Efficient Refrigeration Research Articles

Large reversible magnetocaloric effect across the first-order magneto-structural transition in (Mn0.45Fe0.55) (Ni0.6Co0.4) Si alloy

Magnetic materials with reversible magnetocaloric effect across their respective first-order magneto-structural transitions (MST) have vital significance for further advancement towards the ultimate goal of practical magnetic cooling applications. In this present study, the reversibility of the MST is investigated by analyzing the isofield curves under different minor and major thermal hysteresis loops and the isothermal curves under different magnetic field cycles. The reversibility of the magnetocaloric effect (MCE) depends upon the width of the nucleation energy barrier existing across the MST. Minor hysteresis loops are found to be minimizing the energy loss by preventing the nucleation of the martensite phase and can be easily returned to the austenite phase immediately while switching from cooling to heating. A large reversible isothermal magnetic entropy change ΔSM of −14.4 J kg−1 K−1 nearly at 322 K is observed for the (Mn0.45Fe0.55) (Ni0.6 Co0.4) Si alloy under a low magnetic field change of 3 T. The observed large reversible MCE, very low magnetic field-induced hysteresis loss, and large reversible RCeffe ∼ 155 J kg−1 will be beneficial for reducing the energy loss during several magnetic field cycles in practical cooling applications which makes this alloy promising for the development of efficient magnetic refrigerants.

A new two-phase passive temperature control system for a wine fermenter

Thermal control of a fermenter tank is fundamental to guarantee a high-quality final product, especially in wine-making processes. Indeed, temperature is a crucial parameter for alcoholic fermentation in the production of wine, since it could modulate the generation of secondary products of fermentation in specific aromatic compounds. Fermentation is an exothermic process, and an efficient refrigeration system in fermenter tanks is necessary. Usually, to achieve this aim in fermentation tanks for wine-making processes, an external shell is implemented where a cooling fluid, normally water, flows. The circulation of the service fluid is triggered only when the temperature in the fermenter overcomes a critical value; however, this classical system could generate oscillation and stratification of the must temperature, reducing the goodness of the fermentation process. In this work, a substitutive cooling system based on heat pipe technology is proposed, and its feasibility is studied. It presents the benefit of always working and, for this reason, keeping a more constant and uniform value of temperature in the fermenter for the entire process duration. Additionally, the presented solution is completely passive, lowering energetic and economical costs. The obtained outcomes proved that the practical adoption of the proposed cooling system is achievable and that it constitutes an encouraging option.

Experimental investigation on the feasibility of a solution regenerator unit using freeze concentration for heat source tower heat pump system

Freeze concentration, which is often used in water treatment and the food industry, has a good regeneration effect and is easy for latent heat utilization. Therefore, a solution regenerator unit using freeze concentration with a heat pump system (SRFCHP) is proposed in this paper. In winter, SRFCHP can achieve weak antifreeze solution concentration, and the heat capacity of frozen phase transition is used to raise the supply water temperature. To investigate the performance of the SRFCHP system, a test was built in the enthalpy difference laboratory. Results shown that the SRFCHP system was able to regenerate the dilute solution from 13 % to 15 % in five regeneration cycle cycles. Around 34.5 % of ice production was able to be separated and the average loss mass of solute was about 0.95 kg per test in the regeneration cycle. Moreover, the SRFCHP system has a better performance on energy efficiency. About 62.5 % of total heat capacity had been recovered effectively. The solute recovery rate was 69.1 %. The coefficient of performance of refrigeration efficiency and heat recovery efficiency were 2.01 and 3.01, respectively. The specific ice production rate was 11.03 kg/kWh. These results demonstrate that the proposed system can be used in frosting regions to regenerate the dilution liquid.

Varying cross-sectional area of regenerator for improving efficiency of 4 K pulse tube refrigerator

Stirling-type pulse tube refrigerators (SPTRs) working at the liquid-helium temperatures are attractive in space applications. However, the refrigeration efficiency is as low as 0.5% of the Carnot efficiency or less. A method for improving the performance of the 4 K refrigerator by increasing the cross-sectional area of the regenerator at the colder part is numerically analyzed in this paper, and it is verified through experiments for the first time. The no-load temperature of the variable cross-sectional refrigerator reaches 3.87 K, which is 0.14 K lower than that of the uniform one, and the coefficient of performance (COP) is increased by 66% at 4.2 K. The reason for reducing the heat-associated enthalpy flow is the increment both in the heat transfer area and the total heat capacity of the matrix at the colder part. It is found that the lower the refrigeration temperature, the more significant the improvement is. Meanwhile, this method brings about some side effects that hinder the positive effects. The improvement of the COP tends to vanish at about 6 K. This new method provides a reference for further improving the performance of the SPTRs and other types of regenerative refrigerators working at liquid-helium temperatures.

