Journal of Fluid Flow, Heat and Mass Transfer (JFFHMT)

ISSN: 2368-6111

Exploring the Utilization of Newtonian Fluids in Heat Transfer Applications

Surupa Shaw^1,2, Dominga Guerrero^1,2

¹Texas A&M University | Department of Multidisciplinary Engineering
400 Bizzell St, College Station, United States
¹²Texas A&M Higher Education Center at McAllen
6200 Tres Lagos Blvd., McAllen, United States
surupashaw@tamu.edu | dguerr56@tamu.edu

Abstract - This paper presents a comprehensive review of theoretical investigations concerning the influence of Newtonian fluids on heat transfer processes. Newtonian fluids are characterized by a constant viscosity that remains unaffected by variations in shear rate. Their widespread utilization in heat transfer applications is attributed to their consistent and stable flow behaviour, facilitating easier modelling and analysis. A prominent exemplification of the application of Newtonian fluids in heat transfer lies in electronic cooling systems. These fluids, typified by substances like water or oil, efficiently dissipate the heat generated by electronic components through circulation within the cooling system. Moreover, Newtonian fluids play a pivotal role as heat transfer agents in heat exchangers, wherein an array of tubes facilitates the exchange of thermal energy between two fluids separated by a conductive partition. In addition, within the realm of industrial processes, Newtonian fluids find utility in mixing tanks and reactors for tasks ranging from heat transfer between different phases to the maintenance of uniform temperatures within the vessel. The consistent behaviour and low viscosity of Newtonian fluids render them exceptionally effective in mediating heat transfer across diverse applications. This paper presents a comprehensive comparative study between air and Newtonian fluids as heat transfer media in various industrial applications. The objective is to assess the advantages, limitations, and suitability of each medium in different scenarios, considering factors such as thermal efficiency, cost-effectiveness, ease of implementation, and environmental impact. This study embarks on an exploration of the multifaceted utilization of Newtonian fluids in both industrial and consumer contexts, shedding light on their indispensable role in enhancing heat transfer processes.

Keywords: Newtonian, Heat transfer, Heat exchangers, Fluids, Reactors, Mixing tanks.

© Copyright 2023 Authors - This is an Open Access article published under the Creative Commons Attribution License terms Creative Commons Attribution License terms. Unrestricted use, distribution, and reproduction in any medium are permitted, provided the original work is properly cited.

Date Received: 2023-08-20
Date Revised: 2023-09-25
Date Accepted: 2023-10-04
Date Published: 2023-10-18

1. Introduction

Newtonian fluids renowned for their heat transfer attributes are extensively employed across a spectrum of engineering and industrial applications. Their burgeoning popularity can be attributed to their exceptional characteristics and user-friendliness. These fluids are distinguished by their capability to facilitate efficient heat transfer while maintaining the quintessential Newtonian fluid trait of consistent viscosity across varying shear rates. Franco et al.[1] considers Newton’s law of Viscosity:

where the shear stress τ of a fluid is equal to the product of its dynamic viscosity μ and the rate of shear deformation du/dy. Among the commonly employed fluids that satisfy this criterion are water, air, oil, gasoline, alcohol, glycerol, organic solvents, motor oil, and honey. These fluids exhibit a decrease in viscosity with rising temperatures, a consequence of heightened molecular kinetic energy, which, in turn, leads to more frequent molecular collisions. This phenomenon results in reduced flow resistance and lower viscosity. The temperature dependence of viscosity is best described by the Arrhenius equation:

where viscosity µ is measured in pascals/sec, μ_o is a constant value measured in pascals/sec, and E_A is the activation energy a molecule must experience before taking part in a reaction, measured in kJ/mol, R is the universal gas constant, 0.00831434 kJ/mol K and T is the absolute temperature in Kelvin. The equation suggests that the viscosity of a fluid decreases exponentially with increasing temperature. Yanniotis et al.[2] utilized the Arrhenius equation satisfactorily to predict the dependency of the viscosity of honey on temperature, proving the Newtonian behavior of honey.

