Available online at ScienceDirect. Energy Procedia 74 (2015 )

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1 Available online at ScienceDirect Energy Procedia 74 (015 ) International Conference on Technologies and Materials for Renewable Energy, Environment and Sustainability, TMREES15 Impact of Temperature Gradient on Thermoacoustics Refrigerator Nasser Yassen * General Mechanics department, Faculty of mechanical and Electrical Engineering, University Of Damascus.Syria Abstract In an extended search for suitable parameters of the project base on "Solar thermoacoustic refrigerator" funded by University of Damascus, which has built in the faculty, early softwares were developed to be a core of sizing Thermoacoustic cooler and prime mover, included the modeling equations for designation. Since high technologies were required, it was necessary to change the design strategies in order to allow the usage of low technology especially in stack fabrication, as well as to achieve building large sized tunnel that is used in air conditioning based on solar prime mover. In this paper, the new design strategy were modified to obtain a new software for sizing a Thermoacoustic device that would simply be built manually, in addition to find the impact of affecting temperature gradient over the stack. Some parameters like the heating capacity, cooling capacity, mean pressure, and stack spacing were chosen to fit the needs, fabrication, and simplicity requirements. The optimum temperature gradients were included in this paper Published The Authors. by Elsevier Published Ltd. This by is Elsevier an open Ltd. access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD). Peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) Keywords: Thermoacoustic, solar refrigeration, solar prime mover, stack sizing software, optimum temperature gradient. Nomenclature a K cp angular frequency sound velocity Gas thermal conductivity Gas density Gas heat capacity * Mob: , address: Dr.naser58@hotmail.com Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Euro-Mediterranean Institute for Sustainable Development (EUMISD) doi: /j.egypro

2 Nasser Yassen / Energy Procedia 74 (015 ) l yo f A Z() Qc Qh Qcn Qhn D Po Pm tm k v kn xs xn Pr Tm Tmn B Ls Lsn A Wn W Lt -l k l D1 D Lt Gas Viscosity Half stack plate thickness half plate spacing Operating frequency Stack cross sectional area Stack perimeter acoustic impedance cooling power heating power Dimensionless cooling power Dimensionless heating power Drive ratio Dynamic Pressure, Average Pressure Average temperature thermal penetration depth viscous penetration depth Normalized thermal penetration depth Stack center position Normalized center position Ratio of isobaric to isochoric specific heats Prandtl Number Temperature difference Normalized Temperature difference Blockage ratio or porosity stack length Normalized stack length Stack cross sectional area Dimensionless acoustic power Acoustic Power the length of the small diameter tube Wave number, Length of the large diameter tube Diameter of large tube Diameter of small tube Total length of resonator 1. Introduction A project of building a friendly environmental refrigerator based on "Thermoacoustics" for the refrigeration laboratory in the Faculty of Mechanical and Electrical Engineering in Damascus University is done. The project consists of a refrigerator attached to a modulating driver that is driven by a computer which generates an electronic sinuous wave with specific parameters. These waves are amplified then emitted through speakers to create a sound wave which drives the thermoacoustic refrigerator that has no moving part. The sinuous wave generator were an electronic circuit solar powered to generate a stand wave in the thermoacoustic refrigerator, which has four essential parts, known as driver, resonator, stack, and two heat exchangers. The proposed system and the four parts are labelled in Figure1: The common thermoacoustic refrigerator parts are shown in Figure (1). However, there are other models for thermoacoustic refrigerators. Nevertheless, every design carries out the four basic functions shown down in some way [5].

3 1184 Nasser Yassen / Energy Procedia 74 (015) PV Module Dc-AC Convertor Battary with charger Modulator f= Hz Ampl. Hhx Chx Driver Ls compliance Proposed TAR Figure.1-a: proposed thermoacoustic solar refrigerator Chx Hhx Driver Slope Stack compliance Resonator Figure.1-b: Essential parts of a thermoacoustic refrigerator The driver creates either a standing or travelling wave in the refrigerator. The wave created by the driver is generally at or near the resonant frequency of the resonator in which the wave oscillates. The stack is located within the resonator and serves in creating more surface area across which the Thermoacoustic effect can take place. Finally, the heat exchangers are used to take heat from a refrigerated region and pump heat to the outside. These components are each described individually in details in the coming sections. Russel [1] describes a cheap and easy way to build thermoacoustic refrigerator. The refrigerator is for demonstration purposes only; hence it is not very powerful nor efficient. However, it is an excellent starting point for those interested in the field. Actually, Tijani [11] published a paper describing the process used to design a thermoacoustic refrigerator from scratch in details. The project we are working on is nearly finished, but the stack required a higher technology which is not available. Alternative solutions were sought, one is bigger spacing. In this paper the equations that are being used has reviewed including gas thermo physical properties for air with the specific pressure of 0.1 [MPa], with the final design of the thermoacoustic refrigerator.

