建环资料外文

ICR07-A1-156

PARAMETRIC STUDIES OF THERMOACOUSTIC REFREIGERATORS

DRIVEN BY SOLAR ENERGY

Guozhong DING, Xiaoqing ZHANG, Fangzhong GUO, Suyi HUANG

School of Energy and Power Engineering,Huazhong University of Science and

Technology,Wuhan,Hubei,430074,P.R.China

Fax:86-27-87540724 email:ding_guo_zhong@https://www.sodocs.net/doc/632521905.html,

ABSTRACT

The article discusses the technical feasibility of thermoacoustic refrigerator driven by solar energy. A concept of a thermoacoustic stack (TARS)is proposed and the thermoacoutic Stirling scheme is adopted as a basic system for parametric study of a refrigeration energy transducer driven by solor energy. The relationships between pressures of input pressure, resonator pressure and output pressure and between working frequency and buffer volume are discussed, and a series of problems have been investigated by computation modeling . The main problems are the limitation of specific cold capacity in unit volume, the preferred resonance frequency and the required thermal properties of working medium in TA system. Based on the presented study an experimental prototype of the proposed system is being established.

INTRODUCTION

Over the last three decades, with the fast development of the thermoacoustic technology, thermoacousic engines(refrigerators and prime movers) reached a great benefit in terms of simplicity, reliability and cost. Moreover, the employment of nonpollution working fluids makes thermoacoustic devices being very attracitive from an environmental point of view. A comprehensive review of the principles of thermoacoustic heat transport can be found in the tutorial article of Swift[1,2].Usually solar energy power density is about 800W/m 2。For a 20m 2 air-conditioning room, 3000W refrigeration capacity supply is required. Suppose the temperatures of two heat source of a refrigerator is 400K and 300K and the effective absorb coefficient is 0.5, 400W/m 2 power can be absorbed, then Carnot efficiency is 25.0=η, the required solar energy area is 30m 2 under the condition of Carnot efficiency. The best efficiency of thermoacoustic engines is 0.4 of Carnot efficiency reported by G . Swift reported[3]. It is obvious that the refrigeration capacity is insufficient if supplied only by solar energy. Whether is there a technical feasibility of thermoacoustic refrigerator driven by solar energy? In order to solve the problem, the power density for application has to be estimated. According to current thermoacoutic refrigerator ’s levels and there are being some problems, such as power density, critical temperature and feasibility, effectiveness. A original scheme of thermoacoustic refrigerators stacks(TARS) can be exploited, it can be assembled by a lot of TARS chips according to the requirement of target objects.

The most significant problem with prior thermoacoustic engines and refrigerators is that they have a very low power density. They are typically much larger and more massive for the amount of output work they produce, than other types of engines and refrigerators. A compound engine by coupling Ceperley ’s

torus-shaped traveling-wave engine with a cylindrical standing-wave resonator, made by Greg Swift[3], in an effort to produce greater output power from the traveling-wave component, without damping the standing-wave oscillator. But the engine develops low energy density because the design still relies mainly on geometry to produce an engine that is acoustically resonant.H. Sugita et al. [4] reported an experimental study on thermally actuated pressure wave generator for space cryocooler, the maximum work amplification ratio of 1.6 was obtained in the work amplifier with solid displacers. It is the best level in thermoacoustic refrigetators so far. The paper will adopt Sugita model and the analysis of the influence of buffer volume on working frequency will be also discussed. According to the prototype, the power density of thermoacoutic refrigerator that is estimatly compared with that of target objects to decide the numbers of TARS chips. Another key problem of thermoacoustic refrigeration driven by solar energy is that the influence of temperature difference of heat sources on the performance of thermoacoustic refrigeration, which decides the technical feasibility of thermoacustic refrigerator. This will be also discussed in the paper.

1. SCHEME STUDY OF THE TECHNICAL FEASIBILITY OF THERMOACOUSTIC

REFRIGERATOR DRIVEN BY SOLAR ENERGY

The paper proposes a conceptual scheme that the key component is a thermoacoustic stacks(TARS) with resonator and buffer volume. Its optimistic target is unit volume refrigeration capacity, which decides the number of TARS in one square meter. In terms of required refrigeration, the number of TARS calculated can be compared with the maximum number TARS that can be laid in one square meter. According to the compared results, the scheme of thermoacoustic refrigerator driven by solar energy whether is with reason can be verdicted.

