Introductory Chapter: Low-Temperature Technologies

1. Introduction

This book has introduced low-temperature technology, its aspects, and applications. Further, it has covered low-temperature resources and their deployment technologies. Sterilization and preservation techniques and their engineering and scientific aspects are incorporated. Ultra-low-temperature refrigeration is a crucial requirement in some research and industrial applications, which is considered in depth in this issue. Azeotropic, zeotropic, and non-zeotropic refrigerants and their mixtures are highlighted in detail along with their applications and economic aspects. Cryogenics, low temperature, and vacuum systems for industrial applications are incorporated. Global energy resources, energy crisis, the principle of conservation of energy, alternative sources of energy for low-temperature technologies, and their application in refrigeration, process industries, and electronic equipment and parts manufacturing industries are considered here. Enhancement of efficiency of the system along with the economic aspects is incorporated. At the end, modeling, design efficiency, and enhancement of efficiency of low-temperature cooling process are elaborately discussed.

2. Overview of low-temperature technologies

In a refrigeration system, the used refrigerant could be either a pure compound or a mixture (blend) of two or more compounds or refrigerants. R12, R22, and R134a are the pure refrigerants, whereas the mixture refrigerants are R502, R404A, and R407C [1]. A mixture of compounds used in a refrigeration loop can behave either as a pure refrigerant (azeotropic mixtures), or differently (non-azeotropic or zeotropic, mixtures). Azeotropic mixtures contain two or more refrigerants and the mixture at a certain pressure evaporates and condenses at a constant temperature. It behaves like pure refrigerants in all practical aspects. For a given pressure, the temperature is constant in the liquid-vapor mixture region. Among the non-azeotropic/zeotropic mixtures, the zeotropic mixtures have gliding evaporation and condensing temperature. At the evaporation temperature, the most volatile component boils off first and the least volatile component boils off last. The opposite happens when a gas condenses into liquids and the temperatures changes in the liquid-vapor mixture at a given pressure. It caused a raised evaporation and condensing temperature along the heat transfer surface. In general, there is a negative effect on the heat transfer coefficient due to mass transport phenomena in the refrigerant during the evaporation and condensation of zeotropic. This negative effect is neutralized by the high turbulence and good mixing in the heat exchanger, which also suggests that Brazed Plate Heat Exchangers (BPHEs) have an advantage over Shell and Tube Heat Exchangers (S&Ts). If the refrigerant liquid is allowed to accumulate somewhere in the circuit, then the problems arise at the suction line of the accumulators, flash tanks, receivers, or pool boiling/flooded evaporators (often S&T) [1]. The unpredictable performance could be observed from a change in the composition of the refrigerant circulating through the system. Thus, all components should have a continuous flow of refrigerant to avoid unpredictable performance. Thus, for systems containing mixtures with glide, the flooded evaporators will probably disappear. A considerable leak of refrigerant in the liquid-vapor region can lead to the same problems, as appears in the case of the changed composition of the remaining refrigerant charge, which produces unpredictable system performance.

Plasmas (low-temperature plasmas [LTPs]) at low temperature have characteristic electron energies of a few eV–10 eV with ionization of typically lower degrees but they can reach tens of percent in arc discharges. These energetic electrons can efficiently generate radicals, excited states, photons, and charged species. Particularly at low pressure, the space charge sheaths at the boundary of plasmas accelerate and deliver fluxes of ions to surfaces with adjustable energies ranging from a few to hundreds of eVs. Surface modifications are enabled by these ion fluxes, which alter surfaces by sputtering, activation, etching, and deposition that are essential to technological devices. Many industrial applications are performed by plasma created by microwave, arc, and inductively coupled plasma discharges that operate close to thermal equilibrium [2, 3].

