Potassium formate and potassium acetate, as well as their blends are known as environmentally friendly secondary fluids with good thermophysical properties. The aim of this work was to investigate properties of cesium formate, cesium acetate and ammonium acetate solutions. Results showed that various alkali metal ions such as potassium, sodium, cesium or ammonium are affecting the freezing point, thermal conductivity, viscosity and specific heat capacity in different ways. Among examined salts, ammonium formate showed the best performance by giving the highest specific heat capacity and highest thermal conductivity and the lowest dynamic viscosity compared to potassium formate and other salts. Cesium formate solutions had the lowest viscosity among all tested salts. This study shows that both cesium formate and sodium formate could be used as different additives to enhance different properties of potassium formate and potassium acetate secondary based fluids.

Potassium organic salts like formates and acetates are known as environmentally friendly secondary fluids. The most important advantages of salts compared to aqueous solutions of alcohols and glycols are good thermophysical properties, low toxicity and non-flammability. The purpose of this work is to investigate properties of different formate salt based secondary fluids like: lithium formate, ammonium formate and sodium formate at low temperatures in order to propose new blends of formate salts that could be used as secondary fluids for low temperature applications. Studies showed that different alkali metal ions like sodium, lithium or ammonium are affecting the solubility level, freezing point, thermal conductivity, dynamic viscosity and specific heat capacity in different way. Among examined formate salts, ammonium formate showed the best performance by giving the lowest freezing point as well as the highest specific heat capacity and highest thermal conductivity and similar dynamic viscosity. Lithium formate salts had the highest dynamic viscosity among all samples and despite high specific heat capacity and thermal conductivity values these salts cannot be recommended for low temperature applications. 30 wt-% sodium formate and 36 wt-% lithium formate were recrystallizing at lower temperatures than 0 degrees C when fast cooling rate was applied. Thus, the possible application for these salts is rather limited to higher temperatures only. As seen, different type of cation group in the formate salt can result in different properties, thus, further studies to investigate ammonium formate as well as different acetate salts are recommended.

The most common secondary fluid used for the borehole heat exchangers in Sweden is aqueous solution of ethyl alcohol (EA). Commercially available ethyl alcohol based fluids in Sweden and other Euro ...

Ethylene and propylene glycol water based secondary solutions are very popular due to their low corrosivity character, low freezing point, high boiling point and low fire hazards. The main drawback of ethylene glycol solutions is its potential toxicity both to the environment, animals and food products. Therefore, propylene glycol is the most common substitute for ethylene glycol. The biggest disadvantage of propylene glycol solutions is its very high viscosity at low temperatures, which results in higher pumping power and lower system performance. For very low temperatures, it is common to use non-aqueous synthetic fluids, which have lower viscosities at these temperatures. Thus, the aim of this paper is to propose a new generation of synthetic iso-paraffins having better thermophysical properties compared to existing synthetic products used for very low temperature applications.The first results showed that the new generation of iso-paraffins having the freezing temperature of 50 degrees C or lower had significantly lower viscosity (between 75 % and 98 %) at very low temperatures compared to 60 wt-% propylene glycol (PG 60 %) and 60 wt-% ethylene glycol solution (EG 60 %). Iso-paraffin 1 showed better performance than iso-paraffin 2 by giving the lowest freezing point, the lowest dynamic viscosity and kinematic viscosity as well as the highest thermal conductivity. Instead, iso-paraffin 2 had higher specific heat capacity. As seen, the different composition of iso-paraffin mixture can result in different properties and operating temperature ranges. Thus, iso-paraffins could become an interesting alternative for very low temperature cooling applications.

The most common secondary fluid used for the borehole heat exchangers in Sweden is an aqueous solution of ethyl alcohol (EA) due to its relatively good thermophysical properties and low toxicity. C ...

In Sweden, there are more than 500 000 small and about 500 relatively large ground source heat pumps (GSHP) having a total installed capacity of about 5.6 GW delivering approximately 15 TWh. yr-1 o ...

