Milind Atrey

Indian Institute of Technology Bombay | IIT Bombay · Department of Mechanical Engineering

Availability of ultra-high pressure ratio turboexpanders present numerous options to the helium liquefier/refrigerator designer as it allows to conceptualize a compact plant by making use of high-pressure process compressors and eliminates placement of turboexpanders in series for large pressure heads in the process cycle. Setting out with this obj...

Experimental investigations of two variants of a high pressure ratio cryogenic turboexpander, from a new series of turboexpanders for Bhabha Atomic Research Centre (BARC), are presented in the article. Both the variants are designed based on an earlier reported enhanced midstream method. The new turboexpanders are designed with larger turbine impel...

In Current work, experimental investigations are carried out on a high-frequency thermoacoustic engine used for driving a pulse tube cooler. During the course of work, two different working gases namely Helium and Nitrogen, two different lengths of engine stack, two heater housing configurations and two different configurations of the ambient heat...

Experimental investigations are performed on a half-wavelength standing wave type thermoacoustically driven thermoacoustic refrigerator also known as TADTAR. Present TADTAR device conceived to be a quarter wavelength standing wave type thermoacoustic engine (TAE) coupled to a quarter wavelength standing wave thermoacoustic refrigerator (TAR). A TAE...

An enhanced midstream design method for cryogenic turbomachines is presented in this article by reformulating that given by Hasselgruber and Balje. The enhanced formulation incorporates non-idealities such as turbomachinery inefficiency and flow angle deviation. Moreover, certain other issues faced by high speed cryogenic turbomachinery operating i...

The idea of adsorption based refrigerator was conceived in the year 1961 by Vickers. The present work reports development of a sorption compressor based J-T refrigerator with R134a alone as a working fluid and a three component mixture of R134a, Ethane and Methane. Commercially available activated carbon, obtained from coconut shell, is used as an...

Because of the absence of any moving components at the cold region, low vibration and high reliability, two stage GM type pulse tube refrigerator (PTR) is nowadays preferred compared to conventional GM refrigerator for cooling of superconducting magnets, SQUIDs, and cryopumping applications. The second stage regenerative material plays an importan...

To meet the growing demands of vibration free and compact cooling devices for various space and military based application, Pulse tube cryocoolers (PTC) are in focus. Several modifications have been attempted in recent past to increase the performance of the PTC. These includes different geometric configurations, phase shift mechanism, multi-stagin...

Chill down of cryogenic transfer lines is a crucial part of cryogenic propulsion as chill down ensures transfer of single phase fluid to the storage tanks of cryogenic engines. It also ensures single phase liquid flow at the start of the engine. Chill down time depends on several parameters such as length of the pipe, pipe diameter, orientation, ma...

Thermoacoustic engines (TAEs) are devices which convert heat energy into useful acoustic work whereas thermoacoustic refrigerators (TARs) convert acoustic work into temperature gradient. These devices work without any moving component. Study presented here comprises of a combination system i.e. thermoacoustic engine driven thermoacoustic refrigerat...

Mixed refrigerant Joule-Thomson (MRJT) cryocoolers can produce cryogenic temperatures with high efficiency and low operating pressures. As compared to the high system pressures of around 150–200 bar with nitrogen, the operational pressures with non-azeotropic mixtures (e.g., nitrogen-hydrocarbons) come down to 10–25 bar. With mixtures, the heat tra...

Experimental investigations are carried out using a specially developed three-layer plate fin heat exchanger (PFHE), with helium as the working fluid cooled to cryogenic temperatures using liquid nitrogen (LN2) as a coolant. These results are used for validation of an already proposed and reported numerical model based on finite volume analysis for...

In J–T cryocoolers operating with mixed refrigerants (nitrogen-hydrocarbons), the recuperative heat exchange takes place under two-phase conditions. Simultaneous boiling of the low pressure stream and condensation of the high pressure stream results in higher heat transfer coefficients. The mixture composition, operating conditions and the heat exc...

Thermoacoustic Refrigerators (TARs) use acoustic power to generate cold temperatures. Apart from the operating frequency and the mean temperature of the working medium, the charging pressure and the dynamic pressure in the TAR govern its attainable cold temperature. The effect of charging pressure on the dynamic pressure in a loudspeaker driven gas...