Artificial Neural Networks as Artificial Intelligence Technique for Energy Saving in Refrigeration Systems—A Review

The refrigeration industry is an energy-intensive sector. Increasing the efficiency of industrial refrigeration systems is crucial for reducing production costs and minimizing CO2 emissions. Optimization of refrigeration systems is often a complex and time-consuming problem. This is where technologies such as big data and artificial intelligence play an important role. Nowadays, smart sensorization and the development of IoT (Internet of Things) make the massive connection of all kinds of devices possible, thereby enabling a new way of data acquisition. In this scenario, refrigeration systems can be measured comprehensively by acquiring large volumes of data in real-time. Then, artificial neural network (ANN) models can use the data to drive autonomous decision-making to build more efficient refrigeration systems.

Manipulation of thermal hysteresis and magnetocaloric effect in the Ni-Co-Mn-In alloys through lattice contraction: Effect of Ge substitution for In

First-order magnetostructural transformation can be utilized to generate giant magnetocaloric effect for the magnetic refrigeration applications, but the intrinsic hysteresis always cripples the refrigeration efficiency. In this work, the strategy of lattice contraction was exploited to manipulate the thermal hysteresis and magnetocaloric response in the Ni-Co-Mn-In magnetocaloric alloys. Such strategy was effectuated by using Ge to replace In on account of the relatively smaller atomic radius of Ge, yielding a significant reduction in the thermal hysteresis. In a Ni46Co3Mn37In10Ge4 alloy with the combination of low thermal hysteresis of ∼4 K and large magnetization difference of 83.1 Am2kg−1 associated with the magnetostructural transformation, giant effective refrigeration capacity RCeff of 311 Jkg−1 and reversible entropy change ΔSM up to 22.8 Jkg−1K−1 were demonstrated by varying the field of 5 T. Besides, a large reversible adiabatic temperature change ΔTad of –3.0 K was also obtained by using a low field change of 1.5 T. Based on the displacement gradient tensor determined by the orientation relationship governing the martensitic transformation, it was presented that Ge substation for In effectively decreased the lattice misfit, thus lowering the elastic energy accompanying the structural transformation and the related transformation hysteresis.

Vehicle Routing Optimization for Vaccine Distribution Considering Reducing Energy Consumption

In recent years, the energy consumption of vehicles has gained widespread attention due to the increasing importance of energy and environmental issues. Coupled with the explosive demand for vaccines that has spawned the massive deployment of refrigerated trucks, energy savings and efficiency improvement are the goals pursued by pharmaceutical logistics companies while getting the vaccine distribution task done. In order to evaluate the fuel consumption of refrigerated trucks during vaccine distribution, in this paper, we construct a mathematical model for the vehicle routing problem with time windows (VRPTW) for vaccine distribution with the aim of minimizing the total cost, including fossil fuel cost and penalty cost. Due to the NP-hardness and nonlinearity of the model, a genetic algorithm with a large neighborhood search operator (GA-LNS) and TSP-split encoding method is customized to address the large-scale problem. Numerical experiments show that the algorithm can obtain a near-optimal solution in an acceptable computational time. In addition, the proposed algorithm is implemented to evaluate a case of vaccine distribution in Haidian, Beijing, China. Insights on the effects of seasonal temperature, vehicle speed, driver working hours, and refrigeration efficiency are also presented.

