ASHRAE IJHVAC 8-4: 美国采暖与制冷工程研究期刊

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"ASHRAE IJHVAC 8-4.pdf" 是一份由ASHRAE（美国采暖与制冷工程协会）发布的专业期刊文章，属于国际供暖、通风、空调及制冷研究（International Journal of Heating, Ventilating, Air-conditioning and Refrigerating Research）。该期刊由知名专家Reinhard Radermacher教授担任主编，并有来自全球各地的学者作为副编辑，如Michael J. Brandemuehl、James E. Braun、Alberto Cavallini、Arthur L. Dexter、Leon R. Glicksman和Richard R. Gonzalez等，他们分别在相关领域有深厚的学术背景和实践经验。 ASHRAE是北美乃至全球建筑环境科学与技术的权威机构，致力于推动暖通空调（HVAC）和制冷行业的技术进步，制定相关标准和指南，以及提供教育和研究支持。这篇PDF文件可能包含关于 HVAC 和制冷系统的最新研究成果、技术创新、能源效率提升方法、室内环境质量改进、系统设计策略等内容。由于具体文章内容未给出，以下将就ASHRAE和HVAC行业的一般性知识点进行详述： 1. **HVAC系统**：HVAC代表供暖、通风和空调，是建筑环境中不可或缺的部分，负责维持室内舒适度。这些系统通常包括热源（如锅炉或热泵）、冷却设备（如冷却塔或空调机组）、通风设备（如风机和风管）以及控制系统。 2. **能源效率**：ASHRAE在其标准中强调了提高HVAC系统的能源效率，如ASHRAE 90.1，这是一套建筑能效标准，规定了新建和改扩建建筑物的最低能效要求。ASHRAE的研究成果常常推动了高效设备的设计和应用。 3. **室内空气质量（IAQ）**：ASHRAE也关注室内空气质量，研究如何通过通风和空气净化策略来改善室内的空气质量和居住者的健康。 4. **制冷技术**：在制冷方面，ASHRAE涉及冷藏存储、食品处理设施和空调系统中的制冷技术，涵盖了制冷剂的选择、环保替代品的开发和制冷系统的优化。 5. **标准和指南**：ASHRAE制定了一系列标准和指南，如ASHRAE 62.1，用于规定建筑物的通风需求；ASHRAE 189.1则关注绿色建筑的能源和环境设计。 6. **研究和创新**：ASHRAE的期刊通常会发布关于新技术、材料、设计方法和分析工具的研究论文，这些研究成果对行业实践有重要指导作用。 7. **持续教育**：为了保持行业人员的专业技能，ASHRAE提供多种培训课程和研讨会，帮助专业人士了解最新的技术发展和法规变化。 "ASHRAE IJHVAC 8-4.pdf" 可能包含与HVAC和制冷相关的深入研究、技术应用和行业动态，对于从事相关领域的工程师、设计师、研究人员和教育工作者来说，是非常有价值的信息资源。

346

O00

8000

-c

4000

HVAC&R

RESEARCH

0.0

0.1

0.2

0.3

0.4

0.0

0.3

0.6

0.9

Ax,

kgkg

Ax,

kglkg

Figure

Overall Heat Transfer and Pressure-Drop Results for

R-404A

Microfin Tube at

Ta,

5OC

repeating the test conditions shown in Figure 4. When

(i.e., heat flux) increases further, the

role of the EHD force components changes. Specifically, the polarization forces [an extraction

phenomenon primarily from the second term on the right-hand side of Equation

(i)]

start to play

a more significant role as more energy is added to the flow. If the extraction phenomenon is

large enough, for a given set of operating conditions, it will strip the liquid layer from the wall,

causing local dryout, which will result in suppression of the heat transfer. This is evident in Fig-

ures 3 and 4 for

mass flux of approximately 100 kg/(m2*s) and change

quality greater than

0.5.

kV there is little or no heat transfer enhancement, but at 15 kV the extraction phenom-

enon is large enough to significantly suppress heat transfer.

Figures 3 through

indicate that application of EHD forces provide enhancement at low qual-

ities and suppression at qualities higher than

0.5

under the conditions

this research.

this

work the change in quality was achieved by increasing the heat flux. Thus, heat flux and quality

both influence the net effect of application of electric forces

heat transfer. In this work, when

was low, heat flux was low in all test sections, usually resulting in EHD enhancement. High

corresponded to high heat flux in all test sections. Only for R-134a in the smooth and micro-

fin tubes at

100 kg/(m2.s) and

T,,

5°C

(see Figures 3 and 4) did total heat transfer sup-

pression occur at the highest heat fluxes.

