Food water and securities lab

1. Experiment No-12 Heat pump drying system
Name of course: Renewable energy applications for food, energy and water (FEW) security.
Course code: 20ME404T.
Course Coordinator: Dr. Anurag Mudgal.
Aim: Observe the total drying time and net energy consumption during the entire process.
And performance analysis of Heat Pump based drying system. To improve the product
quality extension of shelf life and reducing the volume and mass with the help of heat pump
drying system.
Theory: Drying is an ancient, popular and well-known unit operation or method for
preservation of food materials. But due to more energy and time consumption it has limited
application for drying of fruits and vegetables i.e. higher moisture content food material/more
susceptible to perish.
While in the case of heat pump assisted drying, it is an energy-efficient process because the
heat is recoverable and has lowest operating cost. However, the economic feasibility of the
heat pump dryer (HPD) is debatable so far, because of using high grade energy (electricity)
and now a question is arising which drying system will be more feasible and efficient, and
how it can be recognise etc.
Although tray, rotary, flash, spray, fluidized bed, vacuum, freeze and batch dryers are
classified as conventional, there is great number of areas suitable for further improvement. It
is identified various areas and aspects that need further research and development efforts.
Some of the areas (including limitations) and characteristics addressed by researchers in
recent years.
The basic principle of heat pump assisted drying (hybrid) is same as that of heat pump drying
(pure) heat pump can be thought of as a heat engine operating in reverse. The heat pump
works on the principle of refrigeration that cools an air stream and condenses the water
contained in it. This renders the air dry and recovers the latent heat of evaporation through
water vapour removal which permits air recirculation.
Roll No Name
20BME154 Vishesh Raisinghani
20BME155 Dhruvansh Panchal
20BME157 Hemal Gol
20BME158 Vedansh Harani
20BME160 Urvil Shah

2. The process of removal of excess moisture from a product by the use of thermal energy in the
form of heat to a safer moisture level, up to which it can be stored easily without any
microbial damage is called drying or dehydration.
The water content of most fruits and vegetables is higher than 80%, which limits their shelf
life and make them susceptible to chemical or microbial damage. Drying is a complex
operation involving transient transfer of heat and mass along with several rate of processes
such as physical or chemical transformations.
The main purpose of drying is to improve the product quality, extension of shelf life and
reduction of volume and mass, which in turn reduces the storage and transportation cost. The
loss of moisture in the product during drying results in increasing concentration of taste and
nutrients in the dried mass.
Heat pump technology have wide range of applications in industrial and domestic
applications for heating, ventilation and air conditioning. Heat pump drying is widely used in
agricultural sector for prevention of post-harvest losses. Heat pump drying system is
combination of two engineering systems that are heat pump and dryer.
A controllable drying environment is provided in the heat pump dryer which give rise to high
quality product in an energy efficient way, in comparison with other conventionally used
drying techniques. The design of heat pump drying is simple having energy saving ability
along with less drying time.
Working of heat pump drying system:
Figure 1 Components of Heat pump drying system
The figure shows the working of heat pump drying system. Major components of heat pump
are – Evaporator, Condenser, Compressor and an expansion valve. In this system, refrigerant
is used as the working fluid which is at low pressure. The heat from surrounding is used to
evaporate the refrigerant in the evaporator section.
The enthalpy of the refrigerant is raised at the compressor from where it is discharged as high
pressure superheated vapor. After removal of heat from the working fluid, then it is supplied
to the condenser.
The hot air which h is rejected from the condenser is made to pass through the drying
chamber which is utilized for drying. After throttling of working fluid from condenser to low

3. pressure line it again passes through the evaporator for completion of cycle. The hot and
humid air is made to pass through the exhaust from the drying chamber.
Procedure and apparatus: An experiment was performed in a heat pump drying system for
drying of 40kg Indian Cucumber.
Figure 2 Apparatus used for experiment
➢ First, we need to cut the product to be dried into slices of uniform thickness and
spread them evenly into the drying trays followed by loading them into the drying
chamber.
➢ Switch on the MAIN switch and VCR cycle. Set the drying temperature at 550C and
note the initial starting time and energy meter reading.
➢ After switching ON the VCR cycle, the temperature of the drying chamber increases
up to 550C.
➢ As the drying chamber temperature reaches 550C, the VCR cycle stops by its own.
Then the drying chamber temperature starts decreasing and reaches 520C, at this stage
the VCR cycle starts by its own.