Experimental Research of the Entire Wave System Inside a Wave Rotor Refrigerator and the Impact of Pressure Ratios on the Equipment Performance

Abstract The wave rotor refrigerator (WRR) is an efficient refrigeration technology. For the purpose of investigating the gas wave characteristics inside the rotor channels of WRR device, the performance and pressure monitoring experiments were conducted at various pressure ratios in this study, and the main findings are as follows: the computation method can produce an accurate design of pressure ports though the post-wave gas pressure of numerical computation has a certain difference with the experiment because of the actual gap leakage and friction loss. The deviation of working pressure ratio from the design values results in the reversed/reflected compression waves or worsens gas leakage, which lowers the equipment performance. When the expansion ratio α is constant, the efficiency reduction ratio does not exceed 11.9% as the relative variation rate of the compression ratio is less than 150%; When the compression ratio β is constant, the efficiency is relatively lowered by a proportion less than 16.4% as the relative increasing ratio of α is less than 63%. This study improves the mechanism of WRR and demonstrates the strong ability of WRR to resist fluctuations in working conditions.

Thermophysical properties of cassava during its cooling: Experiment, determination by inverse method, and simulation

AbstractMinimal processing consists in eliminating inedible parts of agricultural products, through cutting, reducing them to smaller portions, ready for immediate consumption or subsequent preparation. Despite the practicality, this resource is responsible for the first physical alterations in the tissues of food, contributing to its perishability. However, cooling of minimally processed products increases their shelf life. Designing refrigerators and calculating the costs of cooling require that the thermophysical properties of the product be known, making it possible to describe its cooling kinetics. The objective of this study was to present a methodology that includes experimental data and two computer programs for determining these properties referring to cylindrical pieces of cassava. A solver with the solution of the two‐dimensional diffusion equation was created for the direct problem, assuming the boundary condition of the third kind. For the inverse problem, an experimental data set of temperature in the center of the cassava pieces during cooling, the solver, and LS Optimizer software were used. The values obtained for thermophysical properties were consistent with those reported in the literature, while the cooling simulation was consistent with the experimental data, with χ2 = 1.7588 and R2 = 0.9992.Practical ApplicationsThe main contribution of this article is to present a methodology to determine thermophysical properties of agricultural products, including the uncertainties of these properties, during their cooling. This is a transient process, involving an interval of temperatures, and not one constant temperature, within which thermal properties are usually determined. With the information obtained for the thermal properties of cassava pieces, one can design an efficient refrigerator for the product and reliably calculate the cost for cooling the product during its minimal processing.

Design and Analysis of Charge‐Reduced Refrigerant Cycles Using R290

AbstractR290 is one of the most promising refrigerants for heat pumps and cooling processes working in a temperature range of –15 to 70 °C. The nearly neglectable global warming potential and attractive thermodynamic properties allow the design of climate‐friendly and efficient refrigeration systems and heat pumps. However, R290 is flammable, and the use of charge‐reduced components and designs should be the first central step to reduce safety risks. Whereas the prediction of heat capacity, temperatures and pressure drops are sufficiently precise the prediction of refrigerant charge is not very accurate when using computer‐aided design tools. The article presents a method to enhance accuracy for refrigerant cycles with less than 500 g of R290.

Selecting optimal R6TX2 intermetallics (R = Gd, Tb, Dy; T = Mn, Fe, Co, Ni; X = Sb, Te) for magnetic refrigeration.

A complete experimental study of the physical properties playing a relevant role in the magnetic refrigeration application (structural, magnetic, magnetocaloric and thermal) has been performed over nine selected Fe2P-type R6TX2 (R = Gd, Tb, Dy; T = Mn, Fe, Co, Ni; X = Sb, Te) intermetallic compounds, to work close to room temperature. Two magnetic phase transitions are observed for these materials: a paramagnetic to ferromagnetic transition in the range of 182-282 K and a spin reorientation transition in the range of 26-76 K. As a consequence, two peaks related to a direct magnetocaloric effect (DMCE) appear with the magnetic entropy change, generating a wide table-like plateau region in between both peaks, which is required to improve the efficiency of refrigerators following an Ericsson cycle. The highest magnetic entropy peak value for μ0ΔH = 5 T is found for Tb2Dy4FeSb2, with 7.72 J kg-1 K-1 around 182 K. For the same applied field the other compounds show moderate values around room temperature (2.88-4.53 J kg-1 K-1). However, the superposition of the two peaks results in huge refrigerant capacity values, up to RCFWHM(5 T) = 1103.04 J kg-1 in the case of Tb2Dy4FeSb2. The thermal diffusivity, thermal effusivity, thermal conductivity and specific heat capacity have been measured at room temperature, and the temperature dependence of the former has been obtained around the relevant magnetic phase transition region, with values in the range of 1.3-2.3 mm2 s-1, which are good for magnetic refrigerators at high working frequencies. The study is completed with a rigorous critical behavior analysis of the second order PM-FM transition. The critical exponent γ points to long range order interactions, in general, while β values are in the range of 0.59-0.90, indicating a deviation from theoretical models as a reflection of the magnetic complexity in these compounds. The critical exponents have been used to confirm the scaling relations of magnetocaloric properties, and the scaling of refrigerant capacity (RC) values in materials exhibiting two magnetic phase transitions is addressed, concluding that for a correct scaling of RC the magnetic entropy change peak must be considered symmetric. The role of each atom in the properties of the compounds is discussed.

