Compression Work Research Articles

Thermal Study of Carbon-Fiber-Reinforced Polymer Composites Using Multiscale Modeling.

The layered fibers of carbon-fiber-reinforced polymer (CFRP) composites exhibit low thermal conductivity (TC) throughout their thickness due to the poor TC of the polymeric resin. Improved heat transmission inside the hydrogen storage tank during the filling process can reduce further compression work, and improved heat insulation can minimize energy loss. Therefore, it is crucial to understand the thermal properties of composites. This paper reports the thermal behavior of plain-woven CFRP composite using simulation at the micro-, meso-, and macro-scales. The TC was predicted numerically and compared to experimental findings and analytical models. Good results were found. Using the approach of multi-scale modeling, a parametric study was carried out to analyze in depth the influence of certain variables on thermal properties. The study revealed that both fiber volume fraction and temperature significantly influenced the TC of the composite, with the interphase fiber/matrix thickness following closely in terms of impact. The matrix porosity was found to have a relatively slighter impact, particularly within the porosity range of 5 to 15%.

Performance of hybrid electric vehicle air-conditioning using SiO2/POE nanolubricant

The automobile air-conditioning (AAC) system uses the most energy among all auxiliary components in hybrid electric vehicles (HEV) with an electrically-driven compressor (AAC-EDC). Incorporating nanolubricant improves AAC-EDC performance and reduces battery and AAC component size. This study aims to assess the performance of an AAC-EDC system by employing SiO2/POE nanolubricants. The performance of the AAC-EDC was examined using SiO2/POE with a volume concentration of up to 0.01 %, a refrigerant charge of 120–160 g, and a compressor speed of 1200–3840 rpm. The performance of the AAC system was measured by its heat absorption, compressor work, coefficient of performance (COP), and EDC power consumption. The SiO2/POE was stable for 30 days with a zeta potential of 102.5 mV. The SiO2/POE demonstrated superior performance over the pure POE lubricants. The compressor work and power consumption were reduced to 26.17 % and 11.97 %, respectively. The lowest expansion valve discharge temperature of 9.6 °C was achieved at 160 g refrigerant charge and compressor speed of 3840 rpm. The nanolubricant attained the highest COP of 3.36 at 1860 rpm speed and 160 g charge. The SiO2/POE nanolubricant with a volume concentration of 0.01 % is highly recommended for optimal performance in the AAC-EDC system.

Improving the Sealing Efficiency of Compressor Cylinders of Gas Engine Compressors in the System of Gas-Lift Production of Offshore Fields

An increase in the efficiency of gland seals in compressor cylinders with cast iron rings pressed against the contact surface of the piston rod using a steel spring in reciprocating compressors used in offshore oil and gas-condensate fields for gas-lift oil production systems is considered. Studies of a gas engine reciprocating compressor working directly on the operating gas-lift system have shown that in order to increase the time of normal operation of gland seals, it is necessary to adjust the clearance using lubricant up to 0.1 mm. After increasing the spring stiffness, the serviceability and number of working hours of the gland seal increased twofold, from 850 to 1700 h.

Study on planar compression properties of multi-layered spacer fabrics

Due to the thickness of the spacer fabric, it is usually assembled in a multi-layered manner as a cushion material. However, few studies have been conducted on the compression properties of the multi-layered spacer fabrics. Firstly, this paper analyzes the factors affecting the compression properties of multi-layered spacer fabrics, and explains the influencing mechanisms. Results show that the fixing condition between the sample and the indenter, the fixing condition between layers, the overlaying direction and the compression speed have little effect on the compression property. However, when overlaying spacer fabrics with different moduli, a better compression property can be obtained by placing the fabric with a higher modulus on top. Secondly, this paper focuses on the relationship between the layers and the compression property of the spacer fabrics. It shows that the relation between the compression work and the number of layers is linear, with a high correlation coefficient. The relationship between the modulus and the number of layers is in the form of a cubic function with a good correlation coefficient. Finally, the Kelvin model is modeled and is found to be suitable for characterizing the stage II compressive properties of multi-layered spacer fabrics. The above quantitative analysis provides theoretical support for the design of cushion materials with different moduli and support performance in different regions, and has practical guiding significance.

