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1、A review of water heating system for solar energy applications☆A(yù). Jamar a, Z.A.A. Majid b, W.H. Azmi a,c,?, M. Norhafana d, A.A. Razak ea Faculty of Mechanical Engineering, Universiti Malaysia Pahang, 26600 Pekan, Pahang
2、, Malaysia b Kulliyyah of Allied Health Sciences, International Islamic University of Malaysia, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia c Automotive Engineering Centre, Universiti Malaysia Pahang, 26600 Pe
3、kan, Pahang, Malaysia d Department of Mechanical Engineering, Kulliyyah of Engineering, International Islamic University Malaysia, P.O. Box 10, 50728, Kuala Lumpur, Malaysia e Faculty of Engineering Technology, Universit
4、i Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Pahang, Malaysiaa b s t r a c t a r t i c l e i n f oAvailable online 25 May 2016 Solar energy is one of the widely used renewable energy that can be harnessed eithe
5、r by directly deriving energyfrom sunlight or indirectly. Solar water heating system, on the other hand, is one of the applications of solarenergy that has drawn great attention among researchers in this field. Solar col
6、lectors, storage tanks and heattransfer fluids are the three core components in solar water heater applications, which are reviewed in thispaper. This paper discusses the latest developments and advancement of a solar wa
7、ter heater based on thethree basic components that may affect the thermal performance of the system. It also reviews the developmentof various types of solar collectors in solar water heater, including both the non-conce
8、ntrating collectors (flatplate collector, evacuated tube collector) and the concentrating collectors (parabolic dish reflector, parabolictrough collector). All these are studied in terms of optical optimization, heat los
9、s reduction, heat recuperationenhancement and different sun tracking mechanisms. Among the non-concentrating and concentratingcollectors, the parabolic dish reflector collectors show the best overall performance. The use
10、 of nanofluids as aheat transfer fluid was also discovered in this paper.© 2016 Elsevier Ltd. All rights reserved.Keywords:Solar energySolar water heating systemSolar water heaterRenewable energyContents1. Introduct
11、ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1792. Development of solar water heating system . . . . . . . . . . . . . . . . . . . . . .
12、. . . . . . . . . . . . . . . . . . . . . . . . . . 1793. Solar water heating system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1793.1. Active system . .
13、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1803.2. Passive system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14、. . . . . . . . . . . . . . . . 1803.2.1. Thermosiphon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1803.2.2. Integrated collector storage . . . . . . . . .
15、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814. Components of solar water heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16、 1814.1. Solar collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814.1.1. Solar collector selection . . . . . . . . . . . . . . . . . . . . . .
17、 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1824.1.2. Types of solar collector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1824.2. Storage tank . . . . .
18、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1834.3. Heat transfer fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19、. . . . . . . . . . . . . . . 1845. Latest development and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1856. Conclusions . . . . . . . . . . . . . .
20、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21、. . . . . . . . . 185References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185International Communications in Heat and Mass Transfer
22、76 (2016) 178–187☆ Communicated by W.J. Minkowycz.? Corresponding author.E-mail addresses: akasyahj@gmail.com (A. Jamar), amzafri@iium.edu.my (Z.A.A. Majid), wanazmi2010@gmail.com (W.H. Azmi), norhafana@yahoo.com (M. Nor
23、hafana),amirrazak@outlook.com (A.A. Razak).http://dx.doi.org/10.1016/j.icheatmasstransfer.2016.05.0280735-1933/© 2016 Elsevier Ltd. All rights reserved.Contents lists available at ScienceDirectInternational Communic
24、ations in Heat and Mass Transferjournal homepage: www.elsevier.com/locate/ichmtelectricity and fossil fuels used for water heating [49]. Generally, thesystem is very simple because it requires only sunlight to heat thewa
25、ter. It works when the working fluid is brought in contact with adark surface (high absorptive) that is exposed to sunlight, which thencauses the temperature of the fluid to rise [3]. This fluid may be causedby the water
26、 being heated directly, which is called a direct system, or itmay be a heat transfer fluid (such as a glycol or water mixture) that ispassed through some form of a heat exchanger and called an indirectsystem. These syste
27、ms can be classified into two main categories; activesystem and passive system [50] as shown in Fig. 1. The active system canbe divided into two which are the open loop and close loop systemwhereas the passive system use
28、s the system of thermosiphon andintegral collector storage (ICS).Almost all solar water heating systems used in temperate climatesare active systems that make use of pumps to circulate the heat transferfluids [24]. Theor
