Measurement of Kinematic Viscosity of Refrigeration Oil and R1234yf Mixture

Refrigerant dissolves in refrigeration oil which is used to lubricate the compressor. Because the viscosity of the oil in which the refrigerant is dissolved is significantly reduced, the rate of the reduction is important information to select a proper oil. However, viscosities have not been sufficiently measured for mixtures of refrigeration oil and new refrigerants which are HFOs and mixtures of HFO and HFC. In order to utilize HFO refrigerants in alternative refrigeration systems, viscosity data of mixtures of refrigeration oil and HFO are essential. In this study, mixture of a refrigeration oil and refrigerant (R410A and R1234yf) viscosity are measured with temperature from 40 to 80 ℃ (313 – 353 K) and the oil mass concentration from 80 to 100 % using the tandem capillary tubes method. In this method, the test fluid flows inside two different length and same diameter capillary tubes connected in series in order to eliminate the pressure drop at the inlet and outlet therefore the measurements have better accuracy than the single capillary tube method

Condensation and evaporation local heat transfer characteristics of the refrigerant mixture of R1123 and R32 inside a plate heat exchanger

In the present study, condensation and evaporation local heat transfer coefficients of the refrigerant mixture of R1123 and R32 inside a brazed plate heat exchanger were investigated by using a test section which is combined with two grooved stainless steel plates. In the test section, wall temperature distribution was measured. The test section consists of eight plates; two of them were processed herringbone for refrigerant flow channel other two flat plates are set for cooling plate for refrigerant, and another consist on cooling water flow channel. In order to measure local heat transfer and temperature distribution, five thermocouples were set on flow direction for each wall temperature measurement of the refrigerant side and heat source water side. Local heat transfer coefficient were calculated from local wall temperature of refrigerant side, saturation temperature and local heat flux obtained by temperature gradient between heat transfer surface of refrigerant side and heat source side

Experimental Study on Boiling and Condensation Heat Transfer in a Horizontal Mini Channel

This paper presents experimental results on boiling and condensation heat transfer coefficient in rectangular and rectangular grooved minichannels with hydraulic diameters of 0.81 and 0.64 mm, respectively. The boiling and condensation heat transfer coefficients were measured for saturated condition of R134a flowing in the horizontally placed minichannel tube. Length of the minichannel ube is 852 mm and it was heated or cooled by the water that flows through the upper and lower side of the minichannel tube. Wall temperature was measured by 18 thermocouples embedded in the tube surface

Local Heat Transfer Characteristics of the R1234ze(E) Two Phase Flow Inside a Plate Heat Exchanger

In the present study, condensation and evaporation local heat transfer coefficients of the R1234ze(E) inside a brazed plate heat exchanger were investigated by using a test section which is combined with two grooved stainless steel plates. In the test section, wall temperature distribution was measured. The test section consists of eight plates; two of them were processed herringbone for refrigerant flow channel other two flat plates are set for cooling plate for refrigerant, and another consist on cooling water flow channel. In order to measure local heat transfer and temperature distribution, five thermocouples were set at not only flow direction but also in the right and left sides of plates. Local heat flux and heat transfer coefficient were calculated from wall temperature distribution for downward and upward flow condition. And, the local heat transfer characteristics were discussed.

Experimental Study on Boiling and Condensation Heat Transfer of R1234yf Inside a Plate Heat Exchanger

In this study, boiling and condensation heat transfer characteristics of refrigerant R1234yf flowing inside a channel of plate heat exchanger were experimentally investigated. The test section consists of 8 plates where the refrigerant flow channel is formed by two plates grooved chevron pattern. Other plates are used to measure local temperature distribution and to form cooling /heating water channel. In this experiment three vertical flow channel exist in the test section and where the refrigerant flows in the middle channel (upward or downward directions) depending on evaporation or condensation process. In case of evaporation process the refrigerant flows upward in the middle channel and heat source water flows downward in the outer two channels. In condensation, refrigerant flows downward in the middle channel and the cooling water flows upwards in the two outer channels. In the test section, there are 160 measurement points in total with 4 sets of 8 symmetrical points in the horizontal direction and 5 symmetrical points in the vertical direction. In order to measure local heat transfer characteristics of the R1234yf, 20 thermocouples were set in the test section for measurement of wall temperature of the refrigerant and heat source water side. Local heat transfer coefficient was obtained under the experimental conditions of the mass flux of 10kg/(��2s) and 50 kg/(��2��). The local heat transfer coefficient is varied in horizontally and vertically. Local dryout in evaporation process was identified. The data of the R1234yf was also compared with the R32

Experimental Performance Estimations of Horizontal Ground Heat Exchangers for GSHP System

Horizontal ground heat exchanger in ground source heat pump systems is susceptible to ground surface variations thus affecting its thermal performance. However, this configuration is desirable due to low installation costs as it mainly involved burying pipes in shallow trenches. In this study, the numerical simulation of thermal performance for slinky horizontal ground heat exchanger (GHE) loops in several operation modes is conducted in order to estimate the performance. This study also deals with experimental investigation of slinky type GHE buried in 1.5 m depth of the ground

Analysis of Short Time Period of Operation of Horizontal Ground Heat Exchangers

Ground source heat pump (GSHP) systems have been proven to have higher efficiency compared to conventional air source heat pump systems for space heating and cooling applications. While vertical ground heat exchangers (GHE) are favorable in GSHP installation, this type of configuration requires higher capital costs as opposed to horizontal configuration. Numerical simulation has been used to accurately predict the thermal performance of GHE. In this paper, numerical analysis of thermal performance for slinky horizontal GHE loops in different orientations and operation modes is discussed. It was found that the loop orientation is not so important due to the little effect it has on thermal performance. While the mean heat exchange rate of copper loop increases 48% compared to HDPE loop, the analysis supports the common claim that heat exchange rate is predominantly limited by the thermal conductivity of the ground. With the same amount of circulation work, the mean heat exchange rate increases by 83%–162% when operated in parallel loops operations. The performance in these operations can be further optimized to 10%–14% increase when spacing between adjacent loops was provided. The spacing helps to minimize interference of heat flow that would penalize the overall thermal performance

CFD-Based Approach to Propose a Zigzag-Shaped Tube Heat Exchanger without Fins

This study explores the application of zigzag-shaped, finless tubes in enhancing heat transfer performance within heat exchangers. Using three-dimensional numerical simulations, we examined the heat transfer per unit area and the volume of the pressure drop, comparing these findings with a traditional parallel tube heat exchanger. This innovative design strategy involved arranging zigzag-shaped tubes at varying distances, and the thermal transfer and frictional characteristics were tested at different air speeds. This research suggests that the introduction of zigzag heat exchangers, as opposed to traditional fin-and-tube designs, led to a significant improvement in heat transfer. This enhancement is attributed to the swirling flow created around the zigzag tubes, which increased the total heat transfer area. Furthermore, we found that the heat transfer area increased by 14.2%, 32.1%, and 63.9% for tube zigzag angles of 30°, 45°, and 60°, respectively, when compared to a parallel tube heat exchanger. Consequently, the zigzag-shaped tube heat exchanger demonstrated not only superior heat transfer, but also a reduction in frictional pressure loss