ASHRAE IJHVAC 8-3: 美国采暖与制冷工程研究期刊

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"ASHRAE IJHVAC 8-3.pdf" 是一份由美国采暖与制冷工程协会(American Society of Heating, Refrigerating and Air-Conditioning Engineers, 简称ASHRAE)出版的国际期刊《加热、通风、空调与制冷研究》(International Journal of Heating, Ventilating, Air-conditioning and Refrigerating Research)的文章或专辑。该资源可能包含了一系列关于这些领域的最新研究成果、技术发展、标准更新和行业动态。 ASHRAE是全球知名的非营利组织，致力于推动建筑环境领域的科技进步，其工作涵盖了供暖、通风、空调和制冷系统的各个方面。该协会制定并维护了一系列标准和指南，对建筑设计、设备性能和能源效率有着深远的影响。期刊的部分内容可能包括但不限于以下几个方面： 1. **热力学与传热学**：探讨各种工质的热力学性质，以及在 HVAC 系统中的传热过程，例如冷却、加热、湿度控制等。 2. **空气流动与通风**：研究室内空气品质（IAQ）、气流组织和通风效率，旨在提供健康且舒适的室内环境。 3. **制冷技术**：涵盖制冷系统的设计、制冷剂的选择与应用，以及能源效率提升的策略。 4. **能源效率**：讨论最新的能源节约技术和策略，包括高效设备设计、节能标准和政策。 5. **建模与仿真**：介绍使用计算机模拟来预测和优化 HVAC 系统性能的方法。 6. **环境影响**：分析 HVAC 技术对环境的影响，包括温室气体排放、废热回收和可持续性问题。 7. **系统控制与自动化**：探讨智能控制系统如何提高 HVAC 系统的运行效率和用户舒适度。 8. **建筑集成**：研究 HVAC 系统如何更好地与建筑物的结构、材料和设计相结合，实现整体性能的提升。 9. **实验研究**：报告实验室测试的结果，验证新理论或技术的有效性。 10. **案例研究**：分享实际项目中的经验和教训，为行业实践提供参考。编辑团队由来自不同国家的学者和专家组成，他们不仅有深厚的学术背景，还在教学和实践中积累了丰富的经验。通过他们的工作，ASHRAE 的期刊为专业人士提供了有价值的学术交流平台，推动了 HVAC 领域的持续创新和发展。请注意，由于无法提供具体文章的详细内容，以上概述是基于 ASHRAE 期刊通常涵盖的主题。如需了解文章的具体信息，建议直接阅读或通过 ASHRAE 的资源库访问该PDF文件。

228

HVAC&R

RESEARCH

30%

10 kW/m

30%.

1425

kPa

100

kg/(d.S)

10 15

APPLIEDVOLTAGE, kV

R-404a

SMOOTH TUBE

30%

30°C,

i=&,

1425 kPa

10 kWlm

100

kg/(m2.s)

G=200

kg/(ds)

300

kg/(ds)

kg/(m2.s)

APPLIED VOLTAGE, kV

(6)

Figure

(A) Heat Transfer Enhancements and

(B)

Pressure Drop

Penalties for R-404a in Smooth Tube (Mass Flux Variation)

Table

Ratio

Mean EHD Pressure to Rate

Axial Momentum Flux

(4"

kW/(mZ.K),

Tsat

3OoC,

kv)

Parametric

Condition

W(m%

Xave9

Ratio

0.3

1.4

200

0.5

0.9

0.3

0.75

0.32

4.5

0.35

the

100

ks/(m2.s) curve at 15

applied voltage, but the enhancements for

200

kg/(m2.s) and

300

kg/(m2

are always below those for mass flux of

kg/(m2.

s).

The net EHD enhancement

is a function of the balance of Maxwell stresses, interfacial shear, and mass transfer resistance in

the case of mixtures. The mass transfer resistance decreases

with increasing mass flux; interfacial

shear increases with increasing mass

flux.