Compact plate-fin heat exchangers (PFHE) having very high effectiveness (>0.95) are key equipment of modern helium liquefaction/refrigeration systems. Effectiveness (e) of these heat exchangers strongly influences the overall system performance. Apart from basic fluid film resistances, various secondary parameters such as axial heat conduction (AHC...

The work presented aims to develop a numerical model which can be used to design a vapour shielded liquid helium (LHe) Dewar without LN2 Shield. This model can compute the position of shields and the Net Evaporation Rate (NER) based on the capacity and number of vapour cooled shields (VCS) given by the user. The effect of neck dimensions on the hea...

Thermoacoustics have been recent area of investigations due to its noticeable advantages like simplicity, structural stability, absence of moving component, high reliability, minimal or no maintenance etc. In addition to these, thermoacoustic devices can use different noble gases and their mixtures as working fluid as well as they can use low grade...

Pulse Tube Cryocoolers (PTCs) have been investigated in recent times with the focus on achieving much lower temperature and reliable operation. Lower temperatures can be obtained by cascading the stages of the PTC. These stages can either be gas coupled or thermal coupled. This paper presents the design and development of two different configuratio...

In many cryogenic applications, Joule-Thomson (J-T) effect is used to produce low temperatures. The isenthalpic expansion of gas results in lowering of temperature only if the initial temperature of the working fluid is below its characteristic temperature, called the inversion temperature. Inversion curves are helpful in studying the inversion tem...

Applications of thermoacoustic engines are not limited to driving pulse tube cryocoolers. The performance of a thermoacoustic engine is governed by various design parameters like type of resonator, stack geometry, frequency, type of working gas etc. and various operating parameters like heat input, charging pressure etc. It is very important to arr...

Research on Stirling type Pulse Tube Cryocooler (PTC) is focused on achieving lower temperatures by cascading the stages or by multi-staging. Multi-staging can be done either by gas coupling or by thermal coupling of the stages. In the thermal coupling option, either a two stage cooler can pre-cool a single stage PTC to reach lower temperatures or...

The overall efficiency of a mixed refrigerant Joule-Thomson (MR J-T) cryocooler is governed by the performance of the recuperative heat exchanger. In the heat exchanger, the hot stream of the mixed refrigerant undergoes condensation at high pressure while the cold stream gets evaporated at low pressure. The pressure drop in the low pressure stream...

Transient analysis of single stage GM type double inlet pulse tube cryocooler is carried out using a one dimensional numerical model based on real gas properties of helium. The model solves continuity, momentum and energy equation for gas and solid to analyse the physical process occurring inside of the pulse tube cryocooler. Finite volume method i...

The recuperative heat exchanger is the most critical component of a mixed refrigerant Joule-Thomson cryocooler. The heat transfer process in such a heat exchanger takes place under two-phase conditions due to simultaneous boiling of the cold stream and condensation of the hot stream. This results in higher heat transfer coefficients as compared to...

Transient analysis of single stage GM type double inlet pulse tube cryocooler is carried out using a one dimensional numerical model based on real gas properties of helium. The model solves continuity, momentum and energy equation for gas and solid to analyse the physical process occurring inside of the pulse tube cryocooler. Finite volume method i...

The objective of this work is to study the effect of the reservoir pressure and volume on the cool-down behavior of a miniature Joule-Thomson (J-T) cryocooler considering the distributed J-T effect. As the supply pressure to the J-T cooler reduces in case of a reservoir with finite capacity, the volume and the initial pressure of the reservoir are...

Cryosurgery is a widely regarded minimally invasive surgery for treatment of various types of cancers. It involves destruction of cancer cells within a limited spatial domain by exposing them to very low temperatures while minimizing injury to surrounding peripheral healthy tissues. Surprisingly, despite increasing demands for cryosurgery, there ha...

The work presented aims to develop a numerical model which can be used to design a vapour shielded liquid helium (LHe) Dewar without LN2 Shield. This model can compute the position of shields and the Net Evaporation Rate (NER) based on the capacity and number of vapour cooled shields (VCS) given by the user. The effect of neck dimensions on the hea...

The aim of this work is to develop a transient program for the simulation of a miniature Joule-Thomson (J-T) cryocooler to predict its cool-down characteristics. A one dimensional transient model is formulated for the fluid streams and the solid elements of the recuperative heat exchanger. Variation of physical properties due to pressure and temper...

