experimental study on performance of celdek packed liquid ... · experimental study on performance...

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Heat Mass Transfer (2016) 52:1821–1832DOI 10.1007/s00231-015-1704-2

ORIGINAL

Experimental study on performance of celdek packed liquid desiccant dehumidifier

Rakesh Kumar1 · A. K. Asati2

Received: 18 August 2014 / Accepted: 22 October 2015 / Published online: 29 October 2015 © Springer-Verlag Berlin Heidelberg 2015

Subscriptsa Dry airai Inlet of airao Outlet of airav Averageeq Equilibriumi Inleto Outlets Solutionsi Inlet of solutionso Outlet of solution

Greek lettersε Effectivenessω Specific humidity (kg/kg of dry air)dω Change in specific humidity (kg/kg of dry air)

AbbreviationsCFC Chlorofluoro carbonCaCl2 Calcium chlorideDBT Dry bub temperatureLiBr Lithium bromideLiCl Lithium chlorideLPH Liter per hourMRR Moisture removal rateRTD Resistance temperature detectorTEG Tri ethylene glycolVCS Vapour compression systemWBT Wet bulb temperature

1 Introduction

Desiccant dehumidification system is ecofriendly in com-parison to conventional vapour compression system (VCS).

Abstract Dehumidifier is the main component of liq-uid desiccant dehumidification system. Effect of the inlet parameters on various outlet parameters of the dehumidifier is studied in the present paper with structured pads as pack-ing material and calcium chloride as liquid desiccant to process the air. The outlet parameters are change in specific humidity, mass transfer coefficient, moisture removal rate, air temperature, solution temperature, effectiveness and the corresponding inlet process parameters; mass flow rate of air, temperature of air, temperature and flow rate of desic-cant solution. It is observed that mass transfer coefficient and moisture removal rate increase with increasing mass flow rate of the air and desiccant while these parameters decrease with increasing temperature of air and desiccant solution. Dehumidifier effectiveness gets increased with increasing solution flow rate. The present investigations are compared with the results of the researchers in the past.

List of symbolsA Area of packing (m2)ṁ Mass flow rate (kg/s)T Temperature (°C)K Mass transfer coefficient (kg/m2 s)w Uncertainty

* Rakesh Kumar [email protected]

A. K. Asati [email protected]

1 Punjab Technical University, Jalandhar-Kapurthala Highway, Kapurthala, Punjab, India

2 SBS STC Ferozepur, Ferozepur, Punjab, India

http://crossmark.crossref.org/dialog/?doi=10.1007/s00231-015-1704-2&domain=pdf

1822 Heat Mass Transfer (2016) 52:1821–1832

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In VCS, humidity of the air is controlled by cooling below its dew point temperature. Therefore, evaporator in con-ventional air-conditioning systems is required to work at low temperature to fulfil the requirements of latent cool-ing load. Global warming potential of CFCs is high and they also cause depletion of the ozone layer. Due to these reasons, several alternative methods are discovered to pre-serve high-grade energy. Liquid desiccant system is extra beneficial because it is more flexible and absorbs organic and inorganic chemicals available in atmosphere [1–3]. Low moisture is gained at the outlet of the dehumidifier by retaining low temperature and high concentration of desiccant at inlet of the dehumidifier [4]. A simple model is described for preliminary design of an air dehumidifica-tion process in a packed bed using liquid desiccant [5]. Air dehumidification by liquid desiccant solution has numer-ous benefits comprising lower consumption of high grade energy, use of renewable energy/waste heat, lower use of CFCs and improved indoor air quality with removal of airborne bacteria and particulate matter. The experimen-tal findings of Chung et al. [2] have discussed that a 95 % by weight triethylene glycol solution purifies the air con-taining pollutants of formaldehyde (0.02 ppm), toluene (3 ppm), 1,1,1-trichloroethane (24 ppm) and carbon dioxide (1000 ppm) by removing all toluene and 1,1,1-trichloroeth-ane, 56 % of the carbon dioxide and 30 % of formaldehyde.

The study of dehumidifier is carried out by various researchers [6–18]. Chung and Wu [6] have designed packed dehumidifier with an inverse U-shaped tunnel and tested for the dehumidification of air. The mass transfer performance of the dehumidifier has also been discussed by them. Patnaik et al. [8] designed and installed 10.5 kW open cycle liquid desiccant cooling system, using Tripack No. 1/2 polyethylene spheres as packings and lithium bro-mide as solution. Liu et al. [9] has investigated that MRR in the dehumidifier increases with increasing air flow rate, solution flow rate, air inlet specific humidity and inlet con-centration of desiccant. The performance of desiccant cool-ing system is studied in the form of moisture removal rates and effectiveness of dehumidifier and regenerator [10]. Experimental investigations on the performance of the structured packing cross flow liquid desiccant dehumidifi-cation system are carried out [11] by using CaCl2 as des-iccant. Mass transfer coefficient, moisture removal rate, effectiveness and the coefficient of performance were used as performance parameters of the system. The significant increase in mass transfer coefficient and MRR for both the dehumidifier and regenerator has been detected with increasing air flow rate and solution flow rate.

