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ItemExperimental Investigations on 20 K Stirling-Type Two-Stage Pulse Tube Cryocooler with Inline Configuration(Georgia Institute of Technology, 2008-05) Tendolkar, M. V. ; Narayankhedkar, K. G. ; Atrey, M. D.Multistaging in a Stirling-type Pulse Tube Refrigerator (PTR) is employed to reach the temperature range of 20 K and below. Various configurations of two-stage PTRs can be used, where the former stage provides precooling for the next stage. There are several candidate twostage configurations, each with advantages and limitations. These include: inline, ‘U’ type, coaxial, and combinations of these. In addition to the above, the configuration can be of integral or split type, depending if the compressor is directly attached to the pulse tube assembly or is remote. The present work describes experimental investigations carried out on an integralconfiguration Stirling-type two-stage PTR with inline pulse tubes for both stages. This pulse tube configuration is thermodynamically advantageous as it involves the least dead space and flow resistance. Inertance tubes are used as the phase shift mechanism for both stages. The secondstage alone has an added double-inlet valve along with the inertance tube. A linear compressor is used to provide the PV power to the PTR and is maintained at 350 W. The investigations are carried out for different operating conditions.
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ItemInvestigations on a Standing Wave Thermoacoustic Refrigerator(Georgia Institute of Technology, 2008-05) Dhuley, R. C. ; Atrey, M. D.The dynamic pressure inside a Thermoacoustic Refrigerator (TAR) is an important parameter which governs the cold temperature and the cooling power. The present work aims to investigate the effect of two operating parameters: the resonant frequency and charging pressure on the dynamic pressure inside a TAR. A simple theoretical model is used to predict the behavior of dynamic pressure with charging pressure and resonant frequency. Experimental investigations have been carried out using a gas filled column driven by a moving coil loudspeaker. It has been observed that at small excitation levels, the results from theory and experiment closely match. Large deviations have been observed due to non linear effects at high excitation levels. One such non linear effect, periodic shocks, has been observed.
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ItemPhasor Analysis of Pulse Tube Refrigerator(Georgia Institute of Technology, 2008-05) Mohanta. L. ; Atrey, M. D.A phasor diagram for a pulse tube refrigerator (PTR) is a vectorial representation of mass flow rate, pressure, and temperature at different locations as a function of time. With the help of a phasor diagram, the operation of different types of pulse tube refrigerators can be well understood. Phasor analysis based on these diagrams gives an idea regarding the underlying complex phenomena of the PTR. In the present work, a simplified model has been presented based on the assumption that there is no phase difference between temperature and pressure throughout the working space. The phasor analysis is extended to a two-stage Orifice Pulse Tube Refrigerator (OPTR) and to a Double Inlet PTR (DIPTR). The important contribution of the work is that it highlights the condition for which the DIPTR will work better than the OPTR.
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ItemTheoretical and Experimental Investigation of 30 K Single Stage GM-Type Pulse Tube Cryocooler(Georgia Institute of Technology, 2008-05) Desai, S. ; Desai, K. P. ; Naik, H. B. ; Atrey, M. D.Theoretical modeling of thermodynamic performance plays an important role in the design and development of pulse tube cryocoolers. In the present work, a thermodynamic model of a GMtype double-inlet pulse tube cryocooler has been developed. It includes calculation of ideal refrigeration power, various losses, and hence net refrigeration power. An experimental setup was designed and fabricated to carry out experimental investigations on the GM-type double-inlet pulse tube cryocooler. Experiments were conducted, and the results obtained were used for comparison with the isothermal model developed in the present work. The effect of orifice valve opening, double-inlet valve opening, and frequency on the performance of cryocooler was studied in terms of net refrigeration power and no-load temperature.
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ItemTheoretical and Experimental Investigation of Flow Straighteners in U-type Pulse Tube Cryocoolers(Georgia Institute of Technology, 2008-05) Badgujar, A. D. ; Atrey, M. D.The U-type Pulse Tube Cryocooler (PTC) involves a change in the direction of gas flow as it proceeds from the regenerator to the pulse tube. The sharp U-bend has an adverse effect on pulse tube cooling action due to formation of eddies and undesirable mixing in the cold end of the pulse tube. The present work deals with experimentation and CFD modeling related to U-type PTCs. Two cases of ‘U’ bends have been studied; gradual ‘U’ bends and sharp ‘U’ bends. Experimentation has been carried out using copper screens of 100-mesh size as flow straighteners. The optimum performance in terms of low temperature for the case of a gradual U bend was achieved with a stack of 18 flow-straightener screens. The no-load temperature for this case of a gradual ‘U’ bend, with and without flow straighteners, was 57.7 K and 88.8 K, respectively, for a charging pressure of 16 bar. When the gradual 180 degree bend at the cold end was replaced by a sharp U bend, the no load temperature increased from 88.8 K to 137 K without flow straighteners. In order to understand the role of flow straighteners in PTC, a CFD model was developed in FLUENT. The flow straighteners are modeled as a homogeneous porous medium. The results show that the flow straighteners significantly affect velocity patterns in the pulse tube. The theoretical study showed that there exists an optimum number of flow straighteners which improve the cooling power and efficiency of the pulse tube cryocooler. This was in agreement with the experimental results obtained earlier.
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ItemDesign of Standing Wave Type Thermoacoustic Prime Mover for 300 Hz Operating Frequency(Georgia Institute of Technology, 2008-05) Mehta, S. M. ; Desai, K. P. ; Naik, H. B. ; Atrey, M. D.Thermoacoustically driven pulse tube cryocoolers are gaining significant interest in the recent time due to the key advantage of complete absence of moving components for the entire system. The present work gives a simple design procedure for a 300 Hz Standing Wave-Type Thermoacoustic Prime Mover having a parallel plate type stack. The necessary code is written in MATLAB for solving the Rott’s wave equation. The code is validated by comparing the results with those available in the literature. The work further reports the effect of operating and geometrical parameters on the performance of the standing wave-type thermoacoustic prime mover. The system performance, mainly in terms of acoustic power and pressure ratio, is influenced significantly by the operating and geometrical parameters. The operating parameters are heat input, hot end temperature, frequency, filling pressure. The geometrical parameters are the stack length, the stack position, the resonator length and the dimensions of the acoustic amplifier, etc.