Power output of the TARS depends on the physical dimensions of the pistons and heat exchangers in the device, the static pressure of the working fluid and the thermal gradient across the device. The frequency of operation is determined by the engineering properties of all the heat exchangers, and to a less extent, by the geometry of the acoustic cavity. When affixed to a blackened metal absorber panel, or other radiant-energy absorbing material, and to a cooling means on its opposite face, the TAR can convert heat from radiant energy, such as sunlight, into electrical energy. In this respect, the TAR responds to a wider bandwidth of radiant energy than photovoltaic cells. It can absorb and use wavelengths that are below the photovoltaic threshold for most materials.Energy conversion efficiencies are directly related to the temperature gradient across the TAR. According to above said description, key parameters of thermoacoustic refrigerator driven by solar energy, which decided by optimistic target of unit volume refrigeration capacity, are the relationship between input pressures, resonator pressure and output pressure, and the relationship between working frequency and buffer volume,and the location of stack and wire mesh have an important effect on performance of TARS.

The calculation scheme of thermoacoutic Stirling amplifer is shown below[4]:

Fig. 1 Schematic diagram of work amplifer

1.1 Basic equation of thermoacoustic systems

The network scheme figure of resonator of Stirling engine is shown below[5]:

Fig.2 the network scheme of variation volume resonator for Stirling engine

s R is the sum of dissipation of the engine system, s p m m + is the total mass of vibration, s k is strain coefficient of spring systems, TA R is the actual load of the Stirling engine system.

It is obvious that the characteristic frequency of the system is as follows: s s m k f π21

0=

(1) where dr m ech gas s k k k k ++=, dr p s m m m m ++=0s .

This is a optimation frequency of the system for the design of thermoacousitc Stirling engine.In fact, the length ,geometry and diameter of resonator and void volume have an important effect on the resonance frequency.

The network model of resonator is expressed as follows[6]:

??

????''??????-=??????''in in end end J p a V i J p 1/012ρω (2) The network transport equation of thermoacoustic components is expressed as follows[6]:

???????????

???????+++-+-++++=??????----in in x x

x x x x x x J p e e e e z e e z e e J p 21212121212211212121211212)()(1)(γγγγγγγγγγγγγγγγγγγγγγγγγγ (3) yz 4212121++-=ααγ, yz 4212122++=ααγ

The equation is suitable for all kinds of stacks such as parallel plates, circular pores, meshes, and pin-array . the work flux is then given by[7,8]

t r u p x I ?????=11)( (4)

The symbol t >?

written as follows:

?c o s ||||5.0)(11q p x W = (5)

For modeling the output work and pressure variation of TARS, momentum equation and pressure equations respect to thermoacoustic components need to be established according to Fig. 1[11].

1.2 Influence of buffer volume on working frequency

As shown in Fig.1, the equations of continuity and mass conservation lead to

04030201P P P P ===

004030201=+++Q Q Q Q

where P is gas pressure and Q is volume flow rate.

In terms of the fluid network principle, for a pipe with length L and flow area A, when the gas viscosity is ignored, the relation between the input impedance and output impedance of the system, is given[9]

L

C L L C Z a L Z Z i a L Z Z i

Z ωωt a n 1t a n 10++= (6) where a is acoustic speed, C Z is characteristic impedance which is equal to A a /ρ to an idealized pipe, ρ is fluid density, ω is angular frequency, 0Z is input impedance, L Z is output impedance. In terms of the definition of impedance, we get:

0111104

030201=+++Z Z Z Z (7) Using Eq.(6), the frequency equation can be expressed as

011t a n 1t a n 1t a n 1t a n 10403222222

2221111111=+++++++Z Z a V i a L Z Z i a L Z Z i a V i a L Z Z i a L Z Z i

L C C L L C C L ρωωωρωωω (8) 1.3 Influence of temperature difference on performance of TARS

The thermoacoustic refrigerator driven by solar energy has a low temperature difference between the hot end and the cold ends of the regenerator (stack), a gamma-configuration engine requireds a normal 90 degree phase angle between the displacer and the power piston. Some characteristics of the low temperature difference Stirling refrigerator are as follows:(1)Displacer to power piston swept volume ratio is large;(2)Diameter of displacer cylinder and displacer is large;(3)Displacer is short;(4)Displacer stroke is small;(5)Working frequency is low.The characteristics are the same with external actuacted thermoacoustic Stirling engine.