Thermodynamic Performance Enhancement of an Air Conditioner With Dew Point Evaporative Cooler

Abstract The vapor-compression-based conventional split air conditioners (CACs) consume a large portion of total electrical power and pose an alarming threat to global environment. The present work aims to reduce cooling load and power consumption of CAC by employing a dew point evaporative cooler (DPEC). DPEC consists of a counter flow type heat and mass exchanger with alternate layers of dry and wet channels. The intake air is sensibly cooled before entering the cooling room through the evaporator coil of the air conditioner. Also, the working air (a part of outlet air in dry channel), after absorbing sensible heat of intake air and water vapors from the wet channel surface, is allowed to pass across the condenser coils. The intake dry-bulb temperature (T0 = 29–44 °C) and specific humidity (ω0 = 6–22 g/kg) are taken as input parameters. While the cooled air entering the evaporator decreases the cooling load on the conditioned space, the compression work is also reduced due to increased heat transfer in the condenser. The maximum reductions in cooling load and monthly energy consumption at T0 = 44 °C and ω0 = 6 g/kg are found as 59.54% and 340 kW h, respectively. The water consumption for different months of the cooling season varies from 1037.8 L to 2905.95 L. The average energy savings with the DPEC system for hot-dry climate (from April to June) and hot-humid climate (from July to September) of New Delhi, India, are observed to be 479.6 kW h and 79.1 kW h, respectively. The proposed system is found to payback in about 3.37 years.

STUDI EKSPERIMENTAL NATURAL REFIGERANT DENGAN VARIASI DIAMETER TiT-HEAT EXCHANGER TERHADAP REFRIGERATOR PERFORMANCE

ABSTRACT
 Almost all households in Indonesia use a refrigerator as a place to store food that is more durable. But behind these needs, refrigerators are identified as one of the household appliances that use high electrical energy. Therefore, this study aims to examine the use of Tube in Tube Heat Exchanger (TiTHX) with refrigerant R290 in the refrigerator system to reduce household electricity consumption. This research was conducted experimentally by varying the 3 diameter ratios on TiTHX. The results showed that the use of TiTHX with the most optimum value was obtained at the variation diameter ¼ : ½ increasing refrigerator performance by 3.7%. and also reduce the consumption of electricity costs up to Rp. 17,544.44 per month. This is because the difference between the evaporation pressure and condensation pressure is smaller in systems using TiTHX which then results in lower compression work.

Performance enhancement and optimization of residential air conditioning system in response to the novel FAl2O3-POE nanolubricant adoption

This paper aims to evaluate residential air conditioning systems' performance enhancement and optimization by adopting a novel functionalized Al2O3 (FAl2O3)–Polyolester (POE) nanolubricant. Comprehensive discussions were conducted on key performance parameters, including heat absorption, compressor work, cooling capacity, coefficient of performance (COP), and power consumption. Novel FAl2O3 nanoparticles were dispersed into the POE lubricant using a two-step method. The findings reveal that FAl2O3–POE nanolubricant exhibits superior heat absorption compared to pure POE. Heat absorption decreases with an increased initial refrigerant charge, while cooling capacity performance improves with an increased initial refrigerant charge. The COP shows an increasing trend at all concentrations of FAl2O3–POE nanolubricant when operating with R32. FAl2O3–POE/R32 demonstrates an enhanced range of 3.12%–32.26% for COP. The results suggest that applying novel FAl2O3–POE nanolubricant with R32 can reduce electrical power consumption by 13.79%–19.35%. The central composite design (CCD) offers an optimal condition for FAl2O3–POE nanolubricant with a concentration of 0.11 vol%, an initial refrigerant charge of 0.442 kg, resulting in a COP of 3.982, a standard error of 0.019, and a desirability of 1.0.

Isobaric Expansion Engines–Compressors: Thermodynamic Analysis of Multistage Vapor Driven Compressors

Isobaric expansion (IE) engines can directly convert heat into mechanical energy, making them particularly attractive for applications such as vapor-driven pumps and compressors. A recent initial assessment investigating the utilization of IE engines as vapor-driven reciprocating compressors has revealed that the vapor use efficiency is inherently low in the case of the simplest direct-acting compressor designs. Based on this analysis, it was anticipated that multistage compression can offer significant advantages for vapor-driven compressors. Therefore, this paper aims to conduct a comprehensive analytical thermodynamic analysis of direct vapor-driven multistage reciprocating compressors. The analysis considers processes without intercooling and processes with intercooling of the compressed gas between stages. The findings demonstrate that, for vapor-driven compression, the benefits of multistage compression are superior to those known for conventional compression processes. Multistage vapor-driven compression not only reduces compression work and temperature elevation but, more importantly, mitigates the adverse effects on vapor compression of the driving vapor, thereby enabling a substantial improvement in vapor utilization efficiency. Furthermore, the total volume of the IE engine compressor experiences a significant decrease with an increasing number of stages. Consequently, under specific process parameters, the overall dimensions of the engine-compressor system may also decrease as the number of stages increases. The results offer significant opportunities for energy savings in energy-intensive compression processes by replacing electrical energy with readily available low-grade heat sources (<100 °C). Such processes include hydrogen, air, and ethylene compression at high pressure.

