Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Performance evaluation of a heat pump-driven vacuum humidification- dehumidification desalination system Emad Ayati, Zohreh Rahimi-Ahar, Mohammad Sadegh Hatamipour ⁎ , Younes Ghalavand Chemical Engineering Department, University of Isfahan, Isfahan, Iran HIGHLIGHTS • Heat pump is added to two variable pressure humidification-dehumidification systems. • Specific power consumption and desalination rate determine the process efficiency. • Liquid ring vacuum pump enhances system performance more than the throttle valve. • Using heat pump in process 2 improves the specific power consumption by 9%. • A maximum desalination rate of 2.24 kg·h -1 is obtained in more efficient process. ARTICLE INFO Keywords: Humidification Dehumidification Heat pump Desalination rate Specific power consumption ABSTRACT In this study, the vacuum desalination technology coupled with a heat pump was investigated. Two vacuum humidification-dehumidification desalination systems were experimented. The proposed systems involved the over-atmospheric and atmospheric pressure dehumidification operations denoted by Processes 1 and 2, re- spectively. The more efficient process was determined through a parametric study based on the desalination rate and specific power consumption. The results indicated that decreasing the humidifier pressure and using a heat pump at the optimum value of saline water to air mass flow rate ratio, a maximum desalination rate of 1.12 kg·h -1 (per 1 m 2 of solar water heater aperture area) was obtained. Coupling the heat pump to the efficient process had desirable effects on the desalination rate and produced water cost, with a negligible negative impact on the specific power consumption. Although the airflow rate was considered constant in simulation, its fixing was not possible in experimental work. In actual operation, a reduction in airflow rate was occurred by hu- midifier pressure reduction, which led to system performance reduction. 1. Introduction Freshwater is one of the most important resources used by humans, being of great importance for social, economic and environmental ac- tivities. The existence of freshwater resources is a prerequisite for life on the Earth and is an enabling or limiting factor for any social or technical development [1]. Though 71% of the Earth's surface is cov- ered by water, 2.5% of this water is fresh. Uneven distribution of po- table resources throughout the world and its unavailability create water shortage. Although activities such as optimizing the use of existing water resources or reducing transmission losses appropriately minimize the water consumption, these activities are not sufficient owing to the industrial and population growth. Another solution for overcoming the water shortage can be the water desalination process. In recent years, water desalination has been a top priority for countries experiencing water shortage [2]. Numerous efforts have been made to provide fresh water based on the thermal and membrane desalination technologies. Each of these technologies has its advantages and disadvantages, and each method is recommended for a specific region. One of the main thermal desalina- tion techniques, especially at the domestic scale, is the humidification- dehumidification (HDH) process. The HDH process is based on the principle that air can transport significant amounts of water vapor. In the humidification section, saline water and air come into direct contact with each other, during which water vapor transfers to the air. In the dehumidification section, water vapor of the humidified air condenses, producing freshwater [3]. Several studies have been conducted on HDH systems to enhance their performance. The options for HDH perfor- mance enhancement include operating at different pressures [4], heat recovery through brine recirculation [5], multi-stage humidification https://doi.org/10.1016/j.applthermaleng.2020.115872 Received 25 February 2020; Received in revised form 27 June 2020; Accepted 7 August 2020 ⁎ Corresponding author. E-mail address: hatami@eng.ui.ac.ir (M.S. Hatamipour). Applied Thermal Engineering 180 (2020) 115872 Available online 11 August 2020 1359-4311/ © 2020 Published by Elsevier Ltd. T