Eric Granryd

Hydrocarbons as refrigerants — an overview

Possibilities and problems of using hydrocarbons as working fluids in refrigerating equipment are discussed. An overview of safety standards is given. Different hydrocarbon alternatives are listed and characteristics in terms of thermodynamic cycles as well as heat transfer are shown. The general conclusion is that hydrocarbons offer interesting refrigerant alternatives for energy efficient and environmentally friendly refrigerating equipment and heat pumps. However, safety precautions due to flammability must be seriously taken into account. For some applications this can be done without adding noticeably to the total installation cost, but not in the general case.

Experimental and theoretical study on flow condensation with non-azeotropic refrigerant mixtures of R32/R134a

Abstract Experiments on flow condensation have been conducted with both pure R32, R134a and their mixtures inside a tube (10 m long, 6 mm ID), with a mass flux of 131–369 kg m −2 s −1 and average condensation temperature of 23–40°C. The experimental heat transfer coefficients are compared with those predicted from correlations. The maximum mean heat transfer coefficient reduction (from a linear interpolation of the single component values) occurs at a concentration of roughly 30% R32 for the same mass flux basis, and is approximately 20% at Gr = 190 kg m −2 s −1 , 16% at Gr = 300 kg m −2 s −1 . Non-ideal properties of the mixture have a certain, but relatively small, influence on the degradation. Among others, temperature and concentration gradients, slip, etc. are also causes of heat transfer degradation.

Heat transfer and pressure drop of HFC134a-oil mixtures in a horizontal condensing tube

Abstract The paper reports the results of condensation heat transfer and pressure drop from tests with pure and oil-contaminated refrigerant HFC134a in a horizontal tube (10 m in length, 6 mm ID). The experimental results are compared with prediction from correlation. The heat transfer coefficient in the case of oil-contaminated refrigerant is shown to depend strongly on the definition of the saturation temperature. Using the pure refrigerant saturation temperature (hence disregarding the influence of oil on the vapour pressure), the results for average heat transfer coefficient show only minor effect of the oil contents. If the saturation temperature of the refrigerant—oil mixture is used, there is thus a significant degradation of the heat transfer coefficient (as expected) with increasing oil concentrations.

Flow Pattern, Heat Transfer and Pressure Drop in Flow Condensation Part I: Pure and Azeotropic Refrigerants

This study concerns the flow pattern, heat transfer, and pressure drop for flow condensation. The experimental results are recorded in tests with a smooth horizontal tube of 6 mm inner diameter and 2 to 10 m long. This manuscript, which is part I of a two part series, focuses on pure and azeotropic fluids. Part II describes results with non-azeotropic refrigerant mixtures. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with pure and azeotropic fluids in this work. However, the Froude number is found to be a good additional indicator to identify transition between annular and wavy flows. The transition occurs mostly at Fr = 15 to 20 for both pure and azeotropic fluids. In the case of pure and azeotropic fluids, the heat transfer coefficient was found to be independent of the mass flux in wavy flow regions, but increased with an increasing mass flux in the annular flow regions. For pure and azeotropic fluids, a modified Tandon et al. correlation agreed best with experimental data from tests with R-12, R-22, R-134a, and R-502. For the local pressure drop it is correlated within ±15% by using the Lockhart-Martinelli parameters. The experimental data for pure and azeotropic refrigerants can be predicted by using a correlation for overall pressure drop.

Flow pattern, heat transfer and pressure drop in flow condensation part II : Zeotropic refrigerants mixtures (NARMs)

This paper, which is part II of a study on flow condensation is focused on zeotropic (or non-azeotropic) refrigerant mixtures (NARMs). In the experiments, condensation in a horizontal tube of inner diameter 6 mm and 10 m length were studied with fluids R-404A, R-407C, and three mixtures of R-32 and R-134a. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with NARMs studied in this work. Most tests recorded are in the annular or semi annular flow region. The Froude number is, however, found to be an additional indicator to identify transition between annular and wavy flows. The transition in the experiments occurs mostly at Fr = 15 to 20 for the fluids tested. For NARMs with a small temperature glide (e.g. R-404A), as observed in the case of pure and azeotropic fluids, the heat transfer coefficient is independent of the mass flux in wavy flow regions, and increases with an increasing mass flux in annular flow regions. For other NARMs tested, the heat transfer coefficient (starting from a lower level) always increases with an increasing mass flux within the tested ranges. The heat transfer data from the tests with R-404A, R-407C, and R-32/R-134a mixtures can be predicted reasonably well by a modified Tandon et al. (1985b, 1995) equation with a correction proposed by Granryd (1989) for NARMs. The classical correlations for the pressure drop do not work well. Instead, the data for local pressure drop are correlated within ±15% by means of the same correlation as for the pure and azeotropic fluids. A simple correlation for the overall pressure drop based on the experimental data for pure and azeotropic fluids is good also for R-404A (with a small glide), but overpre-dicts the pressure drop (by up to 50%) for NARMs with glide, such as R-407C.

Performance of a Single-Family Heat Pump at Different Working Conditions Using Small Quantity of Propane as Refrigerant

The performance of a domestic heat pump that uses a low quantity of propane as refrigerant has been experimentally investigated. The heat pump consists of two minichannel aluminium heat exchangers, a scroll compressor, and an electronic expansion valve. It was charged with the minimum amount of refrigerant propane required for the stable operation of the heat pump without permitting refrigerant vapor into the expansion valve at incoming heat source fluid temperature to the evaporator of +10°C. The inlet temperature of the heat source fluid passing through the evaporator was varied from +10°C to −10°C while holding the condensing temperature constant at 35°C, 40°C, 50°C, and 60°C, respectively. The minimum refrigerant charges required at above-tested condensing temperatures were found to decrease when the condensing temperature increased and were recorded as 230 g, 224 g, 215 g, and 205 g, respectively. The results confirm that a heat pump with 5 kW capacity can be designed with less than 200 g charge of refrigerant propane in the system. Due to the high solubility of propane in compressor lubrication oil, the amount of refrigerant which may escape rapidly in case of accident or leakage is less than 150 g.

A simple experimental investigation of saturated vapour pressure for HFC134a-oil mixtures

Abstract A new refrigerant , HFC134a, seems to be the most promising substitute for CFC12. The vapour pressure of HFC134a-oil mixtures is one parameter that is important for a proper analysis of the operation of refrigeration systems. This paper presents vapour pressure curves for HFC134a and three kinds of representative oil for different oil percentages, and for the temperature range from -20 to +40°C (253.15–313.15 K).

Ground Source Heat Pump Developments

ABSTRACT In a Nordic climate, as that of Sweden, the use of the ground as a heat source for heat pumps is of special interest. Two developments are discussed: A new antifreeze solution based on potassium carbonate in water solutions and with a corrosion inhibitor, is shown to have beneficial properties from a thermal, as well as an environmental point of view. Thermal properties for the fluid and experiences from several years of field testing are given. Properties for secondary refrigerants for indirect systems are compared. A few relations are given between the the heat transfer, the pumping power and the influence of the fluid properties. For energy efficient operation it is of importance to operate the system at close to optimal conditions. A relation is shown for the “specific pumping power” resulting in a maximum of the total COP. The investment cost, especially for small residential heat pump systems, must be kept to a minimum. One way to minimize the cost is to use direct systems, with the evaporator coil buried directly in the ground. To some extent such systems have been successful on the market. A few details of the systems are described.