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EXPERIMENTAL STUDY ON THE THERMOSIPHON SOLUTION ELEVATION PUMP

WITH MULTIPLE LUNATE CHANNELS USED IN MINITYPE SOLAR

AIR-CONDITIONDING SYSTEM

Li Zhengliang

Guangxi Normal College, Nanning City, 530001

, China

Wang Daxi

Guangxi University of Technology, Liuzhou, 545006, China

Zhang Xiang, Zheng Hongfei

School of Mechanical and Vehicular Engineering, Beijing,

Institute of Technology, Beijing, 100081, China

ABSTRACT

A special structure thermosiphon solution elevation pump

with multiple lunate channels used in minitype solar

air-condition system was designed and experimentally

measured on its elevating effects. Under the determinate

operation conditions, its transient state performances were

tested. The curves of the temperature and strong solution

elevation volume with operating time were given out.

Researches indicate that only 20 minutes is required from

start-up to steady operation. Under the steady state

conditions, the elevating rate of the strong solution and the

distilled water yield rate versus the operating temperature

were investigated. The minimum start-up operating

temperature under different the immersing heights and the

weak solution concentration were determined. The ex-

perimental results show that under the operating

temperature condition of 85ć, the strong solution elevation

rate could reach 32 ml/s for 45% weak solution concen-

tration. If all distilled water is evaporated, the refrigeration

capability of the chiller can reach about 9 kW. At the same

time, the heat transfer density of the lunate channel wall is

about 10.2 kW/m

1. INTRODUCTION

There is a couple of significance of saving energy and

protecting environment for humankind to use the solar

energy to drive air-conditioner. The most important

characteristic for without-pump LiBr absorption solar

chiller is to use the thermosiphon elevation solution pump

to replace electric pump[1]. This unit utilizes the

thermosiphon elevation solution pump with multiple lunate

channels. Due to the special structure of the lunate channels,

the superheat of the solution boiling temperature is

decreased efficiently. The boiling and elevation of the

LiBr solution can be realized under lower heating water

temperature[2,3]. This unit has the characteristic of solution

elevating amount bigger and more steady than that of the

thermosiphon solution elevation pump with single lunate

channel[2].

2. OPERATION PRINCIPLE OF UNIT

Schematic diagram of the experimental system is shown in

Fig.1. It is consist of gas-solution separator, condenser,

solution elevating pump, storage solution tank, simulation

solar heater and some pipes. The structure and material of

the equipments were presented in reference [4].

The operation principle of the unit is: the heating water

yielded by simulation solar heater is pumped into the

heating tube, in which the heating water heats LiBr weak

solution through the beside of the lunate channel. At the

same time, another loop heating water is pumped into the

inner tube of the lunate channel from its bottom end, in

which the heating water heats LiBr weak solution through

the inside of the lunate channel. So, LiBr weak solution is

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

913

heated from two sides (outer and inner tube). The weak

solution enters the elevating channel from the bottom of the

storage solution tank, in which it is heated continuously

until boiling and changed into two phase liquid. And then,

forced by the weight pressure coming from the solution in

storage solution tank, the solution is elevated into

gas-solution separator to change the strong solution. The

vapor goes into the condenser, in which it is condensed to

change stilling water. The stilling water and the strong

solution together go into the storage solution tank through

different pipes and meters, separately, as shown in Fig. 1.







input of

cooling

wtaer

output of

heating

water

input of

heating

water

























1.storage solution tank; 2.distilled water pipe; 3.solution flow meter; 4.distilled

water flow meter; 5.solution pipe; 6.pressure equilibrium pipe; 7.vaccum meter;

8.cooling water flow meter; 9. gas-solution separator, 10. solution elevating

pump; 11. lunate channel pipe; 12.heating water flow meter.

Fig. 1: Schematic diagram of the experimental system.

3. EXPERIMENTAL RESULTS AND ANALYSIS

The experimental conditions: the pressure range of unit is

4̚6kpa, the input temperature of the cooling water is 17 , ć

the flow rate of the cooling water is 0.2kg/s, the heating

water flow rate is 0.3kg/s, ambient temperature range is

20~22ć.

3.1 Transient State Performance Test

Transient state performance of unit is that characteristic

during which unit operates from starting up until steady

state operation. It is an important index to reflect the heat

mass of unit. Under the determinate conditions, some

parameters versus operating time were tested when the unit

transient state operate. During the test, the heating water

temperature was 80

C. The immersing height of the weak

solution was 650mm.