1.4 Influence of kinds and location of stacks(regenerator) on performance of TARS

Work gain has a peak with the length of stacks under the condition of different wire mesh. The influence of

stack can be calculated by DeltaE and the result show that an optimistic length of stacks(regenerator) must be choosed.

2 THE CALCULATION RESULT AND DISCUSSION OF A PROTOTYPE SCHEME 2.1 The input work and loss of TARS

Fig. 3 Input work at an actuator

PV work is shown in Fig.3 under the condition of different working frequency。This is the input work at the compressor piston. It tells us that a larger input work under the condition of the same amplification ratio is more benificial. Fig.4 is the dissipated work at the displacer. The narrow PV shape indicates the high quality factor of the resonator to generate the standing wave.

Fig. 4 Lost work at buffer volumes

2.2 The relationship between pressures of TARS

Fig.5 Pressure variation with time

The pressure variation is shown in Fig.5. It is obvious that there are a phase angle difference between the compression piston and displacer and buffer volume. It tells us that the three components need optimistic design to produce resonant working frequency under the condition of three inherent charcteristic frequency. From Fig.5, a difference of the amplification between pressures can be found. It tells us that a larger input pressure can reach a larger output work at the condition of the same pressure ratio.

2.3 influence of buffer volume on working frequency

The computed result of the dependence of specific buffer volume on resonance frequency with helium as the working fluid is shown in Fig.6. The resonance frequency of the resonator can be decreased by means of increasing the buffer volume in each arrangement[10]. The arrangement of Fig.1 is the best for the frequency reduction.

Fig. 6 Relationship between resonance frequency and buffer volume

From Fig.6 we can find that an optimical buffer volume is coincided with the design resonance frequency.

2.4 Influence of kinds and location of stacks on performance of TARS

Fig.7 Influence of the length of stacks and wire mesh on performance of TARS

From Fig.7 the length of stack and wire mesh must be an optimistic choice.

CONCLUSION

In this paper, we proposed a prototype scheme of a thermoacoustic refrigerator driven by solar energy. The relationships between input pressure, resonator pressure and output pressure and between working frequency and buffer volume indicate the conditions of technical feasibility of a thermoacoustic refrigerator. By discussing the parameters, a Stirling scheme of thermoacoustic refrigerator driven by solar energy must adopte work amplifier and buffer volume, and correspongding to a certain resonance frequency, there is an optimical buffer volume and a stack(regenerator). By stacking the modules of the thermoacoustic stacks, a required refrigeration capacity can be capable of satisfaction.

ACKNOWLEDGEMENT

The projects is sponsored by natural science foundation of China(50676068).

REFERENCES

1. G.W.Swift, 1988,Thermoacoustic engines,J.Acoust. Soc.Amer.84(8): 1145-1180.

2. S.Backhaus and G.W. Swift, 2000,A thermoacoustic-Stirling heat engine:Detailed study, J.Acoust.

Soc.Amer.107(6):3148-3166.

3. S. Backhaus and,G..W. Swift, 1999,A thermoacoustic Stirling heat engine, Nature 399:335-338.

4. H. Sugita et al., 2004,Experimental study on thermally actuated pressure wave generator for space

cryocooler, Cryogenics 44:431-437.

5. Qiu Tu et al., 2003, Influence of temperature gradient on acoustic characteristic parameters of stack in

TAE , Int. J. Engineering Science 41(12):1337-1349.

6. Q. Tu et al., 2003,Network model approach for calculating oscillating frequency of thermoacoustic prime

mover, Cryogenics 43(6):351-357.

7. Arnott WP, Bass HE, Raspet R. 1991,General formulation of thermoacoustics for stacks having arbitrarily

shaped pore cross sections, J.Acoust. Soc.Amer. 90(6):3228-37

8. A.Tominaga, 1995,Thermodynamic aspects of thermoacoustic theory, Cryogenics 35(7):427-440.

9. J.M. Kirshner, S. Katz, 1975,Design theory of fluidic components. New York:Academic Press.

10. G.B. Chen et al., 2002,Influence of buffer on resonance frequency of thermoacoustic engine, Cryogenics

42:223-227.