Most of the low-temperature plasmas substantially deviate from thermodynamic equilibrium, along with the electron temperature T_e being significantly higher than the heavy particle temperature and gas temperature T_g. A chemically rich environment could be generated by LTP sources at close to room temperature both at reduced and at ambient pressures, which is an exclusive condition that facilitates the delivery of highly reactive plasma species in a non-destructive and useful way to extremely heat-sensitive surfaces. The microelectronics industry formed the technological base of modern society. Currently, the beneficial plasma-surface interactions deposited and removed the nanometer resolution in the fabrication of microprocessors [4]. This useful contact with surfaces later extended to liquids, organic tissues, and wounds, which directed to the arena of plasma medicine [5]. There could be an interaction between LTPs and surfaces with the plasma, non-destructively and beneficially [6]. They synthesized nanomaterials as particles or aerosol-laden dusty plasma that assisted nanomaterial synthesis. It was observed that LTPs can be generated and sustained within liquids and bubbles in liquids. Currently, they are investigated for medical applications, chemical processing, and in the context of environmental stewardship [7]. Thus, there are enormous extraordinary societal benefits of low-temperature plasmas. Low-temperature plasmas are remarkably interdisciplinary and have a wide range of applications. LTP discipline joined varieties of research fields, such as fluid dynamics, electrodynamics, thermodynamics, heat transfer, statistical physics, atomic and molecular physics, material and surface science, chemistry, electrical engineering, chemical engineering, and recently even biology and medicine.

Considering the enormous diversity in applications, investigations on non-equilibrium plasma kinetics and the interactions of plasmas with the matter should be encouraged. Research on Plasma Agriculture and Innovative, Plasmas in Analytical Chemistry, Plasma Metamaterials, and Plasma Photonic Crystals are the new additions in this activity area. Applications of plasmas in the areas of energy, flow control and material processing, synthesis, transport, and catalysis are also highlighted in many reviews. There are scopes of study on the dominant mode of energy transfer and chemical reaction processes in transient plasmas, the physical and chemical interaction of plasmas with materials and liquids, and the mechanisms, origins of the formation of complex self-organizing structures in plasmas, etc. Research on the low-temperature plasma field is at stake. It is observed that the support of fundamental research in the past has provided good results. Application of low-temperature plasmas depends on culturing and maintaining new generations of researchers engaged in plasma science, modeling, and diagnostics. Thus, more involvement should be encouraged in the fundamentals of plasma science that strengthens this technological development and enables the career progress of the next generation [8].

Application of steel-stiffened panels is commonly used in offshore, navel, mechanical, and civil engineering structures. Sometimes, they get in contact with cryogenic conditions, such as the sudden release of liquefied gas, such as LNG (liquefied natural gas) or liquefied hydrogen [9]. For the design of steel-stiffened plate structures, the ultimate strength is a primary criterion. Thus, it is necessary to characterize the effects at cryogenic conditions on the ultimate strength of such structures [10, 11]. Some works introduced a sequel to examine under cryogenic conditions, the brittle fracture of stiffened-plate steel structures. On some occasions, rupture, ductile fracture, and brittle fracture were investigated. In the case of fracture, the inherently brittle materials show different behavior than the ductile materials such as carbon steel. Slow and stable crack growth is generally exhibited during crack extension in the ductile materials. Similar behavior to brittle materials could be seen in certain environments such as very low temperatures or lower than the ductile-to-brittle fracture transition temperatures (DBTT), impact loading etc. Here, the Bauschinger effect of materials cannot be neglected at cryogenic conditions because the material behavior in compression is distinct from that in tension [10, 12, 13]. Some constitutive equations of materials were proposed to compute the failure behavior of structures at cold (sub-zero) temperatures (or higher than the ductile-to-brittle fracture transition temperatures). It is identified that there is a lack of investigation applicable to entirely brittle fracture at cryogenic conditions [14, 15, 16, 17]. The research compared the ultimate compressive strength of steel-stiffened plate structures by nonlinear finite element method (NLFEM) using the multi-physics software package LS-DYNA implicit code. The tested structure was fabricated from high-strength steel of grade AH32. Mechanical properties were considered, tension and compression tests at low temperatures and cryogenic conditions, and later, a phenomenological relation of engineering stress versus engineering strain of the material was formulated, and then, the model was used into the LS-DYNA implicit code. Comparison results of the NLFEM model data with the experimental results from the full-scale test presented the similarity of the trends [18, 19].

