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Showing papers on "Subcooling published in 2008"


Journal ArticleDOI
TL;DR: In this paper, the authors investigate different methods for differential scanning calorimetry (hf-DSC) analysis, namely the dynamic method and the step method, and test their accuracy in the determination of the enthalpy-temperature relationship of PCM.
Abstract: Thermal energy storage by latent heat allows storing high amounts of energy working in narrow margins of temperature. The use of phase change material (PCM) for the latent heat storage has been studied in different applications and it has been commercialized in containers to transport blood, products sensible to temperature, to decrease their energy demand. The use of PCM in cooling and refrigeration has been attracting a lot of interest lately, but for all applications, the properties of these materials need to be known with sufficient accuracy. Regarding heat storage, it is necessary to know the enthalpy as a function of temperature. The most widely used calorimeter is the heatflux differential scanning calorimetry (hf-DSC). The objective of this study is to investigate different methods for hf- DSC analysis, namely the dynamic method and the step method, and to test their accuracy in the determination of enthalpy–temperature relationship of PCM. For the dynamic method, a strong influence of heating/cooling rate was observed. For the step method, the resulting enthalpy–temperature relationship is independent of heating/cooling rate. Commercial PCM RT27 was chosen as sample material to avoid subcooling and kinetic effects in the test measurements. The approach introduced in this study can be used to carry out similar investigations for other classes of PCM and/or other DSC instruments.

169 citations


Journal ArticleDOI
TL;DR: In this article, a thermodynamic analysis of carbon dioxide-ammonia (R744-R717) cascade refrigeration system is presented to optimize the design and operating parameters of the system.
Abstract: A thermodynamic analysis of carbon dioxide–ammonia (R744–R717) cascade refrigeration system is presented in this paper to optimize the design and operating parameters of the system. The design and operating parameters considered in this study include (1) condensing, subcooling, evaporating and superheating temperatures in the ammonia (R717) high-temperature circuit, (2) temperature difference in the cascade heat exchanger, and (3) evaporating, superheating, condensing and subcooling in the carbon dioxide (R744) low-temperature circuit. A multilinear regression analysis was employed in terms of subcooling, superheating, evaporating, condensing, and cascade heat exchanger temperature difference in order to develop mathematical expressions for maximum COP, an optimum evaporating temperature of R717 and an optimum mass flow ratio of R717 to that of R744 in the cascade system.

165 citations


Journal ArticleDOI
TL;DR: In this article, a new cooling scheme is proposed where the primary working fluid flowing through a micro-channel heat sink is pre-cooled to low temperature using an indirect refrigeration cooling system.

144 citations


Journal ArticleDOI
TL;DR: In this article, a combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycles, and a parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle.

141 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the influence of subcooling on spray performance and critical heat flux (CHF) from a 1.0×-1.0 cm2 test surface.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explore experimentally stabilizing flow boiling water in ten parallel micro-channel heat sinks with a diverging cross-section design and show that the stability boundary is plotted on the plane of the subcooling number against the phase change number (Npch).
Abstract: This paper explores experimentally stabilizing flow boiling water in ten parallel microchannel heat sinks with a diverging cross-section design. Each diverging microchannel has a mean hydraulic diameter of 120 µm and a diverging angle of 0.5° while the channel depth is uniform at 76 µm. Flow visualization shows that heat flux and mass flux significantly affect the stability of flow boiling in the parallel microchannels. The extent of pressure drop oscillations may be regarded as an index for the onset of flow boiling instability. The stability boundary is plotted on the plane of the subcooling number (Nsub) against the phase change number (Npch) and compared with microchannels with a uniform cross-section design in the literature. The present study confirms that, in terms of stability performance, the flow boiling in the parallel microchannel heat sinks with a diverging cross-section design is superior to a uniform cross-section design.

94 citations


Journal ArticleDOI
TL;DR: In this paper, a high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process, and the bubble departure frequencies were obtained from the video for a total of 58 test conditions.

93 citations


Journal ArticleDOI
TL;DR: In this article, a stable dropwise condensation (DWC) of saturated steam has been achieved on an aluminum alloy Al 6951 disc with an average surface finish of about 0.15μm by means of ion beam implantation technology with an ion dose of 1016 n + cm−2 and an implantation energy of 20 keV.