The coefficient of performance of the desiccant dehu-midification system is evaluated by Bakhtiar et al. [12].

Energy consumption of dehumidification system is reduced by applying thermodynamic balancing by mass with-drawal and injection [13]. Thermodynamic balancing of the humidifier or the dehumidifier has been proposed through mass extraction and injection as a potential means of reduc-ing the energy consumption of these systems. Bouzenada et al. [14] have performed an experimental study on dehu-midification/regeneration processes using LiBr as liquid desiccant in direct contact with the air at different operating conditions.

The performance of dehumidifier in terms of moisture removal rate and dehumidification effectiveness has been studied for structured packed liquid desiccant air dehumidi-fier using TEG as desiccant [15]. Two models have been developed using stepwise multiple regression method for the condensation rate and the dehumidification effective-ness. Kumar et al. [16] have simulated and analyzed the steady-state performance of stand-alone liquid desiccant systems. Falling film designs of absorber and regenera-tor has been selected for the study due to lower pressure drop. Outlet and performance parameters of dehumidifica-tion and regeneration processes have been found out using a simple model. Mohammad et al. [17] devised a simula-tion to predict the distribution of air specific humidity, air temperature, concentration and temperature of desiccant solution in a dehumidifier. They compared their results with experimental cross flow dehumidification system [16]. Bassuoni [18] proposed a simple mathematical model to study the air dehumidification in a cross flow dehumidifier by using CaCl2 desiccant solution. A maximum deviation of +6.63 % and −5.65 % in the moisture removal rate has been found between analytical solution and experimental results.

2 Desiccant and packing materials

Desiccants can add or absorb moisture from air, depend-ing on the vapor pressure difference between the desiccant solution and surrounding air. People are generally aware with solid desiccants such as silica gel packages those are included with new electronics or textile products. Liquid desiccants are preferred to use in desiccant cooling sys-tems as these have several advantages over solid desic-cants. The pressure drop through the liquid desiccant is lower than that through a solid desiccant system. A num-ber of small units can be coupled to meet demands of large buildings because liquid desiccant can be pumped from one place to another. Liquid desiccants include TEG, cal-cium chloride, lithium chloride, lithium bromide, and their mixtures. CaCl2 is used as liquid desiccant in current paper

1823Heat Mass Transfer (2016) 52:1821–1832

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because it is cheaper than other desiccants. Chung and Luo [19] experimentally measured the vapour pressure of aque-ous desiccants and found lowest for glycols followed by LiCl, CaCl2 and highest for LiBr. A brief review of dif-ferent desiccants used by various researchers is given in Table 1.

Packing material used in current paper is structured type celdek pads with dimensions 0.57 m × 0.27 m × 0.34 m and surface area 390 m2/m3. Figure 1 presents the differ-ent views of celdek structured packing. These pads com-prise of particularly impregnated and corrugated cellulose paper sheets with 45° flute angles are bonded together. These pads are self-supporting with great absorbance. Celdek pads have more advantages over other packings. These pads give high evaporation efficiency. Pressure drop through these pads in wet condition is very low as com-pared with other packings. Operating cost of these pads is also less. Drift carry over through these pads is negligible. These pads are strong and self-supporting and have long life time. It is very easy to install these pads. Celdek pads are also environment friendly.

Oberg and Goswami [3] have used 2.54 cm polypropyl-ene Rauschert Hiflow rings packing with TEG and studied different design variables such as airflow rate, humidity

ratio, desiccant temperature, desiccant concentration and the packed bed height. Abdul-Wahab et al. [15] have used three different structured packing densities of 77, 100 and 200 m2/m3 to study the impact of number of design vari-ables on the performance of dehumidification process. Chung and Ghosh [29] have compared the efficiency of random and structured packings for dehumidification of process air in a packed column using LiCl as desiccant solutions. Both packings were found to be equally efficient in dehumidifier to process the air under same working envi-ronments. Elsarrag [30] have worked with rigid cellulose media pads and try-ethylene glycol to analysis the conse-quence of different design parameters.

Tri-ethylene glycol as liquid desiccant has been used by many researchers but only a limited research is avail-able with CaCl2. The performance of structured packing desiccant dehumidifier has been studied by Bassuoni [11] in cross flow manner with calcium chloride as desiccant. Combination of celdek pads as packing material and cal-cium chloride as liquid desiccant in counter flow direction has not been used by any researcher. So, current paper is focused on the study of a liquid desiccant cooling system in a counter flow of desiccant solution and air in the presence of structured type packing.

