The Relationship between Temperature and Performance of Solar

Desalination Plants

Ahror Jafarov

and Zaynalobudin Kobuliev

Technological University of Tajikistan, 63/3, Nemat Karabaev street, Dushanbe, Tajikistan

Institute of Water Problems, Hydropower and Ecology of the National Academy of Sciences of Tajikistan, 12, Parvin

street, Dushanbe, Tajikistan

Keywords: Temperature Regime, Thermal Resistance, Thermal Conductivity, Thermal Effect, Solar Radiation,

Condensation, Heat Exchange, Heat Flux, Recuperation.

Abstract: This article considers the analysis of studies on increasing the productivity of solar desalination plants through

the rational use of falling solar energy on the surface of installations, as well as the dependence of the

efficiency of solar desalination plants on the parameters of external thermal effects and determining the

temperature regime of these installations. To determine the temperature regime of the desalter, a calculation

method was applied based on finding the temperature functions in the form of Fourier series. It has been

established that the heat transferred by radiation from the surface of the water to the surface of the transparent

coating can be reduced by installing additional transparent screens between the evaporating zone of the

desalter and its roof. This technical solution made it possible to increase the productivity of sloped-stepped

type installations by 1.5 times in comparison with single-layer glazing.

1 INTRODUCTION

According to the annual addresses of the Founder of

Peace and National Unity – Leader of the Nation,

President of the Republic of Tajikistan Emomali

Rahmon to the Majlisi Oli of the Republic of

Tajikistan, hydropower comprises for 98% of

electricity production in Tajikistan. This has become

the basis for Tajikistan to be on the 135th place in

terms of greenhouse gas emissions into the

atmosphere on a global scale, which is assessed as a

valuable contribution of the Republic of Tajikistan to

the solution of global problems of mankind.

The value of this indicator shows that on a

regional scale, the specific quantitative characteristics

of greenhouse gas emissions in Tajikistan is the

smallest indicator for each person, which is

considered Tajikistan's contribution to improvement

and enhancement of the ecological situation in the

region and, particularly, the planet. This helps to

achieve widespread use of renewable energy sources

(RES), first of all, hydropower. It was also noted that

the vast use of renewable energy sources, especially

https://orcid.org/0000-0003-1105-068X

https://orcid.org/0000-0003-0272-0792

water resources, may explore one of the main sources

of "green energy" generation and the development of

a "green economy".

In connection with the statements made above and

according to the main actions, in order to achieve the

set strategic goals of the National Development

Strategy of the Republic of Tajikistan for the period

up to 2030 and its initial stage. The initial stage is

included in the Medium-Term Development Program

of the Republic of Tajikistan for 2016-2020, which

indicated that to ensure energy security, as well as

efficient use of electricity, it is necessary to diversify

generating energy sources with the development of

hydropower resources, both large and small rivers,

the development of existing capacities in the oil and

gas and coal sector, the exploration and development

of new fossil fuel deposits, the creation and provision

of technical capabilities with the purpose of using

non-traditional (renewable) energy sources (solar,

wind, biological, geothermal), modernization and

rehabilitation of existing ones, as well as the

construction of new hydroelectric power plants

(HPPs) and thermal power plants (TPPs).

Jafarov, A. and Kobuliev, Z.

The Relationship between Temperature and Performance of Solar Desalination Plants.

DOI: 10.5220/0011367600003350

In Proceedings of the 5th International Scientiﬁc Congress Society of Ambient Intelligence (ISC SAI 2022) - Sustainable Development and Global Climate Change, pages 525-533

ISBN: 978-989-758-600-2

525

The above-mentioned statement will serve as the

reason to consider the research topic relevant and

timely. The aim of the research is the rational use of

solar energy through the development of theoretical

and applied models and the improvement of low-

potential solar installations in the climatic conditions

of the Republic of Tajikistan.

To achieve the goal, the following tasks were set

and solved:

- Assessment of the state and development of the

use of non-traditional energy sources in Central Asia,

including in Tajikistan.

