Thermal evaluation of an indirect air heating system using solar collectors

One of the current problems is the use of energy obtained from fossil fuels, especially due to the emission of greenhouse gases. An option to replace fossil fuels is the use of alternative energies such as solar or wind energy. The objective of this work is to carry out a thermal and energy analysis of an indirect air heating system that receives energy through solar collectors that operate with water as the thermal fluid used in a food dehydration system, in order to know the efficiency of the system and therefore, make improvements to the circuit, in addition to the characterization of the water storage tank of the system, obtain the amount of energy that can be provided and the behavior of temperatures at different operating flows. According to the methodology, the temperature profile was obtained inside the hot water tank in two modes of operation (heating and energy extraction) reaching temperatures of 50 to 70 ° C, where the optimum temperature for drying is found and in turn reaching an efficiency 84%, compared to a conventional drying system that uses LP gas.

CFD MODELING OF VORTEX AFTERBURNING OF BIOMASS GASIFICATION PRODUCTS IN A FLUIDIZED BED FURNACE

CFD modeling of the afterburning of biomass gasification products in a fluidized bed furnace with a vortex supply of secondary air has been carried out. The effect of secondary air heating on the ecological characteristics of flue gases has been determined. Modeling has shown that gasification products swirl in the primary chamber with the formation of a central vortex, which obeys the law of solid-body rotation. An increase in the temperature of the secondary air leads to an increase in its tangential velocity and, as a consequence, to an increase in centrifugal mass forces. Calculations have shown that with an increase in the secondary air temperature, the maximum of the kinetic energy of turbulence shifts to the periphery and increases in absolute value. This results in more efficient mixing of the central (producer gas) and peripheral (secondary air) streams. As a result, this leads to a more complete combustion. The influence of secondary air heating on the ecological characteristics of the furnace has been determined. As a result of air heating from 30° C to 300° C, the concentration of carbon monoxide decreases by more than 1.5 times. The concentration of nitrogen oxides practically does not change and amounts to 3.5 mg /nm3.

Experimental Investigation on Effect of Inclination Angle of a Flat Plate Solar Air Collector

This study investigates the effect of inclination angle of a flat plate solar air collector in Kampar, Malaysia. Flat plate solar air collectors have been investigated since the early 1950s for air heating and crop drying. Their performances under natural convection air cooling are very similar to a photovoltaic (PV) panels for power production. A PV panel becomes hot when operating under hot weather which will affect the efficiency and lifespan. The panel could be cooled down by providing an air duct underneath which allowing natural convection air circulating inside the duct. The degree of cooling would depend upon the angle of inclination of the panel. This paper presents some experimental results on the effect of inclination angle on the performance of a flat plate solar air collector under natural convection air cooling.

Optimization of the operation mode of regenerative heat exchangers

The paper considers the operation of regenerative heat exchangers with a fixed checkerwork. Such a checkerwork allows for high-temperature heating of gases and is made of refractory materials with a relatively high heat capacity, but low thermal conductivity. The article presents calculations of regenerative heat transfer for devices with block checkerwork. It is shown that a decrease in the equivalent diameter of the channel d e leads to an increase in the average air heating temperature over the period. An increase in the relative water section of the checkerwork f also leads to an increase in the air heating temperature, but only to a certain limit. On the one hand, with an increase in the relative water section, the specific heat exchanger surface increases. On the other hand, at a certain value f, the accumulating mass of the checkerwork significantly decreases, and as a result, the air heating temperature decreases. For the same reason, for checkerwork with a high value of the relative water section, it is necessary to reduce the duration of the heating/cooling periods of the checkerwork. The paper also examines several types of compact checkerwork, which are very promising, including in heat storage systems. It is noted that the use of such attachments in conventional regenerate heat exchangers is impossible. First, it is necessary to increase the water section of the heat exchanger and significantly reduce its height, otherwise, the pressure loss will increase sharply. Secondly, it is necessary to significantly reduce the duration of the heating/cooling periods, otherwise, due to more intense heat exchange, the air temperature at the outlet of the regenerative heat exchanger changes much more than in the block checkerwork.

Laboratory observation of interior surface heat transfer at balcony door

This paper informs about laboratory experiments studying heat transfer phenomena at the interior side of balcony doors. A well-insulated testing space representing a typical room with a balcony door equipped with floor heating and warm air heating was used. In the first step, an opaque panel with similar thermal transmittance as a triple glazed balcony door was installed in the opening for reference. A combination of temperature measurements and particle imaging velocimetry (PIV) was used here to study the surface heat transfer in detail for both types of space heat distribution and obstacles by curtains. From the measured data, the surface heat transfer coefficient along the height of the door was evaluated and discussed.

Determining the speed and acceleration of the separator for grass leaf part in horizontal and vertical directions

Vitamin-grass flour is the main component of mixed fodders intended for all types of livestock and poultry. Earlier and currently, the vitamin-grass flour has been prepared from legumes by a high-temperature drying technique. However, existing techniques have high operating costs and require very expensive technical tools. To reduce the specific operating costs and the price of equipment in the production of VGF, a technique has been proposed that involves the main drying of grass to a moisture content of 30‒35 % on a swath while the post-drying of grass is performed in a small-sized channel under the haystack without air heating. Next, the dried mass is pre-crushed. At the same time, the delicate leaf part of the hay, while falling between the side walls of hammers and counter-hammers, is ground and finely crushed, and the stems are processed into large fractions. From pre-crushed hay, the leaf part is separated and fed into the crusher to produce flour. In this case, the main machine that determines the performance of the line is the separator of the leaf part of the grass. The results of the theoretical research have established the speed and acceleration of hay movement on the surface of the sieve. These values determine the productivity of separation of the leaf part from pre-crushed hay and the reliability of the selected structural and technological scheme of the separator. The production tests have confirmed the reliability and economic efficiency of the proposed technique. Comparing the proposed technique for obtaining vitamin-grass flour by existing high-temperature methods has shown that the carotene content in flour was 1.6 times higher while the specific operating costs and equipment price were 6‒7 times lower