The input and output temperature of the heating and

cooling water versus operating time are shown in Figs. 2

and 3. The elevating rate of the strong solution and the

stilling water yield rate versus operating time is shown in

Fig. 4. The experimental results indicate that the output

temperature of the heating and cooling water have

remarkable change from start-up until steady state

operation. Only 5 minutes, a litter solution and stilling

water is elevated to gas-solution separator. Their yield rate

fleetly increases with the operating time, as shown in Fig. 4.

After 20 minutes, the solution elevating rate and stilling

water yield rate slowly go up to steady. At this time, the

0 5 10 15 20 25 30

Temperature, T/ C

Operation time, t/min

heating water input

heating water output

Fig. 2: The input and output temperature of the heating

water versus operating time.

0 5 10 15 20 25 30

Temperaure, T/ C

Operation time, t /min

cooling water output

cooling water input

Fig. 3: The input and output temperature of the cooling

water versus operating time.

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

914

output temperature of the heating and cooling water also go

up to steady.

0 5 10 15 20 25 30

Elevating rate, m/(mL/s)

Operation time, t/min

solution elevating rate

stilled water rate

Fig. 4: The elevating rate of the strong solution and the

stilling water yield rate versus operating time.

3.2 Steady State Performance Test

Steady state performance of the unit is an important index

to indicate elevating ability. It is also an important basis to

instruct the optical design and utilization of the unit. So, the

steady state experiments about parameters having influence

on the solution elevating rate and distilled water yield rate

had been carried out.

3.2.1 Influence of the Operating Temperature on the

Solution Elevating Rate

The heating water temperature is the operating temperature.

The solution elevating rates versus the operating tempera-

ture are shown in Fig.5. The immersing height of the weak

solution was 650mm in the test. The elevating pump can

not operate if the operating temperature is extremely low.

The start-up operating temperature of the unit is about

76~78 when the concentration of LiBr solution is 45ć ˁ.

If the concentration of LiBr solution is 40ˁ, then the

start-up operating temperature of the unit is decreased to

71~72 . ć

The experimental results shown in Fig. 5 indicate that the

operating temperature has notable influence on the

elevating rate of the solution. The elevating rate of the

solution freely increases with the operating temperature.

72 76 80 84 88

120

Solution elevating rate, M /(ml/s)

Operation temperature, T/ C

ξ=50%

ξ=45%

ξ=40%

Fig. 5: The variation of the strong solution elevation rate

versus the operating temperature.

It can be found from the experiments that the elevating rate

of the strong solution is about 30ml/s when the weak

solution concentration is 45% and the heating water

temperature is 80 . In this time, the distilled water yield ć

rate is about 3.8g/s. If the distilled water is evaporated

completely (evaporation temperature is 7 ), the ć

refrigeration ability can reach 9kw. It is shown that this

pump has corking elevating ability. Based on the

experimental results, the heat transfer density through the

lunate channel wall can be calculated also. Supposing, A is

the area of the channel wall, m

. ΔT is the temperature

difference between input and output of the heating water.

is the flow rate of the heating water. Then, the total heat

energy provided by the heating water is,

kWTcMQ

4.105.818.43.0 =××=Δ=

where c

is the specific heat of water. It is known that

A=0.256m

, where A is the total area of the lunate channel

inner tube and outer tuber wall. If heat loss in other

components is ignored, the heat transfer density through the

lunate channel wall can be calculated as follow,

/2.10

mkW

q ==

It is found that the heat transfer density through the lunate

channel wall is very big.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

915

3.2.2 Influence of the Immersing Height of the Weak

Solution on the Start-up Temperature

Immersing height of the weak solution is the height from

the bottom of the channel to the surface of the weak

solution in channel when unit do not operate. Immersing

height of the weak solution has remarkable influence on the

solution elevating rate. If the immersing height is too low,

the solution can not be elevated to the gas-solution

separator. In fact, there is a coincidence relation among the

immersing height, solution concentration, operating

temperature and operating pressure. In order to know the

immersing height influence on the performance of the

thermosiphon solution elevation pump with multiple lunate

channels. Some especial tests with different immersing

height have been completed. In the tests, the weak solution

concentration is 40%, 45ˁ and 50%, respectively. The

experimental results is shown in Fig. 6.

500 550 600 650 700 750 800

Start-up elevating temperature, T/ C

The immersing height of the weak solution, h/mm

ξ=40%

ξ=45%

ξ=50%

Fig. 6: Start-up temperature versus immersing height of the

weak solution.

It can be found from Fig.6 that the immersing height has

remarkable influence on the start-up temperature. If the

immersing height increases, the start-up temperature will

decrease.

4. CONCLUSIONS

(1) The experimental results show that this pump has the

notable advantages of lower start-up temperature and wider

range of operating temperature and more steadily running

than that with other figure of channels because of the

solution heated through double directions and the superheat

degree decreased by the enhanced heat transfer of the

narrow slot.

