Thermodynamic and Operational Fundamentals in .NET Creator 39 barcode in .NET Thermodynamic and Operational Fundamentals

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Thermodynamic and Operational Fundamentals use none none creation toattach none on none GS1-8 refrigerant vapor 6 Qcond condenser 7 mrefrig (liquid). 1 generator Qgen 1 mconc solution heat exchanger mdilute 2 mrefrig (vapor) 8 refrigerant pump solution pump Qevap 8 evaporator 3 absorber Qabs m6h6 m5 h5 generator Qgen m1 h1 m4 h4 mrefrig h2 absorber Qabs mdilute h2 Figure 2.23: Sc none none hematic of the absorption cycle, highlighting the components, heat flows and flow rates used in solving the problem. Subscripts on variables reflect the state point numbering of Table 2.

5.. The refrigerant mass flow rate mrefrig is obtained from the prescribed cooling power and the specific enthalpy values in Table 2.4:. mrefrig = Qevap h8 - h7 3068 = 1.322 kg none for none s 1 . 2509.

71 - 188.41. Then the mass f low rate of the concentrated and dilute solutions, mconc and mdilute, respectively, are m conc = mrefrig CR = (1.322) (13.31) = 17.

60 kg s 1 m dilute = mconc mrefrig = 17.60 1.322 = 16.

28 kg s 1 . Now we are set to calculate the principal heat flows in the cycle. We have been given the evaporator heat extraction, Qevap = 3068 kW.

The absorber, condenser and generator heat flows are calculated as follows (with the numerical subscripts referring to the state points listed in Table 2.5)..

Cool Thermodyna none for none mics Mechanochemistry of Materials 1) Absorber heat removal Qabs = m dilute h 2 + mrefrig h8 m4 h 4 = (16.28) (185.2) + (1.

322) (2509.71) (17.60) (126.

10) = 4114 kW .. 2) Condenser he at rejection Qcond = m 6 h6 m7 h7 = (1.322) (2683.05) (1.

322) (188.41) = 3298 kW . 3) Generator heat input Qgen = m1 h 1 + m6 h6 m 5 h 5 = (16.

28) (261.39) + (1.322) (2683.

05) (17.60) (196.64) = 4342 kW .

. Finally, we che none none ck the overall energy balance: Qin = Qgen + Q evap = 4342 + 3068 = 7410 kW Qout = Qcond + Qabs = 3298 + 4114 = 7412 kW . According to the First Law, Q in and Q out should be equal (the very small difference here is due to round-off error)..

D. THERMOACOUST IC CHILLER In thermoacoustic refrigeration, high-intensity sound waves are used instead of compressors to set up a standing wave in a closed resonator tube filled with inert gases, and in which a stack of plates is inserted with heat exchangers at its ends [Swift 1988; Garrett & Hofler 1992] (see Figure 2.24).

The gas is compressed by the acoustic standing wave, warms up, and transfers heat to the stack plates. The temperature difference that develops along the stack plates is called the thermoacoustic effect. A heat exchanger rejects part of this heat, and the remaining cooled gas is used to chill the load via the other heat exchanger.

The process is cyclic. The basic but involved physics and thermodynamics underlying thermoacoustic processes are already well understood [Wetzel & Herman 1997]. The two predominant irreversibilities are viscous dissipation in the working fluid, and finite-rate heat transfer at the heat exchangers.

The most notable use of the thermoacoustic refrigerator to date has been as a cryocooler in satellites [Garrett & Hofler 1992], where using low input power and having large temperature spans (100 200 K) are critical (in contrast, for example, to commercial mechanical chillers. Thermodynamic and Operational Fundamentals acoustic generator power input hot-side heat exchanger stack of plates cold-side heat exchanger resonator Figure 2.24: Schematic of a thermoacoustic chiller. which have far none none higher input power and far smaller temperature spans). We ll return to the thermoacoustic chiller in 10 to examine how its performance data compare with the universal aspects of the chiller models that will be developed in the ensuing chapters..

E. THERMOELECTR IC CHILLER When an electrical current I is passed through two dissimilar thermoelectric materials (denoted by A and B in Figure 2.25, usually metal or semiconductor alloys), one heats up while the other grows colder.

Referred to as the Peltier effect, it forms the basis for thermoelectric refrigeration [Ioffe 1957; Goldsmid 1960]. A principal virtue of thermoelectric chillers is that they are solid state devices with no moving parts and no fluids. They accept DC power input, and can be temperature controlled with great precision.

The niche applications for thermoelectric devices are miniaturized cooling loads, unlike conventional mechanical chillers. They are commonly used in military, aerospace, consumer product and medical instrument applications, among others. The dimensions of just the thermoelectric module itself are typically 2.

5 2.5 0.5 cm, and some commercial units are as small as 0.

4 0.4 0.2 cm.

A complete commercial thermoelectric chiller package may occupy only around 300 500 cm 3 of space. Typically, commercial thermoelectrics comprise semiconductors, most commonly bismuth telluride. The semiconductor material is doped to.

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