Table 1 Researchers for various liquid desiccants

S. No. Name of liquid desiccant Researchers

1. Lithium Bromide Patnaik et al. [8]; Jain et al. [10]; Bouzenada et al. [14]; Factor and Grossman [20]; Jain et al. [21]; Lazzarin et al. [22] etc

2. Lithium Chloride Chung et al. [1]; Chung et al. [7]; Kessling et al. [23]; Salarian et al. [24] etc

3. Calcium Chloride Gandhidasan [5]; Bassuoni [11]; Alizadeh and Saman [25]; Rahamah et al. [26] etc

4. Triethylene Glycol Oberg and Goswami [3]; Kumar et al. [16]; Abdul-Wahab et al. [15]; Chung and Wu [27]; Zurigat et al. [28]; Elsarrag [30] etc

Fig. 1 Orthographics and enlarged views of celdek struc-tured packing


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3 Experimental set‑up

The details of experimental set-up used for dehu-midification are shown in Fig. 2. The overall dimen-sions of the dehumidifier are 0.6 m × 0.3 m × 0.9 m (Length × Width × Height). The humid air is introduced at the bottom of the dehumidifier through the duct by a cen-trifugal blower. A regulator is attached with blower to con-trol the air flow rate in the dehumidifier. Digital tempera-ture controller with RTD is attached in the solution tank to control the temperature of solution. The desiccant solution is pumped at the top of the packing through rotameter by a distribution tray. The desiccant solution and air flow in counter direction with respect to each other. The weak des-iccant solution runs to the storage tank by gravity. A bypass system is used to control the solution flow rate in the dehu-midifier. Three wire RTDs with digital indicator are used to measure dry bulb temperature, wet bulb temperature and

desiccant solution temperature at inlet and outlet of the dehumidifier. Range of the RTDs is 0–100 °C with resolu-tion of 0.1 °C. The flow rate of desiccant solution is meas-ured with a rotameter with range 40 LPH (0.04 m3/h) to 500 LPH (0.5 m3/h). The air flow rate is measured with a vane type portable digital anemometer. RTDs were calibrated with standard points such that freezing and boiling points of distilled water. Calibration of rotameter was carried out by catch and bucket method corresponding to concentration and temperature of the desiccant solution. Anemometer was calibrated by first principal with the help of pitot static tube. Concentration of desiccant solution is measured with hydrometer. Hydrometer with range 1.300–1.500 and accu-racy of 0.001 is used to measure specific gravity of solution and it is converted to concentration by using tables of prop-erties of solution from DOW’s handbook of calcium chlo-ride [31]. Detail of specifications and uncertainty errors of different measuring instruments is given in Table 2.

The experiments are run in hot and humid outdoor condi-tions. The inlet process parameters for the study are tempera-ture of the air, mass flow rate of the air, temperature and flow rate of the desiccant solution. Different outlet parameters are change in specific humidity, mass transfer coefficient, mois-ture removal rate, outlet temperature of air, outlet tempera-ture of desiccant solution and effectiveness of the dehumidi-fier. The inlet parameters are varied as temperature of the desiccant solution from 25 to 35 °C, inlet temperature of the air from 30.9 to 39.7 °C, air flow rate from 0.02 to 0.07 kg/s and desiccant solution flow rate from 0.056 to 0.112 kg/s.

Fig. 2 Schematic diagram of the experimental set up

Table 2 Specifications and uncertainty errors of instruments

Device Type Uncertainty Operating range

Thermometers RTD ±0.1 °C 0–100 °C

Flow meter Rotameter ±2 % 40–500 LPH (0.04–0.5 m3/h)

Anemometer Vane ±0.1 m/s 0.4–30 m/s

Hydrometer Hand ±0.001 1.300–1.500


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Different observations are recorded at steady state for the above mentioned variations of the inlet parameters.

4 Performance parameters

The performance of the dehumidifier is assessed in the form of moisture removal rate, mass transfer coefficient and effectiveness of dehumidifier. Moisture removal rate from the air is assessed from Eq. (1)

The dehumidifier effectiveness, ε, is defined as the ratio of the actual difference in specific humidity of the air in the dehumidifier to the maximum possible difference in spe-cific humidity under a certain set of working environments. It is expressed mathematically as:

Here ωeq is the specific humidity of air in equilibrium state with the desiccant at its inlet condition, which is a function of the temperature and concentration of desiccant at inlet of dehumidifier.

The average mass transfer coefficient is defined as the rate of moisture flux passing through a unit area (kg/m2 s). It can be obtained from the measured data as follows:

where, A is the interfacial area of contact between liquid desiccant and air inside the dehumidifier.

