Convective Heat Losses in Pulse Tube Coolers: Effect of Pulse Tube Inclination

Thummes, G.; Schreiber, M. R.; Landgraf, R.; Heiden, C.

doi:10.1007/978-1-4615-5869-9_46

Cited by 39 publications

(23 citation statements)

References 8 publications

(5 reference statements)

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“…However, the total heat flux is over-estimated in a range of about 1 − 2W depending on the inclination angle. The correlation of Thummes et al [6] shows an increasing heat flux beginning with γ = 0 • . The further profile of the correlation differs in the fact that the maximum value is achieved at an inclination of γ = 90 • .…”

Section: Correlations and Data Comparisonmentioning

confidence: 84%

“…The paper of Thummes et al [6] gives experimental data for a tilted pulse tube. In addition, the same configuration was analyzed numerically by He et al [11].…”

Section: Experimental and Numerical Datamentioning

confidence: 99%

“…In a later stage of this paper we will extend this comparison also to our data. The used conditions from Thummes et al [6] are given above. show the same characteristic as the baseline data.…”

Section: Correlations and Data Comparisonmentioning

confidence: 99%

“…Further, the correlation is not able to include any influence effects of the pipe wall material, such as heat conduction along the pipe or transversely the main flow inside. However, the correlation of Thummes et al [6] is the only one which is applicable to get at least a very rough estimation of the total heat flux. The correlation of Schneider and Straub [4] shows also a different characteristic in comparison to the baseline case.…”

Section: Correlations and Data Comparisonmentioning

confidence: 99%

“…If no such modification is applied an unphysical behavior of the correlation will occur. The correlation of Thummes et al [6] is originally a compilation of various equations developed by Fujii and Imura [7], Hollands et al [8,9] and Globe and Dropkin [10]. The correlation of Thummes et al can be applied for aspect ratios of L/D ≤ 10 which includes very short pipes, at least from the cryogenic point of view.…”

Section: Introductionmentioning

confidence: 99%

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Natural convection in inclined pipes - A new correlation for heat transfer estimations

Langebach¹,

Haberstroh²

2014

AIP Conference Proceedings

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Abstract. Heat intake minimization is one of the main challenges during the design process of cryogenic storage tanks. It is widely known that connection pipes significantly contribute to this residual heat transfer from ambient temperature conditions to the cold inner vessel. A certain pipe inclination can cause a convective flow field within the fluid. This effect usually increases the total heat transfer much more dramatically than anticipated. In several previous papers we discussed the impact of pipe geometry as well as boundary conditions intensively. However, there is no suitable correlation in literature available which could be used to estimate the total heat transfer properly. The large number of experimental data we gained during our investigations allows us to propose a new correlation in order to predict the total heat transfer through an inclined pipe in function of the inclination angle. In this paper we derivate this new correlation and show its application for heat transfer estimations. Several comparisons are carried out against our own measurements as well as literature data.Keywords: Natural convection, inclined pipe, heat transfer, storage vessels INTRODUCTIONA primary concern in the design process of low loss cryogenic storage tanks is the minimization of the overall heat intake in order to increase the dormancy time as much as possible. A major contribution to the overall heat intake is caused by connection pipes mounted between the warm outer vessel and the cold inner vessel. Depending on to the inclination angle γ we can observe a substantial change of the heat transfer characteristic. The inclination angle is defined to be γ = −90 • for the vertical pipe with the cold end down and the warm end up, γ = 0 • for a horizontal configuration and γ = 90 • for a vertical pipe with the warm end down and the cold end up. Typical dimensions for these pipes are several millimeters in diameter and a length lower than one meter. In terms of high-pressure connection pipes a certain wall thickness of several millimeters also need to be taken into account. In case the warm end of the pipe is positioned above the cold end (γ = −90 • ), the fluid inside can be seen as stagnant and therefore no natural convection is present. In this case the amount of transported heat can be calculated from the equations for pure heat conduction. In case the warm end of the pipe is positioned much below or even at the same height as the cold end (γ = 0 • ..90 • ), a natural convective flow field occurs. The total heat flux usually increases substantially. In previous studies [1, 2] we already discussed the theoretical background on natural convection in inclined connection pipes and emphasized the relevance of this topic with a special focus to high-pressure cryogenic storage tanks. In literature only a very low number of references covering this topic is available. Moreover, there are no relevant data or correlations available to appropriately predict the total heat flux except of CFD analysis. Therefore, we see a tremend...

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Section: Correlations and Data Comparisonmentioning

confidence: 84%

“…The paper of Thummes et al [6] gives experimental data for a tilted pulse tube. In addition, the same configuration was analyzed numerically by He et al [11].…”

Section: Experimental and Numerical Datamentioning

confidence: 99%

Section: Correlations and Data Comparisonmentioning

confidence: 99%

Section: Correlations and Data Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Natural convection in inclined pipes - A new correlation for heat transfer estimations

Langebach¹,

Haberstroh²

2014

AIP Conference Proceedings

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Visualization of DC Gas Flows in a Double-Inlet Pulse Tube Refrigerator with a Second Orifice Valve

Shiraishi¹,

Takamatsu

Murakami

et al. 2002

Cryocoolers 11

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We have observed the secondary flow induced in a double-inlet pulse tube refrigerator by using a smoke-wire flow visualization method and investigated the effects of the opening of the bypass valve on the flow behavior of the secondary flow, especially of the DC flow. Also, the effect of a second orifice valve on the secondary flow has been visually investigated. Based on the observations, the relationship between the cooling performance and the dynamic behavior of the secondary flow has been determined. It has been found that for the double-inlet pulse tube refrigerator, a DC flow is induced by opening the bypass valve, and that the DC flow is strengthened with additional opening of the valve. Further, the behavior of secondary flow in the pulse tube is well modeled as a superposition of the DC flow and the convection of acoustic streaming driven by the oscillating main flow. The valve opening for optimum cooling performance is found to be that that balances the DC flow and the acoustic streaming to reduce the net velocity of the secondary flow to zero in the core region of the pulse tube. Similarly, it is found for a double-inlet pulse tube refrigerator with a second orifice valve, that the optimum cooling performance again corresponds to near zero secondary flow in the core region.

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