4. Figure 3 Working of heat pump drying system
➢ The above-mentioned process goes on without any interruption. In this way drying
takes place inside the chamber.
➢ When the texture of the product inside the drying chamber becomes brittle, we can
understand that drying is complete. We have to notice that the colour of the product
should not get altered.
Some literature surveys are done to study conceptual facts about heat pump drying
system
➢ Fayose& Huan (Fayose& Huan, 2016) experimented on the use of HPD for drying of
food in Sub Saharan Africa. This research showed the conditions for the optimal use
of HPD. It was concluded that heat pump drying is an energy efficient technique, not
only maintains the quality of dried product but also enhances several properties such
as microbial safety, better colour, rehydration, nutrient retention etc.
➢ Kivevele& Huan (Kivevele& Huan, 2014) researched about the development of heat
pump drying system in South Africa. The results showed that in HPD the control of
temperature of drying air, rate of air flow and relative humidity is easy and also it
have high ability to save energy, but the overall of industrialization of HPD is a slow
process.
➢ An experiment was performed by Prasertan& Saen-saby (Prasertsan& Saen-saby,
1998) to dry rubber wood and banana. It was observed that MER and SMER
decreased with drying time when the compressor power was kept constant. Maximum
MER and SMER can be achieved when less than 10% moisture are present in wood

5. whereas in case of banana drying maximum average MER and SMER is obtained in
case of maximum drying load.
Observation Table:
Temperature of Apparatus-
TI - Ambient Temp.
T2- Dryer Temp.
T3- Cooling Box Temp.
T4- Evaporator Air Outlet Temp.
T5- Comp. Discharge Temp
T6- Condenser outlet
T7- Evaporator inlet
T8- Evaporator Outlet
Result and discussion-
Initial Condition of Sample-
Sample Time
Interval
(Min)
T1 T2 T3 T4 T5 T6 T7 T8
NEEM
LEAVES 1
20 32.1 60 18.7 30.2 91.2 53.4 17.6 32.9
NEEM
LEAVES 2
24 33.6 70 22 30.9 106.9 60.3 14.8 35
FLOWER 1 20 32.1 60 18.7 30.2 91.2 53.4 17.6 32.9
FLOWER 2 24 33.6 70 22 30.9 106.9 60.3 14.8 35

6. Sample Condition at 60°C-
Sample Condition at 70°C-

7. The sample observation table is provided at the end of this document.
Experimental calculations:
Moisture Content:
1.WetBasis = = 91.6%
2.DryBasis = = 109.1%
SMER = = 1.130kg/kWh
Governing equation for heat transfer:
Q = -KA
Net Efficiency of the system = η = = 70% (Based on experimental values)
WhereT1, T2, Ta are dryer inlet, exhaust gas and ambient temperature respectively.
Result Table:
The sample observation table is provided at the end of this document
Conclusion:
By performing this experiment, we are able to know how the experiment is carried out what
all are the important components of the experiment. Apart from that, we also calculated the
moisture content on both wet and dry basis and finally found out the overall efficiency of the
machine.
mi − mf
mi
mi − mf
mf
Amount of moisture removed
Total energy supplied
dt
dx
T1 − T 2
T1 − Ta

8. Applications of heat pump dryer:
Heat pump drying have wide range of applications in food processing industries for drying of
fruits/vegetables/grains/marine products for prevention of post-harvest losses.
Apart from that heat pump dryers are used in timber, rubber and automobile industries.
The heat pump dryers have been used in several experiment swith medical and biological
active solutions.
It is also used in pharma as well as fragrance industries for coating of pharmaceuticals tablets
and drying of flowers for extracting perfumes respectively.
Future scope of heat pump drying system:
Heat pump drying technique have some distinct characteristics such as low drying time,
appropriate drying, improved quality product along with its energy saving capacity, which
make this technique distinct from other drying processes.
The opportunities for further R&D in heat pump drying with increase the product quality and
system efficiency.
The future R&D development on HPD must focus on increasing the efficiency of the system,
simple design of the system, reduction of the operational cost and payback period. This will
further require the help of various multi-disciplinary engineering sub fields and will also
increase the cooperation between industry and academic institute.
Sample Observation Table:
Mass of
product before
drying (mi)
(kg)
Mass of
product after
drying (mf)
Amount of
moisture removed
during drying
Total time
required for
drying (hrs)
Net energy
consumption
(Kwh)
45 3.776 45-3.776 = 41.224 27.6 36.46

9. Sample Result Table:
Wet basis (%) Dry basis (%) SMER (kg/kwh) Net efficiency (%)
91.6 1091 1.130 70