29、etically, these systems commonly use flat plates orevacuated tube collectors, which absorbs both diffused and directsolar radiation and function even under clouded skies. Water is heatedin the collectors and a pump is us
30、ed to circulate a water glycol mixtureused as the heat transfer fluid [51]. A solar controller triggers the pumpwhen the difference between the temperature of water at the bottom ofthe tank and the heat transfer fluid at
31、 the outlet from the collectorexceeds a set value. A solar coil at the bottom of the hot water tank isused to heat water. This fluid has some desirable properties such aslow freezing and high boiling points. Their ease o
32、f operation and lowcost makes them suitable for low temperature applications below80 °C. An auxiliary heating system is used to raise the water tempera-ture during periods when there is less heat available from the
33、solarcollector [52]. The solar water heating system proves to be an effectivetechnology for converting solar energy into thermal energy. Theefficiency of solar thermal conversion is around 70% when comparedto the solar e
34、lectrical direct conversion system that has an efficiencyof only 17% [53].There are two types of solar water heating systems; active andpassive solar heating systems. The active system consists of the openloop system and
35、 closed loop system; whereas the passive system con-tains thermosiphon and integrated collector storage (ICS).3.1. Active systemActive solar water heating systems use collectors to heat a fluid, stor-age units to store s
36、olar energy until needed and distribution equipmentto provide the solar energy to the heated spaces in a controlled manner[54]. In combination with conventional heating equipment, a solarwater heating system provides the
37、 same levels of comfort, temperaturestability and reliability as a conventional system. A building that hasbeen heated is often referred to as a “solar house”. The term solarhouse is also applied to buildings that includ
38、e integral parts of the build-ing elements that admit, absorb, store and release solar energy and thusreduce the needs for supporting energy to comfort heating [55]. Insimple definition, the active system uses electrical
39、 pumps [56], valvesand controllers to circulate water or other heat transfer fluids troughthe collectors [57]. This system is also known as forced circulationsystem and it can be an open loop (direct) active system or a
40、closedloop (indirect) active system [50]. Open loop (direct) active systemheats the actual household water in the solar collectors. Once heated,the water is pumped into a storage tank and then piped to spouts foruse in h
41、ome [58]. Since this system uses regular household water inthe collectors, it should only be used in areas that do not experiencefreezing conditions. However, a closed loop (indirect) active systemuses heat to transfer f
42、luids that is usually a water-antifreeze mixture[58]. After the heat-transfer fluid is heated in the solar collectors, it ispumped into a storage tank where a heat-exchanger transfers the heatfrom the fluid to the househ
43、old water [59].3.2. Passive systemOn the other hand, a passive solar water heating system can be well-defined by comparing with the active system in terms of two bases; thefirst is the role of the collector and storage t
44、hat are combined togetherinto a structure of the building. For example, windows and rooms canserve as collectors while storage can provide sensible heat of thebuilding structure and their contents as temperature changes
45、[46].Meanwhile, the second is that this system delivers no moving fluids(mechanical energy) but fluid and energy is moved by virtue of the tem-perature gradients established by absorption of radiation [5]. In otherwords,
46、 the passive system uses the method of natural convection heattransfer [56] and without mechanical devices [54], to circulate wateror transfer fluids between a collector and an elevated storage tankwhich is placed above
47、the tank [60] as shown in Fig. 2. In this system,if the fluid is gradually heated up, it will result in the decreasing of thefluid density. Starting with the collector, for example the flat plate col-lector (FPC), it col
48、lects the radiation from the sun and at that moment,the fluid in the collector will absorb the heat, causing the fluid densityto decrease as well as affecting the upsurge of fluid to the top of the col-lector and gushing
49、 into the storage tank. Afterward, the fluid will turnout to be cool at the bottom of the tank and flow back to the collector.This phenomenon will circulate continuously until there is no sun asthe source of energy [50].
50、3.2.1. ThermosiphonThe best examples of passive systems are the thermosiphon in Fig. 3and the integrated collector storage (ICS) [61]. The thermosiphonsystem is the most common type of solar water heating system in thema
51、rket and most commercially available [62]. It uses this type of roof-mounted flat plate collector, storage tank and connecting pipe together[63,64]. However, caution and care should be taken when installingsuch a system
52、as the combined weight of the solar collector, storagetank and the water itself might be too much for the design of thesupporting roof [65]. Moreover, the thermosiphon's concept is justsimple and requires less mainte
53、nance due to the absence of controlforces and instrumentations [28]. The efficiency of a collector dependsFig. 1. Solar water heating system. Fig. 2. Passive solar heating system [50].180 A. Jamar et al. / International
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