economic medium stone high efficiency concentrator for sale in nur sultan

economic medium stone high efficiency concentrator for sale in nur sultan

Evacuated tube solar collectors operate in a different way from the collectors presented so far. These usually consist of a heat pipe inside a vacuum-sealed glass tube. As the area of one tube is small, to increase the heat collection area a number of tubes are connected to one manifold although just one tube is shown in Fig. 8. Depending on the collector size 10–20 tubes are used. The ETC usually employs a fin with a tube as in FPC as shown in the cross-sectional detail of Fig. 8

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Compared to FPCs, higher temperatures can be obtained from ETCs due to the combination of selective surface which is more feasible to be used in these collectors due to the small size of the fin and the effective convection suppressor achieved because of the vacuum insulation. Like FPCs they collect both direct and diffuse radiation, their efficiency however compared to FPCs is higher at low incidence angles, which gives an advantage to the ETC in day-long performance [2]

ETCs use the liquid–vapor phase change as a heat pipe to transfer heat effectively from the collector to the heat transfer medium. The heat pipe is a sealed copper pipe, which is attached to a black thin copper fin and forms the collector absorber plate as shown in Fig. 8. Each tube is terminated to a metallic vessel which is attached to the sealed pipe and acts as a condenser. The heat pipe contains a small amount of volatile fluid (usually methanol or ethanol) which, as long as there is sunshine, undergoes an evaporating-condensing cycle. The solar heat evaporates the liquid and converts it into a vapor which due to its lower density risers to the heat sink (metallic vessel) where it condenses by transferring its latent heat to the flowing fluid, usually water. The condensed fluid then returns back to the solar collector due to gravity. The cycle is repeated as long as there is sunshine and thus solar heat to evaporate the fluid. Water or water-glycol mixture usually flows through the manifold heated up from the condensation of the vapor. The circulated heated liquid is then directed either through a heat exchanger to supply heat to a process or is stored in a storage tank for later use

evacuated tube solar collector - an overview

Perhaps the greatest advantage, which is a unique feature of the evacuated heat pipe collector, is the fact that because no evaporation or condensation above the phase-change temperature is possible, the heat pipe offers inherent protection to the collector from freezing and overheating [2]

Another important design of ETC that exists in the market, suitable for low-temperature applications, consists of an all-glass Dewar-type ETC, also called a wet-tube ETC. In this design, two concentric glass tubes are used, like a thermos, separated by a vacuum space. The selective coating is deposited on the outside surface of the inner glass tube which is domed at one end. A second larger diameter domed glass tube is then inserted on the outside of the first tube and these are joined at the open end. This design has the advantage that it is made entirely from glass and avoids the necessity to penetrate the glass envelope for the riser tube supplying vapor to the condenser used to extract the heat from the tube. This eliminates possible leakage losses and the collector is cheaper than the single envelope system [2]

The tubes are not usually installed very close to each other therefore some space is wasted between the tubes. It is thus very much cost effective to install a diffuse reflector at the back of the tubes either as a flat surface or as a gasp design as shown in Fig. 7 to utilize any, otherwise wasted, solar radiation. For example, a diffuse reflector with reflectivity, ρ = 0.6, mounted behind the tubes spaced one tube diameter apart, increases the absorbed energy in each tube by > 25% for normal incidence

The use of involute or CPC-type reflectors instead of a flat surface is used to effectively concentrate the solar radiation onto the tubes. Evacuated tube arrays with this type of stationary concentrators may have operating temperatures exceeding 150°C

evacuated tube solar collector - an overview

In another design, evacuated tubes are made with internal, inside the glass tube, reflectors. This collector design is called integrated compound parabolic collector (ICPC). The design of an ETC is shown in Fig. 8 in which at the bottom part of the glass tube a reflective material is used [16]. To allow solar radiation to reach the reflector more efficiently, no fin is used in this case, Fig. 9A, or if it is used it is of a triangular shape as shown in Fig. 9B. Depending on the operating temperature required, either a CPC reflector or a cylindrical reflector is used, which is a much more cost-effective method as it is obtained by depositing a reflective coating on the bottom semicircle of the glass tube. The CPC-type ETC combines into a single unit the advantages of vacuum insulation and non-imaging stationary concentration. This can be steady or tracking ICPC which is suitable for higher temperature applications [17]