Water reigns as the predominant Newtonian fluid in utilization, primarily attributable to its exceptional thermal conductivity and specific heat capacity, rendering it an exceptionally effective heat transfer medium. Moreover, water enjoys widespread availability and affordability in comparison to alternative heat transfer fluids. In addition to water, other prominent Newtonian fluids endowed with heat transfer capabilities encompass various oils, glycols, and refrigerants. These versatile fluids find application in diverse sectors, including HVAC systems, refrigeration, power generation plants, and chemical processes. Furthermore, they are integral components in heat exchangers, facilitating the transfer of heat between two distinct fluids. Prabhanjan et al.[3] utilized tap water as a heat transfer fluid when comparing the heat transfer coefficient of a helical coil heat exchanger and a straight tube heat exchanger. They found that the water’s temperature was affected by the coil geometry of the fluid, thus causing an increase in heat transfer to the helical coil heat exchanger compared to the straight tube heat exchanger. Rudresha et al.[4] investigated a two-phase pulsating heat pipe(PHP) system that used water as the coolant and ethylene glycol as the working fluid at different filling ratios to determine the heat transfer performance under different heat inputs. The results show that the heat transfer increases with the filling ratio and displayed lower thermal resistance up at a 70% filling ratio.

Air, while not as thermally efficient as liquids for heat transfer, remains a prevalent choice in various heat transfer applications owing to its wide availability, cost-effectiveness, and safety considerations.

Within HVAC systems, “air” assumes a pivotal role as the primary heat transfer medium, serving to ensure thermal comfort for occupants. The process involves heating or cooling air by passing it through respective heating or cooling coils. Subsequently, the conditioned air is distributed throughout the building via ductwork. The air's capacity to absorb and release heat significantly influences the system's efficiency and its effectiveness in maintaining desired temperatures. In refrigeration systems, air serves as a secondary heat transfer medium, tasked with expelling heat from the refrigerant. Here, the refrigerant undergoes cooling as it passes over a coil that is itself cooled by air. The efficiency of this process relies heavily on the air's ability to extract heat from the coil, ensuring the refrigeration system's effectiveness. Within cooling systems, air stands as the primary heat transfer medium for dissipating heat from equipment or industrial processes. Conventionally, air is blown over surfaces to facilitate heat removal through convection. The air's prowess in heat dissipation is paramount for maintaining the optimal temperature of various industrial equipment and processes. Vlasogiannis et al.[5] tested a two-phase air-water flow as a cold stream in a plate heat exchanger and a single-phase hot water heat stream. When comparing the heat transfer, they found that it is always higher in the two-phase flow due to the presence of air.

Oil finds widespread application as a coolant across various domains, notably in high-performance engines and machinery subjected to substantial heat loads. The use of oil as a coolant boasts several merits, such as its exceptional heat absorption and transfer capabilities, its inherent lubrication attributes, and its resistance to thermal deterioration and breakdown. Shen et al.[6] investigated the use of mineral oil as a dielectric coolant for transformers, along with alternative dielectric oils that are plant-based. They concluded that the plant-based oils are the superior coolant for transformers as they are environment-friendly and satisfy fire-safety requirements.

Newtonian fluids exhibit changes in viscosity primarily in response to temperature variations rather than alterations in shear rate. This behavior results in reduced friction and wear on the equipment employing them. Wurzel[7] describes the uses of glycerol, a Newtonian fluid used in several industries, such as food, pharmaceutical, personal care, printing, and even for creating dynamite (nitro-glycerine).

The process of heat transfer within Newtonian fluids transpires via conduction, convection, and radiation mechanisms. The rate of heat transfer hinges on an interplay of factors encompassing the fluid's thermal conductivity, viscosity, density, specific heat capacity, emissivity, and velocity, alongside the system's geometry and the temperature differential between the fluid and its surrounding environment. Zhang et.al.[8] experimented with forced convection of water, where they studied the freezing behaviour of water subjected to forced convection and emphasized its importance in predicting the frosting of the engine air precooler. They found that while under forced convection, the convective heat transfer between the airflow and liquid phase of water leads to an increase in the temperature of the liquid phase.

The thermal management of technology is increasingly dependent on heat transfer as components are consuming higher amounts of power to increase their productivity. Liquid and air cooling continue to be analysed and innovated to meet the requirements of next-generation devices. Traditionally, air cooling has been used in managing electronics due to its mechanical simplicity, as stated by Etemoglu [9]. Distilled water is conventionally used in liquid cooling systems for electronics as it is electrically non-conductive and has a high thermal capacity and low viscosity. Tie et al.[10] studied the influence of jet arrays [with distilled water] on heat transfer and found the enhancement of heat transfer by increasing Reynold’s number with small jets instead of large jets. He et al.[11] used an internal indirect water-cooled heat sink cycle and an external cooling tower cold source cycle to decrease the power consumption of a server tower. They found the ideal water temperature for different ambient temperatures of the server tower and were able to generate a 21.3% reduction in power consumption. This paper also presents a comprehensive comparative study between air and Newtonian fluids as heat transfer media in various industrial applications. The objective is to assess the advantages, limitations, and suitability of each medium in different scenarios, considering factors such as thermal efficiency, cost-effectiveness, ease of implementation, and environmental impact. The study encompasses a range of industrial sectors, including HVAC systems, power generation, chemical processing, and manufacturing, where heat transfer plays a pivotal role. The thermal properties, heat transfer mechanisms, and practical considerations of both air and Newtonian fluids are evaluated to provide a comprehensive perspective on their performance.