At temperatures higher than the temperature of the ductile-to-brittle fracture transition, the ductile-dominated behavior of structural steel is observed. The material behaves predominantly in a brittle manner with partial or no ductility at the approaching cryogenic condition. Ductile-to-brittle fracture transition temperature (DBTT) has to be clarified further. However, it is reported in a few investigations the evidence for brittle fracture behavior of steel structures at the cryogenic condition and their dependence on the type of materials and loading conditions (e.g., quasi-static or impact), in addition to other relevant factors. In some investigations, the ductile fracture in steel tubes under quasi-static loads at −60°C during the crashing test was observed. The brittle fracture was reported in dropped object impact testing of steel-stiffened plate panels at −60°C. Collapse testing of a steel-stiffened plate structure under axial-compressive loading in the presence of brittle fracture the ultimate strength was reached. In the presence of flexural-torsional buckling at room temperature, the structures reached the ultimate strength. On the other hand, brittle fracture caused the global failure of the material structure at cryogenic conditions.

In this book, it has attempted to develop a new fracture criterion based on the hypothesis that crack initiates if an equivalent stress exceeds a critical value. In this book, the effects of brittle fracture on the ultimate compressive strength of stiffened plate steel structures under cryogenic conditions have thoroughly been investigated. To analyze the ultimate compressive strength of steel-stiffened plate structures, the developed computational models were applied considering brittle fracture, under cryogenic conditions. Here, a material model for the high-strength steel at cryogenic condition is proposed, considering the Bauschinger effect, and implemented into a nonlinear finite element solver (LS-DYNA). The researchers obtained a good agreement between computational predictions and experimental measurements for the ultimate compressive strength response of a full-scale stiffened plate steel structure. Thus, a practical method was introduced to compute the ultimate compressive strength of steel-stiffened plate structures at cryogenic conditions triggered by brittle fracture. A recommendation suited for the adoption of NLFEM (nonlinear finite element method) simulations.

In the refrigeration process, the low-temperature technology is achievable, especially in the vapor compression refrigeration system (VCRS) [20, 21]. With reference to the issue of environmental challenges, the appropriate selection of refrigerant is essential to protect the environment from the greenhouse effect and stratospheric ozone layer depletion. Based on their safety, thermo-physical and thermodynamics properties, and economic factors, the refrigerants can be selected [22, 23].

As a refrigerant, ammonia has an increased coefficient of performance at a low cost, favorable transport, high enthalpy of vaporization, and good thermodynamic properties. Due to toxicity, it is prevented for domestic purposes [24, 25, 26]. Later, halocarbon refrigerants were developed. They have high thermal efficiency but imposed a threat to the ozone layer. Finally, the hydro-chlorofluorocarbon refrigerants were found as the best short-term alternative replacement for chlorofluorocarbon. Later, its application was also becoming limited. Du Pont said the HCFC substances’ production should be ceased but would persist in making it available for existing equipment until their expiry period [27, 28, 29].

The hydrofluorocarbon refrigerant (R134a) has zero ODP with a high GWP of 1430, which promotes its application as a working fluid that creates a threat to the immediate surroundings. The challenge of climate change engaged the researchers toward discovering and applications of environmentally friendly refrigerants in the heating and air-conditioning systems that also diminish greenhouse gas and enable energy savings [30, 31, 32].