The average specific humidity (ωav) and average equi-librium specific humidity

(

ωav,eq

)

of process air across the dehumidifier are given as

5 Uncertainty analysis

The uncertainties in the experimental results are calcu-lated by analytical method given by Kline and McClin-tock [32]. This method needs a mathematical expression for the measurement of uncertainty. Let X be the function of several independent variables, X = f (x1, x2, x3, . . . , xn), where, x1, x2, x3, . . . , xn are independent variables. Let wx1, wx2, wx3, …, wxn be the uncertainty of independent vari-ables x1 , x2, x3, . . . , xn respectively and wx be the result-ant uncertainty. Equation 6 gives uncertainty in result as follows:

(1)MRR = (ωi − ωo)ma

(2)ε =ωi − ωo

ωi − ωeq

(3)K =MRR

A(ωav − ωav,eq)

(4)ωav =ωi − ωo

2

(5)ωav,eq =ωi,eq − ωo,eq

2

The uncertainties of different experimental results are given in Table 3.

6 Results and discussion

To have the insight into the working and performance of the dehumidifier, a number of experiments have been per-formed and the observations so obtained with respect to various inlet, outlet and performance parameters are shown in Table 4. The graphical representation for effect of mass flow rate of the air, inlet air temperature and inlet solution temperature on outlet parameters is given in Figs. 3, 4 and 5. The effect of the solution flow rate is also included in all these figures. Error bars obtained for the experimental measurements by using standard deviation of input and out-put parameters are also shown in Figs. 3a–f, 4a–f and 5a–f.

6.1 Effect of mass flow rate of air

The effect of air flow rate and solution flow rate on the outlet parameters is shown in Fig. 3a–f. The Fig. 3a represents that the change in specific humidity across the dehumidifier decreases by 18 % for the air flow rate variation from 0.02 to 0.07 kg/s. When air mass flow rate is increased, the outlet specific humidity increases due to the reduced residence time between air and des-iccant solution. With increase in the air flow rate, mass transfer coefficient between air and desiccant solution is increased by 113 % as shown in Fig. 3b. This increase in mass transfer coefficient across the dehumidifier is responsible for increase in moisture removal rate by 144 % as shown in Fig. 3c. Outlet temperature of the air seems to be marginally increased with increas-ing air flow rate as shown in Fig. 3d. This might be due to recompense of higher condensation heat by the increased mass flow rate of the air itself. Solution outlet

(6)

wX =

√

(

∂X

∂x1

)2

(wx1)2+

(

∂X

∂x2

)2

(wx2)2+ · · · +

(

∂X

∂xn

)2

(wxn)2

Table 3 Uncertainty errors of the results

S. No. Quality Uncertainty

1. Temperature ±0.1 °C

2. Velocity of air ±0.1 m/s

3. Mass of condensate (MRR) ±0.02 kg/s

4. Specific humidity ±5.13 × 10−4 kg/kg of dry air

5. Effectiveness of dehumidifier ±0.08


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Table 4 Experimental observations of dehumidification of the air

Inlet parameters Outlet parameters Performance parameters

ṁa (kg/s) DBTi (°C) WBTi (°C) ṁs (kg/s) Tsi (°C) Csi (%) DBTo (°C) WBTo (°C) Tso (°C) Cso (%) MRR (g/s) ε