Energy efficiency evaluation method of refrigeration and air conditioning in intelligent buildings based on improved entropy value method

In order to improve the accuracy and precision of the evaluation of cold source energy efficiency, this paper proposes an evaluation method of cold source energy efficiency of refrigeration and air conditioning in intelligent buildings based on the improved entropy method. On the basis of analysing the energy efficiency ratio composition of refrigeration and air conditioning system, the calculation process of energy efficiency ratio is refined by using refrigeration energy efficiency transport function. Then the AHM improved entropy method was used to optimise the weight ratio process, and the efficient and accurate evaluation of the cooling source energy efficiency of refrigeration and air conditioning was completed by adjusting the weight ratio. The experimental results show that the average evaluation accuracy of the proposed method is 95.9% and the average evaluation accuracy is 96.3%, which proves that the proposed method achieves the design expectation.

Modern refrigeration solutions for maritime sector and marine refrigeration transport

New coming environmental regulations from International Maritime Organization put each involved actor from ship manager, ship owner to cargo owner into a hard situation for a short time period to change the data collection process, to determine gups considering operating needs, to create an improvement plan according to specific requirements, needs, and goals. It is one more signal, in order to reach the sustainability goal, the industry digitalization process, and available efficient and effective use of technologies should be pushed forward. From cold chain digitalization, refrigeration system maintenance, and retrofitting processes, in particular, data science, process science, and data mining can be used. Refrigeration system retrofitting process modelling is presented by data mining technology. A lack of knowledge and investment in cold chain best practices and infrastructure lead to projects failing. Efficient, controlled, and smart Refrigeration is a challenge for the sustainable refrigeration sector. The global reefer transport market will expand up to 6% from 2020 to 2027 and it is vital for countries involved in military operations as well. The results of energy, exergy, and exergoeconomic analysis of different solutions intended for marine refrigeration transport, the cascade refrigeration system with R717-R744 refrigerants is presented. It was found that the optimum condensation temperature for the refrigerant of the high-temperature circuit is 40 °C, while the boiling temperature of the lower-temperature circuit is -50 °C. The temperature mode can be considered optimal ceteris paribus. The article provides an analysis of ejector refrigeration systems that can be used to improve the energy performance of marine refrigeration plants. It is a recommended issue to consider not only industrial requests but policies, and regulations in the force and in projects development status that can change an organization’s vision and aims of a strategic packet in own turn it can be affected a project budget change for labs, research institutions, shipyards.

Proposal and performance study on a component-based double-stage compression auto-cascade refrigeration cycle

It is difficult for the conventional single-stage compression auto-cascade refrigeration cycle to achieve higher refrigeration efficiency and lower refrigeration temperature, because the stream rich in high boiling point component from the phase separator bottom undergoes a single-stage compression process of high pressure lift ratio. Based on the concept of the evaporating temperature of the high/low boiling point component matching the grade compression of two streams from the phase separator, a component-baseddouble-stagecompressionauto-cascaderefrigeration (CDACR)cycle using R170/R600a is proposed in this paper. In the novel cycle, one dedicated compressor with two suction ports is used as the substitute for a conventional compressor with the sole suction port to realize grade compression process of the component of the refrigerant mixtures, and the stream enriched with high boiling point component from the separator bottom is sucked into the high-pressure suction port and undergoes the low-pressure-lift-ratio compression process, while the stream rich in low boiling point component from the separator top is sucked into the low-pressure suction port and executes the high-pressure-lift-ratio compression process, so as to cut down the compressor power consumption and obtain a lower refrigeration temperature. The mathematical model of the proposed cycle is developed to evaluate the thermodynamic performance of the system and comparisons with the conventional single-stage compression auto-cascade refrigeration (SCACR) cycle are also discussed. The results indicate that application of the component-based grade compression to the conventional auto-cascade refrigeration cycle dramatically improves the performance of the CDACR cycle, and there is optimum composition ratio of refrigerant mixtures for the CDACR cycle to obtain the highest coefficient of performance (COP). It is also shown that the performance of the CDACR cycle is significantly better than that of the SCACR cycle. As compared with those of the SCACR cycle, the compressor power consumption of the CDACR cycle decreases by 44.83%-53.17%, and its COP increases by 0.34–0.43, as the evaporating temperature at the evaporator outlet ranges from −60°C to −40°C. In addition, at the condenser outlet temperature in the range of 26°C- 40°C, the compressor power consumption for the proposed cycle is 37.74%-47.03% lower than that for the SCACR cycle, while COP of the CDACR cycle is 0.29–0.42 higher than that of the SCACR cycle.