Regulatory bodies (Kyoto and Montreal protocols) have called for banning pure fluid, which is posing a threat of high global warming and ozone depletion [33, 34, 35]. Halogen-free refrigerants (HFRs) are an alternative to halocarbon refrigerants in the refrigeration system. They are eco-friendly refrigerants with an organic composition of hydrogen and carbon atoms, such as butane, propane, isobutene, propylene [23]. It is miscible with mineral oil, which provides a smooth running of the single hermetic reciprocating compressor (SHRC). It has got zero ozone depletion and negligible global warming potential. The critical temperature of HFR refrigerant is high that enhances the domestic refrigerator’s efficiency. It preserves the environment and serves as an energy reduction substance [36, 37, 38, 39, 40, 41, 42].

In a closed system, the halogen-free refrigerant is applicable with relatively less mass charge. It is used in significant engineering systems such as deep freezers, water dispensers, domestic refrigerators, vending machines, and industrial refrigeration system. Some investigators used isobutane (R600a) and hydrofluorocarbon (R134a) as refrigerants and compared their performance characteristics. It was observed that the role of HTM (working fluid) in the heating ventilation and air-conditioning industries are highly significant [23, 43].

Considering the thermodynamic properties, the conventional refrigerants have predominantly been used. Hydrocarbon refrigerants such as isobutane were later picked because of their negligible global warming potential, zero ozone depletion, and eco-friendly behavior. It was reported that a better absorption of refrigerant into a refrigeration system could increase the coefficient of performance (COP). By using R600a and R134a, the performance was raised. Researchers have developed acceptable suggestions for working fluid (refrigerant) that would be suitable for a domestic refrigeration system. It could also enable the cooling performance of a computation system at a lower minimum level. Based on the comparative performance of R600a and R134a refrigerants in the vapor compression refrigeration system, the overall efficiency and refrigeration effect of the cooling system are greatly influenced by the working fluids. The researchers reiterated that the use of isobutane could secure the surroundings from global warming, ozone depletion, improvement of energy conservation etc.

The application of cryogenic fluids for keeping temperature and maintaining electronic circuits was successfully demonstrated by many authors with the emerging field of quantum computing, and the study of CMOS devices at low and very low temperatures, below 100 K, has received a revived attention [44, 45, 46, 47, 48]. Recently, in advanced CMOS technologies, outstanding characteristics were demonstrated at 4.2 K [49, 50, 51, 52], specifically for Fully Depleted Silicon-On-Insulator (FDSOI) [53, 54, 55]. Low-power electronics, threshold voltage tune ability, and back bias ability were designed by applying FDSOI, which offered low variability due to the un-doped channel [56]. The low-temperature operation can provide many advantages such as better electrical performance of MOSFETs, higher carrier drift velocity, higher on-state drain current and transconductance, steeper subthreshold slope, lower leakage current, etc. [45, 52]. The temperature dependence of carrier transport properties and thermal effects needed to be incorporated to obtain accurate models [57, 58]. Due to low-temperature operation, the appeared physical phenomena need to be properly modeled [52]. This book presents a review of recent results obtained on 28-nm FDSOI transistors operated down to deep cryogenic temperatures. The major device electrical properties in terms of transfer characteristics and MOSFET parameters as a function of temperature are elaborately discussed. It is reported that the self-heating phenomena could alter the performance of the FDSOI device. It also contains the matching and variability properties of scaled transistors and their limitations in the analog applications. It presented the development of a compact model necessary for FDSOI circuit design at deep cryogenic temperatures and the operation of elementary circuits at very low temperatures regarding inverter delay and oscillator frequency.

The investigation of CMOS technology performance at cryogenic temperatures was encouraged for its applications in high-performance computing and energy physics. The advanced CMOS node could support the larger bandwidth at low-temperature applications of quantum computers. For co-integration between qubits and consistent engineering of control and read-out, the FDSOI technology appears as a valuable solution. For the advanced CMOS node behavior at deep cryogenic operation, more investigations are required. Thus, this book contains a review of electrical characterization and modeling results recently obtained on modern FDSOI MOSFETs down to 4.2 K.