Experimental investigation on a closed-cycle single-stage turbo-refrigerator for deep freezing

Turbo-refrigerator based on reverse Brayton cycle is an attractive solution for providing refrigeration at ultra-low temperatures below −60 °C for deep freezing. Employing a motor-driven turboexpander compressor (MTEC) not only allows the turbo-refrigerator to achieve high compactness, reliability and flexibility, but also leads to new operating characteristics especially in a closed cycle. This paper aims to investigate the operating characteristics of a closed-cycle single-stage turbo-refrigerator with a MTEC. A high-speed turbo-refrigerator system with the design refrigeration temperature of −86 °C was manufactured and then tested under variable rotating speeds and refrigeration conditions. Test results show that a refrigeration temperature below −96.4 °C was obtained in a pull-down progress. Compared with a fixed-speed operation, variable-speed operation enables the independent control of the refrigeration temperature and the cooling capacity. With the decrease in the refrigeration temperature (or in the cooling capacity), the rotating speed has a greater effect on the COP than that on the cooling capacity (or on the refrigeration temperature). The mass flow rate along with the compression and expansion work shows a decreasing trend as the refrigeration temperature decreases at a fixed speed of the MTEC. The advanced exergy analysis shows a total exergy efficiency of 0.42 (with a COP of 0.62 at refrigeration temperature of −86 °C) could be expected with component improvement in the near future, and it is of the priority to increase the efficiency of the turboexpander.

Analysis of the Coefficient of Performance (COP) on the Car’s Air Cooling System Using a Training Kit with Constant Rotation

The performance of the air condition system is strongly influenced by the compressor work, the condenser cooling temperature. So that the compressor working pressure (suction) and condenser cooling play a very important role in the performance of the air conditioning system which will have an impact on compressor work, compressor power, refrigeration impact, isentropic efficiency and coefficient of performance (COP) of the car air conditioning system. From the research, data will be obtained which include the pressure value on the refrigerant, namely P1 and P2, the temperature on the refrigerant, namely T1, T2, T3 and Tcabin, at the point of installation of the Manifold Gauge and Thermocouple. The research data is then processed and analyzed to obtain performance at constant rotation with variations in compressor working time both actual and theoretical as well as the efficiency of the ac system. From the results of the study, it was found that the compressor rotation was 2300 rpm with a constant rotation then measured the pressure and temperature of the refrigerant, then temperature data was obtained and analyzed to obtain the enthalpy value, thus obtaining the coefficient of performance (COP) of the car air conditioning system. The coefficient of performance (COP) of the resulting system is greater than the actual COP, the optimal COP occurs at P1 30 psi and P2 340 psi working pressures, the actual COP is 3.4848 and the theoretical COP is 4.1500, with an efficiency of 83.97% at 360 seconds.

Performances Investigation of the Eco-friendly Refrigerant R13I1 used as Working Fluid in the Ejector-Expansion Refrigeration Cycle

Knowing that from 2030 refrigerants used in refrigerating engineering should have a global warming potential (GWP) of less than 150. Searching for eco-friendly refrigerants with good performance and minimal environmental impact to substitute conventional working fluids such as R134a (GWP=1430) represents a great challenge for researchers.
 The present research aims to investigate and compare the performances of the eco-friendly refrigerant R13I1 (Zero GWP) used as a possible new working fluid in the ejector-expansion refrigeration cycle (EERC) with the commonly used R134a which has good performances but a high GWP. To reach this objective, a numerical program was developed using MATLAB software to evaluate the coefficient of performance (COP), the entrainment ratio (µ), the exergy destruction and the exergy efficiency for both refrigerants. Furthermore, the effect of the diffuser efficiency of the ejector on the COP and the compressor work was explored. Furthermore, the effect of the diffuser efficiency of the ejector on the COP, and the compressor work were explored. The simulation was realized for Tc selected between 30 and 55 °C and Te ranging between -10 and 10 °C. Results proved that the use of R13I1 as a working fluid in the EERC system exhibited a higher COP, µ, and exergy efficiency, as well as lower exergy destruction compared with R134a under the same operating temperatures. On another hand, the energetic analysis revealed that as Tc increases the COP and µ decrease. However, as Te varies from -10 and 10 °C, the COP and µ increase. Regarding exergy analysis, it should be noted that both exergy destruction and exergy efficiency are sensitively influenced by Tc more than Te. Overall, the study confirms that R13I1 could be a suitable substitute for the phase-out R134a in terms of performance and environmental protection.

