Refrigerant-induced noises, which occur irregularly at special thermodynamic cycle conditions, are frequently cited by residential customers who use refrigerators. However, these noises are very difficult to resolve and their root causes cannot usually be exactly identified. In this research, the root causes of the irregular refrigerant-induced noise are estimated through the theories of two-phase flow and bubble dynamics. Also, by using refrigerant-supplying equipment that can continuously supply refrigerant to the test unit at typical cycle conditions, the flow patterns of the evaporator in vertical and horizontal pipes are inspected and their noises are simultaneously measured. Through the observation of the relationship between the flow pattern and the refrigerant-induced noise, the root causes of this irregular refrigerant noise can be identified and verified.

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Analysis of the root causes of refrigerant-induced noise in refrigerators †

The acoustic characteristics of a long-shaped cylindrical bubble for slug or churn flow in a pipe are different from those of a freely rising spherical bubble in infinite liquid. In this research, the theoretical estimation of the natural frequency of the long-shaped cylindrical bubble was derived using the energy conservation law for a single bubble in a pipe. The acoustic characteristics of bubbles in a pipe were also investigated with the R600a refrigerant, which is widely used in refrigerators when the flow pattern in a pipe is slug or churn flow. In order to make slug and churn flow artificially, refrigerant-supplying equipment was designed and developed. Using this test equipment, the frequency characteristics of the long-shaped cylindrical bubble in 2-phase flow were investigated experimentally.

Frequency characteristics of the noise of R600a refrigerant flowing in a pipe with intermittent flow pattern

Various refrigerant flow patterns can produce a range of noise types according to their cycle conditions. Consequently, the identification of flow patterns in a tube is crucial to reducing refrigerant-induced noise. Because of the obstacles involved in identifying them accurately by experiment, in this paper, these flow patterns are estimated from the flow pattern map. Working from the assumption that the refrigerant-induced noise for an air conditioner in the heating mode comes from slug flow in the condenser-outlet pipe, the reduction of refrigerant-induced noise by avoiding slug flow in a tube is examined. To fully understand the conditions under which the refrigerant-induced noise occurs, cycle simulator equipment for an outdoor unit is developed. With this cycle simulator, noise tests of 4-way cassette type indoor units are performed under the conditions that the refrigerant-induced noise occurs. Increasing the mass flux in a tube by reducing the diameter of the condenser-outlet pipe can avoid slug flow, and the refrigerant-induced noise can therefore be reduced. The results of the cycle simulator can be verified with an outdoor unit 5HP system multi air conditioner and the results are well in line with simulator results.

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Experimental analysis for reducing refrigerant-induced noise of 4-way cassette type air conditioner

The shell side heat transfer and pressure drop in counterflowing water were experimentally investigated on the basis of the overall heat transfer coefficient. The investigation was intended to identify ways to get higher performance for the cooler in a BWR nuclear power plant. The following three conclusions were reached in the study. (1) Predicted performance of the heat exchanger, using the overall heat transfer coefficient based on the outside area of the tube Ko, indicated an enhancement by 92% compared with the measured performance of the conventional segmental baffle-type heat exchanger. (2) The tube side pressure drop ΔPt=20 kPa and the shell side pressure drop ΔPs=70 kPa were obtained, and were within the allowable value ΔPa=80 kPa. The shell side pressure drop of the low-pressure drop spacer could be decreased by 20% as compared with that of the standard spacer. (3) The enhancement constant of the shell side heat transfer using the low-pressure drop spacer was about 1.2 times as large as that of the standard spacer, regardless of the pumping power. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(5): 455–471, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10097

Enhancement of shell side forced convective heat transfer in the shell tube-type heat exchanger using thin plate-type supports