- Analysis of existing methods for determining the

formation of the process of heat exchange of

constructions, under the influence of solar thermal

effects and their improvement;

- Technical and economic justification and

practical implementation of low-grade solar

installations and developed models for the use of

renewable energy sources in the conditions of the

Republic of Tajikistan.

The scientific novelty of the obtained results

consists of determining the temperature regime of

closed volumes and channels with a coolant under

periodic fluctuations in the parameters of the thermal

effect and a developed model for regulating the

temperature regime of a homogeneous structure

under periodic fluctuations in the temperature of the

medium on its lateral surface, on the basis of which

the calculated parameters of the thermal

characteristics of the coolant in duct exposed to the

thermal effect of the environment with periodically

changing temperature.

The practical significance lies in the fact that the

thermal state of structures in a closed volume is

determined in the absence and presence of sources

and sinks of heat and filtration of outdoor air, as well

as an algorithm for calculating and controlling the

parameters of the temperature state of structures of

solar desalination plants has been developed.

The researches were conducted and completed

using the current regulatory methods for studying the

physicochemical and biotechnological properties of

low-grade solar installations (Sokolov and Hershgal,

1990; Le Pierrèset et al., 2003; Ma et al., 2018; Zhu

et al., 2019). In the processing stage, a mathematical

and statistical technique was used to process

experimental data. For the theoretical part, there were

used analytical and numerical methods to solve the

problem of heat and mass transfer, regarding the

research objects (Safarov et al., 2003).

The authors contribution in this study is to

conduct joint research, starting with the formulation

of the research objectives, methodological support for

their solutions and the analysis of the results of

monitoring the water interrogation process obtained

by the authors. The research mainly relies on the

results of researches conducted by the authors over

the last years on the problems of rational use of water

resources.

The 21st century will be characterized by a further

exacerbation of the shortage of fresh water on a global

scale. At the same time, it is noted that two-thirds of

drinking water is consumed for the implementation of

agro-technical activities (for example, for irrigation

and growing crops). The problem of desalination of

sea and ocean water is aggravated by the fact that the

world's population is growing rapidly (more than 80

million people per year) and by 2025 at least 2 billion

people on the planet will systematically face an acute

shortage of fresh water (Ruy et al., 2007).

It is also necessary to note that fresh water is used

in different ways by the population of different

countries. So, the water consumption in the homes of

US residents is on average about 380 liters per person

per day, while millions of people on the planet

(especially in underdeveloped countries) use about 19

liters of water per day, and 46% of the world's

inhabitants do not access to the supplied running

water. All this indicates that there is a problem with

fresh water, the demand for water will only start to

grow. Therefore, people need to take care not only of

water supplies, but also learn to rationally use

precious moisture with care (Ruy et al., 2007).

In recent years, the problem of the shortage of

fresh water has become more and more urgent for

many regions of the world. As a result of

desertification of large areas, pollution of water

bodies and an increase in water consumption, there is

already a shortage of drinking water for 1.2 billion

people. It becomes obvious that in the future

humanity will face a global catastrophe of lack of

drinking water. In such conditions, it is important to

develop not only methods for the efficient use of

water resources, but also projects for the purification

and desalination of sea water.

2 EXTERNAL THERMAL

INFLUENCE PARAMETERS

The external thermal impact on constructions located

in the open area is manifested in the form of

convective heat fluxes during heat exchange with the

outside air, radiant heat fluxes during heat exchange

with the atmosphere, the surface of the Earth and the

surrounding objects, as well as solar irradiation.

ISC SAI 2022 - V International Scientiﬁc Congress SOCIETY OF AMBIENT INTELLIGENCE

526

It is known that the outside air temperature

changes over time in all regions of the Earth, and the

temperature changes have a periodic oscillatory

nature. Like any oscillatory process, temperature

changes are characterized by periods and amplitude

of fluctuations. The period of temperature

fluctuations outside the air is the time interval during

which there is one complete oscillation. In

hydrometeorology it is accepted to distinguish

annual, monthly and daily fluctuations of outdoor air

temperature with a period of change of one year, one

month and one day, respectively. The amplitude of

temperature fluctuations is the largest deviation from

the average value for the period of fluctuations. The

amplitude of outside air temperature fluctuations, as

well as its average values for the period of

fluctuations, depends on the geographical location of

the area on the earth's surface.

Numerous observations of changes in outdoor air

temperature (Gidrometeoizdat, 1966) show that the

daily amplitude of temperature fluctuations in

summertime for almost all localities is significantly

greater than the amplitude of temperature fluctuations

in wintertime. Maximum air temperatures are

observed in July and minimum air temperatures in

January. Temperature fluctuations of recurring

pattern in summer and winter can be repeated for 5-

10 days, i.e. repeatedly. It is important because the

temperature fluctuations of environment repeatedly

repeat the temperature state of bodies in it gets the

established periodical character (Lykov, 1967) that

allows to consider a heat transfer in elements of

constructions exposed to external thermal influence

as quasi-stationary process with the established

periodical character of temperature and heat flows

changes.

Constructions located in open areas, in addition to

heat exchange with the outside air, are exposed to

solar radiation. The total impact of solar radiation on

the surfaces of constructions consists of direct

irradiation (direct solar radiation) and irradiation by

the atmosphere scattering the sun's rays (scattered

radiation).

Thermal influence of solar rays on surfaces of

constructions is characterized by solar radiation

intensity which is the quantity of heat referred to unit

of time and unit of the irradiated surface area, and

changes in the same units as heat flux density

(W/m2).

The path the sun's rays take in the atmosphere

increases as the Sun approaches the horizon line. The

intensity of solar radiation reaching the Earth's

surface decreases sharply. When the height of the Sun

above the horizon h is less than 5°, the thermal impact

of solar radiation can be ignored.

For values h more than 5° the intensity of direct

solar radiation on the surface, perpendicular to the

direction of the rays, is approximated by the

simplified formula of Kastrov-Savinov (Kiteyev,

1962).

𝐼

пр

= 1360

𝑠𝑖𝑛ℎ

𝑠𝑖𝑛ℎ +

1−𝑝

𝑝

Вт/м

𝟐

(1)

where h is the height of the Sun, deg;

p - atmospheric transparency coefficient, varying

from 0.7 to 0.8.

The height of the Sun h is calculated by the

formula

h = arc sin (sin φ sinδ + cos φ cos δ cos γ) (2)

where φ - geographic latitude, deg;

δ - declination of the Sun (deg.) depending on the

time of the year (from -23.4° in December to 23.4° in

June);

γ - hour angle in degrees, determined by the ratio

γ = 15(τ1-12), (3)

where τ1 - local time, h.

Due to the refraction of light in the atmosphere,

the apparent height of the Sun slightly differs from

the actual height, especially at sunrise and sunset.

However, this phenomenon is neglected when

calculating the thermal effects of solar radiation.

Intensity of direct solar radiation on flat horizontal

and vertical surfaces of constructions is defined by

dependences

𝐼

пр.г

=𝐼

пр

sinℎ;

(4)

𝐼

прв

=𝐼

пр

cosℎsin

𝛼−𝑥

(5)

where x is the angle determining the position of

the vertical surface relative to the meridian;

α is the azimuth of the Sun, calculated by the ratio

cos α = sinφ cos т - cos φ sin т cos А

(6)

The intensity of total solar radiation is defined as

the sum of direct and scattered radiation. The

dependence of the intensity of scattered solar

radiation affecting the horizontal surface under a

cloudless sky as a function of angle h is as follows:

The Relationship between Temperature and Performance of Solar Desalination Plants

527

10 20 30 40 50 60 70

рr

31,4 43,1 52,4 60,5 65,2 67,5 68,6

The intensity of scattered solar radiation for

vertical surfaces is determined by the approximate

dependence

𝐼

пр

=0,5 𝐼

рг

(7)

The scattering that the sun's rays pass through the

atmosphere varies depending on the position of the

Sun in relation to the horizon line, which is the reason

for the periodic change in the intensity of solar

radiation reaching the Earth and affecting the surfaces

of various constructions.

More complete data on measurements of solar

radiation intensity for different times of the year and

any regions of the USSR are given in the reference

book on the climate of the USSR (Gidrometeoizdat,

1966), which summarizes the results of observations

of changes in the outside air temperature in the

territory of the Tajik SSR.

3 METHODOLOGIES

The main method of obtaining fresh water is based on

the heating and evaporation of salt water, its

subsequent condensation on the surface of the heat

exchanger and removal of the brine, which remains

after heating the mixture with a high salt content. Any

heat carrier that produces a sufficient amount of

energy can serve as a source of heat for the

desalination plant. There are installations based on

fossil fuels, chemical sources and fuel cells, with

electric heating and even on the basis of nuclear fuel.

Due to the fact that the greatest shortage of fresh

water is observed in regions of the world with

increased solar radiation, solar desalination plants are

of particular interest. Solar collector desalination -

plant for desalination of water by the method of

thermal distillation. The main advantages of solar

desalination plants are due to the energy source,

namely the absence of the need for fuel supplies,

environmental friendliness, and affordability.

There are two main technologies for desalination

of water, widely used in the world: a method based on

a change in the phase state of a substance (thermal

method), and membrane, which can be provided by

several methods.

Phase change technology includes:

- multistage distillation;

- highly efficient distillation;

- steam pressure: thermal and mechanical

compression of steam;

- other processes including distillation,

humidification, dehumidification using solar

installations.

Membrane technologies, in addition to membrane

distillation, include two main processes: reverse

osmosis and electrodialysis. These two technologies

use membranes to remove salts from water.

Both processes require a lot of energy to

overcome the existing osmotic pressure between

fresh and salt water. Electrodialysis technologies, as

a rule, are used only for brackish waters, in which

salts from the water stream are attracted by

membranes and pass through them under the action

of an electric current.

Despite significant advances in the use of solar

energy for desalination of salt water, the problem of

creating optimal methods for desalination of water

and the theory of their calculation is still unresolved.

(Achilov, 1976; Kolodin, 1981; SNiP, 1983; Baum,

1985)

To measure the impact of the climatic parameters

of the outside air and solar radiation, we can use the

reference data of the place of the experiment.

(Gidrometeo-Izdat, 1990; Dorvlo and Ampratwum,

1998; Stathopoulos and Zacharias, 2004; Hasni et al.,

2012; Smirnov, 2013; Adeala et al., 2015). The solar

desalination process generally proceeds as follows.

Before starting work, the solar water-maker,

which is a "hot box" in design, is filled with salt

water. Solar energy passes through the transparent

coating of the desalter almost completely (up to 90%)

and is absorbed by the surface of the salt water, which

heats up and evaporates.

Next, the saturated steam-air mixture comes into

contact with the colder transparent wall of the

desalter, and water vapor condenses on its surface. As

it accumulates, fresh water condensate is discharged

from the installation, and the desalter is replenished

with a new portion of salt water. The desalination

process is carried out continuously until the end of the

effect of solar radiation on the design of the

desalination plant.

The performance of solar plants is a function of

the salt water and condensation surface temperatures,

which in turn depend on the outside temperature and

the intensity of solar radiation. Since the parameters

of the external thermal effect, to which the desalter is

exposed, change during the daylight hours over a

fairly wide range, the temperature regime and

productivity of the installation are impermanent.

To measure the temperature regime of the

desalter, let us consider a calculation method based

ISC SAI 2022 - V International Scientiﬁc Congress SOCIETY OF AMBIENT INTELLIGENCE

528

on finding the temperature functions in the form of

Fourier series.

