The Effect Of Seasonal Variation On Thermal Performance Of Horizontal Slinky-Loop Ground Heat Exchanger

For ground-source heat pump (GSHP) installations, it is important to predict the thermal performance and economic feasibility prior to the introduction of the system. Numerical modelling can be used as an analytical method to accurately predict the thermal performance of such system. It is desirable that the modelling to incorporate seasonal variation during long period of operation, which would lead to a better understanding of the overall performance and provide more reliable results. In this work, numerical modelling performed using computational fluid dynamic software presented the heat exchange rate for different operation of slinky loop ground heat exchanger using time- and position-varying parameters. Each operation were carried out in short and long simulation periods during winter and summer conditions of southwest of Japan, specifically in Saga City

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

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

Developments of next generation refrigerants and heat transfer

Since the effect of refrigerants which are widely used in heat pump and refrigeration systems on the global warming has become a big environmental issue, researches and developments on the next generation refrigerants are being conducted intensively. Values of global warming potential (GWP) of most of currently used refrigerants are grater than 1000. R32 which becomes popular as a refrigerant of domestics air-conditioners for years has GWP=675. Recently, some hydrofluoroolefins (HFOs) are getting attention and their thermophysical properties and heat transfer characteristics are being clarified experimentally because GWP of HFOs are very small in which the values of some HFOs are less than 1 and those of others are less than around 10. For example, R1234yf and R1234ze(E) are promising candidate of R134a. In this paper, recent developments of the next generation refrigerants and its heat transfer characteristics are introduced