Overall, the widespread adoption of Newtonian fluids with heat transfer capabilities is underpinned by their prowess in facilitating efficient heat transfer, user-friendly characteristics, and ready availability. As emerging technologies unfold and the quest for enhanced, sustainable heat transfer solutions gains momentum, the utilization of these fluids is poised to expand further in response to evolving demands.

2. PROPERTIES OF POPULAR NEWTONIAN FLUIDS

All Newtonian fluids have the unique characteristic of “their viscosity changing with temperature and their ability to resist shear rate” in common. Although true, it does not make all Newtonian fluids equally suitable for the same applications.

2.1. Thermophysical Properties of Newtonian Fluids

Considering the thermophysical properties of Newtonian fluids, as described in Table 1, one can select the fluid to be used based on design specifications for different applications and devices.

2.2. Advantages, Disadvantages, and Applications of Popular Newtonian Fluids

The choice of the appropriate Newtonian fluid for a heat transfer application must be accompanied by highlighting its advantages and disadvantages. Depending on a Newtonian fluid’s environment, its

characteristics might be detrimental to its surroundings, making them only acceptable in certain applications. Table 2 highlights the advantages, disadvantages, and applications of fluid groups of popular Newtonian fluids.

2.2.1. Advantages

1. Predictable Flow Behavior: Newtonian fluids exhibit a reliable and uniform flow behavior, simplifying their modeling and analysis in heat transfer applications. This predictability enables engineers to make precise predictions regarding flow rates, pressure fluctuations, and heat transfer rates, streamlining the design process.
1. Good et al.[12] utilized air to replace thermal oil as a heat transfer fluid in a novel Concentrating Solar-thermal Power (CSP) solar receiver. This was done to overcome the limited operating temperature of 450°C with thermal oil, which they could do and increased to 650°C with air. In this situation, air was more desirable than thermal oil due to its availability, cost, and low toxicity.
2. Coupled with CSP systems is Thermal Energy Storage (TES), where molten can be used as a heat transfer medium to replace thermal oil. Bonk et al.[13] investigated five molten salt variations: Solar Salt, HitecXL, LiNaK-Nitrate, Hitec, and CaLiNaK, and determined the thermophysical properties of each. Due to their low melting temperature, they found that salt mixtures such as Hitec, HitecXL, LiNaK-Nitrate, and CaLiNaK are candidates for HTF in CSP TES systems.
3. Jithin et al.[14] investigated using deionized water, mineral oil, and engineered fluid in a single-phase immersion cooling for a lithium-ion battery. They found that when using the deionized water, the heat is removed from the battery almost at the same rate as heat generated. When comparing the viscosity of the fluids, it was noticeable that the pressure drop and power consumption were greater for the mineral oil and engineered fluid. Therefore, deionized water, as expected is best suited for decreasing power consumption.
2. High Thermal Stability: Certain Newtonian fluids, including mineral oils, demonstrate remarkable thermal stability, allowing them to withstand high temperatures without experiencing degradation or breakdown. Consequently, these fluids prove highly suitable for demanding high-temperature applications such as power generation and industrial processes.
4. Li et al.[15] proposed using liquid metals to replace water as the working fluid to enhance heat transport in heat exchangers, as liquid metals have higher thermal conductivity than water.
5. Trimbake et al.[16] utilized mineral oil as a coolant in jet impingement immersion cooling of lithium-ion batteries due to its thermal stability. They found that the mineral oil maintained a uniform temperature along and within the cells of the batteries compared to natural air convection cooling.
3. Compatibility with Equipment: Newtonian fluids frequently exhibit compatibility with an extensive array of heat transfer equipment, encompassing heat exchangers, boilers, and piping systems. This inherent versatility renders them a flexible and adaptable option for a multitude of heat transfer applications.
6. Garrett et al.[17] compared water, carbon dioxide, and helium as coolants in a nuclear reactor model, finding that water could maintain the fusion reactor temperature better than carbon dioxide and helium.
7. Qin et al.[18] used silicone oil in a model to measure the heat dissipation of light-emitting diodes (LEDs) by submerging a LED in the oil. They chose silicone oil because of its good electrical heat dissipation and high heat capacity, causing it to avoid catching fire easily.
8. Velasco et al. [19] experimented with the performance of a CO2 water-to-water heat pump and a water storage tank for domestic hot water (DHW) production to increase water temperature distribution. At high water flow rates at the gas cooler it reduced the systems coefficient of performance (COP) due to a reduction of water temperature at the top of the storage tank, reduction of the COP of the CO2 heat pump, increasing the use of the compressor to get the water at the top of the tank to the desired temperature.