In active solar heating systems solar energy is converted into useful heat in an active way. Collection of solar energy and its conversion into heat take place in solar collectors. Heat gained by solar collectors can be used directly or stored in a storage unit to be supplied later to the consumer in a planned way. The operation of active systems is possible thanks to mechanical devices, which enforce circulation of the working medium, ie, the heat transfer medium. Those devices are circulation pumps in water heating systems and fans in air heating systems

Active solar space heating systems are equipped with flat plate or evacuated tube solar collectors. In Europe the most popular collector type is a flat plate solar collector with a selective absorber coating. It can be mentioned that at the global scale evacuated tube collectors dominate, mainly owing to applications in Asia (but they are mainly used for DHW heating). Active solar space heating systems are always equipped with auxiliary heaters (devices or systems), working the whole year for the individual heating purposes of the user in the residential sector, public buildings, and others in the tertiary sector [9,10]. It should be emphasized that auxiliary heaters could be in the form of traditional electrical heaters (eg, electrical immersion heaters in storage tanks); traditional boilers fired by coal, gas, or oil; or nontraditional devices and systems based on renewables. There is always a heat store or stores in a space heating system. They are very often recognized as the key elements of the solar heating system. Thus the main elements of active space heating systems are as follows:

evacuated tube solar collector - an overview

The University of Chicago in collaboration with the GTE Research Laboratories (Waltham, Mass.) has designed and fabricated an advanced evacuated tube solar collector in which the outer glass vacuum envelope forms a nonimaging concentrator of the CPC type. The resulting low thermal losses and high optical throughput combine to permit high temperature operation (to ∼300ºC) in a fully stationary design. The design and fabrication methods have been described previously (1-3) and will not be discussed in detail here. The essential elements of the concentrating tube are indicated in the profile drawing inset in Fig. 1. The selective coating and geometrical concentration ratio of 1.6X, together with a vacuum of less than 10−6 torr, have reduced thermal losses per unit aperture area at 200ºC to levels comparable to those achieved by fully tracking line focus parabolic troughs. At the same time the single glazing and front surface silver reflectors maintain relatively low optical losses so that a high solar to thermal operating efficiency can be attained. The wide acceptance half angle θc = ±35º not only permits fully stationary operation (no tracking or tilt adjustments throughout the year) but also collects a large fraction of the diffuse component of insolation which is unavailable to high concentration devices

Eighty prototype tubes have been fabricated and 45 of these have been assembled into a test panel described previously (2,3) which is illustrated schematically in Fig. 1. The individual tubes have an active length of 91 cm (a portion of the total length is optically blocked to allow for seals and expansion bellows) and a width of 4.9 cm, yielding a net active collecting area for the panel of 2.0 m2. Assembly of the full panel was completed in late August 1981 and a comprehensive series of operational and performance tests was begun. This paper is an interim report on the results of these measurements conducted during the fall and winter of 1981/82 at our test facility on the campus of the University of Chicago

