A cryogenic fluid heating system, comprising: a fluid conduit having a conduit upstream end, a conduit downstream end and a conduit wall having a conduit inner surface and a conduit outer surface, the conduit upstream end fluidly coupled to a cryogenic fluid source, wherein the conduit upstream end is configured to receive a cryogenic fluid which flows through the fluid conduit in a downstream direction toward the conduit downstream end; a heating mechanism located on a downstream portion of the fluid conduit and configured to heat the conduit wall so that the cryogenic fluid nearest the conduit inner surface is warmer than a downstream-moving main flow of the cryogenic fluid located toward the center of the fluid conduit; an upstream valve mounted to the fluid conduit at a location upstream of the heating mechanism and configured to be operable for control of an upstream-valve mass flow rate of the cryogenic fluid, wherein the upstream-valve mass flow rate comprises an upstream-valve non-buoyant mass flow rate of cryogenic fluid flowing through the upstream valve in the downstream direction minus an upstream-valve buoyant mass flow rate of any buoyant flow flowing past the upstream valve in the upstream direction; a downstream valve located downstream of the heating mechanism and configured to be operable for control of a downstream-valve mass flow rate of the cryogenic fluid; an upstream flowmeter for measuring the upstream-valve mass flow rate of the cryogenic fluid passing through an upstream valve opening of the upstream valve along the downstream direction; a downstream flowmeter for measuring the downstream-valve mass flow rate of the cryogenic fluid passing through a downstream valve opening of the downstream valve along the downstream direction; and a controller configured to adjust a size of the upstream valve opening to a choked position, wherein the controller is further configured to continuously receive data representative of the upstream-valve mass flow rate and the downstream-valve mass flow rate, and continuously adjust the upstream valve opening such that the upstream-valve non-buoyant mass flow rate substantially matches the downstream-valve mass flow rate, and the flow of the buoyant flow past the upstream valve is blocked. a fluid conduit having a conduit upstream end, a conduit downstream end and a conduit wall having a conduit inner surface and a conduit outer surface, the conduit upstream end fluidly coupled to a cryogenic fluid source, wherein the conduit upstream end is configured to receive a cryogenic fluid which flows through the fluid conduit in a downstream direction toward the conduit downstream end; a heating mechanism located on a downstream portion of the fluid conduit and configured to heat the conduit wall so that the cryogenic fluid nearest the conduit inner surface is warmer than a downstream-moving main flow of the cryogenic fluid located toward the center of the fluid conduit; an upstream valve mounted to the fluid conduit at a location upstream of the heating mechanism and configured to be operable for control of an upstream-valve mass flow rate of the cryogenic fluid, wherein the upstream-valve mass flow rate comprises an upstream-valve non-buoyant mass flow rate of cryogenic fluid flowing through the upstream valve in the downstream direction minus an upstream-valve buoyant mass flow rate of any buoyant flow flowing past the upstream valve in the upstream direction; a downstream valve located downstream of the heating mechanism and configured to be operable for control of a downstream-valve mass flow rate of the cryogenic fluid; an upstream flowmeter for measuring the upstream-valve mass flow rate of the cryogenic fluid passing through an upstream valve opening of the upstream valve along the downstream direction; a downstream flowmeter for measuring the downstream-valve mass flow rate of the cryogenic fluid passing through a downstream valve opening of the downstream valve along the downstream direction; and a controller configured to adjust a size of the upstream valve opening to a choked position, wherein the controller is further configured to continuously receive data representative of the upstream-valve mass flow rate and the downstream-valve mass flow rate, and continuously adjust the upstream valve opening such that the upstream-valve non-buoyant mass flow rate substantially matches the downstream-valve mass flow rate, and the flow of the buoyant flow past the upstream valve is blocked.