90 citations


Journal ArticleDOI
TL;DR: In this article, a simultaneous visualization and measurement study has been carried out to investigate stable and unstable flow boiling phenomena of deionized water in a single microchannel having a hydraulic diameter of 155 µm with a bottom Pyrex glass wall.

89 citations


Journal ArticleDOI
TL;DR: In this paper, a convective flow boiling of refrigerant R-113 in a vertical annular channel has been simulated by a CFD (Computational Fluid Dynamics) code CFX.

85 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that a significant CHF enhancement can be achieved with as little as 0.01% by volume concentration of alumina nanoparticles in flow experiments at atmospheric pressure, low subcooling 20° C, and relatively high mass flux 1000 kg/m 2 s.
Abstract: Many studies have shown that addition of nanosized particles to water enhances the critical heat flux (CHF) in pool boiling. The resulting colloidal dispersions are known in the literature as nanofluids. However, for most potential applications of nanofluids the situation of interest is flow boiling. This technical note presents first-of-a-kind data for flow boiling CHF in nanofluids. It is shown that a significant CHF enhancement (up to 30%) can be achieved with as little as 0.01% by volume concentration of alumina nanoparticles in flow experiments at atmospheric pressure, low subcooling 20° C, and relatively high mass flux 1000 kg/ m 2 s. DOI: 10.1115/1.2818787

Journal ArticleDOI
TL;DR: In this article, a model considering the forces acting on departing bubbles at the heated surface is employed, coupled with a three-dimensional two-fluid and population balance equations based on the modified MUSIG (MUltiple-SIze-Group) model, the behavior of an upward forced convective subcooled boiling flows in a vertical annular channel is simulated.

Journal ArticleDOI
TL;DR: In this article, the results of series of experiments that systematically investigated nucleate boiling of both FC-72 and HFE-710 dielectric liquids on a plain porous graphite surface measuring 10 × 10 mm were compared.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the single-phase and two-phase cooling performance of a hybrid micro-channel/micro-jet impingement cooling scheme using HFE 7100 as working fluid.

Journal ArticleDOI
TL;DR: In this article, performances of two-phase cooling of a chip at very high heat flux with refrigerant R236fa in a silicon multimicrochannel heat sink were presented. But the performance of the chip was not compared with an extrapolation of the present results.
Abstract: This paper presents performances of two-phase cooling of a chip at very high heat flux with refrigerant R236fa in a silicon multimicrochannel heat sink. This heat sink was composed of 134 parallel channels, 67 mum wide, 680 mum high, and 20 mm long, with 92- mum -thick fins separating the channels. The base heat flux was varied from 3 to 255 W/cm2 , the volume flow rate from 0.18 to 0.67 I/min, and the exit vapor quality from 0 to 80%. The working pressure and saturation temperature were set at 273 kPa and 25 degC, respectively. The present database includes 1040 local heat transfer coefficients. The base temperature of the chip could be maintained below 52 degC while dissipating 255 W/cm2 with 10 degC of inlet subcooling and 90 kPa of pressure drop. A comparison of the respective performances with an extrapolation of the present results shows that two-phase cooling should be able to cool the chip 13 K lower than liquid cooling for the same pumping power at a base heat flux of 350 W/cm2.

Patent
24 Mar 2008
TL;DR: In this article, a system consisting of a compressor having a motor and a refrigeration circuit including an evaporator and a condenser fluidly coupled to the compressor is described, and the system may further include a first sensor producing a signal indicative of one of current and power drawn by the motor, a second sensor producing an indicator of a saturated condensing temperature, and a third sensor indicating a liquid line temperature.
Abstract: A system is provided and may include a compressor having a motor and a refrigeration circuit including an evaporator and a condenser fluidly coupled to the compressor. The system may further include a first sensor producing a signal indicative of one of current and power drawn by the motor, a second sensor producing a signal indicative of a saturated condensing temperature, and a third sensor producing a signal indicative of a liquid-line temperature. Processing circuitry may processes the current or power signal to determine a derived condenser temperature and may compare the derived condenser temperature to the saturated condensing temperature received from the second sensor to determine a subcooling associated with a refrigerant charge level of the refrigeration circuit.

Journal ArticleDOI
TL;DR: In this paper, a 2-mm water jet of 5-80-k subcooling and 3-15m/s velocity was impinged on the flat surface of a cylindrical steel/brass block.

Journal ArticleDOI
TL;DR: In this paper, the interfacial flow structure of subcooled water boiling flow in a subchannel of 3 × 3 rod bundles is presented, where 9 rods are positioned in a quadrangular assembly with a rod diameter of 8.2mm and a pitch distance of 16.6 mm.
Abstract: In this paper, the interfacial flow structure of subcooled water boiling flow in a subchannel of 3 × 3 rod bundles is presented. The 9 rods are positioned in a quadrangular assembly with a rod diameter of 8.2mm and a pitch distance of 16.6 mm. Local void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter, and liquid velocity have been measured using a conductivity probe and a Pitot tube in 20 locations inside one of the subchannels. A total of 53 flow conditions have been considered in the experimental dataset at atmospheric pressure conditions with a mass flow rate, heat flux, inlet temperature, and subcooled temperature ranges of 250–522 kg/m s, 25–185 kW/m2, 96.6–104.9°C, and 2–11 K, respectively. The dataset has been used to analyze the effect of the heat flux and mass flow rate on the local flow parameters. In addition, the area-averaged data integrated over the whole subchannel have been used to validate some of the distribution parameter and drift velocity constitu...

Journal ArticleDOI
TL;DR: In this article, the behavior of multichannel system two-phase flow instability is studied theoretically, and a physics model that includes the entrance section, heater section and riser section is built.

Journal ArticleDOI
TL;DR: In this article, a detailed direct numerical simulation study of condensing stratified flow, involving a sheared steam-water interface under various thermal and turbulent conditions, has been conducted, and scaling laws for the normalized heat transfer coefficient (HTC) have been derived for both the steam and liquid phases.
Abstract: The paper discusses the results of a detailed direct numerical simulation study of condensing stratified flow, involving a sheared steam-water interface under various thermal and turbulent conditions. The flow system comprises a superheated steam and subcooled water flowing in opposite directions. The transport equations for the two fluids are alternately solved in separate domains and then coupled at the interface by imposing mass, momentum, and energy jump conditions with phase change. The effects induced by changes in the interfacial shear were analyzed by comparing the relevant statistical flow properties. New scaling laws for the normalized heat transfer coefficient (HTC), K + , have been derived for both the steam and liquid phases. The steam-side law is found to compare with the passive-scalar law obtained hitherto by (Lakehal et al.(2003, "Direct Numerical Simulation of Turbulent Heat Transfer Across a Mobile, Sheared Gas-Liquid Interfaces, " ASME J. Heat Transfer, 125, pp. 1129-1139) in that HTC scales with Pr -3/5 . A close inspection of the transfer rates on the liquid side reveals a consistent relationship between K + , the local wave deformation or curvature and the interfacial shear stress. The surface divergence model of Banerjee et al. (2004, "Surface Divergence Models for Scalar Exchange Between Turbulent Streams," Int. J. Multiphase Flow, 30(8), pp. 965-977) is found to apply in the liquid phase, too.

Journal ArticleDOI
C.A. Chen1, W.R. Chang1, K.W. Li1, Y.M. Lie1, T.F. Lin1 
TL;DR: In this paper, the authors investigated how the channel size affects the subcooled flow boiling heat transfer and the associated bubble characteristics of refrigerant R-407C in a horizontal narrow annular duct with the gap of the duct fixed at 1.0 and 2.0 mm.

Patent
07 Jul 2008
TL;DR: In this article, a closed loop single mixed refrigerant provides most of the refrigeration to the refloor, together with an auxiliary refrigeration system, coupled in such a manner that waste heat generated by a gas turbine drive of the compressor in the closed-loop single-mixed refrigerant drives the auxiliary driveline system and the auxiliary DR system cools the inlet air of the gas turbine.
Abstract: A process and system for liquefying a hydrocarbon gas is provided. The hydrocarbon feed gas is pre-treated to remove sour species and water therefrom. The pre-treated feed gas is then passed to a refrigeration zone where it is cooled and expanded to produce a hydrocarbon liquid. A closed loop single mixed refrigerant provides most of the refrigeration to the refrigeration zone together with an auxiliary refrigeration system. The auxiliary refrigeration system and closed loop single mixed refrigerant are coupled in such a manner that waste heat generated by a gas turbine drive of the compressor in the closed loop single mixed refrigerant drives the auxiliary refrigeration system and the auxiliary refrigeration system cools the inlet air of the gas turbine. In this way, substantial improvements are made in the production capacity of the system.