Seawater is the most common fluid on earth and ice generating machines are increasingly used on fishing vessels to produce ice slurry from the seawater with up to 60 % ice to be poured over the catch. In this study, new measurements of thermophysical properties of standard seawater have been carried out to complement a recent literature search made to establish thermophysical property data of seawater as function of salinity and temperature. These single-phase measurements have been made for salinity 20, 30 and 35 g kg(-1) (2.0, 3.0 and 3.5 % total salt content) and include measurements of freezing point, density, dynamic viscosity, thermal conductivity, specific heat capacity and specific enthalpy. The obtained experimental results generally confirm recent literature search and experimental results only call for minor adjustments of viscosity values. Hence, experimental results confirm the following published ice slurry properties: enthalpy, ice fraction and ice slurry density.

Currently available commercial ethyl alcohol (EA) based secondary fluids in Sweden and other Nordic countries contain up to 10 wt-% denaturing agents (in concentrate alcohol) in form of propyl alcohol and n-butyl alcohol but no corrosion inhibitors. These studies were initiated due to a growing need for providing any protection against corrosion and extending the lifetime of the system. A literature search has been made to find the compatible corrosion inhibitors that can effectively protect the system. Afterwards, measurements have been performed to investigate the effect of these corrosion inhibitors on the thermophysical properties of the base fluid. Results showed that the different corrosion inhibitors can affect the thermophysical properties even when added in small concentrations. The presences of corrosion inhibitor had a positive effect and decrease the freezing point. Additionally, the presence of corrosion inhibitor in 30 wt-% ethyl alcohol samples had no significant effect on the dynamic viscosity and only EA25 + 0.01 SG (sodium gluconate) sample showed lower dynamic viscosity value by up to 10 %. The corrosion inhibitors had negative effect on the thermal conductivity in the full temperature range. EA25 and EA30 samples containing sodium gluconate, benzotriazole and sodium molybdate had higher specific heat capacity than the pure solutions. This study showed that both benzotriazole and 2-mercaptobenzothiazole seem to be the most promising corrosion inhibitor for ethyl alcohol based secondary fluids.

Seawater is the most common fluid on earth and ice generating machines are increasingly used on fishing vessels to produce ice slurry from the seawater with up to 60 % ice to be poured over the catch. In this study, new measurements of thermophysical properties of standard seawater have been carried out to complement a recent literature search made to establish thermophysical property data of seawater as function of salinity and temperature. These single-phase measurements have been made for salinity 20, 30 and 35 g kg(-1) (2.0, 3.0 and 3.5 % total salt content) and include measurements of freezing point, density, dynamic viscosity, thermal conductivity, specific heat capacity and specific enthalpy. The obtained experimental results generally confirm recent literature search and experimental results only call for minor adjustments of viscosity values. Hence, experimental results confirm the following published ice slurry properties: enthalpy, ice fraction and ice slurry density.

Ground source heat pumps are commonly used in Sweden. The dominating method of exchanging heat with the ground is by circulation of a secondary fluid through borehole heat exchangers inserted into energy wells. Due to the environmental reasons and relatively good thermophysical properties, aqueous solutions of ethanol are recommended and are commonly used for the borehole heat exchanger application in Sweden and other Nordic countries. The primary idea of using these fluids is to decrease the freezing point of the fluid since many borehole loops in Northern Europe operate near or below the freezing point of water. The available ethanol based commercial products consist of ethyl alcohol with up to 10% of denaturing agents without any corrosion inhibitors. The main denaturing agents used to prevent from drinking are mixtures of isopropyl alcohol, n-butanol, acetone, methyl ethyl ketone and methyl isobutyl ketone. These denaturing agents in commercial secondary fluids can influence the fluid’s thermophysical properties and thereby affect the pressure drop and heat transfer in the borehole heat exchanger. These not well defined effects of additives can cause uncertainties in the ground source heat pump design and operation. The thermophysical properties of a few aqueous ethanol solutions are experimentally studied in this paper including a field sample, a pure mixture of ethanol and ethanol including additives are compared with reference data. The density of 20 wt-% solution of ethanol including additives and the field sample were higher than pure 20 wt-% ethanol sample. The additives increased the specific heat capacity by 2.3% at -10 oC and 1% at 0 oC. A decrement by 10.5% in the dynamic viscosity was observed. Presence of additives increased the thermal conductivity values by around 1.5% at -8 oC and 4.3% at +40 oC. Some implications in terms of pressure drop and fluid to pipe thermal resistance are observed when these properties are applied in borehole heat exchangers, as the occurrence for laminar or turbulent varies at given temperature levels. An alternative would be to replace the denaturing agents with corrosion inhibitors to decrease the concentration of additives, improve corrosion protection of the systems and still fulfill the market recommendations.