A novel technique to measure the cryogenic temperature distribution of a helically coiled Tube-in-Tube (TIT) heat exchanger using Fiber Bragg Grating (FBG) array has been reported. The measured temperature distribution will help in estimating the heat exchanger efficiency and will be used to investigate its performance. The measurement of the tempe...

In mixed refrigerant Joule–Thomson cryocooler, a multi–component mixture of nitrogen–hydrocarbons undergoes evaporation and condensation process in a helical coiled heat exchanger simultaneously at different pressures. Experimental data and the empirical correlations for predicting heat transfer coefficients of evaporating and condensing streams of...

The performance of a miniature Joule–Thomson cryocooler depends on the effectiveness of the heat exchanger. The heat exchanger used in such cryocooler is Hampson-type recuperative heat exchanger. The design of the efficient heat exchanger is crucial for the optimum performance of the cryocooler. In the present work, the heat exchanger is numericall...

The heat exchanger of a mixed refrigerant Joule–Thomson (MR J–T) cryocooler forms a very important component of the cycle. The working fluid in such a heat exchanger consists of a mixture of gases which undergo condensation and boiling heat transfer simultaneously. The design of these heat exchangers, therefore, is crucial; however, heat transfer d...

A model based on finite volume analysis is presented here for multistream plate fin heat exchangers for cryogenic applications. The heat exchanger core is discretised in both the axial and transverse directions. The model accounts for effects of secondary parameters like axial heat conduction through the heat exchanger metal matrix, parasitic heat...

To achieve lower temperatures is a subject of recent research and development activities in the field of pulse tube cryocoolers. To reach a temperature of 20 K, multi-staging is necessary in Stirling-type pulse tube cryocoolers. In the present work, Sage software is used to design a three-stage gas-coupled as well as thermal-coupled pulse tube cryo...

Cryosurgery is fast gaining popularity as a minimally invasive surgery for treatment of various types of cancers. It involves destruction of cancer cells within a limited spatial domain by exposing them to very low temperatures while minimizing injury to the surrounding healthy tissues. The volumetric extent of the critical isotherm in the ice ball...

The overall performance of a mixed refrigerant Joule-Thomson (MR J–T) cryocooler depends on the efficiency of the heat exchanger used to cool the refrigerant prior to J-T expansion. The multi-component refrigerant mixture gets condensed and evaporated simultaneously at different pressures in the recuperative heat exchanger which is responsible to i...

Modern helium liquefaction/refrigeration systems employ compact plate-fin heat exchangers having very high effectiveness (>0.95). Performance of such systems is a strong function of effectiveness of heat exchangers used. The calculation of heat exchanger effectiveness in such cases needs considerations of several secondary parameters apart from bas...

The present work aims to determine thermo-physical properties such as mass density, specific heat capacity, viscosity, enthalpy and thermal conductivity of argon at cryogenic temperatures and high pressures up to 20 MPa. The deviations from the ideal gas law led to development of many empirical models based on equation of state (EOS) such as van de...

A capillary tube is commonly used in small capacity refrigeration and air-conditioning systems. It is also a preferred expansion device in mixed refrigerant Joule-Thomson (MR J-T) cryocoolers, since it is inexpensive and simple in configuration. However, the flow inside a capillary tube is complex, since flashing process that occurs in case of refr...

The need of a cooler with no electromagnetic interference and practically zero vibration has led to sorption compressor based Joule-Thomson (J-T) coolers. These are useful for sophisticated electronic, ground based and space borne systems. In a Sorption compressor, adsorbed gases are desorbed into a confined volume by raising temperature of the sor...

A one-dimensional theoretical model is developed to describe the transient state phenomena in a low cooling standing wave Thermoacoustic Refrigerator. The model is based on the Linear Theory of Thermoacoustics. It uses Implicit Finite Difference method to calculate the temporal evolution of temperature and steady state temperature distribution in...

Thermoacoustic devices have drawn considerable attention of researchers due to their several advantages like simplicity of construction, maintenance free operation etc. It is known that the working gas for these systems should have lower prandtl number for their better performance. Gaseous mixtures are found to be more suitable due to their lower v...