Thermoeconomic and environmental analyses based single objective optimization of subcooled compression-absorption cascaded refrigeration system using evolutionary techniques

ABSTRACT This article analyses a subcooled compression-absorption cascaded refrigeration system (SCRS) in comparison with a standalone compression-absorption cascaded refrigeration system (CRS) based on thermoeconomic optimization. Three different absorbent solution/solution mixture-refrigerant combinations have been tested as working pairs in vapor absorption refrigeration system (VARS), whereas four environmentally friendly refrigerants have been utilized in vapor compression refrigeration system (VCRS). The total annual cost of the system is formulated using energy, exergy, and economic performance of the system and is minimized for optimal operational parameters by implementing five recent evolutionary optimization techniques. The effect of compression subcooling on various operational parameters of the cascaded system is reported. Amid all absorbent solution/solution mixture-refrigerant-refrigerant combinations, R290 combined with (CaCl2-LiBr-LiNO3)-H2O provides the minimum total annual cost of 13,164.8 US$ yr−1 and 15,401.9 US$ yr−1 for CRS and SCRS, respectively. Sanitized Teaching Learning Based Optimization (sTLBO) and Coyote Optimization Algorithm (COA) obtain the optimal total annual cost for most VARS-VCRS absorbent solution/solution mixture-refrigerant-refrigerant combinations. Though the coefficient of performance (COP) of an optimal SCRS is about 250% higher than its optimal CRS, higher compressor work results in a higher penalty cost for the optimal SCRS, which is almost 190% higher than the optimal CRS. A quick convergence is observed for sTLBO and COA.

Performance analysis of ice plant using R134a/POE blended with MWCNTs nano-refrigerant–An experimental approach

Ice plant is used for producing ice at a large scale from water filled in standard cans placed inside rectangular tanks filled with brine solution. Ice plant works on the vapour compression refrigeration (VCR) cycle, the researchers are focusing on minimizing compressor work and improving the cycle's performance by introducing nanoparticles with higher thermophysical properties. In this experimental investigation, the performance analysis of the test rig of an ice plant using varied masses of 0.05 g, 0.10 g, 0.15 g, 0.20 g, and 0.25 g of multi-walled carbon nanotubes (MWCNTs), dispersed in 250 ml polyolester (POE) oil charged with masses 175 g, 200 g, and 225 g of tetrafluoro ethane (R134a) refrigerants is carried out separately. REFPROP 9.1 software is used to obtain the properties of refrigerants. The evaluated parameters are pull-down time, cooling capacity, coefficient of performance (COP), Compressor work input, economic analysis, pressure ratio, thermal conductivity, absolute viscosity, and density. It is observed that in comparison to the pure refrigerant, the refrigerator's pull-down time and compressor work are reduced by 17.9% and 21.46%, whereas, COP and cooling capacity improved by 40.09% and 11.29% for 225 g mass of R134a with 250 ml POE respectively. In addition, thermal conductivity, density, and absolute viscosity improved at both the suction side and discharge side of the compressor.

Effect of Performance by Excessive Advanced Fuel Injection Timing on Marine Diesel Engine

The injection timing of fuel in a diesel engine affects the combustion condition. Advanced fuel injection prolongs the ignition delay, positively impacting the increase in maximum combustion pressure and improving output. However, excessively advanced fuel injection can cause knocking. Moreover, premature ignition results in increased compression work when the maximum combustion pressure occurs before top dead center (TDC). This study aimed to diagnose and rectify starting failures, noise, and vibrations in a commercially operated ship engine by measuring the combustion pressure during low load operation. The target engine was a 4-stroke diesel, and the fuel injection system was mechanically controlled by a camshaft. The measured engine exhibited a 4.5 °CA error between the TDC, determined by the flywheel mark and the actual TDC. This discrepancy was influenced by excessively advanced fuel injection timing. It was confirmed that fuel injection and ignition were excessively advanced in all cylinders. After readjusting the engine by delaying the fuel injection timing by approximately 10 °CA, the combustion pressure was remeasured. The ignition was delayed by approximately 6.5 °CA at the same load, and the ignition intervals were uniformly adjusted. As the ignition timing was retarded, the compression work decreased and the expansion work increased in each cylinder, resulting in improved output across all cylinders. The amplitude of crankshaft angular velocity variation significantly decreased, improving uneven rotational force.