Indirect systems with secondary (working) fluid circuits are often used where there are many places to be cooled or where long pipes are required. Examples of systems with many places to be cooled ...

Ice generating machines are more and more used on fishing vessels to produce ice slurry from seawater. Because slurry with up to 60% ice can be handled and poured over the catch, there is excellent potential for long preservation of the catch on board and during transport, improving seafood quality for the end user. A literature search has been made to establish physical property data of seawater as a function of salinity and temperature. Ice slurry properties of seawater have been generated and are presented by means of an enthalpy phase diagram and related diagrams giving ice concentration, enthalpy change, density and viscosity of fine crystalline ice slurry. These studies also confirm that an initial salt content of 2–3% will give optimal performance. Seawater is known to be corrosive and a brief discussion of corrosion factors and problems, use of corrosion inhibitors and choice of materials is included in the paper.

Methyl and ethyl alcohol based secondary fluids are commonly used in different indirect refrigeration systems due to relatively good thermophysical properties. Methyl alcohol is considered toxic an ...

Seawater is the most common fluid on earth and ice generating machines are increasingly used on fishing vessels to produce ice slurry from seawater with up to 60% ice to be poured over the catch. An experiment using this method has recently shown that sensitive fish immersed in ice slurry, when flown from Japan to Taiwan, arrived in better condition than fish chilled by ordinary procedure. In this study, a literature search has been made to establish physical property data of seawater as function of salinity and temperature. Ice slurry properties of seawater have been generated and are presented by means of an enthalpy-phase diagram and related tables with ice concentration, enthalpy change and density. This material confirms that an initial salt content of 2-3 % is optimal and it can help determine the potential for long preservation of catch on board and during transport. As seawater is known to be corrosive, a brief discussion on corrosion factors and problems, the use of corrosion inhibitors and choice of machine and transport materials is included in this paper.

Ethyl alcohol (ethanol) based secondary fluids are commonly used in different types of indirect refrigeration systems in Scandinavia due to low toxicity, relatively good thermophysical properties and environmental regulations regarding leakage. Ethyl alcohol based commercial products available in Scandinavia contain different types of denaturing agents but no corrosion inhibitors. The most common denaturing agents are isopropyl alcohol (isopropanol), n-butyl alcohol (n-butanol), methyl ethyl ketone and methyl isobutyl ketone. Property measurements recently performed at KTH showed that presence of these additives in ethyl alcohol based secondary fluid improved thermophysical properties especially in terms of specific heat, thermal conductivity, and dynamic viscosity. Additionally, it was found that the specific heat capacity tendency is different than previously reported.

Most refrigeration systems have been constructed as direct expansion systems but indirect systems with secondary circuits have long been used. Today, indirect systems with secondary (working) fluids (secondary refrigerants or coolants, heat transfer fluids, brines) are used for a number of applications from solar heating to freezers in supermarkets. What needs to be considered when using secondary fluids in indirect systems? This paper takes up two rather new publications and a DVD that have been produced as tools for a successful use of secondary working fluids in indirect systems. One publication, Properties of Secondary Working Fluids for Indirect Systems (Melinder 2010), covers thirteen types of aqueous solutions and includes a few non-aqueous heat transfer fluids as a comparison. The fluid should be chosen considering the thermal properties at the operation temperature and certain other aspects such as toxicity, environmental impact and the effect of corrosion on metals and other materials in the system. A comparison of the fluid types is given for several applications. Properties of phase changing secondary working media or fluids are considered, evaporating CO2 to some extent and ice slurry properties more extensively. The publication contains an extensive section with tables and charts of thermo-physical properties of the various types of aqueous solution. A DVD includes an Excel calculation program using equations presented in the publication and an Excel prop-am to make fluid property values available for computer programs of the user. The second publication on indirect refrigeration and heat pump system has been produced in Swedish in cooperation with over twenty companies and persons involved in the field (Melinder 2009). Information from books, reports, magazine articles, company information has been taken in consideration. An English version, Handbook on indirect refrigeration and heat pump systems, is planned to be published in the near future. The chapters in this handbook deal among else with the following topics: direct contra indirect systems, indirect systems solutions, components in secondary circuits, secondary (working) fluids, corrosion, environmental aspects, design, dimensioning, construction, installation, control and optimization of indirect systems. An expectation is that this handbook will prove to be a useful tool to understand and work with indirect systems.