0.024 37.3 27.3 0.056 34.5 36.42 34.8 25.6 37.1 36.08 0.046 0.56

0.036 37.3 27.2 0.056 34.5 36.42 34.7 25.6 37.4 36.00 0.061 0.52

0.048 37.4 27.2 0.056 34.5 36.42 34.8 25.7 37.9 35.92 0.073 0.48

0.060 37.3 27.2 0.056 34.5 36.42 34.9 25.8 38.3 35.75 0.086 0.44

0.072 37.4 27.2 0.056 34.5 36.42 34.8 25.8 38.7 35.58 0.098 0.42

0.024 38.1 28.1 0.07 34.5 36.42 35.5 26 37.6 36.00 0.064 0.59

0.036 38.1 28.1 0.07 34.5 36.42 35.6 26.2 38 35.92 0.092 0.56

0.048 38.1 28.2 0.07 34.5 36.42 35.6 26.3 38.4 35.75 0.117 0.51

0.060 38.2 28.1 0.07 34.5 36.42 35.6 26.3 38.9 35.50 0.130 0.48

0.072 38.1 28 0.07 34.5 36.42 35.6 26.4 39.3 35.33 0.146 0.44

0.024 38.5 28.6 0.098 34.5 36.42 35.8 26.2 38.1 35.75 0.078 0.61

0.036 38.4 28.6 0.098 34.5 36.42 35.8 26.3 38.5 35.67 0.112 0.58

0.048 38.5 28.6 0.098 34.5 36.42 35.7 26.3 38.9 35.58 0.145 0.57

0.060 38.6 28.7 0.098 34.5 36.42 35.8 26.5 39.2 35.42 0.172 0.52

0.072 38.5 28.6 0.098 34.5 36.42 35.8 26.6 39.5 35.17 0.182 0.47

0.024 39 29.2 0.112 34.5 36.42 35.9 26.2 38.5 35.83 0.102 0.67

0.036 39.1 29.3 0.112 34.5 36.42 36 26.4 38.8 35.67 0.147 0.63

0.048 39.2 29.3 0.112 34.5 36.42 35.9 26.4 39 35.50 0.192 0.62

0.060 39.1 29.4 0.112 34.5 36.42 36 26.6 39.3 35.33 0.236 0.59

0.072 39 29.4 0.112 34.5 36.42 35.8 27.1 39.5 35.08 0.264 0.55

0.048 30.9 22.8 0.056 27.7 35.67 27.3 20.8 30.2 35.5 0.0665 0.55

0.048 31.7 23.0 0.056 27.7 35.67 28.2 21.1 30.5 35.5 0.0627 0.53

0.048 32.5 23.2 0.056 27.7 35.67 28.7 21.3 30.9 35.3 0.0579 0.49

0.048 33.0 23.3 0.056 27.7 35.67 29.2 21.5 31.4 35.3 0.0517 0.45

0.048 33.5 23.4 0.056 27.7 35.67 29.8 21.7 31.7 35.1 0.0431 0.39

0.048 32.9 23.7 0.07 28.3 36.08 29.5 21.8 30.8 35.7 0.0689 0.58

0.048 33.7 23.9 0.07 28.3 36.08 30.3 21.9 31 35.5 0.0646 0.56

0.048 34.2 24.0 0.07 28.3 36.08 30.5 22.2 31.3 35.4 0.0569 0.50

0.048 34.8 24.1 0.07 28.3 36.08 31.1 22.4 31.7 35.3 0.0526 0.47

0.048 35.3 24.2 0.07 28.3 36.08 31.7 22.6 32 35.1 0.0459 0.43

0.048 35.9 25.0 0.098 28.3 36.08 32.6 22.9 31.5 36.1 0.0924 0.59

0.048 36.3 25.1 0.098 28.3 36.08 33.2 23.1 31.8 36.0 0.0895 0.57

0.048 37.0 25.2 0.098 28.3 36.08 33.8 23.3 32.1 35.9 0.0809 0.54

0.048 37.5 25.3 0.098 28.3 36.08 34.3 23.5 32.3 35.8 0.0742 0.50

0.048 38.1 25.4 0.098 28.3 36.08 34.9 23.7 32.6 35.6 0.0670 0.46

0.048 37.5 25.6 0.112 28 36.08 33.6 23.2 31.7 36.0 0.1062 0.61

0.048 38.0 25.7 0.112 28 36.08 34.1 23.4 31.9 35.9 0.0995 0.58

0.048 38.6 25.8 0.112 28 36.08 34.6 23.5 32.2 35.8 0.0919 0.55

0.048 39.2 25.9 0.112 28 36.08 34.9 23.7 32.5 35.5 0.0857 0.52

0.048 39.7 26.0 0.112 28 36.08 35.4 23.9 32.8 35.3 0.0790 0.49

0.048 38.1 28.1 0.056 25 36.42 28.9 22.1 27.8 36.1 0.178 0.51

0.048 38.1 28.1 0.056 27.5 36.42 29.7 22.8 29.9 36.0 0.137 0.48

0.048 38.1 28.1 0.056 30 36.42 30.5 23.8 32.3 35.9 0.088 0.42

0.048 38.2 28.1 0.056 32.5 36.42 31.5 24.6 34.9 35.8 0.052 0.36

0.048 38.1 28 0.056 35 36.42 32.3 25.1 37.3 35.6 0.027 0.32

0.048 38.1 28.1 0.07 25 36.42 29.5 22.1 28.1 36.0 0.190 0.54


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temperature is increased with increasing air flow rate as shown by Fig. 3e. This is mainly due to larger part of condensation heat transfer to the solution during dehu-midification of the air. Figure 3f shows variation in effectiveness of the dehumidifier, which is decreased by 22.7 % when air flow rate is increased from 0.02 to 0.07 kg/s. This is because of increase in specific humid-ity of the air at outlet with increasing air flow rate. The equilibrium humidity at the inlet of desiccant solution remains constant with increasing air flow rate. So, dif-ference in specific humidity between inlet of air and equilibrium humidity (ωi − ωeq) is more as compared with change in specific humidity (ωi − ωo) across the packing.