2.2.2. Disadvantages

1. Susceptibility to Fouling: Newtonian fluids may exhibit susceptibility to fouling, characterized by the accumulation of deposits on the heat transfer equipment's surface. Such fouling can result in a diminished efficiency of heat transfer and an escalation in maintenance expenditures.
1. Liu et al.[20] investigated the use of glycol as an antifreeze in cooling tower’s solar generation systems, as they are sensitive to freezing in winter and affect the solar system's performance. The glycol was added to the water of the cooling tower, which decreased the heat transfer efficiency of the tower, thus rendering it unsuitable for this application.
2. Limited Temperature Range: Certain Newtonian fluids, including water and various oils, possess a restricted operational temperature range. For instance, water's boiling point at 100°C can impose limitations on its suitability for high-temperature applications.
2. Fernández et al.[21] evaluated the replacement of mineral oil as the liquid insulation in power transformers with vegetable-based and silicone-based dielectric oils. They described the harmful effects of mineral oil, such as being non-biodegradable and a fire hazard. They found that using vegetable-based dielectric oils was a better alternative due to their high flash points.
3. Limited Stability: Certain Newtonian fluids may deteriorate or degrade with the passage of time, especially when subjected to elevated temperatures or harsh environmental conditions. Such degradation can curtail their serviceable lifespan, resulting in the need for more frequent replacements or maintenance procedures.
3. Vignarooban et al.[22] discusses the effect of different HTF, such as air, water/steam, thermal oils, organic fluids, molten salts, and liquid metals in CSP systems. They found molten salts most advantageous due to their extremely high boiling points. Consequently, molten salt proposed dangers due to its high-corrosive nature with the pipes and containers of CSP systems made of metal alloys.
4. Soni et al.[23] discuss the disadvantages of using mineral oil as transformer oil. It is considered an environmental hazard in spillage, limited stock, and flammability, which has caused explosions in mineral-based transformers.
4. Scarcity: Availability of certain Newtonian fluids varies globally, creating the need to explore and research substitute fluids for applications where these Newtonian fluids are traditionally used.
5. Du Plessis[24] describes water scarcity in water-stressed areas, deducing that industrial applications are responsible for the degradation of water around the globe. Finding alternatives for water in industries, such as heat transfer applications, can be more helpful to the environment.

3. COMPARISON OF LIQUID COOLING VS AIR COOLING IN ELECTRONICS

Inadequate heat dissipation can occur when the thermal design of any electronic device is insufficient or when the cooling system is not properly sized for the heat load generated by the components. Liquid and air cooling provide a thermal control that allows the component to maintain a temperature at its functional and allowable limits. Table 3 showcases the comparison between liquid and air cooling of the electronics.

3.1. Applications of Heat Transfer

1. Heat exchanger: This apparatus facilitates the transfer of heat between two fluids while ensuring they remain isolated in separate chambers, preventing any mixing. Heat exchangers come in diverse forms, including shell and tube, spiral, loop, fin and flat, among others. One notable industrial application for heat exchangers is within HVAC (Heating, Ventilation, and Air Conditioning) systems.
1. Jouhara et al.[36] investigated water as a working fluid in a wraparound loop heat pipe (WLHP) heat exchanger in HVAC systems. The results showed that the thermal performance of water as the working fluid was higher than with conventional HVAC systems that use refrigerants.
2. Missaoui et al.[37] investigated the helical coil heat exchanger with water as the working fluid, for domestic refrigeration and water heating, and determined the variable pitch coils on the heat exchanger improved the overall heat transfer coefficient by 36.48% when compared to a normal coil. They found that the design of the helical coil directly impacts the water temperature distribution.
2. Mixing tanks: These are mechanically stirred containers designed to uphold a consistent temperature. When dissimilarly heated fluids are combined within the mixing tank, the agitation process facilitates heat transfer, ensuring an even distribution of heat throughout the mixture. Newtonian fluids excel in this context due to their ability to maintain viscosity despite variations in mixing speed within the tank. This technology finds valuable application in the food and beverage industry.

iii.  Śmieja et al.[38] describes the pasteurization applications of milk, a Newtonian fluid that has to be held at a constant temperature for a set period to ensure the product’s shelf life is not reduced due to bacteria buildup. Agitated systems use water heated by an external source as a heat transfer medium to distribute the heat evenly throughout the milk.

