A downhole tool (100) including an open loop cooling system (110) having a pressurized container (120) disposed within a tool string, and has a refrigerant (122). The cooling system further includes a tank (150) in fluid communication with the pressurized container (120), and a heat exchanger (160) associated with tank (150), where the heat exchanger exchanges heat between the refrigerant (122) and a downhole payload (164). The cooling system further includes a low pressure apparatus that creates a low pressure region proximate the pressurized container. The low pressure apparatus can include a venturi (180). The venturi has a drilling mud passage (188) therethrough, and drilling mud flowing through a convergence (186) creates a low pressure adjacent the tank (150).