Study of refrigeration system with minichannel condenser using R1234ze, R134a, R152a, R600a, R290 and mixture of R290/R600a (50/50)

A versatile vapor compression refrigeration (VCR) system is designed, developed and manufactured for testing different alternative refrigerants to R134a. The refrigerants such as R1234ze, R152a, R600a, R290 and mixture of R290/R600a (50/50) refrigerants are tested with an aluminum minichannel condenser which is designed for R134a. All the refrigerants are experimented for condensation temperature varying from 40 to 55°C while evaporation temperature varying from −10 to +15°C for every condensing temperature. The performance parameters like volumetric refrigerating capacity, actual work consumption of compressor, coefficient of performance (COP) and condenser capacity are compared for different alternative refrigerants. Aluminum minichannel condenser has reduced condensing temperature by 2–3°C with an increase in COP by 10%. The ratio of volumetric refrigerant capacities for R152a, R1234ze, R600a, R290 and HC mixture of R290/R600a (50/50) with respect to R134a are found to be 1.296, 1.143, 0.736, 1.749 and 1.067, respectively which is useful to select specific compressor. The ratio of compressor work for R600a, R290, HC mixture of R290/R600a, R152a and R1234ze with respect to R134a are found to be 1.81, 1.812, 1.867, 1.6 and 1.1, respectively. The ratios of condenser capacity of R600a, R290, HC mixture of R290/R600a, R152a and R1234ze with respect to R134a are found to be 1.914, 2.061, 1.939, 1.65 and 1.064, respectively. It is found that COP of R152a, R600a and R1234ze are larger by 11.53, 5.38 and 27% over R134a whereas COP of R290/R600a (50/50) and R290 are decreased by 0.75% and 14.23% over R134a, respectively. The exergy loss analysis for VCR system components is carried out at condensing temperature of 44°C while evaporating temperature ranging from −10 to +15°C for all the refrigerants and found that total exergy loss is more for R600a among all refrigerants.

Dynamic Investigation of a Solar-Driven Brayton Cycle with Supercritical CO2

The exploitation of solar irradiation is a critical weapon for facing the energy crisis and critical environmental problems. One of the most emerging solar technologies is the use of solar towers (or central receiver systems) coupled with high-performance thermodynamic cycles. In this direction, the present investigation examines a solar tower coupled to a closed-loop Brayton cycle which operates with supercritical CO2 (sCO2) as the working medium. The system also includes a storage system with two molten salt tanks for enabling proper thermal storage. The sCO2 is an efficient fluid that presents significant advancements, mainly reduced compression work when it is compressed close to the critical point region. The novelty of the present work is based on the detailed dynamic investigation of the studied configuration for the year period using adjustable time step and its sizing for achieving a continuous operation, something that makes possible the establishment of this renewable technology as a reliable one. The analysis is conducted with a developed model in the Modelica programming language by also using the Dymola solver. According to the simulation results, the yearly solar thermal efficiency is 50.7%, the yearly thermodynamic cycle efficiency is 42.9% and the yearly total system efficiency is 18.0%.

Comparative performance investigation of a dual evaporator cycle using an ejector with the conventional cycle using a pressure reducing valve

The performance of a dual evaporator cycle using ejector is compared with a conventional cycle employing pressure reducing valve. In both the systems, high temperature evaporator is considered as a flooded evaporator, thus a separator is employed after the high temperature evaporator. However, low temperature evaporator is a kind of conventional dry evaporator. The comparison of both systems, i.e., conventional and ejector assisted, is done for the same cooling capacities and same dryness fraction at the exit of high temperature evaporator with R134a, R152a, and R1234yf refrigerants. The effects of varying the states of refrigerant at the exit of flooded evaporator, and temperatures of both the evaporators and the condenser are analyzed using Engineering Equation Solver. It is found that the compressor work is reduced in both the cycles with the rise in low temperature evaporator temperature; however, a little variation is observed in the total cooling effect. The cooling effect in high temperature evaporator is increased with the increase in dryness fraction at the exit of the high temperature flooded evaporator, but it is decreased in low temperature evaporator.