11. Y. Matsubara et al., 2003,Pressure wave generator for a pulse tube cooler, Cryocoolers 12:343-348.

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基于Multisim的锁相环解调系统仿真毕业论文

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致谢 (50)

第1章绪论 1.1 研究背景 实现调频波解调的方法有很多，而锁相环鉴频是利用现代锁相环技术来实现鉴频方法，具有工作稳定失真小，信噪比高等优点，所以被广泛用在通信电路系统中。锁相环路是一种反馈电路，锁相环的英文全称是Phase-Locked Loop，简称PLL。其作用是使得电路相位同步。因锁相环可以实现输出信号频率对输入信号频率的自动跟踪，所以锁相环通常用于闭环跟踪电路。锁相环在工作的过程中，当输出信号的频率与输入信号的频率相等时，输出电压与输入电压保持固定的相位差值，即输出电压与输入电压的相位被锁住，它还具有载波跟踪特性。作为一个窄带跟踪滤波器，可提取淹没在噪声中的信号；用高稳定的参考振荡器锁定，可提供高稳定的频率源；可进行高精度的香味与频率测量等等。如今锁相环解调器在通信、雷达、测量和自动化控制等领域应用极为广泛，随着电子技术的发展，对锁相环解调的研究和应用得到了越来越多的关注。 现在通过分析与研究，加深对锁相环解调方式的理解，并根据它的原理，设计出2FSK、2PSK、2ASK的调制电路，并通过锁相环解调出来。 1.2 研究现状 锁相环解调技术的发展十分迅速，如今已经在很多领域都应用了锁相环解调的理论。可用于手机中、SDH网络中、在汽车MP3无线发射器中‘测量汽车转速都是十分典型的应用。调频波的特点是频率随调制信号幅度的变化而变化，压控振荡器的振荡频率取决于输入电压的幅度。当载波信号的频率与锁相环的固有振荡频率ω0相等时，压控振荡器输出信号的频率将保持ω0不变。若压控振荡器的输入信号除了有锁相环低通滤波器输出的信号uc外，还有调制信号ui，则压控振荡器输出信号的频率就是以ω0为中心，随调制信号幅度的变化而变化的调频波信号。当然，锁相环的许多优越性使得锁相环解调技术在很多我们周围都可以见到的物品中发挥着其巨大的功效。 如今，锁相环路理论与研究日臻完善，应用围遍及整个电子技术领域。随着通信及电子系统的飞速发展，促使集成锁相环和数字锁相环突飞猛进。现在品种齐全繁多，提高系统的工作稳定性和可靠性和小型化，目前仍朝着集成化，数字化，多用化方向迅速发展。

模具毕业设计外文翻译(英文+译文)

Injection Molding The basic concept of injection molding revolves around the ability of a thermoplastic material to be softened by heat and to harden when cooled .In most operations ,granular material (the plastic resin) is fed into one end of the cylinder (usually through a feeding device known as a hopper ),heated, and softened(plasticized or plasticized),forced out the other end of the cylinder, while it is still in the form of a melt, through a nozzle into a relatively cool mold held closed under pressure.Here,the melt cools and hardens until fully set-up. The mold is then opened, the piece ejected, and the sequence repeated. Thus, the significant elements of an injection molding machine become: 1) the way in which the melt is plasticized (softened) and forced into the mold (called the injection unit); 2) the system for opening the mold and closing it under pressure (called the clamping unit);3) the type of mold used;4) the machine controls. The part of an injection-molding machine, which converts a plastic material from a sold phase to homogeneous seni-liguid phase by raising its temperature .This unit maintains the material at a present temperature and force it through the injection unit nozzle into a mold .The plunger is a combination of the injection and plasticizing device in which a heating chamber is mounted between the plunger and mold. This chamber heats the plastic material by conduction .The plunger, on each stroke; pushes unbelted plastic material into the chamber, which in turn forces plastic melt at the front of the chamber out through the nozzle The part of an injection molding machine in which the mold is mounted, and which provides the motion and force to open and close the mold and to hold the mold close with force during injection .This unit can also provide other features necessary for the effective functioning of the molding operation .Moving

建筑-外文翻译

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