Assuming that the water temperature has

insignificant volume fluctuations, and the thermal

resistance of the transparent wall, through which the

heat flux from solar radiation enters the desalination

tank, it is possible to record the heat balance

equations for water and the transparent wall of the

desalination tank (Kutateladze, 1979; Brdlik, 1983;

Baum, 1985; Timakova, 2006; Nokali, 2007;

Temerov, 2008; Usmanov, 2019):

𝐶

𝜌

𝛿

𝑑𝑡

𝑑𝜏

=𝜀

𝛽

𝐼

−𝐾

тс

𝑡

−𝑡

ус



−𝐾

ти

𝑡

−𝑡

,

(1)

𝐶

𝜌

𝛿





𝐴

𝐼

−𝐾

(

𝑡

−𝑡

)

−

𝛼

(

𝑡

−−𝑡

)

(2)

here Cc, ρc, δc - specific heat, density and

thickness of the transparent wall of the desalter; Cв,

ρв, δв - specific heat, density and thickness of the

water layer; Ас, βс - absorption and throughput

capacity of the transparent wall of the desalter; Кп -

heat transfer coefficient from water to transparent

wall; Ктс, Kти - heat transfer coefficients of the

transparent wall and insulation of the desalter; α_н-

total heat transfer coefficient of the desalter; Iс - the

intensity of solar radiation on the surface of the

transparent wall; tc, tв, tн – respectively, the

temperatures of the transparent wall, water and

outside air; τ - time.

Since the daily changes in the temperature of the

outside air and the intensity of solar radiation are

periodic in nature, and the thermal capacity of the

installation is relatively small, it seems possible to

look for the dependences of the temperatures tc and

tв on time in the form of harmonic Fourier:

𝑡

=𝑡

с

∑



𝑥



𝑐𝑜𝑠𝑘









+𝑦



𝑠𝑖𝑛𝑘







(3)

𝑡

=𝑡

в

∑



𝜇



𝑐𝑜𝑠𝑘









+𝜂



𝑠𝑖𝑛𝑘







(4)

where the average values of temperatures tc0, tв0

and the coefficients of the series xk, yk, μ_k, η_k

should be determined during the solution; the value k

= 1, 2, 3 ... is an integer variable; z - period of change,

equal to 24 hours.

To find a solution to equations (1) and (2) in the

form (3) and (4), series (3) and (4) are conveniently

written using a complex number i:

𝑡



=𝑡



+𝜃



𝑒















(5)

𝑡

=𝑡

в

+𝜃

в

𝑒















(6)

where θ_ck, θ_vk are the amplitude-phase

characteristics of the simple harmonic components of

the temperatures of the transparent wall and water.

The amplitude-phase characteristics are related to the

coefficients of the series (5) and (6):

𝜃



=𝑥



−𝑖𝑦



(7)

𝜃

в

=𝜇



−𝑖𝜂



(8)

As already noted, the outside air temperature and

the intensity of solar irradiation can also be

represented in the form of Fourier series:

𝑡

=𝑡

н

∑



𝛼



𝑐𝑜𝑠𝑘









+𝑏



𝑠𝑖𝑛𝑘







(9)

𝐼=𝐼



∑



𝐶



𝑐𝑜𝑠𝑘









+𝑑



𝑠𝑖𝑛𝑘







;

(10)

where the average values of tн0, I0 and the

coefficients of the series ak, bk, ck, dk are determined

by harmonic analysis of daily fluctuations in the

outside air temperature and the intensity of solar

radiation. By analogy with relations (5) - (8), we have

𝑡

=𝑡

н

+𝜃

н

𝑒















(11)

𝐼=𝐼



+𝜃





𝑒















(12)

𝜃

н

=𝑎



−𝑖𝑏



(13)

𝜃





=𝑐



−𝑖𝑑



(14)

Let us determine the time derivatives of

temperatures tc and tв from equations (5) and (6):

The Relationship between Temperature and Performance of Solar Desalination Plants

529

𝑑𝑡



𝑑𝜏

=𝑘

2𝜋𝑖

𝑧







𝜃



𝑒









(15)

𝑑𝑡

𝑑𝜏

=𝑘

2𝜋𝑖

𝑧







𝜃

в

𝑒









(16)