A major application of PCMs in the moderate-temperature range is in domestic solar hot-water applications. A heat transfer fluid, such as water or glycol, circulated through a flat plate or an evacuated tube solar collector, collects solar radiation as heat to be used to heat water for household use. This type of system can replace or supplement electric- or gas-powered hot-water heaters, for substantial energy savings and reduction in CO2 emissions. Solar hot-water systems require energy storage, sensible or latent. Water could be heated and stored in a large tank to be used directly or by heat exchange with cold water, when there is insufficient solar gain to heat cool water. This type of sensible storage is, however, necessarily quite large and massive, possibly ruling out its use in some domestic or commercial locations, especially for retrofitting where space is problematic. If, instead, latent heat storage with a PCM is used, the volume and mass requirements are much lower [54], in some instances allowing use of solar thermal hot water when otherwise only nonrenewable sources would be feasible. In this case, solar energy can be used to charge a much smaller volume of a PCM, and cool water can then be heated by circulating through a heat exchanger in the PCM tank

evacuated tube solar collector - an overview

Choice of PCM is important for this application. It is desirable to have a high melting point PCM to provide water at a higher temperature. However, if the melting point of the material is chosen based on the maximum achievable temperature in the heat transfer fluid from the collector on a day with high solar gain, on days with less ideal conditions the PCM would only melt partially, if at all. In the latter case the bulk of the PCM would only provide sensible heat storage. Transfer of heat to the PCM also is important. The time during the day when there would be sufficient solar gain on the collector to melt the PCM is limited, so heat must be transferred efficiently. Most moderate-temperature PCMs have low thermal conductivity, so the heat exchange system must be designed to promote melting across the entire PCM. Numerous solar water heater designs employing PCMs have been explored [55–59]

Fig. 5.109 presents a schematic diagram of the experiment setup which was proposed by A. Khalil et al. [43]. The saline water, which is working in a closed loop, is heated by an evacuated tube solar collector as an energy source in order to save electrical energy. Air working in an open loop is injected into the evaporation chamber from the bottom through sieve plates with 1200 holes of 1, 3, and 5 mm diameter. The characteristics of generating bubbles are changed by using different hole diameters of sieve plates. The study includes the effect of water temperature and level, air flow rate, and orifice diameter of the sieve plate on the unit performance

Figure 5.109. Experimental setup schematic diagram [43]. C.C, cooling coils; CV, control valve; DEH, dehumidifier; FM, flow meter; FWT, freshwater tank.; GL, graduate level; HUM, humidifier; P, pump; PCV, pressure control valve; PG, pressure gauge; RH, relative humidity sensor; SP, sieve plate; SWC, solar water collector; TC, thermocouple; TST, thermal storage tank

evacuated tube solar collector - an overview

The unit main components are HUM (humidifier), DEH (dehumidifier), and SWS (solar water collector). The system consists of two loops, a closed water loop and open-air loop. In the closed water loop, the hot water at (1) is pumped to the HUM inlet (2) through CV (control value) and FM (flow meter) that heats in the evacuated tube solar collector. At HUM exit (3) the hot water is pumped through CV and FM to TST (thermal storage tank) at (5). The hot salt water is circulated in a closed loop between HUM and TST. High salt concentration saline water is rejected from CV at (6). HUM is made of an acrylic plastic sheet of 10 mm thickness with 580 mm × 580 mm cross-section, and 900 mm height

In the open-air loop, air at (7) is supplied from the reservoir of a compressor containing 220 L at a pressure of 10 bar. The desired pressure and flow rate of air at (8) could be adjusted by a PCV (pressure control valve) and CV (control valve) then it is passed through the FM and PG (pressure gauge) that indicate the pressure before the HUM. The air at (9) enters the HUM through the sieve plate which is located at the bottom of the HUM. Three different sieves are used, with 1200 holes each, with 1, 3, and 5 mm hole diameter. The air flow is humidified by passing through the water level in HUM and carries vapor water to DEH. Then, the produce water through a tube is desalinated to the FWT (freshwater tank). DEH is a shell and tube heat exchanger. The shell is made of 0.7-mm-thick steel with dimensions of 400 mm × 400 mm, and 900 mm height. Inside the shell, the cooling water tube is fixed