6.2 Effect of inlet air temperature

Figure 4 shows the effect of temperature of the air and solution flow rate on the outlet parameters. When tem-perature of the air is increased from 30.9 to 39.7 °C, there is an average decrease in change in specific humid-ity of the air by 42.7 % as shown in Fig. 4a. When inlet temperature of the air is increased, temperature of the desiccant solution in the dehumidifier is also increased, which in turn increases the vapour pressure of desic-cant solution. Therefore, vapour pressure difference between air and desiccant solution is decreased and less moisture is absorbed by the solution, which appears as higher specific humidity at the outlet. The mass trans-fer coefficient is decreased by 6.5 % with increasing

air temperature as shown in Fig. 4b. The moisture removal rate is decreased by 42 % with increase in the temperature of air within above specified limit as shown by Fig. 4c because it is directly proportional to the change in specific humidity across the dehumidi-fier. When temperature of the inlet air is increased, outlet temperature of air and solution are increased by 7.2 and 40 % respectively as shown in Figs. 4d, e. The Fig. 4f shows that the effectiveness of dehumidifier is decreased by 30.8 % which is due to increase in outlet specific humidity of the air. The equilibrium humidity also increases with increase in temperature of desiccant but its increment is less in comparison to the increment of outlet specific humidity.

6.3 Effect of inlet solution temperature

Effect of inlet solution temperature and its flow rate on different outlet parameters is shown in Figs. 5. When temperature of the desiccant solution is increased from 25 to 35 °C, change in specific humidity is decreased by 84.1 % as shown in Fig. 5a. Basically increased solu-tion temperature causes increase in vapour pressure of the desiccant and decrease in absorption of moisture from the air, which in turn gives lesser change in the specific humidity in the dehumidifier. The mass trans-fer coefficient is decreased by 24.1 % as shown in Fig. 5b. Decrease in change in specific humidity (dω) is responsible for the decrease in moisture removal rate as shown in Fig. 5c. At high desiccant temperature,

Table 4 continued

Inlet parameters Outlet parameters Performance parameters

ṁa (kg/s) DBTi (°C) WBTi (°C) ṁs (kg/s) Tsi (°C) Csi (%) DBTo (°C) WBTo (°C) Tso (°C) Cso (%) MRR (g/s) ε

0.048 38.1 28.1 0.07 27.5 36.42 30 22.9 30.7 35.9 0.144 0.50

0.048 38.1 28.1 0.07 30 36.42 30.9 23.8 33.2 35.8 0.095 0.46

0.048 38.2 28.1 0.07 32.5 36.42 31.7 24.5 35.6 35.4 0.058 0.40

0.048 38.1 28.1 0.07 35 36.42 32.6 25.1 38.2 35.3 0.029 0.35

0.048 38.1 28.1 0.098 25 36.42 30.1 22 28.4 35.8 0.210 0.60

0.048 38.1 28.1 0.098 27.5 36.42 30.7 22.9 31 35.6 0.157 0.54

0.048 38.1 28.1 0.098 30 36.42 31.6 23.9 33.6 35.3 0.101 0.49

0.048 38.1 28.1 0.098 32.5 36.42 32.7 24.7 35.9 35.1 0.062 0.41

0.048 38.1 28.1 0.098 35 36.42 33.6 25.3 38.6 35.0 0.034 0.38

0.048 38.2 28.1 0.112 25 36.42 31.3 22.2 29 35.4 0.220 0.63

0.048 38.1 28.1 0.112 27.5 36.42 32.2 23.1 31.4 35.2 0.173 0.60

0.048 38.1 28.1 0.112 30 36.42 33.2 24.1 34.1 35.0 0.119 0.55

0.048 38.1 28.1 0.112 32.5 36.42 34.1 25 36.2 34.8 0.067 0.46

0.048 38.1 28.1 0.112 35 36.42 35 25.6 38.8 34.5 0.037 0.40


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lower potential for mass transfer also reduces the moisture removal rate. When temperature of the solu-tion is increased, outlet temperature of air is increase by 10.3 % as shown in Fig. 5d and solution temperature at outlet increases by 25.9 % as shown in Fig. 5e. The effectiveness of dehumidifier is decreased by 34.1 % with increase in solution temperature as shown in Fig. 5f. This is due to the effect that difference in spe-cific humidity at inlet and outlet positions is more as

compared with difference in specific humidity at inlet and equilibrium conditions.

6.4 Effect of mass flow rate of desiccant solution

When solution flow rate is increased from 0.056 to 0.112 kg/s, there is increase in change in specific humid-ity, mass transfer coefficient, moisture removal rate, air outlet temperature, solution outlet temperature and the

Tai=37.3:39.2 oC, Tsi=34.5oC, Csi=36.42%

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

dω(k

g/kg

of d

ry a

ir)

ṁa (kg/s)

ṁs = 0.056 kg/s ṁs = 0.07 kg/sṁs = 0.098 kg/s ṁs = 0.112 kg/s

0.71

1.31.61.92.22.52.8

K (1

0-3kg

/m2 .s

)

ṁa (kg/s)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

0

0.05

0.1

0.15

0.2

0.25

0.3

MR

R (g

/s)

ṁa (kg/s)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

34.4

34.9

35.4

35.9

36.4

T ao

(o C)

