Experimental Investigation of Thermal Performance Parameters of Drying Air Unit with a Different Flowrate of Liquid Desiccant Solution

The air conditioning industry has become more interested in desiccant dehumidification devices in recent years [1]. Statistics show that an individual's performance in a conditioned space is superior to that in an untreated setting [2]. Moreover, there has been a resurgence of interest in solar-powered air conditioning [3]. Because the cooling load is closely connected to overall solar availability, solar cooling is a viable use of solar thermal technology [4]. Desiccant dehumidification is a technology that has long been used in both industrial and agricultural applications, such as humidity management in textile mills and post-harvest crop drying. In stores, they are drying. In the last few years, all cooling coils including (DX) and chilled-water coils are ineffective moisture removes [5]. Desiccants, on the other hand, can be useful tools and help maintain a pleasant and healthy indoor environment [6]. When compared to traditional compression refrigeration devices, these systems offer the potential to minimize energy usage for humidity management by using low-temperature waste heat [7]. Furthermore, both sensible and latent cooling loads can be separately regulated [8]. The rising demand for air conditioning has resulted in a huge increase in energy resource consumption. One of the ecologically friendly approaches that might assist solve the problem is solar powered cooling [9, 10]. The climate has a big role in deciding which type of evaporative cooler to use [2]. The partial water vapor pressure of the air rises as the air inlet humidity ratio rises, increasing the mass transfer potential, according to Moon et al. [11]. Furthermore, Ahmed and Abdalla in 2012 [12] proved that the moisture removal rate was enhanced by increasing the inlet air flow rate and the inlet air humidity ratio. In the work of Ahmed and Kamal (2012) [13] the rate of moisture removal was tested in an experiment during which the entry parameters such as: rate, humidity ratio, desiccant flow rate, and concentration are changed. Bouzenada et al. (2015) [14] investigated experimentally the effectiveness of a low-flow falling-film liquid desiccant air-conditioner. The dehumidifier is one of the most important components in open-cycle liquid desiccant air-conditioning systems. Zouaoui et al. (2016) used packed bed of silica gel particles in order to investigate the air dehumidification and regeneration operations experimentally during adsorption and desorption phases [15]. Rafique et al. (2017) [16] presented an experimental tests to enhanced liquid desiccant evaporative cooling system. The impact of weather and other factors on device efficiency have been investigated. Ou et al. (2018) [17] studied the heat and mass transfer properties of a liquid desiccant cooling and dehumidification system in an experimental setting (LDCD). The heat efficiency and moisture efficiency improve as the chilled water flow rate, desiccant solvent flow rate, and concentration increase. Recently, Ebrahimpour et al. used lithium chloride as fluid in liquid desiccant air conditioners [18]. Previously, most published research focused on utilizing an expensive desiccant to remove moisture from air in a basic system such as a pipe or duct [19, 20]. In the current study, the authors combined an indirect evaporative cooling system with a calcium chloride desiccant, which is the cheapest and most readily available desiccant for modern air conditioning applications. In this work, to exchange moisture between the air and the liquid desiccant, the scientists used an experimental counter-flow enthalpy exchanger. The ambient air moisture content reduced by roughly 20% during the dehumidification process and increased by around 14.28 percent during the regeneration phase, according to the findings.

The main aim of this research is to study the effect of the primary air flow rate and desiccant flow rate on desiccant system parameters such as: the moisture removal, efficiency of moisture, enthalpy efficiency, sensible heat ratio and mass transfer coefficient. For this the experiment test rig shown Figure 1 was used. According to that, the main contribution is using calcium chloride as a desiccant solution in the air conditioning system of the present work which includes two air passages one for the primary air and the second for secondary air and joined by cross flow heat and mass exchanger and for the desiccant solution regeneration process, a flat plate solar collector was employed.

The performance of desiccant system can be evaluated by calculation the moisture removal rate (MR) from Eq. (1) [21], the rate of moisture removal is [22]:

$M R=\dot{m}_{a}\left(W_{i-} W_{o}\right)$       (1)

where, $\dot{m}_{a}$ the mass flow is rate of air with unit of Kg/s and (W_i-W_o) is the difference between the moisture content at inlet and outlet with units of Kg_v/Kg_dryair, respectively. According to the concept of efficiency, the performance of process of removing moisture from the air in the desiccant drter system can be expressed in terms of both the moisture efficiency and the enthalpy efficiency, which can be calculated, respectively, from Eqns. (2) and (3) as follows [23].

$\eta_{m}=\frac{\left(W_{i-} W_{o}\right)}{\left(W_{i-} W_{e}\right)}$      (2)

$\eta_{h}=\frac{\left(h_{i-} h_{o}\right)}{\left(h_{i-} h_{e}\right)}$      (3)

The sensible heat ratio which is defined as the ratio between the sensible heat load and the total heat load of the air represents the needed handling capability of the air conditioner's various components.

Therefore, Calculating Sensible Heat Ratio (SHR) based on inlet and output air parameters might be used to assess cooling and dehumidify introduction the humidity and temperature, it can be calculated as shown in Eq. (4) [24]:

$S H R=\frac{C_{a}\left(t_{i-} t_{o}\right)}{\left(h_{i-} h_{o}\right)}$      (4)

The Antoine equation is one of the most widely used formulas for determining the vapor pressure of desiccant solution. It can commonly be written as follows [19]:

$\mathrm{p}_{s o l}=a \exp \left(A-\frac{\mathrm{B}}{\mathrm{T}+\mathrm{C}}\right)$      (5)

where, A, B, and C are constants depending on the liquid desiccant temperature and concentration of the desiccant solution.

$a=a_{0}+a_{1} x_{m}+a_{2} x_{m}^{2}+a_{3} x_{m}^{3}+a_{4} x_{m}^{4}$      (6)

in which x_m represents the concertation of the solution. Regarding calcium chloride solution used as a liquid desiccant in the Antoine equation for listed in the following Table 1:

Table 1. Antoine’s equation constant for calcium chloride solution

The equilibrium humidity ratio (W_e) of the moisture air in contact with calcium chloride solution can be written for an ideal gas as follows Eq. (7):

$W_{e}=0.626185\left(\frac{p_{\text {sol }}}{p_{a t m}+p_{s o l}}\right)$      (7)

In term of equilibrium humidity ratio, the following equation is used to compute the coefficient of mass transfer between calcium chloride solution and the processed air.

$K_{d}=\frac{m_{a}\left(w_{i-} w_{o}\right)}{A \rho\left(w_{i-} w_{e}\right)}$      (8)