4 Nasser Yassen / Energy Procedia 74 (015 ) Working Gas thermo physical Properties Based on the National Institute of Standard and Technology (NIST) Data [9], the polynomial equations which describe thermo physical properties for Air as a function of tm when pm=0.1 [MPa], are: (t)= e-16*t^ e-13*t^ e-10*t^ e-08*t^ e-05*t^ *t cp(t)= e-3*t^ e-0*t^ e-17*t^ e-14*t^ e-1*t^ e-11*t^ e-07*t^ e-05*t (t)= e-3*t^ e-1*t^ e-18*t^ e-15*t^ e-1*t^ e-09*t^ e-08*t^ e-05*t (t)= e-16*t^ e-14*t^ e-11*t^ e-08*t^ e- 05*t^ *t (t)= e-17*t^ e-14*t^ e-11*t^ e-08*t^ e- 05*t^ *t pr(t)= e-3*t^ e-0*t^ e-17*t^ e-14*t^ e-1*t^ e-10*t^ e-08*t^ e-05*t a(t)= e-15*t^ e-1*t^ e-09*t^ e-06*t^ e- 4*t^ *t Modified design Strategy The developed strategy is based on Tijani's strategy, but has been modified to fit the specific requirements [13]; it contains the four essential parts: stack, resonator, heat exchangers, and driver. The strategy is shown in figure (). Design equations are listed in table 1(begins with stack and ends with acoustic driver) Table (1): Design equations Used in software (sizer) element STACK Resonator Design Equations K y k k k k f m c p 1.1 mcp f mcp y o Lsn = -0.3 * (Cop) * (Cop) * (Cop) xn = * (Lsn) * (Lsn) * (Lsn) Lsn =Ls.k; Xs=xn.k y0 B y l Tm Tc Tmn. tanxn 1B. Lsn 0, Po 1 k D 1 Pr. Pr kn kn a, Pm,, knd sin. x n 1 Pr Pr Qcn Pr. 1 Pr Qcn Qc / Pm a A LsnD 4. A Qc / Qcn. Pm. a kn k / y Pr Pr. kn kn W n -1B cos. xn. 1 Pr sin. xn Wn W / Pm a A /4-resonator D/D1 =0.54 l x s+ls/. x D1 cot(k l)= tanklt l D 1 L t 1 1 Pr atan l kn LsnD 4. B D / D1 k cot(k l)

5 1186 Nasser Yassen / Energy Procedia 74 ( 015 ) Cold heat exchanger Hot heat exchanger Acoustic driver 1 1 u p x o 1 sink x m a optimum length of the cold heat exchanger ~x1 optimum length of the Hot heat exchanger ~4x1 W W t s COPt =Qc/Wt W res W chx W hhx Start Gas Data, y0, B, Tmn, D,COP,Qc f, Xn,Lsn, Qcn Ls,xs,A,D1,D, Lt,COPt,CHx, HHx,Ws Ls,xs,A,D1,D, Lt,COPt,CHx, HHx,Ws End Figure.: Modified design strategy of a thermoacoustic refrigerator [13]

Nasser Yassen / Energy Procedia 74 (015 ) 118 1191 1187 3. Modified Software and Results The modified software was developed in VB6. The interface is shown in figure ().

of tm, yo, and B on COPt and for the specified range. The calculated results are saved in a text file with the name of desired fixed Parameters.

6 Nasser Yassen / Energy Procedia 74 (015 ) Modified Software and Results The modified software was developed in VB6. The interface is shown in figure (). Figure 3-a: Input form showing desired Parameters used to calculate refrigerator sizes Figure 3-b: Output form showing calculated refrigerator sizes The command button named "Auto" calculates impacts of tm, yo, and B on COPt and for the specified range. The calculated results are saved in a text file with the name of desired fixed Parameters. Results will be saved in a text file with the name of desired fixed Parameters. For several values of "B" the functions COP and were graphed (figure 4). As shown in figure 4-b (as an example), COP decrease by tm increasing while is increase. To determine Maximum t, the function fu=copt.