Detail of the self-healing phenomena was characterized and provided valuable information about the actual device temperature as a function of power dissipation and the thermal resistance that limits the heat dissipation in the FDSOI structure specifically at low temperatures. Considering the threshold voltage and drain current statistical variability analysis, the matching properties were studied and enlightening the mismatch in FDSOI transistors that increases about 30–40% at deep-cryogenic temperatures. On the other hand, Poisson-Schrodinger simulations were carried out with success down to zero Kelvin, giving access to valuable information about the gate charge control in FDSOI structures as a function of temperature, which provided physical insight to the development of compact model mandatory for FDSOI circuit design at deep cryogenic temperatures. The operation of elementary circuits such as ring oscillators and voltage-controlled oscillators was validated in terms of inverter delay and clock frequency down to deep-cryogenic temperatures.

The powerful advantage of FDSOI over bulk technology is highlighted in this book, which is led by the back biasing capability, and it allows the managing power consumption and performance, which mitigates the thermal effect. These are crucial aspects of cryoelectronics. Involving a combination of heat and mass transfer, the stratification in cryogenic liquid storage systems is a complicated yet inexorable thermodynamic phenomenon. Cryogenic liquids having a very low-boiling point are susceptible to heat entry from the ambient. A large temperature gradient exists between the storage and atmospheric temperature, and is the cause of heat ingress during ground parking. Due to aerodynamic heating (during flight) and space radiation, an overwhelming increase in heat ingress occurs, although these are not as significant as obtained during the coast phase. The propellant tanks receive the insulation of foam that is relatively less effective compared to vacuum or multi-layered insulation (MLI). The temperature of liquid adjacent to the walls is raised due to the mentioned leakage, which induced natural convection currents. Due to buoyancy, the heated liquid starts flowing up and accumulates at the liquid-vapor interface, which creates an axial temperature gradient called thermal stratification. Here, with time the depth of this stratified layer increases. On the other hand, due to vaporization, the tank pressure keeps increasing and it creates the requirement of proper design of venting devices and insulation systems. Thus, for designing the rocket fuel tanks, the thermal stratification is a crucial design criterion for consideration.

On thermal stratification and self-pressurization of a cryogenic storage vessel, a wide variety of experimental and numerical studies have been conducted and reported by researchers across the globe. They studied the effect of rib shape and material thermal conductivity on the development of stratification by considering cylindrical ribbed tanks with a certain percentage (50%) filled volume and rib shapes of rectangular and semi-circular [59]. They observed for rib materials of low thermal conductivity produced lower tank pressurization. Lesser self-pressurization was observed in the semi-circular ribbed tank in comparison with the rectangular ribbed case for the same rib cross-sectional area and locations.

To minimize the thermal stratification in LH2 tanks, some researchers carried out numerical investigations and observed about 30% reduction in the stratification parameter by the application of transverse wall ribs on the inner surface of the cylindrical tank [60]. For the tank with the ribbed inner surface, they noticed a delayed stratification, as well as a lesser natural heat transfer coefficient, in comparison with those output for the smooth wall tank.

Transient natural convection on a vertical ribbed wall was investigated by some researchers [61] and they observed a reduction in convective heat transfer coefficient below the initial rib and enhancement was noticed after that region. Other researchers observed a reduction in heat transfer performance for a natural convective airflow over a heated ribbed plate [62]. To reproduce the thermal field, the Schlieren optical technique was used, and it was found that the induced flow creates thermally inactive regions just upstream and downstream of each protruding element.

