Performance analysis of heat pump and infrared–heat pump drying of grated carrot using energy-exergy methodology Mustafa Aktas ß a , Ataollah Khanlari b , Ali Amini c , Seyfi S ßevik d,⇑ a Gazi University, Technology Faculty, Energy Systems Engineering, 06500 Ankara, Turkey b Gazi University, Natural and Applied Science Institute, 06500 Ankara, Turkey c Atatürk University, Natural and Applied Science Institute, 25240 Erzurum, Turkey d Hitit University, Vocational School of Technical Sciences, Electrical and Energy, 19169 Çorum, Turkey article info Article history: Received 28 July 2016 Received in revised form 1 November 2016 Accepted 14 November 2016 Keywords: Heat pump Infrared Energy Exergy Grated carrot Drying abstract In this study, a hybrid drying system that combines all of the advantages of different drying methods was developed. This study aims to compare experimental results of a heat pump dryer (HPD) and an infrared assisted heat pump dryer (IRAHPD), to determine the energy and exergy efficiency of dryers and to ana- lyze the drying kinetic of grated carrot for observing the effectiveness of the dryers. Samples were dried at 45 °C and 50 °C set temperatures and 0.5 m/s air velocity. According to dry basis calculation, initial moisture content amount was 7.06 g water/g dry matter and amount of final moisture content of dry matter was obtained as 0.14 g water/g dry matter. Energy efficiency varied between 5.3% and 50%. Minimum and maximum coefficients of performance for the whole system ðCOP ws Þ were 2.11 and 2.96 respectively. Maximum exergy efficiency was obtained 66.8% while minimum exergy efficiency was 31.6%. It was concluded that during the time to reach a stable state of system, the exergy efficiency increased in response to exergy loss decreases. This study shows a successful and efficient combination of heat pump and infrared heater in food drying. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction The world population is increasing rapidly that makes difficult to access affordable and healthy perishable foods such as fresh fruits and vegetables throughout the year. The easiest way of con- tinuous supply of perishable products is to dry them. Thus, all- year-round consumption of summer produce can be carried out. Drying of agricultural products has always been in great attention for the preservation of food. This process provides effective and practical preservation in order to reduce the losses after harvest [1]. Moisture removal of agricultural products need vaporizing water content of products that is energy intensive and time con- suming process, so economic side of this treatment should be con- sidered in analysis [2,3]. Deceleration of drying rate is caused by falling down the water content. Besides that, low thermal conduc- tivity of food products is a limitation factor during convection heat transfer [4]. High quality production with minimum after treat- ment processes and energy requirement needs more scientific studies in food drying industries. Researchers had used different drying methods or combination of them to catch an optimum point in terms of drying time, energy consumption and product quality for different agricultural products. Some researchers studied various dryers for drying vegetables and fruits. Akpinar (2005) evaluated practical convective heat transfer coefficient of various crops (potato, apple and pumpkin) in cyclone type dryer [5]. She indicated that air velocity was more effective variable than air temperature in forced convection phe- nomena. It was claimed that some parameters such as porosity, moisture content (MC), shape and size of crops, thermophysical properties, experimental working condition and experimental setup properties affect the heat transfer coefficient significantly. Heat pump dryer (HPD) is one of the effective methods in drying of product [6–8]. Closed loop dryers have some advantages due to hygienic conditions, efficient relative humidity control and high efficiency. The high oxygen amount in drying air leads to browning of product during the drying process. It is limited the oxygen amount in drying air due to usage of closed loop air circulation [9]. However, the arrival time to desired drying air temperature prolongs because of the dehumidification of drying air in closed air cycle. Their study shows that working period is shortened by http://dx.doi.org/10.1016/j.enconman.2016.11.027 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: mustafaaktas@gazi.edu.tr (M. Aktas ß), ata_khanlari@yahoo. com (A. Khanlari), ali82amini@gmail.com (A. Amini), seyfisvk@hotmail.com (S. S ßevik). Energy Conversion and Management 132 (2017) 327–338 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman