Development of a Miniature Vapor Compression Refrigeration System for Electronic Cooling

2009 ◽  
Author(s):  
Gareth F. Davies ◽  
Ian W. Eames ◽  
Paul B. Bailey ◽  
Michael W. Dadd ◽  
Adam Janiszewski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Small Computer ◽  
Vapor Compression ◽  
Transfer Coefficients ◽  
Space Applications ◽  
Transient Behaviour ◽  
Vapor Compression Refrigeration

Computer chips have generally been cooled by means of a heat sink/fan device; however, such systems are now approaching their limits and in future alternative techniques/devices will be needed. A 3-year project, involving collaboration between groups at three UK universities, is being undertaken to develop a miniature refrigeration device for the cooling of future microprocessors and electronic systems. Using conventional vapor compression refrigeration technology for the cooling of small computer packages has generally resulted in low heat fluxes, however, microchannel devices have shown heat transfer coefficients up to 16 times greater, and porous medium channels even higher heat transfer rates. Porous media heat exchangers are being developed by Newcastle University and some results from this work are reported here. Surface contamination by lubricating oil from the compressor often causes problems with small passage heat exchangers. Oxford University’s Cryogenics Group have developed specialised oil-free compressors for low temperature cooling systems for space applications. Such a compressor is being adapted for use in the miniature vapor compression refrigeration device. The paper discusses development work on the compressor design. Conventional size refrigeration systems have sufficient capacity to dampen out transient behaviour resulting from variations in local temperatures and flow rates, but this is not the case for miniature systems. Based on earlier work at London South Bank University, a model has been developed to study transient behaviour in miniature refrigeration systems. The basis of the mathematical model is explained within the paper, as well as providing provisional results from the simulations. The paper identifies the potential need for computer cooling and highlights the opportunity to develop specific cooling solutions. Previous relevant work in this area is also highlighted. The paper provides details of novel work being carried out on modelling, micro-heat transfer and compressor development.

Boiling Heat Transfer With Freon 11 (R11) in Brazed Aluminum, Plate-Fin Heat Exchangers

1983 ◽  
Vol 105 (3) ◽  
pp. 605-610 ◽  
Author(s):  
J. M. Robertson ◽  
P. C. Lovegrove
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Industrial Process ◽  
Heat Fluxes ◽  
Test Fluid ◽  
Transfer Coefficients ◽  
Simple Method ◽  
Wide Range

The results of laboratory experiments with Freon 11 (R11) flowing in an electrically heated, serrated-fin test section to measure local boiling coefficients over a wide range of vapor quality, with mass fluxes up to 150 kg/m2 s, heat fluxes to 4 kW/m2, and pressure from 3–7 bar, are reported. These low mass and heat fluxes reflect the industrial process application of these heat exchangers where exceedingly small temperature differences may exist between streams. Results are compared with the very similar boiling characteristics previously reported elsewhere for the same test section, with liquid nitrogen as a test fluid under comparable flow conditions. A simple method using the Reynolds number of the total flow regarded as a liquid has been used to correlate boiling heat transfer coefficients with quality for both fluids. The use of a liquid-film flow model to produce a nondimensional correlation connecting the Nusselt, Reynolds, and Prandtl numbers of the film is discussed.

Comparison of Selected Forced-Convection Supercritical-Water Heat-Transfer Correlations for Vertical Bare Tubes

2010 ◽  
Author(s):  
Amjad Farah ◽  
Krysten King ◽  
Sahil Gupta ◽  
Sarah Mokry ◽  
Wargha Peiman ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Supercritical Water ◽  
Heat Exchangers ◽  
Power Plants ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Correlations ◽  
Bare Tube

This paper presents an extensive study of heat-transfer correlations applicable to supercritical-water flow in vertical bare tubes. A comprehensive dataset was collected from 33 papers by 27 authors, including more than 125 graphs and wide ranges of parameters. The parameters ranges were as follows: pressures 22.5–34.5 MPa, inlet temperatures 85–350°C, mass fluxes 250–3400 kg/m2s, heat fluxes 75–5,400 kW/m2), tube heated lengths 0.6–27.4 m, and tube inside diameters 2–36 mm. This combined dataset was then investigated and analyzed. Heat Transfer Coefficients (HTCs) and wall temperatures were calculated using various existing correlations and compared to the corresponding experimental results. Three correlations were used in this comparison: Bishop et al., Mokry et al. and modified Swenson et al. The main objective of this study was to select the best supercritical-water bare-tube correlation for HTC calculations in: 1) fuel bundles of SuperCritical Water-cooled Reactors (SCWRs) as a preliminary and conservative approach; 2) heat exchangers in case of indirect-cycle SCW Nuclear Power Plants (NPPs); and 3) heat exchangers in case of hydrogen co-generation at SCW NPPs from SCW side. From the beginning, all these three correlations were compared to the Kirillov et al. vertical bare-tube dataset. However, this dataset has a limited range of operating conditions in terms of a pressure (only one pressure value of 24 MPa) and one inside diameter (only 10 mm). Therefore, these correlations were compared with other datasets, which have a much wider range of operating conditions. The comparison showed that in most cases, the Bishop et al. correlation deviates significantly from the experimental data within the pseudocritical region and actually, underestimates the temperature at most times. On the other hand, the Mokry et al. and modified Swenson et al. correlations showed a relatively better fit within the most operating conditions. In general, the modified Swenson et al. correlation showed slightly better fit with the experimental data than other two correlations.

Free Jet Impingement Heat Transfer of a High Prandtl Number Fluid Under Conditions of Highly Varying Properties

1999 ◽  
Vol 121 (3) ◽  
pp. 592-597 ◽  
Author(s):  
J. E. Leland ◽  
M. R. Pais
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Jet Impingement ◽  
Turbulent Jets ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Constant Property ◽  
Wide Range

An experimental investigation was performed to determine the heat transfer rates for an impinging free-surface axisymmetric jet of lubricating oil for a wide range of Prandtl numbers (48 to 445) and for conditions of highly varying properties (viscosity ratios up to 14) in the flowing film. Heat transfer coefficients were obtained for jet Reynolds numbers from 109 to 8592, nozzle orifice diameters of 0.51, 0.84 and 1.70 mm and a heated surface diameter of 12.95 mm. The effect of nozzle to surface spacing (1 to 8.5 mm), was also investigated. Viscous dissipation was found to have an effect at low heat fluxes. Distinct heat transfer regimes were identified for initially laminar and turbulent jets. The data show that existing constant property correlations underestimate the heat transfer coefficient by more than 100 percent as the wall to fluid temperature difference increases. Over 700 data points were used to generate Nusselt number correlations which satisfactorily account for the highly varying properties with a mean absolute error of less than ten percent.

The Analysis of Heat Transfer in Automotive Turbochargers

2009 ◽  
Author(s):  
Nick Baines ◽  
Karl D. Wygant ◽  
Antonis Dris
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Internal Heat ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Internal Surfaces ◽  
The Difference

Heat transfers in an automotive turbocharger comprise significant energy flows, but are rarely measured or accounted for in any turbocharger performance assessment. Existing measurements suggest that the difference in turbine efficiency calculated in the conventional way, by means of the fluid temperature change, under adiabatic conditions differs considerably from the usual diabatic test conditions, particularly at low turbine pressure ratio. In the work described in this paper, three commercial turbochargers were extensively instrumented with thermocouples on all accessible external and internal surfaces in order to make comprehensive temperature surveys. The turbochargers were run at ranges of turbine inlet temperature and external ventilation. Adiabatic tests were also carried out to serve as a reference condition. Based on the temperature measurements, the internal heat fluxes from the turbine gas to the turbocharger structure, and from there to the lubricating oil and the compressor, and the external heat fluxes to the environment, were calculated. A one-dimensional heat transfer network model of the turbocharger was demonstrated to be able to simulate the heat fluxes to good accuracy, and that the heat transfer coefficients required were ultimately found to be mostly independent of the turbochargers tested.

The Analysis of Heat Transfer in Automotive Turbochargers

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Nick Baines ◽  
Karl D. Wygant ◽  
Antonis Dris
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Internal Heat ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Internal Surfaces ◽  
The Difference

Heat transfers in an automotive turbocharger comprise significant energy flows, but are rarely measured or accounted for in any turbocharger performance assessment. Existing measurements suggest that the difference in turbine efficiency calculated in the conventional way, by means of the fluid temperature change, under adiabatic conditions differs considerably from the usual diabatic test conditions, particularly at low turbine pressure ratio. In the work described in this paper, three commercial turbochargers were extensively instrumented with thermocouples on all accessible external and internal surfaces in order to make comprehensive temperature surveys. The turbochargers were run at ranges of turbine inlet temperature and external ventilation. Adiabatic tests were also carried out to serve as a reference condition. Based on the temperature measurements, the internal heat fluxes from the turbine gas to the turbocharger structure and from there to the lubricating oil and the compressor, and the external heat fluxes to the environment were calculated. A one-dimensional heat transfer network model of the turbocharger was demonstrated to be able to simulate the heat fluxes to good accuracy, and the heat transfer coefficients required were ultimately found to be mostly independent of the turbochargers tested.

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Comparison of Existing Supercritical Carbon Dioxide Heat Transfer Correlations for Horizontal and Vertical Bare Tubes

2012 ◽  
Author(s):  
Prabu Surendran ◽  
Sahil Gupta ◽  
Tiberiu Preda ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Wall Temperature ◽  
Statistical Error ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Correlations ◽  
Supercritical Carbon

This paper presents a thorough analysis of ability of various heat transfer correlations to predict wall temperatures and Heat Transfer Coefficients (HTCs) against experiments on internal forced-convective heat transfer to supercritical carbon dioxide conducted by Koppel [1], He [2], Kim [3] and Bae [4]. It should be noted the Koppel dataset was taken from a paper which used the Koppel data but was not written by Koppel. All experiments were completed in bare tubes with diameters from 0.948 mm to 9 mm for horizontal and vertical configurations. The datasets contain a total of 1573 wall temperature points with pressures ranging from 7.58 to 9.59 MPa, mass fluxes of 400 to 1641 kg/m2s and heat fluxes from 20 to 225 kW/m2. The main objective of the study was to compare several correlations and select the best of them in predicting HTC and wall temperature values for supercritical carbon dioxide. This study will be beneficial for analyzing heat exchangers involving supercritical carbon dioxide, and for verifying scaling parameters between CO2 and other fluids. In addition, supercritical carbon dioxide’s use as a modeling fluid is necessary as the costs of experiments are lower than supercritical water. The datasets were compiled and calculations were performed to find HTCs and wall and bulk-fluid temperatures using existing correlations. Calculated results were compared with the experimental ones. The correlations used were Mokry et al. [5], Swenson et al. [6] and a set of new correlations presented in Gutpa et al. [7]. Statistical error calculations were performed are presented in the paper.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

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