The interdependence of the convective boiling parameters and the

EHD parameters can be

seen by comparing the results shown in Figures 3 through

EHD enhancement was greater

for R-134a in the smooth tube, but not in the microfin tube when compared to R-404A for the

same applied voltage, electrode design, and saturation temperature. This behavior is prima-

rily attributed to differences in the fluid properties, as shown in Table 4. The fact that

R-404A is a mixture (near-azeotropic blend of R-125, R-l43a, and R-134a) may play a role

weil because of the differences

the electrical and thermophysical properties of the mix-

ture components.

Provided by IHS under license with ASHRAE

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Not for Resale, 01/19/2008 02:24:14 MST

No reproduction or networking permitted without license from IHS

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348

HVAC&R

RESEARCH

0.75

0.50

0.25

0.00

EQUATION

(6)

EQUATION

(7)

BASED ON

EQUATION

(6)

cm SECTION

0.00 0.01 0.02

0.03

0.04

0.05

0.06

0.00

0.03

0.06

0.09

0.12

(

xoup

kglkg

0.00'

BASED ON

EQUATION

(6)

SECTION

0.00

0.06

0.12

0.18

0.24

0.00

0.07

0.14 0.21

0.28

0.35

Xoup

Wkg

X0Mv

Wkg

Figure

7. EHD

Power Versus Quality for

R-134a

Smooth

Tube

kV,

300.4

kg/(m2.s),

and

T,,

24.9OC

The amount of liquid and vapor present will influence the amount of EHD power consumed.

quality increases, EHD power decreases, because the amount of vapor (less conductive than

the liquid phase) is increasing. This can be supported analytically by using the theoretical

approach presented by Bryan and Seyed-Yagoobi

(2000)

to calculate EHD power

from

Equation

(5)

based on the first term in Equation (4). Table

lists the equations for

and

CJ~,~

based on the

theoretical approach of Bryan and Seyed-Yagoobi (2000). Experimental

data

and analytical

results for EHD power as a function of quality are shown in Figure

for different test sections

with R-134a in the smooth tube at

300.4 kg/(m2.s) and

Tsat

24.9"C.

Both the experimental data and the analytical results indicate that a large portion

the cur-

rent flow derives

from

electric conduction, the first term

the right-hand side of Equation (4).

The electric field calculated based on Equation

(6),

given in Table

assumes that all the liquid

in the tube surrounds the energized electrode. The liquid extraction phenomenon promotes this

by attracting the liquid, which has higher permittivity than the vapor, toward the energized elec-

trode. However, as flow momentum increases, the attraction of the liquid to the energized elec-

trode will decrease for a given applied voltage. Thus, if the EHD power

only

from

electric

conduction, then the EHD power should lie within the analytical results shown in Figure

Most

Provided by IHS under license with ASHRAE

Licensee=Naval Aviation Depot/5918326100

Not for Resale, 01/19/2008 02:24:14 MST

No reproduction or networking permitted without license from IHS

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VOLUME

NUMBER

OCTOBER

2002 349

O00

10000

8000

æm

6000

4000

2000

100

150

200

250

300

350

400

kg/(m*.c)

1.75

1.50

1.25

1.00

I-

0.75

0.50

0.25

0.00

Figure

Average Heat Transfer and

EHD

Power Versus Mass Flux for R-134a

Smooth

Tube at

Tsar

25OC

of the data in Figure

follow this trend. The presence of the electric charge density' (from impu-

rities andíor interfacial gradients) would increase EHD power further. In Figure'

EHD power

consumption for each test section is theoretically presented using

two

different equations for the

electric field. Specifically, Equation

(6),

which is based on the electric field calculated by

assuming that only the liquid phase

present around the energized electrode, corresponds

the

lowest EHD power consumption. On the other hand, using Equation

(7)

results in the highest

EHD power consumption as long as electric conduction is the only component of the electric

current. At low quality values, Equation

(8)

is used instead of Equation

(7)

because the low

quality corresponds to a more homogeneous mixture of liquid and vapor surrounding the elec-

trode than the vapor alone.