The electric-body force cannot be quantified simply in

such

situation with multicomponent refrigerant with local permittivity and fluid density

gradients. The complex interplay of these three forces can give rise to the behaviors shown in

Provided by IHS under license with ASHRAE

Licensee=Naval Aviation Depot/5918326100

Not for Resale, 01/19/2008 02:24:00 MST

No reproduction or networking permitted without license from IHS

--`,`,`,``,,`,`,,,`,``,,,`,`,,``-`-`,,`,,`,`,,`---

230

HVAC&R

RESEARCH

+x,,=

10%

x,,

30%

voltage until the liquid breaks down. Being a high-temperature glide mixture, R-407c encoun-

ters a mass transfer resistance and does not respond to EHD in the same manner as the

single-component refrigerant R- 134a or the near-azeotrope R-404a. For certain parametric con-

ditions, there is an optimum voltage beyond which the enhancement stays constant or even

decreases with further increase in the applied voltage. This

observed for R-407c for mass flux

values less than

200

kg/(m2.s). This new finding has not been reported previously in the

literature.

A plateau in augmentation in heat transfer enhancement has been observed for external con-

densation and in-tube boiling experiments but not for in-tube condensation experiments.

EHD-enhanced in-tube condensation results for R-l34a (Singh 1995) showed a continuous

increment in heat transfer enhancement with the applied EHD voltage until the breakdown of the

liquid. On the other hand, the pressure drop penalty increases continuously with the applied

EHD voltage for the limited data collected (Figure 7B). The pressure drop data could not be

collected for R-407~ condensing inside smooth tubes for mass

flux

values of

200

kg/(m2.s) and

300 kg/(m2.

s).

Figure

and B depicts the effect of the variation of vapor qualities on EHD heat transfer

enhancements and pressure drop penalties inside the smooth tube, keeping all other parameters

constant. Typical quality change during condensation was about

to 7%.

shown in the fig-

ure, lower vapor qualities produce higher enhancements and higher pressure drop penalties.

x,=

10%

R407c

SMOOTH

TUBE

100

kg/(m2.s)

kW/m2

Tsa,

3OoC,

Ps,,

1250

kPa

30%

-A-

x,,

50%

APPLIED VOLTAGE,

(B)

Figure

(A)

Heat Transfer Enhancements and

(B)

Pressure Drop Penalty

for

R-407c

in Smooth Tube (Vapor Quality Variation)

Provided by IHS under license with ASHRAE

Licensee=Naval Aviation Depot/5918326100

Not for Resale, 01/19/2008 02:24:00 MST

No reproduction or networking permitted without license from IHS

--`,`,`,``,,`,`,,,`,``,,,`,`,,``-`-`,,`,,`,`,,`---

VOLUME

NUMEIER

JULY

2002

maximum enhancement of 3.5-fold is obtained at a quality of 10% compared (at 9 kV applied

voltage) to an enhancement of 2.4-fold at a quality of 50% (at 18 kV). The maximum pressure

drop penalties are 4.1 and 2.7, for qualities

10% and 50% respectively, both at 18 kV.

lev-

eling-off in heat transfer enhancements is observed at lower qualities

(40%)

corresponding to

stratified and stratified-wavy flow regimes, similar to that observed for mass flux values below

200

kg/(m2.s). At higher vapor qualities with wavy-annular and annular flow regimes, the

enhancements increase continuously with the applied EHD voltage up to the highest applied

voltage of 18 kV. These observations follow from the fact that, at low vapor qualities, the flow

pattern is mostly stratified and stratified-wavy, where the EHD forces are dominant compared to

the axial momentum flux, resulting in higher extraction and vigorous cross-motions of the liquid

film. As the quality increases, the flow pattern transitions to shear-governed wavy-annular and

annular flow regimes, making the liquid extraction phenomenon difficult and resulting in lower

heat transfer enhancements and lower pressure drops.

the other hand, the pressure drop pen-

alty increases continuously with the applied voltage.