The type of SWC is an evacuated tube solar collector. It consists of 25 evacuated glass tubes with 58 mm diameter and 1.8 m length. The capacity of the TST is 250 L. The tilt angle of the solar collector is 30° all day

evacuated tube solar collector - an overview

This solar cooling system is in the laboratory of Institute of Built Environment and Energy Efficiency, CABR, in the Shunyi District of Beijing. The total building area of the laboratory for solar air conditioning is 1850 m2. U-type glass–metal evacuated-tube solar collectors measuring 524 m2 are installed on the roof of the laboratory. The slope angle of the collector is 10°. Figure 10.14 shows the solar collectors of the system. The efficiency equation of the collector based on aperture area is η = 0.732–2.371 Ti. There is one 176 kW lithium bromide absorption refrigerating machine, one 15 m3 hot water storage tank, one 8 m3 cold water storage tank, and one monitoring system in the system. The auxiliary heat source of the system is one 232 kW biomass boiler. The lithium bromide absorption refrigerating machine has a very wide range of working temperature from 70 to 95 °C, and the COP of the machine can reach 0.7 when the input hot water temperature from the solar collector is at 70 °C

In summer 2013, the National Center for Quality Supervision and Testing of Solar Heating Systems (Beijing) tested this system. Testing was done for 4 days, from which different solar daily irradiation and solar daily irradiation was H < 8 MJ/m2, 8 ≤ H < 12 MJ/m2, 12 ≤ H < 16 MJ/m2, H ≥ 16 MJ/m2, respectively, in these 4 days. From the testing data, the energy-saving effect of the system for the whole summer can be computed and was analyzed according to the methods in GB/T 50801

Enhanced thermal conductivity of nanofluid is the key factor, which increases the performance of thermal systems including solar collectors. Some review papers (Leong et al., 2016; Muhammad, Muhammad, Che Sidik, & Muhammad Yazid, 2016; Sarsam, Kazi, & Badarudin, 2015) have highlighted the prospects of using nanofluid in a solar collector. Mahian, Kianifar, Kalogirou, Pop, and Wongwises (2013) compiled some literature and found an improvement of solar collector efficiency by using nanofluids. Nanofluids are promising to use in different types of solar collectors that include but are not limited to direct absorption, flat plate, parabolic trough, wavy, heat pipe, and evacuated tube solar collectors (ETSCs) (Hussein, 2016). According to Hussein (2016), most of the solar collectors operated in nanofluid studies are related to direct absorption and flat plate types

evacuated tube solar collector - an overview

Tyagi, Phelan, and Prasher (2009) numerically studied the efficiency improvement of a direct absorption solar collector for various parameters including nanoparticle size, concentration, and collector geometry. They observed that collector efficiency was improved according to particle concentration and collector height. However, they could not find a strong relation of particle size and collector length on efficiency. Otanicar, Phelan, Prasher, Rosengarten, and Taylor (2010) studied the advantages of using nanofluids in a smaller size of direct absorption solar collector (5×3 cm size). They observed that higher volume fraction but lower diameter of nanoparticles increased collector efficiency. Yousefi, Veysi, Shojaeizadeh, and Zinadini (2012) conducted experiments with a flat-plate solar collector and alumina–water nanofluid as shown in Fig. 8-5. They selected smaller particles of 15 nm diameter with 0.2 and 0.4 wt.% particle concentrations and the nanofluid mass flow rates were 1–3 L/min throughout the investigations. They found better efficiency for nanofluids (as shown in Fig. 8-6) where the highest efficiency enhancement was observed as 28.3% for 0.2 wt.% concentration of alumina particles. It can be seen in Fig. 8-6 that, in most cases, efficiency for 0.2 wt.% is found to be higher than that for 0.4 wt.%. Again, they observed that nanofluid with surfactant has higher efficiency than that without surfactant