3. Fluidized bed reactors (FBR): These systems harness the thermal properties of Newtonian fluids like air and steam to optimize heat transfer between a fluid and a solid medium. The process involves the passage of the fluid through a high-velocity flow bed of solid particles, effectively heating or cooling the solid material.
4. The industrial application in chemical processing has been explored by Li et al.[39], who utilized the steam generated using distilled water to fluidize the catalyst of a fluidized bed reactor in a catalytic cracking of cottonseed oil. The produced fluid was liquid rich in gasoline and diesel. The role of distilled water in this experiment was to facilitate the heat transfer of steam and temperature control to the fluidized bed reactor.
4. Consumer Consumption Applications: They make use of heat transfer with Newtonian fluids, such as the following:
5. Water heaters: Taira [40] proposed using CO2 to replace refrigerants in water heaters in residential homes. They found that using CO2 could reduce the power output from their home while still being capable of heating water to 90° C. The heat transfer of the CO2 and other refrigerants were comparable, with CO2 having greater benefits in reducing greenhouse gases. Ihiourne et al.[41] conducted an experimental study using a water-to-air heat exchanger to replace the use of a boiler in a greenhouse, resulting in lower CO2 emissions of 142g/day compared to 41,000 g/day, along with an improvement in the greenhouse’s internal air temperature at night of 4℃ to 5℃.
6. Electronics cooling: In our electronic devices, such as mobile phones, laptop computers, and tablets, heat transfer is used to cool the devices as it is essential to maintain a certain operating temperature. Alnaimat [42] experimented on the use of air-water mist evaporating cooling in a heat sink compared to air cooling, finding an increase of 158% in heat transfer when using the mist at 1-6% in the heat sink. Heat sinks such as these can be used in microelectronic cooling systems.
5. Competition for Newtonian Fluids: Non-Newtonian Power-Law fluids, also known as shear-thinning fluids, exhibit viscosity that varies with shear rate and they follow the Power-Law model, where viscosity (η) is related to shear rate (γ) by the equation: η = K * γ^n , where K is the consistency coefficient, and n is the flow behavior index. The value of n determines the degree of shear-thinning: n < 1 indicates significant shear-thinning behavior. They are widely used in a variety of industries [where heat transfer capabilities of power-law fluids play a vital role], like food processing [ketchup, mayonnaise, etc.], oil and gas industry [Crude oil, drilling mud, hydraulic fracturing fluid, etc.], polymer processing, pharmaceuticals, wastewater treatment [sludge] and nanofluids used for electronic cooling.

6. Conclusion

In summary, the examination of Newtonian fluids' role in heat transfer applications has revealed a spectrum of advantages and drawbacks. Newtonian fluids play a pivotal role in the realm of heat transfer, offering a multitude of advantages that significantly enhance their suitability for various applications. These fluids exhibit desirable attributes such as predictable flow behaviour, low viscosity, ease of handling, exceptional thermal stability, and compatibility with equipment, rendering them an appealing choice for numerous heat transfer scenarios. Predictable flow behaviour of Newtonian fluids simplifies their modelling and analysis, allowing for precise predictions of flow rates, pressure drops, and heat transfer rates. These fluids efficiently transfer heat due to their stable viscosity, which makes them well-suited for applications where precise control of temperature and heat dissipation is critical. The high thermal stability of Newtonian fluids allows them to operate at elevated temperatures without breaking down or degrading, which leads to their compatibility with a wide range of heat transfer equipment, including heat exchangers, boilers, and piping systems. Newtonian fluids are generally safe to handle, and their properties are well-understood, minimizing risks associated with heat transfer processes. The reliable nature of Newtonian fluids simplifies the design and modelling of heat transfer systems. These advantages collectively underscore the significance of Newtonian fluids in optimizing heat transfer efficiency and effectiveness across a myriad of industrial and consumer applications. As technology advances and the demand for more efficient and sustainable heat transfer solutions continues to grow, Newtonian fluids are expected to maintain their prominent role as reliable and versatile heat transfer media.

Nonetheless, it is essential to acknowledge certain limitations, including their susceptibility to high shear stress and the potential for fouling and corrosion. The selection of a fluid for a specific heat transfer application necessitates a nuanced consideration of various factors, encompassing the unique requisites of the application, the fluid's inherent properties, and any potential constraints imposed by the fluid's characteristics. Future research endeavours hold the promise of deeper insights into the properties and behaviours of Newtonian fluids in the realm of heat transfer, thereby paving the way for the development of more efficient and effective heat transfer systems.

References