Journal ArticleDOI
TL;DR: In this article, a generalized correlation for predicting the refrigerant mass flow rate through the adiabatic capillary tube is developed with approximate analytic solutions based on the extensive data for R12, R22, R134a, R290, R600a, RC, R410A, R407C, and R404A.
Abstract: The capillary tube is often served as an expansion device in small refrigeration and air-conditioning systems. In this paper, a generalized correlation for predicting the refrigerant mass flow rate through the adiabatic capillary tube is developed with approximate analytic solutions based on the extensive data for R12, R22, R134a, R290, R600a, R410A, R407C, and R404A, in which a homogeneous equilibrium model for two-phase flow is employed, and there is a subcooled liquid or saturated two-phase mixture at the inlet of the capillary tubes. The collected database about capillary tubes covers the inner diameter from 0.5 mm to 2 mm, the tube length from 0.5 m to 5 m, the condensing temperature from 20 °C to 60 °C, the subcooling from 0 °C to 20 °C, and the quality from 0 to 0.3 at the inlet. Assessments for the correlation are made with some experimental data for R12, R22, R134a, R290, R407C, R410A, and R404A obtained from the open literature and some existing correlations based on the experimental database also. The present correlation yields an average deviation of −0.83% and a standard deviation of 9.02% from the database.

Journal ArticleDOI
TL;DR: In this paper, a Computational Fluid Dynamics (CFD) analysis for a thermal mixing test was performed for 30 s to develop the methodology for a numerical analysis of the thermal mixing between steam and subcooled water and to apply it to Advanced Power Reactor 1400 MWe (APR1400).

Journal ArticleDOI
TL;DR: In this article, a temperature-controlled pool boiling (TCPB) device has been developed to study the bubble behavior and heat transfer in pool boiling phenomenon both in normal gravity and in microgravity.
Abstract: A temperature-controlled pool boiling (TCPB) device has been developed to study the bubble behavior and heat transfer in pool boiling phenomenon both in normal gravity and in microgravity. A thin platinum wire of 60 mu m in diameter and 30 mm in length is simultaneously used as heater and thermometer. The fluid is R113 at 0.1 MPa and subcooled by 26 degrees C nominally for all cases. Three modes of heat transfer, namely single-phase natural convection, nucleate boiling, and two-mode transition boiling, are observed in the experiment both in microgravity aboard the 22nd Chinese recoverable satellite and in normal gravity on the ground before and after the space flight. Dynamic behaviors of vapor bubbles observed in these experiments are reported and analyzed in the present paper. In the regime of fully developed nucleate boiling, the interface oscillation due to coalescence of adjacent tiny bubbles is the primary reason of the departure of bubbles in microgravity. On the contrary, in the discrete bubble regime, it's observed that there exist three critical bubble diameters in microgravity, dividing the whole range of the observed bubbles into four regimes. Firstly, tiny bubbles are continually forming and growing on the heating surface before departing slowly from the wire when their sizes exceed some value of the order of 10(-1) mm. The bigger bubbles with about several millimeters in diameter stay on the wire, oscillate along the wire, and coalesce with adjacent bubbles. The biggest bubble with diameter of the order of 10 mm, which was formed immediately after the onset of boiling, stays continuously