Faizal, Saidur, Mekhilef, Hepbasli, and Mahbubul (2015) studied the overall performances (energetic, economic, and environmental) analyses of a flat-plate solar collector by using SiO2–water nanofluid in an outdoor environment in Kuala Lumpur, Malaysia. The schematic diagram of the experiment is shown in Fig. 8-7. Unlike, Yousefi et al. (2012), they found higher efficiency for higher particle concentration as well as for higher volume flow rate of the fluid (as can be seen in Fig. 8-8). They reported that the use of SiO2 nanoparticles in the solar collector can save 26.2% energy, and also that there will be 170 kg less CO2 emissions

Figure 8-7. A schematic diagram of the experiment: 1—flat plate solar collector, 2—water tank, 3—heat exchanger, 4—flow meter, 5—drain, 6—pump, 7—valve, 8—thermocouple (plate temperature), 9—thermocouple (working fluid out), 10—thermocouple (working fluid in), 11—thermocouple (ambient), 12—thermometer, 13—TES 1333R solar meter, 14—PROVA (AV M-07) Anemometer, 15—data logger, 16—pressure transducer

evacuated tube solar collector - an overview

In comparison to the flat plate solar collector, the ETSC is promising for better thermal performance as it has lower heat losses (Sabiha, Saidur, Hassani, Said, & Mekhilef, 2015). Mostly, flat-plate solar collectors are used for low-temperature applications, whereas ETSC are used in high-temperature processing. ETSC can increase temperature more than the flat-plate solar collector. In stationary case, evacuated tube collector temperature range is 50–200°C, whereas it is only 30–80°C for a flat-plate collector (Kalogirou, 2004)

There are few studies available about ETSC operated with nanofluids. Mahendran, Lee, Sharma, Shahrani, and Bakar (2012) studied the performance of an ETSC using TiO2–water nanofluid. The experiment was conducted in Pahang, Malaysia, on a clear sky day when the highest solar irradiance was 958 W/m2. They observed that the system efficiency was increased up to 16.67% by using the 0.3 vol.% of the nanofluid. Hussain, Jawad, and Sultan (2015) studied the thermal efficiency of an ETSC by using Ag–distilled water and ZrO2–distilled water nanofluids with 1–5 vol.% of nanoparticles. They used three different mass flow rates (30, 60, and 90 L/h·m2). They observed that nanofluids improved the thermal performance of the solar collector. Comparatively, better efficiency was observed for the Ag nanoparticles. The reasons could be the higher thermal conductivity and lower particle size of Ag. In a recent study, Ghaderian and Sidik (2017) used Al2O3–water nanofluid in an ETSC. They changed the volume fractions of nanoparticles and mass flow rates. They observed higher efficiency with increasing nanoparticle concentrations and mass flow rates. Sabiha et al. (2015) studied the energy performance of an ETSC with single-walled carbon nanotubes (SWCNTs)–water nanofluid as shown in Fig. 8-9. The system was operated on both a cloudy day and a clear sky day in Kuala Lumpur, Malaysia. Firstly, the authors operated the ETSC system with water. Later, nanofluids with three different volume concentrations from 0.05% to 0.2% were used in place of water to be heated up by the ETSC and the mass flow rates of the working fluids were changed as 0.008, 0.017, and 0.025 kg/s correspond to 1, 2, and 3, respectively, in Fig. 8-10. They observed that higher mass flow rate and higher nanoparticle volume concentration could increase the efficiency of the system. However, maximum outlet temperature and temperature difference were observed at higher nanoparticle volume concentrations with lower mass flow rate (as can be seen in Fig. 8-10). [Section (8.3) is adapted from Mahbubul et al. (2018), copyright (2018), with permission from Elsevier.]

Here, Qu is the useful energy gained, m. is the mass flow rate of working fluid, Cp is the specific heat capacity of fluid, To is the outlet temperature, and Ti is the inlet temperature of the solar collector

evacuated tube solar collector - an overview

They (Sabiha et al., 2015) developed a correlation as Eq. (7.130) to predict the efficiency of an evacuated tube solar collector when operated with nanofluid by considering the improved thermal conductivity of nanofluids

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