international standard for testing devices that directly convert sunlight into thermal energy has been developed. Uncontrollable variables such as ambient temperature, wind speed, relative humidity, and amount of solar radiation will alter the test results if they differ significantly from certain limits. [2]. Methods for estimating optical efficiency factors for solar cookers are proposed [3]. Optimizing methods in the design of a parabolic solar cookers are reviewed and analyzed [4]. Parabolic solar cookers provide higher temperatures in a shorter time for boiling, roasting, and baking than other solar cookers. Most paraboloid solar cookers use aluminum foil as a reflector. Many studies and limited modeling work on thermal storage have been presented [5]. “Фан ва технологиялар тараққиёти” Илмий–техникавий журнал №3/2025 23 Техника, технология и оборудование Mathematical model. The heat process generated in the solar concentrator is stationary, heat balance equations are used in developing its mathematical model [6], [7], [8].   T T kF I A dt dT cm a T c    . where - is the specific heat capacity of water; - mass of water; - water temperature; - time; - heat transfer coefficient; - the surface of the object placed in focus; - ambient temperature. The heat transfer coefficient is determined as follows 1 1             k   2 1 where and – respectively, the heat exchange coefficient of the liquid with the wall of the object placed at the focus and the wall with the environment; - wall thickness; - heat transfer coefficient of the wall. due to the convenience of solving using numerical methods, we use a differential scheme in the form of revealing equation (1) [6], [8].    t t t T T kF I A t   t a T c T T cm     We find the next temperature by deriving one time step from the equation (3). T c a t t t I A cm t T cm tkF T kF cm t T                1 . Using the resulting equation, it is possible to determine the change in temperature of the liquid in the solar cooker over time based on the given values. This, in turn, makes it possible to choose the geometric dimensions of the solar cooker for the considered environment. Experimental device. The diameter of the main part of the paraboloid is . The main part of the paraboloid is made of concrete and covered with square mirror pieces. The focal length of the paraboloid is . There is a mechanical screw that vertically moves the parabolic base vertically to increase the energy efficiency of the device and convert the incident solar energy into thermal energy as much as possible. To make it easier to point to the sun, wheels were installed on the three existing support parts of the base. Fig. 1. Overview of the experimental device. “Развитие науки и технологий” Научно–технический журнал №3/2025 24 Техника, технология ва жиҳозлар By obtaining different geometric dimensions of the solar cooker, its most effective values are searched (Table 1) [4]. Table 1. Options for determining geometric dimensions. Options Option 1 2 400 30 Option 2 2 700 25 Option 3 2.5 500 30 Option 4 1 1000 25 Option 5 1.5 1000 -10 Option 6 2.5 500 0 Option 7 1.5 400 10 Option 8 1 700 -10 Option 9 2.5 1000 25 Option 10 1.5 700 0 Option 11 2 500 10 Thermal-physical parameters used in theoretical calculations for a solar cooker: ; ; ; ; . Based on the parameters listed above, the following calculation algorithm was created Fig.2. Calculation algorithm of heat processes in a solar cooker. THE BEGINNING Entering geometric dimensions Determination of thermal-physical properties of the device Determination of liquid temperature No t>tmax Yes Outputting results END “Фан ва технологиялар тараққиёти” Илмий–техникавий журнал №3/2025 25 Техника, технология и оборудование Results and analysis. The results of calculations performed based on the above conditions and equations (2), (4) and the algorithms presented in Fig. 3 are presented graphically in the following drawings. Temperature, K 1 2 3 4 5 6 7 8 9 10 11 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280 time, min “Развитие науки и технологий” Научно–технический журнал №3/2025 26