(2) Operating temperature has remarkable influence on

solution elevating rate and distilled water yield rate. It has

not good effect until operating temperature over 80

C for

45% weak solution concentration. If the weak solution

concentration is 40%, it will have good effect when

operating temperature is about 75̚80

(3) There is a coincidence relation among the immersing

height, solution concentration, operating temperature and

operating pressure. When solution concentration and

operating pressure are determinate, the immersing height of

the weak solution has remarkable influence on the start-up

temperature. In general, when the immersing height

increases 60̚80mm, the start-up operating temperature

will decrease about 1

5. ACKNOWLEDGEMENT

This work was supported by the Natural Scientific

Foundation of China (No. 50576004) and the Basic

Research Foundation of Guangxi Province (No.0639034 ).

6. REFERENCES

(1) Q. Wang, X. Zhang, H. Zheng, Y. Wu, Study on little

temperature difference heat transfer of phase change in

LiBr solar energy absorbing air conditioning system[J],

fluid machinery, 2002, 30(9): 46-49

(2) H. Zheng ongfei, Y. Wu, H. Jiang, etc. The study of the

thermosiphon solution on elevation tubes with lunate

channel in solar absorption chiller[J], Acta Energiae

Solaris Sinica, 2003, 24(4): 466-471

(3) L. Zhang

, Y. Wu, H. Zheng, J. Guo, D. Chen. An ex-

perimental investigation on performance of bubble

pump with lunate channel for absorption refrigeration

system. Int. J. of Refrigeration, 2006, 29˄5˅˖815-822

(4) J. Fang, H. Zheng, Z. Li, M. Xie. Study on performance

of the thermosiphon solution elevation tubes with

multi- tube lunate channels in minitype solar

air-conditionding system. Acta Energiae Solaris Sinica,

2007, 28(3): 291-295

SOLAR-POWERED ADSORPTION CHILLER WITH CPC COLLECTION SYSTEM:

COLLECTOR DESIGN AND EXPERIMENTAL RESULTS

Manuel I. González

Physics Department, University of Burgos

Avda. Cantabria s/n

Burgos 09006, Spain

miglez@ubu.es

Luis R. Rodríguez

Physics Department, University of Burgos

C/ Villadiego s/n

Burgos 09001, Spain

ABSTRACT

A new class of compound parabolic concentrator (CPC)

useful in solar, solid sorption cooling is presented. The

main feature of this class of CPC is that only a portion of

its tubular receiver is exposed to sunlight. During the daily

phase of the refrigeration cycle the non-exposed portion is

covered with a thermal insulation, which is removed at the

beginning of the nightly phase, in order to improve the

natural cooling of the sorption bed.

Geometric characteristics of the proposed CPC are given as

a function of the concentration factor and the fraction of

receiver area which is exposed to radiation

A prototype of chiller using this type of collector and the

activated carbon – methanol pair is described. The

concentration factor is 1.41 and the receiver area is exactly

half exposed to sunlight. The prototype was tested in

Burgos (Spain) and the measured solar COP ranged from

0.078 to 0.096.

1. INTRODUCTION

Many of the solar adsorption machines described in the

literature are based on the flat-plate collector geometry [1].

Porous beds of some other prototypes are enclosed

in tubular receivers, evacuated or non-evacuated. Very

little attention in this field has been paid to concentrating

collectors such as compound parabolic concentrators (CPC).

An exception is Headley’s work [2], which reports COP’s

of about 2% and the ability to produce ice even in overcast

days.

This work deals with the use of CPC collectors suitable for

solar refrigerators. A new class of CPC concentrators is

presented and some of their geometric characteristics are

given. Section 3 describes a prototype of solar refrigerator

based on CPC geometry, built and tested in Burgos (Spain);

the working pair is methanol – activated carbon. Finally,

section 4 shows typical experimental results obtained with

this unit.

2. CPC WITH PARTIALLY EXPOSED TUBULAR

RECEIVER

A logical configuration of CPC collection system for

adsorption machines consists of placing the porous bed

inside the tubular, fully exposed to sunlight, receiver.

However, this solution leads to a difficult compromise

between the adsorbent mass and the geometric parameters

of the concentrator, mainly the concentration factor.

A suggested solution is what we call ‘CPC with partially

exposed tubular receiver’, in which only a portion 2α of the

angular perimeter of the tube is effectively exposed to solar

radiation (Fig. 1).

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

917

Fig. 1: A CPC with partially exposed tubular receiver

suitable for adsorptive refrigerators. ζ is the

acceptance half-angle.