ṁa (kg/s)


40

40.4

40.8

41.2

41.6

42

42.4

0.015 0.035 0.055 0.075 0.015 0.035 0.055 0.075

0.015 0.035 0.055 0.075 0.015 0.035 0.055 0.075

0.015 0.035 0.055 0.075 0.015 0.035 0.055 0.075

T so

(o C)

ṁa (kg/s)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

0.35

0.44

0.53

0.62

0.71

0.80

ε

ṁa (kg/s)


(a) (b)

(c) (d)

(e) (f)

Fig. 3 Variation of the air flow rate on output parameters


1 3

dehumidifier effectiveness as shown in the Fig. 3a–f. The increased mass flow rate of desiccant solution gets larger capacity to absorb moisture with better wetting of the Celdek pads, which provide higher vapour pressure differ-ence till last contact surface of the air and solution. Thus more quantity of moisture is absorbed by the desiccant and change in specific humidity across the dehumidifier increases as shown in Fig. 3a. With increasing solution flow rate, mass transfer coefficient between air and desiccant solution also increases as shown in Fig. 3b, which is due

to physical and flow conditions to provide greater diffu-sion of vapour condensate towards the solution. The mois-ture removal rate through the dehumidifier also increases (Fig. 3c) due to increased change in the specific humidity and mass transfer coefficient. The latent heat of condensa-tion is increased due to the increased moisture removal rate, therefore the air and solution outlet temperatures increase with solution flow rate as shown in Fig. 3d, e. Because of the increased change in specific humidity (dω) at higher solution flow rate, the dehumidifier effectiveness increases.

Tsi=28 oC, Csi=36.08% ṁa=0.048 kg/s

0.0005

0.001

0.0015

0.002

0.0025

30 32 34 36 38 40 30 32 34 36 38 40

30 32 34 36 38 40 30 32 34 36 38 40

30 32 34 36 38 40 30 32 34 36 38 40

dω(k

g/kg

of d

ry a

ir)

Tai (oC)


2.6

2.7

2.8

2.9

3

3.1

3.2

K (1

0-3kg

/m2 .s

)

Tai (oC)


0.03

0.05

0.07

0.09

0.11

MR

R (g

/s)

Tai (oC)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

26

28

30

32

34

36

T ao(o C

)

Tai (oC)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

30

30.5

31

31.5

32

32.5

33

T so(oC)

Tai (oC)


0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

ε

Tai (oC)


(a) (b)

(c) (d)

(e) (f)

Fig. 4 Variation of air inlet temperature on output parameters


1 3

The Figs. 4a–f and 5a–f also include effect of variation of the solution mass flow rate on the said parameters with increasing air and solution inlet temperatures respectively, which shows almost similar trends as in case of increased mass flow rate of air.

The results of the present study are compared with the previous studies as given in Table 5. The table provides the parameters describing the performance, process variables and ranges covered. The effect of each inlet parameter on the outlet parameters is presented by arrows as explained

in the table. Compared to the previous studies, the desic-cant flow rate and air flow rate used in this study are signifi-cantly lower. The range of inlet temperatures of air is wider than [3, 8, 24] and inlet temperature of desiccant is wider than [5, 8, 24]. So, it seems that it is possible to work at low desiccant flow rates with structured packing. The previous researchers had mainly studied moisture removal rate and effectiveness of dehumidifier. This paper adds the experi-mental study of change in specific humidity, mass transfer coefficient, outlet temperatures of the air and desiccant.

Tai=38.1oC, Csi=36.42%, ṁa=0.048 kg/s

0

0.001

0.002

0.003

0.004

0.005

dω(k

g/kg

of d

ry a

ir)

Tsi (oC)


1

1.5

2

2.5

3

K (1

0-3kg

/m2 .s

)

Tsi (oC)


0

0.05

0.1

0.15

0.2

0.25

MR

R (g

/s)


282930313233343536

T ao

(o C)


27.5

29.5

31.5

33.5

35.5

37.5

24 26 28 30 32 34 36 24 26 28 30 32 34 36

T so(oC)

Tsi (oC)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

0.30

0.37

0.44

0.51

0.58

0.65

ε

Tsi (oC)

24 26 28 30 32 34 36 24 26 28 30 32 34 36

24 27 30 33 36 24 26 28 30 32 34 36

Tsi (oC) Tsi (oC)

ṁs = 0.056 kg/s ṁs = 0.07 kg/s

ṁs = 0.098 kg/s ṁs = 0.112 kg/s

(a) (b)

(c) (d)

(e) (f)