Abstract This paper presents a state-of-the-art review of the literature concerning flow-induced noise in expansion devices. The topics covered are theoretical natural frequency models of bubbles with spherical and cylindrical shapes and flow-induced noise in capillary tubes, such as orifice, thermal and electric expansion valve. Several parametric conditions affect the flow-induced noise in capillary tubes, such as outlet capillary geometry, capillary inner diameter and length, flow orientation, outlet vapor quality, mass velocity, pressure drop, in/outlet flow pattern, evaporation temperature, and refrigeration cycle operational conditions. Despite the broad use of orifice, there is a lack of knowledge in the literature of flow-induced noise in these devices. The flow-induced noise seems primarily a function of mass velocity, vapor quality, and flow pattern. It seems that outlet intermittent flow patterns lead to significant noise in capillary tubes and expansion valves. In general, for the noise evaluated outside the expansion device, electric expansion valves exhibited higher sound pressure levels than capillary tubes. Furthermore, the present literature review indicates that efforts should be made to perform tests for a wide range of conditions evaluating the noise within and outside the expansion device, device wall acceleration and flow topology for current and new refrigerants, simultaneously.

A State-of-the-Art Review on Two-Phase Flow-Induced Noise in Expansion Devices

An experimental investigation was made on heat transfer and pressure drop using a spacer in a rectangular channel, and the basic characteristics of the spacer were obtained. These included the local heat transfer coefficient and static pressure drop distribution. A heat transfer enhancement was caused by the effect of turbulence at the spacer outlet region, not as the effect of increased velocity in the spacer ; and then the flow diffusion and contraction around the spacer caused a larger pressure drop. Four dimensionless parameters were defined as spacer specifications : blockage ratio e, gap ratio α, spacer length ratio β, and spacer existence ratioθ. Among the parameters, blockage ratio e had the most influence on performance enhancement. The total performance between heat transfer and pressure drop were estimated under the condition of a constant fluid transportation power. The spacers with blockage ratio e=0.5 and spacer existence ratio θ=0.2 gave excellent performances.

薄い平板状障害物による矩形流路内強制対流熱伝達の促進 : 第1報,単相流における伝熱・圧力損失基本特性

Presently, in our quest to develop low-noise air conditioning equipment, it is important to reduce the refrigerant flow noise. To date, this problem has been investigated on the basis of trial and error. Fundamental cause and mechanism of the flow noise must be analyzed before a drastic reduction of noise can be achieved. In this study, air-water two-phase flow was used to create a slug flow with single large gas bubble for the purpose of modeling the problem. We investigated the relations among gas bubble state, static pressure pulsation and flow noise caused by single gas bubble passing through the orifice, In the results, it is shown that the noise level increases twice while the gas bubble passes through the orifice and that there exist correlations among flow state, static pressure pulsation and flow noise.

単一大気泡が絞りを通過するときの気液二相流の流動音 : 第1報,空気-水系気液二相流による実験的研究

The shell side heat transfer and pressure drop to water flowing parallel with the Eggcrate Support Plate was experimentally investigated in order to get higher performance for the cooler in a Boiling Water Reactor power plant. The following three conclusions were reached in the study. (1) The shell side heat transfer characteristics with the Eggcrate Support Plate were twice as large as those of the shell side parallel flow. An equation using the Reynolds number of the Eggcrate Support Plate could predict the heat transfer coefficient. (2) The shell side pressure drop characteristics with the Eggcrate Support Plate were about five to six times as large as those of the shell side parallel flow. (3) The enhancement constant of heat transfer with the Eggcrate Support Plate, using the Colburn's j factor and friction factor f, was the same as that of the ROD-baffle type, and was about two times as large as that of the segmental baffle type.

中村昭三

Papers

薄い平板状障害物による矩形流路内強制対流熱伝達の促進 : 第1報,単相流における伝熱・圧力損失基本特性

単一大気泡が絞りを通過するときの気液二相流の流動音 : 第1報,空気-水系気液二相流による実験的研究

薄板状伝熱管支持材を設置した胴側並行流の熱伝達特性〔熱工学, 内燃機関, 動力など〕

中村 昭三

Papers

薄い平板状障害物による矩形流路内強制対流熱伝達の促進 : 第1報,単相流における伝熱・圧力損失基本特性

単一大気泡が絞りを通過するときの気液二相流の流動音 : 第1報,空気-水系気液二相流による実験的研究

薄板状伝熱管支持材を設置した胴側並行流の熱伝達特性 〔熱工学, 内燃機関, 動力など〕

中村昭三

薄板状伝熱管支持材を設置した胴側並行流の熱伝達特性〔熱工学, 内燃機関, 動力など〕