2.1 The profile of the Proposed CPC

The general algorithm to calculate the profile of a CPC is

explained in [3]. The basic idea is that every solar ray

whose incidence angle is exactly the acceptance half-angle

ζ should be tangent to the receiver after being reflected by

the sheet (see Fig. 2).

Fig. 2: Geometric construction to determine the profile of a

CPC with partially exposed tubular receiver.

Although the details of the calculation will be omitted, a

short explanation must be given. Let ϕ be the angle giving

the position of the point Q(ϕ) where the reflected ray

reaches the receiver, and let P(ϕ) be the point of the

reflective sheet where the reflection occurs. The distance

a(ϕ) between P and Q, expressed in units of the receiver

radius, is given by:

ϕαϕ −=)(a (points between M and N) (1)

)sin(1

)cos(

)(

ζϕ

ϕζα

++−−+

(points over N) (2)

These two expressions permit an easy calculation of the

sheet profile in Cartesian coordinates.

In order to manufacture the CPC, the height and the length

of the sheet must be known. Although (1) and (2) are exact,

no attempt has been made to find closed expressions for

both parameters. Instead, they have been computed

numerically. Figures 3 and 4 show the results as a function

of the angles ζ and α.

Fig. 3: The height of a non-truncated CPC with partially

exposed tubular receiver. The height is measured

from the centre of the receiver to the top of the

reflective sheet.

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

918

Fig. 4: Total length of the reflective sheet vs. concentration

factor for various values of the angle α.

3. THE PROTOTYPE

A prototype of solar chiller with a CPC as described in the

previous section and using the methanol / activated carbon

pair was built and tested in Burgos (Spain). The generator

is an array of four CPC collector with tubular receivers

oriented in the EW direction (see figures 5 and 6). The

chosen concentration ratio is 1.41 (i.e. ζ = 45º) and half the

receiver perimeter is exposed to sunlight (α = 90º). Total

aperture area is 0.55 m

; the porous bed contains 7.6 kg of

activated carbon.

Fig. 5: Schematic view of the prototype.

Fig. 6: Front view of the prototype.

The condenser is a cylindrical chamber crossed by an array

of parallel water pipes; the condensation occurs inside the

chamber. The total exchange area is 0.33 m

. The cooling

water is stored in a 100-litre tank annex to the unit (Fig. 7).

The evaporator consists of a grid of vertical tubes, where

the liquid methanol is stored as the condensation proceeds.

Each tube is surrounded by a cylindrical reservoir

containing the water to be chilled. Thermal insulation is

provided by 8 cm thick polystyrene walls, including a cover.

During the daily phase of the cycle the cover is removed

(see Fig. 7). When the solar radiation ceases the cold box is

covered and the bottom insulation of the generator is

removed.

Fig. 7: Rear view of the prototype.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

919

Measuring equipment includes a pyranometer; various

thermocouple probes: ambient air, receiver surface, cold

box; and three pressure meters: generator, top of the

evaporator, bottom of the evaporator. The two latter allow

knowing the amount of liquid methanol inside the

evaporator and hence the concentration of methanol in the

porous bed.

4. EXPERIMENTAL TEST

This prototype was tested in the summer of 2005 in Burgos

(Spain). Table 1 shows a summary of experimental results

for some selected cycles. As we can see, measured COP’s

ranged from 0.078 to 0.096.

TABLE 1: SUMMARY OF EXPERIMENTAL RESULTS

DAY G M

cond

COP

1 July 19.5 2.45 1.62 0.096

5 July 27.2 2.96 1.98 0.082

6 July 22.0 1.76 1.82 0.093

7 July 26.6 2.05 1.84 0.078

8 July 28.2 2.16 1.95 0.078

11 July 27.5 2.91 2.25 0.092

12 July 27.7 2.29 2.09 0.085

13 July 27.4 2.15 20.5 0.084

14 July 26.1 2.15 2.09 0.089

15 July 25.9 2.27 2.04 0.088

(G): daily irradiation (MJg m ); (M ): condensed mass (kg m ); (M ):

evaporated mass (kggm

Referring to Table 1 it should be noted that both the

condensed and the evaporated masses have been

measured directly, since our experimental setup allows

continuous record of methanol concentration in the

porous bed, as explained before. The bed temperature

was not measured but estimated with the help of the

Dubinin – Astakhov equation, whose parameters were

previously found in [4].

