İki kapılı buzdolabında soğuma sürecinin deneysel ve sayısal incelenmesi
An experimental and numerical investigation of cooling process on a two door household refrigerator
Yazar: BUĞRA SEMİH ERSAN
Danışman: DOÇ. DR. LEVENT ALİ KAVURMACIOĞLU
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Günümüzde buzdolapları, evler için vazgeçilmez bir ihtiyaçtır ve evlerin enerji 
sarfiyatının büyük bir kısmını oluşturmaktadır. Bu sebeple buzdolapları, beyaz eşya 
üreticileri için iç sıcaklık ve enerji tüketimi konularında sürekli bir optimizasyon 
problemi oluşturmaktadır. Bu çalışmada iki kapılı bir buzdolabının sanal bir ikizinin 
nasıl yaratılabileceği ve oluşturulacak bu modelin gerçek sonuçlarla uyumlu olup 
olmadığı sayısal ve deneysel olarak araştırılmıştır. Oluşturulan 3 boyutlu Hesaplamalı 
Akışkanlar Dinamiği modeli her iki kabin için hava dağıtım sistemi ve kabin içi 
sıcaklık dağılımı konuları özelinde incelenmiştir. Ayrıca model buharlaştırıcı 
modellemesi konusunda literatür çalışmalarına kıyasla birtakım yenilikler 
barındırmaktadır.
Çalışmanın ikinci kısmında dolabın hava dağıtım sistemi ve çalışma debilerini 
belirlemek için yapılan rüzgâr tüneli deneyleri ve kabin içi sıcaklıklarını belirlemekle 
birlikte çalışma algoritmasını ortaya dökmek amacıyla sıcaklık bakımından
şartlandırılmış bir odada farklı ortam ve ayar sıcaklıklarında yapılan deneyler 
incelenmiş, yapılan deneylerde kullanılan test elemanları anlatılmıştır.
Çalışmanın üçüncü kısmında oluşturulan 3 boyutlu sayısal modelin HAD metodolojisi 
incelenmiş, sayısal çözüm ağı, model oluşturulurken kullanılan sınır koşulları ve
çözüm modelleri ve algoritmaları anlatılmış ve yapılan varsayımlardan 
bahsedilmiştir. 
Çalışmanın üçüncü ve son bölümünde ise hem deneysel hem de sayısal çalışmaların 
çıktıları incelenmiş, elde edilen sonuçlar birbiriyle karşılaştırılmış ve oluşturulan 
sayısal modelin eksileri ve artıları tartışılmıştır. Elde edilen sonuçlara göre hava 
dağıtım sistemine ait deneysel ve sayısal sonuçlar birbirleriyle uyum içerisindedir.
Kabin içi sıcaklıklar incelendiğinde ise taze gıda kabininde kabin raflarına ait ortalama 
sıcaklıklar maksimum 1.1°C, dondurucu için ise maksimum 2°C'lik bir hata ile tespit 
edilebilmektedir. Dolabın çalışma ve durma süreleri de incelendiğinde elde edilen 
sıcaklık sonuçları deneysel sonuçlarla uyumludur.

Abstract:
Today, refrigerators are an indispensable need for homes and constitute a large part of 
the energy consumption of homes. For this reason, refrigerators create a constant 
optimization problem for white goods manufacturers in terms of internal temperature 
and energy consumption. When the studies in the literature are investigated, although 
the air distribution and temperature distribution in refrigerators are examined, there is 
no CFD model for the whole refrigerator, which includes vapor cycle effects. Although 
CFD studies for refrigerators gave close values on issues such as average temperature 
inside the cabinet, these studies remained far from obtaining a detailed temperature 
analysis as a result of the assumptions made. In this study, how a virtual twin of a 
refrigerator can be created and whether this model to be created is compatible with 
real results was investigated numerically and experimentally. The 3D CFD model 
created has been examined specifically for the air distribution system and interior 
temperature distribution for both cabins. In addition, the model contains some 
innovations in the evaporator modeling compared to the literature studies. Another 
purpose of this model is to calculate the interior temperatures of the refrigerator and 
the air distribution system at a very low error rate compared to the reality, and to reveal 
the results of a change or effect on the refrigerator over time without the need for a 
physical prototype or experiment. This means both financial and time savings for 
refrigerator manufacturers.
In the second part of the study, the wind tunnel experiments performed to determine 
the air distribution system and operating flow rates of the cabinets. Wind tunnel tests 
were carried out in two different sizes of wind tunnels. The purpose of these tests is to 
determine the operating flow rates of refrigerator fans and to extract the operating 
curves of these fans. Thus, appropriate boundary conditions will be used for the CFD 
model. In addition, a temperature test matrix was created and temperature tests were 
carried out to determine the operating temperatures and performance of the refrigerator xvii
in different situations. The temperature experiments conducted in a temperature and 
moisture conditioned room at different ambient and set temperatures in order to reveal 
the working algorithm as well as to determine the interior temperatures. Temperature 
experiments were carried out with 35 thermocouples placed on the refrigerator. These 
thermocouples are placed on the shelves in fresh food and freezer cabinets, on the 
evaporator surfaces and at the air suction and blowing places. 
In the third part of the study, the CFD methodology of the 3-dimensional numerical 
model was examined. Preparation of analysis geometry, meshing studies and grid 
independency, models and algorithms used in the solution are discussed in this section.
The boundary conditions, the algorithm evaporator model which is dependent to time
and assumptions used while creating the model also were mentioned in this section.
The k-ω SST turbulence model is used for flow field. Flow equations are solved 
steady-state however, the energy equations are solved in transient. The time step for 
transient analysis was 60 seconds to be compatible with experimental studies. For grid 
independence, three different mesh structures with 14 million, 20 million and 24 
million elements were examined and the best results were obtained in a structure with 
24 million elements. Natural convection and radiation effects are ignored in order to 
have less effect on the heat transfer and reduce the computational power.
In the fourth and last part of the study, the outputs of both the experimental and the 
numerical studies were examined, the results obtained were compared with each other 
and the pros and cons of the numerical model created were discussed. According to 
the results obtained, the experimental and numerical results of the air distribution 
system are in agreement with each other. A difference of 2% in a fresh food cabinet 
and a 5% difference in a freezer cabinet was found between the experimental and 
numerical studies on air flow. When the cabin temperatures are examined, average 
temperatures of the cabin shelves in the fresh food cabinet can be detected with an 
error of maximum 1.1°C and a maximum of 2°C for the freezer. When the working 
and stopping times of the cabinet are examined, the obtained temperature results are 
consistent with the experimental results. Run times obtained experimentally in the 
fresh food cabinet are quite compatible with the numerical results. The working and 
stopping times of the refrigerator were found to be very close to each other. Although 
the working time obtained experimentally in the freezer food cabinet was compatible 
with CFD in total, the working and stopping times differed from each other. The main 
reason for this situation is that the generated User Defined Function code cannot 
simulate the freezer cabinet working algorithm. In addition, at the end of the fourth 
part, some suggestions have been made to increase the performance and accuracy of 
this virtual twin. Among these suggestions, the most important are modeling the 
rotational effects of the fan, adding natural convection and radiation effects to the 
model and adding the working algorithm of the freezer cabinet to the UDF in case the 
cabinets work together.