Researchers [63] studied the flow behavior of air over a heated wall with single and repeated, two-dimensional, rectangular roughness elements. They did not notice the enhancement of heat transfer in the presence of wall ribs. The volume of fluid (VOF) method was used to investigate the depressurization and thermal stratification behavior of a liquid nitrogen tank with different baffle structures under microgravity conditions [64]. A reduction of up to 54% in pressurization rate was achieved by optimizing the baffle setting. The effect of isogrid on thermal stratification inside propellant tanks was investigated by researchers [65]. They observed that the boundary layer thickness on the wall in a forced-free stream flow was distinctly thicker (150–700%) than the equivalent flat plate boundary layer thickness. Depending upon roughness size and tank conditions, the isogrids can either enhance or suppress the stratification rate compared with smooth tanks. The boundary layer behavior over the propellant tank with mass saving isogrid structures was investigated and observed development of more than 200% thicker velocity boundary layer over isogrid wall than a smooth wall, which led to rapid self-pressurization and enhanced fluid mixing [66].

Thus, the liquid fuels held in liquid form at cryogenic temperature and gas at normal temperatures are used in cryogenic engines. Minimal heat infiltration causes thermal stratification and self-pressurization because the propellants are stored at their boiling temperature or subcooled condition. The state of propellant inside the tank varies due to stratification, and it is essential to keep the propellant properties in a predefined state for restarting the cryogenic engine after the coast phase. Here, cavitation could happen and create destruction of the flight vehicle if the inlet temperature is above the cavitation value. To reduce the stratification phenomenon in a cryogenic storage tank, some investigations are going on to find some effective methods, such as the shape of the inner wall surface of the storage tank plays an essential role in the development of the stratified layer. To predict the rate of self-pressurization in a liquid hydrogen container, an established CFD model could be used. To predict the liquid-vapor interface movement, the Volume of Fluid (VOF) method was used by researchers, whereas the Lee phase change model was adopted for evaporation and condensation calculations.

A detailed study was conducted on a cylindrical storage tank by some researchers with an isogrid and rib structure. Free convection flow of buoyancy-driven support over isogrid structure resulted in significantly different velocity and temperature profiles from a smooth wall case. Thus, the isogrid-type obstruction provided a more significant thermal boundary layer, and those obstructions induced streamline deflection and recirculation zones, which improved the heat transfer to bulk liquid. With an isogrid structure, a larger self-pressurization rate was observed for tanks. A reduction of upward buoyancy flow near the tank surface was obtained with the presence of ribs, whereas with it streamline deflection and recirculation zones were also noticeable. It nullified the effect of the formation of recirculation zones with the increase in the number of ribs. The self-pressurization rate was reduced by about 32.89% with the incorporation of the rib structure in the tank wall.

Thermal stratification is reduced in the presence of roughness elements. The conductivity of ribs on heat transfer performance for the flat vertical and horizontal heated plates has been studied extensively with the variation of spacing to height ratios of transverse ribs, protrusion length, etc. Thus, further investigation is needed to realize the influence of ribs and grid structure on the reduction of stratification on a cryogenic cylindrical tank.

The improvement of manufacturing technology and the expansion of the semiconductor market caused the rise in wafer size and well-integrated semiconductor devices. Due to higher integration, the heat produced in the semiconductor manufacturing process is required to be at a lower level, so the temperature of the supplied cooling medium from the chiller is needed to keep at a lower level. Therefore, the Joule-Thomson cooling cycle is used and, in the process, a mixed refrigerant (MR) is used to produce the cooling medium at a level of −100°C, which is required for the semiconductor process. This technique has gained great attention, where a mixture of refrigerants (MR) is used, and the chiller performance is heavily influenced by the composition and proportions of the refrigerant charged to the chiller system. The application of MR in the cooling system to achieve the required low temperature of −100°C in the semiconductor manufacturing process and the use of different proportions and the compositions of MR and results are represented by some researchers. It was observed that the increased proportion of high-boiling point refrigerant could shorten the time for cooling the process and it keep the device pressure at a lower level. On the other hand, the reduction of the proportion of the mass ratio of the high-boiling point refrigerant enhances the cooling capacity of the refrigerants. However, it was reported that the MR refrigerants could reach the target temperature of the process in a short time and the cooling capacity is high when R290 is used as the high-boiling point refrigerant among R290 and R600a [67].