Fig. 8 shows the time evolution of one of these cycles in a

log P vs. estimated bed temperature diagram. As we can see,

the bed temperature ranges between 37 ºC and 117 ºC –the

latter, rather high value is possible thanks to the

concentration provided by the CPC. The maximum and

minimum methanol concentrations in the porous bed were

210 and 50 g/kg, respectively. The condensation

temperature was 27 ºC at the beginning of the condensation

stage and 33 ºC at its end. This increase is caused by the

progressive heating of the water tank. The evaporation

temperature drops from 15 ºC to -8 ºC as evaporation phase

proceeds.

Bed temperature (ºC)

ln (P / mbar)

Saturation temperature (ºC)

Fig. 8: The 12 July cycle in a (t, ln P) diagram. (Diagonal

lines): isosters.

The average gross cold production for the cycles shown in

Table 1 was 2.2 MJ per m

collection area. About 35 % of

this quantity was extracted from the 9 kg per m

chilled

water, whose temperature dropped from 25 ºC to about 1 ºC

in every single cycle.

5. CONCLUSIONS

The CPC with partially exposed tubular receiver seems to

be an interesting option as a collection system for solar

adsorptive refrigerators. The characteristic half angles ζ

and α can be varied in various manners, but future work

must be conducted to achieve the best compromise between

daily collection efficiency, adsorbent mass per unit

collection area and nightly cooling of the sorption bed.

6. ACKNOWLEDGMENTS

The authors acknowledge the financial support provided by

the Spanish Ministerio de Ciencia y Tecnología (Grant

REN-2003-09684-C02-01).

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

920

7. REFERENCES

(1) A. O. Dieng and R. Z. Wang. “Literature review on

solar adsorption technologies for ice-making and

air-conditioning purposes and recent developments in

solar technology”. Renewable and Sustainable Energy

Reviews 2001; 5: 313-42.

(2) O. StC. Headley, A. F. Kothdiwala, and I. A. McDoom,

“Charcoal–methanol adsorption refrigerator powered

by a compound parabolic concentrating solar collector”.

Solar Energy 1994; 53(2): 191-7.

(3) J. A. Duffie and W. A. Beckman, “Solar Engineering of

Thermal Processes”, 3

ed. John Wiley & Sons, New

York 2006.

(4) M. I. González, Thesis “Refrigeración Solar por

Adsorción con Sistema de Captación CPC: Experimentos

y Modelo”, University of Burgos (Spain), 2006.

STUDY ON SOLAR SPACE HEATING FOR BUILDINGS WITH TIME-SCHEDULED

ROOM TEMPERATURE SETBACK

Guoqing Yu, Chuanzhen Feng

Department of Building Environment and Equipment

Engineering

University of Shanghai for Science and Technology

Shanghai 200093, China

guoqing.yu@163.com

Yujie Li

Shanghai United Architectural Design Group

Stock Exchange Building 528 South Pudong Road,

Shanghai 200120, China

ABSTRACT

This paper will focus on solar heating for intermittently

occupied buildings such as offices, classrooms, workshops

which generally are unoccupied during nights and

weekends. If we lower the room temperature and maintain

the temperature above 5

C to prevent freezing during nights

and weekends, a large portion of energy will be saved. This

paper call this is time scheduled heating. In the paper, a

simple building is assumed and a solar assisted space

heating system is designed for it. Hourly simulations during

January will be conducted under various conditions, such

as different building envelopes, different control strategies

(reducing flowrate or cut off space heating) and so on.

Some conclusions are obtained.

1. INTRODUCTION

In the whole world, the energy consumption for space

heating in winter accounts for a large proportion of energy

consumption. How to improve the efficiency of heating

system and to save energy is of great importance for the

sustainable development of the world.

Solar assisted heating is one important way to reduce

energy used for space heating. Today lots of research and

application of solar heating are focused on residential

buildings. This paper will focus on solar heating for

buildings such as offices, classrooms, workshops which

generally are unoccupied during nights and weekends. If

we lower the room temperature and maintain the

temperature above 5

C to prevent freezing during nights

and weekends, a large portion of energy will be saved. This

paper call this is time scheduled heating.

However, it is not so simple to use time scheduled heating.

If we stop heating during nights, can the room temperature

drop below zero and encounter the risk of freezing? How

much energy will be saved by night setback? How to

reduce the fluctuation of the room temperature during

daytime?

In the paper, a simple building is assumed and a solar space

heating system is designed for it. Hourly simulations during

January have been conducted under various conditions,

such as different building envelopes, different control

strategies.

2. THE RESEARCH OBJECTS

2.1 The Shematic of the Solar Space Heating Systems

A solar space heating system is designed for a house. The

schematic of the solar heating system is shown in Fig. 1. It

includes a heat source (solar collectors), pumps, an air

heater (radiator, or water-air heater), a thermal storage tank

and the load (a house).

Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2

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