Patent
01 Oct 2008
TL;DR: In this paper, the electronic expansion valve is provided in a refrigerant circulation loop of equipment, the circulation loop is also provided with an evaporator, characterized in that the control method includes following steps: S10: starting the electronic expand valve to process initialization, setting the opening of the electronic enlargement valve in a predetermined initial value; S20: after starting the predetermined time, determining the real superheat/subcooling of the Electronic expansion valve according to the difference between the outlet temperature and the inlet temperature of the evaporator; S30: comparing the object super
Abstract: The present invention provides a control method of an electronic expansion valve, the electronic expansion valve is provided in a refrigerant circulation loop of equipment, the circulation loop is also provided with an evaporator, characterized in that the control method includes following steps: S10: starting the electronic expansion valve to process initialization, setting the opening of the electronic expansion valve in a predetermined initial value; S20: after starting the predetermined time, determining the real superheat/subcooling of the electronic expansion valve according to the difference between the outlet temperature and the inlet temperature of the evaporator; S30: comparing the object superheat/subcooling with the real superheat/subcooling, determining the optimal opening range of the electronic expansion valve; S40: adjusting the opening of the electronic expansion valve to the optimal opening range. The invention realizes the automatic control of refrigerant volume and throttle degree of equipment, and capable of adapting the working condition to control automatically, so as to protect the optimal state in the system operation ,ensuring credibility and safety operation.

Journal ArticleDOI
TL;DR: In this article, two models for the prediction of flow boiling heat transfer coefficients are presented for binary and ternary mixtures of acetone, isopropanol and water.

01 Jan 2008
TL;DR: In this paper, the authors describe performance measurements on a prototype miniature rotary compressor with refrigerant R134a using a compressor load stand based on a hot-gas bypass design.
Abstract: This paper describes performance measurements on a prototype miniature rotary compressor with refrigerant R134a using a compressor load stand based on a hot-gas bypass design. The hermetically sealed rolling piston compressor runs on a 24 V DC power supply. Because of its small size and compact form factor, it can potentially be used in a miniature vapor compression refrigeration system for electronics cooling applications. Compressor tests are conducted for varying suction pressures, pressure ratios, and rotational speeds. For each test, the refrigerant mass flow rate, electrical power consumption, and the suction and discharge temperature and pressure are recorded, at a suction superheat of 5 K. Using the experimental data, the compressor volumetric and overall isentropic efficiencies are calculated. Also, by assuming a subcooling of 5 K in the condenser, a hypothetical cooling capacity of the system and the corresponding COP are calculated. The volumetric efficiency ranges from 73% to 90% and the overall isentropic efficiency varies from 44% to 70% for pressure ratios between 2 and 3.5. For this range of pressure ratios, the estimated cooling capacity and the COP vary from 163 W to 489 W and 2.1 to 7.4, respectively.

Proceedings ArticleDOI
28 May 2008
TL;DR: In this article, the authors provide a complete set of models/correlations that are required for designing an optimum spray cooling system and a new user-friendly CHF correlation is recommended which shows excellent predictive capability for the entire database.
Abstract: Recent studies provide ample evidence of the effectiveness of two-phase spray cooling at dissipating large heat fluxes from electronic devices. However, those same studies point to the difficulty predicting spray performance, given the large number of parameters that influence spray behavior. This paper provides a complete set of models/correlations that are required for designing an optimum spray cooling system. Several coolants (water, FC-72, FC-77, FC-87 and PF-5052) are used to generate a comprehensive spray-cooling database for different nozzles, flow rates, subcoolings, and orientations. High-speed video motion analysis is used to enhance the understanding of droplet formation and impact on the device's surface, especially near the critical heat flux (CHF) point. A previous CHF correlation for normal sprays is modified for both inclination and subcooling effects. A new user-friendly CHF correlation is recommended which shows excellent predictive capability for the entire database. Also discussed in this paper is a new theoretical scheme for assessing the influence of spray overlap on cooling performance.

Journal ArticleDOI
TL;DR: In this article, surface treatments were performed with sandpapers, building micro structures by etching, and micro-porous coating, and the effect of wall superheat, surface orientation, and subcooling on treated surfaces were also investigated.
Abstract: Pool boiling heat transfer characteristics on treated surfaces were investigated experimentally. Surface treatments were performed with sandpapers, building micro structures by etching, and micro-porous coating. Copper blocks of 20 mm × 20 mm were used as test sections and PF5060 was used as a working fluid. The effect of wall superheat (0–35 K), surface orientation (0°, 45°, 90°), and subcooling (0, 5, 10 K) on treated surfaces were also investigated. Heat transfer performance on inclined surface was better than that of horizontal surface in all test sections. Because bubble generation was suppressed by subcooling, higher wall superheat was needed to initiate boiling in all surfaces. Micro-porous coated surface showed the highest heat transfer enhancement among tested surfaces.