Highly efficient Pulse Tube Cryocooler (PTC) is subject of recent research and development activities. High efficiency can be obtained by increasing the available refrigeration effect at desired temperature. Various geometrical and operating parameters affect the performance of PTC. Pressure drop is one of the significant parameters. A major pressu...

The recuperative heat exchanger governs the overall performance of the mixed refrigerant Joule–Thomson cryocooler. In these heat exchangers, the non-azeotropic refrigerant mixture of nitrogen-hydrocarbons undergoes boiling and condensation simultaneously at cryogenic temperature. Hence, the design of such heat exchanger is crucial. However, due to...

The design of the recuperative heat exchanger used to pre-cool the refrigerant mixture prior to J-T expansion is crucial for the efficient operation of the mixed refrigerant Joule- Thomson (MR J-T) cryocooler. The multi-component non-azeotropic refrigerant mixture undergoes boiling and condensation heat transfer simultaneously in the heat exchange...

A standing wave type thermoacoustic pressure wave generator for 300 Hz operating frequency is designed and developed for helium as a working fluid. The device is designed as a half wave length resonator. A parallel plate type SS 304 stack is designed and fabricated. An electric heater is used for heat supply to the hot end heat exchanger while a...

The requirement of a cryocooler with minimum vibrations for space borne system and highly sophisticated electronic devices for ground application, has led to the development of sorption compressor type J-T cryocooler. The adsorption capacity of any adsorbent material increases with an increase in pressure and decreases with an increase in temperatu...

This paper reports the Simulation, Design, fabrication and preliminary testing results of a single channel, open cycle miniature Joule-Thomson (JT) refrigerator. Miniaturization of the refrigerator is aimed at providing an alternative that would suffice both the requirements of milli watt cooling as well as high portability owing to its light weigh...

The requirement of cooling with minimum vibrations for space borne system and highly sophisticated electronic devices for ground application has led to the development of sorption type compressor. In a sorption compressor, adsorbed gases are desorbed into a confined volume by raising temperature of the sorption bed. This results in increase in gas...

Thermoacoustic Refrigerators (TARs) use acoustic power to generate cold temperatures. Apart from the operating frequency and the mean temperature of the working medium, the charging pressure and the dynamic pressure in the TAR govern its attainable cold temperature. The effect of charging pressure on the dynamic pressure in a loudspeaker driven gas...

Thermoacoustic Refrigerators (TARs) use acoustic power to generate cold temperatures. Apart from the operating frequency and the mean temperature of the working medium, the charging pressure and the dynamic pressure in the TAR govern its attainable cold temperature. The effect of charging pressure on the dynamic pressure in a loudspeaker driven gas...

The requirement of a cryocooler, with practically zero vibrations in space borne surveillance system and highly sophisticated electronic devices for ground applications, have led to the development of non-mechanically driven Sorption compressor type J-T cryocooler. The sorption capacity of any adsorbent is a function of temperature and adsorption p...

Multistage high frequency Pulse Tube Refrigerators (PTR) are subject of recent research and development activities. In multistage PTR the stages are cascaded to provide cooling for the next stage. This paper reports on design and experimental investigations on the Stirling type two stage split PTR with U type configuration for both the stages. The...

The mixed refrigerant Joule–Thomson (MR J–T) cryocoolers have a wide application area covering the temperature range from 80K to 200K. The significant advantages of the system are simplicity of its design and working reliability with high level performance. The present paper discusses the experimental results of MR J–T cooler with different flammab...

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 pred...

There are plenty of complex physical phenomena which remain to be studied and verified experimentally for building an optimized superconducting magnet. The main problem for experimental validations is due to the unavailability of suitable sensors. This paper proposes a Fiber Bragg Gratings (FBG) sensor for this purpose which allows access to the lo...

Pulse tube refrigerators (PTRs) are categorized into various types based on the type of phase shifting mechanism involved in it: Basic pulse tube refrigerator (BPTR), Orifice pulse tube refrigerator (OPTR), Double inlet pulse tube refrigerator (DIPTR) and Inertance tube pulse tube refrigerator (ITPTR). ITPTR has thin capillary tube (called as Inert...

Pulse Tube Refrigerator (PTR) is a special class of regenerative cryocooler where there is no moving part at the cold end. Due to this, it has inherent advantages of higher reliability, reduced vibrations and light weight. Based on the arrangement of regenerator and pulse tube in a PTR, there are various configurations possible like inline, U-shape...