Comparative Analysis of the Environmental Load of Natural Refrigerant (R290)

Due to the detrimental environmental consequences of synthetic refrigerants, natural refrigerants have gained renewed interest as alternative refrigerants for a variety of applications due to their minimal ozone depletion potential (ODP) and insignificant global warming potential (GWP). This study compares the performance characteristics of R32-based Air Source Heat Pump (ASHP) to those of R290 and R410A refrigerants. In this study, analyses of the cooling effect, heat output, compressor work input, and coefficient of performance (COP) for various refrigerants will be undertaken. Additionally, the environmental consequences of R32, R410A, and R290 are discussed. The results indicate that R290 is the most efficient refrigerant in terms of performance coefficient, followed by R410A and R32. Considering environmental protection aspects, R290 is a favorable substitute medium.

Effect of the micro-textured piston on the performance of a hermetic reciprocating compressor

A hermetic reciprocating compressor is one of the most critical parts for the energy efficiency of a household refrigerator. Piston-cylinder contact in the hermetic compressor accounts for most of the energy loss. The tribological performance of the piston-cylinder pair can be enhanced by introducing micro-texturing on the piston surface. In this research, an experimental study is presented to tribologically assess the effect of the micro-textured piston on the performance of the hermetically sealed reciprocating compressor. The micro-texture on the piston surface was prepared by the laser surface texturing method. Four different micro-textures were studied: radial micro-grooves, axial micro-grooves, mesh micro-grooves, and micro-dimples. The textures’ size, shape, and depth were studied using scanning electron microscopy (SEM) and white light interferometry (WLI) techniques. The results were compared with the non-textured piston compressor. It was found that the radial, axial, and mesh micro-grooves pistons have a negative effect on the coefficient of performance of the hermetic reciprocating compressor. However, the piston with the micro-dimples texture increased the compressor's coefficient of performance by 1%. Refrigerant leakage from the piston-cylinder clearance was also investigated and it was observed that micro-dimples on the piston surface decrease the refrigerant leakage by 35% due to the presence of a continuous oil film between piston and cylinder. The compressor's cooling capacity (Qc) was observed to be increased by 1 W in the case of a micro-dimpled piston.

Enhancing the elastocaloric effect and thermal cycling stability in dendritic-like Ni50Mn31.6Ti18.4 single crystal

Solid-state cooling based on elastocaloric effect possesses potential for refrigeration. The improvement of elastocaloric effect and thermal cycle stability is beneficial to enhance the refrigeration efficiency and service life of refrigeration equipment. Here, single-crystal Ni50Mn31.6Ti18.4 shape-memory alloys were successfully prepared using directional solidification technique. The microstructure, martensitic transformation, isothermal stress-strain responses and elastocaloric effect of the single crystals with different solidification rates have been systematically studied. The single crystal solidified at 10 µm s−1 exhibits lower stress hysteresis Δσhy and much more superior adiabatic temperature |ΔTad| than those of alloys solidified at 100 µm s−1 and 500 µm s−1, with the values of 34 MPa and 24.8 K. In addition, the single crystal at low solidification rate also performs excellent cyclic stability. All these results show that the single crystal with larger austenite primary dendrite arm spacing (PDAS) can effectively enhance the elastocaloric effect and thermal cycling stability in Ni50Mn31.6Ti18.4 alloys. This work sheds a bright light on the relationship between the elastocaloric performance and microstructure for shape-memory alloys.

