The efficient cooling of servers in data center offers a unique challenge to reduce the worldwide energy consumption and liquid inventory of working fluid. Presently, single phase cooling techniques are widely used for CPU cooling in data centers. Such techniques are proving to be inefficient, as the heat flux generated in CPU cores is very high, limiting the clock speed of the processors. Also, single phase coolers require external pumping power adding cost to the system. The great potential of a thermosiphon system as a replacement of currently used cooling techniques is studied in the presented work.

A thermosiphon loop using two-phase heat and mass transfer process uses latent heat of the working fluid. The latent heat is much more efficient than sensible heat improving the heat dissipation ability of the system. The thermosiphon system is a gravity driven loop thus reducing the power consumption and the cost of the system. However, the system performance is limited by Critical Heat Flux (CHF) and Heat Transfer Coefficients (HTC). An increase in CHF offers wide temperature operating range while the HTC defines the efficiency of the process. In the proposed design of the cooling solution, a manifold with a taper is employed over the heater surface to guide vapor away from the surface along the flow length. The incoming liquid flows over the heating surface unobstructed developing separate liquid-vapor pathways.

Two taper angles, 3.4ᵒ and 6ᵒ in the manifold are tested for the benchtop configuration of the thermosiphon loop. A heat transfer coefficient of 27.3 kW/m2ᵒC and 33.4 kW/m2ᵒC was achieved for 3.4ᵒ and 6ᵒ taper angles respectively. The heat transfer performance was analyzed with HFE7000 as the working fluid. The performance of the benchtop thermosiphon loop was evaluated for three liquid fill volumes resulting in three different liquid heads available in the thermosiphon loop. Based on the benchtop thermosiphon loop performance a new cooler was designed and built for CPU cooling in RIT’s data center. The performance of the new thermosiphon loop used in CPU cooling was compared with the air and water based coolers currently used in the data center. The maximum CPU temperature achieved for thermosiphon loop was 84.4ᵒC under the stress test. The maximum CPU temperatures for air based and water based coolers were 82.6ᵒC and 63.4ᵒC respectively under the stress test.

Publication Date


Document Type


Student Type


Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)


Satish G. Kandlikar

Advisor/Committee Member

Agamemnon Crassidis

Advisor/Committee Member

Michael Schrlau


RIT – Main Campus