Limitations of disciplined compressors led to the development of linear, electromagnetically driven compressors which utilize either moving coil or moving magnet type linear motor drive. Linear compressors are more reliable than the conventional compressors because of fewer moving parts, flexure bearings and lubrication free operation. The power dr...

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 mode...

Feasibility of employing Fiber Bragg Gratings (FBG) for measuring thermodynamic parameters of superconducting (SC) coils has been studied. The distribution of mechanical stress and temperature inside the coil are important for an optimized magnet design. Standard sensors with electrical connections like resistance thermometer and strain gauges can...

A metal recoated fiber Bragg grating sensor has been designed, fabricated and tested to study its temperature response at cryogenic temperature around 15 K. Metals like aluminium (Al), copper (Cu), lead (Pb) and indium (In) are considered for recoating the FBG sensors. Indium recoated FBG (IRCFBG) sensors showed a higher sensitivity at around 15 K...

Many researchers have shown that pulse tube refrigerator (PTR) performance depends significantly on the pressure waveforms generated by the rotary valve in a Gifford McMahon (GM) type PTR. Some literature has shown this effect experimentally for various waveforms. The design of the rotary valve therefore is very critical in order to generate an opt...

A two-stage, split Stirling cryocooler with a capacity of 2 W at 100 K and 0.5 W at 50 K is designed. A second order cyclic analysis is used to decide the final geometry of the unit. A compressor with an opposed piston configuration is developed. A flexure stack suspended piston and displacer are used. A moving coil linear motor is developed. Senso...

Mixed Refrigerant Joule Thomson (MR J-T) cryocoolers have obvious advantages, such as low cost, high reliability, higher cooling effect at 80 K, low vibrations and simplicity in design layout. As a result of this, their use for different applications has become a major threat to conventional cryocoolers such as Stirling coolers. The performance of...

In the current work, cyclic analysis has been utilised for simulation of two-stage miniature Stirling cryocooler. In cyclic analysis, the cycle is divided into equal number of intervals. Pressure and volume variation for each interval are calculated. These pressures and volumes are then utilised for calculating the ideal refrigerating effect (ʃP*dV...

Oxford Instruments Superconductivity has developed a new closed cycle cooling circuit based on a Pulse Tube Refrigerator (PTR) to cool a Cold Probe for NMR applications. By replacing the existing Gifford McMahon (G-M) cryocooler with a PTR, levels of vibration at the probe can be reduced by an order of magnitude, essential for NMR experiments. Anot...

High field NMR spectrometers have been an essential tool for biomolecular scientists for many years. They have been instrumental in the pursuit of understanding of the structure, function and dynamics of proteins and other biological molecules. In addition, NMR is increasingly used for small molecule applications such as metabonomics, providing cap...

The ratio of swept volume of the compression space to the swept volume of the expansion space is an important design parameter for the Stirling cryogenerator. The swept volume ratio can be varied by changing diameter either of the piston, displacer or both of them. In this paper cyclic simulation of Stirling cycle has been carried out to predict th...

Counter flow heat exchangers are commonly used in cryogenic systems because of their high effectiveness. In addition to operating and design parameters, the thermal performance of these heat exchangers is strongly governed by various losses such as longitudinal conduction through wall, heat in leak from surrounding, flow maldistribution, etc. Desig...

The present paper gives a thermodynamic analysis of the Collins helium liquefaction cycle with two reciprocating expanders. The results of the analysis make it clear that, for a given efficiency of expanders and effectiveness of heat exchangers, there exists an optimum mass flow fraction of total helium gas mass flow rate that should be diverted th...

A computer model developed recently to determine the performance of free-displacer Stirling cryocoolers was extended to include an optimization routine. This was applied to a two-stage, free-displacer Stirling cryocooler to determine the optimized dimensions for the displacer. The design parameters taken for the optimization were the diameters and...

Computer modelling of cryocoolers has emerged as a major research area in the last 4–5 years. In this paper, the authors describe a computer model for two-stage Gifford-McMahon cycle cryocooler. The model is developed based on certain simplifying assumptions. It starts with the computation of ideal refrigeration effect that can be obtained from the...