Aqueous solutions used as single-phase secondary fluids can also be used below the freezing point as ice slurry, a fluid consisting of liquid and ice. It is not as easy to determine thermophysical properties when aqueous solutions are used as two-phase ice slurry as when used for single-phase liquids. One main reason is that ice particles in a system change form and size with time. Values obtained from measurements in lab rigs are strictly valid only for the batch in case and at that specific time. Results from experiments done over the years in various lab rigs in research centres have often been compared to what equations for liquids with solid particles give although the values at times differ much. Such equations may be used to compare ice slurry properties for different fluid types and to find optimal conditions in a particular application. This paper presents ice fraction, density, enthalpy, viscosity and thermal conductivity for aqueous solutions of ethylene glycol and potassium formate based on fluid properties and mentioned equations. Diagrams help us compare the fluids for certain operational temperatures and initial freezing point temperatures or additive fractions. The relative differences between fluids and operational conditions will likely be similar to what ice slurry in a real plant gives, providing valuable clues for choice of fluid and suitable operational conditions. A conclusion from examples given is that the best performance is obtained with an initial freezing point equal to the operation temperature at the end of the user unit, giving maximal change in ice fraction and enthalpy. The dynamic viscosity does not differ very much from the viscosity of single-phase while the thermal conductivity is higher. The high density of potassium formate may give less even distribution of ice in pipes.

Indirect systems with aqueous solution used as secondary working fluids (secondary refrigerants or coolants) have long been used making it possible to minimize the charge and leakage of (primary) refrigerant. In ice slurry applications such aqueous solutions are used below the freezing point, benefiting from the enthalpy change resulting from ice melting. Accurate thermophysical property data and a general knowledge of other secondary fluid properties are useful for choice of suitable fluid and for technical calculations of the system. An extensive research with the aim to establish reliable data resulted in an IIR publication (Melinder 1997). Since then work has been carried out to update and extend such data for a new IIR publication intended to be published in 2009. Property values have been included for lower concentrations of the additive where ice slurries have best potential. Two tables arc as an example here given for aqueous solutions of sodium chloride. One table gives density, mixing properties, index of refraction, surface tension and specific conductance at 20 C. The other table gives thermophysical fluid properties, here only for low concentrations. Polynomial equations and coefficients used in an Excel-program for simple technical calculations are outlined. The new IIR publication includes other properties and aspects of the aqueous solutions used and it considers corrosion and material compatibility as well as environmental impact of such fluids. A summary is given with characteristics of aqueous solutions used for ice slurries. Property relations are given of ice and of fine crystalline ice slurry as well as enthalpy phase diagrams and charts with equilibrium values of ice mass fraction, enthalpy and density of ice slurries of sodium chloride and water. Hopefully this new IIR publication will prove to be useful for industry and researchers working with single-phase as well as ice slurry applications.

Heat transfer of ice slurry flow based on ethanol-water mixture in a circular horizontal tube has been experimentally investigated. The secondary fluid was prepared by mixing ethanol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 degrees C). The heat transfer tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 22% depending on test performed. Measured heat transfer coefficients of ice slurry are found to be higher than those for single phase fluid, especially for laminar flow conditions and high ice mass fractions where the heat transfer is increased with a factor 2 in comparison to the single phase flow. In addition, experimentally determined heat transfer coefficients of ice slurry flow were compared to the analytical results, based on the correlation by Sieder and Tate for laminar single phase regime, by Dittus-Boelter for turbulent single phase regime and empirical correlation by Christensen and Kauffeld derived for laminar/turbulent ice slurry flow in circular horizontal tubes. it was found that the classical correlation proposed by Sieder and Tate for laminar forced convection in smooth straight circular ducts cannot be used for heat transfer prediction of ice slurry flow since it strongly underestimates measured values, while, for the turbulent flow regime the simple Dittus-Boelter relation predicts the heat transfer coefficient of ice slurry flow with high accuracy but only up to an ice mass fraction of 10% and Re-cf > 2300 regardless of imposed heat flux. For higher ice mass fractions and regardless of the flow regime, the correlation proposed by Christensen and Kauffeld gives good agreement with experimental results. (C) 2009 Elsevier Ltd and IIR. All rights reserved.