Performance of a computerized refrigeration cycle test rig for varying concentrations of (CuO-Al2O3/MO) hybrid nano-lubricants and R600a refrigerant charges: an energetic and exergetic approach

ABSTRACT This article examined the energetic and exergetic performance evaluations of a computerized refrigeration cycle test rig for different concentrations of (CuO-Al2O3/MO) hybrid nano-lubricants and R600a refrigerant mass charges. In this particular investigation, three different refrigerant mass charges of 80 g, 100 g, and 120 g were employed, together with four different hybrid nano-lubricant concentrations of 0.1 g/L, 0.2 g/L, 0.3 g/L, and 0.4 g/L. A number of significant parameters, including COP, compressor power consumption (W), refrigerator pull-down time (minutes), second law efficiency (%), and total exergy destruction (W) of mineral oil without nanoparticles and nano-doped mineral oil using (CuO/Al2O3) hybrid nanoparticles as the lubricant, were examined in the course of this investigation. The optimum condition is achieved at 0.2 g/L of (CuO-Al2O3/MO) with 100 g mass of R600a refrigerant. At optimal conditions (0.2 g/L concentration of hybrid nano-lubricant and 80 g refrigerant mass charge), compressor work and total exergy destruction are lowered by (2.20–23.53%) and (4.51–49.00%), respectively. It is also observed that at optimum condition COP and second law efficiency grew within the range of (0.93–28.97%) and (3.38 to 25.42%), respectively. In conclusion, the performance of the computerized refrigeration cycle test rig altered with (CuO-Al2O3/MO) hybrid nano-lubricant concentrations and R600a refrigerant charges.

Experimental and numerical investigations on thermal-hydraulic characteristics of supercritical CO2 flows in printed circuit heat exchangers

In the supercritical CO2 (SCO2) Brayton cycle, the pre-cooler is employed to cool SCO2 to be near the pseudo-critical point state to minimise compression work and achieve high cycle efficiency. The dramatic variation in thermophysical properties of SCO2 makes heat transfer and flow very complex in the pre-cooler, bringing a lot of difficulty to the design of the related components and system. This study attempts to address this issue. The experiment and simulation are carried out to analyse the influences of mass flux, inlet temperature, and pressure on the thermal-hydraulic characteristics of SCO2 flows in a straight-channel printed circuit heat exchanger (PCHE) employed as a pre-cooler, and the underlying heat transfer mechanism is analysed as well. The local heat transfer coefficient (h) is higher when the phenomenon that the local temperature of SCO2 (Tf) is equal to the pseudo-critical temperature (Tpc) appears in the laminar sublayer than when this phenomenon appears in the buffer layer. The new heat transfer and flow correlations are presented, and the genetic algorithm and back-prediction (GA-BP) neural network is employed to predict the local heat transfer and flow performance. The maximum relative error between the Nusselt number (Nu) predicted by the new heat transfer correlation and Nu obtained via experiment and simulation is within ±20%. The maximum relative error between the Nu predicted by the GA-BP neural network and the Nu obtained through experiment and simulation is within ±15%. The maximum relative error between the Fanning friction factor (f) predicted by the new friction factor correlation and f obtained via experiment and simulation is within ±5%. The maximum relative error between f predicted by the GA-BP neural network and f obtained through experiment and simulation is within ±4%. The present investigations analyse the thermal-hydraulic characteristics of SCO2 in the pre-cooler prototype and could provide useful guidance for the design of pre-coolers for the SCO2 Brayton cycle.

Grease material properties from first principles thermodynamics

AbstractThermodynamics has historically been used to derive characteristic material properties. In this study, fundamental thermodynamics is applied to grease. First‐principle formulations of existing material properties—heat capacity and storage modulus—and new properties—thermal strain and stress coefficients, chemical resistance and thermo‐chemical decay coefficient—are derived, some of which are experimentally determined. A new group of Maxwell relations is introduced by replacing the classical compression work with the grease shearing work . The physical interpretations and implications of these properties on grease behaviour and performance are presented. Experimental measurements of the derived properties are performed in accordance with the theoretical formulations. Six different grease types are studied. Obtained results are shown to conform with anticipated, observed and established grease behaviours. The proposed properties can be used in grease performance and degradation analyses, as well as grease selection for lubrication applications.