The increase in mass flux corresponds to

increase in flow momentum, which would cause

EHD power to increase toward the curve defined by Equation

(8)

at low qualities and Equation

(7)

at qualities greater than 0.05. This is mainly because of the change in the liquidívapor distri-

bution with the increase in flow momentum (e.g., liquid being forced to the tube wall as flow

momentum increases). Additionally, if there is a small electric charge density present, then it

will contribute to the total EHD power as mass flux increases because of the convective current

term [i.e., the second term on the right-hand side of Equation (4)]. Note that the fluid velocity in

Equation

(4)

contributing to the current density is primarily in the radial direction for the elec-

trode design of this study. However, an increase in the axial fluid velocity also Corresponds to an

increase in the radial velocity. Experiments were conducted to validate these statements. The

average heat transfer coefficient and the EHD power consumption, both versus mass flux, are

shown in Figure

for R-134a in the smooth tube at

Tsar

25°C.

indicated in Figure

the

quality range was held approximately constant through the range of mass fluxes. perefore, the

EHD power consumption increases due to the increase in mass flux, which indicates the pres-

ence of some electric charge density.

The EHD power consumption relative to the total heat transferred

(QEH~lQtot,J

in all

data

shown in Figures

and

was less than 1.5%. The

maximum

QEHDIQtotar

shown in Figure

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350

HVAC&R

RESEARCH

1.27% and occurs in the 20 cm section at the lowest quality and heat flux.

the heat flux (heat

transferred) increases,

QEHD

decreases as described previously because the amount

vapor is

increasing. The maximum

QEHD/Qtotul

shown in Figure

is 0.094% and occurs at the lowest

mass flux

101.4 kg/(m2.s). As the mass flux increases,

QEHD/Qtotul

decreases because

Qtotal

increases at a greater rate than

QEHo.

Transient EHD Enhancement

The application

EHD forces to the convective boiling process enhanced and even sup-

pressed heat transfer when compared to heat transfer without EHD. All the results published in

the literature as weil as the data given in this paper

far have been at steady state. Several inter-

esting observations were made when real-time temperature measurements were observed imme-

diately after applying the electric fields. The most profound behavior in the evaporator

temperatures was recorded with R-404A in the smooth tube at

Tsut

25OC, when

EHD

forces

were applied at 15

after the system had reached steady state without EHD. When

EHD

forces

were applied, the evaporator outlet refrigerant temperature began to rise rapidly. Then, after a

time lag, the same occurred for the evaporator inlet refrigerant temperature. This indicates that

EHD forces were initially enhancing heat transfer upon the application of 15 kV. However, the

enhancement eventually decayed and resulted in suppression, as indicated by a lower saturation

temperature after

min. This behavior was also influenced by mass flux, as shown in Figure 9.

The highest initial enhancement appears to occur between

of 248.0 and 299.6 kg/(m2.s) and it

decreases to the point of suppression upon application of 15 kV at

=102.4 kg/(m2.s), with the

change in quality of approximately

0.60. It is important to note that the change in quality was

measured after the system reached steady state, which occurred after the

80 min mark shown in

Figure 9. The quality and saturation conditions were changing substantially during the time

before the 80 min mark.

The water reservoir temperature, local surface temperatures, refngerant temperature, refriger-

ant pressure, and the section pressure drop

a function

time for the

cm and 50 cm test

section locations are shown in Figures 10 and

11,

respectively, for

299.6 kg/(m2.s). From

these figures, the initiai enhancement can easily be detected on each test section location. The

initial enhancement is most pronounced on the top of the tube at each location. The tube surface

temperature at the bottom does not change significantly, and after 3600

(60 min) there is stili a

small enhancement. After 60 min at the top of the tube, suppression has started to occur, with the

greatest occurring in the

cm section. There

also suppression starting in the middle of the

tube in the

cm section after 60 min. The rapid decrease in the pressure drop in both the 30 and

50 cm test sections is misleading, because the refrigerant saturation pressure is rising rapidly

because of the sudden increase in absorbed energy. This is shown in both Figures 10 and

where the pressure-drop decay coincides with the saturation pressure rise. The fluctuation in the

two-phase pressure-drop signal is substantial. This is common for two-phase flow; however, it

increases the difficulty in measuring the pressure drop. The instantaneous pressure-drop mea-

surements in two-phase flow vary significantly because of the flow regime structure and the

application of EHD forces. The following conjectures are presented to explain the enhancement:

Upon the application of 15 kV, the EHD forces start to influence the liquid-vapor interface.

This influence can result in liquid attraction toward the energized electrode at the center of the

tube and/or instabilities at the liquid-vapor interface. The vapor bubbles, as they are formed,

will also be forced to the tube wall.

Initially, the instabilities and liquid and vapor motion can lead to heat transfer enhancement.

The instabilities and liquid motion can thin the liquid layer near the wall, promoting greater

evaporation.

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No reproduction or networking permitted without license from IHS

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