Substituting relations (5), (6), (11), (12), (15), (16)

into equations (1) and (2), separating constant and

variable components in them, we obtain equations for

constant and variable components heat flows:

- for constant components

𝐴

𝑇



+𝐾

(

𝑡

в

−𝑡

с

)

−𝛼

(

𝑡

с

−𝑡

н

)

=0;

(17)

𝜀

𝐼



𝐼



−



𝐾



+𝐾



(

𝑡

в

−𝑡

н

)

=0;

(18)

- for k-x simple harmonic components of heat flux

densities



𝜌



𝛿



𝑘





𝜃



𝑒









𝐴



𝜃





𝑒









+𝐾

(

𝜃

в

−𝜃



)

∗

* 𝑒





+𝛼

(

𝜃

н

−𝜃



)

𝑒





;

(19)

𝜌

𝛿

𝑘





𝑖𝜃



𝑒









𝜀

𝑇



𝜃





𝑒









+(𝐾



+𝐾

)

(

𝜃

н

−𝜃

в

)

𝑒









;

(20)

From equations (17) and (18) we determine the

constant components of the desired temperatures

𝑡

в

=𝑡

н

𝜀

𝑇

(𝐾



+𝐾

)

𝐼



;

(21)

𝑡



𝐴

𝐼



+𝐾

𝑡

в

+𝛼

𝑡

н

𝐾

+𝛼

(22)

Making a cancellation by e ^ (k ^ (2πτ / z i)) from

equations (19) and (20), we determine the

dependences for finding the amplitude-phase

characteristics of the k-x components of the desired

temperatures:

𝜃

в

𝜀

𝑇

𝜃





+(𝐾



+𝐾

)𝜃

н

𝜌

𝛿

𝑘

2𝜋

𝑧

𝑖+(𝐾



+𝐾

)

;

(23)

𝜃



𝐴



𝜃





+𝐾

+𝜃

в

+𝛼

𝜃

н



𝜌



𝛿



𝑘

2𝜋

𝑧

𝑖+𝐾

+𝛼

(24)

The values θ_ink and θ_ck are generally complex

numbers. Using relations (7) and (8), we obtain the

dependences for determining the coefficients of the

Fourier series:

𝑥



=𝑅𝑒

(

𝜃



)

;𝑦



=−𝐼



(

𝜃



)

(25)

𝜇



=𝑅𝑒

(

𝜃

в

)

;𝜂



=−𝐼



(

𝜃

в

)

(26)

where Re (θ_ck), Re (θ_vk) - real parts of

complex numbers;

I_m (θ_ck), I_m (θ_vk) are the coefficients of the

imaginary parts of the complex numbers θ_ck and

θ_vk.

Correlations (23) and (24) are algebraic

expressions and make it easy to determine the

amplitude-phase characteristics, and hence the

coefficients of the Fourier series. Rows (3) and (4)

should have as many components as are contained in

the external thermal effect. As already noted, the

outside air temperature and the intensity of solar

radiation are well described by the first three

harmonic components, therefore, dependencies (23)

and (24) will also contain three harmonic

components.

The outlined method was used to determine the

temperature regime of solar desalination plants of

inclined-step type by analogy with previous studies

(Garg, 1987; Hamed et al., 1993; Roca, 2008; Al-

Othman, 2018; Zheng et al., 2021).

4 RESULTS AND DISCUSSION

The results of temperature calculations based on the

obtained dependences and experimental data (see

Figure), Coinciding with an error not exceeding 7-

10%, allow us to assess the validity of the described

method for calculating the temperature regimes of

solar desalination plants and the possibility of its

application to analyze the operation of various low-

potential plants.

Note that the greatest difficulty in calculating the

temperature regime of a solar desalter is the

determination of the heat transfer coefficients in the

inner volume of the desalter, since heat transfer

occurs simultaneously when there is convection,

radiation and phase transformations on the heat

exchange surfaces.