7 1188 Nasser Yassen / Energy Procedia 74 ( 015 ) COP Air tm=-5 [C o ] Pm=0.1 [MPa] 0 B= B=0.1 B=0.3 B=0.5 B= Figure 4-a: Output for calculated "COPt" as a function of "tm" for all range of B when: Gas= Air, and tm=-5 [C]. tm COPt Air, B=0.9 tm=-5 [C o ] Pm=0.1 [MPa] Figure 4-b: Output for calculated "" and "COPt" as a function of "tm" for B=0.9 when: Gas= Air, and tm=-5 [C]. 4. Results As an example, results of calculation listed in table. Figure 4 shows the graphed values of calculation. tm

8 Nasser Yassen / Energy Procedia 74 (015 ) Table (): results of calculation when B=0.7 (desired), t m = -5[C o ], Gas=Air, p m =1 [bar]. "B" "tm [C] " "" "COPt" "" "COPf" Max{"" "COPf"}= >1 it becomes Prime mover

9 1190 Nasser Yassen / Energy Procedia 74 ( 015 ) fu 0.8 Max T B=0.3 B=0.5 B=0.7 B= Figure 5: Output for calculated "fu= COPt" as a function of "t" for several B values when: Gas= Air, and tm=-5 [C]. T Input tm Pm Qc D B tm Yo gas Data -5[C o ] 0.1[MPa] 30[Watt] [C o ] 0.5 [mm] [Air] Table (3): final design sizes W Lt f l Ls Xs D1 D Chx Hhx Driver [Watt] 14.3 [cm] 385[Hz] 0.06 [mm] 33 [mm] 3 [mm] 3. [cm] [cm] [mm] 4 [mm] -6.9 [Watt] 5. Conclusion Every blockage ratio has a temperature gradient that affects the operation mode (prime mover refrigerator). The higher "B" is, the higher "tm" is. fu= COPt is the parameter which determines the optimum values. The suitable o maximum tm for our case is 45[CP P] since it counters maximum "fu" when B=0.5. Similar results are reported in [13] fig (9.6-c). Air is good for each prime mover and heat pump. Pm has no impact on the performance of refrigerator using "Air" with B>0.8. But it has for prime movers with B<0.7. The lower "B" is, the higher the impact is. To use air in prime movers with low pressure, "tm" must be higher and "B" must be lower. References [1]. Tijani,M.E.H Loudspeaker-Driven Thermoacoustic Refrigeration Ph.D. Thesis University of Eindhoven, Netherlands. []. M.E.H Tijani, J.C.H Zeegers and A.T.A.M Waele,00. Construction and Performance of a Thermoacoustics Refrigerator Cryogenics 4 (00) [3]. M.E.H Tijani, J.C.H Zeegers and A.T.A.M Waele, 00. The Optimal Stack Spacing for Thermoacoustic Refrigeration J. Acoustical Society of America 11(1)

10 Nasser Yassen / Energy Procedia 74 (015 ) [4]. Wheatley,J., Hofler,T., Swift,G.W., Migliori,A Understanding Some Simple Phenomena in Thermoacoustics with Applications to Acoustical Heat Engines J. Acoustical Society of America. 74(1). [5]. Daniel George Chinn. " PIEZOELECTRICALLY-DRIVEN THERMOACOUSTIC REFRIGERATOR". Master of Science, University of Maryland, College Park. 010 [6]. Normah M Ghazali, Prof Dr Azhar Abd Aziz, Srithar Rajoo, Nor Aswadi Che Sidek. "ENVIRONMENTALLY FRIENDLY REFRIGERATION WITH THERMOACOUSTIC", Fakulti Kejuruteraan Mekanikal, Universiti Teknologi Malaysia. Research Vote No: [7]. Hofler TJ. "Thermoacoustic refrigerator design and performance". Ph.D. dissertation, Physics Department, University of California at San Diego, [8]. Garrett SL, Adeff JA, Hofler TJ. Thermoacoustic refrigerator for space applications. J Thermophys Heat Transfer 1993;7: [9]. National Institute of Standard and Technology (NIST) Database. [10]. Ivan Johansen. "Graph". Versions 4.3 build [11]. M.E.H Tijani, J.C.H Zeegers and A.T.A.M Waele,001. Design of a Thermoacoustics Refrigerator Cryogenics 4 (00) [1]. D. A. Russel and P. Weibull, Tabletop thermoacoustic refrigerator for demonstratio demonstrations, Am. J. Phys. 70 (1), 131 (00) [13]. Panhuis Peter," Mathematical Aspects of Thermoacoustics", Eindhoven University of Technology Library ISBN , (009). [14] konaina and yassin, Thermoacoustic solar cooling for domestic usage sizing software, Energy Procedia 18 ( 01 ) [15] Konaina.et. al. Thermoacoustic prime mover sizing software, Energy Procedia 50 ( 014 )

Available online at ScienceDirect. Energy Procedia 74 (2015 ) Ekhlas Alkhwildy * Issa Morad

Available online at ScienceDirect. Energy Procedia 74 (2015 ) Ekhlas Alkhwildy * Issa Morad Available online at www.sciencedirect.co ScienceDirect Energy Procedia 74 (05 ) 643 65 International Conference on Technologies and Materials for Renewable Energy, Environent and Sustainability, TMREES5