Fig. 5 Variation of inlet solution temperature on output parameterss


1 3

7 Conclusions

The effect of different operating inlet parameters on the outlet and performance parameters for the structured packed dehumidifier using calcium chloride as desiccant is investigated experimentally. The performance of the dehu-midifier is studied in the form of change in specific humid-ity, mass transfer coefficient, moisture removal rate, outlet air temperature, outlet solution temperature and effective-ness of the dehumidifier. It is observed that when the air flow rate is increased, outlet parameters; moisture removal rate, temperature of solution and mass transfer coefficient are increased while change in specific humidity and effec-tiveness of the dehumidifier decreases. Decrease in mass transfer coefficient, change in specific humidity, MRR and dehumidifier effectiveness are observed with increasing

inlet temperature of the process air, while temperature of air and solution are increasing. When the temperature of the desiccant solution is increased, there is decrease in change in specific humidity, moisture removal rate and effectiveness whereas air and solution outlet temperature are increased. Celdec structured packing works efficiently using low flow rate of desiccant solution. Researchers; Gandhidasan [5], Patnaik et al. [8], Abdul-Wahab et al. [15], Salarian et al. [24] and Elsarag [30] have studied only MRR for the dehumidifier and Oberg and Goswami [3], Bassuoni [11], Zurigat et al. [28] have studied MRR and effectiveness as performance parameters. The Present paper adds the study of change in specific humidity, mass transfer coefficient, outlet temperature of air and desiccant along with MRR and effectiveness of the dehumidifier. The combination of celdec structured packing and desiccant

Table 5 The effect of inlet parameters investigated in this study as well as reported in literature

↑ Performance parameter increases with increasing variable, ↓ performance parameter decreases with increasing variable, ↑↓ variable has no significant effect on the performance parameter

Author Desiccant Packing material Performance parameters

Inlet parameters

ṁa Tai Tsi ṁs

Present study CaCl2 Celdec structure packing

0.024–0.072 kg/s 30.9–39.7 °C 25–35 °C 0.056–0.112 kg/s

dω ↓ ↓ ↓ ↑K ↑ ↓ ↓ ↑MRR ↑ ↓ ↓ ↑Tao ↑ ↑ ↑ ↑Tso ↑ ↑ ↑ ↑ε ↓ ↓ ↓ ↑

Zurigat et al. [28] TEG Aluminium 1.5–2.613 kg/m2 s 25.4–44.0 °C 28–45 °C 0.13–1.00 kg/m2 s

MRR ↑ ↑ ↑ ↑ε ↑ ↑ ↑ ↑

Gandhidasan [5] CaCl2 Rashing rings 32–36 °C 3.5–6.0 kg/m2 s

MRR – – ↑↓ ↑Oberg and Goswami

[3]TEG Polypropylene

rauschert hilflow rings

0.5–2.0 kg/m2 s 25–35 °C 25–35 °C 4.5–6.5 kg/m2 s

MRR ↑ ↑↓ ↑ ↑↓ε ↓ ↑↓ ↑↓ ↑↓

Patnaik et al. [8] LiBr Polyethylene spheres

1.3–1.9 kg/m2 s 24–36 °C 24–32 °C 0.6–1.7 kg/m2 s

MRR ↑↓ ↓ ↑↓ ↑Salarian et al. [24] LiCl Polypropylene

rauschert hilflow rings

0.35–1.5 kg/m2 s 22–27 °C 20–25 °C 0.35–1.5 kg/m2 s

MRR ↑ ↓ ↓ ↑

Elsarrag [30] TEG Celdec structure packing

0.94–2.2 kg/m2 s 1.75–2.2 kg/m2 s

MRR ↑↓ – – ↑Abdul-Wahab et al.

[15]TEG Stacked plates 1.5–2.613 kg/m2 s 25–45 °C 28–45 °C 0.13–1.00 kg/m2 s

MRR ↑ ↓ ↑↓ ↑ε ↑↓ ↓ ↑ ↑

Bassuoni [11] CaCl2 Celdec structure packing

0.022–0.014 kg/s – 14–30 °C 0.014–0.058 kg/s

MRR ↑ ↓ ↑ε ↓ ↑ ↑


1 3

solution seems very useful in the area of desiccant cooling systems.

Acknowledgments Authors are thankful to the Punjab Techni-cal University, Jalandhar, Head and faculty members of Mechanical Engineering Department, IET Bhaddal Ropar, Punjab for their valu-able support to carry out this research. We also express our sincere thanks to respected Dr. Sanjeev Jain, Professor, IIT Delhi for provid-ing consistent help in the research work.

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http://dx.doi.org/10.1016/j.enconman.2010.12.052

http://dx.doi.org/10.1016/j.enconman.2010.12.052

http://dx.doi.org/10.1016/j.energy.2011.02.004

http://dx.doi.org/10.1016/j.procs.2014.05.476

http://dx.doi.org/10.1007/s00231-013-1198-8

http://dx.doi.org/10.1016/S0196-8904(03)00109-2

http://dx.doi.org/10.1016/S0196-8904(03)00109-2

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