ISC SAI 2022 - V International Scientiﬁc Congress SOCIETY OF AMBIENT INTELLIGENCE

530

It is important to describe the total coefficients of

the fluxes using the method of successive

approximations, since the convective and radiant

components of heat fluxes are functions of the

temperatures of the heat exchange surfaces, which are

determined in the process of thermal engineering

calculation of the desalter.

Figure 1: Temperature range of solar desalination plant: 1 -

water temperature; 2 - temperature of the transparent

coating; a - calculation; b - experiment.

Research analysis on increasing the productivity

of solar desalination plants (Achilov, 1976; Baum,

1985) shows that the improvement of their designs is

possible through the most rational use of incident

solar energy while minimizing some energy losses.

Thus, the heat transferred by radiation from the

surface of the water to the surface of the transparent

coating can be reduced by installing additional

transparent screens between the evaporating zone of

the desalter and its roof, by analogy with work

(Timakova, 2006; Temerov, 2008; Prakash, 2019).

This technical solution makes it possible to increase

the productivity of inclined-step type installations by

1.5 times in comparison with single-layer glazing.

Solar absorption and reflection of energy from the

transparent wall and the condensate layer, which

make up to 20% of the incident energy (Baum, 1985),

can be reduced by applying an interference layer to

the roof material (Brdlik, 1983) and organizing film

condensation, which eliminates reflection from

condensate droplets. In this respect, clean degreased

glass is a fairly acceptable structural material, but it is

fragile.

As a material with acceptable optical and strength

properties, it is possible to recommend a lavsan film

coated with polyvinyl spirit, which increases its

wettability. However, such a film is not strong

enough and after some time is partially washed off,

therefore, the problem of creating strong materials

that are well wetted and sufficiently well to transmit

solar energy remains one of the urgent problems at

the present time.

A promising direction in increasing the

productivity of solar desalination plants is the use of

recuperation of the heat flux supplied to the

condensation surface due to a phase transition, which

is removed by convection and radiation into the

environment and thus becomes the most significant

loss of energy. Known technical solutions for the use

of this heat flux for heating desalinated water (SNiP,

1983; Slesarenko, 1991; Smirnov, 2013), for

example, adding to the design of the desalinator

(Achilov, 1976) just one additional layer of the

condenser-evaporator. At the same time, an increase

in its productivity was established by almost 40%.

The heat flow, which is removed by the flowing

hot distillate, also refers to significant heat loss and

can be largely recovered. So, a heat exchanger can be

connected to the distillate drain line, in which the

water supplied to desalination will be preheated.

Thus, an increase in the performance of solar

desalination plants can be achieved by recovering

heat and minimizing heat losses that cannot be

recovered.

5 CONCLUSIONS

1. To determine the temperature regime of the

desalter, a calculation method was applied based on

finding the temperature functions in the form of

Fourier series.

2. The outlined method is applied to determine the

temperature regime of inclined-step type solar

desalination plants. The results of temperature

calculations based on the obtained dependences and

experimental data, which coincided with an error not

exceeding 7-10%, make it possible to assess the

legality of the described method for calculating the

temperature regimes of solar desalination plants and

the possibility of its application to analyze the

operation of various low-potential plants.

3. One of the promising areas for increasing the

productivity of solar desalination plants is the use of

recuperation of the heat flow supplied to the

condensation surface due to the phase transition,

which is removed by convection and radiation into

the environment and thus becomes the most

significant loss of energy. Known technical solutions

for the use of this heat flux for heating desalinated

water by adding one additional layer of the

condenser-evaporator to the design of the desalinator,

in which an increase in its productivity is established

by almost 40%.

The Relationship between Temperature and Performance of Solar Desalination Plants

531

4. Analysis of studies on increasing the

productivity of solar desalination plants shows that

the improvement of their designs is possible through

the most rational use of falling solar energy while

minimizing some energy losses. Thus, the heat

transferred by radiation from the surface of the water

to the surface of the transparent coating can be

reduced by installing additional transparent screens

between the evaporating zone of the desalter and its

roof. This technical solution made it possible to

increase the productivity of the inclined-step type

installations by 1.5 times in comparison with single-

layer glazing.

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