Refrigerants R-404a and R-134a showed a continuous increase in heat transfer enhancement

and pressure drop penalty with the applied EHD voltage, as is expected from the flow regimes.

For detailed quantitative information on the heat transfer enhancement magnitudes, see Gidwani

(1 998).

The effect of saturation temperature on heat transfer enhancements and pressure drop penal-

ties for R-l34a is plotted in Figure 9A and

Increasing the saturation temperature yields higher

T,,=

1íPC

I-

T,,

20%

T,,

4wc

R-134a

CORRUGATED TUBE

100

kgl(m2.s)

30%

kWh2

APPLIEDVOLTAGE, kV

(A)

T,r=

10%

T,,

20%

T,,

30%

T,,

40%

R-134a

CORRUGATED TUBE

kg/(m*.s)

30%

kWlm2

10 15

APPLIEDVOLTAGE, kV

(B)

Figure

(A) Heat Transfer Enhancements and

(B)

Pressure Drop Penalties

for R-134a in Corrugated Tube (Saturation Temperature Variation)

Provided by IHS under license with ASHRAE

Licensee=Naval Aviation Depot/5918326100

Not for Resale, 01/19/2008 02:24:00 MST

No reproduction or networking permitted without license from IHS

--`,`,`,``,,`,`,,,`,``,,,`,`,,``-`-`,,`,,`,`,,`---

232

HVAC&R

RESEARCH

enhancements.

EHD enhancement of 2.7-fold is observed at a saturation temperature of

10°C, as compared to an enhancement of 6.2-fold at a saturation temperature of 40°C, the corre-

sponding pressure drop penalties being 5.0 and 10.7 (Figure 9B), respectively. The smooth tube

results of Singh (1995) show a similar trend.

As temperature increases, the liquid density, vis-

cosity, and the interfacial surface tension decrease. The lower surface tension values allow more

vigorous motions to be induced by the EHD force, resulting in higher interfacial area and higher

liquid extraction, and thereby, higher heat transfer enhancements. This is supported by Singh's

(1995) empirical correlation predicting EHD enhancements for R-l34a for the same tube-elec-

trode configuration. Based on Singh's work, the enhancement is proportional to the surface ten-

sion EHD number, which

proportional to

E2/S.

Furthermore, the ratio of mean EHD pressure

to momentum flux rate for R-134 at 30°C is 1.4 as against a value of 0.84 at a lower saturation

temperature of 10°C, demonstrating stronger effects of EHD force at higher saturation

temperatures.

The effect of heat flux on the heat transfer enhancement and pressure drop penalties for

R-404a

plotted in Figure

10A

and B. The heat transfer characteristics are insensitive to the heat

flux variations for the range of parameters tested. This could be attributed to the fact that the set

of parametric conditions tested was limited

the stratified

wavy

flow regime, which was not

affected much by the increase in the heat flux values. The negligible change in the flow regime

implies a negligible difference in the performance of refrigerant with EHD at the various heat

10 15

APPLIED VOLTAGE,

(A)

kwlmz

R4Wa

CORRUGATED TUBE

kWh2

100

kdd4

"I I

-cQ=30kW/m2

Xem=30%

i,,

30%.

P,,

1425 kPa

kwlmz

R4Wa

CORRUGATED TUBE

-c

kW/m2

Xe,

30%

i,,

30%.

P,,

1425 kPa

kWh2

100

ke/(d,s)

5 10 15

APPLIED VOLTAGE, kV

(6)

Figure

10.

(A)

Heat Transfer Enhancements and

(B)

Pressure Drop Penalties

for R-404a in Corrugated Tube (Heat Flux Variation)

Provided by IHS under license with ASHRAE

Licensee=Naval Aviation Depot/5918326100

Not for Resale, 01/19/2008 02:24:00 MST

No reproduction or networking permitted without license from IHS

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