Colossal barocaloric effect achieved by exploiting the amorphous high entropy of solidified polyethylene glycol

The barocaloric effect (BCE) has emerged as an intense research topic in regard to efficient and clean solid-state refrigeration. Materials with solid-liquid phase transitions (SL-PTs) usually show huge melting entropies but cannot work in full solid-state refrigeration. Here, we report a colossal barocaloric effect realized by exploiting high entropy inherited from huge disorder of liquid phase in amorphous polyethylene glycol (PEG), which is solidified by introducing 5 wt.% polyethylene terephthalate (PET). Transmission electron microscopy (TEM) combined with X-ray diffraction (XRD) demonstrates the amorphous nature of the high-temperature phase after fixation by PET. Although PEG loses its –OH end mobility in amorphous solid, high entropy still retains owing to the retained high degrees of freedom of its molecular chains. The remaining entropy of amorphous PEG is up to 83% of that of liquid PEG in PEG10000/PET15000, and the barocaloric entropy change reaches ΔSp ∼ 416 J·kg−1·K−1 under a low pressure of 0.1 GPa, which exceeds the performance of most other BCE materials. Infrared spectra combined with density function theory (DFT) calculations disclose conformational change from the liquid to amorphous state, which explains the origin of the large entropy retained and hence the colossal BCE of the solidified PEG. This research opens a new avenue for exploring full solid-state barocaloric materials by utilizing genetic high entropy from huge disordering of liquid phases in various materials with SL-PTs.

Design and Optimization of Automotive Air Conditioning Duct Based on CFD Algorithm

Nowadays, the air conditioner (AC), as an important guarantee for driving comfort and endurance, has attracted more and more attention. The pipe connecting the air conditioner refrigerator and the air outlet of the cockpit instrument panel is known as the air duct. Its structural characteristics and fluid flow characteristics are related to the refrigeration efficiency of the whole air conditioning system. The air supply performance of the air duct directly affects the uniformity of the temperature field and speed field in the car, thus affecting the comfort performance of the car [2]. Limited by the layout space, the design of air conditioning duct is the most difficult part of the design of automobile air conditioning system [1]. Therefore, how to optimize the air duct of automotive air-conditioning to meet the size design of the car while being more energy-efficient is an important research direction. This paper focuses on the simulation design and further optimization of the model of the air duct of automotive air conditioning through CFD algorithm. The author uses the Soildworks software for preliminary modeling, meshes the established model with Meshing, and applies the Fluent software to simulate the fluid flow characteristics in the pipe. By inputting a given flow to the inlets, the air volume of each outlet can be simulated. Based on the initial air-conditioning duct model of a vehicle model, the pipe turbulence problem and the uneven distribution of air volume at each outlet in the simulation process are improved under the condition of ensuring the existing size, and finally the rationality of the improvement is verified.

Semi-clathrate hydrate slurry as a cold energy storage and transport medium: Rheological study, energy analysis and enhancement by amino acid

Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate is an attractive phase change material for cold energy storage and transport. The high viscosity of hydrate slurry is a major challenge for process design and causes large pumping power consumption, not to mention the significant discrepancy of viscosity data observed in the literature. In this study, the discrepancy was clarified by studying the rheology of TBAB semi-clathrate hydrate slurry (SHS) using a rheometer with seed-induced in-situ formation of hydrate up to a high hydrate fraction (∼0.51). TBAB SHS exhibited a non-Newtonian shear-thinning behavior. Its apparent viscosity increased exponentially with the increase of hydrate fraction. Type B TBAB SHS was recommended due to its lower apparent viscosity than type A TBAB SHS. Energy analysis revealed that TBAB SHS with appropriate hydrate fractions could outperform chilled water to provide the same cooling capacity but consume less pumping power. Furthermore, to reduce the viscosity, an environmentally benign additive l-tryptophan was identified and employed for the first time. Addition of l-tryptophan up to 1.0 wt% in TBAB SHS significantly decreased the apparent viscosity and lead to a 68.7% reduction of pumping power consumption compared with chilled water. This work demonstrated the potential of TBAB SHS as a more efficient next-generation secondary refrigerant and the addition of a small dosage of l-tryptophan would considerably enhance its economic strength in cooling applications.